Cooperative interaction of protonated hexamethylenetetramine with a hexaarylbenzene-based receptor: Experimental and theoretical study
2012
Makrlík, Emanuel | Toman, Petr | Vaňura, Petr | Rathore, Rajendra
From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium HL⁺(aq)+1·Cs⁺(nb)⇄1·HL⁺(nb)⁺Cs⁺(aq) taking place in the two-phase water–nitrobenzene system (HL⁺ =protonated hexamethylenetetramine, 1=hexaarylbenzene-based receptor; aq=aqueous phase, nb=nitrobenzene phase) was evaluated as logKₑₓ (HL⁺, 1⋅Cs⁺)=0.5±0.1. Further, the stability constant of the 1⋅HL⁺ complex in nitrobenzene saturated with water was calculated for a temperature of 25°C as logβₙb(1⋅HL⁺)=5.8±0.2. Finally, by using quantum mechanical DFT calculations, the most probable structures A and B of the 1⋅HL⁺ complex species, which are obviously in a dynamic equilibrium, were indicated. In both of these structures of the resulting complex 1⋅HL⁺ having C₃ symmetry, the cation HL⁺ synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene bottom of the parent receptor 1 via cation–π interaction.
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