Monodisperse benzyl -ester derivatives of poly(α, L-glutamate) and poly(α, L-aspartate) modeling nature's delicate state of matter

• Main Author: Soto, Carissa M
• Language: ENG
• Published: ScholarWorks@UMass Amherst 2000
• Subjects: Polymers|Biochemistry
• Online Access: https://scholarworks.umass.edu/dissertations/AAI9960791

Biosynthesis of monodisperse poly(α,L-aspartic acid) and optimization of poly(α,L-glutamic acid) production have been accomplished. Protein design having as ultimate goal the synthesis of monodisperse benzyl-ester derivatives of α-helical polypeptides by genetic engineering has been performed. This comprises design of a monomeric DNA cassette, cloning, multimerization, ligation into an expression vector, and expression of the target gene followed by purification of the resultant protein. Advantages of such techniques include control of molecular size, composition, sequence and stereochemistry of the synthesized polymers. 1H NMR (nuclear magnetic resonance), amino acid analysis, and MALDI-MS (matrix-assisted laser desorption mass spectrometry) analytical techniques were employed for characterization of monodisperse poly(α, L-amino acid)s. Modification of conventional purification and cyanogen bromide cleavage reactions are included as part of the strategy to obtain monodisperse poly(α, L-aspartic acid). Optimization of polymer production was achieved by means of utilization of a variety of Escherichia coli strains and plasmids, modification of large scale fermentation conditions, and alterations of purification procedures. Monodisperse poly(α,L-amino acid)s were benzylated by treating the acid forms of the polymers with phenyldiazomethane. Polarized light optical microscopy was used to observe textures from birefringent samples of poly(β-benzyl α,L-glutamate) and poly(β-benzyl α,L-aspartate). Small-angle X-ray diffraction data shows evidence of smectic ordering of monodisperse poly(β-benzyl α,L-glutamate) (DP = 76). poly(γ-4-(hexadecyloxy)benzyl α,L-glutamate) DP = 300, was synthesized by methods developed in our laboratories. Differential scanning calorimetry (DSC) and polarized light optical microscopy (POM) data is presented as evidence for thermotropic liquid crystal behavior.