Pressure and Temperature Probe for Studies of Biological Materials

In our previous paper [1] a high pressure technique for monitoring pressure up to 700 MPa and temperature from m 40 °C to +100 °C in several pressure vessels simultaneously was reported. This technique, applied in Unipress High Pressure Multivessel Apparatus for studies of biological materials, revealed some limitations. In this paper we propose a new solution which allows to overcome them. In this solution two different pressure media are used, separated from each other: one suitable for biological studies and the other proper for electric sensors. A new integrated pressure/temperature probe is presented in which manganin pressure gauge is confined in a metal bellows separating the two pressure transmitting media. The bellows can be easily assembled or disassembled, allowing promptly to refill pressure medium or to replace the pressure gauge. Temperature is measured by constantan/copper thermocouple. The probe is linked to data acquisition system. Taking into account temperature dependence of the manganin pressure gauge, simultaneous measurements of the resistance of pressure gauge and thermocouple voltage allow to compute pressure at any temperature. The new probe is integrated with the bottom closure of the pressure vessel which also incorporates capillary inlet. Such a design leaves free access from the top of the vessel, allowing easy mounting the studied samples as well as other additional probes.     

Multiparticle continuum in the excitation spectrum of the compound CsNiCl

Recent neutron scattering experiments on CsNiCl₃ reveal some features that are not well described by the standard nonlinear σ model, nor by numerical simulations, for isolated S = 1 spin chains. In particular, in real systems at the antiferromagnetic point of the Brillouin zone, the intensity of the continuum of multiparticle excitations, at T = 6 K, is about 5 times greater than predicted. Also, the spin gap is higher and the correlation length is smaller than predicted. We propose a theoretical scenario where the interchain interaction is approximated by an effective staggered magnetic field, and that yields a correct prediction for the observed quantities. Received 2 October 2002 / Received in final form 19 March 2003 Published online 7 May 2003     

Theoretical Studies of Water''s and Methanol''s Effects on Alcoholysis of N-Benzyl-3-oxo-β-sultam

The mechanisms about the water's and methanol's effects on the alcoholysis of N-benzyl-3-oxo-β-sultam together with their differences have been studied by using density functional theory at the B3LYP/6-31G* level. The results, in comparison with a previous study on the relative reaction without the assistance of water and methanol, show that the added water or methanol can remarkably reduce the energy barrier of alcoholysis reaction of N-benzyl-3-oxo-β-sultam and the most favorite pathway is the breaking of C-N bond instead of S-N. It is also found that the reaction energy barrier of methanol-assisted alcoholysis is a little higher than that of the water-assisted one.     

A theoretical analysis of the magnetic properties of La<Subscript>2</Subscript>CuO<Subscript>4</Subscript>

The magnetic properties of the La₂CuO₄ are analyzed by means of the paramagnetic solution of the Hubbard model within the composite operator method. The experimental findings of the inelastic neutron magnetic scattering [R. Coldea et al., Phys. Rev. Lett. 86, 5377 (2001)] for the spin spectrum, the spin-wave intensity and the behavior of the dispersion at the zone boundary are well described by our results although the difference in phase. The Hubbard model emerges has a minimal model capable to describe the anomalous magnetic behavior of such a strongly correlated material. Received 29 July 2002 / Received in final form 2 January 2003 Published online 14 March 2003     

Ligand-Controlled Regiodivergence in Nickel-Catalyzed Vinylcyclopropane Rearrangement

A ligand-controlled regiodivergence in Ni-catalyzed rearrangement of vinylcyclopropanes to 1,4- or 1,5-disubstituted cyclopentenes is reported. The 1,4- or 1,5-disubstituted cyclopentene is selectively obtained depending on the choice of ligands. Detailed kinetic studies and density functional theory calculations on the catalytic cycle revealed that the product selectivity is determined at the reductive elimination step from the six-membered η₁-allyl intermediate.     

