排序方式: 共有73条查询结果,搜索用时 31 毫秒
51.
Bhattarai KM del Amo V Magro G Sisson AL Joos JB Charmant JP Kantacha A Davis AP 《Chemical communications (Cambridge, England)》2006,(22):2335-2337
Cholic acid has been converted into triamine with the all-trans polycyclic allocholanoyl skeleton and co-directed, axial amino groups; the potential of this system as a scaffold is illustrated by conversion to a preorganised anion receptor. 相似文献
52.
Singh TD Sumitra Ch Bag GC Devi MI Singh NR 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(1):154-159
Pr(III) and Nd(III) are hard acceptors in HSAB (hard and soft acid base) sense and hence are known to exhibit practically a little affinity towards electrons. At the same time these metal ions show strong preference for oxygen donor chelating ligands. The ligands chosen for this study are structurally related diols, viz. butane-1,4, butene-1,4 and butyne-1,4-diols which form identical seven membered chelate ring by coordinating to metals in a bidentate manner through oxygen on 1 and 4 positions of the diol molecules. Complexation of these diols with Pr(III) and Nd(III) was carried out in DMF, CH3OH, CH3CN and their equimolar binary mixtures using comparative absorption spectrophotometry of 4f-4f transitions. The variation of oscillator strengths (P) of different 4f-4f bands as well as the magnitude and variation of Judd-Ofelt electric dipole intensity parameters (T lambda, lambda = 2, 4, 6) was discussed. They correlate the interaction between the metal 4f-orbitals of Pr(III) and Nd(III) with the pi-electron densities of the double and triple bonds present in butene-1,4 and butyne-1,4-diols, respectively. The value of empirical intensity parameter [T lambda(complex)/T lambda (aquo)] was calculated and its plot against oscillator strength (P) is drawn. 相似文献
53.
Precise measurements on the electrical conductivity of sodium polystyrenesulfonate in acetonitrile–water-mixed solvent media
containing 20 and 40 vol.% of acetonitrile at 308.15, 313.15, and 318.15 K are reported. The mobility of the polyelectrolyte
solute was found to be influenced by the polyelectrolyte concentration, the relative permittivity of the medium, and the temperature.
The Manning counterion condensation theory for salt-free polyelectrolyte solution failed to describe the experimental results.
The data have, therefore, been analyzed on the basis of a new model for semidilute polyelectrolyte conductivity which takes
into account the scaling arguments to obtain the fractions of uncondensed counterions which were found to depend on the polyelectrolyte
concentration. The effects of the temperature and the relative permittivity of the medium on the equivalent conductivity as
well as on the fraction of uncondensed counterions have also been discussed. 相似文献
54.
Young-Hee Lee Govinda Bhattarai Santosh Aryal Min-Ho Lee Eun-Chung Jhee Ho-Keun Yi 《Applied Surface Science》2010,256(20):5882-5887
This study examined the gelatin nano gold (GnG) composite for surface modification of titanium in addition to insure biocompatibility on dental implants or biomaterials. The GnG composite was constructed by gelatin and hydrogen tetrachloroaurate in presence of reducing agent, sodium borohydrate (NabH4). The GnG composite was confirmed by UV-VIS spectroscopy and transmission electron microscopy (TEM). A dipping method was used to modify the titanium surface by GnG composite. Surface was characterized by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The MC-3T3 E1 cell viability was assessed by trypan blue and the expression of proteins to biocompatibility were analyzed by Western blotting. The GnG composite showed well dispersed character, the strong absorption at 530 nm, roughness, regular crystal and clear C, Na, Cl, P, and Au signals onto titanium. Further, this composite allowed MC-3T3 E1 growth and viability compared to gelatin and pure titanium. It induced ERK activation and the expression of cell adherent molecules, FAK and SPARC, and growth factor, VEGF. However, GnG decreased the level of SAPK/JNK. This shows that GnG composite coated titanium surfaces have a good biocompatibility for osteoblast growth and attachment than in intact by simple and versatile dipping method. Furthermore, it offers good communication between cell and implant surfaces by regulating cell signaling and adherent molecules, which are useful to enhance the biocompatibility of titanium surfaces. 相似文献
55.
S. Bobby Singh H.B. Sharma H.N.K. Sarma Sumitra Phanjoubam 《Physica B: Condensed Matter》2008,403(17):2678-2683
Ferroelectric barium strontium titanate (Ba0.7Sr0.3TiO3)(BST) thin films have been prepared from barium 2-ethylhexanoate [Ba[CH3(CH2)3CH(C2H5)CO2]2], strontium 2-ethylhexanoate [Sr[CH3(CH2)3CH(C2H5)CO2]2] and titanium(IV) isopropoxide [TiOCH(CH3)2]4 precursors using a modified sol-gel technique. The precursor except [TiOCH(CH3)2]4 were synthesized in the laboratory. Transparent and crack-free films were fabricated on pre-cleaned quartz substrates by spin coating. The structural and optical properties of films annealed at different temperatures have been investigated. The as-fired films were found to be amorphous that crystallized to the tetragonal phase after annealing at 550 °C for 1 h in air. The lattice constants “a” and “c” were found to be 3.974 A and 3.990 A, respectively. The grain sizes of the films annealed at 450, 500 and 550 °C were found to be 30.8, 36.0 and 39.8 nm respectively. The amorphous film showed very high transparency (∼95%), which decreases slightly after crystallization (∼90%). The band gap and refractive index of the amorphous and crystalline films were estimated. The optical dispersion data are also analyzed in the light of the single oscillator model and are discussed. 相似文献
56.
