Tautomerism and isomerism of guanine–cytosine DNA base pair: Ab initio and density functional theory approaches

The relative stabilities of guanine–cytosine (G–C) DNA base pairs are theoretically investigated with a focus on the keto–enol tautomerism as well as on the cis–trans enol isomerism by using both ab initio method and the density functional theory. The G–C pairs of the keto tautomers turn out to be in general more stable than those of the enol tautomers, 9H-guanine pair, 9KK (see the notation below), being the most stable one. The stability of the G–C pairs appears to be affected by various factors including the keto–enol tautomerization, cis–trans enol isomerization, and the steric hindrance between two tautomeric pairs. Although the B3LYP calculations tend to underestimate the binding energies, in addition, it is shown that the binding energy of G–C pairs interacting through hydrogen bonds can be reasonably calculated with the DFT method, contrary to the base pairs with stacked configurations.     

Elemental analysis in liver,ascites, and blood of tumor-bearing mice

The contents of twelve minor and trace elements in liver, ascites, and blood of sarcoma-180 tumor-bearing mice were determined by instrumental neutron activation analysis at various tumor growing stages. Biological samples were irradiated by reactor neutrons and subsequently subject to direct analysis using a high-resolution HPGe -spectrometer. A statistically significant difference for the concentration of Na and Cl in all tumor samples relative to those in a normal control group is found. During the tumor growing period, concentration of Mg, K, Fe, Se, Rb, Cu, Zn, and Mn in liver and ascites of tumored mice vary with respect to the tumor size. Each elemental concentration and its biological function in the tumored mice is discussed and possible correlation to humans is analyzed.     

水溶性钯－膦配合物催化1－己烯加氢反应研究

研究了水溶性钯－膦配合物ＰｄＣｌ２（ＴＰＰＴＳ）２催化１－己烯加氢反应，考察了两相催化体系中添加表面活性剂ＣＴＡＢ，膦配体ＴＰＰＴＳ，以及溶液ｐＨ值等对反应的影响，证明了１－己烯加氢反应中有一诱导期．反应中涉及两种催化活性物种．一种是由ＰｄＣｌ２（ＴＰＰＴＳ）２还原生成的低氧化态催化物种，它在一定的ＣＴＡＢ浓度下，可以保持相当的稳定性．另一种是被ＴＰＰＴＳ或Ｈ２还原形成的钯黑．根据ＰｄＣｌ２和ＴＰＰＴＳ反应过程的３１ＰＮＭＲ研究，对ＰｄＣｌ２（ＴＰＰＴＳ）２分子中Ｐｄ被还原和ＴＰＰＴＳ被氧化提出了解释     

SYNTHESIS OF NEW HIGH MOLECULAR WEIGHT AND REACTIVE LADDERLIKE POLYSILSESQUIOXANES*

Ladderlike polychloropropylsilsesquioxane (CP-T) was first synthesized by "stepwise coupling polymerization".The molecular weight of CP-T is as high as 1.7×10~5. It is a tough, elastic reactive ladderlike polymer and has good heat-resistant and adhesive properties. CP-T can further react with many nucleophilic reagents to generate new ladderlike reactivepolysilsesquioxanes, which can be used as potential precursors in the synthesis of functional ladderlike polymers.     

Characterization of yeast deoxyhypusine synthase: PKC-dependent phosphorylation in vitro and functional domain identification

The biosynthesis of hypusine [Nepsilon-(4-amino-2-hydroxybutyl)-lysine] occurs in the eIF-5A precursor protein through two step posttranslational modification involving deoxyhypusine synthase which catalyzes transfer of the butylamine moiety of spermidine to the epsilon-amino group of a designated lysine residue and subsequent hydroxylation of this intermediate. This enzyme is exclusively required for cell viability and growth of yeast (Park, M.H. et al., J. Biol. Chem. 273: 1677-1683, 1998). In an effort to understand structure-function relationship of deoxyhypusine synthase, posttranslational modification(s) of the enzyme by protein kinases were carried out for a possible cellular modulation of this enzyme. And also twelve deletion mutants were constructed, expressed in E. coli system, and enzyme activities were examined. The results showed that deoxyhypusine synthase was phosphorylated by PKC in vitro but not by p56lck and p60c-src. Treatment with PMA specifically increased the relative phosphorylation of the enzyme supporting PKC was involved. Phosphoamino acid analysis of this enzyme revealed that deoxyhypusine synthase is mostly phosphorylated on serine residue and weakly on threonine. Removal of Met1-Glu10 (deltaMet1-Glu10) residues from amino terminal showed no effect on the catalytic activity but further deletion (deltaMet1-Ser20) caused loss of enzyme activity. The enzyme with internal deletion, deltaGln197-Asn212 (residues not present in the human enzyme) was found to be inactive. Removal of 5 residues from carboxyl terminal, deltaLys383-Asn387, retained only slight activity. These results suggested that deoxyhypusine synthase is substrate for PKC dependent phosphorylation and requires most of the polypeptide chains for enzyme activity except the first 15 residues of N-terminal despite of N- and C-terminal residues of the enzyme consist of variable regions.     

Environmental monitoring of134Cs in beach sand using a coincident spectrometer

Environmental samples of beach sand taken at northern Taiwan have been monitored using a coincident gamma-ray spectrometer. The concentration of¹³⁴Cs, under intense interference from natural and other artificial radioactivity, is determined as low as 0.2 Bq/kg dry. The accumulation of trace levels of¹³⁴Cs originates from the discharge of nuclear power plants nearby.     

The synthesis and biological characterization of a ceramide library

A facile synthesis of a combinatorial ceramide library and their activities in the NF-kappaB pathway and in apoptosis induction/prevention were demonstrated. A novel NF-kappaB activating molecule was discovered among ceramide containing beta-galactose, and the structural requirements of ceramides for apoptosis induction was elucidated.     

Molecular mass determination of polyamic acid ionic salt by size-exclusion chromatography

A methodology was developed for the determination of molecular weight aveages of polyamic acid ionic salt (PAS) by size-exclusion chromatography (SEC). Polystyrene standards were used for calibration and THF-DMF 1:1 by volume containing 0.06 M LiBr and 0.06 M H3PO4 was used as the mobile phase. The proposed methodology was found to be reproducible.