The Solubility of Proteins and Proteoses in Aldehydes and other Organic Solvents.

ALTHOUGH the action of aqueous solutions of aldehydes upon proteins has been extensively studied, the behaviour of aldehydes in the anhydrous state does not seem to have been investigated in detail, except for the single observation of Mathewson [1906] that gliadin appeared to be somewhat soluble in impure benzaldehyde. Apart from its chemical interest such an investigation might lead to improved methods of separation and purification of proteins and proteoses. The present methods of fractionation depend largely on the use of inorganic salts, and there is a considerable field for the application of organic solvents in protein chemistry. Observations were made in the first place with benzaldehyde. It was found that, whilst gelatin, egg-albumin, gliadin, and proteoses (Witte's peptone) were precipitated from their solutions in anhydrous phenol by paraldehyde, the addition of benzaldehyde had no effect. Egg-albumin was, furthermore, slightly soluble in benzaldehyde alone, and was reprecipitated on the addition of alcohol. Gelatin, gliadin and caseinogen, however, appeared to be insoluble in benzaldehyde. Glycine and alanine were similarly insoluble, but proteoses dissolved in benzaldehyde with great readiness at ordinary room temperature, only a small residue being left undissolved. The proteoses were precipitated by the addition of various organic solvents (alcohol, acetone, chloroform, paraldehyde, mesityl oxide), or even by warming the benzaldehyde alone to 370; on cooling the proteoses re-dissolved. Benzaldehyde is thus characteristic (1) in exerting a selective solvent action upon intermediate hydrolytic products of proteins, amino-acids and proteins themselves being almost insoluble; (2) in being efficacious as a solvent for proteoses within only a very restricted range of temperature (approx. room temperature). Similar experiments were carried out with many other aldehydes and derivatives, and the results are as follows: