Type
Text
Type
Thesis
Advisor
Reeder, Richard. | Phillips, Brian L | Rasbury, Troy
Date
2015-08-01
Keywords
Geochemistry | Calcite, Coprecipitation, NMR spectroscopy, Organic, Phosphorus
Department
Department of Geosciences.
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/77674
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
The interaction between calcite and dissolved organic phosphate is important to biomineral and geochemical systems. Organic molecules and phosphates can be adsorbed to the calcite surface and incorporated as impurities in the matrix during crystal growth. Although 31P NMR spectroscopy has been extensively used to study the nature of P in a wide variety of natural samples, a lack of understanding of spectroscopic characteristics of organic P occluded in calcite hinders NMR application in this area. Here, a methodology based on 31P NMR is proposed to help determine the speciation of P at low concentrations in calcite based on spectroscopic characteristics of organophosphoesters coprecipitated with calcite, and succeeded in characterizing the organic P occluded in a natural calcite sample, calcitic moonmilk. By dissolving in the 13C-enriched carbonate (anion) syringe an amount sufficient to yield a Ca:P ratio of approximately 1000:1, we succeeded in coprecipitating various phosphoesters (e.g. monoesters and diesters) with calcite in seeded constant-rate-of-addition experiment. 31P NMR experiments such as 31P{1H} CP/MAS (cross polarization under magic-angle spinning condition) and 1H<&rarr>31P{13C} CP/ REDOR (rotation-echo double resonance) were carried out to study the chemical environment of phosphorus in the coprecipitate samples. In all cases, we find minor differences in the 31P{1H} CP NMR spectra between the organic phosphates and their corresponding coprecipitates, demonstrating that the molecules remain intact during precipitation. Detailed analysis of the chemical shift and chemical shift anisotropy revealed systematic differences among the coprecipitates. None of the coprecipitate chemical shifts overlap that for inorganic orthophosphate coprecipitated with calcite. The differences in delta δ values can differentiate monoester from diester in coprecipitates based on whether delta δ exhibits a positive or negative value, which can be easily recognized in the SSB pattern. For monoesters, compared to the first SSB(+) on the left side of central band, the intensity of the first SSB(<&ndash>) on the right side is larger for each monoester coprecipitate and smaller for each diester coprecipitate. 31P{13C} REDOR experiments of all coprecipitates exhibit strong dephasing signal, demonstrating multiple 31P - 13C pairs within about 4 <Å> distances and hence that these P-esters are occluded in the calcite structure. The 31P NMR spectra present here reveal significant differences (e.g. chemical shift, chemical shift anisotropy, spinning sidebands) between different phosphate esters occlude in calcite structure, providing a spectroscopic method to determine the speciation of phosphorus at low-concentration in carbonate minerals. Moonmilk samples obtained from cave Coel Zelà , Italy were bleached to remove extra-crystalline organic matter. CP/MAS (cross polarization under magic angle spinning conditions) was exclusively applied to obtain the NMR signals of 31P and 13C from these moonmilk samples, considering the anticipated low concentration of P in moonmilk and low abundance of 13C in nature. XRD revealed that these moonmilk samples are composed dominantly of calcite. 31P spectra of moonmilk samples significantly resembles that of a well characterized stalagmite calcite and orthophosphate/calcite coprecipitate, which suggests that the main P content is inorganic and present as structural defects. The dominant peak (δ P-31=3.45 ppm) is somewhat larger in peak width (FWHM about 5.2 ppm) and value of the chemical shift anisotropy (delta δ around <&ndash>40 ppm) than that of orthophosphate defect, indicating that the inorganic P appears to be non-protonated and structurally distorted. Detailed analysis revealed that a small 31P resonance δ P-31 at <&ndash>2.0 ppm exhibits significant spinning sideband effect, which can be attributed to organic phosphate. Substantial 13C resonances from carbon-bearing groups other than calcite carbonate confirms that these moonmilk samples contain organic matter, mainly fatty acids. Taken together, 31P and 13C CP/MAS reveal that rich organic matter, minor inorganic phosphate, and trace amount of organophosphate present in the moonmilk calcite as structural defects. Most significantly, even though the P speciation in moonmilk closely resembles stalagmite calcite, monetite is absent in moonmilk due to the Ca2+ deficiency caused by organic compounds. This study demonstrates the advantage of using solid-state NMR spectroscopy in characterizing organic phosphates in calcite mineral particular at low phosphorus concentrations, and provides a valuable methodology and data that complement previous