Affinity quantitative aspects

The study of the interactions between organic compounds and aUtali-metal cations, in the gas phase, is related to many topics such as ion solvation, catalysis and molecular recognition. Furthermore, mass spectrometry has been used for the analyses of organolithium compounds and supramolecular assemblies that contain lithium cations. Alkali cationization is an important ionization technique, implemented for the analyses of a wide range of organic compounds. Finally, gas-phase studies are also useful for the quantitative determination of lithium cation affinity. The interaction between lithium cation and organic substances is thus related to different aspects of gas-phase chemistry and mass spectrometry. 

Hage, D.S. and Chen, J., Quantitative affinity chromatography Practical aspects, in Handbook of Affinity Chromatography, 2nd edn., Hage, D.S., Ed., CRC Press, Boca Raton, EL, 2005, Chap. 22. 

To study the range of possibilities the first molecular dynamics simulations of a DNA duplex tethered to a surface was performed [35,36] The technical aspects of simulations near surfaces are nontrivial, especially as concerns reliable boundary conditions [37], Molecular dynamics provides a more quantitative picture of the salt gradients and DNA structures near the surface responsible for changes in hybridization affinities and specificities than approximate (PB level mean field) theory and so may be used as a check on the simple analytical picture derived above. In addition simulation provides mechanistic clues which can form additional hypotheses for testing. 

The two quantities, catalytic proficiency (which has the dimensions in the example above) and rate enhancement (which is dimensionless in the example above), give a valid account of two aspects of enzyme catalysis. The catalytic proficiency, as the equilibrium constant for transition-state binding to the free enzyme, measures quantitatively the affinity of the free enzyme for the transition state. The free-energy equivalent of the catalytic proficiency gives the total transition-state stabilization by the enzyme. The rate enhancement, as the equilibrium constant for the expulsion of a substrate molecule from the active site of the enzyme and its replacement by a transition-state molecule, quantitatively describes the relative affinity of the enzyme for the transition state compared to the reactant-state substrate. 

One of the most important yet common trends in organic chemistry is the increase in carbocation stability with additional alkyl substituents. This stability relationship is fundamental to understanding many aspects of reactivity, especially of nucleophilic substitution. In recent years, it has become possible to put the stabilization effect on a quantitative basis. One approach incorporates gas phase measurements, which determine the proton affinity of alkenes leading to... 

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