Absorption microspectroscopy, theory and applications in the case of the photosynthetic compartment

We performed microspectroscopic evaluation of the pigment composition of the photosynthetic compartments of both algae and higher plants. The feasibility of microspectroscopy for discriminating among species and/or phylogenetic groups was tested on laboratory cultures. Gaussian bands decompositions, and a fitting algorithm, together with fourth-derivative transformation of absorbance spectra, provided a reliable discrimination among chlorophylls, phycobiliproteins and carotenoids. Comparative analysis of absorption spectra highlighted the evolutionary grouping of the algae into three main lineages in accordance with the most recent endosymbiotic theories.     

A new crown ether as vesicular carrier for 5-fluoruracil: synthesis, characterization and drug delivery evaluation

Niosomes have shown promise as cheap and chemically stable drug delivery systems. In this paper a novel crown ether amphiphile, 1,16-hexadecanoyl-bis-(2-aminomethyl)-18-crown-6 (Bola A-16), has been synthesized with the aim of developing a long time stable controlled release system. Niosomes have been prepared with different molar ratios of amphiphile and cholesterol and their morphological properties have been determined by quasi-elastic light scattering and transmission electron microscopy. The composition of niosomes affects the entrapment efficiency and the release rate of 5-fluorouracil, a well-known antineoplastic molecule. In addition, other two known azacrown ether amphiphiles (4,7,10,13-pentaoxa-16-aza-cyclooctadecane)-hexadecanedioc acid diamide (Bola D-16) and ,ω-(4,7,10,13-pentaoxa-16-aza-cyclooctadecane)-hexadecane (Bola C-16), have been synthesized and the obtained vesicles have been characterized for comparison. Furthermore, the release profile of 5-fluorouracil in vitro, from these niosomes, has been studied over a period of 6 h in order to simulate a hematic adsorption.     

A new approach to 4,6-disubstituted-3,4-dihydropyran-2-ones by Domino Michael addition-cyclization reaction under PTC conditions

Domino Michael addition-cyclization reactions of α,β-unsaturated carbonyl compounds with activated 1,3-dithiane-2-carbothioate esters under solid-liquid phase transfer catalysis conditions provide 4,6-disubstituted-3,4-dihydropyran-2-one-3,3-dithioacetals in good chemical yield. Desulfurization proceeds chemoselectively under mild conditions affording 3,4-dihydropyran-2-ones in high yields.     

The electro-optical response of nematic emulsions

Switchable nematic emulsions are micron-sized droplets of nematic liquid crystal, floating in isotropic fluid matrices. Such droplets can be switched from an opaque (off) to a transparent (on) state by application of very low electric fields. It is known that the electro-optical properties of liquid crystal dispersions are affected by several parameters, including the liquid crystal loading. The electro-optical response of nematic emulsions has been investigated as a function of liquid crystal weight percentage. Almost transparent films with a reduced contrast ratio are obtained with lower liquid crystal contents. A macroscopic phase separation is observed when liquid crystal content exceeds 45 wt %. On the contrary, large contrast ratios and very low switching fields can be obtained if liquid crystal ranges from 25 to 35 wt %. Consequently, nematic emulsions prepared in this liquid crystal range can be used as promising systems for electro-optical applications. In addition to technological developments, these results can help computational and basic studies of phase separation in novel multiphase liquid crystalline materials.     

Evolution of paper chromatography: from Runge''s perceptions to Tswett''s adsorption

Summary The historical development of paper chromatography is reviewed from the work of Runge up to the contribution of Tswett. The type of support, the path of substances and the forces responsible for the phenomenon are discussed in detail.     

Phase transition in saturated porous media: Pore-fluid segregation in consolidation

Consider the consolidation process typical of soils; this phenomenon is expected not to exhibit a unique state of equilibrium, depending on external loading and constitutive parameters. Beyond the standard solution also, pore-fluid segregation can arise. Pore-fluid segregation has been recognized as a phenomenon typical of the short time behavior of a saturated porous slab or a saturated porous sphere, during consolidation. In both circumstances, the Biot three-dimensional model provides time increasing values of the water pressure (and fluid mass density) at the center of the slab (or of the sphere), at early times, if the Lamé constant μ of the skeleton is different from zero. This localized pore-fluid segregation is known in the literature as the Mandel-Cryer effect. In this paper, a nonlinear poromechanical model is formulated. The model is able to describe the occurrence of two states of equilibrium and the switching from one to the other by considering a kind of phase transition. Extending the classical Biot theory, a more than quadratic strain energy potential is postulated, depending on the strain of the porous material and the variation of the fluid mass density (measured with respect to the skeleton reference volume). When the consolidating pressure is strong enough, the existence of two distinct minima is proven.     

Comparison of Finite Volume Canonical and Grand Canonical Gibbs Measures: The Continuous Case

We consider a continuous gas with finite range positive pair potential and we assume that the cluster expansion convergence condition holds. We prove a sharp bound on the difference between the finite volume grand canonical and canonical expectation of local observable. The bound is given in terms of the support of the observable, of its grand canonical variance and of the volume on which the system is confined.     

Anaerobic oxidation of non-activated secondary alcohols over Cu/Al2O3

A liquid phase, transfer dehydrogenation reaction promoted by an 8% Cu/Al(2)O(3) catalyst allows complete conversion of secondary alcohols into ketones under very mild conditions and in short times without any additives.     

FN+Cl Ions from Ionized F2NCl: a Computational Investigation on the Structure and Reactivity toward H2O

We have used various ab initio methods and basis sets to ascertain that the FN⁺Cl cation has a singlet ground state, ¹A′, which is more stable than the triplet state ³A″ by ca. 30 kcal mol^?1. We have subsequently used the Gaussian‐3 (G3) theory to explore the potential‐energy profile for the reaction between singlet FN⁺Cl and H₂O. The process commences by the effortless formation of a FN⁺Cl/H₂O complex, which, in principle, can undergo several alternative processes, including isomerization to N‐protonated FN(Cl)OH, 1,2‐elimination of HX (X=F or Cl), and 1,1‐loss of H₂. However, the energy barriers of all these processes are invariably larger than the energy (+18.1 kcal mol^?1) required for the formation of FN⁺Cl/H₂O from FN⁺Cl and H₂O, thus suggesting that, under gas‐phase thermal conditions, FN⁺Cl should be essentially unreactive toward H₂O. Comparing these theoretical findings with those concerning the reaction between FN⁺H, ClN⁺H, F₂N⁺, and H₂O, the reactivity order FN⁺H>F₂N⁺>ClN⁺H>FN⁺Cl, was derived, which parallels the trend we recently found by G2MS calculations concerning the Lewis acidity of these ions. This suggests the conceivable occurrence of correlations between the reactivity and thermochemical properties of these simple halonitrenium ions.