Thermodynamics of coupled reactions by the amplitudes of chemical relaxation

The amplitudes of the relaxation curves, as obtained by the Temperature-jump method have been used to measure simultaneously equilibrium constant and enthalpy for the reaction of complex formation of Ni²⁺ ion by 2,6-dihydroxobenzoic acid in the presence of a buffer. The experiments have been performed by changing the concentration of metal ion at constant ligand concentration andpH as in a complexometric titration. The points of such ‘dynamic titrations’ have been analysed by means of the concept of ‘normal reactions’ which enabled us to transform a set of coupled individual steps into a set of kinetically independent reactions. The potentialities of the dynamic titrations are discussed.     

Spatiotemporal dynamics of damped propagation in excitable cardiac tissue

Compared to steadily propagating waves (SPW), damped waves (DW), another solution to the nonlinear wave equation, are seldom studied. In cardiac tissue after electrical stimulation in an SPW wake, we observe DW with diminished amplitude and velocity that either gradually decrease as the DW dies, or exhibit a sharp amplitude increase after a delay to become an SPW. The cardiac DW-SPW transition is a key link in understanding defibrillation and stimulation close to the refractory period, and is ideal for a general study of DW dynamics.     

DTI of trabecular bone marrow

The development of NMR diffusion imaging and diffusion tensor imaging (DTI) has offered the possibility of studying the porous structures beyond anatomical imaging. In fact, random molecular motions, within tissue components, probe tissue microstructures. Up to now, the DTI method was mainly used to investigate cerebral morphology and study white matter diseases. In this study, it has been applied to trabecular bone marrow analysis to obtain structural information on spongy bone tissue. Our first results show that DTI could represent an important tool in studying the microstructural architecture of the trabecular bone as well as the microarchitecture of porous media.     

Coordination properties of 3-functionalized beta-cyclodextrins. Thermodynamic stereoselectivity of copper(II) complexes of the A,B-diamino derivative and its exploitation in LECE

The bis-amino AB derivative of beta-cyclodextrin on the secondary rim was synthesised and spectroscopically characterised by different techniques. Its binary systems both with protons and copper(II) were thermodynamically characterised by pH-metric potentiometry. In addition the ternary systems with each of the enantiomers of tryptophan and alanine were investigated. A thermodynamic stereoselectivity was observed for the tryptophan enantiomers and this was exploited to separate them by capillary electrophoresis through a ligand exchange mechanism (LECE). LECE separation of racemates of phenylalanine and tyrosine was also obtained.     

A comparative chemotaxonomic study on Vinca sardoa steam and Vinca difformis pourret

The phytochemical analysis of iridoidic fraction of the aerial parts of Vinca sardoa and Vinca difformis, gave the identification of loganic acid in V. difformis as unique iridoid glucoside, while loganin is also present in V. sardoa. The two taxa highly differ in alkaloids, so the chemotaxonomic classification in two different species is supported.     

Photochemical synthesis of copper nanoparticles incorporated in poly(vinyl pyrrolidone)

The effect of the presence of poly(vinyl pyrrolidone) (PVP) on the copper nanoparticle formation, obtained by UV irradiation of ethanol solution of Cu(acac)₂ (acac = 2,4-pentanedionato), was investigated. At 254 nm, in conditions of light completely absorbed by complex, the PVP exhibited protective and stabilizing effects, as shown by the formation of a colloidal copper solution and by a block of the heterogeneous process, which leads to thin film formation on the quartz walls. The colloidal solution was tested for several months by plasmon position and it was found that it remained unaltered in inert atmosphere, but returned to the starting complex on contact with air. The PVP ability to control the particle size was investigated by carrying out photoreduction sensitized by Hacac at 254 and 300 nm, in the presence of PVP concentration varying from 0 to 0.2 M. In this range it was possible to obtain copper nanoparticles of dimensions decreasing from 30 to 4 nm. Besides this, the PVP (0.005–0.05 M) role as sensitizer was investigated by irradiating solutions of Cu(acac)₂ at 300 nm which is an inactive wavelength for copper reduction by direct light absorption. It was found that the PVP was an efficient sensitizer of the copper photoreduction. The nanoparticles were characterized by plasmon band, Trasmission Electron Microscope (TEM) as well as Dynamic Light Scattering (DSL) analysis. The overall results evidence the advantages of the PVP use in the nanoparticle copper formation through the photochemical technique such as the exclusive formation of colloidal copper, their size control, stable colloidal solution and complete return to the starting complex.     

SELECTIVE PHOTOSENSITIZED OXIDATION OF THE METHIONYL RESIDUES IN ELASTASE

In recent years, significant advances have clarified the mechanism of photosensitized oxidations (see, for example, Foote, 1968), especially as regards the nature of the reactive oxidizing agents. This fact stimulated the development of reaction systems which allow selective photooxidation of specific components of biological macromolecules (Spikes and Livingston, 1969; Spikes and MacKnight, 1970). In the field of proteins, the selective conversion of the methionyl residues to the sulfoxide can be achieved by irradiation with visible light in the presence of hematoporphyrin at neutral or acid pH (Jori et al. , 1969).     

Photophysical and photobiological behavior of antimalarial drugs in aqueous solutions

This article describes the results of a combined photophysical and photobiological study aimed at understanding the phototoxicity mechanism of the antimalarial drugs quinine (Q), quinacrine (QC) and mefloquine (MQ). Photophysical experiments were carried out in aqueous solutions by stationary and time-resolved fluorimetry and by laser flash photolysis to obtain information on the various decay pathways of the excited states of the drugs and on transient species formed on irradiation. The results obtained showed that fluorescence and intersystem crossing account for all the adsorbed quanta for Q and MQ (quantum yield of about 0.1 and 0.9, respectively) and only for 24% in the case of QC, which has a negligible fluorescence quantum yield (0.001). Laser flash photolysis experiments evidenced, for QC and MQ, the occurrence of photoionization processes leading to the formation of the radical cations of the drugs. The effects of tryptophan and histidine on the excited states and transient species of the three drugs were also investigated. In parallel, the photoactivity of the antimalarial drugs was investigated under UV irradiation on various biological targets through a series of in vitro assays in the presence and in the absence of oxygen. Phototoxicity on 3T3 cultured fibroblasts and lipid photoperoxidation were observed for all the drugs. The photodamage produced by the drugs was also evaluated on proteins by measuring the photosensitized cross-linking of spectrin. The combined approaches were proven to be useful for understanding the mechanism of phototoxicity induced by the antimalarial drugs.     

Use of peptide nucleic acid probes for detecting DNA single-base mutations by capillary electrophoresis

Peptide nucleic acid (PNA) oligomers can be used as probes in pre-gel hybridization experiments, as an alternative to Southern hybridization. In this technique, the PNA probe is hybridized to a cyanine-5 labeled DNA sample denatured at low ionic strength, and the mixture is directly injected for size separation into a capillary electrophoresis (CE) system equipped with laser-induced fluorescence (LIF) detector. The neutral backbone of PNA allows hybridization to occur at low ionic strength and assures an efficient CE separation of the PNA/DNA hybrids from both double-stranded and single-stranded DNA. We have used as a model system the cystic fibrosis R553X and R1162X single-base mutations and we have assessed the influence of various factors, such as temperature and denaturants concentration on DNA/PNA hybrid stability in order to achieve the high specificity required for a single base pair discrimination.