Polarographic Examination of Sialic Acids

Abstract

WE have investigated systematically the polarographic wave of neuraminic acid derivatives with a dropping-mercury electrode (m = 2.86 mgm./sec., t = 2.98 sec.). The existence of a sialic acid wave was anticipated from the fact that structurally related substances such as pyruvic acid^1,2 and fructose^3,4 give well-defined polarographic waves. Three type of waves could be observed in N-acetylneuraminic acid solution (NANA): (a) a hydrogen wave in 0.1 M LiCl or in 0.01–0.1 M tetramethylammonium bromide (TMABr) under pH. 7. The apparent half-wave potential is − 1.65 V. (s.c.e.) in 0.01 M TMABr and − 1.48 V. in 0.01 M TMABr. There is a linear relationship between the height of the wave and the square root of the height of the mercury column up to 45 cm. ; and, under defined conditions, a linear relationship between NANA concentration and the height of the wave. Under identical conditions, pyruvic acid (4.05 × 10⁻⁴ M in 0.01 M TMABr, under nitrogen) gives a hydrogen wave of the same height (36.7 µamp.) as NANA (39 µamp.). The slope of the straight line in which the height of the wave is plotted as the function of concentration of NANA is 0.3 µamp./µgm./ml. or 92.7 µamp./µ/ml. (at 30° C. in 0.01 M TMABr). There is a marked sensitivity of the wave to ionic strength and also to the presence of oxygen.