Beta-lactoglobulin (beta-LG) was treated with high hydrostatic pressure (HHP) at 600 MPa and 50 degrees C for selected times as long as 64 min. The intrinsic tryptophan fluorescence of beta-LG indicated that HHP treatment conditions induced a conformational change. HHP treatment conditions also promote a 3-fold increase in the extrinsic fluorescence of 1-anilinonaphthalene-8-sulfonate and a 2.6-fold decrease for cis-paraneric acid, suggesting an increase in accessible aromatic hydrophobicity and a decrease in aliphatic hydrophobicity. Far-ultraviolet circular dichroism (CD) spectra reveal that the secondary structure of beta-LG converts from native beta-sheets to non-native alpha-helices following HHP treatment, whereas near-ultraviolet CD spectra reveal that the native tertiary structure of beta-LG essentially disappears. Urea titrations reveal that native beta-LG unfolds cooperatively, but the pressure-treated molecule unfolds noncooperatively. The noncooperative state is stable for 3 months at 5 degrees C. The nonaccessible free thiol group of cysteine121 in native beta-LG became reactive to Ellman's reagent after adequate HHP treatment. Gel electrophoresis with and without beta-mercaptoethanol provided evidence that the exposed thiol group was lost concomitant with the formation of S-S-linked beta-LG dimers. Overall, these results suggest that HHP treatments induce beta-LG into hydrophobic molten globule structures that remain stable for at least 3 months.

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Three metal complexes[Re(bpy)(CO)3(CN-t-Bu)]Cl (1) (where bpy = 2,2-bipyridine), Bu4N[Ir(ppy)2(CN)2] (2), and Ir(ppy)3 (3) (where ppy = 2-phenylpyridine and Bu4N = tetrabutylammonium cation)were evaluated as oxygen sensors in poly((n-butylamino)thionylphosphazene) (nBuPTP) matrixes. The phosphorescent dyes 2 and 3 exhibit long lifetimes and high quantum yields in degassed dichloromethane and toluene solutions and when dissolved in the polymer matrix. These two dyes exhibited exponential decays both in solution and in the polymer films, with somewhat longer lifetimes (for 2, τ0 = 4.78 μs; for 3, τ0 = 1.40 μs) in the polymer film. All three dyes gave linear Stern−Volmer plots, but 1 was rather sensitive to photodecomposition. The slopes of the Stern−Volmer plots for these dyes were compared to those measured previously for platinum octaethyl porphine (PtOEP) and ruthenium tris-diphenylphenanthroline chloride ([Ru(dpp)3]Cl2. Attempts to explain the differences in slope using τ0 as the sole scaling parameter were unsuccessful. To explain these results, we calculated the effective capture radius for quenching by oxygen, which was 1.7 nm for 2 and 2.7 nm for 3, relative to a value of 1.0 nm for PtOEP. Thus, dye 3 is 2.7 times more sensitive to quenching by oxygen than PtOEP and more than 5 times more sensitive than [Ru(dpp)3]Cl2.

We describe direct nonradiative energy transfer (DET) experiments on mixtures of two symmetrical poly(isoprene-b-methyl methacrylate) block copolymers of similar molar mass and composition, bearing different dyes at the junction. One polymer has a donor dye (9-phenanthrene) at the junction, and the other has an acceptor dye (2-anthracene). Small-angle X-ray scattering experiments show that films of the mixed diblock copolymers have a lamellar morphology with a spacing that varies with composition from 24 to 26 nm. Fluorescence decay profiles from these films were analyzed in terms of an energy transfer model that takes account of the distribution of junctions across the interface. On the basis of the value R 0 ) 2.3 nm for the characteristic ET distance and an assumed value of 〈κ 2 〉 ) 0.476 for the preaveraged orientation parameter for randomly oriented immobile dipoles, we calculate an interface thickness of 1.6 ( 0.1 nm. This value is independent of the acceptor/donor ratio (i.e., the acceptor concentration) in the films.