DETECTION OF ACTIVE RADICALS FORMED DURING THE SONOLYSIS OF POLYMERS

Active radicals formed during the sonolysis of PVK (polyvinyl carbazole) and PMMA (polymethylmethacrylate) have been studied with the combination of spin thepping technique and ESR spectroscopy-The results show that: 1. For PVK, radicals CA and--CH_2--CH--are produced during the ultrasonic irradiationand only the later can be trapped by MNP. 2. For PMMA, radicals --C and --CH_2 are grnerated by sonolysis and both can be trappedby ND.     

MOLECULAR VOLUMES OF SALTS. WITH TRIANGULAR RADICALS

The present paper discusses some characteristics of the molecular volumes of carbonates, nitrates and borates. It confirms that the molecular volume of H_2O in the hydrates of this kind of salts approximates to a constant. When the coordination numbers of cations in mixed salts are identical with those in the single salts, the additivity of the molecular volume is quite accurate. Over 100 sets of data demonstrate that a general additivity is true, the average relative error being ±2.31%. The concept of the topological molecular volume is proposed based, on the additivity. For salts with the same radical and equally charged cations, the molecular volume varies linearly with the cation radius. The volume effects of CO_3~(2-) NO_3~- and BO_3~(3-) in packing can be obtained by extrapolation. They are equal to a large sphere whose volume is the sum of those of three O~(2-). This paper also discusses the possibility of compiling a table of ionic volumes.     

ESR STUDY OF FREE RADICALS IN IRRADIATED POLYAMIDE-1010

Polyamide-1010 samples were irradiated in vacuum at room temperature by Cobalt-60 γ-rays. The free radicals formed in irradiation were studied by means of electron spin resonance (ESR)techniques.The ESRspectra consisted of a quartet and a superimposed singlet which were attributed to radical -CO-NH-CH-CH_2 and -CH_2-C=O, respectively. The effects of temperature and crystaUinity on the radicals were discussed and the mechanism for the production and decay of the radicals was also proposed.     

DNA SYNTHESIS INHIBITION OF NITROXIDE RADICALS ON LEUKEMIA CELLS

4-isothiocyanate-2,2,6,6-tetramethyl-piperidine-l-oxyl has the strongest effects on the DNA synthesis and viability of isolated leukemia 7712 cells. This compound is a very potent inhibitor of DNA synthesis with 50% inhibition of cell DNA synthesis occurring at 2.2 μg/ml, while the LD50 for white mice is 277 mg/kg. During the concentration of 50 μg/ml, the inhibition of DNA synthesis is 99.7%, which is unable to damage the DNA replicate templet. The inhibition of this compound, a combination of nitroxide and isothiocyanate, appears to be stronger than that of the sum of the two separate actions. Much more moderate effects are seen for all the other nitroxide radicals. After reducing nitroxide to hydroxyla-mine, there is no inhibition for DNA synthesis. The free radical mechanism of carcinogene-sis and antitumor action has been discussed.     

ENDOR AND ESR STUDIES OF RADICALS FORMED IN FRIEDEL-CRAFTS REACTIONS

The present study deals with the study of some Friedel-Crafts alkylating system and the accurate measurement of hyperfine coupling constants by ESR and ENDOR techniques. The results indicate that the observed ESR spectra are due to polycyclic aromatic radical cations formed from their parent hydrocarbons.It is suggested that benzyl halides produced in the Friedel-Crafts alkylating reaction undergo Scholl condensation reaction to give polycyclic aromatic hydrocarbons, which were converted into the corresponding polycyclic aromatic radical cations in the presence of aluminum chloride.     

PHOTOCATALYTIG DECOMPOSITION OF METHANOL BY VC1_2 AND TRANSFER OF HYDROGEN AND METHYL FREE RADICALS

The photocatalytic decomposition of methanol in the presence of vanadium dichloride and the transfer of hydrogen and methyl free radicals to the additives and dinitrogen were reported.     

TERMINATION AND TRANSFER OF THE CHAIN RADICALS IN THE POLYMERIZATION OF ACRYLONITRILE INITIATED BY VANADIUM(V)-THIOUREA REDOX SYSTEM

The dependence of the molecular weights on the concentration of reactants in the polymerization of acrylonitrile initiated by vanadium (V)-thiourea redox system has been investigated. It was found that the molecular weights of the polymer change nonlinearly with increasing concentrations of nitric acid and thiourea. Probably, the composition of the complexes exert a great influence on the chain initiation and termination. The reaction of "complextermination" gives rise to the decrease of the molecular weights markedly while the concentrations of thiourea and vanadium (V)in the range from one to three molar ratios.     

