Counterintuitive torsional barriers controlled by hydrogen bonding.

The torsional barriers along the Caryl-Caryl axis of a pair of isosteric disubstituted biphenyls were determined by variable temperature 1H NMR spectroscopy in three solvents with contrasted hydrogen bond accepting abilities (1,1,2,2-tetrachloroethane-d2, nitrobenzene-d5 and dimethyl sulfoxide-d6). One of the biphenyl scaffolds was substituted at its ortho and ortho' positions with N'-acylcarbohydrazide groups that could engage in a pair of intramolecular N-HO=C hydrogen bonding interactions at the ground state, but not at the transition state of the torsional isomerization pathway. The torsional barrier of this biphenyl was exceedingly low despite the presence of the hydrogen bonds (16.1, 15.6 and 13.4 kcal mol-1 in the three aforementioned solvents), compared to the barrier of the reference biphenyl (15.3 ± 0.1 kcal mol-1 on average). Density functional theory and the solvation model developed by Hunter were used to decipher the various forces at play. They highlighted the strong stabilization of hydrogen bond donating solutes not only by hydrogen bond accepting solvents, but also by weakly polar, yet polarizable solvents. As fast exchanges on the NMR time scale were observed above the melting point of dimethyl sulfoxide-d6, a simple but accurate model was also proposed to extrapolate low free activation energies in a pure solvent (dimethyl sulfoxide-d6) from higher ones determined in mixtures of solvents (dimethyl sulfoxide-d6 in nitrobenzene-d5).

Aromatic foldamers as scaffolds for metal second coordination sphere design.

As metalloproteins exemplify, the chemical and physical properties of metal centers depend not only on their first but also on their second coordination sphere. Installing arrays of functional groups around the first coordination sphere of synthetic metal complexes is thus highly desirable, but it remains a challenging objective. Here we introduce a novel approach to produce tailored second coordination spheres. We used bioinspired artificial architectures based on aromatic oligoamide foldamers to construct a rigid, modular and well-defined environment around a metal complex. Specifically, aza-aromatic monomers having a tethered [2Fe-2S] cluster have been synthesized and incorporated in conical helical foldamer sequences. Exploiting the modularity and predictability of aromatic oligoamide structures allowed for the straightforward design of a conical architecture able to sequester the metal complex in a confined environment. Even though no direct metal complex-foldamer interactions were purposely designed in this first generation model, crystallography, NMR and IR spectroscopy concurred to show that the aromatic oligoamide backbone alters the structure and fluxional processes of the metal cluster.

[Mortality and functional independence one year after hip fracture surgery: extracapsular fracture versus intracapsular fracture]. / Mortalité et indépendance fonctionnelle un an après chirurgie pour fracture de l'extrémité supérieure du fémur : comparaison fracture extracapsulaire versus fracture intracapsulaire.

OBJECTIVES: Outcome in hip fracture patients tends to be poor, with an associated death rate of 20 to 33%. The primary aim of our monocentric retrospective study was to compare mortality rates one year after surgery in patients with extracapsular fracture versus patients with intracapsular fracture of the proximal femur. Our secondary aims were the evaluation of functional independence and the rate of institutionalization one year after surgery. METHODS: We compared two groups of 100 patients. The first group had an average age of 83.2 years, and the patients underwent total hip replacement for intracapsular fracture. Patients in the second group, who underwent osteosynthesis for extracapsular fracture, were aged 83.6 years on average. RESULTS: One year post-surgery, there was not a significant difference in mortality between the two groups (23% for extracapsular fracture vs 22% for intracapsular fracture). The rate of independent walking was significantly better in the intracapsular fracture group (42.3% vs 27.3%, p=0.047), and the rate of institutionalization was significantly higher in the extracapsular fracture group (35.8% vs 17.3%, p=0.043). CONCLUSION: Elderly patients with hip fracture are prone to poor outcomes. When compared with osteosynthesis, total hip replacement does not lead to higher mortality rates though it is a more complex surgery. Our findings raise questions regarding of treatment for extracapsular fracture and the choice between osteosynthesis or total hip replacement with a reconstruction of the proximal femur.