Getting a library of activities from a single compound: tunability and very large shifts in acidity constants induced by sol--gel entrapped micelles.
Acidity constants (in terms of K(i) values) can be fine-tuned, their values can be pushed to extremes, and their location can be placed either at the basic or acidic range of the pH scale, by tailoring intra-cage properties of SiO(2) sol--gel materials with surfactants. With the entrapped "solid-state pseudomicelles", an 8-orders magnitude K(i) shift--from the high-basic pH region to the acidic one--was obtained for acid fuchsin (AF); and tunability of the pK(i) values of the solvatochromic dye E(T)(30) and of crystal violet over much of the pH scale was achieved. This tailoring of various activities from the same dopant was achieved either by utilizing surfactants of different nature or by utilizing mixtures of anionic/cationic surfactants. The extraction of a wide range of reactivities from a single compound and the ability to fine-tune it is a powerful concept with potential extensions beyond acid/base reactions.
Rottman
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Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Avnir
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