13 research outputs found
Optimisation of Amphiphilic-Polymer Coatings for Improved Chemical Stability of NaYF4-based Upconverting Nanoparticles
NaYF4 nanoparticles codoped with Yb3+ and Tm3+ exhibit upconversion fluorescence in near-infrared and visible spectral range. Consequently, such upconverting nanoparticles (UCNPs) can be used as contrast agents in medical diagnostics and bioassays. However, they are not chemically stable in aqueous dispersions, especially in phosphate solutions. Protective amphiphilic-polymer coatings based on poly(maleic anhydride-alt-octadec-1-ene) (PMAO) and bis(hexamethylene)triamine (BHMT) were optimised to improve the chemical stability of UCNPs under simulated physiological conditions. Morphologies of the bare and coated UCNPs was inspected with transmission electron microscopy. All samples showed intense UC fluorescence at ~800 nm, typical for Tm3+. The colloidal stability of aqueous dispersions of bare and coated UCNPs was assessed by dynamic light scattering and measurements of zeta potential. The dissolution of UCNP in phosphate-buffered saline at 37 °C, was assessed potentiometrically by measuring the concentration of the dissolved fluoride. Protection against the dissolution of UCNPs was achieved by PMAO and PMAO crosslinked with BHMT
Alkaloids and Selected Topics in Their Thermochemistry
Alkaloid chemistry is varied and complex. Many alkaloids attract a great deal of interest because of their physiological activity, yet surprisingly little is known about the thermochemistry of these compounds, especially in the gas phase. In this paper, we investigate the thermochemical characteristics, specifically demethoxylation enthalpies rather than those derived from trans-methoxylation reactions, of a series of biologically relevant alkaloids in their condensed phase
Nitrosyl and dioxygenyl cations and their salts-Similar but further investigation needed
The O-2(+) ion is sufficiently similar in size to NO+ and so the difference in lattice energy in salts with a common anion can be expected to be negligible. Comparative analysis of O2F vs. NOF and of O-2(+) vs. NO+-salts is given in this paper and some surprising and unexpected differences between corresponding species are discussed. (C) 2009 Elsevier B.V. All rights reserved
Dissolution Mechanism of Upconverting AYF<sub>4</sub>:Yb,Tm (A = Na or K) Nanoparticles in Aqueous Media
The dissolution of
upconverting AYF<sub>4</sub>:Yb,Tm (A = Na or
K) nanoparticles (UCNPs) in aqueous media was systematically studied.
UCNPs with a cubic structure and sizes of between 10 and 33 nm were
synthesized solvothermally in ethylene glycol at 200 °C. The
UCNPs of both compositions showed an upconversion fluorescence emission
characteristic of Tm<sup>3+</sup>. The effects of the A cation, the
particle size, the temperature, the pH, and the composition of the
aqueous medium on the dissolution of the UCNPs were evaluated. The
degree of dissolution was determined from the fraction of dissolved
fluoride (F<sup>–</sup>) using potentiometry. Unexpectedly,
the composition of aqueous media had the most significant effect on
the dissolution of the UCNPs. The highest degree of dissolution and
rate were measured for the phosphate-buffered saline (PBS), which
can be explained by the formation of stable lanthanide compounds with
phosphates. The degree of dissolution was much lower in water and
in the phthalate buffer, which was attributed to the release of F<sup>–</sup> as a result of the hydrolysis of the UCNPs’
surfaces
Chemical Aspects of human and environmental overload with fluorine
[Image: see text] Over the last 100–120 years, due to the ever-increasing importance of fluorine-containing compounds in modern technology and daily life, the explosive development of the fluorochemical industry led to an enormous increase of emission of fluoride ions into the biosphere. This made it more and more important to understand the biological activities, metabolism, degradation, and possible environmental hazards of such substances. This comprehensive and critical review focuses on the effects of fluoride ions and organofluorine compounds (mainly pharmaceuticals and agrochemicals) on human health and the environment. To give a better overview, various connected topics are also discussed: reasons and trends of the advance of fluorine-containing pharmaceuticals and agrochemicals, metabolism of fluorinated drugs, withdrawn fluorinated drugs, natural sources of organic and inorganic fluorine compounds in the environment (including the biosphere), sources of fluoride intake, and finally biomarkers of fluoride exposure
Optically Detected Degradation of NaYF<sub>4</sub>:Yb,Tm-Based Upconversion Nanoparticles in Phosphate Buffered Saline Solution
In a proof-of-concept study, we assessed
different analytical and
spectroscopic parameters for stability screening of differently sized
β-NaYF<sub>4</sub>:20 mol % Yb<sup>3+</sup>, 2 mol %
Tm<sup>3+</sup> upconversion nanoparticles (UCNPs) exemplarily in
the bioanalytically relevant buffer phosphate buffered saline (PBS;
pH 7.4) at 37 and 50 °C. This included the potentiometric determination
of the amount of released fluoride ions, surface analysis with X-ray
photoelectron spectroscopy (XPS), and steady-state and time-resolved
fluorescence measurements. Based on these results, the luminescence
lifetime of the 800 nm upconversion emission was identified as an
optimum parameter for stability screening of UCNPs and changes in
particle surface chemistry