Spiropyran-Containing Polypeptides

Sunlight-induced Conformational Transitions in Spiropyran-containing Polypeptides 13.2.2.1 Spiropyran-modified Poly(L-glutamate)s... 

F. Ciardelli, D. Fabbri, O. Pieroni, and A. Fissi, Photomodulation of polypeptide conformation by sunlight in spiropyran-containing poly(L-glutamic acid), J. Am. Chem. Soc. Ill, 3470-3472... 

N., and Lenci, F. (1999) Photoresponsive polypeptides, photochromic and conformational behavior of spiropyran-containing poly(l-glutamate)s under acid conditions. Macromolecules, 32, 7116—7121. 

The effect of light on CD spectra at various solvent compositions, for a polymer containing 85 mol% spiropyran units, is shown in Figure 11. When methanol concentration is below 5%, both the dark-adapted and the irradiated samples show the typical CD pattern of disordered polypeptides. In HFP/MeOH = 90/10, the sample kept inthedark is random coil, whereas the sample exposed to light displays the standard CD pattern of the a-helix. The intensity of the bands indicates that under these conditions light causes the full conversion from random coil to 100% a-helix. With increasing methanol con-... 

The spiropyran-modified poly(L-glutamic acid) PGA-2 undergoes a coil helix transition upon exposure to visible light in hexafluoro-2-propanol solution. In the dark, the polypeptide, containing 30-80 mol% chromophore units in the open charged form, adopts a random coil conformation. Irradiation causes isomerization in the side chains, as indicated by complete bleaching of the colored solution (see Scheme 5.4). The formation of the colorless and uncharged spiropyran form induces spiralization of the polypeptide chain. The coil helix transition can be followed with the aid of CD spectra, as shown in Fig. 5.4. 

Fissi, A., Pieroni, O., Ciardelli, F., Fabbri, D., Ruggeri, G., and Umezawa, K. (1993) Photoresponsive polypeptides photochromism and conformation of poly(L-glutamic acid) containing spiropyran units. Biopolymers, 33,1505-1517. 

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