Direct Observation of Molecular Recognition Mediated by Triple Hydrogen Bonds at a Water/Oil Interface: Time-Resolved Total Internal Reflection Fluorometry Study

Molecular recognition mediated by hydrogen-bonding interactions at a water/CCl4 interface was investigated directly by means of time-resolved total internal reflection (TIR) fluorescence spectroscopy. The TIR fluorescence decay profile of riboflavin (RF) in the absence of a guest in the CCl4 phase was fitted satisfactorily by a single-exponential function. In the presence of N,N-dioctadecyl-[1,3,5]triazine-2,4,6-triamine (DTT) as a guest in the CCl4 phase, on the other hand, the fluorescence decay profiles were best fitted by double-exponential functions with the relevant amplitude (Ai) being varied with the concentration of DTT. Furthermore, the rotational reorientation time of RF at the interface determined by fluorescence dynamic anisotropy was 210 ps in the absence of DTT, while fast (160-220 ps) and slow (670-750 ps) rotational reorientation times were observed in the presence of DTT. This slow rotational reorientation time was shown to ascribe to that of the RF-DDT complex formed at the water/CCl4 interface. These results indicate that molecular recognition mediated by complementary hydrogen bonding takes place effectively at the water/CCl4 interface, which was observed directly by both fluorescence dynamics and fluorescence dynamic anisotropy measurements under the TIR conditions.