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Stability and structure of complexes between silver (I) and l-methionine (L) deduced from potentiometric and 1H NMR measurements allow to assume the prevailing of several protonated species. The experimental data are compatible with the formation of the following complexes: AgL, AgL2, AgH2L, AgH1L2, AgH2L2, AgH3L2 and AgH4L2. The coordination sites are obtained by 1H NMR spectra, showing that only the bond between the methylthioether sulfur atom and silver (I) is responsible of the complex stability. The system is studied potentiometrically with silver and glass electrodes at 25 °C and 1.00 mol·dm−3 NaClO4 as ionic medium. Amino acids containing sulfur are few and not extensively studied. In particular, l-methionine, even if it is the most important, enantiomer and their complexes with silver (I) present anticarcinogenic properties, is quite not investigated. In the same experimental conditions, l-methionine protonation constants are determined. The 1H NMR data allow one to assume that, in moderately alkaline solution, silver (I) is bond with six membered chelate rings with sulfur and amino nitrogen, while carboxylic groups are not involved. No polynuclear species are present. The high stability of the complex with ratio 1:2 (silver (I)/l-methionine), involving also two hydrogen ions, predominating in a wide range of hydrogen ion concentration suggests to propose a study for the preparation of an electrode to measure the deprotonated l-methionine concentration.

Alzheimer's disease (AD) is a multifactorial pathology that requires multifaceted agents able to address its peculiar nature. Increasing evidence has shown that aggregation of amyloid β (Aβ) and oxidative stress are strictly interconnected, and their modulation might have a positive and synergic effect in contrasting AD-related impairments. Herein, a new and efficient fragment-based approach towards tyrosol phosphodiester derivatives (TPDs) has been developed starting from suitable tyrosol building blocks and exploiting the well-established phosphoramidite chemistry. The antioxidant activity of new TPDs has been tested as well as their ability to inhibit Aβ protein aggregation. In addition, their metal chelating ability has been evaluated as a possible strategy to develop new natural-based entities for the prevention or therapy of AD. Interestingly, TPDs containing a catechol moiety have demonstrated highly promising activity in inhibiting the aggregation of Aβ40 and a strong ability to chelate biometals such as CuII and ZnII .

The solubility of folic acid was determined at 25 °C in 1.00 mol dm−3 and in 0.15 mol dm−3 NaCl (physiological solution) spectrophotometrically by measuring the absorbance of saturated solution at different hydrogen ion concentrations. Five protonation constants of folate were determined both from the dependence of the solubility on the hydrogen ion concentration as well as from potentiometric titrations carried out in the presence of solid folic acid and in alkaline solution, in which folate is relatively soluble. Corresponding to the protonation constants, nuclear magnetic resonance and florescence spectra were also obtained at different hydrogen ion concentrations to determine the protonation positions in acid, neutral and alkaline solutions. An approach through circular dichroism was also applied to study the eventual polymerization of folate in alkaline solution.

Mitidjospirone, a new spiridioxynaphthalene, was isolated from the mycelial extract of a strain of

The contamination of environments by heavy metals has become an urgent issue causing undesirable accumulations and severe damages to agricultural crops, especially cadmium and lead which are among the most widespread and dangerous metal pollutants worldwide. The selection of proper species is a crucial step in many plant-based restoration approaches; therefore, the aim of the present work was to check for early morphophysiological responsive traits in three cultivars of Cynara cardunculus (Sardo, Siciliano, and Spagnolo), helping to select the best performing cultivar for phytoremediation. For all three tested cultivars, our results indicate that cardoon displays some morphophysiological traits to face Cd and Pb pollution, particularly at the root morphology level, element uptake ability, and photosynthetic pigment content. Other traits show instead a cultivar-specific behavior; in fact, stomata plasticity, photosynthetic pattern, and antioxidant power provide different responses, but only Spagnolo cv. achieves a successful strategy attaining a real resilience to metal stress. The capacity of Spagnolo plants to modify leaf structural and physiological traits under heavy metal contamination to maintain high photosynthetic efficiency should be considered an elective trait for its use in contaminated environments. Supplementary Information The online version contains supplementary material available at 10.1007/s11356-021-13242-9.

