Electrostatic Basis for Enzyme Catalysis

It can be useful to describe the Gibbs free energy changes for the binding to a protein of a molecule, A—B, and of its component parts, A and B, in terms of the “intrinsic binding energies” of A and B, ΔGAi and ΔGBi, and a “connection Gibbs energy,” ΔGs that is derived largely from changes in translational and rotational entropy. This empirical approach avoids the difficult or insoluble problem of interpreting observed ΔH and TΔS values for aqueous solutions. The ΔGi and ΔGs terms can be large for binding to enzymes and other proteins.

https://www.pnas.org/content/pnas/78/7/4046.full.pdf

On the attribution and additivity of binding energies.

The molecular constitution of viscoelastic gels is customarily described in terms of networks, which may have a transient or permanent character. Such supermolecular structures are often observed in biological or macromolecular systems, but can even occur in dilute solutions of some detergents. Surfactant molecules in solution, under suitable conditions, assemble reversibly into large aggregates of rod-like geometry. Depending on the ionic strength of the solution, these particles may be completely stiff or semiflexible. At low concentrations, when the lengths of the rods are much smaller than their mean distance of separation, there exists a sol state which is highly sensitive to shear forces. At higher surfactant concentrations, where the lengths of the rod shaped micelles become comparable to their mean distance, one observes gel formation and the solutions exhibit pronounced elastic properties. In analogy to polymer systems, these elongated, rod shaped micelles are strongly entangled; this leads to co...

Viscoelastic surfactant solutions: model systems for rheological research

Binding Energy, Specificity, and Enzymic Catalysis: The Circe Effect

The increasing demand for stable isotopically labeled compounds has led to an increased interest in H/D-exchange reactions at carbon centers. Today deuterium-labeled compounds are used as internal standards in mass spectrometry or to help elucidate mechanistic theories. Access to these deuterated compounds takes place significantly more efficiently and more cost effectively by exchange of hydrogen by deuterium in the target molecule than by classical synthesis. This Review will concentrate on the preparative application of the H/D-exchange reaction in the preparation of deuterium-labeled compounds. Advances over the last ten years are brought together and critically evaluated.

The renaissance of H/D exchange.

A rapid and convenient method for measuring the swelling of coals by solvents

Alkylation and depolymerization reactions of coal: a selective review with supplementary experiments☆

Heats of transfer of a variety of salts from water to solutions of hexadecyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), and sodium dodecyl sulfate (NaLS) were measured. Lyotropic series for both cations and anions were observed for all soaps, the series for the 2 cationic soaps being almost identical. The dependence of the observed heats of transfer for anions from H/sub 2/O to CTAB and DTAB solutions and for cations from H2O to NaLS solutions on the hydrated radii of the ions involved supports the contention that favorable binding of counterions depends on how closely they can approach the charged micellar surfaces. It is clear that a lyotropic series similar to that existing for proteins exists for ion binding to micelles. The controlling factor in this binding seems to be the distance of closest approach of the ion to the micelle, although polarizable organic ions may be the exceptions. Chain length has little effect on binding. It is felt that the work discussed has established the usefulness of a calorimetric investigation and the use of ion-specific electrodes for characterizing surfactant systems containing more than one species of counterions. (37 refs.)

John W. Larsen

Papers

A rapid and convenient method for measuring the swelling of coals by solvents

Alkylation and depolymerization reactions of coal: a selective review with supplementary experiments☆

Calorimetric and counterion binding studies of the interactions between micelles and ions. The observation of lyotropic series

Effect of aqueous alcoholic solvents on counterion-binding to CTAB micelles

Coal swelling in binary solvent mixtures: pyridine―chlorobenzene and N,N-dimethylaniline―alcohol