Stabilising Peptoid Helices Using Non‐Chiral Fluoroalkyl Monomers

Stability towards protease degradation combined with modular synthesis has made peptoids of considerable interest in the fields of chemical biology, medicine, and biomaterials. Given their tertiary amide backbone, peptoids lack the capacity to hydrogen‐bond, and as such, controlling secondary structure can be challenging. The incorporation of bulky, charged, or chiral aromatic monomers can be used to control conformation but such building blocks limit applications in many areas. Through NMR and X‐ray analysis we demonstrate that non‐chiral neutral fluoroalkyl monomers can be used to influence the K_cis/trans equilibria of peptoid amide bonds in model systems. The cis‐isomer preference displayed is highly unprecedented given that neither chirality nor charge is used to control the peptoid amide conformation. The application of our fluoroalkyl monomers in the design of a series of linear peptoid oligomers that exhibit stable helical structures is also reported.     

Kinetic and calorimetric study of the adsorption of dyes on mesoporous activated carbon prepared from coconut coir dust

Mesoporous activated carbon has been prepared from coconut coir dust as support for adsorption of some model dye molecules from aqueous solutions. The methylene blue (MB) and remazol yellow (RY) molecules were chosen for study of the adsorption capacity of cationic and anionic dyes onto prepared activated carbon. The adsorption kinetics was studied with the Lagergren first- and pseudo-second-order kinetic models as well as the intraparticle diffusion model. The results for both dyes suggested a multimechanism sorption process. The adsorption mechanisms in the systems dyes/AC follow pseudo-second-order kinetics with a significant contribution of intraparticle diffusion. The samples simultaneously present acidic and basic sites able to act as anchoring sites for basic and acidic dyes, respectively. Calorimetric studies reveal that dyes/AC interaction forces are correlated with the pH of the solution, which can be related to the charge distribution on the AC surface. These AC samples also exhibited very short equilibrium times for the adsorption of both dyes, which is an economically favorable requisite for the activated carbon described in this work, in addition to the local abundance of the raw material.     

Gluing semigroups: when and how

Semigroup Forum - Given two semigroups $$\langle A\rangle$$ and $$\langle B\rangle$$ in $${\mathbb {N}}^n$$ , we wonder when they can be glued, i.e., when there exists a semigroup $$\langle...     

New rheological developments for reactive processing of poly(ε-caprolactone)

This short review aims to show how an integrated activity on reactive processing have been developed these last years in our laboratory. We can say that the originality of this approach is based on combining developments in chemistry, in line instrumentation, and rheology aspects. Our rheological works can be divided into four important contributions: rheo-physics, rheo-chemistry, rheo-mixing and rheo-processing. These different parts are illustrated from the ε-caprolactone polymerisation in bulk and dispersed media. Rheo-physics studies allowed us to calculate the molecular weight distribution and chain structures of in situ polymerised poly(ε-caprolactone) samples. From rheo-chemistry works, we are now able to predict the variation of the complex shear modulus versus the extent of the polymerisation. The developments of new rheological tools such as rheo-mixer enable us to investigate complex mixing situations encountered in reactive polymer blends and formulations. Lastly, a rheo-processing approach based on the in-line measurement of the viscosity in a slit rheometer at the die exit of the extruder allows us to envisage its application to the experimental control of the reactive processing in extruder. To cite this article: P. Cassagnau et al., C. R. Chimie 9 (2006).     

Li + HCl RIOSA cross section calculations on parallel computers

Summary Reactive Infinite Order Sudden Approximation calculations have been performed using a computational procedure restructured to run on parallel computers. Computationally intensive sections of the code are analyzed and speedups obtained from a parallel restructuring discussed. The significant speedup obtained on a shared-memory parallel machine has allowed us to perform extensive calculations of the energy dependence of the integral and differential reactive cross sections of the Li+HCl system. A comparison with results of a quasiclassical and an experimental study is also performed.     

