José L. Beltrán

Speciation of the Ionizable Antibiotic Sulfamethazine on Black Carbon (Biochar)

Adsorption of ionizable compounds by black carbon is poorly characterized. Adsorption of the veterinary antibiotic sulfamethazine (SMT; a.k.a., sulfadimidine; pK(a1) = 2.28, pK(a2) = 7.42) on a charcoal was determined as a function of concentration, pH, inorganic ions, and organic ions and molecules. SMT displayed unconventional adsorption behavior. Despite its hydrophilic nature (log K(ow) = 0.27), the distribution ratio K(d) at pH 5, where SMT(0) prevails, was as high as 10(6) L kg(-1), up to 10(4) times greater than literature reported K(oc). The K(d) decreases at high and low pH but not commensurate with the decline in K(ow) of the ionized forms. At pH 1, where SMT(+) is predominant and the surface is positive, a major driving force is π-π electron donor-acceptor interaction of the protonated aniline ring with the π-electron rich graphene surface, referred to as π(+)-π EDA, rather than ordinary electrostatic cation exchange. In the alkaline region, where SMT(-) prevails and the surface is negative, adsorption is accompanied by near-stoichiometric proton exchange with water, leading to the release of OH(-) and formation of an exceptionally strong H-bond between SMT(0) and a surface carboxylate or phenolate, classified as a negative charge-assisted H-bond, (-)CAHB. At pH 5, SMT(0) adsorption is accompanied by partial proton release and is competitive with trimethylphenylammonium ion, signifying contributions from SMT(+) and/or the zwitterion, SMT(±), which take advantage of π(+)-π EDA interaction and Coulombic attraction to deprotonated surface groups. In essence, both pK(a1) and pK(a2) increase, and SMT(±) is stabilized, in the adsorbed relative to the dissolved state.

Study of solvent effects on the acid–base behaviour of adenine, adenosine 3′,5′-cyclic monophosphate and poly(adenylic) acid in acetonitrile–water mixtures using hard-modelling and soft-modelling approaches

Abstract The acid–base behaviour of adenine, adenosine 3′,5′-cyclic monophosphate and poly(adenylic) acid was studied at 37xa0°C by spectrometric titration in acetonitrile–water mixtures. Hard-modelling and soft-modelling approaches were used for this purpose. The first one, which requires the assumption of a previous chemical model, was used for the study of monomeric compounds and the second one, an alternating least-squares multivariate curve resolution procedure, was used for the study of poly(adenylic) acid, because it does not require any previous chemical model. The p K a values were correlated with either macroscopic or microscopic parameters, such as solvatochromic parameters. The influence of solvent composition on the intramolecular and solute/solvent interactions such as base stacking and hydrogen-bonding, affects the structure, solubility and the number of species detected.

Chiral macrocyclic polyethers incorporating a tetraoxaspiro[5.5]undecane or trioxa-azaspiro[5.5]undecane moiety

Abstract New macrocyclic polyethers possessing chirality due to a spiro ring junction are prepared from 2,8-dihydroxymethylated (+)-1,4,7,10-tetraoxaspiro[5.5]undecane 1 and (+)-1,4,7-trioxa-10-azaspiro[5.5]undecane 2 , both ( E,E ). N -Functionalization of compounds derived from 2 is also examined. The complexing properties of representative ligands 3 , 4 , 5 measured by spectrophotometry in THF, for alkaline and alkaline-earth cations, indicate that these spheric positively-charged species are weakly associated.

Spectrofluorimetric method for the simultaneous determination of zinc and cadmium.

The simultaneous determination of zinc and cadmium using derivative synchronous and multiwavelength synchronous spectrofluorimetry is described. Effects of experimental variables on the fluorescence intensities and on the spectral resolution of the fluorescent chelates of these metals with 8-(p-toluenesulfonamido)-quinoline (TSQ) in a sodium lauryl sulfate micellar medium have been studied. Mixtures containing 10–200 μg L−1 Zn and 15–250 μg L−1 Cd have been analyzed with good results. The proposed method has been applied to a biological sample.

Sorption of Enrofloxacin and Ciprofloxacin in Agricultural Soils: Effect of Organic Matter

Large amounts of fluoroquinolones (FQs), highly used antimicrobials in veterinary medicine, enter the soil directly through the application of manure contaminated with these chemicals. The environmental mobility of this contaminant is mainly governed by its retention in soil. The aim of this study was to examine the contribution of humic acid (HA), an organic matter (OM) surrogate, to the sorption of FQs in natural soils. Sorption of enrofloxacin and ciprofloxacin was studied in two completely different Spanish agricultural soils with similar pH. The soils tested were amended with different concentrations of HAs (0%, 1%, 3% and 5%; wt/wt). The results showed that addition of HA to the soil samples increased the magnitude of sorption and changed the sorption behaviour. However, the effect was only apparent at 3–5% HA content and its extent was dependent on both the sorbent and the sorbate. At soil pH around 7.5, when zwitterionic species predominate in the solution, sorption of FQs onto the soil seems to be governed by OM content, which provides a source of available sites for cation-exchange mechanisms.