Mitidjospirone, a new spiridioxynaphthalene, was isolated from the mycelial extract of a strain of Lasiodiplodia mitidjana, a recently described species belonging to the family Botryosphaeriaceae. Its structure was elucidated by extensive spectroscopic analysis and the absolute configuration was determined by electronic circular dichroism (ECD) experiment. Furthermore, several known compounds were identified during the screening of secondary metabolites produced by four strains of L. mitidjana.

Harzianic acid is a secondary metabolite of Trichoderma, structurally belonging to the dienyltetramic acid subgroup of the tetramic acids. Biological activities of harzianic acid are of great interest for its antimicrobial and plant growth-promoting activities, which might be related to its chelating properties. In the present work harzianic acid, isolated from cultures of a strain of Trichoderma pleuroticola associated to the gastropod Melarhaphe neritoides, was studied as a complexant agent of a number of biologically relevant transition metals (i.e., Zn2+, Fe2+, Cu2+, and Mn2+), using UV-VIS, potentiometry, MS and NMR techniques. Our findings show the coordination capacity of harzianic acid toward the above cations through the formation of neutral or charged complexes in a variable ratio depending on the metal and pH conditions.

pH-sensitive surfactants find applications in many fields, including responsive drug delivery and smart material design. The rational design of the surfactant molecular structure leads to species presenting strong variations of the micellization parameter (e.g., critical micelle concentration, cmc, and aggregate dimension) in a controlled pH range. In the present work, the micellization of the branched amine oxide surfactant N,N-dimethyl-2-propylheptan-1-amine oxide (C10DAO-branched) is studied as a function of pH in dilute aqueous mixtures. Its behavior is compared with that of the linear isomer N,N-dimethyldecan-1-amine oxide (C10DAO-linear). The samples are investigated by potentiometric titrations, fluorescence spectroscopy, and Dynamic Light Scattering (DLS). With increasing pH, micellized C10DAO-branched presents a higher tendency to remain in the protonated/cationic form with respect to the linear isomer. As a consequence, the minimum cmc value, observed when the protonated and the deprotonated/zwitterionic forms of the surfactant coexist in the micelles, is shifted to higher pH values. The volume of these C10DAO-branched “mixed micelles” is more than one order of magnitude higher than that of completely protonated or deprotonated aggregates. This is a singularity of the branched surfactant, not observed for the linear isomer. Overall, the results highlight that the branched molecular architecture of the surfactant tail, favoring the formation of low-curvature aggregates, enhances H-bonding between the protonated and deprotonated headgroups, which synergistically stabilizes the flatter surface of bulkier aggregates. Taking into account the good biodegradability of surfactants with a limited number of short side chains, purposely designed branched surfactants appear as a suitable option to accurately tune supramolecular aggregation in pH-responsive formulations.

The presence and mobilization of toxic metal cations represents under many aspects a current and important problem in the environmental field. In this research, as cation lead (II) ion was studied. The formation of complexes between glutathione and lead (II) was studied at 25 °C and in 1.00 M NaCl as ionic medium by means of measurements of electromotive force (e.m.f.) of cells containing glass and lead amalgam electrodes. In the same experimental conditions, the protonation constants of glutathione were determined potentiometrically, using a cell containing the glass electrode. In the same experimental conditions, by considering glutathione (GSH) completely deprotonated, four protonation constants were determined. Potentiometric data could be explained by assuming the formation of 1:1 complexes between GSH and Pb2+ and with the participation of hydrogen ions. The stability constants of the assumed complexes were determined. The 1:1 ratio between GSH and lead (II) was confirmed by spectrophotometric investigations. Measurements by Infrared Rays (IR) and protonic Nuclear Magnetic Resonance (1H NMR) provide information on the structure of the found complexes.

The aim of this work is to compare new and traditional extraction methods to obtain silymarin from

The aim of this work is to compare new and traditional extraction methods to obtain silymarin from Silybum marianum, a biennial herbaceous plant of the Asteraceae family, present throughout the Mediterranean basin and used to treat several diseases. Silymarin primarily contains flavonolignans and flavonoids and is used in some pharmaceutical preparations to improve of liver function and as a protective against some hepatotoxins. In six extracts obtained by new and traditional extraction methods, the total contents of silymarin and its main flavonolignans, total phenols and condensed tannins were evaluated in addition to their respective antioxidant capacities. By the Naviglio extractor, that is a rapid solid-liquid dynamic extraction method, it is possible to obtain a fraction quantitatively more abundant than other methods, and with a lower content of tannins and phenolic compounds but with a higher content of flavonolignans, rare and expensive, and therefore easier to separate and purify.

