Molecular dynamics simulations of conserved Hox protein hexapeptides. I. Folding behavior in water solution

Molecular dynamics simulations of hexapeptides TFDWMK and LFPWMR; the highly conserved regions of Hox proteins Hox B1 and Hox B8, respectively, are carried out starting from extended structures to investigate their conformational space in water solution. In addition, we have studied TADWMK and TADAMK, where the aromatic residues Phenylalanine and Tryptophan were successively substituted for Alanine to investigate effects from the presence/absence of aromatic amino acids and interactions between them to folding behavior. The backbone of the hexapeptides in all simulations folds to a similar conformation found in experimental studies in solution. Intramolecular, hydrophobically driven interactions between the aromatic residues and internal hydrogen bonds are found to stabilize the conformations.     

三元配合物钯（Ⅱ）-2,2''-联吡啶-L-天冬氨酸与DNA作用研究

The ternary complex Pd(Ⅱ)-2,2‘-bipyridine-L-asparagic acid was synthesized and characterized by elemental analysis, IR-spectra and molar conductance. The formula of the complex is Pd(bipy)(L-asp). The interaction of the complex with DNA has been studied by UV-spectra, fluorescence spectra, CD-spectra and gel electrophoresis. The results showed that the interaction of the complex with DNA performed mainly in intercalative mode and the extent of interaction was dependent on the concentration of the complex.     

Dipyrrolo[1,2-a;2',1'-c]pyrazines. 6. Electrophilic Substitution in a Series of Dipyrrolo[1,2-a;2',1'-c]pyrazine and 5,6-Dihydrodipyrrolo[1,2-a;2',1'-c]pyrazine Derivatives. Phosphorylation of Dipyrrolo[1,2-a;2',1'-c]pyrazines

We have studied the behavior of asymmetrically substituted dipyrrolo[1,2-a;2',1'-c]pyrazines and their 5,6-dihydro analogs under phosphorylation reaction conditions.     

Electrochemical study of some bromo-substituted [2.2]paracyclophanes

The potentials of electrochemical oxidation ( ) and reduction ( ) of monobromo- and isomeric di- and tribromo[2.2]paracyclophanes as well as of mono-, di-, and tribromobenzenes were measured in acetonitrile. The similarity between the properties ofpseudo-para-disubstituted cyclophanes andmeta-disubstituted benzenes, on the one hand, andpseudo-meta-disubstituted cyclophanes andpara-disubstituted benzenes, on the other hand, was confirmed by the existence of a linear relationship between of bromo-substituted [2.2]paracyclophanes and of the corresponding bromo-substituted benzenes. The results were explained in terms of the qualitative theory of molecular orbitals, taking into account a through space interaction between the -systems of the benzene rings.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 839–845, May, 1994.The authors wish to express their gratitude to Professor R. Hoffmann (Cornell University, USA) for a useful discussion and criticisms of the text of this paper.This work was financially supported by the Russian Foundation for Basic Research (Project 93-03-5246).     

Intramolecular proton transfer induced by divalent alkali earth metal cation in the gas state

Interactions between divalent alkali earth metal (DAEM) ions M (M?Be, Mg, Ca, Sr, Ba) and the second stable glycine conformer in the gas phase, which can transfer into the ground‐state glycine‐M²⁺ (except the glycine–Be²⁺) among each corresponding isomers when these divalent metal ions are bound, are studied at the hybrid three‐parameter B3LYP level with three different basis sets. Proton transfers from the hydroxyl to the amino nitrogen of the glycine without energy barriers have been first observed in the gas phase in these glycine–M²⁺ systems. The interaction between the glycine and these DAEM ions except beryllium and magnesium ion only create an amino hydrogen pointing to the original hydroxyl due to their weaker interaction relative to those divalent transition metal (DTM) ion‐bound glycine derivatives, being obviously different from that between the glycine and DTM ions, in which two amino hydrogens point to the original hydroxyl oxygen when these metal‐chelated glycine derivatives are produced. The interaction energy between the glycine and divalent magnesium would be the boundary of one or two amino hydrogens pointing to the hydrogyl oxygen, i.e., the ?170.3 kcal/mol of binding energy is a critical point. Similar intramolecular proton transfer has also been predicted for those DTM ion‐chelated glycine systems; however, that in the gas state has not been observed in the monovalent metal ion‐coordinated glycine systems. The binding energy between some monovalent TM ion and the glycine is similar to that of the glycine–Ba²⁺, which has the lowest binding strength among these DAEM–ion chelated glycine complexes. The difference among them only lies in the larger electrostatic and polarized effects in the latter, which favor the stability of the zwitterionic glycine form in the gas phase. According to these observations, we predict that the zwitterionic glycine would exist in the field of two positive charges in the gas phase. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 205–214, 2003     

