Microscopic calculation of friction in heavy ion reaction using linear response theory

We present a realistic calculation of the frictional coefficients for²⁸Si+²⁰Ne system using the two-center shell model on the basis of the linear response theory. Adopting the center separationR and the deformationδ as collective variables we study the dependence of frictional coefficients γ _RR , γ _Rδ and γ_δδ on those variables, for various values of the neck parameter?, the temperatureT and the smearing widthΓ. The direct application of the linear response theory to the two-center potential gives non-vanishing friction for the simple translational motion of the two fragments even when they are far apart. A method to avoid this energy dissipation is proposed and is used in the calculation. Results show that the form factor of the frictional force is surface-peaked and the peak becomes lower as the prolate deformation or neck formation increases. Temperature dependence is mild, but is not negligible. We compare our γ _RR and γ_δδ with other models.     

Infrared spectra of polymer solutions. I. Conformational stability of isotactic polymer chains in solution

The infrared spectra of isotactic polystyrene, polypropylene, and poly-p-chlorostyrene were measured in dilute solutions or gels at various temperatures ranging from room temperature to ?100°C. For isotactic polystyrene and polypropylene, all the absorption bands characteristic of the helical conformation of the molecules increase in intensity with decreasing temperature, and show intensities at low temperature as strong as in the highly crystallized samples. This suggests that the molecules can assume very regular conformations even in solution. Similar temperature dependence of the spectra was observed for a homogeneous gel of isotactic poly-p-chlorostyrene, which is believed to be noncrystalline. These experimental facts lead to the conclusion that the stability of the TG type helical conformation of these isotactic polymers may be ascribed to the intramolecular forces within a molecule. The fact that these spectral changes are reversible has permitted a thermodynamic treatment of the conformational regularity in solution on the basis of the infrared data. The temperature dependence of the absorption intensities has been interpreted quantitatively by a simple statistical mechanical model, and the enthaply and the entropy differences between the helical and the random states of the monomeric residue in the molecular chain have been estimated.     

Solution-phase synthesis of alpha-rat atrial natriuretic peptide (alpha-rANP)

alpha-Rat atrial natriuretic peptide (alpha-rANP) was synthesized by assembling five peptide fragments in solution, followed by HF-dimethylselenide-m-cresol deprotection and subsequent air-oxidation. Synthetic alpha-rANP exhibited more potent diuretic and natriuretic activity in rats than synthetic alpha-hANP.     

Selective ring opening reactions of 3,7-diarylsulfonyl-1,3,5,7-tetrazabicyclo[3.3.1] nonaries

The selective formation of 1,3,5,7-tetrazacyelooctanes from the title compounds is described. Exclusive cleavage of the IN-CH₂-N bonds at the bridge methylene is shown to be a facile process, thus providing a convenient route to tetrazacyclooctane derivatives.     

Grafting onto wool. IV. Interaction of polymer radicals in the viscous media of wool fibers

In order to study the termination reaction of polymer radicals in the viscous media of wool fibers, reduced, methylated, and S-carboxymethylated wool fibers were used for graft copolymerization of methyl methacrylate and styrene. With termination of poly(methyl methacrylate) radicals, two different termination reactions, recombination and disproportionation, were together involved in the grafting systems studied. The occurrences of two termination reactions in the system could be correlated with the mobility of the wool chain controlling the radical end mobility. With decreasing disulfide content in the fibers, disproportionation predominantly takes place among the mobilized chains. At a constant disulfide, the thiol content or the concentration of thiol anions becomes the determining factor for the termination reaction. A possible explanation for these phenomena in terms of the thiol and disulfide interchange reaction is presented. On the grafting of styrene, additional evidence was obtained that prevention and retardation of the interchange reactions followed mechanochemical bond scission of the disulfide and other covalent bonds and produced new free radicals which could initiate chain reactions.     

Precipitation of magnesium ammonium phosphate from homogeneous solution by means of hydrolysis of p-nitrophenylphosphate with an alkaline phosphatase

In the precipitation of magnesium ammonium phosphate from homogeneous solution, phosphate ions were generated by means of hydrolysis of p-nitrophenylphosphate with an alkaline phosphatase. Conditions for the gravimetric determination of magnesium ion as magnesium ammonium phosphate hexahydrate were investigated.