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81.
82.
The synthesis and the crystal properties of new selenides of formula MxMo3Se4 are described. If M = Zn, Ag, Cd, Sn and Pb, they are stoichiometric with x = 0.6; if M = Fe, Mn, Cr, V, Ti, triclinic solid solutions are observed with 0.5 < x < 0.7; if M = Cu, Co, Ni, rhombohedral solid solutions are obtained with 0 < x < 1.4 for M = Cu, 0 < x < 0.7 for M = Co and 0 < x < 0.8 for M = Ni All these phases can be deduced from the Mo3Se4 structure by introducing metal atoms into the tunnels between the “Mo6Se8” metal atom cluster configuration. 相似文献
83.
The 4,6-bis(10-mesityl-5,15-di-p-tolylporpyrinyl)dibenzothiophene (H4DPSN) free base was obtained in five steps from commercially available materials. The metalation of DPSN2- with zinc(II), copper(II), and palladium(II) led to three new homobimetallic systems, (Zn)2DPSN, (Cu)2DPSN, and (Pd)2DPSN, respectively. The cofacial structures of these molecules offer the possibility of having dioxygen molecules inside the cavity for a period of time, allowing dynamic (collisional) phosphorescence quenching to be more efficient. The bimolecular excited-state deactivation rate constant for deactivation by dioxygen (kQ: (Pd)2DPB, 2.98x10(9); (Pd)2DPSN, 3.99x10(9); (Pd)2DPX, 6.94x10(9); (Pd)TPP, 8.95x10(9); (Pd)2DPS, 8.95x10(9) M-1 s-1) of (Pd)2DPSN, which exhibits an intense phosphorescence at 699 nm, was compared to those observed for (Pd)TPP, (Pd)2DPS, (Pd)2DPX, and (Pd)2DPB (TPP2-=tetraphenylporphyrin dianion, DPS4-=4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzothiophene tetraanion, DPX4-=4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene tetraanion, and DPB4-=1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]biphenylene tetraanion). These collision-induced deactivation data were interpreted by estimating a series of physical parameters such as the surface area and bisporphyrin radii, the diffusion coefficient of the bismacrocycles, and the theoretical deactivation efficiency for the five compounds addressing the role of steric hindrance of the macrocycles on each other and the aryl groups at the meso positions. For sensing purposes, (Pd)2DPX is characterized by a Stern-Volmer constant kSV of 2.91x10(6) M-1, placing the lower detection limit for [O2] in solution at 0.58 ppm, which is better than that for (Pd)TPP (kSV=2.31x10(6) M-1; lower detection limit of 0.73 ppm), the classically used monoporphyrin complex. 相似文献
84.
Photodegradation of Polychlorinated Dibenzo-p-dioxins in Liquid Samples by Near UV Light Irradiation
Photodegradation of 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) in hexane solution was studied under controlled near-UV light exposure in the spectral region from 325 to 269 nm. GC-MS was used to detect the amount of unreacted dioxin and to characterize the relevant degradation products. Irradiation experiments carried out at a constant light energy (700 mJ) showed that the percentage of 1,2,3,4-TCDD left in the solution after irradiation changed from about 55 to 75%, with a minimum of 55% at 310 nm. Further irradiation experiments carried out at two wavelengths, namely 310 and 269 nm, and light energy ranging from 0 to 4000 mJ, showed that the photodegradation reaction of the TCDD always followed a pseudo-first-order kinetic, with a rate constant of 8 × 10−4and 5 × 10−4mJ−1, respectively. These experiments also showed that trichloro- and dichloro-dibenzo-p-dioxins were produced with less than 15% of the initial quantity of TCDD, leading to the conclusion that the dechlorination process is a minor photolysis pathway. 相似文献
85.
Queiroz MJ Abreu AS Ferreira PM Oliveira MM Dubest R Aubard J Samat A 《Organic letters》2005,7(22):4811-4814
[structure: see text] A new photochromic thieno-2H-chromene alpha-amino acid derivative was prepared by C-N palladium-catalyzed cross-coupling of a bromothieno-2H-chromene with the aminated aromatic side chain of the methyl ester of a N,N-diprotected amino acid. Its good photochromic properties demonstrated by flash photolysis and continuous irradiation indicate a possible application in ophthalmic lenses. It may also be inserted into peptides to give photoinduced reversible structural changes. 相似文献
86.
