Hyper chromic effect

The solvent often exerts a profound influence on the quality and shape of the spectrum. For example, many aromatic chromophores display vibrational fine structure in non-polar solvents, whereas in more polar solvents this fine structure is absent due to solute-solvent interaction effects. A classic case is phenol and related compounds which have different spectra in cyclohexane and in neutral aqueous solution. In aqueous solutions, the pH exerts a profound effect on ionisable chromophores due to the differing extent of conjugation in the ionised and the non-ionised chromophore. In phenolic compounds, for example, addition of alkali to two pH units above the pKa leads to the classical red or bathochromic shift to longer wavelength, a loss of any fine structure, and an increase in molar absorptivity (hyper chromic... 

The influence of temperature, ionic strength, pH and various additives on the circular dichroism spectra of pectic solutions has been reported. On a pH change from 7.5 to 2.0, hyper- and hypso-chromic effects were observed. The molecular ellipticity (0) contribution from the free carboxy-group was the same as that from the methyl esterified carboxy-group. The gelling of pectins caused by a change in the solvent composition led to an increase in 0. If the ionization level was kept constant, 0 for the carboxy chromophore could be used as a probe for the interpretation of intermolecular interactions. 

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