Biocatalytic deacylation studies on tetra-O-acyl-β-D-xylofuranosyl nucleosides: synthesis of xylo-LNA monomers

A Novozyme-435 catalytic methodology has been developed for selective deacylation of one of the acyloxy functions involving a primary -OH group over the other acyloxy functions involving primary and secondary -OH groups in 4'-C-acyloxymethyl-2',3',5'-tri-O-acyl-β-D-xylofuranosyl nucleosides. Optimization of the biocatalytic reaction revealed that tetra-O-butanoyl-β-D-xylofuranosyl nucleosides are the best substrates for the enzyme. The possibility of acyl migration during enzymatic deacylation reactions has been ruled out by carrying out biocatalytic deacylation reactions on mixed esters of 4'-C-hydroxymethyl-2',3',5'-tri-O-acetyl-β-D-xylofuranosyl nucleosides. The developed methodology has been used for the efficient synthesis of xylo-LNA monomers T, U, A, and C in good yields.     

Photocatalytic properties of nanocrystalline TiO<Subscript>2</Subscript> thin films doped with Tb

In this work photocatalytic properties of TiO₂ thin films doped with different amount of Tb have been described. Thin films were prepared by high energy reactive magnetron sputtering process. Comparable photocatalytic activity has been found for all doped TiO₂ thin films, while different amounts of Tb dopant (0.4 and 2.6 at. %) results in either an anatase or rutile structure. It was found that the terbium dopant incorporated into TiO₂ was also responsible for the amount of hydroxyl groups and water particles adsorbed on the thin film surfaces and thus photocatalytic activity was few times higher in comparison with results collected for undoped TiO₂ thin films.     

Observation of a resonancelike structure in the pi +- psi' mass distribution in exclusive B-->Kpi +- psi' decays

A distinct peak is observed in the pi +/- psi' invariant mass distribution near 4.43 GeV in B-->K pi +/- psi' decays. A fit using a Breit-Wigner resonance shape yields a peak mass and width of M=4433+/-4(stat)+/-2(syst) MeV and Gamma=45-13+18(stat)-13+30(syst) MeV. The product branching fraction is determined to be B(B 0-->K -/+Z+/-(4430)) x B(Z+/-(4430)-->pi+/-psi')=(4.1+/-1.0(stat)+/-1.4(syst)) x 10(-5), where Z+/-(4430) is used to denote the observed structure. The statistical significance of the observed peak is 6.5 sigma. These results are obtained from a 605 fb(-1) data sample that contains 657 x 10(6) BB pairs collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+ e- collider.     

The Impact of Retinal Configuration on the Protein–Chromophore Interactions in Bistable Jumping Spider Rhodopsin-1

Bistable rhodopsins have two stable forms that can be interconverted by light. Due to their ability to act as photoswitches, these proteins are considered as ideal candidates for applications such as optogenetics. In this work, we analyze a recently crystalized bistable rhodopsin, namely the jumping spider rhodopsin-1 (JSR1). This rhodopsin exhibits identical absorption maxima for the parent and the photoproduct form, which impedes its broad application. We performed hybrid QM/MM simulations to study three isomers of the retinal chromophore: the 9-cis, 11-cis and all-trans configurations. The main aim was to gain insight into the specific interactions of each isomer and their impact on the absorption maximum in JSR1. The absorption spectra were computed using sampled snapshots from QM/MM molecular dynamics trajectories and compared to their experimental counterparts. The chromophore–protein interactions were analyzed by visualizing the electrostatic potential of the protein and projecting it onto the chromophore. It was found that the distance between a nearby tyrosine (Y126) residue plays a larger role in the predicted absorption maximum than the primary counterion (E194). Geometric differences between the isomers were also noted, including a structural change in the polyene chain of the chromophore, as well as changes in the nearby hydrogen bonding network.     

Spin–orbit and correlation effects in platinum hydride (PtH)

The low-lying electronic states of PtH were studied by all-electron one- and two-component variational calculations on the multireference CI levels. The orbital optimization is performed within a one-component formalism, whereas the further refinement of the wave functions follows two different schemes: The most demanding approach introduces spin–orbit coupling in the CI optimization step, giving a simultaneous treatment of electron correlation and spin–orbit coupling. The second, considerably less demanding approach, corresponds almost to a perturbational treatment, introducing spin–orbit coupling as a final step after the CI optimization by diagonalizing the resulting Hamiltonian matrix over CI states. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 53–64, 1998     

Phage Langmuir monolayers and Langmuir–Blodgett films

Stable, insoluble Langmuir monolayer films composed of Staphylococcus aureus-specific lytic bacteriophage were formed at an air–water interface and characterized. The phage monolayer was very strong, withstanding a surface pressure of ～40 mN/m at 20 °C. The surface pressure–area (Π–A) isotherm possessed a shoulder at ～7 × 10⁴ nm²/phage particle, attributed to a change in phage orientation at the air–water interface from horizontal to vertical capsid-down/tail-up orientation as surface pressure was increased. The Π–A-dependence was accurately described using the Volmer equation of state, assuming horizontal orientation to an air–water interface at low surface pressures with an excluded area per phage particle of 4.6 × 10⁴ nm². At high pressures phage particles followed the space-filling densely packed disks model with a specific area of 8.5 × 10³ nm²/phage particle. Lytic phage monolayers were transferred onto gold-coated silica substrates from the air–water interface at a constant surface pressure of 18 mN/m by Langmuir–Blodgett method, then dried and analyzed by scanning electron microscopy (SEM) and ellipsometry. Phage specific adsorption (Γ) in Langmuir–Blodgett (LB) films measured by SEM was consistent with that calculated independently from Π–A isotherms at the transfer surface pressure of 18 mN/m (Γ = 23 phage particles/μm²). The 50 nm-thickness of phage monolayer measured by ellipsometer agreed well with the horizontal phage average size estimated by SEM. Surface properties of phage Langmuir monolayer compare well with other monolayers formed from nano- and micro-particles at the air–water interface and similar to that of classic amphiphiles 1,2-diphytanoyl-sn-glycero-3-phosphocholine (phospholipid) and stearic acid.