Alan M. Bond Roger J. OHalloran Ivica Ruzic Donald E. Smith 《Journal of Electroanalytical Chemistry》1978,90(3):381-388
Rate laws presented to date for analysis of a.c. cyclic voltammetric data have invoked the so-called “slow scan limit approximation” which requires that ΔEω ? v, where Δ E and ω are the applied a.c. potential amplitude and angular frequency, respectively, and v is the d.c. potential scan rate. To provide a more useful guideline for the experimentalist than this qualitative condition, a pure digital simulation approach has been used to compute the a.c. cyclic time domain waveform for a reversible process under small amplitude conditions. The a.c. content of this waveform is extracted by the digital FFT alogirthm. Results of this study are presented here. Among the conclusions reached are more quantitative limitations for the slow scan limit rate laws describing the fundamental and second harmonic responses (approximately 128 a.c. cycles/d.c. cyclic sweep and 512 a.c. cycles/d.c. cyclic sweep, respectively) and an interesting prediction that the latter limitations can be relaxed further by a current waveform subtraction strategy, to as low as about 16 a.c. cycles/d.c. cyclic sweep for the fundamental and second harmonics. The cycles/sweep values assume one triangular wave potential scan of ±200 mV is encompassed. 相似文献
87.
Excess enthalpies and excess volumes were determined at 298.15 K for: dimethoxymethane+heptane, diethoxymethane+heptane, 1,1-dimethoxyethane+heptane, 1,1-diethoxyethane+heptane, 2,2-dimethoxypropane+heptane and 1,1-diethoxypropane+heptane. 相似文献
88.
Work which has recently appeared on the structures of Celastraceae alkaloids in addition to physical and chemical evidence adduced with respect to cathidine D permits formulation of structure 7a or 7b for this component of Catha edulis. 相似文献
89.
Tomás Moya-Pizarro Roger Salmon Léopold Fournes Gilles Le Flem Barbara Wanklyn Paul Hagenmuller 《Journal of solid state chemistry》1984,53(3):387-397
Single crystals of the high-temperature form of NaFeP2O7 have been grown by a flux technique. II-NaFeP2O7 crystallizes in the monoclinic space group with lattice parameters: a = 7.298(2) Å, b = 7.874(2) Å, c = 9.536(3) Å, β = 111.85(2)°. The structure refined from 1481 independent reflections leads to R = 0.044 and confirms the work previously published by M. Gabelica-Robert, M. Goreaud, P. Labbe, and B. Raveau (J. Solid State Chem.45, 389, 1982). Magnetic Mössbauer resonance studies have shown the existence of antiferromagnetic ordering with a weak ferromagnetic component below 30 K. The FeO bond is markedly ionic in character due to the highly polarizing power of phosphorus in tetrahedral site. 相似文献
90.
Wong DM Greenblatt HM Dvir H Carlier PR Han YF Pang YP Silman I Sussman JL 《Journal of the American Chemical Society》2003,125(2):363-373
Acetylcholinesterase (AChE) inhibitors improve the cognitive abilities of Alzheimer patients. (-)-Huperzine A [(-)-HupA], an alkaloid isolated from the club moss, Huperzia serrata, is one such inhibitor, but the search for more potent and selective drugs continues. Recently, alkylene-linked dimers of 5-amino-5,6,7,8-tetrahydroquinolinone (hupyridone, 1a), a fragment of HupA, were shown to serve as more potent inhibitors of AChE than (-)-HupA and monomeric 1a. We soaked two such dimers, (S,S)-(-)-bis(10)-hupyridone [(S,S)-(-)-2a] and (S,S)-(-)-bis(12)-hupyridone [(S,S)-(-)-2b] containing, respectively, 10 and 12 methylenes in the spacer, into trigonal TcAChE crystals, and solved the X-ray structures of the resulting complexes using the difference Fourier technique, both to 2.15 A resolution. The structures revealed one HupA-like 1a unit bound to the "anionic" subsite of the active-site, near the bottom of the active-site gorge, adjacent to Trp84, as seen for the TcAChE/(-)-HupA complex, and the second 1a unit near Trp279 in the "peripheral" anionic site at the top of the gorge, both bivalent molecules thus spanning the active-site gorge. The results confirm that the increased affinity of the dimeric HupA analogues for AChE is conferred by binding to the two "anionic" sites of the enzyme. Inhibition data show that (-)-2a binds to TcAChE approximately 6-7- and > 170-fold more tightly than (-)-2b and (-)-HupA, respectively. In contrast, previous data for rat AChE show that (-)-2b binds approximately 3- and approximately 2-fold more tightly than (-)-2a and (-)-HupA, respectively. Structural comparison of TcAChE with rat AChE, as represented by the closely related mouse AChE structure (1maa.pdb), reveals a narrower gorge for rat AChE, a perpendicular alignment of the Tyr337 ring to the gorge axis, and its conformational rigidity, as a result of hydrogen bonding between its hydroxyl group and that of Tyr341, relative to TcAChE Phe330. These structural differences in the active-site gorge explain the switch in inhibitory potency of (-)-2a and 2b and the larger dimer/(-)-HupA potency ratios observed for TcAChE relative to rat AChE. The results offer new insights into factors affecting protein-ligand complementarity within the gorge and should assist the further development of improved AChE inhibitors. 相似文献