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Spherical structures built from uni- and multilamellar lipid bilayers (LUV and MLV) are nowadays considered not just as nanocarriers of various kinds of therapeutics, but also as the vehicles that, when coupled with gold (Au) nanoparticles (NPs), can also serve as a tool for imaging and discriminating healthy and diseased tissues. Since the presence of Au NPs or their aggregates may affect the properties of the drug delivery vehicle, we investigated how the shape and position of Au NP aggregates adsorbed on the surface of MLV affect the arrangement and conformation of lipid molecules. By preparing MLVs constituted from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in the presence of uncoated Au NP aggregates found i) both within liposome core and on the surface of the outer lipid bilayer, or ii) adsorbed on the outer lipid bilayer surface only, we demonstrated the maintenance of lipid bilayer integrity by microscopic techniques (cryo-TEM, and AFM). The employment of SERS and FTIR-ATR techniques enabled us not only to elucidate the lipid interaction pattern and their orientation in regards to Au NP aggregates but also unequivocally confirmed the impact of Au NP aggregates on the persistence/breaking of van der Waals interactions between hydrocarbon chains of DPPC. [ABSTRACT FROM AUTHOR]

A detailed study of Zn(II)-D-mannosamine and mixed ligand complex Zn(II)-D-mannosamine-glycine in aqueous solution ( θ = 25 °C, I c = 0.55 mol L −1 ) was carried out by voltammetry and potentiometry, allowing their characterization. Redox process of the [ZnManN] 2+ complex was registered at E p ∼ −1.01 V, [ZnGly] + at −1.02 V, ZnGly 2 at −1.18 V, while [ZnManNGly] + at −1.12 V (pH = 8.0). Stoichiometry and stability constants of Zn (II) complexes were determined by potentiometric titrations. Calculated stability constants were found to be: log   β ZnManN 2 + = 2.7, log   β MaNZnGly + = 7.7 and log   β MaNZnGlyH − 1 = −0.15. Voltammetric and potentiometric data were in good agreement, both indicating formation of two different ternary complexes, i.e. [ZnGlyManN] + and [ZnGlyManNH −1 ]. Calculated speciation revealed the presence of the [ZnManN] 2+ complex, as well as ternary complexes ([ZnManNGly] + ) in significant amount. This study was the first attempt to quantify complexation processes of Zn (II) with naturally occurring amino sugar and mixed complex with amino acid, important for bioavailability of zinc (II) in seawater. [ABSTRACT FROM AUTHOR]

Speciation of iron(III) ( c Fe = (0.5 - 40) × 10 −5 mol dm −3 ) and indirectly of iron(II), in aqueous solution of L-aspartic acid and aspartic acid - glycine mixture was investigated by square-wave voltammetry on a static mercury drop electrode. A reversible, one-electron reduction process of iron(III)-aspartate complexes with peak potential between +0.04 and -0.17 V was recorded, depending on the solution pH (4.5–8.6) and concentration of aspartic acid ( c Asp = 0.01 - 0.4 mol dm −3 ). Cumulative stability constants of iron(III)-aspartate complexes: FeAsp + (log K = 13.16 ± 0.01), FeAspOH 0 (log β = 20.76 ± 0.02), FeAsp(OH) 2 − (log β = 27.77 ± 0.12) and Fe(Asp) 2 − (log β = 17.62 ± 0.10); and iron(II)-aspartate complexes: FeAsp 0 (log K = 4.17 ± 0.11) and Fe(Asp) 2 2− (log β = 6.53 ± 0.11), were determined at I c = 0.5 mol dm −3 and 25 ± 1 °C. In the solution with mixture of amino acids, aspartic acid and glycine, a formation of mixed (Fe(III)-aspartate-glycine) complexes occurred. The reduction process was also shown to be reversible, so stability constants of mixed complexes (iron(III): FeAspGly 0 (log β = 17.35 ± 0.02), FeAspGly(OH) − (log β = 23.87 ± 0.33), and iron(II): FeAspGly − (log β = 6.83 ± 0.23)) were calculated, as well. [ABSTRACT FROM AUTHOR]

