Comment on Dutia et al. Limited Recovery of β-Cell Function After Gastric Bypass Despite Clinical Diabetes Remission. Diabetes 2014;63:1214−1223

The article in this issue of Diabetes by Dutia et al. (1) shows that in obese diabetic patients returning to normal glucose tolerance (NGT) after gastric bypass β-cell function appears to recover if evaluated through oral glucose tolerance test (OGTT), but not if evaluated through isoglycemic glucose clamp. In fact, the plot indicating Δinsulin/Δglucose (insulin release [IR]) versus 1/homeostasis model assessment of insulin resistance (HOMA-IR) (insulin sensitivity [IS]) grows during OGTT, but stays flat or moves right, indicating

NMR study of the Superconducting gap variation near the Mott transition in Cs3_{3}C60_{60}

Former extensive studies of superconductivity in the \textit{A}$_{3}$C$_{60}$ compounds, where \textit{A} is an alkali, have led to consider that Bardeen Cooper Schrieffer (BCS) electron-phonon pairing prevails in those compounds, though the incidence of electronic Coulomb repulsion has been highly debated. The discovery of two isomeric fulleride compounds Cs$_{3}$C$_{60}$ which exhibit a transition with pressure from a Mott insulator (MI) to a superconducting (SC) state clearly re-opens that question. Using pressure ($p$) as a single control parameter of the C$_{60}$ balls lattice spacing, one can now study the progressive evolution of the SC properties when the electronic correlations are increased towards the critical pressure $p_{c}$ of the Mott transition. We have used $^{13}$C and $^{133}$Cs NMR measurements on the cubic phase A15-Cs$_{3}$C$_{60}$ just above $p_{c}=5.0(3)$ kbar, where the SC transition temperature $T_{c}$ displays a dome shape with decreasing cell volume. From the $T$ dependence below $T_{c}$ of the nuclear spin lattice relaxation rate $(T_{1})^{-1}$ we determine the electronic excitations in the SC state, that is $2\Delta$, the SC gap value. We find that $2\Delta$ increases with decreasing $p$ towards $p_{c}$, where $T_{c}$ decreases on the SC dome, so that $2\Delta /k_{B}T_{c}$ increases regularly upon approaching the Mott transition. These results bring clear evidence that the increasing correlations near the Mott transition are not significantly detrimental to SC. They rather suggest that repulsive electron interactions might even reinforce elecron-phonon SC, being then partly responsible for the large $T_{c}$ values, as proposed by theoretical models taking the electronic correlations as a key ingredient.Comment: 5 pages, 4 figures, Supplemental Materia

NMR investigation of the pressure induced Mott transition to superconductivity in Cs3C60 isomeric compounds

The discovery in 1991 of high temperature superconductivity (SC) in A3C60 compounds, where A is an alkali ion, has been initially ascribed to a BCS mechanism, with a weak incidence of electron correlations. However various experimental evidences taken for compounds with distinct alkali content established the interplay of strong correlations and Jahn Teller distortions of the C60 ball. The importance of electronic correlations even in A3C60 has been highlighted by the recent discovery of two expanded fulleride Cs3C60 isomeric phases that are Mott insulators at ambient pressure. Both phases undergo a pressure induced first order Mott transition to SC with a (p, T) phase diagram displaying a dome shaped SC, a common situation encountered nowadays in correlated electron systems. NMR experiments allowed us to establish that the bipartite A15 phase displays N\'eel order at 47K, while magnetic freezing only occurs at lower temperature in the fcc phase. NMR data do permit us to conclude that well above the critical pressure, the singlet superconductivity found for light alkalis is recovered. However deviations from BCS expectations linked with electronic correlations are found near the Mott transition. So, although SC involves an electron-phonon mechanism, correlations have a significant incidence on the electronic properties, as had been anticipated from DMFT calculations.Comment: 9 pages, 6 figures, invited at M2SHTSC Conference Washington (2012

Spin Dynamics at the Mott Transition and in the Metallic State of the Cs_{3}C_{60} Superconducting Phases

We present here ^{13}C and ^{133}Cs NMR spin lattice relaxation T_{1} data in the A15 and fcc-Cs_{3}C_{60} phases for increasing hydrostatic pressure through the transition at p_{c} from a Mott insulator to a superconductor. We evidence that for p>> p_{c} the (T_{1}T)^{-1} data above T_{c} display metallic like Korringa constant values which match quantitatively previous data taken on other A_{3}C_{60} compounds. However below the pressure for which T_{c} goes through a maximum, (T_{1}T)^{-1} is markedly increased with respect to the Korringa values expected in a simple BCS scenario. This points out the importance of electronic correlations near the Mott transition. For p > p_{c} singular T dependences of (T_{1}T)^{-1} are detected for T >> T_{c}. It will be shown that they can be ascribed to a large variation with temperature of the Mott transition pressure p_{c} towards a liquid-gas like critical point, as found at high T for usual Mott transitions.Comment: 6 pages, 6 figures, submitted to EP

