环硅氧烷负离子乳液聚合中活性中心浓度的变化规律

以八甲基环四硅氧烷(D4)为单体,十二烷基二甲基苄基氢氧化铵(BDAH)为乳化剂兼催化剂,进行环硅氧烷负离子乳液聚合,采用凝胶色谱(GPC)测定聚合产物的转化率及分子量.在此基础上,分析基元反应,提出活性中心生成机理,并应用环硅氧烷开环聚合普适动力学模型计算乳液聚合平衡之前的活性中心浓度变化规律.结果发现,聚合温度较低时,活性中心浓度随时间逐渐增加,最终恒定;聚合温度较高时,活性中心浓度随时间仅单调递增.结果与机理相符.     

Characterization of polyimide films exposed at the mir orbital space station

Polyimide films remained unchanged upon an exposure at the Mir orbital space station under quartz plates, which protected them from bombardment by atomic oxygen with an energy of ～5 eV and transmitted solar radiation with λ ≥ 200 nm. The films underwent considerable degradation under the simultaneous action of atomic oxygen and solar radiation. The large weight loss and the mechanical destruction of one-sidedly aluminized polyimide films were caused by the participation of an aluminum coating in the polyimide destruction process. The accelerated degradation of the aluminum-polyimide composition can be explained by the photoeffect mechanism, the scavenging of photoelectrons emitted from aluminum by imide and benzene groups, and the formation and photochemical conversion of light-sensitive centers.     

Interaction of polymers with fullerene C60

The fundamentals of the method for estimating the fullerene-binding power of polymer macromolecules and supramolecular formations are developed for fullerene C₆₀. Polymers with covalently attached anthracene groups (one group per macromolecule) whose luminescence decreases in the presence of fullerene in solution in direct proportion to the stability of the fullerene-polymer complex are used. The effect of the anthracene mark on the fullerene-binding power of a luminescent-marked polymer is taken into account or discarded on the basis of an analysis of the interaction between fullerene and low-molecular models of luminescent marks.     

Study of one-side aluminized polyimide films exposed on the Mir orbital space station

During exposure on the Mir space station, external polyimide films aluminized on one side substantially lost mass and mechanical strength and their outer surfaces became hydrophilic. The surface tension and polar plots of brightness of the exposed films acquired an anisotropic character. Spatially-oriented nano- and microsized entities, whose size and shape depend on the time of exposure, were detected by the scanning electron and atomic-force microscopy techniques on the outer surfaces of external films. The orientation axes of drops on the surface of the films, polar plots of brightness, and spatially oriented structures coincided with the direction of the station movement. It was assumed that one of the main factors of outer space responsible for mass loss and the formation of the anisotropic nano- and microsized structures is the impact of a flux of oxygen atoms onto the surface of the external film. The efficiency of the reaction of atomic oxygen with polyimides was estimated. A possible (photoelectron) mechanism of the influence of the metal on polyimide degradation is discussed.     

Stability of transition metal complexes with sulfonated polymers

Stability constants of macromolecular metallocomplexes of transition metal ions (Ag⁺, Cu²⁺, Ni²⁺, Fe³⁺) with sulfonated polymers in water and aqueous HCl and NaCl solutions were determined from quenching by transition metal ions of the luminescence of macromolecules labeled with luminescent groups.     

Identification of shrimp species in raw and processed food products by means of a polymerase chain reaction-restriction fragment length polymorphism method targeted to cytochrome b mitochondrial sequences

A novel PCR-RFLP method has been developed for the identification of six commercially relevant penaeid shrimp species in raw and processed food products. The method can be completed within 8 h. To implement the method, PCR amplification with the crustF/crustR primers, targeted to the amplification of a ca. 181 bp region of the cytochrome b (cytb) mitochondrial gene in penaeid shrimps, was coupled to restriction analysis with CviJI, DdeI and NlaIV. The method was also applied successfully to the identification of shrimp species in complex processed foods, including this type of shellfish as an added-value food ingredient. The small size of this molecular target facilitates amplification from fresh, frozen, or precooked samples, where DNA fragmentation may be relevant and fragment size critical. We also report the first cytb mitochondrial sequences described to date for the species Farfantepenaeus notialis, Parapenaeus longirostris and Pleoticus muelleri, and these nearly triplicate current knowledge of reference nucleotide sequences in this mitochondrial region for this group of species. The cytb mitochondrial gene may also be considered as a molecular marker for identification and phylogenetic purposes in penaeid shrimp species.     

Toward efficient nanoporous catalysts: controlling site-isolation and concentration of grafted catalytic sites on nanoporous materials with solvents and colorimetric elucidation of their site-isolation

We report that the polarity and dielectric constants of solvents used for grafting organosilanes on mesoporous materials strongly affect the concentration of grafted organic groups, the degree of their site-isolation, and the catalytic properties of the resulting materials. Polar and nonpolar organosilanes as well as polar-protic, dipolar-aprotic, and nonpolar solvents were investigated. Polar-protic solvents, which have high dielectric constants, resulted in smaller concentrations ( approximately 1-2 mmol/g) of polar organic groups such as 3-aminopropyl groups, higher surface area materials, site-isolated organic groups, and more efficient catalytic properties toward the Henry reaction of p-hydroxybenzaldehyde with nitromethane. On the other hand, dipolar-aprotic and nonpolar solvents resulted in larger concentrations ( approximately 2-3 mmol/g) of grafted polar functional groups, lower-to-higher surface area materials, more densely populated catalytic groups, and poor-to-efficient catalytic properties toward the Henry reaction. Both the polar-protic and dipolar-aprotic solvents resulted in significantly lower concentration of grafted groups for nonpolar organosilanes such as (3-mercaptopropyl)trimethoxysilane compared to corresponding grafting of the polar amino-organosilanes. The relationship between the solvent properties and the percentage and degree of site-isolation of the grafted functional groups was attributed to differences in solvation of the organosilanes and silanols in various solvents and possible hydrogen-bonding between the organsilanes and the solvents. The degree of site-isolation of the amine groups, which affect the material's catalytic properties, was elucidated by a new colorimetric method involving probing of the absorption maxima (lambdamax) on the d-d electronic spectrum of Cu2+ complexes with the amine-functionalized materials and the colors of the samples. The absorption lambdamax and the colors of the materials were found to be uniquely dependent on the type of solvents used for grafting the organoamines. For instance, the monoamine- and diamine-functionalized samples grafted in methanol resulted in pale blue and light purple colors with lambdamax at approximately 720 and 650 nm, respectively. These correspond to CuNO5 and CuN2O4 structures, respectively, which are indicative of the presence of site-isolated organoamines in samples grafted in methanol. The monoamine and diamine samples grafted in toluene resulted in purple and deep purple colors with lambdamax at approximately 590 and 630 nm, respectively. These correspond to CuN2O4 and CuN4O2, which are indicative of the presence of closely spaced organoamines in samples grafted in toluene. The samples grafted in isopropanol gave colors and lambdamax intermediate between those of samples grafted in toluene and methanol.     

Side-chain chiral centers of amino acid and helical-screw handedness of its peptides

Both diastereomeric right-handed (P) and left-handed (M) 310-helices exist in homopeptides having twelve chiral centers at the side-chain bicyclic skeletons.