Nuclear Magnetic Resonance (NMR) Spectroscopy tome… · Nuclear Magnetic Resonance (NMR)...
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Nuclear Magnetic Resonance (NMR) Spectroscopy to assess Biogeochemical Interfaces Marko Bertmer 1 , Alexander Jäger 1,2 and Gabriele E. Schaumann 2 1 Universität Leipzig, Institut für Experimentelle Physik II, Abteilung MQF, Linnéstr. 5, 04103 Leipzig. [email protected] 2 Universität Koblenz-Landau, Institute for Environmental Sciences, Department of Environmental and Soil Chemistry, Fortstr. 7. 76829 Landau. [email protected] References Introduction Physical-Chemical Background All nuclei with a magnetic moment can be accessed by NMR (nuclear magnetic resonance). Due to a different magnetogyric ratio for each isotope, the technique is element-selective. In an external magnetic field, frequency dependent spectra can be obtained by irradiation with radiofrequency pulses. The different NMR interactions influence the resulting NMR spectra in a well-known fashion that can be calculated exactly. The dynamics of nuclei and respectively of molecules or functional groups is mainly reflected by their linewidth, with higher mobility leading to more narrow spectral lines. The electronic surrounding of the nuclei gives rise to a frequency shift, thereby allowing for assignment of different functional groups. In 1 H NMR, the shift range is rather small (on the order of 10 ppm) and high- resolution solid-state NMR spectra are complicated to obtain and need sophisticated measurement techniques, i. e., pulse sequences. In 13 C NMR, the spread of frequencies is larger (on the order of 250 ppm) and therefore 13 C NMR spectroscopy is a standard technique for organic chemistry to assign different functional groups. However, due to the multitude of chemical compounds present in soil, overlapping spectral lines are present that nevertheless can be analyzed by dividing the spectra into several chemical shift ranges. The data shown here were measured using a 9.4 T magnet giving rise to frequencies of 400 MHz for 1 H and 100 MHz for 13 C. Application Examples Example 1: 1 H NMR deconvolution [1] of static (non rotating samples), access to mobility 1 H and 13 C NMR spectroscopy is a versatile and flexible tool to reveal a multitude of information about soil material. Within this priority program, 1 H NMR investigations on static (non rotating) and MAS (magic angle spinning) samples will be employed to study the different mobilities of water molecules and organic matter as well as the structural assignment of different 1 H containing components. 13 C NMR gives information on the organic matter and the quantification of different functional groups. In combination, the mobility of soil components, their spectroscopic assignment as well as the interaction between soil components is investigated. [1] G. E. Schaumann, M. Bertmer, “Do water molecules bridge soil organic matter molecule segments?”, Eur. J. Soil Sci. 59 (2008) 423-429. [2] J E. Vinogradov, P. K. Madhu, S. Vega, "High-resolution proton solid-state NMR spectroscopy by phase-modulated Lee-Goldburg experiment", Chem. Phys. Lett. 314 (1999) 443-450. [3]. Schaefer, E. O. Stejskal, "Carbon-13 Nuclear Magnetic Resonance Polymers Spinning at the Magic Angle", J. Am. Chem. Soc. 98 (1976) 1031-1032. Example 2: 1 H high-resolution spectra (2D-PMLG[2]): signal assignment Example 3: 13 C CPMAS[3] spectra: quantification of functional groups of SOM - peat and soil have different linewidth for Lorentzian line, which clearly indicates a higher water mobility in the peat compared to the soil samples - with this method, mobility changes due to heating are followed, for details see project poster - analysis with two lines is oversimplified in these heterogeneous compounds. Probably a distribution of mobilites (linewidths) are present, though it reveals a good estimate of the major components and their relations with regard to mobility (Hz) -100000 -50000 0 50000 100000 (Hz) -100000 -50000 0 50000 100000 FS 001 FM 001 experiment full simulation Lorentzian line Gaussian line - differentiation of aromatic (a), aliphatic (c), and water protons (b) possible - decrease of water signal intensity with heating in open sample holder or deuteration - identification of functional groups possible - large differences between sapric and fibric peat in the aliphatic region 1 wet sample 2 air dried sample 3 heated sample δ / ppm Assignment [1] 0–45 Alkyl-C 45–110 O- and N-alkyl 45–60 Aliphatic C-N, methoxyl 60–95 Alkyl-O (carbohydrates, alcohols) 95–110 Acetal and ketal carbons (carbohydrates) 110–160 sp 2 -hybridized C 110–140 Aryl-H and aryl-C carbons, olefinic carbons 140–160 Aryl-O and aryl-N carbons 160–220 Carbonylic -C/carboxylic-C/amide-C 160–185 Carboxyl and amide-C 185–220 Aldehyde and ketone carbons NMR spectroscopy is a non- destructive method. Samples can be used without further preparation. For heating/cooling cycles, samples have to be sealed in glass ampules prior to measurement. Special Requirements / Sample preparation MAS rotor (4 mm o. d.) glass insert Example 4: heat-induced changes to poly(methylene) components of soil cryst. amorph. FS FB FL 0 10 20 30 40 50 60 70 80 rel. ratio to total signal integral 220-160 ppm 120-110 ppm 110-45 ppm 45-0 ppm - measurements itself done at room temperature - heating and subsequent fast cooling increases the amorphous amount of the poly(methylene) signal b a c c b b
Transcript of Nuclear Magnetic Resonance (NMR) Spectroscopy tome… · Nuclear Magnetic Resonance (NMR)...
