Band-Selective HSQC and HMBC Experiments Using Excitation Sculpting and PFGSE

Variants of the HSQC and HMBC experiments are described. They allow the restriction of the heteronuclear chemical shift domain without causing spectral folding. Selectivity is introduced in the HSQC experiment by means of excitation sculpting. The selective element of the pulse sequence is a double pulsed field gradient spin echo. It may be used either split by the t(1) evolution period, or not. The selectivity profile depends on the scheme used as well as on the number of protons attached to the heteronucleus. The selective HMBC experiment requires only a single echo sequence as no strict control of the signal phase is required. A complex glycoconjugate is used as a test compound for the new pulse sequences.     

Etude rheologique de gels mixtes de poly(alcool vinylique) et d'alginate de sodium

Snake-cage hydrogels were prepared by the association of poly(vinyl alcohol) (PVA) and sodium alginate. The aim of this work is to study the viscoelastic properties of PVA networks having different molecular weights and trapping alginates of various mannuronate/guluronate ratios, molecular weights and aqueous concentration. The elastic and viscous moduli, G′ and G″, were found to depend on alginate concentration. With the sodium alginate (mannuronate/guluronate =1.78, M̄w=380 000), the elasticity was observed to be independent of the PVA molecular weight in the 7.5% to 10% (w/w) concentration range. Hydrogels elasticity was found to be sodium alginate nature-dependent only in the case of PVA with M̄w =22 000. Moreover, it seems that the viscoelastic parameters G′ and G″ become increasingly insensitive to the nature of sodium alginate as the molecular weight of PVA increases.     

The Enantioselectivity and the Stereochemical Course of Copper‐Catalyzed Intramolecular CH Insertions of Phenyliodonium Ylides

The Cu‐catalyzed intramolecular CH insertion of phenyliodonium ylide 1b was investigated at 0° in the presence of several chiral ligands. Enantioselectivities varied in the range 38–72%, and were higher than those resulting from reaction of the diazo compound 1c at 65°. The intramolecular insertion of the enantiomerically pure methyl diazoacetate (R)‐ 20 and of the corresponding phenyliodonium ylide (R)‐ 21 proceeded to (R)‐ 23 with retention of configuration with [Cu(hfa)₂] (hfa=hexafluoroacetylacetone=1,1,1,5,5,5‐hexafluoropentane‐2,4‐dione) and [Rh₂(OAc)₄]. These results are consistent with a carbenoid mechanism for the Cu‐catalyzed insertion with phenyliodonium ylides. However, the insertion of the perfluorosulfonated phenyliodonium ylide (R)‐ 29 afforded with [Cu(hfa)₂] as well as with [Rh₂(OAc)₄] the cyclopentanone derivative 30 as a cis/trans mixture with only 56–67% enantiomeric excess.     

Description of complementary actions of mineral and organic additives in thermoplastic polymer composites by Flame Retardancy Index

This work visualizes the complementary actions of organic and mineral additives in model thermoplastic polymer composites in terms of Flame Retardancy Index (FRI). Thermal and flame retardancy behaviors of ethylene‐vinyl acetate copolymer (EVA) composites containing calcium carbonate (CC) mineral and ammonium polyphosphate (APP) organic additives were studied varying composition of additives in the 80/20 EVA/(xCC + (20 ? x)APP) composites with x denoting 0, 5, 10, 15, and 20 wt%. Thermogravimetric analysis (TGA) revealed that the onset temperature of composites and the remaining residue were increased by combination of APP and CC, while cone calorimetry results were indicative of a promising flame retardancy performance at a given composition of APP and CC. Based on FRI values, we made distinguished samples from flame retardancy performance viewpoint, where the best flame retardancy was obtained by combination of 15 wt% APP and 5 wt% CC, as reflected in FRI value of 3.08. By contrast, samples containing only APP or CC revealed low resistance against flame, as signaled by FRI values of 0.99 and 0.89, respectively. X‐ray diffraction (XRD) analysis was made on remaining residue collected at the end of cone calorimetry measurements. Moreover, Raman analysis confirmed barrier effect of flame retardancy for EVA/(5APP + 15CC) sample, featured by a higher graphitization level as well as a thicker yet more homogenous char layer. Mechanical behavior analysis of composites revealed an acceptable level of properties, particularly high elongation at break, which was almost independent of formulation. However, a minor loss in yield stress was observed, especially for EVA(10CC + 10APP) sample.     

