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81.
Lee CH Na HK Yoon DW Won DH Cho WS Lynch VM Shevchuk SV Sessler JL 《Journal of the American Chemical Society》2003,125(24):7301-7306
Three calix[4]pyrroles bearing m-orcinol-derived diether straps of different lengths on one side of the tetrapyrrolic core have been synthesized and characterized. Structural information for an analogous diester bridged strapped system reported previously (Yoon, D. W.; Hwang, H.; Lee, C. H. Angew. Chem., Int. Ed. Engl. 2002, 41, 1757-1759) is also provided as are bromide and chloride anion affinities for all four systems determined by Isothermal Titration Calorimetry (ITC) in acetonitrile. Although both sets of the strapped calix[4]pyrroles displayed enhanced affinities for chloride and bromide anion, differences were seen among the various receptors that support the conclusion that the anion binding ability of calixpyrrole-type systems can be effectively tuned by modifying the length and nature of the bridging straps. In the specific case of the diether systems, the largest chloride affinity was seen with the shortest strap, whereas the largest affinity for bromide anion was recorded in the case of the longest strap. On the basis of these findings, as well as supporting (1)H NMR spectroscopic studies, it is postulated that not only cavity size per se, but also the ability of the aryl portion of the strap to serve as a CH hydrogen bond donor site are important in regulating the observed anion affinities. 相似文献
82.
83.
Wiskur SL Lavigne JJ Ait-Haddou H Lynch V Chiu YH Canary JW Anslyn EV 《Organic letters》2001,3(9):1311-1314
[structure in text] The pK(a) values and the geometries of secondary and tertiary amines adjacent to boronic acids were determined using potentiometric and (11)B NMR titrations. The studies showed that the secondary ammonium ion has a pK(a) similar to that of the tertiary ammonium species, which leads to the formation of tetrahedral boron centers at pH values above approximately 5.5. Therefore, secondary amines as well as tertiary amines, when placed proximal to boron centers, can be used to create tetrahedral boronic acids at neutral pH for diol complexation. 相似文献
84.
85.
Michael J. Quast Gary E. Martin Vincent M. Lynch Stanley H. Simonsen John G. Stuart Marvin L. Tedjamulia Raymond N. Castle Milton L. Lee 《Journal of heterocyclic chemistry》1986,23(4):1115-1118
The crystal structure of 9-methylphenanthro[4,3-a]dibenzothiophene, C25H16S, Mr = 348.47, has been determined. Monoclinic, P21/c, a = 11.364(3), b, = 14.257(3), c = 11.575(2)Å, β = 116.26(2)°, V = 1681.9(7)Å3, Z = 4, Dx = 1.38 g/cc, MoKα radiation λ = .71069 Å, F(000) = 728, T = 163K, R = .0458 for 2330 reflections. The structure compares favorably with that of hexahelicene and methylated derivatives. The thiophene moiety increases the helical core radius and decreases the pitch with respect to hexahelicene and its derivatives. 相似文献
86.
87.
88.
89.
Summary The method of iterative target transformation factor analysis (ITTFA) used in conjunction with second derivative peak finding
has shown to be a practical method for the peak deconvolution and reconstruction of HPLC chromatograms and spectra. The second
derivative method of peak finding is acceptable for resolutions above 0.5 for peaks of similar heights. Above 0.5 resolution
the labelling gives correct results where the spectra are substantially different and also when reasonably similar. Below
this value the peak labelling was still accurate where the spectra were different. Solvent effects on the spectra of the compounds
studied are small and do not hinder the peak labelling process. Thus small “local” libraries are feasible.
Presented at the 17th International Symposium on Chromatography, September 25–30, 1988. Vienna, Austria. 相似文献
90.
A. Factor J. C. Lynch F. H. Greenberg 《Journal of polymer science. Part A, Polymer chemistry》1987,25(12):3413-3422
Previous studies of the photodegradation of bisphenol A polycarbonate (BPA PC) indicate that both alkyl side chain and ring oxidation play significant roles. In order to determine the relative importance of these two pathways in the photoyellowing that accompanies photodegradation, side chain free polycarbonates based on 3,3′-dihydroxydiphenyl ether were synthesized and tested. Both accelerated weathering experiments using a QUV test apparatus and outdoor weathering indicated that these polymers photoyellowed faster than BPA PC. This suggests that ring oxidation is an important source of photoyellowing of aromatic polycarbonates. 相似文献