Lupine Publishers | Kinetic Isotherm Studies of Azo Dyes by Metallic Oxide Nanoparticles Adsorbent

Lupine Publishers | An archive of organic and inorganic chemical sciences

Abstract

We reported the synthesis of Cu4O3 nanoparticles fabricated by Camellia Sinensis (green tea) leaves extract as reducing and stabilizing agent and studied the azo dyes removal efficiency. The formation of copper oxide nanoparticles was confirmed after change in solution of salt and plant extract from green to pale yellow. Subsequently, the above said nanoparticles were characterized by SEM, XRD, FTIR, and UV spectrophotometer for size and morphology. The average particle size of copper oxide nanoparticle was found to be 17.26nm by XRD shrerrer equation, average grain diameter by SEM was calculated 8.5×10-2mm with spherical and oval shaped. UV spectroscopy range was between 200-400nm. These copper oxide nanoparticles were applied as azo dyes (Congo red and malachite green) degradation. Effect of reaction parameters were studied for optimum conditions. Kinetic models like Langmuir, Freundlich and elovich models were applied. Finally, concluded that these particles are effective degradation potential of azo dyes at about 70-75% from aqueous solution.

Keywords: Green Tea; Cu4O3; Green synthesis; XRD; Congored; Malachite Green

Background

With elevating improvement in technology, the Scientific developments are approaching to new horizons [1]. Besides supplementary needs, the stipulation of industrial wastewater has increased swiftly, supervened in the huge amount of wastewater including azo dyes. Azo dyes are the foremost group of commercial pollutants [2]. Azo dyes are class of synthetic dyes with a complex aromatic structure and contain two adjacent nitrogen bond (N=N), that can accompany color to materials [3]. Furthermore, the aromatic structures of dyes form them sturdy and not- biodegrade [4]. Textile consume prodigious quantities of hazardous chemicals particularly in dyeing operations. This work is constructed on malachite green and congored azo dyes. The toxic Habit of the azo dyes can be elaborated by fact that upon decomposition it breaks up into hazardous products [5]. The MG and CR azo dyes toxic dye which has been removed from water samples through the physical, chemical and biological methods. Azo dyes are toxic, probably cause aesthetic problems and mutagenic and carcinogenic effects on human health, so must be degraded [6]. Therefore, the adsorption method by using copper oxide metal nanoparticles for wastewater treatment comprised with azo dyes. Cu4O3 nanoparticle were applied as an adsorbent for the degradation of MG and CR dyes and its kinetic and isotherm studies. Biogenic technology is regarded an emerging advancement of the current time which has been utilized to synthesize nanoparticles of a desired shape and size by using plant extract [7]. Consequently, the synthesized nanoparticles using innovative techniques which is used as cost-friendly reagent and less reactive. The work symbolizes application of conventional physical and also chemical methods for decolorization of azo dyes. physical method includes osmosis, filtration, adsorption and flocculation. the chemical method (oxidation, electrolysis) and biological method (microorganism, enzymes) are also applicable [8]. Green technology deals with the manipulation of matter at size typically b/w 1-100nm range. Nanoparticles having high surface to volume ratio responsible for enhanced properties [9]. Specific area is appropriate for adsorption property and other relevant properties such as dye removal [10].

Azo dye normally has aromatic structure and N=N bond that’s why they are hardly biodegradable [11,12]. These dyes have also mutagenic and carcinogenic effect. Normally, conventional methods have considerably less potential of degradation. Copper oxide nanoparticles have efficient power of dyes removal [12-17]. Most probably, copper oxide are low cost and novel adsorbent of azodyes. Copper oxide nanoparticle has efficiency of azo dyes removal from wastewater [12]. Malachite green dye (C23H25N2 with molar mass364.911g/mol) is organic in nature. Its lethal dose is 80mg/kg the structure of malachite green dye is in Figure 1 below. Congo red an azo dye is sodium salt of 3,3′-bis structure. Congo red dye is water soluble, its solubility is enhanced in organic solvents. Its molecular formula is C32H22N6Na2O6S2 with molar mass of 696.665 g/mol [13- 14]. The structure is given below Figure 2. The Camellia synesis is evergreen small tree. The Camellia synesis leaves act as capping and reducing agent during the synthesis of metal nanoparticle. There are certain properties of green tea extract such as antitumor, antioxidant, anticoagulant, antiviral, blood pressure and lowering activity [18-22] (Figure 3). Plant extract has some chemicals like phenols, acid, vitamins, responsible for reduction of metal [23]. Camellia synesis leaves have polyphenols, catechins (ECG), OH groups which cause copper metal reduction (Table 1). Copper oxide Cu4O3 is known as paramelaconite material in tetragonal shape. Plants contain a wide range of secondary metabolites included phenolics help a vital role in the reduction of copper metal ions yielding nanoparticles [24]. Thus, ideally be used for the biosynthesis of nanoparticles. Copper oxide Cu4O3 is known as paramelaconite material in tetragonal shape. Copper nanoparticles synthesis by using green tea has Nano range particle size confirmed by characterization [25-28]. This is One-step processes in which no surfactants and other capping agents used.

Aims of Study

The main aim of the study was

To extract copper nanoparticles using camellia sinensis leaves

a) To characterize the copper NPs

b) To study its potential to degrade azodyes

c) To find out the effect of different experimental parameters on %degradation.

d) Kinetic study of adsorption of congored and malachite green dye

Method

Material and Method

The material used for the preparation of copper nanoparticles Cu4O3 includes copper sulfate (CuSO4.5H2O from Sigma Aldrich) and camellia sinensis leaves (from botanical garden of institute) for the preparation of green tea extract. All chemicals used were of analytical grade and pure (Figure 4).

