Interaction of protonated tyramine with a hexaarylbenzene-based receptor: Extraction and DFT study

From extraction experiments and gamma-activity measurements, the extraction constant corresponding to the equilibrium HL+(aq) + 1.Cs+(b) double left right arrow 1.HL+(nb) + Cs+(aq) taking place in the two-phase water-nitrobenzene system (HL+ = protonated tyramine, 1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K-ex (HL+, 1.Cs+) = -0.3 +/- 0.1. Further, the stability constant of the 1.HL+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 degrees C as log beta(nb) (1.HL+) = 4.7 +/- 0.2. Finally, by using quantum mechanical OFT calculations, the most probable structure of the 1.HL+ complex species was predicted. In the resulting "asymmetrical" cationic complex 1.HL+, the cation HL+ synergistically interacts with the polar ethereal oxygen fence by means of the corresponding three H-bonds and with the central hydrophobic benzene bottom of the parent receptor I via cation - pi interaction. (C) 2013 Elsevier B.V. All rights reserved.