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Unimolecular rate constants, K sub et, are reported for the one-electron electroreduction of pentaamminecobalt (III) anchored to mercury, gold, or copper electrodes via various thiophenecarboxylate ligands where the thiophene sulfur acts as the surface binding group and the carboxylate is coordinated to the cobalt reactants. At mercury, the rate parameters were found to be sensitive to the bridging ligand structure, substantially (ca. 10-20 fold) smaller values of K sub et being found for ligands containing one or more methylene groups between the thiophene sulfur and carboxylate oxygen than those featuring uninterrupted bond conjugation between the metal surface donor and Co(III) acceptor sites. Various contributions to these reactivity differences are asse-sed on the basis of the measured variations in the stability constants of the adsorbed precursor state, the rate constants for the homogeneous reduction of these complexes by hexammineruthenium (II), the unimolecular frequency factors obtained from the electrochemical activation parameters, and by comparison with ele-trochemical outer-sphere rate data. Taken together, these results provide strong evidence that the smaller values of K sub et values of the electronic transmission coefficient than are achieved with the conjugated ligands. Comparison is made with analogous results for intramolecular electron transfer via extended organic ligands in homogeneous solution. (Author)

Etude de la cinetique de reduction a 1 electron des cryptates d'Eu (Eu(2.2.1) 3+ et Eu(2.2.2) 3+ ) par les ions V aq 2+ et Eu aq 2+ et d'oxydation de Eu(2.2.1) 2+ par Co(IVH 3 ) 6 3+ , par polarographie

The nature of the redox-induced structural changes of cyclooctatetraene iron tricarbonyl are explored using fourier transform infrared spectroelectrochemistry. The results provide a simple demonstration of the detailed mechanistic information that can be obtained by employing FTIR instrumentation along with a thin-layer electrochemical arrangement. Keywords: Infrared spectroelectrochemistry, Redox kinetics.

A circuit has been designed for the automatic control of potential modulation for subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) using an IBM IR/90 series FTIR spectrometer. This device enables the potential modulation to remain synchronized with the spectral data collection under all conditions.

The near-infrared absorption parameters for bicobaltocene monocation, (Cp2Co)2+, evaluated in several solvents, are compared with corresponding data for biferrocene cation, (Cp2Fe)2+, in order to ascertain the consequence of metal substitution upon the degree of redox-site electronic coupling. From the markedly (ca. 5 fold) larger intervalence band intensities, narrower bandwidths, and milder solvent dependence of the band energy observed for the former system, the degree of Co(III)-Co(II) electronic coupling is deduced to be substantially greater than for Fe(III)-Fe(II). A similar conclusion is reached from a comparison of near-infrared spectra for bis(fulvalene)-dicobalt and -diiron monocations. These differences are also reflected in more negative comproportionation free energies for the cobalt mixed-valence analogs, as derived from electrochemical data. These findings are consistent with orbital symmetry considerations, since electron transfer for the Co(III)-Co(II) system is expected to involve a ligand-centered 4e1g orbital, as compared with strongly metal-localized 4e2 or 8a1g orbitals that are apparently utilized in the Fe(III)-Fe(II) metallocene case. Keywords: Mixed valence compounds, Donor acceptor orbital overlap, Electronic coupling, Biferrocene, Bicobaltocene.

Objective:To determine the degree and sources of variability in faculty evaluations of residents for the American Board of Internal Medicine (ABIM) Clinical Evaluation Exercise (CEX). Design:Videotaped simulated CEX containing programmed resident strengths and weaknesses shown to faculty evaluators, with responses elicited using the openended form recommended by the ABIM followed by detailed questionnaires. Setting:University hospital. Participants:Thirty-two full-time faculty internists. Intervention:After the open-ended form was completed and collected, faculty members rated the resident’s performance on a five-point scale and rated the importance of various aspects of the history and physical examination for the patient shown. Measurements and Main Results:Very few of the resident’s strengths and weaknesses were mentioned on the openended form, although responses to specific questions revealed that faculty members actually had observed many errors and some strengths that they had failed to document. Faculty members also displayed wide variance in the global assessment of the resident: 50% rated him marginal, 25% failed him, and 25% rated him satisfactory. Only for performance areas not directly related to the patient’s problems could substantial variability be explained by disagreement on standards. Conclusions:Faculty internists vary markedly in their observations of a resident and document little. To be useful for resident feedback and evaluation, exercises such as the CEX may need to use more specific and detailed forms to document strengths and weaknesses, and faculty evaluators probably need to be trained as observers.

