Authors:J. C. Benegas, A. Di Blas, S. Paoletti, and A. Cesàro
It is shown that calorimetric experiments on the dilution process of polyelectrolytes, i.e. on the excess enthalpy of electrostatic origin, can give information on the conformational state of the polymer. Analytical expression are obtained relating the enthalpy of dilution to the charge density on the polymer, from Manning's theory. The experimental data reported on some ionic biopolymers are interpreted on the basis of the theoretical prediction of the electrostatic contribution to the enthalpy of dilution in water of a polyelecrolytic salt and of a weak polyacid.
Various approaches to the modeling of metal and radionuclide interactions with macromolecular ligands, proteins, polysaccharides
and humic substances in particular, their chemical and sorption equilibria, and the techniques used for their investigation
are concisely compared. To predict radionuclide mobility in the natural and semi-natural aqueous environment, the estimation
of the effective interaction constants, related to specific species of polyelectrolytes which are linked with the absorbancy
or absorbancy ratio in their electronic absorption spectra, should probably be preferred and developed as standard. For characterization
of the binding sites of specific molecular forms of polyelectrolyte ligands, the Scatchard plot analysis at macroconcentrations
of the metal and also, though not so effectively, the two-phase distribution at trace concentrations of radionuclide or metal
can be applied.
Authors:Ö. Malay, D. Yalçın, A. Batıgün, and O. Bayraktar
This study aimed the characterization of the films casted from the aqueous mixtures of the pH induced complexes between silk
fibroin (SF) and hyaluronic acid (HA). The insoluble and transparent films were subjected to scanning electron microscopy
(SEM) analyses to show the morphological changes. Thermal analysis of complex films was determined by a differential scanning
calorimeter (DSC). The changes in the crystalline state were monitored by X-ray diffractometer (XRD) and Fourier transform
infrared spectroscopy (FTIR). It was shown that the complexation between HA and SF was dominantly induced by pH. It was shown
that the complex films comprised mixtures of crystalline and non-crystalline regions.
Authors:S. Bayülken, G. Yüce, A. Erkol, Z. Mustafaeva, and M. Mustafaev
Aqueous solution of polyacrylic acid (PAA), poly-N-isopropylacrylamide (PNIPAAm), bovine serum albumin (BSA), superoxide dismutase
(SOD) and their mixtures (PAA-BSA, PAA-Cu-BSA, PNIPAAm-BSA, PAA-SOD) were irradiated in the presence of oxygen in neutral
media (pH 7.0) with 60Co γ-rays. In addition, aliquots of aqueous solutions of PAA, PAA-Cu2+, BSA and PAA-Cu2+-BSA saturated with N2 and N2O were also irradiated. The decomposition rate of irradiated solutions were measured by UV-visible spectrophotometry, fluorescence
spectroscopy, and high performance liquid chromatography (HPLC). Protective effect of copper ions on radiolysis of aqueous
solution of PAA-Cu-BSA and conversion of Cu(II) to Cu(I) was observed. The possible mechanism of this phenomenon is discussed.
Humic acid has been shown to play a significant role in the environmental behavior of many metal cations as it can function as both a complexant and a redox agent. A number of models have been proposed to explain their complexing role, but most use quite different chemical descriptions of the metal-humate interactions. Two of these models which have been applied to humic acid interaction with actinide cations are briefly discussed. In one model in which humics are treated as anionic polyelectrolytes, cations can bind to specific anionic donor sites (site binding) as well as be attracted by the net anionic charge of the macromolecules (the Polyelectrolyte Model). In the second model (the Charge Neutralization Model), the binding for each cation is assumed to be associated with a number of carboxylate groups equal to the cationic charge. It is concluded that the Charge Neutralization Model is more useful in geochemical calculation codes, whereas the Polyelectrolyte Model can provide more insight into the chemical behavior of the humic acids.
Authors:A. Paulenová, P. Rajec, J. Kandráč, G. Sasköiová, E. Tóthová, P. Bartoš, V. Švec, and R. Góra
Complexation equilibrium of metals by three humic acids of different origin with ultrafiltration method was investigated at pH 4 a 5 and ionic strength I = 0.1M NaClO4. Commercial (Aldrich) and two original humic acids (peat and soil, obtained by six step isolation process from the material from Trnava county, close to the NPP Jaslovské Bohunice) were used in this study. For the evaluation of the results, the model of metal ion charge neutralization upon humic acid functional group proposed by the Kim and Czerwinski was used. Complexation constants were calculated using the terms of this model (operational concentration, loading capacity). The values of log = 5.39±0.16 for yttrium, 6.15±0.16 for americium and 5.20±0.08 for lead were found. Correlation of free metal concentration and ratio of molar fraction of complexing functional groups confirms the validity of charge neutralisation model for metal and polyelectrolyte complexation study.
A theoretical description of the proton dissociation process of weak polyacids is given. Incorporation of conformational variability in the free energy of a polyelectrolyte system provides quantitative fitting of experimental data. In addition, it extends the validity of the theory to cases in which a cooperative order-disorder transition takes place. Biopolymers considered are: poly(L-aspartic acid), poly(L-glutamic acid), samples of poly(uronic acid) and some carboxylic derivatives of a gelling bacterial polysaccharide.
Authors:A. Paulenová, P. Rajec, M. Žemberyová, G. Sasköiová, and V. Višacký
The binding of strontium by humic acid was studied in systems designed to model soil leaching conditions. Ultrafiltration experiments were conducted for a wide range of CaCl and NaCl concentrations and for the pH range 4 to 7. It was found that the recovery of humic acid slowly decreased with increasing pH. This occurred because at neutral and basic solutions the increasing degree of ionization of the carboxylate groups leads to the full repulsion state of the humic acid and to increasing of the strontium binding (strontium recovery 60% at pH 7) with this natural polyelectrolyte. The strontium complexation in the presence of calcium was studied in different series of metal concentrations at pH 5 and the ionic strength 0.1M NaCl. The results were explained on the base of the metal ion charge neutralization model of humic complexation (CNM). Loading capacity (cca 40%) and complexation constants and Sr (3.51±0.27) and Ca (3.10±0.29) with Aldrich humic acid were found.
be a significant concern for human health. The possible impurities include surface-active agents [ 3 ] or inorganic salts such as Na 2 SO 4 [ 5 ]. The presence of these impurities has a strong effect on the polyelectrolyte properties like viscosity