studies on carbonate minerals and biomineralization. | The interaction between calcite and dissolved organic phosphate is important to biomineral and geochemical systems. Organic molecules and phosphates can be adsorbed to the calcite surface and incorporated as impurities in the matrix during crystal growth. Although 31P NMR spectroscopy has been extensively used to study the nature of P in a wide variety of natural samples, a lack of understanding of spectroscopic characteristics of organic P occluded in calcite hinders NMR application in this area. Here, a methodology based on 31P NMR is proposed to help determine the speciation of P at low concentrations in calcite based on spectroscopic characteristics of organophosphoesters coprecipitated with calcite, and succeeded in characterizing the organic P occluded in a natural calcite sample, calcitic moonmilk. By dissolving in the 13C-enriched carbonate (anion) syringe an amount sufficient to yield a Ca:P ratio of approximately 1000:1, we succeeded in coprecipitating various phosphoesters (e.g. monoesters and diesters) with calcite in seeded constant-rate-of-addition experiment. 31P NMR experiments such as 31P{1H} CP/MAS (cross polarization under magic-angle spinning condition) and 1H<&rarr>31P{13C} CP/ REDOR (rotation-echo double resonance) were carried out to study the chemical environment of phosphorus in the coprecipitate samples. In all cases, we find minor differences in the 31P{1H} CP NMR spectra between the organic phosphates and their corresponding coprecipitates, demonstrating that the molecules remain intact during precipitation. Detailed analysis of the chemical shift and chemical shift anisotropy revealed systematic differences among the coprecipitates. None of the coprecipitate chemical shifts overlap that for inorganic orthophosphate coprecipitated with calcite. The differences in delta δ values can differentiate monoester from diester in coprecipitates based on whether delta δ exhibits a positive or negative value, which can be easily recognized in the SSB pattern. For monoesters, compared to the first SSB(+) on the left side of central band, the intensity of the first SSB(<&ndash>) on the right side is larger for each monoester coprecipitate and smaller for each diester coprecipitate. 31P{13C} REDOR experiments of all coprecipitates exhibit strong dephasing signal, demonstrating multiple 31P - 13C pairs within about 4 <Å> distances and hence that these P-esters are occluded in the calcite structure. The 31P NMR spectra present here reveal significant differences (e.g. chemical shift, chemical shift anisotropy, spinning sidebands) between different phosphate esters occlude in calcite structure, providing a spectroscopic method to determine the speciation of phosphorus at low-concentration in carbonate minerals. Moonmilk samples obtained from cave Coel Zelà, Italy were bleached to remove extra-crystalline organic matter. CP/MAS (cross polarization under magic angle spinning conditions) was exclusively applied to obtain the NMR signals of 31P and 13C from these moonmilk samples, considering the anticipated low concentration of P in moonmilk and low abundance of 13C in nature. XRD revealed that these moonmilk samples are composed dominantly of calcite. 31P spectra of moonmilk samples significantly resembles that of a well characterized stalagmite calcite and orthophosphate/calcite coprecipitate, which suggests that the main P content is inorganic and present as structural defects. The dominant peak (δ P-31=3.45 ppm) is somewhat larger in peak width (FWHM about 5.2 ppm) and value of the chemical shift anisotropy (delta δ around <&ndash>40 ppm) than that of orthophosphate defect, indicating that the inorganic P appears to be non-protonated and structurally distorted. Detailed analysis revealed that a small 31P resonance δ P-31 at <&ndash>2.0 ppm exhibits significant spinning sideband effect, which can be attributed to organic phosphate. Substantial 13C resonances from carbon-bearing groups other than calcite carbonate confirms that these moonmilk samples contain organic matter, mainly fatty acids. Taken together, 31P and 13C CP/MAS reveal that rich organic matter, minor inorganic phosphate, and trace amount of organophosphate present in the moonmilk calcite as structural defects. Most significantly, even though the P speciation in moonmilk closely resembles stalagmite calcite, monetite is absent in moonmilk due to the Ca2+ deficiency caused by organic compounds. This study demonstrates the advantage of using solid-state NMR spectroscopy in characterizing organic phosphates in calcite mineral particular at low phosphorus concentrations, and provides a valuable methodology and data that complement previous studies on carbonate minerals and biomineralization. | 116 pages
Recommended Citation
Zhang, Zelong, "NMR Investigation of Organic Phosphorus in Calcite" (2015). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 3466.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/3466