Leon A. P. Kane-Maguire

Chiral conducting polymers

This critical review describes the preparation and properties of a relatively new class of chiral macromolecules, namely chiral conducting polymers. It focuses in particular on examples based on polypyrrole, polythiophene and polyaniline. They possess remarkable properties, combining not only chirality with electrical conductivity but also the ability to undergo facile redox and pH switching. These unique properties have opened up a range of exciting new potential applications, including as chiral sensors, as novel stationary phases for chiral separations, and as chiral electrodes for electrochemical asymmetric synthesis (153 references).

Enantioselective electropolymerization of aniline in the presence of (+)- or (−)-camphorsulfonate ion: a facile route to conducting polymers with preferred one-screw-sense helicity

Abstract The first and remarkably facile synthesis of optically active polyaniline has been achieved via the enantioselective electropolymerization of aniline on indium-tin-oxide-coated glass electrodes in aqueous solution containing (1S)-(+)- or (1R)-(−)-10-camphorsulfonic acid (HCSA). The dark green films of conducting polyemeraldine salt formed under electrostatic conditions (+ L1 V versus Ag/AgCl) exhibited strong circular dichroism (c.d.) spectra typical of polymers possessing helical chirality. The quantitative reversal of the c.d. spectrum of the salt grown in (+)-HCSA as opposed to (−)-HCSA suggests that electropolymerization is highly enantioselective, with one helical screw of the polymer chain being preferentially produced depending on the hand of the CSA − anion incorporated. The ready electrosynthesis of optically active polyanilines should facilitate studies of their use in asymmetric synthesis and in chiral chromatography.

Manipulating and Monitoring Biomolecular Interactions with Conducting Electroactive Polymers

The use of conducting electroactive polymers (CEPs) to monitor and manipulate biomolecular interactions is reviewed in this article. Examples involving simple amino acids, more complex protein structures, DNA, and even whole living cells are discussed. The work described clearly demonstrates that the ability of CEPs to interact with biomolecular systems is dependent on polymer composition and on electrical stimuli applied to the polymer in situ. This provides a versatile molecular platform that is proving useful in the development of new biosensing and bioseparation technologies as well as providing a new means of cellular communications. This latter aspect is particularly exciting in that it has already been demonstrated that nerve cell growth can occur on these new platforms and electrical stimulation can be used to encourage neurite outgrowth.

Chemical generation of optically active polyaniline via the doping of emeraldine base with (+)- or (−)-camphorsulfonic acid

Abstract Optically active polyaniline salts can be readily generated in solution via the enantioselective acid doping of the neutral emeraldine base form of aniline with either (+)- or (−)-camphorsulfonic acid in a variety of organic solvents (1-methyl-2-pyrrolidinone (NMP), dimethylformamide, dimethylsulfoxide, CHCI3). Strong mirror-imaged circular dichroism (CD) spectra were observed for the deep green polymer solutions obtained with (+)- and (−)-camphorsulfonic acid (HCSA), respectively, suggesting that the acid doping is enantioselective, with one helical screw of the polymer chain being preferentially produced depending on which hand of the CSA− anion is incorporated. In contrast, no CD bands were observed for related polytoluidine salts in NMP, consistent with a model proposed for the above enantioselectivity. Films of the optically active polyaniline salts were also obtained by casting from the acid-doped solutions onto glass plates, and showed similar CD spectra.

Conductive Electroactive Polymers : Intelligent Polymer Systems, Third Edition

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Facile preparation of optically active polyanilines via the in situ chemical oxidative polymerisation of aniline

Abstract Optically active polyaniline in the non-doped emeraldine oxidation state and as the polymer doped with HCl have been synthesised via the facile in situ deposition of films from an aqueous solution of aniline undergoing oxidative polymerisation. Films of optically active polyaniline doped with (+)- or (−)-10-camphorsulfonic acid (PAn.HCSA) were first deposited from a solution of aniline by ammonium persulfate in the presence of (+)- or (−)-HCSA. Their UV–visible and circular dichroism (CD) spectra suggest significant structural differences to PAn.HCSA salts prepared electrochemically. De-doping of the in situ deposited films with aqueous NH 4 OH gave optically active emeraldine base films, which could be re-doped with HCl vapour or 1.0 mol dm −3 aqueous HCl to generate optically active PAn.HCl films with retention of polymer configuration.

