Statistical mechanics of worm-like polymers from a new generating function

We present a mathematical approach to the worm-like chain model of semiflexible polymers. Our method is built on a novel generating function from which all the properties of the model can be derived. Moreover, this approach satisfies the local inextensibility constraint exactly. In this paper, we focus on the lowest order contribution to the generating function and derive explicit analytical expressions for the characteristic function, polymer propagator, single chain structure factor, and mean square end-to-end distance. These analytical expressions are valid for polymers with any degree of stiffness and contour length. We find that our calculations are able to capture the fully flexible and infinitely stiff limits of the aforementioned quantities exactly while providing a smooth and approximate crossover behavior for intermediate values of the stiffness of the polymer backbone. In addition, our results are in very good quantitative agreement with the exact and approximate results of five other treatments of semiflexible polymers.     

An effective synthesis method for secondary fluorinated alcohols via the reaction of esters of polyfluorinated acids with trialkylalanes

Unlike nonfluorinated analogs, complex esters of polyfluorinated acids in reactions with trialkylalanes produce only polyfluorinated secondary alcohols.Department of Fine Organic Synthesis, Institute of Organic Chemistry, Urals Branch, Russian Academy of Sciences, 450054 Ufa. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2339–2341, October, 1992.     

Cycloadditions dipolaires-1,3-XXV: Formation sous controle cinetique d'invertomeres stables lors des cycloadditions d'esters nitroniques

The addition of nitronic esters to α,β-diactivated olefins leads to the formation under kinetic control of invertomers of N-alkoxy isoxazolidines. These results and the conformational properties of the heterocycles are discussed in terms of the anomeric effect and ‘gauge effect”.     

Oscillations in solvent fraction of polyelectrolyte multilayers driven by the charge of the terminating layer

We have investigated polyelectrolyte multilayers of poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) in contact with D2O by neutron reflectometry. The study particularly focuses on the changes in the solvent fraction of the system upon addition of a layer. When the layers are deposited at a low salt concentration (0.25 M NaCl), no significant changes in the solvent fraction are detected. In contrast, at a larger salt concentration (1 M NaCl), oscillations in the solvent fraction are detected when a new layer is deposited. In this case, addition of PSS systematically increases the solvent volume fraction, and addition of PAH decreases the solvent fraction. The results suggest that one of the parameters driving the oscillations in solvent fraction is the uncompensated charges present in the layers. This study opens new perspectives on results previously published by other authors: in addition to polymer desorption, water uptake or release might contribute to the different regimes of multilayer growth reported in the literature (linear, asymmetric, or exponential growth). In addition, comparison to NMR results previously reported allows for conclusions about the mobility of the solvent in the multilayers: the average rotational correlation time of the water molecules in the polyelectrolyte layers decreases upon addition of PSS and increases upon addition of PAH.     

Structural elucidation of a new delta2-pyrazoline derivatives using 1H and 13C NMR spectroscopy

This paper describes the unequivocal structural elucidation of a new kind of Delta2-pyrazoline derivatives carried out by means of monodimensional 1H and 13C NMR spectroscopies, bidimensional ones such as HMBC and HMQC experiments, and NOEDIFF effects. Conformational analysis of this molecule agrees very well with the experimentally NOEDIFF effects found.     

Role of hydrogen bonds in the fast dynamics of binary glasses of trehalose and glycerol: a molecular dynamics simulation study

Trehalose-glycerol mixtures are known to be effective in the long time preservation of proteins. However, the microscopic mechanism of their effective preservation abilities remains unclear. In this article we present a molecular dynamics simulation study of the short time, less than 1 ns, dynamics of four trehalose-glycerol mixtures at temperatures below the glass transition temperature. We found that a mixture of 5% glycerol and 95% trehalose has the most suppressed short time dynamics (fast dynamics). This result agrees with the experimental analysis of the mean-square displacement of the hydrogen atoms, as measured via neutron scattering, and correlates with the experimentally observed enhancement of the stability of some enzymes at this particular concentration. Our microscopic analysis suggests that the formation of a robust intermolecular hydrogen bonding network is most effective at this concentration and is the main mechanism for the suppression of the fast dynamics.     

(RS)-, (R)- and (S)-3-benzyl-3-ethyl 2-oxetanone polymerization with chiral and achiral initiators

The polymerization of 3-benzyl-3-ethyl 2-oxetanones leads to three types of polymers: polyRS (enantiomer excess,ee=0), polyR or polyS (Ree >See) and polyracemate. All these polymers are crystalline and the thermal properties (T _g, meltingT _M and H _M) depend mainly on theee of the polymer. The propagation of the polymerization is not stereospecific. The use of heating-cooling cycles leads to a pure crystalline form melting at the highest temperature. The polyracemate has the behaviour of a pure polymer which melts at a lower temperature, a prolonged heating in the melt induces a strong racemization.

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Zusammenfassung Die Polymerisation von 3-benzyl-3-ethyl 2-oxetanon führt zu drei Polymer Typen: PolyRS (überschuss des Enantiomers,EE=0), PolyR oder PolyS (REE > SEE) und Polyracemate. Alle Polymere sind kristallin und die thermischen Eigenschaften (T _g, SchmelzeT _M und H _M) hängen wesentlich vonEE des Polymers ab. Die Fortpflanzung der Polymerisation ist nicht stereospeeifisch. Die Verwendung von Aufheitzen Abkühl Zyklen führt zu einer reinen kristallinen Form, die bei der höchsten Temperatur schmilzt. Das Polyracemat verhält sich wie ein reines Polymer, das bei niedrigeren Temperatur schmilzt; es racemisiert im Laufe einer verlängerten Erhitzung im Schemlzfluss.