The voltammetric detn. of trace amts. of gold was studied using a chem. modified electrode. The role played by the host mol. attached to a glassy carbon electrode (GCE), i.e. 8,9,17,18-dibenzo-1,7-dioxa-10,13,16-triazacyclooctadecane (DDTC), was examd. by electrochem. and spectrochem. techniques. Cathodic stripping voltammetry (CSV) was applied to study the various parameters affecting the affinity of gold ions by a DDTC modified electrode as well as the interferences by other ions. Finally, the method was successfully applied to det. gold traces in a geol. sample. In addn., the formation of an AuCl4--DDTC complex was followed and its formation const. was detd. by spectrophotometry. [on SciFinder(R)]

The scanning electrochem. microscope was applied to drive the deposition of Ni(OH)2 structures. Nickel hydroxide was deposited from aq. solns. onto platinum surfaces as a result of changing the pH locally on the electrode surface. The increase in pH is driven by an oxidn.-redn. process, i.e., N,N'-dimethyl-4,4'-bipyridinium, MV2+, which is reduced at an ultramicroelectrode, diffuses to the surface where it is regenerated upon the redn. of protons, causing a local increase of pH and the deposition of Ni(OH)2. The different parameters that control the efficiency of the deposition, such as the pH and the concn. of the buffer, were examd. [on SciFinder(R)]

A glassy carbon electrode (GCE) coated with 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8.]hexacosane, Kryptofix-222, was used for the very sensitive and selective detn. of very low levels of mercury. A detection limit lower than 10-12 M (<0.2 ppt) was obtained applying anodic stripping voltammetry (ASV). The parameters that governed the sensitivity and possible interferences by other ions have been examd. in detail. The electrode has been successfully applied for detg. mercury in seawater, wastewater, and also in human saliva and amniotic fluid. The modified electrode exhibited high stability and, therefore, could be used repeatedly without mech. regeneration. [on SciFinder(R)]

Self-assembled monolayers of ω-mercaptocarboxylic acids, HS(CH2)nCO2H (n = 1, 2, 5, 10), on mercury film (MF) and gold electrodes have been used for the very sensitive and selective anal. of ultralow levels of cadmium(II). The authors find that shorter ω-mercaptocarboxylic acids provide superior sensitivity. Other parameters that govern the sensitivity and selectivity of this system have been examd. in detail. Optimizing these factors resulted in a detection limit of 4 × 10-12 M (0.45 ppt). The method has been verified by detg. cadmium in std. solns. and it has been successfully applied to the anal. of cadmium in seawater. [on SciFinder(R)]

Selective detn. of ultra low levels of mercury (<10-12M) is described using a glassy carbon electrode spin coated with 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (Kryptofix-222). The electrode was used for the detn. of mercury in sea water by anodic stripping voltammetry. [on SciFinder(R)]

A cross-linked polymer composed of polyethylenimine (PEI) reacted with 1,4-dibromobutane coated on a glassy C electrode (GCE) and contg. neg. charged ions, Fe(CN)63-/4-, is proposed as a ref. electrode in org. solvents. The system exhibits a relatively stable potential (±10 mV) over a period of several days in MeCN and a reasonable potential stability for several hours in DMF and CH2Cl2. The different parameters that affect the behavior of the GCE/PEI/Fe(CN)63-/4- are characterized. [on SciFinder(R)]

Self-assembled monolayers of ω-mercapto carboxylic acids, HS(CH2)nCO2H (n = 2, 5, 10), Cm on gold electrodes were used as a means to induce electrochem. differentiation between a neurotransmitter, dopamine, and ascorbic acid. Optimum differentiation is found for n = 5, and it is attributed to a compromise between a well-organized system that requires long ω-mercapto carboxylic acids and a reasonable rate of electron transfer which is obsd. with short ω-mercapto carboxylic acids. [on SciFinder(R)]

