Enhanced binding strength

Mutations in the specificity pocket of trypsin, designed to change the substrate preference of the enzyme, also have drastic effects on the catalytic rate. These mutants demonstrate that the substrate specificity of an enzyme and its catalytic rate enhancement are tightly linked to each other because both are affected by the difference in binding strength between the transition state of the substrate and its normal state. 

It is quite interesting that ln(r°/r0°), where r0° is the open-circuit preexponential factor, also varies linearly with Uwr and O (Figs. 4.35 to 4.37) and in fact, when plotted as kbT0ln(r°/ro°) where T is the isokinetic temperature discussed below, with the same slope as EA. This decrease in apparent preexponential factor with increasing <3> can be attributed to the reduced binding strength and thus enhanced mobility of chemisorbed oxygen on the catalyst surface. 

Adsorption of cyanide anions can be affected by adsorption of cations. In the solutions containing nonspecifically adsorbed anions, the nature of alkali metal cations was found to influence the measured value of the electrode capacitance at potentials more negative than —0.6 V (versus standard hydrogen electrode (SHE)). At < —l.OV adsorption of CN ions was enhanced in the presence of Li+ and Na+ cations, and inhibited in the presence of Cs+ ions [81]. A combined SERS and density-functional theory has been applied to study cyanide adsorption at Au electrode [82]. The authors have arrived at the conclusion that the polarity of Au—CN bonds falls between that of Au—Cl and Au—Br surface bonds. The binding strength for three different gold surfaces decreased in the order ... 

In order to minimize swelling, MIP is often synthesized in a polar solvent, such as dimethylformamide (DMF) or ACN [113]. Most importantly, a (cross-linker)-to-(functional monomer) mole ratio affects the chemosensor performance. That is, a high (5 1) ratio enhances mechanical strength of an MIP film and favours formation of binding sites. But a low (1 5) ratio leads to a flexible MIP film of improved template memory and stronger adherence to the transducer surface [114]. Therefore, this ratio must be compromised for preparation of MIP of superior performance [114]. 

A ditopic receptor 71, comprising a semitubular calix[4]arene system [91] for cation recognition and urea moieties for anion recognition, was reported very recently. The complexation of sodium or potassium cations into the central ethylene glycol cavity invokes substantial enhancement of the binding strength (more than one order of magnitude) towards selected anions (halides, acetate). 

The sensitivity of the energetic aspects of the H-bonds to the level of theory is reported in Table 2.42. The inclusion of polarization functions reduces the interaction energy somewhat, probably due largely to reduction of BSSE. With these d-functions included, there is little difference between water or methanol as proton donor. Correlation enhances the binding strength, as noted in other systems. Comparison with other complexes is difficult as the authors did not remove the BSSE from their data. On the other hand, the authors have compiled a list of thermodynamic quantities for a number of related systems, all at the SCF76-31G level, so there is some basis for comparison here. 

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