Abstract:

Measurements of the temperature dependence of the circular dichroism spectra of l-stercobilin and d-urobilin show that the conformations of these optically-active urobilinoids change with temperature between 163 and 297 degrees K. These conformational changes depend critically on the hydrogen bonding characteristics of the solvent. Thus, in methanol-glycerol (9:1), the chiral sense of the helical conformation of the dipyrrylmethene chromophore is reversed on lowering the temperature, whereas in chloroform, reversal does not occur.

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Circular Dichroism Studies at Variable Temperature: Urobilinoid Conformation<sup><a href="#fn1" rid="fn1" class=" fn">*</a></sup>

Abstract

Measurements of the temperature dependence of the circular dichroism spectra of l-stercobilin and d-urobilin show that the conformations of these optically-active urobilinoids change with temperature between 163 and 297°K. These conformational changes depend critically on the hydrogen bonding characteristics of the solvent. Thus, in methanol-glycerol (9:1), the chiral sense of the helical conformation of the dipyrrylmethene chromophore is reversed on lowering the temperature, whereas in chloroform, reversal does not occur.

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GRAY CH, JONES PM, KLYNE W, NICHOLSON DC. Optical activity of stercobilin and d-urobilin. Nature. 1959 Jul 4;184:41–42. [PubMed] [Google Scholar]
MOSCOWITZ A, KRUEGER WC, KAY IT, SKEWES G, BRUCKENSTEIN S. ON THE ORIGIN OF THE OPTICAL ACTIVITY IN THE UROBILINS. Proc Natl Acad Sci U S A. 1964 Nov;52:1190–1194.[PMC free article] [PubMed] [Google Scholar]
Moscowitz A, Wellman KM, Djerassi C. SOME EFFECTS OF SOLVATION UPON OPTICALLY ACTIVE MOLECULES. Proc Natl Acad Sci U S A. 1963 Nov;50(5):799–804.[PMC free article] [PubMed] [Google Scholar]

^§DEPARTMENT OF CHEMISTRY OF THE UNIVERSITY OF CALIFORNIA, LOS ANGELES, CALIF. 90024

^{Department of Nuclear Medicine, UCLA.}

^{Chemistry Department, University of Minnesota, Minneapolis.}

^{Supported by the National Science Foundation (GP-9533 and GB-5578X) and the National Institutes of Health, U.S. Public Health Service (AM-11193 and AM-10539).}

^{Contribution no. 2703.}

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Abstract

Measurements of the temperature dependence of the circular dichroism spectra of l-stercobilin and d-urobilin show that the conformations of these optically-active urobilinoids change with temperature between 163 and 297°K. These conformational changes depend critically on the hydrogen bonding characteristics of the solvent. Thus, in methanol-glycerol (9:1), the chiral sense of the helical conformation of the dipyrrylmethene chromophore is reversed on lowering the temperature, whereas in chloroform, reversal does not occur.

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