Quantitative evaluation of noncovalent interactions between glyphosate and dissolved humic substances by NMR spectroscopy

Interactions of glyphosate (N-phosphonomethylglycine) herbicide (GLY) with soluble fulvic acids (FAs) and humic acids (HAs) at pH 5.2 and 7 were studied by (1)H and (31)P NMR spectroscopy. Increasing concentrations of soluble humic matter determined broadening and chemical shift drifts of proton and phosphorus GLY signals, thereby indicating the occurrence of weak interactions between GLY and humic superstructures. Binding was larger for FAs and pH 5.2 than for HAs and pH 7, thus suggesting formation of hydrogen bonds between GLY carboxyl and phosphonate groups and protonated oxygen functions in humic matter. Changes in relaxation and correlation times of (1)H and (31)P signals and saturation transfer difference NMR experiments confirmed the noncovalent nature of GLY-humic interactions. Diffusion-ordered NMR spectra allowed calculation of the glyphosate fraction bound to humic superstructures and association constants (K(a)) and Gibbs free energies of transfer for GLY-humic complex formation at both pH values. These values showed that noncovalent interactions occurred most effectively with FAs and at pH 5.2. Our findings indicated that glyphosate may spontaneously and significantly bind to soluble humic matter by noncovalent interactions at slightly acidic pH and, thus, potentially pollute natural water bodies by moving through soil profiles in complexes with dissolved humus.     

Nonideal binding between dissolved humic acids and polyaromatic hydrocarbons

Interactions between hydrophobic organic chemicals (HOCs) and dissolved organic matter (DOM) are of environmental significance due to their influence on mobility and bioavailability of HOCs. The linear dissolution concept has been widely used to describe the interactions between HOCs and DOM, but it may not be correct. To date there is no systematic evaluation of nonideal interactions between HOCs and DOM. Therefore, this study employed a dialysis method to investigate sorption, desorption, and competition of two polyaromatic hydrocarbons (PAHs), phenanthrene (PHE) and pyrene (PYR), by two DOMs at pHs of 4, 7, and 11. Nonlinear interactions between PAHs and DOM and desorption hysteresis were consistently observed. The isotherm nonlinearity factor, nvalue, increased significantly after the addition of cosolutes, indicating the occupation of specific binding sites by the cosolute molecules. Significant influence of pH on PAHs-DOM interaction was also observed (higher binding coefficients, stronger desorption hysteresis, and increased nonlinearity at lower pH). This study for the first time systematically showed the nonideal binding behavior of PAHs by DOM. A more complete model rather than linear distribution is required to describe the interactions between HOCs and DOM. Conformation changes of DOM molecules were proposed to explain the interactions between HOCs and DOM.     

Adsorption of humic substances on goethite: comparison between humic acids and fulvic acids

The adsorption of humic acids (HA) to goethite (at pH 3-11) and the proton co-adsorption (at pH 4.0, 5.5, and 7.0) were measured, and the results were compared to those of fulvic acids (FA). Compared to FA, the adsorption of HA is stronger and more ionic strength dependent. The adsorption of both HA and FA decreases with increasing pH. The relative change of the adsorption with pH is bigger for HA than for FA at relatively low pH. At relatively high pH, it is the opposite. Protons are released at pH 4.0 and co-adsorbed at pH 5.5 and 7.0 upon the adsorption of both HA and FA. The observed pH dependency of HA and FA adsorption is in agreement with the proton co-adsorption data. Model calculations show that the adsorbed FA particles are on average located in the Stern layer, whereas the adsorbed HA particles protrude beyond the Stern layer. The closer location to the surface of the adsorbed FA leads to stronger electrostatic interactions between the FA particles and the surface, which explains the larger amount of protons released at low pH and co-adsorbed at high pH with each mass unit of FA adsorbed than that with HA adsorbed. The model also revealsthatfor FA a mean-field (smeared-out) approximation is reasonable, but for HA a patchwise approach is more appropriate at relatively low loading.     

Arsenite and arsenate binding to dissolved humic acids: influence of pH, type of humic acid, and aluminum

The fate of arsenic in the aquatic environment is influenced by dissolved natural organic matter (DOM). Using an equilibrium dialysis method, conditional distribution coefficients (Dom) for As(III) and As(V) binding onto two commercial humic acids were determined at environmentally relevant As/dissolved organic carbon (DOC) ratios and as a function of pH. At all pH values, As(V) was more strongly bound than As(III). Maximum binding was observed around pH 7, which is consistent with H+ competition for binding sites at low pH values and OH- competition for the arsenic center at high pH. For both oxidation states, Dom values increased with decreasing As/DOC ratios. Dom values were fitted as a function of the As/DOC ratio for As(III) and As(V). Compared to the aquatic humic acid, the terrestrial humic acid had a higher affinity for arsenic binding with 1.5-3 times higher Dom values under the same conditions. Al3+ in excess to arsenic successfully competed for strong binding sites at low As/DOC ratios. Under environmentally relevant conditions, about 10% of total As(V) may be bound to DOM, whereas >10% of As(III) is bound to DOM at very low As/DOC ratios only. Binding of arsenic to DOM should be considered in natural systems.     

