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81.
The discovery of selective cyclooxygenase-2 (COX-2) inhibitors represents a major achievement of the efforts over the past few decades to develop therapeutic treatments for inflammation. To gain insights into designing new COX-2-selective inhibitors, we address the energetic and structural basis for the selective inhibition of COX isozymes by means of a combined computational protocol involving docking experiment, force field design for the heme prothetic group, and free energy perturbation (FEP) simulation. We consider both COX-2- and COX-1-selective inhibitors taking the V523I mutant of COX-2 to be a relevant structural model for COX-1 as confirmed by a variety of experimental and theoretical evidences. For all COX-2-selective inhibitors under consideration, we find that free energies of binding become less favorable as the receptor changes from COX-2 to COX-1, due to the weakening and/or loss of hydrogen bond and hydrophobic interactions that stabilize the inhibitors in the COX-2 active site. On the other hand, COX-1-selective oxicam inhibitors gain extra stabilization energy with the change of residue 523 from valine to isoleucine because of the formations of new hydrogen bonds in the enzyme-inhibitor complexes. The utility of the combined computational approach, as a valuable tool for in silico screening of COX-2-selective inhibitors, is further exemplified by identifying the physicochemical origins of the enantiospecific selective inhibition of COX-2 by -substituted indomethacin ethanolamide inhibitors. 相似文献
82.
83.
Rongbiao?WangEmail author Herbert?Schmiedel Bernd-Reiner?Paulke 《Colloid and polymer science》2004,283(1):91-97
Isothermal titration calorimetry (ITC) measurements of the mixture of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) with negatively charged, hairy copolymer latices (poly-(2,3-epoxypropylmethacrylate-co-methacrylic acid) in different ratio) at high water excess indicate a monomer adsorption mechanism of CTAB by the polymer particles. The number of adsorbed CTAB molecules at saturation corresponds approximately to the number of negative elementary charges bound at the surface of the latices. The mixing enthalpy is the sum of demicellization and sorption enthalpies. At 25 °C for CTAB the demicellization enthalpy amounts to 10 kJ/mol, whereas the adsorption enthalpy varies from –7 kJ/mol (surface charge density of the latices
=–0.37 C/m2) to +3 kJ/mol (=–0.085 C/m2). The hydrodynamic radius
RH of the latex particles upon titration of cationic detergent and salt (NaBr) decreases by about 2 nm until the onset of aggregation near the isoelectric point. Titration of nonionic or anionic detergents has much less influence on the hydrodynamic radius and produces no measurable adsorption heat. The results are consistent within a model of latex particles with extended negatively charged polymer chains interacting predominantly via Coulombic forces with detergents. 相似文献
84.
Veronica?StigssonEmail author G?ran?Kloow Ulf?Germg?rd Niclas?Andersson 《Cellulose (London, England)》2005,12(4):395-401
Controlling the reduction in molecular weight of the cellulose chains is essential in the production of carboxymethyl cellulose
(CMC). Such a reduction can be achieved by the addition of cobalt during the process of cobalt(II) ions, which act as a catalyst
for oxidative cleavage, and the influence thereof has been studied under a variety of conditions. This study has resulted
in a model that summarises the effects of the added amount of cobalt, the time for the cobalt reaction, the temperature in
the mercerisation stage of the CMC-manufacturing process and finally the effect of the temperature in the etherification stage.
It is shown that it is important for cobalt to be present during the mercerisation stage in order to achieve the desired viscosity. 相似文献
85.
Kimmo Smolander Risto J?rnstr?m Annika Sajalinna 《Fresenius' Journal of Analytical Chemistry》1989,335(4):392-394
Summary The matric effect of boric acid was investigated in the determination of iron in the primary circuit coolant water of nuclear power plants by furnace atomic absorption spectrometry. The effect of boric acid was of particular interest. The method was applied during refuelling and maintenance periods and the results were used to interpret the chemical changes in the water.
Einfluß von Borsäure auf die Bestimmung von Eisen in Reaktorkühlwasser durch GF-AAS相似文献
86.
87.
