Amino Acid Schiff Base Complexes Research Articles

Structure explication, biological evaluation, DNA interaction, electrochemistry and antioxidant activity of iron (II) tri- and tetra-dentate Schiff base amino acid complexes

Structure explication, biological evaluation, DNA interaction, electrochemistry and antioxidant activity of iron (II) tri- and tetra-dentate Schiff base amino acid complexes

Trinuclear nickel(II) amino acid Schiff base complex containing phenolato and acetato bridges: Structural and functional resemblance of urease

A novel phenolato and acetato bridged trinuclear Ni(II) complex [Ni3L2] was synthesized by the reaction between the amino acid Schiff base, N-o-vanillylidene-l-histidine(L) and Ni(OAc)2·2H2O. Single crystal X-ray analysis reveals that the trinuclear structure of Ni3L2 is built by linking two terminal NiN2O4 cores with one NiO6 centre core (NiN2O4⋯NiO6⋯NiN2O4) and each Ni(II) ion exists in an octahedral environment. Variable-temperature magnetic susceptibility data represent the antiferromagnetic interactions of the Ni3L2 mediated by a single Ni-O-Ni bridge. The bond length and bond angles around each terminal nickel centre match the nickel centre in urease enzyme of native bacteria Klebsiella aerogenes, Bacillus pasteurii and Helicobacter pylori. The catalytic activity of Ni3L2 on the hydrolysis of urea into ammonia and carbon dioxide was established by the absorption spectral method. The urea binding propensity of the nickel complex Ni3L2 was compared with jack bean urease by using molecular docking studies.

Transition metal complexes constructed by pyridine–amino acid: fluorescence sensing and catalytic properties

Four amino acid Schiff base complexes—one with a 3D network structure ({[Cd2(PYSA)2(H2O)]·3H2O}n (1)) and the other three with a supramolecular network structure {[Co(PYSA) (H2O)2]·H2O}n (2), {([Zn(PYSA)(H2O)2]·H2O}n (3), {[Mn(PYSA)(H2O)2]·H2O}n (4)), (PYSA = (S-2-(pyridine-4-ylmethylamino) succinic acid)—were successfully obtained under hydrothermal conditions. Among the four complexes, photoluminescence analysis revealed that complex 1 exhibited high selectivity and sensitivity in the detection of iron ions. In particular, it was able to qualitatively and quantitatively detect iron ions at low concentrations without interference from other ions. With a Fe3+ concentration of 0.01 mol/L, the detection limit was 0.81 μM, Ksv = 2.46 × 104 L/mol. In addition, complex 2 exhibited excellent catalytic performance toward 4-nitrophenol (4-PNP). Four amino acid Schiff base complexes 1–4 were synthesized by a hydrothermal method. Among the four, complex 1 exhibited good fluorescence sensing performance in the detection of Fe3+ in water. In addition, the catalytic activity of complex 2 for 4-PNP was preliminarily investigated, which showed an ability to reduce 4-PNP to 4-PAP.

SBA-16 supported amino acid Schiff base complexes of molybdenum as new heterogeneous molybdenum catalysts

Immobilization of molybdenum complexes of amino acid Schiff bases within the SBA-16 nanocages produced new heterogeneous catalysts for the epoxidation of olefins. First, amino acid Schiff bases were obtained through the reaction of amino acids with salicylaldehyde. Then, complexation of the prepared amino acid Schiff bases with molybdenum (VI) produced the molybdenum complexes of amino acid Schiff bases. Immobilization of the molybdenum complexes into the SBA-16 nanocages followed by silylation with triethoxyoctylsilane gave the heterogenized molybdenum catalysts. The obtained catalysts were characterized with several physicochemical techniques. FT-IR and inductively coupled plasma optical emission (ICP-OES) spectroscopies approved the inclusion of molybdenum complexes within the SBA-16 nanocages. The results of X-ray diffraction (XRD) and nitrogen adsorption-desorption (BET method) analyses illustrated that surface properties of SBA-16 were maintained upon the inclusion of molybdenum complexes. The prepared catalysts exhibited good activities and excellent selectivities (>99%) in the epoxidation of olefins with tert-butyl hydroperoxide (TBHP).