Mechanism of interactions between Hg(II) and Demeton S: an NMR study

The chemical fate of organophosphorus pesticides (OPs) has been proven to depend strongly on the chemistry of their aquatic environment. In particular, metal ions (and metal oxide surfaces) have been known to play an important role in the hydrolytic fate of OPs. Various postulates regarding the mechanism of metal-ion-promoted hydrolysis of OPs have been made over the years. However, direct spectroscopic evidence to pinpoint the hydrolytic products and the exact interaction between metal ions and organophosphorus pesticides are still lacking. We report herein the first in-situ study of the interaction between an aqueous solution of Hg(II) and Demeton S using 1H- and 31P NMR spectroscopy. It was found that the interactions between Hg(II), a soft Lewis acid, and Demeton S tend to be a strong function of the aqueous speciation of Hg(II), and the bonding between Hg2+ and Demeton S does not involve the central P=O bond but rather Hg2+ bonds with the two sulfur atoms in the Demeton S side chain and subsequently stabilizes the Demeton S molecule, a phenomenon not previously reported for any metal ion-OP systems studied. On the basis of this study, generalizations regarding the nature of metal ion binding even within a given class of OPs (i.e., phosphorodithioates, phosphorothioates, phosphorothiolates, etc.) should be avoided or only made with extreme caution.     

Mechanisms of humic acids degradation by white rot fungi explored using 1H NMR spectroscopy and FTICR mass spectrometry

Enzymatic activities involved in decay processes of natural aromatic macromolecules, such as humic acids (HA) and lignin by white rot fungi, have been widely investigated. However, the physical and chemical analysis of degradation products of these materials has not been intensively explored. Fourier transform cyclotron resonance mass spectrometry (FTICR MS) and 1H NMR as well as CHNOS and size exclusion chromatography were employed to study the mechanisms of HA degradation by Trametes sp. M23 and Phanerochaete sp. Y6. Size exclusion chromatography analyses demonstrate and provide evidence for HA breakdown into low MW compounds. The 1H NMR analysis revealed oxidation, a decrease in the aromatic content, and an indication of demethylation of the HA during biodegradation. Evidence for oxidation was also obtained using CHNOS. Analysis of FTICR MS results using a new software program developed by our group (David Mass Sort) revealed consecutive series of masses suggesting biochemical degradation trends such as oxidation, aromatic cleavage, and demethylation. These results are in agreement with the 1H NMR analysis and with the suggested role of the ligninolytic system leading to HA degradation.     

Immobilizing humic acid in a sol-gel matrix: a new tool to study humic-contaminants sorption interactions

Humic substances originated from aquatic, soil, or sediment environments are mixtures of humic compounds with various characteristics. Sorption interactions with isolated, well defined humic fractions can be studied either in an aqueous phase ("dissolved humic substances"), or in a solid-phase, by coating mineral particles with the humic materials, or simply by working with humic acid particles (powder) at low pH to minimize dissolution. Each attitude, by definition, can be studied by different experimental techniques and has a different meaning for understanding natural environmental processes. In this study, a new tool for studying sorption interactions is presented. Sol-gel was used as an inert matrix to immobilize (entrap) various humic acids (HAs), and then used to study the interactions of several polycyclic aromatic hydrocarbons (PAHs) with the entrapped HA. Linear and nonlinear sorption coefficients were highly correlated with contaminant hydrophobicity. Sorption of pyrene to immobilized HA was in the order of soil HA > Aldrich HA approximately = peat HA. It was concluded that the entrapped HAs retained their original properties in the gel matrix and were accessible to the external contaminant through the pore network. Additionally, binding coefficients of pyreneto dissolved humic substances and to dissolved organic matter (DOM) were determined from the reduction in pyrene sorption to immobilized HA in the presence of dissolved humic material or DOM in solution. Binding coefficients of pyrene were in the order of the following: dissolved Aldrich HA > dissolved peat fulvic acid (FA) > DOM derived from mature compost > DOM derived from fresh compost.     

