Syntheses, Crystal Structures and Antibacterial Activities of Two Heterocyclic Schiff Base Compounds

Two heterocyclic Schiff bases were synthesized via the condensation reactions of primary amines with carbonyl compounds. 2-[（4-pyridylmethylene）-amino] phenol （compound 1） was synthesized by the interaction of 4-pyridinecarboxaldehyde with o-aminophenol in ethanol solvent; N,N＇-bis（3-（furan-2-yl）allylidene）benzene-1,4-diamin （compound 2） was synthesized by the interaction of 3-（2-furyl）acrolein with p-phenylenediamine in ethanol medium. The compounds were characterized by elemental analysis, IR, MS and single-crystal X-ray diffraction. Compound 1 （C12H10N2O） crystallizes in the monoclinic system, space group P21/c with α = 7.0771（7）, b = 7.2820（7）, c = 19.849（2）, b = 96.3390（10）°, V = 1016.66（17） ？3, Z = 4, Mr = 198.22, Dc = 1.295 g/cm3, F（000） = 416, GOOF = 1.060, m = 0.085 mm-1, the final R = 0.0371 and wR = 0.0929 for 1497 observed reflections with I 〉 2σ（I）. Compound 2 （C20H16N2O2） crystallizes in the orthorhombic system, space group Fdd2 with α = 26.344（15）, b = 48.50（3）, c = 5.293（3）, V = 6764（7） ？3, Z = 16, Mr = 316.35, Dc = 1.243 g/cm3, F（000） = 2656, GOOF = 1.043, m = 0.081 mm-1, the final R = 0.0526 and wR = 0.1267 for 2059 observed reflections with I 〉 2σ（I）. 1 and 2 molecules are connected through hydrogen bonds to generate a 2D network and a 1D chain structure, respectively. The preliminary antibacterial activity results showed that the title compounds display excellent antibacterial activities to Escherichia coli, Staphylococcus aureus and Bacillus subtilis.

Syntheses, Crystal Structures and Antibacterial Activities of Schiff Base Ligand and Its Nickel(Ⅱ) Complex

A complex [NIL2] was synthesized, in which L, or to be exact, a Schiff base ligand （HL）, was derived from the condensation of 1-phenyl-3-methyl-4-phenylacetyl-5-pyrazolone （PMPAP） with L-phenylalanine methyl ester. They were characterized by IR and single-crystal X-ray diffraction. Green block crystals of both ligand and its complex were grown at room temperature. The ligand, which consists of two individual fragments, crystalizes in the P1 space group （a = 5.6268（5）, b = 10.6892（11） and c = 19.4869（18） A）. The complex crystalizes in the P21 space group （a -- 21.4076（18）, b = 9.4792（8） and c = 25.287（2） A）, which consists of a nickel six-coordinated compound. Every fragment is a distorted octahedron with four oxygen and two nitrogen atoms. The Schiff base ligand （HL） and its complex have been tested in vitro to evaluate their antibacterial activity against bacteria Escherichia Coli and Bacillus subtilis. It is found that the complex has higher activity than the corresponding free Schiff base ligand （HL） against the same bacterial.

Syntheses, Characterizations, Crystal Structures and Antibacterial Activities of Two Zinc(II) Complexes with a Schiff Base Derived from o-Vanillin and p-Toluidine

Two new zinc（Ⅱ） complexes, [Zn2L2Ch].2[ZnL（CH3OH）Cl2] 1 and [ZnL2（NO3）2] 2, were synthesized by reacting ZnX2.nH2O （X = Cl^-, NO3^-） and a Schiff base ligand 2-[（4-methylphenylimino）methyl]-6-methoxyphenol （C15HIsNO2, L） which was obtained by the condensation of o-vanillin （2-hydroxy-3-methoxybenzaldehyde） with p-toluidine. Both 1 and 2 were characterized by single-crystal X-ray diffraction technique, elemental analysis, molar conductance, FT-IR, UV-Vis, IH-NMR spectra and thermogravimetrie analysis. The Schiff base ligand and its zinc（Ⅱ） complexes have been tested in vitro to evaluate their antibacterial activity against bacteria, viz., Escherichia Coli, Staphylococcus aureus and Bacillus Subtilis. The results show that these complexes have higher activity than the corresponding free Schiff base ligand against the same bacteria.

