An ESR study of intrachannel mobility in DOCA clathrates. Effects due to photochemical reactivity between guest and host

Eva Meirovitch

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

ESR spectra of deoxycholic acid channel type inclusion compounds doped with 2,2,5,5-tetramethyl-3-carbamidopyrrolinyl-1-oxyl (Tempyo) and 2,2,6,6-tetramethylpiperidinyl-1-oxyl-4-ol (Tanol) free radicals were recorded as a function of temperature, radical concentration, and photochemically triggering UV irradiation. At room temperature the spin probes are immobile and isotropically dispersed within the channels. Onset of isotropic molecular reorientation is observed upon increasing the temperature to 50-70°C and nearly complete motional averaging is achieved between 120 and 140°C with activation energies of the order of 6-8 kcal/mol. For 5-30% molar enrichment of the guest with the paramagnetic dopant, second-order rate constants for bimolecular encounters of 1.65 × 109 M-1 s-1 at 130°C and a related activation energy of 5 kcal/mol are measured from concentration-dependent spin exchange effects on the ESR line shape. Clustering is observed for radical concentrations relative to the guest of the order of 0.2 M. With acetophenone as guest we find that, following the photochemical reaction between host and guest, the rate for rotational reorientation and the rate constant for bimolecular encounters are slowed down considerably.

Original languageEnglish
Pages (from-to)5237-5243
Number of pages7
JournalJournal of Physical Chemistry
Volume86
Issue number26
DOIs
StatePublished - 1982
Externally publishedYes

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