Phenylpropanoids are secondary metabolites widely distributed in plants. They are believed to protect human cells against oxidative stress and in turn, to prevent various diseases associated with it, such as cancer, cardiovascular, and neurodegenerative disorders as well [2,3]. Recently, many natural phenylpropanoids have emerged as a particularly promising class of small molecules able to inhibit β-amyloid aggregation and disrupt preformed amyloid fibrils that represent important targets in the development of pharmacological treatments of Alzheimer’s disease (AD) [4]. Unfortunately, natural phenylpropanoids often have poor pharmacokinetic properties and low bioavailability. In this frame an interesting approach in the design of new bioactive compounds could be the combination of two or more polyphenolic "fragments". This "natural-fragment-based drug-discovery" approach would allow the assembly, also in a combinatorial manner, of libraries based on complex polyphenols in a few steps. This strategy provides us with the possibility of easily modifying both scaffold and decorations and modulating pharmacodynamic and pharmacokinetic properties [5]. Therefore, we planned to join two "tyrosol-fragments" by a phosphodiester bridge to obtain a new class of phosphate-linked compounds [6], which are potentially more bioactive than the corresponding precursors. We report here the general synthetic strategy to obtain new phosphate-linked tyrosol dimers in good yield and their full characterization. Since oxidative stress, as well as metal ion dyshomeostasis, are known to play important roles in AD pathogenesis, preliminary studies are focused on the evaluation of their antioxidant activity, metal chelating ability and their ability to inhibit β-amyloid aggregation.

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 (C 10 DAO-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 C 10 DAO-branched is dramatically different from that of the linear analog N,N-dimethyldecyl-1-amine oxide (C 10 DAO-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 C 10 DAO-branched is less sensitive to pH variations. Foaming tests show that C 10 DAO-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.

The utilization of isotopes of transition metals for the development of novel therapeutic or diagnostic compounds is limited by the fact that they must be stabilized by chelating systems in coordination complexes. Important roles in the targeting approach are played by the tricarbonyl complexes of Technetium(I) and Rhenium(I) because they can be readily conjugated to biomolecules to form stable probes. Additionally, Ga-67 and Ga-68 isotopes of gallium are considered an obvious alternative to 99mTc (M. D. Bartholoma, A. S. Louie, J. F. Valliant and J. Zubieta, Chem. Rev., 2010, 110, 2903-2920) for SPECT and PET applications. We have previously reported the characterization of the peptide CCK8 decorated with a bis-histidine-based chelator (pHis2) labeled with 99mTc-tricarbonyl. In order to study the molecular properties of the histidine-based chelator pHis2, we here present the characterization in solution of its complexes with the metals Re(I) and Ga(III) using potentiometry and NMR. We detail the solution equilibria reporting pHis2 acid-base behavior, the coordination properties of pHis2 toward fac-[Re(H2O)3(CO)(3)](+) and Ga(III) and the atomic details of the formed complexes. Interestingly, two different metal coordination modes were found highlighting the plasticity of this bifunctional chelator.

Background Reactive oxygen species (ROS) in biological tissues of elected biosentinels represent an optimal biomarker for eco-monitoring of polluted areas. Electron spin resonance (ESR) is the most definitive method for detecting, quantifying and possibly identifying radicals in complex systems. Objective A non-invasive method for monitoring polluted areas by the quantitative determination of ROS in frog skin biopsy is presented. Methods We assessed by ESR spectroscopy the ROS level in adult male of Pelophylax bergeri, specie not a risk of extinction, collected from the polluted Sarno River (SA, Italy) basin. The spin-trap ESR method was validated by immunohistochemical analysis of the well-assessed pollution biomarkers cytochrome P450 aromatase 1A (CYP1A) and glutathione S-transferase (GST), and by determining the poly(ADPribose) polymerase (PARP) and GST enzymatic activity. Results ROS concentration in skin samples from frogs collected in the polluted area is significantly higher than that determined for the unpolluted reference area. Immunohistochemical analysis of CYP1A and GST supported the reliability of our approach, even in the absence of evident morphological and ultrastructural differences. PARP activity assay, connected to possible oxidative DNA damage, and the detoxification index by GST enzymatic assay give statistically significant evidence that higher levels of ROS are associated to alterations of the different biomarkers. Conclusions ROS concentration, measured by ESR on isolated frog skin, through the presented non-lethal method, is a reliable biomarker for toxicity screening and represents a useful basic datum for future modelling studies on environmental monitoring and biodiversity loss prevention.

