Androstane alkaloids from musk of Moschus moschiferus

Two androstane alkaloids were isolated from the musk of Moschus moschiferus. The structures were elucidated to be 3alpha-ureido-androst-4-en-17-one (1) and 3alpha-ureido-androst-4-en-17beta-ol (2) by two-dimensional NMR analysis (HMQC, 1H-1H COSY, HMBC, and NOESY).     

Effect of surface composition on the adsorption of photosystem I onto alkanethiolate self-assembled monolayers on gold

We have used self-assembled monolayers (SAMs) prepared from omega-terminated alkanethiols on gold to generate model surfaces and examine the effect of surface composition on the adsorption of Photosystem I (PSI), stabilized in aqueous solution by Triton X-100. Triton-stabilized PSI adsorbs to high-energy surfaces prepared from HO- and HO2C-terminated alkanethiols but does not adsorb to low-energy surfaces. The inhibition of PSI adsorption at low-energy surfaces is consistent with the presence of a layer of Triton X-100 that adsorbs atop the hydrophobic SAM and presents a protein-resistant poly(ethylene glycol) (PEG) surface. While the presence of the PEG surface prevents the adsorption of PSI, the displacement of the inhibiting layer of Triton X-100 by dodecanol, a more active surfactant, greatly enhances the adsorption of PSI. This inhibiting effect by Triton X-100 can be extended to other protein systems such as bovine serum albumin.     

Triterpenoids from Psidium guajava leaves

Three pentacyclic triterpenoids including one new guajavanoic acid (2) and two known obtusinin (1) and goreishic acid I (3) have been isolated from the leaves of Psidium guajava. The new constituent 2 has been characterized as 2alpha-hydroxy-3beta-p-E-coumaroyloxyurs-12, 18-dien-28-oic acid through 1H-NMR and 13C-NMR (broad band and DEPT). This is the first report of isolation of compound 1 and 3 from the genus Psidium.     

Contrasting linear and quadratic nonlinear optical behavior of dipolar pyridinium chromophores with 4-(dimethylamino)phenyl or ruthenium(II) ammine electron donor groups

In this article, we contrast the optical properties of dipolar chromophores having 4-(dimethylamino)phenyl electron donor (D) and pyridinium acceptor (A) groups with those of closely related cations having pyridyl-coordinated Ru(II) donors. A range of physical data, including that from Stark (electroabsorption) spectroscopy, permits unprecedented quantitative comparisons, most notably regarding the effects of extension of bridging polyene chains. The purely organic compounds display normal optical properties in that their intense, visible pi --> pi intramolecular charge-transfer (ICT) bands red-shift as the number of E-ethylene units (n) increases from 1 to 3 and the associated static first hyperpolarizabilities beta(0) increase steadily with n. The related Ru(II) complexes show intense, visible d --> pi metal-to-ligand charge-transfer (MLCT) bands, which are found to lower energy when compared with the ICT transitions of the corresponding organics. Abnormally, these MLCT bands blue-shift as n increases, and beta(0) maximizes at n = 2. Time-dependent density-functional theory and finite field calculations verify these empirical trends for both types of compound, which can be rationalized as arising from the differing orbital structures of the chromophores and the associated degrees of D-A electronic coupling.     

Analysis of 1,2(2,3)- and 1,3-positional isomers of diacylglycerols from vegetable oils by reversed-phase high-performance liquid chromatography

Separation of 1,2(2,3)- and 1,3-positional isomers of diacylglycerols (DAG) from vegetable oils by reversed-phase high-performance liquid chromatography (RP-HPLC) is investigated. The method is based on isocratic elution using 100% acetonitrile and UV detection at 205 nm. The following elution order of DAG molecular species is identified: 1,3-dilinolein < 1,2-dilinolein < 1,3-dimyristin < 1-oleoyl-3-linoleoyl-glycerol < 1,2-dimyristoyl-rac-glycerol < 1(2)-oleoyl-2(3)-linoleoyl-glycerol < 1-linolenoyl-3-stearoyl-glycerol < 1(2)-linolenoyl-2(3)-stearoyl-glycerol < 1,3-diolein < 1-palmitoyl-3-oleoyl-glycerol < 1,2-dioleoyl-sn-glycerol < 1(2)-palmitoyl-2(3)-oleoyl-glycerol < 1-linoleoyl-3-stearoyl-glycerol < 1,3-dipalmitin < 1(2)-linoleoyl-2(3)-stearoyl-glycerol < 1-oleoyl-3-stearoyl-glycerol < 1,2-dipalmitoyl-rac-glycerol < 1-palmitoyl-3-stearoyl-sn-glycerol < 1,3-distearin < 1,2-distearoyl-rac-glycerol. Linearity is observed over three orders of magnitude. Limits of detection and quantitation range 0.2-0.7 microg/mL for 1,3-dilinolein to 0.6-1.9 microg/mL for 1,2-dioleoyl-sn-glycerol, respectively. Precision and accuracy of the method are also demonstrated. The method is developed to separate mixtures of DAG molecular species produced from edible oils.     

Effect of N-glycinylmaleamic acid on microstructural characteristics and solubilization properties of sodium dodecyl sulfate micellar assemblies

The cosurfactant activity of N-glycinylmaleamic acid (NGMA) in sodium dodecyl sulfate (SDS) micelles has been demonstrated. The complementary techniques of electron spin resonance (ESR) and fluorescence spectroscopy have been used to draw information on hydration index (H), microviscosity (eta), and aggregation number (N) of micellar assemblies. The estimate of the critical micelle concentration of SDS in the presence of NGMA suggests a synergistic effect of NGMA. The enhanced solubilization of butyl propionate in the presence of NGMA in SDS micelles is explained on the basis of availability of larger interfacial area calculated from a simple spherical geometric model, combined with a low hydrophilicity index as estimated from ESR. Thus, addition of NGMA contributes to an increase of about 50% in ratio of area of polar shell (AP)/volume of hydration (Vh) ratio. The decrease in H accompanied by a decrease in eta with the incorporation of butyl propionate probably arises from solubilization of a butyl component inside the core with the adsorption of propionate ester on the interface.     

Effect of simulated microgravity on aged pea seed vigour and related physiological properties

We used simulated microgravity to treat aged pea seeds, in order to observe its effect on seed vigour and related physiological properties. The result shows that microgravity obviously promotes the germination rate, vitality index, germination index, and keeps the activity of protective enzyme, with conductivity and the content of MDA decreased. These effects gradually disappeared for a certain period after the microgravity administration.     

用小平顶炭极提高光谱定量分析的灵敏度——溶液干渣法

溶液光谱分析的各种方法近年有了较全面的总结。用溶液干渣法进行测定具有最高的绝对灵敏度,其常用技术有下列三种:(1)石墨火花法、(2)铜极火花法、(3)石墨交流电弧干渣法。这三法虽各有利弊,但均用6毫米直径电极,对于试液消耗量     

多孔离子交换树脂内的扩散

本文评论了多孔离子交换树脂内的离子扩散过程研究的近期发展,着重讨论了二级分散扩散模型的应用;利用该模型处理和分析实验结果,获得了某些重要的结论。