Molecular modeling of soil organic matter: Squaring the circle?

Schaumann, Gabriele E.; Thiele‐Bruhn, Sören

doi:10.1016/j.geoderma.2011.04.024

Cited by 67 publications

(49 citation statements)

References 109 publications

(78 reference statements)

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“…The latter have been only lately attributed to the semi-reversible disruption of water molecule bridges (WaMB) between individual molecule segments, which leads to an increased physical stability of the organic matter matrix (Schaumann and Bertmer 2008;Aquino et al 2009Aquino et al , 2011Schaumann and Thiele-Bruhn 2011). The combination of DSC (Schaumann and Bertmer 2008;Hurraß and Schaumann 2007;Hurrass and Schaumann 2005) and advanced 1D and 2D nuclear magnetic resonance (NMR) spectroscopy methods (Jaeger et al 2011) with targeted heating-coolingageing experiments (Schaumann and Bertmer 2008) as well as results obtained from molecular modelling (Aquino et al 2009) support the hypothesized WaMB transitions.…”

Section: Introductionmentioning

confidence: 77%

“…Verification will be conducted applying detailed investigations of the low-temperature range transitions including reversibility, heating rate dependence and reaction on changes in moisture conditions, as discussed in earlier studies Hurrass and Schaumann 2005). The lack of compression in the low temperature indicates a higher physical stability of peat than of charcoal, which is on the one hand surprising, but could potentially be explained by the stabilizing capacity of the hypothesized WaMB (Schaumann and Thiele-Bruhn 2011;Aquino et al 2009Aquino et al , 2011. After disruption of WaMB above >80-90°C, the collapse of an aggregate or pore structures as assumed for manure and charcoal, respectively, could explain the compression phase in the higher temperature region.…”

Section: Sapric Peatmentioning

confidence: 99%

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Potential of AFM–nanothermal analysis to study the microscale thermal characteristics in soils and natural organic matter (NOM)

Schaumann

Mouvenchery

2011

J Soils Sediments

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Purpose This exploratory study evaluates the potential of nanothermal analysis (nTA) coupled with atomic force microscopy (AFM) of soil samples for understanding physicochemical processes in soil and for linking the nanospatial and microspatial distribution of thermal characteristics with the macroscopic properties of soil samples. Materials and methods Soil and reference samples were investigated by differential scanning calorimetry and AFMnTA. nTA was conducted on 16 points of each AFM image in two subsequent heating cycles (55-120°C and 55-300°C, respectively). Thermograms were subdivided into characteristic types and their spatial distribution was compared between sample replicates and materials. Results and discussion Thermogram types consisted of partly structured expansion and compression phases, suggesting material-specific thermal profiles. The distribution of thermogram types reflected sample-dependent nanoscale and microscale heterogeneity. Indications for water molecule bridge transitions were found by nTA in peat and soil. Organic materials generally revealed strong expansion and irreversible compression phases, latter probably due to the collapse of pore and aggregate structures. In contrast to charcoal and manure, peat shows strong expansion below 120°C and compression only above 120°C. Conclusions All investigated samples are heterogeneous on the nanoscale and microscale with respect to thermal behaviour. AFM-nTA allows distinguishing numerous different materials on nanometre and micrometre scales in soil samples. The material-dependent characteristics will help in understanding and learning more about the nanoscale distribution of different materials and properties. Related to the macroscopic thermal behaviour, this will allow studying links between the properties of biogeochemical interfaces and the processes governed by them.

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Section: Introductionmentioning

confidence: 77%

Section: Sapric Peatmentioning

confidence: 99%

Potential of AFM–nanothermal analysis to study the microscale thermal characteristics in soils and natural organic matter (NOM)

Schaumann

Mouvenchery

2011

J Soils Sediments

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“…This can be understood in a way that heating destroys water molecule bridge (WaMB) (Schaumann and Thiele-Bruhn, 2011) networks, and therefore, originally bound water molecules with high linewidth (contributing to PR2) become more mobile upon the heating event and contribute to a Lorentzian line after heating (Jaeger et al, 2011;Schaumann and Bertmer, 2008). The increase in Lorentzian line before and after the heating event is larger for the soil samples, indicating that relatively more bound, but easily mobilised water is present in the soil samples.…”

