Structure-activity relationships of pyrethroid insecticides. Part 2. The use of molecular dynamics for conformation searching and average parameter calculation

Summary Molecular dynamics simulations have been performed on a number of conformationally flexible pyrethroid insecticides. The results indicate that molecular dynamics is a suitable tool for conformational searching of small molecules given suitable simulation parameters. The structures derived from the simulations are compared with the static conformation used in a previous study. Various physicochemical parameters have been calculated for a set of conformations selected from the simulations using multivariate analysis. The averaged values of the parameters over the selected set (and the factors derived from them) are compared with the single conformation values used in the previous study.     

31P solid state NMR studies of metal selenophosphates containing [P2Se6]4-, [P4Se10]4-, [PSe4]3-, [P2Se7]4-, and [P2Se9]4- ligands

31P solid-state nuclear magnetic resonance (NMR) spectra of 12 metal-containing selenophosphates have been examined to distinguish between the [P(2)Se(6)](4-), [PSe(4)](3-), [P(4)Se(10)](4-), [P(2)Se(7)](4-), and [P(2)Se(9)](4-) anions. There is a general correlation between the chemical shifts (CSs) of anions and the presence of a P[bond]P. The [P(2)Se(6)](4-) and [P(4)Se(10)](4-) anions both contain a P[bond]P and resonate between 25 and 95 ppm whereas the [PSe(4)](3-), [P(2)Se(7)](4-), and [P(2)Se(9)](4-) anions do not contain a P[bond]P and resonate between -115 and -30 ppm. The chemical shift anisotropies (CSAs) of compounds containing [PSe(4)](3-) anions are less than 80 ppm, which is significantly smaller than the CSAs of any of the other anions (range: 135-275 ppm). The smaller CSAs of the [PSe(4)](3-) anion are likely due to the unique local tetrahedral symmetry of this anion. Spin-lattice relaxation times (T(1)) have been determined for the solid compounds and vary between 20 and 3000 s. Unlike the CS, T(1) does not appear to correlate with P-P bonding. (31)P NMR is also shown to be a good method for impurity detection and identification in the solid compounds. The results of this study suggest that (31)P NMR will be a useful tool for anion identification and quantitation in high-temperature melts.     

Lithiation and electrophilic substitution of 8-chlorodibenz[b,f][1,4]-oxazepine-10-tert-butylcarbamate: The preparation of novel fused heterocyclic derivatives of 8-chlorodibenzoxazepine

Lithiation of 8-chlorodibenz[b,f][1,4]oxazepine-10-tert-butylcarbamate ( 1 ) is described. Electrophilic substitution of the resulting N-Boc dibenzoxazepine α- lithioamine 2 with ketones, aldehydes, nitriles, iso-cyanates and imines, followed by an in-situ cyclization, gave fused carbamates 5–26 , fused 2H-imidazol-2-ones 27–29 , fused hydantoins 30–32 , and fused ureas 33–35 , respectively, in 11–66% yield.     

Rh complexes of 1-(2,4,6-triisopropylphenyl-)3-methyl-1H-phosphole: preparation and use as catalysts in the hydroformylation of styrene

In the series of 1-(2,4,6-trialkylphenyl-)3-methyl-1H-phospholes (1a–c) that are to a certain extent of aromaticity, only the isopropyl substituted one (1a) entered into reaction with dimeric (pentamethylcyclopentadienyl)rhodium dichloride to afford Rh(III) complex (2a) in a reversible manner. After a careful workup, (2a) could be prepared and characterized whose stereostructure was elucidated by B3LYP/3–21G*, B3LYP/6–31G* and LANL2DZ calculations. Complex (2a) as a preformed catalyst, as well as the Rh(acac)(CO)₂ + 2(1a) in situ catalytic system were useful in the hydroformylation of styrene and gave the branched aldehyde in regioselectivities of 65–96%.     