Homogenised constitutive model coupling damage and debonding for reinforced concrete structures under cyclic solicitations

A new stress resultant constitutive model for reinforced concrete plates under cyclic solicitations is presented. This model is built by the periodic homogenisation approach using the averaging method and couples damage of concrete and periodic debonding between concrete and steel rebar. In one-dimensional situations, we derive a closed-form solution of the local problem useful to verify and set up the plate problem. The one dimensional macroscopic constitutive model involves a limited number of parameters, the sensibility of which is studied. Comparison to experimental results underlines the pertinence of the model by considering internal debonding in order to properly represent the mechanical dissipation occurring during cyclic loadings on reinforced concrete panels.     

Impact of N-Truncated Aβ Peptides on Cu- and Cu(Aβ)-Generated ROS: CuI Matters!

In vitro Cu(Aβ_1–x)-induced ROS production has been extensively studied. Conversely, the ability of N-truncated isoforms of Aβ to alter the Cu-induced ROS production has been overlooked, even though they are main constituents of amyloid plaques found in the human brain. N-Truncated peptides at the positions 4 and 11 (Aβ_4–x and Aβ_11–x) contain an amino-terminal copper and nickel (ATCUN) binding motif (H₂N-Xxx-Zzz-His) that confer them different coordination sites and higher affinities for Cu^II compared to the Aβ_1–x peptide. It has further been proposed that the role of Aβ_4–x peptide is to quench Cu^II toxicity in the brain. However, the role of Cu^I coordination has not been investigated to date. In contrast to Cu^II, Cu^I coordination is expected to be the same for N-truncated and N-intact peptides. Herein, we report in-depth characterizations and ROS production studies of Cu (Cu^I and Cu^II) complexes of the Aβ_4–16 and Aβ_11–16 N-truncated peptides. Our findings show that the N-truncated peptides do produce ROS when Cu^I is present in the medium, albeit to a lesser extent than the unmodified counterpart. In addition, when used as competitor ligands (i.e., in the presence of Aβ_1–16), the N-truncated peptides are not able to fully preclude Cu(Aβ_1–16)-induced ROS production.     

Nitroxyl radical self assembled monolayers: Ion pairing investigation in organic and aqueous media

Self assembled monolayers (SAMs) formed from TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) derivative thiols have been studied by electrochemical quartz crystal microbalance (EQCM) in both aqueous and non-aqueous solvents. The in situ study of the mass transport occurring during the oxidation of TEMPO provides evidence of a ion pair formation without incorporation of solvent in densely packed nitroxyl radical SAMs. For SAMs having a low nitroxyl radical surface coverage, the effect of mixed SAMs is evidenced and seems to avoid the solvent incorporation.     

Versatile Functionalization of Nanoelectrodes by Oligonucleotides via Pyrrole Electrochemistry

Surface modification at the nanometer scale is a challenge for the future of molecular electronics. In particular, the precise anchoring and electrical addressing of biological scaffolds such as complex DNA nanonetworks is of importance for generating bio‐directed assemblies of nano‐objects for nanocircuit purposes. Herein, we consider the individual modification of nanoelectrodes with different oligonucleotide sequences by an electrochemically driven co‐polymerization process of pyrrole and modified oligonucleotide sequences bearing pyrrole monomers. We demonstrate that this one‐step technique presents the advantages of simplicity, localization of surface modification, mechanical, biological and chemical stability of the coatings, and high lateral resolution.