MICROWAVE SYNTHESIS CHARACTERIZATION AND ANTIMICROBIAL STUDIES OF NOVEL LIGAND (2, 6 DIACETYLPYRIDINE AND 5 AMINO 1, 3, 4 THIADIAZOLE 2 THIOL) AND ITS METAL COMPLEX

www.wjpr.net Vol 3, Issue 8, 2014. 467 MICROWAVE SYNTHESIS- CHARACTERIZATION AND ANTIMICROBIAL STUDIES OF NOVEL LIGAND (2, 6- DIACETYLPYRIDINE AND 5-AMINO-1, 3,

4-THIADIAZOLE-2-THIOL) AND ITS METAL COMPLEX

1

Dr.Mohammed.Fakruddin Ali Ahamed*, 2Segni Asafa

Department of chemistry, College of Natural Science, Jimma University, Post-Box No:

378-Ethiopia.

ABSTRACT

Metal complexes of Cu (II) with a new Schiff base derived from

2,6-Diacetyl pyridine-5-amino -1,3,4-thiadiazole -2-thiol (DAPATT) in

methanol are reported. The complexes have been characterized using

chemical analysis, (IR, UV-VIS, H1-NMR), conductometric data.

According to these data, we propose an octahedral geometry for metal

(II) complexes. The invitro antibacterial activities of the investigated

complexes were evaluated against few microorganisms by well

diffusion technique. It was found that the metal complexes have higher

activity that the standard drugs. Antibacterial activity of the ligand and

its complexes were studied against to gram positive bacteria;

Staphylococcus aureus and bacteria Salmonella typhi and

Escherichia coli.

KEYWORDS: Hexa-dentate Schiff base, 2,6Diacetyl pyridine5amino 1,3,4thiadiazole -2-thiol (DAPATT), Biological activity.

INTRODUCTION

A microwave is a form of electromagnetic energy, which falls at the lower end of the

electromagnetic spectrum. Recently, Microwave heating has emerged as a powerful

technique to promote a variety of chemical reactions[1,2].Microwave synthesis is attractive in

offering reduced pollution, low cost, saving time and offer high yields together with

simplicity in processing and handling [3].The recent introduction of single-mode technology

assures safe and reproducible experimental procedures and microwave synthesis has gained

acceptance and popularity among the synthetic chemist community.

Volume 3, Issue 8, 467-480. Research Article ISSN 2277 – 7105

Article Received on 22 July 2014,

Revised on16 August 2014, Accepted on 10 Sept 2014

*Correspondence for Author

Dr. Mohammed. Fakruddin Ali Ahmed

Department of chemistry,

College of Natural Science,

Jimma University, Post-Box

www.wjpr.net Vol 3, Issue 8, 2014. 468 Microwave irradiation now a day is an accepted tool for accelerating the organic and

inorganic reactions. It leads to the higher reaction selectivity and utilization of the

inexpensive reagents. In addition to providing an eco-friendly “green chemistry” approach to

the reaction, it is free of environmental impacts [4-7].the application of microwave irradiation

towards the acceleration of wide range of organic and inorganic reactions has received

concealable attention [8-13] .It also allowed a greener approach [14]. Schiff base of an important

class of ligands in coordination chemistry and have many applications [15], in different fields.

The chemistry of Schiff base complexes continues to attract many researchers [16, 17]. because

of their wide application in food industry, dye industry ,analytical chemistry catalysis

,antimicrobial activity, agro-chemical activity[18] and pharmacological applications [19]. The

application of microwave irradiation to organic synthesis has been the focus of considerable

attention in recent years and is becoming an increasingly popular technology.

Schiff bases are generally bi-or tri- dentate ligands capable of forming very stable complexes

with transition metals. Schiff bases have number of applications. Some are used as liquid

crystals. In organic synthesis, Schiff base reactions are useful in making carbon-nitrogen

bonds. Schiff bases appear to be an important intermediate in a number of enzymatic

reactions involving interaction of an enzyme with an amino or a carbonyl group of the

substrate. One of the most important types of catalytic mechanism is the biochemical process

which involves the condensation of a primary amine in an enzyme usually that of a lysine

residue, with a carbonyl group of the substrate to form an imine, or Schiff base.

