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  • Organic Compounds
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  • 1
    Language: English
    In: The journal of physical chemistry. A, 30 March 2017, Vol.121(12), pp.2367-2376
    Description: Water molecules in soil organic matter (SOM) can form clusters bridging neighboring molecular segments (water molecule bridges, WaMBs). WaMBs are hypothesized to enhance the physical entrapment of organic chemicals and to control the rigidity of the SOM supramolecular structure. However, the understanding of WaMBs dynamics in SOM is still limited. We investigated the relation between WaMBs stability and the physicochemical properties of their environment by treating a sapric histosol with various solvents and organic chemicals. On the basis of predictions from molecular modeling, we hypothesized that the stability of WaMBs, measured by differential scanning calorimetry, increases with the decreasing ability of a chemical to interact with water molecules of the WaMBs. The interaction ability between WaMBs and the chemicals was characterized by linear solvation energy relationships. The WaMBs stability in solvent-treated samples was found to decrease with increasing ability of a solvent to undergo H-donor/acceptor interactions. Spiking with an organic chemical stabilized (naphthalene) or destabilized (phenol) the WaMBs. The WaMBs stability and matrix rigidity were generally reduced strongly and quickly when hydrophilic chemicals entered the soil. The physicochemical aging following this destabilization is slow but leads to successive WaMBs stabilization and matrix stiffening.
    Keywords: Humus – Research ; Organic Compounds – Chemical Properties ; Polar Molecules – Chemical Properties;
    ISSN: 10895639
    E-ISSN: 1520-5215
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  • 2
    Language: English
    In: Organic Geochemistry, 2011, Vol.42(8), pp.917-925
    Description: H wideline NMR spectra of soil samples offer the possibility to analyze soil material based on their proton mobility. Care has to be taken to remove unwanted signal contributions from the probe background. We demonstrate that unstructured wideline spectra can be analyzed quantitatively by a combination of a Gaussian line for rigid and a Lorentzian line for mobile protons. This is used to study effects of hydrogen-bonded water networks upon heat treatment for a series of different soil samples with varying water content as a contribution to study physical aging of soil organic matter (SOM). Results are combined with H projections from C 2D WISE (wideline separation) experiments representing solely the broad Gaussian line. Furthermore, for the first time applied to soils, H structural information from soil samples is obtained from 2D PMLG phase modulated Lee–Goldburg measurements under magic angle spinning (MAS). Low water contents improve the resolution of main functional groups significantly.
    Keywords: Geology
    ISSN: 0146-6380
    E-ISSN: 1873-5290
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  • 3
    Language: English
    In: Agriculture, Ecosystems and Environment, 02 January 2017, Vol.236, pp.43-51
    Description: Disposal of olive mill wastewater (OMW) is a well-recognized environmental and agricultural problem. Spreading on agricultural lands and roads, which is one way of discharging OMW, may result in multiple effects on soil environment, including changes in the potential of the soil to interact with organic compounds. There is a lack of knowledge regarding the persistence and temporal dynamics of effects of prior OMW land application on the sorption of organic compounds to soil, and the role of application season. This knowledge is also important for better understanding of dynamics of organic matter in soil environments. Therefore, in this work sorption of diuron, an urea pesticide, was determined in lab batch experiments on soil sampled from two depths (0–5 and 5–10 cm) in the field, in different time intervals (up to 18 months) following OMW application in various seasons (Spring, Summer and Winter), where Summer application was carried out in “dry” and “wet” (with previous moistening) regimes. The application of typical (local) OMW to the field (in Bait Reema village in Palestinian Authority) enhanced diuron-soil interactions. A greater enhancement effect was on the soil samples from the 5–10 cm layer as compared with that on the samples from the 0–5 cm layer. Larger extents of diuron sorption enhancement, following the prior OMW-soil interactions, were observed at higher diuron concentrations in soil solution. The enhancement effect of OMW on soil sorption of diuron mitigated with time. It was also “season”- dependent such that the OMW field application when carried out in summer led to smaller impacts on diuron sorption, as compared with the application in spring and winter. This work emphasized the importance of long-term observations in understanding the environmental fate of organic compounds in areas affected by OMW disposal and experiencing the “pressure” of anthropogenic organic contaminants.
