Role Of Imidazole Research Articles

Role of Imidazole and Chelate Ring Size in Copper Oxidation Catalysts: An Experimental and Theoretical Study.

In this work, the structural, solution, electrochemical, and catalytic properties of the complexes with ligands derived from imidazole and pyridines were studied. A comparative study of five bioinspired copper catalysts with or without coordinated imidazole and with different chelate ring sizes is presented. Catalytic efficiency on the oxidation of 3,5-di-tert-butylcatechol (DTBC) and ortho-aminophenol (OAP) in a MeOH/H2O medium was assessed by means of the Michaelis-Menten model. Catalysts comprising imidazole-containing ligands and/or a six-membered chelate ring proved to be more efficient in both oxidation reactions. Determination of stability constants and electrochemical parameters of the copper complexes supported the explanation of the catalytic behavior. A catalytic cycle similar for both reactions has been proposed. The results of density functional theory (DFT) free energy calculations for all five complexes and both catalytic reactions agree with the experimental results.

The role of imidazole and benzimidazole heterocycles in Chagas disease: A review.

The haemoflagellate protozoan Trypanosoma cruzi (T.cruzi) is the causative agent of Chagas disease (CD), a potentially life-threatening disease. Little by little, remarkable progress has been achieved against CD, although it is still not enough. In the absence of effective chemotherapy, many research groups, organizations and pharmaceutical companies have focused their efforts on the search for compounds that could become viable drugs against CD. Within the wide variety of reported derivatives, this review summarizes and provides a global vision of the situation of those compounds that include broadly studied heterocycles in their structures due to their applications in medicinal chemistry: imidazole and benzimidazole rings. Therefore, the intention of this work is to present a compilation, as much as possible, of all the reported information, regarding these imidazole and benzimidazole derivatives against T.cruzi, as a starting point for future researchers in this field.

Role of biologically important imidazole moiety on the antimicrobial and anticancer activity of Fe(III) and Mn(II) complexes

Currently, most pathogens influencing a number of epidemics outline a notable warning to human health. It has pushed researchers to design new antimicrobial drugs using transition metals that are studied in proceeding fewer years for their antimicrobial properties. Henceforth, in this work, two mononuclear complexes [Imz-H][Fe(pda)2]⋅1⋅3H2O (1) and [Mn(Imz)6]⋅2Cl-⋅2H2O (2) [Imz = imidazole and H2pda = 2,6 pyridine dicarboxylic acid] are isolated and characterized systematically by various spectral and single-crystal XRD studies. The antimicrobial activity of the present hexadentate complexes of Fe(III) and Mn(II) against Gram-positive as well as Gram-negative bacteria is also assessed. Augmented activity against standard isolates of Staphylococcus aureus with a minimum inhibitory concentration (MIC) is observed. Similar activity was also observed toward Escherichia coli, Klebsiella pneumoniae and Listeria monocytogenes. 1 and 2 have excellent bactericidal activity, and no resistant mutant for S. aureus was seen. The compound also unveiled antibiofilm activity and was capable to disrupt significantly the pre-formed biofilms and this property was confirmed by XTT assay experiment. The MTT assay data indicate that 1 and 2 can be used as anticancer agents toward the RAW 64.7 (human macrophage/monocyte) cell line. Further, the molecular docking study reveals that the role of imidazole is very important in the biological activity of these complexes. Moreover, our results suggest that 1 and 2 with its effective anti-microbial, anti-biofilm and cytotoxicity activity can be used to treat bacterial and fungal infections and could be appraised clinically for further applications. Communicated by Ramaswamy H. Sarma

Effects of Imidazole-Type Ligands in CuI/TEMPO-Mediated Aerobic Alcohol Oxidation

