Hydroxylation structural studies

The views perpendicular to b, on the other hand, show considerably more asymmetry. The lack of a two-fold axis in the crystal is most evident in the view along c. In all three of the PbTX-1 structures studied, a short intermolecular distance is calculated between the 012 hydroxyl and the 05 ether oxygens. The two molecules involved in the short contact are related by a C-centerihg (or pseudo C-centering) operation. In the PbTX-1 dimethyl acetal crystal, the 012-05 distance is 2.87 A, in PbTX-1 it is 2.86 A, and in dihydro PbTX-1 it is 2.84 A. Dihydro... 

PEMFC)/direct methanol fuel cell (DMFC) cathode limit the available sites for reduction of molecular oxygen. Alternatively, at the anode of a PEMFC or DMFC, the oxidation of water is necessary to produce hydroxyl or oxygen species that participate in oxidation of strongly bound carbon monoxide species. Taylor and co-workers [Taylor et ah, 2007b] have recently reported on a systematic study that examined the potential dependence of water redox reactions over a series of different metal electrode surfaces. For comparison purposes, we will start with a brief discussion of electronic structure studies of water activity with consideration of UHV model systems. 

Per-iodic acid oxidation78-80 has been used by many investigators in structural studies because this reagent oxidizes selectively the hydroxyls on adjacent carbon atoms. In the course of their studies, McDonald and Jackson81 found that difructose anhydrides I, II and III and diheterolevulosan reduce per-iodic acid to iodic acid in the following respective molecular ratios 2, 1, 1, and 4 moles of acid per mole of anhydride. 

As regards the l,l-bis(acylamido)-l-deoxyalditols, the first structural study was that of Fletcher and coworkers,69 who conducted oxidations with lead tetraacetate. These authors postulated an empirical relationship between the position of the oxidation curve in a graph and the number of hydroxyl groups present. They compared the curves afforded by a series of l,l-bis(acetamido)-l-deoxyalditols with those of alditols having the same number of free hydroxyl groups, and observed a close correspondence. At present, periodate oxidation is widely applied to these mono- or di-saccharide derivatives. Under controlled conditions, the methylation technique can also be applied.42... 

This is of relevance to the mechanism of carbonic anhydrase. This enzyme, which catalyzes the hydration of C02, has at its active site a Zn2+ ion ligated to the imidazole rings of three of its histidines. The classic mechanism for the reaction is that the fourth ligand is a water molecule which ionizes with a pKa of 7.37 The reactive species is considered to be the zinc-bound hydroxyl. Chemical studies show that zinc-bound hydroxyls are no exception to the rule of high reactivity. The H20 in structure 2.31 ionizes with a pKa of 8.7 and catalyzes the hydration of carbon dioxide and acetaldehyde.38... 

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