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Surface structure active sites

A. A. Chuiko and Yu. I. Gorlov, Chemistry of Silica Surface Surface Structure, Active Sites and Adsorption Mechanisms, Kiev, Naukova Dumka, 1992 (in Russian). [Pg.280]

Chuiko, A.A. Gorlov, Yu.I. Silica Surface Chemistry Surface Structure, Active Sites, Sorption Mechanisms Nauk. Dumka 1992. (In Russian). [Pg.359]

The stereochemical specificity of enzymes depends on the existence of at least three different points of interaction, each of which must have a binding or catalytic function. A catalytic site on the molecule is known as an active site or active centre of the enzyme. Such sites constitute only a small proportion of the total volume of the enzyme and are located on or near the surface. The active site is usually a very complex physico-chemical space, creating micro-environments in which the binding and catalytic areas can be found. The forces operating at the active site can involve charge, hydrophobicity, hydrogen-bonding and redox processes. The determinants of specificity are thus very complex but are founded on the primary, secondary and tertiary structures of proteins (see Appendix 5.1). [Pg.280]

Further, the active sites co-exist with the rest of the surface and bulk of the heterogeneous catalyst, and there is keen interest in determining the relationship between the bulk, surface, and active site structure in any given catalytic system. [Pg.19]

The overall structures of all MMP catalytic domains known so far are very similar (Fig. 2). These MMP catalytic domains are shaped like an oblate ellipsoid, with a small active-site cleft, harboring the catalytic zinc ion, notched into the flat ellipsoid surface. The active site cleft is defined by helix hB, which provides two histidine residues that coordinate to the catalytic zinc ion, and the catalytic Glu in between, all belonging to the zinc-binding consensus sequence HEYZHYZGXZH (5, 22, 23). The active-site helix ends at a Gly residue, where the peptide chain bends, presenting the third zinc-liganding His. The zinc ion also coordinates to a water molecule that... [Pg.1071]

When water is present in the gas stream, it reacts with the SO, and O2 to produce sulfuric acid on the carbon surface, and can subsequently desorb. The overall SO adsorption capacity is enhanced due to its solubility in the water film that forms on the carbon surface. Conversely, active sites for SO2 capture are simultaneously reduced by water coverage. In general, the SO2 adsorption characteristics of an activated carbon are dependent upon its physical form, the pore structure, the surface area, and the surface chemistry. Similarly, both temperature and contact time also affect the efficiency of the process. The temperature for practical application is usually between ambient and 200°C, with ambient to 50°C being favored due to the decreasing solubility of SO2 in water at higher temperatures. [Pg.23]

Kanungo, S.B., Parida, K.M., and Sant, B.R., Studies on MnOj—II. Relationship between physicochemical properties and electrochemical activity of some synthetic MnO2 of different crystallographic forms. Electrochim. Acta, 26, 1147, 1981. Pivovarov, S., Surface structure and site density of the oxide-solution interface, J. Colloid Intetf. Sci., 196, 321, 1997. [Pg.943]

Realistic simulations should ultimately take into account the electronic structure of reactants, products, the surface, and active sites. The Car-Parrinello simulation scheme seems to be the most appropriate method for the future. First steps into this direction were made by Price and Halley, using a hybrid scheme [285]. [Pg.68]

The deactivation of zeolites which occurs during the reactions of organic compounds is mainly due to the formation of secondary products heavier than the reactant(s) and the desired product(s). These secondary products remain blocked either in the pores of the zeolite, on the outer surface of the crystallites or in both positions. As has been shown in various reviews [1-4] the rate of their formation and their composition depend on numerous parameters pore structure, active sites, nature of the reactant(s), temperature... [Pg.437]

The catalytic activity per surface active site (TOP) toward a specific reaction is the right parameter to obtain reliable surface structure-activity correlations. The knowledge of the TOFs values dismissed the believes that the catalytic activity is influenced by bulk properties and that monolayer supported oxide catalysts are more active than bulk oxide catalysts. There is no doubt that the specific activity would contribute to design more active and selective catalytic materials at a molecular level. [Pg.386]

Van Etten, R.L., Davidson, R., Stevis, P.E., MacArthur, H., and Moore D.L., 1991, Covalent structure, disulfide bonding, and identification of reactive surface and active site residues of human prostatic acid phosphatase./. Biol. Chem. 266 2313-2319. [Pg.184]

The molecular surface of receptor site regions cannot be derived from the structure infoi mation of the molecule, bth represents the form ofthe active site of a protein surrounded by a ligand. This surface representation is employed in drug design in order to illustrate the volume of the pocket region or the molecular interaction layers [186. ... [Pg.128]

Active site of an enzyme is the binding site where catalysis occurs. The structure and chemical properties of the active site allow the recognition and binding of the substrate. The active site is usually a small pocket at the surface of the enzyme that contains residues responsible... [Pg.13]

After the somewhat tedious parametrization procedure presented above you are basically an expert in the basic chemistry of the reaction and the questions about the enzyme effect are formally straightforward. Now we only want to know how the enzyme changes the energetics of the solution EVB surface. Within the PDLD approximation we only need to evaluate the change in electrostatic energy associated with moving the different resonance structures from water to the protein-active site. [Pg.167]

The elucidation of the X-ray structure of chymotrypsin (Ref. 1) and in a later stage of subtilisin (Ref. 2) revealed an active site with three crucial groups (Fig. 7.1)-the active serine, a neighboring histidine, and a buried aspartic acid. These three residues are frequently called the catalytic triad, and are designated here as Aspc Hisc Serc (where c indicates a catalytic residue). The identification of the location of the active-site groups and intense biochemical studies led to several mechanistic proposals for the action of serine proteases (see, for example, Refs. 1 and 2). However, it appears that without some way of translating the structural information to reaction-potential surfaces it is hard to discriminate between different alternative mechanisms. Thus it is instructive to use the procedure introduced in previous chapters and to examine the feasibility of different... [Pg.171]


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