Jacob A. Marinsky

A unified physicochemical description of the protonation and metal ion complexation equilibria of natural organic acids (humic and fulvic acids). 1. Analysis of the influence of polyelectrolyte properties on protonation equilibria in ionic media: fundamental concepts.

Explication quantitative de la forte sensibilite des proprietes potentiometriques des polyelectrolytes acides faibles a la force ionique du milieu

A unified physicochemical description of the protonation and metal ion complexation equilibria of natural organic acids (humic and fulvic acids). 2. Influence of polyelectrolyte properties and functional group heterogeneity on the protonation equilibria of fulvic acid.

Potentiometric studies of the neutralization of several fulvic acid sources with standard base in aqueous and nonaqueous media have been conducted. Analysis of the results with a recently developed unified physicochemical model has shown that the protonation behavior of these fulvic acid sources is a reflection of their polyelectrolyte nature and their heterogeneity. It has been possible to ascribe the polyelectrolyte properties observed to a rather inflexible fulvic acid molecule whose variably charged surface is impermeable to simple electrolyte. 42 references, 24 figures, 4 tables.

The interaction of Cu(II) ion with humic acid

Abstract The interaction of Cu(II) ion with a humic acid gel was carefully examined as a function of ionic strength and degree of dissociation to test the utility and validity of the fundamental approach developed by the authors for the unambiguous analysis of the protolytic and metal-ion complexation properties of such organic acid substances. Several of the equations developed earlier have been useful for this purpose. Two complexed species, CuS2, where S is believed to be an oxygen atom accessible from ether, aldehyde, ketone, or phenolic groups contained in the three-dimensional array of aromatic rings and their side chains which determine the structure of humic acid, and (RCOOCu+)ν are believed to be the only Cu(II)-bound entities formed. The stability constant of the more strongly complexed CuS2 is approximately 1 × 104; the formation constant of (RCOOCU+)ν is ∼18, a value not too different from the formation constant that has been reported for this particular species when formed by the interaction of Cu(II) with mononuclear carboxylic acid molecules. The sizable variation in pK(HA)νapp of three orders of magnitude, attributed initially to the heterogeneity of humic acid samples, was found to be more likely a consequence of differences in the accessibility of the functional units (RCOOH)ν, (RCOO−)ν, and (RCOOCu+)ν in these condensed systems.

Ultrafiltration as a technique for studying metal-humate interactions: studies with iron and copper.

Abstract An ultrafiltration method was employed to study Fe(II)/Fe(III) and Cu(II) binding by Armadale Horizon fulvic acid. The results of the Fe—fulvate studies indicate the formation of “aggregates” between Fe and the fulvic acid molecule. The reduction of Fe(III) to Fe(II) by fulvic acid is also observed. Results for Cu(II)—fulvate electrode method. An algorithm developed previously for the prediction of metal ion binding by fulvic acid at different pH and salt concentration levels was tested further by comparing Cu 2+ ion binding predictions with their measured values.

A unified physicochemical description of the equilibria encountered in humic acid gels

Abstract Though numerous publications have appeared relating metal-ion binding to humic substance properties no unified physicochemical description of the equilibria encountered has been available to provide a unique analysis of these systems. A fundamentally sound approach for the achievement of this goal is developed here in an attempt to rectify this situation. In particular the physical chemical basis for the unambiguous analysis of the protolytic and metal-complexation behavior of humic acid gels during potentiometric investigation is detailed. Complication introduced into the analysis by heterogeneity encountered in humic substances is examined briefly as well.

Gel speciation studies-I The intrinsic dissociation constant of weakly acidic cation-exchange gels.

The arid-dissociation properties of three weakly acidic cation-exchange gels, CM-Sephadex C-50-120, Biogel CM-2 and CM-Biogel A, have been studied. Each of the gels was equilibrated in sodium polystyrene sulphonate (NaPSS) solutions at three different concentration levels (0.1, 0.01 and 0.001M). The volume of the gels was measured as a function of a (their degree of neutralization), and C(p) (the NaPSS concentration); pH and pNa were also measured at each alpha-value. Intrinsic pK values of 3.25 and 4.55 have been found for CM-Sephadex C-50-120 and Biogel CM-2 respectively.

Influence of counterion concentration on equilibria and conformational properties of linear weak-acid polyelectrolytes

Abstract Since linear, weak-acid polyelectrolytes respond to neutral salt just like their crosslinked analogs, their equilibria have been presumed to be as amenable to analysis with the Gibbs-Donnan approach as the gels. To examine this possibility this approach has been used to estimate solvent uptake by carboxymethyldextran and poly(acrylic acid) in the course of their neutralization with standard base. These estimates have been compared with estimates obtained for the same parameter by using the ion-condensation model of Manning.

Gel speciation studies—II: An extension of earlier studies of the protonation equilibria of cross-linked carboxymethyldextran

The potentiometric properties of the rigidly cross-linked Sephadex gel CM-25 have been studied. The gel was equilibrated in sodium perchlorate at fixed concentration levels (0.010 and 0.0010M) and with variable concentration levels of NaClO(4) (from 0.0010 to 0.10M). The volume of the gel was measured for every equilibrated sample simultaneously with the solution pH and pNa. The pK computed after correction for a Donnan potential term was found to be independent of alpha, the degree of neutralization, and ionic strength; its value of 3.35 +/-0.15 was in excellent agreement with the intrinsic pK measured earlier for the flexible CM-50 Sephadex gel and reported for its linear polyelectrolyte analogue, carboxymethyldextran. An interesting observation from these studies is the efficient screening of the charged surface by the counter-ions in the presence of a three-dimensional charged network.

Computational scheme for the prediction of metal ion binding by a soil fulvic acid

The dissociation and metal ion binding properties of a soil fulvic acid have been characterized. Information thus gained was used to compensate for salt and site heterogeneity effects in metal ion complexation by the fulvic acid. An earlier computational scheme has been modified by incorporating an additional step which improves the accuracy of metal ion speciation estimates. An algorithm is employed for the prediction of metal ion binding by organic acid constituents of natural waters (once the organic acid is characterized in terms of functional group identity and abundance). The approach discussed here, currently used with a spreadsheet program on a personal computer, is conceptually envisaged to be compatible with computer programs available for ion binding by inorganic ligands in natural waters.

Metal complexation of negatively charged polymers: Evaluation of the electrostatic effect on the complexation equilibria

A unified analytical treatment of metal complexation equilibria in weak-acid linear polyelectrolyte and gel polyelectrolyte systems is presented. Complexation equilibria of monovalent (Ag+) and divalent (Ca2+ and Zn2+) ions with carboxymethyldextran, CmDx, and the gel analogues, CM-Sephadex C-25 and C-50 (Pharmacia, Sweden), have been investigated in sodium salt media at 25°C. It was revealed that the formation of monodentate ligand complexes, AgA0, CaA+, and ZnA+ (A−= carboxymethyl group) is predominant. The stability constants of the complexed species, AgA0, CaA+, and ZnA+ have been determined to be 2.7, 3.8, and 4.8 mol−1dm3 , respectively, in good agreement with the stability constants of the respective acetate complexes, the monomer analogues of the CmDx and the cross-linked CmDx complexes.