An efficient chemo-enzymatic approach to (+)-meroquinene

Meroquinene (+)-1 was prepared in an efficient and stereocontrolled fashion from (1R-2S)-4-cyclohexene dimethanol monoacetate (−)-8. Key steps are the enzyme-catalyzed hydrolysis of the available diacetate 5 to (−)-8 and of the intermediate diester 17 to hemiester 18, which allow the stereo- and regiocontrolled elaboration of the vicinal vinyl and carboxymethyl groups.     

Instabilities of the Stewartson layer Part 2. Supercritical mode transitions

We investigate, both experimentally and numerically, the fluid flow in a spherical shell with radius ratio r_i/r_o=2/3. Both spheres rotate about a common axis, with _i>_o. The basic state consists of a Stewartson layer situated on the tangent cylinder, the cylinder parallel to the axis of rotation and touching the inner sphere. If the differential rotation is sufficiently large, non-axisymmetric instabilities arise, with the wavenumber of the most unstable mode increasing with increasing overall rotation. In the increasingly supercritical regime, a series of mode transitions occurs in which the wavenumber decreases again. The experimental and numerical results are in good agreement regarding this basic sequence of mode transitions, and the numerics are then used to study some of the finer details of the solutions that could not be observed in the experiment.     

Holding and spinning molecules in space

We illustrate, experimentally and theoretically, a laser-based method to control the rotations of polyatomic molecules in 3D space. A linearly polarized nanosecond pulse strongly aligns the most polarizable axis of an asymmetric top molecule along its polarization axis while an orthogonally polarized, femtosecond pulse sets the molecules into controlled rotation about the aligned axis. As a result, strong three-dimensional (3D) alignment occurs shortly after the femtosecond pulse and is repeated periodically, reflecting coherent revolution about the molecular axis. Our method opens new directions for research in orientationally confined complex molecules.     

Quantum dynamical phase transition in a system with many-body interactions

Recent experiments, [G.A. Álvarez, E.P. Danieli, P.R. Levstein, H.M. Pastawski, J. Chem. Phys. 124 (2006) 194507], have reported the observation of a quantum dynamical phase transition in the dynamics of a spin swapping gate. In order to explain this result from a microscopic perspective, we introduce a Hamiltonian model of a two level system with many-body interactions with an environment whose excitation dynamics is fully solved within the Keldysh formalism. If a particle starts in one of the states of the isolated system, the return probability oscillates with the Rabi frequency ω₀. For weak interactions with the environment , we find a slower oscillation whose amplitude decays with a rate . However, beyond a finite critical interaction with the environment, , the decay rate becomes . The oscillation period diverges showing a quantum dynamical phase transition to a Quantum Zeno phase consistent with the experimental observations.     

Light trapping and guidance in plasmonic nanocrystals

We illustrate the possibility of light trapping and funneling in periodic arrays of metallic nanoparticles. A controllable minimum in the transmission spectra of such constructs arises from a collective plasmon resonance phenomenon, where an incident plane wave sharply localizes in the vertical direction, remaining delocalized in the direction parallel to the crystal plane. Using hybrid arrays of different structures or different materials, we apply the trapping effect to structure the eigenmode spectrum, introduce overlapping resonances, and hence direct the light in space in a wavelength-sensitive fashion.     

An application of ergodic theory to a problem in geometric ramsey theory

LetE be a measurable subset of ℝ ^k ,k>2, with XXX(E)>0. LetV = {0,υ ₁, …,υ _k+1} ε ℝ ^k , whereυ ₁, …,υ _k+1 are affinely independent. We show that forr large enough, we can find an isometric copy ofrV arbitrarily close toE. This is a generalization of a theorem of Furstenberg, Katznelson and Weiss [FKW] showing a similar property for ℝ²,V = {0,υ ₁,υ ₂}.     

Electrospray Mass Spectrometry with Consecutive Fragmentation Steps (ESI‐MSn) as a Tool for Rapid and Sensitive Analysis of Ginsenosides and Their Galactosyl Derivatives

The ginsenosides Rb₁ ( 3 ) and Rg₁ ( 4 ) isolated from Panax ginseng were enzymatically modified with galactosyltransferase to furnish new derivatives carrying galactose units in one or both sugar chains at position C(20) and/or C(3) or C(6) of the protopanaxadiol and protopanaxatriol aglycones 1 and 2 , respectively. To determine the linkage position(s) of the introduced galactose unit(s), an electrospray‐ionization MS analysis with consecutive fragmentation steps (ESI‐MSⁿ) was carried out using an ion‐trap mass spectrometer (Figs. 2 and 3). It was shown that both sugar moieties, located at different positions of the protopanaxadiol and protopanaxatriol aglycone, can be easily differentiated and analyzed in the subsequent fragmentation steps. Collision‐induced dissociation (CID) of the Na⁺‐ionized molecule (MS²) leads to cleavage of the most labile O−C(20) glycosidic bond, liberating the C(20) oligosaccharide fragment ion that can be analyzed in a subsequent fragmentation step (MS³). MS³ of the C(20) monodeglycosylated ginsenoside leads to cleavage of the second sugar moiety, allowing structure analysis of this fragment ion (MS⁴). By this method, the linkages of the monosaccharides and branching positions can be rapidly determined using only a few μl of a 10⁻⁵ M sample solution.     

Antibody for Serine 65 Phosphorylated Ubiquitin Identifies PLK1-Mediated Phosphorylation of Mitotic Proteins and APC1

Deciphering the protein posttranslational modification (PTM) code is one of the greatest biochemical challenges of our time. Phosphorylation and ubiquitylation are key PTMs that dictate protein function, recognition, sub-cellular localization, stability, turnover and fate. Hence, failures in their regulation leads to various disease. Chemical protein synthesis allows preparation of ubiquitinated and phosphorylated proteins to study their biochemical properties in great detail. However, monitoring these modifications in intact cells or in cell extracts mostly depends on antibodies, which often have off-target binding. Here, we report that the most widely used antibody for ubiquitin (Ub) phosphorylated at serine 65 (pUb) has significant off-targets that appear during mitosis. These off-targets are connected to polo-like kinase 1 (PLK1) mediated phosphorylation of cell cycle-related proteins and the anaphase promoting complex subunit 1 (APC1).