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The influence of protonation on molecular structure and physico-chemical properties of gossypol Schiff bases.

Authors
Type
Published Article
Journal
Organic & Biomolecular Chemistry
1477-0539
Publisher
The Royal Society of Chemistry
Publication Date
Volume
8
Issue
24
Pages
5511–5518
Identifiers
DOI: 10.1039/c0ob00288g
PMID: 20959900
Source
Medline
License
Unknown

Abstract

Protonation of gossypol Schiff bases (S1 and S2), possessing different numbers of basic N-atoms, was studied using potentiometric, spectroscopic, ESI MS and PM5 methods. Titration of S1 and S2 with HClO(4), monitored by the FT-IR and (1)H NMR, indicated that the change from the enamine-enamine into the protonated imine-imine tautomeric form occurs at different Schiff base-H(+) ratio. The FT-IR and PM5 results show that for S1 the first protonation step occurs at Schiff base moiety whereas for S2 it is realised at N-atom of the morpholine. The formation of N(+)-HO hydrogen bond between morpholine moieties within S2 contributes to high pK(a(ACN)) = 22.65.

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