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 sensitive to the acetone-water composition. Near 50% acetone content, a discontinuous macroscopic volume phase transition (VPT) occurred. The gel was found to emit intrinsic blue fluorescence at 415 nm, which is attributed to the formation of dimeric species of tyrosine (bityrosine) in the gelatin network. 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 volume phase transition (VPT). With the increasing acetone concentration, I-B/I-M continuously increased till VPT, and then dropped little, revealing a high 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 collapsed 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.