New silibinin phosphodiester glyco-conjugates were synthesized by efficient phosphoramidite chemistry and were fully characterized by 2D-NMR. A wide-ranging study focused on the determination of their pKa and E° values as well as on their radical scavenging activities by different assays (DPPH, ABTS+ and HRSA) was conducted. The new glyco-conjugates are more water-soluble than silibinin, and their radical scavenging activities are higher than those of silibinin. The conjugation therefore improves both the water solubilities and antioxidant activities of the flavonolignan moieties. The serum stability was evaluated under physiological conditions, and the glyco-conjugates degraded with half-lives of 40-70 h, making them useful in pro-drug approaches. We started by treating androgen-dependent prostate cancer (PCa) LNCaP cells and then expanded our studies to androgen-independent PCa PC3 and DU145 cells. In most cases, the new derivatives significantly reduced both total and live cell numbers, albeit at different levels. Anti-HIV activities were evaluated and the glucosamine-phosphate silibinin derivative showed higher activity (IC50 = 73 μM) than silibinin.

The aim of this study is to investigate the effect of the concentration of sulphur dioxide and steam, in the flue gas subjected to CO2 capture by calcium looping, on the performance of two limestone-based sorbents. The experimental calcium looping tests were carried out in a purposely-designed Twin Bed lab-scale apparatus (consisting of two identical interconnected bubbling fluidised bed reactors), able to reproduce a realistic particle thermal/chemical/mechanical history. The two natural limestones (particle size range 0.4–0.6 mm) were selected in view of their remarkably “high” and “poor” reactivity to CO2, respectively. Calcium looping tests consisted of ten calcination/carbonation cycles (plus an eleventh calcination). Carbonation was carried out at 650 °C in an atmosphere containing 15% CO2 to simulate a typical combustion flue gas, while calcination was operated at 940 °C at 70% CO2 to simulate oxy-combustion conditions. Six different operating conditions for carbonation were tested to study the effect of SO2 and/or H2O, where steam (when present) was fed at 10%, and SO2 (when present) either at 75 ppm (a typical concentration in a pre-desulphurised combustion flue gas) or 1500 ppm (raw flue gas). The CO2 capture capacity was calculated for each carbonation stage, and the attrition rate was obtained by collection of elutriated fines from both reactors. At the end of the test, sorbent particles were further analysed for the determination of: degree of calcium sulphation, particle size distribution, porosimetric and microscopic properties. Relationships among sorbent type, operating conditions and experimental results are here discussed in detail, with the aim of originally outlining general trends arising from the comparison of the performance of the two limestones, which are characterised by very different reactivity.

Only a few studies have been made on the ion product of variscite, Al(III) phosphate dihydrate, AIPO 4 .2H 2 O, a parameter of fundamental importance in clarifying the fixation of soluble phosphates in acid soils. The solubility of variscite in H 3 PO 4 solutions of molality ranging from 1 x 10 -4 to 0.1 mol kg -1 was determined at 25°C. The data were explained with a value of the ion product equal to 10 -3.14 mol -1 kg (at the infinite dilution reference state) and assuming the formation of complexes AlPO 4(aq) , AlHPO 4 + , and Al(H 2 PO 4 ) 2 + . 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 3+ ion as the unique soluble Al 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.

The use of isotopes of transition metal has opened many perspectives in the development of novel compounds utilizable for therapeutic or diagnostic purposes. In order to be exploited, though, they must be stabilized by chelating systems in coordination complexes. The tricarbonyl complexes of Technetium(I) and Rhenium(I) have assumed important roles in these fields as they are readily conjugated to biomolecules to form stable probe useful in the targeting approach. In this context the amino acid histidine represents a valuable ligand for bioconjugation. Since little is reported on the chemistry and speciation of Re(I) and Tc(I) in aqueous solution, here, we analyze the interaction of fac-[Re(H2O)(3)(CO)(3)](+) with histidine or with the simple imidazole ring by means of potentiometric and spectroscopic techniques. We describe in details the equilibria that arise in solution, calculate the constants of each equilibrium reaction and report coordination properties and atomic details of the formed complexes. Our data represent a valuable contribute towards the exploitation in nuclear medicine of histidine containing biomolecules complexing Tc (I) and Re(I).

