Chemical cross-linking gelatin with natural phenolic compounds as studied by high-resolution NMR spectroscopy.
Cross-linking gelatin with natural phenolic compound caffeic acid (CA) or tannic acid (TA) above pH 9 resulted in formation of insoluble hydrogels. The cross-linking reactivity was controlled by variation of pH, the concentration of the gelatin solution, or the amount of CA or TA used in the reaction. The cross-linking chemistry was studied by high-resolution NMR technique in both solution and solid state via investigation on small molecular model systems or using (13)C enriched caffeic acid (LCA) in the reaction with gelatin. Direct evidence was obtained to confirm the chemical reactions occurring between the phenolic reactive sites of the phenolic compounds and the amino groups in gelatin to form C-N covalent bonds as cross-linking linkages in gelatin matrix. The cross-linked network was homogeneous on a scale of 2-3 nm. The cross-linking resulted in a significant decrease in the molecular mobility of the hydrogels, while the modulus of the films remained at high values at high temperatures.
CSIRO Materials Science and Engineering, Private Bag 33, Clayton South MDC, Clayton South, Victoria 3169, Australia. xiaoqing.zhang@csiro.au
Xiaoqing
X
Zhang
My Dieu
MD
Do
Philip
P
Casey
Adrian
A
Sulistio
Greg G
GG
Qiao
Leif
L
Lundin
Peter
P
Lillford
Shansha
S
Kosaraju
D002109:Caffeic Acids / Q000737:chemistry / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D005780:Gelatin / Q000737:chemistry / Q000378:metabolism*; D020100:Hydrogels; D009682:Magnetic Resonance Spectroscopy; D008422:Materials Testing; D008958:Models, Molecular; D015394:Molecular Structure; D013634:Tannins / Q000737:chemistry / Q000378:metabolism*
D002109:Caffeic Acids; D003432:Cross-Linking Reagents; D020100:Hydrogels; D013634:Tannins; D005780:Gelatin; C040048:caffeic acid