[RU-2(II)(TTHA)(H2O)(2)](2-) IS A RAPID NO SCAVENGER (TTHA(6-) = TRIETHYLENETETRAMINEHEXAACETATE)

The reaction of NO(aq.) with [Ru-2(II)(ttha)(H2O)(2)](2-) = (A) and [R u-2(II)(ttha)(bpy)(H2O)](2-) = (B), (ttha(6-) = triethylenetetraminehe xaacetate; bpy = 2.2'-bipyridine) was monitored by electrochemical met hods (cyclic voltammetry, differential pulse polarography). Each of tw o sites of [Ru-2(II)(ttha)] may be represented by [LRu] for convenienc e. Waves for the [LRuII(NO .)] --> (-1e-) [LRuII(NO+)], 2[LRuII(NO2-)] --> (-2e-) [LRuIII(NO3-)] + [LRuIII(NO+)], and [LRuII(NO+)] --> (-1e- ) [LRuIII(NO+) oxidations were identified at -0.06, +0.98, and 1.14 V vs normal hydrogen electrode, respectively. The protonated form of [LR uII (NO .)], [LRuII(NOH)] was detected as a separate Ru-II/III wave at +0.10 V. The pK(a) of [LRuII(NOH)] is 1.80. The rate of substitution of NO on (A) is 22.7 M(-1)s(-1) at 22 degrees C indicating a normal ra te of neutral ligand substitution on Ru-II-polyaminopolycarboxylates v ia dissociative intermediates. The identical waves fm the nitrosylated (B) indicate that the nitrosyls of (A), [(Ru-II(NO .))(2)(ttha)](2-) = (C), are terminally coordinated rather than a single bridged nitrosy l. The nitrosyl (C) does not react with H-2, precluding a catalytic sc avenging of NO by (A) followed by H-2 reduction for environmental cont rol purposes. However, the nitrosyl (C) is robust and dissociates very slowly under Ar purging. Thus the parent complex [Ru-2(ttha)(H2O)(2)] (2-) and related mononuclear Ru-II-polyaminopolycarboxylates such as [ Ru-2(bedta)(H2O2- have several features that lend them toward uses as antisepsis agents for the control of septic shock. [Ru-2(III)(ttha)(H2 O)(2)] also reacts directly with NO, forming [Ru-II(NO+))(2)(ttha)] wh ich exhibits the same waves as [Ru-II(ttha)(NO)(2)](2-) since the Ru-I I(NO+) units readily reduce electrochemically at glassy carbon to the Ru-II(NO .) complex (C) below -0.06 V. It was observed that the [LRuII I(NO+)] catalyzes the electrochemical oxidation of NO to NO+ and, henc e HNO2 at 1.14 V at glassy carbon. (C) 1997 Elsevier Science Inc.