Nitrogen Atom Of Imidazole Ring Research Articles

Probing the Adsorption Sites of 5‐amino‐2‐mercaptobenzimidazole Conformations on Colloidal Gold Nanoparticles Investigated by SERS and DFT

AbstractGold nanoparticles (AuNP) have shown great potential in biomedical applications due to their unique and tunable properties. Understanding the ligand conformation on AuNP has profound interest in nanoparticle research leading to a precise drug delivery system. Colloidal AuNPs were synthesized using trisodium citrate as reducing agent. Normal Raman spectrum (NRS) in solid and aqueous phase identifies that 5‐amino‐2‐mercaptobenzimidazole (5A2MBI) mainly exist as thione form. Surface enhanced Raman scattering (SERS) investigation of 5A2MBI depending on pH was performed to explore the adsorption mechanism of thiolate and thione conformations on AuNPs. Density functional theory (DFT) calculations were used to find the band assignments and molecular electrostatic potential (MEP) mapping to identify the electron rich site where metal can interact preferentially. Using SERS spectral analysis and DFT results, surface adsorption scheme was proposed. At basic pH, 5A2MBI adsorbs on AuNP as thiolate form bidentately via Sulfur and nitrogen atom of imidazole ring with tilted geometry. However, in acidic condition the thione form adsorbs on nanosurface with perpendicular orientation.

Imidazole derivative with an intramolecular hydrogen bond as thermal latent curing accelerator for epoxy/phenolic resins

AbstractOne‐component epoxy systems with long shelf life during storage or transportation, while high curing reactivity during molding as well as satisfactory mechanical and thermal performances after curing, are extremely essential for industrial application. Herein, we used salicylaldehyde and o‐phenylenediamine to synthesize 2‐(2′‐hydroxyphenyl)‐1H‐benzimidazole (HPBI), an imidazole derivative with an intramolecular hydrogen bond between the phenolic hydroxyl group and the pyridine‐type nitrogen atom of imidazole ring, and further employed HPBI as a thermal latent curing accelerator for epoxy/phenolic resins. The intramolecular hydrogen bond endowed HPBI with inert activity toward resins at room temperature, making the one‐component resin system a long‐term storage stability (21 days of shelf life at 30°C). Once rising the temperature to a high degree, a rather high activity of HPBI to accelerate the curing process of epoxy/phenolic resins. It was attributed to the effective release of high activity of the pyridine‐type nitrogen by breaking the intramolecular hydrogen bond at high temperature. In addition, the resulted thermosets from HPBI also possessed the comparable Tg (>130°C, determined by DMA) and thermostability (Td‐5% > 380°C) with that from common curing accelerators. Therefore, HPBI was proved to be a promising thermal latent curing accelerator applied in electronic packaging field.

Thermal latent curing agent for epoxy resins from neutralization of 2‐methylimidazole with a phosphazene‐containing polyfunctional carboxylic acid

A novel thermal latent curing agent, 2MZS, was obtained through the reaction of 2‐methylimidazole (2MZ) and a symmetrically carboxyl‐functionalized star‐shaped molecule based on cyclotriphosphazene (N3P3‐COOH). In the complex, the resonance of N3P3‐COOH reduced the activity of lone electron pairs on the pyridine‐type nitrogen atom of imidazole ring, suppressing the nucleophilic attack and crosslinking reaction between 2MZ and epoxy resin. As a result, the storage stability was improved distinctly for the one‐pot epoxy compound, which could be steadily stored at room temperature for nearly 1 month. Nonisothermal DSC revealed a delayed initiation curing mechanism of the prepared one‐pot system, and which could undergo rapid curing reaction upon raising the temperature. Moreover, the introduction of terminally polyfunctional star‐shaped phosphazene derivative could promote the curing process at elevated temperature, as well as improve the chain rigidity of the cured resin by chemical incorporation into the cross‐linked network, thus endowing the cured resin with enhanced glassy storage modulus. The epoxy thermoset exhibited the highest glass transition temperature and thermal degradation temperature when 20 wt% of 2MZS was used. It is suggested that the novel latent curing agent is potential for high‐performance one‐pot epoxy compound, particularly recommended for application in electronic packaging fields.

