Host‐guest complexes of protonated (AcH+) and neutral (Ac) forms of biologically important acridine dye with p‐sulfonatocalix[4]arene (SCX4) and their responses towards acetylcholine (AcCh) as a competitive binder has been investigated using photochemical studies. Unlike Ac, the AcH+ undergoes strong binding with SCX4 and their differential binding results in a large upward pKa shift for the bound dye. Dye binding to SCX4 causes a drastic fluorescence quenching, witnessing a strong fluorescence “turn OFF”, which is switched to strong fluorescence “turn ON” by the presence of neurotransmitter, AcCh, acts as a stimulus cum competitive binder. This is a unique system showing controlled binding and release for both AcH+ and Ac forms of the dye triggered by AcCh, convincingly established through absorption, pKa tuning, fluorescence modulation and NMR shift. Fluorescence “OFF/ON” switching observed in this study demonstrates an efficient indicator displacement methodology, achieving a control over the selectivity in binding and release of the dye/analyte, having prospective uses in designing new optical sensors and smart functional materials for analytical and biological applications.

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Summtary. The biosynthesis of apiose was investigated in cell wall polysaccharide of Lemna gibba G3 (duckweed) and in detached leaves of Petroselinum crispumt (parsley). Lemnna grown either in short days or in continuous light incorporated 1;C from a mediuim containing miiyo-inositol-2-'4C into D-apiosyl and D-XylOSyl units of cell wall polysaccharides. Labeled D-apiose was characterized by paper chromatography, by formatioun of labeled crystalline di-O-isopropylidene D-apiose, and by gas chromatography of trimethylsilyl derivatives of apiose and of its sodium borohydride reduction product, apiitol. Periodate oxidation of labeled apiose revealed 86 to 94 % of the '4C was located in formaldehyde fragmenits corresponding to C3' and C4. Comparison of this restult with work reported by Grisebach and Doebereiner and by Beck and Kandler supports the concltusion that mnvo-inositol-2-14C was coInverted to D-apiose labeled specifically at C4.WVhen iJarabinose-l-14C was supplied to Lemntta, both L-arabinosyl and D-xylosyl uinits of cell wall polvsaccharides became labeled, buit no 14C was folund in D-apiose. Analysis of the medium external to the plants revealed the presence of a polysaccharide-like polymer that also contained labeled xylose and arabinose.Petroselinimn leaves uitilized mnvo-inositol-2-3H for the synthesis of apiose in apiiin.These results provride direct evidence for a pathway of apiose biosynthesis invOIlvillg D-gicticronic acid metabolism.Bell, Isherwood, and Hardwick (7) observed that mild acid hydrolysis of dried fresh leaves or fibers from Posidonia australis release free D(+)-apiose in sulbstantial yield. Subsequently, others fo,und D-apiose as a constittleint of cell wall polysaccharides in several plant species (4,5,13,28

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