Biological and electronic transition studies of the previously reported organotin (IV) dithiocarbamates of p-Fluoro- Nmethylbenzylaminedithiocarbamate

Four organotin(IV) complexes of p-Fluro-N-methylbenzylaminedithiocarbamate with general formula R2SnL2 where (R= dimethyl, diphenyl and dibutyl)and R3SnL (R = triphenyl) synthesized earlier in the group were tested for their bioactivity. Antibacterial assay against four Gram-negative and Gram-positive strains including Salmonella typhi, Escherichia coli, Pneumoniae and Staphylococcus aureus, while antifungal activity against Aspergillus Niger of the compounds were carried out using standard procedures.The tested compounds were found significantly active against Aspergillus Niger. Whereas, the antibacterial activity of compounds wasfound moderate as compared to their antifungal activities.


Synthesis of organotin (IV) complexes
The organotin (IV) complexes of p-Fluro-N-methylbenzylaminedithiocarbamate were synthesized by adding 5 mmol methanolic solution of ligand in 2.5 mmol of diorganotin (IV) dichloride dissolved in the same solvent in 2:1 molar ratio.

Scheme3. Synthesis of triphenyltin (IV) p-FluroN-methylbenzylaminedithiocarbamate
Antibacterial assay Disc diffusion method had been utilized for the determination of antibacterial activity of synthesised organotin (IV) dithiocarbamate complexes [23].The inhibition zones were measured against Gram negative bacteria including Escherichia coli and Salmonella thyphi and Gram positive including Bacillus cereus and Staphylococcus.Molar Hinton Agar were prepared following its instructions.Agar were spread on petri plates and bacterial strains were cultured on 25ml of medium.Organotin (IV) dithiocarbamatecomplexes were dissolved in dimethylsulfoxide (DMSO) and a 100ml stock solution (4mg/mL in DMSO) compounds were added in wells.These petri plates were incubated at 37 °Cfor 24 hours.The bactericidal activity of compounds was recorded by measuring the diameter of inhibition zone.Doxycycline (DO 30mg) and DMSO were used as negative and positive control.

Antifungal Assay
The fungi Aspergillus Niger was isolated from environment.The solutions of compounds used for antifungal activity were freshly prepared inDMSO (0.02mg/5ml) tested against AspergillusNiger fungus.Diffusion method was adopted to measure the antifungal activity [24].These fungal strains were properly grown in sabouraud dextrose agar slants.The fungal spores sabouraudon to dextrose agar plates.The compounds were dissolved in final concentration from 10-20mg for fungal cultures could stay in the walls.The petri plates were incubated for 4 days and spores were observed after 4, 7 and 14 days.The inhibition zone and activity of all compounds were measured compared with control.

Result and discussion 1 HNMR spectroscopy
In spectra of complexes, slight variation is observed in the absorptions of methyl groups attached with nitrogen and aromatic protons which indicates formation of complexes and the values are in accordance with the previous reports.
In the spectra of ligand, methyl group attached with nitrogen atom shows absorbance at2.89 ppm in ligand's spectrum.The aromatic protons of ligand appear in the range 6.99 and 7.25 ppm.Whereas, the aromatic protons of complexes show multipletsin the range6.97-7.98 ppm.In spectrum of dimethyltin(IV), the methyl group attached with tin is observed at 1.56 ppm.In dibutyltin (IV) complex,the methylene protons appear at 5.09 ppm [25].

Infrared spectroscopy
The solid state vibrational spectra are recorded for the dithiocarbamateligand and its complexes in the range 4000-370 cm -1 which matches the exact value already reported by Naqeebet al. [26].The appearance of C-N peak in spectra of ligand at 1472 cm -1 confirms the formation of ligand.The C=S peak is observed at 954 cm -1 .The slight variation in main peaks along with appearance of Sn-S wave numbers in their respective ranges confirm the formation of four coordinated organotin(IV) complexes as reported earlier.The dithiocarbamate ligand are coordinated only via singly bonded sulphur donor site exhibiting four coordinated complexes and in accordance with the NMR spectral interpretations [27, 28].

Ultraviolet spectroscopy
The Ultraviolet absorbance of these ligands and complexes is studied for the first time.UV-Vis spectroscopy is carried out to observe the change in the electronic transitions of ligands and their complexes.Dimethylsulfoxide (DMSO) was used to make the solutions of ligands and complexes.The concentration for the complexes are 1.00 x 10 -4 M and 1.00 x 10 -3 M and the wavelengths were in the range of 200-400 nm.In UV spectrum of ligand two bands appear at 264 and 379 nm due to π-π* and n-π*.The n-π* in spectrum ligand is because of transition of lone pair of electrons of sulphur atom to π* orbital.Whereas, in UV spectra of complexes, the π-π* and n-π* are observed in the range238-265 nm and 262-301, respectively.The slight variation in absorption values of π-π* and n-π* in spectra of complexes confirms the formation of complexes.The UV studies of the ligand and its complexes have been performed  and E.coli and other strains.Different biological impacts of organotin (IV) complexes is ascribedto the existence of different organic groups attached with tin centre.Antibacterial activity is because of the interaction of organotin moiety with deoxyribose nucleic acid (DNA) of bacteria.The dimethyltin(IV) complex shows good activity against all the tested and it might be due toits low molecular mass and greater penetration through cell wall of bacteria [32].

Antifungal Activity
The antifungal assay of the synthesized compound has been performed by diffusion method.The obtained results of these compounds show strong antifungal activity against Aspergillus Niger.All the compounds inhibit the fungus growth completely as shown in figure 1.The amazing antifungal activity of these compounds might be due to their easy penetration through fungal cell wall [33].It may also be associated with different composition of cell wall structures of fungal and bacterial cells.The bacterial cell wall is composed of cellulose while the fungal cell wall is composed of chitin.The assayed compounds exhibit strong fungicidal activity in comparison to bacterial activity.All the tested compounds inhibit the fungal growth completely as compared to standard drug.The antifungal activity is given below in figure 1.

Figure1. Antifungal Activity of organotin (IV) dithiocarbamates complexes Conclusion
The ligandp-Fluro Nmethylbenzylaminedithiocarbamate and its complexes were resynthesized in the Department of Chemistry,University of Balochistan.Antibacterial assay against four Gram-negative and Gram-positive strains includingS.typhi, E. coli, Pneumoniae and S. aureus were noted using disc diffusion method.The ligands and its complexes show moderate against these four strains while the antifungal activity of these compounds is very high which completely inhibit the fungal growth as compared with control.Moreover, the electronic transitions of these compounds were in the range of 200-400nm.