Synergy of diffraction and spectroscopic techniques to unveil the crystal structure of antimonic acid.

The elusive crystal structure of the so-called 'antimonic acid' has been investigated by means of robust and state-of-the-art techniques. The synergic results of solid-state magic-angle spinning nuclear magnetic resonance spectroscopy and a combined Rietveld refinement from synchrotron X-ray and neutron powder diffraction data reveal that this compound contains two types of protons, in a pyrochlore-type structure of stoichiometric formula (H3O)1.20(7)H0.77(9)Sb2O6. Some protons belong to heavily delocalized H3O+ subunits, while some H+ are directly bonded to the oxygen atoms of the covalent framework of the pyrochlore structure, with O-H distances close to 1 Å. A proton diffusion mechanism is proposed relying on percolation pathways determined by bond-valence energy landscape analysis. X-ray absorption spectroscopy results corroborate the structural data around Sb5+ ions at short-range order. Thermogravimetric analysis and differential scanning calorimetry endorsed the conclusions on the water content within antimonic acid. Additional 0.7 water molecules per formula were assessed as moisture water by thermal analysis.

Strongly reduced lattice thermal conductivity in Sn-doped rare-earth (M) filled skutterudites M x Co4Sb12-y Sn y , promoted by Sb-Sn disordering and phase segregation.

CoSb3 thermoelectric skutterudite has been filled with rare-earth metals (M = La, Ce, Yb) and partially doped with Sn in specimens of M x Co4Sb12-y Sn y stoichiometry. This has been achieved under high-pressure conditions at 3.5 GPa in a piston-cylinder hydrostatic press. A structural investigation using synchrotron X-ray diffraction data reveals a phase segregation in twin skutterudite phases with filling fraction fluctuation and different unit-cell sizes. As a result of three effects acting as phonon scatterers, namely the rattling effect of M at the wide 8a cages of the cubic Im3̄ structure, the phase segregation, and the intrinsic disorder introduced by Sn substitution at the Sb sublattice, the total thermal conductivity (κ) dramatically falls to reach minimum values under 2 W m-1 K-1, well below those typically exhibited by other thermoelectric materials based upon single-filled skutterudites. The power factor is substantially enhanced to 1.11 mW m-1 K-2 in Yb0.5Co4Sb11.6Sn0.4 with respect to the unfilled composition, as a result of the charge transfer promoted by the filler.

Prophylactic therapy with valganciclovir in high-risk (cytomegalovirus D+/R-) kidney transplant recipients: a single-center experience.

BACKGROUND: A prospective study was performed in kidney transplant patients at risk of developing cytomegalovirus (CMV) infection (CMV D+/R-). They were treated with valganciclovir (VGC) for 3 months as prophylactic therapy. The aim was to determine the safety and efficacy of prophylactic therapy with VGC. METHODS: Antigenemia and/or polymerase chain reaction CMV was routinely performed every 2 weeks up to month 3, monthly to month 6, and every other month until the end of the first year posttranplantation, as well as when clinically indicated. RESULTS: From July 2007 to April 2010, 366 renal transplantations were performed at our center, including 34 (9%) high-risk patients for CMV infection. The median age was 47 years; 19 were males and 15 females. Twelve (35%) patients developed CMV infections: 10 (34%) gastrointestinal disease and 3 viral syndromes. The timing of the clinical manifestations was 16% (3/12) between months 1 and 3, 75% (8/12) between months 4 and 6, and 8% (1/12) in month 9 posttransplantation. CONCLUSION: Treatment with intravenous ganciclovir followed by oral VGC was successful in all patients. No opportunistic infections or allograft rejection were observed; only 1 patient developed thrombocytopenia as an adverse event to VGC.

Familial hypokalemia-hypomagnesemia or Gitelman's syndrome: a further case.

A woman aged 33 years presented hypokalemia and hypomagnesemia associated with renal potassium and magnesium wasting. Her mean 24-hour urinary calcium excretion was strikingly low despite normocalcemia, normal creatinine clearance, normal serum PTH and calcitriol. Normal distal fractional chloride reabsorption [CH2O/(CH2O + CCl)] was noted during water load but was reduced during hypotonic saline infusion. In response to intravenous furosemide (1 mg/kg), the patient showed significant increments in sodium, chloride and magnesium excretion as well as abolition of hypocalciuria. The association of renal calcium transport from magnesium transport together with exaggerated natriuresis after furosemide suggests the presence of a defect in the distal tubule rather than in the loop of Henle. We propose that our patient is affected by the syndrome of primary renotubular hypomagnesemia-hypokalemia with hypocalciuria, known as Gitelman's syndrome.