Solvent effects on infrared spectra of methyl 4-hydroxybenzoate in pure organic solvents and in ethanol/CCl4 binary solvents

Infrared spectroscopy studies of methyl 4-hydroxybenzoate (MHB) in 17 different organic solvents and in ethanol/CCl4 binary solvent were undertaken to investigate the solvent-solute interactions. The frequencies of carbonyl stretching vibration nu(C=O) of MHB in single solvents were correlated with the solvent acceptor number (AN) and the linear solvation energy relationships (LSER). The assignments of the two bands of nu(C=O) of MHB in alcohols and the single one of that in non-alcoholic solvents were discussed. The shifts of nu(C=O) of MHB in ethanol/CCl4 binary solvents showed that several kinds of solute-solvent hydrogen bonding interactions coexisted in the mixture solvents, with a change in the mole fraction of ethanol in the binary solvents.     

Thermally responsive polymeric micellar nanoparticles self-assembled from cholesteryl end-capped random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide): synthesis, temperature-sensitivity, and morphologies

Cholesteryl end-capped thermally responsive amphiphilic polymers with two different hydrophobic/hydrophilic chain-length ratios were synthesized from the hydroxyl-terminated random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) and cholesteryl chloroformate. The hydroxyl-terminated precursor polymers with narrow molecular weight distributions were synthesized by free-radical polymerization using 2-hydroxyethanethiol as a chain-transfer agent. The aqueous solutions of the cholesteryl end-capped copolymers exhibited reversible phase transitions at temperatures slightly above human body temperature, with the lower critical solution temperature values being 37.7 and 38.2 degrees C, respectively. The critical micelle concentration values of the two cholesteryl end-capped polymers were 9 and 25 mg/L, respectively. Polymeric micellar nanoparticles were prepared from the amphiphilic polymers using a dialysis method as well as a direct dissolution method. Transmission electron microscope studies showed that the micellar nanoparticles existed in different morphologies, including spherical, star-like, and cuboid shapes. Pyrene as a model hydrophobic compound could be readily encapsulated in these polymeric nanoparticles, at loading levels of 1.0 and 0.8 mg/g for the two cholesteryl end-capped polymers, respectively. The temperature sensitivity and unusual morphology of these novel polymeric nanoparticles would make an interesting drug delivery system.     

Optical properties of ZnO and ZnO:In nanorods assembled by sol-gel method

Self-assembled zinc oxide (ZnO) and indium-doping zinc oxide (ZnO:In) nanorod thin films were synthesized on quartz substrates without catalyst in aqueous solution by sol-gel method. The samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), Raman-scattering spectroscopy, room-temperature photoluminescence (PL) spectra, and temperature-dependent PL spectra measurements. XRD and Raman spectra illustrated that there were no single In2O3 phase in ZnO lattice after indium doping. The PL spectra of ZnO showed a strong UV emission band located at 394 nm and a very weak visible emission associated with deep-level defects. Indium incorporation induced the shift of optical band gap, quenching of the near-band-edge photoluminescence and enhanced LO mode multiphonon resonant Raman scattering in ZnO crystals at different temperatures. Abnormal temperature dependence of UV emission integrated intensity of ZnO and ZnO:In samples is observed. The local state emission peak of ZnO:In samples at 3.37 eV is observed in low-temperature PL spectra. The near-band-edge emission peak at room temperature was a mixture of excitons and impurity-related transitions for both of two samples.     

Subsolidus phase relations and crystal structure of compounds in the PrOx-CaO-CuO system

The subsolidus phase relations of the PrO_x-CaO-CuO pseudo-ternary system sintered at 950-1000°C have been investigated by X-ray powder diffraction. In this system, there exist one compound Ca₁₀Pr₄Cu₂₄O₄₁, one Ca₂Pr₂Cu₅O₁₀-based solid solution, seven three-phase regions and two two-phase regions. The crystal structures of Ca₁₀Pr₄Cu₂₄O₄₁ and Ca₂Pr₂Cu₅O₁₀-based solid solution have been determined. Compound Ca₁₀Pr₄Cu₂₄O₄₁ crystallizes in an orthorhombic cell with space group D_2h²⁰−Cccm, Z=4. Its lattice parameters are a=11.278(2) Å, b=12.448(3) Å and c=27.486(8) Å. The crystal structure of Ca₂Pr₂Cu₅O₁₀-based solid solution is an incommensurate phase based on the orthorhombic NaCuO₂ type subcell. The lattice parameters of the subcell of the Ca_2.4Pr_1.6Cu₅O₁₀ are a₀=2.8246(7) Å, b₀=6.3693(5) Å, c₀=10.679(1) Å, and those of the orthorhombic superstructure are with a=5a₀, b=b₀, c=5c₀. The Ca_2.4Pr_1.6Cu₅O₁₀ structure can also be determined by using a monoclinic supercell with space group C_2h⁵−P2₁/c, Z=4, a=5a₀, b=b₀, and β=104.79(1)° or 136.60(1)°, V=5a₀b₀c₀.     

