Calcium-induced aggregation of bovine caseins: effect of phosphate and citrate

The formation of colloidal particles by Ca²⁺ precipitation of whole caseinates in the presence of phosphate (Pi), citrate (Cit), or both of the anions in concentrations found to be effective in previous works was followed comparing the colloidal particle size and the ionic and proteic composition of the precipitates obtained. Ca²⁺ was incorporated to the precipitate and colloidal particles in a different way than Pi, differences which were related to the presence of Pi and/or Cit in the media. A sequential salting-out process due to progressive Ca²⁺ binding to at least two kinds of sites was observed. The precipitation curves were fitted, and the affinity constants and binding site numbers were calculated with a modification of the Farrell’s equation based on the concept of Wyman’s linked functions. Precipitates obtained at low total Ca²⁺ concentrations in different conditions varied their casein composition. Colloidal particles appeared at the beginning of the second salting-out step, in different amount, and in average size according to the presence or absence of Pi and/or Cit in the media. Consideration of these differences showed that Cit favored the formation of bigger colloidal particles, acting especially in the first steps of the casein aggregation and conditioning the mechanism of this process.     

Stereo-differentiation in the excited state behaviour of naphthalene-thymine dyads

Using two diastereomeric dyads containing naphthalene and thymine units, significant chiral discrimination has been found in the photophysical processes involving the naphthalene excited states: singlet deactivation by hydrogen bonding molecules, singlet-singlet energy transfer from thymine and triplet decay.     

Capillary electrophoresis and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry for analysis of the novel erythropoiesis-stimulating protein (NESP)

NESP (novel erythropoiesis-stimulating protein) is a recently approved hyperglycosylated analogue of human erythropoietin (EPO) with a long-lasting effect. In this work, the capillary electrophoresis (CE) methodology proposed by the European Pharmacopoeia for the separation of EPO glycoforms has been modified for the separation of NESP glycoforms. Optimization of pH of the separation electrolyte has been fundamental in order to achieve baseline resolution of seven peaks corresponding to NESP glycoforms. Intact NESP has also been characterized by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). An accurate approximation to an average molecular mass of the NESP molecule has been obtained, taking into account the strong influence of laser intensity upon the MALDI-TOF mass spectra found.     

Liquid–liquid phase behaviour,liquid–liquid density,and interfacial tension of multicomponent systems at 298 K

Experimental liquid–liquid phase diagrams are presented for the multicomponent systems isooctane–benzene–(80 mass% methanol + 20 mass% water)–5 mass% isobutyl alcohol (2-methyl-1-propanol) and isooctane–benzene–(80 mass% methanol + 20 mass% water)–15 mass% isobutyl alcohol, at 298.15 K. The density and interfacial tension of conjugate phases of concentration located in the isothermal binodal have been determined at 298.15 K for the partially miscible systems: isooctane–benzene–methanol, isooctane–benzene–(80 mass% methanol + 20 mass% water), isooctane–benzene–(80 mass% methanol + 20 mass% water)–5 mass% isobutyl alcohol, and isooctane–benzene–(80 mass% methanol + 20 mass% water)–15 mass% isobutyl alcohol. The experimental tie-line data define the binodal or coexistence curve of the two studied multicomponent systems and depending on the initial isobutyl alcohol concentration the liquid–liquid phase diagram is either of type II, with low alcohol concentration, or type I, with high concentration of alcohol, which is a clear indication that the solubility of the partially miscible systems is greatly enhanced via the co-solvency phenomenon. It is observed that both the density of each conjugate phase and the interfacial tension of each tie-line are valuable indicators of the degree of solubility of the multicomponent systems. Furthermore the experimental tie-lines data were correlated with the NRTL and UNIQUAC solution models with satisfactory quantitative results.     

Energetics and bonding in beryllium metallized carbon clusters

Small carbon clusters C, C₂ and C₃ metallized with beryllium were studied by first principles within the hybrid density functional approach with generalized gradient correction. Cluster isomer structures for the ground state and several excited states where systematically calculated for C_xBe_y with x = 1–3 and y = 1–4 including the vibrational analysis of all states. Ionization potentials and electron affinities are calculated for the ground state cluster isomers. The thermal stability of the ground state isomers was verified within the harmonic approximation of the Helmholtz free energy up to temperatures of about 1000 K. Within the family of clusters studied, C₂Be₃ undergoes a solid-like structural transition at about 260 K changing from a planar structure at low temperatures to a linear isomer at high temperatures.     

On M–multisplittings of singular M–matrices with application to Markov chains

Given a singular M–matrix of a linear system, convergent conditions under which iterative schemes based on M–multisplittings are studied. Two of those conditions, the index of the iteration matrix and its spectral radius are investigated and related to those of the M-matrix. Furthermore, a parallel multisplitting iteration scheme for solving singular linear systems is suggested which can be applied to practical problems such as Poisson and elasticity problems under certain boundary conditions, the Neumann problem, and in Markov chains. A discussion of that multisplitting scheme, based on Gauss–Seidel type splittings is given for computing the stationary distribution vector of Markov chains. In this case a computational viable algorithm can be constructed, since only the nonsingularity of one weighting matrix of the multisplitting is needed. © 1998 John Wiley & Sons, Ltd.     

Synthesis and Crystal Structure of Dichlorobis(dimethylsulfoxide)oxoperoxo Molybdenum(VI)

Hydrogen peroxide reacts with [MoO₂Cl₂(dmso)₂] to produce orange crystals of the title complex, [MoO(O₂)Cl₂(dmso)₂]. The structure is orthorhombic with distorted pentagonal bipyramidal geometry around the molybdenum ion. A short O‐O bond length suggested the presence of a superoxide, but electron paramagnetic resonance measurements definitely supported the peroxo structure.     

Characterization of latex particle arrays by gas adsorption

Assemblies of colloidal particles are frequently used in novel applications, and this requires nondestructive methods allowing overall characterization of the sample and collection of information about the quality of the arrays. From suspensions of polystyrene, poly[styrene-co-(2-hydroxyethylmethacrylate)], poly[styrene-co-acrylic acid], and poly[styrene-co-methacrylic acid], assemblies of spherical particles were obtained by elimination of the solvent in different ways-evaporation, gravity deposition, and filtration. These latex particle packings were characterized by scanning and transmission electron microscopy and by gas adsorption to determine the efficiency of packing. The surface area, total pore volume, and pore size distributions obtained from the adsorption and desorption data were related to characteristic parameters calculated for cubic close-packed spherical particles.