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The similarity between 2,6-Bis(2-hydroxyarylidene)cyclohexanones and 2′-hydroxychalcones in generating respectively styrylflavylium and flavylium cations was explored. The complex pH and light dependent multistate of species of the asymmetric of 2,6-Bis(2-hydroxyarylidene)cyclohexanone bearing a diethyl amine in position 7 of the flavylium cation was studied by pH jumps, monitored by UV–vis spectrophotometry, stopped flow, and NMR. The possible structural isomers corresponding to the migration of the amine substituent at the benzopyrylium to ring B of the flavylium cation via chalcone, or spiro species were not detected. However, cis and trans isomers from the pendent arm take place and a photochromic system involving flavylium cation switching from red to blue was characterized. In acidic medium the flavylium cation and the hemiketal protonated at the amine substituent are the equilibrium species. In moderately acidic solutions the spiro is the most stable species and in very basic medium the ionized trans -chalcone. The spiro and the ionized chalcone are key compounds to define the multistate of chemical species of compound 1. The spiro is stable in moderately acidic medium and gives cis -flavylium and ionized chalcone respectively in acidic and basic medium. The chalcone is stable only at very basic medium, and gives trans -flvaylium cation in acidic medium. Image 1 • 2,6-Bis(arylidene)cyclohexanones possesses 17 species that are reversibly interconnected by pH and light external stimuli. • There are for each species cis-trans and structural isomers, except for the trans-trans and cis-cis chalcones and the spiro. While the structural isomers may communicate through these 3 common species, as observed in other similar systems, no evidence for this behavior was achieved. • The cis-trans isomers lead to a photochromic system. [ABSTRACT FROM AUTHOR]

Abstract The thermodynamic and kinetic behavior of 4-(2,4-dihydroxybenzylidene)-6-hydroxy-1,2,3,4-tetrahydroxanthylium chloride was studied in detail. Similarly to anthocyanins, this compound generates a multistate of species that are reversibly interconverted by pH stimuli. The multistate system was studied by NMR and UV–visible (conventional spectroscopy and stopped-flow techniques). A theoretical approach adapted from the one reported for anthocyanins and related compounds was used to rationalize the complex multistate. In particular, the thermodynamic diagram where all the species are positioned was extended to the ionized species. Cis and trans isomers of flavylium cation, quinoidal bases, and ionized chalcone at extremely high pH values were identified. The multistate is dominated in the range 5 < pH < 8 by the spiro form in equilibrium with a small fraction of quinoidal bases. The spiro opening rates follow a different route and pH dependence in very acidic or moderately acidic pHs. Graphical abstract Image 1 Highlights • 2,6-bis(2-hydroxybenzylidene)cyclohexanones follow the general anthocyanins multistate of species. • A thermodynamic and kinetic model adapted from the one reported for anthocyanins and related compounds, was used to rationalize the complex multistate data for 4-(2,4-dihydroxybenzylidene)-6-hydroxy-1,2,3,4-tetrahydroxanthylium chloride. • A spiro derivative is the species that differentiates the present system from anthocyanins. It was fully characterized by NMR and is the dominant species in the pH range 5

Abstract: The sol–gel immobilization of Celite-supported lipase from Pseudomonas fluorencens (Lipase AK) was systematically studied using ternary silane precursor systems consisting of alkyltriethoxysilane (alkylTEOS), phenyltriethoxysilane (PhTEOS) and tetraethoxysilane (TEOS). The parameters investigated were the surface coverage at various enzyme-Celite ratios (between 1:1 and 1:10) and the effect of molar ratio of alkylTEOS (alkyl=propyl, hexyl, octyl, 1H,1H,2H,2H-perfluorooctyl, decyl, dodecyl, octadecyl), PhTEOS and TEOS (seven series of alkylTEOS:PhTEOS:TEOS from 0.1:0.9:1 to 0.9:0.1:1 in 0.1 steps) on the catalytic properties of the sol–gel biocatalysts. For comparison, the corresponding binary systems (1:1 molar ratios of alkylTEOS:TEOS and PhTEOS:TEOS) were also studied. The ternary and binary sol–gel lipase preparations were evaluated by their catalytic behavior in enantiomer selective acetylation of racemic 1-phenylethanol and 2-heptanol. For each alkylTEOS precursor, one or more alkylTEOS/PhTEOS/TEOS ternary systems were superior biocatalysts compared to the corresponding alkylTEOS/TEOS preparations. The best overall results were achieved with the medium-chain octylTEOS and perfluorooctylTEOS-containing ternary systems. [ABSTRACT FROM AUTHOR]