Electrostatic interactions classification

Metal ions, effect of size, 200-205 Metalloenzymes, see also Enzyme cofactors classification of, by cofactor and coupled general base, 205-207, 206 electrostatic interactions in, 205-207 SNase, 189-197... 

Ahrland s (1973) classification distinguishes incompletely hydrolyzed ions into types a and b. Cations of type a form stable complexes with electronic donors of the first row of the periodic chart through electrostatic interactions those of... 

We review the subject of noncovalent interactions in proteins with particular emphasis on the so-called weakly polar interactions. First, the physical bases of the noncovalent electrostatic interactions that stabilize protein structure are discussed. Second, the four types of weakly polar interactions that have been shown to occur in proteins are described with reference to some biologically significant examples of protein structure stabilization and protein-ligand binding. Third, hydrophobic effects in proteins are discussed. Fourth, an hypothesis regarding the biological importance of the weakly polar interaction is advanced. Finally, we propose adoption of a systematic classification of electrostatic interactions in proteins. 

As has already been stressed, the classification of acceptors as (a) and (b) has been founded on their behaviour in aqueous solution. For media of lower D, and consequently stronger electrostatic interactions, any given acceptor will display more (a) -character than in water, j udged by the fundamental criteria given above. In the gas phase, almost all metal ion acceptors seem in fact to show (a)-sequences. This was pointed out by Pearson already in his first paper (2), and has later on been very convincingly elaborated by Pearson and Mawby (8), as will be more discussed below. 

In capillary electrophoresis (CE), several criteria can be applied to classify solvents [e.g., for practical purposes based on the solution ability for analytes, on ultraviolet (UV) absorbance (for suitability to the UV detector), toxicity, etc.]. Another parameter could be the viscosity of the solvent, a property that influences the mobilities of analytes and that of the electro-osmotic flow (EOF) and restricts handling of the background electrolyte (BGE). For more fundamental reasons, the dielectric constant (the relative permittivity) is a well-recognized parameter for classification. It was initially considered to interpret the change of ionization constants of acids and bases according to Born s approach. This approach has lost importance in this respect because it is based on too simple assumptions limited to electrostatic interactions. Indeed, a more appropriate concept reflects solvation effects, the ability for H-bonding, or the acido-base property of the solvent. 

It is assumed that systems with fast decaying non-electrostatic interactions (class 1 of our classification) are very well understood nowadays and that they thus do not pose any problem for theory anymore. It is therefore the range of the Coulomb interactions and its effect on the properties of fluids which is of the main concern. To investigate this effect for fluids of class 2 and 3, trial potentials of a different range, uT, are constructed from the given parent model u so that,... 

We have introduced this classification among continuous methods at the beginning of our exposition as the technical details about the specific model exploited to describe the electrostatic interactions axe the most used features in characterizing and discussing continuum solvation methods. To be more effective in presenting extensions of the basic procedure it is convenient to go a step back. 

There are three broad types of intermolecular forces of adhesion and cohesion (7) quantum mechanical forces, pure electrostatic forces, and polarization forces. Quantum mechanical forces account for covalent bonding. Pure electrostatic interactions include Coulomb forces between charged ions, permanent dipoles, and quadrupoles. Polarization forces arise from dipole moments induced by the electric fields of nearby charges and other permanent and induced dipoles. Ideally, the forces involved in the interaction at a release interface must be the weakest possible. These are the polarization forces known as London or dispersion forces that arise from interactions of temporary dipoles caused by fluctuations in electron density. They are common to all matter and their energies range from 0.1 to 40 kJ/mol. Solid surfaces with the lowest dispersion-force interactions are those that comprise aliphatic hydrocarbons, and fluorocarbons, and that is why such materials dominate the classification table (Table 1) and the surface energy table (Table 2). 

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