Studies on the structure and properties of nickel complexes in a set of amide-based 13-membered macrocyclic ligands

This work reports a systematic investigation to understand the structural, spectroscopic and redox properties of Ni(II) ion in a set of 13-membered amide-based macrocyclic ligands. Four macrocyclic ligands containing e⁻-donating/withdrawing substituents and their Ni(II) complexes have been synthesized and characterized. Structural analysis shows that the macrocyclic ligands create a square-planar environment and nicely accommodate the Ni(II) ion. Electrochemical results suggest that the complexes are capable of undergoing metal-centered oxidation. The electron-donating substituents on ligand lowers the redox potentials and better stabilizes the +3 oxidation state of metal. The electrochemically generated Ni^III species are shown to have rich spectroscopic features. For majority of complexes, the oxidized species are concluded to be Ni^III by their anisotropic EPR spectra typical for Ni^III ion in square-planar geometry. The absorption and EPR spectra for nickel complex bearing an -OMe group on the ligand; however, suggest a Ni(II) complex with a ligand-based radical.     

N-methyl-bis(2-bromo 6-pyridylmethyl)amine: high yield synthesis, and spectroscopic properties of the dichloroferrous complex with trigonal bipyramidal geometry

The new tridentate title ligand has been synthesized by a very convenient and high yield method. The dichloroferrous derivative was prepared in order to provide spectroscopic bases for solution studies of trigonal bipyramidal derivatives with aminomethylpyridyl containing ligands. Its crystal structure is reported, together with UV-Vis, ¹H NMR and molecular conductivity data. The absence of any MLCT in UV-Vis, significant broadening of the β and β′ resonances in ¹H NMR and neutral electrolytic behavior are reported and taken together, these parameters can now unequivocally serve as criteria to detect any tridentate coordination mode of the tripod in the chemistry of dichloroferrous complexes with tris-(2-pyridylmethyl)amine type ligands.     

Interaction of drug based binuclear mixed-ligand complexes with DNA

Here in we tried to increase an antibacterial activity of ciprofloxacin drug due to formation of mixed-ligand complexes. Synthesized compounds were found to be more potent compare to drugs, ligands and metal salt against selective gram^(+ve) and gram^(?ve) organisms. Interaction of the complexes with nucleic acid (DNA) were investigated using spectroscopic technique, viscosity measurement and gel electrophoresis and it was found that the complexes bind to DNA via intercalative mode.     

DNA-interaction and in vitro antimicrobial studies of some mixed-ligand complexes of cobalt(II) with fluoroquinolone antibacterial agent ciprofloxacin and some neutral bidentate ligands

Six new mixed-ligand complexes of Co(II) with ciprofloxacin (Cip) and neutral bidentate ligands have been synthesized and characterized. Binding and cleavage of DNA with the complex were investigated using spectroscopic method, viscosity measurements and gel electrophoresis techniques. Antibacterial activity has been assayed against two Gram^(?ve) and three Gram^(+ve) microorganisms using the doubling dilution technique.     

Synthesis and structure of the complex tetra-μ-prolinatodirhodium(II)

The dinuclear Rh^IIRh^II complex with proline [Rh₂(pro₄][NEt₄]₂ was synthesized and its structure studied by means of spectroscopic (IR, EPR and ESCA) and magnetochemical methods. It was shown that two proline molecules serve as bridging ligands, while the other two are only axially coordinated through their N atoms.     

Synthesis, characterization and antitumor activity of polymeric copper(II) complexes with thiosemicarbazones of 3-methyl-5-oxo-1-phenyl-3-pyrazolin-4-carboxaldehyde and 5-oxo-3-phenyl-3-pyrazolin-4-carboxaldehyde

New polymeric copper(II) complexes with two tridentate ONS thiosemicarbazone ligands containing substituted pyrazolone moiety were synthesized and characterized by means of spectroscopic, electrochemical and crystallographic techniques. While both ligands exist as different tautomers in the solid state and DMSO-d₆ solution, Cu(II) ion coordinates the ligands from the same tautomeric form with square-pyramidal geometry around each Cu atom. In the crystal structures, the copper(II) complex cation forms polymeric chains {[Cu(L)Cl]⁺}_n with a bridging chlorine atom. One of the complexes was found to have a significantly higher cytotoxic potential in comparison with cisplatin in inhibition of several cell lines (HL60, REH, C6, L929 and B16). The results obtained on the basis of flow cytometry indicated that apoptosis could be possible mechanism of cell death.     

