Polymorphic behavior in protein-surfactant mixtures: the water-bovine serum albumin-sodium taurodeoxycholate system

Mixtures containing water, bovine serum albumin (BSA), and sodium taurodeoxycholate (NaTDC), a component of the bile in mammals, have been investigated in a wide range of composition and pH. Depending on the concentration of both solutes and the pH, solutions, precipitates, and gels are formed. Under spontaneous pH conditions, the transport properties in dilute solutions indicate the occurrence of significant interactions between BSA and the surfactant. Conversely, acidic media favor the formation of nonsoluble protein-surfactant complexes, with subsequent precipitation. The nucleation kinetics of the protein-surfactant complexes in solid form and the related precipitation processes can be slow or fast, depending on the overall solute content and the mole ratio. At high concentrations, a gel, extending on both sides of the charge neutralization line, and two-phase regions are observed. Gels shrink in open air and swell in the presence of excess water. Depending on concentration and temperature, the gels transform from an essentially liquidlike behavior to that peculiar to true gels (when G' > or = G'). The thermal gelation threshold, the temperature above which G' > or = G', depends on BSA and NaTDC content and is concomitant to moderate heat effects, inferred by differential scanning calorimetry (DSC). The above data also indicate that the protein thermal denaturation in the gel is shifted to higher temperatures compared to water. Such a stabilizing effect is presumably related to the occurrence of both electrostatic and hydrophobic interactions with NaTDC. Water self-diffusion in the gels is slightly slower than that in the bulk and poorly sensitive to composition: it is about 65% the value of neat H2O in a wide concentration range, irrespective of the BSA, or NaTDC, concentration. A peculiar behavior is also observed in 23Na longitudinal and transverse relaxation rates. The T1 and T2 values, measured at 105.75 MHz on BSA-NaTDC gels, indicate that the motions determining the NMR relaxation of the sodium ions in the hydration layer of the protein-surfactant aggregates are not slow, having frequencies comparable with the Larmor one. The above properties, especially the rheological and the spectroscopic ones, are important for understanding the behavior of gels based on protein-surfactant mixtures.     

Absolutely Convergent Extensions of Nonclosable Positive Linear Functionals

The existence of extensions of a positive linear functional ω defined on a dense *-subalgebra \mathfrakA₀{\mathfrak{A}_0} of a topological *-algebra \mathfrakA{\mathfrak{A}}, satisfying certain regularity conditions, is examined. The main interest is focused on the case where ω is nonclosable and sufficient conditions for the existence of an absolutely convergent extension of ω are given.     

Simple modules over the multiparameter quantum function algebra at roots of 1

We construct essentially all the irreducible modules for the multiparameter quantum function algebraF [G], whereG is a simple simply connected complex algebraic group, and is a root of unity.     

The effect of changing the TiO2 content (0-6%) on the structure and thermal evolution of glasses obtained from porphyric sands and dolomite

Glasses have been obtained from mixtures of porphyric sands and dolomite. The influence of changes in the TiO₂ content (0-6%) on the glass structure and the formation of crystalline phases on reheating has been studied. The experimental results suggest that in the studied system TiO₂ promotes glass-in-glass phase separation and plays the role of a nucleating agent. The activation energy for crystal growth, E_C = 486 kJ mol⁻¹, and the Avrami parameter (m = 1) have been evaluated by means of thermoanalytical techniques in the case of the base glass (no TiO₂ added). The value of the Avrami parameter (m = 1) agrees well with SEM observations of dendritic crystal growth from surface nuclei. In the other glasses, lath-like crystals were observed, the microstructure being finer the greater the TiO₂%. The first addition of TiO₂ (2%) gives, on quenching, a partially devitrified product; subsequent additions of titania, surprisingly, allow glasses to be formed more easily. The experimental results suggest that Na₂O and K₂O, present in the porphyric sands and therefore in the glasses (to a total amount of ≈ 5.6%), segregate preferentially into the titania-rich phase with respect to MgO. Taking into account that Na₂O and K₂ are useful in lowering the liquidus temperature of glasses but are known to have a negative effect on the mechanical properties, this can be important in the production of glass ceramics.     

Characterization of n-alkanes and PAHs in PM10 samples in Prato (Italy)

This study reports the characterization of n-alkanes and PAHs in 13 PM10 samples collected in the South area of Prato (Italy) during the period April-July 2002. n-Alkanes concentrations ranged between 9.45 and 182.64 ng/mc while PAHs concentrations ranged from 3.058 to 22.048 ng/mc. No correlation was evidenced between benzo(a)pirene and PM10 concentrations. Total carbonaceous aerosol was also measured and it meanly accounted for 21.5% of the PM10 mass ranging from 12.4% to 27.1%.     

Energy loss of deuterons in 3He gas: a threshold effect

The energy loss of deuterons in ³He gas was measured at E _d = 15 to 100 keV using the ³He pressure dependence of the ³He(d,p)⁴He cross-section at a given incident energy. At the highest energies, the observed energy loss is in good agreement with a standard compilation. However, with decreasing energy the experimental values drop steadily below the theoretical values and near E _d = 18 keV they drop sharply (within 1 keV) reaching the domain of nuclear stopping power. This threshold behavior is due to the minimum 1s → 2s electron excitation of the He target atoms, i.e. it is a quantum effect. Some consequences are discussed.     

Annealing and Crystallization of Fe40Ni40P14B6 Glassy Alloy. A DSC study

In this paper a DSC study is reported of the behavior of Fe₄₀Ni₄₀P₁₄B₆ alloy produced by rapid quenching. The experimental results show that relaxation phenomena can be studied directly from the DSC curves. From these experiments, the spread of the E _c values in the literature is attributed to differences in the quenching rates and the presence of variable number of quenched-in nuclei. It is also shown that the microstructure (number and size of crystals) of the non-isothermally devitrified metallic alloy changes with the heating rate; this is a consequence of the shift of crystallization temperatures and, therefore, of the change of the ratio of nucleation and crystal growth rates. This revised version was published online in July 2006 with corrections to the Cover Date.