Application of Liquid Crystalline NMR Solvents to a Mixture of Ketones

A series of dilute liquid crystalline solvents are used to study the effect of slight anisotropy caused by partial alignment on chemical shift and residual dipolar coupling (RDC) in small molecules. The residual dipolar couplings between protons in solutes are found to be almost independent of the local environment. It is also found that the chemical shift does not change over the concentration range observed. A linear relationship between residual dipolar coupling and liquid crystal concentration is observed at relatively low concentrations, but is severely violated at high concentrations.     

互贯磺酸树脂的离子交换平衡性质

本文研究凝胶型互贯磺酸树脂的热力学性质。测定了一系列第一网和第二网重量比及交联度不同的互贯磺酸树脂对多种离子交换反应的△G~0、△H~0和△S~0值。归纳了二重网重量比和交联度对△H~0、△S~0值变化影响规律。提出了用积分持水量来表达互贯磺酸树脂的平衡常数与持水量关系,并探讨了这类树脂在离子交换色谱等方面应用的可能性。     

Laser-assisted electron capture by a fast proton from a hydrogen atom

The first Born approximation is used to study the laser-assisted electron capture by a fast proton from a hydrogen atom. The laser modification on differential cross section peaks sharply in the forward direction. With the impact energy increasing, the change in integral cross section becomes notable. The more intense the laser, the greater the cross section is; the lower the frequency, the greater the cross section.     

Preparation and Characterization of a Sol-Gel Prepared Ferroelectric Sandwich Structure

A novel silicon-based PbTiO₃/Pb(Zr,Ti)O₃/PbTiO₃ (PT/PZT/PT) sandwich structure has been prepared using a sol-gel method. The annealing temperature is greatly reduced compared with those structures without PT layers. Capacitance-voltage (C-V), leakage current-voltage (I-V), polarization-field (P-E), dielectric-frequency response and polarization fatigue of the sandwich structure are examined. The relative dielectric constant, the coercive field and the remanent polarization of the PZT films are measured to be about 900, 18 kV/cm and 16 C/cm² respectively. The current density is less than 5 × 10^–9 A/cm² below 200 kV/cm. The dielectric constant of the structure remains constant at low frequency, and decreases to some degree at high frequency. The retained polarization does not change significantly after 8 × 10⁹ read/write cycles. The PZT films are proved to have very good dielectric and ferroelectric properties. The new PT/PZT/PT sandwich structure can be valuable for memory devices and other applications.     

TiO2 sol-gel derived amperometric biosensor for H2O2 on the electropolymerized phenazine methosulfate modified electrode

A novel hydrogen peroxide biosensor was developed based on the immobilization of horseradish peroxidase (HRP) in a TiO(2) sol-gel matrix on an electropolymerized phenazine methosulfate (PMS) modified electrode surface. Such membranes are of interest due to their high surface area, biological compatibility, and ease of fabrication. HRP entrapped in the TiO(2) matix was stable and retained its activity to a large extent. Cyclic voltammetry and amperometric measurements were employed to demonstrate the feasibility of electron transfer between immobilized HRP and the glassy carbon electrode via electropolymerized PMS. The influence of various experimental parameters such as operating potential, pH, temperature, and stability was investigated for optimum analytical performance. The biosensor provided a wide linear calibration range from 4.0x10(-6) M to 1.0x10(-3) M, with a detection limit of 8.0x10(-7) M at a signal-to-noise ratio of 3. The sensor retained 80% of its original activity after two months of operation.     

Studies on the inactivation of bovine liver enoyl-CoA hydratase by (methylenecyclopropyl)formyl-CoA: elucidation of the inactivation mechanism and identification of cysteine-114 as the entrapped nucleophile

The inhibitory properties of (methylenecyclopropyl)formyl-CoA (MCPF-CoA), a metabolite derived from a natural amino acid, (methylenecyclopropyl)glycine, against bovine liver enoyl-CoA hydratase (ECH) were characterized. We have previously demonstrated that MCPF-CoA specifically targets ECHs, which catalyze the reversible hydration of alpha,beta-unsaturated enoyl-CoA substrates to the corresponding beta-hydroxyacyl-CoA products. Here, we synthesized (R)- and (S)-diastereomers of MCPF-CoA to examine the stereoselectivity of this inactivation. Both compounds were shown to be competent inhibitors for bovine liver ECH with nearly identical second-order inactivation rate constants (k(inact)/K(I)) and partition ratios (k(cat)/k(inact)), indicating that the inactivation is nonstereospecific with respect to ring cleavage. The inhibitor, upon incubation with bovine liver ECH, labels a tryptic peptide, ALGGGXEL, near the active site of the protein, where X is the amino acid that is covalently modified. Cloning and sequence analysis of bovine liver ECH gene revealed the identity of the amino acid residue entrapped by MCPF-CoA as Cys-114 (mature sequence numbering). On the basis of gHMQC (gradient heteronuclear multiple quantum coherence) analysis with [3-(13)C]-labeled MCPF-CoA, the ring cleavage is most likely induced by the nucleophilic attack at the terminal carbon of the exomethylene group (C(2)'). We propose a plausible inactivation mechanism that involves relief of ring strain and is consistent with examples found in the literature. In addition, these studies provide important clues for future design of more efficient and selective inhibitors to control and/or regulate fatty acid metabolism.