DNAzyme amplification of molecular beacon signal

This paper reports an improved catalytic molecular beacon. Addition of the target oligonucleotide activates a DNA enzyme (DNAzyme), which, in turn, activates multiple copies of molecular beacons (MB) and gives rise to a strong fluorescence signal. In a previous design, the activated DNAzyme could oligomerize, especially dimerize, and result in inactivation of the DNAzyme. The current design avoids this problem, upon activated by the target DNA, the DNAzyme will stay constantly active. With the improved method, a detection of 10 pM DNA has been demonstrated, which is 1000 times more sensitive than the method previously reported.     

A new approach to the synthesis of oligomers. Application to the synthesis of p-phenylene thioether wires

Oligothioethers 4-RC₆H₄(SC₆H₄-4)_nX (n = 1-3; X = Br, I; R = NO₂; X = Br; R = MeO. n = 1 and 2; X = I; R = MeO. n = 4; X = Br; R = NO₂) have been prepared through a process involving (i) palladium-catalyzed C-S coupling between 4-RC₆H₄(SC₆H₄-4)_n−1I and 4-BrC₆H₄SH to give 4-RC₆H₄(SC₆H₄-4)_nBr and (ii) copper-catalyzed replacement of Br by I.     

Synthesis of β3‐Homophenylalanine‐Derived Amino Acids and Peptides by Suzuki Coupling in Solution and on Solid Support

β‐Peptides and, to a certain extent, also mixed α,β‐peptides, are resistant to degradation by a variety of proteolytic enzymes that rapidly degrade natural α‐peptides. This is one of many characteristics that make β‐peptides an attractive class of compounds for drug‐discovery studies. On the other hand, modern organometallic reactions such as the Suzuki–Miyaura cross‐coupling have become standard tools in industry laboratories to derivatize side chains of α‐peptidic compounds to build up libraries of unnatural peptides. Combining both features, we prepared (4‐bromo)‐β³‐homophenylalanine derivatives 3 – 5 and 12 as precursors for Suzuki–Miyaura couplings. From these bromo compounds, we synthesized biaryl‐substituted β‐homoamino acids 6 , and analogs 13 and 15 of the anti‐AIDS drug Saquinavir.     

B20N20团簇的结构与稳定性

B3LYP/6-31G* density functional theory calculations have been carried out on the structure and stability of ten B20N20 clusters. It was found that two new proposed isomers with two octagons, twelve hexagons, eight squares in Cab and C2 symmetry were more stable than the isomer with sixteen hexagons and six squares in C2 symmetry which was previously deemed to the most stable by 79.5 and 13.8 kJ/mol respectively. The isomer with two decagons in S10 symmetry is much higher in energy than the most stable structure in C4h symmetry by 637.2 kJ/mol.     

Quantum-chemical analysis of the CuCl2 molecule

This paper reports on quantum-chemical analysis of the linear structure of CuCl₂ by Hartree-Fock (HF) and density functional theory (DFT) methods and also by time-dependent HF (TD HF) and DFT (TD DFT) techniques. Using pure DFT exchange correlation functional (B3LYP) yields the best agreement with the experimental electronic spectra of CuCl₂. In this case, the odd electron is delocalized over the molecule, spin density on copper being 0.27. The ground state of the CuCl₂ molecule is ²Π_g with linear geometry.     

Ab initio and DFT studies on hydrolyses of phosphorus halides

Hydrolyses of phosphorus halides, (RO)(2)POX where R = H or Me and X = F or Cl, in the gas phase and in the reaction field have been investigated theoretically with ab initio and the density functional theory (DFT). The free energy of activation in the reaction field was also estimated using the Onsager method with a correction of entropy change and basis set superposition error (BSSE). The reaction of (MeO)(2)POF proceeds through a path with bifunctional catalysis regardless of the medium, but the reaction of (MeO)(2)POCl proceeds through bifunctional and general base catalysis in the gas phase and in water, respectively. The estimated free energy barrier of 23 kcal/mol for the hydrolysis of (MeO)(2)POF is in good agreement with the experimental values of 24 kcal/mol, and relative barrier of 3 kcal/mol to the (MeO)(2)POCl is also in good agreement with the experimental values of 5 kcal/mol of diisopropyl phosphorus halides ((Pr(i)O)(2)POX, X = F and Cl).     

苯酚和草酸二甲酯在不同分子筛催化下的酯交换反应

研究了以TS－1、H－ZSM－5、Hβ和H－丝光沸石等不同分子筛为催化剂，苯酚和草酸二甲酯酯交换合成草酸二苯酯反应。通过对催化剂进行吸附吡啶的红外光谱和NH3－TPD表征，考察了不同分子筛催化剂的酸性和酸强度对草酸二苯酯合成反应的影响，确定了催化剂上的弱酸中心是催化苯酚和草酸二甲酯酯交换合成草酸二苯酯反应的活性位，且催化剂的酸性中心越多，酸量越大，催化活性越好。催化剂上的强酸中心促进了副产物苯甲醚的生成。     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.     

Nonideal mixing of 16-(9-anthroyloxy) palmitic acid and fatty acid in monolayer

The surface pressure-molecular area curve of the mixed monolayer of 16-(9-anthroyloxy) palmitic acid (16AP) and fatty acid (palmitic or stearic acids) showed various kink points which indicated the phase transitions of the monolayer. On the basis of the surface phase rule, the phase diagrams of the mixed monolayer were elucidated. The bifunctional molecule, 16AP, takes two orientations in a monolayer state, that is, horizontal and vertical ones. Horizontally oriented 16AP and vertically oriented fatty acid form a mixed monolayer but this exhibits deviation from the ideal mixing, which was interpreted in terms of the surface regular solution theory. On the other hand, the 16AP molecule in the vertical state was found to be immiscible with the fatty acid molecule in a monolayer de spite both molecules being vertical to the surface and parallel to each other. This was caused by the participation of the 9-anthroyloxy moiety of 16AP in the interaction of 16AP and fatty acid in the hydrophobic region of the monolayer.     

On a resonance energy model based on expansion in terms of acyclic moments: Exact results

Summary The new concept of the resonance energy in conjugated hydrocarbons introduced by Jiang Y, Zhang H (1989) Theor Chim Acta 75:279 is further developed. This model is based on expansion of the -electron energy in terms of moments which are also equal to numbers of closed walks in a molecular graph. The reference system is established by counting only acyclic walks, i.e. those tracing only on acyclic subgraphs. Because acyclic walks could be counted only up to some finite length, the energy of the reference system has been evaluated by truncating higher terms in the expansion. In this paper a finite expression for the energy of the same reference system is derived, thus allowing its exact evaluation. The exact values differ significantly from the truncated ones. This difference, as well as the discrepancy between exact results and chemical experience, are discussed.