Enantioselective total synthesis of (+)-gigantecin: exploiting the asymmetric glycolate aldol reaction

The enantioselective synthesis of the potent, selective, cytotoxic, annonaceous acetogenin, (+)-gigantecin, has been completed. An asymmetric glycolate aldol serves to establish the stereocenters at C13,14 and at C21,22. A Carreira asymmetric acetylide addition is used to establish the C17 stereocenter.     

Oxidative reactivity of S-nitrosoglutathione with Hantzsch 1,4-dihydropyridine

[formula: see text] S-Nitrosoglutathione oxidized 4-substituted Hantzsch 1,4-dihydropyridines in CH3CN/H2O or CH3CN/phosphate aqueous buffer solution to give aromatic products in various yields.     

Survival paths for reaction dynamics in fluctuating environments

We study rate processes in general Gaussian fluctuating environments using a path integral formalism. We derive a variational equation for the dominant survival path when the fluctuations relax exponentially or according to a stretched exponential law. In the case of a slowly varying barrier, the equilibrium regression approximation which is used by Frauenfelder and coworkers emerges. In this approximation, the survival path follows the ordinary law of relaxation to equilibrium. If the rate coefficients vary rapidly with environmental variables, however, the dominant survival paths exhibit more complex behaviour. Many phenomena analogous to geometrical optics occur. These include reflection off of rapid variations in rate constant, as well as refraction, giving paths very different from the equilibrium relaxation properties. A model with a piece-wise linear rate exhibits the basic phenomena, and the survival path equation is exactly solved for the general stretched exponential relaxing environment.     

A NEW ONE-STEP REDUCTIVE N-ALKYLATION OF AMINO ACIDS AND THEIR ESTERS

The reductive alkylation of amine with carbonyl compounds usingsodium hydrogen telluride has been investigated in recent years.Application of this method to the synthesis of N-alkyl derivativesof biologically important amino acids and their esters is described.     

Synthesis of a novel 18β-glycyrrhetinic acid derivative

A novel compound, biotinylated 18β-glycyrrhetinic acid (BGA), was synthesized. It is a compound of 18β-glycyrrhetinic acid linked with biotin. Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 266–267, May–June, 2006. An erratum to this article is available at .     

Investigations on adsorption potentiometry-part VIII. Determination of ultratrace copper in food by derivative adsorption chronopotentiometry

An electroanalytical method, based on derivative chronopotentiometry of the copper complex with 4-[(4-diethylamino-2-hydroxyphenyl) azo]-5-hydroxy-naphthalene-2,7-disulphonic acid (Beryllon III) accumulated on the surface of a hanging mercury drop electrode, for determining trace copper in food has been developed. The dependence of the peak height of reduction of the copper complex on the preconcentration time and preconcentration potential are discussed. Optimum experimental conditions include 0.01 M HOAc, 0.01M NaOAc, 1.0 x 10(-6) Beryllon III and a preconcentration potential of 0.10 V (vs. SCE). Under these conditions the detection limit and the linear range are 4 x 10(-11)M and 6 x 10(-11) -4 x 10(-7)M, respectively. The method was applied to samples of digested rice.     

Dye-sensitized solar cells based on composite solid polymer electrolytes

The ionic conductivity of polymer electrolytes and their interfacial contact with dye-attached TiO2 particles were enhanced markedly by the addition of amorphous oligomer into polymer electrolytes, resulting in very high overall energy conversion efficiency.     

Surface-initiated growth of poly d(A-T) by Taq DNA polymerase

In this paper, we report surface-initiated d(A-T) polymerization by Taq DNA polymerase as a method for constructing DNA-tethered surfaces using an enzyme. The enzymatic polymerization was conducted successfully via two steps: tethering of oligo d(A-T)s onto the surface presenting carboxylic acids by amide coupling and surface-initiated polymerization using Taq DNA polymerase. In this enzymatic polymerization process, the design and construction of carboxylic acid-presenting surfaces were found to be an important factor: DNA growth did not occur on the gold surface coated only with the self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (MHDA), but effectively proceeded on the surfaces presenting mixed SAMs of MHDA and 1-pentadecanethiol. The coupling of oligo d(A-T)s and the subsequent DNA polymerization reaction were characterized by polarized infrared external reflectance spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy.     

K对Mn—Co—O的结构及氧化活性的影响

利用XRD,TPD,TFD-MS及催化氧化反应等实验技术,研究了K对Mn-Co-O的结构及氧化活性的影响。XRD结果表明,Mn-Co-O系已形成反尖晶石型的MnCo_2O_4结构;K-Mn-Co-O系中除MnCo_2O_4型结构外,还有新相KMnO_2存在。根据O_2的TPD-MS及吡啶的TPD结果,Mn-Co-O中添加适量的K能提高供氧活性和增加供氧数目,但酸中心数目减少,强度降低。K对Mn-Co—O催化剂氧化活性的影响随反应物分子结构的不同而异,对乙酸乙脂、苯甲酰氯等极性有机物的完全氧化反应,K能提高氧化活性,但对苯、正己烷等非极性有机物的完全氧化反应,K使其活性降低。