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51.
Alexei?VernitskiEmail author Laila?Tunsi Colette?Ponchel Alexei?Lisitsa 《Semigroup Forum》2018,97(1):75-86
It is known that a knot (link) is rational if and only if its \(\pi \)-orbifold group is dihedral. A semigroup version of this result has been formulated as a conjecture. Working towards proving the conjecture, we describe certain semigroups associated with twist links, clarify how these semigroups are related to dihedral groups and find defining relations of these semigroups. 相似文献
52.
The 35-Cl NQR spectra of diazepam and some of its related compounds are reported; they yield information about the hydrogen bonded complex that diazepam forms with chloral hydrate. The results reflect large changes in electron distribution at the CCl3 group while the diazepam chlorine at the 7 position remains almost unaffected. 相似文献
53.
Ladame S Fauré R Denier C Lakhdar-Ghazal F Willson M 《Organic & biomolecular chemistry》2005,3(11):2070-2072
A new series of "bi-substrate" analogues have been synthesized as potential inhibitors of the glyceraldehyde-3-phosphate dehydrogenase and one lead compound has been identified that inhibits the enzyme from Trypanosoma cruzi with good affinity and very high (50-fold) specificity. 相似文献
54.
Gautier-Luneau I Merle C Phanon D Lebrun C Biaso F Serratrice G Pierre JL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(7):2207-2219
Despite the crucial role of "iron(III) citrate systems" in the iron metabolism of living organisms (bacteria as well as plants or mammals), the coordination chemistry of ferric citrate remains poorly defined. Variations in the experimental conditions used for the preparation of so-called ferric citrates (iron salt, Fe:cit molar ratio, base, pH, temperature, solvent) lead to several different species, which are in equilibrium in solution. To date, six different anionic complexes have been structurally characterized in the solid state, by ourselves or others. In the work described herein, we have established the experimental conditions leading to each of them. Five were obtained from aqueous solution. With the exception of a nonanuclear species (of which fragments have been detected), all were identified in aqueous solution on the basis of electrospray ionization mass spectrometry. In addition, the spectra revealed a new trinuclear species, which could not be crystallized. Kinetic studies of iron uptake from citrate species by iron chelators confirmed the results indicated by the ESI-MS studies. These studies also allowed the relative molar fraction of mononuclear versus polynuclear complexes to be determined, which depends on the Fe:cit molar ratio. 相似文献
55.
Boskovic C Brechin EK Streib WE Folting K Bollinger JC Hendrickson DN Christou G 《Journal of the American Chemical Society》2002,124(14):3725-3736
The reaction of (NBu(n)(4))[Mn(8)O(6)Cl(6)(O(2)CPh)(7)(H(2)O)(2)] (1) with 2-(hydroxymethyl)pyridine (hmpH) or 2-(hydroxyethyl)pyridine (hepH) gives the Mn(II)(2)Mn(III)(10) title compounds [Mn(12)O(8)Cl(4)(O(2)CPh)(8)(hmp)(6)] (2) and [Mn(12)O(8)Cl(4)(O(2)CPh)(8)(hep)(6)] (3), respectively, with X = Cl. Subsequent reaction of 3 with HBr affords the Br(-) analogue [Mn(12)O(8)Br(4)(O(2)CPh)(8)(hep)(6)] (4). Complexes 2.2Et(2)O.4CH(2)Cl(2), 3.7CH(2)Cl(2), and 4.2Et(2)O.1.4CH(2)Cl(2) crystallize in the triclinic space group P1, monoclinic space group C2/c, and tetragonal space group I4(1)/a, respectively. Complexes 2 and 3 represent a new structural type, possessing isomeric [Mn(III)(10)Mn(II)(2)O(16)Cl(2)] cores but with differing peripheral ligation. Complex 4 is essentially isostructural with 3. A magnetochemical investigation of complex 2 reveals an S = 6 or 7 ground state and frequency-dependent out-of-phase signals in ac susceptibility studies that establish it as a new class of single-molecule magnet. These signals occur at temperatures higher than those observed for all previously reported single-molecule magnets that are not derived from [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(x)]. A detailed investigation of forms of complex 2 with different solvation levels reveals that the magnetic properties of 2 are extremely sensitive to the latter, emphasizing the importance to the single-molecule magnet properties of interstitial solvent molecules in the samples. In contrast, complexes 3 and 4 are low-spin molecules with an S = 0 ground state. 相似文献
56.