ESR STUDIES OF SPIN-TRAPPED RADICALS IN GAMMA-IRRADIATED POLYCRYSTALLINE PYRIMIDINE NUCLEOSIDES——THYMIDINE AND DEOXYCYTIDINE HYDROCHLORIDE

Room-temperature free radicals produced in gamma-irradiated polyerystalline thymidine and deoxy-cytidine hydrochloride were studied by spin-trapping and ESR methods with NtB (nitroso-t-butane) serv-ing as the spin trap. Three types and two types of base radicals were identified for them respectively,which was completely consistent with the results in single-crystal ESR studies, and thereby standard ESRspectra of their R·spin adducts were obtained. In addition, ribose radicals HOC(5')HC(4')H 相似文献   

TWO-DIMENSIONAL DISTRIBUTIONS OF TEMPERATURE AND OH, C_2 AND CH RADICALS IN FLAME DETECTED BY LASERINDUCED FLUORESCENCE

The in situ, high spatial resolution, two-dimensional distributions of OH(X), C_2(X) and CH(X) radicals in premixed paraffin/air flames are first reported. The measurements were done with the laser-induced fluorescence spectroscopies (LIFS) of the transitions of OH(A~Σ~+←→X~2Π), C_2(A~3Π←→X~3Π) and CH(B~2Σ←→X~2Π), (A~2△→X~2Π). The results show that OH(X) populated the edge of the outer flame, while C_2(X) and CH(X) the edge of the inner cone of the flame.The local rotational temperature of OH radical for a small zone was detected by the saturated laser-induced fluorescence spectroscopy of A~2Σ~+, v′=0←→X~2Π, v=″0 transition. The two-dimensional temperature distribution for the flame was measured through moving the position of the burner.     

ESR STUDIES OF SPIN-TRAPPED RADICALS IN GAMMA-IRRADIATED POLYCRYSTALLINE PYRIMIDINE NUCLEOSIDES——CYTIDINE, DEOXYCYTIDINE, URIDINE AND DEOXYURIDINE

Room-temperature free radicals produced in four gamma-irradiated polycrystalline pyrimidine nucleosides (cytidine, deoxycytidine, uridine and deoxyuridine) were studied by an improved spin trapping and ESR methods with NtB (nitroso-t-butane) serving as the spin trap. The presence of three types of radicals was ascertained in all samples, i.e. —C(5)H—C(6) H_2—and —C(5)H_2—C(6)H— base radicals, and —C(5')H_2— ribose radical evolving from HOC(5')H—C(4')H<. In addition, radicals in which the unpaired electron was located on ribose C(1') and C(4') sites were tentatively distinguished. Stress was laid on the discussion of the mechanism of formation of ribose radicals.     

STUDIES ON THE ESR CHARACTERISTICS OF FOUR PIPERIDINE NITROXYL RADICALS——CHARACTERISTICS IN THE SOLID STATE,CONCENTRATION EFFECTS AND SOLVENT EFFECTS IN SOLUTIONS

The ESR characteristics are studied for four piperidine nitroxyl radicals in the solidstate and in solutions. They all exhibited singlet ESR spectra in the solid state, but tripletspectra in solutions at a concentration lower than 1×10~(-2)M. The effects of the free radi-eal coneentration and the polarity trod the viscosity of solvents were observed and comparedon five ESR spectral parameters. Linear correlations could be found between the hyperfinesplitting constant A_N and the solvent polarity parameter, namely, Kosower Z value, Ex-perimental data showed also linear relations of the rotational correlation time τ of free rad-icals with the solvent viscosity, η. We have further found that the relative height of thehigh-field peak varied inversely with η. These ESR characteristics of nitroxyl radicals arediscussed.     

THEORETICAL ANALYSIS OF KINETICS OF NONISOTHERMAL CRYSTALLIZATION OF POLYMERS

The classical crystallization theories proposed by Avrami, Evans, and Mandelkern wereextended to the nonisothermal situation. The expressions derived from the classical equations canbe expressed in either the differential form or the integral form. A method was provided so as toobtain the parameters characterizing the crystallization rate and mechanism from DSC curves withseveral constant heating or cooling rates. The rate constants of crystallization obtained from bothisothermal and nonisothermal curves of poly(ethylene terephthalate)were compared.     

DIASTEREOSELECTIVITY OF ALLYBORATION OF ALDEHYDES

Reaction of(Z)-Crotyldiisopinocampheylborane with a series of alde-hydes have been examined,and the ratio of erythro to threo products varies fr-om 20:1 to 1:1.The results are discussed in detail.     