Some likely influences of the solvent medium upon the kinetics of simple electrochemical reactions are described, and illustrated with recent results from the author’s laboratory.

Surface-enhanced Raman (SER) spectra are reported for several adsorbates at underpotential deposited (upd) layers of mercury, thallium, and lead on an electrochemically roughened gold electrode. For upd mercury monolayers, SER bands were obtained for the surface-halide stretching mode, ν M-X , of adsorbed chloride and bromide that are of comparable intensities to those observed on the unmodified gold substrate. The ν M-X peak frequencies are downshifted by 15–24 cm −1 on the former relative to the latter surface, consistent with a smaller extent of halide bond covalency on mercury. These spectral changes induced by upd formation could be reversed by anodic stripping of the mercury monolayer. Comparable results were also obtained by prior formation of the upd monolayer in a separate solution followed by electrode transfer rather than by deposition in the solution of interest. Satisfactory SER spectra at upd mercury are reported additionally for thiocyanate and pyridine, as are similar experiments for upd thallium and lead layers on gold. Of the above adsorbates, only pyridine yielded easily measurable SER spectra for these layers, having 2–3 fold smaller signal intensities than on unmodified gold. The SERS intensity decreases upon thallium, and lead upd formation exhibited both irreversible and reversible components. Differential capacitance-potential plots for upd mercury indicate some similarities to liquid mercury interfaces. The results indicate that overlayers on gold provide a means of extending SERS to metals that in themselves do not exhibit suitable Raman scattering enhancements.

Publisher Summary This chapter describes mechanistically simple electrochemical reactions in relation to contemporary theoretical treatments of single electron-transfer steps. Although these treatments have been developed primarily in conjunction with homogeneous redox processes, they are equally applicable to electrochemical reactions with suitable modifications. Besides emphasizing the close connections between heterogeneous and homogeneous redox processes, this approach serves to clarify the various structural factors expected to influence electrochemical kinetics. Selected comparisons are made with experiment to examine the strengths and limitations of the theoretical treatments and to suggest possible directions for future experimental and theoretical work. The chapter discusses contemporary theoretical treatments of single electron-transfer steps and relates them to experimental electrochemical-rate parameters in the same manner as for the more widely considered reactions between pairs of redox couples in homogeneous solution. The role of one of the reacting centers (electron acceptor or donor) is taken by the metal surface, which provides a rigid two-dimensional environment where reaction occurs. The extant theoretical models enable, at least in principle, to predict reactivities for individual electrochemical reactions, given knowledge of the relevant thermodynamic and structural parameters, for comparison with the experimental kinetics.

Hydrogen 1 NMR spectra have been obtained for the Rhodium (II) complex (eta-C6Me6)RhCp*)+, Cp* = 5-C5Me5, at 200 MHz, and 470 MHZ. A single resonance was observed for te arene CH3 protons between 298 K and 183 K in Methylene Chloride. The temperature dependence of the resonance was consistent with a doublet state formulation of the Rh(II) complex. At 298 K, the CH3 chemical shifts were 56 ppm for the arene substituents and 123 ppm for the cyclopentadienyl substituents. The magnetic equivalence of the methyl arene resonances is consistent with a planar arene structure in the complex. It is shown that a structural formulation including a highly fluxional bent arene is unlikely. The results demonstrate eta 4-arene hapticity, the one-electron intermediate can retain the planar arene structure, even if this results in a 19 e- metal.

Rate parameters have been gathered for the electroreduction of a number of Cr(III) complexes attached to silver electrodes via one or more thiocyanate, azide, chloride, or bromide bridging ligands. Unimolecular rate constants k sub et (per sec) for electron transfer within the adsorbed states as well as the surface concentration of the adsorbates were obtained directly using rapid linear sweep voltammetry. These data are also compared with corresponding kinetics and adsorption measurements at mercury electrodes in order to deduce the structure factors responsible for the substantially greater overall reactivities (i.e., larger apparent rate contents k sub app) seen at silver. Marked differences in k sub et, as well as k sub app, were found between silver and mercury surfaces these differences being sensitive to the nature of the nonbridging as well as the bridging ligands. This indicates that the metal surface exerts a significant influence upon the energetics of the elementary electron-transfer step as well as upon the stability of the precursor intermediate. Explanations for the observed structural influences upon k sub et are sought in terms of 'electronic communication' effects between the redox center and the metal surface.

