Intermediates in the photochemistry of of carbonato-amine complexes of cobalt(III). Carbonate(-) radicals and the aquocarbonato complex

Abstract

The 254-nm irradiation of neutral, buffered, solutions of Co(NH3)4C03+ and Co(en)2C03+ produces Coaq2+ with a relatively low quantum yield (0.06 and 0.02, respectively); Co(NH3)6CQ3+ also is photoreduced. The irradiation of Co(NH3)4C03+ also generates Co(NH3)4(OH2)23+ with a quantum yield of 0.11 ± 0.03. The flash photolysis of the three complexes yields a transient intermediate which has 600 nm and which is identified as the C03~radical. The flash photolysis of the bidentate carbonato complexes also reveals a long-lived tail absorption in the 300-nm region which decays via pH-dependent first-order kinetics. The behavior of this intermediate is identical with that of the aquocarbonato species proposed as an intermediate in the acid-catalyzed aquation of the bidentate carbonato complexes. It is proposed that photochemical excitation of these complexes in the intense ligand-to-metal charge-transfer band produces the charge-transfer singlet state (1CT) which generates, via

Oxidation of Guanine by Carbonate Radicals Derived from Photolysis of Carbonatotetramminecobalt(III) Complexes and the pH Dependence of Intrastrand DNA Cross‐Links Mediated by Guanine Radical Reactions

“…Time-resolved, transient absorption experiments have shown that the photolysis of [Co(NH 3 ) 4 CO 3 ] + complexes induced by 248 nm KrF excimer, or 266 nm Nd: Yag laser pulses, yields CO 3 •− radicals. [19, 24, 25] Here we show that CO 3 •− radicals can also be produced easily by 308 nm XeCl excimer laser pulse excitation because the UV absorption spectrum of [Co(NH 3 ) 4 CO 3 ] + extends beyond 300 nm (i.e., beyond the absorption threshold of the normal DNA bases).…”

“…[17] The conjugate acid (HCO 3 • ) is a strong acid (p K a < 0) and, at pH > 0, these radicals exist in the anion form, CO 3 •− . [29] The UV irradiation of [Co(NH 3 ) 4 CO 3 ] + complexes has been shown to generate different products according to two pathways : [19, 24, 25] …”

Influence of bicarbonate and carbonate ions on sonochemical degradation of Rhodamine B in aqueous phase

“…For many years, by analogy to the carbonate and bicarbonate anions, it was assumed that this radical normally exists as the protonated form (HCO 3 • ) in the neutral to basic pH range, but it is now firmly established that no protonation of CO 3 •− (reaction (10)) could be observed in the pH range of 0-10 [8], which leaves CO 3 •− as the only relevant carbonate radical species to be considered in this study and in most aquatic chemistry applications. This radical is a strong one-electron oxidant (1.78 [9] and 1.59 V [10] vs. Normal Hydrogen Electrode (NHE) at pH 7.0 and 12.5, respectively). Carbonate radical may be formed when using ultrasound for water treatment (quenching of hydroxyl radical by HCO 3 − and CO 3 2− ).…”

The effect of neighboring methionine residue on tyrosine nitration and oxidation in peptides treated with MPO, H2O2, and NO2− or peroxynitrite and bicarbonate: Role of intramolecular electron transfer mechanism?

“…Carbonato tetrammine cobalt(III) perchlorate [Co(NH 3 ) 4 CO 3 ]ClO 4 was synthesized in two steps, as described elsewhere: (1) synthesis of [Co(NH 3 ) 4 CO 3 ]Cl [49] and (2) exchange of chloride anion with perchlorate anion [50]. …”

“…The carbonate radical anion (CO 3 •- ) was generated in situ by irradiation of the samples placed in quartz cuvettes with UV light [50; 51]. Photolysis was carried out using a 300 W Xe high pressure compact arc lamp (Eimac Model VIX 300 UV).…”