Detail of "41085-99-8"

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Single-molecule orientations determined by direct emission pattern imaging

Single-molecule orientations determined by direct emission pattern imaging. Lieb, M. 41085-99-8 and 9011-14-7 are also occured in this study. Andreas; Zavislan, James M.; Novotny, Lukas (Institute of Optics, University of Rochester, Rochester, NY 14627, USA). Journal of the Optical Society of America B: Optical Physics, 21(6), 1210-1215 (English) 2004 Optical Society of America. CODEN: JOBPDE. ISSN: 0740-3224. DOCUMENT TYPE: Journal CA Section: 74 (Radiation Chemistry, Photochemistry, and Photographic and Other Reprographic Processes) Section cross-reference(s): 73 We demonstrate a new method of detg. the three-dimensional dipole orientations of single mols. by direct imaging of the emission patterns in the back focal plane of a high-numerical-aperture objective lens. We compare the reconstructed emission-dipole orientations with a previously established method of absorption-dipole mapping. We find that, for a given no. of emitted photons, emission pattern imaging provides better accuracy (1°-2°) than absorption-dipole mapping of single mols. Compared with some other methods for emission-dipole mapping, the presented method is (1) less sensitive to optical aberrations and adjustment and (2) data anal. is simplified because radiation patterns can be expressed in a simple anal. form. .

pH dependence of tailing in reversed-phase chromatography of a cationic dye: measurement of the strong adsorption site surface density

pH dependence of tailing in reversed-phase chromatography of a cationic dye: measurement of the strong adsorption site surface density. Smith, Emily A.Several substances are used for example 41085-99-8 which is its cas registry number.; Wirth, Mary J. (Department of Chemistry, University of Arizona, Tucson, AZ 85721-0041, USA). Journal of Chromatography, A, 1060(1-2), 127-134 (English) 2004 Elsevier B.V. CODEN: JCRAEY. ISSN: 0021-9673. DOCUMENT TYPE: Journal CA Section: 66 (Surface Chemistry and Colloids) Section cross-reference(s): 80 A question that has interested Dr. J.J. Kirkland is addressed: what is the nature of the silanols that cause tailing to persist at low pH in reversed-phase chromatog. Chromatograms for a cationic dye, 1,1'-didodecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate (DiI), were studied at varying pH using an Agilent SB-C8 column and 80% ACN/water for six DiI concns. ranging from 0.9 to 316 mM. The chromatograms showed increased retention and tailing from pH 1 to 5, as expected. Simulations of the chromatograms agreed well with expt. for a bi-Langmuir isotherm with weak (C8) and strong (silica) adsorption sites. The simulation parameters revealed that the no. of strong adsorption sites decreases by 40% from pH 1 to 5, which indicates that the silanols causing tailing are in the SiOH, not the SiO-, form. This seems paradoxical because tailing increases with increasing pH. The simulation parameters reveal that this increased tailing from pH 1 to 5 owes to doubling of the partition coeff. for DiI to the strong adsorption site, which more than compensates for the decreasing no. of sites. We attribute this increased partition coeff. to increased long-range coulombic interactions with the increasingly abundant SiO- groups at higher pH, which boosts DiI's partition coeff. for both the C8 and SiOH sites. The picture thus emerges that for DiI, higher pH causes increased tailing because the SiO- groups exacerbate tailing that actually originates from adsorption to SiOH groups. .