Preparation of Green Tea Extract

Green tea leaves of 30g were taken and then washed with distilled water. further, the leaves were dried and then ground. The powder of green tea was used in the formation of extract [29]. The 100ml of deionized water was used. Later, the solution was boiled for 10 minutes and subsequently kept at low temperature after filtration.

Preparation of Cu4O3 Nanoparticles

A copper sulfate soln. of 50ml was added into 5ml of green tea extract. Magnetic stirrer was used for stirring. The color changed from green to pale yellow and finally dark brown confirmed the formation of nanoparticles. After the formation of nanoparticles, solution was centrifuged at the speed of 1000rpm for 20 mins. After the removal of supernatant copper oxide nanoparticles were dried and washed with ethanol. At the end calcination was performed at 500 degree for one hour and resultantly black colored particles were collected for characterization [27-29].

Results

Characterization of Cu4O3 Nanoparticles

UV spectrophotometer, X-ray diffractometer (XRD), Fourier transform infrared spectrophotometer (FTIR) and Scanning electron microscope (SEM) were used in order to characterize the size, shape, chemical and structural composition of Cu4O3 nanoparticles [30]. During the study, the green color soln. transformed into dark brown which confirm the formation of copper oxide nanoparticles.

X-Ray Diffraction Studies

The X-ray diffraction pattern of copper oxide nanoparticles were examined by x-ray diffractometer. To determine the intensity of copper oxide nanoparticles, the powder was added in the XRD cubes for analysis. The resultant pattern of the copper oxide nanoparticles was matched with JCPDS card number (033-0480), the peaks at 2θ intensity 28.09, 30.61, 36.14 and 44.14 and have 112, 103, 202 and 213 patterns respectively. However, average crystal size calculated by the Scherrer equation keeping lemda at 0.154 and FWHM value calculated 0.5 found was 17.2nm. The shapes of the particles of Cu4O3 nanoparticles in XRD was tetragonal [31-33].

Name and Formula

Reference code: 00-033-0480

Mineral name: Paramelaconite

Compound name: Copper OxideEmpirical formula: Cu4O3

Chemical formula: Cu4O3

Ultraviolet Spectroscopy:

The range at which copper oxide nanoparticles appeared was 200-400nm. The maximum absorption peak was confirmed at 280nm which confirmed the copper oxide nanoparticles (Figure 6).

FTIR Analysis:

In the current study, FTIR spectrum was examined to determine the copper nanoparticles functional group peaks. The overall peak was observed in ranged from 400 to 4000cm-1. The spectrum at peak 3310.7cm and 1611.2cm revealing the (Figure 7) presence of alcoholic group. The bands at 3310.7cm- 1, and 2850cm-1 another functional group present are listed in table below (Table 2).

SEM Analysis:

The average particle size of copper nanoparticle was analyzed by SEM model (JSM-6480). The range of grain of copper oxide nanoparticle was calculated about 8.5 ×10-2mm by SEM micrograph. The prepared copper oxide nanoparticles were well dispersed. It was observed that particles were smooth with a tetragonal shape (Figure 8).

Removal of Malachite Green and Congo Red Azo Dye by Cu4o3 Nanoparticles

Preparation of Standard Solution: In 1-liter distilled water, the dye was dissolved to prepare 1000ppm solution of malachite green and Congo red. From stock solution different concentrations of dyes were prepared. After dilution from 1000ppm solution to 100ppm solution was prepared. From that 150, 200, 250-ppm solution were prepared. Efficiency of Color removal was calculated by percentage degradation formula

% decolorization of dye= A-B /A×100.

Where A and B are absorbance of dye solution without nanoparticles and with particles respectively.

Mechanism of Azodye Degradation

50 microliter of the hydrogen peroxide H2O2 was added as the oxidizing agent to yield hydroxyl radical. Catalytic activity process mainly depends on the formation of superoxide anion radical and hydroxyl radical. The concentration of CR and MG dyes in aqueous solutions were measured by UV–vis spectrophotometer. A reducing agent H2O2 was added with adsorbent to check the adsorption capacity.

Effect of Experimental Parameters On % Degradation of Dye Removal

Time effect: Effect of time on percentage degradation of azo dyes was also studied by UV spectrophotometer. The samples of copper oxide NPs synthesized by green tea C-1, C-2(GT) were calculated. The time required for removal of above said dye was between (40-45min) and percentage removal was observed for all samples between 70-75%. The result of graphs clearly shows the time effect on color degradation of azo dye malachite green-MG and acid red 28-CR by using adsorbent copper oxides nanoparticles. The experimental conditions during experiment were kept constant just like temperature 308 kelvin and initial concentration of adsorbent was within ranges from 20- 250mg/l. Samples C-1, C-2 are samples codes synthesized by camellia sinensis leaves extract at different temperatures. In figure below C-1 sample is dye+ adsorbent +H202 and C-2 sample without reducing agent. It was concluded from graphs %degradation enhanced in presence of reducing agents. Figure 9 Effect of time by copper oxide nanoparticles samples C-1, C-2(Green tea mediated) on malachite green dye and Congo red dye calculated by ultraviolet spectrophotometer DB-20.

Adsorption Kinetics Studies: The kinetics of azo dye adsorption was carried under selecting optimum operating conditions. The kinetic parameters are helpful for the estimation of adsorption rate. A solution prepared by dissolving 20mg of adsorbent in 50ml of 10ppm dyes and continuously stirred.

