Thursday, 18 August 2022

Prediction of Physico-Chemical Properties for Polycyclic Aromatic Hydrocarbons Based on Electronic Characteristics of Molecules


Abstract

QSPR models have been developed to predict of polycyclic aromatic hydrocarbons (PAHs) based on quantum chemical and integral spectroscopic descriptors. The first ionization potentials calculated from the energies of the highest occupied molecular orbital (HOMO), relative autocorrelation empirical parameters and the total number of electrons of non-ionized molecules were used as quantum chemical descriptors. Ionization potentials, electron affinities, boiling points, molecular masses, saturation vapor pressure of PAHs were studied as physical-chemical properties. Ionization potentials and electron affinities (IPs and EAs) are calculated by the use of density functional theory (DFT). The predictive power of resulting model is demonstrated by testing it on unseen data that were not used during model generation. The obtained models make it possible to estimate physical and chemical properties with sufficient accuracy for practical applications.

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Monday, 15 August 2022

Value Chain Analysis for Medicinal Plant based products in India: Case Study of Uttarakhand

Abstract

Value chain concepts and approaches can be used to understand the integration of producers of high value products in developing countries with regional and global markets. A value chain is a description of range of activities that involves processes of production, delivery and final disposal of the product after use. The value chain analysis involves the study of the structure, actors, and dynamics of value chains that connect farm and forest products. The participants, linkages, structure of cost and benefit and dynamics of the value chain are studied.

The standardization of the production procedures in case of medicinal plant industry is important to develop a uniformity and acceptability in all parts of the world. The various processes of the value chain i.e. cultivation, maintenance, harvesting, processing, storage, packaging of the medicinal and aromatic plant industry are required to be standardized to meet the criteria for the certification as well as for the assessment of the quality and safety norms of the product and extracts thus produced. Certifications and the standardization define the safety and quality of the product that are essential in the international markets for the commodities to be traded abroad. The analysis discusses about the current scenario of value chain of the medicinal plant industry and how the standardization of the value addition contributes in the trade of medicinal and aromatic plants.

Read more about this article: https://lupinepublishers.com/chemistry-journal/fulltext/value-chain-analysis-for-medicinal-plant-based-products-in-india-case-study-of-uttarakhand.ID.000176.php 

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Friday, 19 February 2021

Lupine Publishers | Experimental Approach, Computational DFT Investigation and a Biological Activity in the Study of an Organic Heterocyclic Compound

 Lupine Publishers | An archive of organic and inorganic chemical sciences


Abstract

The title compound TZ1 was synthesized by N-alkylation reaction, and its structure was confirmed by 1H NMR, 13C NMR and IR, it was screened for their in vitro antibacterial activity by the agar well diffusion method against four bacteria, Gram-positive (Bacillus cereus, Staphylococcus aureus) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa). The molecule was studied with the density functional theory (DFT) at B3LYP/6–31G (d,p) level in order to determine the relationship between the molecular structure and the antibacterial inhibition behavior. The molecular geometry, frontier molecular orbitals and Mulliken atomic charge of the compound are investigated to get a better insight of the molecular properties. The molecular electrostatic potential (MEP) for a compound was determined to check their electrophilic or nucleophilic reactivity. The theoretical parameters offer significant assistance to understand the antibacterial inhibition mechanism indicated by the molecule and are in full agreement with the experimental results.

Keywords:5-Chlorosatin derivatives; N-alkylation reaction; antibacterial activity; DFT; Molecular electrostatic potential

 

Introduction

The 5-Chloroisatin is well documented as an important heterocyclic compound in the field of medicinal chemistry. My recently published book and review [1,2] contain a special chapter, dedicated to the chemistry of 5-Chloroisatin and their derivatives.

The 5-chloro-1H-indole-2 3-dione structure is a heterocyclic compound which easily participates in chemical reactions. Its bonding sites are analogous to pyrrole. As shown in Scheme 1, 5-Chloroisatin is reactive at four different positions including the carbon atom 3, nitrogen atom 1, the C2–C3 p-bond and the C2–N sigma bond.

This moiety of 5-Chloroisatin and their derivatives possess pharmacological and chemotherapeutic properties such as anti- cancer [3], anti-diabetic [4], anti-inflammatory [5], anti-malarial [6], anti-bacterial [7], anti-fungal [8], anti-viral [9] and others drugs for treatment of several diseases [10].

Density functional theory (DFT) has become a convenient method to decipher experimental results, in antibacterial activity; this technique makes it possible to accurately predict the inhibition efficiency of organic compounds on the basis of electronic and molecular properties as well as reactivity indexes [11]. The objective of current study is to explore relationship amongst structure and electronic properties of the synthesized 5-chloro-1- (2- (dimethylamino) ethyl) indoline-2,3-dione (TZ1) using DFT. Then, the evaluation of its antibacterial activity. (Scheme1)

 

Experimental Details

Chemistry

Melting points were determined using the kofler bench apparatus and uncorrected. The spectra of 1H NMR spectra were recorded in CDCl3 on the Brucker Avance-300 spectrometer, operating at 300MHz and at 75MHz for 13C-NMR using TMS as an internal standard and Spin resonances are reported as chemical shifts (d) in parts per million (ppm). Infrared Spectra were run on AVATAR 320 AEK0200713 spectrometer and frequencies are reported in cm-1. The purity of the synthesized compound was confirmed by thin layer chromatography (TLC), performed on Silica gel 60 coated plates. UV light was used for the visualization of TLC spots [12].

General procedure

The 5-Chloroisatin derivatives TZ1 was prepared by mixing 0.2g (1.1 mmol) of 5-chloro-1H-indole-2,3-dione, (0.23g, 1.16mmol) of potassium carbonate in 15mL of N-N dimethylformamide (DMF) and (0.035g, 0.10mmol) of BTBA, then, the reagent is slowly added, the mixture is left at room temperature for 48 hours. The reaction mixture was concentrated by using rota vapor. The solid was separated out by filtration. It was carefully checked by thin layer chromatography. The compound was isolated by column chromatography by using different fractions of n-hexane and ethyl acetate [13-16].

Yield=89%; mp: 114 °C ; 1H NMR (CDCl3) δppm 7.53-7.54 (m, H, HAr); 7.51 (d, H, HAr, J=9Hz); 6.90 (d, H, HAr, J=9Hz); 3.85 (t, 2H, CH2, J=9Hz); 3.75 (t, 2H, CH2, J=9Hz); 2.15 (m, 6H, CH3). 13C NMR (CDCl3) δppm: 184.59 (C=O); 164.45 (N-C=O); 146.22, 141.13, 110.39 (Cq); 138.59, 126.08, 113.36 (CHAr); 55.90, 46.79 (CH2); 45.09 (CH3). Infra Red (KBr) cm-1: 3565, 3174, 30815 (C-H), 2975, 1720 (C=O), 1607 (NC=O), 1445, 1472 (C=C) 1185,1123 (N-C), 654 (C-Cl).

Antibacterial screening

Synthesized compound TZ1 was screened for their antibacterial activity against two Gram positive (Bacillus cereus and Staphylococcus aureus) and two Gram negative (Escherichia coli and Pseudomonas aeruginosa) bacteria by the agar well diffusion method, using LB medium (Luria Bertani medium: yeast extract 5.0g, peptone 10.0g, sodium chloride 5.0g, distilled water 1000mL). This technique was recommended by CLSI [17].

A sterile paper disk was placed on the surface of each plate and impregnated with 5μL of the TZ1 solution at a final concentration of 10mg/mL. Then, the plates were incubated at 4 °C for 2 hours to permit good diffusion before incubation at 37±2 °C for 24 hours. The diameters of the inhibition zones were measured in mm with the caliper. A disc impregnated with 2% dimethylsulfoxide as a negative control was made the experiment was carried out in triplicate.

