Indications for chlororespiration in relation to light regime in the marine diatom Thalassiosira weissflogii

The marine diatom Thalassiosira weissflogii was cultured under a light regime simulating the daily rise and fall of the sun. The light regime caused a daily cycle in non-photochemical quenching. Remarkable were the changes in fluorescence directly after a light-to-dark transition that occurred in addition to the changes induced by non-photochemical quenching. A transient non-photochemical reduction of PQ and of Q(A) was indicated by a transient increase in apparent F(o) and by changes in the shape of the fluorescence induction curve. The observed changes developed approximately the first 100-120 s after a light-to-dark transition and could be reversed by the application of far-red illumination. Chlororespiration is thought to cause the reduction of PQ and, as the PQ-pool is in equilibrium with Q(A), also a reduction of Q(A). The function and ecological relevance of chlororespiration are discussed.     

Use of sol–gels as solid matrixes for laser-induced breakdown spectroscopy

Silicon, zirconium and aluminum sol–gels were investigated as suitable starting materials for tunable matrix calibration standards for laser-induced breakdown spectroscopy. A fast and simple preparation method was developed, using aluminum i-propoxide as the precursor in the sol–gel synthesis, which allows one to quickly prepare solid calibration standards offering very homogenous analyte distribution in the matrix, low optical spectral background, as well as reproducible behavior towards laser ablation and vaporization. The surface of the calibration targets and the morphology of the ablation craters were examined by optical and scanning electron microscopy, and the material ejection process was observed by shadowgraph imaging. Low μg/g detection limits and 4–15% relative standard deviation were measured by laser induced breakdown spectroscopy for Pb, Cr and Be used as internal standards.     

Reversing Dane’s strategy: a new, concise, enantioselective synthesis of the steroid nucleus

Reversing the polarity of the cycloaddition partners in Dane’s steroid synthesis provides ready access to enantiomerically pure, functionally-rich steroidal structures.     

Profiling lithium distribution in Sn anode for lithium-ion batteries with neutrons

Measuring the distribution of lithium in high capacity lithium-ion battery (LIB) electrodes is essential to understanding the coulombic losses during the lithiation/delithiation processes that occur while charging and discharging the cell. In this research, two half-cell prototypes were fabricated by electrochemically lithiating Sn foil anodes in 1M LiBF₄ in a 1:1 (wt:wt) ethylene carbonate and dimethyl carbonate solutions at a constant potential of 0.50 and 0.67 V (vs. Li/Li⁺). The neutron depth profiling (NDP) technique was employed to study the Li distributions in the anodes. Li concentration profiles were resolved for the samples lithiated under different conditions for LIB studies. In addition, this paper demonstrated an in situ NDP measurement of an electrochemical cell with a thin window design, which reveals the dynamics of lithium distribution within the Sn anode.     

Distributed Online Frequency Assignment in Cellular Networks

A cellular network is generally modeled as a subgraph of the triangular lattice. The distributed online frequency assignment problem can be abstracted as a multicoloring problem on a weighted graph, where the weight vector associated with the vertices models the number of calls to be served at the vertices and is assumed to change over time. In this paper, we develop a framework for studying distributed online frequency assignment in cellular networks. We present the first distributed online algorithms for this problem with proven bounds on their competitive ratios. We show a series of algorithms that use at each vertex information about increasingly larger neighborhoods of the vertex, and that achieve better competitive ratios. In contrast, we show lower bounds on the competitive ratios of some natural classes of online algorithms.     

Boric acid inhibits adenosine diphosphate-ribosyl cyclase non-competitively

Adenosine diphosphate-ribosyl cyclase (ADP-ribosyl cyclase) is a ubiquitous enzyme in eukaryotes that converts NAD+ to cyclic-ADP-ribose (cADPR) and nicotinamide. A quantitative assay for cADPR was developed using capillary electrophoresis to separate NAD+, cADPR, ADP-ribose, and ADP with UV detection (254 nm). Using this assay, the apparent Km and Vmax for Aplysia ADP-ribosyl cyclase were determined to be 1.24+/-0.05 mM and 131.8+/-2.0 microM/min, respectively. Boric acid inhibited ADP-ribosyl cyclase non-competitively with a Ki of 40.5+/-0.5 mM. Boric acid binding to cADPR, determined by electrospray ionization mass spectrometry, was characterized by an apparent binding constant, KA, of 655+/-99 L/mol at pH 10.3.     

Enantioselective synthesis of diversely substituted quaternary 1,4-benzodiazepin-2-ones and 1,4-benzodiazepine-2,5-diones

Benzodiazepines are privileged scaffolds in medicinal chemistry, but enantiopure examples containing quaternary stereogenic centers are extremely rare. We demonstrate that installation of the di(p-anisyl)methyl (DAM) group at N1 of 1,4-benzodiazepin-2-ones and 1,4-benzodiazepine-2,5-diones derived from enantiopure proteinogenic amino acids allows retentive replacement of the C3-proton via a deprotonation/trapping protocol. A wide variety of carbon and nitrogen electrophiles function well in this reaction, providing the corresponding quaternary benzodiazepines with excellent enantioselectivity. Deprotonation/trapping experiments on a pair of diastereomeric 1,4-benzodiazepine-2,5-diones provide evidence for a key role of conformational chirality in these enantioselective reactions. Acidic removal of the DAM group is fast and high-yielding and can be performed selectively in the presence of a N-Boc indole. Thus the synthesis of quaternary benzodiazepines with diverse N1 functionality can now be accomplished.     

Nanosized polymetallic resorcinarene-based host assemblies that strongly bind fullerenes

Polymetallic nanodimensional assemblies have been prepared via metal directed assembly of dithiocarbamate functionalized cavitand structural frameworks with late transition metals (Ni, Pd, Cu, Au, Zn, and Cd). The coordination geometry about the metal centers is shown to dictate the architecture adopted. X-ray crystallographic studies confirm that square planar coordination geometries result in "cagelike" octanuclear complexes, whereas square-based pyramidal metal geometries favor hexanuclear "molecular loop" structures. Both classes of complex are sterically and electronically complementary to the fullerenes (C(60) and C(70)). The strong binding of these guests occurred via favorable interactions with the sulfur atoms of multiple dithiocarbamate moieties of the hosts. In the case of the tetrameric copper(II) complexes, the lability of the copper(II)-dithiocarbamate bond enabled the fullerene guests to be encapsulated in the electron-rich cavity of the host, over time. The examination of the binding of fullerenes has been undertaken using spectroscopic and electrochemical methods, electrospray mass spectrometry, and molecular modeling.     

Dynamical forcing of circular groups

In this paper we introduce and study the notion of dynamical forcing. Basically, we develop a toolkit of techniques to produce finitely presented groups which can only act on the circle with certain prescribed dynamical properties.

As an application, we show that the set consisting of rotation numbers which can be forced by finitely presented groups is an infinitely generated -module, containing countably infinitely many algebraically independent transcendental numbers. Here a rotation number is forced by a pair , where is a finitely presented group and is some element, if the set of rotation numbers of as varies over is precisely the set .

We show that the set of subsets of which are of the form

where varies over countable groups, are exactly the set of closed subsets which contain and are invariant under . Moreover, we show that every such subset can be approximated from above by for finitely presented .

As another application, we construct a finitely generated group which acts faithfully on the circle, but which does not admit any faithful action, thus answering in the negative a question of John Franks.

     

Promoting essential laminations

We show that a co-orientable taut foliation of a closed, orientable, algebraically atoroidal 3-manifold is either the weak stable foliation of an Anosov flow, or else there are a pair of very full genuine laminations transverse to the foliation.