Adsorption Kinetic Studies of Copper Oxide NPs: The pseudo-second-order model was found to explain the adsorption kinetics most effectively. The results indicated a significant potential of nanoparticles as an adsorbent for azo dye removal. The straight line shows that nanoparticles follow pseudo-second-order kinetics rather than first orde

Adsorption Reaction Isotherm Models

Langmuir Isotherm Model: The Langmuir isotherm is applicable for adsorption of a solute as monolayer adsorption on a surface having few numbers of identical sites. Langmuir isotherm model provide energies of adsorption onto the plain. That’s why, the Langmuir isotherm model is selected for adsorption capacity relating to monolayer surface of adsorbent. Adsorption process fits the Langmuir and pseudo-second-order models. Langmuir isotherm or single crystal surfaces describes well adsorption at low medium coverage, adsorption into multilayer is ruled out. Parameters of different models studied in this research are listed below in Table 3.

Freundlich Isotherm Model: The Freundlich isotherm model is suitable for the adsorption of dye on the adsorbent. Freundlich equation is stated below

In qe = Kf qm+ 1/n InCe

qe is the amount used of azo dye in unit of mg/g, Ce is the equilibrium concentration of the azo dye and Kf and n are constants factors affecting the capacity of adsorption and adsorption speed. The graph between lnqe versus ln Ce shows linearity. The adsorption reaction isotherms are fitted to models by linear square method. The result shows in this study that Langmuir model fit better than the Freundlich model. The adsorption activity of copper oxide nanoparticle samples prepared by green source were observed against the degradation of malachite green and congored azodyes (Figure15).

Discussion

In present we reported an eco-friendly and cost-efficient preparation of copper oxide nanoparticles by leaf extract of camellia sinensis. the characterization of particles were performed by SEM, UV, XRD, FTIR analysis. UV spectroscopy peak was observed at 280nm and a broadband observed which confirmed nanoparticles existence. The particle size was calculated by Scherrer equation was 17.26nm. The SEM results confirmed tetragonal shape of cu403 particles with grain average diameter 8.5×10-2nm, and FTIR spectra indicated the peaks of OH, C=C, C-H functional groups, which is due to thin coating of extract on nanoparticles. The calculated surface area of nanoparticles was 65m2/g. The %degradation of azo dyes malachite green and congored range were b/w70-75% at maximum 0.2g/l and 20mg/l dosage of adsorbent and dye. The optimum time was b/w 30-40mint, PH 3-4, temperature 70-80 Co for maximum degradation. The effect of different experimental parameters was studied on percentage degradation of dyes. The azo dyes congored and malachite green dyes adsorption isotherm models were studied. The reaction kinetics followed pseudo second order for both dyes rather than first order. The Langmuir model fit better with linearity rather than Freundlich, which confirmed by graph having r2 0.98,0.99and0.95 values for models. The elovich model also linear fit. In conclusion, copper oxide nanoparticles keep excellent azo dyes degradation potential.

Conclusion

In present we reported an eco-friendly and cost-efficient preparation of copper oxide nanoparticles by leaf extract of camellia Sinensis. According to kinetic study it proved that Cu4O3 NPs keep excellent adsorption capability for MG and CR azo dyes.

https://lupinepublishers.com/chemistry-journal/pdf/AOICS.MS.ID.000174.pdf

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Lupine Publishers | Phytochemical and Antimicrobial Screening of the Leaves of Crotalaria Lachnosema Against Staphylococcus Aureus, Salmonella Typhi, Escherichia Coli and Klebsiella Pneumoniae

 Lupine Publishers | An archive of organic and inorganic chemical sciences

Abstract

The leaves of Crotalaria lachnosema were freshly collected, dried under-shade and ground into powder. The ethanolic extract of the sample was obtained by cold extraction and was fractionated with solvent of varied polarity. The fractions were analyzed for their phytochemicals and screened antimicrobial against Staphylococcus aureus, Salmonella typhi and Escherichia coli. The phytochemicals were distributed among the test fractions. Tannins were found to be present in all the fractions and methanol fraction contains all the other tested phytochemicals except alkaloids and cardiac glucosides. The activities of the fractions were found to be more pronounced against E. coli than against the other test organisms.

Keywords: Phytochemical Screening; Antimicrobial; Crotalaria lachnosema; Staphylococcus aureus; Salmonella aureus; Salmonella typhi; Escherichia coli; Klebsiella pneumoniae

Introduction

For many centuries, man explores and utilizes the natural endowment offered by both the species of flora and fauna to provide the basic necessity of life such as clothing, shelter, food and indeed health care. Medicinal plants are the richest and commonest natural resource used in traditional medicine. Of the 250, 000 higher plant species on earth, more than 80,000 are medicinal [1]. Although plants had been priced for their medicine, flavoring effect and aromatic qualities for centuries, but the synthetic products of the modern age had for some time surpassed their importance. However, the blind dependence on synthetics is over and people are returning to the naturals with hope of safety and security [1]. The development of drug resistance in human pathogens against commonly used antibiotics has necessitated a search for new antimicrobial substances from other sources including plants [2]. Many reports have attested the efficacy of herbs against microorganisms, as a result, plant is one of the bedrocks of modern medicine to attain new principles [3]. The therapeutic properties of plants may not be unconnected to the variety of chemical substances biosynthesized by the plants as “secondary metabolites’’ that bring about definite physiological action in the human body. The most important of these bioactive constituents of plants are alkaloids, tannins, flavonoids, saponins and etc. [4]. Presently many governments and major health institutions including the World Health Organization [5] have recognized, pharmacologically validated and improved many traditional herbal medicines and eventually integrated them in formal health care system [1]. Thus, in light of the evidence of rapid global spread of resistant clinical isolates, the need to find new antimicrobial agent is of paramount importance. However, the past record of rapid, widespread emergence of resistance to newly introduced antimicrobial agents, indicates that even new families of antimicrobial agents will have a short life expectancy [6]. For this reason, researchers are increasingly turning their attention to herbal products, looking for new leads to develop better drugs against MDR microbe strains [7].