In order to determine the Minimum inhibitory concentration (MIC) values, we started by the dilution of the TZ1 was prepared in a Mueller Hinton broth supplemented with bacteriological agar, to reach a final concentration between 5mg/mL and 0.004mg/ mL, 50μL of bacterial inoculum was added to each well at a final concentration of 106CFU/mL. DMSO (2%) was used as a negative control. The final concentration of our product was between 5mg mL-1 (3rd well) and 0.019mg mL-1 (well 11). Plates were incubated at 37 °C for 24 hours. After 2 hours of a subsequent incubation, bacterial growth was revealed by reduction of blue dye resazurin to pink resorufin [18].

Including, the minimum bactericidal concentrations (MBC) which is the last step in the protocol, a bactericidal control is carried out 24 hours earlier by streaking on a platelet agar, after microdilution to the broth by spreading 5μL of the negative wells on Luria Bertani agar plates.

Theoretical calculations

The computational studies of compound TZ1 were performed using the GAUSSIAN 09W [19] program package and visualized with the Gauss View on a personal computer using density functional theory (DFT) method with 6−31G (d,p) as the basis set [20]. The using HOMO and LUMO orbital energies, the ionization energy and electron affinity can be expressed as: IP = -EHOMO, EA = -ELUMO, respectively. The total hardness, η and electronegativity χ were given by the following relations: [21].

Result and Discussion

Synthesis of 5-chloro-1-(2-(dimethylamino) ethyl) indoline- 2,3-dione (TZ1) is outlined in Scheme 2, it was prepared according to a similar previous procedure [22]. 5-chloroisatin was used as a starting material for the synthesis of various substituted indole derivatives [23-27].

The (TZ1) was synthesized by the N-alkylation reaction of 5-chloro-1H-indole-2,3-dione in DMF, a base K2CO3 and a TBAB catalyst was added to a stirred solution at room temperature, Chloro-N,N-dimethylethanamine was added dropwise to the mixture under conditions of catalysis by phase transfer for 48 hours, the reaction was monitored by thin layer chromatography. After this time, the mixture was filtered and concentrated and dried under vacuum to afford the required product. The complex was obtained in good yield, stable in air, and is colored solid, soluble in methanol, chloroform, DMF, and DMSO.

The 1H-NMR, 13C-NMR and IR were used to assign the structure of synthesized compound. (Scheme 2)

Antibacterial activity

The In vitro antimicrobial screening tests of synthesized compound TZ1 was carried out as an antibacterial activity. the tested compound showed biological activity against different types of Gram-positive (Bacillus cereus and Staphylococcus aureus) and Gram negative bacteria (Pseudomonas aeruginosa, Escherichia coli), it showed zones of inhibition of MIC/MBC values ranging from 0.156/0.156 to 0.313/0.313mm against the Gram-positive bacteria and between 0.625/0.625 and 1.25/1.25mm against Gram-negative bacteria.

Coordination enhances the antibacterial activity and the TZ1 in the present study are more active against Gram-positive than Gram-negative bacteria [28]. On the other hand, it should also be noted that the presence of nitrogen and oxygen atoms which are the highest values of the negative charge on the molecule TZ1 suggesting that these centers have the maximum electron density and would preferentially interact with the micro-organisms Gram positive then increases the antibacterial potential.

Computational details

Frontier orbital energy analysis and other global reactivity descriptors: The all optimized structures along with the numbering scheme of TZ1 at DFT/B3LYP level using the 6-31+G (d,p) basis are shown in Figures 1-3.

The HOMO-LUMO orbitals help to characterize the chemical reactivity and kinetic stability of the molecule.

The analysis of the HOMO highlights the areas of the molecule that can donate electrons to electrophilic species while the analysis of the LUMO predicts the regions of the molecule with high affinity to accept electrons from nucleophilic species. The calculated HOMO–LUMO energy gap value is found to be 3.1673 eV.

The dipole moment (μ(debye= 5.6982) tells about the polarity of the molecule. The higher value of dipole moment in case of TZ1 molecule is mainly attributed to an overall imbalance in charge from one side of a molecule to the other side is also evident from the MESP plot. DFT calculation gives an idea about the substance reactivity and site selectivity of the frameworks. By the computed value of HOMO and LUMO energy values for the TZ1, the electronegativity (χ), total hardness (η), Softness (σ), can be calculated. The significance of (η) and (σ) is to evaluate both the reactivity and stability [31].

Molecular electrostatic potential (esp) map: The molecular electrostatic potential mapped surfaces show the charge distributions of molecules three dimensionally which give clear and special signature of the interactions of the compounds [31].

The molecular electrostatic potential is related to the electronic density and a very useful descriptor for determining sites for electrophilic attack and nucleophilic reactions as well as hydrogenbonding interactions [32].

The MEP mapped surface of the compound TZ1 was calculated by DFT/B3LYP at 6 31G (d,p) basis set and MEP surface are plotted in Figure 6. Red, blue and green colors represent regions of the most electro negative, most electro positive electrostatic and zero potential, respectively [33].

Mulliken charges analysis

The Mulliken atomic charges have a significant role in the application of quantum chemical calculations to molecular systems, by determining the electron population of each atom as defined by the basis function [34]. Table 3 exhibits the calculated mulliken atomic charges except for atoms H by DFT/B3LYP at 6 31G (d,p) basis set. Also, the color range in the scale of positive and negative charge and graphical representation for Mulliken atomic charges of TZ1 is shown in Figure 7.

From the listed tabulated values (Table 3) of atomic charge, we can summary that the charge on the carbon atom (C6) is greater than other carbon atoms in the all compounds because it is connected to electronegative chloride atom (Cl10). Then, all nitrogen and oxygen atoms (N13, N22, O14 and O15) are the most negatively charged ones, suggesting that these centers have the maximum electron density, which can interact with the positively charged part of the receptor easily.

Conclusion

In summary, we report the synthesis and characterization of 5-chloro-1- (2- (dimethylamino) ethyl) indoline-2,3-dione (TZ1) in excellent yield. The antibacterial activity of TZ1 has been explored experimentally and by quantum calculations. The frontier orbital energy analysis, mulliken atomic charges and electrostatic potential were also studied by using the DFT method at B3LYP/6–31G (d,p). The antibacterial bioassay showed that it possessed excellent activity.

Acknowledgements

The author would like to thank all the people who helped to carry out this work such as 1H NMR, 13C NMR, IR, and for antibacterial activity.

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Friday, 12 February 2021

Lupine Publishers | Value Chain Analysis for Medicinal Plant based products in India: Case Study of Uttarakhand

 Lupine Publishers | An archive of organic and inorganic chemical sciences


Abstract

Value chain concepts and approaches can be used to understand the integration of producers of high value products in developing countries with regional and global markets. A value chain is a description of range of activities that involves processes of production, delivery and final disposal of the product after use. The value chain analysis involves the study of the structure, actors, and dynamics of value chains that connect farm and forest products. The participants, linkages, structure of cost and benefit and dynamics of the value chain are studied.

The standardization of the production procedures in case of medicinal plant industry is important to develop a uniformity and acceptability in all parts of the world. The various processes of the value chain i.e. cultivation, maintenance, harvesting, processing, storage, packaging of the medicinal and aromatic plant industry are required to be standardized to meet the criteria for the certification as well as for the assessment of the quality and safety norms of the product and extracts thus produced. Certifications and the standardization define the safety and quality of the product that are essential in the international markets for the commodities to be traded abroad. The analysis discusses about the current scenario of value chain of the medicinal plant industry and how the standardization of the value addition contributes in the trade of medicinal and aromatic plants.