Selective aerobic oxidation of benzyl alcohol to benzaldehyde by a (bpy)CuI(IM)/TEMPO catalyst (IM represents differently substituted imidazoles) has been studied by simultaneous operando electron paramagnetic resonance/UV-vis/attentuated total reflectance infrared spectroscopy in combination with cyclic voltammetry to explore the particular role of imidazole in terms of ligand and/or base as well as of its substitution pattern on the catalytic performance. For molar ratios of IM/Cu ≥ 2, a (bpy)CuI/II(IM)a(IM)b complex is formed, in which the Cu-N distances and/or angles for the two IM ligands a and b are different. The coordination of a second IM molecule boosts the oxidation of CuI to CuII and, thus, helps to activate O2 by electron transfer from CuI to O2. The rates of CuI oxidation and CuII reduction and, thus, the rates of benzaldehyde formation depend on R of the R-N moiety in the IM ligand. Oxidation is fastest for R = H and alkyl, while reduction is slowest for R = H. The CuI/CuII interplay leads to decreasing total benzaldehyde formation rates in the order R (I+ effect) > R (conjugated system) > R = H.

The role of imidazole in peptide cyclization by transesterification: parallels to the catalytic triads of serine proteases

The improved bioavailability, stability and selectivity of cyclic peptides over their linear counterparts make them attractive structures in the design and discovery of novel therapeutics. In our previous work, we developed an imidazole-promoted preparation of cyclic depsipeptides in which we observed that increasing the concentration of imidazole resulted in the concomitant increase in the yield of cyclic product and reduction in dimerization, but also resulted in the generation of an acyl-substituted side product. In this work, we used transition state analysis to explore the mechanism of the imidazole-catalyzed esterification of one such peptide, Ac-SAFYG-SCH2φ, and determined the acyl substitution product to be an intermediate in a competing reaction pathway involving acyl substitution of the thioester by imidazole. Our findings indicate that imidazole plays an essential role in this side-chain to C-terminal coupling, and by extension, in transesterifications in general, through a concerted mechanism wherein imidazole deprotonates the nucleophile as the nucleophile attacks the carbonyl. The system under study is identical to the histidine-serine portion of the catalytic triads in serine proteases and it is likely that these enzymes employ the same concerted mechanism in the first step of peptide cleavage. Additionally, relatively high concentrations of imidazole must be used to effectively catalyze reactions in aprotic solvents since the overall reaction involves imidazole acting both as an acid and as a base, existing in solution as an equilibrium distribution between the neutral form and its conjugate acid.

Catalytic activity of carbon nanotube supported iron(III) and manganese(III) porphyrins in oxidation of olefins with tert-butyl hydroperoxide: Higher activity of the iron(III) porphyrin

Abstract Oxidation of olefins with tert-butyl hydroperoxide (TBHP) catalyzed by carbon nanotube supported iron(III) and manganese(III) complexes of meso-tetrakis(4-hydroxyphenyl)porphyrin is reported. The results show higher catalytic activity of the Fe(III) complex compared to the Mn(III) one. With the exception of cyclooctene which gives cyclooctene oxide as the sole product, oxidation of styrene, α-methyl styrene and cyclohexene leads to the formation of benzaldehyde, acetophenone and cyclohexene-1-one as the major product, respectively. In this study, acetonitrile has been found to be the best solvent for reaction performed in the presence of the manganese and iron porphyrin. In comparison of the two metalloporphyrins, catalytic activity of the manganese porphyrin is more sensitive to the type of solvent than the iron one. In spite of the crucial role of imidazole (ImH) on catalytic performance of the manganese porphyrin, the presence of ImH has a negative effect on the activity of the iron porphyrin. The nano-tube supported iron porphyrin may be recovered and reused at least four times without significant loss of the catalytic activity.

Identification and characterization of aging products in the glyoxal/ammonium sulfate system – implications for light-absorbing material in atmospheric aerosols

Abstract. In this study we report the identification of bicyclic imidazoles in aqueous aerosol mimics using HPLC-ESI-MS/MS. 2,2'-Biimidazole was identified to be a major contributor to the 280 nm absorbance band observed in mixtures of glyoxal and ammonium sulfate, despite the fact that its production rate is two orders of magnitude lower than the previously reported production rates of imidazole or imidazole-2-carboxaldehyde. The molar absorptivity of 2,2'-biimidazole was determined to be (36 690 ± 998) M−1 cm−1. This demonstrates the necessity of molecular product identification at trace levels to enable a better understanding of relevant absorbing species. Additionally, the formation of lower polarity products including formamides of imidazoles is proposed. The role of imidazoles and other light-absorbing species in the formation of SOA and optical properties of SOA is discussed and potentially interesting fields for future investigations are outlined.

