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In this review, attention is initially focused upon the evolution of the Newton–Laplace Equation, that links the measured speed of sound in a fluid in conjunction with its density, to a reliable estimate of its isentropic compressibility κS. Definitions of ideal and excess isentropic quantities are formulated on the premise that the thermodynamic properties of an ideal mixture are mutually related in the same manner as are those of a real mixture or a pure substance. It is shown that both intensive and extensive properties can be derived from the ideal Gibbs energy. Different approaches previously used to calculate ideal isentropic quantities are examined and some subtle errors are identified. The consequences of using conflicting definitions are pointed out. Isentropic pressure derivatives obtained under different conditions and empirical models for estimating the differences between ultrasonic speeds in real and ideal liquid mixtures are discussed.

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Inclusion modes in complexes with a-and byclodextrins in water have been investigated by NMR spectroscopy at 400 or 500 MHz, and compared with structures obtained by computer-aided molecular modelling and with calorimetric data. The NOEs observed on 0-and m-aryl protons upon irradiation of either H3 or H5 inside the CD cavity indicate for all phenols an inclusion mode with the hydroxy group at the wide cavity end, and an increasingly deep immersion for phenol or phenolate with iodine compared with this nitro group, aspara-substituent. This is found to be in line with the complexationinduced NMR shifts. Adamantane-l-carboxylate is indicated by distinct NOEs to be fully immersed into the PCD cavity; the corresponding complex with a-CD shows contact only at the wider rim and a tilted conformation which allows formation of a hydrogen bond between the guest COO-and the 2-OH group of the CD. The same conformation is found by CHARMm calculations, including simulations in a water box. The results, together with some A@ values derived from N M R titrations, are in line with data from calorimetric studies. These show for complexes with tight fit (in a-CD) large enthalpies of up to 43 W mol-l as the predominating driving force against sizeable entropy disadvantages (TAS" < -24 kJ mol-'), particularly for guest molecules of higher electron density and/or polarizibility. These observations point to predominating dispersive interactions. In contrast, inclusion in the wider fLCD cavity suffers less from entropy disadvantage (TAS" < -11 W mol-*); the binding, however, is still dominated by AH", pointing to predominant cohesive and not entropic hydrophobic forces.

Key features of an isothermal titration microcalorimeter (ITC) are described together with a general equation which forms the basis of the analysis of the calorimetric results. Recent applications of titration microcalorimetry to four subject areas concerned with the properties of aqueous solutions are reviewed. The four subjects covered are (i) pairwise enthalpic soluteÈsolute interaction parameters in aqueous solution, (ii) deaggregation of micelles formed by ionic surfactants, (iii) proteinÈligand interactions and (iv) adsorption of adsorbates on polymeric adsorbents.