Lan-Chi Königsberger

Low-temperature thermodynamic model for the system Na2CO3−MgCO3−CaCO3−H2O

Abstract A comprehensive low-temperature thermodynamic model for the geochemically important Na2CO3−MgCO3−CaCO3−H2O system is presented. The model is based on calorimetrically determined ΔfH°298 values, S°298 values and C°p(T) functions taken from the literature as well as on μ°298 values of solids derived in this work from solubility measurements obtained in our laboratories or by others. When these thermodynamic quantities were combined with temperature-dependent Pitzer parameters taken from the literature, solubilities calculated for a wide range of conditions agree well with experimental data. The results for several subsystems were summarized by depicting the respective phase diagrams. For the MgO−CO2−H2O subsystem, it was found that the commonly believed stability relations must be revised, i.e., in the temperature range covered, nesquehonite never becomes more stable than hydromagnesite at pCO2 ≤ 1 atm. Although the recommended set of thermodynamic data on sparingly soluble solids was derived from experimental results on mainly NaClO4 systems, it can be incorporated in databanks containing additional Pitzer parameters for modeling more complex fresh- or seawater systems.

Complexation of iron (III) and iron (II) by citrate. Implications for iron speciation in blood plasma

Estimates of the concentrations and identity of the predominant complexes of iron with the low-molecular-mass ligands in vivo are important to improve current understanding of the metabolism of this trace element. These estimates require a knowledge of the stability of the iron-citrate complexes. Previous studies on the equilibrium properties of the Fe(III)-citrate and Fe(II)-citrate are in disagreement. Accordingly, in this work, glass electrode potentiometric titrations have been used to re-determine the formation constants of both the Fe(III)- and Fe(II)-citrate systems at 25 degrees C in 1.00 M (Na)Cl and the reliability of these constants has been evaluated by comparing the measured and predicted redox potentials of the ternary Fe(III)-Fe(II)-citrate system. The formation constants obtained in this way were used in computer simulation models of the low-molecular-mass iron fraction in blood plasma. Redox equilibria of iron are thus included in large models of blood plasma for the first time. The results of these calculations show the predominance of Fe(II)-carbonate complexes and a significant amount of aquated Fe(II) in human blood plasma.

Thermodynamic modeling of crystal deposition in humans

The prevention and treatment of crystal deposition in the human body are based on the understanding of the physicochemical properties underlying the precipitation of the substances involved. Among these properties, the solubilities of the crystals are very important. Recently, experimentally determined solubility data of substances related to urolithiasis, such as calcium oxalate hydrates, uric acid and urates, cystine, and xanthine, were critically assessed. Unfortunately, reported solubilities of these substances were found to be either scarce or in large disagreement. Consequently, detailed studies were carried out in our laboratory, and the results will be discussed in this communication with emphasis on the thermodynamic consistency of the experimentally determined data. Since proper modeling of the solubilities of these substances in artificial urine solutions serves as a prerequisite for solubility predictions in real urine, the Joint Expert Speciation System (JESS) software package was employed to create a comprehensive computer model including the relevant, low-molecular inorganic and organic components of urine. The results of the simulations lead to some useful suggestions regarding the prevention and treatment of stone disease.

Biomineralization – Medical Aspects of Solubility

Summary This title takes an interdisciplinary approach to the central role of solubility in pathological biomineralisation, ranging from traditional thermodynamics and kinetics to unusual concepts such as the PILP process. The scientific background and expertise of the contributors, ranges accordingly from solubility modelling and database development, renal stone and bone implant research, Mossbauer spectroscopy and structural chemistry to biochemistry and crystallisation. The chapters all have a quantitative, physico-chemical component rather than giving purely phenomenological descriptions. The contributors deal with aspects and concepts that have not previously been common in the study of pathological biomineralisation processes.