The second dissociation constant of salicylic acid (H 2 L) has been determined, at 25° C, in NaCl ionic media by UV spectrophotometric measurements. The investigated ionic strength values were 0.16, 0.25, 0.50, 1.0, 2.0 and 3.0 M. The protolysis constants calculated at the different ionic strengths yielded, with the Specific Interaction Theory, the infinite dilution constant, log β 1 ° = 13.62 ± 0.03, for the equilibrium L 2- + H + ←→ HL - . The interaction coefficient between Na + and L 2- , b(Na + , L 2- ) = 0.02 ± 0.07, has been also calculated.

The solubility, at 25°C, of calcium citrate, Ca3(C6H5O7)2. 4H2O, in NaClO4 solutions in the molality (m) range 0–3.5, has been determined by potentiometric titration with EDTA, using the Hg2+/Hg half-cell. The increase of solubility with m has been explained with the specific interaction theory by assuming, for Ca3(C6 H5 O7)2.4 H2 O(s) ⇄3Ca2+ + 26H55O7 3−, log Ks0= −17.81 ± 0.03 and the interaction coefficient between Na+ and C6H5O7 3− ions equal to 0.08 ± 0.03 −(0.06 ± 0.01)m. This coefficient allows the extrapolation to the infinite dilution reference state of stability constants determined in concentrated ionic media. Results of calculations compare well with those of the literature.

The adsorption of hydrogen ions on precipitated hydrous FePO4(am) (HFP) was studied. The experiments were carried out in 0.3 mol·dm–3 KNO3 solutions and NaClO4 solutions at ionic strengths of (0.002, 0.010, 0.030, 0.1, 0.3, and 1.0) mol·dm–3. The acidity of surface ferrihydrols, >FeOH, and phosphohydrols, >POH, groups was evaluated from potentiometric acid–base titration curves. The pH values ranged from 2.5 to 5.5. The adsorption equilibria were found to be slow but showed good reversibility. Effects by medium ions were studied using two amorphous hydrated solids obtained with different procedures: (a) precipitation and washed by dialysis (HFP(dialyzed)); (b) precipitation in situ in the presence of the ionic medium in question HFP (in situ). On the exchange of protons at the interface HFP solution, a charged surface results with positively, >FeOH2+, and negatively, >PO–, charged sites. The charge is a function of the solution acidity and is regulated by the acid–base equilibria:>FeOH2+⇄>FeOH+H+⁣logFeKa1...

*Background* Based on previous findings, we have estimated that, in injured coronary artery tissue, the low molecular weight disulfides homocystine and cysteine-homocysteine, otherwise identified as oxidized homocysteine equivalents (OHcyE), may achieve a total concentration that is higher than the aqueous solubility of homocystine at room temperature. In order to verify whether or not OHcyE could reach their saturation limit in the vascular tissue, we have measured the solubility of homocystine in physiological-like condition. *Materials and methods* The solubility of homocystine has been measured in aqueous sodium chloride solutions at 37 °C by differential pulse polarography based on the reduction of homocystine to homocysteine. *Results* We have estimated that the concentration achieved by OHcyE in injured coronary artery tissue is at least near-saturating, because the solubility of homocystine in physiological-like condition, above which deposition of homocystine and/or cysteine-homocysteine as solid phase occurs, almost exactly matches its value. Near-saturation levels of OHcyE within the vascular tissue means that significant leakage of intracellular fluid can promote OHcyE crystallization in tissue fluids, which may serve to initiate inflammation. *Conclusions* We speculate that deposition of OHcyE crystals could damage blood vessels and act as a primer of homocysteine-triggered inflammation, thus being along the causal pathway that leads to vascular dysfunction.

The title compound, catena-poly[[[dioxouranium(VI)]-bis(micro-2-hydroxybenzohydroxamato)] dihydrate], [[U(C(7)H(6)NO(3))(2)O(2)].2H(2)O](n), is a uranyl coordination polymer based on the salicylhydroxamate ligand. The ligand acts both as a chelate, forming five-membered rings, and as a bridge between two U atoms. The coordination around each U atom is a distorted hexagonal bipyramid. Infinite chains running along [001] are formed via bridging salicylhydroxamate O atoms. The chains have C(2) symmetry, with U atoms in special positions on twofold axes. The water molecules are not coordinated to the metal but crosslink, through hydrogen bonding, adjacent coordination polymer chains in the [110] and [110] directions.

