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Novel Method of Constructing Two-Dimensional Correlation Spectroscopy without Subtracting a Reference Spectrum
journal contribution
posted on 2017-12-27, 00:00 authored by Anqi He, Yiwei Zeng, Xiaoyan Kang, Shigeaki Morita, Yizhuang Xu, Isao Noda, Yukihiro Ozaki, Jinguang WuIn
this study, we propose a new approach to generate two-dimension
spectra to enhance the intensity of cross peaks relevant to intermolecular
interaction. We investigate intermolecular interaction between two
solutes (denoted as P and Q, where P has a characteristic peak at XP) dissolved in the same solvent via the near
diagonal cross peaks around the coordinate (XP, XP) in a two-dimensional (2D)
asynchronous spectrum of generalized spectroscopy. Because of physical
constrains in many cases, the variation ranges of the initial concentrations
of P or Q must be kept very narrow, leading to very weak cross peak
intensities. The weak cross peaks vulnerable to noise bring about
difficulty in the investigation of subtle intermolecular interaction.
Herein, we propose a new of way constructing a 2D asynchronous spectrum
without the subtraction of the average spectrum often used as a reference
spectrum. Mathematical analysis and computer simulation demonstrate
that the near diagonal cross peaks around the coordinate (XP, XP) in the 2D
asynchronous spectrum using the new approach possess two characteristics:
(1) they can still reflect an intermolecular interaction reliably;
2) the absolute intensities of the cross peaks are significantly stronger
than those generated by the conventional method. We incorporate the
novel method with the DAOSD (double asynchronous orthogonal sample
design scheme) approach and applied the modified DAOSD approach to
study hydrogen bonding behavior in diethyl either/methanol/THF system.
The new approach made the weak cross peaks, which are not observable
in 2D asynchronous spectrum generated using conventional approach,
become observable. The appearance of the cross peak demonstrate that
When a small amount of THF is introduced into diethyl solution containing
low amount of methanol, THF breaks the methanol–diethyl ether
complex and forms methanol-THF complex via new hydrogen bond. This
process takes place in spite of the fact that the content of diethyl
ether is overwhelmingly larger than that of THF. The above result
demonstrates that the new approach described in this article is applicable
to enhance intensity of cross peaks in real chemical systems.