Abstract
AbstractNew chiral aniline copolymers containing L-cysteine substituent have been first prepared from unsubstituted polyaniline, utilizing a concurrent reduction and substitution reaction performed in the solid-state matrix of polyaniline.The chemical, electrical and chiroptical properties of the resultant copolymer powder have been characterized by XPS, ATRIR, CV, UV-vis, CD ( circular dichroism ) spectroscopy. The resultant copolymer powder was found to contain ca. 24 mol % (based on atomic ratio S/(N-S) measured by XPS ) of L-cysteine group and are very conductive (2 S/cm ). XPS spectra of PAN-L-Cys show a newly appeared S 2p line at around 163.6 eV, confirming the formation of the sulfide linkage. The ATRIR spectrum of the resulting aniline copolymer powder clearly showed reduction in the intensities of the peaks associated with diiminoquinoid ring at 1600 cm-1 (C=C stretching vibration of diiminoquinoid ring ). The oxidation potential E0 of the resulting aniline copolymer was lower than that of parent polyaniline. This result is consistent with the expectation that the attachment of electron-donating L-cysteine group that help lower the oxidation potential of polyaniline backbone . The UV-vis spectra of the resulting aniline copolymer showed that the lmax of the p-p* transition band is longer than the corresponding band of the parent unsubstituted polyaniline, possibly due to the enhanced electron density of the copolymer backbone as contributed by the electron-donating L-cysteine group. The corresponding CD spectra for PAN-L-Cys and PAN-D-Cys ( in NMP solutions ) are mirror image of each other, indicating that these two chiral form of polyaniline possess opposite handedness.