A de-doping/re-doping study of organic soluble polyaniline

Abstract Polyaniline (PAn·HA) doped with dinonylnaphthalene sulfonic acid (DNNSA) is highly soluble in organic solvents making it attractive from a processing viewpoint. In a number of applications, however, it is desirable to use specific counterions to obtain particular properties. The exchange of the DNNSA counterion has been investigated by a de-protonation/re-protonation cycle involving aqueous and methanolic base and acid solutions. More effective counterion exchange occurs when the polymer is de-protonated using the methanolic base solution, since the DNNSA counterion has limited solubility in water. De-protonation also occurs upon extended immersion in neutral methanol due to simple dissolution of the counterion. Re-protonation of the polyaniline to the emeraldine salt is possible using a wide range of acids to produce doped PAn·HA having simple counterions (e.g. Cl − ), polymeric counterions (e.g. polyvinylphosphate) and even sulfonated polyaniline as the counterion. Re-doping is also achieved with neutral salt solutions, such as zinc nitrate. In most cases, the quality of the coatings is not compromised by the de-protonation/re-protonation cycle and the re-protonated polyanilines remained conductive and electroactive. However, significant conformational changes occur in the polymer following de-protonation/re-protonation as indicated by UV–visible–near-infrared spectral changes.

Influence of the chiral dopant anion on the generation of induced optical activity in polyanilines

Abstract Emeraldine base (EB) is doped with (1S)-(+)-3-bromocamphor-10-sulfonic acid and a novel chiral acrylamidesulfonic acid (4) in NMP and DMF solvents to give new optically active polyaniline salts (PAn.HA). The conjugate base anions (A − ) of these chiral dopants (as with the previously studied (+)-camphor-10-sulfonic acid, HCSA) contain SO 3 − and carbonyl (C=O) groups that may maintain the polyaniline chains in a preferred one-sense helical screw via simultaneous electrostatic and H-bonding. Optically active polyaniline salts are also produced via analogous doping of EB (in NMP or DMF) with the chiral dicarboxylic acids (+)- or (−)-tartaric acid and O,O′-dibenzoyl- d -tartaric acid, which possess quite different structural motifs to HCSA. A common feature of all the dopants successful in generating optically active polyaniline salts is their bidental nature, allowing attachment of the dopant to the polymer backbone at two places simultaneously.

Facile synthesis of optically active polyaniline and polytoluidine

Abstract Films of optically active polyaniline salts (PAN/HCSA) have been obtained by casting from solutions of emeraldine base doped with (1S)-(+)- or (1R)-(−)-10-camphorsulfonic acid (HCSA) in various solvents (NMP, DMF, DMSO or CHCl 3 ). The mirror-imaged circular dichroism spectra for the salt films derived using (+)- and (−)-HSA, respectively, indicate enantioselectivity in the doping process. The first optically active ring-substituted polyanilines, namely poly( o -toluidine)/(+)-HCSA and poly( o -toluidine)/(−)HCSA, have also been produced in solution and as films via a similar doping procedure in DMSO.

Comparison of electrospray mass spectrometry with other soft ionization techniques for the characterisation of cationic π-hydrocarbon organometallic complexes

Abstract Electrospray (ES) mass spectrometry provides a convenient method for the characterisation of a wide range of π-hydrocarbon complex salts of the general types [FeCp(η-arene)]BF 4 , [M(CO) 3 (η-C 7 H 7 )BF 4 (MCr, Mo, W), [Fe(CO) 2 L ( η 5 -dienyl)]BF 4 L  CO or PPh 3 ; dienyl  C 6 H 7 , 2-MeOC 6 H 6 , or C 7 H 9 ), [CpFe(CO) 3 ] PF 6 and [CpFe(CO) 2 ( η -C 2 H 4 )]BF 4 . At low skimmer voltages (20 V), principal (molecular) ions are generally the only observed species. For the arene complexes, [FeCp( η -arene)]BF 4 , high skimmer voltages (80–135 V) are required before fragmentation is observed. However, for the carbonyl containing cations, moderate skimmer voltages (40–55 V) also give rise to [MCO] + ,[M2CO] + and [M3CO] + ions. Very similar behaviour is observed with phosphonium and imidazolium adducts of the type [Fe(CO) 3 (η 4 -diene. Nuc)] + ( diene  C 6 H 7 or C 7 H 9 ; Nuc PPh 3 or Im) and [CpFe(CO) 2 ( η 1 -C 2 H 4 ·PPh 3 )] + . comparison with fast atom bombardment (FAB) and field desorption (FD) mass spectra for the same complex salts indicates that fragmentation decreases along the series FAB > ES > FD, and that ES mass spectrometry is the most convenient and informative of the three soft ionization techniques.