Of Dogs and Fleas: The Dynamics of N Uncoupled Two-State Systems

The historical Ehrenfest model dating back to 1907 describes the process of equilibration together with fluctuations around the thermal equilibrium. This approach represents a special case in the dynamics of N uncoupled two-state systems. In this article we present a generalization of the original model by introducing an additional parameter p which denotes the probability of a single state change. Analytical solutions for the probability distribution of the system's state as well as the fluctuation distribution are derived. Interestingly, close inspection of the fluctuation distribution reveals an intrinsic time scale. Sampling the system's state at much slower rates yields the familiar macroscopic exponential distribution for equilibrium processes. For faster measurements a power law extends roughly over log₁₀ N orders of magnitude followed by an exponential tail. At some point, further increases of the sampling rate merely result in a shift of the fluctuation distribution towards higher values leaving plateau at small fluctuation sizes behind. Since the generic solution is rather unwieldy, we derive and discuss simple and intuitive analytical solutions in the limit of small p and large N. Furthermore, we relax the quantization of time by considering a complementary approach in continuous time. Finally we demonstrate that the fluctuation distributions resulting from the two different approaches bear identical characteristic features.     

Characterization of low-molecular weight peptides in champagne wine by liquid chromatography/tandem mass spectrometry

This paper reports the use of an on-line LC–ESI–MS/MS method for the identification and quantification of di- and tripeptides in champagne wine without laborious sample pretreatment. The identification of these compounds, in their underivatised form, is based on identical retention times and ESI–MS spectra to those of reference standards. The presence of nine dipeptides (Arg–Ile, Ile–Arg, Ile–Val, Lys–Phe, Lys–Tyr, Phe–Lys, Tyr–Gln, Tyr–Lys, Val–Ile) and the absence of two tripeptides (Phe–Arg–Arg and Lys–Met–Asn) have been evidenced in the matrix. Calibration curves for each analyte were established using Phe–Arg as internal standard. The calibration curves were linear in the concentration range 0.1–10 mg L⁻¹ with a determination coefficient, r², better than 0.992. The accuracy for the calibration standard was estimated at between 92 and 102%. This method allows high recovery and satisfies the necessary requirements with respect to accuracy, repeatability and sensitivity. The first application of this analytical method to the measurement of di- and tri-peptides in different vintages of champagne wine is reported. Compositional changes in the peptides occurred depending on the vintage.     

Multicomponent synthesis of epoxy-tetrahydronaphthyridine and structural diversification by subsequent fragmentation

Three-component reaction of an α-isocyanoacetamide 7, an homoallylamine 8 and an aldehyde 9 in methanol at room temperature provides oxa-bridged tricycle 4 in good to excellent yield as a mixture of two separable diastereoisomers. In this one-pot multicomponent process, one C-N, one C-O and three C-C bonds are formed with concomitant creation of five asymmetric centers and three rings. Fragmentation of epoxy-tetrahydronaphthyridine 4 affords differentially substituted 5,6,7,8-tetrahydro-1,7-naphthyridine (5, 6) depending on the reaction conditions, providing thus additional structural diversity. A one-pot three-component synthesis of 5,6,7,8-tetrahydro-1,7-naphthyridine (6) from 7, 8 and 9 is also documented.     

Q-switched Yb-doped nonlinear microstructured fiber laser for the emission of broadband spectrum

We report on an innovative configuration of a supercontinuum laser based on an Yb-doped nonlinear microstructured fiber. Due to this particular fiber design combining amplification and nonlinear properties, a wideband output spectrum is generated in the fiber under the Q-switched regime. By exploiting stimulated Brillouin scattering, high peak power pulses are achieved and contribute to a spectral broadening due to a nonlinear wavelength conversion process. Both infrared (1000-1200 nm) and visible (650-750 nm) spectra are generated with an average power of 200 mW.     

Contribution of Cytosine‐Containing Cyclobutane Dimers to DNA Damage Produced by Photosensitized Triplet–Triplet Energy Transfer

Mutagenic cyclobutane pyrimidine dimers (CPDs) can be induced in DNA through either direct excitation or photosensitized triplet–triplet energy transfer (TTET). In the latter pathway, thymines are expected to receive the excitation energy from the photosensitizer and react with adjacent pyrimidines. By using state‐of‐the art analytical tools, we provide herein additional information on the formation of cytosine‐containing CPDs. We thus determined the yield of all possible CPDs upon TTET in a series of natural DNAs with various base compositions. We show that the distribution of CPDs cannot be explained only by excitation of individual thymines. We propose that the mechanism for TTET involves at least dinucleotides as the minimal targets. The observation of the formation of cytosine–cytosine CPDs also suggests that additional pathways are involved in this photosensitized reaction.     

