James J. Christensen

Ion binding by synthetic macrocyclic compounds.

The existence of synthetic macrocyclic molecules with hydrophilic cavities containing multiple binding atoms and with hydrophobic exteriors gives rise to extraordinary possibilities with respect to the design and synthesis of molecules with specific cation and anion binding properties. The preparation of many new macrocyclic compounds has recently been reported, but few practical applications for them have been suggested. From the information available, it is becoming clear that it should be possible to synthesize macrocycles that will have specified, or selected, ion binding properties. Cavity size can be varied to accommodate only those cations or anions within a specified narrow band of sizes. Numbers and types of coordinating atoms can be chosen to give essentially electrostatic or covalent bonding or a combination of the two in a metalmacrocycle complex. The metal ligand bond appears to be predominantly ionic in the case of the cyclic polyethers but the covalent character increases on substitution of sulfur or nitrogen for oxygen donor atoms. The essential hydrophobic exteriors of the macrocycles can be modified by the addition of side chains and groups to facilitate the solution of anions and cations in organic solvents. The structures of many macrocycles can be made to approximate naturally occurring molecules, that is, cyclic polyethers similar to macrocyclic antibiotics of the valinomycin and nonactin types and cyclic polyamines similar to porphyrins. Macrocycles are also useful as model compounds for the study of metal interactions with biological systems. The synthetic macrocycles thus represent an intriguing new area of coordination chemistry, the systematic study of which should lead to many interesting and useful chemical applications in the field of metal complexation in solution.

Determination of equilibrium constants by titration calorimetry: Part II. Data reduction and calculation techniques

Abstract Techniques of data reduction and methods of calculation have been given for the determination of equilibrium constants by titration calorimetry. It has been shown how, starting with typical titration calorimetry data, the apparent heat liberated in the reaction vessel can be calculated, corrected for extraneous heat effects, and used to solve for the equilibrium constant and enthalpy change value(s) for the reaction(s) under investigation. Equations are given for calculating the energy contributed to the overall heat effects measured in the reaction vessel by processes other than chemical reactions such as heat of stirring, heat losses, heat of dilution, etc., and by chemical reactions other than the one(s) for which equilibrium constant(s) are sought. Mathematical techniques and equations are presented for calculating equilibrium constants and enthalpy change values from titration data by least squares analysis.

Determination of equilibrium constants by titration calorimetry: Part I. Introduction to titration calorimetry☆

Abstract Techniques for determining thermodynamic equilibrium constants by titration calorimetry have been developed for a wide spectrum of reactions. The method is still relatively new and improvements and extensions are foreseeable. Chief among the advantages of the method is its university. It can be used in any solvent to determine equilibrium constants for proton ionization and metal ion—ligand interactions over a large pH range for simple and complex equilibria. It yields a good overall picture of the stoichiometry of the reaction(s) taking place and the experimentation and data analysis can be done rapidly. The chief drawback of the method has been the initial expense of the calorimeter and the unavailability of commercial calorimeters. However, this is partially offset by the fact that commercial calorimeters are now available from LKB Instruments (Rockville, Maryland) and Tronac (Orem, Utah). Computer programs have been worked out for most types of reactions and are available in Fortran IV computer language (see Part II and III, pp. 219Δ-246). Simple and inexpensive apparatus can be built for demonstration and laboratory classwork in which the equilibrium constants for simple interactions can be obtained by the solution of simultaneous equations.

Macrocycle-Facilitated Transport of Ions in Liquid Membrane Systems

Abstract Ion transport in various liquid membrane systems is discussed in terms of those factors which create the environment for efficient and selective transport. The following parameters which affect ion transport are discussed: membrane configuration, cation-macrocycle complex stability, macrocycle partitioning between membrane and water phases, proton ionization of acidic macrocycles, macrocycle concentration, anion type, ion concentration, membrane solvent type and receiving phase composition. A summary of existing models of ion transport is given along with possible applications to macrocycle-facilitated liquid membraneion transport.