Spectroscopic and theoretical investigations of Schiff base metal complexes with intraligand charge-transfer behavior

Nickel and zinc complexes of hydroxy or mercapto substituted glyoxaldianiles exhibit unusual long-wavelength absorptions. The electronic structure and spectroscopic properties of the compounds are investigated by means of electron spectroscopic studies and qualitative MO considerations. The deep color of the complexes is caused by intraligand charge-transfer transitions from the oxygen or sulphur-containing donor part to the diimine substructure of the ligand. The transition energies depend sensitively on the nature of the donor part of the ligand, and on the solvent polarity. The close structural relationship between these complexes and the d⁸ mixed-ligand complexes with S/O-donor and N-acceptor ligands is discussed.     

The fluorescence of transparent polymer films of rare earth complexes

Fluorescence films of rare earth (Eu³⁺ or Tb³⁺) β-diketone chelates dispersed in a PMMA polymer matrix were prepared and their fluorescence properties were investigated. Dependence of rare earth contents on emission properties and transparencies of the films are also given. Influence of the substituents of the ligand on spectroscopic properties and fluorescence intensities were discussed. The strongest red and green fluorescence was obtained when DBM (dibenzoylmethane) was used as a ligand for the Eu-film and AcA (acetylacetone) for the Tb-film. The relation between the nature of ligands and efficiencies of energy transfer in the film systems was also studied.     

Metal complexes of 3-acetamido-5-methylpyrazole

In this paper, we present the complete synthesis of the 3-Acetamido-5-methylpyrazole (3-Ac-AMP) from 3-amino-5-methylpyrazole and acetic acid anhydride, including its full spectroscopic characterization. The solid-state structure shows extensive H-bonding involving the acyl and pyrazole moieties. Upon coordination to Co²⁺, Zn²⁺, and Cd²⁺, the system adopts a geometry that allows it to bind to metal centres as a O,N-chelate. 3-Ac-AMP coordination to Zn and Cd was monitored by ¹H NMR showing the formation of presumably tetrahedral 2:1 complexes. In the solid state, Co and Zn complexes are centrosymmetric and octahedral having two 3-Ac-AMP ligands in the equatorial plane and two methanol ligands occupying axial positions. The systems form a layered structure in which the ClO₄ ⁻ counter ion links the layers via H-bonding.     

Exploring the binding interactions of structurally diverse dichalcogenoimidodiphosphinate ligands with α-amylase: Spectroscopic approach coupled with molecular docking

Postprandial hyperglycemia has orchestrated untimely death among diabetic patients over the decades and regulation of α-amylase activity is now becoming a promising management option for type 2 diabetes. The present study investigated the binding interactions of three structurally diverse dichalcogenoimidodiphosphinate ligands with α-amylase to ascertain the affinity of the ligands for α-amylase using spectroscopic and molecular docking methods. The ligands were characterized using ¹H and ³¹P NMR spectroscopy and CHN analysis. Diselenoimidodiphosphinate ligand (DY300), dithioimidodiphosphinate ligand (DY301), and thioselenoimidodiphosphinate ligand (DY302) quenched the intrinsic fluorescence intensity of α-amylase via a static quenching mechanism with bimolecular quenching constant (Kq) values in the order of x10¹¹ M^-1s^-1, indicating formation of enzyme-ligand complexes. A binding stoichiometry of n≈1 was observed for α-amylase, with high binding constants (Ka). α-Amylase inhibition was as follow: Acarbose > DY301>DY300>DY302. Values of thermodynamic parameters obtained at temperatures investigated (298, 304 and 310 K) revealed spontaneous complex formation (ΔG<0) between the ligands and α-amylase; the main driving forces were hydrophobic interactions (with DY300, DY301, except DY302). UV–visible spectroscopy and Förster resonance energy transfer (FRET) affirmed change in enzyme conformation and binding occurrence. Molecular docking revealed ligands interaction with α-amylase via some key catalytic site amino acid residues (Asp197, Glu233 and Asp300). DY301 perhaps showed highest α-amylase inhibition (IC₅₀, 268.11 ± 0.74 μM) due to its moderately high affinity and composition of two sulphide bonds unlike the others. This study might provide theoretical basis for development of novel α-amylase inhibitors from dichalcogenoimidodiphosphinate ligands for management of postprandial hyperglycemia.     

Molybdenum complexes with O,N,S donor ligands as models for active sites in oxotransferases and hydroxylases

A series of homologous mononuclear dioxomolybdenum complexes were prepared and fully characterized with structurally related thiosemicarbazone ligands supplying a tridentate O,N,S donor set to the central metal atom. The ligands are derived from the prototype 2-hydroxybenzaldehyde-4-triphenylmethylthiosemicarbazone (H₂L). Within this series the crystal structures of 11 complex compounds [MoO₂(LRⁿ)(dmf)] and [MoO₂(LRⁿ)(MeOH)] were determined showing characteristic differences in the gross structural properties of the central metal core. From the variation of substituents in this ligand library the influences of electronic ligand effects on the spectroscopic, electrochemical, and functional properties of these biomimetic model complexes for molybdenum-containing oxotransferases are reported.     