Preparation and properties of phenylene oxide–aryl ether sulphone block copolymers and their blends

We have prepared triblock copolymers of poly(phenylene oxide) (PPO) and polysulphone (PSF) of the form PPO–PSF–PPO in order to assess their intrinsic mechanical properties and their potential as interfacial compatibilizers in polystyrene/PSF blends. For sufficiently long polysulphone block lengths, we observed microphase separation both in the triblock copolymers and in their blends with polystyrene. The triblock polymers, nevertheless, showed very similar microdeformation behavior to the PPO homopolymer, suggesting the phase separation to play a minor role. On the other hand, the compatibility of the poly(phenylene oxide) blocks and polystyrene ensured a high degree of interphase adhesion in blends containing both polystyrene and free PSF, even for relatively high homopolymer molecular weights. © 1996 John Wiley & Sons, Inc.     

Surface chemistry and optimization of focused ion beam iodine-enhanced etching of indium phosphide

Focused ion beam physical sputtering and iodine-enhanced etching of indium phosphide (InP) were performed. Up to 15× enhanced etching rates over sputtering were measured at room temperature, due to the addition of iodine to the sputter-process. Reaction mechanisms and products are discussed and characterized. The reaction is limited by the desorption of indium triiodide (InI₃) at room temperature. InI₃ has to be removed by sputtering, which simultaneously amorphizes the underlying substrate. Surface roughness and stoichiometry of InP are compared for sputtering and etching. Gallium-contamination and the damaged zone in InP are significantly reduced by iodine-enhanced etching. Based on the reaction mechanisms, an optimum beam scanning strategy is proposed which allows precise microfabrication in reduced time and minimizes damage to the substrate. The method is also applicable for other halide gas etching processes of III-V semiconductors.     

Automating a 96-well microtiter plate assay for identification of AGEs inhibitors or inducers: application to the screening of a small natural compounds library

Advanced glycation end-products (AGEs) are involved in the pathogenesis of numerous affections such as diabetes and neurological diseases. AGEs are also implied in various changes in tissues and organs. Therefore, compounds able to break them or inhibit their formation may be considered as potential drugs, dietary supplements, or bioactive additives. In this study, we have developed a rapid and reliable (Z′ factor calculation) anti-AGEs activity screening based on the overall fluorescence of AGEs. This method was successfully evaluated on known AGEs inhibitors and on a small library of natural compounds, yielding coherent results when compared with literature data.     

Induced Chiroptical Changes of a Water‐Soluble Cryptophane by Encapsulation of Guest Molecules and Counterion Effects

We report the synthesis of the water‐soluble cryptophanol derivative 1 and the study of the chiroptical properties of its two enantiomers (>99 % ee) by polarimetry, electronic circular dichroism (ECD), and vibrational circular dichroism (VCD). We show that cryptophanol 1 exhibits unusual chiroptical properties in water under basic conditions (pH>12). For instance, the shapes of the ECD and VCD spectra of 1 in water were strongly dependent on the nature of the alkali metal ions (Li⁺, Na⁺, K⁺, Cs⁺) surrounding the cryptophane and whether or not a guest molecule is present inside the cavity of the host. To the best of our knowledge, this is the first example in which the nature of these counterions governs the chiroptical properties of a host molecule. Moreover, specific ECD spectra were obtained depending on the size of the guest molecules. This makes 1 a good sensor for small neutral molecules in aqueous solvent. Finally, VCD experiments associated with DFT calculations show that the chiroptical changes can be directly correlated to the presence of charges close to the aromatic rings and with a conformational change of the alkyl chains upon encapsulation.     

The excited state dipole moments of betaine pyridinium investigated by an innovative solvatochromic analysis and TDDFT calculations

This work reports on the solvatochromic properties of a simple heterocyclic betaine pyridinium, 2-(1-pyridinio)benzimidazolate (SBPa), having promising potentialities in non-linear optics. From advanced PCM-TDDFT calculations, the solvatochromism of SBPa was found to be unusual, involving two different electronic states for absorption (S(0)→ S(2)) and emission (S(1)→S'(0)). To account for this behavior, we developed an innovative physical treatment which consists in a non-linear fit of the solvatochromic data using the Bilot-Kawski theoretical model and visualizing the least-square coefficient χ(2) on a 2D map as a function of the solute polarizability and gas phase absorption energy. In parallel, Kamlet-Taft correlations were undertaken to select a propitious set of electrostatic solvents usable in this treatment. Protic solvents that lead to specific interactions and nonpolar solvents that favor dimerization processes were excluded. From a choice of aprotic solvents with sufficiently high polarity, 4 dipole moments μ(g)(S(0)) = +9.1 D, μ(e)(S(2)) = -1.5 D, μ(e)(S(1)) = 0 D and μ(g)(S'(0)) = +3.31 D were determined, the 3 former values being in close agreement with TDDFT values, although the solute polarizability values seem underestimated. Anyhow, disregarding this discrepancy, we evaluated the static hyperpolarizability to β(0) = -64 × 10(-30) esu from the solvatochromic data in close agreement with DFT calculations.