Studies of Polymers Carrying Medium-Sensitive Fluorophores

Department of Chemistry Polytechnic Institute of New York 333 Jay Street Brooklyn,NY 11201 

The use of 1-dimethylamino-5-naphthyl sulphonate ( dansyl ) as a label was first introduced in 1952 for the determination of the rotational diffusion of protein molecules from the anisotropy of the dansyl fluorescence (1). Somewhat later, (2) it was found that the emission intensity of fluorophores of this type is strongly increased when they are adsorbed from water solution on proteins This increase in quantum yield of emission (accompanied by a blue-shift of the emission spectrum) could be correlated with a decreasing polarity of the medium (3). The effect can be explained as follows If the dipolar interaction of the excited chromophore with the solvent is smaller than this interaction in the ground state, the emitted quantum will be increased at the same time, the probability of nonradiative deactivation will be reduced, increasing the quantum yield of fluorescence (4). If the fluorescent label can be attached to a well-defined site on a protein, its emission characteristics will report about the polarity of this site (5) and the use of 

Winnik (ed.). Photophysical and Photochemical Tools in Polymer Science, 85-95. 

In the case of synthetic polymers, the utility of medium-sensitive fluorescent labels has been demonstrated in studies of two types (a)Cer-tain ionizable polymers exhibit a sharp transition from a contracted to an expanded state at a critical charge density along the chain molecule. This expansion increases the contact between dansyl groups attached to the polyion with the aqueous medium and this is reflected in a decreased fluorescence intensity, (b) When an aqueous solution of a dansyl-labeled polymer forms an association complex with another polymer, the label is shielded from contact with water molecules and such associations can, therefore, be monitored by fluorimetry. 

In our laboratory we used the changes in the fluorescence of dansyl labels attached to PMA to follow in a stopped-flow apparatus the kinetics of the chain expansion or contraction after a pH jump (14). 

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STUDIES OF POLYMERS CARRYING MEDIUM-SENSITIVE FLUOROPHORES. 

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