Biocatalysis and biorecognition in nonaqueous media. Some perspectives in analytical biochemistry

Biocatalysis and, to a lesser extent, biorecognition in non-aqueous media (including organic solvents as well as supercritical fluids and gases) constitute at present an exciting research area which has already demonstrated its biotechnological potential in numerous, varied applications. Less attention, however, has been paid to its analytical possibilities, even though many advantages have been postulated and a wide range of poorly water-soluble analytes are present in samples (or waste materials) from food and drink, petrochemical, pharmaceutical, military and other industries. The main approaches, developed in recent years to exploit the use of enzymes, antibodies or antibody mimics in water-restricted environments for analytical purposes, as well as possible future directions are briefly discussed.     

The relative permittivity of 1,2-dimethoxyethane and N,N-dimethylformamide mixtures from −10 to 40°C

Binary solutions of N,N-dimethylformamide and 1,2-dimethoxyethane have been investigated by means of dielectric measurements at temperatures ranging from –10 to +40°C, and for nine mixtures covering the whole miscibility field expressed by the mole fraction of one component (0X₁1). The experimental data were used to study the dependence of on T and X₁, of the type = (T), = (X₁), and = (T,X₁). Further, the excess mixing function _E has been evaluated in order to identify particular patterns of interaction between unlike molecules and any other factor that could modify such patterns. The minimum in the _E vs. composition plots suggests the formation of an adduct of stoichiometric ratio DMFDME=11 at all the investigated temperatures.     

Structural and Transport Properties of Mg1−xMnxMn2O4±δ Spinels

The synthesis and structural properties of Mg_1−xMn_2+xO₄, for 0≤x≤1 are described. Complete miscibility in the solid state exists for this system. For the material with the correct stoichiometry, i.e. MgMn₂O₄, the effect of temperature on the cation distribution was investigated= above 600°C the inversion degree (m) starts increasing. The electrical conductivity shows a small dependence on P(O₂) which is consistent with the small oxygen non-stoichiometry determined by means of thermogravimetry. The main contribution to the transport properties arises from the inversion equilibrium. Two distinct conductivity regimes, below and above the inversion threshold, can be assumed to explain the electrical conductivity and thermoelectric power results.     

Non-destructive in situ determination of pigments in 15th century wall paintings by Raman microscopy

Raman microscopy has been applied to the study of 15th century wall paintings in a chapel of St. Orso Priory palace (Aosta, Italy) in view of their restoration. The use of a transportable instrument has made it possible to work non-destructively in situ without sampling. The main inorganic pigments used by the unknown artist, namely mercury sulphide, azurite, white lead, red and yellow ochre, carbon black and lead tin yellow type I have been identified, and the presence of organic substances and of some decay products (calcium sulphate and oxalate) has been observed.     

Liquid-Phase Selective Oxidation of Propane on Silica-Supported Nafion Catalysts

The liquid-phase partial oxidation of propane in the presence of the Fen+/H2O2 Fenton system at 70℃ and 1.4 atm on silica supported Nafion catalysts has been investigated. The reaction proceeds via a radical reaction path the efficiency of which is improved by silica-supported Nafion catalysts. Because of the direct relationship between reaction rate and concentration of sulphonic acid sites of Nafion catalysts, it is inferred that the active phase enahnces the kinetics of propane conversion by promoting the rate of active radicals generation.     

Fused Mesoionic Heterocycles: Synthesis of 1,2,4-triazolo(4,3-b)-1,2,4-triazole derivatives

A number of mesoionic compounds derivatives of the bicyclic system 1,2,4-triazolo(4,3-b)-1,2,4-triazole have been prepared from 4-amino-1-methyl-3,5-bis(methylthio)-1,2,4-triazolium iodide and aryl isothiocyanates.     

Defect and dopant properties of MgTa2O6

Atomistic computer simulation techniques have been used, for the first time, to reproduce the crystal structure of MgTa₂O₆ and to investigate the defect chemistry and dopant properties of this material. The calculated defect energetics suggest that the concentration of intrinsic atomic defects in this phase is insignificant and that the system is probably stable to both oxidation and reduction. Dopant solution energy versus ion size trends are found for both isovalent and aliovalent dopant incorporation at Mg and Ta sites. Divalent dopants (e.g. Ca, Cu) preferentially occupy the Mg site whereas dopants with higher charge (e.g. Sc, Zr, Nb) are more favorable on the Ta site. High migration activation energies (>2 eV) predict limited ionic conductivity in this material.     

