Medium strength hydrogen bond

Medium-strength hydrogen bonds are by far the most common type encountered for hydrogen attached to electronegative atoms (particularly oxygen), and are ubiquitous in biological systems, particularly in the stabilisation of protein tertiary structure. Hydrogen bonded distances may vary over more than... 

Formation of a dihydrogen bond MH HA, as any medium strength hydrogen bond, entails elongation of the proton donor H-A bond. Consequently, vah vibrations shift to lower frequencies and a new, much wider and more intense band appears with the band shift... 

Wojcik [91] developed a theory that is applicable to weak and medium-strength hydrogen bonds. The basic physical mechanism responsible for the energy and intensity distribution is the coupling between the high-frequency hydrogen-stretching... 

The magnitude of the copigmentation is influenced by pH value, pigment and copigment concentrations, chemical structure of anthocyanin, temperature, and ionic strength of the medium. As to the effect of the solvent, the important issue is the hydrogen-bonded molecular structure of the liquid water, not the polarity of the medium. ... 

The absorption spectra of the hydroxyphenylbenzo-triazole derivatives in various solvents and polymer films indicate that two ground-state forms of the molecules exist. These species are proposed to be a planar and non-planar form of the stabilizers. The position of the equilibrium between these two forms is affected by both the polarity and the hydrogen-bonding strength of the medium. The blue fluorescence (A.max = 400 nm) observed for these stabilizers originates from an excited-state species in which intramolecular proton transfer is disrupted. 

Clearly, the strength of hydrogen bonds depends on the reaction medium. In practice, the nonpolar solvent toluene is routinely used. It can be considered to mimic a hydrophobic binding pocket of an enzyme and clearly supports the formation of moderate (1.5-2.2A) and even strong (1.2-1.5 A) hydrogen bonds [42]. 

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