Synthesis, Structure and Antibacterial Activities of 4-BBTS Schiff Base and Its Complexes

4-Bromobenzaldehyde thiosemicarbazone Schiff base （4-BBTS） and its Cu（Ⅱ）, Zn（Ⅱ）, Co（Ⅱ） and Ni（Ⅱ） complexes were synthesized and characterized by elemental analysis, UV, IR, MS, ^1H NMR, and molar conductivity. Using disc diffusion method, the antibacterial activity tests were conducted. The results revealed that the ligand as well as all the complexes exhibits good antibacterial activities against E. Coli. and S. Aureus. Moreover, Cu（Ⅱ） complex shows the best antibacterial activity, which provides beneficial reference for studying the relationship between the structures and performances.

Synthesis, Characterization and Antibacterial Activities of Polydentate Schiff Bases, Based on Salicylaldehyde

Three Schiff bases L1, L2 and L3 were synthesized by condensing salicylaldehyde with 4-aminoantipyrine, ethylendiamine and 2-aminophenol respectively and subsequently characterized by various physicochemical investigations. All the three compounds were screened for their In-vitro antibacterial activity against two gram positive bacteria, Staphylococcus aureus (S.A), Staphylococcus epidermidis (S.E) and two gram negative bacteria Klebsiella pneumoniae (K.P) and Pseudomonas aeruginosa (P.A) by agar diffusion method. On comparing the results obtained with the activity of commercially available antibiotics such as Ciprofloxacin and Chloramphenicol, the newly synthesized compounds showed comparable antibacterial activities. The solvent methanol exhibit activity against all bacterial species with IZs ranging from 8 ± 0.25 to 17 ± 0.29 mm while the standard antibiotics Ciprofloxacin and Chloramphenicol exhibited an activities with IZs varying from 21.3 ± 0.31 to 28.3 ± 0.32 and 26.3 ± 0.24 mm to 32.3 ± 0.23 mm, respectively. However, the newly synthesized Schiff bases L1, L2 and L3 showed IZs ranging from 7.4 ± 0.23 to 32.5 ± 0.14, 3 ± 0.57 to 12 ± 0.28 and 10 ± 0.20 to 32 ± 0.36 respectively. Among the Schiff bases, L3 showed the activity (32 ± 0.36) against S.E and P.A which is higher than the activity of standard antibiotics Ciprofloxacin and Chloramphenicol against the same bacterial strains. The results obtained revealed that all the synthesized Schiff bases exhibit appreciable antibacterial activity against all the bacteria species which potentially makes them, to apply as wide range antibacterial drugs, after further in-vivo cytotoxicity investigations. Their activity can also be further modified by changing the functionality of precursors for Schiff base condensation.

Synthesis, Characterization, Antimicrobial and DNA Binding Studies of a Tetradentate N2O2 Amino Acid Schiff Base and Its Coordination Compounds

Aminoethanoic acid undergoes condensation with 1,4-benzenedicarboxaldehyde to form an O, N, N, O donor Schiff base, N,N'-di(carboxymethylene) terephthalaldehyde, Ligand L. Coordination compounds of this Schiff base using Ni (II), Cu (II), VO (IV) and Co (II) were then obtained in-situ. The Schiff base and the complexes were evaluated for their antimicrobial and DNA binding abilities. Molecular docking studies of the ligand and synthesized compounds were also carried out. Evidence for the formation of the Schiff base coordination compounds and the coordinating atoms was obtained from 1H NMR, infrared and ultraviolet spectral data, EDX, EDTA complexometric titration and magnetic susceptibility measurement. The results obtained are consistent with octahedral geometry for Ni (II) complex, the metal ion coordinating to one molecule of Ligand L and with additional coordination with two oxygen atoms of two molecules of the solvent. A square-planar geometry was suggested for both Co (II), and Cu (II) complexes and a five-coordinate, square pyramidal geometry for the VO (IV) complex. The results further indicated that the carboxylic acid of Ligand L was not deprotonated both in the free base and also the complexes. In addition, the results showed that Compound 2 elicited the best antimicrobial activity potential. Generally, the compounds exhibited considerable good affinity to CT-DNA.

