Selective interaction in solution between ammonium groups of a cationic starch and aromatic probes revealed by fluorescence emission

Two fluorescent sensors A1 and A2, designed to complex selectively ammonium groups of cationic starch were synthesized and their fluorescence properti es evaluated. They display fluorescence intensity enhancement (FIE) due to the complexation of ammonium group by the 1,2-diazacrown-6 moiety and the s ide arm of the molecule that limits the electron donor-acceptor interaction between the amine and the anthracene part. The location of the benzene rin g in the middle of the side arm in A2 provides better performance for this compound. The FIE presented by A1 and A2 is found quite selective for ammon ium compared to sodium, potassium and calcium cations but the response is n ot linearly related to the ammonium concentration. Also, the FIE is found c onsiderably reduced in water solution. This behavior precludes an easy quan titative application. By contrast, the commercial fluorescent whitening age nt (FWA) in water solution displays a quantitative and selective fluorescen t response versus the ammonium concentration of cationic starch. This might allows an easy and sensitive way to estimate the amount of ammonium groups (range 10(-6)-10(-5) mol l(-1)) presented by a cationic starch in water so lution. (C) 2001 Elsevier Science B.V. All rights reserved.