Operator product expansion and quark condensate from lattice QCD in coordinate space

We present a lattice QCD determination of the chiral quark condensate based on a new method. We extract the quark condensate from the operator product expansion of the quark propagator at short euclidean distances, where it represents the leading contribution in the chiral limit. From this study we obtain , in good agreement with determinations of this quantity based on different approaches. The simulation is performed by using the -improved Wilson action at on a volume 32³ × 70 in the quenched approximation.Received: 8 March 2005, Revised: 15 April 2005, Published online: 18 May 2005PACS: 11.15.Ha, 11.30.Rd, 12.38.-t, 12.38.Gc     

Stochastic resonance phenomenon in Monte Carlo simulations of silver adsorbed on gold

The possibility of observing the stochastic resonance phenomenon was analyzed by means ofMonte Carlo simulations of silver adsorbed on 100 gold surfaces. The coverage degree was studied as a function ofthe periodical variation of the chemical potential. The signal-noise relationship wasstudied as a function of the amplitude and frequency of chemical potential andtemperature. When this value is plotted as a function of temperature, a maximum is found,indicating the possible presence of stochastic resonance.     

Experimental and Kinetic Modeling Study of C2H2 Oxidation at High Pressure

A detailed chemical kinetic model for oxidation of acetylene at intermediate temperatures and high pressure has been developed and evaluated experimentally. The rate coefficients for the reactions of C₂H₂ with HO₂ and O₂ were investigated, based on the recent analysis of the potential energy diagram for C₂H₃ + O₂ by Goldsmith et al. and on new ab initio calculations, respectively. The C₂H₂ + HO₂ reaction involves nine pressure‐ and temperature‐dependent product channels, with formation of triplet CHCHO being dominant under most conditions. The barrier to reaction for C₂H₂ + O₂ was found to be more than 50 kcal mol^?1 and predictions of the initiation temperature were not sensitive to this reaction. Experiments were conducted with C₂H₂/O₂ mixtures highly diluted in N₂ in a high‐pressure flow reactor at 600–900 K and 60 bar, varying the reaction stoichiometry from very lean to fuel‐rich conditions. Model predictions were generally in satisfactory agreement with the experimental data. Under the investigated conditions, the oxidation pathways for C₂H₂ are more complex than those prevailing at higher temperatures and lower pressures. Acetylene is mostly consumed by recombination with H to form vinyl (reducing conditions) or with OH to form a CHCHOH adduct (stoichiometric to lean conditions). Both C₂H₃ and CHCHOH then react primarily with O₂. The CHCHOH + O₂ reaction leads to formation of significant amounts of glyoxal (OCHCHO) and formic acid (HOCHO), and the oxidation chemistry of these intermediates is important for the overall reaction.     

Indirect Study of the 2H(d,p)3H and 2H(d,n)3He Reactions at Astrophysical Energies via the Trojan Horse Method

The ²H(d,p)³H and ²H(d,n)³He reactions have been indirectly studied by means of the Trojan Horse Method applied to the quasi-free ²H(³He, p³H)¹H?²H(³He, n³He)¹H reaction at 18?MeV of beam energy. This is the first experiment where the spectator (here ¹H) has been detected in coincidence with the charged participant, avoiding the limitations of standard neutron detectors. The d ? d relative energy has been measured from 1.5?MeV down to 2?keV, at center of mass angles from 40° to 170°. Indirect angular distributions are compared with the direct behaviour in the overlapping regions.     

Peptide Modifications Differentially Alter G Protein‐Coupled Receptor Internalization and Signaling Bias

Although G protein‐coupled receptors (GPCRs) are targeted by more clinically used drugs than any other type of protein, their ligand development is particularly challenging. Humans have four neuropeptide Y receptors: hY₁R and hY₅R are orexigenic, while hY₂R and hY₄R are anorexigenic, and represent important anti‐obesity drug targets. We show for the first time that PEGylation and lipidation, chemical modifications that prolong the plasma half‐lives of peptides, confer additional benefits. Both modifications enhance pancreatic polypeptide preference for hY₂R/hY₄R over hY₁R/hY₅R. Lipidation biases the ligand towards arrestin recruitment and internalization, whereas PEGylation confers the opposite bias. These effects were independent of the cell system and modified residue. We thus provide novel insights into the mode of action of peptide modifications and open innovative venues for generating peptide agonists with extended therapeutic potential.