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71.
用自散焦介质观测Ce:BaTiO3晶体的自泵浦相位共轭频移 总被引:2,自引:1,他引:1
提出利用自散焦介质作为载体测量光折变晶体自泵浦相位共轭的微小频移的新方法,适宜用于区分二波耦合,四波辊频对频移的贡献,为研究光折变自泵浦相位共轭频移的产生机制提供了一种新的可能的途径。 相似文献
72.
73.
Xin Qi Sook Kyung Kim Su Jung Han Ah Young Jee Chongmok Lee Minyung Lee Sung-Jin Kim Juyoung Yoon 《Tetrahedron letters》2008,49(2):261-264
A new tripod fluorescent system was developed, which bears a triazine core for combining three different functional groups, such as fluorophore (BODIPY), ligand, and auxiliary group. This concept was confirmed by photophysical properties due to the different auxiliary subunits. 相似文献
74.
The Carr-Purcell-Meiboom-Gill (CPMG) transverse relaxation dispersion NMR experiment is a powerful means for detecting and characterizing conformational exchange. This experiment reports the exchange of chemical shifts and therefore can monitor all chemical exchange phenomena, not only intramolecular conformational exchange. Here, we report a CPMG transverse relaxation dispersion study for the monomer-dimer equilibrium of the GB1 point mutant, Ala-34-Phe (GB1(A34F)). This variant exists predominantly as a side-by-side dimer at high concentration (>1 mM). We demonstrate that the dispersion experiment is exceptionally valuable for studying association equilibria since it is extremely sensitive to the minor population in the equilibrium. Twenty-eight individual amide sites in the GB1(A34F) dimer protein were monitored via a 2D (15)N-(1)H HSQC spectroscopy, and all relaxation-derived data are consistent with predominantly an exchange process between dimer and monomer species. 相似文献
75.
Company A Jee JE Ribas X Lopez-Valbuena JM Gómez L Corbella M Llobet A Mahía J Benet-Buchholz J Costas M van Eldik R 《Inorganic chemistry》2007,46(22):9098-9110
A study of the reversible CO2 fixation by a series of macrocyclic dicopper complexes is described. The dicopper macrocyclic complexes [Cu2(OH)2(Me2p)](CF3SO3)2, 1(CF3SO3)2, and [Cu2(mu-OH)2(Me2m)](CF3SO3)2, 2(CF3SO3)2, (Scheme 1) containing terminally bound and bridging hydroxide ligands, respectively, promote reversible inter- and intramolecular CO2 fixation that results in the formation of the carbonate complexes [{Cu2(Me2p)}2(mu-CO3)2](CF3SO3)4, 4(CF3SO3)4, and [Cu2(mu-CO3)(Me2m)](CF3SO3)2, 5(CF3SO3)2. Under a N2 atmosphere the complexes evolve CO2 and revert to the starting hydroxo complexes 1(CF3SO3)2 and 2(CF3SO3)2, a reaction the rate of which linearly depends on [H2O]. In the presence of water, attempts to crystallize 5(CF3SO3)2 afford [{Cu2(Me2m)(H2O)}2(mu-CO3)2](CF3SO3)4, 6(CF3SO3)4, which appears to rapidly convert to 5(CF3SO3)2 in acetonitrile solution. [Cu2(OH)2(H3m)]2+, 7, which contains a larger macrocyclic ligand, irreversibly reacts with atmospheric CO2 to generate cagelike [{Cu2(H3m)}2(mu-CO3)2](ClO4)4, 8(ClO4)4. However, addition of 1 equiv of HClO4 per Cu generates [Cu2(H3m)(CH3CN)4]4+ (3), and subsequent addition of Et3N under air reassembles 8. The carbonate complexes 4(CF3SO3)4, 5(CF3SO3)2, 6(CF3SO3)4, and 8(ClO4)4 have been characterized in the solid state by X-ray crystallography. This analysis reveals that 4(CF3SO3)4, 6(CF3SO3)4, and 8(ClO4)4 consist of self-assembled molecular boxes containing two macrocyclic dicopper complexes, bridged by CO32- ligands. The bridging mode of the carbonate ligand is anti-anti-mu-eta1:eta1 in 4(CF3SO3)4, anti-anti-mu-eta2:eta1 in 6(CF3SO3)4 and anti-anti-mu-eta2:eta2 in 5(CF3SO3)2 and 8(ClO4)4. Magnetic susceptibility measurements on 4(CF3SO3)4, 6(CF3SO3)4, and 8(ClO4)4 indicate that the carbonate ligands mediate antiferromagnetic coupling between each pair of bridged CuII ions (J = -23.1, -108.3, and -163.4 cm-1, respectively, H = -JS1S2). Detailed kinetic analyses of the reaction between carbon dioxide and the macrocyclic complexes 1(CF3SO3)2 and 2(CF3SO3)2 suggest that it is actually hydrogen carbonate formed in aqueous solution on dissolving CO2 that is responsible for the observed formation of the different carbonate complexes controlled by the binding mode of the hydroxy ligands. This study shows that CO2 fixation can be used as an on/off switch for the reversible self-assembly of supramolecular structures based on macrocyclic dicopper complexes. 相似文献
76.