Schiff bases are important class of compounds due to their flexibility, structural similarities

with natural biological substances and also due to presence of imine (N=CH-) which imports

in elucidating the mechanism of transformation and racemization reaction in biological

system which have capable of forming coordinate bonds with many of metal ions through

either/both azomethine nitrogen and phenolic oxygen. A large number of Schiff bases and

their complexes are of significant interest and attention because of their biological activity

including anti-tumor, antibacterial, fungicidal, anti-carcinogenic and catalytic activity [20,21].

Heterocyclic amineshave been widely used for the synthesis of new Schiff’s bases. Azoles,

thiadiazole and their derivatives continue to draw the attention of synthetic organic and

inorganic chemists due to the large group of compounds possessing a wide spectrum of uses.

Heterocyclic compounds possessing the 1, 3, 4-thiadiazole ring system shows antifungal,

www.wjpr.net Vol 3, Issue 8, 2014. 469 number of compounds which display biological activity. The biological activity of the

compounds is mainly dependent on their molecular structures.1, 3, 4-thiadiazoles are very

interesting compounds due to their important applications in many pharmaceutical, biological

and analytical field.

N

C H

C H

N

O

N

N

S

S H

Proposed structure of ligand-fig-1 MATERIALS AND METHODS

The entire chemical used was of analytical grade. The solvents were dried and distilled before

use according to standard procedures. Melting points were determined in a Electro thermal

9200.H1NMR spectra in CDCl3 and DMSO were recorded on NMR spectrophotometer. The

IR spectra (methanol/KBr) were recorded in the range400-4000 cm-1 by KBr pellet using

Perkin-Elmer 457 spectrophotometer. Conductance was measured in DMF at room

temperature using a Digital conductivity bridge. The UV-Visible spectra in CH3OH were

recorded on a shimadzu UV 1800 spectrophotometer. The metal contents were determined

gravimetrically.

Preparation of DAPATT

The reaction mixture containing 2,6-Diacetyl pyridine , (2g,0.077mol in 20ml of methanol )

5-amino -1,3,4-thiadiazole -2-thiol (0.848g ,0.077 mol in 20ml of methanol dissolved in hot

condition) was taken in 250‐ml round bottom flask and refluxed for 8h. On cooling the reaction mixture, deep-red coloured product was formed. It was collected by filtration and

washed with hot water and 50 % cold methanol. This compound was recrystallised from

www.wjpr.net Vol 3, Issue 8, 2014. 470

N

CH

CH

O

O

+

N

N

S

SH

NH

Con HCl

Reflux

N

CH

CH

N

O

N

N

S

SH

Fig. 2: preparation of Ligand – DAPATT

RESULT AND DISCUSSION Physical characteristics

The details of physical characterization of the ligand and metal complexes are tabulated in

table 1.

Table 1.Analytical and physical data for the ligand and its complex

Compound Colour M.pt (oC) Tield% Physical appearance Ligand

(DAPATT) brown 195-197 74.82 Powder Cu Complex of

(DAPATT) green 276-277 71.24 Powder

Molar Conductance Measurements

The molar conductance of Cu complex was measured in 10-3 M solution in DMSO as

solvents at room temperature. It showed a molar conductivity values 139.4 µs/cm. So the

molar conductance of this Cu complex 139.4 Ω-1 cm2 mol-1.From this concluded that Cu

complex is electrolyte.

Chemistry of Ligand and Its Copper Complex

The purity of the synthesized Schiff bases and its copper complex was checked on TLC

plates and the spot was visualized under ultraviolet light. Also their purity was checked on

melting point. The functional group on synthesized ligands was established through

spectroscopic data IR. The below spectra presents the characterization of the compounds,

www.wjpr.net Vol 3, Issue 8, 2014. 471

Fig 1.IR spectra of ligand (DAPATT)

fig 2. IR spectra of Cu complex

The Data Stated From The Above IR Spectra f Ligand (DAPATT) And Its Cu Complex Compound  (C-N)

cm-1

 (C-S) cm-1

(C=N) cm-1

(C=O

) cm-1

(-CH3)