Crotalaria lachnosema belongs to the family Fabaceace (Leguminoseae), sub-family Papilionoideae. It is a woody plant with a height of about 2 cm high. The plant is known as ‘Fara birana’ in Hausa, ‘komp’ in Yoruba, ‘Ake dinwo’ in Ibo and Birjibei in Fulani [8]. The genus Crotalaria is widespread in the tropics and subtropical region and has about 550 species [9]. C. lachnosema was found to be important in the treatment of scabies. The whole plant grounded and mixed with water are fed to animals to treat liver disease [8]. The presence of resins and balsams might support the use of the plant as emollient as well as for treatment of sore throat, rheumatism, wounds and burns. Since some basalms and resins has antiseptic properties [3]. Few species of Crotalaria have been assessed against some pests. For example, under greenhouse condition, C. retusa and C. juncea have been found to be resistant to attack by the nematode, Pratyylenchus zeae and also that C. retusa has shown a higher degree of resistance to attack by the nematode, Rotylenchus rnifirmis Linford and Olivera. It was also reported that, the non-polar extract of C. retusa contain some active ingredients for controlling flea beetle a pest on okro plant. So, could be useful in pest management [10].

Materials and Methods

Sampling and Sampling Sites

The leaves of Crotalaria lachnosema were freshly collected on 4^th July 2011 at an uncultivated land in Damanko village about 9km west of Zaria main town, Zaria Local Government, Kaduna State. The plants were identified and authenticated by Mallam Umar Shehu Galla of the Herbarium unit, biological science, Ahmadu Bello Univesity, Zaria. The leaves of the plant were dried under-shade for seven days and ground into powder using clean pestle and mortar.

Extraction and Fractionation of Plant Materials

Cold extraction (Percolation) was adopted in this research, this is part of the appropriate measure to preserve constituents that may potentially be active and retain their original identities in the course of preparing the extract [11]. 200g of the powdered plant sample was weighed and sucked in1000cm3 of ethanol for 14 days. The crude extract was prepared by decantation, filtration and concentration of the filtrate using Rota vapor machine (RVO) at 400C and finally by drying the concentrated crude ethanol extract. Fractions of various degrees of polarities were obtained from ethanol extract by macerating the ethanol extract with different solvents in sequence starting with solvent of least polarity to the one of highest polarity [12]. For the fractionation, 30cm3 of n-hexane was poured into the beaker that contained the dried and gummy ethanol extract and stirred for 5minutes and the liquid portion was then drained into another cleaned and empty beaker. This process was repeated until a clear solution was obtained at the end. The entire procedure was repeated with other solvents in the series; chloroform, ethyl acetate and methanol. Four fractions were thus obtained from the exercise and were labeled as followed: n-hexane fraction, chloroform fraction, ethyl acetate fraction and methanol fraction.

Phytochemical Screening of Plant Sample

The phytochemical analyses of the fractions were conducted by subjecting the fractions to different standard confirmatory tests. This is to determine the presence of certain phytochemical classes.

Test for Alkaloids: Each fraction (0.5g) was stirred with 5ml of 1 percent aqeous hydrochloric acid on a steam bath; 1ml of the filtrate was treated with a few drops of Mayer’s reagent and a second 1ml portion was treated similarly with Dragendoff’s reagent. Turbidity or precipitation with either of these reagents was taken as evidence for the presence of alkaloids in the extract being evaluated [13].

Test for Saponins: Each fraction (0.5g) was shaken with water in a test tube. Frothing which persists on warning confirmed the presence of saponins [14].

Test for Tannins: Each fraction (0.5g) was stirred with 10ml of water. This was filtered, and ferric chloride reagent was added to the filtrate, a blue-black precipitate indicated the presence of tannins [15].

Test for Flavonoids: A portion of each fraction was heated with 10ml of ethylacetate over a steam bath for 3mins. The mixture was filtered and 4ml of the filtrate was shaken with 1ml of dilute ammonia solution. A yellow colouration indicated the presence of flavonoid.

Test for Reducing Sugar: 1ml of each fraction was taken in five separate test tubes. These were diluted with 2ml of distilled water followed by addition of Fehling’s solution (A+B) and the mixtures were warmed. Brick red precipitate at the bottom of the test tube indicated the presence of reducing sugar [16].

Test for Cardiac Glycosides: 2ml of each fraction was placed in a sterile test tube. This was followed by adding 3ml of 3.5% iron III chloride (FeCI3), then 3ml ethanoic acid. This gave a green precipitate and a dark colored solution respectively. Finally, concentrated H2SO4 was carefully poured down the side of the test tub e which resulted in the formation of brownish red layer, at the interface. This confirms the presence of cardiac glycosides.

Antimicrobial Activity Test

Agar disc diffusion technique was adopted for the sensitivity test as described by [17].

