Amino Acid Schiff Base Research Articles

Effect of bromide salts on the acid hydrolysis of anti-bacterial hydrophilic Schiff base amino acid iron(II) complexes

Salt effects on the kinetics of acid hydrolysis of some novel hydrophilic iron(II) complexes have been investigated in aqueous medium. The ligands are derived from the condensation of amino acids (glycine, L-alanine, L-leucine, L-isoleucine, DL-methionine, DL-serine or L-phenylalanine) and sodium 2-hydroxybenzaldehyde-5-sulfonate. The reaction was studied under conditions of pseudo first order kinetics. The general rate equation was suggested as follows: rate = kobs[complex], where kobs = k2[H+]. The reaction rate decreases with an increase of the salt concentration.

Kinetic study of the hydroxide ion attack on and DNA interaction with high spin iron(II) Schiff base amino acid chelates baering ONO donors

Kinetic study of some novel high spin Fe(II) complexes of Schiff base ligands derived from 5-bromsalicyaldehyde and amino acids with the OH− ion and DNA has been carried out. Based on the kinetic data, the rate law and a plausible mechanism were proposed. Kinetic data of the base catalyzed hydrolysis imply pseudo first-order double stage process due to the presence of mer- and fac-isomers. The observed rate constants kobs were correlated with the effect of a substituent R in the structure of ligands. The rate constants and activation parameters are in good agreement with stability constants of the studied complexes. Reactivity of the complexes towards DNA correlated well with the reported binding constants.

Reactivity Trends and Kinetic Inspection of Hydroxide Ion Attack and DNA Interaction on Some Pharmacologically Active Agents of Fe(II) Amino Acid Schiff Base Complexes at Different Temperatures

ABSTRACTThe reactivity of few novel high‐spin Fe(II) complexes of Schiff base ligands derived from 2‐hydroxynaphthaldehyde and some variety of amino acids with the OH− ion has been examined in an aqueous mixture at the temperature range from 10 to 40°C. Based on the kinetic investigations, the rate law and a plausible mechanism were proposed and discussed. The general rate equation was suggested as follows: rate = kobs[complex], where kobs. = k1 + k2[OH−]. Base‐catalyzed hydrolysis kinetic measurements imply pseudo–first‐order doubly stage rates due the presence of mer‐ and fac‐isomers. The observed rate constants kobs are correlated with the effect of substituent R in the structure of the ligands. From the effect of temperature on the rate base hydrolysis reaction, various thermodynamic parameters were evaluated. The evaluated rate constants and activation parameters are in a good agreement with the stability constants of the investigated complexes. Moreover, the reactivity of the investigated complexes toward DNA was examined and found to be in a good agreement with the reported binding constants.

Synthesis, CMC determination and nucleic acid-binding interaction of a surfactant copper(II) complex containing amino acid–Schiff base ligand:[Cu(sal-ala)(bpy)(DA)

The surfactant copper(II) complex, [Cu(sal-ala)(bpy)(DA)] (sal-ala = amino acid Schiff base, bpy = 2,2′-bipyridyl, DA = dodecylamine) has been synthesized and characterized by elemental analysis, UV–Vis, IR and EPR spectra. The critical micelle concentration (CMC) values of this surfactant copper(II) complex in aqueous solution was obtained from conductance measurements. Specific conductivity data (at 303, 308, 313. 318 and 323 K) served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (Δ $$G_{\text{m}}^0$$ , Δ $$H_{\text{m}}^0$$ and Δ $$S_{\text{m}}^0$$ ). Absorption, fluorescence, cyclic voltammetry, circular dichroism spectroscopy and viscosity experiments have been carried to study the interaction of this surfactant complex with nucleic acids. The results suggest that the complex could bind to nucleic acids by intercalation via salicylidene aromatic chromophore into the base pairs of CT DNA. The long aliphatic chain of the surfactant complex increases the hydrophobic interaction between the complex and nucleic acid. The surfactant copper(II) complex was screened for their antibacterial and antifungal activities against various microorganisms. The results were compared with the standard drugs, amikacin (antibacterial) and ketokonazole (antifungal).

