Amino Acid Schiff Base Research Articles

Cellular and computational studies of proteasome inhibition and apoptosis induction in human cancer cells by amino acid Schiff base–copper complexes

Proliferation and apoptosis pathways are tightly regulated in a cell by the ubiquitin–proteasome system (UPS) and alterations in the UPS may result in cellular transformation or other pathological conditions. Indeed, the proteasome is often found to be overactive in cancer cells. It has also been found that cancer cells are more sensitive to proteasome inhibition than normal cells, and therefore proteasome inhibitors are pursued as antitumor drugs. The use of the proteasome inhibitor Bortezomib for treatment of multiple myeloma and mantle cell lymphoma has proved this principle. Recent studies have suggested that copper complexes can inhibit proteasome activity and induce apoptosis in some human cancer cells. However, the involved molecular mechanism is unknown. In this study, we investigated the biological activities of four amino acid Schiff base–copper(II) complexes by using human breast (MDA-MB-231 and MCF-7) and prostate (PC-3) cancer cells. The complexes C1 and C3, but not their counterparts C2 and C4, inhibit the chymotrypsin-like activity of purified 20S proteasome and human cancer cellular 26S proteasome, cause accumulation of proteasome target proteins Bax and IκB-α, and induce growth inhibition and apoptosis in concentration- and time-dependent manners. Docking analysis shows that C1, but not C2 has hydrophobic, pi–pi, pi–cation and hydrogen bond interactions with the proteasomal chymotrypsin-like pocket and could stably fit into the S3 region, leading to specific inhibition. Our study has identified the mechanism of action of these copper complexes on inhibiting tumor cell proteasome and suggested their great potential as novel anticancer agents.

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).

Synthesis, thermal characterization, and antimicrobial activity of lanthanum, cerium, and thorium complexes of amino acid Schiff base ligand

Metal complexes of La(III), Ce(IV), and Th(IV), with the amino Schiff base ligand, [N-(2-hydroxybenzyl)-l-methionine acid](H3L), were prepared in the presence of triethylamine as a deprotonating agent. All synthesized compounds were identified and confirmed by mass spectra, elemental analyses, molar conductivities, and spectral analyses (UV–Visible, IR, 1H NMR, and 13CNMR). Conductance measurements suggest the non-electrolytic nature and the complexes were isolated in 1:1 ratios. The thermal decomposition of the complexes was discussed in relation to structure. The data from thermogravimetric analysis clearly indicated that the decomposition of the complexes proceeds in four or five steps and the organic part of the complexes decomposed in one or two intermediates. The decomposition of all complexes ended with metal oxide and carbon residue. The Schiff bases and their complexes were screened for their antibacterial (Escherichia coli, Staphylococcus aureus) and antifungal (Aspergillus flavus and Candida Albicans) activities.

Binuclear cobalt complex with Schiff base ligand: Synthesis, characterization and catalytic properties in partial oxidation of cyclohexane

A new binuclear cobalt complex with Schiff base ligand and amino acid was synthesized and characterized using XRD, elemental analysis, IR spectroscopy, XPS and electrochemical measurements. The presence of cobalt in the oxidation state 3+ in this complex was proved. The catalytic activity of this complex was investigated in the reaction of partial cyclohexane oxidation with air, and high activity and selectivity for cyclohexanol and cyclohexanone formation were demonstrated. The possibility of complex reuse in cyclohexane oxidation was studied and it was shown that the activity slightly decreases in a second oxidation cycle along with changes in main product distribution due to partial transfer of Co3+ to Co2+.

Water-soluble platinum(II) complexes of reduced amino acid Schiff bases: synthesis, characterization, and antitumor activity

A series of water-soluble platinum(II) complexes of reduced amino acid Schiff bases were synthesized as potential anticancer agents and characterized by 1H NMR, EA, MS, IR, and molar conductivity. These compounds were tested for their DNA interaction with salmon sperm DNA, and their in vitro anticancer activities have been validated against HL-60, KB, BGC-823, and Bel-7402 cell lines by the MTT assay. The cytotoxicity of one complex (5g) is better than that of cisplatin against BGC-823 and HL-60 cell lines, and show close cytotoxic effect against Bel-7402 cell line.