Preparation of Test Fractions’ Concentration: Discs of about 6mm diameter were punched from Whatman’s No 1 filter paper using a paper puncher. Batches of 10 of the paper discs were transferred into vial bottles and sterilized in an oven at 1400C for 60 minutes. Stock solutions of 100mg/ml of the fractions were prepared by dissolving 200mg of each fraction in 2ml of DMSO (Dimethyl sulphoxide). By means of 1ml sterile syringe, 0.1ml, 0.2ml, 0.5ml and 1.0ml were transferred into labeled vial bottles preoccupied with 10 paper discs from a stock solution of each fraction and the solution were subsequently diluted with 0.9ml, 0.8ml, 0.5mland 0.0ml (i.e. without dilution) of DMSO that correspondingly resulted to 1mg/disc, 2mg/disc, 5mg/disc and 10mg/disc concentration. The prepared concentrations of the test fractions in the labeled bottles were kept in refrigerator until required for use.

Preparation of Inoculum from the Test Micro-Organisms: Staphylococcus aureus, Salmonella typhi, Escherichia coli and Klebsiella pneumoniae that were sourced from Microbiology unit of Aminu Kano Teaching Hospital (AKTH) Kano, were the microorganisms used for the research. The identities of the microorganisms were confirmed by standard biochemical test [18]. The test organism was cultured and maintained in a nutrient agar slant at 40C. The organism was then inoculated into nutrient broth and incubated overnight at 370C for 24 hrs. They were then diluted with normal saline until they give concentration of bacterial cells equivalent to 0.5 McFarland standard of Barium sulphate solution (1% v/v) [19].

Antibacterial Susceptibility Test (Bio Assay)

A suspension of nutrient agar (28g in 1000ml of distilled water) was prepared and autoclaved at 1210C for 15mins according to the manufacturers’ instruction. It was then carefully poured into sterile petri-dishes and allowed to solidify. The standardized inoculums of the bacteria were swabbed on the surface of the solid nutrient agar plates by means of sterile wire loop for the confluent growth of the bacteria. Four paper discs of 10mg/disc, 5mg/disc, 2mg/ disc, 1mg/disc concentrations were taken from the prepared test fraction solutions and were carefully and aseptically placed on the inoculated surface of the nutrient agar and a positive control disc (Tetracycline 1mg/disc) was placed at the centre of the plate. The plates were incubated inverted at 370C for 18 hours. The diameters of clear areas surrounding the discs where growths of the organisms were impeded (Zone of inhibition) were measured in millimeter and recorded. The assay was repeated two more times. The mean and the standard deviation (±SD) for the triplicate values were then calculated.

Results and Discussion

Tables 1-3 Mean of the triplicates ± S.D (standard deviation). A total ethanolic extract of 16.05g was produced from the 200g powdered plant sample. The highest percentage mass (63.05%) of the total mass macerated was methanol fraction and the least percentage mass (0.56g) was the pet. ether fraction. The result of phytochemical analysis revealed the availability of some secondary metabolites in the fractions of the plant sample. The presence of these secondary metabolite’s accounts for the activities of the plants. This complied with several reports by researchers that plants contain bioactive substances. Tannins were detected in all the fractions of the plant sample and tannins were reported to have various physiological effects like anti-irritant, anti secretolytic, antiphlogistic, antimicrobial and antiparasitic effect. Phytotherapeutically, tannins containing plants are used to treat non-specific diarrhea, inflammations of mouth and throat and slightly injured skins [20-22]. While cardiac glucosides which are used as lexative and carthatic drugs were confirmed in chloroform and ethyl acetate fractions. Alkaloids that were present in n-hexane and chloroform fractions act as antimalarial and anti-amoebic agents [22]. The antimicrobial sensitivity test result revealed a varied degree of activities exhibited by the fractions of the plant against the test organisms. Although, the plant sample exhibited low activities when compare to the control, the results show that activity of the different fractions may increase further if the concentrations of the fractions were to be increased. The result also showed that the activities of the plant fractions were comparatively more pronounced against E. coli than against S. aureus, S. typhi. and K. pneumoniae. With the exception of chloroform fraction that demonstrated some activities against S. aureus with zone of inhibition of 12mm at1000ug/disc all other fractions were inactive against S. aureus. However, n-hexane and ethyl acetate fractions exhibited low activities against S. typhi.

Conclusion

The activities of the fractions of the plant sample are more pronounced against E. coli than against the other test organisms. E. coli can cause diarrhea, urinary tract infections, respiratory illness, bloodstream infections and other illness. So, the plant leaves can be used in the treatment of the aforementioned illnesses. However, the relative low activities of the plant sample fractions against S. typhi and K. pneumoniae revealed its un-befitting nature as an antityphoid and anti-pnuemoniie drug.

Recommendation

The other parts of the plant should also be exploited. To harness its full medicinal potential, the plant sample fractions should be tested against other bacteria isolates and further research should be carried out to isolate and characterize the active compounds in the plant.

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Lupine Publishers | Structures and Electrical Properties of Some Biologically Active Nucleic Acid Constituents

 Lupine Publishers | An archive of organic and inorganic chemical sciences

Abstract

Zinc II, cadmium II and mercury II complexes derived from barbituric acid (BA), 5-nitrobarbituric acid (NBA), phenobarbital (PB) and 2-thiouracil (TU) were synthesized. The analytical results assigned the formation of complexes with the stoichiometries 1:1 and 1:2. The infrared spectral measurements assigned, and bands. The tetrahedral geometries are given for these complexes. The capacitance (CP) and the dielectric constant of the complexes are decreased with increasing the applied frequency and increased with increasing temperature. The behavior of the dielectric loss (e”) indicated a polar polarization mechanism. The loss tangent (tan d) is decreased with increasing frequency and increased with increasing temperature while the impedance (Z) is mostly decreased with increasing both of frequency and temperature. Cole-Cole diagrams for the complexes at different temperatures reveal non-Debye type of the complexes. The relaxation time (t) for each relaxator becomes smaller as the temperature increases. In most complexes, the conductivity – temperature relationship is characterized by a phase transition temperature. Two pathways for the conduction of electricity may be expected at lower and upper temperature regions: n ® p* and p ® p* transitions, respectively. The relative permittivity, dielectric loss and conductivity values for the complexes revealed semiconducting features based mainly on the hopping mechanism. The lower values of the activation energy (DE) may be understood assuming that the metal ion forms a bridge with the ligands, thus facilitating the transfer of current carriers with some degree of delocalization in the excited state.