cm-1

(C-H) cm-1

(Cu-N) cm-1

ν(Cu-O) cm-1 L ~1500 ~1000 ~1625 1700–

1721

2856

2931 - -

[CuLH2O]SO4-2 1458 1150 1595 1617 2856 2931 490 554

Infra-Red Spectroscopy

Spectroscopy is the study of the interaction of energy and matter. Absorption of energy of

different magnitudes causes different changes in matter. The magnitude of energy absorbed is

determined by the structure of the matter under study. If we understand how the structure of

matter influences the energy absorbed, we can work backwards to elucidate certain features

www.wjpr.net Vol 3, Issue 8, 2014. 472 A spectroscopic method that determines the functional groups is infrared (IR) spectroscopy.

In this technique, we expose the molecule in question to infrared photons. Functional groups

absorb infrared photons of characteristic energies. We then make a plot of photon energy

versus intensity of absorption, called the infrared spectrum. Therefore IR spectroscopy allows

us to deduce the functional groups that arepresent and absent in a molecule.

Bond Polarity and Absorption Intensity

Like any other type of spectrum, an IR spectrum is a plot of energy (expressed as frequency

or wavelength of photons) versus intensity of absorption or transmittance. Bond polarity and

absorption intensity show correlation IR spectra; less polar bonds cause weaker absorptions

(smaller peaks) than more polar bonds. For example, the C-H bonds are slightly polar

whereas the C≡C bond is non polar (because it is symmetrical). In the IR spectrum, the C–H

stretches appear at 2963-2669 cm-1 whereas the C≡C stretch which usually occurs ~2200 Cm

-1

so weak that it cannot be seen.

The 4000-1450 cm-1 portion of the IR spectrum, sometimes called the functional group

region. The segment of the IR spectrum below 1450 cm-1 is called the fingerprint region. The

fingerprint region contains much absorption. Features that influence stretching frequency

(ring strain, conjugation, hydrogen bonding, electron-withdrawing or electron-donating

effects, etc.)

In case of this study FTIR spectrum of the ligand (L) showed some characteristic stretching

bands at: 2931, 2856, 1700, assigned to–CH3, C-H and C=O bond respectively which could

be found in complexes and 2760, 1625,673 assigned to S-H, C = N of thiadiazole ring, and

the last one is for stretching of C-S bond, respectively which could be found in Cu complex

[22- 24] .

The band of S-H in the ligand was disappeared when complexation occur. Characteristic

absorption new bands for (Cu-N) and (Cu-O) of the complexes appear respectively at

stretching frequency 490 cm-1and 554 cm-1[25].And the band of C = N and C=O is shifted to

the lower frequency due to complexation, but the other bands such as - CH3, C-H aromatic

were didn’t show any shifting because they aren’t participate in the complexation[26].

NMR Spectroscopic Analysis of the Schiff Base Ligand (DAPATT)

Over the past fifty years nuclear magnetic resonance spectroscopy, commonly referred to as

www.wjpr.net Vol 3, Issue 8, 2014. 473 compounds. Of all the spectroscopic methods, it is the only one for which a complete analysis

and interpretation of the entire spectrum is normally expected. Nuclear Magnetic Resonance

(NMR) spectroscopy is an analytical chemistry technique used in quality control and research

for determining the content and purity of a sample as well as its molecular structure. For

example, NMR can quantitatively analyze mixtures containing known compounds. For

unknown compounds, NMR can either be used to match against spectral libraries or to infer

the basic structure directly. Once the basic structure is known, NMR can be used to determine

molecular conformation in solution as well as studying physical properties at the molecular

level such as conformational exchange, phase changes, solubility, and diffusion.

DEPT spectra

DEPT stands for Distortion less Enhancement by Polarization Transfer. It is a very useful

method for determining the presence of primary, secondary and tertiary carbon atoms.

The DEPT experiment differentiates between CH, CH2 and CH3 groups by variation of the

selection angle parameter (the tip angle of the final 1H pulse):

1. 135° angle gives all CH and CH3 in a phase opposite to CH2

2. 90° angle gives only CH groups, the others being suppressed

3. 45° angle gives all carbons with attached protons (regardless of number) in phase

Signals from quaternary carbons and other carbons with no attached protons are always

absent (due to the lack of attached protons).

