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Open AccessArticle

Intramolecular Hydrogen Bond in Biologically Active o-Carbonyl Hydroquinones

1
Laboratorio de Síntesis Asimétrica, Instituto de Química de los Recursos Naturales, Universidad de Talca, Talca, Casilla 747, Chile
2
Departamento de Química, Facultad de Ciencias, Universidad de Chile, Santiago, Casilla 653, Chile
3
Departamento de Química Orgánica y Fisicoquímica, Facultad de Ciencias Químicas Y Farmacéuticas, Universidad de Chile, Santiago, Casilla 233, Chile
*
Authors to whom correspondence should be addressed.
Molecules 2014, 19(7), 9354-9368; https://doi.org/10.3390/molecules19079354
Received: 9 May 2014 / Revised: 18 June 2014 / Accepted: 27 June 2014 / Published: 3 July 2014
(This article belongs to the Special Issue Intramolecular Hydrogen Bonding)
Intramolecular hydrogen bonds (IHBs) play a central role in the molecular structure, chemical reactivity and interactions of biologically active molecules. Here, we study the IHBs of seven related o-carbonyl hydroquinones and one structurally-related aromatic lactone, some of which have shown anticancer and antioxidant activity. Experimental NMR data were correlated with theoretical calculations at the DFT and ab initio levels. Natural bond orbital (NBO) and molecular electrostatic potential (MEP) calculations were used to study the electronic characteristics of these IHB. As expected, our results show that NBO calculations are better than MEP to describe the strength of the IHBs. NBO energies (∆Eij(2)) show that the main contributions to energy stabilization correspond to LPàσ* interactions for IHBs, O1O2-H2 and the delocalization LPàπ* for O2-C2 = Cα(β). For the O1O2-H2 interaction, the values of ∆Eij(2) can be attributed to the difference in the overlap ability between orbitals i and j (Fij), instead of the energy difference between them. The large energy for the LP O2àπ* C2 = Cα(β) interaction in the compounds 9-Hydroxy-5-oxo-4,8, 8-trimethyl-l,9(8H)-anthracenecarbolactone (VIII) and 9,10-dihydroxy-4,4-dimethylanthracen-1(4H)-one (VII) (55.49 and 60.70 kcal/mol, respectively) when compared with the remaining molecules (all less than 50 kcal/mol), suggests that the IHBs in VIII and VII are strongly resonance assisted. View Full-Text
Keywords: hydroquinone; hydrogen bond; DFT; molecular electrostatic potential; natural bond orbital hydroquinone; hydrogen bond; DFT; molecular electrostatic potential; natural bond orbital
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Martínez-Cifuentes, M.; Weiss-López, B.E.; Santos, L.S.; Araya-Maturana, R. Intramolecular Hydrogen Bond in Biologically Active o-Carbonyl Hydroquinones. Molecules 2014, 19, 9354-9368.

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