Kinetic study of the helix to coil dark reaction of poly(spiropyran-L-glutamate)

Kinetic study of the helix to coil dark reaction of poly(spiropyran-L-glutamate)

An investigation of kinetics of the helix to coil dark reaction of light adapted poly(spiropyran-L-glutamic acid) (PSLG) dissolved in hexafluoroisopropanol was performed. The reaction was associated with the spiropyran (SP) to merocyanine (MC) ring opening. The ring opening reaction monitored with U...

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Bibliographic Details
Published in:Photochemistry and photobiology Vol. 55; no. 1; p. 1
Main Authors: Cooper, T M, Obermeier, K A, Natarajan, L V, Crane, R L
Format: Journal Article
Language:English
Published: United States 01-01-1992
Subjects:
Benzopyrans - chemistry
Circular Dichroism
Darkness
Kinetics
Polyglutamic Acid - analogs & derivatives
Polyglutamic Acid - chemistry
Protein Conformation
Spectrophotometry
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Summary:An investigation of kinetics of the helix to coil dark reaction of light adapted poly(spiropyran-L-glutamic acid) (PSLG) dissolved in hexafluoroisopropanol was performed. The reaction was associated with the spiropyran (SP) to merocyanine (MC) ring opening. The ring opening reaction monitored with UV/VIS spectroscopy showed first order kinetics. Chromophore and polypeptide backbone circular dichroism data fit to an expression consistent with a single intermediate series mechanism. By FTIR, we monitored the polypeptide alpha-helix amide I, the MC chromophore--C = C--stretch and the protonated unmodified carboxylate C = O stretch bands. During the first step of the series mechanism, changes in the hydrogen bonding of the unmodified carboxylate groups occurred, suggesting breakup of polypeptide aggregates. The second step of the proposed series mechanism was dominated by the helix to coil transition and the ring opening of SP to MC. The CD spectrum of MC in the dark adapted PSLG was red shifted and had a narrower bandwidth than the UV/VIS spectrum. The kinetic and spectroscopic data suggested that a fraction (population I) of the MC chromophores experienced optical activity induced by the chiral polypeptide environment, while the remainder of the MC chromophores (population II) were solvated and enantiomeric.
ISSN:0031-8655
DOI:10.1111/j.1751-1097.1992.tb04202.x