The polyanionic, water-soluble, and non-micro-oxo dimer-forming iron porphyrin (hexadecasodium iron 54,104,154,204-tetra-t-butyl-52,56,102,106,152,156,202,206-octakis[2,2-bis(carboxylato)ethyl]-5,10,15,20-tetraphenylporphyrin), (P16-)FeIII, with 16 negatively charged meso substituents on the porphyrin was synthesized and fully characterized by UV-vis and 1H NMR spectroscopy. A single pKa1 value of 9.90 +/- 0.01 was determined for the deprotonation of coordinated water in the six-coordinate (P16-)FeIII(H2O)2 and as attributed to the formation of the five-coordinate monohydroxo-ligated form, (P16-)FeIII(OH). The porphyrin complex reversibly binds NO in aqueous solution to yield the nitric oxide adduct, (P16-)FeII(NO+)(L), where L = H2O or OH-. The kinetics for the reversible binding of NO were studied as a function of pH, temperature, and pressure using the stopped-flow technique. The data for the binding of NO to the diaqua complex are consistent with the operation of a dissociative mechanism on the basis of the significantly positive values of DeltaS and DeltaV, whereas the monohydroxo complex favors an associatively activated mechanism as determined from the corresponding negative activation parameters. The rate constant, kon = 3.1 x 104 M-1 s-1 at 25 degrees C, determined for the NO binding to (P16-)FeIII(OH) at higher pH, is significantly lower than the corresponding value measured for (P16-)FeIII(H2O)2 at lower pH, namely, kon = 11.3 x 105 M-1 s-1 at 25 degrees C. This decrease in the reactivity is analogous to that reported for other diaqua- and monohydroxo-ligated ferric porphyrin complexes, and is accounted for in terms of a mechanistic changeover observed for (P16-)FeIII(H2O)2 and (P16-)FeIII(OH). The formed nitrosyl complex, (P16-)FeII(NO+)(H2O), undergoes subsequent reductive nitrosylation to produce (P16-)FeII(NO), which is catalyzed by nitrite produced during the reaction. Concentration-, pH-, temperature-, and pressure-dependent kinetic data are reported for this reaction. Data for the reversible binding of NO and the subsequent reductive nitrosylation reaction are discussed in reference to that available for other iron(III) porphyrins in terms of the influence of the porphyrin periphery. 相似文献
77.
Sacroiliitis in patients with ankylosing spondylitis: association of MR findings with disease activity 总被引:3,自引:0,他引:3
The purpose of this study was to determine whether MR findings can correlate disease activity as measured by laboratory markers in ankylosing spondylitis. MR images in 19 patients with ankylosing spondylitis were retrospectively analyzed for cartilage abnormality, periarticular erosion, synovial enhancement, and bone marrow edema. Each MR finding was correlated with laboratory inflammatory markers (erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)) and the sum of ESR + CRP. Synovial enhancement showed a significant correlation with ESR (r=0.58; p<0.01) and increased activity at bone scan (r=0.74; p<0.005), whereas there was no significant correlation with CRP. A significant correlation was found between ESR + CRP and synovial enhancement (r=0.54; p<0.05). Synovial enhancement was more common when ESR + CRP was greater than 30 (p<0.05). In conclusion, synovial enhancement at MR imaging could correlate disease activity as measured by laboratory inflammatory markers in ankylosing spondylitis. 相似文献
78.
Liu Y Jung JH Xu T Long L Lin X Yin H Yang B Zhou XF Yang X 《Natural product research》2011,25(6):648-652
Guided by the brine shrimp lethality assay, a new cyclitol derivative, sarcotride D (1), was isolated from a marine sponge Sarcotragus species. The structure was established based on NMR and MS analyses. 相似文献
79.
Here we describe the synthesis and the physicochemical and preliminary pharmaceutical assessment of a novel class of hemifluorinated dibranched derivatives: M(1)diH(x)F(y). These compounds have the remarkable ability to completely stop the Ostwald ripening commonly associated with nanoemulsions. The developed synthesis is modular and allows easy incremental structural variations in the fluorophilic (fluorous chains), lipophilic (alkyl spacer head), and hydrophilic (polar head) domains. Furthermore, the synthesis can be easily scaled up and highly pure compounds can be readily obtained through silica gel and fluoro-silica gel column chromatography, without any need to use HPLC or other time-consuming techniques. Surface properties such as micelle formation, critical aggregation concentration (CAC), and emulsion stability studies demonstrated the different behavior of the dibranched hemifluorinated surfactant M(1)diH(x)F(y) with respect to that of single-chain semifluorinated analogues M(z)F(y). Remarkably, the new polymer M(1)diH(3)F(8) drastically slowed the ripening of nanoemulsions of the commonly used fluorinated anesthetic sevoflurane over a period of more than 1 year. During this time, the nanodroplet size did not increase to more than 400 nm. This result is very promising for inducing and maintaining general anesthesia through intravenous delivery of volatile anesthetics, eliminating the need for the use of large and costly vaporizers in the operating room. 相似文献
80.
Jee J Jeon H Hwang D Sommer P Park Z Cechetto J Dorval T 《Combinatorial chemistry & high throughput screening》2012,15(8):656-665
Embryonic stem cells, due to their self-renewal and pluripotency properties, can be used to repair damaged tissues and as an unlimited source of differentiated cells. Although stem cells represent an important opportunity for cell based therapy and small molecules screening (in the context of drug or target discovery) many drawbacks are still preventing their widespread use. One of the most significant limitations is related to the complexity, as well as the reliability, of current protocols driving stem cells into any homogeneously differentiated cellular population. In this respect there is a strong demand for molecular agents promoting differentiation and thereby enabling robust, efficient and safe production of differentiated cells. In order to identify novel molecules that enhance early stages of differentiation, we developed an image based high content screening (HCS) approach using human embryonic stem cells (hESC). In our approach, we took advantage of custom image mining software specifically adapted for the selection of stem cell differentiation agents and the rejection of false positive hits. As a proof of concept ~3500 small molecules originating from commercial libraries were screened and a number of molecules of interests were identified. These molecules show stem cell differentiation properties comparable to the phenotypic signature obtained with the reference compound retinoic acid. 相似文献