Differential effects of metal ligands on synaptic membrane glutamate binding and uptake systems

The high affinity, Na⁺-independentl-[³H]glutamate binding process in synaptic membranes and in the purified binding protein was shown to be inhibited to an almost equal extent by the metal ligands NaN₃, KCN, ando-phenanthroline, and by 2,4,5-trihydroxyphenylalanine (6-OH DOPA). The high affinity, Na⁺-dependent glutamate transport activity in these membranes was almost totally insensitive to NaN₃,o-phenanthroline, KCN, and 6-OH DOPA. These agents, especially 6-OH DOPA, may be useful tools in achieving a discrimination between putative physiologic receptors and uptake carrier sites forl-glutamate in synaptic membranes. The sensitivity of the glutamate binding sites to the effects of the metal ligands may be correlated to the presence of an iron-sulfur center in the purified glutamate binding protein. Some of the characteristics of this metallic center were explored by optical and paramagnetic resonance spectroscopic techniques and are described in this study.This research was supported by grants DAAG29-79-C-0156 from the Army Research Office and AA 04732 from NIAAA.     

Control of asymmetric induction in the organometallic synthesis of 3-methyl-(E)-4-hexen-2-one

Bis(μ-methyl-1,3-dimethyl-η³-allylnickel) reacts in the presence of phosphorus(III) ligands (phosphines, phosphites) with CO to give 3-methyl-(E)-4-hexen-2-one. Systematic experiments were performed using chiral ligands containing menthyl or menthoxy groups and different achiral groups on the P atom to determine the influence of ligand structure and concentration on the direction and extent of chiral induction in this ketone synthesis. It could be shown that reversion of enantioselectivity can be obtained not only by the obvious method of reversing the absolute configuration of the ligand (“parity control”) but also by modifying the nonchiral substituents of the phosphorus ligand (“complementarity control”). The synthesis, physical, and spectroscopic properties of several new menthyl phosphines and phosphites are reported.     

Synthesis,spectral characterization,in vitro microbial and cytotoxic studies of lanthanum(III) and thorium(IV) complexes with 1,2,4-triazole Schiff bases

A series of metal complexes of La(III) and Th(IV) have been synthesized with newly derived biologically active ligands. These ligands were synthesized by the condensation of 3-substituted-4-amino-5-hydrazino-1,2,4-triazole with 8-formyl-7-hydroxy- 4-methylcoumarin. The structure of the complexes has been proposed by elemental analyses, spectroscopic data i.e. i.r., ¹H nmr, Uv-Vis, FAB-mass and thermal studies. The elemental analyses of the complexes conform to the stoichiometry of the type [La(L)·3H₂O]·2H₂O and [Th(L)(NO₃)·2H₂O]·2H₂O where (L = L^I-L^IV). All the complexes are soluble in DMF and DMSO and are non-electrolytes in DMF and DMSO. All these ligands and their complexes have also been screened for their antibacterial (Escherichia coli, Staphylococcus aureus, Staphylococcus pyogenes and Pseudomonas aeruginosa) and antifungal activities (Aspergillus niger, Aspergillus flavus and cladosporium) by the MIC method. The brine shrimp bioassay was also carried out to study their invitro cytotoxic properties.     

Molecular basis of negative co-operativity in rabbit muscle glyceraldehyde-3-phosphate dehydrogenase

The interactions of rabbit muscle glyceraldehyde-3-phosphate dehydrogenase with NAD⁺ and with its fluorescent derivative 1, N⁶-etheno-adenine dinucleotide were investigated using a variety of spectroscopic methods. These techniques included: difference spectroscopy, circular dichroism, fluorescence and circular polarized luminescence. It was found that the greatest structural change in the protein tetramer occurs upon binding of the first mole of coenzyme. We have also demonstrated that progressive structural changes occur at the adenine subsite in the NAD⁺ binding site as a function of coenzyme saturation. These conformational changes are probably responsible for the progressive decrease in the affinity towards the coenzyme. It was also found that every NAD⁺ molecule induces the same conformational change of the nicotinamide subsite. These results offer a molecular explanation for the negative co-operativity in the binding of the coenzyme, without a change in the catalytic power of the NAD⁺ site as a function of coenzyme saturation. These results also offer a new explanation for the fact that enzyme exhibits half-of-the-sites reactivity towards certain ligands and full-site reactivity towards others. It is suggested that those ligands interacting at the adenine subsite of the NAD⁺ binding site induce the half-of-the-sites reactivity.Our results support the view that both the negative co-operativity in coenzyme binding and half-of-the-sites reactivity are due to ligand-induced conformational changes on an a priori symmetric glyceraldehyde-3-phosphate dehydrogenase molecule.     