Hydrous ferric oxide: evaluation of Cd-HFO surface complexation models combining Cd(K) EXAFS data,potentiometric titration results,and surface site structures identified from mineralogical knowledge

The surface properties of ferrihydrite were studied by combining wet chemical data, Cd(K) EXAFS data, and a surface structure and protonation model of the ferrihydrite surface. Acid-base titration experiments and Cd(II)-ferrihydrite sorption experiments were performed within 3<-log[H(+)]<10.5 and 0.5<[Cd(t)]<12 mM in 0.3 M NaClO(4) at 25 degrees C, where [Cd(t)] refers to total Cd concentration. Measurements at -5.5triple bond Fe-OH(-1/2),logk((int))=-8.29, assuming the existence of a unique intrinsic microscopic constant, logk((int)), and consequently the existence of a single significant type of acid-base reactive functional groups. The surface structure model indicates that these groups are terminal water groups. The Cd(II) data were modeled assuming the existence of a single reactive site. The model fits the data set at low Cd(II) concentration and up to 50% surface coverage. At high coverage more Cd(II) ions than predicted are adsorbed, which is indicative of the existence of a second type of site of lower affinity. This agrees with the surface structure and protonation model developed, which indicates comparable concentrations of high- and low-affinity sites. The model further shows that for each class of low- and high-affinity sites there exists a variety of corresponding Cd surface complex structure, depending on the model crystal faces on which the complexes develop. Generally, high-affinity surface structures have surface coordinations of 3 and 4, as compared to 1 and 2 for low-affinity surface structures.     

Analysis of the effects of catalytic bleaching on cotton

Hydrogen peroxide can be catalyzed to bleach cotton fibers at temperatures as low as 30°C by incorporating dinuclear tri-μ-oxo bridged manganese(IV) complex of the ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (MnTACN) as the catalyst in the bleaching solution. The catalytic system was found to be more selective under the conditions applied than the non-catalytic H₂O₂ system, showing better bleaching performance while causing slightly lower decrease in degree of polymerization (DP) of cellulose. In order to gain fundamental knowledge of the bleach effect on cotton fibers and cellulose as its main component, especially after catalytic bleaching, X-ray Photoelectron Spectroscopy (XPS) was used to study surface chemical effects. The Washburn method was applied to investigate wetting properties, and liquid porosity was used to obtain pore volume distribution (PVD) plots. Parallel analyzes performed on model cotton fabric, i.e. “clean” cotton fabric stained with morin - a pigment regularly found in native cotton fiber, helped to differentiate between pigment oxidation and other bleaching effects produced on the (regular) industrially scoured cotton fabric. Bleaching was not limited to the chemical action but also affected cotton fiber capillary parameters most likely due to the removal of non-cellulosic materials as well as chain-shortened cellulose.     

Density and Volume Properties of the 2-Chloroethanol + 2-Methoxyethanol + 1,2-Dimethoxyethane Ternary Solvent System at Different Temperatures

The density of the 2-chloroethanol (CE) + 2-methoxyethanol (ME) + 1,2-dimethoxye- thane (DME) ternary mixtures has been measured at different temperatures ranging from –10 to 80^°C, and over the entire composition range. The experimental data have been used to check the validity of some relationships accounting for the dependence of the density on temperature and composition domains. Starting from the primary data, some derived quantities, such as excess molar volumes V ^E, partial molar volumes and partial excess molar volumes , have been obtained. In these mixtures, V ^E is always positive for the [CE(1) + ME(2)] binaries, while it is generally negative at all other experimental conditions, showing the greatest deviations along the binary axes corresponding to the binary subsystems in the sequence [CE(1) + DME(2)] < [CE(1) + ME(2)] < [ME(1) + DME(2)]. The results are compared and discussed to in terms of changes in molecular association and structural effects in these solvent systems.