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31.
Bibal C Pink M Smurnyy YD Tomaszewski J Caulton KG 《Journal of the American Chemical Society》2004,126(8):2312-2313
The reaction of [(Cymene)RuCl2]2 with the chelate LiHC(PPh2NPh)2 occurs to remove both chloride ligands, to furnish a cationic Ru(II) complex with the monoanionic ligand bound eta3, through two N and an sp3 carbon. This cation is also produced from the conjugate acid of the ligand H2C(PPh2NPh)2 because this molecule can serve as a Br?nsted base, to deprotonate the acidic carbon of another molecule of H2C(PPh2NPh)2. DFT calculations show an energy surface where (Cymene)RuHC(PPh2NPh)2L is more stable with a Ru-CH(PPh2NPh)2 bond and with L = Cl- or MeCN not coordinated to Ru, than to an eta2-HC(PPh2NPh)2 structure with coordinated L; this is tested experimentally. The greater tendency for this ligand to be coordinated eta3 vs analogous diketiminates is discussed. The nucleophilicity of Cgamma in structure 1, vs that of donors L = Cl- or MeCN, is evaluated to understand the preference of the bis(phosphinimino)methanide to be bidentate or tridentate. 相似文献
32.
Bond AD Derossi S Jensen F Larsen FB McKenzie CJ Nelson J 《Inorganic chemistry》2005,44(17):5987-5989
Treatment of cryptand L(1) with Cu(II) generates a H3O2(-)-bridged dicopper(II) cryptate, 2, where the guest anion has responded to steric constraint by a significant shortening of the O-O distance to 2.325(9) A; computational optimization at the B3LYP/6-31(d) level suggests that the bridging O-H...O H-bond is bent (approximately 157 degrees) but that the barrier to interchange of the bridging H atom is low (<4 kJ mol(-1)). This cryptate, rather than the [Cu2L(1)muCN]3+ species recently claimed to derive from cleavage of the C-C bond of the solvent, is the product of acetonitrile recrystallization of the initially formed reaction product, 1. 相似文献
33.
Peter C Oostenbrink C van Dorp A van Gunsteren WF 《The Journal of chemical physics》2004,120(6):2652-2661
While the determination of free-energy differences by MD simulation has become a standard procedure for which many techniques have been developed, total entropies and entropy differences are still hardly ever computed. An overview of techniques to determine entropy differences is given, and the accuracy and convergence behavior of five methods based on thermodynamic integration and perturbation techniques was evaluated using liquid water as a test system. Reasonably accurate entropy differences are obtained through thermodynamic integration in which many copies of a solute are desolvated. When only one solute molecule is involved, only two methods seem to yield useful results, the calculation of solute-solvent entropy through thermodynamic integration, and the calculation of solvation entropy through the temperature derivative of the corresponding free-energy difference. One-step perturbation methods seem unsuitable to obtain entropy estimates. 相似文献
34.
A variety of human cancers become resistant or are intrinsically resistant to treatment with conventional chemotherapy, a phenomenon called multidrug resistance. This broad-based resistance results in large part, but not solely, from overexpression of members of the ATP-binding cassette (ABC) superfamily of membrane transporters, including P-glycoprotein, various members of the multidrug resistance associated proteins (MRPs), and ABCG2, also known as MXR1, BCRP, and ABCP. When overexpressed in cell lines, ABCG2 has the ability to confer high levels of resistance to anthracyclines, mitoxantrone, bisantrene, and the camptothecins topotecan and SN-38. This review focuses on the discovery, the biochemistry and the normal physiology of human ABCG2, a novel ABC half transporter expressed abundantly in placenta, as well as in liver, intestine and stem cells. ABCG2 may serve a protective function by preventing toxins from entering cells as well as potentially playing a role in regulating stem cell differentiation. We also discuss the involvement of ABCG2 in multidrug resistance in cancer, especially with regard to acute myeloid leukemia. The mechanism by which substrates are recognized by ABCG2 and how the energy of ATP hydrolysis is transduced into transport remain elusive. A complete understanding of the mechanism and biological function of ABCG2 will be important for understanding its normal physiology as well as potentially for the development of novel chemotherapeutic treatment strategies. 相似文献
35.
Sophie Griveau Dimitri Mercier Christine Vautrin-Ul Annie Chauss 《Electrochemistry communications》2007,9(12):2768-2773
We propose in this study a simple and rapid way to produce stable amino-derivatized conductive surfaces for the subsequent immobilization of (bio)molecules. This was achieved through the use of (4-aminoethyl)benzenediazonium salt (AEBD), which was immobilized on glassy carbon and gold electrodes by its electrochemical reduction. The presence of terminal grafted amino functions was evidenced with XPS by analyzing N1s core level. Besides this conventional surface characterisation, an electrochemical strategy is proposed here to evidence the presence of immobilized amines, in which the chemical reactivity of amines towards 2,4,6-trinitrobenzenesulfonic acid (TNBS) is used. Surface-bound TNBS served as an electrochemical marker and was detected by cyclic voltammetry. Additionally, pre-modified gold electrodes with amino functions can be derivatized with biomolecules such as glutathione (GSH). Glutathione attachment was evidenced by studying the electrochemical behaviour of ferri/ferrocyanide redox before and after its immobilization. The functionalized electrodes were then used for the detection of copper ions in neutral aqueous solutions. 相似文献
36.
The new tetra-aryl trans-A2B2-porphyrin with two fluoren-2-yl and two phenyl groups at the meso-positions has been synthesized and characterized, together with the analogous bi-aryl trans-A2-porphyrin incorporating only the fluorenyl groups. The photophysical properties of these new compounds in solution are reported. The two additional phenyl groups in the A2B2 porphyrin stabilize the first excited singlet state by approximately 500 cm−1 compared to the A2 system, as revealed by the red-shift of the absorption Q bands and of the fluorescence emission bands. Both compounds display enhanced emission quantum yields compared to tetraphenylporphyrin: the augmentation is higher for the tetra-aryl than for the bi-aryl system, although not as high as for tetrafluorenylporphyrin. Fluorescence lifetime measurements of the series of four compounds suggest that the trends can be interpreted in terms of the larger influence of fluorenyl over phenyl groups in increasing the fluorescence radiative rate constant of the porphyrin, kf. 相似文献
37.
Retsek JL Drain CM Kirmaier C Nurco DJ Medforth CJ Smith KM Sazanovich IV Chirvony VS Fajer J Holten D 《Journal of the American Chemical Society》2003,125(32):9787-9800
The ground- and excited-state metal-ligand dynamics of nonplanar nickel(II) 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (NiDPP) and two fluorinated analogues (NiF(20)DPP and NiF(28)DPP) have been investigated using static and time-resolved absorption spectroscopy in toluene and in ligating media that differ in basicity, aromaticity, and steric encumbrance. Because of the electronic and steric consequences of nonplanarity, NiDPP does not bind axial ligands in the ground state, but metal coordination does occur after photoexcitation with multistep dynamics that depend on the properties of the ligand. Following the structural relaxations that occur in all nickel porphyrins within approximately 10 ps, ligand binding to photoexcited NiDPP is progressively longer in pyridine, piperidine, and 3,5-lutidine (25-100 ps) but does not occur at all in 2,6-lutidine in which the ligating nitrogen is sterically encumbered. The transient intermediate that is formed, which nominally could be either a five- or six-coordinate species, also has a ligand-dependent lifetime (200-550 ps). Decay of this intermediate occurs partially via ligand release to re-form the uncoordinated species, in competition with binding of the second axial ligand and/or conformational/electronic relaxations (of a six-coordinate intermediate) to give the ground state of the bis-ligated photoproduct. The finding that the photoproduct channel principally depends on ligand characteristics along with the time-evolving spectra suggests that the transient intermediate may involve a five-coordinate species. In contrast to NiDPP, the fluorinated analogues NiF(20)DPP and NiF(28)DPP do coordinate axial ligands in the ground state but eject them after photoexcitation. Collectively, these results demonstrate the sensitivity with which the electronic and structural characteristics of the macrocycle, substituents, and solvent (ligands) can govern the photophysical and photochemical properties of nonplanar porphyrins and open new avenues for exploring photoinduced ligand association and dissociation behavior. 相似文献
38.
A solution-phase synthesis of bicyclic prolines containing four points of diversity has been developed by a two-step synthesis involving 1,3-dipolar cycloaddition of perfluoroalkylsulfonyl-protected hydroxybenzaldehydes followed by Pd-catalyzed Suzuki coupling reaction of fluorous sulfonates with boronic acids. Both reactions are conducted under microwave irradiation and reaction mixtures are purified by solid-phase extractions without performing chromatography. 相似文献
39.
The synthesis of aza-2 pyrrolo[1,2-a]indole derivatives was achieved by a 1,3-dipolar cycloaddition reaction of dimethylacetylenedicarboxylate with a mesoionic ion. 相似文献
40.
Max Robba Daniel Maume Jean-Charles Lancelot 《Journal of heterocyclic chemistry》1979,16(6):1193-1196
The 1,2-dihy dro-1,2,4-triazino[4,5-a] indole-1-thiones 2 and 3 obtained by sulphurization of the 1,2-dihydro-1,2,4-triazino-[4,5-a] indol-1-ones 1 and 4 with phosphorus pentasulphide are intermediate products in the synthesis of 1,2,4-triazino[4,5-a]-indolc 10 and 4-methyl-1,2,4 omdp;e 19. The thiolactam-thiolactim tautomerism was studied using the ir and nmr spectra and allowed N. and S.substitutions. The methylation with dimethyl sulphate afforded mixtures of N. and S. methyl derivatives which were separated by chromatographic analysis and identified by |21|0H nmr and unequivocal synthesis. 相似文献