Fluoride and Aluminium in Tea (Camellia sinensis L.)-Tea Quality Indicators and Risk Factors for Consumers.

In recent years, the quality and sourcing of tea have gained importance in Europe, but information remains scarce. The aim of this study was to determine the concentrations of fluoride (F-) and total aluminium (Al) species in infusions of commercially available teas in Slovenia, and thus in Europe, and to relate them to tea quality and their impact on consumer safety. F- concentrations were determined using a fluoride-ion-selective electrode and Al concentrations using inductively coupled plasma optical emission spectroscopy. A comparison of the results obtained for four selected tea samples using the calibration curve and a standard addition technique showed good agreement, with no interferences caused by the sample matrix. The concentrations of 35 commercial teas ranged from 0.34 to 4.79 and 0.51 to 8.90 mg/L for F- and Al, respectively. The average concentrations of the two elements followed the same descending order: black filter > green filter > black leaves ≈ green leaves. Single and multivariate statistical methods supported the categorisation of teas by packaging but not by type, with tea in filter bags being more expensive than loose tea. The linear relationship between F- and Al concentrations in infusions (C(Al) = 1.2134 · C(F-)) allows for the determination of one element and estimation of the other, leading to a significant reduction in laboratory effort and cost. This research advances tea assessment by proposing Al concentration alongside F- as a quality indicator and provides the basis for tea-monitoring protocols. Finally, the daily consumption of larger quantities of tea (≈1 L) with elevated F- and Al concentrations could potentially pose a health risk.

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.

NaYF4-based upconverting nanoparticles with optimized phosphonate coatings for chemical stability and viability of human endothelial cells.

The increasing interest in upconverting nanoparticles (UCNPs) in biodiagnostics and therapy fuels the development of biocompatible UCNPs platforms. UCNPs are typically nanocrystallites of rare-earth fluorides codoped with Yb3+and Er3+or Tm3+. The most studied UCNPs are based on NaYF4but are not chemically stable in water. They dissolve significantly in the presence of phosphates. To prevent any adverse effects on the UCNPs induced by cellular phosphates, the surfaces of UCNPs must be made chemically inert and stable by suitable coatings. We studied the effect of various phosphonate coatings on chemical stability andin vitrocytotoxicity of the Yb3+,Er3+-codoped NaYF4UCNPs in human endothelial cells obtained from cellular line Ea.hy926. Cell viability of endothelial cells was determined using the resazurin-based assay after the short-term (15 min), and long-term (24 h and 48 h) incubations with UCNPs dispersed in cell-culture medium. The coatings were obtained from tertaphosphonic acid (EDTMP), sodium alendronate and poly(ethylene glycol)-neridronate. Regardless of the coating conditions, 1 - 2 nm-thick amorphous surface layers were observed on the UCNPs with transmission electron microscopy. The upconversion fluorescence was measured in the dispersions of all UCNPs. Surafce quenching in aqueous suspensions of the UCNPs was reduced by the coatings. The dissolution degree of the UCNPs was determined from the concentration of dissolved fluoride measured with ion-selective electrode after the ageing of UCNPs in water, physiological buffer (i.e., phosphate-buffered saline-PBS) and cell-culture medium. The phosphonate coatings prepared at 80 °C significantly suppressed the dissolution of UCNPs in PBS while only minor dissolution of bare and coated UCNPs was measured in water and cell-culture medium. The viability of human endothelial cells was significantly reduced when incubated with UCNPs, but it increased with the improved chemical stability of UCNPs by the phosphonate coatings with negligible cytotoxicity when coated with EDTMP at 80 °C.

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.

Formation of phosphonate coatings for improved chemical stability of upconverting nanoparticles under physiological conditions.

