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Analysis of swelling process of protein by positron annihilation lifetime spectroscopy and differential scanning calorimetry
Authors:Yoko Akiyama  Yuji Shibahara  Shin‐ichi Takeda  Yoshinobu Izumi  Yoshihide Honda  Seiichi Tagawa  Shigehiro Nishijima
Institution:1. Graduate School of Engineering, Osaka University, 2‐1 Yamadaoka, Suita, Osaka 565‐0871, JapanGraduate School of Engineering, Osaka University, 2‐1 Yamadaoka, Suita, Osaka 565‐0871, Japan;2. Graduate School of Engineering, Osaka University, 2‐1 Yamadaoka, Suita, Osaka 565‐0871, Japan;3. The Institute of Scientific and Industrial Research, Osaka University, 8‐1 Mihogaoka, Ibaraki, Osaka 567‐0047, Japan
Abstract:The change in the nanoscopic structure and bound state of water in the protein gel were investigated using positron annihilation lifetime spectroscopy (PALS) and differential scanning calorimetry (DSC). Gelatin was used as a protein. To examine the bound state of water in gelatin gel, the amount of freezing and nonfreezing water in gelatin gels were evaluated by fusion enthalpy of DSC curves. Below water content of 40% (w/w), the whole amount of water was nonfreezing water, whereas above water content of 40% (w/w), the amount of freezing water increased according to increase in water content. To investigate the nanoscopic spatial structure under coexistence of polymer and water, positron annihilation lifetime measurement was performed. The lifetime of o‐Ps or the pore size increased according to increase in water content, particularly below the water content of 40% (w/w). When the water penetrates into the gelatin network, the water molecules form hydrogen bonds with hydrophilic groups inside the helical structure in gelatin gel. The water molecules inside the helical structure expand the structure outward, leading to increase in pore size. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2031–2037, 2007.
Keywords:biopolymers  differential scanning calorimetry (DSC)  free volume  positron annihilation lifetime spectroscopy  swelling
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