Quantum tunneling of magnetization in a new [Mn18]2+ single-molecule magnet with s = 13 总被引:3,自引:0,他引:3
Brechin EK Boskovic C Wernsdorfer W Yoo J Yamaguchi A Sañudo EC Concolino TR Rheingold AL Ishimoto H Hendrickson DN Christou G 《Journal of the American Chemical Society》2002,124(33):9710-9711
The reaction between 2-(hydroxyethyl)pyridine (hepH) and a 2:1 molar mixture of [Mn3O(O2CMe)6(py)3](ClO4) and [Mn3O(O2CMe)6(py)3](py) in MeCN leads to isolation of [Mn18O14(O2CMe)18(hep)4(hepH)2(H2O)2](ClO4)2 (1) in 10% yield. The complex is 2MnII,16MnIII and consists of a Mn4O6 central unit to either side of which is attached a Mn7O9 unit. Magnetization data collected in the 2.0-4.0 K and 20-50 kG ranges were fit to yield S = 13, g = 1.86, and D = -0.13 cm-1 = -0.19 K, where D is the axial zero-field splitting parameter. AC susceptibility studies in the 0.04-4.0 K range at frequencies up to 996 Hz display out-of-phase (chiM' ') signals, indicative of a single-molecule magnet (SMM). Magnetization vs applied DC field scans exhibit hysteresis at <1.0 K, confirming 1 to be a SMM. DC magnetization decay data were collected on both a microcrystalline sample and a single crystal, and the combined data were used to construct an Arrhenius plot. Between 3.50 and 0.50 K, the relaxation rate is temperature-dependent with an effective barrier to relaxation (Ueff) of 14.8 cm-1 = 21.3 K. Below ca. 0.25 K, the relaxation rate is temperature-independent at 1.3 x 10-8 s-1, indicative of quantum tunneling of magnetization (QTM) between the lowest energy Ms = +/-13 levels of the S = 13 state. Complex 1 is both the largest spin and highest nuclearity SMM to exhibit QTM. 相似文献
57.
Colette Deschamps-Vallet Michle Meyer-Dayan Jean Andrieux Jacques Riboulleau Bernard Bodo Darius Molho 《Journal of heterocyclic chemistry》1977,14(3):489-492
5-Oxo-5H,7H-[2]benzopyrano[4,3-b][1]benzopyran ( 2 ) has been synthesized from 3-(o-hydroxybenzylidene)isochroman-1,4-dione ( 3 ) by reductive cyclization, and from 5H,7H[2]benzo-pyrano[4,3-b][1]benzopyran-5,7-dione ( 4 ) by selective hydro-genation. This second method affords the dihydro compound 6 or 6a,12a-dihydro-5H,7H-[2]benzopyrano[4,3-b] [1 ]benzopyran-5-one as reaction time increases. 相似文献
58.
Gilbert Michel Breuil Colette Yaguchi Makoto Saddler J. N. 《Applied biochemistry and biotechnology》1992,(1):247-259
Thielavia terrestris 255B, a thermophilic ascomycete, produced two major forms of xylanase with pIs of 4.6 (xylanase I) and 6.1 (xylanase II).
The latter enzyme could be purified to > 99% homogeneity using anion-exchange chromatography and gel filtration. Xylanase
II had a mol wt of 25.7 kDa (SDS-PAGE) and a pH and a temperature optimum of 3.6–4.0 and 60–65°C, respectively. The ratio
of the enzyme’s activity against xylan and carboxymethylcellulose was 500–1000 to 1, indicating a possible application of
this enzyme in biobleaching processes. The amino acid sequence of this protein is being determined, and initial data suggest
that the enzyme belongs to a group of low-mol wt xylanases that have been isolated from both bacteria and fungi. 相似文献
59.
Philippe Demont Daniel Chatain Colette Lacabanne Michel Glotin 《Macromolecular Symposia》1989,25(1):167-186
The retardation and relaxation behaviour of poly(ether-block-amide)s PEBA copolymers was investigated as a function of hard polyamide sequence length by using thermally stimulated creep (TSCr) and Current (TSCu). Two primary TSCr and TSCu peaks, called ßPE and ßPA were observed in the temperature range 150–300 K. The “low temperature” peak ßPE was characterized by a peak position T ßPE which depends poorly upon hard segment content as the corresponding DSC glass transition temperature TgPE. The peak position TßPA of the “high temperature” relaxation showed a progressive shift towards higher temperatures as the hard segment average length was increased as it is observed in series of pure polyamide oligomers. So, complex spectra suggest that an amorphous phase separation occurs in PEBA copolymers. The TSCr ßPE and ßPA modes were analysed by thermal sampling method (TS). The elementary TSCr processes isolated in the ßPE and ßPA distributed retardation modes were characterized by retardation times following a compensation law. The comparison of activation and compensation parameters confirmed the existence of a biphasic amorphous phase in PEBA. In TSCr spectra, an additional peak, noted α, is observed at a temperature close to the DSC melting point TmPE of the poly(tetramethylene glycol) segments. 相似文献
60.