Recovering Metallicity in A4C60: The Case of Monomeric Li4C60

The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remarkable feature for a member of the A4C60 family (A = alkali metal), invariably found to be insulators. Structural and resonance technique investigations on Li4C60 at T > 600 K, show that its fcc structure is associated with a complete (4e) charge transfer to C60 and a sparsely populated Fermi level. These findings not only emphasize the crucial role played by lattice symmetry in fulleride transport properties, but also re-dimension the role of Jahn-Teller effects in band structure determination. Moreover, they suggest the present system as a potential precursor to a new class of superconducting fullerides.Comment: 4 pages, 3 figure

Pressure tuning of light-induced superconductivity in K3C60

Optical excitation at terahertz frequencies has emerged as an effective means to manipulate complex solids dynamically. In the molecular solid K3C60, coherent excitation of intramolecular vibrations was shown to transform the high temperature metal into a non-equilibrium state with the optical conductivity of a superconductor. Here we tune this effect with hydrostatic pressure, and we find it to disappear around 0.3 GPa. Reduction with pressure underscores the similarity with the equilibrium superconducting phase of K3C60, in which a larger electronic bandwidth is detrimental for pairing. Crucially, our observation excludes alternative interpretations based on a high-mobility metallic phase. The pressure dependence also suggests that transient, incipient superconductivity occurs far above the 150 K hypothesised previously, and rather extends all the way to room temperature.Comment: 33 pages, 17 figures, 2 table

Characterisation of strontium-containing apatite-wollastonite porous scaffolds

Porous strontium-doped apatite-wollastonite scaffolds were evaluated as potential substitutes for enhanced bone regeneration and the prevention of peri-prosthetic infections. Parent glasses of composition 35.5SiO2-7.1MgO-0.4CaF2-7.1P2O5-(49.9-x)CaO-xSrO mol%, where x = 0, 6.2, 12.5, 18.7, 24.9 or 37.4, were produced via the melt-quench route, ground and sieved <45 μm. Porous scaffolds were obtained following the foam-replication method and heat-treated at 1050 °C for 2 h for controlled nucleation and growth of the crystal phases. All six glasses produced were amorphous. Differential scanning calorimetry showed that the formation of the calcium silicate phase strongly depended on the amount of strontium contained in the parent glass, linearly moving to higher temperatures with increasing strontium. Morphological evaluation (scanning electron microscopy and micro-computed tomography) proved that the obtained scaffold porosity, about 55 vol%, did not depend on the strontium content. X-ray diffraction showed that strontium preferentially substituted in apatite, while only higher strontium compositions formed a strontium magnesium calcium silicate phase. Compressive and biaxial flexural strength were both comparable to cancellous bone. Compositions containing 0 %, 6.2 % and 12.5 % strontium showed excellent apatite forming ability when submerged in simulated body fluid, which then decreased with increasing strontium for the three higher-strontium compositions. Microbiological tests carried out on strontium-containing salts showed no effective antibacterial properties for strontium as a free element. Amongst the six strontium-containing glasses, only the 37.4 % strontium oxide glass showed antimicrobial effects against Pseudomonas aeruginosa in broth dilution tests. Proliferation and osteogenic differentiation of porous scaffolds were tested on human bone cells. No conclusive results were obtained for the G292 cell line. When scaffolds were tested with human primary mesenchymal stromal cells, an increase in DNA content was observed with increasing strontium, while enhanced alkaline phosphatase activity and increased collagen production were found for low strontium compositions

Synthesis of the Aglycones of Pseudopterosins

The stereocontrolled and efficient syntheses of the aglycones of the potent anti-inflammatory pseudopterosins A-F and K-L have been achieved starting from convenient monoterpenic units and using a novel benzannulation protocol partially developed in or laboratories. For the synthesis of the K-L compounds a completely substrate-controlled stereoselective route was devised starting from commercial isopulegol using a sequence of epoxidation and Lewis acid-promoted oxirane opening followed by benzannulation and Friedel-Crafts type sulphone displacement to generate the tricyclic structure of 3.2.1.13. The route to pseudopterosins A-E started from (-)-citronellal and employed catalytic asymmetric reduction of , -unsaturated ester 8.2.1.5. After the formation of the aromatic ring, the second approach was convergent to the enantiomers of intermediates used in the first route. Oxidation with Fremy's salt led to the unstable aglycones of the natural compounds under mild conditions. (Fig. 3876A