2007 Fiscal Year Final Research Report Summary
Characterization of Hydrogen-bond Correlation Involved in the Helical Structure of Polypeptides and Application to the Molecular Design of Synthetic Polymers
| Project/Area Number |
18550111
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Polymer chemistry
|
|---|
| Research Institution | Tokyo Polytechnic University |
|---|
Principal Investigator |
ABE Akihiro Tokyo Polytechnic University, Nano-Science Research Center, Professor (50114848)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
MATSUMOTO Toshihiko Tokyo Polytechnic University, Department of Nano-Chemistry, Professor (50181780)
HIEJIMA Toshihiro Tokyo Polytechnic University, Department of Nano-Chemistry, Associate Professor (30288112)
|
|---|
| Project Period (FY) |
2006 – 2007
|
| Keywords | Poly(L-aspartate)s / Mechanism of Helix-Coil Transition / Inversion of α-Helical Screw / Random Copolymers / Hydrogen Bond Correlation / Helix Inversiuon in the Solid State / Main Chain Liquid Crystals / Saccharide Chains |
|---|
| Research Abstract |
The molecular mechanism involved in the helix-sense reversal characteristic of poly(L-aspartic acid ester)s has been investigated. These man-made polymers are known to form an α-helix in either the right-n or left-handed screw depending on the chemical constitution of the ester group (X) in the side chain. While poly(β-benzyl L-aspartate) (PBLA) remains in the left-handed form in conventional helicoidal solution at all temperatures, poly(β-phenethyl L-aspartate) (PPLA) exhibits transformation from the right-to the left-handed form with increasing temperature. In this work, random copolymers comprising residues of the two opposite screw-sense preference, BLA and PLA, were chosen to investigate the stability of the α-helical hydrogen-bond array in a helix-forming solvent such as chloroform or tetrachloroethane (TCE). Sharp S-shaped transitions of the helix sense were observed for copolymers in the range PLA>50%. ^2H NMR studies of partially deuterated samples in the nematic liquid crystalline environment indicate that the thermally induced helix-sense inversion takes place highly cooperatively along the a-helical backbone. These observations strongly suggest a zipper-type propagation process starting from one terminal to the other. The driving force of the transformation has been traced back to the thermal variation of the side chain conformation. For given copolymer samples, the transition temperatures observed in dilute isotropic solution are nearly identical to those obtained in the liquid crystalline state, suggesting that the transition mechanism remains more or less the same in both media. A theoretical formula prescribed within the Zimm-Bragg concept has been successfully used in interpreting these helix-helix transition phenomena.
|
