Induction and inversion of chirality in poly-L -lysine and methyl orange complex

Abstract

The mechanism of complexation of poly-L-lysine (PLL) with methyl orange (MO) and the appearance of induced circular dichroism (ICD) were investigated as a function of dye concentration and temperature and compared with that of the PLL-ethyl orange complex. The formation of stoichiometric complexes with uniform size and intensities of ICDs depended on the length of alkyl groups (methyl and ethyl) as determined from quartz crystal microbalance measurement, absorption spectra, and CD spectra data. Furthermore, at constant PLL concentration, a dependence of the inversion of the ICD on the MO concentration (CMO) was observed in the PLL-MO complexes, which to our knowledge has not been reported for a constant dye concentration system. The positive ICD in the PLL-MO complexes observed at CMO lower than 2.0 × 10−5 M showed reversible changes in response to heating and cooling, whereas the negative ICD in PLL-MO complexes observed at higher CMO inverted to positive ICD values in response to a decrease in temperature. These results demonstrate the alkyl group substituent in the dye, dye concentration, and temperature play important roles in the formation of PLL-azo dye complex and ICD appearance. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011