The absorption and the emission spectra of the four ionic species formed by 3-hydroxyquinoline in aqueous solution have been measured, and it is shown that a 2-naphthylmethyl anion model accounts for the observed band positions. The constants governing the prototropic equilibria between the four ionic species in the lowest electronically excited state are estimated from the transition energies, and, independently, from the change in the fluorescence spectrum with hydrogen-ion concentration. It is found that the hydroxy-group of 3-hydroxyquinoline is more acidic, and the ringnitrogen atom more basic, in the excited than in the ground electronic state, as required by the 2-naphthylmethyl anion model, and that the difference between the free energy of ionic dissociation in the ground and the excited state is due primarily to a change in the heat, and not in the entropy, of ionisation.

Spectroscopic studies of alternating polypeptides, prepared by polymerizing dipeptides containing one l and one d residue, indicate that in helicogenic solvents they adopt conformations with properties different from those of the normal a helix. The properties of such polypeptides in which polymerization has been accompanied by appreciable racemization are similar to those of poly(L-aspartic esters), and a distorted type of a helix is suggested; when racemization is negligible a new conformation, the nature of which is uncertain, appears to be formed. This paper is concerned primarily with the conformations adopted in solution by "alternating" sequential polypeptides of the type H-f AB^-"OH, where A and B are amino acid residues which give rise to poly(amino acids), HA"OH and HB"OH, with -helical conformations of opposite sense