Adsorption of hydrogen ions from aqueous NaCl solutions at the Pyrex glass-water interface was investigated by acid-base titration (glasselectrode) at 25 degrees C and at the ionic strengths 0.010, 0.030, 0. 10, 1.0, and 3.0 mol dm(-3). The pH values ranged from 2 to 7. The Pyrex samples had a specific surface area of 19.2 x 103 m(2) kg(-1) and a porous structure (pores 2.4 nm thick, 280 nm long). The reactions were found to be extremely slow but showed good reversibility. The potentiometric data, due to the small effect of ionic strength on the equilibria, were fitted with a simple nonelectrostatic model based on strong specific interactions of medium ions with deprotonated silanol, >SiO-, and boranol, >BO-, as well as with protonated sites. The acid-base properties are described by the reactions and equilibrium constants at the infinite dilution reference state: >SiONa + H+reversible arrow >SiOHNa+, log(Si)beta 110 = 3.1 +/- 0.2; >SiONa + 2H(+) + Cl- reversible arrow >SiOH2Cl + Na+, log(Si) beta 201 = 6.75 +/- 0.15; >SiONa + H+ reversible arrow >SiOH + Na+, log (Si beta)100 = 1.8 +/- 0.2, >BONa + H+ reversible arrow >BOH + Na+, log(B) beta 100 = 6.4 +/- 0.2; >BONa + H+ reversible arrow >BOHNa+, 0 log(B)beta 110 10 = 6.6 +/- 0.2; >BONa + 2H(+)reversible arrow >BOH2++ Na+, log (B)beta 200 = 11.56 +/- 0.15

Strengite, FePO(4)(.)2H(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(Fe(III)), dissolved while keeping strengite in contact with H3PO4 solutions. The acid concentration, mp ranged from 0.001 to 0.1 mol kg(-1). In solutions of m(P) < 0.01 mot kg(-1) m(Fe(III)), results were constant within the limits of experimental error. This was ascribed to the predominance of a soluble species FePO4(aq). Soluble complexes, mainly Fe(H(2)pO(4))(3)(aq) and FeH3(PO4)(2)(aq), were responsible for the increased solubility at m(P) >= 0.02 mol kg(-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(-6.70) met(-1) kg at the infinite dilution reference state.

The protolysis equilibria of 2-hydroxybenzohydroxamic acid, H(2)SAX, have been studied at 25degreesC in different ionic media by potentiometric titration with a glass electrode. The media were 0.513, 1.05, 2.21 and 3.5 mol/kg NaClO4. The constants beta(-p)(H(2)SAXreversible arrowH(2-p)SAX(-p)+pH(+)), combined with salting effects of NaClO4 on H(2)SAX deduced from solubility determinations, were processed by the specific interaction theory, SIT, to give equilibrium constants at infinite dilution, log beta(-1)degrees = -7.655+/-0.013 and log beta(-2)degrees = -1 7.94+/-0.04, as well as specific interaction coefficients b(HSAX(-),Na+) = 0.12+/-0.01 and b(SAX(2-),Na+) = 0.17+/-0.02, molal(-1).

The formation of ternary UO2(2+)-(OH-)-SO4(2-) complexes has been studied at 25 degrees C in 3 M NaClO4 ionic medium by measurements with a glass electrode. The solutions had uranium concentrations between 0.3 and 30 mM, sulfate between 20 and 200 mM, and 1.66or = [SO4(2-)]/[U(VI)]or = 300. The hydrogen ion concentration ranged from 10(-3) M to incipient precipitation of basic sulfates. This occurred, depending on the metal concentration, at [H+] between 10(-4) and 10(-5.3) M. In the interpretation of the data the stabilities of binary complexes were assumed from independent sources. The data could be explained with the mixed complexes and equilibria (beta(pqr)(3sigma) refers to pUO2(2+) + qH2O + rSO4(2-)==(UO2)p(OH)q(SO4)r(2p-q-2r) + qH+): logbeta222 = -2.94 +/- 0.03, logbeta341 = -9.82 +/- 0.06, logbeta211 = -0.30 +/- 0.09, logbeta212 = 1.09 +/- 0.09, logbeta351 = -15.04 +/- 0.09 and logbeta462 = -14.40 +/- 0.06. The fit could be improved by including UO2OH+ with logbeta110 = -5.1 +/- 0.1. The identity of the minor species remains, however, an open question.