Upconverting nanoparticles (UCNPs) are being extensively investigated for applications in bioimaging because of their ability to emit ultraviolet, visible, and near-infrared light. NaYF4 is one of the most suitable host matrices for producing high-intensity upconversion fluorescence; however, UCNPs based on NaYF4 are not chemically stable in aqueous media. To prevent dissolution, their surfaces should be modified. We studied the formation of protective phosphonate coatings made of ethylenediamine(tetramethylenephosphonic acid), alendronic acid, and poly(ethylene glycol)-neridronate on cubic NaYF4 nanoparticles and hexagonal Yb3+,Er3+-doped upconverting NaYF4 nanoparticles (ß-UCNPs). The effects of synthesis temperature and ultrasonic agitation on the quality of the coatings were studied. The formation of the coatings was investigated by transmission electron microscopy, zeta-potential measurements, and infrared spectroscopy. The quality of the phosphonate coatings was examined with respect to preventing the dissolution of the NPs in phosphate-buffered saline (PBS). The dissolution tests were carried out under physiological conditions (37 °C and pH 7.4) for 3 days and were followed by measurements of the dissolved fluoride with an ion-selective electrode. We found that the protection of the phosphonate coatings can be significantly increased by synthesizing them at 80 °C. At the same time, the coatings obtained at this temperature suppressed the surface quenching of the upconversion fluorescence in ß-UCNPs.

Chemical Aspects of Human and Environmental Overload with Fluorine.

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.

Influence of Anodization-Electrolyte Aging on the Photocatalytic Activity of TiO2 Nanotube Arrays.

TiO2 nanotubular films prepared using the anodic oxidation process applied to various forms of metal titanium are promising materials for photocatalytic applications. However, during successive anodizations in batch-anodization cells, the chemical composition of the NH4F- and water-based ethylene glycol electrolyte changes with each subsequent anodization, which greatly affects the final photocatalytic properties of the annealed TiO2 nanotubular films. In the present study, 20 titanium discs (Φ 90 mm) were sequentially anodized in the same anodization electrolyte. The chemical composition of the electrolyte was measured after each anodization and correlated with the anodization current density, temperature, electrical conductivity, and pH of the electrolyte and with the morphology, structure, composition, and photocatalytic activity of the resulting TiO2 nanotube films. It was found that the length of the TiO2 nanotubes decreased with the age of the electrolyte due to its lower conductivity. The subsurface chemical composition was evaluated by time of flight secondary ion mass spectrometry (ToF SIMS) analyses, and the integrated ToF SIMS signals over a depth of 250 nm for the TiO2 nanotube films showed that the concentration of F- in the annealed TiO2 film increased with each subsequent anodization due to the increased pH value of the electrolyte. As a consequence, the concentration of the OH- and O2 - species decreased, which is a major reason for the reduced photocatalytic activity of the TiO2 films. It is proposed that the length of the TiO2 nanotubes does not play a decisive role in determining the photocatalytic activity of the TiO2 nanotube films. Finally, the best measured degradation results of 60% for caffeine were thus achieved for the first anodized titanium discs. After that the efficiency gradually decreased for each subsequent anodized disc.

Fluorine in vegetation due to an uncontrolled release of gaseous fluorides from a glassworks: A case study of measurement uncertainty, dispersion pattern and compliance with regulation.

This study was initiated after the appearance of chlorotic and necrotic lesions on vegetation in the vicinity of a glassworks. The aim was to establish whether the cause was an uncontrolled release of gaseous fluorides. Five different plant species (Norway spruce, peach, common hornbeam, common bean, common grape vine) were collected in the influenced area, and the fluorine (F) content was determined by a fluoride ion selective electrode after prior total sample decomposition by alkaline carbonate fusion. The measurement results were reported together with their measurement uncertainties (MUs), which were evaluated according to the Guide to the Expression of Uncertainty in Measurement. The F contents at comparable distances from the emitter and in a clean area, free from natural or anthropogenic fluoride emissions, were 87-676 and 10 µg g-1, respectively, thereby confirming the release of gaseous fluorides from the glassworks. The F contents in samples of Norway spruce taken at various radial distances from the emitter suggest that the emitted gaseous fluorides were spread about evenly in all directions from the source following an inverse-power function. Estimated distances at which the F content would decrease to 50 µg g-1 (allowed maximum content of F in feeding stuffs) and 21 µg g-1 (maximum fluoride content in vegetables and fruits in relation to the upper limit of fluoride intake for humans) were 378 m and 571 m, respectively, from the emitter. Evaluation of our results for compliance with specification revealed a lack of regulation on fluoride content in the diet of humans and animals as well as a lack of guidelines on how to take into account MU.

Fluoride in Human Health and Nutrition.