Sevim?Hamamci Veysel?T.?YilmazEmail author William?T.?A.?Harrison 《Structural chemistry》2005,16(4):379-383
The first silver(I) complex of saccharinate (sac) with pyridine (py), [Ag(sac)(py)]n has been synthesized and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffractometry. The complex crystallizes in chiral, trigonal space group P3121 (No. 152) with unit cell parameters of a = 11.2605(2) Å, c = 17.3300(4) Å, V = 1903.02(6) Å3 and Z = 6. [Ag(sac)(py)]n contains monomeric [Ag(sac)(py)] units linked into infinite helices by way of Ag⋅sAg interactions [d(Ag⋅sAg) = 2.909(2) and 2.985(1) Å]. The distorted square-planar environment of Ag is completed by an N-bonded sac [Ag—N = 2.084(2) Å] and a py molecule [Ag—N = 2.116(2) Å]. The Nsac—Ag—Npy angle is 173.85(10)∘. The one-dimensional chains are crosslinked by C—H⋅sO interactions involving the carbonyl and sulfonyl O atoms of sac and aromatic-ring hydrogen atoms of both sac and py. The thermal stability of the title complex was investigated using thermogravimetry and differential thermal analysis in a static atmosphere of air. The first decomposition stage between 90 and 160∘C corresponds to removal of the py molecule in a single stage, while the degradation of the sac moiety occurs at two stages in the temperature range 370–515∘C, giving an end product of metallic Ag. 相似文献
88.
An enzymatic assay for glucose based on the use of the fluorescent probe for hydrogen peroxide, europium(III) tetracycline (EuTc), is described. The weakly fluorescent EuTc and enzymatically generated H2O2 form a strongly fluorescent complex (EuTc–H2O2) whose fluorescence decay profile is significantly different. Since the decay time of EuTc–H2O2 is in the microseconds time domain, fluorescence can be detected in the time-resolved mode, thus enabling substantial reduction of background fluorescence. The scheme represents the first H2O2-based time-resolved fluorescence assay for glucose not requiring the presence of a peroxidase. The time-resolved assay (with a delay time of 60 s and using endpoint detection) enables glucose to be determined at levels as low as 2.2 mol L–1, with a dynamic range of 2.2–100 mol L–1. The method also was adapted to a kinetic assay in order to cover higher glucose levels (mmol L–1 range). The latter was validated by analyzing spiked serum samples and gave a good linear relationship for glucose levels from 2.5 to 55.5 mmol L–1. Noteworthy features of the assay include easy accessibility of the probe, large Stokes shift, a line-like fluorescence peaking at 616 nm, stability towards oxygen, a working pH of approximately 7, and its suitability for both kinetic and endpoint determination. 相似文献
89.
The apparent molar volumes, V,2, of glycine, L-alanine, DL--amino-n-butyric acid, L-valine, and L-leucine have been determined in aqueous 0.25, 0.75, 1.0, and 1.5 mol-dm–3 tetraethylammonium bromide (TEAB) solutions by density measurements at 298.15 K. These data have been used to calculate the infinite dilution apparent molar volumes, V2,m, for the amino acids in aqueous tetraethylammonium bromide and the standard partial molar volumes of transfer (tr V2,m) of the amino acids from water to the aqueous salt solutions. The linear correlation of V2,m for a homologous series of amino acids has been utilized to calculate the contribution of the charged end groups (NH3+, COO–), CH2 group, and other alkyl chains of the amino acids to V2,m. The results of the standard partial molar volumes of transfer from water to aqueous tetraethylammonium bromide have been interpreted in terms of ion–ion, ion–polar, and hydrophobic–hydrophobic group interactions. The volume of transfer data suggest that ion–ion or ion–hydrophilic interactions are predominant in the case of glycine and alanine, and hydrophobic–hydrophobic group interactions are predominant in the case of DL--amino butyric acid, L-valine, and L-leucine. 相似文献
90.
Kalagouda?B.?GudasiEmail author Ramesh?S.?Vadavi Rashmi?V.?Shenoy Manjula?S.?Patil Siddappa?A.?Patil Munirathinam?Nethaji 《Transition Metal Chemistry》2005,30(6):661-668
The synthesis of cobalt(II), nickel(II) and zinc(II) complexes of 2-pyridine-2-yl-3(pyridine-2-carboxylideneamino)-1,2-dihydroquinazolin-4(3H)-one is described. The ligand and metal complexes were characterized by elemental analysis, conductivity measurements, spectral (u.v.–vis., i.r., 1D n.m.r., 2D hetcor and mass) and thermal studies. The cobalt(II) complex crystallizes as pink crystals in the monoclinic crystal system, space group P21/n with a = 10.066(6) Å, b = 15.929(9) Å, c = 12.624(7) Å, α = 90.00(9)°, β = 110.850 (8)°, γ = 90.00, V = 1891.5 (18) Å3 and Z = 4. The geometry around the cobalt atom is distorted trigonal bipyramidal with τ = 0.83 [structural parameter, τ = (β − α)/60; where α and β are the two basal angles in a five coordinate complex]. 相似文献