Catalytic generation of nitric oxide from S-nitrosothiols using organoselenium species and development of amperometric S-nitrosothiol sensors.

Novel nitric oxide (NO) generating polymeric materials possessing organoselenium (RSe) catalysts have been developed with the goal of improving the biocompatibility of blood-contacting surfaces in biomedical devices. Low-molecular-weight diselenides were covalently linked to model polymeric materials, e.g., cellulose filter paper and polyethylenimine. Such RSe-derivatized polymers were shown to generate NO from S-nitrosothiols (RSNOs) in the presence of thiol reducing agents (e.g., glutathione). The likely involvement of both immobilized selenol/selenolate and diselenide species for NO liberation from RSNOs is suggested in the proposed catalytic cycle. The new RSe-polymers clearly exhibit the ability to generate NO from RSNO species even after prolonged contact with fresh animal plasma. Such NO generating capability could render RSe-containing polymeric materials more thromboresistant when in contact with flowing blood containing endogenous RSNOs, owing to NO's activity to inhibit platelet adhesion and activation. Efforts were also undertaken to utilize the new immobilized RSe catalysts to detect RSNO species. To apply a planar-type amperometric NO(g) sensor for directly detecting RSNOs in biological samples (e.g., fresh blood), the NO selectivity was quantitatively examined over both ammonia and nitrite, and compared with other types of amperometric NO sensors. It was found that the NO selectivity coefficient of the planar-type NO sensor can be significantly enhanced up to a thousand fold by treating the porous gas-permeable membrane with a Teflon AFRTM solution. Finally, novel electrochemical devices for the direct detection of RSNO species were developed by modifying the selectivity-improved NO sensor with thin polymeric layers containing immobilized RSe- or copper-based catalysts. Such polymeric layers are capable of decomposing RSNOs to generate NO(g) at the distal tip of the NO sensor. Under optimized conditions, these RSNO sensors were shown to reversibly and quantitatively detect various RSNO species in test solutions down to 0.1 muM concentration. Basic performance parameters (e.g., limit of detection and lifetime, etc.) and factors influencing sensor sensitivity were identified for both the RSe- and copper-based RSNO sensors. The new sensors were shown to be useful in assessing the NO-generating ability of fresh blood samples by effectively detecting the total level of reactive RSNO species present in such samples.Ph.D.Analytical chemistryPolymer chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126375/2/3253230.pd

Rapid Hydrolysis of Organophosphates Induced by U(IV) Nanoparticles: A Kinetic and Mechanistic Study using Spectroscopic Analysis

The heterogeneous interactions of colloidal U particles with organophosphates, leading to the formation of U-phosphate minerals, can retard the migration of U in contaminated sites. Here, we studied the hydrolytic mechanism of p-nitrophenyl phosphate (NPP) on the surfaces of tetravalent uranium nanoparticles (U(IV)NPs), resulting in the formation of U-phosphate precipitates. Our study shows that the reaction rate of NPP hydrolysis is significantly enhanced by U(IV)NPs through a multi-step heterogeneous reaction on the particle surfaces. The end products of the reaction were identified as U(IV)NPs-aggregates with surface-bound phosphates. Colloidal properties, such as high positive values of the zeta-potential (>+30 mV) and large surface areas of U(IV)NPs due to their unique cluster structures consisting of relatively small primary UO2(cr)-particles, are correlated with their reactivity towards hydrolysis reaction. Reaction kinetic modeling studies using spectrophotometric data indicated the presence of two distinct reaction intermediates as the surface complexes of NPP on U(IV)NPs. We suggest the involvement of the NPP inner-sphere complexes in the rate-determining step based on the results obtained by analyzing the ATR-FTIR spectra and the surface-enhanced infrared absorption of NPP bound to substrate surfaces

Electronic Effect on the Molecular Motion of Aromatic Amides: Combined Studies Using VT-NMR and Quantum Calculations

Rotational barrier energy studies to date have focused on the amide bond of aromatic compounds from a kinetic perspective using quantum calculations and nuclear magnetic resonance (NMR). These studies provide valuable information, not only regarding the basic conformational properties of amide bonds but also the molecular gear system, which has recently gained interest. Thus, we investigate the precise motion of the amide bonds of two aromatic compounds using an experimental rotational barrier energy estimation by NMR experiments and a theoretical evaluation of the density functional theory calculation. The theoretical potential energy surface scan method combined with the quadratic synchronous transit 3 method and consideration of additional functional group rotation with optimization and frequency calculations support the results of the variable temperature 1H NMR, with deviations of less than 1 kcal/mol. This detailed experimental and theoretical research strongly supports molecular gear motion in the aromatic amide system, and the difference in kinetic energy indicates that the electronic effect from the aromatic structure has a key role in conformational movements at different temperatures. Our study provides an enhanced basis for future amide structural dynamics research.© 2018 by the authors

Study of Aqueous Am(III)-Aliphatic Dicarboxylate Complexes: Coordination Mode-Dependent Optical Property and Stability Changes

