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Conductance
About: Conductance is a research topic. Over the lifetime, 8088 publications have been published within this topic receiving 235961 citations.
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TL;DR: The voltage-activated H+ selective conductance of rat alveolar epithelial cells was studied using whole-cell and excised-patch voltage-clamp techniques and the effects of substituting deuterium oxide for water, H2O, on both the conductance and the pH dependence of gating were explored.
Abstract: The voltage-activated H+ selective conductance of rat alveolar epithelial cells was studied using whole-cell and excised-patch voltage-clamp techniques. The effects of substituting deuterium oxide, D2O, for water, H2O, on both the conductance and the pH dependence of gating were explored. D+ was able to permeate proton channels, but with a conductance only about 50% that of H+. The conductance in D2O was reduced more than could be accounted for by bulk solvent isotope effects (i.e., the lower mobility of D+ than H+), suggesting that D+ interacts specifically with the channel during permeation. Evidently the H+ or D+ current is not diffusion limited, and the H+ channel does not behave like a water-filled pore. This result indirectly strengthens the hypothesis that H+ (or D+) and not OH- is the ionic species carrying current. The voltage dependence of H- channel gating characteristically is sensitive to pH0 and pHi and was regulated by pD0 and pDi in an analogous manner. shifting 40 mV/U change in the pD gradient. The time constant of H+ current activation was about three times slower (T(act) was larger) in D2O than in H2O. The size of the isotope effect is consistent with deuterium isotope effects for proton abstraction reactions, suggesting that H+ channel activation requires deprotonation of the channel. In contrast, deactivation (T(tail)) was slowed only by a factor < or = 1.5 in D2O. The results are interpreted within the context of a model for the regulation of H+ channel gating by mutually exclusive protonation at internal and external sites (Cherny, V.V., V.S. Markin, and T.E. DeCoursey. 1995. J. Gen. Physiol. 105:861-896). Most of the kinetic effects of D2O can be explained if the pKa of the external regulatory site is approximately 0.5 pH U higher in D2O.
112 citations
TL;DR: First principles density functional calculations demonstrate a better delocalization of the frontier orbitals as well as a stronger electronic coupling between the azobenzene moiety and the electrode for the cis configuration over the trans one.
Abstract: A new azobenzene-thiophene molecular switch is designed, synthesized and used to form self-assembled monolayers (SAM) on gold. An "on/off" conductance ratio up to 7x1E3 (with an average value of 1.5x1E3) is reported. The "on" conductance state is clearly identified to the cis isomer of the azobenzene moiety. The high "on/off" ratio is explained in terms of photo-induced, configuration-related, changes in the electrode-molecule interface energetics (changes in the energy position of the molecular orbitals with respect to the Fermi energy of electrodes) in addition to changes in the tunnel barrier length (length of the molecules). First principles DFT calculations demonstrate a better delocalization of the frontier orbitals, as well as a stronger electronic coupling between the azobenzene moiety and the electrode for the cis configuration over the trans one. Measured photoionization cross-sections for the molecules in the SAM are close to the known values for azobenzene derivatives in solution.
111 citations
TL;DR: In this paper, a new azobenzene−thiophene molecular switch is designed, synthesized, and used to form self-assembled monolayers (SAM) on gold.
Abstract: A new azobenzene−thiophene molecular switch is designed, synthesized, and used to form self-assembled monolayers (SAM) on gold. An “on/off” conductance ratio up to 7 × 103 (with an average value of 1.5 × 103) is reported. The “on” conductance state is clearly identified to the cis isomer of the azobenzene moiety. The high on/off ratio is explained in terms of photoinduced, configuration-related changes in the electrode−molecule interface energetics (changes in the energy position of the molecular orbitals with respect to the Fermi energy of electrodes) in addition to changes in the tunnel barrier length (length of the molecules). First principles density functional calculations demonstrate a better delocalization of the frontier orbitals as well as a stronger electronic coupling between the azobenzene moiety and the electrode for the cis configuration over the trans one. Measured photoionization cross sections for the molecules in the SAM are close to the known values for azobenzene derivatives in solution.
111 citations
TL;DR: In this paper, the NO2 gas sensing behavior of nano-particular SnO2 is studied at room temperature under illumination, and two main effects have been observed: the conductance is increased and the time constant for NO2 desorption is drastically reduced.
Abstract: The NO2 gas sensing behaviour of nano-particular SnO2 is studied at room temperature under illumination. SnO2 samples were sputtered on interdigital contact (IDC) substrates for conductance measurements and Pt-coated Si-substrates for work function potential measurements by Kelvin probe. Moreover, we used spectral filters and attenuation filters to study light induced gas adsorption and desorption mechanisms. Two main effects have been observed: the conductance is increased and the time constant for NO2 desorption is drastically reduced. Furthermore, the gas induced baseline shift has been reduced. The results can be explained with a surface photovoltaic model.
111 citations
TL;DR: In this article, the authors investigated electrical transport through the molecular model systems benzenedithiol, benzenediamine, hexanedithiol and hexanediamine and found that the spread in single-molecule conductance is not reduced by amino anchoring groups.
Abstract: We have investigated electrical transport through the molecular model systems benzenedithiol, benzenediamine, hexanedithiol and hexanediamine. Conductance histograms under different experimental conditions indicate that measurements using mechanically controllable break junctions in vacuum are limited by the surface density of molecules at the contact. Hexanedithiol histograms typically exhibit a broad peak around 7 * 10^{-4} G_0. In contrast to recent results on STM-based break junctions in solution we find that the spread in single-molecule conductance is not reduced by amino anchoring groups. Histograms of hexanediamine exhibit a very wide peak around 4 * 10^{-4} G_0. For both benzenedithiol and benzenediamine we observe a large variability in low-bias conductance. We attribute these features to the slow breaking of the lithographic mechanically controllable break junctions and the absence of a solvent that may enable molecular readsorption after bond breaking. Nevertheless, we have been able to acquire reproducible current-voltage characteristics of benzenediamine and benzenedithiol using a statistical measurement approach. Benzenedithiol measurements yield a conductance gap of about 0.9 V at room temperature and 0.6 V at 77 K. In contrast, the current-voltage characteristics of benzenediamine-junctions typically display conductance gaps of about 0.9 V at both temperatures.
111 citations