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Anne Lesage

Publications and source records attributed to Anne Lesage.

32 records · Page 2Linked to original sources
PubMed2004

Molecular understanding of the formation of surface zirconium hydrides upon thermal treatment under hydrogen of [([triple bond]SiO)Zr(CH2tBu)3] by using advanced solid-state NMR techniques.

The reaction of [([triple bond]SiO)Zr(CH(2)tBu)(3)] with H(2) at 150 degrees C leads to the hydrogenolysis of the zirconium-carbon bonds to form a very reactive hydride intermediate(s), which further reacts with the surrounding siloxane ligands present at the surface of this support to form mainly two different zirconium hydrides: [([triple bond]SiO)(3)Zr-H] (1a, 70-80%) and [([triple bond]SiO)(2)ZrH(2)] (1b, 20-30%) along with silicon hydrides, [([triple bond]SiO)(3)SiH] and [([triple bond]SiO)(2)SiH(2)]. Their structural identities were identified by (1)H DQ solid-state NMR spectroscopy as well as reactivity studies. These two species react with CO(2) and N(2)O to give, respectively, the corresponding formate [([triple bond]SiO)(4-x)Zr(O-C(=O)H)(x)] (2) and hydroxide complexes [([triple bond]SiO)(4-x)Zr(OH)(x)] (x = 1 or 2 for 3a and 3b, respectively) as major surface complexes.

Journal Article↗
PubMed2004

Internalization of human 5-HT4a and 5-HT4b receptors is splice variant dependent.

The family of 5-HT4 receptors comprises 16 putative splice variants. We have previously shown that there are differences in signal transduction of the h5-HT(4a) and h5-HT(4b) receptors. In the present study, the internalization of these two splice variants following receptor stimulation was investigated with confocal microscopy on living cells. Chimeric receptors, h5-HT(4a)-GFP and h5-HT(4b)-GFP were generated by fusing the coding sequence of the 5-HT4 receptor with the coding sequence of the GFP. The agonist stimulation of fluorescent receptors resulted in a time-dependent internalization of the h5-HT(4b)-GFP receptor, but not of the h5-HT(4a)-GFP receptor. The h5-HT(4b) receptor displays a dual coupling to G(alpha)i,o and G(alpha)s proteins, in contrast to the h5-HT4a receptor, which couples to Galphas proteins only. We investigated whether the difference in internalization of the two splice variant receptors was related to their differential coupling. Therefore, we performed agonist-stimulation of the receptor following inhibition of the G(alpha)i,o protein coupling using PTX. The h5-HT(4b) receptor internalization is PTX insensitive. We co-transfected the fluorescent chimeric receptors with other wild-type variants, which did not produce an alteration of the receptor trafficking. These findings provide the first evidence of differential internalization between the two splice variants, 5-HT(4a) and 5-HT(4b) receptors.

Alternative Splicing↗
PubMed2004

Complicated acute myocardial infarction requiring mechanical ventilation in the intensive care unit: prognostic factors of clinical outcome in a series of 157 patients.

OBJECTIVE: To determine prognostic factors associated with death in patients with complicated acute myocardial infarction requiring mechanical ventilation. DESIGN: Retrospective chart-based analysis. SETTING: A 22-bed medical intensive care unit in a university hospital. PATIENTS: A total of 157 consecutive patients with acute myocardial infarction requiring endotracheal intubation and mechanical ventilation admitted to an intensive care unit during a 6-yr period. INTERVENTIONS: Coronary reperfusion strategy within 12 hrs following symptom onset. MEASUREMENTS AND MAIN RESULTS: Clinical characteristics at admission of survivors (n = 77) and nonsurvivors (n = 80) were similar regarding demographics, medical history, and Glasgow Coma Scale score. Twenty-eight-day intensive care unit mortality rate was 51%. The following criteria were higher for nonsurvivors: Simplified Acute Severity Score II, 79 +/- 18 vs. 64 +/- 17 (p <.0001); Acute Physiology and Chronic Health Evaluation (APACHE) II, 33 +/- 13 vs. 25 +/- 6 (p <.0001); incidence of cardiogenic shock (p =.0085) and failing organs (p <.0001); coronary artery disease extension (p =.045); and delay between symptom onset and coronary reperfusion (p =.0348). Nonsurvivors also had higher serum urea and creatinine and lower urine output, arterial pH, and left ventricular ejection fraction (p <.05). Mortality rate was higher in patients with PaO2/FiO2 ratio <200 than in patients with PaO2/FiO2 ratio >200 at admission (log-rank, 5.016; p =.0251). By multivariate analysis, only three factors were independently associated with death: APACHE II >29 (odds ratio, 1.132; 95% confidence interval, 1.013-1.265, p =.0287), serum creatinine >180 micromol/L (odds ratio, 6.151; 95% confidence interval, 1.446-26.166, p =.0139), and initial left ventricular ejection fraction <0.4 (odds ratio, 1.121; 95% confidence interval, 1.049-1.347, p =.0316). Overall, good discrimination was achieved for the risk score model (c-index, 0.852). CONCLUSIONS: We confirmed the high mortality rate of patients admitted to an intensive care unit with acute myocardial infarction requiring mechanical ventilation. In these patients, the main risk factors for death found, namely high APACHE II, early development of acute renal failure, and low resting left ventricular function, reflected the severity of the myocardial infarction.

APACHE↗
PubMed2003

High-resolution NMR correlation spectra of disordered solids.

We show how high-resolution NMR spectra can be obtained for solids for which the spectra are normally broadened due to structural disorder. The method relies on correlations in the chemical shifts between pairs of coupled spins. It is found experimentally that there are strong correlations in the chemical shifts between neighboring spins in both phosphorus-31 and carbon-13 spectra. These correlations can be exploited not only to provide resolution in two-dimensional spectra, but also to yield "chains" of correlated chemical shifts, constituting a valuable new source of structural information for disordered materials.