Syntheses, Crystal Structures and Antibacterial Activities of Cobalt(Ⅱ) and Manganese(Ⅱ) Complexes with Schiff Base Ligand Derived from Tryptamine

Two new mononuclear complexes, namely [Co（L）2]（1） and [Mn（L）2]（2）（HL = N-（3-methylsalicylidene）tryptamine）, have been synthesized by the reactions of the ligand with cobalt acetate or manganese acetate in anhydrous ethanol. The crystal structures of the complexes were characterized by IR spectrum, elemental analysis, PXRD and single-crystal X-ray diffraction analysis. Complex 1 crystallizes in monoclinic, space group C2/c, with a = 23.146（2）, b = 9.4864（10）, c = 13.9261（15）A, β = 102.898（2）°, V = 2980.6（5） ？3, Z = 4, Dc = 1.367 g/cm3, F（000） = 1284 and μ = 0.616 mm^-1. Complex 2 crystallizes in monoclinic, space group P21/n, with a = 14.807（11）, b = 13.118（10）, c = 16.663（13） A, β = 111.237（14）°, V = 3017（4） A^3, Z = 4, Dc = 1.342 g/cm^3, F（000） = 1276 and μ = 0.477 mm-1. The units of complex 1 are linked by intermolecular N–H…π hydrogen bonds into infinite 1D chains, which are further extended into a 3D supramolecular structure by a series of π···π stacking interactions. The units of complex 2 are linked by intermolecular N–H…π hydrogen bonds and C–H…π hydrogen bonds into an infinite 3D supramolecular structure. Meanwhile, the antibacterial activities of the ligand and its complexes have been tested against four kinds of bacteria. The results show that the three compounds all have excellent antibacterial activities and that 1 and 2 possess stronger inhibiting effects against the bacteria than the Schiff base.

Synthesis, Characterization and Antibacterial Activity of New Ln(Ⅲ) Complex with Unsymmetrical Schiff Base Ligand

A new unsymmetrical Schiff base ligand (H_2LLi) was synthesized using L-lysine, o-vanillin and salicylaladyde. Three solid metal complexes of this ligand [Ln(H_2L)(NO_3)] NO_3·2H_2O (Ln=Sm, Ho, Tm) were prepared and characterized by elemental analyses, IR spectra, UV spectra, TG-DTG and molar conductance. The ligand synthesized are chelating agent. The nitrogen atoms of Schiff base, oxygen atoms of hydroxybenzene, methoxide and carboxyl are all coordinated to the metal ions. Carboxyl and the nitrate ion within the coordination sphere are coordinated to the metal ion in a mondentate or bidentate fashion. Water molecules are lied in crystal substances. The antibacterial activity of the ligand and its complexes was also studied. The antibacterial experiments indicate that they have antibacterial activity to E. coli, S. aureus, B. subtilis and the complexes have higher activity than the ligand.

Biological Activities of Schiff Bases and Their Complexes: A Review of Recent Works

Schiff bases are the most widely used organic compounds. They have been shown to exhibit a broad range of biological activities, including antifungal, antibacterial, antimalarial, antiproliferative, anti-inflammatory, antiviral, and antipyretic properties. This review summarizes the synthesis and biological activities of Schiff bases and their complexes.

Synthesis of Pyridyl Polyheterocyclic Oxime-ether Schiff Bases Containing s-Triazole and Oxadiazole Subunits

4-Amino-5-pyridin-4-yl-s-triazole-3-thiol （1） was sequentally reacted with 3-chloro-1- phenylpropan-1-one to afford 3-（4-amino-5-pyridin-4-yl-s-triazole-3-sulfanyl）-1-phenylpropan-1- one （2） followed by oximation with hydroxylamine hydrochloride and etherification with 5-aryl-[13,4]oxadiazole-2-cbloromethanes to the corresponding oxime （3） and oxime-ethers （4a-e）, respectively. The condensation of compounds 4 with salicylaldehyde gave the title compounds （5a-e）. The antibacterial activity in vitro against Gram-postive （G^＋） and Gram negative （G） bacteria was primarily evaluated.

Synthesis of thiadiazole-based Schiff base metal complexes and their inhibition rate to superoxide anion free radical

A new series of Schiff base ligands were synthesized by the condensation of 2-amino-5-mercaptan-l,3,4-thiadiazole and salicylaldehyde or 2,4-dihydroxybenzaldehyde and their derivatives with choroacetic acid, and further reaction with corresponding metal acetate to form metal complexes. The compositions and structures of the ligands and their complexes were characterized by elemental analysis, molar conductivities, electronic absorption spectra and infra-red spectra. Their inhibition rates to free radical, such as O2, were also tested. The results show that all of the obtained complexes display significant activities, among which the copper（Ⅱ） complexes have the best inhibitive effects.