IUPAC-NIST Solubility Data Series. 90. Hydroxybenzoic Acid Derivatives in Binary, Ternary, and Multicomponent Systems. Part I. Hydroxybenzoic Acids, Hydroxybenzoates, and Hydroxybenzoic Acid Salts in Water and Aqueous Systems

The solubility data for well-defined binary, ternary, and multicomponent systems of solid-liquid type are reviewed. One component, which is 2-, 3-, and 4-hydroxybenzoic acids, 4-hydroxybenzoate alkyl esters (parabens), or hydroxybenzoic acid salts, is in the solid state at room temperature and another component is liquid water, meaning that all of the systems are aqueous solutions. The ternary or multicomponent systems include organic substances of various classes (hydrocarbons of several structural types, halogenated hydrocarbons, alcohols, acids, ethers, esters, amides, and surfactants) or inorganic substances. Systems reported in the primary literature from 1898 through 2000 are compiled. For seven systems, sufficient binary data for hydroxybenzoic acids or parabens in water are available to allow critical evaluation. Almost all data are expressed as mass and mole fractions as well as the originally reported units, while some data are expressed as molar concentration.

IUPAC-NIST Solubility Data Series. 90. Hydroxybenzoic Acid Derivatives in Binary and Ternary Systems. Part II. Hydroxybenzoic Acids, Hydroxybenzoates, and Hydroxybenzoic Acid Salts in Nonaqueous Systems

The solid-liquid solubility data for well defined nonaqueous binary and ternary systems are reviewed. One component includes hydroxybenzoic acid, hydroxybenzoate, and hydroxybenzoic acid salt, and another component includes a variety of organic compounds (hydrocarbons, alcohols, halogenated hydrocarbons, carboxylic acids, esters, et al.) and carbon dioxide. The ternary systems include mixtures of organic substances of various classes and carbon dioxide. The total number of compilation sheets is 270 for six types of system. Almost all data are expressed as mass percent and mole fraction as well as the originally reported units, while some data are expressed as molar concentration. Critical evaluation was carried out for the binary nonaqueous systems of 2-, 3-, and 4-hydroxybenzoic acids and hydroxybenzoates (methylparaben, ethylparaben, propylparaben, and butylparaben) in alcohols, 1-heptane, and benzene.

Solubility and body fluids

Solubility phenomena (i.e. dissolution and precipitation reactions) are the physicochemical basis of numerous biological processes. These include, for instance: • gas solubilities in respiratory and photosynthetic processes; the solubility of volatile anaesthetics; • the crystallisation, both in biologically controlled and pathological processes, of biogenic minerals in a variety of body fluids; the resorption of mineralised tissue; • the accumulation, due to their higher solubility, of lipophilic substances, such as pesticides, in liquid fat contained, e.g. in adipose tissue or human milk; • the incorporation of metal ions such as strontium (including the radioactive 90Sr isotope) in bone, by co-precipitation and solid-solution formation. Since Sr stabilises bone apatite crystals (i.e. decreases solubility), it may retard the resorption of the calcified matrix and thus have therapeutic potential in the prevention and treatment of osteopenic disorders [1]. In dental enamel, a combination of strontium and fluoride was reported to be more effective in stabilising the apatetic structure than each element alone [2]. This results in an improved crystal resistance to degradation by bacterial acids and hence may be useful for the prevention of dental caries [3]. All of these solubility phenomena are governed by the laws of thermodynamics and kinetics. The human body is essentially an isothermal system (a notable exception, related to gout, has been reported in the literature – see below). Thus, the pertinent in vitro measurements have almost always been performed at 37_C. However, reactions in body fluids are complicated by the presence of organic complexing agents which affect the speciation of metal ions (i.e. their distribution among these complexes). Computer speciation modelling of biofluids, which has a long history [4], has also to be considered in the modelling of solubility equilibria. The presence of organic macromolecules such as proteins provides templates or matrices which control the crystallisation of biogenic minerals and modify their morphologies. The mineral phase in organic/inorganic composites (such as teeth or bone) may form nanosized crystals, which exhibit unusual dissolution and crystallisation behaviour [5]. A new biomineralisation mechanism invoking liquid precursors and their importance for normal and pathological biomineralisation processes has been proposed [6]. These and other aspects of normal and pathological biomineralisation processes have been reviewed recently [7].

Editorial: Special Issue in Memoriam Heinz Gamsjäger

Professor Heinz Gamsjager was an Associate Editor of Monatshefte fur Chemie/Chemical Monthly since 1998...