Fluorine is in the form of fluorides ubiquitous in nature and as such an inevitable part of our environment. In small amounts, it is known to have beneficial effects on dental health. On the other hand, excessive chronic intakes can result in adverse effects including the development of dental fluorosis in children and/or skeletal fluorosis in both children and adults. The adequate intake has been set, based on empirical observations, at 0.05 mg/day/kg body weight however, the threshold between beneficial and harmful effects is narrow. Despite numerous studies, knowledge on the fluoride toxicity is still relatively poor. In this review, the role and the effects of fluoride on human health are enlightened. Some of the fluoride controversies are discussed and future research directions suggested.

Amphiphilic coatings for the protection of upconverting nanoparticles against dissolution in aqueous media.

Upconverting nanoparticles (UCNPs) of ß-NaYF4, co-doped with Yb3+ and Tm3+ and 21-36 nm large, were synthesized using a modified thermal decomposition method. The as-synthesized UCNPs were coated with oleic acid and dispersed in nonpolar media. Their morphology, size and crystal structure were analysed with transmission electron microscopy and X-ray diffraction. The UCNPs showed a fluorescence emission spectrum characteristic of Tm3+. Their dissolution in water (pH ∼ 4-5) and phosphate buffered saline (PBS, pH = 7.4) was determined from the fraction of dissolved fluoride ions using a fluoride-ion-selective electrode. The dissolution of bare UCNPs was much more prominent in PBS than in water. Two amphiphilic coatings, poly(maleic anhydride-alt-1-octadecene)-bis(hexamethylene)triamine (PMAO-BHMT) and d-α-tocopheryl polyethylene glycol succinate (TPGS) were tested for their effects on the dissolution of the UCNPs. The coatings were formed directly on the as-synthesized UCNPs as was confirmed with electrokinetic measurements, infrared spectroscopy and thermogravimetric analyses. Both coatings enabled the dispersion of UCNPs in water, and improved the fluorescence emission intensity with respect to the bare UCNPs. However, only the PMAO-BHMT coating provided an effective protection against the dissolution of the UCNPs and long-term colloidal stability in PBS, and did not show cytotoxicity in EAhy926 endothelial cells.

Optically Detected Degradation of NaYF4: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 ß-NaYF4:20 mol % Yb3+, 2 mol % Tm3+ 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.

Dissolution Mechanism of Upconverting AYF4:Yb,Tm (A = Na or K) Nanoparticles in Aqueous Media.

The dissolution of upconverting AYF4: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(3+). 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(-)) 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(-) as a result of the hydrolysis of the UCNPs' surfaces.

Influence of the Synthesis Parameters on the Properties of NaYF4:Yb3+,Tm3+ Nanoparticles.

Fluorescent nanoparticles, especially fluorides, have received a great deal of interest due to their optical properties, making them suitable for applications in bio-imaging. For this reason they need to exhibit a superior chemical stability in aqueous media. We have studied the influence of the synthesis parameters on the chemical stability of NaYF(4) nanoparticles co-doped with Yb(3+) and Tm(3+). These nanoparticles have different crystal structures, and were synthesized hydrothermally or with thermal decomposition. The samples were characterized with X-ray diffraction and transmission electron microscopy. The up-conversion fluorescence of nanoparticles dispersed in water was measured at 400-900 nm. The partial dissolution of the fluorine in water was detected with an ion-selective electrode for all the samples. The dissolution of the other constituent ions was analysed with an optical emission spectrometer using inductively coupled plasma. The nanoparticles with a hexagonal crystal structure and sizes of around 20 nm that were synthesized with thermal decomposition showed a superior chemical stability in water together with a superior up-conversion fluorescence yield.

An overview of the understanding of ions containing solely fluorine atoms.

We discuss in the current paper ions containing solely fluorine atoms, F-, F2- and F3-, their corresponding cationic and/or multiply charged counterparts. While the emphasis of the paper is on gas phase species, their energetics and reactions, aqueous solutions are also discussed. In particular, biomedical and analytical aspects of F- are also considered. The new trichotomy of convenience, anthropocentrism and folksonomy is also applied to the understanding of our fluorine-containing ions.

New methods applicable for calibration of indicator electrodes.

The new methods applicable for calibration of indicator electrodes, based on standard addition and standard subtraction methods, are suggested. Some of the methods enable the slope of an indicator electrode and equivalence volume V(eq) to be determined simultaneously from a single set of potentiometric titration data. Some other methods known hitherto were also taken into account. A new model, based on a standard addition method, applicable also in nonlinear range for the ISE slope (S) is suggested, and its applicability was confirmed experimentally in calibration of calcium ISE.