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Item The binding of 4-ethylguaiacol with polyaniline-based materials in winesAutores: Marican, A.; Carrasco-Sanchez, V.; John, A.; Laurie, VF.; Santos, LS.4-ethylguaiacol (4-EG) is one of the important compounds responsible for the "Brett character" (i.e. spicy and smoky aromas) found in wines contaminated with Brettanomyces yeast. In this trial, the ability of polyaniline-based materials (PANI-EB and PANI-ES) was tested as a potential fining agent for the removal of 4-EG in wine. First, a screening study was developed in order to determine the binding capacity of 4-EG by PANI materials in 12% ethanol solution. Then, the capturing ability of PANI against 4-EG was evaluated with a solution containing gallic acid (GA), 4-methyl-catechol (4-MC), in which the concentration of the phenolic compounds were maintained as in the real wine. The results obtained showed that the retention percentage varied between 0 to 100% (4-EG), 13.81% to 72.32% (GA), and 0 to 17.39% (4-MC), depending on the interaction time and amount of the PANI used. Finally, the capturing capacity of PANI-EB and PANI-ES against 4-EG was evaluated in a real wine sample containing originally 3.10 +/- 0.13 mg L-1 of 4-EG and 2.55 +/- 0.10 g L-1 of other total phenolic compounds. The analyses performed indicated that PANI-EB is more effective in removing 4-EG than PANI-ES, with retention percentages varying between 36 and 50%. (C) 2014 Elsevier Ltd. All rights reserved.Item Intramolecular Hydrogen Bond in Biologically Active o-Carbonyl HydroquinonesAutores: Martinez-Cifuentes, M.; Weiss-Lopez, BE.; Santos, LS.; Araya-Maturana, R.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 (Delta E-ij((2))) show that the main contributions to energy stabilization correspond to LP ->sigma* interactions for IHBs, (O1O2)-O-center dot center dot center dot-H-2 and the delocalization LP ->pi* for O-2-C-2 = C-alpha(beta). For the (O1O2)-O-center dot center dot center dot-H-2 interaction, the values of Delta E-ij((2)) can be attributed to the difference in the overlap ability between orbitals i and j (F-ij), instead of the energy difference between them. The large energy for the LP O-2 ->pi* C-2 = C-alpha(beta) interaction in the compounds 9-Hydroxy-5-oxo-4,8, 8-trimethyl-1, 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.