ISOT_Calc: A versatile tool for parameter estimation in sorption isotherms

Geochemists and soil chemists commonly use parametrized sorption data to assess transport and impact of pollutants in the environment. However, this evaluation is often hampered by a lack of detailed sorption data analysis, which implies further non-accurate transport modeling. To this end, we present a novel software tool to precisely analyze and interpret sorption isotherm data. Our developed tool, coded in Visual Basic for Applications (VBA), operates embedded within the Microsoft Excel™ environment. It consists of a user-defined function named ISOT_Calc, followed by a supplementary optimization Excel macro (Ref_GN_LM). The ISOT_Calc function estimates the solute equilibrium concentration in the aqueous and solid phases (Ce and q, respectively). Hence, it represents a very flexible way in the optimization of the sorption isotherm parameters, as it can be carried out over the residuals of q, Ce, or both simultaneously (i.e., orthogonal distance regression). The developed function includes the most usual sorption isotherm models, as predefined equations, as well as the possibility to easily introduce custom-defined ones. Regarding the Ref_GN_LM macro, it allows the parameter optimization by using a Levenberg-Marquardt modified Gauss-Newton iterative procedure. In order to evaluate the performance of the presented tool, both function and optimization macro have been applied to different sorption data examples described in the literature. Results showed that the optimization of the isotherm parameters was successfully achieved in all cases, indicating the robustness and reliability of the developed tool. Thus, the presented software tool, available to researchers and students for free, has proven to be a user-friendly and an interesting alternative to conventional fitting tools used in sorption data analysis.

Complexation of Ni (II) and Zn(II) ions by 3-(1-naphthyI)-2-mercaptopropenoic acid

The complexation equilibria between Ni(II) and Zn(II) metal ions with 3-(1-naphthyl)-2-mercaptopropenoic acid (H2NMP) were studied by glass electrode potentiometry, at 25 °C and 1.0 mol·dm−3 in NaClO4 as constant ionic medium in 50% (v/v) water-ethanol solutions. Formation constants for the complexes Ni(NMP), Ni(NMP)22−, Zn(NMP) and Zn(NMP)22−, refined by the MINIGLASS program, are reported.

Thermodynamic properties of the dissociation of 2-mercaptopyridine, 2-mercaptopyrimidine and 2-thiobarbituric acid

Abstract The changes in free energy, enthalpy and entropy for the dissociation and neutralization of 2-mercaptopyridine, 2-mercaptopyrimidine and 2-thiobarbituric acid have been determined at 25°C in aqueous potassium nitrate medium of 0.1 M ionic strength. The changes in dissociation free energy were calculated from dissociation constants determined potentiometrically and refined using the program MINIGLASS. The neutralization enthalpy changes were determined by direct thermometric titration, using linearization methods and the least-squares program MINITERM.

A potentiometric study on complex formation of nickel(II) and zinc(II) ions with 3-(2-naphthyl)-2- mercaptopropenoic acid

Abstract Protonation and complex formation equilibria between zinc and nickel ions with 3-(2-naphthyl)-2-mercaptopropenoic acid (NMPA) have been studied in 50% (v/v) water-ethanol solutions containing 1 M NaClO4 as constant ionic medium at 25°C using glass electrode potentiometry. Initial estimates of complex formation constants were refined with the MINIGLASS program. Protonation constants for the ligand and formation constants for the complexes Ni(NMPA), Ni(NMPA)2, Zn(NMPA)H, Zn(NMPA) and Zn(NMPA)2 are reported.

Thermodynamic properties of the dissociation of several α-oxooximes

The changes in free energy, enthalpy and entropy for the dissociation of several α-oxooximes (phenylglyoxal aldoxime, glyoxylanilide oxime,N-ethyl-glyoxylanilide oxime and 1-phenyl-1,2-propanedione-2-oxime) have been determined in water-ethanol medium (50% v/v) at 0.5M ionic strength (NaNO3) and 25 °C. The changes in dissociation free energy were calculated from the pKa values determined by glass-electrode potentiometry, and refined by using the programs MINIGLASS and SUPERQUAD. The dissociation enthalpies were determined by direct thermometric titration, and refined by using the programs MINITERM and MULTITERM.