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871.
Dr. Michèle Cristau Dr. Muriel Amblard Dr. Sonia Cantel Prof. Christine Enjalbal Dr. Karine Puget Prof. Jean Martinez Dr. Gilles Subra 《化学:亚洲杂志》2011,6(9):2382-2389
The synthesis and use of novel polymer‐supported reagents for disulfide bond formation is described. This family of supported reagents consists of a series of oxidized methionines grafted onto a solid support. Their cost and the simplicity of their preparation through N‐carboxyanhydride polymerization on beads make them reactants of choice for the formation of disulfide bridges in peptides. 相似文献
872.
The estimator proposed recently by Delmas and Jourdain for waste-recycling Monte Carlo achieves variance reduction optimally with respect to a control variate that is evaluated directly using the simulation data. Here, the performance of this estimator is assessed numerically for free energy calculations in generic binary alloys and is compared to those of other estimators taken from the literature. A systematic investigation with varying simulation parameters of a simplified system, the anti-ferromagnetic Ising model, is first carried out in the transmutation ensemble using path-sampling. We observe numerically that (i) the variance of the Delmas-Jourdain estimator is indeed reduced compared to that of other estimators; and that (ii) the resulting reduction is close to the maximal possible one, despite the inaccuracy in the estimated control variate. More extensive path-sampling simulations involving an FeCr alloy system described by a many-body potential additionally show that (iii) gradual transmutations accommodate the atomic frustrations; thus, alleviating the numerical ergodicity issue present in numerous alloy systems and eventually enabling the determination of phase coexistence conditions. 相似文献
873.
Gilles Gnacadja 《Journal of mathematical chemistry》2011,49(10):2137-2157
Chemical Reaction Network Theory uses mathematics to study systems of reactions and infer their properties from their structure.
At the onset is an abstract definition of a chemical reaction network which is very general and is pertinent beyond chemistry,
e.g. in modeling interactions of microscopic and macroscopic living species. This allows the theory to provide widely applicable
theorems. It also results in that the idea of chemical composition is mostly used implicitly in examples to illustrate theorems,
not explicitly to establish new properties. In this paper we propose a formalism for species composition in a way that generalizes
the idea of atomic composition—for instance, elementary species will extend the idea of atoms. We envision that this formalism
could lead to more theorems on classes of networks that are of interest in biochemistry. Toward that prospect, we prove that
if there is no isomerism among elementary species, and if a newly formalized and widely applicable reversibility condition
holds, then a reaction network is vacuously persistent: no species will tend to extinction if all species are implicitly present
at initial time. This paper is the second in a series of three articles. The first paper studies vacuous persistence and the
third one probes a class of enzymatic networks. 相似文献
874.
Ulrich G Goeb S De Nicola A Retailleau P Ziessel R 《The Journal of organic chemistry》2011,76(11):4489-4505
A general method for the synthesis of difluorobora-diisoindolomethene dyes with phenyl, p-anisole, or ethyl-thiophene substituents has been developed. The nature of the substituents allows modulation of the fluorescence from 650 to 780 nm. Replacement of the fluoro ligands by ethynyl-aryl or ethyl residues is facile using Grignard reagents. Several X-ray molecular structures have been determined, allowing establishment of structure-fluorescence relationships. When the steric crowding around the boron center is severe, the aromatic substituents α to the diisoindolomethene nitrogens are twisted out of coplanarity, and hypsochromic shifts are observed in the absorption and emission spectra. This shift reached 91 nm with ethyl substituents compared to fluoro groups. When ethynyl linkers are used, the core remains flat, and a bathochromic shift is observed. All the fluorophores exhibit relatively high quantum yields for emitters in the 650-800 nm region. When perylene or pyrene residues are connected to the dyes, almost quantitative energy transfer from them to the dye core occurs, providing large virtual Stokes shifts spanning from 8000 to 13,000 cm(-1) depending on the nature of the dye. All the dyes are redox active, providing the Bodipy radical cation and anion in a reversible manner. Stepwise reduction or oxidation to the dication and dianion is feasible at higher potentials. We contend that the present work paves the way for the development of a new generation of stable, functionalized luminophores for bioanalytical applications. 相似文献
875.
The angular power spectrum of a stationary random field on the sphere is estimated from the needlet coefficients of a single realization, observed with increasingly fine resolution. The estimator we consider is the one recently used in practice by (Faÿ et al. 2008) to estimate the power spectrum of the Cosmic Microwave Background. The consistency of the estimator, in the asymptotics of high frequencies, is proved for a model with a stationary Gaussian field corrupted by heteroscedastic noise and missing data. 相似文献
876.
Deraemaeker A Tondreau G Bourgeois F 《The Journal of the Acoustical Society of America》2011,129(2):681-690
When a voltage is applied across the electrodes of a flat piezoelectric transducer attached to a thin plate structure, the transducer acts as equivalent loads applied to the host plate structure. In this paper, analytical expressions of these equivalent loads are derived for the general case of an orthotropic piezoelectric actuator using Hamilton's principle and two different mathematical approaches leading to the same results: Green's theorem and derivation using the theory of distributions. The equivalent loads are a function of the material properties as well as the normal to the contour of the transducer. Examples of applications to simple geometric shapes (triangle, rectangle, and circle) are given. 相似文献
877.
