The influence of aggregation on the redox chemistry of humic substances

2009 ◽  
Vol 6 (2) ◽  
pp. 178 ◽  
Author(s):  
Noel E. Palmer ◽  
Ray von Wandruszka
Keyword(s):  
Ionic Strength ◽  
Humic Substances ◽  
Reduction Potential ◽  
Divalent Cations ◽  
Redox Chemistry ◽  
Fulvic Acids ◽  
Monovalent Cations ◽  
Fluorescence Excitation ◽  
Reduction Potentials ◽  
Fluorescence Excitation Emission Matrices

Environmental context. The ability of humic substances (decaying plant and animal matter) to partake in redox reactions in the environment depends on the extent to which the various humic polymers aggregate in solution to form larger particles. This aggregation, in turn, is predicated on the solution conditions, especially ionic strength, the pH, and the types of cations present. Abstract. Aggregation and conformation play an important role in the aqueous redox chemistry of humic substances (HS). The reduction potentials of dissolved humic and fulvic acids vary with pH, ionic strength, and type of humate used, and depending on the solution conditions, they can abiotically reduce various species. Changes in HS reduction potential ranged from 60 to 140 mV on addition of divalent cations, whereas no significant changes were observed with equivalent additions of monovalent cations. Dynamic light scattering measurements showed that this behaviour paralleled the size changes obtained with humic aggregates under the same conditions. The effect was more pronounced at higher pH, where divalent cations caused a significant decrease in the average hydrodynamic radius, whereas monovalent cations did not. At pH 4, neither mono- nor divalent cations substantially affected aggregate sizes. Quinoid moieties, which are known to play an important role in the redox chemistry of HS, displayed fluorescence excitation–emission matrices with features related to changes in the reduction potential of HS. An increase in the reduction potential (Eh) induced by the addition of Ca2+, for instance, caused a red shift in the excitation–emission matrix maximum.

On-the-Fly Fluorescence Lifetime Detection of Humic Substances in Capillary Electrophoresis

2003 ◽  
Vol 57 (3) ◽  
pp. 256-265 ◽  
Author(s):  
Joseph D. Hewitt ◽  
Linda B. McGown
Keyword(s):  
Humic Substances ◽  
Fluorescence Lifetime ◽  
Spectral Characteristics ◽  
Emission Spectra ◽  
Fulvic Acids ◽  
Fluorescence Decay ◽  
Fluorescence Excitation ◽  
Lifetime Analysis ◽  
Decay Profile ◽  
Fluorescence Lifetime Detection

On-the-fly fluorescence lifetime detection was investigated as a tool for studying humic substances in capillary zone electrophoresis (CZE). Humic substances are complex, heterogeneous mixtures of natural products that tend to migrate in a single, broad CZE peak. The intrinsic fluorescence lifetime of five humic substances from the International Humic Substances Society (IHSS) was monitored using excitation at 488 or 364 nm to produce intensity-lifetime electropherograms for each of the substances. Each frequency-domain lifetime measurement, collected at sub-second intervals during the CZE run, contains the equivalent of a complete decay profile. Lifetime analysis of each decay profile was used to construct a lifetime-resolved electropherogram for each lifetime component, from which the variation in relative intensity contributions of each lifetime across the broad CZE peak could be determined. Absorption spectra, fluorescence excitation–emission spectra, and lifetime profiles of batch solutions of the samples were determined as well. It was found that, whereas absorption and fluorescence spectral characteristics tended to discriminate between humic acids and fulvic acids, the batch solution lifetime profiles discriminated instead between samples from different sources, regardless of fraction. On-the-fly lifetime detection provided a more detailed view of the fluorescence decay of the samples, including greater resolution of lifetimes for two of the fulvic acids and greater discrimination among samples based on lifetime profiles across the CZE peaks.

Cell-Glass Separation Depends on Salt Concentration and Valency: Measurements on Dictyostelium Amoebae by Finite Aperture Interferometry

1982 ◽  
Vol 54 (1) ◽  
pp. 299-310
Author(s):  
DAVID GINGELL ◽  
SHEILA VINCE
Keyword(s):  
Ionic Strength ◽  
Cell Membrane ◽  
Divalent Cations ◽  
Optical Measurements ◽  
Surface Glycoprotein ◽  
Monovalent Cations ◽  
Cell Surface Glycoprotein ◽  
Cellular Slime ◽  
Finite Aperture ◽  
Interacting Surfaces

Using pre-aggregation amoebae of the cellular slime mould Dictyostelium discoideum we have investigated the influence of cation concentration and valency on cell-glass separation. For computing the separation we used interference reflection microscopy and converted measured image irradiance to distance by finite aperture theory. Alterations in ionic strength caused virtually instantaneous reversible changes in the interference image due to changes in cell membrane-glass separation. In solutions containing monovalent cations, a change in ionic strength from 20 mM to 0.5 mM increased the separation of the plasmalemma from the glass by 60 nm. Divalent cations were better than monovalent cations at maintaining a small separation. Our results show that both divalent and trivalent cations adsorb to one or both of the interacting surfaces, in addition to acting as electrostatic double-layer counterions. The optical measurements also show that the cell membrane-glass gap is not reduced to zero by counterion screening; this is apparently due to the presence of a cell surface glycoprotein coat.