Keywords: Ligands and Complexes; IR Spectra; Dielectric Properties; Electrical Conductivity; Cole-Cole Diagrams and Activation Energy

Introduction

In today’s age of molecular biology purines and pyrimidines are probably best known as the basic constituents of the nucleic acids which are biomolecules that store genetic information in cells or that transfer this information from old cells to new cells. A number of pyrimidines were tested for their ability to inhibit nuclear and mitochondrial (uracil- deoxyribonucleic acid (DNA) glycosylase) activities also, 2-thiouracil, a ribonucleic acid (RNA) synthesis inhibitor, reduces the fertility of photoperiod sensitive genic male- sterile rice. Some nucleobase analogous were screened as inhibitors of dihydrouracil dehydrogenase (DHU dehydrogenase) from mouse liver. 5-Nitrobarbituric acid was identified as a potent inhibitor [1]. Since most living systems contain metal ions which are essential for proper functioning, question arises as to study the effect of such metal ions on nucleic acids. Any elucidation of metal ions effects on the pyrimidine nucleus could possibly lead to a better understanding of complex biological processes occurring in living system. Transition metals possess great biological activity when associated with certain metal-protein complexes which participate in the transport of oxygen and electronic transfer reactions [2]. Platinum group metal complexes of nucleic acid bases and their derivatives attracted considerable attention because of their antitumor and antibacterial activity [3]. The biological activity of cisplatin is due to its ability to bind the guanine-cytosine of the DNA strand and stop the replication process [4]. Cisplatin has been used in treating several human tumors of the genito-urinary type [5].

DNA strands can curl up to produce some amazing structures, and they can bind to metal ions. DNA has served as an ingenious storage device for genetic data for more than three billion years. But only few years ago, it has also emerged as a powerful material for building complex structures at the nanometer scale. Masoud and coworkers published a series of papers about pyrimidine complexes, the most recent references are cited [6-12]. So, in a sequel of continuation, the present paper is focused to study the complexing properties and electrical applications of some biologically active nucleic acid constituents (barbituric acid, 5-nitrobarbituric acid, phenobarbital, and 2-thiouracil).

Experimental

A- Synthesis of Complexes

The required metal salts were dissolved and mixed with the required weight of the ligand solutions. The selected ligands are shown in the following (Scheme 1).

Barbituric acid (BA), 5-nitrobarbituric acid (NBA), phenobarbital (PB), and 2-thiouracil (TU).

I. Metal ion content

The complexes were digested and decomposed with aqua regia. The contents of Zn²⁺, Cd²⁺ and Hg²⁺ were determined by the usual complexometric titration procedures [13].

II. Carbon, hydrogen, nitrogen and sulfur contents were analyzed as usual.

C- Instruments and Working Procedures

Infrared Spectrophotometer

The spectra of ligands and their complexes were recorded using Perkin-Elmer Spectrophotometer model 1430 covering the frequency range 4000-200cm^-1, by the KBr disc method.

Dielectric and Electrical Conductivity Measurements

i Four test parameters including impedance |Z|, phase angle θ, parallel equivalent static capacitance CP and loss tangent tan δ were measured for the complexes Zn(BA)₂, Cd(BA)₂.2H₂O, Zn(NBA).2H₂O, Cd(PB)₂.H₂O and Zn(TU).H₂O in the solid state at constant voltage 0.80 volt. The measurements were taken at different temperatures (26-190°C) and variable frequencies (4 kHz-100 kHz) using HIOKI “3532-50 LCR HITESTER” instrument.

ii The complexes were prepared in the form of tablets at a pressure of 4 tons/cm2.The tablets were hold between two copper electrodes and then inserted with the holder vertically into cylindrical electric furnace. The potential drop across the heater was varied gradually through variable transformer to produce slow rate of increasing the temperature to get accurate temperature measurements using a pre-calibrated Cuconstantan thermocouple attached to the sample.

iii The dielectric constant ε, the dielectric loss e², real part of impedance Z′, imaginary part Z″, the conductivities σ_a.c. the relaxation times τ_o , τ and the activation energies ΔE of the complexes were calculated [14] and correlated with the structures.

Results and Discussion

Mode of Bonding and Stereochemistry of the Prepared Complexes

The IR spectra of the free ligands and their metal complexes were studied, usually, a charge transfer takes place from the ligand to the metal ion resulting in a decrease in the force constant of the bond reflecting a red shift of the band position. In some cases, a blue shift occurs for a reverse process, i.e. electrons are donated from the metal ion to the coordinated groups leading to increase the bond order of the groups bonded to the metal ion [15]. Most of the prepared complexes contain water. Generally, lattice water absorbs at 3550-3200cm^-1 (asymmetric and symmetric OH stretchings) [16], and at 1630-1600cm^-1 (HOH bending). Also, the rocking and metaloxygen stretching modes will become infrared active if the metaloxygen bond is sufficiently covalent. The presence of these bands in aqua complexes was reported at 880-850cm^-1 and assigned to the rocking mode of coordinated water [17]. Infrared data illustrated the following main points

b) Shifts of the band of the free ligand occurred upon complexation, due to the existence of coordinated water molecules or M-O and hydrogen bond formations [19], However, is assigned.

