Studies On Thermodynamics Of Supramolecular Chemistry Via ESI-MS

Professor J. M. Lehn had proposed the concept of supramolecular chemistry in 1978 firstly. He pointed out that the supramolecular chemistry is the studies of the complex with specific functions formed by two or more chemical species via weak molecule interactions instead of chemical bond. From then on, supramolecular chemistry developed rapidly as a new interdisciplinary, especially its special properties in molecular self-assembly and molecular. Electrospray ionization(ESI), as a soft ionization technology, could make non-covalent complexes ionization without destroying the non-covalent bonds. The feature made it possible that the ESI-MS technology could be employed in the studies of supramolecular chemistry. In fact, it has already become an important method in the field with rapidly, sensitively, intuitively.This paper was the studies on thermodynamics of several reaction systems of host-guest via ESI-MS:1. The interactions of cucurbit[n]uril(CB [n], n = 7, 8) with several carbazole derivatives were studied by ESI-MS respectively. Firstly, it was founded that the reaction time didn’t affect the ion counts of the complex at room temperature, so the influence of reaction time on the reaction could be ignored. Then, the conditions of chromatography and mass spectrometry were optimized respectively by adjusting the ratio of the mobile phase, the temperature of the drying gas and the voltage of the fragmentor. After that, full MS scans of the mixtures of the host and guest molecules were made at the optimum analytical conditions and the ion counts of the complexes and the guest molecules were counted. Linear equations were plotted on the 1/△Ir to 1/CH and the correlation coefficients were all not less than 0.9. Finally, the binding constants of the host-guest complexes were calculated by the linear intercept and slope.2. The interactions of CB [7], CB [8] with two coumarin derivatives were also studied. MS/MS characteristicses of the guest molecules and the complexes were carried out. The inclusion models of the complexes could be drawn by elaborating the fragmentation pathways. Then, the binding constants of the host-guest complexes were also calculated by the same method above-mentioned. And it were found that the binding constants of XDS-3CMV and XDS-6CMV with CB [7] were greater than that of CB [8]. It is possible that the size of guest molecules were small which could match better with smaller cavity of CB [7] and the complexes was more stabilization.3. The interactions of β-cyclodextrin(β-CD) with racemic betaxolol and levobetaxolol were studied respectively. The MS spectra verified that β-CD could form 1:1 complexes with betaxolol and levobetaxolol. MS/MS characteristicses of the complexes showed that no matter how much voltage was applied to the collision of the complexes, the fragmention were always the m/z 308.2([Betaxolol+H]+, [Levobetaxolol+H]+), which offered a method to protect betaxolol. The binding constants of the host-guest complexes were calculated and found that the constants of the two systems were difference. The reason was that the cavity of β-CD was a chiral environment which could match better with dextrobetaxolol, so that the complex was more stabilization. The discoveries were important for the chiral recognition of the host-guest interactions. And also, it would be beneficial to the studies of the controlled release formulation of betaxolol and levobetaxolol.