An electrochem. pretreated glassy carbon electrode (GCE) modified with an aza crown ether, 8,9,17,18-dibenzo-1,7-dioxa-10,13,16-triazacyclooctadecane (DDTC), has been used for the very sensitive and selective anal. of trace amts. of gold(III). A detection limit of 4.2 × 10-10 M was obtained by applying anodic stripping voltammetry. The parameters that affect the sensitivity and possible interferences by other ions have been examd. in detail. The modified electrodes exhibit high stability and, therefore, have been used repeatedly without mech. regeneration. Finally, the method has been successfully applied to det. gold traces in a geol. sample. [on SciFinder(R)]

Selective detn. of ultra low levels of mercury (<10-12M) is described using a glassy carbon electrode spin coated with 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (Kryptofix-222). The electrode was used for the detn. of mercury in sea water by anodic stripping voltammetry. [on SciFinder(R)]

A modified polymer, i.e. benzylated polyethyleneimine (PEI), coated on a glassy C electrode in which neg. charged quinones were incorporated, was used for voltammetric measurement of pH. A linear dependence of the av. of the peak potentials as a function of pH was obsd. The system was successfully applied also to ultramicroelectrodes. [on SciFinder(R)]

An easy approach for constructing gold electrodes embedded in glass is described. A special "soft" glass, with a thermal expansion coeff. matching that of gold has enabled assembling gold electrodes which exhibit good sealing and thus excellent electrochem. response. [on SciFinder(R)]

During a study of the electrooxidn. of SnCl2 at Au and Pt electrodes by cyclic voltammetry, a remarkable hysteresis was assocd. with the oxidn. of SnCl2 that is attributed to the adsorption of SnCl2 on the Au electrode. The adsorbed SnCl2 inhibits the oxidn. of the bulk SnCl2 and therefore shifts the potential for oxidn. to more pos. values. However, once the adsorbed SnCl2 is oxidized, the dissolved SnCl2 is oxidizable at less pos. potentials. This inhibition by adsorbed SnCl2 also affects other inner-sphere electrode reactions (e.g., oxidn. of I-), but not outer-sphere reactions. This inhibition is explained in terms of the need of a bridging ligand to facilitate electron transfer in inner sphere reactions. This inhibition is even more pronounced on Pt electrodes, where no oxidn. wave for SnCl2 is obsd. However, adsorption of Cl- ions, 2-mercaptoethanol, or iodide causes desorption of the SnCl2 and the appearance of an irreversible wave for oxidn. of the Sn(II) in soln. [on SciFinder(R)]

High resoln. (-μm£ etching of semiconductors has been achieved by applying the scanning electrochem. microscope (SECM) in the feedback mode. Strong oxidants, such as bromine, were electrogenerated in situ at an ultramicroelectrode UME and the surface. The variables that affect the size and shape of the etched pattern, the required properties of the redox couple, and the mechanism of the etching process are discussed. This approach was successfully applied to several III-V and II-V semiconductors: gallium arsenide, gallium phosphide, cadmium telluride, and mercury cadmium telluride. . [on SciFinder(R)]

A scanning electrochem. microscope (SECM) was used as an anal. tool to study the etching of GaAs surfaces. Hole injection from several electrogenerated oxidants to n-type, p-type, and undoped GaAs was examd. by the feedback mode of the SECM. Assignment of the process as a hole injection from the oxidized form of the redox couple into the valence band and assignment of the energy of the valence band edge in the semiconductor were made by studying the behavior of the feedback current at various pHs and with different redox couples. The nature of the dopant strongly affected the etching process. Both n-GaAs and undoped GaAs were etched by using the feedback mode while p-GaAs was completely resistive toward etching. The differences between n-GaAs and p-GaAs are explained in terms of semiconductor-electrolyte interactions. [on SciFinder(R)]

Au and Pd electrodeposition in polymer films immersed in soln. with high resoln. has been accomplished using the scanning electrochem. microscope (SECM). The SECM was used in the feedback mode, where Ru(NH3)63+ was reduced at an ultramicroelectrode (UME) and diffused to a protonated polyvinylpyridine-coated surface. When metal anions e.g., AuCl4- or PdCl42-, were incorporated in the polymeric matrix, the diffusion of reduced mediator, Ru(NH3)2+, from the UME to the polymer film resulted in metal deposition. The different factors that det. the size and pattern of deposited metal were examd. The difference between Au and Pd deposition was studied by several techniques and interpreted in terms of kinetic and thermodn. properties of the mediator and the metal complex. [on SciFinder(R)]

