Biomedical subjects

Concetta De Stefano

Publications and source records attributed to Concetta De Stefano.

12 recordsLinked to original sources

PubMed2006

Speciation of phytate ion in aqueous solution. Cadmium(II) interactions in aqueous NaCl at different ionic strengths.

Interactions between myo-inositol 1,2,3,4,5,6-hexakis(dihydrogen phosphate) (phytic acid) and cadmium(II) were studied by using potentiometry (at 25 degrees C with the ISE-H+ glass electrode) in different metal to ligand (Phy) ratios (1:1< or =Cd(2+):Phy< or =4:1) in NaCl(aq) at different ionic strengths (0.1< or =I/mol L(-1)< or =1). Nine Cd(i)H(j)Phy((12-2i-j)-) species are formed with i=1 and 2 and 4< or =j< or =7; and trinuclear Cd3H4Phy2-. Dependence of complex formation constants on ionic strength was modeled by using Specific ion Interaction Theory (SIT) equations. Phytate and cadmium speciation are also dependent on the metal to ligand ratio. Stability of Cd(i)H(j)Phy((12-2i-j)-) species was modeled as a function of both the ligand protonation step (j) and the number of metal cations bound to phytate (i), and relationships found were used for the prediction of species other than those experimentally determined (mainly di- and tri-protonated complexes), allowing the possibility of modeling Phy and Cd(II) behavior in natural waters and biological fluids. A critical evaluation of phytate sequestering ability toward cadmium(II) has been made under several experimental conditions, and the determination of an empirical parameter has been proposed for an objective "quantification" of this ability. A thorough analysis of literature data on phytate-cadmium(II) complexes has been performed.

Cadmium↗

PubMed2006

Sequestration of biogenic amines by alginic and fulvic acids.

The interaction of natural (alginic and fulvic acids) and synthetic (polyacrylic acid 2.0 kDa) polyelectrolytes with some protonated polyamines [diamines: ethylendiamine, 1,4-diaminobutane (or putrescine), 1,5-diaminopentane (or cadaverine); triamines: N-(3-aminopropyl)-1,4-diaminobutane (or spermidine), diethylenetriamine; tetramine: N,N'-bis(3-aminopropyl)-1,4-diaminobutane (or spermine); pentamine: tetraethylene-pentamine; hexamine: pentaethylenehexamine] was studied at T=25 degrees C by potentiometry and calorimetry. Measurements were performed without supporting electrolyte, in order to avoid interference, and results were reported at I=0 mol L(-)(1). For all the systems, the formation of (am)L(2)H(i) species was found (am=amine; L=polyelectrolyte; i=1...4, depending on the amine considered). The stability of polyanion-polyammonium cation complexes is always significant, and for high-charged polycations, we observe a stability comparable to that of strong metal complexes. For example, by considering the formation reaction (am)H(i)+2L=(am)L(2)H(i) we found log K(i)=6.0, 6.5 and 10.8 for i=1, 2 and 3, respectively, in the system alginate-spermidine. Low and positive formation DeltaH(degrees) values indicate that the main contribution to the stability is entropic in nature. The sequestering ability of polyelectrolytes toward amines was modelled by a sigmoid Boltzman type equation. Some empirical relationships between stability, charges and DeltaG(degrees) and TDeltaS(degrees) are reported. Mean values per salt bridge of formation thermodynamic parameters (DeltaX(degrees) (n)) are DeltaG(degrees) (n)=-5.8+/-0.4, DeltaH degrees (n)=0.7+/-0.5 and TDeltaS(degrees) (n)=6.5+/-0.5 kJmol(-)(1) for all the systems studied in this work.

Alginates↗

PubMed2006

Speciation of phytate ion in aqueous solution. Sequestering ability toward mercury(II) cation in NaClaq at different ionic strengths.

