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Structures in solid state and solution of dimethoxy curcuminoids: regioselective bromination and chlorination
Petra Galer1, Amalija Golobič, Jože Koller
1Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000, Ljubljana, Slovenia. boris.sket@fkkt.uni-lj.si.
Chemistry Central Journal
|June 27, 2013
Summary
The position of methoxy groups influences dimethoxy curcuminoid structures in solids, while solution states show fast tautomeric equilibrium. Halogenation at the alpha-position maintains the cis keto-enol form.
Area of Science:
- Organic Chemistry
- Solid-State Chemistry
- Computational Chemistry
Background:
- Curcumin and its derivatives exhibit diverse structures in solid and solution states.
- Solid-state curcumin structures feature symmetrical hydrogen bonds in the enolone fragment.
- Solution structures are influenced by solvent interactions, stabilizing specific tautomers.
Purpose of the Study:
- To investigate how methoxy group positions affect dimethoxy curcuminoid molecular conformation.
- To determine the impact of alpha-position halogenation on molecular structure.
- To explore the solid-state and solution behaviors of these compounds.
Main Methods:
- Synthesis of six dimethoxy curcuminoid isomers.
- X-ray single crystallography and solid-state NMR (1H MAS, 13C CPMAS) for structural analysis.
- Theoretical calculations (HOMO/LUMO energies) and regioselective halogenation (bromination/chlorination).
Main Results:
- Solid-state conformations of dimethoxy curcuminoids are dependent on methoxy group placement.
- Polymorphism observed in crystalline 3,4-diOCH3 and 3,5-diOCH3 derivatives.
- Halogenated compounds predominantly exist in the cis keto-enol form in solution.
Conclusions:
- Methoxy group position significantly dictates solid-state structures and influences polymorphism.
- Dimethoxy curcuminoids exist as rapidly equilibrating tautomers in solution.
- Alpha-halogenation does not alter the preferred cis keto-enol conformation observed in parent compounds.
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