The complexation equilibria between UO2(2+) and SO4(2-) ions have been studied at 25 degrees C in the ionic medium 3 M NaClO4 by potentiometry, by spectrophotometry and by solubility measurements of UO2(IO3)2. The potentiometric investigation was carried out with the Hg-Hg2SO4(s)-SO4(2-) half-cell and glass electrode in the sulfate concentration range 0.005 to 0.07 M. The optical absorbances in the UV-visible region and the solubility data cover the ligand concentration range 0.005 to 0.3 M. The data could be explained by assuming the complexes and equilibrium constants [Table: see text]. The constants in the infinite dilution reference state, log beta1o = 3.08 +/- 0.15 and log beta2o = 4.28 +/- 0.15, estimated by assuming the validity of the specific interaction theory, are practically coincident with literature data.

The equilibria have been investigated at 25 degrees C in 3 M NaClO4 using potentiometry, glass and redox Fe3+/Fe2+ half-cells, and UV optical absorptiometry. The concentration of the reagents was chosen in the intervals: 10(-4)or = [Fe(III)]or = 5.10(-3) M, 0.01or = [SO4(2-)]totor = 0.65 M. The value of [H+] was kept at 0.1 M or more to reduce the hydrolysis of the Fe3+ ion to less than 1%. Auxiliary constants, corresponding to the formation of Fe(II)-sulfate complexes and to the association of H+ with SO4(2-) ions, were taken from previous determinations. The experimental data could be explained with the equilibria [formula: see text] Equilibrium constants at infinite dilution, log beta 101 degrees = 3.82 +/- 0.17, log beta 102 degrees = 5.75 +/- 0.17 and log beta 111 degrees = 3.68 +/- 0.35, have been evaluated by applying the specific interaction theory.

The ternary Fe (III)-OH(-)-SO4(2-) complexes have been investigated at 25 degrees C in 3 M NaClO4 by potentiometric titration with glass electrode. The metal and sulfate concentrations ranged from 2.5 x 10(-3) to 0.03 M and from 5.10(-3) to 0.060 M, respectively. [H+] was decreased from 0.05 M to incipient precipitation of basic sulfate which occured at log[H+] between -2.3 and -2.5 depending on the concentration of the metal. For the interpretation of the data stability constants of HSO4(-), of binary hydroxo complexes (FeOH2+, Fe(OH)2+, Fe2(OH)2(4+), Fe3(OH)4(5+), Fe3(OH)5(4+)) and of sulfate complexes (FeSO4+, FeHSO4(2+), Fe(SO4)2-) were assumed from independent sources. The data are consistent with the presence of FeOHSO4, log beta 1-11 = -0.49 +/- 0.03. Equilibrium constants are defined as beta pqr for pFe3+ +qH+ +rSO4(2-) [symbol: see text] FepHq(SO4)r3p+q-2r. No substantial better fit could be found by adding a second mixed complex. Only a slightly smaller agreement factor resulted introducing as minor ternary complex Fe3(OH)6(SO4)3(3-) with log beta 3-63 = -5.8 +/- 0.5. Its evidence, however, cannot be considered conclusive.

The complex formation equilibria between iron(II) and sulfate ions have been studied at 25 degrees C in 3 M NaClO4 ionic medium by measuring with a glass electrode the competition of Fe2+ and H+ ions for the sulfate ion. The concentrations of the metal and of the ligand were varied in the ranges 0.01 to 0.125 and 0.01 to 0.250 M, respectively. The analytical concentration of strong acid was chosen to be 0.01 or 0.03 M. The potentials of the glass electrode, corrected for the effect of replacement of medium ions with reagent species, have been interpreted with the equilibria [formula: see text] Stability constants valid in the infinite dilution reference state, logK zero = 1.98 +/- 0.16, log beta 1 zero = 2.1(5) +/- 0.2 and log beta 2 = 2.5 +/- 0.2, have been estimated by assuming the validity of the specific interaction theory.