Synthesis and characterization of higher amino acid Schiff bases, as monosodium salts and neutral forms. Investigation of the intramolecular hydrogen bonding in all Schiff bases, antibacterial and antifungal activities of neutral forms

Schiff bases derived from 5-nitro-salicylaldehyde and 4-aminobutyric acid, 5-aminopentanoic acid and 6-aminohexanoic acid were synthesized both as monosodium salts (1a–3a) and neutral forms (1b–3b). The monosodium-Schiff bases were characterized by elemental analysis, 1H/13C NMR, IR, powder XRD, UV–vis spectra and conductivity measurements. The neutral-Schiff bases were characterized by elemental analysis, 1H/13C NMR, 2D NMR (HMQC), mass, IR, powder XRD, UV–vis spectra and conductivity measurements. The intramolecular hydrogen bonding and related tautomeric equilibria in all the Schiff bases were studied by UV–vis and 1H NMR spectra in solution. Additionally, the neutral-Schiff bases were screened against Staphylococcus aureus-EB18, S. aureus-ATCC 25923, Escherichia coli-ATCC 11230, Candida albicans-M3 and C. albicans-ATCC 16231.

Two 2D grid-based Co(II) amino acid Schiff base complexes with left- and right-handed helical chains: Structures and magnetism

Two layered Co(II) amino acid Schiff base complexes, [Co(napala)(tbpe)0.5]n (1) and [Co(napgly)(tbpe)0.5]n (2) [H2napala=N-(2-hydroxy-1-naphthylmethylidene)-d/l-alanine, H2napgly=N-(2-hydroxy-1-naphthylmethylidene)-glycine and tbpe=trans-1,2-bis(4-pyridyl)ethylene], have been synthesized by solvothermal methods and characterized using single-crystal X-ray diffraction. The bridging of Schiff base ligands napala2− or napgly2− with Co(II) forms one-dimensional (1D) left- and right-handed helical chains which are further pillared by tbpe to build a two-dimensional (2D) grid-based hcb-type framework. Moreover, both complexes show high thermal stability and exhibit antiferromagnetic coupling between the Co(II) centers mediated by the syn–anti-COO−-bridges.

Exploring DNA binding and nucleolytic activity of few 4-aminoantipyrine based amino acid Schiff base complexes: A comparative approach

A series of novel Co(II), Cu(II), Ni(II) and Zn(II) complexes were synthesized from Schiff base(s), obtained by the condensation of 4-aminoantipyrine with furfural and amino acid (glycine(L1)/alanine(L2)/valine(L3)) and respective metal(II) chloride. Their structural features and other properties were explored from the analytical and spectral methods. The binding behaviors of the complexes to calf thymus DNA were investigated by absorption spectra, viscosity measurements and cyclic voltammetry. The intrinsic binding constants for the above synthesized complexes are found to be in the order of 102 to 105 indicating that most of the synthesized complexes are good intercalators. The binding constant values (Kb) clearly indicate that valine Schiff-base complexes have more intercalating ability than alanine and glycine Schiff-base complexes. The results indicate that the complexes bind to DNA through intercalation and act as efficient cleaving agents. The in vitro antibacterial and antifungal assay indicates that these complexes are good antimicrobial agents against various pathogens. The IC50 values of [Ni(L1)2] and [Zn(L1)2] complexes imply that these complexes have preferable ability to scavenge hydroxyl radical.

Green Route for Efficient Synthesis of Novel Amino Acid Schiff Bases as Potent Antibacterial and Antifungal Agents and Evaluation of Cytotoxic Effects

Green chemical one-pot multicomponent condensation reaction of substituted 1H-indole-2,3-diones (1), various amino acids (2), and thiosemicarbazide (3) is found to be catalyzed by lemon juice as natural acid using water as a green solvent to give the corresponding Schiff bases (4) in good to excellent yields. This method is experimentally simple, clean, high yielding, and green, with reduced reaction times. The product is purified by simple filtration followed by washing with water and drying process. The synthesized compounds are characterized by FT-IR,13CNMR, and1HNMR spectroscopy and are screened for their antifungal activity againstAspergillus niger,Penicillium notatum,Fusarium oxysporum,Alternaria brassicicola,Chaetomium orium, andLycopodium sp.and antibacterial activity against Gram-positive bacteria,Bacillus licheniformis,Staphylococcus aureus, andMicrococcus luteus,and Gram-negative bacteria,Pseudomonas aeruginosaandEscherichia coli. Compounds have also been evaluated for cytotoxic effects against human colon cancer cell line Colo205.

