Ignacio Moreno-Villoslada

Water-soluble polymer–metal ion interactions

Abstract The interactions between metal ions and water-soluble polymers (WSP) have gained great interest due to their intrinsic properties as well as their potential applications, such as superconducting materials, ultra-high strength materials, liquid crystals, and biocompatible polymers. This review attempts to provide a general coverage of various scientific aspects of the WSP–metal ion interactions in aqueous solution and their applications. It includes fundamental aspects on synthesis of water-soluble polymers, as well as different activities and properties. A particular emphasis is given to the study the WSP–metal ion interactions, under different experimental procedures, through the liquid-phase polymer based retention (LPR) technique, which combines the use of WSP and membrane ultrafiltration. Theoretical work on this WSP–metal ion interaction has been elaborated to explain the counterion binding to polyelectrolytes, and the polymer–metal ion complex formation.

Influence of the linear aromatic density on methylene blue aggregation around polyanions containing sulfonate groups.

The aggregation of methylene blue around different polyelectrolytes is studied by diafiltration, UV-vis, and (1)H NMR spectroscopies. Poly(sodium acrylate-co-sodium maleate) induces the formation of higher-order aggregates, showing a typical polyelectrolyte behavior dominated by long-range electrostatic interactions with the dye which are highly dependent on the ionic strength. Poly(sodium 4-styrenesulfonate) presents a high dispersant ability of methylene blue, showing what we can call a typical polyaromatic-anion behavior characterized by the presence of short-range aromatic-aromatic interactions with the dye which are less dependent on the ionic strength. An intermediate behavior is found for the copolymers poly(sodium 4-styrenesulfonate-co-sodium maleate) at two different comonomer compositions, related to a different probability of the polymers to form and stabilize ion pairs in hydrophobic environments. Their behavior is a function of the linear aromatic density, which is related to the comonomeric structure.

Chelation properties of polymer complexes of poly(acrylic acid) with poly(acrylamide), and poly(acrylic acid) with poly(N,N-dimethylacrylamide)

The metal-complexing properties of intermolecular complexes of poly(acrylic acid) with poly(acrylamide), and poly(acrylic acid) with poly(N,N-dimethylacrylamide) were studied by means of the liquid-phase polymer based retention (LPR) technique. The metal ion retention ability at pH 5 for 400 μg of Cu(II), Cd(II), Co(II), Cr(III), Hg(II), Ni(II), Pb(II), and Zn(II) was investigated due to their environmental and analytical interest in the presence of 1.1 M of carboxylic acid units and variable amounts of amide groups. The retention profiles of the intermolecular complexes were compared with those of the correspondent homopolymers and copolymers. The retention capacity of poly(acrylic acid) is 100% for all metal ions except for Co(II), Ni(II), and Zn(II) whose values were about 90%, while poly(acrylamide) does not retain any of the metal ion studied. The presence of poly(acrylamide) decreases the retention capacity down to 60% for Co(II) and Ni(II) and to 70% for Zn(II). The decrease on the retention values is dependent on the polymer ratio. A smaller effect is observed by the addition of poly(N,N-dimethylacrylamide) which also decreases the retention capacity down to 80% for Co(II) and Ni(II) for a ratio poly(acrylic acid)/poly(N,N-dimethylacrylamide) = 1/2. The metal ion binding behavior of the interpolymer complexes is very close to that of the copolymers.

Comparative study of the self-aggregation of rhodamine 6G in the presence of poly(sodium 4-styrenesulfonate), Poly(N -phenylmaleimide- co -acrylic acid), poly(styrene- alt -maleic acid), and poly(sodium acrylate)

The interaction between rhodamine 6G and different polyelectrolytes is analyzed. Structural aspects differentiate these polyelectrolytes, such as the presence of aromatic groups and the number and localization of their respective charges, which may be directly attached to the aromatic groups or to the polymeric main chain. In the case of poly(sodium acrylate), which does not bear aromatic groups, the polyelectrolyte induces cooperative self-stacking between the dyes which is highly sensitive to the ionic strength, due to the predominance of long-range electrostatic interactions between the polymer and the dye. In the case of poly(sodium 4-styrenesulfonate), whose charge is directly attached to the aromatic groups, a high dispersant ability of the dyes is found and the interaction is less dependent on the ionic strength, due to the predominance of short-range aromatic-aromatic interactions between the dye and the polymer. Among the two polyelectrolytes studied for which the polymeric charge is directly attached to the main chain, and separated from the aromatic group, poly(styrene-alt-maleic acid) shows a lower dependence of the interaction on the ionic strength than poly(N-phenylmaleimide-co-acrylic acid) at a comonomer composition of 1:2, due to a higher linear aromatic density and a lower linear charge density, indicating the importance of hydrophobic forces. Both copolymers exhibit a high ability to induce cooperative self-aggregation of the dye.

Poly(sodium 4‐styrenesulfonate)–metal ion interactions

The metal ion-binding properties of poly(sodium 4-styrenesulfonate) in conjunction with membrane filtration were investigated for Cu(II), Cd(II), Co(II), Cr(III), Hg(II), Ni(II), Pb(II), Zn(II), and Fe(II). Different experiments were carried out at different pHs, metal ion concentrations, polymer concentrations, and molecular weight fractions. Only Fe(II) and Cr(III) were retained at pH 1, which allows a selective separation of these metals from all the other metal ions. At pH 3 the retention ability of this polymer increased for all the metal ions. On the other hand, the metal ion-retention properties are dependent on the polymer/metal ratio.