Anionic oxide‑vanadium Schiff base amino acid complexes as potent inhibitors and as effective catalysts for sulfides oxidation: Experimental studies complemented with quantum chemical calculations

Three anionic oxide‑vanadium Schiff base N-salicylidene amino acid complexes are derived from the reaction of sodium salicylaldehyde-5-sulfonate with phenylalanine (VO-1), alanine (VO-2) or glycine (VO-3), followed by mixing with vanadyl sulfate monohydrate. Inhibition effect of VO-1, VO-2 and VO-3 is investigated for the corrosion of carbon steel in chloride acid solution. From the electrochemical measurements, VO-complexes protect carbon steel form corrosion, yielding maximum inhibition efficiency up to 94.7% in the presence of 1.0mM VO-1 inhibitor. All VO-complexes act as mixed-type inhibitors. The SEM and EDX investigations provided the appearance of an inhibitor layer encasement the steel surface. Catalytic efficiency of VO-complexes is measured in the symmetric and asymmetric oxidation of sulfides by using an aqueous H2O2. All complexes show high catalytic potentials towards sulfides oxidation. VO-1, VO-2 and VO-3 are optimized at B3LYP/GEN and B3LYP/LANL2DZ levels of theory in gas and aqueous phases. Theoretical results agree with the experimental reactivity of the VO-complexes, as corrosion inhibitors and catalysts for sulfides oxidation.

Binding interactions of mixed ligand copper(II) amino acid Schiff base complexes with biological targets: Spectroscopic evaluation and molecular docking

AbstractThree mixed ligand copper(II) complexes [Cu(o‐vanillin‐l‐tryptophan Schiff base)(diimine)] (diimine =2,2′‐bipyridine (1), 1,10‐phenanthroline (2) and 5,6‐dimethyl‐1,10‐phenanthroline(3)) were synthesized and characterized using analytical and spectral methods. The molecular structures of 1–3 were optimized using density functional theory (DFT) at B3LYP/LanL2DZ levels in the gas phase. Spectral and DFT studies suggest a distorted square pyramidal geometry around the copper ion. Binding interactions of 1–3 with calf thymus DNA and bovine serum albumin protein were studied using UV–visible and fluorescence spectroscopies, viscometric titrations and cyclic voltammetry and also using molecular docking analysis. Studies of the binding of the complexes with calf thymus DNA reveal intercalation, which is supported by molecular docking simulation. The DNA cleavage nature of 1–3 with pUC19 DNA shows that the complexes can cleave DNA without any external agents, and the efficiency follows the order 1 > 3 > 2. Synchronous and three‐dimensional fluorescence spectral studies suggest that the secondary structures of the protein are altered by the complexes. Antioxidant studies reveal that the complexes have significant radical scavenging activity against DPPH. In vitro cytotoxic activity of the complexes was evaluated against breast cancer cells (MCF‐7), revealing that complex 2 exhibits higher cytotoxicity than the other complexes. Nuclear chromatin condensation and fragmentation were observed with DAPI staining assay. The mitochondrial membrane potential damage was studied by FITC staining assay. Flow cytometric analysis suggests that all the metal complexes induce cell apoptosis.

Kinetic Screening for the Acid‐Catalyzed Hydrolysis of Some Hydrophobic Fe(II) Schiff Base Amino Acid Chelates and Reactivity Trends in the Presence of Alkali Halide and Surfactant

ABSTRACTKinetics of acid‐catalyzed hydrolysis of some high‐spin Fe(II) Schiff base amino acid complexes were followed spectrophotometrically at 298 K under pseudo–first‐order conditions. The studied ligands were derived from the condensation of 5‐bromosalicylaldehyde with different four amino acids (phenylalanine, aspartic acid, histidine, and arginine). The acid hydrolysis reaction was studied in aqueous media and in the presence of different concentrations of the alkali halide (KBr) and cationic surfactant (cetyl‐trimethyl ammonium bromide, CTAB). The general rate equation was suggested to be rate = kobs[complex], where kobs = k2[H+]. The increase in [KBr] enhances the reactivity of the reaction, and the addition of CTAB to the reaction mixture accelerates the reaction reactivity. The obtained kinetic data were used to determine the values of δmΔG# (the change in the activation barrier) for the studied complexes when transferred from “water to water containing different [KBr]” and from “water to water containing altered [CTAB].”

Kinetics of acid hydrolysis and reactivity of some antibacterial hydrophilic iron(II) imino-complexes

Kinetic study of acid hydrolysis of some hydrophilic Fe(II) Schiff base amino acid complexes with antibacterial properties was performed using spectrophotometry. The Schiff base ligands were derived from sodium 2-hydroxybenzaldehyde-5-sulfonate and glycine, L-alanine, L-leucine, L-isoleucine, DL-methionine, DL-serine, or L-phenylalanine. The reaction was studied in aqueous media under conditions of pseudo-first order kinetics. Moreover, the acid hydrolysis was studied at different temperatures and the activation parameters were calculated. The general rate equation was suggested as follows: rate = k obs [Complex], where k obs = k 2 [H+]. The evaluated rate constants and activation parameters are consistent with the hydrophilicity of the investigated complexes.

