
%0 Journal Article
%A Stunzi, H 
%T Can chelation be important in the antiviral activity of isatin &#946;-thiosemicarbazones?
%J Australian Journal of Chemistry
%D 1982/06/01
%V 35
%N 6
%P 1145-1155
%K 
%R https://doi.org/10.1071/CH9821145
%U https://www.publish.csiro.au/paper/CH9821145 
%X The stability constants of 5-sulfonatoisatin &#946;-thiosemicarbazone (&#946;-thiosemicarbazonoisatin-5- sulfonate) [sibt,(3)] with Zn2+ and Fe2+ have been determined from slow pH titrations (I 0.15M KNO3, 37º). At pH 7.4, the conditional stability constants for the sibt complexes are logK1' 4.5 (Zn2+), 3.1 (Fe2+) and log &#946;2' 8.9 (Zn2+), 6.5 (Fe2+). The mixed ligand complexes Zn(sibt)L (L = histidine or glycine) have conditional stability constants log &#946;1110' 8.8 and 7.0, respectively, at pH 7.4. Copper(I) complexes of sibt and bishistidinato-copper(II) coexist in mixtures of Cu2+, sibt and histidine. [In solutions of copper ions, sibt (complexes Cu+) and histidine (chelates Cu2+), the response of the Orion cupric-ion-selective electrode is not stoichiometric.] Also studied was 1-methyl-5-sulfonatoisatin &#946;-thiosemicarbazone [msibt,(4)] which behaves like sibt. 5-Sulfonatoisatin &#946;-semicarbazone and p-sulfonatobenzaldehyde thiosemicarbazone (p-thiosemicarbazonomethyl- benzenesulfonate) are weak ligands. Comparison of the stability constants with those of complexes of biologically relevant chelating agents showed that isatin &#946;-thiosemicarbazones are not expected to form stable complexes with zinc and iron in vivo. Bidentate thiosemicarbazones, such as benzaldehyde thiosemicarbazones, form even weaker complexes. Both classes of thiosernicarbazones have a similar activity against vaccinia virus; this activity seems not to depend on metal ion chelation. 
