Insights on Stability Constants and Structures of Complexes between Coumarin Derivatives and Pb(II) in Aqueous Media.

In the frame of a systematic study on the sequestering ability of natural antioxidants towards metal cations, here the complexation of coumarin-3-carboxilic acid (HCCA) with Pb(II) and the overall stability constants of the resulting complexes, at 37 °C and in 0.16 M NaClO4, are discussed. Reaction of Pb(ClO4)2 with HCCA in an aqueous medium at a pH range from 2 to 6 and various ratios (1:1-1:10) yielded the Pb-CCA complexes, which were characterized spectrometrically by laser desorption ionization mass spectrometry (LD-MS). LD-MS has provided the composition and structure of Pb-CCA species according to the speciation model proposed on the basis of the potentiometric data. The graphic representation of the complex's concentration curves is given by the distribution diagram, which provides a whole depiction of the species present in the solution at the selected pH ranges.

Transition metal cations catalyze 16O/18O exchange of catechol motifs with H218O.

Catechol motifs are ubiquitous in nature, as part of plant, animal and microbial metabolites, and are known to form complexes with various metal cations. Here, we report for the first time that complexation with transition metal cations, especially Fe(III), results in rapid 16O/18O exchange of the catecholic hydroxyl groups with H218O. We discuss the implications of this finding for mechanistic studies using H218O and potential relevance for production of 18O-labeled catechol derivatives.

Modeling the Solubility of Phenolic Acids in Aqueous Media at 37 °C.

In this work, the solubility of vanillic, gallic, syringic, p-coumaric, ferulic and caffeic acids was determined at 37 °C under different conditions, namely pure water and two different ionic media, NaCl(aq) and NaClO4(aq), at different ionic strengths (i.e., 0.16, 0.50, 1.0, 2.0 and 3.0 M). The solubility in water of all the acids was found to be higher than that in both of the ionic media. Moreover, the solubility of hydroxycinnamic acids was lower than that of hydroxybenzoic acids. The activity coefficients of neutral species were calculated from these data; this knowledge is necessary when modeling the dependence of equilibrium constants on the ionic strength. Results obtained in this work can be useful for further studies regarding complex formation equilibria between these ligands and bioavailable metal cations.

A Review on Coordination Properties of Al(III) and Fe(III) toward Natural Antioxidant Molecules: Experimental and Theoretical Insights.

This review focuses on the ability of some natural antioxidant molecules (i.e., hydroxycinnamic acids, coumarin-3-carboxylic acid, quercetin, luteolin and curcumin) to form Al(III)- and Fe(III)-complexes with the aim of evaluating the coordination properties from a combined experimental and theoretical point of view. Despite the contributions of previous studies on the chemical properties and biological activity of these metal complexes involving such natural antioxidants, further detailed relationships between the structure and properties are still required. In this context, the investigation on the coordination properties of Al(III) and Fe(III) toward these natural antioxidant molecules might deserve high interest to design water soluble molecule-based metal carriers that can improve the metal's intake and/or its removal in living organisms.

Interleukin-13 increases pendrin abundance to the cell surface in bronchial NCI-H292 cells via Rho/actin signaling.

Interleukin-13 (IL13) is a major player in the development of airway hyperresponsiveness in several respiratory disorders. Emerging data suggest that an increased expression of pendrin in airway epithelia is associated with elevated airway hyperreactivity in asthma. Here, we investigate the effect of IL13 on pendrin localization and function using bronchiolar NCI-H292 cells. The data obtained revealed that IL13 increases the cell surface expression of pendrin. This effect was paralleled by a significant increase in the intracellular pH, possibly via indirect stimulation of NHE. IL13 effect on pendrin localization and intracellular pH was reversed by theophylline, a bronchodilator compound used to treat asthma. IL13 upregulated RhoA activity, a crucial protein controlling actin dynamics, via G-alpha-13. Specifically, IL13 stabilized actin cytoskeleton and promoted co-localization and a direct molecular interaction between pendrin and F-actin in the plasma membrane region. These effects were reversed following exposure of cells to theophylline. Selective inhibition of Rho kinase, a downstream effector of Rho, reduced the IL13-dependent cell surface expression of pendrin. Together, these data indicate that IL13 increases pendrin abundance to the cell surface via Rho/actin signaling, an effect reversed by theophylline.

HSP90 and pCREB alterations are linked to mancozeb-dependent behavioral and neurodegenerative effects in a marine teleost.

