The synthesis and crystal structures of bis(S-methylisothiouronium) (MSTUH)+, N,N′-bis((3-
guanidinopropyl)piperazinium (PipeC3GuaH4)4+ and hexamidinium (HexaH2)2+ tetrachloro platinate(ll) salts ( called hereafter PtMSTU, PtPipeC3Gua and PtHexa respectively ) were
investigated. These compounds contain the “amidine” function (- C(=NH)NH2 ) in which the H
atoms supplied by the acid have become attached to the imino group of each terminal amidino
function. Moreover, in PtPipeC3Gua, the nitrogen atoms of the chair-piperazine moiety are also
protonated. The influence of tetrachloroplatinate(ll) counteranion ( versus sulfate, nitrate and
diisethionate ) in the in vivo nitrite inhibition by the (MSTUH)+, (PipeC3GuaH4)4+ and (HexaH2)2+
cations was investigated. The three tetrachloroplatinate(ll) salts, unexpectedly, do not inhibit
significantly the in vivo nitrite production in comparison with the other salts (sulfate, nitrate and
diisethionate and their corresponding previous countercations) which exhibit NO synthase
inhibition, especially bis(S-methylisothiouronium) sulfate, a selective and potent inducible NO
synthase (iNOS) inhibitor commonly used as standard.