Synthesis,Crystal Structure,and Antioxidant and Antibacterial Activities of3,5-Dihydroxy-N'-(4-nitrobenzylidene)benzohydrazide

A new compound, 3,5-dihydroxy-N＇-（4-nitrobenzylidene）benzohydrazide （I）, has been synthesized and characterized by single-crystal X-ray diffraction. The title compound crystallizes in the monoclinic system, space group P21/c with a = 9.632（12）, b = 12.256（15）, c = 11.425（14） A, β = 105.306（11）°, Z = 4, V = 1301（3） A3, Dc = 1.538 g/cm3, F（000） = 704,μ = 0.276 and S = 1.011. The final R = 0.0444 and wR = 0.1186 for 3808 observed reflections with I〉 20（I）. We used methods such as ABTS, DPPH assays and in vitro hydroxyl radical scavenging experiment to assess the in vitro antioxidant activity of the new compound, and found that its IC50 value was 48.59 μg/mL for scavenging ABTS radicals, 48.04 μg/mL for scavenging DPPH radicals, and 1.03 mg/mL for scavenging hydroxyl radicals, indicating that it had a good in vitro antioxidant activity. We also test the antibacterial activities of this compound against three bacteria, and it showed considerable antibacterial activity against S.aureus. The MIC values of S.aureus, K.pneumoniae and P. aeruginosa are respectively 0.156, 0.625 and 1.25 mg/mL.

Substituent effect on spectral and antimicrobial activity of Schiff bases derived from aminobenzoic acids

The dependence of electronic absorption spectra antimicrobial property on the substituent position was investigated using three Schiff bases derived from salicylaldehyde and isomeric aminobenzoic acids in three solvents of different polarities. The absorption maxima in all three solvents exhibited dependence on the position of substituent with the absorption maxima undergoing a red shift as solvent polarity increased. The in vitro antibacterial activity of the compounds against some clinically important bacteria namely Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Staphylococcus aureus (ATCC 25923), Enterococcus feacalis (ATCC 29212) was determined in N,N”-dimethylformamide and 1,4-dioxane using the agar dilution method. The results revealed that the ortho and meta substituted Schiff bases exhibited better antimicrobial activity in the non-polar solvent.

Synthesis and Characterization of Schiff Base Metal Complexes Derived from Cefotaxime with 1<i>H</i>-indole-2,3-dione (Isatin) and 4-N,N-dimethyl-aminobenzaldehyde

This work involved the synthesis of two Schiff base derivatives of cefotaxime antibiotic (CFX) namely: [sodium3-(acetoxymethyl)-7-((Z)-2-(methoxyimino)-2-(2-((E)-2–oxoindolin-3-ylide-neamino) thiazol-4-yl)acetamido)-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate]. (0.5) Methanol (LI) and [sodium3-(acetoxymethyl)-7-((2Z)-2-(2-(4-dimethylamino) benzylideneamino) thiazol-4-yl)-2-(methoxyimino)acetamido)-8-oxo-5-thia-1-azabicyclo [4.2.0] oct-2-ene-2-carboxylate]. (0.5) Methanol (LII) from the condensation reaction of the antibiotic with 1H-Indole-2,3-dione(isatin) and -N, N-dimethyl amino benzaldehyde respectively. Metal complexes of the two Schiff base ligands with Co(II), Ni(II), Cu(II), Cd(II), Pd(II) and Pt(IV) ions were prepared by reacting each ligand with the metal salts in refluxing ethanol. The chemical structures of the two ligands as well as the stereo-chemical structures and geometries of the studied metal complexes were suggested depending the results obtained from CHN and TG analysis, NMR, FTIR, and atomic absorption spectrophotometry, electronic spectra, magnetic moments and conductivity measurements. The mole ratio of the ligands to the metal ion was 1:1 with tridentate bonding behaviors of the coordinating ligands with the metal ions.

Synthesis, Structure Characterization, Antibacterial Activity and Fluorescence Studies of a Ni(Ⅱ) Compound with Schiff-base Ligand

We synthesized one novel Schiff-base ligand by modifying the aromatic aldehyde： H2L^1（H2L^1 = N,N？-bis（2-oxy-acetate-3-methoxyl）benzylpropylene（1,3-propane）diamine）. [Ni（C（23）H（24）N2O8）]·6H2O]（1） was prepared by the reaction between H2L^1 and NiCl2·6H2O in C2H5 OH. Compound 1 was structurally characterized by elemental analysis, IR, H NMR and single-crystal X-ray diffraction. 1 crystallizes in monoclinic system, space group P21/n with a = 1.3952（4）, b = 1.3746（9）, c = 1.6121（0） nm, β = 112.66（3）°, V = 2.8533（4） nm^3, Z = 4, Mr = 623.25 and Dc = 1.451 g·cm^（-3）. The Ni（Ⅱ） atom is hexa-coordinated to furnish a slightly distorted octahedral geometry. Lattice water molecules are found in 1, and the H-bonding intersections formed novel water clusters. The IR, antibacterial activity and luminescence of 1 are studied.