Journal Article↗
PubMed2003

Perhydrocarbyl ReVII complexes: comparison of molecular and surface complexes.

The molecular complex [Re(=CtBu)(=CHtBu)(CH2tBu)2] 1 reacts with a silica partially dehydroxylated at 700 degrees C to give syn-2, [(=SiO)Re(=CtBu)(=CHtBu)(CH2tBu)], as a single isomer according to mass-balance analysis, IR, and solid-state NMR spectroscopy. 1D and 2D solid-state NMR (HETCOR and long-range HETCOR) on a 13C-labeled-2 has allowed us to observe the chemical shifts of all carbons (including those that are not labeled) and ascertain their assignments. Moreover, EXAFS data are consistent with the presence of two carbons at a relatively short distance (1.79 A), which cannot be deconvoluted, but which are consistent with the presence of alkylidene and alkylidyne carbons along with two other first neighbors at a longer distance (2.01 A), the alkyl carbon and the O atom by which the Re is attached to the surface. Moreover, the data also suggest the presence of a siloxane bridge of the silica surface at 2.4 A in the coordination sphere of the Re center. Thermal and photochemical treatment allow us to observe the anti isomer, which was also fully characterized by 1D and 2D solid-state NMR. This behavior parallels the reactivity of molecular Re complexes, and their respective 1H and 13C chemical shifts match those of the corresponding molecular analogues syn- and anti-2m and n. Finally, the grafting of 1 onto silica involves the reaction of both the alkyl and the alkylidene ligand with an equiprobability, leaving the alkylidyne as a spectator ligand. Noteworthy is the formation of 2 [(=SiO)Re(=CtBu)(=CHtBu)(CH2tBu)], rather than the corresponding trisneopentyl-neopentylidyne Re complex, monografted on silica, [(=SiO)Re(=CtBu)(CH2tBu)3], which would have been expected from the reactivity of 1 with various molecular Brönsted acids and which also suggests that a proximal siloxane bridge forces the alpha-H abstraction process, leading to syn-2a.

Journal Article↗
PubMed2003

Carbon-13 lineshapes in solid-state NMR of labeled compounds. Effects of coherent CSA-dipolar cross-correlation.

The experimental lineshapes of the carboxyl and methyl carbon resonances of fully 13C enriched L-Alanine are studied in detail at different MAS frequencies and decoupling field strengths. Complex lineshapes at intermediate spinning speeds were explained by the joint effect of off rotational resonance and coherent CSA-dipolar cross-correlation. Whereas off rotational-resonance effects lead to complex lineshapes due to a splitting of some energy levels, coherent CSA-dipolar cross-correlation introduces either a differential intensity and/or a differential broadening of the lines of the J-multiplet. The conditions which lead to such effects are explained and experimentally verified. Additional simulations show that these effects can be expected over a wide range of static magnetic fields and are not restricted to L-Alanine.

Alanine↗
PubMed2003

Experimental aspects of proton NMR spectroscopy in solids using phase-modulated homonuclear dipolar decoupling.

In this paper we demonstrate experimentally that the continuously phase-modulated homonuclear decoupling sequence DUMBO-1 is suitable for high-resolution proton NMR spectroscopy of rigid solids. Over a wide range of experimental conditions, we show on the model sample L-alanine as well as on small peptides that proton linewidths of less than 0.5 ppm can be obtained under DUMBO-1 decoupling. In particular the DUMBO-1 sequence yields well resolved proton spectra both at slow and fast MAS. The DUMBO-1 decoupling scheme can in principle be inserted in any multi-nuclear or multi-dimensional solid-state NMR experiment which requires a high-resolution 1H dimension. An example is provided with the 13C-1H MAS-J-HMQC experiment.

Alanine↗
PubMed2003

Spin-state selection in solid-state NMR.

Spin-state selection in solid-state NMR is demonstrated, using similar pulse sequences as used in liquid-state NMR. The different transitions of all three carbon resonances in fully 13C-labeled L-alanine are separated in different spectra. By selecting spin-states, the contribution of the J-coupling to the linewidth is removed, leading to a considerable enhancement in resolution. The spin-state-selective technique is demonstrated for magic-angle spinning frequencies from 6 to 35kHz. Other experimental conditions affecting the sensitivity of the experiments are discussed. Sensitivity losses due to the introduction of the spin-state-selective filter are shown to be acceptable. Finally, spin-state selection was used to experimentally confirm the differential broadening expected for the two transitions of the CH3 resonance.

Alanine↗
PubMed2002

Neurotrophic and antileukemic daphnane diterpenoids from Synaptolepis kirkii.

Biological assay guided fractionation of a dichloromethane extract of Synaptolepis kirkii led to the isolation of four new and five known daphnane-type diterpene orthoesters, whose structure was established by spectroscopic data. Full spectroscopic data of the new and known natural products are reported here for the first time. Pronounced neurotrophic and substantial antileukaemia activities of these compounds were found in in vitro assays.

Animals↗
PubMed2001

Molecular Insight Into Surface Organometallic Chemistry Through the Combined Use of 2D HETCOR Solid-State NMR Spectroscopy and Silsesquioxane Analogues We are also indebted to the CNRS, ENS Lyon, and ESCPE Lyon for financial support. M.C. is grateful to the French ministry of education, research, and technology (MENRT) for a pre-doctoral fellowship. E.A.Q. gratefully acknowledges Università di Pisa and S.N.A.M. for financial support. 2D HETCOR=two-dimensional heteronuclear correlation.

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Journal Article↗