The complexing capacity for Cu ions (LT) and the apparent stability constant values (logKapp) were measured in throughfall (TF) and open field bulk deposition (BD), at two Mediterranean forest ...ecosystems of western Greece. LT was measured for the first time in the TF of natural forests.
Concentrations of LT were three-to-four-fold higher in TF (mean ± st.dev: 2014 ± 769 nM for Varetada and 1565 ± 595 nM for Karpenissi) compared to those in BD (531 ± 517 nM and 468 ± 321 nM, respectively). In all TF and BD samples, LT concentrations were significantly higher than the corresponding total Cu concentrations, indicating that Cu was fully complexed. The LT/TOC ratios in TF were found comparable between the two study sites (235 ± 149 nM mg−1 C for Varetada and 256 ± 233 nM mg−1 C for Karpenissi) and with those of BD (226 ± 257 and 163 ± 163 nM mg−1 C, respectively). The determined mean logKapp values were almost identical in TF (6.8 ± 0.7 at Varetada; 6.8 ± 0.6 at Karpenissi) and BD (6.5 ± 0.6 at Varetada; 6.8 ± 0.3 at Karpenissi), pointing to the fact that regardless of the enrichment of TF in ligands (LT(TF) > LT(BD)) the type of binding sites remain the same. The logKapp values which were obtained herewith are similar to those obtained for humic-like substances (HULIS), indicating them as the most widespread type of ligands in BD and TF.
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•Cu complexation in forest throughfall was studied for the first time by DPASV.•Samples were collected from two different Mediterranean forest ecosystems.•In throughfall (TF) and bulk deposition (BD) copper was fully complexed.•Cu ligands concentrations were determined 3–4 fold higher in TF than in BD.•HULIS seem to be the most widespread type of ligands in both type of precipitations.
Melanoidins, condensation products of sugars and amino acids, represent a key link in the transformation of polysaccharides to humic material in the marine environment. We investigated the complexing ...capacity of melanoidins that were prepared in deionized water and seawater and separated into different molecular mass fractions. The copper complexing properties of humic material isolated from marine lagoon sediments were determined for comparison. Melanoidins prepared using condensation times longer than two days exibit complexation properties towards copper ions that appear to depend on the basicity of the amino acid precursor and the molecular mass of the product. Pseudomelanoidins, prepared from glucose only, do not complex copper ions at all, regardless of the molecular mass. The highest copper complexing capacity value among melanoidins was measured for a glucose–lysine melanoidin with molecular mass fraction >
10 kD (L
T
=
2.1
×
10
−
7
molCu
2+/L). Melanoidin prepared from glucose and glutamic acid >
10 kD was similar in complexing capacity to fulvic acid (1–20 kD molecular mass) isolated from lagoon sediments. The presence of calcium and magnesium ions and other macro and microconstituents in the seawater used to prepare melanoidins influences its complexing properties towards metal ions.
Sensitive electrochemical techniques were combined with photometric and chromatographic assays to characterize the organic matter, determine selected bioactive compounds, and evaluate antioxidant ...properties of popular coffee brews. Physicochemical properties of organic material released in Greek/Turkish, espresso, filter, and instant coffee brews were investigated measuring copper-complexing ligands (
L
T
), surface active substances (SAS), and catalytically active compounds (CAC). In addition, organic carbon, total and individual phenolics, and caffeine were measured. The content of Maillard reaction products was estimated. Antioxidant potential was primarily assessed measuring DPPH-radical scavenging capacity and ferric-reducing antioxidant power. The potential inhibition of human serum lipoprotein oxidation in vitro was also investigated. The effect of fast or slow sipping of Greek/Turkish coffee was investigated as regards organic matter release and antioxidant activity. Coffee brews release Cu complexing ligands at different concentrations (74.6 and 364 mM in filter and Greek/Turkish coffees, respectively). Coffee brews contained 50.1–445 mg caffeoylquinic acids (CQAs) per 100 mL, the 47–53% being chlorogenic acid. Among coffee brews, espresso contained more CAC, SAS, copper-complexing ligands, caffeine, browned compounds, and phenolics. In addition, espresso exhibited higher antiradical activity and reducing power, while Greek/Turkish coffees higher resistance to serum lipid oxidation.
•Catalytic “peak HPS” was produced in the solution of κ, ι-, and λ-carrageenan.•Peak increased at negative accumulation potentials due to breakdown of associations.•AdT CPS conditions for κ, ι-, and ...λ-carrageenan analysis in seawater were defined.•Only λ-carrageenan could be detected in the mixture with κ- and/or ι-carrageenan.