Synthesis of Phenylhydrazone and Amino acid Schiff Base of Pyropheophorbide-a

Methyl pyropheophorbide-a was used as starting material for the synthesis of phenylhydrazone and amino acid Schiff base by reactions of carbonyl group at 13-position. The maximum absorption wavelength of phenylhydrazone caused a red shift. The water-solubility of Schiff base was incremented, and the maximum absorption wavelength shifted hypsochromically. The structures of all these compounds were characterized by H NMR, MS and elemental analysis.

Newer mixed ligand Schiff base complexes from aquo-N-(2′-hydroxy acetophenone) glycinatocopper(II) as synthon: DFT, antimicrobial activity and molecular docking study

Synthesis of a series of newer mixed ligand copper(II) complexes of aminoacid Schiff base of the type [CuL(X)] (L=N-(2′-hydroxy acetophenone) glycinate, X=imidazole (im) 2, benzimidazole (benz) 3, pyridine (py) 4, hydrazine (hz) 5,8-hydroxyquinoline (8-hq) 6, pyrrolidine (pyrr) 7, piperidine (pip) 8, and nicotinamide (nic) 9) have been accomplished from the interaction of an aquated Schiff base complex, [CuL(H2O)]·H2O, 1 with some selected neutral nitrogen-donor ligands. The copper(II) Schiff base complex, [CuL(H2O)]·H2O, L=N-(2′-hydroxy acetophenone) glycinate was synthesized from the reaction of glycine and 2′ hydroxy acetophenone and copper(II) acetate. The compounds were characterised by elemental analysis, spectral, magnetic and thermal studies. The density functional theory calculations were performed using LANL2DZ and 6-311 G(d, p) basis sets with B3LYP correlation functional to ascertain the stable electronic structure, HOMO–LUMO energy gap, chemical hardness and dipole moment of the mixed ligand complexes. A distorted square planar geometry has been conjectured for the complexes. Antibacterial activities of the ligand and its metal complexes have been tested against selected gram-positive and gram-negative strains and correlated with computational docking scores.

Hydrophobicity, reactivity trends of base catalyzed hydrolysis of some novel high spin Fe(II) Schiff base amino acid chelates in some binary aqueous solvent mixtures: Initial-transition state analysis

Rate constants for the base hydrolysis of bis(naphthylidene alanate)iron (II) (nali), bis(naphthylidene phenylalanate)iron(II) (nphali), bis(naphthylidene aspartate)iron(II) (nasi), (naphthylidene histidinate)iron(II) (nhi), bis(naphthylidene arginate)iron(II) (nari) have been reported in different binary aqueous solvent mixtures at 298K. The observed reactivity trends are discussed in terms of the hydrophilic and hydrophobic forms of the complexes investigated, as well as the transfer chemical potentials of the hydroxide ion and the complex. Both the solvent–solute and solvent–solvent interactions have been considered. The hydrophobic character of the complexes studied was manifested by a decrease in reactivity. Solvent effect on reactivity trends of the investigated complexes have been analyzed into initial and transition state components. This can be achieved by using the transfer chemical potentials of the reactants and the kinetic data of the studied compounds. The decrease in the observed rate constant values (kobs) of the base hydrolysis of the investigated complexes with increase of solvent% is dominated by the initial state (IS).

Synthesis, Characterization, and Antimicrobial Activities of New N-(2-hydroxy-1-naphthalidene)-amino Acid (L-Tyrosine, L-Arginine, and L-Lysine) Schiff Bases and Their Manganese(III) Complexes