Formamide,a water substitute XIV (1) waterless microemulsions 8. Structural analysis by X-ray scattering of CTAB aggregates in formamide and in the microemulsion system (formamide,CTAB, isooctane, 1-butanol)

X-ray scattering was used to analyse the structures of aggregates of CTAB in various formamide-containing media.Firstly, CTAB micelles were detected in formamide solutions. A spherical micelle model was proposed; at values close to the CMC, smaller micelles were observed in formamide than in water.Secondly, the structure of microemulsions in the isooctane-rich zone of the system (formamide/CTAB=2, isooctane, 1-butanol) was studied by X-ray scattering. The structure was found to be quite different in this zone from that normally observed in aqueous microemulsions. Structures compatible with small filaments of formamide were detected. The results were related to previous measurements of electrical conductivity.     

P(i-PrNCH2CH2)3N: An efficient nonionic catalyst for the regioselective Michael addition of a β,γ-unsaturated ester and a nitrile

Michael additions of a β,γ-unsaturated ester and a nitrile to a variety of α,β-unsaturated ketones can be effected with high regioselectivity and in good yields using P(i-PrNCH₂CH₂)₃N as a catalyst.     

Chemistry of <Emphasis Type="Italic">N,N</Emphasis>-bis(silyloxy)enamines 7. Quaternization of tertiary amines and nitrogen-containing heterocycles by <Emphasis Type="Italic">N,N</Emphasis>-bis(silyloxy)enamines

Coupling of N,N-bis(silyloxy)enamines with tertiary amines and nitrogen-containing heterocycles affording the corresponding functionalized ammonium or iminium salts was studied. The area of its application was determined, and optimal procedures for the synthesis of the target products were proposed. The mechanism including the formation of conjugated nitroso alkene or a silylnitrosonium cation as key intermediates is discussed.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2137–2143, October, 2004.     

Cp*Me5P6C5: Ein neues Carbaphosphan mit einem Strukturelement aus dem Hittorfschen Phosphor

Cp*Me₅P₆C₅: A New Carbaphosphane with a Structure Unit of Hittorf-Phosphorus The thermolysis of 1,2,3-tris(pentamethylcyclopentadienyl)cyclotriphosphane [(Cp*P)₃, 1 ] or 2,3,4,6-Tetrakis(pentamethylcyclopentadienyl)bicyclo[3.1.0]hexaphosphane [Cp*₄P₆, 2 ] leads in addition to the known 3,4-bis(pentamethylcyclopentadienyl)tricyclo[3.1.0.0^{2, 6}]hexaphosphane [Cp*₂P₆, 3 ] to the pentacyclic carbaphosphanes 3,4,5,6,11-pentamethyl-endo-9-pentamethylcyclopentadienyl- 3,4,5,6,11-pentacarba-pentacyclo [6.1.1^1,8.1^3,6.0^2,70^10,11]-4-en-undecaphosphane and 3,4,5,6,11-pentamethyl-exo-9-pentamethylcyclopentadienyl-3,4,5,6,11-pentacarba-pentacyclo [6.1.1^1,8.1^3,6.0^2,70^10,11]-4-en-undecaphosphane [Cp*Me₅P₆C₅, 4a, 4b ]. Furthermore, other polyphosphanes are formed, like 1,2,3,4-tetrakis(pentamethylcyclopentadienyl)cyclotetraphosphane [(Cp*P)₄, 5 ] and 2,4-bis(pentamethylcyclopentadienyl)-tetraphosphabicyclo[1.1.0]butane [(Cp*P)₂P₂, 6 ]. The structure of 4a and 4b is determined by NMR-spectroscopy. The molecule contains a P₅C₃-cunean-unit, to which a C₂Me₂-brigde and a PCp*-brigde is bonded.     

GC-MS监测生活饮用水输配水管材及防护材料中溶出的挥发性有机物

我国的生活饮用水行业中,目前常使用的管材分为金属类管材和非金属类管材两种。由于金属类管材本身的化学特性,行业内必须在此类管材的内壁上进行防腐处理,通常采用一些高分子防腐涂料。可用于给水行业的涂料品种繁多,涂料质量好坏直接影响到水质。我们针对一些常用产品作了浸泡试验,用吹扫捕集-GC-MS方法对水中溶出的可挥发性有机物进行了检测,发现一些产品在水中溶出了大量的甲苯、乙苯、二甲苯、甲乙苯等苯系物,且浸泡30d后仍有溶出物。这些物质长期存在会导致人体中枢神经系统紊乱,严重危害人体健康。行业内关于水源水中此类有机物污染的监测比较充分,而对于防护涂料可能污染水质的状况并未引起足够重视。