Synthesis and Spectroscopic Characterization of Diphenylargentate, [(C6H5)2Ag](.).

We present the structural and optical properties of the isolated diphenylargentate anion, which has been synthesized by multistage mass spectrometry in a quadrupole ion trap. The experimental photodetachment spectrum has been obtained by action spectroscopy. Comparison with quantum chemical calculations of the electronic absorption spectrum allows for a precise characterization of the spectroscopic features, showing that in the low-energy regime, the optical properties of diphenylargentate bear a significant resemblance to those of atomic silver.

Structural and photochemical properties of organosilver reactive intermediates MeAg2(+) and PhAg2(+).

Although there is growing interest in silver promoted carbon-carbon bond formation, a key challenge in developing robust and reliable organosilver reagents is that thermal and photochemical decomposition reactions can compete with the desired coupling reaction. These undesirable reactions have been poorly understood due to complications arising from factors such as solvent effects and aggregation. Here the unimolecular decomposition reactions of organosilver cations, RAg(2)(+), where R = methyl (Me) and phenyl (Ph), are examined in the gas phase using a combination of mass spectrometry based experiments and theoretical calculations to explore differences between thermal and photochemical decompositions. Under collision-induced dissociation conditions, which mimic thermal decomposition, both PhAg(2)(+) and MeAg(2)(+) fragment via formation of Ag(+). The new ionic products, RAg(+•) and Ag(2)(+•), which arise via bond homolysis, are observed when RAg(2)(+) is subject to photolysis using a UV-vis tunable laser OPO. Furthermore, comparisons between the theoretical and experimental UV-vis spectra allow us to unambiguously determine the most stable structures of PhAg(2)(+) and MeAg(2)(+) and to identify the central role of the silver part in the optical absorption of these species. The new photoproducts result from fragmentation in electronic excited states. In particular, potential energy surface calculations together with the fragment charges highlight the role of triplet states in these new fragmentation schemes.

Quantitative determination of the size dependence of surface plasmon resonance damping in single Ag@SiO(2) nanoparticles.

The optical extinction spectra of single silver nanoparticles coated with a silica shell were investigated in the size range 10-50 nm. Measurements were performed using the spatial modulation spectroscopy technique which permits independent determination of both the size of the metal nanoparticle under study and the width of its localized surface plasmon resonance (LSPR). These parameters can thus be directly correlated at a single particle level for the first time. The results show a linear increase of the width of the LSPR with the inverse diameter in the small size regime (less than 25 nm). For these nanoparticles of well-controlled environment, this can be ascribed to quantum confinement of electrons or, classically, to increase of the electron surface scattering processes. The impact of this effect was measured quantitatively and compared to the predictions by theoretical models.

Optical properties and relaxation processes at femtosecond scale of bimetallic clusters.

The optical properties of Au-Ag and Ni-Ag clusters are measured by linear optical absorption spectroscopy and the time-resolved pump-probe femtosecond technique allowing a study of the influence of alloy or core-shell structure.

Asymmetric top rotors in electric fields. II. Influence of internal torsions in molecular beam deflection experiments.

We report on electric deflection experiments of aminobenzonitrile and (dimethylamino)benzonitrile molecules. They are used as prototypes to study the influence of the asymmetry and rotation-vibration couplings in deflection experiments. Experimental deflection profiles are compared to results of ab initio calculations in the frame of the rigid rotor Stark effect and of the statistical linear response. The change in symmetry and the introduction of methyl groups lead to a transition from the rigid rotor response to the linear response. From the experimental results, a total dipole of mu = 6.2 +/- 0.6 D has been deduced for the m-(dimethylamino)benzonitrile molecule (MDMABN).

Performances of Wang-Landau algorithms for continuous systems.

The relative performances of different implementations of the Wang-Landau method are assessed on two classes of systems with continuous degrees of freedom, namely, two polypeptides and two atomic Lennard-Jones clusters. Parallel tempering Monte Carlo simulations serve as a reference, and we pay particular attention to the variations of the multiplicative factor f during the course of the simulation. For the systems studied, the Wang-Landau method is found to be of comparable accuracy as parallel tempering, but has significant difficulties in reproducing low-temperature transitions exhibited by the Lennard-Jones clusters at low temperature. Using a complementary order parameter and calculating a two-dimensional joint density of states significantly improves the situation, especially for the notoriously difficult LJ(38) system. However, while parallel tempering easily converges for LJ(31), we have not been able to get data of comparable accuracy with Wang-Landau multicanonical sampling.

Comparison of the fragmentation pattern induced by collisions, laser excitation and electron capture. Influence of the initial excitation.

Collision-induced dissociation, laser-induced dissociation and electron-capture dissociation are compared on a singly and doubly protonated pentapeptide. The dissociation spectrum depends on the excitation mechanism and on the charge state of the peptide. The comparison of these results with the conformations obtained from Monte Carlo simulations suggests that the de-excitation mechanism following a laser or an electron-capture excitation is related to the initial geometry of the peptide.

Asymmetric top rotors in electric fields: influence of chaos and collisions in molecular beam deflection experiments.

