| Research Abstract |
Polypeptide conjugated with the porphyrin is expected to gather with each other in aqueous system. We have shown that the acyclic peptides, Ac-Cys(por)-Lys-Val-Lys-Val-NH_2 and Ac-Cys(por)-Lys-Val-Ser-Val-Lys-Val-NH_2, linking porphyrins took the amphiphilic β-sheet structure in aqueous solution. Because the free peptides without porphyrins were of the random structure, the hydrophobia porphyrins were supposed to gather each other, which induced the peptideβ-sheet structure. The CD spectra of the porphyrin-linked polypeptide showed the exciton coupled Cotton effect in the porphyrin region, suggesting the assembly of the porphyrin rings.
In DMSO-d_6 or in CD_3OD, Ac-Cys(por)-Lys-Val-Lys-Val-NH_2 and Ac-Cys(por)-Lys-ValSer-Val-Lys-Val-NH_2 showed the expected ^1-NMR spectra and all the ID and 2D signals were successfully assigned. However in D_2O-CD_3OD (7/3, v/v), the signals of the porphyrin rings were not detected at all. Because porphyrin signals were not observed in H_2O-CH_3OH (7/3, v/v), the H-D exchanges of the porphyrin rings were not in the case. In D_2O-CD_3OD (5/95, v/v), the signals of the porphyrin rings were detected with weak intensities (〜60 % of the calculated values). In this D_2O-CD_3OD (5/95, v/v) solvent, the porphyrin signals were extremely broaden. For instance, the peak width at the half height was 66 Hz for the pyjrole proton (at 9.0 ppm) in D_2O-CD_3OD (5/95, v/v at 303 K), while it was the 〜3 Hz peak width at the half height in CD_3OD.
The ^1H-NMR relaxation times (T1 and T2) were measured. The peptide protons showed similar T1 and T2 values in both solvents. The pyrrole-proton of the porphyrin ring showed T1 of 1.9 sec in both solvent but the T2 value was 200 msec in CD_3OD and 100 msec in D_2O-CD_3OD (5/95, v/v). The difference of T2 may bring about the drastic decrease of the intensity of the porphyrin signal in D_2O-containing solvent.
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