Oligomeric silazanes

High conversions of oligomeric silazanes that are not volatile at 200°C/0.1 mm are obtained when hexamethylcyclotrisilazane or octamethylcyclotetrasilazane is heated with a molar deficiency of dichlorodimethylsilane at 175°C. The oligomers, which show moderate solvolytic stability, contain disilazane, trisilylamine, and cyclodisilazane units. They are structurally similar to materials that have been prepared by others from hexamethylcyclotrisilazane and ammonium bromide. When the oligomers are treated with ammonia and heated to 325°C, evidence can be found in their spectra for the presence of oligocyclodisilazane structures.     

Helicity Induction and Memory of the Macromolecular Helicity in a Polyacetylene Bearing a Biphenyl Pendant

A novel, cis‐transoidal poly‐(phenylacetylene) bearing a carboxybiphenyl group as the pendant (poly‐ 1 ) was prepared by polymerization of (4′‐ethoxycarbonyl‐4‐biphenylyl)acetylene with a rhodium catalyst followed by hydrolysis of the ester groups. Upon complexation with various chiral amines and amino alcohols in dimethyl sulfoxide (DMSO), the polymer exhibited characteristic induced circular dichroism (ICD) in the UV/Vis region due to the predominantly one‐handed helix formation of the polymer backbone as well as an excess of a single‐handed, axially twisted conformation of the pendant biphenyl group. Poly‐ 1 complexed with (R)‐2‐amino‐1‐propanol showed unique time‐dependent inversion of the macromolecular helicity. Furthermore, the preferred‐handed helical conformation of poly‐ 1 induced by a chiral amine was further “memorized” after the chiral amine was replaced with achiral 2‐aminoethanol or n‐butylamine in DMSO. In sharp contrast to the previously reported memory in poly((4‐carboxyphenyl)acetylene), the present helicity memory of poly‐ 1 was accompanied by memory of the twisted biphenyl chirality in the pendants. Unprecedentedly, the helicity memory of poly‐ 1 with achiral 2‐aminoethanol was found to occur simultaneously with inversion of the axial chirality of the biphenyl groups followed by memory of the inverted biphenyl chirality, thus showing a significant change in the CD spectral pattern.     

Oligomeric oxidation products of the flavonoid quercetin

Some of the main oxidation products of quercetin were shown to be compounds formed by oligomerization of the starting flavonoid. Conditions for the preparative synthesis of these compounds were developed. Their structures were established using HPLC-MS and NMR methods. Quercetin oligomers in the natural sample, outer leaves of modified runners of Allium cepa L., were found using chromatographic procedures. The use of quercetin oligomers as indicators of its oxidation was proposed. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 344–347, July–August, 2008.     

Hyperconjugation Is the Source of Helicity in Perfluorinated n-Alkanes

Hyperconjugative, steric, and electrostatic effects were evaluated as possible sources of the helicity in linear perfluorinated alkanes through analysis of natural bond orbitals and classical electrostatics. Contrary to previous rationalizations, which indicate dominating steric or electrostatic effects, this analysis indicates that hyperconjugative stabilization through σ_CC→σ*_CF interactions are the underlying driving force for the origin of the observed helicity in perfluoroalkanes.     

Oligomeric organosilicon dicyano ethers

Conclusions We synthesized and characterized some oligomeric organosilicon dicyano ethers that offer promise as monomers for the preparation of heat-resistant polymers.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2803–2806, December, 1976.     

Oligomeric stilbenes from the root of Caragana stenophylla

Caragaphenol A (1), a new trimeric stilbene, was isolated from the roots of Caragana stenophylla (Leguminosae) along with three known oligomeric stilbenes: (+)-alpha-viniferin (2), miyabenol C (3) and kobophenol A (4). The stereostructure of 1 was elucidated by one- and two-dimensional (1D- and 2D-)-NMR spectral studies.     

三聚甲醛解聚的研究

一般普通中学化学实验室购置的甲醛试剂是含甲醛36-50%的甲醛水溶液。放置久了就会析出固体—三聚甲醛,影响使用。为回收药品,节约费用,我们查了一些资料。     

Oligomeric nucleic acids as antivirals

Based on the natural functions and chemical characteristics of nucleic acids, a variety of novel synthetic drugs and tools to explore biological systems have become available in recent years. To date, a great number of antisense oligonucleotides, RNA interference-based tools, CpG?containing oligonucleotides, catalytic oligonucleotides, decoys and aptamers has been produced synthetically and applied successfully for understanding and manipulating biological processes and in clinical trials to treat a variety of diseases. Their versatility and potency make them equally suited candidates for fighting viral infections. Here, we describe the different types of nucleic acid-based antivirals, their mechanism of action, their advantages and limitations, and their future prospects.     

Oligomeric proanthocyanidin glycosides ofRhodiola pamiroalaica

Two oligomeric proanthocyanidin glycosides have been isolated from the roots ofRhodiola pamiroalaica and their structures and relative configurations have been established: — RP-1 - and — RP-2. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 484–491, July–August, 1998.     

Oligomeric proanthocyanidin glycosides ofClementsia semenovii

Five new proanthocyanidins have been isolated from the roots ofClementsia semenovii A. Bor. The structures of two of these compounds have been established by various chemical and physical methods: 7-0-[6-0-galloyl-β-D-Glcp 0-β-D-Glcp 0-βD-Glcp 0-β-D-Glcp ]-(+)-gallocatechin-(4a-8)-(+)-gallo-catechin-(4a-8)-(-)-epigallocatechin-(4β-8)-(-)-epigallocatechin-(4β-8)-(-) -epigalloactechin-(4β-8)-(+)-catechin - CS-1 and 3-0-galloyl-7-0-(β-D-Glcp 0-B-D-Glcp)-(-)-epigallocatechin-(4β-8)-[3-0-galloyl-(-)-epigallocatechin]-(4β-8)-[3-0-galloyl-5-0-(6-0-galloyl-0-β-D-Glcp)]-(-)-epicatechin - CS-2. 1) Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (371) 120 64 75; 2) Osh State University, Osh, fax (33 222) 2 23 73. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 756–763, November–December, 1998.     

