Chemical ionization mass spectrometry of nitrosamines

The mass spectra of eight nitrosamines have been recorded, with excitation by chemical ionization (CI) and electron impact (EI). Comparison of the intensities of the base peaks under CI and El conditions gives intensity ratios in the range 1.4-1.9 for low resolution measurements and up to 10 for high resolution measurements, confirming the enhanced sensitivity available in the CI mode.     

Modification chimique des polyalcadiènes par les composés du type CX3Z—I Addition catalysée des composés CCl3Z sur les polybutadiènes-1,2

The influence of catalysis on chemical modification of 1,2-polybutadienes (M_n < 10,000) by CX₃Z reagents (X = halogen; Z = functional group or halogen), in order to obtain polymers soluble in common solvents, has been studied. The work has been carried out with carbon tetrachloride, trichloromethylphosphonyldichloride (CCl₃POCl₂) and ethyl trichloroacetate (CCl₃CO₂Et) in the presence of solvents such as C₆H₆, CH₂Cl₂. Among the compounds tested as catalysts for the addition of CX₃Z to 1,2-polybutadiene (transition metal salts and complexes; radical initiators) only the systems formed with metal salts such as CuCl₂, FeCl₃, RuCl₃ 3H₂O, Fe₂(CO)₉ and Cl₂Ru(PPh₃)₃ were found to show high catalytic activity. The most active is Cl₂Ru(PPh₃)₃: used without or with cocatalysts (Et₃NHCl/benzôin, alcohols), it leads always, to the best yields whatever the nature of CX₃Z. The activity of the other catalysts is generally dependent on CX₃Z structure. Some secondary reactions (cross-linking, cyclization, transesterification) have been found.     

Use of reference pools to compare the qualitative and quantitative determination of polychlorinated biphenyls by packed and capillary gas chromatography with electron capture detection. Part 1. Serum

Serum for reference pools of in vivo polychlorinated biphenyls (PCBs) was obtained from four goats that had received one dose (100 mg kg-1) of a selected technical Aroclor (AR) (1016, 1242, 1254 or 1260) and were allowed to recover for 30 d. These pools were used to assess the differences in an analytical method that determines and quantifies PCBs using packed-column gas chromatography (PCGC) (quantified on the basis of mean mass percent. data for grouped PCB peaks) and capillary-column gas chromatography (CCGC) (quantified on the basis of percent. composition data for specific congeners). With CCGC, results were statistically significantly different (p less than or equal to 0.0002) from results with PCGC for ARs 1016, 1242 and 1254 but not for AR 1260 (p = 0.23). When comparing these gas chromatographic methods using bovine serum spiked in vitro with the same ARs at 17-25 p.p.b., it was found that the methods were not statistically significantly different for any of the ARs (p = 0.30-0.92). Levels of serum PCB determined by the two methods for 12 persons, divided into two groups according to exposure, were compared using the paired t-test. Group 1 consisted of three persons with dietary and/or environmental exposure; one with dietary and/or environmental exposure in addition to occupational exposure dating back 20 years. Group 2 consisted of eight persons with recent occupational exposure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Variable step molecular dynamics: An exploratory technique for peptides with fixed geometry

A new algorithm is presented for performing molecular dynamics simulations of peptides with fixed geometry, with the aim of simulating conformational changes and of exploring conformational space. The principle of the method is to expand the potential energy as a Taylor's series in the coordinates around the current point, retaining the force and its first two derivatives, and obtain a series solution of the resulting differential equations using a method due to Lyapunov. By choosing the time step so that the second term in the series is small compared to the first, the true solution can in principle be approximated to any desired degree of accuracy. The algorithm has been used to solve numerically Lagrange's equations of motion for N-acetyl alanine amide and N-acetyl methionide amide, regarded as fixed at their C-termini, under the influence of the ECEPP/2 potential energy function, and time steps of 15–30 fsec have been achieved with little variation in the total energy. Possible directions for future development are discussed.     

Persulphate initiated polymerisation of methacrylamide—I: Kinetics and molecular weight dependences

A kinetic study of the aqueous persulphate initiated polymerisation of methacrylamide has shown that the rate of polymerisation is represented by the equation $\text{R}{}_{\mathrm{p}}\text{= k [}\text{M}\text{] [}\text{I}\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ where the overall rate constant, $\text{k = 1.3 × 10}{}^9\text{exp}\text{(?18,400/}\text{RT}\text{) 1}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{mol}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{s}{}^{\mathrm{?1}}$. Chain transfer with monomer, where C_M = 5.4 × 10^?3 at 60°, is shown to be the dominant transfer step. Comparison with kinetic studies of the analogous acrylamide polymerisation shed doubt on the ‘cage effect’ interpretation of complex orders with respect to monomer. An alternative explanation is proposed.     

Application of ESCA to polymer chemistry. VIII. Surface structures of AB block copolymers of polydimethylsiloxane and polystyrene

The surface morphology of a number of films of AB block copolymers of polydimethylsiloxane and polystyrene was examined by ESCA and contact angle measurements. In all cases the immediate surface is shown to consist of an essentially pure polydimethylsiloxane component. By comparing the intensities of elastic peaks corresponding to photoionizations from core levels without energy loss for polydimethylsiloxane and polystyrene with those for the block copolymers and by consideration of shake-up phenomena specific to the polystyrene component, an estimate of the thickness of the polydimethylsiloxane outer layer of the latter may be obtained. This is shown to vary between ～13 and 40 Å, depending on the method of formation of copolymer film.     

A Photoelectron-spectroscopic investigation of the Homoconjugative Interaction between π- and Walsh-Orbitals in endo- and exo-Cyclopropano-norbornene

Photoelectron spectra of endo- and exo-cyclopropano-norbornene ( = endo- and exo-tricyclo[3.2.1.0^2.4]octa-6-ene) show that a significant homoconjugation exists between the π-orbital of the double bond and the symmetric Walsh-es-orbital of the cyclopropane ring in the exo-isomer, whereas the interaction is negligeable in the endo-derivative.     

The determination of the thermodynamic characteristics of Lennard-Jones fluids under isobaric conditions by the method of molecular functions

Integral equation theory for partial distribution functions was used to suggest an effective method for calculating the derivative of radial distribution function with respect to temperature under isobaric conditions. The thermodynamic expansion, compression, and pressure coefficients and isobaric and isochoric heat capacities were calculated for Lennard-Jones fluids. The calculation results were in close agreement with the known thermodynamic relations.     

Isopoly-molybdic acids

From the measurements of conductivity, diffusion coefficient etc., Jander indicated the presence of several isopoly-anions of molybdenum under different pH conditions. He and subsequent workers in the field dealt with solutions only. In the present work one free molybdic acid, and one ammonium acid molybdate were isolated in solid condition at pH 4.6 and 2. On analysis, their compositions were found to be H₄Mo₃O₁₁ and NH₄H₅Mo₆O₂₁ (or (NH₄)₂H₄Mo₇O₂₄) respectively.     

The method of non-paired spatial orbitals

The calculation of non-paired spatial orbitals and alternant molecular orbital wavefunctions for the benzyl radical is described. The NPSO and AMO methods give comparable energy lowerings which indicate that they make substantial allowance for electron correlation. The calculated spin densities are not in very good accord with experiment and it is thought that this reflects inadequacies in the integral approximations used.