Varying solvent polarity to tune the enantioselective quenching of a calixarene host

Abstract

Calixarene L1 has been designed to behave as a fluorescent molecular sensor capable of distinguishing between chiral amines on the basis of their size and chirality.Fluorescence quenching studies of calixarene L1 in methanol demonstrated no enantiomeric selectivity for a short chain amino alcohol, phenylglycinol, while excellent selectivity was observed for a longer chain amino alcohol, phenylalaninol (PA). The effect of solvent on the fluorescent properties of this calixarene in the presence of PA has been studied, and demonstrates that varying solvent polarity allows the wavelength of enantiomer selectivity to be tuned from 227nm to 440nm. While enantiomeric selectivity is observed in methanol at 227nm, no discrimination is achieved in acetonitrile. Chiral discrimination is statistically possible with L1 and PA in chloroform at 227nm, but it is not comparable with the extent of discrimination achieved in methanol. In chloroform a new emission band at a longer wavelength (440nm) is formed with R-PA in solution with L1, an effect that is not observed with the S-enantiomer. This new band in chloroform at 440nm allows very effective chiral discrimination and has been attributed to the presence of two different conformations of calixarene L1, which is reinforced by 1 H-NMR studies and molecular modelling studies.__________________________________________________________________________

Fluorescence quenching of p-tert-buthylthiacalix[4]arene by 1-ethyl-3-methylimidazolium bromide

“…Comparable results have been reported, since the addition of phenylalanilol did not modify the fluorescence lifetimes of propranolol-amide-calix4arene from a fluorescence static quenching phenomenon [36]. In this paper, the values of lifetimes obtained were of 9.4 ns and 4.6 ns in methanol.…”

“…The different lifetimes were attributed to the conformations that can be adopted by the calixarene macrocycle since the naphthalene groups could be oriented in different positions depending on the calixarene conformer [36]. Also, an average fluorescence lifetime of 0.49 ns was determined for a calix [4]arene di methoxycarbonyl methyl ester, also owing to the fluorescence of the aryl moieties of the monomers [37].…”

Recent Advances in Development of Chiral Fluorescent and Colorimetric Sensors

“…Diamond and co-worker reported calixarene 151 as a fluorescent molecular sensor for chiral amines based on their size and chirality (Figure ) . Based on the fluorescence quenching studies, calixarene 151 did not show any significant enantiomeric selectivity for short chain amino alcohols, such as phenylglycinol in methanol.…”

Rapid determination of enantiomeric excess: a focus on optical approaches

“…Derivatization at the upper and lower rims of calixarenes allows for functionality and incorporation of chirality. 102 Calixarenes can be tuned for selectivity by the size of the cavity, and are known to bind ammonium cations through their aromatic cone cavity through cation-p interactions. 103,104 In addition, many groups have used the atropisomers of the easily derivatizable 1,1 0 -bi-(2-naphthol) (BINOL), for enantioselective discrimination due to the chirogenic unit and the chromophore already present.…”