Molecular motions of β-carotene and a carotenoporphyrin dyad in solution. A carbon-13 NMR spin-lattice relaxation time study

S. Li, S. L. Swindle, S. K. Smith, R. A. Nieman, Ana L Moore, Thomas A Moore, John Devens Gust

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Analysis of 13C NMR spin-lattice relaxation times (T1) yields information concerning both overall tumbling of molecules in solution and internal rotations about single bonds. Relaxation time and nuclear Overhauser effect data have been obtained for B-carotene and two related molecules, squalane and squalene, for zinc meso-tetraphenylporphyrin, and for a dyad consisting of a porphyrin covalently linked to a carotenoid polyene through a trimethylene bridge. Squalane and squalene, which lack conjugated double bonds, behaves essentially as limp string, with internal rotations at least as rapid as overall isotropic tumbling motions In contrast, B-carotene reorients as a rigid rod, with internal motions which are too slow to affect relaxation times. Modeling it as an anisotropic rotor yields a rotational diffusion coefficient for motion about the major axis which is 14 times larger than that for rotation about axes perpendicular to that axis. The porphyrin reorients more nearly isotropically and features internal librational motions about the single bonds to the phenyl groups. The relaxation time data for the carotenoporphyrin are consistent with internal motions similar to those of a medieval military flail, consisting of a rigid, rod-like carotenoid and ball-like porphyrin linked by a flexible chain of single bonds. Intemal reorientation about this linkage is approximately 100 times faster than triplet-triplet energy transfer from the porphyrin to the carotenoid, which is mediated by such motions.

Original languageEnglish
Pages (from-to)3371-3378
Number of pages8
JournalJournal of Physical Chemistry
Volume99
Issue number10
Publication statusPublished - Mar 9 1995

Fingerprint

carotene
carbon 13
Time and motion study
Spin-lattice relaxation
Carotenoids
porphyrins
spin-lattice relaxation
Relaxation time
carotenoids
Porphyrins
Carbon
relaxation time
Nuclear magnetic resonance
nuclear magnetic resonance
Squalene
Barreling
rods
tumbling motion
librational motion
Overhauser effect

ASJC Scopus subject areas

  • Engineering(all)
  • Physical and Theoretical Chemistry

Cite this

Molecular motions of β-carotene and a carotenoporphyrin dyad in solution. A carbon-13 NMR spin-lattice relaxation time study. / Li, S.; Swindle, S. L.; Smith, S. K.; Nieman, R. A.; Moore, Ana L; Moore, Thomas A; Gust, John Devens.

In: Journal of Physical Chemistry, Vol. 99, No. 10, 09.03.1995, p. 3371-3378.

Research output: Contribution to journalArticle

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