Acid–Base Equilibria of Merocyanine Air–Water Monolayers

Robert A. Hall, Peter J. Thistlethwaite, Franz Grieser, Nobuo Kimizuka, Toyoki Kunitake

    Research output: Contribution to journalArticlepeer-review

    15 Citations (Scopus)

    Abstract

    The acid–equilibrium of air–water monolayers of 1-docosyl-4-(4-hydroxystyryl)pyridinium bromide (HSP) on a range of subphases was investigated. On an aqueous subphase the observed pKa at halfionization was found to be considerably lower than that measured in mixed solvent systems. This difference is attributed in part to the enhanced stabilization of the unprotonated form of HSP in the monolayer environment by keto–enol tautomerization. The pKa of 11.0 measured for HSP monolayers on dextran sulfate solution was rationalized in terms of the acid group of HSP experiencing a net negative surface potential. Reflection spectra of the HSP monolayer on an anionic cyanine dye solution subphase indicated that only the protonated HSP species is complexed by the dye, giving support to the idea that the unprotonated form lacks a site of appreciable positive charge.

    Original languageEnglish
    Pages (from-to)3743-3748
    Number of pages6
    JournalLangmuir
    Volume10
    Issue number10
    DOIs
    Publication statusPublished - Oct 1 1994

    All Science Journal Classification (ASJC) codes

    • General Materials Science
    • Condensed Matter Physics
    • Surfaces and Interfaces
    • Spectroscopy
    • Electrochemistry

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