Title

ESR studies of spin distribution and cation binding in organic and biological systems

Date of Award

1987

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Luis A. Echegoyen, Committee Chair

Abstract

Part I. Bridged bis(cyclooctatetraene), COT-X-COT, showed spin delocalization over the two rings for X = CH$\sb2$. This is not observed when X = Si(CH$\sb3$)$\sb2$ or Ge(CH$\sb3$)$\sb2$ due to their strong stabilizing effect, $-0.82\sp{\rm Kcal}$/$\sb{\rm mol}$ for X = Si(CH$\sb3$)$\sb2$.Study of aryl-COTs showed for the first time a resolved splitting arising from a hydrogen in the aryl group (9-phenanthryl-COT). Puckering of the COT ring was observed in 1-anthryl-COT. Molecular orbital calculations confirmed the experimental observations.Part II. Solution ESR spectra demonstrated VO$\sp{2+}$ binding to calmodulin (CaM) and S100-like proteins. Two classes of binding sites were observed in the rigid limit spectra (frozen) for both proteins. In the case of CaM, a 4:1 (VO$\sp{2+}$/CaM) binding stoichiometry was obtained.Competition of Ca$\sp{2+}$ for the VO$\sp{2+}$ binding sites in calmodulin was investigated, and the results indicated that two of the VO$\sp{2+}$ corresponded to two of the Ca$\sp{2+}$ sites; the other two VO$\sp{2+}$ binding sites may have a higher affinity for VO$\sp{2+}$ than for Ca$\sp{2+}$ or they may correspond to Ca$\sp{2+}$-independent sites.Part III. An attempt to study electron transfer processes in bis-lariat ethers was explored.Coulometry and ESR studies confirmed that the dianionic species was a biradical. No exchange coupling was observed between the two radicals in the absence of a cation. Addition of sodium or potassium perchlorate to the dianion solution produced a drastic, but reversible, change in the ESR signal. This observation was explained as a consequence of the two radicals approaching each other due to the interaction with the complexed cation.This information prompted the study of electron transfer for the anion radical. No experimental support of such a process was observed due to decomposition of the sample under various conditions.

Keywords

Chemistry, Physical

Link to Full Text

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