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.

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.

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.

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.

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.

Microwave Assisted Synthesis and Antioxidant Activity of Vanadium(IV) Complexes of Amino Acid Schiff Bases

Synthesis of some amino acid Schiff base complexes of vanadium(IV) was done using microwave mode of synthesis and aqueous/semiaqueous medium as solvent. Complexes were characterized by using common analytical and spectroscopic tools such as IR, 1H NMR, EI Mass, ESR, and magnetic susceptibility measurements. Single-crystal X-ray analysis of one of the complexes was carried out. Antioxidant activity of the complexes was studied using the DPPH scavenging method. The present work attempts to establish a possible structure and antioxidant activity correlation of the synthesized complexes. Some of the complexes show comparable activity to that of the standard reference (i.e., ascorbic acid).

Spectroscopic characterization of novel d-amino acid-Schiff bases and their Cr(III) and Ni(II) complexes as antimicrobial agents

The aim of this work was to investigate the antibacterial and antifungal activities of novel d-amino acid-Schiff bases including fluorine atom and their Cr(III) and Ni(II) complexes. All these substances have been examined for antibacterial activity against pathogenic strains Listeria monocytogenes 4b ATCC19115, Staphylococcus aureus ATCC25923, Escherichia coli ATCC1280, Salmonella typhi H NCTC 901.8394, Brucella abortus (A.99, UK-1995) RSKK03026, Staphylococcus epidermis sp., Micrococus luteus ATCC9341, and Shigella dysenteria typ 10 NCTC 9351, and antifungal activity against Candida albicans Y-1200-NIH, Tokyo. The antimicrobial test results of these amino acid-Schiff base complexes exhibited better activity than some known antibiotics. In particular, diamagnetic Ni(II) complexes were more potent bactericides than all of the substances synthesized.

Immobilized vanadium amino acid Schiff base complex on Al-MCM-41 as catalyst for the epoxidation of allyl alcohols

Vanadium complexes of N-salicylidene-l-histidine immobilized on Al-MCM-41 designated as VO(Sal-His)/Al-MCM-41, were prepared and characterized by X-ray powder diffraction (XRD), FT-IR, nitrogen adsorption–desorption and chemical analysis techniques. VO(Sal-His)/Al-MCM-41 was found to catalyze the epoxidation of trans-2-hexen-1-ol, cinnamyl alcohol and geraniol with tert-butyl hydroperoxide (TBHP). The successful catalytic behavior of VO(Sal-His)/Al-MCM-41 with 99% conversion and excellent selectivity toward the corresponding epoxides is described herein.

Kinetic investigation of aquation of some Fe(II) Schiff base amino acid complexes

Kinetics of aquation of some Fe(II) Schiff base amino acid complexes was followed spectrophotometrically. The Schiff base ligands were derived from salicylaldehyde and isoleucine, leucine, serine, methionine, tryptophan, or histidine. The reaction was studied in aqueous media, aqua–propanol mixtures, and in the presence of different concentrations of KBr. Moreover, the activation parameters were calculated and discussed for structures and other physical properties observed. The reaction was acid catalyzed and the general rate equation was suggested as follows: rate = kobs [complex], where kobs = k2 [H+]. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 372–379, 2010

DNA binding and cleavage activity of reduced amino-acid Schiff base complexes of cobalt(II), copper(II), and cadmium(II)

Three new reduced amino-acid Schiff base complexes, [Co(HL)2(H2O)2] · 4H2O (1), [Cu(HL)2(H2O)2] · 2H2O (2), and [Cd(HL)2(H2O)3] · 2H2O (3), where H2L is the reduced Schiff-base ligand derived from the condensation of N-(4-hydroxybenzaldehyde) with L-glycine, have been synthesized and characterized by physico-chemical and spectroscopic methods. In these complexes, the two bidentate monoanionic Schiff base ligands coordinate the metal center through the secondary amine N atom and the carboxylate O atom. Water ligands complete a distorted octahedral (1, 2) or a pentagonal bipyramidal coordination geometry (3) around each metal center. The binding interactions of the complexes with CT-DNA have been investigated by UV–visible spectrophotometry and fluorescence quenching methods. The results show that these complexes bind to CT-DNA with an intercalative mode. In addition, DNA cleavage experiments have been also investigated by agarose gel electrophoresis. Complexes 1–3 show oxidative DNA cleavage activity in the presence of H2O2/sodium ascorbate and the reactive oxygen species responsible for the DNA cleavage is most likely singlet oxygen.