Synthesis of s-triazine based tri-imidazole derivatives and their application as thermal latent curing agents for epoxy resin

A series of novel s-triazine based tri-imidazole derivatives were successfully prepared through the substitution reaction of cyanuric chloride with imidazole (IM), 2-methylimidazole (2MI), 2-ethylimidazole (2EI) and 2-ethyl-4-methylimidazole (EMI), respectively. The synthesized tri-imidazole derivatives were applied in epoxy resin (EP) to investigate their curing behaviors and thermal latency. Compared with the EP systems containing the unmodified imidazoles, the curing exothermic peaks of the EP systems containing s-triazine based tri-imidazole derivatives shifted to higher temperature regions. Moreover, the EP systems containing s-triazine based tri-imidazole derivatives had much longer storage stability at room temperature. The s-triazine structure with strong electron withdrawing effect reduced the nucleophilicity of pyridine-like nitrogen atom of imidazole ring, resulting in the suppression of reactivity of the modified imidazole derivatives towards EP at room temperature. Nevertheless, the s-triazine based tri-imidazole derivatives regained fast curing performance towards EP at elevated temperatures.

First principles study on proton transfer between amino acid side chains of histidine and aspartic acid in β-structure

We have demonstrated possibility of proton transfer between nitrogen atom of imidazole ring in histidine and oxygen atom of carboxylic group in aspartic residues inside peptide of Asp-Ala-His+ using density functional theory calculations. Our NBO and AIM analyzes have shown that the proton transfer takes place between side chain of histidine and aspartic acid residues through the hydrogen bond formation. Transition state structures of proton transfer reaction were calculated in gas and solution phases. The calculated reaction rates show that the proton transfer reaction rate in the gas phase is higher than solution phase. The ionization constant (pKa) value of the lysine residue in peptide was estimated to be 1.09 which is lower than intrinsic pKa value of lysine amino acid.

Synthesis and Thermal Study of Co (II), Ni (II), Cu (II) Mixed Ligand Complexes Using Histidine As Tridentate Ligand

The mixed ligand complexes of Co (II), Ni (II) and Cu (II) with histidine (His.) and 8- hydroxyquinoline (Qui.) have been synthesized and characterized.The resulting complexes were characterized by vibrational and electronic spectral data, thermogravimetric studies , metal analysis and molar conductance measurements. The histidine acts as tridentate ligand, coordinating through the two nitrogen atoms of imidazole ring and the amino group and carboxylate oxygen whereas 8-hydroxyquinoline shows a bidentate nature and the coordination occurs through nitrogen of imine group and oxygen of phenol group. The experimental data suggest that a mononuclear octahedral structure with general formula (M (His.)(Qui.) H2O ) where M= Co (II), Ni (II) and (Cu (His.)(Qui.)H2O) .H2O, thermo gravimetric studies reveal the presence of coordinated water molecules in all complexes. The molar conductance measurements reveal non-electrolytic nature of complexes. Mixed ligand complexes of 8-hydroxyquinoline and o-hydroxybenzylidene-1-phenyl-2, 3-dimethyl-4-amino-3- pyrazolin-5-on with Fe (II), Co (II), Ni (II) and Cu (II) ions were synthesized , the molar conductivity of the complexes in DMF solution have non-electrolyte behavior and 8-hydroxyquinoline coordinate through the nitrogen and oxygen atoms. therefore, the complexes have tetrahedral configuration. (12) Several mixed ligand Ni(II),Cu(II) and Zn(II) complexes of 2- amino-3-hydroxypyridine(AHP) and imidazoles viz.,, imidazole (him), benzimidazole (bim), histamine(hist) and L- histidine(his) have been synthesized and characterized, the geometry becomes tetrahedral when mixed ligand complexes are fomed with him, bim and hist for Cu(II) and Zn(II). All Ni (II) and Cu (II) / Zn (II) histidine mixed ligand complexes have octahedral geometry.The complexes exhibited considerable amount of antibacterial activity and Cu (II) complexes cleave DNA yielding scission of the sugar- phosphate backbone . (13) Mixed ligand Zr(IV) complexes prepared with 8-hydroxyquinoline as a primary ligand and amino acids such as L-alanine/L - serine/glycine as a secondary ligand. Zr(II) was used due to its high coordination number and ability to form stable complexes. These complexes were characterized and screened for their antibacterial, antifungal and cytotoxic properties . (14) Kinetics and mechanism of thermal decomposition of o-vanilline-L-histidine complexes of some transition metal ions in which histidine acts as a tridentate ligand and an octahedral structure for the complexes has been reported . (15) Synthesis, structural, coordination and thermal stability studies of mixed ligand complexes of histidine with other ligands (adenine/guanine/ethylenediamine, diethylenetriamine or N,N,N , N ,, ,N ,,, -pentamethyldiethylenetriamine, glycine or L-alanine, histamine and diethylglyoxime) have been carried out .

