Abstract
The following changes have been observed to occur when dl-phenylalanine is exposed to ultraviolet radiant energy:
1. Spiegel-Adolf 1 reported that solutions of phenylalanine exposed to ultraviolet rays become pigmented. Pigment formation was most marked in neutral solution, but acid and alkaline solutions also became red-brown after prolonged irradiation. During the present investigation, these findings were confirmed. Moreover, when dilute sulfuric acid or hydrochloric acid solutions of the amino acid were exposed to the ultraviolet rays, a small amount of dark brown material precipitated; this material formed colloidal solutions in dilute sodium hydroxide solution, but was insoluble in dilute acid solution. Much of the soluble pigment of the irradiated solutions could be removed by alternate additions of strong sodium hydroxide and sulfuric acid solutions; or by extraction from strongly acid solution with butyl alcohol.
2. Irradiated neutral, acid, or alkaline solutions of phenylalanine were found in the present investigation to give positive Millon tests, indicating the formation of a phenol. When this test was carried out under standard conditions, 2 a precipitate (composed chiefly of unchanged phenylalanine) formed. Removal of this precipitate by centrifugation left a clear, red solution whose color closely resembled that of a tyrosine solution tested in the same way.
3. Irradiated solutions developed a faint, orange-red color when they were treated with the nitrite-molybdate reagent. 2 Since irradiated tyrosine solutions give a similar color with this reagent as a result of the formation of dopa, 3 it may be inferred that a portion of the phenol (tyrosine?) formed during the phenylalanine irradiation was converted to a catechol (dopa?).
4. spiegel-Adolf 1 suggested that the characteristic odor produced by irradiating phenylalanine solutions might be due to the formation of phenylacetaldehyde, but she offered no chemical evidence in support of this guess.
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