The pesticide mancozeb (mz) is recognized as a potent inducer of oxidative stress due to its ability to catalyze the production of reactive oxygen species plus inhibiting mitochondrial respiration thus becoming an environmental risk for neurodegenerative diseases. Despite numerous toxicological studies on mz have been directed to mammals, attention on marine fish is still lacking. Thus, it was our intention to evaluate neurobehavioral activities of ornate wrasses (Thalassoma pavo) exposed to 0.2mg/l of mz after a preliminary screening test (0.07-0.3mg/l). Treated fish exhibited an evident (p<0.001) latency to reach T-maze arms (>1000%) while exploratory attitudes (total arm entries) diminished (-50%; p<0.05) versus controls during spontaneous exploration tests. Moreover, they showed evident enhancements (+111%) of immobility in the cylinder test. Contextually, strong (-88%; p<0.01) reductions of permanence in light zone of the Light/Dark apparatus along with diminished crossings (-65%) were also detected. Conversely, wrasses displayed evident enhancements (160%) of risk assessment consisting of fast entries in the dark side of this apparatus. From a molecular point of view, a notable activation (p<0.005) of the brain transcription factor pCREB occurred during mz-exposure. Similarly, in situ hybridization supplied increased HSP90 mRNAs in most brain areas such as the lateral part of the dorsal telencephalon (Dl; +68%) and valvula of the cerebellum (VCe; +35%) that also revealed evident argyrophilic signals. Overall, these first indications suggest a possible protective role of the early biomarkers pCREB and HSP90 against fish toxicity.

Complexation of Al3+ and Ni2+ by l-Ascorbic Acid: An Experimental and Theoretical Investigation.

Despite the potential versatility of Vitamin C as a ligand, only for few metal complexes does full characterization exist. Vitamin C metal complexes, indeed, are difficult to study experimentally because the ligand has multiple protonation and oxidation states, and the metal-ligand complexes are in general not as tight as one might expect and frequently resistant to crystallographic characterization. In most cases, coordination via one of the hypothesized modes is invoked, characterized by monodentate or bidentate coordination via the most acidic oxygen atoms, with the ligand singly or doubly deprotonated. In this study the ability of l-ascorbic acid to form complexes with Al3+ and Ni2+ ions under physiological conditions was investigated by using a combination of potentiometric measurements, 1H NMR spectroscopy, and DFT computations in order to recognize the structural properties of the resulting complexes in aqueous solution. The comparison between the values of the free energies of complexation obtained by using DFT quantum chemical calculations and estimated from experimental stability constants according to the mass action law and by considering the involved equilibria allows to select structure and preferred coordination modes of formed complexes. The protonation constant of the free ligand was also determined using potentiometric data and its reproduction by using computational approaches was critically commented.

Sequestering Ability of a Synthetic Chelating Agent towards Copper(II) and Iron(III): A Detailed Theoretical and Experimental Analysis.

In the continuous effort to identify selective chelators towards bioavailable and toxic metal ions, the potential selectivity of a novel N,O chelating ligand, recently synthesized and claimed to be able to bind to Cu(II) ions forming stable complexes while leaving unaltered the level of essential metal ions, was scrutinized using a combined theoretical and experimental approach. A multistep synthetic procedure was used to synthesize the ligand, whose chelating properties along with the stability of the complexes formed binding Cu(II) and, for comparison, Fe(III) ions were evaluated using potentiometric measurements and UV-Vis spectroscopy. DFT analysis allowed to disclose the structural characteristics of the formed complexes. In the plethora of all the possible structures, a selection of the most reliable ones was achieved by means of a stringent comparison between experimental and simulated UV-Vis spectra. The outcomes of the present investigation demonstrate that the Cu(II) sequestering ability of the ligand is smaller than that towards Fe(III). The strategy used here should allow to check the propensity of ligands in selectively binding metal ions.

Electropolymerizable IrIII Complexes with ß-Ketoiminate Ancillary Ligands.

A series of electropolymerizable cyclometallated IrIII complexes were synthesized and their electrochemical and photophysical properties studied. The triphenylamine electropolymerizable fragment was introduced by using triphenylamine-2-phenylpyridine and, respectively, triphenylamine-benzothiazole as cyclometalated ligands. The coordination sphere was completed by two differently substituted ß-ketoiminate ligands deriving from the condensation of acetylacetone or hexafluoroacetylacetone with para-bromoaniline. The influence of the -CH3 /-CF3 substitution to the electrochemical and photophysical properties was investigated. Both complexes with CH3 substituted ß-ketoiminate were emissive in solution and in solid state. Highly stable films were electrodeposited onto ITO coated glass substrates. Their emission was quenched by electron trapping within the polymeric network as proven by electrochemical studies. The -CF3 substitution of the ß-ketoiminate leads instead to the quenching of the emission and inhibits electropolymerization.