As a contribution to understanding the speciation of mercury in the environment and to the study of the sequestering ability of phytate (Phy) toward heavy metal and organometal cations, this paper describes the results of an investigation (at t = 25 degrees C by potentiometry, ISE-H+ glass electrode) of its interactions with mercury(II) cation in NaCl aqueous solutions at different ionic strengths (I = 0.15 and 1.0 mol L(-1)), in the pH range 2.5 < or = pH < or = 9.5 and considering metal-to-ligand ratios of 1:1 < or = Hg/Phy < or = 4:1. The formation of 11 HgiHjPhy(12-2i-j)(- species with i = 1 and 0 < or = j < or = 7 and i = 2 and 0 < or = j < or = 2 was observed. Their complex formation constant values proved to be fairly dependent on ionic strength. The speciation of phytic acid and mercury(II) is also dependent on the metal-to-ligand ratio; the dependence of the stability of phytate-mercury(II) species on the phytate protonation step was modeled, and an empirical predictive relationship was proposed. From the results obtained, phytate has very good sequestering ability toward Hg2+, even in the presence of considerable excesses of chloride ion, that is, another ligand strongly interacting with mercury; this supports future studies both on the use of plants that naturally synthesize it for phytoremediation purposes and on its direct application in remediation techniques.

Cations↗

PubMed2006

Modeling ATP protonation and activity coefficients in NaClaq and KClaq by SIT and Pitzer equations.

The acid-base properties of Adenosine 5'-triphosphate (ATP) in NaCl and KCl aqueous solutions at different ionic strengths (0<I/mol L(-1)<or=5 for NaCl(aq), 0<I/mol L(-1)<or=3 for KCl(aq)) and at t=25 degrees C were investigated. A selection of literature data on ATP protonation constants and on activity isopiestic coefficients was performed, together with new potentiometric measurements (by ISE-H(+), glass electrode). Both literature and new experimental data were used to model the dependence on ionic strength and ionic medium of ATP protonation by SIT (Specific ion Interaction Theory) and Pitzer equations. In addition to values of first and second ATP protonation constants in NaCl(aq) and KCl(aq) at different ionic strengths, stability constants of NaATP(3-) and KATP(3-) complexes, SIT interaction coefficients and Pitzer parameters were calculated, together with protonation constants at infinite dilution: log (T)K(1)(H)=p(T)K(a2)=7.656+/-0.010 and log (T)K(2)(H)=p(T)K(a1)=4.561+/-0.006 (in the molar concentration scale, +/-95% confidence interval). Both SIT and Pitzer approaches give satisfactory results.

Adenosine Triphosphate↗

PubMed2005

Modelling of proton and metal exchange in the alginate biopolymer.

Acid-base behaviour of a commercial sodium alginate extracted from brown seaweed (Macrocystis pyrifera) has been investigated at different ionic strengths (0.1<or=I/mol l(-1)<or=1.0) and in different supporting electrolytes (Et4NI, NaCl, KCl, LiCl, NaCl+MgCl2), with the aim of examining the influence of ionic medium on the proton-binding capacity and of quantifying the strength of interaction with light metal ions in the perspective of speciation studies in natural aqueous systems. Potentiometric ([H+]-glass electrode) and titration calorimetric data were expressed as a function of the dissociation degree (alpha) using different models (Henderson-Hasselbalch modified, Högfeldt three parameters and linear equations). The dependence on ionic strength of the protonation constants was taken into account by a modified specific interaction theory model. Differences among different media were explained in terms of the interaction between polyanion and metal cations of the supporting electrolytes. Quantitative information on the proton-binding capacity, together with the stabilities of different species formed, is reported. Protonation thermodynamic parameters, at alpha=0.5, are log K H=3.686+/-0.005, DeltaG 0=-21.04+/-0.03 kJ mol(-1), DeltaH 0=4.8+/-0.2 kJ mol(-1) and TDeltaS 0=35.7+/-0.3 kJ mol(-1), at infinite dilution. Protonation enthalpies indicate that the main contribution to proton binding arises from the entropy term. A strict correlation between DeltaG and TDeltaS was found, TDeltaS=-9.5-1.73 DeltaG. Results are reported in light of building up a chemical complexation model of general validity to explain the binding ability of naturally occurring polycarboxylate polymers and biopolymers. Speciation profiles of alginate in the presence of sodium and magnesium ions, naturally occurring cations in natural waters, are also reported.