Keywords: Value chain; Medicinal plants; Uttarakhand; India; Herbal industry; Spices

Introduction

Background

Value addition is the process of economically adding value to a product by altering its current place, time and from one set of characteristics to other characteristics that are more favored in the marketplace [1]. Value addition is the process of creating value in existing value chain of a product. Value addition in medicinal plant industry starts at grass root level of cultivation of medicinal plants and primary processing of medicinal and aromatic plants which includes the procedures like cleaning, drying and sorting of medicinal plants at very initial phase of collection and harvesting of medicinal plants.

The basic theory for calculating the value addition at every level of the production process is the difference between the market price of the product and the total cost of production of the inputs used for the production (Figure 1).

The demand for chemicals and products derived from medicinal and aromatic plants is increasing globally and has opened up opportunities for entrepreneurs to add value to these plants through processing, thereby generating enormous employment avenues [2]. India has abundance of medicinal plants with 8000 medicinal and 2500 aromatic species which are mined for natural chemicals and processed for commercial products that are then exported globally. An upward trend has been recorded in the exports of medicinal and aromatic plants’ products in recent years which have encouraged Government and private organizations for developing processed products with medicinal plants. Value addition through processing involves employment of unskilled rural youth and unemployed, educated urban youth. A number of value added consumer products can be developed from a single medicinal or aromatic plant for trade in national and international markets.

Value chain actors

The returns received by the actors of the medicinal plant value chain namely villagers, middlemen and wholesaler, constitute the total trade in medicinal plants. The villagers constitute the first link in the trade in medicinal plants wherein the cultivators separately or combined collect the medicinal plant produce and take them up to the processors for further refinement. There upon, the middle men intervene in the medicinal plant trade and act as facilitators due to the lack of efficient infrastructure and link the cultivators to the wholesalers for commissions. The wholesalers are the distributors of the medicinal plant products to the ultimate markets and they carry out the work through a complex network of agents and retailers.

The medicinal plant value chain also included the secondary actors which are the industries that use the medicinal plants and their extracts as their input materials and then the value added to them through the processes operated on them through which the end products are obtained. The Pharmaceutical industries and the Cosmetic industries are the prime example of the value addition made to the medicinal plants. These industries use the medicinal and aromatic plants in fixed percentages and the final products made are the blend of multiple such plants and extracts.

Research motivation

The medicinal plant industry in the North Indian state of the Uttarakhand though is established, but the industry lacks a systematic structure and direction which can grant the various actors of the medicinal plant value chain proper guidelines and direction to develop the products that match the international quality standards. The international trade in medicinal plants and allied products is based on certain qualitative and safety standards which should be in place to ensure safety of the medicinal plants traded. The application and adherence of such standards in production of the medicinal plants in the country is eminent in order to explore the entire international trade potential of the medicinal plants.

For the purpose of analyzing the impact of value addition made by different actors of the medicinal plant value chain and the value added by the standardization of the production of medicinal plant products, qualitative method of analysis has been used. The existing studies have primarily focused on determining the value addition made by various actors of the value chain of medicinal plants. A very limited number of studies have explored the benefits of standardization of the various processes that are crucial to the quality of the end products of the medicinal plant industry. This study attempts to do that.

Objectives of the research

1. To understand the value chain processes in medicinal plant industry of Uttarakhand

2. To identify the issues in the value chain processes of the industry

3. To analyze the impact of standardization of active ingredients of value chain on the trade

The study begins with the introduction of the study. The previous studies pertaining to the topic have been discussed in the literature review section. Research gaps have been identified in the same chapter and research framework has been formed. In the next chapter, research methodology has been stated in which the process that has been adopted during the entire course of the investigation has been discussed. Data analysis has been discussed in the succeeding chapter. This chapter is followed by discussions, conclusions, and recommendations for future work.

Literature Review

Value chain of MAPs

Value Chain (VC) defines a complete series of activities which are mandatory to carry the product or service from beginning through the different phases of production to the end consumer and discarding the product after its usage [3]. The value chain concept is an analytical approach that is been deployed used for evaluating the performance of the marketing initiatives of any industry or organization. This kind of analysis helps in identifying the loop holes in the performance system of marketing initiatives and implementing measures for refining the private and public interventions [4].

Medicinal plants and its related products have a wide ranging value chain activities associated with it. Recent estimates suggest that trade related activities of herbs is projected to attain a financial worth of US$ 5 Trillion by 2050. Realizing this increasing demand, it becomes important to assess the activities that can be restructured for smooth flow of medicinal herbs from producers to end consumers. This kind of analysis helps in understanding the difference that prevails in quality of the herbal medicines in different market zones and identify superior quality products over the inferior ones.

The value chain in medicinal plant industry comprises of the producers, collector, processors, wholesalers, exporters and distributors and retailer. The producers, or the cultivators or, the collectors are the upstream actors of the medicinal plant value chain and they provide the industry with the basic raw material and inputs for the other participants to function. While the processors, the wholesalers, the retailers, the traders and the exporters are the downstream actors of the medicinal plant value chain which provide the raw inputs of the medicinal plants with value and the capacity to the trade. The downstream actors enhance the utility of the medicinal plants and impart value to the products through processing and packaging of the products which increases the shelf life of the products.

Producers

The production system of MAPs products comprises of three major groups; wild crafters, plantation operators and cultivators. The three broad categories of producers differ according to the level of power they own, the practices they employ and the benefits they draw from these valuable resources. State Forest Departments are anticipated to control the harvesting of forest produce and are also expected to maintain a record of such produce. Thus, majority of information about the raw materials can directly be obtained from people working in the state forest department.

Collectors

Collectors are those middlemen who gather harvested herbal species from agriculturalists and wild crafters and make them available to processors. Because of the changeable demand of the products, collectors do not involve in the gathering process until they receive an order for the same. Formerly, several cooperative societies in Uttarakhand were assigned the role of collection process. Bhesaj Sangh, was one amongst the trusted collecting agency. But in the year 1986, Kumaon Mandal Vikas Nigam (KMVN) was started by the government officials to undertake activities pertaining to collection process and regulate the unnecessary exploitation of the growers. Thereafter, Garhwal Vikas Mandal Nigam (GVMN) was assigned the authority of regulating the allied activities of the medicinal plant agricultural sector. Despite this, Bhesaj Sangh, because of its consistent attention on collection of medicinal and aromatic plants,wasfar more popular in comparison to their counterpart.

Processors

Processing of the harvested medicinal herbs is done in two stages; semi-processing and alteration in the preparations. The first stage of the processing includes activities like cleaning the organic material stuck to the herbal species by drying; building concentrates, disinfecting, boiling and grinding. Marketing processed products adds value to their produce thereby allowing them charge higher prices for the same. The processing stage involves numerous activities including the drying, packaging, storage which enhance the shelf life and assist the marketing of the medicinal plant products.

Wholesalers and exporters

The wholesalers and the retailers constitute the organized part of the medicinal plant value chain. The links like the cultivators, collectors, processors and handlers in medicinal plant industry in Northern India are inherently unorganized and scattered in nature, while the downstream actors, the wholesalers and retailers are relatively formal in their structure. The wholesalers and the exporters provide the upstream actors of the medicinal plant value chain with valuable information of the trends and patterns of the consumer demand for the medicinal plant products in the domestic as well as in the international markets.

Distribution and retailing

The distributors and retailers play a crucial role in connecting the consumers to the producers through the wholesalers and help the consumers in attaining the products they desire. The medicinal plant cultivation usually is situated in the remote areas of the countries with abundant and rich biodiversity while a majority of the consumers are centered in the clusters of urban areas. The retailers provide the function of connecting the producers with the consumers. The retailers obtain the medicinal plants from the wholesalers and in certain cases, directly from the producers (processors) and offer the medicinal plant products in the market to the consumers for the ultimate consumption. The retail sellers of the medicinal plant industry also performs the function of acquiring the required credential sand certificates for the medicinal plants before such products can enter the consumer markets as the per the national and regional safety and quality norms [5].

The distributors, on the other hand perform, similar functions like the retailers but they interact with both the wholesalers and the retailers while the retailers interact only with the consumers.