c) The shifts or disappearance of both the bands, (Table 1) suggest that these groups are strongly involved in the structural chemistry of the complexes. This is supported either by the probable existence of M-N bands or the free ligand may be subjected to keto enol tautomerism [20,21].

d) New IR bands of the complexes appeared at (528- 523cm^-1) and (316-315cm^-1) assigned as , respectively. The bands of BA are shifted on complexation, indicating M-O interaction.

e) Barbituric acid is of bidentate or tridentate bonding according to the complex stoichiometries, (Scheme 1) The bidentate chelation is suggested to be through N(1) and C(2) O while the tridentate interaction is via C(2)O, N(3) and C(4)O.

In Case Of NBA, (Table 2) The Infrared Data, Illustrated the Following Main Points:

a) The broad band at 3433cm^-1 in the free ligand is shifted to 3561 and 3559cm^-1 for ZnII and CdII complexes, respectively [22]. Two bands for the free ligand at 3173 and 3028cm^-1 are identified. On complexation, the former band for the ligand becomes doublet at (3170, 3146cm^-1) and (3170, 3141 cm^-1) for ZnII and CdII complexes, respectively. However, the latter band is shifted to 3024 and 3025cm^-1 for ZnII and CdII complexes, respectively.

b) The medium CH υ band at 2836cm^-1 for the free ligand excluded the possibility of the formation of an organometallic compound. However, the band in the free ligand (NBA) is not remarkably affected on complexation suggesting that the C=O in position (6) is still exist in the complexes.

c) The observed medium C N υ = band in the free ligand at 1651cm^-1 may be due to tautomerism. It is shifted (-3cm^-1) for both ZnII and CdII complexes in strong feature. Such data suggest that the nitrogen atom of the pyrimidine ring formed by tautomerism is bonded to the metal ion.

d) The nitro group is not involved in coordination.

In case of thiouracil (TU), the NH group either participates in bond formation with the metal ion or tautomerised with the adjacent C=S and C=O groups to form the enol-thiol tautomers. The latter view is verified by the presence of C N υ = , C O υ − and bands at 1626, 1390 and 1001cm^-1, respectively [23]. 2-Thiouracil acts as dianionic and tridentate chelator through C(2)S, N(3) and C(4)O. From the previous findings, together with the elemental analyses, the following structures for NBA complexes are given: (Scheme 2)

B- Dielectric and Electrical Conductivity Measurements

Dielectric Measurements

For a parallel-plate condenser in which a dielectric tablet fills the space between the plates, the capacitance is given by [26]:

 

where o ε is the permittivity of a vacuum and its value is approximately 8.854 × 10-12 F m-1,

ε is the dielectric constant of a dielectric, A and d are the area and thickness of the tablet, respectively.

The real and imaginary parts of the complex impedance are given by:

where Z′ and Z″ are the real and imaginary parts of the impedance, respectively.

Dispersion arising during the transition from full orientational polarization at zero or low frequencies to negligible orientational polarization at high radio frequencies is referred to as dielectric relaxation. The rate of decay and build-up of the orientational polarization, as given by the relaxation time τ, will depend upon the thermal energy of the dipoles as well as upon the internal or molecular friction forces encountered by the rotating dipoles. The dielectric parameters are given in terms of temperature and frequency changes, e.g. Zn(BA)₂ (Figure 1). The more spotlight points could be given as follows:

I. The capacitance (CP) and the dielectric constant decreased with increasing the applied frequency in some different ranges which probably due to that the polarization does not occur instantaneously with the application of the electric field.

II. The variation of the permittivity values with increasing temperature at certain constant frequency revealed small dielectric constant at lower temperatures, where the molecules are rigid, i.e. less oriented forces. By increasing the temperature, the number of molecules capable of rotating about their long axes increased with higher permittivity values. The behavior of the dielectric loss e² values, (Figure 1), indicated a polar polarization mechanism [28], where its values are affected by both temperature and frequency.

III. The relative permittivity and dielectric loss values for the complexes, (Figure 1), revealed semiconducting features based mainly on the hopping mechanism [29].

IV. The loss tangent (tan δ) is decreased with increasing frequency and increased with increasing temperature in most cases, (Figure 1).

V. The impedance (Z) is mostly decreased and illustrated for Zn(BA)₂ and Cd(BA)₂.2H₂O as two different examples at different temperatures, (Figure 2).

The evaluation of experimental dielectric data is much facilitated by certain graphical methods of display, which permit the derivation of parameters by geometrical construction. The earliest and most used of these methods consists of plotting e²(ω) for certain frequency against ε′(ω) at the same frequency, in cartesian coordinates or in the complex plane. For a dielectric with a single relaxation time the Cole-Cole plot is a semi-circle which provides an elegant method of finding out whether a system has a single relaxation time or more [30]. The semi-circle diagram has been used to determine the distribution parameter α [31], which measures the width of distribution of relaxation time and evaluated by measuring the angle between the real part of dielectric constant and radius of the circle. Also, the macroscopic relaxation time to and the molecular relaxation time τ can be determined [30,32]. If the centers of semi-circles lie ε′(ω) axis, α is zero (Debye type). Otherwise the centre is below ε′(ω) axis and α ≠ 0 (non-Debye type). Two intersections between the real axis ε′(ω) and the circular arc, give the relative permittivity at zero frequency (static dielectric constant es) and that at infinite frequency approaching the frequencies of light oscillators (optical dielectric constant ε∞) [32]. A point on the semi-circle defines two vectors u and v. v is the distance on the Cole-Cole diagram between the static dielectric constant es and the experimental point, u is the distance between that point and the optical dielectric constant ε∞. Cole and Cole generalized the representation of a Debye dielectric by a circular arc plot in the complex plane so that it is applied to a certain type of distributions of relaxation times, so