Achieving ‘Desirable and Feasible’ Change: An Application of Soft Systems Methodology

Rational intervention in human affairs, if it is to constitute not only action but also research, so that future interventions may be made more effective, needs a well-defined methodological framework. Soft systems methodology (S.S.M.) provides one such framework. S.S.M. is doubly systemic: it is itself a learning system, and within that system it uses systems models, models of human activity systems. It accepts that such models are not models of parts of the real world, only models of ways of perceiving the real world, that is to say, models relevant to debate about ‘reality’ (one man's ‘terrorism’ is another's ‘freedom fighting’).S.S.M. is here illustrated by means of an account of a systems study of change in the information function of a sophisticated science-based company. The study is described from the point of view of a professional analyst who was helping a team of three managers carry out the study. The course of the study is described, and a separate commentary relates its activity to the seven stages of S.S.M. The study involved three cycles round stages 2–3–4–5 of S.S.M., the stages in which models of relevant human activity systems are built and compared with the real world in order to construct a rich debate about changes whose introduction in the problem situation world be both (systemically) desirable and (culturally) feasible.     

Microheterogeneity in aqueous-organic solutions: Heat capacities,volumes and expansibilities of some alcohols,aminoalcohol and tertiary amines in water

The heat capacities per unit volume and the densities of aqueous solutions of 2-propanol, neopentanol, tert-amylalcohol, 2-amino-2-methylpropanol, triethylamine and diethylmethylamine were measured, in many cases as a function of temperature, over the whole mole fraction or solubility range. Apparent and partial molal heat capacities, volumes and expansibilities were derived. The concentration dependence of these functions suggest the existence of transitions in some of these systems, in the water-rich region, qualitatively similar to micellization. The large relaxation contribution observed with some of the thermodynamic functions of hydrophobic alcohols and amines suggests a reinforcement of hydrophobic hydration due to strong hydrogen-bonding interactions of the polar groups with water.     

Ultraviolet photolysis of CH2I2 in methanol: O-H insertion and HI elimination reactions to form a dimethoxymethane product

Ultraviolet photolysis of low concentrations of CH2I2 in methanol solution found that CH2I2 is converted into dimethoxymethane and some H+ and I- products. Picosecond time-resolved resonance Raman (ps-TR3) experiments observed that the isodiiodomethane (CH2I-I) photoproduct decayed faster as the concentration of methanol increases, suggesting that isodiiodomethane is reacting with methanol. Ab initio calculations indicate isodiiodomethane is able to react with methanol via an O-H insertion/HI elimination to form an iodoether (ICH2-O-CH3) and HI products. The iodoether can then further react via another O-H insertion/HI elimination reaction to form the dimethoxymethane (CH3-O-CH2-O-CH3) observed in the photochemistry experiments. A reaction mechanism consistent with these experimental and theoretical observations is proposed.     

Comparison of the dehalogenation of dihalomethanes (CH2XI, where X = Cl, Br, I) following ultraviolet photolysis in aqueous and NaCl saltwater environments

The ultraviolet photolysis of low concentrations of CH(2)XI (X = Cl, Br, I) were investigated in water and saltwater solutions by photochemistry and picosecond time-resolved resonance Raman spectroscopy. Photolysis in both kinds of solutions formed mostly CH(2)(OH)(2) and HI and HX products. However, photolysis of the CH(2)XI molecules in saltwater resulted in production of some CH(2)XCl products not observed in aqueous solutions without salt present. The appearance of these new products in saltwater solutions is accompanied by a decrease in the amount of CH(2)(OH)(2), HI, and HX products compared to photolysis in aqueous solutions without salt present. The possible implications for photolysis of CH(2)XI and other polyhalomethanes in seawater and other salt aqueous environments compared to nonsaltwater solvated environments is briefly discussed.     

Influence of shell strength on shape transformation of micron-sized,monodisperse, hollow polymer particles

Micron-sized, monodisperse, non-spherical polymer particles with "rugby ball" and "red blood corpuscle"-like shapes were produced by seeded polymerization of the dispersion of (divinylbenzene/vinylbiphenyl/xylene)-swollen polystyrene particles prepared by utilizing the dynamic swelling method which the authors proposed in 1991. Their non-spherical shapes were based on buckling of the shell of the resultant hollow particles. In this article, the reversible shape transformation of the hollow composite polymer particle between spherical and such non-spherical shapes was studied in detail by controlling the shell strength. A part of the shell was buckled by external pressure which was caused by evaporation of xylene from the hollow when the shell had the tensile modulus below the critical value calculated from the pressure-buckling relationship of a spherical shell proposed by Uemura. The plasticization of the shell by a good solvent was one of key factors for the shape transformation.