The reaction entropies lSo,, of a number of transition metal redox couples of the form M ( I I I ) / ( 11) in aqueous solution have bcen determined using nonisothermal electrochemical cells in order to explore the effect of varying the ligand structure upon the nature of the ion-solvent interactions. Examination of six aquo couples of the form M ( O H Z ) , , ~ + ' ~ + with varying metal M yielded ASo,, values in the range 36-49 eu. In order to scrutinize the effect of replacing aquo with ammine and simple anionic ligands, R u ( l I I ) / ( I I ) couples were employed since the relativc substitution inertness of both oxidation states allowed AS',, to be determined using cyclic voltammetry. The stepwise replacement of aquo by ammine ligands results in substantial reductions in ASo,, which are attributed to the smaller extent of ligand-solvent hydrogen bonding for ammine compared with aquo ligands. Substitution of both aquo and ammine by anionic ligands also resulis in substantial reductions in ASo,,. A number of M ( I I I ) / ( I I ) couples containing chelating ligands were also examined. Sizable differcnces in ASo,, were found between Co(lll)/(ll) couples and the corresponding R u ( l l l ) / ( l l ) and Fe(lll)/(ll) couples. Suggested explanations are differences in ligand conformation and electron delocalization effects. The possible contribution of outer-sphere solvent structuring effects to the large reorganization energies observed for electron exchange of aquo complexes is noted. The validity of the assumptions required for the estimation of ASo,, from nonisothermal cell measurements is discussed.

In situ infrared reflection-absorption spectra in the CO stretching (νCO) region for carbon monoxide adsorbed on an ordered Pd(110) electrode in 0.1 M HClO4 as a function of coverage (θCO) and electrode potential (E) are compared with corresponding θCO-dependent spectra reported in previous studies for the same surface in ultrahigh vacuum (UHV). The latter system has been shown from electron diffraction to involve an unusual case of CO-induced surface reconstruction which is reflected also in marked changes in the θCO-dependentνCO spectra. Detailed comparison of the infrared data obtained in the electrochemical and UHV environments therefore enables the possible occurrence of Pd(110) reconstruction in the former system to be assessed. Indeed, rich θCO-dependentνCO spectra were obtained which provide strong evidence that similar surface structural changes also occur at the Pd(110)-aqueous interface. Specifically, dosing CO from dilute (ca. 0.01 mM) solution yields a single νCO band (at 1810–1840 cm−1) at low coverages. These spectra transform for θCO values above ca. 0.4 into a complex multiple-band pattern which contains an additional band near 1930–1940 cm−1 and weaker higher-frequency νCO features along with a peak at ca. 1850–1880 cm−1. Significantly, this spectral pattern, obtained for coverages between ca. 0.4 and 0.75, is similar to that observed in the UHV system over a comparable θCO range, the latter being diagnostic of the CO-induced formation of a (1 × 2) “missing-row” reconstruction. Increasing the coverage further, from 0.75 up to saturation, θCO = 1.0, triggers another spectral transition to a single dominant νCO band at 1960–1965 cm−1, consistent with the formation of a (2 × 1) atop CO adlayer on a (1 × 1) (i.e. unreconstructed) substrate. Further evidence that the freshly prepared surface is unreconstructed prior to CO dosing, as well as in the presence of a saturated adlayer, was obtained from νCO spectra following CO removal and redosing, and also from energetic considerations along with voltammetric data. Intermediate-coverage CO adlayers formed by solution dosing followed by partial electrooxidative removal exhibit much smaller θCO-dependent spectral changes, indicative of adsorbate island formation. However, the νCO spectra for such adlayers transformed within 10–20 min into θCO-dependent patterns comparable to those obtained upon initial solution CO dosing. This “island dissipation” may be driven by the resultant formation of reconstructed nanoscale domains.

