The roles of imidazole in biological systems

Synthesis, DFT Molecular Geometry and Anticancer Activity of Symmetrical 2,2'-(2-Oxo-1H-benzo[d]imidazole-1,3(2H)-diyl) Diacetate and Its Arylideneacetohydrazide Derivatives

To identify new candidate anticancer compounds, we here report the synthesis of benzimidazole derivatives: diethyl 2,2'-(2-oxo-1H-benzo[d]imidazole-1,3(2H)-diyl) diacetate and its arylideneacetohydrazide derivatives, using ultrasonic irradiation and conventional heating. The compounds were confirmed by Nuclear magnetic resonance (NMR) (JEOL, Tokyo, Japan) and Fourier transform infrared spectroscopy (FTIR) spectroscopy (Thermoscientific, Waltham, MA, USA). The molecular structure and electronic properties of the studied compounds were predicted for the acetohydrazide hydrazones. These compounds exist as a mixture of configurational and conformational isomerism as well as amido-amidic acid tautomerism. The NMR spectral data proved the predominance of syn-E amido isomers. In addition, density functional theory (DFT) predicted stability in the gas phase and showed that syn-E amido isomers are the most stable in the presence of an electron donating group, while the anti-isomer is the most stable in the presence of electron-attracting substituents. The anticancer activity of these synthetic compounds 6a, 6b and 6c towards both colon cancer (HCT-116) and cervical cancer (HeLa) cells was examined by MTT assay and DAPI staining. The MTT assay revealed a strong antiproliferative effect against the cancer cells at low concentrations, and interestingly, no significant inhibitory action against the non-cancerous cell line, HEK-293. The IC50 values for HCT-116 were 29.5 + 4.53 µM, 57.9 + 7.01 µM and 40.6 + 5.42 µM for 6a, 6b, and 6c, respectively. The IC50 values for HeLa cells were 57.1 + 6.7 µM, 65.6 + 6.63 µM and 33.8 + 3.54 µM for 6a, 6b, and 6c, respectively. DAPI staining revealed that these synthesized benzimidazole derivatives caused apoptotic cell death in both the colon and cervical cancer cells. Thus, these synthetic compounds demonstrate encouraging anticancer activity as well as being safe for normal human cells, making them attractive candidates as anticancer agents.

Development of Imidazole-Reactive Molecules Leading to a New Aggregation-Induced Emission Fluorophore Based on the Cinnamic Scaffold

In order to obtain new fluorophores potentially useful in imidazole labeling and subsequent conjugation, a small series of Morita-Baylis-Hillman acetates (3a-c) was designed, synthesized, and reacted with imidazole. The optical properties of the corresponding imidazole derivatives 4a-c were analyzed both in solution and in the solid state. Although the solutions display a very weak emission, the powders show a blue emission, particularly enhanced in the case of compound 4c possessing two methoxy groups in the cinnamic scaffold. The photophysical study confirmed the hypothesis that the molecular rigidity of the solid state enhances the emission properties of these compounds by triggering the restriction of intramolecular motions, paving the way for their applications in fluorogenic labeling.

Mode recognition in UV resonance Raman spectra of imidazole: histidine monitoring in proteins

The imidazole side-chains of histidine residues perform key roles in proteins, and spectroscopic markers are of great interest. The imidazole Raman spectrum is subject to resonance enhancement at UV wavelengths, and a number of UVRR markers of structure have been investigated. We report a systematic experimental and computational study of imidazole UVRR spectra, which elucidates the band pattern, and the effects of protonation and deprotonation, of H/D exchange, of metal complexation, and of addition of a methyl substituent, modeling histidine itself. A consistent assignment scheme is proposed, which permits tracking of the bands through these chemical variations. The intensities are dominated by normal mode contributions from stretching of the strongest ring bonds, C(2)N and C(4)C(5), consistent with enhancement via resonance with a dominant imidazole π-π* transition.