The extent of the distribution of relaxation times increases with increasing parameter α. On the other hand, the value of to decreases with increasing temperature. The molecular relaxation time τ could be determined based on the following equation [30]:

The temperature dependence of τ can be expressed for thermally activated processes as [32]:

where to is a constant characteristic relaxation time and represents the time of a single oscillation of a dipole in a potential well, Eo is the energy of activation for the relaxation of the dipole, k is the Boltzmann constant and τ represents the average or most probable value of the spread of the relaxation times. A representative Cole-Cole diagrams for Zn(BA)₂ complex at 30 and 50°C, (Figure 3), reveal non-Debye type of the complex. The dielectric data obtained from the analysis of Cole-Cole diagrams for different complexes are collected in Table 3. The change of central metal ion from Zn to Cd in the complexes results mainly in a decrease of the relaxation time values. to for Cd(PB)₂.H₂O complex is much higher than that for Cd(BA)₂.2H₂O complex at the same temperature in most cases, (Table 3). One must focus the attention that the molecular orientation of Cd(PB)₂.H₂O gave its high restriction. So, this complex is probably associated in its molecular structure.

The variation of ln τ as a function of reciprocal absolute temperature for different complexes, (Figure 4), showed the above relation for Zn(NBA).2H₂O and that for Cd(PB)₂.H₂O assigned that as the temperature increases, the relaxation time for each relaxator becomes smaller in some ranges. The activation energies for the relaxation processes of different complexes are given in Table 4.

Electrical Conductivity Measurements

The frequency dependence of a. c. conductivity for the complexes at different temperatures is illustrated in Figure 5. The behavior shows that the a. c. conductivity increases with increasing the frequency. In the present complexes, the conductivities have a magnitude close to that of semiconductors, where the electrons in the orbitals are not of sufficient mobility to be promoted. The study of the conduction mechanism of organic materials leads to an increasing use of these materials in commercial devices such as solar energy panels, scintillation counter and also in some technological applications such as photocopy process. The electrical conductivity of substances at a given frequency varies exponentially with the absolute temperature according to the Arrhenius relation [33]:

where σ is the electrical conductivity at an absolute temperature T, so is the pre-exponential factor, ΔE is the activation energy and k is the Boltzmann constant. Therefore, the temperature dependence of the electrical conductivity is characterized by the two constants: the activation energy (ΔE) and the pre-exponential factor (so). The variations of ln σ as a function of reciprocal absolute temperature for Zn(NBA)₂.2H₂O and Cd(PB)₂.H₂O complexes at different frequencies are illustrated in Figure 6. The activation energy data and ln so values for the complexes are given in Table 4, from which the ΔE values are in harmony with those calculated from relaxation processes. For the complexes, the curves are characterized by breaks at a transition temperature. So, the behavior is nearly the same till the phase transition temperatures (343-403K) followed by large increase in conductivity by further increase of temperature. This can be ascribed to a molecular rearrangement or different crystallographic or phase transitions [34,35]. The magnitude of the conductivities of the complexes, along with the values of the energy gaps indicated slight semiconducting properties. The most realistic description of the complexes involves an interaction of the metal orbitals with the ligands to give new molecular orbitals (MO), which are delocalized over the whole molecular complex. In view of the high degree of covalency in the M-O and M-N bonds, it is no longer permissible to distinguish the central metal from the ligands, the complexes must be regarded as individual entities.

The conductivity for amorphous semiconductor could be interpreted with an intrinsic two-carrier model which originates with thermally assisted hopping conduction [29]. The relationship between molecular structure and electrical properties was deduced. On the basis of electronic transition within molecules, two pathways for the conduction of electricity may by expected. The first conducting process occurring in the lower temperature region is attributed to n → π* transitions which require less energy to be performed. While in the upper temperature region, conduction could be attributed to π → π* transitions which need more energy to participate in electronic conduction. The observed increment of conduction in the upper temperature region may be attributed to interactions between n → π* and π → π* transitions. The lower temperature range is the region of extrinsic semiconductor where the conduction is due to the excitation of carriers from donor localized level to the conduction band. In the upper temperature range, the intrinsic region is reached where carriers are thermally activated from the valence band to the conduction band. This behavior can be explained as follows: the upper temperature range may be attributed to the interaction between the electrons of d-orbitals and the p-orbitals of the ligand. This interaction will lead to small delocalization of the p-electronic charge on the ligand which tends to increase the activation energy. The presence of d-electrons in a narrow energy band leads to magnetic ordering and degeneracy of d-bands with respect to the orbital quantum number, which is only partially lifted in a crystal field [36].

In all complexes, during temperature increase, an additional increase in electrical conductivity occurs. This is a useful criterion for ascertaining the nature of the metal-ligand bonding [37], so

a) The electrical conductivities increased by increasing the molecular weight of the complexes

b) The activation energy decreased with increasing the atomic number of the metal, which indicates that the presence of holes in the system has little effect on the mobility of charges [38].

The lower values of ΔE may be understood assuming that the metal ion forms a bridge with the ligands, thus facilitating the transfer of current carriers with some degree of delocalization in the excited state during measurements. Meanwhile, this leads to an increase of the electrical conductivity with a decrease in energy of activation [39].

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