Alginates↗

PubMed2005

Interaction of UO2(2+) with ATP in aqueous ionic media.

Interaction of dioxouranium(VI) (uranyl) ion with ATP was studied by ligand/proton and metal/hydroxide displacement technique, at very low ionic strength and at I=0.15 mol L(-1), in aqueous Me4NCl and NaCl solutions, at t=25 degrees C. Measurements were carried out in the pH range 3-8.5, before the formation of precipitate. Computer analysis allowed us to find the quite stable species UO2(ATP)H2(0), UO2(ATP)H-, UO2(ATP)2-, UO2(ATP)2(6-), UO2(ATP)2H2(4-) and UO2(ATP)(OH)3- whose formation constants are (at I=0 mol L(-1)) logbeta(112)=18.21, logbeta(111)=14.70, logbeta(110)=9.14, logbeta(120)=12.84, logbeta(122)=24.82, and logbeta(11-1)=2.09, respectively. Different values were obtained in the above ionic media at I=0.15 mol L(-1) and the dependence on the ionic medium was interpreted in terms of interactions between the negatively charged complex species and cations of supporting electrolytes. The species more stable in NaCl than in Me4NCl are those with the highest negative charge, UO2(ATP)2(6-) and UO2(ATP)2H2(4-), and the extra stability of these species can be attributed to the interaction with Na+. Speciation profiles show that ATP can suppress UO2(2+) hydrolysis, and that in the neutral to slightly alkaline range the yield of complex UO2-ATP species is quite high. Comparison with other metal-ATP systems is also given in order to recognize the possibility of binding competition of uranyl ion in metal-ATP requiring enzymes for biochemical processes.

Adenosine Triphosphate↗

PubMed2005

Speciation of phytate ion in aqueous solution. Dimethyltin(IV) interactions in NaCl(aq) at different ionic strengths.

As the introduction of a systematic study on the sequestering ability of phytate (Phy) towards heavy metal and organometal cations, this paper describes the results of an investigation (at t=25 degrees C by potentiometry, ISE-H(+) glass electrode) of its interactions with dimethyltin(IV) cation [(CH(3))(2)Sn(2+), DMT] in NaCl aqueous solutions at different ionic strengths (0.1< or =I (mol L(-1))< or =1), in the pH range 2.5< or =pH< or =8.5 and considering metal to ligand ratios 1:1< or =DMT:Phy< or =4:1. We observed the formation of 18 DMT(i)H(j)Phy((12-2i-j)-) species: with i=1 and 0< or =j< or =7; i=2 and 0< or =j< or =5; i=3 and 0< or =j< or =3. Their complex formation constant values are fairly dependent on ionic strength and this dependence was modeled by a Debye-Hückel type equation. The speciation of phytic acid and dimethyltin(IV) is also dependent on the metal to ligand ratio; the dependence of the stability of phytate-dimethyltin(IV) species on both the phytate protonation step and the number of cations bound to the ligand has been modeled and an empirical predictive relationship is also proposed. From the results obtained it emerged that phytate has very good sequestering ability towards (CH(3))(2)Sn(2+). Comparisons are made with other ligands, such as ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA) and phosphate.

Hydrogen-Ion Concentration↗

PubMed2003

Dissociation constants of protonated methionine species in NaCl media.