Determination of equilibrium constants by titration calorimetry: Part III. Application of method to several chemical systems☆

The determination of equilibrium constants and enthalpy change values from titration calorimetry data has been demonstrated for three chemical systems. It has been known how, starting with the calorimetric data, the computational methods outlined in the previous papers of this series can be used to calculate the heat, Qc, produced, due to the reaction(s) of interest and from these Qc values the K and ΔDH values can be calculated for the interactions occuring in the calorimeter. Source of computer programs used in the calculations have been given.

New Precision Thermometric Titration Calorimeter

A new solution calorimeter is described which combines the thermometric titration techniques with the precision and accuracy of conventional solution calorimetry. The calorimeter through use of a unique design has a low heat leakage, k = 1.1×10−3 min−1, and a short equilibration period, 1–3 sec. Measurements of quantities of heat as small as 4 calories with an accuracy of 0.1% are possible. The heat of ionization of water at zero ionic strength has been determined to be 13.34±0.02 kcal/mole which is in excellent agreement with the value of 13.34±0.01 kcal/mole determined by conventional solution calorimetry. The large amount of information obtained from a single run makes this type of calorimeter a valuable addition to the field of solution calorimetry.

Excess enthalpies for (ethanol + water) at 298.15 K and pressures of 0.4, 5, 10, and 15 MPa

Abstract The design and construction of a modified isothermal-flow calorimeter with a reproducibility of better than 0.5 per cent is described. This apparatus was used to measure H m E for (ethanol + water) at 298.15 K and pressures of 0.4, 5, 10, and 15 MPa. The 0.4 MPa values are in excellent agreement with published values at atmospheric pressure. A fitting equation was developed which gives a good fit of the H m E results over the composition and pressure ranges investigated. We propose that H m E measurements be made on (ethanol + water) at high temperatures and pressures to establish it as a reference system for testing calorimeters. Agreement of our results with existing literature values suggests that it could now be used for this purpose at 298.15 K and atmospheric pressure.

Binding of Alkali Metal Ions by Cyclic Polyethers: Significance in Ion Transport Processes

Values for the formation constant (log K), the change in enthalpy (▵H�), and the change in entropy (▵S�) have been determined for the interaction of lithium, sodium, potassium, rubidium, and cesium ions with the two isomers of the cyclic polyether, 2,5,8,15,18,21-hexaoxatricyclo[20.4.0.09,14] hexacosane. The stability order of these metal ions with either isomer is identical to the permeability order for these same metal ions with the structurally related antibiotics, valinomycin and monactin.

Heat-loss corrections for small isoperibol-calorimeter reaction vessels☆

A more exact method of calculating the heat loss from isoperibol-calorimeter reaction vessels is described. This method involves corrections for changes in the heat-leak constant and the external power input with changes in the calorimeter contents, and is particularly important for reaction vessels with volumes of less than 25 cm3 or with heat-leak constants greater than about 0.005 min−1. The new calculation has been tested by application to results collected with a titration calorimeter of capacity 3 cm3.

Thermodynamics of proton ionization in dilute aqueous solution. Part XI. pK, ΔH°, and ΔS° values for proton ionization from protonated amines at 25°

A calorimetric study has been made of proton ionization from 69 protonated amines in aqueous solution at 25°. The resulting ΔH° values were combined with pK values to calculate ΔS° values. pK Values were obtained from the literature for 51 compounds and new values were determined for 18 compounds. A compilation of pK, ΔH°, and ΔS° values from the present study and the literature is given for proton ionization from 169 protonated amines. The effect of hydrocarbon chain length and branching on ΔH° and ΔS° values for proton ionization from primary and secondary aliphatic protonated amines is described by simple linear equations. Proton ionization for protonated amines was not found to follow the linear relation between ΔG° and ΔS° predicted by the Bjerrum theory of electrostatics. The changes in the ΔH° and ΔS° values from the first to the second step of ionization for 37 protonated diamines have been examined by using the Bjerrum and Kirkwood–Westheimer theories of electrostatic interactions in aqueous solution. A deviation identical to that previously found for dicarboxylic acids was found between the results derived from the experimental data and those predicted by the Kirkwood-Westheimer theory. Possible reasons for this deviation are discussed.