/ 



CONVERSION OF PROVITAMINS TO VITAMINS D 761 



that the activation probably involves the addition of energy by an electron 

 displacement. The energy required to produce one U.S. P. unit of vitamin 

 D has been calculated by Harris et aZ./*^* as 7.5 X 10'^ quanta. For the 

 production of a healing effect equivalent to one unit of vitamin D on direct 

 irradiation of rats, Knudson and Benford'''^ calculated the following energy 

 values: 2653 A., 287,000 ergs; 2804 A., 226,000 ergs; 2894 A., 395,000; 

 2967 A., 280,000 ergs; 3024 A., 553,000 ergs; 3128 A., 27,545,000 ergs. 

 There is no evidence, however, that the energy used for activation of the 

 provitamin remains stored in the molecule of the vitamin D so produced. 

 Bills and co-workers ^^^ were unable to demonstrate any difference in the 

 heats of combustion of the provitamins D and of the inactivated products. 



A number of factors alter the ease with which the provitamins D are ac- 

 tivated. The effect of the wave length of the light has already been dis- 

 cussed. Variations are dependent upon the physical state of the provita- 

 min. Thus, although dry material can be activated, ^^^ the yield is poor 

 because activation of the provitamin occurs at first only on the surface. 

 Although this less exposed provitamin D can be activated by further ir- 

 radiation, this treatment will cause a destruction of the vitamin D already 

 produced on the surface. Askew and collaborators^'^ describe a method of 

 activation of the provitamin D while in the vapor form. However, the 

 most effective synthesis of vitamin D occurs when the provitamin D is in 

 solution. The yield is increased when the solution of provitamins is agi- 

 tated."^ This can be accomplished very efficiently when a special quartz 

 irradiation chamber is employed which is built concentrically around a 

 mercury vapor lamp"^; the solution of provitamin D is passed continuously 

 through this apparatus, which is so constructed as to cause a considerable 

 agitation of the solution. 



The solvent employed, also, has some influence upon the efficiency of 

 conversion of the provitamins to the vitamins. Activation is said to occur 

 more effectively in ether than in alcohol. "^ Cyclohexane and dioxane have 

 been employed as well, either alone or in a mixture with benzene, ethyl 

 acetate, or triethanolamine. Oil is sometimes used as a solvent for the 

 provitamins. An improvement in yield is claimed when compounds are 



i«» R. S. Harris, J. W. M. Bunker, and L. M. Mosher, ./. Am. Chem. Soc, 60, 2579- 

 2580 (1938). 



"9 C. E. Bills, F. G. McDonald, La M. X. Be-Miller, G. E. Steel, and M. Nussmeier, 

 ./. Biol. Chem., 93, 775-785 (1931). 



i'« H. H. Beard, R. E. Burk, H. E. Thompson, and H. GoklMatt, ./. Biol. Chem., 96, 

 307-312 (1932). 



1" F. A. Askew, R. B. Bourdillon, and T. A. Webster, Biochem. J., 26, 814 (1932). 



^'^ A. Windaus, K. Westphal, F. v. Werder, and O. Rvgh, Nachr. Ges. Wiss. Gottingen 

 Math, physik. Klasse, III, 45-59 (1929). 



''^ F. Seitz, Vitamine uml Hormone uiul Ihre tec.hnische Dar.^tellung. Darstellung von 

 V itamin-Prdpamten, Leipzig, 1939, p. 50; Advance Sciicntific Pub., New York, 1944. 



"^ C. E. Bills, E. ^L Honeywell, and W. M. Cox, ./. BioL Chem., 92, 601-604 (1932). 