A new series of manganese(III) complexes Na[Mn(L1)2].3H2O, Na3[MnL2(CH3COO)4].2H2O, Na[Mn(L3)2].2H2O and amino acid Schiff bases (H2L1); [N-(2-hydroxy-1-naphthylidene)tyrosine], (H2L2); [N-(2-hydroxy-1-naphthylidene)arginine], (H2L3); [N-(2-hydroxy-1-naphthylidene)lysine] have been prepared from 2-hydroxy-1-naphthaldehyde and a-amino acids (L-tyrosine, L-arginine, and L-lysine). The structures of the compounds were identified using elemental analyses, IR, UV-VIS, 1H-NMR spectra, magnetic susceptibility measurements, and thermogravimetric analyses (TGA). All of these substances have been also examined for antibacterial activity against the pathogenic strains S. aureus, Sh. dys. typ 7, L. monocytogenes 4b, E. coli, S. typhi H, S. epidermis, Br. abortus, M. luteus, B. cereus, P. putida, and antifungal activity against C. albicans.

Synthesis, Characterization and Spectrophotometric Studies of Seven Novel Antibacterial Hydrophilic Iron(II) Schiff Base Amino Acid Complexes

A series of new Iron(II) Schiff base amino acid complexes derived from the condensation of amino acid and sodium 2-hydroxybenzaldehyde-5-sulfonate have been synthesized. The complexes were characterized by elemental, electronic, IR spectral analyses and conductance measurements. The stability and solubility of the prepared complexes were determined. Two spectral methods used to determine the stoichiometry of the prepared complexes which exhibited divalent tridentate coordination and formed chelates of octahedral structures. The antibacterial activity of the prepared complexes has been tested against Bacillus cereus, Pseudomonas aeruginosa and Micrococcus bacteria. The effect of HCl on investigated complexes studied spectrophotometrically.

A systematic investigation on biological activities of a novel double zwitterionic Schiff base Cu(II) complex

Double zwitterionic amino acid Schiff base, o-vanillylidene-l-histidine (OVHIS) and its copper complex (CuOVHIS) have been synthesized and characterized. CuOVHIS has distorted octahedral geometry, and OVHIS coordinates the copper ion in a tetradentate manner (N2O2). The pKa of OVHIS in aqueous solution was studied by potentiometric and spectrophotometric methods. DNA binding behavior of the compounds was investigated using spectrophotometric, cyclic voltammetric, and viscosity methods. The efficacy of DNA cleaving nature was tested on pUC19 DNA. The in vitro biological activity was tested against various micro organisms. The effect of CuOVHIS on the surface feature of Escherichia coli was analyzed by SEM. DPPH assay studies revealed that CuOVHIS has higher antioxidant activity. OVHIS inhibits proliferation of HCT117 cells with half maximal inhibition (IC50) of 71.15±0.67. Chelation of OVHIS with Cu(II) ion enhances the inhibition of proliferation action (IC50=53.14±0.67).

Metal based pharmacologically active agents: Synthesis, structural characterization, molecular modeling, CT-DNA binding studies and in vitro antimicrobial screening of iron(II) bromosalicylidene amino acid chelates

In recent years, great interest has been focused on Fe(II) Schiff base amino acid complexes as cytotoxic and antitumor drugs. Thus a series of new iron(II) complexes based on Schiff bases amino acids ligands have been designed and synthesized from condensation of 5-bromosalicylaldehyde (bs) and α-amino acids (l-alanine (ala), l-phenylalanine (phala), l-aspartic acid (aspa), l-histidine (his) and l-arginine (arg)). The structure of the investigated iron(II) complexes was elucidated using elemental analyses, infrared, ultraviolet–visible, thermogravimetric analysis, as well as conductivity and magnetic susceptibility measurements. Moreover, the stoichiometry and the stability constants of the prepared complexes have been determined spectrophotometrically. The results suggest that 5-bromosalicylaldehyde amino acid Schiff bases (bs:aa) behave as dibasic tridentate ONO ligands and coordinate to Fe(II) in octahedral geometry according to the general formula [Fe(bs:aa)2]⋅nH2O. The conductivity values between 37 and 64ohm−1mol−1cm2 in ethanol imply the presence of nonelectrolyte species. The structure of the complexes was validated using quantum mechanics calculations based on accurate DFT methods. Geometry optimization of the Fe-Schiff base amino acid complexes showed that all complexes had octahedral coordination. In addition, the interaction of these complexes with (CT-DNA) was investigated at pH=7.2, by using UV–vis absorption, viscosity and agarose gel electrophoresis measurements. Results indicated that the investigated complexes strongly bind to calf thymus DNA via intercalative mode and showed a different DNA binding according to the sequence: bsari>bshi>bsali>bsasi>bsphali. Moreover, the prepared compounds are screened for their in vitro antibacterial and antifungal activity against three types of bacteria, Escherichia coli, Pseudomonas aeruginosa and Bacillus cereus and three types of anti fungal cultures, Penicillium purpurogenium, Aspergillus flavus and Trichotheium rosium. The results of these studies indicated that the metal complexes exhibit a stronger antibacterial and antifungal efficiency than their corresponding Schiff base amino acid ligands.

