Abstract:Recebido em 3/5/01; aceito em 6/7/01 ELECTRON TRANSFER IN INORGANIC MIXED-VALENCE SYTEMS. This article reports on some basic and conceptual principles concerning electron transfer (ET) and/or intervalence transfer (IT) phenomena in inorganic mixed-valence systems.Keywords: electron transfer; intervalence charge transfer; mixed-valence.
INTRODUÇÃOEm um contexto bastante abrangente, os materiais de valência mista 1 são aqueles que contêm íons em mais de um estado de oxidação formal em uma mesma unidade molecular… Show more
“…2 (ΔE = 130 mV; region IV). As comproportionation constants can be related to the stabilization promoted by the electronic delocalization in the mixed-valence states, [15] according to this evaluation of K c based on the closely-spaced redox potentials, the electronic coupling between the two cluster units does not appear to be particularly strong within the oxidation-state range studied and reported herein. Consistent with these findings are also preliminary results of ongoing theoretical calculations of molecular and electronic structures, which provide additional evidence for the moderate extent of cluster-tocluster electronic communication (despite the obvious metal-ligand mixing and delocalization within each cluster).…”
The pH-dependent electronic and electrochemical properties of a series of triangular μ 3 -oxo-centered trinuclear clusters of the type [Ru 3 O(Ac) 6 (py) 2 (OH x )] n (Ac = acetate; py = pyridine; x = 0, 1, or 2; where the formal oxidation states on the metal ions range from +II to +IV) have been investigated with emphasis on the elucidation of the successive proton-coupled redox processes spanning the interconvertible aqua-(x = 2), hydroxo-(x = 1), and oxo-(x = 0) forms, from which the complete Pourbaix diagram has been proposed. From the spontaneous slow coupling reaction of the monomeric cluster in its
“…2 (ΔE = 130 mV; region IV). As comproportionation constants can be related to the stabilization promoted by the electronic delocalization in the mixed-valence states, [15] according to this evaluation of K c based on the closely-spaced redox potentials, the electronic coupling between the two cluster units does not appear to be particularly strong within the oxidation-state range studied and reported herein. Consistent with these findings are also preliminary results of ongoing theoretical calculations of molecular and electronic structures, which provide additional evidence for the moderate extent of cluster-tocluster electronic communication (despite the obvious metal-ligand mixing and delocalization within each cluster).…”
The pH-dependent electronic and electrochemical properties of a series of triangular μ 3 -oxo-centered trinuclear clusters of the type [Ru 3 O(Ac) 6 (py) 2 (OH x )] n (Ac = acetate; py = pyridine; x = 0, 1, or 2; where the formal oxidation states on the metal ions range from +II to +IV) have been investigated with emphasis on the elucidation of the successive proton-coupled redox processes spanning the interconvertible aqua-(x = 2), hydroxo-(x = 1), and oxo-(x = 0) forms, from which the complete Pourbaix diagram has been proposed. From the spontaneous slow coupling reaction of the monomeric cluster in its
“…In the particular case of triruthenium compounds, usually the electronic interaction among the ruthenium atoms is so strong that the central core [Ru 3 O] ? is totally delocalized, and thus behaves as a single metal centre [1,4]. From an electrochemical viewpoint, it constitutes an appealing electroactive moiety, since the [Ru 3 O] unit displays up to five reversible redox processes in the -1.5 to 2.5 V (vs. SHE) range, and the choice of terminal and bridging ligand modulates its electrochemical behaviour [5,6].…”
The polymetallic [Ru 3 O(CH 3 COO) 6 (py) 2 (BPE)-Ru(bpy) 2 Cl](PF 6 ) 2 complex (bpy = 2,2 0 -bipyridine, BPE = trans-1,2-bis(4-pyridil)ethylene and py = pyridine) was assembled by the combination of an electroactive [Ru 3 O] moiety with a [Ru(bpy) 2 (BPE)Cl] photoactive centre, and its structure was determined using positive ion electrospray (ESI-MS) and tandem mass (ESI-MS/MS) spectrometry. The [Ru 3 O(CH 3 COO) 6 (py) 2 (BPE)Ru(bpy) 2 Cl] 2? doubly charged ion of m/z 732 was mass-selected and subject to 15 eV collision-induced dissociation, leading to a specific dissociation pattern, diagnostic of the complex structure. The electronic spectra display broad bands at 409, 491 and 692 nm ascribed to the [Ru(bpy) 2 (BPE)] charge-transfer bands and to the [Ru 3 O] internal cluster transitions. The cyclic voltammetry shows five reversible waves at -1.07 V, 0.13 V, 1.17 V, 2.91 V and -1.29 V (vs SHE) assigned to the [Ru 3 O] -1/0/?1/?2/?3 and to the bpy 0/-1 redox processes; also a wave is observed at 0.96 V, assigned to the Ru ?2/?3 pair. Despite the conjugated BPE bridge, the electrochemical and spectroelectrochemical results indicate only a weak coupling through the p-system, and preliminary photophysical essays showed the compound decomposes under visible light irradiation.
“…Reações envolvendo transferência de elétrons são essenciais para a vida de diversos organismos e a sua ocorrência nos sistemas biológicos está relacionada com diversos processos metabólicos, como a fosforilação oxidativa e a cadeia respiratória. 1 Processos redox também vêm sendo explorados para o desenvolvimento de fármacos para o tratamento de algumas doenças como as cardiovasculares, doença de Chagas, artrite reumatoide e câncer. [2][3][4][5][6][7][8][9] Alguns tipos de câncer geram tumores sólidos que possuem uma vascularização deficiente, o que leva a um ambiente hipóxico com maior capacidade redutora quando comparado aos tecidos normais.…”
Redox activation has been exploited in the development of drugs for treatment of several diseases, including cancer. Some cancers generate solid tumors that have a poor vascularization, which leads to the generation of hypoxic environments, which in turn, limit the effectiveness of both radio and chemotherapies. These regions have a higher reducing capability when compared to normoxic tissues. Thus, substances capable of circulating intact through the body can be reduced and activated selectively in the hypoxic region of the tumor, becoming cytotoxic. Based on this strategy, five classes of Prodrugs Activated by Hypoxia (PDAHs) are described and include nitro(hetero)cycles (p. eg. nitrogen mustards and nitroimidazoles), aromatic N-oxides, aliphatic Noxides, quinones and transition metal complexes. In this review, some advances in the development of PDAHs are discussed, focusing on the relationship between the redox properties and biological activity.
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