Standardization of MAPs

Lazarowych et al. [6] in their study of the Standardization practices of the botanical drugs and the various strategies used for the standardization, have highlighted the standardization of the medicinal plants and the resultant botanical drugs has enabled the development of the required strategies for the enhancement of the quality of the products of the industry and maintenance of the homogeneity of the medicinal plant products. Well established system of standardization, according to Lazarowych et al. [6] can help to establish efficient control mechanisms for quality of the raw medicinal plants and the processed extracts of the plants. The need for standardization in medicinal plant industry has been further accentuated in a paper by Folashade et al. [7] which corresponds to the issue of standardization of the herbal plant industry. According to Folashade et al. [7] the standardization of the medicinal plant and the herbal product industry is eminent because of the act that the medicinal plants and the processes involved in their value addition are based upon a fine balance of constituents and are precariously time lined. Any deviation from the balance might lead to serious implications on the quality and nature of the end product. Without the standardization of the production and processing stages, the value chain actors may act independently and the resultant products might not be favorable for the consumers for the desired treatment of the ailments. The authors lay the responsibility of ensuring the safety of the consumers and the products that they consume on the Authorities’ shoulders and the safe procedures of production, harvesting, processing and packaging ought to be outlined by the authorities so that the ground rules for the production are set in the industry which can then be used as the basic criteria for judging the products and the assessment of the products can be assisted in similar manner.

Research gaps and framework

Certifications and the standards provide the products with the scientific seals of safety and quality that are essential in the international markets for the commodities to be traded abroad. The current study determines the importance of standardization of value chain processes by examining its impact on trade volume and trade price of Medicinal Plants (Figure 2).

Irrespective of the increasing demand and huge market size of the medicinal products, there is a huge gap in the amount of studies that have been undertaken in the context of value chain of medicinal plants, that too specifically in the context of Uttarakhand. There exist several prior researches which focus on determining the value addition made by the various actors of the value chain of medicinal plants but not many studies explore the benefits of standardization of the various processes that are crucial to the quality of the end products of the medicinal plant industry.

Research Methodology

The aim of the study is to understand the current status of value chain processes of medicinal plants in Uttarakhand and the impact of standardization of value chain processes on trade volume and trade price of medicinal plants. This is done because it has been observed that majority of the trade in this particular sector was happening in its raw form. The data has been collected from various government sources such as State government medicinal Plant websites: NMPB, ENVIS etc. and empirical research papers related to this area. The analysis provides information about the certifications the various systems of AYUSH, value chain practices, cost and benefits and trade related information of medicinal plants. The impact of standardization on trade volume has been analyzed in the data analysis.

For the purpose of satisfying this particular objective, analysis has been performed to ascertain the impact of the standardization on the Indian export of medicinal and aromatic plants and the allied products, the year in which the standards were established in the Indian medicinal plant Industry has been used as the benchmark year and comparative analysis has been done of the Indian trade in medicinal plants five years prior and five years post the standardization of the industry in order to gather the overall impact of the standardization on the economy.

The study is descriptive in nature in the sense that it includes collection of data that explains events and then organizes to come up as a result. Secondary data related to quantity of medicinal plants collected/produced/traded have been collected from the records of the State Forest Departments in many research studies [8,9] (Figure 3).

Findings

Value chain analysis of MAPs in Uttarakhand

The value chain makes addition at every level of the production. The value chain actors are responsible for processing and adding value to the medicinal plants and developing the product to fulfill global demand. The value chain analysis of medicinal plants is done to understand the discrepancies in the process and to assess ways to improve the same.The division of the returns from the trade in medicinal plants among the various actors in medicinal plant trade has been depicted below. All through the medicinal plants under consideration, trend continues wherein wholesalers takes up the largest piece of the pie and get the largest share in the returns from total trade in the medicinal plants and returns to middlemen follow soon after for receiving the second highest share in the total returns from medicinal plant trade. The initial cultivator or villagers are the worst off group of players in medicinal plant trade.

There have been identified issues regarding the distribution of income and an attempt has been made to understand the probable reasons. One such reason can be unregistered and untrained farmers. Lack of training and understanding of the process and acknowledgement of market value of medicinal plants is the reason for unequal distribution of returns arising from sale of medicinal plants.

The analysis of the data set reveals a larger share of medicinal and aromatic plant trade going to the wholesalers which is contradicted by the findings of Shahidullah and Haque (2010) in their study of the relationship between the medicinal plant production and livelihood enhancement in the case of Bangladesh. Their study indicates that the primary and secondary- wholesale markets for the medicinal plants are dominated by the middlemen and not the primary producers and the wholesalers who benefitted from the trade in medicinal plants. According to their findings, the medicinal plant cultivation is sustainable for the relatively economically well off cultivators who usually have access to the better quality of land and the technical equipments. However, Shahidullah & Haque [10] also agreed that the small scale medicinal plant cultivators need to organize themselves in order to gain better holding in the market through an improved control over the quantity supplied in the market and hence the prices which determines their returns.

The value addition in specific species was also assessed. The comparative scrutiny of the value addition made by the cultivators for the given medicinal plants reveals that the value addition was the highest in the case of Chandramul, Kapur Kachari and Sarpgandha at Rs. 13680 while Kali Jiri had the lowest value addition made at the primary stage of cultivation. The value addition in the given data set was lowest for the plant Kali jiri while Kapur Kachari, Sarpgandha and Chandramul had the highest value added at the cultivation level of the medicinal plant value chain.

Standardization of medicinal and aromatic plants and its impact on trade

The certifications of the value chain processes improve the tradability of medicinal plants since it assures the quality of the product to buyers in different countries. Certification programs have been introduced by Indian agencies as well to improve the acceptability of Indian medicinal products abroad. However, the compliance is not made mandatory for the companies and other participants. The systems wise distribution (%) of good manufacturing practice and non-good manufacturing practicecompliant Ayurveda, Yoga and Naturopathy, Unani, Siddha, and Homeopathy pharmacies has been depicted below that suggests that many of the AYUSH pharmacies do not comply to Good Manufacturing Practices and do not even have license.

AYUSH: Ayurveda, Yoga, and Naturopathy, Unani, Sidhha and Homeopathy

GMP: good manufacturing practices: The capacity of trade of medicinal plants in Uttarakhand has been assessed through number of traders present in different districts, amount of wholesale trade and trade through mandis. The district wise distribution of the medicinal plant traders in the state of Uttarakhand in the period ranging from 2008-09 to 2012-13 has been depicted below. In the year 2008-09, the total number of traders in the medicinal plant trade amounted to 571 and the highest number of traders were in the district of Pithoragarh while the lowest were in the districts of Rudraprayag. The year 2009-10, the total number of traders was 600 wherein the highest number of traders was in the Pithoragarh 259 and the lowest numbers of traders were in the Chamoli district of Uttarakhand. In the next year 2010-11, the total number of traders was 864 and the highest number of traders was in the Pithoragarh district while Uttarkashi and Rudraprayag had the lowest number of traders of the medicinal plants. The year 2011-12 witnessed the numbers of traders decline to 594 with the highest number of traders in Pithoragarh (337) and the lowest in Rudraprayag (1). The year 2012-13 witnessed an increase in the number of total traders to 732 with highest number of traders in the Pithoragarh district and the least traders in Rudraprayag. The number of traders in the given period increased from the 571 in 2008-09 to 864 in 2010-11 but declined to 594 thereafter in 2012- 13 (Figure 6).

The impact of standardization on trade has also been assessed. The voluntary scheme of standardization scheme introduced in the year 2009 was adopted by many companies involved in the value processing of medicinal plants. The impact of the scheme on the trade values of medicinal plants has been assessed and for this, pre and post 2009, figures of trade, when standardization was introduced for the medicinal plants has been compared.

