Synthesis and Antibacterial Activities of Some Schiff Bases

Schiff bases p-hydroxybenzylidene-2-carboxyaniline, p-nitrobenzylidene-2-carboxyaniline, p-(N, N-dimethyl)aminobenzylidene-2-carboxyaniline, N-(4-hydroxybezylidene)-benzene-1,2-diamine, N-(4-nitrobezylidene)benzene-1,2diamine,N-(4-(N, N-dimethylaminobezylidene)benzene-1,2-diamine, N-(4-(N,Ndimethylamino)benzylidene)naphthalen-1-amine,N-(4-nitrobenzylidene)naphthalen1-amine,N-(4-chlorobenzylidene)naphthalen-1-amine,sodium-4-(4-(N,N-dimethyl amino)benzylideneamino)naphthalene-1-sulfonate,sodium -4-(4-nitrobenzylideneamino)naphthalene-1-sulfonate and sodium-4-(4-chlorobenzylideneamino) naphthalene-1-sulfonate obtained by condensation of aniline and naphthylamine derivatives with some aromatic aldehydes were characterized by physical and spectral methods. The biological activity of these products were as antibacterial agents against three species of human pathogenic bacteria such as Escherichia coli, Staphylococcus aureus and Klebsiella sp. Nearly 50% of these compounds showed reasonable activity against the bacterial species investigated and we found that the antibacterial activity is dependent on the molecular structure of the compounds.

Application of many new analytical devices requires the presence of organic reagents as essential compounds of the measuring system.Among the organic reagents actually used, Schiff bases possess excellent characteristics, structural similarities with natural biological substances, relatively simple preparation procedures and the synthetic flexibility that enables design of suitable structural properities 5,6 .The antibacterial activity is dependent on the molecular structure of the compound, the solvent used and the bacterial species [7][8][9] .
The Schiff bases prepared are condensation products of aromatic aldehyde derivatives with aromatic amines derivatives and presented below.In this work the spectroscopic characteristics and antibacterial activity against three species of human pathogenic bacteria such as Escherichia coli, Staphylococcus aureus and Klebsiella sp of these Schiff bases are presented.

Experimental
All chemicals and solvents used for synthesis were of reagent grade.All melting points were taken on a melting point apparatus and are uncorrected.IR spectra were recorded on a Shimadzu 5000 instrument. 1 H NMR were run on a Jeol 500 MHz instrument using TMS as internal standard, and DMSO as solvent.The spectral analyses were carried out at the NMR laboratory, Alexandaria University, Alexandaria; the elemental analyses at Microanalytical center Cairo University, Cairo, Egypt The Schiff bases (I-VI) were prepared according to the reported methods [10][11][12] .The procedure is as follows: A solution of the amine derivative (0.01 mol) in absolute ethanol (10 mL) was slowly added to a solution of the aldehyde derivative (0.01 mol) in absolute ethanol (10 mL).After stirring the reaction mixture for 2 h (Compounds I, II and III) and for 5 h at 60-70 o C and cooling (Compounds IV, V and VI), a precipitate was formed which collected by filtration then washed several times with cold ethanol and recrystallised from ethanol.

N-(4-Nitrobezylidene)-benzene-1,2-diamine (V)
It was prepared from o-phenylenediamine and p-nitrobenzaldehyde; pale brown; m.p. 317-318 o C; 1.9 g (81%) yield.IR (KBr, cm The Schiff bases (VII-XII) were prepared according to the reported methods [10][11][12] .The procedure is as follows: A solution of the amine derivative (0.01 mol) in absolute ethanol (10 mL), (with 0.01 mol NaOH for compounds IV-VI), was slowly added to a solution of the aldehyde derivative (0.01 mol) in absolute ethanol (10 mL).After stirring the reaction mixture for 2 h (Compounds I, II and III) and for 5-10 h at 60-70 o C and cooling (Compounds IV, V and VI), a precipitate was formed which collected by filtration then washed several times with cold ethanol and recrystallised from ethanol.

Antibacterial assay
The antibacterial tests were assayed according to the diffusion method.The strains of bacteria used were Escherichia coli, Staphylococcus aureus and Klebsiella sp.All species were isolated from patients in Al-Jamahiriya hospital, Benghazi, Libya.The identity of all the strains was confirmed.A bacterial suspension was prepared and added to the sterilized nutrient agar (OXID/England) medium before solidification.The medium with bacteria was poured into sterilized Petri dishes under aseptic condition.Different weights of Schiff bases (5 mg, 10 mg and 20 mg) were placed on the surface of the culture and incubated at 37 o C for 24 h.After incubation, the average of inhibition zones was recorded (mm).Antibacterial activity was indicated by the presence of clear inhibition zones around the samples.

Results and Discussion
Schiff bases were prepared in this work through condensation of aniline derivatives and naphthylamine derivatives with some aromatic aldehydes, The IR and NMR spectral data confirmed their molecular structure.They showed different effects on bacterial species.
Table 1 shows the mean of inhibition zone of some Schiff bases which were tested at different concentrations of 5, 10 and 20 mg against several species of human pathogenic bacteria.The results from this study indicated that I, II,III, XI and XII had antibacterial activities against Escherichia coli and Klebsilla sp which are known as resistant to most commercial antibiotics used.Also, the compounds I-III and X-XII had effects on Staphylococcus aureus.In contrast, no effect was observed of IV-IX compounds against all bacterial tested.

Table 1 .
The effect of Schiff bases on bacteria growth