Nuclear Magnetic Resonance (NMR) Spectroscopy to assess Biogeochemical InterfacesMarko Bertmer1, Alexander Jäger1,2 and Gabriele E. Schaumann2
1Universität Leipzig, Institut für Experimentelle Physik II, Abteilung MQF, Linnéstr. 5, 04103 Leipzig. [email protected]ät Koblenz-Landau, Institute for Environmental Sciences, Department of Environmental and SoilChemistry, Fortstr. 7. 76829 Landau. [email protected]
References
Introduction Physical-Chemical BackgroundAll nuclei with a magnetic moment can be accessed by NMR (nuclear magnetic resonance). Due to a different magnetogyric ratio for each isotope, the technique is element-selective. In an external magnetic field, frequency dependent spectra can be obtained by irradiation with radiofrequency pulses.The different NMR interactions influence the resulting NMR spectra in a well-known fashion that can be calculated exactly. The dynamics of nuclei and respectively of molecules or functional groups is mainly reflected by their linewidth, with higher mobility leading to more narrow spectral lines.The electronic surrounding of the nuclei gives rise to a frequency shift, thereby allowing for assignment of different functional groups. In 1H NMR, the shift range is rather small (on the order of 10 ppm) and high-resolution solid-state NMR spectra are complicated to obtain and need sophisticated measurement techniques, i. e., pulse sequences. In 13C NMR, the spread of frequencies is larger (on the order of 250 ppm) and therefore 13C NMR spectroscopy is a standard technique for organic chemistry to assign different functional groups. However, due to the multitude of chemical compounds present in soil, overlapping spectral lines are present that nevertheless can be analyzed by dividing the spectra into several chemical shift ranges.The data shown here were measured using a 9.4 T magnet giving rise to frequencies of 400 MHz for 1H and 100 MHz for 13C.
Application ExamplesExample 1: 1H NMR deconvolution [1] of static (non rotating samples), access to mobility
1H and 13C NMR spectroscopy is a versatile and flexible tool to reveal a multitude of information about soil material. Within this priority program, 1H NMR investigations on static (non rotating) and MAS (magic angle spinning) samples will be employed to study the different mobilities of water molecules and organic matter as well as the structural assignment of different 1H containing components.
13C NMR gives information on the organic matter and the quantification of different functional groups.In combination, the mobility of soil components, their spectroscopic assignment as well as the interaction between soil components is investigated.
[1] G. E. Schaumann, M. Bertmer, “Do water molecules bridge soil organic matter molecule segments?”, Eur. J. Soil Sci. 59 (2008) 423-429.[2] J E. Vinogradov, P. K. Madhu, S. Vega, "High-resolution proton solid-state NMR spectroscopy by phase-modulated Lee-Goldburg experiment", Chem. Phys. Lett. 314 (1999) 443-450.[3]. Schaefer, E. O. Stejskal, "Carbon-13 Nuclear Magnetic Resonance Polymers Spinning at the Magic Angle", J. Am. Chem. Soc. 98 (1976) 1031-1032.
Example 2: 1H high-resolution spectra (2D-PMLG[2]): signal assignment
Example 3: 13C CPMAS[3] spectra: quantification of functional groups of SOM
- peat and soil have different linewidth for Lorentzian line, which clearly indicates a higher water mobilityin the peat compared to the soil samples- with this method, mobility changes due to heating are followed, for details see project poster- analysis with two lines is oversimplified in these heterogeneous compounds. Probably a distribution of mobilites (linewidths) are present, though it reveals a good estimate of the major components and their relations with regard to mobility
(Hz)
-100000-50000050000100000(Hz)
-100000-50000050000100000
FS 001 FM 001
experiment
full simulation
Lorentzian line
Gaussian line
- differentiation of aromatic (a), aliphatic (c), and water protons (b) possible- decrease of water signal intensity with heating in open sample holder or deuteration
- identification of functional groups possible- large differences between sapric and fibric peat in the aliphatic region
1 wet sample 2 air dried sample3 heated sample
δ / ppm Assignment [1]
0–45 Alkyl-C
45–110 O- and N-alkyl
45–60 Aliphatic C-N, methoxyl
60–95 Alkyl-O (carbohydrates, alcohols)
95–110 Acetal and ketal carbons (carbohydrates)
110–160 sp2-hybridized C
110–140 Aryl-H and aryl-C carbons, olefinic
carbons
140–160 Aryl-O and aryl-N carbons
160–220 Carbonylic -C/carboxylic-C/amide-C
160–185 Carboxyl and amide-C
185–220 Aldehyde and ketone carbons
NMR spectroscopy is a non-destructive method. Samples can be used without further preparation.
For heating/cooling cycles, samples have to be sealed in glass ampulesprior to measurement.
Special Requirements /Sample preparation
MAS rotor (4 mm o. d.)
glass insert
Example 4: heat-induced changes to poly(methylene) components of soil
cryst.
amorph.
FS FB FL
0
10
20
30
40
50
60
70
80
rel. r
atio t
o t
ota
l sig
na
l in
teg
ral 220-160 ppm
120-110 ppm
110-45 ppm
45-0 ppm
- measurements itself done at room temperature
- heating and subsequent fast cooling increases the amorphous amount of thepoly(methylene) signal
b
a
cc
bb