The exports figures of the medicinal plants in the years prior and post the launch of the standardization scheme by the government in the year 2009-10 have been depicted. The years 2003-04 to 2008-09 have been taken into consideration to grasp the export scenario of the medicinal plants before the launch of the medicinal plant standardization. In the year 2008-09, the total exports of the medicinal plant products was 125.4 million USD which was a major improvement since 2003-04 when the Indian exports of the medicinal plant products to the rest of the world used to be 65.71 million USD. The total exports for the given period amounted to 528.75million USD. The exports reached a high of 233.7 million USD worth of medicinal plant export in the year 2014-15. The total exports in the period ranging from 2009-10 to 2014-15 were almost the double of the total medicinal plant export of the previous period at 1068.22 million USD.The trend of Indian exports of medicinal plants over the period ranging from 2003-04 to 2014-15 and the effect of the standardization on the total exports of the medicinal plants of the country have been analyzed. The year 2008-09 has been taken the bench mark year in which the National medicinal Plant Board of India introduced the standards in the Indian medicinal plant industry. The year post the introduction of the certification policies in the system saw a fall in the export of the medicinal plants for one year which picked up in the corresponding years. The Indian medicinal plant exports have improved over the year’s post the standardization of the industry which implies the positive impact the certification and standardization has had over the industry exports .

The analysis of the data reveals that the standardization of the medicinal plant industry does indeed has improved the foreign trade quantities of the Indian medicinal and aromatic plants in the foreign which is evident in the study of the pattern of trade which corresponds five years prior to the standardization and certification obligation (2004-05 to 2008-09) in the country and five year post the standardization (2009-10 to 2013-14) of the industry. The comparative analysis of the figures shows a boom in the Indian exports to the world in the years after the standardization was made compulsory in the year 2008-09 for the medicinal plant cultivators, processors and the marketers and traders. The basic requirement for the standardization of the medicinal plants is explained by Tierra (2002) in his research article discussing the need for standardization of the medicinal plants and extracts. Tierra emphasizes that the standardization of the medicinal plants and extracts would lead to a higher degree of technological refinement of the products of the industry as compared to unorganized system of the medicinal plants and the resultant products provide safer, stronger and more effective products that are supported by an adequate scientific evidence to substantiate the quality and the authenticity of the medicinal plants and the extracts and oils derived from them.

The standardization process is likely to minimize the gap between the prices offered in Indian market and international markets. Authenticated raw material is the basic starting point for the development and manufacturing of a botanical product. Harvesting, storing, processing and formulating methods may effect on the quality and consistency of the herbal product. Our herbal products are not getting international market because we are not capable to show the international standard of our products. A coordinated effort of all the supply chain actors and improved market facilities is likely to improve the export prices of the medicinal and aromatic plants; as discussed in Table 3. The rising export prices from the year 2008-09 till 2012-2012, shows that significant improvements were made in the traded prices of the medicinal produce. Thereafter the prices declined might be because of ineffective marketing strategies or poor market linkages.

Lazarowych et al. [6] in their study of the Standardization practices of the botanical drugs and the various strategies used for the standardization, have highlighted the standardization of the medicinal plants and the resultant botanical drugs has enabled the development of the required strategies for the enhancement of the quality of the products of the industry and maintenance of the homogeneity of the medicinal plant products. Well established system of standardization according Lazarowych et al. [6] can help to establish efficient control mechanisms for quality of the raw medicinal plants and the processed extracts of the plants. The need for standardization in medicinal plant industry has been further accentuated in a paper by Folashade et al. [7] which corresponds to the issue of standardization of the herbal plant industry. According to Folashade et al. [7] the standardization of the medicinal plant and the herbal product industry is eminent because of the act that the medicinal plants and the processes involved in their value addition are based upon a fine balance of constituents and are precariously time lined. Any deviation from the balance might lead to serious implications on the quality and nature of the end product. Without the standardization of the production and processing stages, the value chain actors may act independently and the resultant products might not be favorable for the consumers for the desired treatment of the ailments [11,12].

Conclusion

The standardization of the production procedures of the medicinal plant industry is eminent for the development of a more systematic, uniform and high quality medicinal and aromatic plant industry in India. The standards of the cultivation, maintenance, harvesting, processing, storage, and packaging function of the medicinal and aromatic plant industry are necessary to set up the criteria for the certification as well as for the assessment of the quality and safety norms of the product and extracts thus produced. Certifications and the standards provide the products with the scientific seals of safety and quality that are essential in the international markets for the commodities to be traded abroad. Further, the analysis talks about the current scenario in the medicinal plant industry wherein the returns are unequally distributed among the various actors of the medicinal plant value chain which leads to the low participation in the industry as well as the poor performance at the grass root level. The wholesalers and the middlemen in the state of Uttarakhand take up a majority of the medicinal plant sector’s revenue while the small scale cultivators receive little which impedes the performance of the sector. Medicinal plant sector in the North Indian state of Uttarakhand needs a systematic organization structure which assists the value chain actors in receiving the quantum of returns due to them and the injection of standardization and uniformity of the commodities produced which further enhances the value of the products in the domestic and the international markets. There are various issues identified in the value chain process of medicinal plants such as distribution of income among the various value chain participants, lack of training and understanding of the process and acknowledgement of market value of medicinal plants and lack of quality of products. These issues can be addressed through standardization of medicinal plants value chain and a strong plan to create awareness among the participants of value chain. The government of India in collaboration with the national medicinal plant board and the state medicinal plant boards has decided permissible level of contaminants in the production of selected medicinal plants. These level needs to be adhered to in order to gain local and state level permission from the authorities to function in the markets.

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Saturday, 6 February 2021

Lupine Publishers | Optimization of Chitosan+Activated Carbon Nanocomposite. DFT Study

 Lupine Publishers | An archive of organic and inorganic chemical sciences

Abstract

First, the minimum energy (geometry optimization DFT-DMol3) is obtained among C48 optimized ring carbon-system, and one non-optimized chitosan copolymer unit. Second, C24 and C9 optimized rings, each one interacting with an optimized chitosan copolymer unit (Ch). With the aim to investigate structural properties, the first case is optimized by applying smearing; and the second without smearing. Two parallel hypothetical carbon chains of 12 carbon atoms, symmetrically arranged are optimized in C24 carbyne ring; and one hypothetical 5 carbon-chain parallel to another 4 carbon-chain end optimized in a cumulene C9-ring. These carbon-ring structures here defined as activated carbons (AC), correspond to big pore size diameter obtained without chemical agent acting on them. Single point calculations are to build potential energy surfaces with GGA-PW91 functional to deal with exchange correlation energies for unrestricted spin, all-electron with dnd basis set. Only in the first case, orbital occupation is optimized with diverse smearing values. To determine structure stability, the minimum energy criterion is applied on AC+Ch nanocomposite. To generate fractional occupation, virtual orbitals are formed in this occupation space, whether homo-lumo gap is small and there is certain density near Fermi level. This fractional occupation pattern depends on the temperature. It must be noticed that when AC and Ch are solids, there is no adsorption; however, by applying smearing it was possible to find potential energy surfaces with a high equilibrium energy indicating glass phase transition in Chitosan due to the chemisorption given at the minimum of energy. AC+Ch molecular complex nanocomposite is expected to be applied not only in medicine but also in high technology.

