Imidazole binding

Ligands assigned by Pearson as hard appear in normal type, borderline in bold, and soft in italics. For Pearson, aliphatic amines are hard and aromatic amines borderline. Since imidazole binds metal ions through a borderline pyridine-type nitrogen, imidazole is also classed as borderline in the hgand scale. Use of CH3Hg+ in place of Hg + yields a virtually identical ordering with a lesser span of 13 log units. 

When Mn tetraphenyl porphyrin (MnTPP) is used as the catalyst, imidazole binding as a fifth ligand acts as a promoter for P450 reaction as has been noted in earlier studiesInterestingly, the hexanol-to-hexanone ratio increases (0.8 1.1) upon replacement... 

Several imidazoles have been found to inhibit NOS, including 1-phenylimidazole, 2-phenylimidazole, and 4-phenylimidazole. These imidazoles bind heme in NOS and other enzymes. A search for isoform-specific inhibitors based on an imidazole structure has led to the discovery of l-(trifluoromethylphenyl) imidazole, N-(4-nitrophenacyl) imidazole, and N-(4-nitrophenyIacyl)-2-methyI-imidazole, below (54). The nitrophenylacylimidazoles are selective for nNOS rather than eNOS inhibition. They appear to bind to the tetrahydro-biopterin site and are competitive inhibitors of tetrahydrobiopterin binding. They are noncompetitive inhibitors of arginine binding. It appears that electron-withdrawing N-1 substituents enhance activity and nNOS selectivity. 

At higher imidazole concentrations, and thus at higher binding rates, the second-order process gives way to first-order behaviour Fig. 4. The binding becomes rate limited at 8/sec by a first-order process which, in this case, may be interpreted as the dissociation (Ar ff) of methionine from the central iron atom of cytochrome c prior to imidazole binding. 

In contrast to the case of imidazoles binding to tetraphenylporphyrins, Wang et a/ have demonstrated that binding of cyanide to high-spin protoporphyrin IX iron(III) chloride in DMSO- ie is a two-step process as shown in equations (38) and (39), and whether DMSO acts as a sixth ligand for the mono-cyano complex is not known ... 

In none of our studies of ligand binding by peroxidases or hemin have we obtained any evidence of inhibition of rate at high hgand concentration which would indicate either a dissociative or ion-pair mechanism (28,29). This lack of evidence does not exclude such mechanisms, however. From a comparison of imidazole binding rate with solvent exchange rate by hemin in an ethanol—water solvent, our results favored an ion-pair mechanism (30, 31). 

The same mechanism with a rate-limiting conformational change that results in loss of the Fe—Met has been proposed for imidazole binding to ferricyts c and C2- Imidazole... 

Goldston. H.M.. Jr. Scribner. A.N. Trammell, S.A. Tender. L.M. A model recognition switch. Electrochemical control and transduction of imidazole binding by electrode-immobilized microperoxidase-11. Chem. Commun. 2002. 416-417. 

Figure 13.55. Strong imidazole binding within the phenanthroline-strap of the ZnP is used as an assembly tool for a series of dyads.

While the approaches summarized above limit the number of active chromo-phores in the vicinity of the surface, the attachment of multiporphyrins more closely resembles the natural process of photon collection. Two recent papers by Kobuke illustrate this approach quite well and take advantage of the axial imidazole binding to zinc porphyrins . The phenomenon is better described by the more recent example in which a heterodimer is formed by self-assembly after the attachment of a zinc porphyrin to a gold surface, as depicted in Figure 13.81 . 

Solubilizate binding constants have been determined for a few reverse micelle -small molecule (phenols, imidazole, simple alcohols) combinations [60, 63, 64]. In the case of imidazole binding to dodecylammonium propionate (DAP) reverse micelles, the use of the chemical shift dependence on DAP concentration for imidazole protons led to nonunique (i. e., proton-dependent) binding constants, a physically unreasonable situation [64]. When one is studying chemical reactions involving reactants which partition among the water pools, with the surfactant layer on the... 

One advantage of the supramolecular polymers constructed by orthogonal assembly is their enhanced responsiveness to multiple external stimuli. Recently, a thermo- and photo-responsive supramolecular polymer based on pillar[5]arene was reported by Yang s group, ° where the anthracene group was used as the photo-responsive unit, and the pillar[5]arene/imidazole binding motif was employed as the thermo-responsive unit. When an anthracene-modified pillararene (7.27) was irradiated with UV light [1 >360 nm), the anthracene unit dimerized and the pillar[5]arene dimer... 

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