An Autocatalytic Experiment to Illustrate Virus Growth P . HERSCH The University, Istanbul, Turkey
T
HE REDUCTION of nickel hydroxide by means of hypophosphite, when performed under special conditions, closely resembles the growth of bacterial colonies on a culture medium. This entirely inorganic reaction system is suggested to illustrate autocatalysis to students of biochemistry. Hypophosphite ion is dehydrogenated by active forms of nickel according to the equation (3,5):
If nickel ion is present, i t is reduced by a part of the nascent hydrogen (4, 6, 7, 8 ) : Ni++ + 2 H Ni f 2 H C
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The reaction product is very active in promoting further dehydrogenation and the whole system is therefore typical of autocatalysis. The reduced nickel is not pure, however, hut is alloyed with metallic phosphorus formed by secondary reactions (7, 8). The mechanism of the dehydrogenation is probably a complex one, as is the case with the autoxydation of hypophosphite (1, 2). The decomposition resembles that of formate: HCOn- + H1O HCOs- 2 H
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which is catalyzed by bacterium coli or palladium (9). The nickel catalyst formed by hypophosphite is also able to decompose fo&ate. The reaction between Ni++ and H2POz- takes place onlv certain conditions of concentration (7). ~ -, - under .. The following method of performing the experiment has always proved successful. Dissolve: A . 7.0 g. of NiSOa7HzO in 45 cc. of water, to give 50 cc. of a 0.5 mol. Ni++ solution; B. 52 g. KHzPOZin 75 cc. of water, to give 100 cc. of a 5.0 mol. hypophosphite solution; C, 5.5 g, of KOH in 48 cc. of water, to give 50 cc, of 2 N KOH.
To prepare the catalyst, mix 1 cc. of A , 2 cc. of B, and 1 cc. of C. Heat the mixture in a large test tube. At about 100°C., the liquid suddenly turns black and effervesces vigorously because of the hydrogen evolved. After decomposition of the excess of hypophosphite, the nickel deposits as a black powder. It is kept under the liquid, which is now clear and colorless. It thus remains active over many weeks. The reaction mixture also consists of A , B, and C in the proportion of 1:2:1 by volume. As a reaction vessel, use a white porcelain saucer, which will subsequently be filled with the reaction mixture to a depth of 2 to 3 mm. To obtain the correct temperature, use a clean water bath a t 50°-550C. Mix A and B and warm the mixture in the water bath. Warm solution C and the saucer also. When the saucer and the two solutions have come to the temperature of the bath, withdraw them, add C to A and B, and pour the resulting green suspension into the saucer. By means of a wire, place very small traces of the previously prepared nickel catalyst on a few distant points of the green reaction liquid. These small "inoculation" spots immediately begin to grow, evolving gas bubbles and forming hlack "colonies" which reach a diameter of 1 to 2 cm. within three minutes. To demonstrate poisoning, place one drop of a 2 per cent KCN solution on one of the spots, which immediately ceases to grow. The other spots continue to expand until finally the whole of the green liquid has turned hlack.
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LITERATURE CITED
(1) BAc~smonr,Natunuirsenrchaflen,22, 170 (1934). (2) B O C K E M ~ ~ LGiil.2. E R . Liebigs Ann. Chem.. 508,263 (1934). (3) BOUGAULT. CATTELAIN, CHABRIER, Bull. so^. chim. mtm., 151, 5, 1699 (1938). (4) BRETEAU, did., [4],9,518 (1911). (5) FRANKE, M6~~~,Liebig~Ann. Chem., 550,1(1941). (6) PAAL, FREIDERICI, Ber., 64,1766 (1931). (7) SCHOLDER, HILKEN, Z. anore. alleem. chem., 198,329 (1931). HECKEL, Bw.. 64,2870 (1931). (8) SCHOLDER, (9) STEPHENSON, STICKLAND, Biochem. J., 26,712 (1932).