Introduction

With the aim to figure out a molecular complex formed through the interaction between a system of 48 carbons arranged in planar way and a copolymer unit of chitosan, potential energy surfaces were built [1,2] using single point step by step calculations. The problem is studied considering that a molecular complex is obtained by changing smearing value according to the energy value convergence. Considering that electrons occupy orbitals with the lowest energies and with an integral occupation number in calculations of density functionals, a smearing change indicates a fractional occupation in virtual orbitals within this space of occupation. The smearing calculations correspond to the explicit inclusion of the fractional occupation numbers of the DFT calculations, requiring an additional term to achieve a functional energy from variation theory [35]. The contribution of this term to the density functional force exactly cancels the correction term as a function of the change in the occupation number. For occupation numbers satisfying a Fermi distribution, the variation total-energy functional is identical in form to the grand potential [3-6]. From the grand canonical distribution or Gibbs distribution, the normalized probability distribution of finding the system in a state with n particles and energy 𝐸𝑛𝑟 [7], the Z grand partition function of the system, and the number of particles remains according to the Fermi energy ℰf =μ(T,V,n). When T = 0 the fermion gas is in the state of minimum energy in which the particles occupy the n states of 𝜓𝑖 of lower energy, since the exclusion principle of Pauli does not allow more than one particle in each state. Therefore, the Fermi function 𝑓(ℰ) gives the probability that certain states of available electron energy are occupied at a given temperature.

Other options for the shape of the occupancy numbers result from the different associated functional with finite temperature to DFT but without physical meaning, such as the temperature or the entropy associated with this term [3]. These terms, although numerically small must be included in the practical calculations that allow numbers of fractional occupation [3,8]. To consider the scope of smearing, it is known that electrons occupy orbitals with the lowest energies, and occupancy numbers are integers; nonetheless, there is a need for a fractional occupation in virtual orbitals within this space of occupation. We apply this when the HOMO-LUMO gap is small and there is especially a significant density near of Fermi level [9], thus in order to obtain the fractional occupation a kT term is implemented. This fractional occupation pattern depends on the temperature. The systems C48 carbinoid, C24 carbyne-ring, and C9 cumulene-ring (almost-planar) are arrangements obtained through DFT geometry optimization of two hypothetical parallel zigzag linear carbon chains. We consider these systems as carbon physically activated, due to the pore size diameter, and since no activating chemical agent has been applied. Carbyne is known as linear carbons alternating single and triple bonds (-C≡C-) n or with double bonds (=C=C=)n (cumulene) [10]. Polyyne is known as a allotrope carbon having H(-C≡C-) nH chemical structure repeating chain, with alternating single and triple bonds [11] and hydrogen at every extremity, corresponding to hydrogenated linear carbon chain as any member of the polyyne family HC2nH [12] with sp hybridization atoms. It is known that polyyne, carbyne and carbinoid have been actually synthesized as documented by Cataldo [13]. Bond length alternation (BLA) of carbyne pattern is retained in the rings having an even number of atoms [10]. Additional care must be taken with carbyne rings since the Jahn-Teller distortion (the counterpart of Peierls instability in non-linear molecules) is different in the C4N and C4N+2 families of rings [14-16]. There is a great variety of applications of activated carbon as an adsorbent material, and it has been used in areas related to the energy, and the environment, generating materials with a high-energy storage capacity [17].

Chitin is, after cellulose, the most abundant biopolymer in nature. When the degree of deacetylation of chitin reaches about 50% (depending on the origin of the polymer), it becomes soluble in aqueous acidic media and is called chitosan [18]. Chitosan is applied to remediation of heavy metals in drinking water and other contaminants by adsorption. The affinity of chitosan with heavy metals makes the bisorption process stable and advantageous, being only by the alginates present in brown algae matched [19]. The glass transition temperature of chitosan is 203°C (476.15 K) according to Sakurai et al. [20], 225°C (498.15 K) according to Kadokawa [21], and 280°C (553.15 K) according to Cardona-Trujillo [22]. One can differentiate specific reactions involving the -NH2 group at nonspecific reactions of -OH groups. This is important to difference between chitosan and cellulose, where three -OH groups of nearly equal reactivity are available [23,24]. In industrial applications, several solids having pores close to molecular dimensions (micropores < 20 Å) are used as selective adsorbents because of the physicochemical specificity they display towards certain molecules in contrast to the mesoporous substrates (20-500 Å) and macropores (> 500 Å). Adsorbents with these selective properties include activated carbon among others [25]. Chitosan-based highly activated carbons have also application for hydrogen storage [26]. In principle, electronic structure of diatomic molecules has been built through the overlapping knowledge of the interacting atomic orbitals [27]. In this case, the orbitals correspond to bonding (σg, πg) and antibonding (σu, πu) orbitals of hydrogen, carbon, nitrogen and oxygen diatomic molecules, whose H2, C2, N2, and O2 groundstate electronic configurations are and with 2, 8, 10 and 12 valence electrons, respectively. Actually, the reactivity sites in a molecule correspond to the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO). HOMO as base (donor), and LUMO as acid (acceptor) are particularly important MOs to predict reactivity in many types of reaction [28,29]. Activated carbon and chitosan have been independently applied as sorption materials to increase environmental quality standards. Then, we expect AC-Ch nanocomposite to have a powerful handleable adsorption property of pollutants that can be applied not only in wastewater treatment, but also in medicine against intoxication, in batteries to increase storage capacity, in electrodes of fuel cells, and in more possible applications, according to the pore size distribution to be generated on this new material.

Methodology

The interaction between an activated carbon molecule (AC) and a unit of the chitosan copolymer (Ch) is studied by means of DFTDMol3 [30-32]. The AC system is a hypothetical model of two parallel linear chains of 24 carbons each one geometrically optimized using DFT, converging into a plane molecular carbon system. In this system six nodes were formed allowing 7 interconnected rings of different bond lengths and sizes: 2 of 6 carbons, 4 of 8 carbons and one of 16 carbons. By summing these quantities gives 54 carbons since the carbons are in the nodes double counted. When subtracted they are the 48 carbons of the AC system. This system has a length of 28.4Å comparable to that of the chitosan copolymer unit (Ch). The reactants are AC + Ch corresponding to C48 + C14H24N2O9.

Single point potential energy curves were constructed [1,2] by using smearing. The following conditions to find AC+Ch (Activated Carbon+Chitosan) interaction energy are: functional GGA-PW91 [31,33-36], unrestricted spin, dnd bases, and orbital occupation with various smearing values. Considering that we obtained a solution for the energy value convergence, the interaction by changing the smearing value was studied. Since electrons occupy orbitals with lower energies and integral occupation numbers in calculations of density functional, a smearing change indicates fractional occupation and virtual orbital within this occupation space [19]. When generating a fractional occupation, virtual orbitals are in this occupation space generated, if the HOMO-LUMO gap is small, and there is certain density near the Fermi level [1], then it is implemented the fractional occupation term kT. This pattern of fractional occupation depends on temperature. Covalent connectivity calculations [37] according to DMol3 on no-bonding to s- and f-shell scheme, bond type, and converting representation to Kekulé, for bond length tolerances from 0.6 to 1.15 Ǻ were accomplished in this molecular complex mostly composed of carbon. Area calculations have been carried out by inserting triangles in each amorphous carbon ring and using the

Heron formula: where P=(a+b+c)/2 is the perimeter of a triangle of a, b, c sides; while the pore size diameter (PSD) is calculated as an approximation to the circle area. Periodic systems can be constructed using amorphous builder of BIOVIA Materials Studio, these are useful to calculate Radial Distribution Functions and the area under the curve on a significant interval.