We report on electric deflection experiments of structural isomers of aminobenzonitrile. They are used as models to study the influence of the asymmetry of a molecule on the molecule-electric field interaction. Experimental deflection profiles are compared to Stark effect calculations. We found increasing deviations from the calculated Stark effect behavior with increasing asymmetry. This deviation is induced by interactions with other particles and is directly related to the chaotic behavior of the rotational motion of asymmetric rotors in a static electric field.

Direct measurement of the single-metal-cluster optical absorption.

The absorption of a single isolated metal cluster is directly measured using a novel far-field optical technique based on modulation of its position. Single gold nanoparticles with average diameters down to 5 nm, dispersed on a transparent substrate, are optically detected and their absolute absorption cross section determined.

Entrapping molecules in zeolites nanocavities: a thermodynamic and ab-initio study.

Adsorption enthalpies of Ar, N2, CO, H2O, CH3CN and NH3 on H-BEA and H-MFI zeolites and on Silicalite, have been measured calorimetrically at 303K in order to assess the energetic features of dispersive forces interactions (confinement effects), H-bonding interactions with surface silanols and specific interactions with Lewis and Brønsted acidic sites. The adsorption of the molecular probes with model clusters mimicking surface silanols, Lewis and Brønsted sites has been simulated at ab-initio level. The combined use of the two different approaches allowed to discriminate among the different processes contributing to the measured (-deltaadsH). Whereas CO and N2 single out contributions from Lewis and Brønsted acidic sites, Ar is only sensitive to confinement effects. For H2O, CH3CN and NH3 the adsorption on Brønsted sites is competitive with the adsorption on Lewis sites. The energy of interaction of H2O with all considered zeolites is surprisingly higher than expected on the basis of -deltaadsH vs PA correlation.

Electron-phonon scattering in metal clusters.

Electron-lattice energy exchanges are investigated in gold and silver nanoparticles with sizes ranging from 30 to 2.2 nm embedded in different environments. Femtosecond pump-probe experiments performed in the low-perturbation regime demonstrate a strong increase of the intrinsic electron-phonon interaction for nanoparticles smaller than 10 nm due to a confinement effect.

Vibration induced electric dipole in a weakly bound molecular complex.

A strong electric susceptibility is measured as a function of temperature in a molecular dimer which is weakly bound by a pair of hydrogen bonds. This system is a remarkable example where the dominant term in the susceptibility is due to a vibration induced electric dipole. As a consequence, the averaged square of the dipole moment varies linearly with the temperature and the susceptibility does not follow the usual 1/T Curie law. this spectacular effect demonstrates the importance of dynamics to interpret the properties of weakly bound complexes.

[Ethical aspects of organ transplantation with living related or unrelated donors]. / Aspects éthiques de la transplantation avec donneur vivant apparenté et non apparenté.

Organ transplantation with living donor, relatively not much used in France, raises a number of ethical questions. It just transgresses the principle of primum non nocere, transgression finally accepted when considering the potential benefit for the sick recipient. It is only possible to use a living donor if a free informed consent is given. This raises some questions and supposes for the doctor in charge the obligation to follow a strict protocol. Commercialization is in the heart of the ethical discussion about living donors. This is universally condemned, but quite largely used in some underdeveloped countries and we are faced now to some professionals arguing in favour of the extension of this practice in Occident. Recently, a new category of donors has appeared, the altruists: they are ethically acceptable if strictly defined, but this category raises also some problems.

Urological complications after renal transplantation using ureteroureteral anastomosis in children.

PURPOSE: Ureterovesical reimplantation is most often performed for renal transplantation in children. We reviewed our experience to evaluate the safety and efficacy of ureteroureteral reimplantation in pediatric renal transplantation. MATERIALS AND METHODS: We retrospectively evaluated the charts of 92 boys and 72 girls who underwent a total of 166 ureteroureteral anastomoses for renal transplantation from January 1990 to December 1999. Spatulated end-to-end anastomosis was performed between recipient and graft ureters without stenting and with a bladder catheter for at least 10 days. RESULTS: Mean patient age at transplantation was 11.2 years (range 1 to 21.5). There were 22 living related donor and 144 cadaveric grafts. Urological anomalies and nephropathy were the cause of end stage renal disease in 146 and 20 patients, respectively. Urological complications were noted in 14 of the 166 transplantations (8.4%) in 10 boys and 4 girls, including 12 initial and 2 repeat grafts from 2 living related and 12 cadaveric donors. Five of these patients had undergone previous urological surgery. The 2 children (1.2%) with acute ureteral obstruction underwent repeat intervention after stent failure. Anastomotic leakage in 7 cases (4.2%) was treated conservatively in 1 and with a Double-J stent (Medical Engineering Corp., New York, New York) only required in 3. Reoperation was required in 3 cases. One patient (0.6%) with late ureteral stenosis underwent repeat anastomosis, 1 (0.6%) required reimplantation for recurrent pyelonephritis due to vesicoureteral reflux in the graft, 1 (0.6%) with a valve bladder required bladder augmentation and ureteral reimplantation, and 1 (0.6%) with lymphocele and 1 (0.6%) with lithiasis were successfully treated conservatively. Complications were associated with acute rejection in 6 cases. Mean followup without graft loss in patients who presented with versus without complications was 58.3 months (range 1 to 112) versus 75 (range 1 to 118). In the former patients with a mean age of 16 years 9 months versus those without urological complications mean serum creatinine was 116 and 108 mol./l., respectively. Two grafts were lost in patients with urological complications, including 1 who died of pulmonary embolism and 1 with refractory chronic rejection. Seven patients were lost to followup after 54 months (range 12 to 113) of adequate graft function. CONCLUSIONS: Ureteroureteral anastomosis is a safe and effective technique for pediatric renal transplantation with a low complication rate, which may be due to better vascularization of the shorter ureteral end of the graft. Our results should encourage the use of this technique in pediatric renal transplantation. Efforts to preserve the recipient ureters should be made at nephrectomy.