1

H - NMR Spectroscopic Analysis of the Schiff Base (DAPATT)

www.wjpr.net Vol 3, Issue 8, 2014. 474 The 1H - NMR spectra of the Schiff bases were recorded in DMSO (Fig 3). For CH aromatic

proton,the ligand shows singlet in the region 8.135 ppm. The1H -NMR signal at =2.694

 ppm sharp and singlet peak is due to –CH3 proton [27, 28] .

13

C - NMR spectroscopic analysis of the Schiff base (DAPATT)

Fig. 4 13C NMR Spectra of Ligand (DAPATT) 13

C NMR showed that carbon (RCH3) (a) of this compound appeared at 25.807 ppm, (R3CH)

(e) at 39.943 ppm, (N=C) azomethine (imines) group at 152.644 ppm, (N=C-R) at 139.401

ppm and carbon(C=C- RH) (d) at 125.003 ppm in pyridine ring. As well as 13C NMR showed

that carbon (N=C-S2) (h) at 181.421 ppm and Carbon (N=C-SN) (g) at 161.940 ppm in

thiadiazole ring. The carbonyl carbon (b) also deshielded and appeared at 199.225ppm due to

inductive effect (Oxygen attracting electron from carbonyl carbon)[29].

www.wjpr.net Vol 3, Issue 8, 2014. 475

The above DEPT-135 Spectra show that the compound contains CH and CH3 carbon (there is

no CH2 carbon).The quaternary carbon was absent.

Electronic spectroscopy

Electronic spectroscopy is an analytical technique to study the electronic structure and its

dynamics in atoms and molecules. Electronic absorption spectra are often very helpful in the

evaluation of results furnished by other methods of structure investigation. The electronic

spectral measurements were used for assigning the stereochemistry of metal ions in the

complexes based on the positions and numbers of d-d transition bands.In general an

excitation source such as X- rays, electrons, or synchrotron radiation will eject an electron

from an inner-shell orbital of an atom. The Beer-Lambert law states that the absorbance of a

solution is due to the solution's concentration. Thus UV/vis spectroscopy can be used to

determine the concentration of a solution. It is necessary to know how quickly the absorbance

changes with concentration.

The method is most often used in a quantitative way to determine concentrations of an

absorbing species in solution, using the Beer-Lambert law:

A= -log (I /I0) =. C. l

Where A is the measured absorbance, I0 is the intensity of the incident light at a given

wavelength, I is the transmitted intensity, / is the path length through the sample, and c is the

concentration of the absorbing species. Samples for UV /vis spectrophotometer are most

often liquids, although the absorbance of gases and even of solids can also be measured.

Samples are typically placed in a transparent cell, known as a cuvette.Cuvettes are typically

rectangular in shape, commonly with an internal width of 1 cm. (This width becomes the path

length, /, in the Beer-Lambert law).

Test tubes can also be used as cuvettes in some instruments. The best cuvettes are made of

high quality quartz, although glass or plastic cuvettes are common. (Glass and most plastics

absorb in the UV, which limits their usefulness to visible wavelengths.) An ultraviolet-visible

spectrum is essentially a graph of light absorbance versus wavelength in a range of ultraviolet

or visible regions. Such a spectrum can often be produced by a more sophisticated

spectrophotometer. Wavelength is often represented by the symbol . For the given

substance, the wavelength at which maximum absorption in the spectrum occurs is called

www.wjpr.net Vol 3, Issue 8, 2014. 476 Electronic spectra of Schiff base (DAPATT) and its complexes

Figure 6.Electronic Spectra of Ligand (DAPATT)

Figure 7.Electronic Spectra of Copper Complex

The UV-Vis spectral data of the ligands (DAPATT) and the Cu complex were recorded in

DMSO in the wavelength range from 800 – 200 nm at room temperature. The UV-Vis spectra

of the ligand(DAPATT) showed bands at 220, nm 260 nm,295 nm,345 nm and 377 nm,

assigned to π → π* and n →π* transition with the molecular, these bands were slightly

shifted to lower wavelength region for the complexes due to coordination with metal ions.

