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Staphylococcus aureus is a Gram-positive bacterium, which can be found, as a commensal microorganism, on the skin surface or in the nasal mucosa of the human population. However, S. aureus may become pathogenic and cause severe infections, especially in hospitalized patients. As an opportunistic pathogen, in fact, S. aureus interferes with the host Ca2+ signaling, favoring the spread of the infection and tissue destruction. The identification of novel strategies to restore calcium homeostasis and prevent the associated clinical outcomes is an emerging challenge. Here, we investigate whether harzianic acid, a bioactive metabolite derived from fungi of the genus Trichoderma, could control S. aureus-induced Ca2+ movements. First, we show the capability of harzianic acid to complex calcium divalent cations, using mass spectrometric, potentiometric, spectrophotometric, and nuclear magnetic resonance techniques. Then, we demonstrate that harzianic acid significantly modulates Ca2+ increase in HaCaT (human keratinocytes) cells incubated with S. aureus. In conclusion, this study suggests harzianic acid as a promising therapeutical alternative against diseases associated with Ca2+ homeostasis alteration. [ABSTRACT FROM AUTHOR]

Rare-earth elements (REEs) are in all respect a class of new contaminants that may have toxic effects on organisms and microorganisms and information on their interactions with natural ligands should be of value to predict and control their diffusion in natural environments. In the current study, we investigate interactions of tripositive cations of praseodymium, europium, holmium, and thulium with harzianic acid (H2L), a secondary metabolite produced by selected strains of fungi belonging to the Trichoderma genus. We applied the same techniques and workflow previously employed in an analogous study concerning lanthanum, neodymium, samarium, and gadolinium tripositive cations. Therefore, in the current study, HPLC-ESI-HRMS experiments, circular dichroism (CD), and UV-Vis spectrophotometric absorption data, as well as accurate pH measurements, were applied to characterize bonding interactions between harzianic acid and Pr3+, Eu3+, Ho3+, and Tm3+ cations. Problems connected to the low solubility of harzianic acid in water were overcome by employing a 0.1 M NaClO4/(CH3OH + H2O 50/50 w/w) mixed solvent. For Pr3+, Ho3+, and Tm3+, only the mono complexes PrL+, HoL+, and TmL+ were detected and their formation constant determined. Eu3+ forms almost exclusively the bis complex EuL 2 − for which the corresponding formation constant is reported; under our experimental conditions, the mono complex EuL+ is irrelevant. Combining the results of the present and previous studies, a picture of interactions of harzianic acid with rare-earth cations extending over 8 of the 17 REEs can be composed. In order to complement chemical information with toxicological information, a battery of bioassays was applied to evaluate the effects of praseodymium, europium, holmium, and thulium tripositive cations on a suite of bioindicators including Aliivibrio fischeri (Gram-negative bacterium), Raphidocelis subcapitata (green alga), and Daphnia magna (microcrustacean), and median effective concentration (EC50) values of Pr3+, Eu3+, Ho3+, and Tm3+ for the tested species were assessed. [ABSTRACT FROM AUTHOR]

Only a few studies have been made on the ion product of variscite, Al(III) phosphate dihydrate, AlP[O.sub.4] x 2[H.sub.2]O, a parameter of fundamental importance in clarifying the fixation of soluble phosphates in acid soils. The solubility of variscite in [H.sub.3]P[O.sub.4] solutions of molality ranging from 1 x [10.sup.-4] to 0.1 mol [kg.sup.-1] was determined at 25[degrees]C. The data were explained with a value of the ion product equal to [10.sup.-3.14] [mol.sup.-1] kg (at the infinite dilution reference state) and assuming the formation of complexes AlP[O.sub.4(aq)], AlHP[O.sub.4.sup.+], and Al[([H.sub.2]P[O.sub.4]).sub.2.sup.+]. The solubility product obtained in this work differs by orders of magnitude from the literature values. The discrepancies are mainly due to the use of solids of different composition as well as to the assumption of the [Al.sup.3+] ion as the unique soluble A1 species. On the basis of equilibrium constants, the fixation in acid soils of soluble phosphates implicates the formation of variscite, while only at higher concentrations does the fixation occur as strengite.