DNA binding ability mode, spectroscopic studies, hydrophobicity, and in vitro antibacterial evaluation of some new Fe(II) complexes bearing ONO donors amino acid Schiff bases

New series of Fe(II) complexes and Schiff base amino acids have been designed and synthesized from the bioactive ligands by condensation of 5-bromo-2-hydroxybenzaldehyde and α-amino acids (l-alanine (ala), l-phenylalanine (phala), l-aspartic acid (aspa), l-histidine (his) and l-arginine (arg)). Elemental analyses, infrared, ultraviolet–visible spectra, as well as conductivity and magnetic susceptibility measurements are used to elucidate the structure of the newly prepared iron(II) complexes. Moreover, the stoichiometry and the stability constants of the prepared complexes have been determined spectrophotometrically. The results suggest that the prepared Schiff base amino acid ligands behave as dibasic tridentate ONO ligands and bind to Fe(II) in octahedral geometry according to the general formula [Fe(bs:aa)2].nH2O. The DNA interaction of these complexes was tested at pH=7.2, by using electronic absorption spectra and viscosity measurements. The experimental results indicated that the investigated complexes could bind to DNA via intercalative mode and showed a different DNA binding activity according to the sequence: bsari>bshi>bsali>bsasi>bsphali. Moreover, the prepared compounds are tested for their in vitro antibacterial activity against three types of bacteria, Escherichia coli, Pseudomonas aeruginosa and Bacillus cereus. The results show that the metal complexes are more reactive with respect to their corresponding Schiff base ligands.

Design, characterization, teratogenicity testing, antibacterial, antifungal and DNA interaction of few high spin Fe(II) Schiff base amino acid complexes

In this study, new Fe(II) Schiff base amino acid chelates derived from the condensation of o-hydroxynaphthaldehyde with l-alanine, l-phenylalanine, l-aspartic acid, l-histidine and l-arginine were synthesized and characterized via elemental, thermogravimetric analysis, molar conductance, IR, electronic, mass spectra and magnetic moment measurements. The stoichiometry and the stability constants of the complexes were determined spectrophotometrically. Correlation of all spectroscopic data suggested that Schiff bases ligands exhibited tridentate with ONO sites coordinating to the metal ions via protonated phenolic-OH, azomethine-N and carboxylate-O with the general formulae [Fe(HL)2]·nH2O. But in case of l-histidine, the ligand acts as tetradentate via deprotonated phenolic-OH, azomethine-N, carboxylate-O and N-imidazole ring ([FeL(H2O)2]·2H2O), where HL=mono anion and L=dianion of the ligand. The structure of the prepared complexes is suggested to be octahedral. The prepared complexes were tested for their teratogenicity on chick embryos and found to be safe until a concentration of 100μg/egg with full embryos formation. Moreover, the interaction between CT-DNA and the investigated complexes were followed by spectrophotometric and viscosity measurements. It was found that, the prepared complexes bind to DNA via classical intercalative mode and showed a different DNA activity with the sequence: nhi>nari>nali>nasi>nphali. Furthermore, the free ligands and their complexes are screened for their in vitro antibacterial and antifungal activity against three types of bacteria, Escherichia coli, Pseudomonas aeruginosa and Bacillus cereus and three types of anti fungal cultures, Penicillium purpurogenium, Aspergillus flavus and Trichotheium rosium in order to assess their antimicrobial potential. The results show that the metal complexes are more reactive with respect to their corresponding Schiff base amino acid ligands.

