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Detailed measurements of infrared absorption and Raman scattering on crystalline acetanilide [(CH3CONHC6H5)"] at low temperature show a new band close to the conventional amide I band.Equilibrium properties and spectroscopic data rule out explanations based on a conventional assignment, crystal defects, Fermi resonance, and upon frozen kinetics between two different subsystems.Thus we cannot account for this band using the concepts of conventional molecular spectroscopy, but a soliton model, similar to that proposed by Davydov for a-helix in protein, is in satisfactory agreement with the experimental data.

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The framework of percolation theory is used to analyze the hydration dependence of the capacitance measured for protein samples of pH 3-10, at frequencies from 10 kHz to 4 MHz. For all samples there is a critical value of the hydration at which the capacitance sharply increases with increase in hydration level. The threshold hc = 0.15 g of water per g of protein is independent of pH below pH 9 and shows no solvent deuterium isotope effect. The fractional coverage of the surface at h, is in close agreement with the prediction of theory for surface percolation. We view the protonic conduction process described 'here for low hydration and previously for high hydration as percolative proton transfer along threads of hydrogen-bonded water molecules. A principal element of the percolation picture, which explains the invariance of hc to change in pH and solvent, is the sudden appearance of long-range connectivity and infinite clusters at the threshold ho. The relationship of the protonic conduction threshold to other features of protein hydration is described. The importance of percolative processes for enzyme catalysis and membrane transport is discussed.In a previous paper we have described the protonic conductivity induced by hydration below monolayer coverage for single molecules of the protein lysozyme (1). Under these conditions, the hydration water is severely disordered (2). Thus, it seems appropriate to consider the protonic conductivity in the framework of the percolation model (3, 4). This model has been shown applicable to a broad range of chemical and physical phenomena where spatially random processes and topological disorder are of vital importance, such as polymer gelation and the electrical conductivity of a network of conducting and nonconducting elements. One of the most appealing aspects ofthe percolation model is the presence ofa percolation transition, where a long-range connectivity among the elements of the system suddenly appears. In this paper we focus on a transition of this kind, a sharp change in dielectric properties in the low hydration region for the protein lysozyme. This analysis extends that reported for the high hydration region (1).MATERIALS AND METHODS A previous paper (1) described the preparation of protein samples of pH 3-10 and the measurement of their dielectric properties at frequencies from 10 kHz to 10 MHz and for hydration levels from wet powder (>0.35 h) to the low hydration limit (h.) where the evaporation rate is zero under these experimental conditions. The data were analyzed previously for the high hydration region, h > 0.2 (1). In this paper we analyze a similar body of data for the low hydration region.For display and analysis, the dielectric properties are presented as a function of hydration level, h. During the measurements the hydration of each sample was varied from the starting conditions, a wet powder obtained by isopiestic equilibration against pure water, to the final limiting low hydration, h.. The dielectric data were collected continuously. Hydra...