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71.
Doriane Gérard Marc Guéroult Leticia Casas-Godoy Jean-Stéphane Condoret Isabelle André Alain Marty Sophie Duquesne 《Tetrahedron: Asymmetry》2017,28(3):433-441
Enzyme-catalyzed enantiomer discrimination is still a great challenge for the development of industrial pharmaceutical processes. For the resolution of ibuprofen, naproxen and ketoprofen racemates, three major anti-inflammatory drugs, only lipases from Candida rugosa present a high selectivity if solvent and surfactant use is discarded. However, their catalytic activities are too low. In the present work, we demonstrate that the lipase Lip2p from the yeast Yarrowia lipolytica has a higher catalytic activity than C. rugosa lipases to hydrolyze the ethyl esters of ibuprofen, naproxen and ketoprofen, but its selectivity is not sufficient [E = 52 (S); 11 (S) and 1.5 (R) respectively]. The enantioselectivity was further improved by site-directed mutagenesis, targeted at the substrate binding site and guided by molecular modelling studies. By investigating the binding modes of the (R)- and (S)-enantiomers in the active site, two amino acid residues located in the hydrophobic substrate binding site of the lipase, namely residues 232 and 235, were identified as crucial for enantiomer discrimination and enzyme activity. The (S) enantioselectivity of Lip2p towards ethyl ibuprofen esters was rendered infinite (E ? 300) by replacing V232 by an A or C residue. Substitution of V235 by C, M, S, or T amino acids led to a great increase in the (S)-enantioselectivity (E ? 300) towards naproxen ethyl ester. Finally, the variant V232F enabled the efficient kinetic resolution of ethyl ketoprofen ester enantiomers [(R)-enantiopreference; E ? 300]. In addition to the increase in selectivity, a remarkable increase in velocity by 2.6, 2.7 and 2.5 times, respectively, was found for ibuprofen, naproxen and ketoprofen ethyl esters. 相似文献
72.
73.
Viret M Samson Y Warin P Marty A Ott F Sondergard E Klein O Fermon C 《Physical review letters》2000,85(18):3962-3965
The resistive effect of domain walls in FePd films with perpendicular anisotropy was studied experimentally as a function of field and temperature. The films were grown directly on MgO substrates, which induces an unusual virgin magnetic configuration composed of 60 nm wide parallel stripe domains. This allowed us to carry out the first measurements of the anisotropy of domain wall resistivity in the two configurations of current perpendicular and parallel to the walls. At 18 K, we find 8.2% and 1.3% for the domain wall magnetoresistance normalized to the wall width (8 nm) in these two respective configurations. These values are consistent with the predictions of Levy and Zhang. 相似文献
74.
The reaction of [(3,5-Me(2)-C(5)H(3)N)(2)Zn(ESiMe(3))(2)] (E = Se, Te) with cadmium(II) acetate in the presence of PhESiMe(3) and P(n)Pr(3) at low temperature leads to the formation of single crystals of the ternary nanoclusters [Zn(x)()Cd(10)(-)(x)()E(4)-(EPh)(12)(P(n)()Pr(3))(4)] [E = Se, x = 1.8 (2a), 2.6 (2b); Te, x = 1.8 (3a), 2.6 (3b)] in good yield. The clusters [Zn(3)Hg(7)Se(4)(SePh)(12)(P(n)()Pr(3))(4)] (4) and [Cd(3.7)Hg(6.3)Se(4)(SePh)(12)(P(n)()Pr(3))(4)] (5) can be accessed by similar reactions involving [(3,5-Me(2)-C(5)H(3)N)(2)Zn(SeSiMe(3))(2)] or [(N,N'-tmeda)Cd(SeSiMe(3))(2)] (1) and mercury(II) chloride. The metal silylchalcogenolate reagents are efficient delivery sources of {ME(2)} in cluster synthesis, and thus, the metal ion content of these clusters can be readily moderated by controlling the reaction stoichiometry. The reaction of cadmium acetate with [(3,5-Me(2)-C(5)H(3)N)(2)Zn(SSiMe(3))(2)], PhSSiMe(3), and P(n)()Pr(3) affords the larger nanocluster [Zn(2.3)Cd(14.7)S(4)(SPh)(26)(P(n)()Pr(3))(2)] (6). The incorporation of Zn(II) into {Cd(10)E} (E = Se, Te) and Zn(II) or Cd(II) into {Hg(10)Se} nanoclusters results in a significant blue shift in the energy of the first "excitonic" transition. Solid-state thermolysis of complexes 2 and 3 reveals that these clusters can be used as single-source precursors to bulk ternary Zn(x)Cd(1)(-)(x)E materials as well as larger intermediate clusters and that the metal ion ratio is retained during these reactions. 相似文献
75.
