470 



NIACIN 



Wright and King^^ obtained nicotinamide crystals which differed in some 

 respects from those of McCrone and Cook. In their work nicotinamide 

 crystallized from ethylene glycol as monoclinic crystals of prismatic habit, 

 elongated parallel to the c axis and showing {110} as the predominant 

 form. All crystals were twinned either about the c axis or across the 100 

 plane. When crystallized from water, acetone, benzene, glycerol, or from 

 mixtures of ethylene glycol and water (50% or more), they appeared as 

 lath-shaped monoclinic crystals, elongated parallel to the c axis and ex- 

 hibiting {010} as the predominant form with a characteristic edge angle 

 of 99°. The optical properties of nicotinamide for sodium light, and the 



0.8 



0.6 



0.4 



0.2 



220 240 260 280 300 



Wavelength (micromoles) 



320 



340 



Fig. 4. Ultraviolet absorption spectrum of nicotinamide (•) and N'-methyl- 

 nicotinamide (O). The concentration of Ijoth compounds was 2 X 10""' M, in water, 

 at pH 7.0. (From Cantoni."*') 



findings from Debye-Scherrer x-ray, oscillation and Weissenberg photo- 

 graphs of nicotinamide crystals are presented in Wright and King's publica- 

 tion. 



(d) Absorption Spectrum. The absorption spectrum of nicotinamide in 

 water was determined by Warburg et al.,^ who found a maximum absorp- 

 tion of 2600 A. with a molecular extinction coefficient of 4.5 X 10^. Kuhn 

 and Vetter^ reported a similar absorption maximum but with a slightly 

 higher extinction coefficient. Figure 4 shows the ultraviolet absorption 

 spectrum of nicotinamide in comparison to N^-methylnicotinamide. 



Jellinek and Wayne^- have studied the ultraviolet absorption spectrum 

 of 0.0003 M nicotinamide solutions at pH values of 5.72 to —1.06 with 

 the results depicted in Fig. 5. They found an absorption maximum at 



^ib G. L. Cantoni, J. Biol. Chem. 189, 203 (1951). 



'2 H. H. G. Jellinek and M. G. Wayne, J. Phys. & Colloid Chem. 55, 173 (1951). 



