Showing papers by "Mark S. Wrighton published in 1988"

Synthesis and Charge Transport Properties of Polymers Derived from Oxidation of 1-H-1'(6-pyrrol-1-yl)-hexyl-4,4'-bipyridinium Bis-hexafluorophosphate and Demonstration of a pH Sensitive Microelectrochemical Transistor Derived from the Redox Properties of a Conventional Redox Center.

Abstract: This article describes the synthesis and electrochemical properties of redox polymers, having a polypyrrole backbone and viologen subunits, derived from oxidative electropolymerization of 1-methyl-1'-(6-(pyrrol-1-yl)hexyl)-4,4'-bipyridinium (P-V-Me/sup 2 +/) and 1-hydro-1'-(6-(pyrrol-1-yl)hexyl)-4,4'-bipyridinium (P-V-H/sup 2 +/). Closely spaced (approx. 1.5 ..mu..M) Au microelectrode arrays (approx. 2.5 ..mu..m wide /times/ 50 ..mu..m long /times/ 0.1 ..mu..m high) modified with the polymers can be used to study aspects of the charge-transport behavior of the viologen redox system. Poly(P-V-Me/sup 2 +/) have been used to investigate the characteristics of microelectrochemical transistors based on a viologen redox center and a similar redox center, protonated, monoquaternized bipyridinium, which is pH dependent. The interesting properties from poly(P-V-Me/sup 2 +/) and poly(P-V-H/sup 2 +/) stem from behavior of the pendant viologen redox centers. The device based on poly(P-V-Me/sup 2 +/) has a narrow region (approx. 200 mV) of gate voltage, V/sub G/, where the source-drain current, I/sub D/, is nonzero and has a sharp, pH-independent peak in the I/sub D/-V/sub G/ plot at approx. 0.53 V versus SCE associated with the reversible, one-electron reduction of viologen. This result is consistent with electron self-exchange between redox centers being the mechanism for charge transport. The device based on poly(P-V-H/sup 2 +/) shows amore » pH-dependent I/sub D/ at fixed V/sub G/, as expected from the electrochemical behavior from reversible protonation of the terminal N of the bipyridinium group of poly(P-V-H/sup 2 +/). The microelectrochemical transistor based on poly(P-V-H/sup 2 +/) illustrates the design of chemically sensitive, molecule-based devices using conventional redox materials.« less

Amperometric electrochemical ion sensors and method for determining ion concentration

Abstract: Electrochemical devices constructed according to the present invention can be used to convert an ion flux into an electric current for determination of ion concentration. The devices are operated without the need for a reference electrode and are specific based on known ion transfer agents. Operation of the devices involves the use of pairs of electrodes modified with electroactive redox materials overlaid with ion selective coatings. An applied potential between a pair of appropriately modified electrodes results in the flow of an electric current between the electrodes which is dependent on the concentration of the ion to be sensed. Devices constructed by combining electrodes overlaid with electroactive polymers and different ion selective films allow simultaneous determination of diverse ions. For example, these devices are useful for measuring the concentration of total cations, total anions, H + , Li + , K + , Ca 2+ , Na + , HCO 3 - , Cl - , other cations and anions, and combinations thereof. The devices are small and stable enough to be used in vivo, for example, as blood monitoring means, or in large scale water quality monitoring or purification/separations techniques.

Potential Dependence of the conductivity of Poly(3-Methylthiophene) in Liquid So2/Electrolyte: A Finite Potential Window of High Conductivity

Abstract: : Poly(3-methylthiophene), I, on Platinum microelectrodes shows reversible oxidation in liquid sulfide/electrolyte, and accompanying oxidation of I are large changes in its conductivity. By using liquid SO2/0.1 M (n-Bu) 4Npf6 as the solvent/electrolyte system it is possible to study the conductivity vs. potential for very positive potentials, to approx. +2.5 V vs. Ag. Over the large potential range explored, I has a broad maximum in conductivity at approx. +0.9 V vs. Ag, and a more positive excursion results in substantially lower conductivity. The width of the region of high conductivity is approx. 1.3 V, substantially wider than that for polyaniline. Results for polythiophene II, in SO2/0.1 M (n-Bu)4Npf6 are similar to those for I. Results for I and II show that it is possible to sufficiently depopulate the highest occupied electronic bands of I and II to render them nonconducting, as suggested by theory. Thiophenes.

Multicomponent redox catalysts for reduction of large biological molecules using molecular hydrogen as the reductant

Abstract: One-electron reduction of the large biological molecules horse heart cytochrome c, sperm whale myoglobin, and horseradish peroxidase using H/sub 2/ as the reductant can be catalyzed by two-component, high surface area heterogeneous catalysts. The catalysts can be prepared by first functionalizing high surface area SiO/sub 2/ with a polycationic polymer into which is dispersed MCl/sub 4//sup 2 -/ (M = Pd, Pt). Reduction with H/sub 2/ yields elemental Pd or Pt dispersed in the polymer. The particles are finally functionalized with a redox polymer derived from hydrolysis of Si(OR)/sub 3/ groups of an N,N'-dialkyl-4,4'-bipyridinium- or from a cobalticenium-based monomer. The two components of the heterogeneous catalysts are the buried noble metal capable of activating the H/sub 2/ and the redox polymer, which can equilibrate both with the noble metal and with the large biological molecule. Reduction of the large biological molecules in aqueous solution can be effected at room temperature and 1 atm H/sub 2/ using the catalysts under conditions where the biological materials would not be reducible with H/sub 2/ alone or when the noble metal alone would be used as the catalyst.

Microelectrochemical devices and method of detecting

Abstract: Novel microelectrochemical devices are provided which consist of closely spaced microelectrodes (24) coated with metal ion based inorganic redox active material such as oxides (22) or mixed oxides of any of the following transition metals: W, Ni, Ru, Co, Rh, Ir, Nb, Mo, V, or any other metal that undergoes a change in electrical conductivity upon electrochemical oxidation or reduction, in contact with an electrolyte. Additionally, other metal based redox materials whose conductivity changes as a function of the movement of ions into or out of the material can be used in the construction of microelectronic devices, for example, Prussion Blue, Fe4[Fe(CN)6]3. ''Metal ion-based microelectrochemical devices'' encompasses all devices based on an inorganic redox active material which incorporate an active ''gate'' region or ''channel'', or exhibit rectification. Included in this classification are devices analogous to diodes, field effect transistors, p-n-p transistors, and n-p-n transistors, and pH sensors, among others.

Thermal Reactions of RuCO)3(C2H4)2 with Acrylic, Non-Conjugated Dienes and Photochemistry of Ru(CO)4(eta squared-diene) Complexes

Abstract: : We wish to report the photochemistry of Ru(CO)4 (ETA squared-diene) (diene = 1,4-pentadiene, 3-methyl-1,4-pentadiene, 1,5-hexadiene, 1,6-heptadiene) complexes and the thermal reaction of Ru(CO)3(C2H4)2 with these dienes. We and others have previously reported the photochemical generation of catalytic intermediates at low temperatures as a means of investigating reactions of alkene complexes. In particular, we examined the photoassisted alkene isomerization catalysts derived from Fe(CO)5 and Ru3(CO)12.10-13. The key intermediate, HM(CO)3(eta3-C3H5), can be observed spectroscopically in a low temperature matrix. However, the absence of synthetic routes to M(CO)n(non- conjugated diene) complexes has hindered mechanistic studies of transition metal carbonyl catalyzed isomerization of non-conjugated dienes. Pentadienes.