scholarly journals Dominating Role of Ionic Strength in the Sedimentation of Nano-TiO2in Aquatic Environments

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Guang’an He ◽  
Rui Chen ◽  
Shushen Lu ◽  
Chengchun Jiang ◽  
Hong Liu ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Natural Organic Matter ◽  
Divalent Cations ◽  
Environmental Water ◽  
Orthogonal Experimental Design ◽  
Aquatic Environments ◽  
Monovalent Cations ◽  
Sedimentation Behavior ◽  
Low Levels

Various factors affect the sedimentation behavior of nanotitanium dioxide (n-TiO2) in water. Accordingly, this study aimed to select the dominating factor. An index of sedimentation efficiency related to n-TiO2concentration was applied to precisely describe the n-TiO2sedimentation behavior. Ionic strength (IS), natural organic matter (NOM) content, and pH were evaluated in sedimentation experiments. An orthogonal experimental design was used to sequence the affecting ability of these factors. Furthermore, simulative sedimentation experiments were performed. The n-TiO2sedimentation behavior was only affected by pH and NOM content at low levels of IS. Moreover, divalent cations can efficiently influence the n-TiO2sedimentation behavior compared with monovalent cations at fixed IS. Seven different environmental water samples were also used to investigate the n-TiO2sedimentation behavior in aquatic environments. Results confirmed that IS, in which divalent cations may play an important role, was the dominating factor influencing the n-TiO2sedimentation behavior in aquatic environments.

Evaluation of the Hg2+binding potential of fulvic acids from fluorescence excitation–emission matrices

2013 ◽  
Vol 12 (2) ◽  
pp. 384-392 ◽  
Author(s):  
Andrea M. Berkovic ◽  
Fernando S. García Einschlag ◽  
Mónica C. Gonzalez ◽  
Reinaldo Pis Diez ◽  
Daniel O. Mártire
Keyword(s):  
Fulvic Acids ◽  
Binding Potential ◽  
Fluorescence Excitation ◽  
Excitation Emission Matrices ◽  
Fluorescence Excitation Emission Matrices

scholarly journals Characterization of Soil Organic Matter Individual Fractions (Fulvic Acids, Humic Acids, and Humins) by Spectroscopic and Electrochemical Techniques in Agricultural Soils

Agronomy ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1067
Author(s):  
Aleksandra Ukalska-Jaruga ◽  
Romualda Bejger ◽  
Guillaume Debaene ◽  
Bożena Smreczak
Keyword(s):  
Molecular Weight ◽  
Organic Matter ◽  
Soil Organic Matter ◽  
Humic Substances ◽  
Humic Acids ◽  
Agricultural Soils ◽  
Fulvic Acids ◽  
Sorption Properties ◽  
Aliphatic Chains

The objective of this paper was to investigate the molecular characterization of soil organic matter fractions (humic substances (HS): fulvic acids-FAs, humic acids-HAs, and humins-HNs), which are the most reactive soil components. A wide spectrum of spectroscopic (UV–VIS and VIS–nearIR), as well as electrochemical (zeta potential, particle size diameter, and polydispersity index), methods were applied to find the relevant differences in the behavior, formation, composition, and sorption properties of HS fractions derived from various soils. Soil material (n = 30) used for the study were sampled from the surface layer (0–30 cm) of agricultural soils. FAs and HAs were isolated by sequential extraction in alkaline and acidic solutions, according to the International Humic Substances Society method, while HNs was determined in the soil residue (after FAs and HAs extraction) by mineral fraction digestion using a 0.1M HCL/0.3M HF mixture and DMSO. Our study showed that significant differences in the molecular structures of FAs, Has, and HNs occurred. Optical analysis confirmed the lower molecular weight of FAs with high amount of lignin-like compounds and the higher weighted aliphatic–aromatic structure of HAs. The HNs were characterized by a very pronounced and strong condensed structure associated with the highest molecular weight. HAs and HNs molecules exhibited an abundance of acidic, phenolic, and amine functional groups at the aromatic ring and aliphatic chains, while FAs mainly showed the presence of methyl, methylene, ethenyl, and carboxyl reactive groups. HS was characterized by high polydispersity related with their structure. FAs were characterized by ellipsoidal shape as being associated to the long aliphatic chains, while HAs and HNs revealed a smaller particle diameter and a more spherical shape caused by the higher intermolecular forcing between the particles. The observed trends directly indicate that individual HS fractions differ in behavior, formation, composition, and sorption properties, which reflects their binding potential to other molecules depending on soil properties resulting from their type. The determined properties of individual HS fractions are presented as averaged characteristics over the examined soils with different physico-chemical properties.

