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521.
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The results presented here provide additional support for our hypothesis based on the relative basicity of the reaction controlling functional group to rationalize experimental observations on intramolecular Diels-Alder reactions with a furan diene (IMDAF) regarding the quantity (0.1 or 1.1 equiv) of Lewis acid required to facilitate the reaction most effectively. Heats of formation, DeltaH(f), and heats of reaction, DeltaH(R), have been obtained using AM1 calculations for 26 IMDAF reactions. These DeltaH(R) are generally exothermic (indicating that these IMDAF reactions are favorable) and can be qualitatively correlated with experimental yields of adduct, thereby providing a means of predicting the feasibility of the IMDAF promoted by 0.1 equiv of Lewis acid. The equilibria involved in the Lewis acid-promoted IMDAF reaction have been qualitatively interpreted using reaction coordinate diagrams and quantitatively investigated by generating a mathematical simulation of the reaction scheme. This demonstrates that the experimental behavior of the IMDAF reaction is well represented by the relative basicity hypothesis and that the LA concentration-dependent behavior should also be observed for other Lewis acid-promoted organic reactions. 相似文献
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C. T. LIN Y. G. CHYAN G. C. KRESHECK HERBERT C. BITTING JR M. A. EL-SAYED 《Photochemistry and photobiology》1989,49(5):641-648
Several spectroscopic techniques (absorption, emission, transient absorption and differential scanning calorimetry--DSC) were used to investigate the deprotonation of dibucaine.HCl in a hydrophobic environment, and the interaction sites and mechanisms of the local anesthetic dibucaine.HCl on bacteriorhodopsin (bR) in purple membrane. The important results are summarized as follows: (1) the visible absorption features of native (lambda max = 568 nm) and deionized (lambda max = 608 nm) bR are sensitive to the amount of dibucaine.HCl added; (2) the emission spectrum of dibucaine.HCl embedded in the retinal-free mutant bR is similar to that of dibucaine free base in Triton X-100 micellar solutions; (3) the phosphorescence emission of dibucaine at 77 K is completely quenched by bR and the fluorescence quenching rate for the incorporated dibucaine.HCl in bR was determined as kq = 4.09 x 10(13) M-1 s-1; (4) the incorporation of dibucaine.HCl in bR inhibits the slow component rate of formation of M412 and decreases the amount of M412 formation in the photochemical cycle of bR; and (5) the thermal stability of native bR was measured by DSC in the presence and absence of dibucaine and yielded an endothermic transition at 95.9 +/- 1.0 degrees C with 13.6 J/g (3.25 +/- 0.12 cal/g) of enthalpy changes. All observations suggest that the action site of the local anesthetic, dibucaine.HCl, is near or at the chromophore, i.e. the retinal Schiff base of bR. The anesthetic action on bR purple membrane is probably via a specific site binding, but not a conformational mechanism. 相似文献
524.
Wu P Malkoch M Hunt JN Vestberg R Kaltgrad E Finn MG Fokin VV Sharpless KB Hawker CJ 《Chemical communications (Cambridge, England)》2005,(46):5775-5777
Unsymmetrical dendrimers, containing both mannose binding units and coumarin fluorescent units, have been prepared using click chemistry and shown to be highly efficient, dual-purpose recognition/detection agents for the inhibition of hemagglutination. 相似文献
525.
Jiang H Granville DJ North JR Richter AM Hunt DW 《Photochemistry and photobiology》2002,76(2):224-231
A new photosensitizer, presently designated QLT0074, may have the potential for the treatment of immune and nonimmune conditions with photodynamic therapy (PDT). The activity of QLT0074 was tested against human peripheral blood T cells and Jurkat T lymphoma cells. At low nanomolar concentrations of QLT0074 in combination with blue light, apoptosis was rapidly induced in Jurkat and blood T cells in vitro as indicated by the expression of the apoptosis-associated mitochondrial 7A6 marker and Annexin-V labeling. Further studies performed with Jurkat T cells showed that PDT-induced apoptosis with QLT0074 was associated with caspase-3 activation and the cleavage of the caspase substrate poly(adenosine diphosphate-ribose)polymerase. Flow cytometry studies revealed that blood T cells with high expression of the interleukin-2 receptor (CD25) took up greater amounts of QLT0074 and were eliminated to a greater extent with PDT than T cells with low levels of this activation marker. This selective action of PDT was confirmed by similar reductions in the percentage of T cells that expressed other activation-related markers, including very late activation antigen-4 (CD49d), human leukocyte antigen DR (HLA-DR), intercellular adhesion molecule-1 (CD54) and Fas (CD95). For activated T cells treated with a specific dose of QLT0074 and light 24 h earlier, CD25 expression density was significantly less, whereas CD54, CD95 and HLA-DR levels were similar to those for control cells treated with light alone. This work shows that PDT with QLT0074 exerts selective, dose-related effects on T cells in vitro. 相似文献
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