Pentacoordinate spirosilicate anion, bis(2,2′-biphenyldiyl)methylsilicate, synthesized by the lithium cleavage of dimethoxyethane

The reaction of spirobisilafluorene (1) with lithium in dimethoxyethane produces lithium 1-methyl-spirobisilafluorenide (2), a stable pentacoordinate silicon compound with five carbon ligands, and lithium 2-methoxyethoxide, which was identified by trapping with Ph₃SiCl to give Ph₃Si-OCH2CH2OCH3 (4). The X-ray crystal structure of 2 shows that the geometry at silicon is an idealized trigonal bipyramid, slightly distorted toward a square pyramid. Methanolysis of 2 cleaves a Si-aryl bond producing a methyl biphenylsilafluorene, 3. Crystal structures are reported for 3 and 4.     

烯烃加成反应活性与烷基极化效应的关系

烯烃的自由基加成和亲电加成速率受不同的因素控制.对于仅仅含烷基取代的简单烯烃:(1)与OH自由基加成速率-log kOH可由π键上烷基极化效应指数的几何平均值GMPEIπ关联:-log kOH=a bGMPEIπ c(GMPEIπ)2; (2)与亲电试剂加成速率log k可由π键两端碳原子所连基团极化效应指数PEI(L)和PEI(S)关联:log k=a bPEI(L) cPEI(S),其中的PEI(L)和PEI(S)分别表示极化效应较大和较小的一端.     

Sterically hindered aliphatic amines in the controlled synthesis of polystyrene

The kinetic features of radical polymerization of styrene in the presence of primary and secondary aliphatic amines combined with benzoyl peroxide and the molecular-mass characteristics of the resulting polymers were studied. In the presence of peroxide initiators, aliphatic amines, as potential sources of stable aminoxyl radicals, provide the synthesis of polystyrene with a controlled molecular mass without gel effect at a relatively high rate. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 159–164, January, 2007.     

Reaction of sulphate radical anion (SO<Superscript>.</Superscript><Subscript>4</Subscript><Superscript>-</Superscript>) with hydroxy-and methyl-substituted pyrimidines: a pulse radiolysis study

Reactions of sulphate radical anion (SO·₄ ^-) with 4,6-dihydroxy-2-methyl pyrimidine (DHMP), 2,4-dimethyl-6-hydroxy pyrimidine (DMHP), 6-methyl uracil (MU) and 5,6-dimethyl uracil (DMU) have been studied by pulse radiolysis at pH 3 and at pH 10. The transient intermediate spectra were compared with those from the reaction of hydroxyl radical (·OH). It is proposed that SO·₄ ^- produces radical cations of these pyrimidines in the initial stage. These radical cations are short-lived except in the case of DMHP where a relatively longer lived radical cation is proposed to be formed. When there is a hydrogen atom attached to the N(1) or N(3) position, a deprotonation from these sites is highly favored. When there is no hydrogen attached to these sites, deprotonation from a substituted methyl group is favored. At acidic pH, deprotonation from nitrogen is observed for DHMP, MU and DMU. At basic pH, the radical cation reacts with OH^- leading to the formation of OH adducts.     

全氟和ω-H-全氟酰基过氧化物与C_(60)的自由基加成反应——全氟和ω-H-全氟烷基化C_(60)的合成

深入研究了C60 与全氟酰基过氧化物的反应 ,通过变温EPR测试证实了此反应的自由基加成机理 .用色谱分析并结合产物的19FNMR结构鉴定 ,首次发现由于加成过程中发生的全氟烷基自由基的 β Scission ,生成了新的氟烷基自由基 ,从而生成了多种氟烷基化的C60 .表面性能研究发现氟烷基化的C60 具有优良的疏水、疏油性 .总之 ,利用C60 与全氟酰基过氧化物的反应 ,成功地对C60 进行了全氟烷基化修饰     

Synthesis and photochemistry of a new class of photocleavable protein cross-linking reagents

A new series of photocleavable protein cross-linking reagents based on bis(maleimide) derivatives of diaryl disulfides have been synthesised. They have been functionalised with cysteine and transient absorption spectra for the photolysis reaction have been recorded by using the pump-probe technique with a time resolution of 100 femtoseconds. Photolysis of the disulfide bond yields the corresponding thiyl radicals in less than a picosecond. There is a significant amount of geminate recombination, but some of the radicals escape the solvent cage and the quantum yield for photocleavage is 30 % in water.     

Tuning of the alpha-terthiophene radical cation coupling reaction using mixed micelles with varying charge density.