Abstract: A detailed study of iron (III)–citrate speciation in aqueous solution (θ =25°C, I c =0.7molL−1) was carried out by voltammetric and UV–vis spectrophotometric measurements and the obtained data were used for reconciled characterization of iron (III)–citrate complexes. Four different redox processes were registered in the voltammograms: at 0.1V (pH=5.5) which corresponded to the reduction of iron(III)–monocitrate species (Fe:cit=1:1), at about −0.1V (pH=5.5) that was related to the reduction of FeL2 5−, FeL2H4− and FeL2H2 3− complexes, at −0.28V (pH=5.5) which corresponded to the reduction of polynuclear iron(III)–citrate complex(es), and at −0.4V (pH=7.5) which was probably a consequence of Fe(cit)2(OH) x species reduction. Reversible redox process at −0.1V allowed for the determination of iron(III)–citrate species and their stability constants by analyzing E p vs. pH and E p vs. [L4−] dependence. The UV–vis spectra recorded at varied pH revealed four different spectrally active species: FeLH (log β =25.69), FeL2H2 3− (log β =48.06), FeL2H4− (log β =44.60), and FeL2 5− (log β =38.85). The stability constants obtained by spectrophotometry were in agreement with those determined electrochemically. The UV–vis spectra recorded at various citrate concentrations (pH=2.0) supported the results of spectrophotometric–potentiometric titration. [Copyright &y& Elsevier]

Abstract: Voltammetric investigations of iron(III)–chrysobactin complexes in aqueous solution at static mercury electrode, were performed. With c Fe =(0.5–30)×10−7 moldm−3 and c Cb =(0.5–100)×10−7 moldm−3 in pH range 6.7–10, reduction peaks with E p −0.64 to −0.74V (1) and E p −0.50 to −0.62V (2) vs. Ag/AgCl, were registered. These reduction processes were time dependent as well as solution composition (c Fe, c Cb and pH). Complexes are adsorbed at the mercury drop surface. Presumed stoichiometry of the detected complexes was FeIIICb3 (1) and FeIIICb2(OH) x (2). Their formation/dissociation processes were described. These investigations are of biological importance as well, since provide an insight into possible reduction mechanism in the bacterial cells that use chrysobactin to acquire the iron. [Copyright &y& Elsevier]

The distribution and speciation of elements along a stream subjected to neutralised acid mine drainage (NAMD) effluent waters (Mátra Mountain, Hungary; Toka stream) were studied by a multi-methodological approach: dissolved and particulate fractions of elements were determined by HR-ICPMS, whereas speciation was carried out by DGT, supported by speciation modelling performed by Visual MINTEQ. Before the NAMD discharge, the Toka is considered as a pristine stream, with averages of dissolved concentrations of elements lower than world averages. A considerable increase of element concentrations caused by effluent water inflow is followed by a sharp or gradual concentration decrease. A large difference between total and dissolved concentrations was found for Fe, Al, Pb, Cu, Zn and As in effluent water and at the first downstream site, with high correlation factors between elements in particulate fraction, indicating their common behaviour, governed by the formation of ferri(hydr)oxides (co)precipitates. In-situ speciation by the DGT technique revealed that Zn, Cd, Ni, Co, Mn and U were predominantly present as a labile, potentially bioavailable fraction (> 90%). The formation of strong complexes with dissolved organic matter (DOM) resulted in a relatively low DGT-labile concentration of Cu (42%), while low DGT-labile concentrations of Fe (5%) and Pb (12%) were presumably caused by their existence in colloidal (particulate) fraction which is not accessible to DGT. Except for Fe and Pb, a very good agreement between DGT-labile concentrations and those predicted by the applied speciation model was obtained, with an average correlation factor of 0.96. This study showed that the in-situ DGT technique in combination with model-predicted speciation and classical analysis of samples could provide a reasonable set of data for the assessment of the water quality status (WQS), as well as for the more general study of overall behaviour of the elements in natural waters subjected to high element loads. [ABSTRACT FROM AUTHOR]

Copper(II) complexes with cysteine and histidine, amino acids that coordinate copper(II) in human body, were investigated. Cu-His and Cu-Cys complexes were detected in pH range from 5.0 to 9.0 using voltammetric techniques. [CuHis2] complex reduces by two-electron reversible process at ≈−0.40 V, while [CuCys] complex by one-electron quasireversible process at −0.6 V, revealing strong adsorption at the electrode surface. When both amino acids are present in the solution, new peak appeared at −0.5 V, which corresponded to the [CuHisCys] complex reduction. Formation and characterization of mixed ligand complex was also supported by UV-Vis spectra recorded at fixed histidine and various cysteine concentrations. Formation of [CuHisCys] complex in the solution was detected and stability constant calculated to amount to log KCuHisCys=16.9±0.3. This study was the first attempt to characterize formation of Cu(II) mixed ligand complexation process with biochemically important amino acids in electron transport and oxygenation reactions in human body. [ABSTRACT FROM AUTHOR]