Synthesis, physicochemical studies, embryos toxicity and DNA interaction of some new Iron(II) Schiff base amino acid complexes

New Fe(II) Schiff base amino acid complexes derived from the condensation of o-hydroxynaphthaldehyde with l-alanine, l-phenylalanine, l-aspartic acid, l-histidine and l-arginine were synthesized and characterized by elemental analysis, IR, electronic spectra, and conductance measurements. The stoichiometry and the stability constants of the complexes were determined spectrophotometrically. The investigated Schiff bases exhibited tridentate coordination mode with the general formulae [Fe(HL)2]·nH2O for all amino acids except l-histidine. But in case of l-histidine, the ligand acts as tetradentate ([FeL(H2O)2]·2H2O), where HL=mono anion and l=dianion of the ligand. The structure of the prepared complexes is suggested to be octahedral. The prepared complexes were tested for their toxicity on chick embryos and found to be safe until a concentration of 100μg/egg with full embryos formation. The interaction between CT-DNA and the investigated complexes were followed by spectrophotometry and viscosity measurements. It was found that, the prepared complexes bind to DNA via classical intercalative mode and showed a different DNA cleavage activity with the sequence: nhi>nari>nali>nasi>nphali. The thermodynamic Profile of the binding of nphali complex and CT-DNA was constructed by analyzing the experimental data of absorption titration and UV melting studies with the McGhee equation, van’t Hoff’s equation, and the Gibbs–Helmholtz equation.

Synthesis of New Zirconium(IV) Complexes with Amino Acid Schiff Bases: Spectral, Molecular Modeling, and Fluorescence Studies

New zirconium(IV) complexes were synthesized with bidentate ligands and characterized by elemental analysis, molar conductance measurements, molecular weight determinations, IR, electronic, NMR (1H and 13C), fluorescence and molecular modeling studies. All the complexes are 1 : 2 electrolytes in nature and may be formulated as [Zr(L)2Cl2] (where L is Schiff bases of amino acids and substituted isatin). The analytical data showed that the Schiff-base ligand acts as bidentate toward zirconium ion via the azomethine nitrogen and carboxylate oxygen. The conductivity values between 8.5–12.6 Ω−1, mol−1, cm2 in DMF imply the presence of nonelectrolyte species. On the basis of spectral and molecular modeling studies, the resulting complexes are proposed to have octahedral geometries.

Synthesis, Crystal Structure, Characterization and DNA Binding Studies of Novel Copper (II) Complex Based on Amino Acid Schiff Base

A novel Schiff base ligand (H2L) from the reaction of 1-phenyl-3-methyl-4-(2-furoyl)-5-pyrazolone with β-alanine and its copper (II) complex [CuLCH3OH]n (1) was synthesized and characterized by elemental analysis, UV, IR, 1H NMR, 13C NMR, MS, EPR, X-ray single crystal diffraction, variable temperature susceptibility measurement and thermogravimetric analysis. The crystal of the complex is a orthorhombic system with crystal parameters: P212121, a= 7.5169(6) Å, b= 13.2788(10) Å, c= 18.5631 (14) Å, α=90.00º, β= 90.00º, γ= 90.00º, V= 1852.9(2) Å3, Z= 4. It was found that the copper (II) complex had a distorted square pyramid coordination environment with two O, one N atoms of H2L ligand and one O atom at carboxyl group of another molecular in the square plane, and with CH3OH at the apex of polyhedron. The complex molecular is a coordination polymer. DNA-Binding properties of the Cu(II) complex and Schiff base ligand have been carried out by UV-vis, fluorescence spectra, circular dichroism spectra and in cleavage of plasmid pGreen DNA. The experimental results indicated that complex 1 and H2L both bind through electrostatic interaction to DNA. A competitive binding study showed that the enhanced emission intensity of ethidium bromide (EB) in the presence of DNA was quenched by the addition of complex 1 and the ligand, indicating that they displace EB from its binding site in DNA. Further, Circular dichroism (CD) spectra of DNA with the addition of the H2L and [CuLCH3OH]n exhibit a decrease in both the positive and negative peaks. Agarose gel electrophoresis shows that they can cleave plasmid pGreen DNA. Keywords: Acylpyrazolone, Amino acid schiff base, Coordination polymer, DNA binding activity, Hyperchromism, DNA cleavage.