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Conformations and interactions of excited states. II. Polystyrene, polypeptides, and proteins
Author(s) -
Longworth J. W.
Publication year - 1966
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1966.360041009
Subject(s) - chemistry , polystyrene , excimer , phosphorescence , polymer , fluorescence , tryptophan , photochemistry , aromatic amino acids , excited state , polymer chemistry , amino acid , organic chemistry , biochemistry , physics , quantum mechanics , nuclear physics
Previous fluorescence and phosphorescence studies of aromatic model compounds have been extended to polymers: “atactic” and isotactic polystyrene, seven aromatic poly‐(amino acids), and two proteins. We have confirmed previous observations that both forms of polystyrene exhibit strong excimer fluorescence emission at room temperature but not at 77°K. Of the poly(amino acids) (all observed in helix‐supporting solvents), poly‐ L ‐phenylalanine, poly(α‐benzyl‐ L ‐aspartic acid), and poly‐1‐benzyl‐ L ‐histidine likewise show excimer emission at room temperature but not at 77°K., while poly‐ L ‐tyrosine, poly‐ L ‐tryptophan, poly(γ‐benzyl‐ L ‐glutamic acid), and poly‐ S ‐benzyl‐ L ‐cysteine exhibit no excimer emission at either temperature. The aromatic residues of bovine serum albumin exhibit only “normal” fluorescence, but, lysozyme appears to be unique among proteins in showing excimer‐like tryptophan emission in the native state; its luminescence becomes “normal” upon denaturation. It appears very probable that none of these polymers has a ground‐state conformation in which the aromatic groups have face‐to‐face orientations appropriate for excimer interaction. It is concluded that at room temperature absorption of light can cause local “melting” of regular (usually helical) structures and thus, in some polymers, permit the attainment of a face‐to‐face arrangement of aromatic rings within the radiative lifetime of their excited singlet states. In certain other polymers (for reasons not clear at present), and in all polymers at 77°K., this does not occur. This concept is extended to provide a bettor basis for understanding the mechanism of formation of the photodimer of thy mine in irradiated DNA.