A poly(ethylene glycol) (PEG)-based new amphiphilic block copolymer bearing the poly(p-dioxanone-co-l-lactide) (PPDO/PLLA) hydrophobic moieties was prepared. Depending on the copolymer composition and molecular weights, solubility of the polymeric samples in water was varied. Its diluted aqueous solution properties were studied by viscometry, dye solubilization, 1H-NMR and dynamic light scattering. 1,6-Diphenyl-1,3,5-hexatriene solubilization and 1H-NMR spectra carried out in CDCl3 and D2O were used to prove the existence of hydrophobic domains as the core of micelle. Average particle size of 60-165 nm with low polydispersity and lower negative zeta (ξ) potential of −3 to −14 mV were observed on the aqueous copolymer dispersion. 相似文献
57.
Ab initio calculation at the MP2/aug-cc-pVTZ level has been performed on the π-hole based N…Si tetrel bonded complexes between substituted pyridines and H2SiO. The primary aim of the study is to find out the effect of substitution on the strength and nature of this tetrel bond, and its similarity/difference with the N…C tetrel bond. Correlation between the strength of the N…Si bond and several molecular properties of the Lewis acid (H2SiO) and base (pyridines) are explored. The properties of the tetrel bond are analyzed using AIM, NBO, and symmetry-adapted perturbation theory calculations. The complexes are characterized with short N…Si intermolecular distances and high binding energies ranging between −142.72 and −115.37 kJ/mol. The high value of deformation energy indicates significant geometrical distortion of the monomer units. The AIM and NBO analysis reveal significant coordinate covalent bond character of the N⋅⋅⋅Si π-hole bond. Sharp differences are also noticed in the orbital interactions present in the N⋅⋅⋅Si and N⋅⋅⋅C tetrel bonds. 相似文献
58.
Sumitra Ch Singh TD Indira Devi M Singh NR 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,66(4-5):1333-1339
Comparative absorption and spectral analysis of 4f-4f transitions of Pr(III) and glutathione reduced (GSH) complex in presence and absence of Zn(II) is carried out in different aquated organic solvents of CH3OH, CH3CN, DMF and dioxane and their equimolar mixtures at different pH (3.0, 4.0, 5.0 and 6.0). The values of experimentally calculated oscillator strengths (P) and computed values of Judd-Ofelt electric dipole intensity parameters, Tlambda (lambda=2, 4, 6) are discussed for different 4f-4f transitions in different experimental conditions. The changes in the values of oscillator strengths (P) and Tlambda parameters suggest the specific correlation between relative intensities, ligand structures and nature of interaction of Pr(III) with GSH in the presence and absence of Zn(II). 相似文献
59.
Ramachandran S Fontanille P Pandey A Larroche C 《Applied biochemistry and biotechnology》2008,151(2-3):413-423
Aspergillus niger spores were used as catalyst in the bioconversion of glucose to gluconic acid. Spores produced by solid-state fermentation were treated with 15 different terpenes including monoterpenes and monoterpenoids to permeabilize and inhibit spore germination. It was found that spore membrane permeability is significantly increased by treatment with terpenoids when compared to monoterpenes. Best results were obtained with citral and isonovalal. Studies were carried out to optimize spores concentration (10(7)-10(10) spores/mL), terpene concentrations in the bioconversion medium and time of exposure (1-18 h) needed for permeabilization of spores. Fed-batch production of gluconate was done in a bioreactor with the best conditions [10(9) spores/mL of freeze-thawed spores treated with citral (3% v/v) for 5 h] followed by sequential additions of glucose powder and pH-regulated with a solution containing 2 mol/L of either NaOH or KOH. Bioconversion performance of the spore enzyme was compared with the commercial glucose oxidase at 50, 60, and 70 degrees C. Results showed that the spore enzyme was comparatively stable at 60 degrees C. It was also found that the spores could be reutilized for more than 14 cycles with almost similar reaction rate. Similar biocatalytic activity was rendered by spores even after its storage of 1 year at -20 degrees C. This study provided an experimental evidence of the significant catalytic role played by A. niger spore in bioconversion of glucose to gluconic acid with high yield and stability, giving protection to glucose oxidase. 相似文献
60.