Organic-coated silver nanoparticles in biological and environmental conditions: Fate,stability and toxicity

This review paper presents the overview of processes involved in transformation of organic-coated silver nanoparticles (AgNPs) in biological systems and in the aquatic environment. The coating on AgNPs greatly influences the fate, stability, and toxicity of AgNPs in aqueous solutions, biological systems, and the environment. Several organic-coated AgNP systems are discussed to understand their stability and toxicity in biological media and natural water. Examples are presented to demonstrate how a transformation of organic-coated AgNPs in an aqueous solution is affected by the type of coating, pH, kind of electrolyte (mono- or divalent), ionic strength, organic ligands (inorganic and organic), organic matter (fulvic and humic acids), redox conditions (oxic and anoxic), and light. Results of cytotoxicity, genotoxicity, and ecotoxicity of coated AgNPs to food chain members (plants, bacteria, and aquatic and terrestrial organisms) are reviewed. Key factors contributing to toxicity are the size, shape, surface coating, surface charge, and conditions of silver ion release. AgNPs may directly damage the cell membranes, disrupt ATP production and DNA replication, alternate gene expressions, release toxic Ag⁺ ion, and produce reactive oxygen species to oxidize biological components of the cell. A progress made on understanding the mechanism of organic-coated AgNP toxicity using different analytical techniques is presented.     

Lanthanide(III) Complexes of 2‐[4,7,10‐Tris(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecan‐1‐yl]acetic Acid (H7DOA3P): Multinuclear‐NMR and Kinetic Studies

The protonation constants of 2‐[4,7,10‐tris(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecan‐1‐yl]acetic acid (H₇DOA3P) and of the complexes [Ln(DOA3P)]^4? (Ln=Ce, Pr, Sm, Eu, and Yb) have been determined by multinuclear NMR spectroscopy in the range pD 2–13.8, without control of ionic strength. Seven out of eleven protonation steps were detected (pK =13.66, 12.11, 7.19, 6.15, 5.77, 2.99, and 1.99), and the values found compare well with the ones recently determined by potentiometry for H₇DOA3P, and for other related ligands. The overall basicity of H₇DOA3P is higher than that of H₄DOTA and trans‐H₆DO2A2P but lower than that of H₈DOTP. Based on multinuclear‐NMR spectroscopy, the protonation sequence for H₇DOA3P was also tentatively assigned. Three protonation constants (pK_MHL, pK_MH2L, and pK_MH3L) were determined for the lanthanide complexes, and the values found are relatively high, although lower than the protonation constants of the related ligand (pK , pK , and pK ), indicating that the coordinated phosphonate groups in these complexes are protonated. The acid‐assisted dissociation of [Ln(DOA3P)]^4? (Ln=Ce, Eu), in the region c_H+=0.05–3.00 mol dm^?3 and at different temperatures (25–60°), indicated that they have slightly the same kinetic inertness, being the [Eu(H₂O)₉]³⁺ aqua ion the final product for europium. The rates of complex formation for [Ln(DOA3P)]^4? (Ln=Ce, Eu) were studied by UV/VIS spectroscopy in the pH range 5.6–6.8. The reaction intermediate [Eu(DOA3P)]* as ‘out‐of‐cage’ complex contains four H₂O molecules, while the final product, [Eu(DOA3P)]^4?, does not contain any H₂O molecule, as proved by steady‐state/time‐resolved luminescence spectroscopy.     

Synthesis of enantiomerically pure (purin-6-yl)phenylalanines and their nucleosides, a novel type of purine-amino acid conjugates

[Chemical reaction: See text] Enantiomerically or diastereomerically pure 4-(purin-6-yl)phenylalanines, a novel type of stable amino acid-purine conjugates, were synthesized by palladium-catalyzed cross-coupling reactions of protected 4-boronophenylalanines or 4-(trimethylstanyl)phenylalanines with diverse 6-halopurines (9-benzyl-6-halopurines and 9-(tetrahydropyran-2-yl)-6-halopurines as well as acyl- and silyl-protected 6-halopurine ribonucleosides and 2-deoxyribonucleosides). Free purine bases and nucleosides bearing (S)- or (R)-phenylalanine in position 6 were obtained after complete deprotection of the products of cross-coupling reactions. Reactivity trends for both of these cross-coupling and deprotection protocols have been compared in terms of practicability, efficiency, and stereoselectivity.     

Cubic β-Fe2O3 as the product of the thermal decomposition of Fe2(SO4)3

Hyperfine Interactions - The thermal decomposition of Fe2(SO4)3 in air has been investigated using transmission Mössbauer spectroscopy, CEMS and X-ray powder diffraction. The hexagonal...     

Pressure-dependent viscosity of powder injection moulding compounds

A single piston capillary rheometer was modified by the addition of a second chamber with a restricting valve (developed at the Polymer Centre, Zlín, Czech Republic), which provides backpressure and increasing the pressure in the melted material during the flow through the die. The Carreau–Yasuda model was employed to fit the measured viscosity data and determine the temperature and pressure coefficients for polyolefin based binder and its compounds with carbide powder. Both temperature and pressure sensitivity coefficients are largely dependent on the structure of a polymer, which should be taken into account for binder-formation’s development. Increasing the loading level of the powder in the compound diminishes the pressure sensitivity of their flow properties.     

A constrained approach to multiscale stochastic simulation of chemically reacting systems

Stochastic simulation of coupled chemical reactions is often computationally intensive, especially if a chemical system contains reactions occurring on different time scales. In this paper, we introduce a multiscale methodology suitable to address this problem, assuming that the evolution of the slow species in the system is well approximated by a Langevin process. It is based on the conditional stochastic simulation algorithm (CSSA) which samples from the conditional distribution of the suitably defined fast variables, given values for the slow variables. In the constrained multiscale algorithm (CMA) a single realization of the CSSA is then used for each value of the slow variable to approximate the effective drift and diffusion terms, in a similar manner to the constrained mean-force computations in other applications such as molecular dynamics. We then show how using the ensuing Fokker-Planck equation approximation, we can in turn approximate average switching times in stochastic chemical systems.