Acid-catalyzed cyclization of epoxyallylsilanes. An unusual rearrangement cyclization process

[reaction: see text]. A new route for the synthesis of epoxyallylsilanes bearing the phenyldimethylsilyl group is reported that involves silylcupration of allene, conjugate addition to enones, and sulfur-ylide-mediated epoxidation. The Lewis acid-catalyzed cyclization of these substrates is presented. The expected normal products derived from 5-exo and/or 6-endo attack are not observed; instead, methylenecyclohexanols resulting from a tandem rearrangement-cyclization process are formed.     

Observation of dislocation line motion in a stressed cholesteric liquid crystal

Summary By means of an optical microscope we observed the instantaneous displacement and motion of dislocation lines in a cholesteric liquid crystal, when the sample was subjected to a mechanical normal strain. It was found that in the linear response regime the equilibrium is reached in a quasi-periodic way. We explain our results just in a phenomenological way. A preliminary account of this work was presented at the IX International Conference on Liquid Crystals, Bangalore (1982).     

Dynamical approach to conformal gravity and the bosonic string effective action

We show that a theory invariant under the full local conformal group in a coset realization contains naturally the massless degrees of freedom of the closed bosonic string. This effective theory is alternative to the bosonic part of SupergravityN=1 as given by Manton and Chapline [4].     

Vacancy formation volume of sodium,aluminium and argon

Summary The whole theory of vacancy formation volume, as developed in parts I, II, III, IV and V of this series, is applied at Al, Na and Ar. In Na the anharmonic terms are found to be responsible for about 35% of the formation volume at 300 K and bring the dominant contribution to its temperature derivative at constant pressure. In fact, we find in this case a negative expansion coefficient for the vacancy, in conflict with the results of Audit and Gilder (1978), who found a positive value, having neglected anharmonicity. The important implications of this result in the interpretation of self-diffusion data are discussed. The analysis of Al confirms the relevant weight of anharmonicity, but also the inadequacy of second-order pseudopotential theory for trivalent metals. Finally, for Ar our conclusions are in full agreement with those reached by Zubov (1980).

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Riassunto Questo articolo presenta l'applicazione a tre elementi (Al, Na e Ar) della teoria riguardante il volume di formazione di una vacanza, quale è sviluppata nelle parti del lavoro già pubblicate. Nel sodio i termini anarmonici risultano responsabili per circa il 35% del volume di formazione a 300 K e portano il contributo dominante alla sua dipendenza dalla temperatura (a pressione costante). Infatti si trova in questo caso un coefficiente negativo di espansione termica per la vacanza, in contrasto con i calcoli di Audit e Gilder (1978), che non tengono conto degli effetti anarmonici. Si discutono le importanti implicazioni di questo risultato nell'interpretazione delle misure di diffusione. L'analisi dell'alluminio conferma il ruolo rilevante giocato dall'anarmonicità, ma nel medesimo tempo l'insufficienza della teoria dello pseudopotentiale al second'ordine per metalli trivalenti. Infine, nel caso dell'argon solido i nostri risultati sono in ottimo accordo con quelli di Zubov (1980).

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Резюме Теория объема образования вакансии, развитая в частях I, II, III, IV и V этой серии, применяется к натрию, алюминию и аргону. Обнаружено, что в натрии ангармонические члены ответственны за 35% объема образования при 300 К и дают доминирующий вклад в зависимость от температуры (при постоянном давлении). Мы получаем в этом случае отрицательный коэффициент теплового расширения для вакансии, в противоположность результатам Аудита и Джилдера, которые получили положительный коэффицент, пренебрегая ангармоничностьй. Обсуждается применение результатов к интерпретации данных по самодиффузии. Анализ для алюминия подтверждает важность ангармоничности, но указывает на неадекватность второго порядка теории псевдопотенциала для трехвалентных металлов. В заключение, отмечается, что наши выводы для аргона хорошо согласуются с теорией, развитой Зубовым.

     

Optical properties of lyotropic mesophases

Summary A brief review of early studies of optical properties of lyotropic mesophases is presented. New results about refractive-index measurements in various phases of a ternary system are shown. Emphasis is given to the optical properties of the different lyotropic nematic mesophases. Finally a short review is then devoted to the optical effects of external applied fields such as magnetic, electric and mechanical ones. Associated to the GNCL (National Discussion Group on Liquid Crystals) and supported by the GNSM of the National Research Council.     

Behaviour of uniaxially preloaded aluminium plates subjected to high-velocity impact

The purpose of this paper is to evaluate the behaviour of structural thin plates made of 7075-T6 aluminium alloy under normal impact of spherical steel projectiles, when they are subjected to uniaxial in-plane tensile preload. Also, nonloaded plates were tested under high-velocity impact. The impact and residual velocity were measured in all tests. From the relationships between the impact and residual velocities, the ballistic limit was estimated by a least-squares method. No significant differences were found between the ballistic limits under the two loaded conditions. Above the ballistic limit in the preloaded plates, unstable cracks that can generate the catastrophic failure of the plate were observed. At similar velocities, this phenomenon was not observed in nonloaded plates.     

