Hui Ma,Dan Luo,Qi Zhao,Rui Liu,Zhenzhou Zhang,Xianglin Hou,Xiaohuan Sun,Yingxiong Wang
Diffusion-ordered spectroscopy (DOSY) is a powerful and efficient technique for the analysis of complex mixtures, relying on their differential in self-diffusion coefficient. However, DOSY is often struggled to separate signals pertaining to isomeric species, especially positional isomers. Here, for the first time, we describe the novel design of 18-crown ether-6 (18C6) and 18C6/K + complex as matrixes to discriminate and identify positional isomeric mixtures of phenylenediamine, nitroaniline, phthalic acid, dimethoxybenzoic acid, aminophthalic acid and even amino acids using 1 H DOSY spectrum. The superior performance of 18C6 and 18C6/K + complex as matrix depends on that they can interact with different components with varying binding energy as demonstrated by MMMF calculations and the DFT calculation. The methodology presented here is simple yet efficient. Moreover, the crown ether and crown ether/K + complex provide the dual mode discrimination for both amino and carboxylic substituted positional isomers.
When diffusion coefficients of different components in a mixture are similar, NMR spectra of pure individual components are difficult to be obtained via a diffusion-ordered spectroscopy (DOSY) experiment. Two-dimensional correlation spectroscopy (2D-COS) is used to analyze the data from the DOSY experiment. Through the properties of the systematic absence of cross-peak (SACP) in the 2D asynchronous spectra, spectra of pure components can be obtained even if their diffusion coefficients are similar. However, fluctuations in peak-position and peak-width are often unavoidable in NMR spectra, which makes SACPs unrecognizable. To address the problem, a 2D quotient spectrum is used to identify the masked SACPs. However, undesirable interference peaks due to the fluctuations in peak-position and peak-width are still present when we extract a spectrum of a component by slicing the 2D asynchronous spectrum across the SACP. A genetic algorithm (GA) is used to select a suitable subset of spectra where the diversities of peak-position and peak-width are significantly reduced. Then, we used the selected spectra to construct a refined 2D asynchronous spectrum so that the spectra of pure components with significant attenuated interference can be obtained. The above approach has been proven to be effective on a model system and a real-world example, demonstrating that 2D-COS possesses a bright perspective in the analysis of the bilinear data from DOSY experiments.
Hui Ma,Christian M. Pedersen,Qi Zhao,Shiyu Jia,Bin Yuan,Xianglin Hou,Yingxiong Wang
Coal chemical wastewater (CCW) with the features of high toxicity and poor biodegradability is a big issue in environmental remediation, posing a great threat to aquatic ecosystems and to human beings. Such complex molecular mixtures are notoriously difficult to characterize without initial physical separation. Herein, we present the 3D diffusion ordered spectroscopy (DOSY) analysis for CCW using DOSY-COSY and DOSY-HSQC methods, the advantages of this strategy have been demonstrated in the analysis of mixtures of aliphatic oxygenates and aromatic compounds, before being implemented on a genuine CCW sample in this study. The results showed that 3D DOSY is a robust and reliable tool for providing superior resolution and virtual separation of complex pollutants, and can be used as a general approach for structural elucidation.
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