Synthesis,spectral studies,thermal behavior,and antibacterial activity of Ni(Ⅱ),Cu(Ⅱ),and Zn(Ⅱ) complexes with an ONO tridentate Schiff base

Three new transition metal complexes have been synthesized with a Schiff base, 3-（2-hydroxy-5-chlorophenylimino）-1,3- diphenylpropen-l-one. In all complexes Schiff base is completely deprotonated and coordinated to metal as tridentate ligand via phenolic and enolic oxygens and imine nitrogen. Thermal decomposition of the complexes has been studied by thermogravimetry. The in vitro antibacterial activity of Schiff bases and their complexes has been evaluated and compared with the standard drugs.

Design,synthesis and evaluation of novel cis-p-menthane type Schiff base compounds as effective herbicides

p-Menthane type monoterpene derivatives were identified as bio-based compounds with high herbicidal activities. In order to search novel p-menthane type monoterpene derivatives in good performance, a series of novel cis-p-menthane type Schiff base derivatives were designed and synthesized. All target products were easily available novel compounds and characterized by FT-IR,^1H NMR,^13 C NMR and ESI＋-MS. Their pre-emergence herbicidal activities against annual ryegrass were evaluated. The bioassays indicated that most of the target compounds displayed excellent herbicidal activities in pre-emergence treatment.

Synthesis,structural characterization and antibacterial activity of diorganotin(Ⅳ) complexes with ONO tridentate Schiff bases containing pyridine ring

Five organotin（IV） complexes, were obtained by reaction of SnR2C12 （R = Ph, Me, Bu） with ONO donor Schiff bases. The synthesized complexes have been investigated by elemental analysis and IR, 1H NMR, and ll9Sn NMR spectroscopy. These data show that the Schiff base acts as a tridentate dianionic ligand and coordinates via the imine nitrogen and two oxygen atoms. The X- ray crystallography of complex 4 shows a dimeric structure for this molecule. The in vitro antibacterial activities of the Schiff bases and their complexes have been evaluated against Gram-positive （Bacillus subtilis and Staphylococcus aureus） and Gram-negative （Escherichia coli and Pseudomonas aeruginosa） bacteria and compared with the standard antibacterial drugs.

Investigation of Antibacterial Activity of Two Kinds of Novel Schiff Bases on Escherichia coil by Microcalorimetry

The microcalorimetric method was used to study the antibacterial activity of two newly synthesized Schiff base compounds （H2L3＇ and H2L3） on Escherichia coli, trying to obtain the action on both of multiplying bacteria and non-multiplying bacteria at one experiment. The metabolic power-time curves of the bacteria treated with the compounds were obtained, and the thermokinetic parameters were analyzed, from which the antibacterial activities of these compounds were evaluated. The results showed that both of the two compounds have good activity on aerobic multiplying metabolism of E. coli, with the value of ICso 75.8 and 168.8 mg/L respectively, but have not effective action on fermentation metabolism of E. coli. The action of the compounds on the non-multiplying metabolism was investigated by taking the heat output of E. coli in the stationary phase as the guideline of the activity. The value of MSCso （minimum stationary-cidal concentration 50） of them is 118 and 187.5 mg/L, respectively. So, H2L^3 has stronger antibacterial action on E. coli than H2L^3 either for multiplying bacteria or non-multiplying bacteria, and their activity on the aerobic multiplying bacteria of E. coil is mainly shown. It does strongly suggest that the calorimetric method should play an important role in the fight against the drug-resistant bacteria.

Antibacterial Activity and Structure-Activity Relationships of Schiff Bases on Staphylococcus aureus by Microcalorimetry

The growth of Staphylococcus aureus under the action of six kinds of Schiff bases（A,B,C,D,E,F） was studied by means of microcalorimetry. Growth constant k and inhibition ratio I were calculated. Also,the antibacterial activity,the action characteristics and the structure-activity relationships of the compounds on S. aureus were analyzed. Results indicate that B,F show good antibacterial activity（IC50：293.6 mg · L-1 and 307.8 mg · L-1） ,D,E show moderate antibacterial activity（IC50：966.3 mg · L-1 and 1 126.7 mg · L-1） ,and A,C just show weak antibacterial activity（IC50 〉1 200 mg · L-1） . The I-c curves mainly present a straight line shape for B,D,E and F,but an inverse ＂S＂ shape for A and C. Structure-activity relationships analysis suggests that the species and position of the substituents determine the antibacterial activity of these Schiff bases,and the charge density distribution is one of the most important influencing factors.