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991.
A new compound (5R, 10R)-3,8-dihydroxy-5,10-diethoxy-5,10-dihydrochromeno[5,4,3-cde]chromene monohydrate was obtained from 3,4-dihydroxybenzaldehyde in aerobic basic aqueous ethanol solution in the presence
of manganese chloride and triethylamine and crystallized in orthorhombic P212121 space group (denoted as 1). When 1 was recrystallized from aqueous methanol, it was transformed to another crystal (2) with the same composition but in P21/n space group. The drastic difference in the extensive hydrogen bond network makes 1 a 3D and 2 a 2D infinite supramolecular structure, respectively. 相似文献
992.
pH-sensitive polyelectrolyte complex gel microspheres composed of chitosan/sodium tripolyphosphate/dextran sulfate: swelling kinetics and drug delivery properties 总被引:10,自引:0,他引:10
Porous chitosan (CS) polyelectrolyte complex (PEC) hydrogel microspheres were prepared via either wet phase-inversion or ionotropic crosslinking with sodium tripolyphosphate (Na+ - TPP) and dextran sulfate (DS). The resulting microspheres were characterized using scanning electron microscopy (SEM) and elemental analysis (EA). The controlled release behavior of ibuprofen (IBU) from these microspheres was investigated. The PEC microspheres were about 700-950 microm in diameter with large pores and open porous structure. The CS/TPP/DS microspheres resisted hydrolysis in strong acid and biodegradation in enzymatic surroundings. The swelling kinetics for CS microspheres was close to Fickian diffusion, whereas those for CS/TPP and CS/TPP/DS were non-Fickian. Furthermore, the equilibrium water content (EWC) and water diffusion coefficient (D) increased with the pH of the media. The release profiles of IBU from CS/TPP/DS microspheres were slow in simulated gastric fluid (SGF, pH 1.4) over 3 h, but nearly all of the initial drug content was released in simulated intestinal fluid (SIF, pH 6.8) within 6 h after changing media. Overall the results demonstrated that CS/TPP/DS microspheres could successfully deliver a hydrophobic drug to the intestine without losing the drug in the stomach, and hence could be potential candidates as an orally administered drug delivery system. 相似文献
993.
5-amino-l,10-phenanthroline (5-AP), as a tautomeric heterocyclic aromatic chelating fluorophore (THACF), can sense Zn^2+ selectively by shifting emission from 495 to 564 nm upon Zn^2+ addition in ethanol. The ratiometric fluorescent sensing behavior has been correlated to the tautomerization of 5-AP affected by solvents and metal chelation. The strategy using THACF as ratiometric fluorescent sensor for Zn^2+ not only simplifies the synthetic procedure but also gives a promising alternative for Zn^2+ ratiometric fluorescent sensor design. 相似文献
994.
995.
A RP-HPLC method for determining fourteen components (gallic acid, chebulic acid, 1,6-di-O-galloyl-D-glucose, punicalagin, 3,4,6-tri-O-galloyl-D-glucose, casuarinin, chebulanin, corilagin, neochebulinic acid, terchebulin, ellagic acid, chebulagic acid, chebulinic acid, and 1,2,3,4,6-penta-O-galloyl-D-glucose) in the fruit of Terminalia chebula Retz. is described. The separation was achieved within 80 min using a binary gradient with mobile phases consisting of a pH 2.7 phosphoric acid solution and an 80% CH3CN solution. Capillary electrophoretic analyses were also attempted, and it was found that CZE (25 mM Na2B4O7, 5 mM NaH2PO4, pH 7.0) was an efficient method for the separation of gallotannins, while an MEKC method (25 mM Na2B4O7, 5 mM NaH2PO4, 20 mM SDS, pH 7.0, and 10% acetonitrile) provided a better separation for most of the tannins examined. The HPLC and CE methods developed were both successfully applied to the assay of tannins in commercial samples of Chebulae Fructus. 相似文献
996.
