Search

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]

Atomic force microscopy (AFM) is a method that provides the nanometer-resolution three-dimensional imaging of living cells in their native state in their natural physiological environment. In addition, AFM's sensitivity to measure interaction forces in the piconewton range enables researchers to probe surface properties, such as elasticity, viscoelasticity, hydrophobicity and adhesion. Despite the growing number of applications of AFM as a method to study biological systems, AFM is not yet an established technique for studying microalgae. Following a brief introduction to the basic principles and operation modes of AFM, this review highlights the major contributions of AFM in the field of microalgae research. A pioneering AFM study on microalgae was performed on diatoms, revealing the fine structural details of diatom frustule, without the need for sample modification. While, to date, diatoms are the most studied class of microalgae using AFM, it has also been used to study microalgae belonging to other classes. Besides using AFM for the morphological characterization of microalgae at the single cell level, AFM has also been used to study the surface properties of microalgal cells, with cell elasticity being most frequently studied one. Here, we also present our preliminary results on the viscoelastic properties of microalgae cell (Dunaliella tertiolecta), as the first microrheological study of microalgae. Overall, the studies presented show that AFM, with its multiparametric characterization, alone or in combination with other complementary techniques, can address many outstanding questions in the field of microalgae. [ABSTRACT FROM AUTHOR]

The properties of engineered nanoparticles (NPs) in the marine environment are influenced not only by the high ionic strength of seawater but also by the interaction of NPs with naturally occurring components of seawater, especially natural organic matter. The aim of this study was to investigate the interaction of engineered silica nanoparticles (SiO2 NPs, diameter of 12 nm) with microalgal extracellular polymers (EPS) released by the marine diatom Cylindrotheca closterium. Dissolved organic carbon (DOC) content of the prepared EPS suspension (200 μg mL−1) used throughout the study was 3.44 mg C L−1. The incorporation of individual SiO2 NPs (height range 10–15 nm) and their nanoscale aggregates (height up to 25 nm, length up to 600 nm) into the EPS network was visualized by atomic force microscopy (AFM), whereas their molecular-level interaction was unraveled by the change in the signal of the Si-O group in their FTIR spectra. AFM imaging of C. closterium cells taken directly from the culture spiked with SiO2 NPs (10 μg mL−1) revealed that the latter are bound to the EPS released around the cells, predominantly as single NPs (height range 10–15 nm). Since AFM and dynamic and electrophoretic light scattering results demonstrated that SiO2 NPs dispersed in seawater without EPS showed enhanced aggregation (aggregate diameter of 990 ± 170 nm) and a 2.7-fold lower absolute zeta potential value compared to that measured in ultrapure water, our findings suggest that the presence of EPS biopolymers alters the aggregation affinity of SiO2 NPs in the marine environment. This might be of outmost importance during microalgal blooms when increased EPS production is expected because EPS, by scavenging and stabilizing SiO2 NPs, could prolong the presence of NPs in the water column and pose a threat to marine biota. [ABSTRACT FROM AUTHOR]

Natural phospholipid (PL)n extract from cultured green algae Dunaliela tertiolecta was used as the main component of cell membranes for studies on the interaction with trace metal Co(II). The phospholipids of the membranes were extracted from other biological components using TiO2-µSPE cartridges selective for the phosphate group according to a completely new protocol. The interaction of Co(II) with natural and standard phospholipids, phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylglycerol (PG) are registered only in the presence of the additional chelating ligand 1,10-Phenathroline (Phen). 1,10-Phenathroline, as a model of humic substances in the marine environment, formed a neutral complex with Co(II) by the substitution of water molecules of central metal ions. The interaction of hydrophobic mixed-ligand complexes with phospholipids was enabled by the substitution of the remaining water molecules in the coordination shell of Co(II), which was registered by voltammetric measurements. The Co(II)-Phen-PL complex is reduced from the adsorbed state at −1.65 V by the transfer of two electrons, followed by its irreversible dissociation and desorption, indicating an EC mechanism. The interaction between the mixed-ligand complexes Co(II)-Phen-lipids was confirmed by atomic force microscopy (AFM). AFM images of PL, PL with Phen mixture and PL, Phen with Co(II) showed different 3D structures on the mica surface, indicating changes caused by the interaction between cobalt(II), 1,10-Phenanthroline and phospholipids. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the effect of positively charged (amine-modified) and negatively charged (carboxyl-modified) polystyrene nanoplastics (PS NPs) on the nanostructural, nanomechanical, and antioxidant responses of the marine diatom Cylindrotheca closterium. The results showed that both types of PS NPs, regardless of surface charge, significantly inhibited the growth of C. closterium during short-term exposure (3 and 4 days). However, longer exposure (14 days) to both PS NPs types did not significantly inhibit growth, which might be related to the detoxifying effect of the microalgal extracellular polymers (EPS) and the higher cell abundance per PS NPs concentration. The exposure of C. closterium to both types of PS NPs at concentrations above the corresponding concentrations that resulted in a 50% reduction of growth (EC50) demonstrated phytotoxic effects, mainly due to the excessive production of reactive oxygen species, resulting in increased oxidative damage to lipids and changes to antioxidant enzyme activities. Diatoms exposed to nanoplastics also showed a significant decrease in cell wall rigidity, which could make the cells more vulnerable. Atomic force microscopy images showed that positively charged PS NPs were mainly adsorbed on the cell surface, while both types of PS NPs were incorporated into the EPS that serves to protect the cells. Since microalgal EPS are an important food source for phytoplankton grazers and higher trophic levels, the incorporation of NPs into the EPS and interactions with the cell walls themselves may pose a major threat to marine microalgae and higher trophic levels and, consequently, to the health and stability of the marine ecosystem. [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]

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]