Section: Assignment Of Structural Features To the Nmr Signalsmentioning

confidence: 98%

Combined proton NMR wideline and NMR relaxometry to study SOM-water interactions of cation-treated soils

Schaumann¹,

Diehl²,

Bertmer³

et al. 2013

Journal of Hydrology and Hydromechanics

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Focusing on the idea that multivalent cations affect SOM matrix and surface, we treated peat and soil samples by solutions of NaCl, CaCl 2 or AlCl 3 . Water binding was characterized with low field 1 H-NMR-relaxometry (20 MHz) and 1 H wideline NMR spectroscopy (400 MHz) and compared to contact angles. From 1 H wideline, we distinguished mobile water and water involved in water molecule bridges (WaMB). Large part of cation bridges (CaB) between SOM functional groups are associated with WaMB. Unexpectedly, 1 H NMRrelaxometry relaxation rates suggest that cross-linking in the Al-containing peat is not stronger than that by Ca.The relation between percentage of mobile water and WaMB water in the context of wettability and 1 H NMR relaxation times confirms that wettability controls the water film surrounding soil particles. Wettability is controlled by WaMB-CaB associations fixing hydrophilic functional groups in the SOM interior. This can lead to severe water repellency. Wettability decreases with increasing involvement of functional groups in CaB-WaMB associations. The results demonstrate the relevance of CaB and WaMB for the dynamics of biogeochemical and hydrological processes under field conditions, as only a few percent of organic matter can affect the physical, chemical, and biological functioning of the entire 3-phase ecosystem.

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“…A recent review paper outlines current understanding of the important effect of cation bridging in NOM aggregation [87]. Indeed, molecular modeling studies of NOM-mineral interfacial systems indicates that cation bridging between NOM and surface sites predominates over direct interactions between NOM functional groups and the surface [88,89], although humic substances can adsorb directly to clay surfaces in confined interlayer environments [90]. In a recent review of soil humic substances, Sutton and Sposito concluded that NOM consists of a "supramolecular association" of small organic molecules linked by short-range interactions dominated by amide-amide interactions [91].…”

Section: Simulations Of Natural Organic Matter (Nom) and Nom-mineral mentioning

confidence: 99%

“…While a number of NOM models based on experimental measurements have been proposed, two recent reviews summarize the few NOM models that have been used in molecular simulations [88,97]. The Temple-Northeastern-Birmingham (TNB) model [7,86,98] of a NOM fragment is an average structure based on spectroscopic and analytical data.…”

Section: Simulations Of Natural Organic Matter (Nom) and Nom-mineral mentioning

confidence: 99%

Interaction of Natural Organic Matter with Layered Minerals: Recent Developments in Computational Methods at the Nanoscale

2014

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Abstract:The role of mineral surfaces in the adsorption, transport, formation, and degradation of natural organic matter (NOM) in the biosphere remains an active research area owing to the difficulties in identifying proper working models of both NOM and mineral phases present in the environment. The variety of aqueous chemistries encountered in the subsurface (e.g., oxic vs. anoxic, variable pH) further complicate this field of study. Recently, the advent of nanoscale probes such as X-ray adsorption spectroscopy and surface vibrational spectroscopy applied to study such complicated interfacial systems have enabled new insight into NOM-mineral interfaces. Additionally, due to increasing capabilities in computational chemistry, it is now possible to simulate molecular processes of NOM at multiple scales, from quantum methods for electron transfer to classical methods for folding and adsorption of macroparticles. In this review, we present recent developments in interfacial properties of NOM adsorbed on mineral surfaces from a computational point of view that is informed by recent experiments.

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Molecular modeling of soil organic matter: Squaring the circle?

Cited by 67 publications

References 109 publications

Potential of AFM–nanothermal analysis to study the microscale thermal characteristics in soils and natural organic matter (NOM)

Potential of AFM–nanothermal analysis to study the microscale thermal characteristics in soils and natural organic matter (NOM)

Combined proton NMR wideline and NMR relaxometry to study SOM-water interactions of cation-treated soils

Interaction of Natural Organic Matter with Layered Minerals: Recent Developments in Computational Methods at the Nanoscale

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