The electronic spectra of copper complex displays bands, which are assigned as an

intraligand charge transfer band (382 nm) and d-d band (700 nm) which is due to 2B1g →2Eg

transition. This d-d band strongly favors square-planar geometry for the copper complex[30].

The various wavelengths, band assignments and the proposed geometry of the complex are

www.wjpr.net Vol 3, Issue 8, 2014. 477 Table 2. Electronic Spectral Data of Schiff Base DAPATT and Its Copper Complexes

Compound (nm) Band assignments Geometry

Ligand (L)

220, 260 295 345 377

π→ π*, n →π*( C=O) (INCT) n →π*( C=O)

n →π*(C=N) n →π*(C=N)

-

[CuLH2O]SO4-2 382 700

INCT 2

B1g →2Eg transition Octahedral INCT-intraligand charge transfer

O H ₂ N

N S

S H

N

C H ₃ C H ₃

N O

M

Cu-complex with ligand Antibacterial Activity of Ligand and Its Metal Complex

Disc Diffusion Assay

The in vitro antibacterial activity of the DMSO, ligand and its metal complexes were tested

against three different bacteria at a concentration of 10-2 M table 2.At this concentration the

Cu complex shows significant antimicrobial activity against the tested pathogens. The degree

of inhibition varied with the nature of the compound. These concentrations of the ligand and

complexes were used to get visible results. The highest zone of inhibition i.e. 2.5 and 3 cm

were measured in salmonella and staphelo coccus aurus when treated with Cu (II) complex.

The zone of inhibition is greatly affected by the thickness of the test agar layer. As the

thickness increases, the zone of inhibition decreases. This can be attributed to the decrease of

concentration of the ligand and its complexes per unit volume of the culture media. Another

factor, which influences the inhibition zone, is inoculum size (concentration of the organism

per unit volume). The diameter of the inhibition zone decreases with increase in the inoculum

www.wjpr.net Vol 3, Issue 8, 2014. 478 Table 3: Antibacterial screening data of investigated ligand (DAPATT) and its Cu complex

Compound

Diameter of Inhibition Zone (mm) Salmonella

typhimurium

Staphylococcus

aureus Escherichia coli

DMSO - - -

Ligand(L) 20 mm - 20 mm

Cu (L) complex 25 mm 30 mm 23 mm

gentamycine 27 mm 29 mm 25 mm

There is a significant reduction in the growth rate of microorganisms due to unfavorable

culture media, low temperature and acidic pH. The activity test was conducted at an optimum

temperature of 37 0C antibacterial activities. Synthesized compounds were investigated for

their antimicrobial activity by agar diffusion method [31].

In case of solvent control disc no zone of inhibition was observed as far as our study is

concerned DMSO, as a solvent is having no effect on the tested bacterial species. Hence we

can effectively conclude here that whole of the antimicrobial effect is due to the nature of the

metal complexes and the ligand used (synthesized) in this study. The antimicrobial behavior

of the Cu complex when compared with standard antibacterial drugs showed momentous and

identical biological properties [32]; even inStaphylococcus aurous showed more activity.

Due to the high antimicrobial activities and chelation of this metal ion in its complex, this

enhances the lipophylic character favoring its permeation through the lipid layer of cell

membrane.

CONCLUSION

A DAPATT ligand was synthesized by microwave method from precursor 5-mercapto-1, 3,

4-thiadiazole-2-thiol with 2, 6-diactylpyridine in purified ethanol. The copper complex was

synthesized by direct method. In direct method, DAPATT and Cu (II) ions were condensed.

Based on conductivity, UV-Vis, IR and NMR spectroscopy studies it is concluded that the

ligand bonds to the metal ion through azomethine nitrogen, carbonyl oxygen (-C=O),

pyridine nitrogen, water molecule oxygen (H2O) and 1, 3, 4-thiadiazole sulfur atoms. The

newly synthesized [CuLH2O] SO4-2 complex is concluded to have an octahedral geometry

with the sixth coordination site benig fulfilled by H2Oion. In addition, the Schiff base ligand

(DAPATT) and its copper complex were evaluated for their in vitro antibacterial activity

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