Poly(phenylacetylene)s bearing a peptide pendant: helical conformational changes of the polymer backbone stimulated by the pendant conformational change.
Optically active, cis-transoid poly(phenylacetylene) derivatives bearing a poly(gamma-benzyl-L-glutamate) [poly(PBGAm)] or poly(L-glutamic acid) [poly(PGAm)] chain as the pendant were prepared by polymerisation of the corresponding macromonomer with a rhodium catalyst followed by hydrolysis of the pendant ester groups. Their conformational changes in solution, induced by a helix-coil transition of the pendant polypeptides, were investigated using circular dichroism (CD) and absorption spectroscopies. A series of macromonomers with a different peptide chain lengths was synthesised by the polymerisation of the N-carboxyanhydride of gamma-benzyl-L-glutamate with a phenylacetylene bearing an alanine residue as the initiator. The obtained macromonomers (PBGAm) were further polymerised with a rhodium catalyst in N,N-dimethylformamide (DMF) to yield novel poly(phenylacetylene)s [poly(PBGAm)] with a poly(gamma-benzyl-L-glutamate) pendant. The poly(PBGAm) exhibited an induced circular dichroism (ICD) in the UV/Vis region of the polymer backbone in dimethyl sulfoxide (DMSO), probably due to the prevailing one-handed helix formation. The Cotton effect signs of a DMSO solution of the poly(PBGAm) were inverted and accompanied by a visible colour change in the presence of an increasing amount of chloroform or DMF containing lithium chloride. The results suggest that poly(PBGAm) may undergo a conformational change such as a helix-helix transition with a different helical pitch responding to a change in the alpha-helix content of the poly(gamma-benzyl-L-glutamate) pendant. Moreover, a water-soluble poly(PGAm) also showed a similar, but dramatic change in its helical conformation with a visible colour change stimulated by a helix-coil transition of the pendant poly(L-glutamic acid) chains by changing the pH in water.
Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan.
Katsuhiro
K
Maeda
Nobuto
N
Kamiya
Eiji
E
Yashima
D000114:Acetylene / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008968:Molecular Conformation; D011099:Polyglutamic Acid / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012997:Solvents / Q000737:chemistry; D013237:Stereoisomerism
D011108:Polymers; D012997:Solvents; C044736:phenylacetylene; C003172:poly-gamma-benzyl-L-glutamate; D011099:Polyglutamic Acid; D000114:Acetylene