    Keywords: Olive Mill Wastewater (Omw) ; Soil Sorption ; Pesticide ; Persistence ; Soil Depth ; Application Season ; Agriculture ; Environmental Sciences
    ISSN: 0167-8809
    E-ISSN: 1873-2305
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  • 4
    Language: English
    In: Journal of Soils and Sediments, 2013, Vol.13(9), pp.1579-1588
    Description: Purpose: Nutrient release, soil wettability, water binding, and matrix rigidity of soil organic matter (SOM) can be affected by cross-links between segments of SOM, cations, and water molecule bridges (WaMB). Not all cation effects on SOM can be explained with the currently accepted idea that multivalent cations cross-link organic matter segments via direct cation bridges (CaB). The objective was to understand these interactions and their effect on SOM matrix rigidity and wettability. Materials and methods: We modified cation composition of two peats and an organic surface layer (OSL) using cation exchange resin to remove cations and solutions of Na super(+), Ca super(2+), or Al super(3+) to enrich samples with cations. SOM matrix rigidity was determined at 4 and 〉8 weeks after treatment via the WaMB transition temperature T*, using differential scanning calorimetry. Wettability was measured via sessile drop contact angle (CA). Results and discussion: The effect of cation removal on T* depended on cation exchange capacity and initial cation content. Cation addition to OSL increased T*. This effect increased with increasing cation loading and valency, and T* correlated with CA. Classical cross-linking can neither explain the higher heterogeneous matrix of Ca-treated than Al-treated samples nor the aging-induced convergence of T* for different cations and concentrations. The latter is likely due to interaction between CaB and WaMB in SOM. Conclusions: Associations of CaB and WaMB evolve slowly and form a supramolecular network in SOM. Those dynamic associations can fix molecular arrangements inducing water repellency and increase kinetic barriers for the release and uptake of water and nutrients from aged soil.
    Keywords: Cross-links ; Differential scanning calorimetry ; Matrix rigidity ; Multivalent cation ; Soil organic matter ; Water molecule bridges (WaMB) ; Water repellency
    ISSN: 1439-0108
    E-ISSN: 1614-7480
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  • 5
    Language: English
    In: Reviews in Environmental Science and Bio/Technology, 2012, Vol.11(1), pp.41-54
    Description: Interactions between cations and natural organic matter (NOM) are central for the stability of organic matter, formation of supramolecular NOM structure, formation of organo-mineral associations, soil aggregation and binding of organic contaminants. The effect of multivalent cations on environmental functionalities of NOM strongly depends on the relative importance between intramolecular complexation and intermolecular cross-linking, the degree of which will be determined by the spatial arrangement of the hydrophilic functional groups in NOM. This literature review seeks to evaluate the current state of the art regarding the relevance of intermolecular cross-links via bridges of multivalent cations. Cross-linking has been suggested to explain among others aggregate stability, retarded dissolved organic matter release, reduced organic matter (OM) solubility as well as increase in degree and nonlinearity of sorption or organic chemicals to NOM. Although the cross-linking mechanism has been suggested in numerous studies, it has not yet been verified directly. The dynamics of the intermolecular cross-links, their persistence as well as their interplay with OM and their influence on stability and bioavailability of organic chemicals is up to now unknown. The major challenge in this context is the development of a suitable combination of experimental and instrumental techniques and relating the results to molecular and physicochemical models on the basis of targeted combination of spectroscopic, molecular modelling and thermoanalytical methods.
    Keywords: Cations ; Natural organic matter ; Cross-linking ; Water molecule bridges ; Cation bridges ; NMR ; Thermal analysis
    ISSN: 1569-1705
    E-ISSN: 1572-9826
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  • 6
    Language: English
    In: Geochimica et Cosmochimica Acta, 2007, Vol.71(3), pp.691-702
    Description: Recent studies indicate that glassiness represents a characteristic feature of soil organic matter (SOM). It is however unknown, to which extent the transitions detected in humic substances and whole soil samples correspond to common models of synthetic polymers providing the theoretical basis for explaining their glass transition characteristics. Physical aging associated with structural relaxation of amorphous substances below their glass temperature is one fundamental basis for the glass transition behavior of synthetic polymers. According to the results of this study, aging processes also occur in SOM. In whole soil samples, this process can be observed by the shift of glass transition-like step transitions to higher temperatures within the time scale of years. Not only the structural relaxation of the macromolecular organic substances, but also interactions with water molecules, which may exhibit both plasticizing and antiplasticizing properties, influence the aging process of SOM. Especially under moistening or drying conditions, a differentiation between the effects of water and of alterations of the SOM structure in the course of time on the rigidity of the macromolecular network is difficult.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 7
    Language: English
    In: Geoderma, 01 April 2017, Vol.291, pp.40-46
    Description: Crystalline aliphatic moieties in soil organic matter (SOM) have been under intensive investigation, but it is still unknown how they interact with organic chemicals in the unfractionated SOM. Our objective was to understand the changes in properties of soil aliphatic crystallites when being in contact with organic chemicals. For this, we treated an organic (sapric histosol) and a mineral soil (gleyic podzol) with phenol and naphthalene dissolved in different solvents. The crystallites were characterized in the unfractionated soil by their melting temperatures determined by differential scanning calorimetry (DSC) and by C CPMAS NMR spectra from the (33.0 ppm) and (30.0 ppm) signals. DSC identified two distinct types of crystalline domains differing in melting temperatures. Their reaction on solvent treatment and spiking allowed for the first time new insights into the nature of these domains in the unfractionated soil samples. Melting temperature and relative crystallinity were generally reduced by the presence of organic chemicals and solvent treatment, but in different way for each domain type. Thus, the domain types differ from each other in chemical nature. The domains melting at 68–75 °C (sapric histosol) responded similar to biopolymer residues and may originate from higher plants, while those melting at 82–93 °C (sapric histosol) and at 76–80 °C (gleyic podzol) responded similarly to lipids and are speculated to be of microbiological origin. These findings open new perspectives for the mechanistic analysis of sorption processes in soil. Aliphatic crystalline domains may have been underestimated with respect to their qualitative relevance for sorption processes in soil.