FEATURES OF Pb ISOTOPIC COMPOSITION OF ORES AND EVOLUTION OF CONTINENTAL CRUST OF CHINA

Based on the Pb isotopic features, the ore leads in the continent of China can be dividedinto four types: (i) single-stage lead of low μ value derived from mantle, (ii) homogeneouslead of crustal source with high μ value, (iii) modern mixing lead between mantle andcrust, and (iv) residual lead of crustal source. As the leads from mantle had possessed single-stage features (μ = 7.8) before the Proterozoic, the ages of continental crust can be calculatedbased on the mixing Pb of type (iii). The results hidicate that the continental crust of Chinawas mainly generated during the Archaean, and the growth rates of crust reached the max-ima by the ages of 3.3-3.4, 2.6 and 1.6-1.7 b.y. The occurrences of residual crust Pbwith high ~(207)Pb/~(204)Pb and ~(208)Pb/~(204)Pb anomalies were associated with the remelting andreconstruction of crust since 1.6 b.y. ago. The lead sources in the continent of China showhigher Th/U ratios (3.3-6.5) and ~(207)Pb anomalies than those in other continents, indicationthe conti     

COMPARISON OF THREE PROGNOSTIC EQUATIONS FOR PROBABILITY OF APPARITION OF STRIPE RUST OF WHEAT

Being used as a mathematical model of the latent period, a prognostic equation for probability of apparition, which is determined mainly by accumulated effective temperatures in the case of wheat stripe rust, is derived on the basis of experimental data.In field inoculation experiments of stripe rust on the susceptible wheat cultivar YD1817, the numbers of rusted leaves that were initiated by the infection that occurred on the i-th day and were just erupting into uredium pustules on the j-th day were observed every day. In the plots with accumulated effective temperatures as abscissa and with accumulated probability of apparition as ordinate, distribution of relevant points for the observed results from 14 experiments follows an S-shaped curve. Among the three models, namely, the Weibull function, logistic model, and Sine-square model, the logistic model seems to be the most fitted one with the determining equation: where PP_i is the accumulated probability of apparition on i-th day and TT_i is the accu     

ASYMMETRIC SYNTHESES OF STEREOTSOMERS OF SECODEMETHYLCLAUSENAMIDE

ＡＳＹＭＭＥＴＲＩＣ　ＳＹＮＴＨＥＳＥＳ　ＯＦ　ＳＴＥＲＥＯＴＳＯＭＥＲＳ　ＯＦ　ＳＥＣＯＤＥＭＥＴＨＹＬＣＬＡＵＳＥＮＡＭＩＤＥ￥ＪｉｎＦＳＤＵ；ＪｉｎＺＨＯＵａｎｄＬｉａｒＨＵＡＮＧ（ＩｎｓｔｉｔｕｔｅｏｆＭａｔｅｒｉａＭｅｄｉｃａ，Ｃｈｉｎｅｓ...     

SYNTHESIS OF ANALOGUES OF HUPERZINE A

A new Lycopodium alkaloid huperzine A (1) possesses a potent inhibitory activity ofacetylcholinesterase. Six structurally simplified analogues of huperzine A, compound 6, 7, 8, 12,13 and 15, were prepared and the inhibitory activities were evaluated.     

THE ORIGIN OF STEROLS: ELEMENTS OF A THEORY OF THE MOLECULAR EVOLUTION OF MEMBRANES

Introduction Cholesterol and its close relatives areuniversal components of the ceils of "high-er" organisms, i. e. of animals and plants,the Eucaryotes (which have a cell nucleus).Yet apart from a few instructive excep-tions, Procaryotes, Bacteria and Cyanobacteria(=blue-green Algae), contain no sterols.     

EQUILIBRIUM HEAT OF FUSION OF POLYTETRAFLUOROETHYLENE

The reliability of the values of equilibrium heat of fusion, △H_m, of polytetrafluoroethylene (PTFE)reported in the literature and the inadequacy of the generally accepted value of 13 .7 or 14.6 cal/gwere discussed. Through extrapolating linear plot of △H_m vs. V_(sp) of the thermally aged PTFE virginas-polymerized samples prepared in accord with ASTM D 1457-81a, △H_m~o=79.6J/g (19.0 cal/g)and V_(sp) (specific volume of amorphous PTFE at 23℃)=0.480 cm~3/g (or ρ_a=2 .08g/cm~3) were ob-tained. The heats of fusion, △H_m, of the thermally aged and γ-irradiated samples are different irrespec-tive of the same V_(sp) value for both samples. A qualitative explanation of this phenomenon was givenbased on the H_v patterns of SALS and Kawai's model.     

THE NATURE OF INTERMEDIATES OF ISOMERISATION AND OF NUCLEOPHILIC SUBSTITUTION OF β-CHLOROALKYLTHIOCARBOXYLIC ACID DERIVATIVES

Abstract

The addition of sulfenchlorides to the derivatives of unsaturated carboxylic acids results in the formation of kinetically controllable adducts, which in solution and even in a solid state isomerize into thermodinamically stable ones. The derivatives of β-chloroalkyl tiocarboxylic acids readily enter nucleophilic substitution reactions, particularly the reaction of hydrolytic splitting of C-C1 bonding. There still remains a problem to be solved concerning the nature of the intermediates which appear in the process of isomerisation and hydrolysis of these compounds. To solve the problem the research was carried out on the effect of chlorine and perchlorate ions concerning the rate of hydrolysis and isomerisation of the derivatives 2(3)-chloro-3(2)-alkylthio-2-methylpropanoic acids.