A review on the technique of electrochem. imaging of a substrate surface by monitoring the tip current when the substrate and tip are part of an electrochem. cell and the tip is scanned in a rastered pattern across the substrate surface. Samples include electrodes, polymer films on electrodes, and biol. materials. The method can be used to control microstructure fabrication by deposition or etching. 28 Refs. [on SciFinder(R)]

Photosensitized redn. of HCO3- to HCO2- proceeds in an aq. system composed of deazariboflavin, dRFl, as photosensitizer, N,N'-dimethyl-4,4'-bipyridinium, MV2+, as primary electron acceptor, sodium oxalate as sacrificial electron donor, and in the presence of a Pd colloid stabilized by β-cyclodextrin, Pd-β-CD. The reaction proceeds with a quantum efficiency of 1.1. Kinetic characterization of the Pd-β-CD catalyst activity reveals the presence of active sites for bicarbonate activation and redn. as well as catalytic sites for H2 evolution. The HCO3- activation sites are specifically inhibited by thiols. The catalytic redn. of HCO3- to HCO2- and the resp. inhibition processes exhibit enzyme-like kinetic properties. The Pd-β-CD colloid shows reversible activities and effects the redn. of MV2+ by formate. Kinetic characterization of the catalyzed redn. of HCO3- to HCO2- and the reverse oxidn. of HCO2- provides a sequential mechanism for the reactions. [on SciFinder(R)]

A review with 110 refs. on photosensitized regeneration of NAD(P)H cofactors by photochem. means. Reductive regeneration of NAD(P)H cofactors proceeds through coupling of photogenerated N,N'-dimethyl-4,4'-bipyridinium radical cation, which acts as electron carrier, to the enzymes lipoamide dehydrogenase, LipDH and ferredoxin reductase, FDR, resp. Regeneration of NAD(P)H is also accomplished by substitution of the enzymes and electron carrier by synthetic rhodium complexes acting as H-donors for the regeneration of NAD(P)H. Oxidn. of NAD(P)H proceeds either by reductive quenching of the excited photosensitizer by NAD(P)H or dark oxidn. of NAD(P)H by the oxidized photoproduct formed in the photosensitized electron-transfer process. The systems are applied in the dehydrogenation of alcs., hydroxy acids, and amino acids. [on SciFinder(R)]

The etching is described of Cu circuit paths using a scanning electrochem. microscope supplied with a redox couple to induce feedback. Very small dimensions (<0.6 μm) are achieved. [on SciFinder(R)]

Photosensitized regeneration of 1,4-dihydronicotinamide adenine dinucleotide phosphate (NADPH) with an artificial photosystem allows the enzymic fixation of CO2 through carboxylation of α-oxo acids using sacrificial electron donors. Pyruvic acid is carboxylated to malic acid and α-oxoglutaric acid is carboxylated to isocitric acid with the malic enzyme and isocitrate dehydrogenase (ICDH) as biocatalysts, ϕ = 1.9%. Malic acid formed through the photosensitized process is used as a synthetic building block for subsequent sequestered enzymic transformations, and its conversion into aspartic acid is accomplished with fumarase and aspartase as biocatalysts. Photoredn. of CO2 to formate is accomplished in the presence of formate dehydrogenase (FDH) as catalyst. Photosensitized redn. of different bipyridinium relay systems, i.e. N,N'-dimethyl-4,4'-bipyridinium (MV2+), N,N'-dimethyl-2,2'-bipyridinium (DM2+), N,N'-trimethylene-2,2'-bipyridinium (DT2+), and N,N'-tetramethylene-2,2'-bipyridinium (DQ2+) to the corresponding radical cations yields reduced relays that act as cofactors for FDH, which mediates the redn. of CO2 to formate. The quantum yield for formate formation is in the range ϕ = 0.5-1.6%. [on SciFinder(R)]