VITAMINS 329 



llic chcniiciil (li\ci,sii\ ol (he vilaniins makes classificaiioii diiricult. 

 As a compromise they are grouped inio water-soluble aud fat-soluble 

 Aitamins and lurther associated where })ossible into the various chemi- 

 cally similar substances fulfilling a single nutritional need in one or 

 more animals. The discovery and study of all these factors represent 

 one of the historically interesting phases of science. See Figure 11-1 

 for an examj)]e of the effect of dietary vitann'ns on growth. 



THIAMINE 



Vitamin B turned out to be a number of essential water-soluble 

 nutrients. Those examples that have been characterized up to now 

 bear individual names assigned more or less at random. The first to 

 be isolated was the antiberiberi factor now called vitamin Bi or 

 thiamine. 



Chemistry 



After thiamine was isolated, structural and synthetic studies cul- 

 minated in 1936 in the complete structural formula and synthesis of 

 the vitamin. By 1957 the compound was commercially available for 

 therapeutic purposes, enrichment of foods, vitamin supplements, etc., 

 at $40/kg., which amounts to about 500,000 daily allowances. 



NH 



+ CH3 CH2CH2OH 



+ 2X" 



CHo — N^ 



thiamine (vitamin Bj) 



At physiological pH values thiamine occurs as a cation with the 

 structure shown, associated with two anions, usually chloride or 

 nitrate. The size and complexity of this molecule account for the dif- 

 ficulties encountered and the time consumed in working out the struc- 

 ture. Its relatively low price is a tribute to the skill of the chemical 

 industry. 



Function 



This vitamin is an important portion of the coenzyme called cocar- 

 boxylase, or more recently thiamine pyrophosphate, written thus: 