Mechanically-induced solvent-less synthesis of cobalt and nickel complexes of cimetidine

Solvent-less synthesis of [Co(CIM)2](SO4) and [Ni(CIM)2](OAC)2 by grinding of CoSO4 and Ni(CH3COO)2.4H2O with cimetidine without any solvent is described. The complexes have been characterized by elemental analysis, melting point, AAS, conductivity measurements, TLC, infrared and UV-Vis spectroscopies as well as X-ray powder diffraction. Cimetidine was found to be bidentate or tridentate ligand. Cobalt ion coordinate with cimetidine through the sulphur atom in the thiol group, nitrogen atom of imidazole ring and the nitrogen atom of the secondary amine to give an octahedral geometry with ligand acting as tridentate whereas nickel ion coordinates through the sulphur atom in the thiol group, nitrogen atom of imidazole ring to give tetrahedral structure with ligand acting as bidentate. X-Ray diffraction patterns of the complex were different from that of the ligand suggesting formation of coordination compounds. The method is quick and gives a quantatively yield, without the need for solvents or external heating. Clearly, it can present higher efficiency in terms of materials, energy and time compared to classical solution phase synthesis.

Potentiometric and spectrophotometric studies of MnII and NiII cimetidine complexes

Cimetidine is an important hydrogen histamine receptor which has the ability to chelate metal ions in blood plasma and in different tissues. This study aimed to determine the stability constants for the cimetidine ligand with MnII and NiII metallic ions, synthesizing complexes and characterizing them by infrared spectroscopy, IR, and hydrogen nuclear magnetic resonance, ¹H NMR. Cimetidine protonation constant regarding to the imidazole group was logK 7.05 and the stability constants for MnII and NiII complexes, ML2 species were logK 3.75 and 2.97, respectively, in 0.100 mol L-1 KCI. The interpretation of IR and H¹ NMR spectra for complexes MnII-cim2 and NiII-cim2 indicated that their formation occurs through the sulfur atoms in the thiol group, nitrogen atoms of imidazole ring, and nitrogen atoms of secondary amine. The nitrile group seems to be involved in the complexation of the NiII-cim2 complex.

DFT STUDY ON GAS-PHASE INTERACTION BETWEEN HISTIDINE AND ALKALI METAL IONS (Li+, Na+, K+); AND INFLUENCE OF THESE IONS ON HISTIDINE ACIDITY

The gas-phase metal affinities of histidine Li +, Na + and K + ions have been determined theoretically employing the hybrid B3LYP exchange–correlation functional and using 6-311++G** basis sets. All computations indicate that the metal ion affinity decreases on going from Li + to Na + and K + for the considered amino acid. Different types of M + coordinations on several histidine conformers/tautomers were considered in detail. The optimized structures indicate that Li + and Na + prefer a tri-dentate coordination, bonding with a nitrogen atom of imidazole ring ( N τ), – NH 2, and an oxygen atom of a carbonyl, while in the K +-histidine lowest-energy conformer, the cation appears to be bi-coordinated to both oxygen atoms of the zwitterionic form by the energy values not too far from that of tri-coordination. We also performed the DFT calculations for proton dissociation energy of histidine both in the presence and absence of alkali metal ions. Our results also reveal that the acidity of histidine dramatically increases upon metal ion complexation.