We demonstrate an efficient dynamical amplification of phase conjugation in the gain medium of a diode-pumped Nd(3+)YVO4 solid-state laser via excitation of its relaxation oscillations. Consequently, enhancement in the modulated amplitude of the phase conjugate wave is observed with up to +30?dB compared to the classical homodyne approach. 相似文献
878.
Bardin L Fauré MC Limagne D Chevallard C Konovalov O Filipe EJ Waton G Krafft MP Goldmann M Fontaine P 《Langmuir : the ACS journal of surfaces and colloids》2011,27(22):13497-13505
We have determined the structure formed at the air-water interface by semifluorinated alkanes (C(8)F(17)C(m)H(2m+1) diblocks, F8Hm for short) for different lengths of the molecule (m = 14, 16, 18, 20) by using surface pressure versus area per molecule isotherms, Brewster angle microscopy (BAM), and grazing incidence x-ray experiments (GISAXS and GIXD). The behavior of the monolayers of diblocks under compression is mainly characterized by a phase transition from a low-density phase to a condensed phase. The nonzero surface pressure phase is crystalline and exhibits two hexagonal lattices at two different scales: a long-range-order lattice of a few tens of nanometers lateral parameter and a molecular array of about 0.6 nm parameter. The extent of this organization is sufficiently large to impact larger scale behavior. Analysis of the various compressibilities evidences the presence of non organized molecules in the monolayer for all 2D pressures. At room temperature, the self-assembled structure appears generic for all the F8Hm investigated. 相似文献
879.
Louguet S Kumar AC Guidolin N Sigaud G Duguet E Lecommandoux S Schatz C 《Langmuir : the ACS journal of surfaces and colloids》2011,27(21):12891-12901
The physical adsorption of PEO(n)-b-PLL(m) copolymers onto silica nanoparticles and the related properties of poly(ethylene oxide) (PEO)-coated particles were studied as a function of the block copolymer composition. Copolymers adopt an anchor-buoy conformation at the particle surface owing to a preferential affinity of poly(L-lysine) (PLL) blocks with the silica surface over PEO blocks when a large excess of copolymer is used. The interdistance between PEO chains at particle surface is highly dependent on the size of PLL segments; a dense brush of PEO is obtained for short PLL blocks (DP = 10), whereas PEO chains adopt a so-called interacting "mushroom" conformation for large PLL blocks (DP = 270). The size of the PEO blocks does not really influence the copolymer surface density, but it has a strong effect on the PEO layer thickness as expected. Salt and protein stability studies led to similar conclusions about the effectiveness of a PEO layer with a dense brush conformation to prevent colloidal aggregation and protein adsorption. Besides, a minimal PEO length is required to get full stabilization properties; as a matter of fact, both PEO(45)-b-PLL(10) and PEO(113)-b-PLL(10) give rise to a PEO brush conformation but only the latter copolymer efficiently stabilizes the particles in the presence of salt or proteins. 相似文献
880.
Legrand YM Gilles A Petit E van der Lee A Barboiu M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(36):10021-10028
Cyclobutadiene ( CBD ), the smallest cyclic hydrocarbon bearing conjugated double bonds, has long intrigued chemists because of its chemical characteristics. The question of whether the molecule could be prepared at all has been answered, but the parent compound and its unperturbed derivatives have eluded crystallographic characterization or synthesis “in water”. Different approaches have been used to generate and to trap cyclobutadiene in a variety of confined environments: a) an Ar matrix at cryogenic temperatures, b) a hemicarcerand cage enabling the characterization by NMR spectroscopy in solution, and c) a crystalline guanidinium–sulfonate–calixarene G4C matrix that is stable enough to allow photoreactions in the solid state. In the latter case, the 4,6‐dimethyl‐α‐pyrone precursor, Me21 , has been immobilized in a guanidinium–sulfonate–calixarene G4C crystalline network through a combination of non‐covalent interactions. UV irradiation of the crystals transforms the entrapped Me21 into a 4,6‐dimethyl‐Dewar‐β‐lactone intermediate, Me22 , and rectangular‐bent 1,3‐dimethylcyclobutadiene, Me2CBDR , which are sufficiently stable under the confined conditions at 175 K to allow a conventional structure determination by X‐ray diffraction. Further irradiation drives the reaction towards Me23&Me2CBDS /CO2 (63.7 %) and Me2CBDR (37.3 %) superposed crystalline architectures and the amplification of Me2CBDR . The crystallographic models are supported by additional FTIR and Raman experiments in the solid state and by 1H NMR spectroscopy and ESI mass spectrometry experiments in aqueous solution. Amazingly, the 4,6‐dimethyl‐Dewar‐β‐lactone, Me22 , the cyclobutadiene‐carboxyl zwitterion, Me23 , and 1,3‐dimethylcyclobutadiene, Me2CBD , were obtained by ultraviolet irradiation of an aqueous solution of G4C{Me21} . 1,3‐Dimethylcyclobutadiene is stable in water at room temperature for several weeks and even up to 50 °C as demonstrated by 1H NMR spectroscopy. 相似文献