The influence of protonation on molecular structure and physico-chemical properties of gossypol Schiff bases.
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.
Faculty of Chemistry, Adam Mickiewicz University, 60-780, Poznań, Grunwaldzka 6, Poland. piotrp@amu.edu.pl
Piotr
P
Przybylski
Krystian
K
Pyta
Justyna
J
Czupryniak
Barbara
B
Wicher
Maria
M
Gdaniec
Tadeusz
T
Ossowski
Bogumił
B
Brzezinski
D006072:Gossypol / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D011522:Protons; D012545:Schiff Bases / Q000737:chemistry
D011522:Protons; D012545:Schiff Bases; D006072:Gossypol