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.

Solvent-Free Synthesis and Characterization of the Zn(II) Complexes with Amino Acid Schiff Base

Three zinc (II) complexes of the amino acid Schiff base were synthesized by the one step reaction of amino acid with aldehyde, zinc acetate in solvent-free. The compositions and structures of the complexes were characterized by elemental analyses, FTIR, XRD, TG-DSC. The compositions of the complexes are ZnL•nH2O (L = sal-leu, sal-ala, van-leu; sal = salicylaldehyde; van = vanillic aldehyde; leu = leucine; ala = alanine). Infrared spectra of the complexes indicate that the Schiff base ligands are formed, zinc ion is coordinated to the Schiff base ligands as terdentate with O, O and N donors from carboxylic, phenolic and imino groups respectively, the coordination numbers of zinc ion is four. The possible pyrolysis reactions in the thermal decomposition process of the complexes, the experimental and calculated percentage mass loss are also given.

Synthesis and Characterization of New Amino Acid-Schiff Bases and Studies their Effects on the Activity of ACP, PAP and NPA Enzymes (In Vitro)

In this study, two new Schiff base compounds derived from the condensation reaction ofL-glycine andL-tryptophan with 4-methylbenzal-dehyde have been synthesized. The Schiff base compounds were characterized by FT-IR, UV and1H NMR spectroscopy. Their effects on the activity of total (ACP), prostatic (PAP) and non prostatic (NPA) acid phosphatase enzymes were studied. The Schiff base derived fromL-glycine (A) demonstrated inhibition effect on the ACP and NPA activities and activation effect on PAP activity. The Schiff base derived fromL-tryptophan (B) demonstrated semi fixed inhibition effects on the ACP and NPA activities at high concentrations (5.5×10-2, 5.5×10-3and 5.5×10-4M) and activator effect at low concentration (5.5×10-5M) while it was exhibits as activator on PAP activity.

Solvent-Free Synthesis and Characterization of the Zn(II) Complexes with Amino Acid Schiff Base

Three zinc (II) complexes of the amino acid Schiff base were synthesized by the one step reaction of amino acid with aldehyde, zinc acetate in solvent-free. The compositions and structures of the complexes were characterized by elemental analyses, FTIR, XRD, TG-DSC. The compositions of the complexes are ZnL•nH2O (L = sal-leu, sal-ala, van-leu; sal = salicylaldehyde; van = vanillic aldehyde; leu = leucine; ala = alanine). Infrared spectra of the complexes indicate that the Schiff base ligands are formed, zinc ion is coordinated to the Schiff base ligands as terdentate with O, O and N donors from carboxylic, phenolic and imino groups respectively, the coordination numbers of zinc ion is four. The possible pyrolysis reactions in the thermal decomposition process of the complexes, the experimental and calculated percentage mass loss are also given.

Catalytic oxidation of alcohols by a novel manganese Schiff base ligand derived from salicylaldehyd and l-Phenylalanine in ionic liquids

Abstract A selective oxidation of alcohols to corresponding carbonyl compounds in ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate([bmim]BF 4 ) was achieved by using a novel salicylaldehyd amino acid Schiff base manganese ligand. The catalytic system can be recycled and reused for four runs without any significant loss of catalytic activity.

