Self-assembled micron-scale fibre structures are formed by amphiphilic decyl ester derivatives of the D- and L-tyrosine amino acids prior to and following enzymatic ring polymerization

In aqueous solution, amphiphilic decyl esters of the amino acids D- and L-t yrosine are capable of self-assembly into aggregates. We present light scat tering measurements that determined the critical micelle concentrations (c. m.c.) of the D- and L-isomers of this compound at pH values of 5.5 (c.m.c. = 0.23 mM) and 6.0 (c.m.c. = 0.17 mM). These data support the notion of an increasing pH dependent self-assembly process involving the deprotonation o f the alpha -NH3+. The self-assembled amphiphilic monomers formed rod or pl ate-like fibres that possess widths of a few microns and lengths ranging fr om tens to hundreds of microns when measured by scanning electron microscop y (SEM). Horseradish peroxidase (HRP) was used to polymerize the monomers i n these self-assembled structures. The kinetics of enzymatic polymerization were not second order above the c.m.c., supporting the model of self-assem bled aggregates being the existing solution structure. SEM provided evidenc e that enzymatic polymerization left the gross shape and diameter dimension s of the fibres unaltered. However, polymerization allowed the existence of much longer fibres, hundreds of microns in length, in contrast to the shor ter length fibres observed before polymerization. These data suggest that t he polymerized fibres are more robust mechanical structures than unpolymeri zed fibres. Also, these data suggest that there is little difference in mac ro-scale self-assembly structure due to isomer differences or to polymeriza tion. However, polymerized fibres possessed a smooth outer surface, in cont rast to the rougher often fibrillar surface of the unpolymerized self-assem bled fibre structures. This suggests a difference in the micro-scale molecu lar organization of the fibre monomer units prior to and following polymeri zation. (C) 2000 Elsevier Science B.V. All rights reserved.