Low-field NMR relaxometry: a study of interactions of water with water-repellant soils

Petroleum-induced water repellency in soils is a problem that has been thought to develop randomly following contamination and then remediation of a site with petroleum. The emergence of the phenomenon can occur within months or years of original contamination and with seemingly no warning. Low-field NMR has been used to study these soils and, specifically, the processes of water uptake that occur in them. Critical aspects in the development of this phenomenon have been identified as well--specifically, a dependence on climatic events in the area and contamination levels that contribute are suggested.     

Measurement of interactions between polysaccharides and flavour compounds by exclusion size chromatography: Advantages and limits

Interactions between flavour compounds and polysaccharides have been studied by exclusion size chromatography, the Hummel and Dreyer method. Hydrogen bonding was found between 2-acetyl thia-zole and dextrines of different degrees of polymerisation. The number of binding sites and the affinity constant increase by increasing the degree of polymerisation. Hydrogen bonding was also responsible for the interactions between xanthane and 1-octen-3-ol or 2-acetyl pyra-zine, with 1 mole of 1-octen-3-ol bound per pentasaccharide repeating unit. Unfortunately, the number of flavour compounds, which can be studied with this method, is limited due to their low water solubility and their low UV absorption.     

Molecular characterization of dissolved organic matter in glacial ice: coupling natural abundance 1H NMR and fluorescence spectroscopy

Glaciers and ice sheets are the second largest freshwater reservoir in the global hydrologic cycle, and the onset of global climate warming has necessitated an assessment of their contributions to sea-level rise and the potential release of nutrients to nearby aquatic environments. In particular, the release of dissolved organic matter (DOM) from glacier melt could stimulate microbial activity in both glacial ecosystems and adjacent watersheds, but this would largely depend on the composition of the material released. Using fluorescence and (1)H NMR spectroscopy, we characterize DOM at its natural abundance in unaltered samples from a number of glaciers that differ in geographic location, thermal regime, and sample depth. Parallel factor analysis (PARAFAC) modeling of DOM fluorophores identifies components in the ice that are predominantly proteinaceous in character, while (1)H NMR spectroscopy reveals a mixture of small molecules that likely originate from native microbes. Spectrofluorescence also reveals a terrestrial contribution that was below the detection limits of NMR; however, (1)H nuclei from levoglucosan was identified in Arctic glacier ice samples. This study suggests that the bulk of the DOM from these glaciers is a mixture of biologically labile molecules derived from microbes.     

Relationships between sensory perception and water distribution determined by low-field NMR T(2) relaxation in processed pork - impact of tumbling and RN(-) allele

The relationships between water distribution, measured with low-field NMR (LF-NMR) transverse (T₂) relaxometry and sensory properties in tumbled and non-tumbled cured-smoked loins from 30 female Hampshire crossbred pigs were investigated. Upon distributed analysis of the T₂ relaxation, three populations centred at about 2, 40 and 600–800 ms, respectively, were detected. Clear differences in the characteristics of the intermediate population (T₂₁) were observed between loins from carriers and non-carriers of the RN⁻ allele, which implies differences in water–protein interactions between the two genotypes. PLS regressions between NMR T₂ variables and sensory attributes revealed significant correlations between NMR T₂ variables and the sensory attributes juiciness, acidulous taste and meat taste, which mainly could be ascribed to the T₂₁ time constant. In addition, the number of unappealing pores assessed by the sensory panel was highly related to the relative T₂ populations, implying that the microstructure is directly reflected in the NMR T₂ populations. However, prediction of the processing yield from NMR T₂ variables was poor. The correlation improved when RN genotypes and tumbling conditions were included as predictors. Thus, other effects of tumbling treatments and RN genotypes unrelated to NMR T₂ relaxation were observed.     

Sorption of very hydrophobic organic compounds (VHOCs) on dissolved humic organic matter (DOM). 2. Measurement of sorption and application of a Flory-Huggins concept to interpret the data

Sorption phenomena of very hydrophobic compounds (VHOCs, log K(OW) > 5) on dissolved humic organic matter (DOM) are overwhelmingly based on partitioning processes. In this respect, DOM is very similar to "rubbery" soil/sediment OM. To exclude system adsorption effects, the DOM sorption coefficients (K(DOM)) of VHOCs were determined using a dynamic approach based on the VHOCs' aqueous solubility enhancement in the presence of DOM. Partition coefficients are strongly correlated to the analytes' Kow across the alkane, PAH, and PCB groups under study. These three "families" are regarded to be good models of hydrophobic partitioning. On the basis of a uniform one-parameter concept characterizing sorption on amorphous polymers, Hildebrand solubility parameters of amorphous polymeric sorbents, including DOM, and of sorbates can be calculated on the basis of partition coefficients. Likewise, partition coefficients can be estimated using Hildebrand solubility parameters. Literature-based partition coefficients on DOM fit very well in this universal one-parameter concept. On using our own sorption data of PAHs, PCBs, and alkanes on DOM, an almost identical solubility parameter for the DOM polymer under study is obtained. The concept is also very useful in understanding both waterborne and airborne bioconcentration processes, which are considered to be partitioning phenomena.     

