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921.
Jenny?ZevallosEmail author Alejandro?Toro-Labbé Otilia?Mó Manuel?Yá?ez 《Structural chemistry》2005,16(3):295-303
High level ab initio and density functional theory calculations have been carried out to investigate the relative stability of the different conformers of hyponitrous acid and its mono- and dithio-derivatives. Geometries and vibrational frequencies were obtained at the B3LYP/6-311+G(d,p) level and final energies through B3LYP/6-311++G(3df,2pd) single point calculations. The reliability of this theoretical scheme has been assessed by comparing these DFT results with those obtained at the G3 level of theory, for some suitable cases. The cis conformers of hyponitrous acid and its mono- and dithio-derivatives are systematically more stable than the
trans ones because in the cis conformation a dative interaction between the nitrogen-lone pairs and the σNX^* antibonding orbital is significantly favored. Quite interestingly, in general, the conformers presenting an intramolecular hydrogen bond (IHB) are not the global minima of the corresponding potential energy surfaces and only for hyponitrous acid the conformer with a OH ⋅s O IHB is slightly more stable than the cis conformer without IHB. The low stability of the tautomers with IHB is closely related with another weak intramolecular interaction which involves the lone-pairs of the chalcogen atoms and the πNN* antibondig orbital, and which is significantly perturbed when the IHB is formed. 相似文献
922.
Photodynamic therapy removes unwanted or harmful cells by overproduction of reactive oxygen species (ROS). Fractionated light delivery in photodynamic therapy may enhance the photodynamic effect in tumor areas with insufficient blood supply by enabling the reoxygenation of the treated area. This study addresses the outcome of fractionated irradiation in an in vitro photodynamic treatment (PDT) system, where deoxygenation can be neglected. Our results show that fractionated irradiation with light/dark intervals of 45/60 s decreases ROS production and cytotoxicity of PDT. This effect can be reversed by addition of 1,3-bis-(2-chlorethyl)-1-nitrosurea (BCNU), an inhibitor of the glutathione reductase. We suggest that the dark intervals during irradiation allow the glutathione reductase to regenerate reduced glutathione (GSH), thereby rendering cells less susceptible to ROS produced by PDT compared with continuous irradiation. Our results could be of particular clinical importance for photodynamic therapy applied to well-oxygenated tumors. 相似文献
923.
Javier Revilla Abdelhamid Ela?&#x;ssari Pascal Carriere Christian Pichot 《Journal of colloid and interface science》1996,180(2):405
The adsorption of bovine serum albumin (BSA) onto polystyrene latexes bearing various amounts of sugar moieties has been investigated as a function of pH and ionic strength and the results were compared to those for bare polystyrene latexes having negative surface charges. The functionalized latexes were produced by seeded copolymerization of (0.3 μm) liposaccharidic monomer onto polystyrene particles obtained by soap-free emulsion polymerization of styrene using potassium persulfate as initiator. At first, the electrophoretic mobility behavior of the various latexes was examined as a function of pH: a significant decrease was observed in the case of saccharide-containing latex particles compared to the bare particles. The adsorption of BSA onto these latexes exhibited a reduced amount of adsorbed BSA for those latex particles bearing saccharide groups. This adsorbed amount depends on the yield of saccharidic monomer incorporated onto the surfaces of the latex particles. 相似文献
924.
Unsal E Durdu A Elmas B Tuncel M Tuncel A 《Analytical and bioanalytical chemistry》2005,383(6):930-937
In this study, a new affinity high-performance liquid chromatography (HPLC) stationary phase suitable for protein separation
was synthesized. In the first stage of the synthesis, uniform porous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate), poly(HEMA-co-EDM), beads 6.2 μm in size were obtained. Homogeneous distribution of hydroxyl groups in the bead interior was confirmed
by confocal laser scanning microscopy. The plain poly(HEMA-co-EDM) particles gave very low non-specific protein adsorption with albumin. The selected dye ligand Cibacron blue F3G-A (CB
F3G-A) was covalently linked onto the beads via hydroxyl groups. In the batch experiments, albumin adsorption up to 60 mg
BSA/g particles was obtained with the CB F3G-A carrying poly(HEMA-co-EDM) beads. The affinity-HPLC of selected proteins (albumin and lysozyme) was investigated in a 25 mm×4.0-mm inner diameter
column packed with CB F3G-A carrying beads and both proteins were successfully resolved. By a single injection, 200 μg of
protein was loaded and quantitatively eluted from the column. The protein recovery increased with increasing flow rate and
salt concentration of the elution buffer and decreased with the increasing protein feed concentration. During the albumin
elution, theoretical plate numbers up to 30,000 plates/m were achieved by increasing the salt concentration. 相似文献
925.
Light-stable micelles with azo dyes were prepared by micelle formation of a nonamphiphilic diblock copolymer containing azobenzene and UV absorbent at ca. 1 mol% as the unit ratios. The nonamphiphilic block copolymer consists of two different kinds of random copolymer blocks: poly[4-(phenylazophenoxymethyl)styrene-co-vinylphenol] (P(AS-co-VPh)) and poly[4-(2-hydroxybenzophenoxymethyl)styrene-co-styrene] (P(HBS-co-St)). This random block copolymer, P(AS-co-VPh)-b-P(HBS-co-St) formed the micelles in the presence of 1,4-butanediamine (BDA) through hydrogen bond cross-linking between the VPh units via BDA. The micelles had the azobenzene moieties at the cores and the UV absorbents at the coronas. The micelles showed a small color difference in color fading experiments, in comparison with the unimers and with micelles having no UV absorbent at the coronas. It is significant that the diblock copolymer forms the micelles and has the UV absorbents at the coronas to suppress the color fading. Furthermore, the chain length of ,-diamines had no effect on the hydrodynamic radius of the micelles, but affected the aggregation number and the cmc. 相似文献
926.