Preparation of Immobilized Chromium Schiff Base Complexes and Their Catalytic Performance for Cyclohexene Epoxidation

Three typical amino acid Schiff base chromium(III) complexes immobilized on MCM-41 were prepared and characterized by various physico-chemical methods such as Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, X-ray powder diffraction, N 2 sorption, and elemental analysis. The obtained immobilized complexes were effective catalysts for the epoxidation of cyclohexene with 30% hydrogen peroxide and they exhibited significantly enhanced catalytic performance compared with their corresponding homogeneous analogues. Under optimal reaction conditions the highest conversion of cyclohexene was 52.6% with 73.5% epoxide selectivity. In addition, the catalytic activity was retained after recycling 6 times. 将 3 种典型的氨基酸-水杨醛 Schiff 碱铬 (III) 配合物固载于介孔 MCM-41 上, 制得非均相 Schiff 碱铬配合物, 用傅里叶变换红外光谱、紫外-可见光谱、X 射线固体粉末衍射、N 2 吸附和元素分析对其结构进行了表征, 并以 30% H 2 O 2 为氧化剂, 考察该配合物对环己烯环氧化反应的催化性能. 结果表明, 均相配合物非均相化后, 其催化活性明显提高. 在较优的反应条件下, 环己烯转化率可达 52.6%, 环氧环己烷选择性为 73.5%, 且该非均相催化剂重复使用 6 次后, 仍保持较高的催化活性. Three promising immobilized complexes were prepared for the epoxidation of cyclohexene. The highest cyclohexene conversion was 52.6% with 73.5% epoxide selectivity. Moreover, catalytic activity was retained after 6 runs.

Ternary oxovanadium(IV) complexes with amino acid-Schiff base and polypyridyl derivatives: Synthesis, characterization, and protein tyrosine phosphatase 1B inhibition

To investigate the structure–activity relationship of vanadium complexes in inhibiting protein tyrosine phosphatase1B (PTP1B), eight mixed-ligand oxovanadium(IV) complexes, [V IVO(SalAla)(NN)] (H 2SalAla for salicylidene alanine, NN for N,N′-donor heterocyclic base, namely, 2,2′-bipyridine (bpy, 1 ), 1,10-phenanthroline (phen, 2 ), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 3), dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 4 )), [V IVO(SalLys)(dpq)] ( 5 ), [V IVO(SalLys)(dppz)] ( 6 ), [V IVO(SalAsp)(dppz)], ( 7 ) and [V IVO(SalTrp)(dppz)] ( 8 )), of which 3– 8 are new, have been prepared and characterized by elemental analysis, infrared, UV–visible, electrospray ionization mass spectrometry and conductivity. The molar conductance data confirmed the non-electrolytic nature of the complexes in DMSO solution. The coordination in [V IVO (SalAla)(phen)] ( 2 ) was confirmed by X-ray crystal structure analysis. The oxidation state of V(IV) with d 1 configuration in 2 was confirmed by EPR. The speciation of VO–SalAla–phen in aqueous solution was investigated by potentiometric pH titrations. The results indicate that the main species are two ternary complexes at the pH range 7.0–7.4. Biochemical assays demonstrate that the mixed-ligand oxovanadium(IV) complexes are potent inhibitors of PTP1B with IC 50 values in the range of 62–597 nM, approximately 3–10 fold weaker in potency than those of similar mixed-ligand oxovanadium(IV) complexes of salicylidene anthranilic acid (SAA) derivative with polypyridyl ligands, except complex 8 , which exhibits comparable or better inhibition activity than those of the mixed-ligand oxovanadium(IV) complexes of SAA derivative with polypyridyl ligands. The results demonstrate that the structures of vanadium complexes influence the PTP1B inhibition activity. Kinetics assays reveal that complex 2 inhibits PTP1B in a competitive manner.

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.

Synthesis, structure, DNA binding, and cleavage activity of two copper(II) complexes

