Electronic and Resonance Raman Spectra of the Hexanuclear Cluster [Ru30(02CCH3)6 {(pyrazine)Ru(NH3)5}3 6+

Abstract

The trinuclear [Ru³0(00CCH³)⁶, (pyrazine)³] cluster reacts with pentaammineruthenium(II) ions, yielding a hexanuclear pyrazine bridged complex. The hexanuclear cluster exhibits a broad absorption band around 1000 nm and a strong band at 533 nm, ascribed to metal-metal and metal-pyrazine charge transfer transitions, respectively. Excitation at the visible band leads to the enhancement of the totally symmetric vibrational modes of pyrazine at 1605, 1230, 1085 and 700 cm?¹, and of a vibrational peak at 335 cm?¹, ascribed to the Ru(peripheral)-N(pyrazine) stretching mode. The spectroscopic data are consistent with a weak coupling between the central and peripheral ruthenium ions.     

Deviation from van't Hoff dependence in RP-LC induced by tautomeric interconversion observed for four compounds

The most encountered situations in reversed-phase liquid chromatography for temperature dependence of retention are those obeying the linear equation known as the van't Hoff plot. When studying compounds that are involved in structural modifications, it is likely that the temperature dependences of their retention factors do not follow this rule. It is the aim of this paper to report some particular cases when compounds involved in tautomeric interconversion have a different retention behavior with temperature: a deviation from the linearity of ln k on 1/T, or, in certain temperature ranges, temperature increase leading to a retention increase. Examples of compounds exhibiting deviation from the van't Hoff temperature dependence are piroxicam, drotaverine, vincamine, and epivincamine. A simple thermodynamic model relying on tautomeric equilibria in mobile phase is proposed for these compounds, which gives a polynomial dependence between ln k and 1/T.     

Investigation of the effects of ultrasound on vegetal tissues during solvent extraction

The paper presents an insight into the mechanism of the ultrasonic enhancement of solvent extraction through the effect of ultrasound on the vegetal material involved. Thus, a series of experiments has been developed to investigate the effect of ultrasonic energy on the vegetal material and the solvent used. Several results concerning the ultrasonic extractive value, ultrasonic swelling index and the effects of frequency on vegetal material are presented.     

The ultrasonically induced reaction of benzoyl chloride with nitrobenzene: an unexpected sonochemical effect and a possible mechanism

A mixture of benzoyl chloride and nitrobenzene is not known to be chemically reactive, indeed the mixture is chemically inert when subjected individually to either ultrasonic irradiation or heating. However, if this system is initially subjected to ultrasound and then heated for several hours at 200 degrees C, a reaction does occur and the products are benzoic anhydride, hydrochloric acid, nitrous and nitric acid together with some minor products. To the best of our knowledge, this is the first example of a reaction where the effect of ultrasound does not appear to be the consequence of the direct action of acoustic cavitation bubbles. A possible explanation of this behaviour is advanced which involves an electron transfer reaction in which nitrobenzene is first activated by ultrasound and then acts as oxidant in the thermal stage of reaction.     

Inequalities between ∥f(A + B)∥ and ∥f(A) + f(B)∥

The conjecture posed by Aujla and Silva [J.S. Aujla, F.C. Silva, Weak majorization inequalities and convex functions, Linear Algebra Appl. 369 (2003) 217-233] is proved. It is shown that for any m-tuple of positive-semidefinite n × n complex matrices A_j and for any non-negative convex function f on [0, ∞) with f(0) = 0 the inequality ?f(A₁) + f(A₂) + ? + f(A_m)? ? ? f(A₁ + A₂ + ? + A_m)? holds for any unitarily invariant norm ? · ?. It is also proved that ?f(A₁) + f(A₂) + ? + f(A_m)? ? f(?A₁ + A₂ + ? + A_m?), where f is a non-negative concave function on [0, ∞) and ? · ? is normalized.