Improvements in the Two‐Dimensional Nuclear Magnetic Resonance Spectroscopy of Humic Substances

Abstract

Understanding pollutant sorption, bioremediation of these pollutants, and their interactions with humic substances requires knowledge of molecular-level processes. New developments with nuclear magnetic resonance (NMR) experiments and labeled compounds have improved the overall understanding of these mechanisms. The advancements made with two-dimensional NMR show great promise, as structural information and hydrogen-carbon bond connectivity can be discerned. This communication presents the application of improved two-dimensional NMR methods, the double quantum filtered (DQF) correlation spectroscopy (COSY) and echo/anti-echo heteronuclear single quantum coherence (HSQC) experiments, for use in structural studies of humic substances. Both experiments were found to produce significant improvements over the conventional COSY and heteronuclear multiple quantum coherence (HMQC) experiments that have been previously employed in similar studies. The more sensitive echo/anti-echo HSQC experiment produced more cross-peaks with higher resolution when compared with the HMQC spectra. The DQF-COSY significantly suppressed the diagonal signals and allowed numerous signals previously hidden in the standard COSY experiment to be observed. These improvements will aid current characterization strategies of humic substances from soils, sediments, and water and their subsequent reactions with pollutants and microorganisms.

A Comprehensive Liquid-State Heteronuclear and Multidimensional NMR Study of Laurentian Fulvic Acid

“…Although multidimensional NMR has long been used, particularly in the field of structural biology, it was not until 1989 that it was first applied to humic materials by Buddrus et al (14). This pioneering work showed the great promise of 2D NMR in the study of humic materials; however, only recently has there been a concerted effort to study humic materials via multidimensional NMR (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32). To date the use of 2D solid-state techniques in the study of humic materials has yielded limited data due to broad peaks (12,25).…”

“…To date the use of 2D solid-state techniques in the study of humic materials has yielded limited data due to broad peaks (12,25). On the other hand, solution-state multidimensional NMR is beginning to emerge as a highly powerful tool in the study of humic materials (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(26)(27)(28)(29)(30)(31)(32). A large number of these studies have used only proton COSY, TOCSY, NOESY, and/ or DOSY spectra (18,19,23,27,28,31), while others used a combination of COSY and/or TOCSY and HSQC and/or HMQC spectra (15,20,22,24,30,32) to obtain both proton and protonated carbon information.…”

Comparative Analysis of Chemical and Microbial Profiles in Estuarine Sediments Sampled from Kanto and Tohoku Regions in Japan

“…The sediment organic matter samples were isolated from 10 g of surface sediments (samples were combined by site and date) by extraction using 0.1 M NaOH; they were subsequently filtered through 0.22-µm filters and subjected to cation exchange to remove the Na + . Thereafter, they were freeze-dried as described previously 1 . The extracted samples (60 mg) were dissolved in DMSO-d 6 solvent (600 µL) and transferred to a 5-mm NMR tube for analysis 2 .…”

The exposome paradigm to predict environmental health in terms of systemic homeostasis and resource balance based on NMR data science

“…The organic matter that accumulates in estuarine environments and provides habitats for various microorganisms can be analysed by using NMR techniques such as HSQC spectroscopy. 248 Dissolved organic matter in water bodies has been extensively investigated by NMR-based approaches. For example, DOM in estuarine environments has been evaluated by 2D correlation spectroscopy using 13 C NMR and FT-IR spectra, 249 solid-and multidimensional solution-state NMR have determined the chemical composition of river DOM, 250 NMR coupled with isotope analysis has revealed refractory proteinaceous compounds in lake DOM, 251 while DOM in a shallow aquifer has been characterized by coupling 13 C NMR spectroscopy with elemental analysis and ultraviolet-visible absorbance spectroscopy.…”