SUGAR-INDUCED CONFORMATIONAL-CHANGES IN BORONIC ACID-APPENDED POLY(L-LYSINE) AND POLY(D-LYSINE) AND SUGAR-CONTROLLED ORIENTATION OF A CYANINE DYE ON THE POLYMERS

Poly(L- and D-lysine)s have been modified with para- or meta-phenylbor onic acid derivatives which act as sugar-binding sites (L-1 and D-1 fo r the para-isomer and L-2 for the meta-isomer). When monosaccharides w ere added to the L-1 solution, the helix content (monitored by CD spec troscopy) increased and the pH which gives the maximum helix content s hifted to a lower pH region. The magnitude of the pH shift was correla ted with the affinity of monosaccharides for phenylboronic acid. The p H dependence of the helix content in the presence of D- or L-fructose was similar although a slight difference was seen at the low pH region . This is a novel attempt towards the control of a polypeptide's confo rmation by sugars. A cyanine dye (4) can be orientated on 1 or 2 in th e presence of saccharides. Judging from the CD spectra, the orientatio n in the presence of 1 is more ordered than that in the presence of 2. The main driving-force for the association of 4 with 1 or 2 is the el ectrostatic attraction between cationic 4 and the anionic centre devel oped on the polymer by complexation of the boronic acid residue with s accharides. The chiral orientation of 4 can be monitored by a CD spect roscopic method: it is mainly governed by the chirality of 1 but not b y the chirality of saccharides. This is a novel system to control the dye orientation by the cooperative action of naturally-originated alph a-amino acids and saccharides.