Shao-Pin Wang

NMR EVIDENCE OF HYDROGEN BOND IN 1-ETHYL-3-METHYLIMIDAZOLIUM-TETRAFLUOROBORATE ROOM TEMPERATURE IONIC LIQUID

The 1-ethyl-3-methylimidazolium-tetrafluoroborate (EMI-BF4) room-temperature molten salt was investigated with NMR techniques. Diffusion coefficients measured at temperatures ranging from 300 to 360 K indicate phase-change occurred in the vicinity of 333 K, which is supported by 11B quadrupolar relaxation rates. Combined with the sizes of diffusion particles obtained form the Stokes-Einstein equation, this phase change is ascribed to that the diffusion particle is transformed from “discrete ion-pair” to “individual ion” at temperatures above 335 K due to decomposition of the EMI-BF4 ion pair. Analysis of the 13C dipole-dipole relaxation rates identifies the formation of hydrogen bond(C2H…F) between the counter ions, EMI+ and BF4 −. That the values of viscosity in EMI-BF4 are higher than those in EMI-AlCl4 at corresponding temperatures is therefore understood according to the viscosity approach employed to investigate the H-bonding in molten salts

Ditopic complexation of selenite anions or calcium cations by pirenoxine: An implication for anti-cataractogenesis

This study investigated whether and how pirenoxine (PRX) interacts with selenite or calcium ions, as these two ions have been proven respectively a factor leading to the formation of lens cataract. UV, NMR, and isothermal titration calorimetry (ITC) analysis indicated that PRX could bind maximum up to six selenite anions and the binding site preference was concentration dependent with the peripheral binding first followed by the π-π interactions with the aromatic moiety; while for calcium cation interaction the 3-carboxylate and β-ketoimine functional groups were responsible for chelating calcium ions. The results obtained by MP2/6-31+G(d) molecular orbital calculations provided theoretical evidence in support of the π-π interactions between selenite and the PRX aromatic framework, and further analysis of the binding energies with the aromatic moiety indicates that these interactions take place most likely at the benzoquinone (ring I) π-system. The calcium binding preferences with PRX were also determined based on the stabilization energy obtained by B3LYP/6-31+G(d) calculations, showing the binding preferences were site 2 > site 1 > site 3 > ring II, consistent with the experimental data. The in vitro study of the reduction of selenite or calcium ions-induced lens turbidity by PRX with ditopic recognition properties was thus demonstrated. These results may provide a rationale for using PRX as an anti-cataract agent and warrant further biological studies.

13C NMR Studies on 3-Aryl-4-Cyanosydnones (II). NMR Spectroscopy and the Chain-Conjugated Structure of Sydnones

Abstract Carbon-13 NMR spectra of 3-aryl-4-cyanosydnones have been analyzed to serve as an electronic structure probe of sydnones. 2-Dimensional INADEQUATE experiments and spin-lattice relaxation time measurements were employed to ascertain exact assignments. Deshielding of the phenyl carbon para to the sydnone ring manifests that N(3) bears positive charge. The electronic-rich property of C(4) is confirmed by shift data of cyano carbons, which have been found by far the most shielded cyano carbons in nitrile-containing compounds yet reported. Shift variations of C(5) resulting from the substitution at C(4) and supplementary oxygen-17 chemical shift data provide evidence in favor of the chain-conjugated structure.

The Comparative Studies of Binding Activity of Curcumin and Didemethylated Curcumin with Selenite: Hydrogen Bonding vs Acid-Base Interactions

In this report, the in vitro relative capabilities of curcumin (CCM) and didemethylated curcumin (DCCM) in preventing the selenite-induced crystallin aggregation were investigated by turbidity tests and isothermal titration calorimetry (ITC). DCCM showed better activity than CCM. The conformers of CCM/SeO32− and DCCM/SeO32− complexes were optimized by molecular orbital calculations. Results reveal that the selenite anion surrounded by CCM through the H-bonding between CCM and selenite, which is also observed via IR and NMR studied. For DCCM, the primary driving force is the formation of an acid-base adduct with selenite showing that the phenolic OH group of DCCM was responsible for forming major conformer of DCCM. The formation mechanisms of selenite complexes with CCM or DCCM explain why DCCM has greater activity than CCM in extenuating the toxicity of selenite as to prevent selenite-induced lens protein aggregation.