© 2020 American Chemical Society. The thermodynamics of Am(III) complex formation in natural groundwater systems is one of the major topics of research in the field of high-level radioactive waste management. In this study, we investigate the absorption and luminescence properties of aqueous Am(III) complexes with a series of aliphatic dicarboxylates in order to learn the thermodynamic complexation behaviors in relation to binding geometries. The formation of Am(III) complexes with these carboxylate ligands induced distinct red shifts in the absorption spectra, which enabled chemical speciation. The formation constants determined by deconvolution of the absorption spectra showed a linear decrease for the three ligands (oxalate (Ox), malonate (Mal), and succinate (Suc)) and a mild decrease for the remaining ligands (glutarate (Glu) and adipate (Adi)). Time-resolved laser fluorescence spectroscopy (TRLFS) was used to obtain information about the aqua ligand, which indirectly indicated the bidentate bindings of these dicarboxylate ligands. A complementary attenuated total reflectance Fourier transform infrared (ATR-FTIR) study on Eu(III), which is a nonradioactive analogue of Am(III) ion, showed that the coordination modes differ depending on the alkyl chain length. Ox and Mal bind to Am(III) via side-on bidentate bindings with two carboxylate groups, resulting in the formation of stable 5- and 6-membered ring structures, respectively. On the other hand, Suc, Glu, and Adi form end-on bidentate bindings with a single carboxylate group, resulting in a 4-membered ring structure. Density functional theory calculations provided details about the bonding properties and supported the experimentally proposed coordination geometries. This study demonstrates that coordination mode-dependent changes in optical properties occur along with thermodynamic stability changes in Am(III)-dicarboxylate complexes11sciescopu

Electronic Effect on the Molecular Motion of Aromatic Amides: Combined Studies Using VT-NMR and Quantum Calculations

Rotational barrier energy studies to date have focused on the amide bond of aromatic compounds from a kinetic perspective using quantum calculations and nuclear magnetic resonance (NMR). These studies provide valuable information, not only regarding the basic conformational properties of amide bonds but also the molecular gear system, which has recently gained interest. Thus, we investigate the precise motion of the amide bonds of two aromatic compounds using an experimental rotational barrier energy estimation by NMR experiments and a theoretical evaluation of the density functional theory calculation. The theoretical potential energy surface scan method combined with the quadratic synchronous transit 3 method and consideration of additional functional group rotation with optimization and frequency calculations support the results of the variable temperature 1H NMR, with deviations of less than 1 kcal/mol. This detailed experimental and theoretical research strongly supports molecular gear motion in the aromatic amide system, and the difference in kinetic energy indicates that the electronic effect from the aromatic structure has a key role in conformational movements at different temperatures. Our study provides an enhanced basis for future amide structural dynamics research

Hindered C–N bond rotation in triazinyl dithiocarbamates

The substituent and solvent effects on the rotation around a C–N amide bond were studied for a series of triazine dibenzylcarbamodithioates. The Gibbs free energies (ΔG‡) were measured to be 16–18 kcal/mol in DMSO-d6 and toluene-d8 using variable-temperature nuclear magnetic resonance (VT-1H NMR) spectroscopy. Density functional theory (DFT) calculations reproduced the experimental observations with various substituents, as well as solvents. From the detailed analysis of the DFT results, we found that the electron donating dibenzyl amine group increased the electron population on the triazinyl ring, which decreased the rotational barrier of the C–N bond in the dithiocarbamate group attached to the triazinyl ring. The higher electron population on the triazine moiety stabilizes the partial double bond character of the S–C bond, which competitively excludes the double bond character of the C–N bond. Therefore, the rotational dynamics of the C–N bond in dithiocarbamates can be a sensitive probe to small differences in the electron population of substituents on sulfur. © 2017 Elsevier B.V

Surface Coverage- and Excitation Laser Wavelength-Dependent Luminescence Properties of U(VI) Species Adsorbed on Amorphous SiO₂

Time-resolved luminescence spectroscopy is usefully used to identify U(VI) surface species adsorbed on SiO2. However, the cause of the inconsistent luminescence lifetimes and spectral shapes reported previously remains undetermined. In this study, the U(VI) surface coverage (Γ) and excitation laser wavelength (λex) were examined as the predominant factors governing the luminescence properties of U(VI) surface species. At neutral pH, the luminescence lifetimes of U(VI) surface species increased with decreasing Γ. In the low-Γ region, where a relatively large number of adjacent surface sites are involved in the formation of multidentate surface complexes, the displacement of more number of coordinated water molecules in the equatorial plane of U(VI) results in a longer lifetime. The pH-dependent luminescence lifetimes of U(VI) surface species at the same U(VI) to SiO2 concentration ratio in the pH range of 4.5–7.5 also explain the effect of the surface binding sites on the luminescence lifetime. The time-resolved luminescence properties of the U(VI) surface species were also investigated at different excitation wavelengths. Continued irradiation of the SiO2 surface with a UV laser beam at λex = 266 nm considerably reduced the luminescence intensities of the U(VI) surface species. The higher the laser pulse energy, the greater the decrease in luminescence intensity. Laser-induced thermal desorption (LITD) of U(VI) surface species is suggested to be the origin of the decrease in luminescence intensity. LITD effects were not observed at λex = 355 and 422 nm, even at high laser pulse energies

Responses of endothelial cells to extremely slow flows

The process of blood vessel formation is accompanied by very minimal flow in the beginning, followed by increased flow rates once the vessel develops sufficiently. Many studies have been performed for endothelial cells at shear stress levels of 0.1–60 dyn∕cm2; however, little is known about the effect of extremely slow flows (shear stress levels of 10−4–10−2 dyn∕cm2) that endothelial cells may experience during early blood vessel formation where flow-sensing by indirect mass transport sensing rather than through mechanoreceptor sensing mechanisms would become more important. Here, we show that extremely low flows enhance proliferation, adherens junction protein localization, and nitric oxide secretion of endothelial cells, but do not induce actin filament reorganization. The responses of endothelial cells in different flow microenvironments need more attention because increasing evidence shows that endothelial cell behaviors at the extremely slow flow regimes cannot be linearly extrapolated from observations at faster flow rates. The devices and methods described here provide a useful platform for such studies