Accurate Detection Of Multiple Components In Complex Systems

Accurate quantitative analysis of complex real samples plays an indispensable role in environmental monitoring,process control,and disease diagnosis.As a powerful method for situ real-time analysis,NMR technology can not only be used to analyze the precise molecular structure of compounds but also capable of tracking the molecular interactions and dynamic changes.However,in the analysis of complex real samples,it is often difficult to interpret the analytical results due to the overlap of NMR signals from different compounds,which affects the accuracy of quantitative analysis.At the same time,the low sensitivity of NMR technology limits its application in the analysis of analytes of low concentration.The combination of heteronuclear NMR technology and chemical sensing is an effective means to overcome these limitations.Among them,¹⁹F NMR has the advantages of high sensitivity and low background signals.Since naturally occurring organic fluorinated compounds are very rare,the ¹⁹F NMR-based detection method avoids the interferences from background signals.By introducing multiple magnetically equivalent fluorine atoms into the probe,the detection sensitivity of the probe can be significantly improved.The chromatogram-like detection signals can be produced when analytes bind with the ¹⁹F-labeled NMR probe in a reversible manner.Under these circumstances,the produced ¹⁹F NMR signals of distinct chemical shifts precisely relate to each individual analyte such that the accurate component information of the sample can be obtained without separation.These excellent detection characteristics make this method have great application potential in the rapid in situ detection of complex real samples.However,when the sample composition to be tested is extremely complex,the ¹⁹F signals of different analytes can still overlap,which to some extent limits the number of analytes that can be simultaneously differentiated.In this dissertation,the influence of ¹⁹F-labeled probe structure and detection medium on the resolution of NMR fluorine spectroscopy was systematically explored.Under optimized test conditions,more than 20 different bioactive molecules were detected simultaneously,and the resolution was similar to that obtained with liquid chromatography.The main research content is divided into the following two parts:1.Investigation of the influence of substitution effect on the resolving ability of ¹⁹F NMR probe.We view the fluorinated palladium pincer complex as an ideal scaffold to introduce diverse substituents adjacent to fluorinated atoms.The manipulation of the polarizability of fluorine atoms can be achieved by changing the substituent adjacent to fluorine atoms,which would influence the width of the ¹⁹F NMR detection window.Moreover,the steric hindrance of the substituents will affect the free rotation of the fluorine-containing sidewall of the probe,thereby affecting the resolving ability of the probe.It is found that even the remote substituents will have a profound impact on the detection results.These findings provide important guidance for further rational design and optimization of probes.2.Investigation of the influence of solvent effect on the resolving ability of ¹⁹F NMR probes.We select eight common solvents as detection media and four structurally similar biogenic amines as model analytes to explore the influence of solvents on the ¹⁹F NMR-based detection.It is found that when using more polar solvents,the ability to distinguish the four types of biogenic amines was reduced,whereas the use of less polar solvents could achieve better resolution.Aromatic hydrocarbon solvents have excellent shielding capabilities,which can further extend the width of the ¹⁹F NMR detection window such that the detection method exhibits excellent resolving power.We have also systematically studied the detection in binary mixed solvents,which provided valuable guidance for the selection of detection media.