(1S,2R,3S)-, (1R,2R,3S)- and (1S,2R,3R)-4-amino-1,2,3-trihydroxybutylphosphonic acids were synthesised. The synthetic strategy involved preparation of the respective 4-azido-2,3-O-isopropylidene-l-threose or -d-erythrose, addition of dialkyl phosphites, separation of C-1 epimeric O,O-dibenzyl phosphonates, the reduction of azides and the removal of the protecting groups. The (2R,3S) and (2R,3R) configurations in the final products were secured by employing diethyl l-tartrate and d-isoascorbic acid as starting materials. The stereochemical course of the addition to the carbonyl groups in 4-azido-2,3-O-isopropylidene-l-threose or -d-erythrose followed that established earlier for 2,3-O-isopropylidene-d-glyceraldehyde and similar (3:1-4:1) diastereoselectivities were achieved. 相似文献
927.
Shuhua?HanEmail author Wanguo?Hou Jun?Xu Zhengmin?Li 《Colloid and polymer science》2004,282(11):1286-1291
Hollow spherical mesoporous silica was synthesized by using sodium silicate as a precursor and a low concentration of cetyltrimethylammonium bromide (CTAB) (0.154 mol dm–3). The resulting hollow spherical particles were characterized with scanning electron microcopy (SEM), small-angle X-ray diffraction (SXRD), transmission electron microscopy (TEM), and N2 gas adsorption and desorption techniques. The results showed that regular spherical mesoporous silica could be obtained only if the molar ratio of propanol to CTAB was in the range of approximately 8:1–9:1. The spherical particles were hollow (inside), and the shell consisted of smaller particles with a pore structure of hexagonal symmetry. With an increase of the molar ratio of propanol to CTAB, the distance (a value) between centers of two adjacent pores increased, and the pore structure of mesoporous silica became less ordered. N2 adsorption–desorption curves revealed type IV isotherms and H1 hysteresis loops; with an increase of the molar ratio of propanol to CTAB, the pore size with Barrett–Joyner–Halenda (BJH) diameter of the most probable distribution decreased, but the half peak width of the pore size distribution peak increased 相似文献
928.
Application of L-Cysteine-Capped ZnS Nanoparticles in the Determination of Nucleic Acids Using the Resonance Light Scattering Method 总被引:2,自引:0,他引:2
Yongxin?LiEmail author Jinlong?Chen Shujuan?Zhuo Yuqin?Wu Changqin?Zhu Lun?Wang 《Mikrochimica acta》2004,146(1):13-19
Nanometer-sized L-cysteine-capped ZnS particles were synthesized by a colloidal aqueous method. The functionalized nanoparticles are water-soluble and suitable for biological applications. In Tris-HCl buffer solution, nucleic acids combine with cysteine-capped nano-ZnS particles by intermolecular forces to form larger nanoparticles. There are two resonance light scattering peaks at 304.5nm and 373.8nm, respectively. The enhanced RLS is related to the concentration of nucleic acids in the range of 0.04 to 1.2µgmL–1 for calf thymus DNA and 0.2 to 1.0µgmL–1 for fish sperm DNA. The detection limits (3) are 19ngmL–1 for calf thymus DNA and 23ngmL–1 for fish sperm DNA, respectively. Four synthetic samples were analyzed satisfactorily. 相似文献
929.
Continuous chemiluminescence determination of formaldehyde in air based on Trautz-Schorigin reaction 总被引:1,自引:0,他引:1
A new continuous method for the determination of formaldehyde in air is described. A cylindrical wet effluent diffusion denuder is used for the collection of formaldehyde from air into a thin film of absorption liquid (distilled-deionized water). Formaldehyde in the denuder concentrate is on-line detected employing a chemiluminescence flow method based on a reaction of formaldehyde and gallic acid with hydrogen peroxide in an alkaline solution. The collection efficiency of formaldehyde is quantitative at the air flow rate of 0.5 L min−1 (absorption liquid flow rate of 336 μL min−1). The limit of detection (S/N = 3) is 0.60 μg m−3 HCHO (0.49 ppb). The calibration graph is linear up to 300 μg m−3 HCHO (244 ppb). The relative standard deviations of chemiluminescence method for 1 × 10−6 and 5 × 10−6 M HCHO are 2.87% and 1.49%, respectively. Acetaldehyde interferes negligible, other compounds do not interfere. The method was employed for formaldehyde measurement in ambient air. The comparison measurement illustrates the good agreement of results obtained by proposed method with those obtained by reference fluorimetric method. 相似文献
930.
Hideo?AkisadaEmail author Masakatu?Ishihara Mitiko?Nishi Masaaki?Higake Seiki?Ishimaru Junko?Nishida 《Colloid and polymer science》2003,281(10):993-997
The partial molal volumes of two series of homologous surfactants, n-alkylammonium decanesulfonates and a, ?-alkanediammonium nonanesulfonates, were measured below and above their CMC in aqueous solution. Their counterions were n-alkylammonium and a, ?-alkanediammonium. The relationship between the partial molal volume and the chain length of the counterion below the CMC had an inflection point. The relationship between them, above the CMC, was almost linear. In the case of the alkylammonium salts, the values of the volume change of micellization were almost the same when the chain length of the counterions was shorter than the butyl, and increased with an increase in the chain length when it was longer than the propyl. In the case of the alkanediammonium salts, the volume change of micellization showed a small decrease with the chain length when it was shorter than octane, and was very large for the nonane ammonium salt. The large positive increase in the volume change with the increase in the chain length of the counterion can be explained by the hydrophobic interaction between the alkyl chain of the counterion and the hydrophobic core of the micelle. 相似文献