Complex Formation Reactions of Dimethyltin(IV) with Some Zwitterionic Buffers

Equilibrium studies in aqueous solution are reported for dimethyltin(IV) complexes of zwitterionic buffers, such as bicine and tricine (L). Stoichiometry and stability constants for the complexes formed were determined at 25°C and ionic strength 0.1M NaNO₃. The results showed the best fit of the titration curves were obtained for complexes MLH, ML, ML₂, MLH_-1, and MLH_-2 with the hydrolysis products of the dimethyltin(IV) cation. The bonding sites of the dimethyltin(IV) complexes with bicine and tricine at different pH were characterized in the solid state by elemental analyses, FTIR, and TG analysis. The molecular formula of the complexes synthesized at pH=3.0 is [(CH₃)₂Sn(L)(H₂O)]Cl while in neutral and alkaline media the hydrolytic species are formed.     

The hydration of caesium chloride in aqueous solutions

Summary The temperature dependence of the adiabatic compressibility of solutions of caesium chloride in water has been determined for different solute concentrations from 14 to 40 wt.%. The compressibility data thus obtained, together with density data, are described in terms of water coordination shells by using a simple model, without the need for further information on the physical properties of the hydration sphere. On the basis of the analysis performed it has been possible to estimate the values of the volume contraction caused by ion-water interactions, the intrinsic volume of ions, the hydration numbers, the compressibility and density of water in hydration shells and their variation with temperature and salt concentration.

---

Riassunto è state misurata la compressibilità adiabatica di soluzioni acquose di cloruro di cesio in funzione della temperatura e della concentrazione di sale nell’intervallo (14÷40)% in peso. I dati di compressibilità, insieme a quelli di densità delle stesse soluzioni, sono stati interpretati facendo uso di un semplice modello che tien conto delle sfere di idratazione degli ioni. Sulla base dell’analisi effettuata è stato possibile valutare la contrazione di volume dovuto all’interazione ione-acqua, il volume intrinseco degli ioni, i numeri di idratazione, la compressibilità e densità dell’acqua nelle sfere di idratazione e la dipendenza di queste quantità dalla temperatura e concentrazione di sale.

---

Резюме Определяется температурная зависимость адиабатической сжимаемости растворов хлорида цезия в воде для различных концентраций в интервале (14÷40) весовых процетов. данные, полученные для сжимаемости, вместе с данными дия плотности описываются в рамках простой модели в терминах водяных координационных оболочек, без использования информации о физических свойствах сферы гидратации. На основе проведенного анализа можно оценить величину объемного сжатия, обусловленного взвимодействиями ионов и воды, собственный объем ионов, числа гидратации, сжимаемость и плотность воды в сфере гидратации и их изменения с температурой и концентрацией соли.

     

A model potential approach for the high-temperature expansion of liquid aluminium

Summary Model potential method, in association with the optimized cluster theory, permits a calculation of hot-expanded-liquid-aluminium properties in good agreement with recent experimental results. The influence of the exchange-correlation correction introduced in the dielectric constant is investigated. Some theoretical results outside the present experimental range are also discussed. To speed up publication, the author of this paper has agreed to not receive the proofs for correction.     

Experimental structure factor of liquid mercury by neutron diffraction

Summary The experimental determination of the static structure factor of liquid mercury at room temperature has been done by employing a neutron beam from a steady source (Triga reactor at Casaccia, Rome). The anomalous behaviour of the structure factor has been found enough in agreement with previous X-ray measurements. The present data have been used to test a potential function including Friedel oscillations, by a Monte Carlo simulation.

---

Riassunto Il fattore di struttura statico del mercurio liquido è stato misurato a temperatura ambiente per mezzo della diffrazione di neutroni termici. L'esperimento è stato realizzato presso la sorgente continua della Casaccia (Reattore Triga, Casaccia, Roma). Il comportamento anomalo del fattore di struttura, trovato in esperimenti di diffrazione di raggi X, è confermato dalla presente misura di neutroni. I dati sperimentali sono stati usati per verificare l'ipotesi di un potenziale interatomico contenente le oscillazioni di Friedel. I risultati di una simulazione Monte Carlo sono presentati.

     

Pseudoclassical approach to electron and ion density correlations in simple liquid metals

Il Nuovo Cimento D - Electron-electron and electron-ion structural correlations in simple liquid metals are treated by using effective pair potentials to incorporate quantal effects into a...