The sulfur-containing amino acid, methionine, has a role in the physiological environment because of its strong interactions with metals. To understand these interactions of metals with methionine, one needs reliable dissociation constants for the protonated methionine species (NH(3)(+)CH(CH(2)CH(2)SCH(3))COOH; H(2)B(+)). The values of stoichiometric dissociation constants, pK(i)*, for protonated methionine species (H(2)B(+) if H(+)+HB, K(1); HB if H(+)+B(-), K(2)) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.25-6.0 mol (kg H(2)O)(-1) and temperature (5-45 degrees C). The results were extrapolated to pure water using the Pitzer equations to estimate the activity of H(+), H(2)B(+), HB and B(-) as a function of ionic strength and temperature. The resulting thermodynamic values of K(1) and K(2) were fit to the equations (T/K): ln K(1)=69.0013-3496.58/(T/K)-10.9153 ln (T/K); ln K(2)=116.4162-10638.02/(T/K)-18.0553 ln (T/K) with standard errors of 0.003 and 0.033, respectively, for ln K(1)* and ln K(2)*. Pitzer interaction parameters (lambda(HB-Na) and zeta(HB-Na-Cl)) for the neutral HB were determined from literature data. The Pitzer parameters (beta(0)(H(2)BCl), beta(1)(H(2)BCl) and C(phi)(H(2)BCl)) for the interactions of H(2)B(+) with Cl(-) and Na(+) with and B(2-) (beta(0)(NaB), beta(1)(NaB) and C(phi)(NaB)) were also determined. These coefficients can be used to make reasonable estimates of the activity coefficients of methionine species and the pK(i)(*) for the dissociation of methionine in physiological solutions, composed mostly of NaCl over a wide range of temperature and ionic strength.

Amino Acids↗

PubMed2003

Speciation of phytate ion in aqueous solution. Alkali metal complex formation in different ionic media.

The acid-base properties of phytic acid [ myo-inositol 1,2,3,4,5,6-hexakis(dihydrogen phosphate)] (H(12)Phy; Phy(12-)=phytate anion) were studied in aqueous solution by potentiometric measurements ([H+]-glass electrode) in lithium and potassium chloride aqueous media at different ionic strengths (0< I mol L(-1)< or =3) and at t=25 degrees C. The protonation of phytate proved strongly dependent on both ionic medium and ionic strength. The protonation constants obtained in alkali metal chlorides are considerably lower than the corresponding ones obtained in a previous paper in tetraethylammonium iodide (Et(4)NI; e.g., at I=0.5 mol L(-1), log K(3)(H)=11.7, 8.0, 9.1, and 9.1 in Et(4)NI, LiCl, NaCl and KCl, respectively; the protonation constants in Et(4)NI and NaCl were already reported), owing to the strong interactions occurring between the phytate and alkaline cations present in the background salt. We explained this in terms of complex formation between phytate and alkali metal ions. Experimental evidence allows us to consider the formation of 13 mixed proton-metal-ligand complexes, M(j)H(i)Phy((12-i-j)-), (M+ =Li+, Na+, K+), with j< or =7 and i< or =6, in the range 2.5< or =pH< or =10 (some measurements, at low ionic strength, were extended to pH=11). In particular, all the species formed are negatively charged: i+j-12=-5, -6. Very high formation percentages of M+-phytate species are observed in all the pH ranges investigated. The stability of alkali metal complexes follows the trend Li+ > or =Na+K+. Some measurements were also performed at constant ionic strength (I=0.5 mol L(-1)), using different mixtures of Et(4)NI and alkali metal chlorides, in order to confirm the formation of hypothesized and calculated metal-proton-ligand complex species and to obtain conditional protonation constants in these multi-component ionic media.

Journal Article↗

PubMed2003

Interactions of diethylenetriaminepentaacetic acid (dtpa) and triethylenetetraaminehexaacetic acid (ttha) with major components of natural waters.

