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SynopsisThe dc conductivity of hydrated bovine Achilles' tendon collagen has been determined as a function of hydration over a limited temperature range. At ambient temperature the conductivity changes from 10-l6 (Q cm)-l in the dry state to about lo-* (Q cm)-l at -24% water content by weight. For all temperatures the conductivity increases exponentially with hydration obeying s(h) = A exp(Oh), where h is a measure of the hydration, A is independent of temperature, and the parameter b -T-1. It is shown that the data may be described by an impurity-type mechanism in which the effective activation energy for the process is dependent on temperature and hydration. Conduction is assumed to be electronic with the impurity (water) acting as a donor. In the solid state the effect of water on the conductivity is reversible indicating the absence of chemical alteration of the hydrated collagen.* 1 eV = 23.05 kcal/mol. 2423

SynopsisThe effect of water on the low-frequency ( 10"106 Hz) complex permittivitv of native, solid-state collagen has been investigated experimentally. Measurements at ambient temperature show that dry collagen exhibits essentially no frequency or temperature dependence. As water is adsorbed, both dielectric constant and loss factor increase simultaneously and rise sharply upward at a hydration level which may be associated with the completion of the primary adsorption layer as determined from independent water adsorption studies. The behavior is qualitatively identical to that observed for other proteins and related materials.Temperaturedependent measurements made under vacuum conditions in the range -196°C to + 100°C are characteristic of the dielectric properties of the water in the sample. Dehydration produced by successive temperature recycling to the maximum temperature effectively eliminates any temperature or frequency dependence. A maximum in the temperaturedependent curves is found at about +4O"C and is explained as the superposition of two processes: (1) the transition of water molecules from bound to freestates, and (2) the diffusion of water molecules out of thesystem. The dielectric constant of dry collagen, after desorption a t ambient temperature, is about 4.5. Desorption a t elevated temperatures reduced the room temperature value to about 2.3 and the liquid nitrogen temperature value to a number indistinguishable from theopticalvalueof n2 = 2.16.

Abstract. A clear correlation has been observed between the resonance Raman (RR) spectra of plaques in the aortic tunica intimal wall of a human corpse and three states of plaque evolution: fibrolipid plaques, calcified and ossified plaques, and vulnerable atherosclerotic plaques (VPs). These three states of atherosclerotic plaque lesions demonstrated unique RR molecular fingerprints from key molecules, rendering their spectra unique with respect to one another. The vibrational modes of lipids, cholesterol, carotenoids, tryptophan and heme proteins, the amide I, II, III bands, and methyl/methylene groups from the intrinsic atherosclerotic VPs in tissues were studied. The salient outcome of the investigation was demonstrating the correlation between RR measurements of VPs and the thickness measurements of fibrous caps on VPs using standard histopathology methods, an important metric in evaluating the stability of a VP. The RR results show that VPs undergo a structural change when their caps thin to 66 μm, very close to the 65-μm empirical medical definition of a thin cap fibroatheroma plaque, the most unstable type of VP.

The real and imaginary parts of the complex index of refraction have been measured in the 3-14-microm region for nine black powders. Data were obtained from specular reflection measurements on pressed powder disks. A vintage prism spectrometer was considerably modified for this study. Polarized radiation, detected with a cooled photoconductor, was used to generate isoreflectance curves from which the optical properties were extracted. With the exception of a bone charcoal sample, the optical constants of the black powders exhibited no spectral features in the wavelength range considered. Measured values were generally in agreement with published data on similar materials. Surface effects were found not to produce a significant limitation on the results of our method.