    Keywords: Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 8
    Language: English
    In: Plant and Soil, 2005, Vol.275(1), pp.1-20
    Description: Variations of soil moisture conditions affect sorption properties of soil organic matter and the pore size distribution of the soils and thus are expected to have an impact on the availability of pollutants and nutrients in soils. At least two principal processes that occur when a soil-water contact is established, are involved. Wetting , which is the very first step, is governed by the interactions of water with the surface of soil organic matter (SOM). The wettability of the pore walls determines the pore accessibility for water. Only in wettable soils, water will occupy the smallest pores first. In the course of wetting, the wettability of the pore walls increases, leading to water redistribution. Swelling of SOM is accompanied by an increase of volume due to the water uptake of the solid SOM phase and will change the SOM polarity. Swelling will thus affect sorption processes in the bulk SOM phase and is expected to change the pore sizes. In this contribution, we investigated swelling and wetting kinetics of soil samples by H-NMR-Relaxometry. We found different effects of wetting and swelling on the development of relaxation time distribution and thus of the pore size distribution. Both swelling and wetting can be slow processes, lasting for up to some weeks. During this time, we found changes in the pore size distribution. For swelling phenomena, we observed a continuous change of the effective pore size, and for wetting phenomena, we found a change in water distribution in a probably rigid pore system. Thus, during swelling and wetting, neither pore size distribution nor sorbent properties of SOM nor hydraulic properties remain constant. Due to the slow kinetics, both processes play an important role in sorption, transport and accessibility for water in hydrophobic areas within a time scale of weeks after e.g. a rainfall event. This will affect the environmental availability and the transport of pollutants and nutrients in the field.
    Keywords: H-NMR-Relaxometry ; kinetics ; soil organic matter ; swelling ; water repellence ; wetting
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 9
    Language: English
    In: Journal of Plant Nutrition and Soil Science, April 2014, Vol.177(2), pp.141-149
    Description: The objective of this study was to investigate the effects of mono‐ and polyvalent cations on sorption of the two hydrophobic compounds nonylphenol (NP) and phenanthrene (Phe). To this end, exchange sites of a sandy soil were saturated with either Na, Ca, or Al and excess salts were removed by washing. The samples were then sterilized and either stored moist, dried at room temperature, or at 20°C, 60°C, or 105°C in a vented oven. Saturation with Na led to an increase of dissolved organic C (DOC) concentration in the soil water extracts, whereas the polyvalent cations Ca and Al decreased it. The H‐NMR relaxometry analyses showed that Al restricted the mobility of water molecules that are confined within the SOM structure to a higher extent than Ca or Na. According to contact‐angle (CA) analyses, cation treatment did not significantly change the wetting properties of the samples. Batch sorption–desorption experiments showed no clear salt‐treatment effects on the sorption and desorption equilibria or kinetics of NP and Phe. Instead, the sorption coefficients and sorption hysteresis of NP and Phe increased in dry soil. With increasing drying temperature the CA of the soils and the sorption of both xenobiotics increased significantly. We conclude that structural modifications of SOM due to incorporation of polyvalent cations into the interphase structure do not modify the sorption characteristics of the soil for hydrophobic compounds. Instead, increasing hydrophobization of organic soil constituents due to heat treatment significantly increased the accessible sorption sites for nonpolar organic compounds in this soil.
    Keywords: Soil Organic Matter ; Sodium ; Calcium ; Aluminum ; Contact Angle ; Wettability ; Relaxation Time
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 10
    Language: English
    In: Geoderma, January 2014, Vol.213, pp.115-123
    Description: An overview of the variety of processes induced by the aluminum cation interacting with carboxyl and carboxylate groups is given by means of quantum chemical density functional theory (DFT) calculations. Different hydration states of Al ranging from the hexaaquo complex down to the unhydrated cation and direct/indirect bonding with the polar groups are considered. The calculations reflect the amphoteric character of the hydrated aluminum complex showing in most cases its acidic character via proton transfer from the water molecules of the hydration shell to the carboxylate group, but in some cases also deprotonation of the carboxyl group. Several additional processes are observed such as interconversion of bidentate and monodentate bonding by the carboxyl/carboxylate groups and strong hydrogen bonding between proton transfer partners. Comparison with analogous previous investigations on cation bridges induced by calcium and sodium shows the pronounced activity of the triply charged aluminum cation. The importance of the strong polarizing and bridging power of the aluminum cation for soil organic matter with low exchange capacities and a low concentration of charged groups is discussed.
    Keywords: Humic Substances ; Cation Bridges ; Water Bridges ; Molecular Simulation ; Density Functional Theory ; Proton Transfer ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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