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

Abstract

The Boreal forest fulvic acid known as Laurentian fulvic acid (LFA) has been interrogated by state of the art heteronuclear and 2D high resolution NMR techniques. It is shown that one can obtain very highly resolved and informative spectra of a traditionally fractionated material. It was possible to observe a proton coupled system of up to seven bonds in the TOCSY spectrum and 329 peaks in the 1H,13C-HSQC spectrum. It is found that the majority of the nitrogen in this sample is in the form of ammonium cations. From the combination of inverse-gated decoupling, APT, and INEPT 13C spectra of LFA it can be concluded that while the aromatic moieties of LFA are highly unfunctionalized, the carbohydrate moieties are highly functionalized. Proton coupled networks are observed in the TOCSY spectrum between and within the aliphatic, functionalized aliphatic, and heteroatom substituted regions and, to a lesser extent, also between the amine/aromatic and heteroatom substituted regions. The HMBC spectrum confirms that both the aliphatic and heteroatom moieties are highly functionalized with carboxylic and alcoholic functional groups, while the aromatic moieties are very sparsely functionalized with phenolic and carboxylic functionalities. Additionally, specific model molecular structures have been identified which are consistent with experimental evidence and are in full agreement with our previously derived meso-model based on solid-state 13C NMR data. Finally, some of the shortcomings of 2D liquid-state NMR for the characterization of humic materials are addressed.

Comparison of Laurentian Fulvic Acid luminescence with that of the hydroquinone/quinone model system: Evidence from low temperature fluorescence studies and EPR spectroscopy

“…A ramp crosspolarization magic-angle spinning (CP-MAS) 13 C NMR spectrum (Cook et al, 1996) has permitted assignment of the functional group distribution. This is 22% aliphatic C, 18 % "carbohydrate" C, 12% aromatic C, 2 % phenolic C, 34% carboxylate and quinonoid C, and 8% ketonic C. 14 N NMR shows that the majority of nitrogen is present as NH 4 + and 31 P NMR shows that a small quantity of phosphate is present along with traces of organophosphorous compounds (Cook et al, 2003). LFA has a number average molecular mass of approx.…”

“…The advantage of using this well characterized fulvic acid is that physical and chemical characterization has been carried out by various research groups and many physical and chemical properties of LFA are well established (Wang et al, 1990;Cook et al, 1996). Highly detailed 1-D and 2-D NMR spectra are now available (Cook et al, 2003). Especially, work on the photophysics of Laurentian and the closely related Mossy Point fulvic acids has been reported elsewhere (Bruccoleri et al, 1993) .…”

A stochastic model for the synthesis and degradation of natural organic matter part II: molecular property distributions

“…Unraveling the complex structures within the NOM assemblage is a challenging analytical problem (Schmitt-Koplin 1998;Cook et al 2003;Hatcher et al 2001). Yet, NOM has attracted attention in spite of its complexity, as it influences a variety of environmental processes, including pollutant solubilization and transport, microbial respiration and growth, light penetration in surface waters, and mineral dissolution (Aiken et al 1985;Chiou et al 1986;Findlay and Sinsabaugh 2003;Zepp et al 1998;Chorover and Amistadi 2001;NamjesnikDejanovic and Maurice 2001).…”

Nuclear Magnetic Resonance Analysis of Natural Organic Matter

“…Similarly, improvements in NMR hardware, stability, and sensitivity have kept pace in both solid -state and solution -state NMR. Thus, it is not surprising that in the last decade the application of multidimensional NMR has grown exponentially (Simpson et al, 1997(Simpson et al, , 2001a(Simpson et al, ,c, 2002a(Simpson et al, , 2003aHaiber et al, 1999Haiber et al, , 2001aFan et al, 2000 ;Kingery et al, 2000 ;Knicker, 2000a ;Simpson, 2001 ;Hertkorn et al, 2002bHertkorn et al, , 2006Cook et al, 2003 ;Kaiser et al, 2003 ;Kim et al, 2003 ;Cardoza et al, 2004 ;Mao and Schmidt -Rohr, 2006 ). In 1989, the fi rst applications of multidimensional NMR were applied to humic substances (Buddrus et al, 1989 ).…”

“…In the same year, Hertkorn utilized 2D NMR to understand the utilization of aquatic humics by microorganisms (Hertkorn et al, 2002a ) and studied peat humic and fulvic acids (Hertkorn et al, 2002b ). The year 2003 saw the introduction of 3D NMR to study NOM (Simpson et al, 2003a ) and studies of a Laurentian fulvic acid (Cook et al, 2003 ). Online hyphenated NMR was introduced in the form of HPLC -NMR and HPLC -SPE -NMR in 2004 (Simpson et al, 2004b ), as well as the use of 2D spectral simulations (Simpson et al, 2004a ), and a review of the fi eld (Cook, 2004 ).…”