On Dielectric Constant and Enzymatic Kinetics : III. Interrelationships of dielectric constant and pH

The dielectric effects on trypsin and alpha-chymotrypsin activities have revealed that at pH 7.8 the active species of the former is the cation while that of the latter is the anion. The present study on the dielectric effects along the pH-activity curves shows that trypsin remains positive within the pH range of 5.5 to 8.5. Conversely, alpha-chymotrypsin is positive from pH 5.5 to 6.6, negative from 6.6 to about 8.1, and at pH 8.25 becomes positive again. The first point of inversion in charge sign shifts from 6.6 to 7.15 with the addition of 0.05 M phosphate buffer. The point of inversion does not seem to be modified significantly by changes in the substrate structure. At pH values near the point of inversion the plots of rate log vs. 100/D are broken lines formed by various straight portions, the slope of each varying progressively from a maximum positive to a maximum negative value. This suggests an effect of resonance possibly attributable to an imidazole group. As an attempt to explain the two observed points of sign inversion in alpha-chymotrypsin, the possibility is suggested that different enzyme configurations are disclosed by the combined action of pH and dielectric constant. On this theoretical basis, it i6s feasible that more than one isoionic point exists.

THE SYNTHESIS AND BACITRACIN-CATALYSED HYDROLYSIS OF ARYL ESTERS OF N-ACYLAMINO ACIDS

1. A new method for synthesizing aryl esters of N-acylamino acids is described. The unsymmetrical anhydride resulting from the interaction of an N-acylamino acid and diphenylketen is allowed to react with a phenol. Cleavage of the anhydride by the phenol usually occurs in the desired direction. 2. Bacitracin has been examined as an enzyme model by determining its catalytic activity towards the hydrolysis of aryl esters. In general, it is less effective than imidazole. The variation of the catalytic constant with pH, together with other evidence, suggests that the histidine residue in bacitracin is the effective catalytic centre. 3. The stereoisomers of N-methoxycarbonylalanine p-nitrophenyl ester were hydrolysed at the same rate, but bacitracin was stereoselective towards the stereoisomers of the corresponding phenylalanine derivative.

Imidazole-buffered osmium tetroxide: an excellent stain for visualization of lipids in transmission electron microscopy

The usefulness of imidazole-buffered osmium tetroxide as a stain for lipids in transmission electron microscopy has been investigated. Rat liver and other tissues were fixed by perfusion with glutaraldehyde and post-fixed with osmium-imidazole and the appearance of lipid droplets was compared with that after post-fixation in unbuffered aqueous osmium tetroxide or an osmium solution buffered otherwise. Prominent electron-opaque staining of lipid droplets and of lipoprotein particles was noted after post-fixation with 2% osmium-imidazole, pH 7.5, for 30 min. The lipid droplets appeared well circumscribed with no evidence of diffusion. In contrast, the intensity of staining was much less and there was some diffusion around lipid droplets in material post-fixed in aqueous or cacodylate-buffered osmium tetroxide. Spot tests on filter paper revealed that unsaturated fatty acids, especially linolenic and linoleic acids reacted more intensely with osmium-imidazole than with aqueous osmium tetroxide. These findings demonstrate that osmium-imidazole provides an excellent stain for lipids in transmission electron microscopy and that most probably it stains lipids with unsaturated fatty acids.

Substrate specificity and kinetic properties of alpha-galactosidases from Vicia faba

1. The hydrolysis of a variety of galactosides and other glycosides by alpha-galactosidases I and II of Vicia faba was studied. 2. The effect of temperature on kinetic parameters was also examined. 3. Both enzymes are inhibited by excess of substrate (p-nitrophenyl alpha-d-galactoside); with enzyme I this is competitive and is caused by the galactosyl moiety. 4. Enzyme I is inhibited by oligosaccharides possessing terminal non-reducing galactose residues and to a smaller extent by l-arabinose and d-fucose. 5. The effect of pH on K(m) and V(max.) values suggests that carboxyl and imidazole groups are involved in the catalytic activity of enzyme I. 6. Photo-oxidation experiments with enzyme I also suggest that an imidazole group is present at the active site.