Results

Chitosan Optimized by Applying Smearing

The default smearing value of 0.005Ha corresponds to T=1578.87 K and P=224.806 atm. We now exhibit electron smearing behavior using the known Fermi-Dirac statistic [38]. Facing two hydrogen atoms and using geometry optimization calculations, we built energy as a function of smearing value. Figure 1 shows the total energy variation when the system is optimized with respect to smearing value [39] (Figure 1). The fractional occupational pattern depends on the temperature, and this is derived from the energy change of Fermi distribution [6] as: 𝛿𝐸 = 𝑇𝑘; where k is Boltzmann constant. Considering a model in which the electrons are free and given that clouds of electrons are being a Fermi gas considered. The pressure is: 2/3 δE/δV [38]. From the latter two previous equations, temperature and pressure change is observed in Table 1 given the 𝛿𝐸 smearing energy. The planar molecular hypothetical system of 48 carbons is built by applying geometry optimization at two linear chains of 24 carbons as shown in Figure 2a, and the chitosan copolymer molecular system is built without applying geometry optimization, as observed in Figure 2b. Approaching enough these two molecular systems we studied a new molecular complex at different smearing values. The molecular model of carbon is symmetrically arranged in planar geometry, and it is physically activated through geometry optimization. We called activated carbon (AC) to the resulting planar carbon system. The length of this planar system is comparable to that one of chitosan (Ch). Each six-carbon ring has an area 4.34 Å2, each eight-carbon ring along with this has an area 8.74 Å2, each eight-carbon ring along with the sixteen-carbon ring has an area 8.55 Å2, and the sixteencarbon ring has an area 27.32 Å2. Considering each one of this area as circle areas the pore size diameter distribution is from 2.35 Å to 5.9 Å, which correspond to micropore size distribution of this carbon system. When considering the whole area of this system for calculating the pore size diameter 9.48 Å [40,41]. Chitosan is very well known to be macropore size [42].

Searching for a new molecular complex, Figure 3 exhibits the potential energy curve of the interaction between AC and Ch having equilibrium at (1.6Å, -1089Kcal/mol). In this case chitosan was not geometrically optimized in order to build the potential energy curve observed in Figures 3b & 3c. It was really easy to build this curve using smearing energy 0.05 Ha for every single point calculated, and hard to build it at 0.03 Ha. We also tried lower values than this, and we obtained poor or none results (Figure 3). After applying geometry optimization at smearing 0.05 Ha, and subsequently at 0.03 Ha. The smearing at 0.02 Ha is shown in Figure 4a. Then, we built the potential energy curve as shown in Figure 4b in step by step single point calculations for AC + Ch face to face interaction, when 2.264 Å is the separation between their corresponding centers of mass. The latter has a potential well depth of 165 Kcal/ mol at a distance of 2.2 Å, meaning formation of a new molecular complex at an adsorption energy greater than 20 kcal/mol in the chemisorption range [43] (Figure 4). Covalent connectivity [37] to the resulting system in Figure 4a was applied under the conditions previously mentioned in methodology, and the molecular complex observed in Figure 5 is obtained. In this complex the reactants and products are C48 + C14H24N2O9 and C49H3O3 + CH2 + C4H6O2 + CH3NO + C2H2O + CH2O + C2H2 + CHNO + CH3, respectively. Carbon bonds are single, double, and triple, as an example the C12 ring has eight double bonds, one triple bond, and three single bonds, where all the carbon valence electrons are shared. Furthermore, C8 and C16 rings have double bonds in one side of the ring, and single and triple bonds in the other side; and C6 ring has four double bonds and two single bonds. This whole carbon system has been activated by chitosan, and double bonds, and single and triple bonds are the representative characteristics of carbine-type molecules (Figure 5).

It must be noticed that geometry optimization of this whole system provides a lowest unoccupied molecular orbital (LUMO - electron acceptor) receiving an electron pair from the highest occupied molecular orbital (HOMO - electron donor). The donor HOMO from the base and the acceptor LUMO from the acid, combine with a molecular orbital bonding, which in our case corresponds to the orbitals 242-HOMO for E=-0.18317 Ha and 243-LUMO for E=- 0.17786, for a Fermi energy of -3136.28 Ha with A as irreducible representation of symmetry C1. The total orbitals number is 274. The orbital occupation is 202 A (2) plus 78 electrons in 65 orbitals, for a total number of 482 active electrons and binding energy of -22.997 Ha, at 2 steps. However, in order to get HOMO and LUMO drawn in this model, we run an energy calculation. Then, this molecular complex as seen in Figures 6a & 6b has HOMO-484 with E=-0.16398 Ha, LUMO-485 E=-0.16196 Ha, and Fermi energy Ef = -3161.44 Ha, for the reactivity sites with 482 active electrons. The total number of valence orbitals is 1070. The orbital occupation is 206 A (1) alpha and 206 A (1) beta, and 35.00 alpha electrons in 62 orbitals plus 35 beta electrons in 62 orbitals. HOMO as base-donor, and LUMO as acid-acceptor are the MOs locating possible reactivity in this reaction. An acid-acceptor can receive an electron pair in its lowest unoccupied molecular orbital from the base-donor highest occupied molecular orbital. That is to say, the HOMO from the base and the LUMO from the acid combine with a bonding molecular orbital in the ground state see Figure 6c.

After applying covalent connectivity [37] to the resulting system in Figure 6, we again applied geometry optimization for smearing 0.02Ha, and we obtain different molecular orbitals in the results, as shown in Figure 7. This molecular complex as seen in Figure 7 has HOMO-482 with E=-0.17650 Ha, LUMO-483 E=0.16060 Ha, and Fermi energy Ef = -3162.004 Ha, for the reactivity sites with 482 active electrons. The orbital occupation is 204 A (1) alpha and 204 A (1) beta, and 37.00 alpha electrons in 62 orbitals plus 37 beta electrons in 62 orbitals. The molecular complex observed in Figure 7 has the same products previously mentioned. It must be noticed that the lowest unoccupied molecular orbitals (LUMO-acceptor) only draw orbitals in the CH3 product, the rest of the molecular orbitals correspond to the highest occupied molecular orbitals (HOMOdonor) complex. Then, this is a very stable molecular system only allowing reactivity through the methyl radical CH3 (Figure 7) The potential energy curve in Figure 3b is very near to physisorption; however, smearing energy in this case corresponds with a very high temperature, which actually occurrs little inside sun surface. In this work, we gradually get down smearing energy searching until reaching the glass transition temperature of chitosan. The smearing energy value 0.02 Ha corresponds with temperature 6315.49 K according to Table 1, and it is still too high; however, is this way we have been achieving geometry optimization to reach right smearing values according to experimental measurements. After successful convergence in geometry optimizations at 0.01, 0.007, 0.005, 0.003, and 0.002 smearing energies, the convergence at smearing energy 0.0017 Ha has been unsuccessful after more than 10000 SCF iterations for an oscillating energy with an energy tolerance of 0.00002 Ha. After these calculations, we continued rising the smearing energy until 0.00175, and after more than 5000 SCF, convergence is successfully accomplished. The temperature 552.6 K reached for smearing at 0.00175 agrees with glass transition temperature range [498.15K, 553.15K] of chitosan, according to experimental measurements [20-22].

Figure 8 illustrates the final stage of the molecular complex formed. We can observe that while C48 has been deformed mainly in its planarity, the chitosan ended broken in the two initial groups of each polymer, also apparently divided in several smaller molecules. This fact is very well known experimentally, because one bonding solution (epichlorhydrine, glutaraldehyde, or EGDE -ethylene glycol glycidyl ether-) is commonly used to keep chitosan copolymer cross-linked for enhancing the resistance of sorbent beads against acid, alkali, or chemicals [19]. The products observed by applying covalent connectivity (under the bonding scheme for no bonding to s- and f- shell, covalent connectivity and bond type, and converting representation to Kekulé) are the following: C51H7NO4 + C4H6O2 + C2H2O + C2H2 + CH3O + CHNO + CH3. As it can be seen part of each polymer remain bonded to the AC system (Figure 8). Then, at smearing 0.00175 Ha we mostly obtain highest occupied molecular orbitals for the molecular complex observed in Figure 9. This output exhibits the orbitals a) HOMO-482 with an eigenvalue of -0.17013 Ha, b) LUMO-483 with an eigenvalue of -0.16923 Ha, and c) HOMOLUMO. The Fermi energy is Ef = 3162.0047053 Ha, for the reactivity sites with 482 active electrons. The orbital occupation is 238 A (1) alpha and 239 A (1) beta, and 2.96 alpha electrons in 5 orbitals plus 2.04 beta electrons in 4 orbitals.

