Thin films with enantioselective properties for electrochemically active chiral probes were developed. Enantioselectivity was accomplished via molecular imprinting. The films were fabricated through the sol-gel technique and were spin-coated on ITO electrodes. The chiral selectivity recognition was detected using two enantiomer pairs: D- and L-3,4-dihydroxyphenylalanine (D- and L-dopa) and (R)- and (S)-N,N'-dimethylferrocenylethylamine [(R)-Fc and (S)-Fc]. A defined chiral cavity was obtained by selection of functional monomers that interact with the template molecule, followed by its removal. Chiral selection properties were measured by cyclic voltammetry and square wave voltammetry. For both template molecules, very good chiral recognition was revealed by electrochemical measurement. The nonspecific adsorption measured for reference nonimprinted films was negligible (less than 5%). Dopa imprinted films revealed both high sensitivity, by the detection of 1 nM (0.2 ppb) concentration, and excellent selectivity, when challenged with a series of catechol derivatives. Fc-imprinted films were able to detect ca. 2 ppm of the target molecule, with very good enantioselectivity and low nonspecific adsorption. To our knowledge, this is the first report of successful molecular imprinting of a ferrocene derivative.[on SciFinder (R)]

A new method has been developed for measuring local adsorption rates of metal ions at interfaces based on scanning electrochemical microscopy (SECM). The technique is illustrated with the example of Ag+ binding at Langmuir phospholipid monolayers formed at the water/air interface. Specifically, an inverted 25 microm diameter silver disc ultramicroelectrode (UME) was positioned in the subphase of a Langmuir trough, close to a dipalmitoyl phosphatidic acid (DPPA) monolayer, and used to generate Ag+ via Ag electro-oxidation. The method involved measuring the transient current-time response at the UME when the electrode was switched to a potential to electrogenerate Ag+. Since the Ag+/Ag couple is reversible, the response is highly sensitive to local mass transfer of Ag+ away from the electrode, which, in turn, is governed by the interaction of Ag+ with the monolayer. The methodology has been used to determine the influence of surface pressure on the adsorption of Ag+ ions at a phospholipid (dipalmitoyl phosphatidic acid) Langmuir monolayer. It is shown that the capacity for metal ion adsorption at the monolayer increased as the density of surface adsorption sites increased (by increasing the surface pressure). A model for mass transport and adsorption in this geometry has been developed to explain and characterise the adsorption process.[on SciFinder (R)]

Handling of a gun results in the formation of invisible impressions, caused by transfer of iron traces to the skin surface. Visualization of these impressions is possible by spraying the palms with a solution of 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT), which forms a magenta complex with iron(II) residues. Hence, mark intensity is directly related to the amounts of iron transferred to the palm. Palmar sweat plays a major role in iron transfer from the firearm to the hand. More factors, however, are involved in this process. Three time-dependent factors have been studied with relation to their effect on the developed mark: the gripping duration of the weapon; the time elapsed from the contact; and the rate of iron dissolution in aqueous solutions containing sweat components in physiological concentrations. We found that the amounts of iron transferred to the palm depend on both, the gripping period and the levels of palmar moisture. Thus, only a few seconds of gripping were required for developing good marks (corresponding to 80ngcm(-2) of iron) on highly-moistured hands, much longer gripping periods were necessary for developing marks of similar intensity on relatively dry hands. Experiments that aimed at studying the effect of sweat components on metallic iron dissolution were carried out in aqueous solutions. It was found that chloride ions in physiological concentrations remarkably enhanced the dissolution, while l-serine, the major amino acid in palmar sweat, had a detrimental effect on this process. Urea, another sweat component, had only a minor effect on the dissolution rate.[on SciFinder (R)]

Thin films with enantioselective properties for electrochem. active chiral probes were developed. Enantioselectivity was accomplished via mol. imprinting. The films were fabricated through the sol-gel technique and were spin-coated on ITO electrodes. The chiral selectivity recognition was detected using two enantiomer pairs: D- and L-3,4-dihydroxyphenylalanine (D- and L-dopa) and (R)- and (S)-N,N'-dimethylferrocenylethylamine [(R)-Fc and (S)-Fc]. A defined chiral cavity was obtained by selection of functional monomers that interact with the template mol., followed by its removal. Chiral selection properties were measured by cyclic voltammetry and square wave voltammetry. For both template mols., very good chiral recognition was revealed by electrochem. measurement. The nonspecific adsorption measured for ref. nonimprinted films was negligible (<5%). Dopa imprinted films revealed both high sensitivity, by the detection of 1 nM (0.2 ppb) concn., and excellent selectivity, when challenged with catechol derivs. Fc-imprinted films were able to detect ∼2 ppm of the target mol., with very good enantioselectivity and low nonspecific adsorption. To the authors' knowledge, this is the 1st report of successful mol. imprinting of a ferrocene deriv. [on SciFinder(R)]

The present invention provides an electrochem. method for depositing a thin film comprising metal oxides or silicon oxides on a conductive surface placed on a non-conductive substrate by electrodeposition of sol-gel precursors on the conductive surface selectively. The sol-gel precursors may further comprise various dopants thereby patterning the conductive layer. [on SciFinder(R)]