Direct evidence for the role of imidazole in disproportionation of hydrogen peroxide by a mononuclear manganese salen complex

It has long been known that imidazole can enhance the catalytic activity of catalase model compounds; however, the role of imidazole is still not well understood. In an attempt to elucidate the role of imidazole in promoting the disproportionation of hydrogen peroxide by model compounds, four mononuclear manganese salen (Mn-Salen) complexes with and without axial imidazole ligands were synthesized and characterized by single-crystal X-ray diffraction, UV–vis spectroscopy, electrochemical and HPLC measurements. By comparing the Mn-Salen compounds with and without imidazole ligands, we demonstrated that the activity enhancement of imidazole originated from coordination of imidazole to the manganese center when less than one equivalent of imidazole was present, and from assisted deprotonation of the substrate when excess imidazole was present. These results provide direct evidence for the mechanism of activity enhancement of imidazole in the catalysis of enzyme model compounds.

ChemInform Abstract: Stereoselective Reduction of Ketones by Histidine‐Alkoxysilane Complexes: The Role of Imidazole in Nucleophilic Substitution at Silicon.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Stereoselective reduction of ketones by histidine-alkoxysilane complexes: The role of imidazole in nucleophilic substitution at silicon

The reduction of carbonyl compounds with transient, hypervalent silicon hydrides is described. Trialkoxysilanes, upon activation by a catalytic amount of lithium imidazolide or the mono or dilithium salt of histidine, but not by neutral imidazole or histidine, reduced the carbonyl groups of various ketones. Enantiomerically enriched product alcohols were recovered in good to excellent yield (70 – 95%) with e.e.'s ranging from 5–75% when catalyzed by histidine derivatives.

Atomic orbitals in the ab initio analysis of imidazole H-bonding

The systems formate-imidazole (A) and formate-imidazole-acrylic acid (B) have been studied in connection with the role of imidazole in biochemical proton transfer. At variance with previous studies, this work has been carried out with the experimental lengths of the H bonds, and attention has been focussed on the in situ hybrid AOs of the various atoms as they appear in the various canonical orbitals obtained from STO-3G computations, and on their possible significance for the stability of the double H-bridge of system B. A discussion mainly referring to the form of B representing the intermediate for concerted proton transfer is given. Hybridisation appears to play an important role, but is not associated with covalent bond formation, and could be associated to through-space interactions within the imidazole ring.

Sulfite oxidase from chicken liver. The role of imidazole and carboxyl groups for the reaction with cytochrome c.

Oxidation of sulfite to sulfate by sulfite oxidase is inhibited when the enzyme is treated with reagents known to modify imidazole and carboxyl groups. Modification inhibits the oxidation of sulfite by the physiological electron acceptor cytochrome c, but not by the artificial acceptor ferricyanide. This indicates interference with reaction steps that follow the oxidation of sulfite by the enzyme's molybdenum cofactor. Reaction with diethylpyrocarbonate modifies ten histidines per enzyme monomer. Loss of activity is concomitant to the modification of only a single histidine residue. Inactivation takes place at the same rate in free sulfite oxidase and in the sulfite-oxidase--cytochrome-c complex. Blocking of carboxyl groups with water-soluble carbodiimides inactivates the enzyme. But none of the enzyme's carboxyl groups seems to be essential in the sense that its modification fully abolishes activity. The pattern of inactivation by chemical modification of sulfite oxidase is quite similar to that observed previously for cytochrome c peroxidase from yeast [Bosshard, H. R., Bänziger, J., Hasler, T. and Poulos, T. L. (1984) J. Biol. Chem. 259, 5683-5690; Bechtold, R. and Bosshard, H. R. (1985) J. Biol. Chem. 260, 5191-5200]. The two enzymes have very different structures yet share cytochrome c as a common substrate of which they recognize the same electron-transfer domain around the exposed heme edge.

The role of imidazole and its natural compounds in the functional activity of the muscles

The role of imidazole and its natural compounds in the functional activity of the muscles