Analytical approaches for 1 H NMR wide line spectra of Soil Organic Matter

1. static 1H NMR spectrum * before heating after heating larger fraction of water with higher mobility heating event Lorentzian line, water with higher mobility 30 min @ 110° C mobilizable fraction: “water molecule bridges” (WAMBs) Gaussian line, organic matter Analytical approaches for 1H NMR wide line spectra of Soil Organic Matter Alexander Jäger1, Marko Bertmer1, Gabriele E. Schaumann2 1Universität Leipzig, Institut für Experimentalphysik II, Abteilung MQF, Linnéstr. 5, 04103 Leipzig ajaeger@physik.uni-leipzig.de, bertmer@physik.uni-leipzig.de 2Universität Koblenz-Landau, Institut für Umweltwissenschaften, AG Umwelt- und Bodenchemie, Fortstr. 7, 76829 Landau schwarzj@uni-landau.de, schaumann@uni-landau.de Introduction 1H NMR Implications from humidity experiments (sapric peat) • wide line NMR is rarely used, but sensitive to mobility of protons and is a fast measurement • protons fixed in SOM structure show broad lines, protons in mobile components (e. g., water) show narrow lines since dipolar interaction is cancelled out by motion, • DEPTH pulse sequence is used to remove probe background signal (two 180° defocusing pulses): • spectra are decomposed using NMR fitting program (dmfit), calculating Gaussian / Lorentzian ratio[1] • all measurements performed at 400.15 MHz (9.4 T magnet) using solid-state NMR probe * dry matter basis 13C NMR total signal • spectra obtained with cross polarization technique under magic angle spinning (CPMAS) • average measurement time (SOM) 5-20 h • measurements at temperatures up to 100° C are possible • spectra are analyzed for chemical composition and structural conformations (phase transitions) • correlation spectroscopy (two dimensional) can be performed addressing proton-carbon connectivity and proton wide line of individual functional groups • • moisture uptake leads to characteristic adsorption isotherm (upper right), • also reflected in 1H NMR Lorentzian fraction (insert in upper right figure) • •1H Lorentzian fraction shows deviation from linear moisture dependency • • mobilizable fraction is decreasing with higher moisture content • higher general mobility with higher moisture content expressing in decreasing Lorentzian line width (right figure), water molecules in WAMBs less rigid, line width of Gaussian fraction is not affected by moisture content 1H line shapes from carbon structural components Improved, extended line fitting model applied to long term data 13C NMR CPMAS spectra 1H NMR spectra analysis assignment & line width: water 1.9 kHz carbohydrates 42 kHz poly-methylene 40 kHz sapric peat (moisture content: 7 %, dry matter basis) broad Lorentzian: aliphatic component poly-methylene Gaussian: carbohydrates + WAMBs second Lorentzian (poly-methylene) water 1.9 kHz carbohydrates 42 kHz poly-methylene 49 kHz carboxylic aromatic compounds broad Lorentzian: aliphatic component poly-methylene first Lorentzian (water molecules) water 5.9 kHz poly-methylene 19.5 kHz no Gaussian: no/small amount of carbohydrates O-alkyl carbohydrate • Lorentzian lines show individual behavior: quick return to initial value for second Lorentzian; slow re-formation for first Lorentzian water 3.6 kHz carbohydrates 44.8 kHz aliphatic compounds only one Lorentzian:  no poly-methylene Conclusions & Outlook • improved model for 1H wide line data [2] is derived out of combined humidity and 13C NMR results • individual effects of aging on certain soil components expected • further analysis of different SOM types with changing parameters (moisture content, composition) planned • advanced mechanistic model required for deeper understanding of soil aging water 1.8 kHz carbohydrates Pake doublet 28.2 kHz (peak distance) high-order Pake doublet:  crystalline carbohydrates please note the project outcome poster: “Dynamic and Structural Effects in SOM after Thermal Treatment observed with 1H, 13C NMR Spectroscopy & DSC” Acknowledgements References SPP 1315 annual colloquium 2012, October 10th – 12th, Dornburg, Jena [1] Jäger, Alexander et al. (2011): Optimized NMR spectroscopic strategy to characterize water dynamics in soil samples; Organic Geochemistry 42, 917–925. We thank the German research foundation (DFG) for funding within the SPP1315 ‘Biogeochemical Interfaces in Soil’ (SCHA849/8-1). [2] Jäger, Alexander et al. (2012): 1H and 13C Solid-State NMR based structural mobility and water adsorption studies of Soil Organic Matter, in preparation. Printed at Universitätsrechenzentrum Leipzig