Background Dispersal of glioblastoma (GBM) cells leads to recurrence and poor prognosis. Accordingly, molecular pathways involved in dispersal are potential therapeutic targets. The mitogen activated protein kinase/extracellular signal regulated kinase (MAPK/ERK) pathway is commonly dysregulated in GBM, and targeting this pathway with MEK inhibitors has proven effective in controlling tumor growth. Since this pathway also regulates ECM remodeling and actin organization − processes crucial to cell adhesion, substrate attachment, and cell motility – the aim of this study was to determine whether inhibiting this pathway could also impede dispersal. Methods A variety of methods were used to quantify the effects of the MEK inhibitor, PD0325901, on potential regulators of dispersal. Cohesion, stiffness and viscosity were quantified using a method based on ellipsoid relaxation after removal of a deforming external force. Attachment strength, cell motility, spheroid dispersal velocity, and 3D growth rate were quantified using previously described methods. Results We show that PD0325901 significantly increases aggregate cohesion, stiffness, and viscosity but only when tumor cells have access to high concentrations of fibronectin. Treatment also results in reorganization of actin from cortical into stress fibers, in both 2D and 3D culture. Moreover, drug treatment localized pFAK at sites of cell-substratum adhesion. Collectively, these changes resulted in increased strength of substrate attachment and decreased motility, a decrease in aggregate dispersal velocity, and in a marked decrease in growth rate of both 2D and 3D cultures. Conclusions Inhibition of the MAPK/ERK pathway by PD0325901 may be an effective therapy for reducing dispersal and growth of GBM cells. Electronic supplementary material The online version of this article (doi:10.1186/s12885-017-3107-x) contains supplementary material, which is available to authorized users.

The surface-enhanced Raman scattering (SERS) properties of rhodium films electrodeposited onto a SERS-active gold substrate are examined as a function of overlayer thickness, using carbon monoxide and thiocyanate as chemisorbate probes in aqueous solution. Although the adsorbate Raman signals obtained for ultrathin (≤10 monolayers, ML) Rh layers emanate from the gold template, a significant or even dominant SERS component for thicker films is identified as arising instead from the transition-metal overlayer itself. The latter contribution was diagnosed and characterized from similar experiments undertaken using SERS-inactive gold and carbon substrates, and from the observation of comparable Raman enhancements obtained with green (514.5 nm) as well as red (632.8 nm) excitation. While the surface enhancement factors for these layers, of the order of 103, are markedly less than those obtained for ultrathin films on SERS-active gold, the signals even for very weak Raman scatterers (such as adsorbed hydrogen) ...

Surface-enhanced Raman scattering (SERS) has been observed for pentaamminepyridineosmium(III) adsorbed at a silver electrode as a function of electrode potential in order to examine the molecular vibrational changes of electrode potential in order to examine the molecular vibrational changes accompanying electron transfer involving a simple surface-bound redox couple. Noticeable alterations in the intensity and frequency of several vibrational bands involving osmium-ligand and pyridine ring modes were observed as the electrode potential was made more negative which are consistent with a variation of the osmium oxidation state from III to II. The effective formal potential for the adsorbed Os(III)/(II) couple determined from SERS, ca -630 mV vs sce, is in reasonable agreement with that obtained from rapid cyclic voltammetry, illustrating the value of SERS for monitoring electron-transfer processes at metal surfaces. (Author)

A circuit has been designed for the automatic control of potential modulation for subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) using an IBM IR/90 series FTIR spectrometer. This device enables the potential modulation to remain synchronized with the spectral data collection under all conditions.

Unimolecular electron-transfer rate constants, k sub et, are reported for the one-electron reduction of pentaaminecobalt (III) attached to gold and mercury electrodes via thioalkylcarboxylate ligands containing varying numbers, n, of alkyl carbons. While similar values of k sub et were found at mercury for each reaction, for close-packed monolayers at gold the k sub et values decreased by circa 10 to the 4th power as an increased from one to five. This effect is identified with increasingly nonadiabatic pathways as an increases, a linear plot of log k sub et versus n being obtained. The results provide estimates of the electronic transmission coefficient as a function of the surface-Co(III) separation distance.

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