钴(II)-联吡啶-α-氨基酸的热力学和动力学研究 总被引:3,自引:0,他引:3
关于联吡啶为第一配体的二元、三元配合物的热力学和动力学性质的研究,以铜(Ⅱ)作为中心离子最为多见,而以钴(Ⅱ)作为中心离子的报导较少.实验表明,过渡金属钻(Ⅱ)能与大多数的生物配体、大π共轭体系形成相当稳定的二元、三元配合物,是生物功能模拟的一个具有应用价值的中心离子·钴(Ⅱ)卟啉可以代替铁(Ⅱ)卟啉,模拟血红蛋白、肌红蛋白[1],在生物体内起到输送氧的作用.为了充分了解钴(Ⅱ)与生物配体的配伍能力、配位方式以及其配位过程的动态行为,为推动钴(Ⅱ)配合物及其生物功能的模拟研究,本文分别采用PH电位法… 相似文献
997.
采用共沉淀法开发了绿铜锌矿型1,4-丁二醇液相合成γ-丁内酯用新型催化剂,经直接还原,1,4-丁二醇转化率约100%,γ-丁内酯收率高于92%;用DSC技术选定了还原条件,运用XRD和XPS等技术优化了催化剂配方;考察了催化剂的稳定性,并获得了反应速率方程。 相似文献
998.
铜(II)-5-取代邻菲啰啉-二氧四胺大环三元体系的稳定性研究 总被引:1,自引:0,他引:1
The stability of copper (Ⅱ)-13-(2'-Hydroxy-3',5'-substituted benzyl)-1,4,8,11-tetraazacyclotetradecane-12, 14-dione(RTADO-14) binary complex compounds and of copper (Ⅱ)-5-substituted-1,10-phenanthrolines(R'TADO)-RTADO-14 ternary complex compounds was studied by means of pH titration method at 25.0±0.1 ℃ and I=0.1mol?dm-3KNO3. The formation constants of binary and ternary complexes were obtained. The structures of the binary and ternary complxes and the effects fo substituents on macrocyclic ligands and on R'Phen were also discussed. 相似文献
999.
Gold nanotubule membranes were prepared by using electroless deposition of gold within the pores and surfaces of polycarbonate track-etched membranes.And the gold nanotubule membrane was used as an electrode for determination of uric acid in urine samples for the first time.In Britton-Robinson buffer of pH 4.56,uric acid exhibited well-defined differential pulse voltammograms.And the interference between coexistent ascorbic acid and uric acid was overcome owing to the attractive ability of the gold nanotubule electrode to yield a large anodic peak difference ca.0.404 V(vs.SCE).The proposed method was then applied to the determination of uric acid in urine without any pretreatment. 相似文献
1000.
Charles Allgood Yi Lin Yee-Chung Ma Burnaby Munson 《Journal of mass spectrometry : JMS》1990,25(10):497-502
Dilute mixtures of C6H6 or C6D6 in He provide abundant [C6H6]+· or [C6D6]+· ions and small amounts of [C6H7]+ or [C6D7]+ ions as chemical ionization (CI) reagent ions. The C6H6 or C6D6 CI spectra of alkylbenzenes and alkylanilines contain predominantly M+· ions from reactions of [C6H6]+· or [C6D6]+· and small amounts of MH+ or MD+ ions from reactions of [C6H7]+ or [C6D7]+. Benzene CI spectra of aliphatic amines contain M+·, fragment ions and sample-size-dependent MH+ ions from sample ion-sample molecules reactions. The C6D6 CI spectra of substituted pyridines contain M+· and MD+ ions in different ratios depending on the substituent (which alters the ionization energy of the substituted pyridine), as well as sample-size-dependent MH+ ions from sample ion-sample molecule reactions. Two mechanisms are observed for the formation of MD+ ions: proton transfer from [C6D6]+· or charge transfer from [C6D6]+· to give M+·, followed by deuteron transfer from C6D6 to M+·. The mechanisms of reactions were established by ion cyclotron resonance (ICR) experiments. Proton transfer from [C6H6]+· or [C6D6]+· is rapid only for compounds for which proton transfer is exothermic and charge transfer is endothermic. For compounds for which both charge transfer and proton transfer are exothermic, charge transfer is the almost exclusive reaction. 相似文献