A review. The implications of organically-modified SiO2-based materials in electrochem. science is reviewed along with some selected recent trends in the field of functionalized and sol-gel SiO2 electrochem. These recent trends include the electro-assisted generation of organosilica films on solid electrode surfaces, the prepn. and applications of sol-gel derived composite (C, Au, nanotubes) electrodes, the electrochem. characterization of mass transfer reactions in porous functionalized silicas, solid-state electrochem. and gas sensors involving sol-gel materials, imprinted functionalized SiO2, and the electrochem. characterization and applications of ordered mesoporous organosilicas. [on SciFinder(R)]

Handling of a gun results in the formation of invisible impressions, caused by transfer of iron traces to the skin surface. Visualization of these impressions is possible by spraying the palms with a soln. of 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT), which forms a magenta complex with iron(II) residues. Hence, mark intensity is directly related to the amts. of iron transferred to the palm. Palmar sweat plays a major role in iron transfer from the firearm to the hand. More factors, however, are involved in this process. Three time-dependent factors have been studied with relation to their effect on the developed mark: the gripping duration of the weapon; the time elapsed from the contact; and the rate of iron dissoln. in aq. solns. contg. sweat components in physiol. concns. We found that the amts. of iron transferred to the palm depend on both, the gripping period and the levels of palmar moisture. Thus, only a few seconds of gripping were required for developing good marks (corresponding to 80 ng cm-2 of iron) on highly-moistured hands, much longer gripping periods were necessary for developing marks of similar intensity on relatively dry hands. Expts. that aimed at studying the effect of sweat components on metallic iron dissoln. were carried out in aq. solns. It was found that chloride ions in physiol. concns. remarkably enhanced the dissoln., while -serine, the major amino acid in palmar sweat, had a detrimental effect on this process. Urea, another sweat component, had only a minor effect on the dissoln. rate. [on SciFinder(R)]

The potential assisted ion-transfer between two immiscible electrolyte solns. has been implemented in scanning electrochem. microscopy (SECM) for depositing metal microstructures on conducting surfaces. An improved approach for local metal deposition is presented, taking advantage from a recently described non-optical shear-force detection system integrated in the SECM, which provided a current-independent tip-surface distance positioning. This allowed positioning of the micropipette in very close proximity to the surface without applying a potential during the approach, and hence, resulted in an improved resoln. for metal deposition. Moreover, it allowed the use of potential pulses for a discontinuous delivery of metal ions over the liq.-liq. interface. The advantages of this approach and its applicability for creating micro- and nanostructures are discussed. [on SciFinder(R)]

A new method was developed for measuring local adsorption rates of metal ions at interfaces based on scanning electrochem. microscopy (SECM). The technique is illustrated with the example of Ag+ binding at Langmuir phospholipid monolayers formed at the H2O/air interface. Specifically, an inverted 25 μm diam. Ag disk ultramicroelectrode (UME) was positioned in the subphase of a Langmuir trough, close to a dipalmitoyl phosphatidic acid (DPPA) monolayer, and used to generate Ag+ via Ag electrooxidn. The method involved measuring the transient current-time response at the UME when the electrode was switched to a potential to electrogenerate Ag+. Since the Ag+/Ag couple is reversible, the response is highly sensitive to local mass transfer of Ag+ away from the electrode, which, in turn, is governed by the interaction of Ag+ with the monolayer. The methodol. was used to det. the influence of surface pressure on the adsorption of Ag+ ions at a phospholipid (dipalmitoyl phosphatidic acid) Langmuir monolayer. The capacity for metal ion adsorption at the monolayer increased as the d. of surface adsorption sites increased (by increasing the surface pressure). A model for mass transport and adsorption in this geometry was developed to explain and characterize the adsorption process. [on SciFinder(R)]

Cyclic voltammetry (CV) and scanning electrochem. microscopy (SECM) were used for studying the binding of protons and Cd(II) ions by 8-mercaptooctanoic acid monolayer that was assembled on an Au surface. Binding of the cations by the monolayer affected the kinetics of electron transfer to neg. charged species, i.e., IrCl63-, in the soln. Increasing the pH of the soln. causes the CV of IrCl63- to become less reversible and the feedback current of the SECM to decrease as the distance between the microelectrode and the surface decreases. However, addn. of Cd2+ to the soln. at pH 6.8 increases the CV reversibility and the feedback current of the SECM of neutralizing the neg. charge of the monolayer by the metallic ions. A model based on the Frumkin correction was used to account for these findings and for extg. the heterogeneous assocn. const. of Cd2+ by the monolayer. [on SciFinder(R)]

Scanning electrochem. microscopy (SECM) can be used in the feedback mode as a 'contactless' method for probing the cond. of ultra-thin films. With this new technique a sample is bathed with one form of a reversible redox (Red/Ox) couple, e.g. Red, and an ultramicroelectrode (UME), located close to the film surface is used to locally convert Red to Ox by diffusion-limited oxidn. Ox diffuses from the UME to the film where it may undergo conversion back to Red. This process is driven by a potential gradient, which depends on the surface cond. A model is developed for the SECM feedback process from which the cond. of the film can be extd. Two routes arising from the model are considered: an approx. method which allows an order of magnitude est. of the film cond. and a more involved approach, which can be used with greater accuracy. The merits of the two approaches are assessed by analyzing exptl. data for the effect of surface pressure on the cond. of a polyaniline monolayer at a water/air interface. [on SciFinder(R)]