Covalent and non‐covalent binding in the ion/ion charge inversion of peptide cations with benzene‐disulfonic acid anions

Protonated angiotensin II and protonated leucine enkephalin‐based peptides, which included YGGFL, YGGFLF, YGGFLH, YGGFLK and YGGFLR, were subjected to ion/ion reactions with the doubly deprotonated reagents 4‐formyl‐1,3‐benzenedisulfonic acid (FBDSA) and 1,3‐benzenedisulfonic acid (BDSA). The major product of the ion/ion reaction is a negatively charged complex of the peptide and reagent. Following dehydration of [M + FBDSA‐H]^? via collisional‐induced dissociation (CID), angiotensin II (DRVYIHPF) showed evidence for two product populations, one in which a covalent modification has taken place and one in which an electrostatic modification has occurred (i.e. no covalent bond formation). A series of studies with model systems confirmed that strong non‐covalent binding of the FBDSA reagent can occur with subsequent ion trap CID resulting in dehydration unrelated to the adduct. Ion trap CID of the dehydration product can result in cleavage of amide bonds in competition with loss of the FBDSA adduct. This scenario is most likely for electrostatically bound complexes in which the peptide contains both an arginine residue and one or more carboxyl groups. Otherwise, loss of the reagent species from the complex, either as an anion or as a neutral species, is the dominant process for electrostatically bound complexes. The results reported here shed new light on the nature of non‐covalent interactions in gas phase complexes of peptide ions that can be used in the rationale design of reagent ions for specific ion/ion reaction applications. Copyright © 2012 John Wiley & Sons, Ltd.     

两例LnⅢ3配合物的构筑、晶体结构及生物活性

利用多齿席夫碱配体H₂L(H₂L=(E)-6-(羟甲基)-N′-((6-甲氧基吡啶-2-基)亚甲基)吡啶酰肼)与Ln(dbm)₃·2H₂O反应,通过溶剂热法,设计与构筑了 2例新的三核稀土配合物[Ln₃(dbm)₅(L)₂(CH₃OH)₂]·CH₂Cl₂,其中 Ln=Pr (1)、Ho (2),Hdbm=二苯甲酰甲烷。单晶 X射线衍射分析表明：配合物 1与 2同构,其结构由 3个 Ln(Ⅲ)离子、5个二苯甲酰甲烷阴离子(dbm^-)、2个席夫碱配体 L^2-、2个配位的 CH₃OH及 1个结晶 CH₂Cl₂分子组成。3个中心 Ln(Ⅲ)离子通过 4个 μ₂-O原子相互连接,形成折线形的 Ln₃核。生物活性研究表明,配体H₂L、Ln(dbm)₃·2H₂O及配合物1和2均具有较好的抑菌活性。与配体H₂L及Ln(dbm)₃·2H₂O相比较,稀土配合物具有更强的抑菌活性。此外,采用紫外光谱法、循环伏安法和荧光光谱法研究了配合物1和2与小牛胸腺DNA(ctDNA)之间的相互作用,结果表明配合物主要以插入键合的方式与ctDNA结合。     

Synthesis,crystal structure,and interaction with DNA and BSA of a chromium(III) complex with naph-gly Schiff base and 1,10-phenanthroline

A new chromium(III) complex, [CrCl(naph-gly)phen]?H₂O (naph-gly = Schiff base derived from 2-hydroxy-1-naphthaldehyde and glycine, phen = 1,10-phenanthroline), has been synthesized and characterized by elemental analysis, electrospray ionization mass spectroscopy, FT-IR, and X-ray single-crystal diffraction. The chromium(III) complex belongs to the trigonal crystal system, P3(1) space group with crystallographic data: a = b = 1.97017(16) nm, c = 1.02991(7) nm, α?=?β?=?90°, γ =120°, V = 3.4621(5) nm³, D_c = 1.476 g?cm^?3, Z = 6, F(0 0 0)?=?1578, R₁ = 0.0508, wR₂ = 0.0907. There are two independent molecules in the crystallographic asymmetric unit of the chromium(III) complex. Each Cr^III is six-coordinate to form an octahedral geometry. In the crystal, a 3-D structure is formed through intermolecular hydrogen bonds. The calf thymus DNA (CT-DNA)- and bovine serum albumin (BSA)-binding properties of the complex have been studied by UV absorption, fluorescence, and circular dichroism (CD) spectroscopy. Results indicate that the chromium(III) complex binds to CT-DNA in an intercalative mode, and it can bind to BSA and cause conformational changes of BSA.     

