Jointly published by Elsevier Science S. A., Lausanne and Akad~miai Kiadd, Budapest Journal of Radioanalytical and Nuclear Chemistry,Articles, Vol. 211, No. 1 (1996) 103-109 POSITRON ANNIHILATION LIFETIME STUDIES OF FREE VOLUME IN OVALBUMIN GELS Y. UCHIYAMA, 1 K. ITO, 1 H.-L. LI, 1 Y. UJIHARA,I N. KITABATAKE, 2 Y. C. JEAN 3 1Research Centerfor Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153 (Japan) 2Research Institutefor Food Science, Kyoto University,Gokasho, Uji, Kyoto 611 (Japan) 3Deparlrnent of Chemistry, University of Missouri-Kansas City, Kansas City, Missouri 64110 (USA) (Received August 26, 1996) The dependence upon concentration of sodium chloride of free volume in ovalbumin gels, a main component of an egg white, is studied by the positron annihilation lifetime technique. The average free-volume radius in ovalbumin gels was about 0.27 nm at 298 K, smaller than those of organic polymers such as low-density polyethylene (0.34 nm at 300 K) and PolYstyrene (0.29 nm at 300 K). These differences suggest that the positronium annihilates in free volumes located close to hydrogen bonds, thus decreasing average free-volume radius. Free-volume content decreased with the increase of NaC1 concentration up to 30 raM. At lower concentrations of NaC1, it seems that a correlation exists between microscopic free volume and macroscopic hardness of the ovalbumin. Ovalbumin gels are the main component of egg white and globular protein which have a characteristic space structure as shown in Fig. 1. The stability of those structural formation participates in some couplings, for example hydrogen bonding between peptide and peptide bonds, hydrphobic bonding between nonpolar side chain and nonpolar side chain, and salt bonding between carboxyl group in acid side chain and ammonium group, between guanidium group and imidazoliurn group in basic side chain, and between side and main chains. These bondings are consequently changed by a gentle environmental conditions, and denaturization occurs. The main factors which cause denaturization are heat, pressure, pH, addition of NaCI, and so on. In the present work, the variation of free volume in ovalbumin gels with the addition of NaCI was studied by the positron annihilation lifetime technique in order to investigate the relation between macroscopic properties and microscopic structure of ovalbumin gels. 0236-5731/96/US $15.0 Copyright 9 1996 Akacl~miai Kiadt, Budapest All rights reserved