Desolvation effects

Comparison of solution pH with the pKa of a side chain informs about the protonation state. A unique pKa, termed the standard or model pKa, can be experimentally determined for each ionizable side chain in solution when it is incorporated in a model compound, often a blocked amino acid residue [73] (Table 10-1). In a protein environment, however, the pKa value of an ionizable side chain can substantially deviate from the standard value, due to desolvation effects, hydrogen bonding, charge-charge, charge-dipole, and other electrostatic interactions with the... 

It should be noted that application of the Marcus theory to these reactions is much more straightforward than application to reactions in solution. Since we are dealing with a single unimolecular step, namely, rearrangement of the reactant complex to the product complex, we need not be concerned with the work terms (2) which must be included in treatments of solution-phase reactions. These terms represent the work required to bring reactants or products to their mean separations in the activated complex, and include Coulombic and desolvation effects. 

Because of the absence of any further contacts with the HIV PR active site residues, the contribution of the quinoline moiety to the free energy of binding remains unclear. Perhaps in solution, a stacking interaction of the PI phenyl ring and the aromatic quinoline restricts the conformational freedom of Ro-31-8959, in effect diminishing the free-energy loss due to the entropic and desolvation effects. 

Extensive structural characterization of many different -ring heterocycles has not yet been done. Difficulties predicting relative potency of these compounds a priori stem from the lack of understanding of solvation/desolvation effects as well as difficulties in characterizing the low-intensity hydrophobic interactions. Consequently, it seems likely that new structure—activity relationships about the A-ring heterocycle will continue to be determined based on empirical findings. 

There exists substantial evidence that in reactions that involve oxyanions or amines as bases or as nucleophiles, their partial desolvation, as they enter the transition state, typically has made greater progress than bond formation. In the context of the PNS, this partial loss of solvation represents the early loss of a reactant stabilizing factor and hence reduces the intrinsic rate constant. As discussed at some length in our 1992 chapter,4 for strongly basic oxyanions this desolvation effect often manifests itself in terms of negative deviations from Br Ansted plots and/or in abnormally low p or pnuc values.58,188 In fact, a number of cases have been reported where the pnuc value was close to zero or... 

Solvation and desolvation effects are of tremendous importance in assessing binding equilibria. 

Solvation/desolvation effects in the cryptand also complicate the expected simple dependence of stability constant on host basicity. For example the aliphatic cryptand O-bistren shows lower formation constants than the less basic aromatic analogues such as R3F, which we attribute to the greater desolvation cost of complexation with the former, more hydrophilic host. 

Electrostatic desolvation effects upon binding can be scored by invoking a Poisson-Boltzmann (PB) formulation of electrostatic binding energies44 of the form... 

Nanooxides such as fumed silica, titania, alumina, etc. (with spherical primary nanoparticles) are used as fillers for complex drugs, enterosorbents, vaccine adjuvants, food additives, etc.1,2 In general nonporous spherical nanoparticles can adsorb solutes in low amounts because the desolvation effect causes an... 

The contribution of hydrogen bonds to the binding affinity strongly depends on solvation and desolvation effects. Here lies the biggest challenge... 

The pneumatic nebulizer has for many years been the most universal sample insertion device for plasma-based spectrometry. The inherent lack of transport efficiency, coupled with the continuing need for increased sensitivity, has promoted research into the use of ultrasonic nebulizers to boost detection capabilities. Such research has focused on various aspects including fundamental aerosol properties [86-88], instrument development [89], nebulizer comparisons [90,91], desolvation effects [92,93], direct nebulization applications [94,95] and speciation [96]. 

The solubility of various liquids in water, and vice versa, is of much interest in different industrial and biological phenomena of everyday importance (Table 3.13). ° In any of these applications, we would encounter instances where a prediction of solubility would be of interest the following such applications are mentioned for general interest. Furthermore, solubilities of molecules in a fluid are determined by the free energy of solvation. In more complicated processes such as catalysis, the reaction rate is related to the desolvation effects. 

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