Oligomeric rod-disc nematic liquid crystals

Six new oligomeric nematic liquid crystals are reported consisting of a triphenylene-based core attached to which are six 4-cyanobiphenyl units via flexible alkyl spacers.     

多面齐聚硅倍半氧烷研究进展

总结了多面齐聚硅倍半氧烷的研究进展,主要介绍了它的合成方法、合成机理和应用,着重介绍了它在二氧化硅模型、树枝状大分子、多孔材料以及聚合物纳米杂化材料中的应用。     

低聚表面活性剂的合成及性能研究

低聚表面活性剂是指通过连接基将两个以上的传统表面活性剂连接在一起而形成的一类新型表面活性剂。相对于对应的传统表面活性剂,这类表面活性剂具有临界胶束浓度(cmc)低、表面活性高等优点。本文介绍了本研究团队近年针对低聚表面活性剂所开展的研究,包括分子结构不对称的双子表面活性剂、同时具有阳离子和阴离子头基的甜菜碱型双子表面活性剂、三聚和四聚阳离子表面活性剂以及通过原子转移自由基聚合制备的低聚表面活性剂等。     

Visible Helicity Induction and Memory in Polyallene toward Circularly Polarized Luminescence,Helicity Discrimination,and Enantiomer Separation

Inspired by biological helices (e.g., DNA), artificial helical polymers have attracted intense attention. However, precise synthesis of one-handed helices from achiral materials remains a formidable challenge. Herein, a series of achiral poly(biphenyl allene)s with controlled molar mass and low dispersity were prepared and induced into one-handed helices using chiral amines and alcohols. The induced one-handed helix was simultaneously memorized, even after the chiral inducer was removed. The switchable induction processes were visible to naked eye; the achiral polymers exhibited blue emission (irradiated at 365 nm), whereas the induced one-handed helices exhibited cyan emission with clear circularly polarized luminescence. The induced helices formed stable gels in various solvents with helicity discrimination ability: the same-handed helix gels were self-healing, whereas the gels of opposite-handed helicity were self-sorted. Moreover, the induced helices could separate enantiomers via enantioselective crystallization with high efficiency and switchable enantioselectivity.     

New Oligomeric Proanthocyanidine from Ziziphus jujuba

Chemical and spectral data establish the structure of an oligomeric proanthocyanidine PZ-5 isolated from Ziziphus jujuba.     

Oligomeric rods of alkyl- and hydridogallium imides

Reaction of [RGa(NMe(2))(2)](2), where R = Me, Et, Bu, and Hx, with ammonia at 150 degrees C in an autoclave produced insoluble white powders formulated as oligomers of [RGaNH](n). The analogous reaction between NH(3) and MeGa[N(SiMe(3))(2)](2) at low temperature (<25 degrees C) formed an isolable intermediate, [MeGa(mu-NH(2))N(SiMe(3))(2)](2), that was characterized using single-crystal X-ray diffraction. Infrared spectroscopy and X-ray diffraction of the oligomers were consistent with a rodlike structure comprised of six-membered, [RGaNH](3) rings stacked perpendicular to the long axis of the rod. The method of synthesis, formula, and diffraction results suggested a structural similarity between the alkyl, [RGaNH](n)(), and the previously reported hydride, [HGaNH](n). The structural and electronic properties of rods having the general formula H(3)[(HXYH)(3)](n)H(3) (XY = GaN, GeC; n = 1-9) were investigated using density functional theory. Atomic electronegativity differences between the group 13/15 and 14/14 systems were found to play important roles in the geometrical structures of the two rods and also caused significant differences in the electronic structures. Energetically, it was found to be increasingly favorable to add additional cyclotrigallazane rings to the GaN rods, while for the GeC rods, there was a roughly constant energy cost associated with each additional ring. The electric dipole moments of the GaN rods increased substantially with length; in the GeC rods, charge separation occurred to a much smaller extent and had a polarization opposite to that found in GaN. In addition, increased dipole moments correlated with smaller electronic excitation energies, as predicted by time-dependent density functional theory. All of the powders exhibited luminescence in the visible spectrum at room temperature. Structure observed in the photoluminescence spectra of [HGaNH](n) and [MeGaNH](n) was interpreted as arising from rods of different length.     

Oligomeric proanthocyanidins: naturally occurring O-heterocycles

This review covers the flavan-3-ols (catechins), flavan-4-ols/flavan-3,4-diols (leucoanthocyanidins), A-type proanthocyanidins, B-type proanthocyanidins including the procyanidins, prodelphinidins, propelargonidins, proteracacinidins, promelacacinidins, procassinidins, probutinidins, and non-proanthocyanidins with flavan-3-ol constituent units. Newly isolated proanthocyanidins, structure elucidation, syntheses, HPLC/MS analysis, NMR/ conformational analysis, and the effects of proanthocyanidins on human nutrition and health are reported. The literature from January 1999 to December 2001 is reviewed, and 130 references are cited.     

Oligomeric pseudorotaxanes adopting infinite-chain lattice superstructures

It's just an illusion: Above a critical chain length, where oligomers contain five or more recognition units, apparently infinite donor-acceptor polypseudorotaxanes are formed in the solid state (see picture). X-ray crystallographic analyses of three different examples have shown that although the oligomeric chains are undoubtedly discrete and monodisperse, they nevertheless appear to be infinite in the crystal.