Plasticizer effect on the dynamics of polyvinylchloride studied by dielectric spectroscopy and quasielastic neutron scattering

We have studied the influence of plasticization on the microscopic dynamics of a glass-forming polymer. For this purpose we studied polyvinylchloride (PVC) with and without the commercially used plasticizer dioctylphthalate (DOP). We used dielectric spectroscopy and inelastic neutron scattering employing the neutron spin echo (NSE) technique. For both kinds of spectra the alpha relaxation could be consistently described by a model involving a distribution of individual relaxations of the Kohlrausch type. In contrast to earlier studies it turned out that an asymmetric distribution is necessary to fit the data at the lower temperatures investigated here. The shape parameters of the distribution (width, skewness) for PVC and PVC/DOP turned out to coincide when the characteristic relaxation times were the same. This means that the plasticizer only induces a remapping of the temperature dependence of the alpha relaxation. Comparison of NSE spectra S(Q,t)S(Q) at different scattering vectors Q gave the result that the slowing down at the structure factor peak Q(max) is surprisingly small for PVC while it is in the normal range for PVC/DOP.     

L^p-gradient Estimates of Symmetric Markov Semigroups for 1 〈 p ≤ 2

For 1 〈 p ≤2, an L^p-gradient estimate for a symmetric Markov semigroup is derived in a general framework, i.e. ‖Γ^/2（Ttf）‖p≤Cp/√t‖p, where F is a carre du champ operator. As a simple application we prove that F1/2（（I- L） ^-α） is a bounded operator from L^p to L^v provided that 1 〈 p 〈 2 and 1/2〈α〈1. For any 1 〈 p 〈 2, q 〉 2 and 1/2 〈α 〈 1, there exist two positive constants cq,α,Cp,α such that ‖Df‖p≤ Cp,α‖（I - L）^αf‖p,Cq,α（I-L）^（1-α）‖Df‖q＋‖f‖q, where D is the Malliavin gradient （[2]） and L the Ornstein-Uhlenbeck operator.     

Sub‐Micromolar Pulse Dipolar EPR Spectroscopy Reveals Increasing CuII‐labelling of Double‐Histidine Motifs with Lower Temperature

Electron paramagnetic resonance (EPR) distance measurements are making increasingly important contributions to the studies of biomolecules by providing highly accurate geometric constraints. Combining double‐histidine motifs with Cu^II spin labels can further increase the precision of distance measurements. It is also useful for proteins containing essential cysteines that can interfere with thiol‐specific labelling. However, the non‐covalent Cu^II coordination approach is vulnerable to low binding‐affinity. Herein, dissociation constants (K_D) are investigated directly from the modulation depths of relaxation‐induced dipolar modulation enhancement (RIDME) EPR experiments. This reveals low‐ to sub‐μm Cu^II K_Ds under EPR distance measurement conditions at cryogenic temperatures. We show the feasibility of exploiting the double‐histidine motif for EPR applications even at sub‐μm protein concentrations in orthogonally labelled Cu^II–nitroxide systems using a commercial Q‐band EPR instrument.     

Extraribosomal cyclic tetradepsipeptides beauverolides: profiling and modeling the fragmentation pathways

Profiling of cyclic tetradepsipeptides beauverolides was tested as a chemotaxonomic tool for fungal strain identification/discrimination. Two new tetradepsipeptides, beauverolides Q and R, were characterized by tandem mass spectrometry. Specific elimination of 113 atomic mass units from both protonated and sodiated molecules of beauverolides is ubiquitous for all 12 most dominant congeners evaluated in this profiling study. Reconstruction of the total ion chromatogram, according to this neutral fragment release, was used for data filtering and selectivity enhancement. Selective ring opening and fragment ion formation of beauverolide I are discussed in detail utilizing high-level theoretical modeling of the fragmentation pathways.     

PHOTOCHEMICAL BEHAVIOR OF BACTERIORHODOPSIN IMMOBILIZED IN NaCl PELLETS

Abstract— Some photochemical reactions of bacteriorhodopsin (BR) embedded in NaCl pellets (BR-NaCI) in the visible region are described here. BR in these preparations is a mixture of two classes of species: a drastically blue-shifted form and the unchanged purple pigment. Depending on the illumination history of the BR before being immobilized, both kinds of BR could be demonstrated in light-adapted (LA) and dark-adapted (DA) forms, but light adaptation was not possible once the pellets were made. Analogously to BR suspensions, the light-adapted blue-shifted BRexhibited an a/l-trans type photocycle, but the thermal steps were greatly slowed down (time constants 1 to 5 min). The parent species absorb at 506 nm. The DA blue-shifted BR exhibited absorption changes resolved into two photoreactions, one all-(rans- like (as in LA-BR) and another, 13-cw like, whose decay rate is also greatly slowed down (recovery time several hours). The parent species of the 13-cis like cycle absorb at 480 nm. That pigment fraction in the pellets whose absorption was not blue-shifted, also exhibited similar photoreactions to BR in suspension, but with an overall turnover rate only one order of magnitude slower. From a previous report (Lazarev and Terpugov, Biochim. Biophys. Acta 590 ,324–338,1980) and this one, it appears that the very slow photocycles in NaCl-BR of low moisture content originate from blue-shifted chromophores rather than from unchanged BR.     

Site‐Specific Iron Substitution in STA‐28, a Large Pore Aluminophosphate Zeotype Prepared by Using 1,10‐Phenanthrolines as Framework‐Bound Templates

An AlPO₄ zeotype has been prepared using the aromatic diamine 1,10‐phenanthroline and some of its methylated analogues as templates. In each case the two template N atoms bind to a specific framework Al site to expand its coordination to the unusual octahedral AlO₄N₂ environment. Furthermore, using this framework‐bound template, Fe atoms can be included selectively at this site in the framework by direct synthesis, as confirmed by annular dark field scanning transmission electron microscopy and Rietveld refinement. Calcination removes the organic molecules to give large pore framework solids, with BET surface areas up to 540 m² g^?1 and two perpendicular sets of channels that intersect to give pore space connected by 12‐ring openings along all crystallographic directions.