Sulphated polysaccharides κ-, ι-, and λ-carrageenan were analysed in seawater by applying adsorptive transfer constant current derivative chronopotentiometric stripping (AdT CPS) method on mercury electrode. Accelerated faradaic (catalytic) nature of the peak (peak HPS) recorded at negative potential was confirmed for all three carrageenans using specific electrochemical criteria. The effect of chronopotentiometric parameters (accumulation potential, accumulation time and stripping current) on the peak HPS height was evaluated for each carrageenan. Optimal CPS parameters for AdT CPS analysis of particular carrageenan in seawater were defined. Regarding the AdT CPS of carrageenans mixture, only λ-carrageenan could be successfully measured in the mixture with ι- and/or κ-carrageenan. This is the first electroanalytical study of a model mixture of sulphated polysaccharides in seawater and it is of great importance for the analysis of organic matter in seawater, especially acidic polysaccharides containing sulphate groups in the structure.
In this communication an ex situ analysis of sulphated polysaccharide (S-PS) chondroitin sulphate (CS) on mercury electrode is reported for the first time. The analysis was performed using adsorptive ...transfer chronopotentiometric stripping (AdT CPS). AdT CPS included three major steps: adsorption, transfer and stripping. S-PS served as “presodium” catalyst of hydrogen evolution revealing two catalytic peaks, H'PS and HPS. The adsorbed CS layer was very stable after the transfer. The reproducibility of the peak HPS was very high. Accumulation potentials more positive than −0.6V (vs. Ag/AgCl(3M KCl)) were appropriate in analysis of a negatively charged twofold helix of CS in water solution.
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► An ex situ technique enabled analysis of sulphated polysaccharide in seawater. ► Sulphated polysaccharide was a “presodium” catalyst of hydrogen evolution. ► Adsorptive transfer chronopotentiometric stripping displayed peaks H'PS and HPS. ► The adsorbed layer of sulphated polysaccharide was very stable after the transfer. ► Detection limit in the range of pmol dm-3 was calculated.
This study demonstrates the potential of the electrochemical methods for the characterization of dissolved organic matter (DOM) in the drainage water of hydroameliorated agricultural areas. A study ...of drainage water could lead to a better understanding of the distribution and fate of terrestrial DOM in the freshwater systems. We have applied the voltammetric techniques which were developed by our group for the characterization of organic matter in the natural waters in general. Studied samples were collected in the experimental amelioration fields in the Sava river valley (45
°
33′ 52″ N/16° 31′ 33″ E, 100 m above sea level), in the hydroameliorated agricultural areas in Croatia. The rough characterization of the type, nature and reactivity of DOM was done through the study of surface activity (SA) of dissolved organic carbon (DOC), copper complexing capacity (CuCC) and apperent stability constants, and measurements of organic and inorganic reduced sulfur species (RSS) fractions. The results confirm that the electrochemical approach gives a valuable and comprehensive insight into physicochemical characteristics of DOM in the drainage water and could be successfully applied to temporal studies in different terrestrial ecosystem.
Cu complexation in wet precipitation samples was measured by the method of differential pulse anodic stripping voltammetry (DPASV), which presumed the existence of 1:1 Cu ion–ligand complexes. The ...wet precipitation samples were collected throughout the rainy period (September 2011–May 2012) from four sampling stations of central and southern Greece, two of which were located in urban coastal areas of its mainland (Athens, n = 24; Elefsina, n = 11) and the other two on the island of Crete (Heraklio, n = 26; Ligortynos, n = 12), comprising different features concerning population density, urban/rural/industrial character and influence from the sea. Total Cu (TCu), total organic and inorganic carbon (TOC, IC), pH, conductivity, several inorganic macro-constituents (Cl−, Br−, NO3−, SO42−, Na+, K+, Ca2+, Mg2+), n-alkanes and polycyclic aromatic hydrocarbons (PAHs) were determined for better characterization of the predominant sources and influences.
Significant complexation of Cu ions was determined in almost all wet precipitation samples examined, with the apparent complexing capacity of Cu ions in unfiltered samples ranging between 0.07 and 1.9 μM and apparent stability constants (logKapp) in the range 6.5–9.6, which corresponds to values comparable to those deriving from a limited number of studies having a common ‘detection window’. The percentage in the mass of TOC complexed with copper was up to 4%.
Among ligands, sources of terrestrial origin appear to be of particular importance. In terrestrial sources, vegetation and anthropogenic emissions seem to have a prominent impact.
•Cu complexation in wet precipitation was examined by DPASV.•Cu ligands ranged between 0.07 and 1.9 μM.•Logkapp were determined in the range 6.5–9.6.•Among ligands, sources of terrestrial origin appear to be of particular importance.•Vegetation and anthropogenic emissions seem to have a prominent impact.
The remobilization of copper, cadmium and zinc in sediments of three selected coastal microenvironments of the Aegean Sea (Eastern Mediterranean) is assessed. Various analytical methods and ...techniques were employed providing concentrations, profiles and forms of metals and organic matter in sediments and pore waters.
