172 



BACTEraOT.OGICAL CHEMISTRY 



solutiuii l»y washijig i\\v exiiaci witli dihitc alkali, wiiicJi 

 converts penicillin into the readily soluble sodium salt ; 

 concentration of the penicillin can be effected at the 

 same time by use of a small volume of alkali. Further 

 purification can be achieved ,by chromatography on 

 alumina or silica gel carrying an alkaline earth carbonate, 

 and conversion to the barium salt. The barium salt is 

 fairly stable iDctAveen j^K 5-5 and 7-5, but is easily in- 

 activated by heating or by acid or alkali. The free acid, 

 penicillin, is hygroscopic and loses its activity readily, 

 although in ether or amyl acetate solution it is stable 

 for some days. It is inactivated by copper or mercury, 

 primary alcohols, ammonia, amines, hydrazine, hydroxyl- 

 amine and oxidising agents. 



Culture filtrates have been shown to contain one or 

 more of several closely related compounds first recognised 

 by somewhat different degrees of activity against various 

 bacteria. They have the general empirical formula, 

 C9H11O4SN2.R, and differ in the nature of the radical R, 

 as is shown : — 



That the penicillins probably have either the ^-lactam 

 structure, I, or the incipient azlactam structure, 11, is 

 in harmony with the following findings : — • 