The binding ability of diethylene triamine pentaacetate (dtpa(5-)) and triethylene tetraamine hexaacetate (ttha(6-)) ligands towards major components, H(+), Na(+), Mg(2+) and Ca(2+), of natural waters was studied in both single and mixed ionic media at different ionic strengths and at T=25 degrees C. Some measurements, performed in Mg(2+)-Ca(2+) mixtures, allowed us to find the formation of new mixed species MgCa(dtpa), MgCa(ttha) and MgCaH(ttha), here reported for the first time. All the complexes formed in the various systems were characterized in terms of both stoichiometry and stability, and an attempt was made to find general rules for the stability of mixed metal complexes in comparison with that of simple species. To obtain quantitative information on the complexing ability of dtpa and ttha in seawater, measurements have been carried out in artificial seawater ionic medium (Na(+), K(+), Ca(2+), Mg(2+), Cl(-) and SO(4)(2-)). Calculations, performed by considering the salt mixture as single salt BA, allowed us to find some quite stable B(i)H(j)L species. Under the natural seawater conditions [S(salinity)=35], we found for the most important species logbeta( B(dtpa))=9.64 and. Literature data comparison is also reported.

Chelating Agents↗

PubMedDate not supplied

Dioxouranium(VI)--carboxylate complexes. Interaction with dicarboxylic acids in aqueous solution: speciation and structure.

In this paper we report the results of an investigation performed by potentiometric (H+-glass electrode) and visible spectrophotometric measurements on the interaction of UO2(2+) ion towards some carboxylic ligands (acetate, malonate, succinate, azelate). The measurements were carried out at T= 25 degrees C in different ionic media (KNO3 and NaCl) at different ionic strengths (0.1 < or = I/mol L(-1) < or = 1.0, NaCl; I/mol L(-1) = 0.1, KNO3). The dependence on ionic strength of formation constants was taken into account by using both a simple Debye-Hückel type equation and the SIT (Specific ion Interaction Theory) approach. Different speciation models (depending on concentration of reagents, ionic strength, pH-range) both for different carboxylates and different ionic media have been obtained. Linear combinations between formation constants, stoichiometric coefficients and length of alkyl chain of dicarboxylates have been observed and predicted formation constants at I= 0 mol L(-1) are reported for the interaction of UO2(2+) with HOOC-(CH2)n-COOH with 1 < or = n < or = 7. Finally, a visible absorption spectrum for each complex reaching a significant percentage of formation in solution (KNO3 medium) has been calculated to characterise the compounds found by pH-metric refinement.

Dicarboxylic Acids↗

PubMedDate not supplied

Thermodynamic parameters for the binding of polycarboxylic anions by fully methyl substituted linear polyammonium cations.

Enthalpy changes for the binding of malonate, citrate, 1,2,3-propanetricarboxylate and 1,2,3,4-butanetetracarboxylate by fully methyl substituted linear polyammonium cations (with the general formula C3nNnH(8n + 2)n+, with n = 1,2,3) were determined calorimetrically. Enthalpy changes were also determined for the binding of malonate by unsubstituted polyammonium cations (with the general formula C2(n - 1)NnH(6n - 2)n+, n = 1...6). delta H0/kJ mol-1 values are always positive and strongly dependent on the charges involved in the formation reaction. Mean values for delta G0 and T delta S0 were obtained as a function of the charge product zeta = Zanion/ Zcation: -delta G0/kJmol-1 = (4.0 +/- 0.4) zeta, T delta S0/kJmol-1 = (5.9 +/- 0.1) zeta (substituted polyamines), and -delta G0/kJmol-1 = (3.5 +/- 0.2) zeta, T delta S0/kJmol-1 = (5.0 +/- 0.4) zeta (unsubstituted polyamines). For both classes of amines it was found that T delta S0 vs. delta G0 is linear with a correlation coefficient of r = 0.9618. Crude approximation gives -delta G0/kJmol-1 = (7.0 +/- 0.4) n-1, T delta S0/kJmol-1 = (10.0 +/- 0.8) n-1 for unsubstituted amines and -delta G0/kJmol-1 = (8.0 +/- 0.8) n-1, T delta S0/kJmol-1 = (11.8 +/- 2.0) n-1 (n = number of possible salt bridges, or single interactions) for substituted amines.

Carboxylic Acids↗