Orexin receptor expression is increased during mancozeb-induced feeding impairments and neurodegenerative events in a marine fish.

Food intake ensures energy resources sufficient for basic metabolism, immune system and reproductive investment. It is already known that food-seeking performances, which are crucially controlled by orexins (ORXs), may be under the influence of environmental factors including pollutants. Among these, mancozeb (mz) is becoming an environmental risk for neurodegenerative diseases. Due to few studies on marine fish exposed to mz, it was our intention to correlate feeding latency, food intake and feeding duration to potential neurodegenerative processes in key diencephalic sites and expression changes of the ORX neuroreceptor (ORXR) in the ornate wrasses (Thalassoma pavo). Hence, fish exposed for 4 days (d) to mz 0.2 mg/l (deriving from a 0.07, 0.14, 0.2, 0.3 mg/l screening test) displayed a significant reduction (p < 0.05) of food intake compared to controls as early as 1d that became more evident (p < 0.01) after 3d. Moreover, significant enhancements of feeding latency were reported after 1d up to 3d (p < 0.001) and even feeding duration was enhanced up to 3d (p < 0.001), which instead moderately increased after 4d (p < 0.05). A reduction (-120%; p < 0.001) of mean body weight was also detected at the end of exposure. Likewise, a notable (p < 0.001) activation of ORXR protein occurred together with mRNA up-regulations in diencephalic areas such as the diffuse nucleus of the inferior lobe (+48%) that also exhibited evident degenerative neuronal fields. Overall, these results highlight an ORX role as a vital component of the neuroprotective program under environmental conditions that interfere with feeding behaviors.

Antiproliferative activity of novel isatinyl/indanyl nitrones (INs) as potential spin trapping agents of free radical intermediates.

A series of ketonitrones derived from isatin and indanone (INs) were synthesized and evaluated for their antiproliferative activities against several human cancer cell lines. Then, the antioxidant properties of these substrates were measured by the DPPH test to report their biological activity in terms of their spin trapping action. In particular, one substrate has showed very high biological and scavenging activity, probably due to the strong correlation between its spin trapping activity and structure.

On the complexation of copper (II) ion with 2-hydroxybenzamide.

The complexation of the Cu2+ ion with 2-Hydroxybenzamide (salicylamide, HL) has been studied, at 25 degrees C, by potentiometric measurements with a glass electrode in NaCIO4 media for ionic strength ranging from 0.5 to 3 mol/dm3. The data are consistent with the formation of the complexes CuH(-1)(HL)+, CuH(-2)(HL)2, Cu2H(-2)(HL)2(2+) and CuH(-2)(HL). The minor species, Cu2H(-2)(HL)2(2+) and CuH(-2)(HL), amount to at least 20% of the total copper. Elaboration of the data according to the Specific Interaction Theory yields the constants valid in the infinite dilution reference state: [formulas: see text] and the interaction coefficients (kg/mol) of complex species with medium ions: b(L-,Na+) = 0.11 +/- 0.03; b(CuH(-1)(HL)+,NaClO4) = 0.17 +/- 0.05; b(CuH(-2)(HL)2,NaClO4) = 0.11 +/- 0.05; b(Cu2H(-2)(HL)2(2+),NaClO4) = 0.2(7) +/- 0.1; b(CuH(-2)(HL),NaClO4) = -0.0(3) +/- 0.1.

Study of the adsorption of mercury (II) on lignocellulosic materials under static and dynamic conditions.

