ESR, STESR, DFT, and MD Study of the Dynamical Structure of Cucurbituril[7]-Spin Probe Guest-Host Complexes.

We study the molecular dynamics and structures of the guest-host complexes of cucurbituril, CB[7], with spin probes through the conventional electron spin resonance (ESR), saturation transfer ESR (STESR), density functional theory (DFT), and molecular dynamics (MD) computations. Protonated TEMPOamine (), a derivative of TEMPO having a positive charge and an octyl group on the quaternary nitrogen atom (), and the neutral spin-labeled indole () are used as guests. To eliminate the overall complex rotation, the solutions of complexes in a solid CB[7] matrix were prepared.

Interaction of Spin-Labeled Lipid Membranes with Transition Metal Ions.

The large values of spin relaxation enhancement (RE) for PC spin-labels in the phospholipid membrane induced by paramagnetic metal salts dissolved in the aqueous phase can be explained by Heisenberg spin exchange due to conformational fluctuations of the nitroxide group as a result of membrane fluidity, flexibility of lipid chains, and, possibly, amphiphilic nature of the nitroxide label. Whether the magnetic interaction occurs predominantly via Heisenberg spin exchange (Ni) or by the dipole-dipole (Gd) mechanism, it is essential for the paramagnetic ion to get into close proximity to the nitroxide moiety for efficient RE. For different salts of Ni the RE in phosphatidylcholine membranes follows the anionic Hofmeister series and reflects anion adsorption followed by anion-driven attraction of paramagnetic cations on the choline groups.

Phase diagram of ternary cholesterol/palmitoylsphingomyelin/palmitoyloleoyl-phosphatidylcholine mixtures: spin-label EPR study of lipid-raft formation.

For canonical lipid raft mixtures of cholesterol (chol), N-palmitoylsphingomyelin (PSM), and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), electron paramagnetic resonance (EPR) of spin-labeled phospholipids--which is insensitive to domain size--is used to determine the ternary phase diagram at 23°C. No phase boundaries are found for binary POPC/chol mixtures, nor for ternary mixtures with PSM content <24 mol %. EPR lineshapes indicate that conversion from the liquid-disordered (L(α)) to liquid-ordered (L(o)) phase occurs continuously in this region.

Wild-type and feedback-resistant phosphoribosyl pyrophosphate synthetases from Bacillus amyloliquefaciens: purification, characterization, and application to increase purine nucleoside production.

Bacillus strains are used for the industrial production of the purine nucleosides inosine and guanosine, which are raw materials for the synthesis of the flavor enhancers disodium inosinate and disodium guanylate. An important precursor of purine nucleosides is 5-phospho-α-D: -ribosyl-1-pyrophosphate, which is synthesized by phosphoribosyl pyrophosphate synthetase (PRS, EC 2.7.