Remarkable alkali cation template effect in 1,5-bridged calix[8]arenes.
Treatment of 1,5-bridged calix[8]arenes 2-4 with alkali metal carbonates produces salts in which an included cation acts as a conformational template. This induces the folding of calix[8]arene skeleton in a conformation in which the triads of contiguous OH-bearing rings adopt a 3/4-cone conformation with all hydroxyls converging toward the same center. The template effect requires the presence of short bridges (ethylene, tetramethylene, diethylene glycol) and became stronger by increasing the cation dimension up to that of Cs(+).
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Istituto per lo Studio delle Sostanze Naturali di Interesse Alimentare e Chimico-Farmaceutico, CNR, Via del Santuario 110, I-95028 Valverde (CT), Italy.
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