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991.
Grangemard I Wallach J Maget-Dana R Peypoux F 《Applied biochemistry and biotechnology》2001,90(3):199-210
The lipopeptide lichenysin (cyclo-[L-Gln1→D-Leu2→L-Leu3→L-Val4→L-Asp5→D-Leu6→L-Ile7-β-OH fatty acid]) produced by Bacillus licheniformis structurally resembles surfactin from Bacillus subtilis. The main difference is the presence of a glutaminyl residue in position 1 of the peptide sequence in place of glutamic acid
in surfactin. This local variation causes significant changes in the properties of the molecule compared to surfactin. Lichenysin
has a higher surfactant power, the critical micellar concentration (c.m.c.) being strongly reduced from 220 to 22 μM and a much higher hemolytic activity because 100% hemolysis was observed with only 15 μM instead of 200 μM. Lichenysin is also a better chelating agent because its association constants with Ca2+ and Mg2+ are increased by a factor of 4 and 16, respectively. This effect is assigned to an increase in the accessibility of the carboxyl
group to cations owing to a change in the side chain topology induced by the Glu/Gln exchange. Additionally, the propensity
of the lipopeptide for extensive hydrophobic interactions, as illustrated by its low c.m.c., contributes to further stabilization
of the cation and an increase in the partitioning of lichenysin into the erythrocyte membrane. Our data support the formation
of a lichensyin-Ca2+ complex in a molar ratio of 2:1 instead of 1:1 with surfactin, suggesting an intermolecular salt bridge between two lichenysin
molecules. Therefore, when Ca2+ ions are present in the solution, micellization occurs via a dimer assembly, with a possible long-range effect on the spatial
arrangement of the micelles or other supramolecular structures. Finally, among all the surfactin peptidic variants so far
known, lichenysin is the one for which the three tested activities are the most substantially improved. 相似文献
992.
Isabelle Dchamps-Olivier Jean-Pierre Barbier Michel Aplincourt Nicolas Oget Franoise Chuburu Henri Handel 《Helvetica chimica acta》1999,82(5):790-795
The acid-base behavior of cyclenphosphine sulfide (cyclenPS) is appreciably different from that of cyclamphosphine sulfide (cyclamPS). The cyclenPS shows five acid functionalities compared to four for cyclamPS. The fifth acidic group in cyclenPS corresponds to the formation of a stable amidure in aqueous solution (pK=12.3). This behavior is due to the strong transannular N→P interaction. The deprotonation sequences were established by 31P-NMR and confirmed by modelling of cyclenPS. 相似文献
993.
Ommochromes are one of the least studied groups of natural pigments, frequently confused with melanin and, so far, exclusively found in invertebrates such as cephalopods and butterflies. In this study focused on the purple color of the shells of a mollusk, Crassostrea gigas, the first evidence of a metabolite of ommochromes, xanthurenic acid (XA), was obtained by liquid chromatography combined with mass spectrometry (UPLC-MS). In addition to XA and various porphyrins previously identified, a second group of high molecular weight acid-soluble pigments (HMASP) has been identified with physicochemical and structural characteristics similar to those of ommochromes. In addition, fragmentation of HMASP by tandem mass spectrometry (MS/MS) has revealed a substructure common to XA and ommochromes of the ommatin type. Furthermore, the presence of melanins was excluded by the absence of characteristic by-products among the oxidation residues of HMASP. Altogether, these results show that the purple color of the shells of Crassostrea gigas is a complex association of porphyrins and ommochromes of potentially ommatin or ommin type. 相似文献
994.
Isabelle Fourr Bernard Silvi Patrick Chaquin Alain Sevin 《Journal of computational chemistry》1999,20(9):897-910
The modifications of bonding in carbonyl and imine compounds upon excitation, electron attachment, and ionization were studied within the framework of the electron localization function (ELF). The topological analysis of ELF allows a partition of the molecular space into regions having a clear chemical meaning: the basins. The electronic populations of the basins associated with bonding and nonbonding character, as well as the basin spin densities, were calculated at the MP2 level of the quantum mechanical calculation. Good agreement was found with the classical view in terms of mesomeric structures corresponding to the dominant localization of electrons contained in frontier molecular orbitals (MOs). The variations of the basins population were compared to the predictions of MO theory. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 897–910, 1999 相似文献
995.
996.