scholarly journals Organic Materials and Their Chemically Extracted Humic and Fulvic Acids as Potential Soil Amendments for Faba Bean Cultivation in Soils with Varying CaCO3 Contents

Horticulturae ◽  
2021 ◽  
Vol 7 (8) ◽  
pp. 205
Author(s):  
Ihab M. Farid ◽  
Mohamed A. El-Ghozoli ◽  
Mohamed H. H. Abbas ◽  
Dalia S. El-Atrony ◽  
Hassan H. Abbas ◽  
...  
Keyword(s):  
Humic Substances ◽  
Faba Bean ◽  
Plant Biomass ◽  
Nitrogenase Activity ◽  
Organic Amendments ◽  
Fulvic Acids ◽  
Mineral N ◽  
Randomized Design ◽  
Long Time ◽  
Factor C

Organic amendments are important sources of nutrients that release upon organic matter degradation, yet the stability of these organics in arid and semi-arid regions is relatively low. In contrast, humic substances (HS) are resistant to biodegradation and can keep nutrients in the soil available for the plant over a long time. Combinations between humic substances (HS) and mineral-N fertilizers are assumed to retain higher available nutrients in soils than those recorded for the sole application of either mineral or organic applications. We anticipate, however, that humic substances might not be as efficient as the organics from which they were extracted in increasing NP uptake by plants. To test these assumptions, faba bean was planted in a pot experiment under greenhouse conditions following a complete randomized design while considering three factors: two soils (calcareous and non-calcareous, Factor A), two organics (biogas and compost, Factor B) and combinations of the organics and their extracts (HA or FA) together with complementary doses of mineral-N ((NH4)2SO4) to attain a total rate of 50 kg N ha−1 (the recommended dose for faba bean plants) (Factor C). Results indicated that nitrogenase activity increased significantly due to the application of the used organics. In this respect, compost manure caused higher nitrogenase activity than biogas manure did. Humic substances raised NP-availability and the uptake by plants significantly; however, the values of increase were lower than those that occurred due to the compost or biogas manure. Moreover, the sole application of the used organics recorded the highest increases in plant biomass. Significant correlations were also detected between NP-availability, uptake and plant biomass. This means that HS could probably retain nutrients in available forms for long time periods, yet nutrients released continuously but slowly upon decomposition of organics seemed more important for plant nutrition.

scholarly journals Spectral Probe for Electron Transfer and Addition Reactions of Azide Radicals with Substituted Quinoxalin-2-Ones in Aqueous Solutions

2021 ◽  
Vol 22 (2) ◽  
pp. 633
Author(s):  
Konrad Skotnicki ◽  
Slawomir Ostrowski ◽  
Jan Cz. Dobrowolski ◽  
Julio R. De la Fuente ◽  
Alvaro Cañete ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Aqueous Solutions ◽  
Absorption Spectra ◽  
Density Functional ◽  
Reduction Potential ◽  
Biological Significance ◽  
Radical Cations ◽  
Basis Sets ◽  
Double Bonds ◽  
Reduction Potentials

The azide radical (N3●) is one of the most important one-electron oxidants used extensively in radiation chemistry studies involving molecules of biological significance. Generally, it was assumed that N3● reacts in aqueous solutions only by electron transfer. However, there were several reports indicating the possibility of N3● addition in aqueous solutions to organic compounds containing double bonds. The main purpose of this study was to find an experimental approach that allows a clear assignment of the nature of obtained products either to its one-electron oxidation or its addition products. Radiolysis of water provides a convenient source of one-electron oxidizing radicals characterized by a very broad range of reduction potentials. Two inorganic radicals (SO4●−, CO3●−) and Tl2+ ions with the reduction potentials higher, and one radical (SCN)2●− with the reduction potential slightly lower than the reduction potential of N3● were selected as dominant electron-acceptors. Transient absorption spectra formed in their reactions with a series of quinoxalin-2-one derivatives were confronted with absorption spectra formed from reactions of N3● with the same series of compounds. Cases, in which the absorption spectra formed in reactions involving N3● differ from the absorption spectra formed in the reactions involving other one-electron oxidants, strongly indicate that N3● is involved in the other reaction channel such as addition to double bonds. Moreover, it was shown that high-rate constants of reactions of N3● with quinoxalin-2-ones do not ultimately prove that they are electron transfer reactions. The optimized structures of the radical cations (7-R-3-MeQ)●+, radicals (7-R-3-MeQ)● and N3● adducts at the C2 carbon atom in pyrazine moiety and their absorption spectra are reasonably well reproduced by density functional theory quantum mechanics calculations employing the ωB97XD functional combined with the Dunning’s aug-cc-pVTZ correlation-consistent polarized basis sets augmented with diffuse functions.

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