Long-term treatment with growth hormone in short children with nephropathic cystinosis.

OBJECTIVE: The objective was to assess the efficacy and safety of growth hormone (GH) treatment in severely growth retarded children with nephropathic cystinosis during conservative treatment and during renal replacement therapy. STUDY DESIGN: The design was an open-labeled prospective trial with a run-in period of 1 year. RESULTS: A total of 74 children with cystinosis (age 3.0 to 18 years) were treated with GH over a mean period of 3.1 years (range 1 to 10 years); 52 patients were receiving conservative treatment (mean age 7.1 years), 7 were receiving dialysis (12.5 years), and 15 had received a renal transplant (14.8 years). The mean standardized height (SD score) was -4.0 in the conservative treatment group, -4.4 in the dialysis group, and -4.9 in the renal transplant group. During the first treatment year, height velocity doubled in the conservative treatment group, increased by 80% in the dialysis group, and increased by 45% in renal transplant group. Within 3 years the height SD score increased by +1.6 (P <.001) in prepubertal patients receiving conservative treatment, and percentile parallel growth was maintained thereafter. These effects of GH were less expressed in peripubertal patients receiving renal replacement therapy. No major side effects were observed. CONCLUSION: Long-term GH treatment is safe and effective in young children with nephropathic cystinosis. GH treatment should be started early in the course of the disease if adequate nutrition and cysteamine treatment do not prevent growth retardation.

Effects of growth hormone on growth factors after renal transplantation.

Growth retardation occurs frequently in renal transplanted children (RTx) and can be improved by growth hormone (GH) treatment. This study retrospectively examines the insulin-like growth factor-1 (IGF-1) and IGF binding protein (IGFBP) profile of ten growth-retarded children previously given renal allografts, after 1 year of GH treatment period. Ten prepubertal patients (nine boys and one girl) were investigated. They had a mean chronological age (CA) of 11.4 +/- 1.1 years and a mean bone age (BA) of 7.3 +/- 0.9 years. Mean height was -3.9 +/- 0.4 SD units below the mean for CA. The mean body mass index (BMI) was 16.9 +/- 0.6 and the mean inulin clearance was 36.5 +/- 4.9 ml/min/1.73 m2. Recombinant hGH was given at 4 IU/m2/day. Plasma GH, total and free IGF-1, IGFBP-2 and -3 were measured by specific radioimmunoassay (RIA). IGFBPs were characterized by SDS PAGE techniques and ligand and immunoblot analyses. Mean velocity was markedly increased (P < 0.01) after 1 year of GH therapy, expressed as SD score for BA. The range of growth response was wide. The total and free plasma IGF-1 increased (P < 0.01) by about 100% (mean values after GH therapy: 95.9 +/- 2.1 nM and 165 +/- 29 pM, respectively). Plasma IGFBP-3 concentrations increased by about 40% (mean value: 148 +/- 18 pM, P < 0.01), with a concomitant increase in both intact IGFBP-3 and its 30-kDa proteolytic fragment. There was no change in plasma IGFBP-2 concentration. Both mean values of inulin clearance and BMI were unchanged during the treatment. In view of the IGF-1/IGFBP concentration changes, there should have been an even better growth response to GH therapy in these patients. This strongly suggests IGF-1 insensitivity, probably as a result of corticosteroid therapy.

PAX2 mutations in oligomeganephronia.

BACKGROUND: Oligomeganephronia (OMN) is a rare congenital and usually sporadic anomaly. It is characterized by bilateral renal hypoplasia, with a reduced number of enlarged nephrons. The mechanisms involved in this deficient nephrogenesis are unknown. The paired box transcription factor PAX2 plays a fundamental role in renal development. Heterozygous Pax2 mutants in mice are characterized by renal hypoplasia and retinal defects, and in humans, PAX2 mutations have been described in the renal-coloboma syndrome. METHODS: To assess whether OMN could be related to PAX2, we searched for PAX2 mutations in nine patients presenting with sporadic and apparently isolated OMN. RESULTS: Heterozygous PAX2 mutations were found in three patients. A limited optic nerve coloboma was secondarily detected in two cases and a very mild optic disk dysplasia in one patient. None of these patients had visual impairment. CONCLUSIONS: Ocular anomaly and PAX2 mutations should be sought in all patients with OMN.