Ce−ZSM-5: A Highly Capable Catalyst for the Construction of Acridines in Water and Their Computational Study against DNA Gyrase Protein

Cerium doped ZSM-5 (Ce−ZSM-5) as an environmentally benign and reusable catalyst for the construction of acridines in aqueous medium. This method produced corresponding acridines with good yields and shorter reaction times. Also avoids the use of hazardous solvents and involves a simple work-up process. The solid catalyst was prepared by doping Ce ions with ZSM-5 (Zeolite Socony Mobil-5) and confirmed by XRD, BET SA-PSD and SEM. The synthesised acridine derivatives were confirmed by ¹H-NMR, ¹³C-NMR and FT-IR spectroscopic data. The docking studies of the synthesised compounds are performed by the PyRx auto dock tool against DNA gyrase protein. The products 5a and 6d are found to be the best fit ligands against DNA gyrase protein.     

Thioamide, urea and thiourea bridged rhenium(I) complexes as luminescent anion receptors

Thioamides, urea and thiourea derivatives of 2,6-pyridinedicarbonyl dichloride, isophthaloyl dichloride and terephthaloyl dichloride have been synthesized. These ligands have been incorporated in dinuclear rhenium(I) diimine tricarbonyl complexes and the anion recognition properties of these complexes have been studied by luminescence, UV-Vis and ¹H NMR spectroscopic methods. The complexes act as receptors for anions via hydrogen bonding and electrostatic interactions. The anion sensing properties of the complexes are compared to earlier amide-based dinuclear rhenium(I) tricarbonyl complexes.     

Impact of ring size on the copper(II) coordination abilities of cyclic tetrapeptides

A new, 14-membered, tetraza cyclic tetrapeptide containing histidine and lysine side-chains, c(β³homoLysdHisβ-AlaHis), was designed, synthesized and characterized; its copper(II) binding properties were investigated in dependence of pH by potentiometric and spectroscopic methods. In line with previous studies of similar systems, the progressive involvement of amide nitrogens in copper(II) coordination was evidenced for pH values greater than 6. At physiological pH the dominant species consists of a copper(II) center coordinated by two amide nitrogens, an imidazole nitrogen and a water molecule. In contrast, at pH values higher than 8.7, a copper(II) coordination environment consisting of four amide nitrogens in the equatorial plane and the axial imidazole ligands is formed as clearly indicated by spectroscopic data and theoretical calculations. The behavior of this 14-membered cyclic tetrapeptide is compared to that of its 12-membered cyclic analog, particular attention being paid to the effects of ring size on the respective copper(II) binding abilities.     

Cu(II)–Protamine interaction. I. The formation and structure of Cu(II)–clupeine Z complexes

The formation and structure of four different Cu(II)–clupeine Z complexes have been studied using potentiometric and spectroscopic (ir and visible absorption, and CD) measurements. The results thus obtained indicate the presence of up to 8 binding sites in the pH range from 6.5 to 10.5. The spectroscopic evidence suggests that the strongest site available contains the α-amino terminal and the adjacent peptide nitrogen, which bind to copper from pH 5 to 6.5 to form the first complex. The stability constant of this first complex has a value of (9.5 ± 0.9) × 10³ mol^?1 1. From pH 6.5 to 8.5, two intervening guanidinium nitrogens of arginine residues occupy the two other corners of the coordination square, giving rise to the second complex. The other sites potentially available from pH 6.5 to 10.5 are formed by two amino nitrogens of arginine residues and two contiguous peptide nitrogens. The first intervene up to pH 8.5, forming the third complex, and the latter from this pH to 10.5, forming the fourth complex. Although the ligands intervening at sites 2–8 appear to be the same, the sites are by no means equivalent. The spectroscopic data enable one to distinguish three different types of binding sites.     

Structure, solution equilibria and magnetic properties of copper(II) complexes with new sulfurated triazoline derivatives of α-amino acids

Two new sulfurated triazoline ligands have been synthesized by functionalization of glycine and l-alanine (HL¹ and HL², respectively) at the carboxylate site with retention of chirality in the latter case. The ligands and their copper(II) complexes have been characterized by spectroscopic methods and their structures were determined by X-ray diffraction. The compound [Cu(H₂L²)₂](H₅O₂)(SO₄)₂(HSO₄) presents a very disordered structure with regard to the anionic counterion and a very unusual elongated crystal cell. In all the complexes the ligands are (N,S) coordinated to copper(II), while the amino groups remain protonated and uncoordinated. The ligands have also been studied in solution and their dissociation constants were determined both by potentiometry and ¹H NMR titrations. Potentiometric studies on the complex [Cu(H₂L²)₂](H₅O₂)(SO₄)₂(HSO₄) were performed to determine the dissociation constants of the ligand once coordinated to the metal. The complex [CuCl₂(H₂L¹)]Cl was studied also by magnetic susceptibility measurements, showing an interesting antiferromagnetic behavior at low temperature which has been interpreted on the basis of its crystal packing.