At Loutropyrgos, a non-industrial site located, however, within an intensively industrialized enclosed gulf, an intense resupply of zinc in pore water from sediment was recorded, correlating with the highest value of weakly bound fraction of zinc determined at this area. The comparatively high zinc concentrations measured in the pore waters (394 nM), exceed considerably those in the overlying seawater (12.5 nM determined by DGT; 13.5 nM total), resulting in the formation of a strong concentration gradient at the sediment–water interface. Potential zinc flux at the sediment–water interface at Loutropyrgos (based on 0.4 mm DGT profile) was calculated equal to 0.8 mmol.m
−2.d
−1. The half lives of trace metals at Loutropyrgos site, based on the aforementioned DGT profiles, amount to 0.1 y (Zn), 2.8 y (Cd), 4.5 y (Cu), 2.2 y (Mn) and 0.4 y (Fe) pointing out to the reactivity of these metals at the sediment–water interface.
The concentration of dissolved organic carbon (DOC) in pore waters of the three selected sites (2.7–5.2 mg/L) was up to four times higher compared to that of the corresponding overlying seawater. Similarly, the concentrations of carbohydrates in pore waters (0.20–0.91 mg/L monosaccharides; 0.71–1.6 mg/L polysaccharides) are an order of magnitude higher than those of seawater, forming a concentration gradient at the sediment–water interface. Total carbohydrates contribute between 34 and 48% of the organic carbon of the pore waters, being significantly higher than those of seawater from the corresponding areas, which were in the range of 15–21%.
The complexing capacity as for copper ions (CCu) determined in pore water ranges widely, from 0.03 μM at Kalamos to 3.76 μM at Molos, whereas the corresponding values for cadmium ions (CCd) were non detectable, except for Kalamos site, where the value for CCd was equal to 0.03 μM. A significant increase in the values of CCu, normalized as for DOC, was observed in pore waters in relation to those of overlying seawater. This indicates an ‘enrichment’ of pore waters in dissolved organic ligands for copper ions per unit of DOC. Up to 72% of DOC could be present as ligands capable to complex copper ions.
► Assessment of copper, cadmium and zinc remobilization in coastal sediments of Aegean Sea. ► Strong concentration gradient of zinc at sediment-water interface. ► Concentration of DOC up to four times higher in pore waters than in overlying seawater. ► Enrichment of pore waters in dissolved organic ligands for copper ions.
The goal of this study was to investigate if transparent exopolymer particles (TEP), carbohydrates, surface-active substances (SAS), reduced sulfur species (RSS), or thio/amino groups contribute ...significantly to the complexing capacity of phytoplankton exudates for Cu (LTOTCu), Cd (LTOTCd), or Fe (LTOTFe). Complexing capacities and apparent stability constants (Kapp) were determined electrochemically for Cu and Cd in cultures of the marine diatomsThalassiosira weissflogiiandSkeletonema costatum, and in a culture of the coccolithophoreEmiliana huxleyi. Furthermore, the complexing capacity with Fe, Cu and Cd of 4 marine polysaccharides (PS) (phytagel, carrageenan, laminarin and alginic acid) was investigated. As expected, more Cu than Cd was complexed in the 3 phytoplankton cultures and in the phytagel solution. Size fractionation of the phytagel solution suggests that the binding capacity for Cu was more significant in the particulate fraction (>0.7 μm), indicating that Cu was preferably trapped within pores and channels of large hydrogels. In contrast, Cd binding sites were predominantly found in the fraction <0.7 μm, suggesting binding to the outer surfaces of gel particles to be of greater importance for larger ions. The Kappof the Cd complexes were higher than those of Cu, indicating stronger binding of Cd ions than of Cu ions. Solutions of carrageenan, laminarin and alginic acid did not form complexes with either Cu or Cd, and Fe-binding properties could not be detected for any of the 4 polysaccharide solutions. Thio/amino groups of sulfur-rich ‘glutathione’ type ligands were found in all phytoplankton cultures and were presumably responsible for the complexation of Cu. No consistent relationship was observed between TEP, carbohydrate concentration, SAS or sulfur content, or with the complexing capacity, emphasizing the high degree of heterogeneity of substance classes responsible for metal binding.
•Copper complexation in herb infusions was examined by anodic stripping voltammetry.•Copper ligands ranged between 8.8 and 112.5μM.•Stability constants (logKapp) of copper ligands were in the range ...6.3–8.7.•Organic matter was studied for the first time electrochemically in infusions.•Copper chelating capacity of infusions is partially attributed to specific organics.
Complex formation is among the mechanisms affecting metals’ bioaccessibility. Evaluating the extent of interactions between trace elements and several constituents of food items is of great interest. This paper examines the release of copper-complexing ligands in herbal infusions of 13 aromatic plants commonly used in Greece. The concentration of ligands (LT) and the copper-binding strength (logKapp) of herbal infusions were determined with Differential Pulse Anodic Stripping Voltammetry (DPASV).
All herbal infusions were found to release Cu complexing ligands, at concentrations ranging from 8.8 to 112.5μM in rosemary and marjoram, respectively. In all infusions the total copper concentrations were lower than the corresponding LT values, indicating that Cu is fully complexed.
Aiming to partially characterise the physico-chemical properties of the released organic material, the surface active substances (SAS), reduced sulphur species (RS) and catalytically active compounds (CAC) were measured, for the first time, in herbal infusions by sensitive electrochemical techniques.
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