Strengite, FeP[O.sub.4]x2[H.sub.2]O, commonly occurs in soils and represents a source of P for plants. The solubility of strengite is thus considerably important in the field of agriculture and environmental geochemistry, but few solubility data are available. Using absorption spectrophotometric techniques, the solubility equilibrium was studied at 25[degrees]C by measuring the total Fe(III), [m.sub.Fe(III)], dissolved while keeping strengite in contact with [H.sub.3]P[O.sub.4] solutions. The acid concentration, [m.sub.P], ranged from 0.001 to 0.1 mol [kg.sup.-1]. In solutions of [m.sub.P] [less than or equal to] 0.01 mol [kg.sup.-1] [m.sub.Fe(III)], results were constant within the limits of experimental error. This was ascribed to the predominance of a soluble species FeP[O.sub.4](aq). Soluble complexes, mainly Fe[([H.sub.2]P[O.sub.4]).sub.3](aq) and Fe[H.sub.3][(P[O.sub.4]).sub.2](aq), were responsible for the increased solubility at [m.sub.P] [greater than or equal to] 0.02 mol [kg.sup.-1], as evidenced in previous investigations. Using the constants evaluated in these investigations, the solubility data can be explained with the ion product equal to [10.sup.-6.70] [mol.sup.-1] kg at the infinite dilution reference state.

Rare-earth elements are emerging contaminants of soil and water bodies which destiny in the environment and effects on organisms is modulated by their interactions with natural ligands produced by bacteria, fungi and plants. Within this framework, coordination by harzianic acid (H2L), a Trichoderma secondary metabolite, of a selection of tripositive rare-earth cations Ln3+ (Ln3+ = La3+, Nd3+, Sm3+, and Gd3+) was investigated at 25 °C, and in a CH3OH/0.1 M NaClO4 (50/50 w/w) solvent, using mass spectrometry, circular dichroism, UV–Vis spectrophotometry, and pH measurements. Experimental data can be satisfactorily explained by assuming, for all investigated cations, the formation of a mono-complex (LnL+) and a bis-complex (LnL2−). Differences were found between the formation constants of complexes of different Ln3+ cations, which can be correlated with ionic radius. Since gadolinium is the element that raises the most concern among lanthanide elements, its effects on organisms at different levels of biological organization were explored, in the presence and absence of harzianic acid. Results of ecotoxicological tests suggest that harzianic acid can decrease gadolinium biotoxicity, presumably because of complex formation with Gd3+. [ABSTRACT FROM AUTHOR]

Amine‐oxide surfactants have emerged as highly stable, nontoxic, and cost‐effective constituents of detergent formulations, specifically as wetting agents and foam boosters. With the aim of enhancing their functional behavior, a new member of this family, N,N‐dimethyl‐2‐propylheptan‐1‐amine oxide, bearing a branched alkyl tail (C10DAO‐branched) was synthesized and purified using a simple and easily scalable strategy starting from 2‐propylheptan‐1‐ol. 2D‐nuclear magnetic resonance (NMR) and mass spectrometry confirm the obtainment of the desired product in high yield and purity. The protonation behavior of the branched surfactant is not affected by alkyl tail branching, as shown by potentiometric titrations. In contrast, surface activity and aggregation behavior of C10DAO‐branched is dramatically different from that of the linear analog N,N‐dimethyldecyl‐1‐amine oxide (C10DAO‐linear), in that it occupies a higher area at the solution interface and aggregates at much higher concentration, forming larger aggregates, as detected using tensiometry and dynamic light scattering (DLS), respectively. Aggregation behavior of C10DAO‐branched is less sensitive to pH variations. Foaming tests show that C10DAO‐branched is a more effective foam booster than its linear analog, in both acidic and basic solutions. The experimental results indicate that the branched surfactant can be used in applications that require enhanced and pH‐independent surface activity and foamability. [ABSTRACT FROM AUTHOR]