In a popular amperometric superoxide sensor, cytochrome c (Cyt c) is covalently immobilized onto a gold electrode previously covered with a self‐assembled monolayer (SAM) of carboxyl‐terminated alkanethiols. Therefore, a study was carried out to reveal the origins of the current response of such sensors. SAMs made of either 3,3′‐dithiodipropionic acid or 11‐mercaptoundecanoic acid and 11‐mercaptoundecanol were used to immobilize either Cyt c or an inert protein onto gold electrodes. The resulting modified electrodes were comparatively investigated by cyclic voltammetry and calibrated for superoxide detection. The obtained results bring evidence that significant part (>70 %) of the current response of the Cyt c‐modified electrodes to superoxide comes from direct oxidation of superoxide on gold (i.e. does not involve Cyt c). 相似文献
76.
A novel, simple and versatile protocol for covalent immobilization of horseradish peroxidase (HRP) on screen‐printed carbon electrode (SPCE) based on the combination of diazonium salt electrografting and click chemistry has been successfully developed. The ethynyl‐terminated monolayers are obtained by diazonium salt electrografting, then, in the presence of copper (I) catalyst, the ethynyl modified surfaces reacted efficiently and rapidly with horseradish peroxidase bearing an azide function (azido‐HRP), thus forming a covalent 1,2,3‐triazole linkage by means of click chemistry. All the experimental results suggested that HRP was immobilized onto the electrode surface successfully without denaturation. Furthermore, the immobilized HRP showed a fast electrocatalytic reduction for H2O2. A linear range from 5.0 to 50.0 µM in a phosphate buffer (pH 5.5) with detection limit of 0.50 µM and sensitivity of 0.23 nA/µM were obtained. The heterogeneous electron transfer rate constant Kct was 1.52±0.22 s?1 and the apparent Michaelis? Menten constant was calculated to be 0.028 mM. The HRP‐functionalized electrode demonstrated a good reproducibility and long‐term stability. 相似文献
77.
García Ruano JL Gamboa AE Gutiérrez LG Martín Castro AM Rodríguez Ramos JH Yuste F 《Organic letters》2000,2(6):733-736
A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group. 相似文献
78.
Pascal Sonnet Sophie Da NascimentoDanielle Marty Nicolas FranceschiniJean Guillon Jean-Daniel BrionJacques Rochette 《Tetrahedron letters》2003,44(16):3293-3296
The first synthesis of two segetalins B and G is described. The corresponding linear peptides were synthesized using standard automated continuous-flow SPPS methods. Ring closure positions were investigated for segetalin B. The best ring closure result was obtained between Val and Gly. 相似文献
79.
Michael T. Marty Hao Zhang Weidong Cui Michael L. Gross Stephen G. Sligar 《Journal of the American Society for Mass Spectrometry》2014,25(2):269-277
Nanodiscs are a promising system for studying gas-phase and solution complexes of membrane proteins and lipids. We previously demonstrated that native electrospray ionization allows mass spectral analysis of intact Nanodisc complexes at single lipid resolution. This report details an improved theoretical framework for interpreting and deconvoluting native mass spectra of Nanodisc lipoprotein complexes. In addition to the intrinsic lipid count and charge distributions, Nanodisc mass spectra are significantly shaped by constructive overlap of adjacent charge states at integer multiples of the lipid mass. We describe the mathematical basis for this effect and develop a probability-based algorithm to deconvolute the underlying mass and charge distributions. The probability-based deconvolution algorithm is applied to a series of dimyristoylphosphatidylcholine Nanodisc native mass spectra and used to provide a quantitative picture of the lipid loss in gas-phase fragmentation. Figure
? 相似文献
80.
Metal complexes with reactive [ESiR3]? (E = S, Se, Te) or [S(SiMe2)]2? ligands provide a means for the delivery of {MEn}m? units in the formation of heterometallic polynuclear complexes and clusters. These complexes can be reacted with M′ salts to promote M–E–M′ interactions via the elimination of a silane side product. This research report summarizes the recent developments in the synthesis of silylchalcogenolate complexes of the d‐block metals with emphasis directed to those for which reactivity studies for the formation of ternary clusters have been carried out. The effects of varying the groups on the silyl moiety on the stability and reactivity of these precursor molecules are also discussed. 相似文献