Binding kinetics thermodynamics

Surface imprinting has recently been used in our laboratory to prepare phosphate and phosphonate receptors in silica xerogels [38]. In an effort to obtain faster on/off binding kinetics and gain thermodynamic control of the host-guest interaction, we positioned the receptor sites as close as possible to the gel surface. This resulted in observed equilibration binding times of less than a minute. 

Despite the tiny dimensions and simple atomic composition, each gas is different in its physical and chemical properties and requires an individual approach. However, it is possible to rationalize kinetics, thermodynamics, and selectivity of molecular hosts for gases on the basis of receptor-substrate electronic and geometrical complementary. It is also clear that widely accepted supramolecular concepts (e.g., the preorganization, multiplication of binding sites, and encapsulation) are applicable for gases. As for all other areas of supramolecular chemistry, spectroscopic techniques and molecular modeling are crucial to elucidate the specific contributions of various binding forces, as well... 

Even if the presentation of the ligands on a spherical or planar polymer surface cannot be rationally coordinated to the complementary receptor positioning but is statistically distributed instead the result is a significantly higher inhibition that can now be reconciled with theoretical methods in terms of binding kinetics (e.g., possibly inaeased rebinding of the ligands) and better thermodynamics. 

Binding thermodynamics defines the average number of active cross-links at any point in time, while the binding kinetics defines how quickly the active cross-links dissociate. This study identifies an important and striking influence on bulk properties as it would seem intuitive that the number of active cross-links (thermodynamics) would dominate over the timescale each cross-link remains active (dissociation kinetics) in determining material properties. However, this study clearly identifies that the dynamic nature of supramoiecuiar interactions is directly responsible for observed properties and for the comparative differences with covalently aoss-linked systems, rather than the relative weakness of the interactions. 

It is interesting to note that catalytic turnover was possible in spite of the closed (as compared to the bowlshaped structures used by Fujita and Rebek, respectively) tetrahedral host structure. Apparently, catalytically active systems rely on an intricate balance of guest-binding kinetics and thermodynamics in order to achieve turnover. 

Water plays a crucial role in the inclusion process. Although cyclodextrin does form inclusion complexes in such nonaqueous solvents as dimethyl sulfoxide, the binding is very weak compared with that in water 13 Recently, it has been shown that the thermodynamic stabilities of some inclusion complexes in aqueous solutions decrease markedly with the addition of dimethyl sulfoxide to the solutions 14,15>. Kinetic parameters determined for inclusion reactions also revealed that the rate-determining step of the reactions is the breakdown of the water structure around a substrate molecule and/or within the cyclodextrin cavity 16,17). 

Real-time spectroscopic methods can be used to measure the binding, dissociation, and internalization of fluorescent ligands with cell-surface receptors on cells and membranes. The time resolution available in these methods is sufficient to permit a detailed analysis of complex processes involved in cell activation, particularly receptor-G protein dynamics. A description of the kinetics and thermodynamics of these processes will contribute to our understanding of the basis of stimulus potency and efficacy. 

The ability to detect discrete rovibronic spectral features attributed to transitions of two distinct conformers of the ground-state Rg XY complexes and to monitor changing populations as the expansion conditions are manipulated offered an opportunity to evaluate the concept of a thermodynamic equilibrium between the conformers within a supersonic expansion. Since continued changes in the relative intensities of the T-shaped and linear features was observed up to at least Z = 41 [41], the populations of the conformers of the He - lCl and He Br2 complexes are not kinetically trapped within a narrow region close to the nozzle orifice. We implemented a simple thermodynamic model that uses the ratios of the peak intensities of the conformer bands with changing temperature in the expansion to obtain experimental estimates of the relative binding energies of these complexes [39, 41]. 

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