PubMed · 7001559
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J F Clayson. 1980. Sub-surface porosity.. https://pubmed.ncbi.nlm.nih.gov/7001559/
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Specific partial volume, partial compressibility, and sound absorption changes induced by the native-to-molten globule state (acid) transition of the human alpha-lactalbumin were measured by means of densitometric and ultrasonic techniques and interpreted in terms of the protein molecule phase transition and interphase water transfer. The molten globule is a highly hydrated state containing about 270 water molecules inside. Intrinsic mass density of the hydrated (swollen) interior of the protein molecule is 5% smaller and the intrinsic compressibility coefficient 2 times higher than those in the native molecule. The obtained intrinsic compressibility falls into the range of values characteristic of highly associated liquids. Water inside the molten globule interior occupies less volume and is less compressible than in solvent phase. The acoustic relaxation was found to increase indicating an appearance of pressure-dependent processes. The commonly used approach to the calculation of the volume fluctuations of protein molecules, based on the well-known relation between the volume fluctuations and compressibility, is of limited applicability to the highly hydrated molten globule state because a large, if not predominant, part of the fluctuations may be determined by the process of water exchange between the molten globule and bulk solvent.
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A method of reading exposed radiochromic film is described which has significant advantages over conventional densitometry. The method employs a document scanner and associated software for imaging the film. The resulting images are easily analysed using standard software to yield high-resolution dose maps. A calibration was performed which relates scanner signal to dose, allowing for the determination of dose at any point on an exposed film. Results obtained using a broad-band densitometer are compared to those where the scanner has been used. The technique was used to measure the dose distribution around a COMS-type ophthalmic applicator.