Elucidation of active site

An alternative to elucidating the active sites on a surface is to synthesize them. For example, a new catalyst for metathesis of alkanes. 

TKase is a homodimeric protein with a subunit of about 70kDa. The X-ray structures of TKase of E. colif S. cerevisiaeX Leishmania mexicana and mize have been solved. In addition, the crystal structures of a number of site-directed mutants have been determined. Schneider and co-workers have reported a series of studies in which they have mutated important residues of active site of TKase to elucidate the reaction mechanism and explain the origin of the stereospecificity of the C—C bond-forming process (Table The conserved... 

Ab initio methods allow the nature of active sites to be elucidated and the influence of supports or solvents on the catalytic kinetics to be predicted. Neurock and coworkers have successfully coupled theory with atomic-scale simulations and have tracked the molecular transformations that occur over different surfaces to assess their catalytic activity and selectivity [95-98]. Relevant examples are the Pt-catalyzed NO decomposition and methanol oxidation. In case of NO decomposition, density functional theory calculations and kinetic Monte Carlo simulations substantially helped to optimize the composition of the nanocatalyst by alloying Pt with Au and creating a specific structure of the PtgAu7 particles. In catalytic methanol decomposition the elementary pathways were identified... 

The nature of active sites elucidated by in situ atomic-resolution electron microscopy... 

Ab inito chemical shielding calculation, combined with solid-state NMR experiment, is a powerful tool to elucidate the structures of active sites in proteins and enzymes. 

The same authors (140) then carried out a number of experiments where the catalyst pretreatment conditions were varied and reagents were added to the reaction mixture (i.e., ammonia, pyridine, and CO) in order to elucidate the type of active site. Rather surprisingly, it was concluded that... 

Dealuminated Y zeolites which have been prepared by hydrothermal and chemical treatments show differences in catalytic performance when tested fresh however, these differences disappear after the zeolites have been steamed. The catalytic behavior of fresh and steamed zeolites is directly related to zeolite structural and chemical characteristics. Such characteristics determine the strength and density of acid sites for catalytic cracking. Dealuminated zeolites were characterized using X-ray diffraction, porosimetry, solid-state NMR and elemental analysis. Hexadecane cracking was used as a probe reaction to determine catalytic properties. Cracking activity was found to be proportional to total aluminum content in the zeolite. Product selectivity was dependent on unit cell size, presence of extraframework alumina and spatial distribution of active sites. The results from this study elucidate the role that zeolite structure plays in determining catalytic performance. 

Much has been accomplished, especially in recent years, toward the goal of elucidating the active sites of galactosyltransferase and a-lactal-bumin. To this end, alteration of specific residues with observations of consequent effects on structure and activity is enlightening, as are metal ion effects. Where the substrate is concerned, we now have some detailed structural information for both galactosyltransferase and the lactose synthase system. 

The elucidation of the site in a molecule at which the metabolism occurs, is one of the most time and sample consuming experimental tasks in the ADME field. In some cases, the experimental methodology does not help one to determine the precise location of metabolism. Nevertheless, the experimental information could be very relevant for exploration of the pharmacological activity or the toxic effect of the formed metabolites. Moreover, knowledge of the site of metabolism could help in the chemical protection of the molecule, making the compound less liable to metabolic reactions. 

A crucial question is. What does the three-dimensional structure of a specific protein look like Protein structure determines function, given that the specificity of active sites and binding sites depends on the precise threedimensional conformation. Nuclear magnetic resonance spectroscopy and x-ray crystallography are two of the most important techniques for elucidating the conformation of proteins. 

T ivalent and ammonium forms of Y zeolite possess catalytic activities for many acid-catalyzed reactions 11, 12, 16, 19). Although it is generally accepted that acidic hydroxyl groups are responsible for the activity of the calcined ammonium form 4, 6,19, 24), the reasons for the activity of the cation forms have been less well elucidated 6, 7, 9,15,19, 20, 25). Since the catalytic activity of the divalent cation forms usually is exhibited when suflBcient cations have been introduced so as to occupy accessible positions in the lattice, it has been suggested that various properties of the cations may be responsible for the introduction of active sites. Properties of the cations such as their electrostatic field and surface diffusion have been suggested 12, 15). Alternatively, it has been suggested that the divalent cations can introduce Bronsted acidity by dissociation of water 3, 5, 6,18,19, 20), thus... 

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