Marianne Fillet Isabelle Bechet Gerhard Schomburg Philippe Hubert Jacques Crommen 《Journal of separation science》1996,19(12):669-673
High resolution could be achieved for the enantiomers of acidic drugs, namely, sulindac, fenoprofen, ketoprofen, warfarin, and hexobarbital, in a buffer of pH 3 by the simultaneous addition of uncharged and charged β-cyclodextrin derivatives. The interaction of the analytes with the anionic sulfobutyl ether β-cyclodextrin provides the analytes with an adequate electrophoretic mobility whereas the interaction with various neutral β-cyclodextrins generates high enantioselectivity. Five neutral cyclodextrins, the native β-cyclodextrin, as well as methyl-, dimethyl-, trimethyl- and hydroxypropyl-β-cyclodextrin, were tested to enhance the enantioselectivity of the electrophoretic system. High resolution values and the shortest analysis times for the five drugs tested were achieved in a buffer made of 100 mM phosphoric acid adjusted to pH 3 with triethanolamine and containing dimethyl- or trimethyl-β-cyclodextrin in addition to sulfobutyl ether β-cyclodextrin. 相似文献
997.
Fahima Bekka-Hadji Isabelle Bombarda Ferhat Djoudi Sofiane Bakour Abdelaziz Touati 《Molecules (Basel, Switzerland)》2022,27(3)
The essential oils were obtained by hydrodistillation from aerial parts of Mentha pulegium L. (M. pulegium L.) and Artemisia herba alba (A. herba alba) Asso. and analyzed by gas chromatography–flame ionization detector chromatograpy (GC–FID) and gaz chromatography–mass spectrometry (GC–MS). The antibacterial activities of the oils were determined by the disk diffusion method and a microdilution broth assay against six bacteria stains. The combinations of these essential oils with antibiotics were evaluated against two multi-drug-resistant bacteria strains: imipenem-resistant Acinetobacter baumannii (IRAB S3310) and methicillin-resistant Staphylococcus aureus (MRSA S19). The chemical analysis of M. pulegium essential oil revealed the presence of pulegone (74.8%) and neoisomenthol (10.0%). A. herba alba essential oil was characterized by camphor (32.0%), α-thujone (13.7%), 1,8-cineole (9.8%), β-thujone (5.0%), bornéol (3.8%), camphene (3.6%), and p-cymene (2.1%). All strains tested except Pseudomonas aeruginosa were susceptible to these oils. The combinations of essential oils with antibiotics exerted synergism, antagonism, or indifferent effects. The best effect was observed with A. herba alba essential oil in association with cefoxitin (CX) against MRSA S19. However, for IRAB S3310, the strongest synergistic effect was observed with M. pulegium in association with amikacin (AK). This study demonstrated that M. pulegium and A. herba alba essential oils have antibacterial activities which could be potentiated by antibiotics especially in the case of IRAB S3310. 相似文献
998.
We describe the synthesis and the incorporation into oligonucleotides of the novel nucleoside building blocks 9, 10 , and 16 , carrying purine‐like double H‐bond‐acceptor bases. These base‐modified nucleosides were conceived to recognize selectively a cytosine⋅guanine (C⋅G) inversion site within a homopurine⋅homopyrimidine DNA duplex, when constituent of a DNA third strand designed to bind in the parallel binding motif. While building block 16 turned out to be incompatible with standard oligonucleotide‐synthesis conditions, UV/triplex melting experiments with third‐strand 15‐mers containing β‐D ‐nucleoside 6 (from 9 ) showed that recognition of the four natural Watson‐Crick base pairs follows the order G⋅C≈C⋅G>A⋅T>T⋅A. The recognition is sequence‐context sensitive, and G⋅C or C⋅G recognition does not involve protonated species of β‐D ‐nucleoside 6 . The data obtained fit (but do not prove) a structural model for C⋅G recognition via one conventional and one C−H⋅⋅⋅O H‐bond. The unexpected G⋅C recognition is best explained by third‐strand base intercalation. A comparison of the triplex binding properties of these new bases with those of 4‐deoxothymine (5‐methylpyrimidine‐2(1H)‐one, 4 HT), previously shown to be C⋅G selective but energetically weak, is also described. 相似文献
999.
1000.
Jean‐Louis Hazemann Olivier Proux Vivian Nassif Hervé Palancher Eric Lahera Cécile Da Silva Aurélien Braillard Denis Testemale Marie‐Ange Diot Isabelle Alliot William Del Net Alain Manceau Frédéric Gélébart Marc Morand Quentin Dermigny Abhay Shukla 《Journal of synchrotron radiation》2009,16(2):283-292
A bent‐crystal spectrometer based on the Rowland circle geometry has been installed and tested on the BM30b/FAME beamline at the European Synchrotron Radiation Facility to improve its performances. The energy resolution of the spectrometer allows different kinds of measurements to be performed, including X‐ray absorption spectroscopy, resonant inelastic X‐ray scattering and X‐ray Raman scattering experiments. The simplicity of the experimental device makes it easily implemented on a classical X‐ray absorption beamline. This improvement in the fluorescence detection is of particular importance when the probed element is embedded in a complex and/or heavy matrix, for example in environmental sciences. 相似文献