MEMBRANE IONIC CURRENT PHOTOMODIFICATION BY ROSE BENGAL and MENADIONE: ROLE OF SINGLET OXYGEN

Abstract –Photosensitized modification of ionic leak current and potassium current was studied in frog cardiac atrial cells using whole cell patch clamp techniques. Rose bengal (RB) and menadione (MQ) were used as photosensitizers. Separate photophysical studies of the photosensitizers in deuterium oxide solution demonstrated that MQ did not produce singlet oxygen as evidenced by the lack of luminescence at 1270 nm, whereas RB was an efficient singlet oxygen generator. Both photosensitizers sensitized block of potassium current in atrial cells, and both sensitized an increase of ionic leak current. However, when photosensitizer concentrations and illumination intensities were adjusted to match the rate of block of potassium current by the two photosensitizers, there were dramatic differences in leak current increase, both quantitatively and qualitatively. Menadione sensitized a much slower increase in leak current than did RB. Further, the leak current sensitized by MQ had a more positive reversal potential than that sensitized by RB, suggesting a less potassium-selective leak current pathway. The results suggest that, while the effects of singlet oxygen and non-singlet oxygen modification of cell membranes may be similar, there may also be significant differences in the resulting membrane permeabilities. The results also demonstrate that MQ and RB may be useful agents to study the role of singlet oxygen versus non-singlet oxygen modification of biological systems.     

Electrochemical and STM studies of 1-thio-β-D-glucose self-assembled on a Au(111) electrode surface

In this study, a Au(111) electrode is functionalized with a monolayer of 1-thio-β-D-glucose (β-Tg), producing a hydrophilic surface. A monolayer of β-Tg was formed on a Au(111) surface by either (1) potential-assisted deposition with the thiol in a supporting electrolyte or (2) passive incubation of a gold substrate in a thiol-containing solution. For each method, the properties of the β-Tg monolayer were investigated using cyclic voltammetry (CV), differential capacitance (DC), and chronocoulometry. In addition, electrochemical scanning tunneling microscopy (EC-STM) was used to obtain images of the self-assembled monolayer with molecular resolution. Potential-assisted assembly of β-Tg onto a Au(111) electrode surface was found to be complicated by oxidation of β-Tg molecules. The EC-STM images revealed formation of a passive layer containing honeycomb-like domains characteristic of a formation of S(8) rings, indicating the S-C bond may have been cleaved. In contrast, passive self-assembly of thioglucose from a methanol solution was found to produce a stable, disordered monolayer of β-Tg. Since the passive assembly method was not complicated by the presence of a faradaic process, it is the method of choice for modifying the gold surface with a hydrophilic monolayer.     

Measurement and Prediction of Thermal Contact Resistance Across Coated Joints

An integrated experimental and numerical investigation of the thermal contact resistance across two nominally flat, coated metallic engineering surfaces in contact is presented. The model consists of a surface deformation computation, which determines the actual contact area and number of contacting asperities at a joint, and a constriction resistance analysis, which determines the constriction resistance through each individual contacting asperity. Predictions from the model are validated against experiments conducted for the purpose. The experiments are performed according to a “design of experiments” approach and evaluated using statistical regression. Three substrates (copper, brass, and aluminum) and three coatings (silver, nickel, and tin) are considered with a variety of coating thicknesses and substrate roughnesses. The contact load is also varied. The experimental measurements show that the best choice of a coating for contact resistance mitigation depends on the substrate material and roughness, and it cannot be prescribed in general. A regression equation developed for the experimental results offers a useful tool for the design of coated contacts. The measured results agree well with predicted values from the numerical model, especially in cases of a rough substrate or hard coating.     

The sticking and dissociation of NH3 on W(110): a three-state model

The kinetics of the adsorption of NH₃ on W(110) and its subsequent dissociation have been investigated using molecular beam techniques and temperature programmed desorption (TPD) for surface temperatures ranging from 140 to 700 K. NH₃ shows a wide desorption peak around 270 K and a smaller peak at 170 K while H₂ and N₂, produced by dissociation, desorbed at 550 and 1350 K, respectively, with kinetic parameters similar to those reported for H and N generated by adsorption of H₂ and N₂. At normal incidence and for a surface temperature of 140 K, the NH₃ sticking coefficient was found to decrease from unity at a beam energy of 0.8 kcal/mol to 0.5 for a beam energy of 5.4 kcal/mol. The sticking coefficient generally decreases with surface temperature to a value of 0.05 at 700 K, but, for a 5.4 kcal/mol beam, it exhibits a relative minimum near 300 K. The reflection coefficient of NH₃, for an angle of incidence of 49°, increases with temperature and incident beam energy in agreement with the sticking measurements. The TPD peak positions, sticking and reflection data are all well reproduced by a three-state model based on simple kinetics. The model assumes that NH₃ initially traps in a molecular state and that dissociation occurs by thermal activation into an intermediate state. At no temperature is the sticking probability enhanced by increasing the kinetic energy of the incident molecules and there is no evidence for a direct dissociation channel which has a translational energy barrier less than 5.4 kcal/mol.     

