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.     

Globalizations, fiber bundles, and envelopes of holomorphy

We describe a relationship between globalizations of local holomorphic actions on Stein manifolds induced by global actions of certain non-compact Lie groups, and holomorphic fiber bundles with smooth Stein base and fiber and connected structure group. To this end we prove a univalence result for particular Stein Riemann domains with a free and properly discontinuous action of a discrete group of biholomorphisms. We then derive some consequences on the existence of Stein globalizations. Received August 11, 1998; in final form March 8, 1999     

Large deviations for posterior distributions on the parameter of a multivariate text{ AR}(p) process

We prove the large deviation principle for the posterior distributions on the (unknown) parameter of a multivariate autoregressive process with i.i.d. Normal innovations. As a particular case, we recover a previous result for univariate first-order autoregressive processes. We also show that the rate function can be expressed in terms of the divergence between two spectral densities.     

Thermal and photochemical transformations of 2-methylthiothiophene in triosmium clusters: photoinduced migrations of MeS from carbon to metal and back again

2-Methylthiothiophene (2-MeSC₄H₃S) oxidatively adds to [Os₃(CO)₁₀(MeCN)₂] with cleavage of the C–H bond at the 3-position to give [Os₃(μ-H)(μ-MeSC₄H₂S)(CO)₁₀] 1, the X-ray structure of which shows that the MeS group is coordinated to osmium through the S atom while the thiophene ring is coordinated to osmium through the 3-carbon atom. Only one invertomer at sulfur is observed in solution and in the crystal the Me group is exo. Thermal treatment of 1 in the dark gives only one product, [Os₃(μ-H)(μ₃-MeSC₄H₂S)(CO)₉] 2 (X-ray structure), derived by loss of a CO from the Os(CO)₄ unit of 1 with concomitant η²-coordination of the thiophene ring of bridging MeSC₄H₂S at the third metal atom. Whereas thermal reaction in the dark leads only to C–H cleavage products, visible irradiation at room temperature leads to various products derived by migration of the MeS group. Thus thermal treatment of 1 in daylight for 2 h gave 2, together with an isomer 3. Cluster 2 converts at room temperature to 3 in daylight while thermal treatment of 2 in the dark (125°C) gave no reaction. Isomer 3 of [Os₃(μ-H)(μ₃-MeSC₄H₂S)(CO)₉] (X-ray structure) is closely related to 2 except that the MeS group and the Os–C σ-bond have interchanged sites at the thiophene ring between the 2- and the 3-positions. Visible irradiation of 1 at room temperature for 3 days in daylight gave further chemical change leading to two bridging thienyl clusters, [Os₃(μ-MeS)(μ-2-C₄H₂S)(CO)₁₀] 4 and [Os₃(μ-MeS)(μ₃-2-C₄H₂S)(CO)₉] 5. Cluster 5 is the ultimate product of daylight irradiation of any of the clusters 1 to 4.     

The reaction between 2-aminobenzenethiol and diethyl oxalate. A structural reassegnement

It is proposed that the reported [2] condensation between 2-aminobenzenethiol and diethyloxalate give rise to 2-ethoxycarbonylbenzothiazole 3 rather than 3-ethoxy-2H-1,4-benzothiazin-2-one 2 .     

Molecular and spectroscopic properties of a polarizer based on a block copolymer of vinylalcohol and acetylene

The preparation of a high efficiency polarizer derived from the block copolymer, poly(vinylalcohol‐b‐acetylene) will be described. The orientations of the polyacetylene chromophore and the polyvinylalcohol matrix have been analyzed by polarized UV/Vis and FTIR spectroscopy, respectively. For moderately stretched films (L/Lo = 3.0‐7.0), the degree of orientation for the polyacetylene segments greatly exceeds that predicted from a simple, pseudoaffine deformation model. For the visible spectral region, dichroic ratios in the range of 60 to 100 are easily achieved, thus permitting films of this polymer to function as a high efficiency, polarizing optical element. Data from a series of sample tilting experiments utilizing polarized UV/Vis radiation are consistent with the polyacetylene segments being distributed uniaxially about the stretching direction. However, analogous experiments in the infrared indicate that the PVA matrix has significant biaxial character. Other novel characteristics of this polarizer will be discussed, such as its thermal and chemical stability.