Thermodynamic flow methods in biochemistry: calorimetry, densimetry, and dilatometry

Phase equilibriums, self-assembly and interactions in two-, three- and four medium-chain length component systems

The Scandinavian surface (surfactant) and colloid science owes much of its success to Per Ekwall and Björn Lindman. In this review the main topics shared by their research groups at Åbo Akademi University in Finland and at Lund University in Sweden are described. The nature of surface active substances (cosolvents, co-surfactants and surfactants) and microemulsions are evaluated. It is shown that the properties of medium-chain length surfactants differ dramatically from long-chain surfactants. The phase equilibriums of binary systems are related to the phase equilibriums of ternary and quaternary systems referred to as microemulsions or more recently also as nanoemulsions. A distinction is made between hydrotrope liquids, detergentless microemulsions, surfactant mixture systems and microemulsions. Three component systems are assembled to "true" quaternary microemulsions. An exceptionally comprehensive network of thermodynamic parameters describing molecular site exchange and micelle formation are derived and related mutually. Gibbs free energy, enthalpy, entropy, volume, heat capacity, expansivity and compressibility can be used to illustrate the degree of aggregation cooperativity and to evaluate whether micelle formation is of a first-, second- or intermediate order phase transition. Theoretical simulations and experimental results show that the associate structures of medium-chain length surfactants are quite open and may be deformed due to small aggregation numbers. The self-assembly occurs over a number of distinct steps at a series of experimentally detectable critical concentrations. Despite the low aggregation tendency their phase behavior equals those of long-chain homologs in surfactant mixture and microemulsion systems. A number of models describing the self-assembly are reviewed. Nuclear magnetic resonance (shift, relaxation rate and diffusion), Laser Raman and infrared spectroscopies were chosen as key instruments for molecular interaction characterization since they were used in the collaboration between the research groups in Åbo and in Lund. A new method is introduced in order to evaluate the traditional procedure for extracting limiting parameters which also enables an illustration of the degree of cooperativity. The focus is laid mainly on aqueous, alcoholic, saline and, to a limited extent oil phases of one-, two-, three- and four component systems of water-sodium carboxylates-alcohol-oil. The extensive thermodynamic characterization of these liquid phases and liquid crystalline phases is left out due to space restrictions.

A stopped-flow mixer device for a batch microcalorimeter application to NAD-NADase reaction

A new molded polypropylene, diamond-like carbon (DLC)-coated mixing cell has been developed for use in the batch microcalorimeter. Reagent volume can be varied from 25 microliters to 100 microliters. A 10 microcalorie reaction heat can be measured to 5%. Repeat reactions can be done as often as every 10 min for a fast reaction. Reactions can be started within 1 h or less after loading. A pre-equilibrator and a temperature-controlled syringe drive unit permit solutions to be stored at 4 degrees C while being run at any temperature from -20 degrees C to 40 degrees C. The kinetics and enthalpy of reaction of NAD-NADase have been measured. delta H is about 21 kcal/mol endothermic.

Thermodynamics of hapten-antibody interactions

Two schools of thought are currently prevalent regarding the thermodynamic mechanism(s) of hapten-antibody interaction(s). While one school is a proponent of the hapten-antibody reaction being driven predominantly by enthalpy, the second school rationalizes the mechanism as an enthalpy-entropy compensation, the magnitude of the latter being dependent on the temperature at which hapten-antibody interaction is carried out.