WHO has declared mercury as one of the most dangerous pollutants for human health. Unfortunately, several cases of rivers and aquifers contaminated by mercury inevitably poses the problem on how to remediate them. Considerable efforts are being addressed to develop cost-effective methodologies, among which the use of low-cost adsorbing materials. In this paper, the adsorption performances of an alternative lignocellulosic material derived from the Spanish broom plant, are presented. This plant is widely diffused in the world and its usage for Hg(II) removal from water in real working conditions requires only minimal pretreatment steps. A thoroughly investigation on the kinetics and thermodynamics of Hg(II) adsorption on Spanish broom is presented, by using Hg(II) polluted aqueous solutions specifically prepared in order to simulate typical groundwater conditions. Several batch experiments, under static conditions, were carried out in order to evaluate the effect of pH, contact time, adsorbent dosage, initial concentration, temperature. A maximum adsorption capacity of 20 mg L-1 can be obtained at pH 5, following a pseudo second order kinetics. Moreover, adsorption experiments in dynamic conditions were carried out using Spanish broom filters. Interestingly, a systematic, unconventional double S-shape breakthrough curve was observed under different experimental conditions, revealing the occurrence of two adsorption processes with different time scales. This behavior has been fitted by a bimodal Thomas model which, unlike the single Thomas fitting, gives satisfactory results with the introduction of a new parameter related to the fraction of surface active sites involved in the adsorption processes.

Multivariate class modeling techniques applied to multielement analysis for the verification of the geographical origin of chili pepper.

Four class-modeling techniques (soft independent modeling of class analogy (SIMCA), unequal dispersed classes (UNEQ), potential functions (PF), and multivariate range modeling (MRM)) were applied to multielement distribution to build chemometric models able to authenticate chili pepper samples grown in Calabria respect to those grown outside of Calabria. The multivariate techniques were applied by considering both all the variables (32 elements, Al, As, Ba, Ca, Cd, Ce, Co, Cr, Cs, Cu, Dy, Fe, Ga, La, Li, Mg, Mn, Na, Nd, Ni, Pb, Pr, Rb, Sc, Se, Sr, Tl, Tm, V, Y, Yb, Zn) and variables selected by means of stepwise linear discriminant analysis (S-LDA). In the first case, satisfactory and comparable results in terms of CV efficiency are obtained with the use of SIMCA and MRM (82.3 and 83.2% respectively), whereas MRM performs better than SIMCA in terms of forced model efficiency (96.5%). The selection of variables by S-LDA permitted to build models characterized, in general, by a higher efficiency. MRM provided again the best results for CV efficiency (87.7% with an effective balance of sensitivity and specificity) as well as forced model efficiency (96.5%).

Rapid discrimination of bergamot essential oil by paper spray mass spectrometry and chemometric analysis.

A novel approach for the rapid discrimination of bergamot essential oil from other citrus fruits oils is presented. The method was developed using paper spray mass spectrometry (PS-MS) allowing for a rapid molecular profiling coupled with a statistic tool for a precise and reliable discrimination between the bergamot complex matrix and other similar matrices, commonly used for its reconstitution. Ambient mass spectrometry possesses the ability to record mass spectra of ordinary samples, in their native environment, without sample preparation or pre-separation by creating ions outside the instrument. The present study reports a PS-MS method for the determination of oxygen heterocyclic compounds such as furocoumarins, psoralens and flavonoids present in the non-volatile fraction of citrus fruits essential oils followed by chemometric analysis. The volatile fraction of Bergamot is one of the most known and fashionable natural products, which found applications in flavoring industry as ingredient in beverages and flavored foodstuff. The development of the presented method employed bergamot, sweet orange, orange, cedar, grapefruit and mandarin essential oils. PS-MS measurements were carried out in full scan mode for a total run time of 2 min. The capability of PS-MS profiling to act as marker for the classification of bergamot essential oils was evaluated by using multivariate statistical analysis. Two pattern recognition techniques, linear discriminant analysis and soft independent modeling of class analogy, were applied to MS data. The cross-validation procedure has shown excellent results in terms of the prediction ability because both models have correctly classified all samples for each category. Copyright © 2016 John Wiley & Sons, Ltd.

The second acidic constant of salicylic acid.

The second dissociation constant of salicylic acid (H2L) has been determined, at 25 degrees 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 beta1(0) = 13.62 +/- 0.03, for the equilibrium L2- + H+ <==> HL-. The interaction coefficient between Na+ and L2-, b(Na+, L2-) = 0.02 +/- 0.07, has been also calculated.

Synthetic, potentiometric and spectroscopic studies of chelation between Fe(III) and 2,5-DHBA supports salicylate-mode of siderophore binding interactions.