Mixed ligand Cu(II) complexes containing o-vanillin-l-tryptophan Schiff base and heterocyclic nitrogen bases: synthesis,structural characterization,and biological properties

[Cu(L)] (1) and mixed ligand copper(II) complexes [Cu(L)(A)] (2 and 3), where L is the Schiff base derived from o-vanillin and l-tryptophan and A is pyridine (2) and imidazole (3), were synthesized and characterized using conventional and spectral techniques. 2 was structurally characterized using single crystal X-ray crystallography showing that Cu(II) is coordinated through N₂O₂ donors in a square plane. The EPR spectra of the complexes in frozen solution support a square-based structure. Electrochemical behavior of the complexes has been studied by cyclic voltammetry. The DNA-binding properties of L and 1–3 with calf thymus DNA were investigated by spectral and kinetic methods. For all the complexes, the maximum value of binding constant (0.38 × 10⁶) was achieved with 3 by spectroscopic titration. The ability of compounds to break pUC19 DNA was checked by gel electrophoresis. The ligand and copper complexes exert cytotoxicity against MCF-7 cell line.     

The formation of a neutral manganese(III) complex containing a tetradentate Schiff base and a ketone – synthesis and characterization

2-Benzoylphenolato-(2,2′-((2,2-dimethylpropane-1,3-diyl)bis((nitrilo)(phenylmethylidyne)))-diphenolato-manganese(III) methanol solvate, [Mn(C₃₁H₂₈N₂O₂)(C₁₃H₉O₂)]·CH₃OH (1), was synthesized and characterized by FTIR, UV–vis, TG-FTIR, TG/DSC, molar conductivity, magnetic moment measurement, and quantum chemical calculations. During the synthesis, partial hydrolysis of ligand is observed. The compound was obtained as amorphous, dark-brown powder. The effects of organic solvents of various polarities on the UV–vis spectra of ligands and complex were investigated. In addition, the IR and UV–vis spectra were also calculated and compared with the experimental data. A single crystal for analysis was obtained by dissolving the amorphous complex in methanol, and slow evaporation of solvent at 4 °C. Single-crystal X-ray analysis indicated that the methanol molecules are not incorporated into the crystal lattice after the recrystallization process ([Mn(C₃₁H₂₈N₂O₂)(C₁₃H₉O₂)] (2)). In the structure Mn(III) is surrounded by two nitrogens and four oxygens of deprotonated Schiff base and α-hydroxy ketone ligands, and adopts a distorted octahedral geometry.     

New Ni(II) Ion-Selective Electrode Based on the N-S Schiff Base Ligand as Neutral Carrier in PVC Matrix

Abstract

A nickel(II) [Ni(II)] ion-selective electrode was prepared by incorporating a new N-S Schiff base ligand, glyoxal-bis(S-benzyldithiocarbazate) (GBSB), as a neutral carrier into the PVC matrix. The proposed electrode exhibits an excellent near-Nernstian response for Ni²⁺ ions, ranging from 2.8 × 10^?7 to 1.0 × 10^?1 mol/L with a detection limit of 1.2 × 10^?7 mol/L and a slope of 31.9 ± 0.3 mV/dec in pH 4.0 nitrate buffer solution at 25°C. It has an appropriate response time and suitable reproducibility and can be used for at least 3 months. The operational pH range of the proposed electrode is 4.0–7.5. The response mechanism is discussed in view of the alternating current (AC) impedance technique. In addition, the electrode was successfully used as an indicator electrode in potentiometric titration of Ni²⁺ ion and in the direct determination of Ni²⁺ ion in milk power and chocolate samples.     

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.     

Synthesis,characterization, and biological activity of metal complexes of 4-ethyl vanillideneamino-3-methyl-5-mercapto-1,2,4-triazole

A series of transition metal–triazole derivatives have been synthesized and characterized by microanalytical, thermal, magneto-chemical, and spectral studies. The synthesized complexes were screened for biological activities. The complexes of Co(II) and Ni(II) emerged as a good antibacterial agent against Gram-negative bacteria such as Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Bacillus subtilis, and Shigella flexneri.     

Studies on oxovanadium(IV), Cr(III), Co(II), Ni(II), and Cu(II) chelates of some bisketimino ligands

The oxovanadium(IV), Cr(III), Ni(II), Co(II), and Cu(II) chelates of some bisketimino Schiff-base ligands (H₂L) obtained by condensation of 4-butyryl-3-methyl-1-phenyl-(or-1,3-diphenyl)-2-pyrazolin-5-ones with thiourea were synthesized and characterized by elemental analyses and thermogravimetric analyses, molar conductivities, magnetic susceptibility measurements, mass, infrared, and electronic spectroscopies. Ligand field parameters, such as splitting energy, Racah parameter, spin–orbit coupling constant, and covalency parameter of the Cr(III), Ni(II), and Co(II) chelates were calculated by band-fitting methods. Based on these studies, tetragonally distorted octahedral environment around OV(IV) and Cu(II) and octahedral Cr(III), Ni(II), and Co(II) have been proposed.     

The synthesis,electrochemical properties and structural characterization of bis ( N -(4-dimethylaminophenyl)-3,5-di- tert -butylsalicylaldiminato)copper(II)

A Cu(II) complex of a Schiff base obtained by the condensation of N,N-dimethyl-1,4-phenylenediamine with 3,5-di-tert-butyl-2-hydroxybenzaldehyde has been synthesized and characterized. The structure of the complex was determined by single-crystal X-ray methods. The four-coordinate Cu(II) ion possesses a compressed tetrahedral coordination environment.