Ion pairs hydrogen bonded

Bacelon et al.43a have confirmed via far-IR studies that R4N halides exist in CC14 in large aggregates, which are dissociated, however, by phenol into ion pairs hydrogen bonded to phenol and multi-solvated anions. 

R)-DNB-Leu molecule also binds to the selector via an ion-pairing mechanism, but it cannot be stabilized by 71-71 stacking interaction that is apparently of crucial importance for the chiral discrimination. In summary, the enantiodiscrimination is achieved by cooperative multiple contact interactions, such as ion pairing, hydrogen bonding, and n-n stacking [62]. A mechanistically similar enantiodiscrimination process of peptide enantiomers on CSP 56 has been proposed [83]. 

Figure 10 Conformational equilibrium for kainate involving separated ions (A) and inter-molecular ion-pair hydrogen bonding (B).

Thermodynamic stability is a global property of the enzyme structure, and contributions of individual amino acids toward the free energy of folding are additive and highly cooperative. Analysis of mutant proteins has defined the contributions of various amino acids toward the overall stability of the protein. Replacements which alter the formation of ion pairs, hydrogen bonds, van der Waals contacts, or hydrophobic interactions each tend to destabilize the folded protein by a qualitatively comparable amount (14). In one approach to this problem, site-specific substitution of amino acids has provided new approaches toward dissecting the kinetic mechanisms of protein folding (27). 

The M-H absorption in the IR spectrum associated with these inter-ion pair hydrogen bonds [K(QNH)]+ -HM-, is shifted by about 10 cm- to lower wave-... 

Similarity search conducts systematic search of functional site databases for chemical groups able to make ion pairs/hydrogen bonds and/or hydrophobic interactions with ligands from which representative sites as surfaces with electrostatic and hydrophobic characteristics are generated (Schmitt et al, 2002). 

A feature of the chromophores in the above compounds is that they can detect and distinguish between hydrogen bonds and ion-pairs. Hydrogen-bond formation is accompanied (as in the infra-red method) by a small (10-30 nm) bathochromic shift of the main absorption peak, with little change in extinction coefficient. However, for strong acids and bases, ion-pairs will be formed, indicated by bathochromic shifts of 100-150 nm, coupled with an extinction coefficient enhancement by a factor of two. Typical examples of systems that have been studied are (i) phenol and dioxan in isooctane [10] and (ii) 2,4-DNP and pyridine in toluene [11]. 

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