Crystal field surface orbital-bond energy bond order (CFSO-BEBO) calculations of adsorption: II. Carbon monoxide,oxygen and carbon dioxide on platinum (111) and oxygen on nickel (111)

The Crystal Field Surface Orbital-Bond Energy Bond Order (CFSO-BEBO) model of chemisorption is applied to the interaction of carbon monoxide, oxygen and carbon dioxide with a (111) platinum surface; and the interaction of oxygen with a (111) nickel surface. No activation energy for molecular adsorption of carbon monoxide on platinum is predicted; however a large activation energy for dissociative chemisorption is calculated. The molecular state has a binding energy of approximately 28 kcal/mole, and vibrational stretching frequencies of 1935 and 1975 cm^?1 are calculated by combining the CFSO-BEBO model with Badger's Rule. The adsorption of oxygen on (111) platinum and (111) nickel are predicted to be different in the following respects: (1) There is an activation energy of 2.1–4.5 kcal/mole on platinum, whereas adsorption on nickel is unactivated; and (2) The dissociative heat of chemisorption on platinum is 58–68 kcal/mole, whereas on nickel it is substantially larger, 112–116 kcal/mole. The adsorption of carbon dioxide on (111) platinum is predicted to be not only highly activated but also endothermic. All of the calculated results are essentially in quantitative agreement with available experimental data.     

Generalized multi-resolution analyses and a construction procedure for all wavelet sets in ℝn

An abstract formulation of generalized multiresolution analyses is presented, and those GMRAs that come from multiwavelets are characterized. As an application of this abstract formulation, a constructive procedure is developed, which produces all wavelet sets in ⁿ relative to an integral expansive matrix.     

Esca studies of polyurethanes: blood platelet activation in relation to surface composition

Segmented polyurethanes (SPU) were synthesized with polyethylene oxide (PEO), polypropylene oxide, or polytetramethylene oxide as the “soft segment,” from the respective polyether diols, of which molecular weight varied from 600 to 2000. The “hard segment” was created from ethylene diamine and tolylene diisocyanate or 4,4′-diphenylmethane diisocyanate. Platelet activation was assessed using columns packed with beads coated with each of the SPU by solutions from which the solvent was subsequently evaporated. Citrated whole human blood was passed through the columns and the platelet count in aliquots leaving the columns was compared with the platelet count in blood that had not contacted the column surface. By this method the fraction of platelets retained in the column averaged for several donors, ρ, was determined. In parallel experiments, SPU surfaces formed under identical conditions by evaporation of solvent were examined by X-ray electron spectroscopy for carbon, oxygen, and nitrogen content of the surface. The carbon C_1s spectra proved to be particularly useful, when analyzed for the components with peaks respectively at 286 eV (carbon not bonded to an ether oxygen) and at 288 eV (carbon bonded to an ether oxygen). The platelet retention index ρ was found to increase nearly linearly with the ratio of the 286-eV intensity to the 288-eV intensity, and extrapolated to nearly zero for zero value of the intensity ratio, which would correspond to amorphous PEO, suggesting that if a surface were only amorphous PEO it would be remarkably inactive toward platelets. In contrast, nitrogen spectra show no systematic relationship with ρ.     

A LEED investigation of the chemisorption of nitrous oxide on a tungsten (100) surface

Nitrous oxide has been adsorbed on the tungsten (100) surface at 295 and 500°K. Flash desorption experiments show two binding states of nitrogen which desorb at 1005 and 1275°K. When both nitrogen states and the oxygen state from the dissociated nitrous oxide molecule are on the surface, there are no new LEED features. When the 1005°K nitrogen state is desorbed, a (4 × 1) LEED pattern occurs. When all the nitrogen is desorbed, a (2 × 1) oxide pattern remains. The oxygen is desorbed as a volatile tungsten oxide. A model of the sorbate surface which is consistent with the facts currently available on the nitrous oxide-tungsten system is described.