Computerized evaluation of mean residence times in multicompartmental linear system and pharmacokinetics

Deriving mean residence times (MRTs) is an important task both in pharmacokinetics and in multicompartmental linear systems. Taking as starting point the analysis of MRTs in open or closed (Garcia-Meseguer et al., Bull Math Biol 2003, 65, 279) multicompartmental linear systems, we implement a versatile software, using the Visual Basic 6.0 language for MS-Windows, that is easy to use and with a user-friendly format for the input of data and the output of results. For any multicompartmental linear system of up to 512 compartments, whether closed or open, with traps or without traps and with zero input in one or more of the compartments, this software allows the user to obtain the symbolic expressions, in the most simplified form, and/or the numerical values of the MRTs in any of its compartments, in the entire system or in a part of the system. As far as we known from the literature, such a software has not been implemented before. The advantage of the present software is that it reduces on the work time needed and minimizes the human errors that are frequent in compartmental systems even those that are relatively staightforward. The software bioCelTer, along with instructions, can be downloaded from http://oretano.iele-ab.uclm.es/~fgarcia/bioCelTer/.     

Seven-membered ring formation from cyclopropanated oxo- and epoxyallylsilanes

A useful strategy for cycloheptane annulations from oxo- and epoxyallylsilanes, prepared by silylcupration of allenes, has been developed, and their application to the stereoselective synthesis of 4-methylenecycloheptan-1-ols is of great potential in the construction of seven-membered ring natural products presented.     

Caracterización de la delaminación en materiales compuestos mediante la teoría de mezclas serie/paralelo

This paper presents a new procedure to deal with the delamination problem found in laminated composites, based in a continuum mechanics formulation. The procedure proposed obtains the composite constitutive performance with the Serial/Parallel mixing theory, developed by F. Rastellini. This theory characterizes composite materials by coupling the constitutive behaviour of the composite components, imposing an iso–strain relation among the components in the fibre (or parallel) direction and an iso-stress relation in the remaining directions (serial directions). The proposed procedure uses a damage formulation to characterize the constitutive behaviour of matrix component in order to obtain the stress-strain performance of this material.With these two formulations, the delamination phenomenon is characterized naturally by the numerical simulation, being unnecessary the definition of special elements or computationally expensive techniques like the definition of contact elements or mesh separation. Matrix failure, as a result of the stress state found in it, leads to a reduction of the stiffness and strength capacity of the composite in its serial directions, among them, the shear component. This stiffness reduction provides a composite performance equivalent to what is found in a delaminated material.To prove the ability of the formulation proposed to solve delamination problems, the End Notch Failure test is numerically simulated and the results obtained are compared with experimental ones. The agreement found in the results with both simulations, numerical and experimental, validate the proposed methodology to solve the delamination problem.     

Molecular Recognition of Rosmarinic Acid from Salvia sclareoides Extracts by Acetylcholinesterase: A New Binding Site Detected by NMR Spectroscopy

Acetylcholinesterase (AChE) inhibition is one of the most currently available therapies for the management of Alzheimer’s disease (AD) symptoms. In this context, NMR spectroscopy binding studies were accomplished to explain the inhibition of AChE activity by Salvia sclareoides extracts. HPLC‐MS analyses of the acetone, butanol and water extracts eluted with methanol and acidified water showed that rosmarinic acid is present in all the studied samples and is a major constituent of butanol and water extracts. Moreover, luteolin 4′‐O‐glucoside, luteolin 3′,7‐di‐O‐glucoside and luteolin 7‐O‐(6′′‐O‐acetylglucoside) were identified by MS² and MS³ data acquired during the LC‐MSⁿ runs. Quantification of rosmarinic acid by HPLC with diode‐array detection (DAD) showed that the butanol extract is the richest one in this component (134 μg mg^?1 extract). Saturation transfer difference (STD) NMR spectroscopy binding experiments of S. sclareoides crude extracts in the presence of AChE in buffer solution determined rosmarinic acid as the only explicit binder for AChE. Furthermore, the binding epitope and the AChE‐bound conformation of rosmarinic acid were further elucidated by STD and transferred NOE effect (trNOESY) experiments. As a control, NMR spectroscopy binding experiments were also carried out with pure rosmarinic acid, thus confirming the specific interaction and inhibition of this compound against AChE. The binding site of AChE for rosmarinic acid was also investigated by STD‐based competition binding experiments using Donepezil, a drug currently used to treat AD, as a reference. These competition experiments demonstrated that rosmarinic acid does not compete with Donepezil for the same binding site. A 3D model of the molecular complex has been proposed. Therefore, the combination of the NMR spectroscopy based data with molecular modelling has permitted us to detect a new binding site in AChE, which could be used for future drug development.