Synthesis of N-functionalized 2,2′-dipyridylamine ligands, complexation to ruthenium (II) and anchoring of complexes to papain from papaya latex

2,2′-Dipyridylamine (dpa) derivatives carrying a thiol-targeted maleimide group located at the end of an alkyl substituent on the central amine were synthesized. Reaction with the organometallic precursors [(η⁶-arene)RuCl₂]₂ (arene = benzene or p-cymene) yielded the half-sandwich cationic complexes [(η⁶-arene)Ru(dpa)Cl]⁺ where the dipyridylamine derivatives were coordinated as bidentate N,N donor ligands. Enzymatic studies showed that these derivatives were able to inactivate the cysteine endoproteinase papain by S-alkylation of the cysteine active site.     

Axially Chiral Facial Amphiphiles with a Dihydronaphthopentaphene Structure as Molecular Tweezers for SWNTs

Syntheses of chiral 6,15‐dihydronaphtho[2,3‐c]pentaphene derivatives of opposite configurations are reported. Starting from anthracene, the strategy involves two key steps: a Diels–Alder reaction on a prochiral dianthraquinone, and an enantiomeric resolution using (?)‐menthol. The final molecules exhibit very strong optical activity, as shown by their circular dichroism spectra, and are examples of chiral facial amphiphiles. Their adsorption at the surface of single‐walled carbon nanotubes (SWNTs) has also been studied, and has been found to occur preferentially on 0.8–1.0 nm diameter nanotubes among the population of a high‐pressure CO conversion (HiPco) SWNT sample (0.8–1.2 nm). The synthesised facial amphiphiles act as nano‐tweezers for the diameter‐selective solubilisation of SWNTs in water. The expected optical activities of the SWNT samples solubilised by each of the chiral amphiphiles have been studied by circular dichroism spectroscopy, but the results are not yet conclusive.     

Surface Fluorination of Carboxylated Nitrile Butadiene Rubber: An XPS Study

Because of their exceptional reactivity, fluorine and fluorinated gases are of primary importance for the modification of the surface properties of materials. This study is devoted to surface treatment of thin nitrile gloves, made of carboxylated nitrile butadiene rubber latex, using either direct fluorination (10% F₂gas diluted in N₂) or plasma-enhanced fluorination in radio-frequency cold plasmas using fluorinated gases (CF₄, CHF₃). Mechanisms of fluorination of these co-elastomers have been proposed on the basis of the assignment of the different components of the XPS spectra. Several mechanisms have been observed depending on the fluorination conditions. Although the modification of nitrile gloves is already effective for fluorination reactions at room temperature, an important activation is observed for experiments carried out at 90°C. When the treatments are carried out at room temperature, a gradual fluorination occurs: in the case of 10% diluted F₂ gas, monofluorinated C—F groups are the species most found at the surface and perfluoro groups CF _n are present in lower amount. An addition reaction takes place at the CH=CH double bonds of the polybutadiene entities, leading to CHF=CHF units. Whatever the fluorination method, thermal activation yields a more massive fluorination of the surface that finally leads to perfluorinated CF₂ groups and terminal —CF₃ groups.     

Chiral relay: a novel strategy for the control and amplification of enantioselectivity in chiral Lewis acid promoted reactions

Chiral Lewis acid catalysis has emerged as one of the premiere method to control stereochemistry. Much effort has gone into the design of superior ligands with increasing steric extension to shield distant reactive sites. We report here an alternative and complementary approach based on a "chiral relay". This strategy focuses on the improved design of achiral templates which may relay and amplify the stereochemistry from ligands. The essence of this strategy is that the chiral Lewis acid would effectively convert an achiral template into a chiral non-racemic template. This approach combines the advantages of enantioselective catalysis (substoichiometric amount of the chiral inducer) with the ones of chiral auxiliary control (efficient and predictable stereocontrol).     

Diastereoselective Radical Reactions Starting from Cyclic Iodohydrin Derivatives

The stereoselectivity of radical reactions using cyclic iodohydrins and 2-alkoxy iodides was investigated on a simple model system obtained from indene (see 1a ? d ). The low level of stereoselectivity inherent to this type of systems could neither be overcome by using large protective group on the O-atom of 1c nor by complexation with Lewis acids. However, starting from the free alcohol 1c , it was possible to obtain very high selectivities (trans/cis > 100:1) by forming an aluminium alkoxide derivative upon treatment with methylaluminium bis[2,6-di(tert-butyl)-4-methylphenoxide] (MAD) before running the radical reaction. Despite the high steric demand of these complexes, the reactions gave satisfactory yields even for the formation of C? C bonds.