Ground and excited state prototropism of 2-(4′-pyridyl)benzimidazole in micelles

The effect of micelles on ground and excited state prototropism of 2-(4′-pyridyl)benzimidazole (4PBI) has been studied by fluorescence spectroscopy. It has been observed that in sodium dodecyl sulfate (SDS) micelle, 4PBI is preferentially protonated at the pyridyl nitrogen atom, in contrast to the situation in neat aqueous solutions, in which imidazole and pyridyl nitrogen atoms have equal propensity for protonation. In SDS, the protonation of the benzimidazole nitrogen occurs only in the excited state. Such effects are not observed in cationic cetyl trimethyl ammonium bromide (CTAB) and neutral Triton X-100 (TX-100). Thus, 4PBI shows very good sensitivity for negatively charged interfaces between aqueous and apolar compartments in microheterogeneous media.

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► Micelles affects prototropism of 2-(4′-pyridyl)benzimidazole (4PBI).
► Tautomer T is formed in SDS micelles in ground state.
► CTAB and TX-100 does not change acid–base equilibria of 4PBI in significant extents.
► 4PBI can thus sense negatively charged interfaces.