Catecholate type enterobactin, a prototype siderophore, comprises 2,3-dihydroxybenzoic acid (2,3-DHBA) cyclically linked to serine in E. coli. The existence of iron-chelating ligands in humans is a recent discovery, however, the basic chemical interactions between 2,5-dihydroxybenzoic acid and Fe(III) ion remain poorly understood. Achieving an accurate description of the fundamental Fe(III) binding properties of 2,5-DHBA is essential for understanding its role in iron transport mechanisms. Here, we show that 2,5-DHBA binds iron in a salicylate mode via a two-step kinetic mechanism by UV spectroscopy. Complexation between Fe(III) salt and 2,5-DHBA initially occurs at 1:1 ratio (of ligand to metal) and binding resulting in higher-order complexes continues at higher concentrations. Through potentiometric measurements we quantify the distribution of Fe(III)-2,5-DHBA complexes with 1:1, 1:2 and 1:3 stoichiometry. The formation of 1:3 complexes is further supported through high-resolution mass spectrometry. Further, using kinetic and equilibrium UV spectroscopy, we report Fe(III)-2,5-DHBA complex formation at a pH range of 2.5-9.0 at 298.15K in water. Maximum complexation occurred at a pH range of 4.5-6.5 consistent with deprotonation of the carboxylic acid proton. Equilibrium measurements and stopped-flow kinetics show that complexation rate constants were independent of concentrations of 2,5-DHBA. Together the data supports a model in which the rate-determining step involves rearrangement of ligands on an initial complex formed by reversible binding between the carboxylate group of 2,5-DHBA and Fe(III).

The hydrogen salicylate ion as ligand. Complex formation equilibria with dioxouranium (VI), neodymium (III) and lead (II).

The complexation equilibria of the hydrogen salicylate ion, HL(-), have been studied, at 25 degrees C, by potentiometric measurements with a glass electrode in 1 M NaClO4 for uranyl and Nd(III) ions and in 3 M NaClO4 for Pb(II) ion. The ligand concentration (CL) was varied between 10(-3) and 0.05 M. In the system with U(VI) the concentrations ranged between: 10(-3) < or = [U(VI)] < or = 0.01 M, 0.5 < or = CL /[U(VI)] < or = 10 and 10(-2) < or = [H+] < or = 10(-5) M; for neodymium system: 2 x 10(-3) < or = [Nd(III)] < or = 0.01, 1 < or = CL /[Nd(III)] < or = 10 and 10(-2) < or = [H+] < or = 10(-7) M; for lead system: 10(-3) < or = [Pb(II) < or = 3 x 10(-3), 1 < or = CL /Pb(II)] < or = 2 and 10(-5) < or = [H+] < or = 10(-7.3) M. The experimental data have been explained with the formation of UO2HL+, UO2L, UO2(OH)L(-), (UO2)2(OH)L2(-) UO2(HL)L(-), NdHL(2+), NdL(+), Nd(OH)L, PbHL(+), PbL and PbL2(2-). Equilibrium constants are given for the investigated ionic media and at infinite dilution.

The effect of ionic strength on the complexation of copper (II) with salicylate ion.

The complexation of Cu2+ with the hydrogen salicylate, HL-, ion has been studied, at 25 degrees C, by potentiometric measurements with a glass electrode in NaClO4 media for an ionic strength range from 0.5 to 3 M. The complexes found were CuL, CuL2(2-) and CuHL+. Stability constants, extrapolated to zero ionic strength by using the Specific Interaction Theory were: [formula: see text]

Equilibria occurring between beryllium (II) and salicylate ions.

The complexation equilibria between Be2+ and the hydrogen salicylate (HL-) ions have been studied, at 25 degrees C, by potentiometric measurements with a glass electrode in 3 M NaClO4. The concentrations of metal (CM) and ligand (CL) were varied between 10(-3) and 0.03 M and 2 x 10(-3) and 0.03 M, respectively, while 1 < or = CL/CM < or = 3. The hydrogen ion concentration ranged from 10(-3) to 10(-5.3) M when basic salts start to precipitate. The equilibria can be written in the general form as: pBe2+ + rHL- <==> Be(p)H(-q) (HL)r(2p-r-q) + qH+, log beta(pqr). The experimental data have been explained with the formation of BeHL+ (log beta101 = 1.46 +/- 0.05), BeL (log beta111 = -0.897 +/- 0.018), BeL2(2-) (log beta122 = -3.746 +/- 0.021), Be2(OH)L2- (log beta232 = -5.23 +/- 0.09), Be3(OH)3L3(3-) (log beta363 = -14.39 +/- 0.12). The uncertainties represent 3sigma. The predominant complex in the whole concentration range studied is the uncharged mononuclear species BeL.