Huizhen Li

Orthogonal Sample Design Scheme for Two-Dimensional Synchronous Spectroscopy and Its Application in Probing Intermolecular Interactions

This paper introduces a new approach to probing intermolecular interactions based on a framework of two-dimensional (2D) synchronous spectroscopy. Mathematical analysis performed on 2D synchronous spectra using variable concentration as an external perturbation shows that the cross-peaks are composed of two parts. The first part reflects intermolecular interactions that manifest in the form of deviation from the Beer–Lambert law. The second part is related simply to the concentration variations of the solutes and is responsible for the generation of interfering cross-peaks not related to the intermolecular interactions in the system. It is the second part that prevents the reliable identification of intermolecular interactions. We propose a way of selecting the concentrations of solutes so that the resultant dynamic concentration vectors of different solutes become orthogonal to one another. Therefore, the contribution of the second part to the cross-peaks can be effectively removed by the dot product of orthogonal vectors. Our new approach has been tested on a simulated chemical system and a real chemical system. The results demonstrate that interfering cross-peaks can be successfully removed from a 2D synchronous spectrum so that the cross-peaks can be used as a reliable tool to characterize or probe intermolecular interactions.

Double Orthogonal Sample Design Scheme and Corresponding Basic Patterns in Two-Dimensional Correlation Spectra for Probing Subtle Spectral Variations Caused by Intermolecular Interactions

This paper introduces a new approach named double orthogonal sample design scheme (DOSD) to probe intermolecular interactions based on a framework of two-dimensional (2D) correlated spectroscopy. In this approach, specifically designed concentration series are selected according to the mathematical analysis on orthogonal vectors to generate useful 2D correlated spectra. As a result, the interfering portion can be completely removed from both synchronous and asynchronous spectra, and complementary information concerning intermolecular interactions can be obtained from the set of 2D spectra. A model system, where intermolecular interactions occur between two solutes in a solution, is used to investigate the behavior of 2D correlated spectra generated by using the DOSD approach. Simulation results demonstrate that the resultant spectral patterns can reflect subtle spectral variation in bandwidths, peak positions, and absorptivities brought about by intermolecular interaction, which are hardly visualized in conventional 1D spectra because of the severe band-overlapping problem. The ability to reveal a subtle variation in a characteristic peak in detail by using the DOSD approach provides a new opportunity to understand the nature of intermolecular interactions from a molecular structural point of view. Intermolecular interactions between iodine and benzene in CCl(4) solutions were investigated by using the proposed DOSD approach to prove the applicability of the DOSD method in real chemical systems.