790 



6. ARSENICALS 



arsenite or dimercaprol alone show no toxic effects but, upon adminis- 

 tration of both, marked toxic symptoms appear. Peters and Stocken 

 (1947) also reported that oxophenarsine-dimercaprol is around 20 times 

 more toxic to Colpidium than oxophenarsine itself. The following two 

 compounds: 



H,N— CONH- 



S— CH2COOH 



As 

 \ 

 S— CH2COOH 



Dithiocarboxymethyl derivative of 

 carbarsone oxide (CC. No. 914) 



HoN— CONH 



HOOC 



\ // 



v\ // 



HOOC 



Dithiocarboxyphenyl derivative of 

 carbarsone oxide (CC. No. 1037) 



were found by Anderson et al. (1949) to be quite effective in amebiasis 

 and to possess certain advantages over carbarsone or its oxide, especially 

 the increased tissue levels in liver and intestine, and a higher therapeutic 

 index. Thioarsenites are now commonly used in African trypanosomiasis, 

 the conjugate of Melarsen oxide and dimercaprol (melarsoprol, Arsobal) 

 being the most noteworthy example (Williamson, 1962). Very little is 

 known about the effects of the thioarsenites on enzymes. Gordon and 

 Quastel (1948) reported that urease in inhibited a good deal more potently 

 by phenylarsenoxide-thioglycolate than by phenylarsenoxide, and in this 

 case it seems that the mechanism of inhibition is not by a reaction 

 with the SH groups. The effects on electron transport systems have been 

 discussed (page 659). 



ARSINE 



Arsine (AsHg) is a colorless gas (b. p. = — 55^) which dissolves in water 

 to the extent of about 20 vol% at ordinary temperatures; a saturated 

 solution is thus around 9 mM. One may calculate the Bunsen absorption 

 coefficient at S7° to be 0.12 and hence about 5.4 mM. The presence of 

 salts decreases the solubility (Jung, 1939); however, physiological concen- 

 trations would lower it only 5%. The solubility of the alkyl arsines is, of 

 course, less than that of arsine. The presence of proteins appreciably 

 increases the solubility. Solutions of hemoglobin and serum proteins absorb 

 more arsine than do corresponding salt solutions and this is proportional 

 to the protein concentration (Wolff, 1936). Such binding seems to occur 

 only aerobically (Jung, 1939). Thus the bound material may not be arsine. 



