The complex permittivity of aqueous myoglobin (Mb) and (for comparison) aqueous polyvinylpyrrolidone (PVP) solutions was measured at 20°C in the frequency range from 2 MHz to 72 GHz. The data were fitted by a sum of Debye type spectral components. For Mb, five terms are needed which are ascribable to the tumbling of the whole Mb molecule (τ1 ≈ 29000 ps) and to free water (τ4 = 10 ps, τ5 = 5 ps). Special attention has been payed to the intermediate region (τ2 ≈ 2500 ps, τ3 ≈ 200 ps for Mb). The comparison of these relaxation times and of the corresponding relaxation strengths with results on PVP shows clearly that the relaxation at about 200 ps is due to bound water while the relaxation in the nanosecond region involves internal motions of the Mb molecule. For the latter, myoglobin is estimated to contribute an appreciable part of the observed squared dipole moment by the independent fluctuation of amide groups and of charges on the residues GLU, ASP, LYS and ARG, where the amplitudes of the motions are taken from the mean square displacements, 〈x2〉, obtained from X‐ray structure analysis.

Dielectrics / Liquids / Molecular InteractionsNine binary mixture systems AB are considered, where A = 2-pyrrolidinone, N-methyl-2-pyrrolidinone or N-cyclohexyl-2-pyrrolidinone and B = water, methanol or ethanediol. Their complex permittivity, as measured in the 20 MHz to 36 GHz range at 20"C, is interpreted by a model supported analysis. It applies in particular an empirical correlation between relaxation time and viscosity as established for the case of rigid molecules, relaxing by rotational tumbling. From this, constraints are obtained for those spectral components which are due to species of that category. The procedure yields, among others, for any system a spectral component which can be ascribed to heteroassociates of probably definite AB or AB2 composition. Again with any system, self association of B type molecules is observed, which is strongly affected by addition of A. Special relaxation features of some substances are also considered.

In an attempt to outline roughly the "normal” dielectric relaxation behaviour of polar liquids as a reference for the investigation of more complex (e.g. associating) systems, some theoretical considerations and experimental results (mainly on two component mixtures) are presented. They show that for a distinct spectral component a simple equation can be used which approximately relates the relaxation strength to the moment of the relaxing moiety. The rotational relaxation time is practically not affected by the static permittivity but is correlated to the molecular size and the macroscopic viscosity, thus allowing for conclusions on the effective radius of the tumbling moieties.

The dielectric relaxation behavior of the title solutions of PVP 40000 is measured in the frequency domain (50 MHz to 36 GHz) at 20 ~ The polymer content of the solutions (up to 0.25 mole fraction of monomer units) is such that it does not yet contribute significantly to dielectric loss. The solvent relaxation shows in all cases a bulk and a slowed down contribution, both characterized by concentration-independent relaxation times. The slow contribution is ascribed to the solvate. Solvation numbers for dilute solutions roughly range between 2 and 4 per PVP repeat unit.

Frequency dependent permittivity measurements on liquid mixtures of both substances in the relaxation region of N-methyl-2-pyrrolidone (MPy) show two spectral components originating from MPy. Pure MPy, on the other hand, exhibits only one component. The components are discussed as due to the microheterogenity of the mixtures.