Two copper(II) complexes, [Cu2(L1)2(H2O)]∞ (1) and {[Cu2(L2)2(H2O)] · H2O}∞ (2), have been synthesized and characterized by elemental analysis, UV-visible absorption spectra, and single-crystal X-ray diffraction. H2L1 is an amino acid Schiff base derived from condensation of N-(2-hydroxybenzaldehyde) and L-methionine. H2L2 is a reduced product of H2L1 by sodium borohydride (scheme 1). Both complexes consist of one-dimensional covalently bonded polymeric chains. Complex 1 has two crystallographic independent copper centers. Cu1 has a distorted octahedral geometry and Cu2 a square pyramid. The copper(II)'s are bridged by carboxylate with a Cu1–Cu2 separation of 3.6399(5) Å. Complex 2 is a double phenolate-bridged complex with a Cu1–Cu2 separation of 3.0148(7) Å, where each copper is square pyramidal. Binding of the complexes with Calf thymus DNA (CT-DNA) has been investigated by UV-visible spectra and fluorescence quenching, showing intercalation to CT-DNA. DNA cleavage experiments have been also investigated by agarose gel electrophoresis. Both complexes show oxidative DNA cleavage in the presence of H2O2/sodium ascorbate. The reactive oxygen species responsible for the DNA cleavage is likely singlet oxygen (). Scheme 1. Schematic structures of H2L1 and H2L2.

Chiral Salarg and its metal complex: Unique extrinsic fluorophores

We present a fluorescence spectroscopic study of a chiral amino acid Schiff base ligand Salarg and its metal complex Mn-Salarg. This study reveals that the Salarg ligand and its metal complex have the properties of a typical extrinsic fluorophore. A detailed comparison has been made with the fluorescence spectroscopic properties of various other extrinsic and intrinsic fluorophores. It is suggested that Salarg and Mn-Salarg, which are economic, efficient, easy to synthesize and environment-friendly extrinsic fluorophores, might be used to label DNA and lipids respectively.

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

Synthesis, structure, and DNA binding of three reduced amino-acid Schiff-base zinc(II), nickel(II), and cadmium(II) complexes

Three new reduced amino-acid Schiff-base complexes, [Zn(HL)2] · H2O (1), [Ni(HL)2] · H2O (2), and [Cd(HL)2] · H2O (3), where H2L is a reduced Schiff base derived from condensation of N-(2-hydroxybenzaldehyde) and L-histidine, have been synthesized and characterized by elemental analysis, UV-Vis absorption spectra and single crystal X-ray diffraction. Complexes 1–3 are isostructural. All metal centers are six-coordinate with O2N4 donor sets in slightly distorted octahedra. Unlike its Schiff-base counterpart, the deprotonated monoanionic ligand HL− has a more flexible backbone and two HL− are tridentate to one metal. Moreover, the binding interactions of these complexes with calf thymus DNA (CT-DNA) have been investigated by UV-Vis spectra and fluorescence quenching, which show that the complexes bind in an intercalative mode.

Investigation of catalytic activities of new heterogeneous molybdenum catalysts in epoxidation of olefins

The mesoporous molecular sieve MCM-41 was covalently grafted with 3-aminopropyl trimethoxysilane and acetyl acetone (acac) successively to give modified MCM-41 (acacAmpMCM-41). Reaction of this material with amino acids, e.g. alanine, phenyl alanine, leucine, isoleucine, histidine and valine afforded the corresponding supported amino acid Schiff base ligands. Subsequent reaction with bis (acetylacetonato)dioxomolybdenum(VI) lead to various molybdenum complexes supported on MCM-41 through propyl chain spacer. Characterization of these materials was carried out with FT-IR, atomic absorption spectroscopy, powder X-ray diffraction (XRD) and BET nitrogen adsorption–desorption methods. The XRD and BET analyses revealed that textural properties of support were preserved during the grafting experiments. The resultant materials successfully catalyzed the epoxidation of cyclooctene, cyclohexene, 1-hexene and 1-octene with tert-butyl hydroperoxide (TBHP) to the corresponding epoxides.

Conformational analysis of pyridoxal amino acid schiff's bases

The conformational properties of a series of pyridoxal amino acid Schiff's bases have been calculated. The calculations were performed using the program CAMSEQ which employs a set of empirical potential energy functions. The cndo/2 charge distributions are also given in this preliminary report. The locations of the local energy minima are consistent with Dunathan's hypothesis that the course of enzymatic reaction is related to the conformation of the pyridoxal phosphate Schiff's base. Calculated results are also in agreement with experiment.

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.