Articolo in rivista, 1999, ENG, 10.1021/ma990796q

Photoresponsive polypeptides, photochromic and conformational behavior of spiropyran-containing poly(L-glutamate)s under acid conditions

Fissi, A (Fissi, A); Pieroni, O (Pieroni, O); Angelini, N (Angelini, N); Lenci, F (Lenci, F)

CNR, Inst Biophys, I-56127 Pisa, Italy Univ Pisa, Dept Chem & Ind Chem, I-56100 Pisa, Italy Univ Sassari, I-07100 Sassari, Italy

High molecular weight poly(L-glutamic acid) was chemically modified with a spiropyran reagent to give polypeptides containing 35 and 85 mol % spiropyran units in the side chains. To investigate the photochromic and conformational behavior in acid conditions, the polypeptides were dissolved in hexafluoro-2-propanol (HFP) and a small amount of trifluoroacetic acid was added (TFA, c = 5 x 10(-4) g/mL). In the absence of acid, the same polypeptides were found to respond to light, giving reversible coil/alpha-helix transitions. In the presence of TFA, by contrast, photoisomerization of the chromophores in the side chains did not; result in any conformational variation of the macromolecular main chains, and CD spectra showed that the macromolecules adopted a random coil structure, both in the dark and after light exposure. However, when appropriate amounts of cosolvents such as methanol (MeOH) or trifluoroethanol (TFE) were added to the HFP/TFA solutions, the system again responded to light giving reversible coil/alpha-helix transitions of the macromolecular structure. The extent of the photoinduced conformational changes depended on solvent composition and the photoresponse could be modulated by the combined action of light; and chemical environment. For HFP/MeOH solvent mixture, it is possible to trigger the photostimulated coil/alpha-helix transition in a narrow window of solvent composition, so that the system is characterized by a gated photoresponse. The molecular processes responsible for the observed photoinduced conformational changes are discussed on the basis of absorption and fluorescence results. These results also allow us to set up a detailed picture of the molecular mechanisms responsible for the described chemo-modulated photosensory system.

Macromolecules (Print) 32 (21), pp. 7116–7121

Keywords

CNR authors

Angelini Nicola, Lenci Francesco

CNR institutes

IBF – Istituto di biofisica

ID: 266892

Year: 1999

Type: Articolo in rivista

Creation: 2013-10-27 17:57:31.000

Last update: 2022-11-17 15:49:21.000

External links

OAI-PMH: Dublin Core

OAI-PMH: Mods

OAI-PMH: RDF

DOI: 10.1021/ma990796q

External IDs

CNR OAI-PMH: oai:it.cnr:prodotti:266892

DOI: 10.1021/ma990796q

ISI Web of Science (WOS): 000083222700033