The photophysics and photochemistry of alpha-terthiophene (alphaT), compartmentalized in mixed nonionic/anionic micelles, have been investigated with focus on the influence of the micellar surface charge density on the formation of the radical coupling product alpha-hexathiophene (alphaH). By varying the ratio of nonionic-to-anionic surfactants, and assuming ideal mixing, the charge density of the mixed micelles was varied. From Poisson-Boltzmann calculations, performed using the cell model, the electrostatic potential and the counterion activity were estimated as a function of the distance from the micellar surface. Upon excitation, the triplet state of alphaT is formed, from which the alphaT radical cation can be formed by absorption of a second photon. The radical cation can form alphaH if it encounters another alphaT radical cation. Under the experimental conditions used, this implies that the alphaH formation only occurs if the compartmentalized radical cation is able to migrate from its host micelle to another micelle, either via the surrounding bulk or by fusion of two micelles followed by mixing of their contents before micellar fission. The formation yield of the radical cation depends on the charge density of the mixed micelle; a lower charge density, that is, an increased amount of nonionic surfactant, lowers the yield. The yield of the coupling product alphaH, however, does not follow the same trend. A maximum yield of alphaH is found at intermediate nonionic surfactant molar ratios. This behavior is understood in terms of the Poisson-Boltzmann simulation results and by comparing charge-density changes as a function of molar fraction with the changes in counterion activity. The alphaH yield is a result of the balance between an increased possibility of radical cation bulk migration and a lowered electrostatic stabilization of the radical.     

Synthesis and Crystal Structure of a New One-dimensional Zn(II) Nitronyl Nitroxide Complex Bridged by Pyridine-2,4-dicarboxylate Anion

1 INTRODUCTION The synthesis and study of transition metal com- pounds incorporating organic free radicals directly bound to their coordination sphere are a major re- search aim in the field of molecular magnetism[1]. Exceptional stability, ease of chemical modification and versatility in their coordination properties have made nitroxide free radicals one of the most attrac- tive spin carriers for the design of molecular magne- tic materials[2, 3]. The structures and magnetic prope- rties …     

Antioxidative effects of flavonols and their glycosides against the free-radical-induced peroxidation of linoleic acid in solution and in micelles

The antioxidative effect of flavonols and their glycosides against the peroxidation of linoleic acid has been studied in homogeneous solution (tBuOH/H(2)O, 3:2) and in sodium dodecyl sulfate and cetyl trimethylammonium bromide micelles. The peroxidation was initiated thermally by the water-soluble initiator 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and the reaction kinetics were studied by monitoring the formation of linoleic acid hydroperoxides. The synergistic antioxidant effect of the flavonols with alpha-tocopherol (vitamin E) was also studied by following the decay kinetics of alpha-tocopherol and the alpha-tocopheroxyl radical. Kinetic analysis of the antioxidative process demonstrates that the flavonols are effective antioxidants in solution and in micelles, either alone or in combination with alpha-tocopherol. The antioxidative action involves trapping the initiating radicals in solution or in the bulk-water phase of the micelles, trapping the propagating lipid peroxyl radicals on the surface of the micelles, and regenerating alpha-tocopherol by reducing the alpha-tocopheroxyl radical. It was found that the antioxidant activity of the flavonols and their glycosides depends significantly on the position and number of the hydroxy groups, the oxidation potential of the molecule, and the reaction medium. The flavonols bearing ortho-dihydroxy groups possess significantly higher antioxidative activity than those without such functionalities, and the glycosides are less active than their parent aglycones. The activity of the flavonols is higher in micelles than in solution, while the activity of alpha-tocopherol is lower in micelles than in solution. This is because the predominant factor for controlling the activity is the hydrogen-bonding interaction of the antioxidant with the micellar surface in the case of hydrophilic flavonols, while it is the inter- and intramicellar diffusion in the case of lipophilic alpha-tocopherol.     

Substituted pyrazine-di-N-oxides as the mediators of catalytic oxidation of organic compounds

The mechanism of oxidation of 2,5-dimethyl-, 2,3,5,6-tetramethyl-, 2,3-dimethyl-5,6-cyclohexa, and 3-phenyl-5,6-cyclohexapyrazine-di-N-oxides is studied by cyclic voltammetry, quantum chemical simulations, and ESR electrolysis. The studies are carried out on electrodes of glassy carbon and Pt in 0.1 M LiClO₄ solutions in acetonitrile. ESR spectra of radical cations of substituted pyrazine-di-N-oxides are recorded. The effects of the temperature, oxygen, and the additions of water, pyridine, and acid on the shape of cyclic voltamograms and the intensity of ESR signals of pyrazine-di-N-oxides are studied. A quantum-chemical simulation of the reaction of pyrazine-di-N-oxide radical cations with acetonitrile is carried out. The oxidation of substituted pyrazine-di-N-oxides is described by the E₁C₁E₂C₂ mechanism, which includes the stage of the formation of a complex between the di-N-oxide radical cation and acetonitrile.