Prediction of the retention values associated to the ultrafiltration of mixtures of metal ions and high molecular weight water-soluble polymers as a function of the initial ionic strength

Abstract The equations that relate the dissociation constants between divalent metal ions and polymer chains in aqueous solutions with the ionic strength are developed from a model previously discussed that gives account for the experimental results obtained in ultrafiltration experiments. The relations found are used to predict the retention values at high filtration factors in ultrafiltration experiments corresponding to the systems poly(sodium 4-styrenesulfonate)/Cd 2+ , and poly(vinylalcohol)/Pb 2+ , respectively, performed under variable initial ionic strength.

Poly[acrylamide‐co‐1‐(2‐hydroxyethyl)aziridine]: An efficient water‐soluble polymer for selective separation of metal ions

Poly[acrylamide-co-1-(2-hydroxyethyl)aziridine], obtained by spontaneous copolymerization, which contains different types of ligand groups as tertiary amines and hydroxyl and amide groups, was tested as a polychelatogen using the liquid-phase polymer-based retention (LPR) technique. The metal ion retention ability of this polymer was found to depend on the pH and it showed a high selectivity to copper(II) at pH 5. The maximum capacity of Cu(II) was determined at pH 5 by using the enrichment variant of LPR. The retention capacities of the polymer with Cu(II), Cd(II), Co(II), Cr(III), Ni(II), Pb(II), Zn(II), and Fe(II) were studied at different pH and the results are compared with those of branched polyethylenimine and poly[1-(2-hydroxyethyl)aziridine] homopolymers.

USE OF ULTRAFILTRATION ON THE EVALUATION AND QUANTIFICATION OF THE INTERACTIONS BETWEEN POLYMERS AND LOW MOLECULAR-WEIGHT MOLECULES IN AQUEOUS SOLUTIONS

The theory and mathematical treatment of the evaluation of the interactions of water-soluble polymers with low molecular-weight molecules is presented. The interaction of the water-soluble polymer poly(sodium 4-styrenesulfonate) with L-tryptophan (Try), L-phenylalanine (Phe), chlorpheniramine maleate (CPM), and 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) is studied by this technique. Ultrafiltration experiments at pH 7.5, and different ionic strength values show weak interactions of the low molecular weight molecules TTC and CPM with the polymer with apparent dissociation constants of 0.26 and 0.32 respectively in the absence of NaNO3, and 2.02 and 1.2 in the presence of 0.10 of NaNO3 and 0.13 M of NaCl respectively. Negligible interactions are found for Try or Phe at pHs ranging between 4 and 10 and NaNO3 concentrations ranging between 0.0 and 0.15 M. This suggests that the interactions are mainly due to both long-range electrostatic forces and short-range interactions that may include hydrophobic forces or charge transfer complexation. The interaction of TTC with PSS in the absence of NaNO3 is reflected in UV-Vis spectroscopic studies by a decrease on the intensity of the maximum at 248 nm

Nanoparticles for the Treatment of Wounds

The treatment of skin wounds represents an important research area due to the important physiological and aesthetic role of this tissue. During the last years, nanoparticles have emerged as important platforms to treat skin wounds. Silver, gold, and copper nanoparticles, as well as titanium and zinc oxide nanoparticles, have shown potential therapeutic effects on wound healing. Due to their specific characteristics, nanoparticles such as nanocapsules, polymersomes, solid lipid nanoparticles, and polymeric nanocomplexes are ideal vehicles to improve the effect of drugs (antibiotics, growth factors, etc.) aimed at wound healing. On the other hand, if active excipients are added during the formulation, such as hyaluronate or chitosan, the nanomedicine could significantly improve its potential. In addition, the inclusion of nanoparticles in different pharmaceutical materials may enhance the beneficial effects of the formulations, and allow achieving a better dose control. This paper aims at reviewing significant findings in the area of nanoparticles and wound treatment. Among the reviewed topics, we underline formulations comprising inorganic, polymeric, surfactant self-assembled, and lipid nanosystems. Among the drugs included in the nanoformulations, the paper refers to antibiotics, natural extracts, proteins, and growth factors, among others. Finally, the paper also addresses nanoparticles embedded in secondary vehicles (fibers, dressings, hydrogels, etc.) that could improve their application and/or upgrade the release profile of the active.

ERROR SIMULATION IN THE DETERMINATION OF THE FORMATION CONSTANTS OF POLYMER-METAL COMPLEXES (PMC) BY THE LIQUID-PHASE POLYMER-BASED RETENTION (LPR) TECHNIQUE

The Liquid-phase polymer-based retention (LPR) technique allows calculating the formation constant of polymer-metal ion complexes (Kf). The dependence of the relative error in Kf (eK) on the error in the total retention coefficient a (ea) has been searched and it was found that its influence is higher as a increases, so that its measurement must be performed with higher precision. In addition, ea is higher for high a values due to the stronger influence of errors in the measurements of the different magnitudes that allow its calculation. In order to achieve a measurement of Kf with a relative error lower than 7 %, the experimental a found should not exceed the value 0.4 when relative errors for the independent variables ranging between 2 % and 5 % are considered