Chiral polypyrroles

Chiral polypyrroles were initially prepared with chiral substituents at the N position [300,301] but optical characterization was scarce. Later, chiral polypyrroles were prepared with aminoacids at the 3 position [302]. These polymers did show a strong Cotton effect. 

Several alkyl aryl sulfides were electrochemically oxidized into the corresponding chiral sulfoxides using poly(amino acid)-coated electrodes448. Although the levels of enan-tioselection were quite variable, the best result involved t-butyl phenyl sulfoxide which was formed in 93% e.e. on a platinum electrode doubly coated with polypyrrole and poly(L-valine). Cyclodextrin-mediated m-chloroperbenzoic acid oxidation of sulfides proceeds with modest enantioselectivity44b. 

The covalent attachment of optically active groups, such as amino acids, to the polymer backbone of polypyrroles and polythiophenes has provided ICPs which have the ability to discriminate between the enantiomers of chiral molecules and ions [29-31]. 

Lee, H.S. Hong, J. Chiral and electrokinetic separation of amino acids using polypyrrole-coated adsorbents. J. Chromatogr., A 2000, 868, 189-196. 

Chiral membranes have also been used to separate isomers. A cellulose tris(3,5-dimethylphenyl carbamate) has been used to separate an amino alcohol /8-blocker, although the S isomer was obtained in only 55% ee and the R isomer in 23% ee.22 On the other hand, a chiral membrane of a poly(L-glutamate) derivative completely resolved racemic tryptophan.23 Apoenzymes (enzymes lacking their usual cofactor) have been placed in the pores of a membrane consisting of a gold film covered with polypyrrole.24 In one of these, D-phenylalanine passed through five times faster than the L-isomer. (For more detail on membrane separations, see Chap. 7.) This method holds considerable promise for catalytic membrane reactors, especially if the unwanted isomer can be racemized in situ. 

Huang, J., Wei, Z., and Chen, J. (2008). Molecular imprinted polypyrrole nanowires for chiral amino acid recognition. Sens. Actuators B. 134, 573-578. 

The electropolymerization of o-methoxyaniline in the presence of (+)-(lS)- or (-)-(ll )-CSA yields an optically active polyaniline derivative. The polymer shows intense CD bands as a film deposited on an electrode. The polymer is soluble in NMP, CHCI3, DMF, DMSO, and MeOH, and the polymer also showed CD absorption in a solution probably based on a chiral main-chain conformation such as a helix. A film made by spin-coating a mixture of polyaniline with CSA also showed strong CD absorptions, which may be based on a helical conformation of the main chain. The electropolymerization method has been applied to the synthesis of an optically active polypyrrole which may have a helical conformation. ... 

An optically active polypyrrole (17 )has also been synthesized by the electropolymerization of pyrrole monomer bearing a homochiral sugar covalently attached to the pyrrole nitrogen. This chiral polymer discriminated between (+)- and (-)-camphorsulfonate ions as potential anionic dopants in cyclic voltammetry studies. 

---