In vitro interactions between DMSA-coated maghemite nanoparticles and human fibroblasts: A physicochemical and cyto-genotoxical study

Although the current production of oxide nanoparticles may be modest, the wide range of proposed applications and forecasted growth in production has raised questions about the potential impact of these nanoparticles on the environment and human health. Iron oxide nanoparticles have been proposed for an increasing number of biomedical applications although in vitro toxicity depending on the particles coating has been evidenced. The aim of this study was to examine the potential in vitro cyto- and genotoxicity on human dermal fibroblasts of DMSA-coated maghemite nanoparticles (NmDMSA) as a function of well-defined physicochemical states. Well-stabilized NmDMSA produced weak cytotoxic and no genotoxic effects. This is attributed in part to the DMSA coating, which serves as a barrier for a direct contact between nano-oxide and fibroblasts, inhibiting a potential toxic effect.     

基于~1H NMR的大米淀粉与马铃薯淀粉水合过程的水状态及分布差异研究

淀粉的水合过程显著影响淀粉食品的品质,尤其在中低水分区域,促进了淀粉类食品的多样性。该文聚焦谷类和薯类淀粉的代表:大米淀粉和马铃薯淀粉,利用1H低场核磁共振技术(LF-NMR)研究水分活度在0.2到1.0的大米淀粉和马铃薯淀粉的水分微观分布和流动情况,并比对差异产生的原因。通过采用反转恢复序列IR和利用自由感应衰减序列FID和多脉冲回波序列CPMG两种测试方法,获得2种淀粉体系的纵向质子弛豫(T1)和横向质子弛豫(T2)特征数据。纵向弛豫的研究结果表明,2种水合淀粉的氢质子分别处于2种不同的环境;横向弛豫的研究结果表明,水合大米淀粉中存在2个氢质子类群,而水合马铃薯淀粉则出现2~4个不同的质子类群。由于两者在粒径和溶胀能力上存在差异,故水合马铃薯淀粉较水合大米淀粉表现出更大的质子自由度和更多的质子量。     

Elucidation of the relationship between cooking temperature, water distribution and sensory attributes of pork - a combined NMR and sensory study

Low-field NMR T(2) relaxation was measured continuously during cooking of pork samples (m. longissimus dorsi) to a final temperature of 75 °C. Simultaneously the remaining muscle was cooked in an oven to a core temperature of either 62 or 75 °C and subsequently evaluated by a sensory panel. Highly significant effects of final cooking temperature on the sensory attributes juiciness (initial and final), hardness, tenderness, crumbliness and chewing time were found. Juiciness and tenderness decreased with increasing temperature, while hardness, crumbliness and chewing time increased with increasing temperature. Distributed T(2) relaxation data revealed marked effects of temperature (62 vs. 75 °C) on the water distribution within the meat. Partial least squares (PLS) regressions were used to examine a potential prediction of sensory attributes from the distributed T(2) relaxation data, and high correlations were obtained. Moreover, loadings from the PLS regressions were analysed to evaluate the alterations in the water distribution as a function of temperature that contribute to changes in juiciness. This analysis revealed that the reduction in juiciness at 75 °C can be ascribed to changes in the size of the pores confining the myofibrillar water together with an expulsion of water.     

1H NMR and Raman spectroscopy of oils and extracts obtained from organic and conventional goji berries: yield,fatty acids,carotenoids and biological activities

The yields of extraction, fatty acid and carotenoid compositions, antioxidant and antimicrobial activities of organic and conventional Lycium barbarum oils and extracts were investigated. Different methods were used in the extraction: Soxhlet, maceration and Bligh & Dyer. Sample characterization was performed by proton nuclear magnetic resonance and Raman spectroscopy. Soxhlet presented a higher yield for organic (4.58%) and conventional (2.83%) fruit. The Goji samples showed a high content of unsaturated fatty acids (UFA) for organic (78.29–84.72%) and conventional (70.74–80.20%) fruit. The main phytochemicals identified in the samples were linoleic acid and zeaxanthin dipalmitate. The maceration method was the most efficient in the extraction of carotenoids with high antioxidant (2.23–40.94 mmolTE 100 g⁻¹) and antimicrobial (3.12–200 mg mL⁻¹) activities. The organic goji samples showed higher yield, UFA, carotenoids and biological activities and these results indicate that this fruit is suitable for cosmetic, pharmaceutical and food applications.