Thermodynamic properties of alkali halides. II. Enthalpies of dilution and heat capacities in water at 25�C

The size and structure of selected hydrated ions and implications for ion channel selectivity

The structures of hydrated sodium (yellow) and potassium (red) ions.

An Investigation of Ion-Pairing of Alkali Metal Halides in Aqueous Solutions Using the Electrical Conductivity and the Monte Carlo Computer Simulation Methods

The ion pairing is, in very dilute aqueous solutions, of rather small importance for solutions' properties, which renders its precise quantification quite a laborious task. Here we studied the ion pairing of alkali halides in water by using the precise electric conductivity measurements in dilute solutions, and in a wide temperature range. The low-concentration chemical model was used to analyze the results, and to estimate the association constant of different alkali halide salts. It has been shown that the association constant is related to the solubility of salts in water and produces a 'volcano relationship', when plotted against the difference between the free energy of hydration of the corresponding individual ions. The computer simulation, using the simple MB+dipole water model, were used to interprete the results, to find a microscopic basis for Collins' law of matching water affinities.

An induction heater device for studies of magnetic hyperthermia and specific absorption ratio measurements

The development of a device for generating ac magnetic fields based on a resonant inverter is presented, which has been specially designed to carry out experiments of magnetic hyperthermia. By determining the electric current in the LC resonant circuit, a maximum intensity of magnetic field around of 15 mT is calculated, with a frequency around of 206 kHz. This ac magnetic field is able to heat powdered magnetic materials embedded in biological systems to be used in biomedical applications. Indeed, in order to evaluate the sensitivity of the device we also present the measurements of the specific absorption rate in phantoms performed with commercially prepared Fe(3)O(4) and distilled water at different concentrations.

Apparent Molar Volumes and Adiabatic Compressibilities of Some Amino Acids in Aqueous Sucrose Solutions at 298.15 K

Apparent molar volumes V ϕ and adiabatic compressibilities K ϕ, s of L-glycine, L-alanine, and L-valine in aqueous sucrose solutions ranging from pure water to 25 mass% of sucrose have been determined at 298.15 K from precise density and sound speed measurements. Partial molar volumes V ϕ 0 and partial molar adiabatic compressibilities K ϕ, s 0 of these amino acids at infinite dilution were evaluated. These values are required for calculating hydration number n H of amino acids. Transfer volumes ΔV ϕ 0 and transfer adiabatic compressibilities ΔK ϕ, s 0 at infinite dilution from water to aqueous sucrose solutions have been calculated. Transfer parameters have been discussed in terms of solute-cosolute interaction on the basis of a cosphere overlap model. Group contributions for the partial molar volumes and adiabatic compressibilities have been determined from the amino acids. All these results indicate that hydrophilic ionic group interactions are stronger than the hydrophilic-hydrophobic interactions in all the amino acids over the whole concentration range of sucrose solutions and decrease with the increase in size of side chain of amino acids.

The osmotic sensitivity of netropsin analogue binding to DNA

The binding of a netropsin analogue to random sequence DNA, monitored by CD, is seen dependent on the concentration of neutral solutes. The binding free energy decreases linearly with solute osmolal concentration and the magnitude of the effect is insensitive to the chemical identity of the solute for betaine, sorbitol, and triethylene glycol. These solutes appear to modulate binding through their effect on water activity and changes in the hydration of the drug and DNA in the complex reaction, not through a direct interaction with the reactants or the product. The dependence of binding constant on solute concentration can be interpreted as an additional binding of some 50-60 extra solute excluding water molecules by the complex. A water sensitivity of drug binding is further seen from the dependence of binding constants on the type of anion in solution. Anions in the Hofmeister series strongly affect bulk water free energies and entropies. The differences in netropsin analogue binding to DNA with Cl-, F-, and ClO4- are consistent with the effect observed with neutral solutes. The ability to measure changes in water binding associated with a specific DNA interaction is a first step toward correlating changes in hydration with the strength and specificity of binding.