Chitosan Optimized Without Smearing

First of all, the C24 carbyne-type ring alternating single and triple bonds is obtained by applying connectivity [37] and bond type to a C24 carbon ring which is the output of the input shown in Figure 10a corresponding to the geometry optimization of two hypothetical C12-carbon chains (Figure 10b). Then, Figure 10c exhibits an alternating single and triple bonds C24-ring. Second, applying clean of BIOVIA Materials Studio on chitosan copolymer molecule designed in Figure 2b, we obtain the input of a chitosan copolymer molecule as in Figure10d, and the Output exhibiting geometry optimization of the previous molecule is shown in Figure 10e. As we can observe, in this case chitosan remained complete. We made this, after suspecting that the initial bonds lengths and angles were not right in our design of chitosan, because broken chitosan is not a satisfactory result. Then, mixing the optimized C24 and Ch systems as shown in Figure 10f in the Input of a C24-ring surrounding a chitosan copolymer molecule, and after applying geometry optimization we obtain the Output of the previous CA-Ch nanocomposite see Figure 10g. Finally, we applied bonding scheme criteria as in Figure 10h.The nanocomposite in Figure 10h is a good example of the possibility of modifying the pore size distribution of chitosan when it is embedded into activated carbon. Here we consider INPUT and OUTPUT for applying geometry optimization on activated carbon and chitosan C14H24N2O9 system after each part has been previously optimized, and we also applied bond criteria for connectivity, bond type and kekulé representation. The C24-ring is carbyne type, and the chitosan copolymer molecule has been optimized in three dimensions in this case. The position of C24- ring surrounding a chitosan copolymer molecule has been only proposed.

From the interaction through geometry optimization of two linear carbon chains of four and five carbon atoms as in Figure 11a, cumulene C9-ring shown in Figure 11b is obtained. This is a clear evidence of Jahn-Teller effect, because we observe double bond lengths alternating long/short with a difference among .02 and .03 Å, and the angles in this non-planar (Figure 11b) cumulene molecule are also different. The expected angles in a planar symmetrical molecule should be the same according to a well-defined symmetry. We considered the interaction of chitosan with another almost planar carbon ring of nine carbon atoms, now one in front to the other as in Figure 11c. Then, in Figure 11d there is another example about building pore size distribution among chitosan and activated carbon. In this case, we consider INPUT and OUTPUT for geometry optimization of cumulene C9-ring and chitosan C14H24N2O9, each one previously optimized by applying geometry optimization to the whole system, and also considering the bond criteria for connectivity, bond type and Kekulé representation as shown in Figure 11e. The cumulene C9-ring and chitosan copolymer molecule have been optimized in three dimensions, and we clearly observe the cumulene passing from face to face to almost T-shape orientation taking three hydrogen atoms from chitosan. The input position of cumulene C9 ring face to face with chitosan in that precise location has been proposed, and the result has been excellent.

Discussion

We consider each carbon ring as physically activated through geometry optimization, due to pore size diameter remains in the average size compared against experimental measurements [41]. The C48 optimized ring carbon-system and one non-optimized chitosan copolymer unit has been studied considering the result after geometry optimization, as a molecular complex obtained when smearing value changes for converging energy values. Different elongation among single and triple carbon bonds in the carbyne-type are due to Jahn-Teller effect [14]. Then, C24 carbynering when we optimize two carbon chains at 3.074 Å of separation distance, is due to the Jahn-Teller effect. The Jahn-Teller effect is also present in C48 carbinoid -ring for their C8- and C4- carbinoid -rings. Carbon rings C4N (N<~8) exhibit a substantial first-order Jahn-Teller distortion that leads to long/short (single/triple) bond alternation decreasing with increasing N [14]. Whether we want to draw HOMO-LUMO orbitals, it is necessary to ask for orbitals in the geometry optimization as input data. At this work, for smearing energy 0.02 Ha we found different HOMO LUMO orbital numbers among the initial system in Figure 5 without asking for orbitals in the geometry optimization calculation, and its output asking for orbitals in a new energy calculation shown in Figure 6. Again after practicing connectivity, bond type, and Kekulé representation at smearing energy 0.02 Ha, we asked for orbitals, and we found in Figure 7 a small change at the orbital numbers previously obtained, and the corresponding energies were little different to the previous ones. We infer that bonding type change produced the differences, and the correct values correspond to the correct bonding type in the new molecular complex system formed.

The strongly dependence on smearing means very closely spaced energy levels (high degeneracy) near Fermi level. When there is a degenerate electron state, any symmetrical position of the nuclei (except when they are collinear) is unstable. As a result of this instability, the nuclei move in such a way that the symmetry of their configuration is destroyed, the degeneracy of the term is being completely removed [44,45]. High degeneracy indicates a high symmetry of the molecule, then the system tends to be distorted, in such way that when moving, the occupied levels are down and the unoccupied ones are up [46]. When levels are very densely spaced, convergence is hard to reach, since very small changes will occupy completely different states, and we get oscillations. These can be damped by smearing out the occupancy over more states, so that we turn off the binary occupancy of the states. We get down smearing width to glass transition temperature by decreasing the smearing parameter in steps to gradually stabilize our molecular complex system at the right temperature.

We initially observe distortion of chitosan system, and then its possible breaking in some products. This is partially in agreement with the results presented by Chigo et al. [46] in a study of the interaction among graphene-chitosan for a relaxed system doped with boron, in which they consider the interaction of pristine graphene with the monomer of chitosan (G + MCh:C6H13O5N) in different configurations, whereas we consider a chitosan copolymer molecule: C14H24N2O9 in only one orientation. While Chigo et al. [46] found a perpendicular chitosan, molecule linked to a carbon nanotube system, we obtained a cumulene carbon ring almost perpendicularly linked to a chitosan copolymer molecule.

Conclusion

We found one mechanism to figure out an optimized big molecular complex system by using DFT geometry optimization. This mechanism is based on smearing calculations, and on decrements of smearing energy in the molecular complex system until reaching the glass transition temperature of one of the components, which in this case correspond to the chitosan copolymer molecule. In order to get a molecular complex system AC + Ch, it is needed a high temperature among them at least to the phase transition temperature of either AC or Ch, because when they are solids there is only a heterogeneous mixture at room temperature. The use of smearing allows to reach high temperatures because according to Table 1 temperature increases as the smearing energy increases. We observed that the use of smearing to optimize a molecule as complex as the chitosan causes this to be fractionated, nevertheless when putting it in a plate of coal we obtained the glass transition temperature of the chitosan reported experimentally. The potential well depth providing chemisorption indicates existence of phase transition in one of our two molecular systems. This phase change is attributed to chitosan, due to carbon is more stable, and because we reach glass transition temperature of chitosan when dealing with the whole molecular complex system. In addition, when applying covalent connectivity, the activated carbon is the most stable molecular system keeping its molecular structure. According to HOMO and LUMO in Figures 6 -9, the sites with the greatest reactivity correspond to double and triple bonds. Besides, Figure 9 exhibits one amine functional group linked to the carbon system now C51 carbon molecular complex formed with a particular pore size distribution. Considering that after geometry optimization physisorption provides bonding in two parts of the chitosan molecule, this is an indication of a more environmental linking than that caused by cross-linking solutions, because cross-linking solutions might be toxic in medicine applications. The first chitosan molecule used, and optimized using smearing resulted to be unstable, because finished broken in several products. The second chitosan molecule used, and optimized without smearing, or with a very small smearing value resulted to be very stable, on which we were able to add activated carbon and to obtain good results. We have been able to optimize chitosan and add activated carbon, and we have observed the change in pore size distribution, even though we are missing its calculation, to assign the type of material obtained (micropore, mesopore, or macropore). We are working on it.

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