Kaiyu Wang

Two-Dimensional J -Resolved NMR Analyses of Fish and Its Products via Spatially Encoded Intermolecular Double-Quantum Coherences

Nuclear magnetic resonance (NMR) spectroscopy provides a powerful tool for food analyses due to its high-throughput information related to component analyses and its non-invasive property without altering detected samples. Current liquid NMR approaches, however, are subject to the influence of field inhomogeneity in direct measurements of biological foods, generally resorting to techniques of tissue extractions or magic-angle spin to eliminate the inhomogeneity. Therefore, we propose an NMR approach based on intermolecular double-quantum coherences (iDQCs) and spatial encoding technique to fast recover high-resolution two-dimensional (2D) J-resolved spectra in inhomogeneous fields. Inheriting from the immunity to field inhomogeneity of iDQCs and the enhancement in acquisition efficiency of the spatial encoding technique, the proposed method can resist the field inhomogeneity in biological foods without superfluous pretreatments and time-consuming shimming procedures, and yield satisfactory 2D J-resolved information for analyses within minutes. Fish and its products, which are closely related to human daily life, capture extensive attentions with the rapid development of the aquaculture. At first, experiments on cod liver oils are implemented in a purposely deshimmed magnetic field to demonstrate the feasibility of the proposed approach. Then, caviars and an intact fish are tested to further show the applicability of the proposed approach for direct measurements on intact biological food samples. Herein, the proposed method may constitute an effective technique in analyzing fish and its products.

A heteronuclear intermolecular single-quantum coherence scheme for high-resolution 2D J-resolved 1H NMR spectra in inhomogeneous magnetic fields

ABSTRACT Based on heteronuclear intermolecular single-quantum coherences between proton (1H) and quadrupolar nuclei (i.e. deuterium 2H), a three-dimensional nuclear magnetic resonance (NMR) pulse sequence is proposed for recovering high-resolution two-dimensional J-resolved NMR spectra from samples mixed with a deuterated solvent in the presence of large magnetic field inhomogeneities. Benefitting from excitation of spins via two different radio frequency (RF) transmit channels, this sequence is suitable for applications in randomly large inhomogeneous fields and the solvent suppression generally required in homonuclear intermolecular multiple-quantum coherence approaches is no longer necessary. Systematic theoretical analyses are given based on the distant dipolar field treatment. Experiment on a sample of corn oil in deuterated acetone and ethyl 3-bromopropionate and acetone dissolved in DMSO-d6 in a deshimmed field with severe inhomogeneous broadening is performed to show the feasibility and applicability of this sequence.

Spin-echo based diagonal peak suppression in solid-state MAS NMR homonuclear chemical shift correlation spectra

The feasibility of using the spin-echo based diagonal peak suppression method in solid-state MAS NMR homonuclear chemical shift correlation experiments is demonstrated. A complete phase cycling is designed in such a way that in the indirect dimension only the spin diffused signals are evolved, while all signals not involved in polarization transfer are refocused for cancellation. A data processing procedure is further introduced to reconstruct this acquired spectrum into a conventional two-dimensional homonuclear chemical shift correlation spectrum. A uniformly 13C, 15N labeled Fmoc-valine sample and the transmembrane domain of a human protein, LR11 (sorLA), in native Escherichia coli membranes have been used to illustrate the capability of the proposed method in comparison with standard 13C-13C chemical shift correlation experiments.

High-resolution heteronuclear correlation spectroscopy based on spatial encoding and coherence transfer in inhomogeneous fields

Two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy has been proven to be a powerful technique for chemical, biological, and medical studies. Heteronuclear single quantum correlation (HSQC) and heteronuclear multiple bond correlation (HMBC) are two frequently used 2D NMR methods. In combination with spatially encoded techniques, a heteronuclear 2D NMR spectrum can be acquired in several seconds and may be applied to monitoring chemical reactions. However, it is difficult to obtain high-resolution NMR spectra in inhomogeneous fields. Inspired by the idea of tracing the difference of precession frequencies between two different spins to yield high-resolution spectra, we propose a method with correlation acquisition option and J-resolved-like acquisition option to ultrafast obtain high-resolution HSQC/HMBC spectra and heteronuclear J-resolved-like spectra in inhomogeneous fields.