Intrinsic fluorescence investigation on the change in conformation of cross-linked gelatin gel during volume phase transition

Gelatin gel cross-linked with glutaraldehyde was prepared. Its volume is se nsitive to the acetone-water composition. Near 50% acetone content, a disco ntinuous macroscopic volume phase transition (VPT) occurred. The gel was fo und to emit intrinsic blue fluorescence at 415 nm, which is attributed to t he formation of dimeric species of tyrosine (bityrosine) in the gelatin net work. The ratio of intensity of bityrosine to that of tyrosine monomer, I-B /I-M, was used to examine the change in conformation of gelatin during volu me phase transition (VPT). With the increasing acetone concentration, I-B/I -M continuously increased till VPT, and then dropped little, revealing a hi gh yield of bityrosine species, which is considered to stem from the closer contact of inter-coil, inter-helix, intra-helix and coil-helix in the coll apsed network. The continuous I-B/I-M change suggests the non-discontinuous volume phase transition of gel occurring in microscale. (C) 2000 Elsevier Science Ltd. All rights reserved.