Real-time quantitative imaging of submolecular layers

Using a recent optical contrast method, real-time and quantitative imaging of submolecular layers was performed with the help of a simple optical microscope. The measuring technique is exposed and documented by three examples. In particular, it allowed label-free detection of peptide-antibody binding interactions with 50 pg/mm2 sensitivity while keeping full optical lateral resolution.     

Synthesis and Properties of TRANSDIP,a Rigid Chelator Built upon a Cyclodextrin Cavity: Is TRANSDIP an Authentic trans‐Spanning Ligand?

The C2-symmetrical diphosphane TRANSDIP was obtained in high yield by treating 6A,6B,6D,6E-tetramesylated, permethylated alpha-cyclodextrin with PPhLi2 in excess. The double cascade cyclisation thus produced is regioselective as phosphinidene capping involves only adjacent glucose units. It is also stereospecific, as both lone pairs on the phosphorus atoms are orientated towards the cyclodextrin axis. The restricted flexibility of the phosphorus atoms, which are part of nine-membered heterocyclic rings, is responsible for JP,C spin-spin couplings with the eight-bond distant CH2OMe carbon atoms of glucose units C and F. The treatment of TRANSDIP with Group 10 metal dihalides quantitatively gave square-planar chelate complexes, in which a M--X bond points towards the centre of the cavitand. The favourable P...P separation and the directional control of the lone pairs on the phosphorus atoms rule out the possibility of forming binuclear complexes or higher oligomers. Further, in all the complexes, the phosphorus atoms are in a trans arrangement. TRANSDIP may therefore be regarded as an authentic trans-spanning diphosphane. In the complex [NiBr2TRANSDIP], the cavity provides effective protection of the encapsulated M--X bond towards nucleophilic attack by MeLi. The same complex, upon activation with methylaluminoxane, efficiently dimerises ethene and propene.     

Characterization of Two Light-Harvesting Subunits Isolated from the Brown Alga Pelvetia canaliculata: Heterogeneity of Xanthophyll Distribution

The main light-harvesting fraction from Pelvetia canaliculata was isolated on a sucrose density gradient from digitonin-solubilized chloroplasts. After further solubilization by dodecyl maltoside, the bulk fraction was separated into two subunits by preparative isoelectric focusing. The more acidic brown fraction was mainly composed of 22 kDa polypeptides having an apparent pI of 4.55. Its pigment composition was very simple, containing chlorophyll (Chi) a, Chi c and fucoxanthin. The in vivo spectral properties of fucoxanthin, namely a shift in light absorption to the green and efficient energy transmission to Chi a, were conserved in this subunit. No xanthophyll associated with photoprotection was found in this band, even when obtained from photoinhibited thalli. The less acidic green band contained predominantly 22 kDa polypeptides that were resolved into numerous components by denaturing isoelectric focusing. Its pigment composition was more complex, containing, in addition, pigments of the so-called xanthophyll cycle. In photoinhibited thalli, about half of the violaxanthin was converted into antheraxanthin and zeaxanthin. All the pigments of the xanthophyll cycle were specifically associated with this subunit, and it may thus have a central role in the thermal dissipation of the absorbed light energy as postulated for light-harvesting complex II isolated from green plants.     

Electrochemistry of vitamin B12: Part VII. Role of the base-off/base-on reaction in the oxido-reduction in the B12r-B12s couple in non-aqueous solvents

The cyclic voltammetric study of vitamin B_12r in DMSO shows the importance of the base-on/base-off reaction in the electrochemical reduction mechanism. Depending upon the flux of electrons flowing through the system. part of the base-on complex is reduced through prior opening of the nucleotide side-chain which gives rise to the more easily reduced DMSO-Co(II) complex. The quantitative analysis of the variations of the peak heights with the sweep rate allows the thermodynamic and kinetic characterization of the base-on/base-off reactions to be determined. DMSO thus appears as a stronger ligand toward Co(II) than water, leading to an increased participation of the base-off complex in the reduction process. The greater stability of the DMSO complex is also related to the observation that electron transfer is significantly slower than in the case of the water complex. The importance of the ligand exchange reactions in the reduction of B_12r is confirmed by the effect of pyridine additions. Three complexes then participate in the reduction process, their reduction potentials lying in the order DMSO >Py >Bzm. The reduction mechanism involving the interconversion of the three complexes is described as a function of the electrode potential, the flux of electrons and the pyridine concentration. An estimation of the equilibrium and rate constants of the three ligand exchange reactions is made, based on the variations of the cyclic voltammograms with the sweep rate and the pyridine concentration.     

Game-perfect digraphs

In the A-coloring game, two players, Alice and Bob, color uncolored vertices of a given uncolored digraph D with colors from a given color set C, so that, at any time a vertex is colored, its color has to be different from the colors of its previously colored in-neighbors. Alice begins. The players move alternately, where a move of Bob consists in coloring a vertex, and a move of Alice in coloring a vertex or missing the turn. The game ends when Bob is unable to move. Alice wins if every vertex is colored at the end, otherwise Bob wins. This game is a variant of a graph coloring game proposed by Bodlaender (Int J Found Comput Sci 2:133?C147, 1991). The A-game chromatic number of D is the smallest cardinality of a color set C, so that Alice has a winning strategy for the game played on D with C. A digraph is A-perfect if, for any induced subdigraph H of D, the A-game chromatic number of H equals the size of the largest symmetric clique of H. We characterize some basic classes of A-perfect digraphs, in particular all A-perfect semiorientations of paths and cycles. This gives us, as corollaries, similar results for other games, in particular concerning the digraph version of the usual game chromatic number.     

New mathematical modelling and simulation of an industrial accumulator for elastic webs

This paper concerns the modelling of an accumulator used in industrial elastic web processing plant such as paper mills, fabric, rolling mills etc. Accumulators are used to allow rewind or unwind core changes while the process continues at a constant web velocity. A new nonlinear model of a pneumatic actuated industrial accumulator including pneumatic jack model, static friction representation and web weight is first detailed which enables to deduce a linear model. These models are derived from physical laws that describe web tension and velocity dynamics in each web span. In a second part, the effects of time-varying mechanical parameters, such as web Young modulus, web length and rollers inertia on accumulator dynamics are presented. The performances of the modeled accumulator are illustrated by simulations in Matlab/Simulink software environment.     

A note on taxation,incentives and risk sharing

The necessary and sufficient conditions for a tax system to guarantee the consistency of private and public evaluation of risky projects are derived. A stochastic dominance approach is used.     

The impact of voters’ preference diversity on the probability of some electoral outcomes

Voting rules are known to exhibit various paradoxical or problematic behaviors, typically in the form of their failure to meet the Condorcet criterion or in their vulnerability to strategic voting. Our basic premise is that a decrease in the number of coalitions of voters that exist with similar preference rankings should generally lead to a reduced propensity of voting rules to yield undesired results. Surprisingly enough, conclusions that are reported by Felsenthal et al. (1990) in an early study do not corroborate this intuition. This study reconsiders and extends the Felsenthal et al. analysis by using a modified Impartial Anonymous Culture (IAC) model. It turns out that the results obtained with this probabilistic assumption are much more consistent with the stated intuitive premise.     

The Structural Nature of the Nerve Functor for n-Groupoids

Given a left exact category B, the construction of the nerve functor _n for n-groupoids in B is related to a certain property of the category S-S i m p l _{n – 1} B of the split (n – 1)-truncated simplicial objects in B, which allows us to define the split n-truncated simplicial objects in B completely internally to S-S i m p l _{n – 1} B and thus to construct intrisincally from it the category S-S i m p l _n B.