19137-07-6Relevant articles and documents
Spin-Doctoring Cobalt Redox Shuttles for Dye-Sensitized Solar Cells
Baillargeon, Josh,Xie, Yuling,Raithel, Austin L.,Ghaffari, Behnaz,Staples, Richard J.,Hamann, Thomas W.
, p. 11633 - 11645 (2018)
A new low-spin (LS) cobalt(II) outer-sphere redox shuttle (OSRS) [Co(PY5Me2)(CN)]+, where PY5Me2 represents the pentadentate ligand 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine, has been synthesized and characterized for its potential application in dye-sensitized solar cells (DSSCs). Introduction of the strong field CN- ligand into the open axial coordination site forced the cobalt(II) complex, [Co(PY5Me2)(CN)]+, to become LS based upon the complex's magnetic susceptibility (1.91 ± 0.02 μB), determined by the Evans method. Interestingly, dimerization and subsequent cobalt hexacyanide cluster formation of the [Co(PY5Me2)(CN)]+ monomer was observed upon long-term solvent exposure or addition of a supporting electrolyte for electrochemical characterization. Although long-term stability of the [Co(PY5Me2)(CN)]+ complex made it difficult to fabricate liquid electrolytes for DSSC applications, short-term stability in neat solvent afforded the opportunity to isolate the self-exchange kinetics of [Co(PY5Me2)(CN)]2+/+ via stopped-flow spectroscopy. Use of Marcus theory provided a smaller than expected self-exchange rate constant of 20 ± 5.5 M-1 s-1 for [Co(PY5Me2)(CN)]2+/+, which we attribute to a Jahn-Teller effect observed from the collected monomer crystallographic data. When compared side-by-side to cobalt tris(2,2′-bipyridine), [Co(bpy)3]3+, DSSCs employing [Co(PY5Me2)(CN)]2+ are expected to achieve superior charge collection, which result from a smaller rate constant, ket, for recombination based upon simple dark J-E measurements of the two redox shuttles. Given the negative redox potential (0.254 V vs NHE) of [Co(PY5Me2)(CN)]2+/+ and the slow recombination kinetics, [Co(PY5Me2)(CN)]2+/+ becomes an attractive OSRS to regenerate near IR absorbing sensitizers in solid-state DSSC devices.
Sequence-specific oxidative degradation of tripeptides by a cobalt(III) complex containing a terpyridine ligand
Jitsukawa, Koichiro,Takahashi, Hiroshi,Hyuga, Ryoji,Arii, Hidekazu,Masuda, Hideki
, p. 4140 - 4145 (2007/10/03)
A sequence-specific oxidative degradation of an oligopeptide consisting of aliphatic amino acids was performed with a ternary cobalt(III) complex. Under aerobic conditions the reaction of [Co(CO3)(OH)(terpy)] and an equimolar amount of tripeptide at 40 °C at pH 8.5 gave two fraction bands (a and b) with water and then two bands (c and d) with NaCl solution, respectively, after column separation. In the case of gly-gly-leu (ggl, 1), [Co(gg'l)(terpy)] [1a, gg'l = glycyl(2-oxoglycyl)leucine], [Co(g'l)(terpy)] [1b, g'l = N-(2-oxoglycyl)leucine], [Co(ggl)(terpy)]+ (1c), and [Co(terpy)2]3+ (1d) were obtained. The crystal structure of 1c, which was the main product, revealed that the starting ggl ligand was cleaved to give a bis-amide compound, g'l, which might be generated by loss of N-terminal glycine and carbonylation of the α-carbon of the N-2 glycine residue. Although the source of the oxygen of the newly generated carbonyl group is not clear, gg'l is supposed to be an intermediate for g'l on the basis of time-dependent HPLC analyses. NMR investigation of other tripeptides [βala-gly-leu (2), gly-gly-phe (3), and gly-gly-ala (4)] containing a bulky C-terminal aliphatic side chain indicated the formation of the corresponding oxidation complexes. On the other hand, peptides containing a C-terminal glycine residue [gly-gly-gly (5) and phe-gly-gly (6)] or an N-2 β-alanine residue [gly-βala-leu (7)] did not give such a transformation product, The crystal structure of [Co(fgg)-(terpy)] (6c) revealed that the tripeptide is coordinated to cobalt with a tridentate N-terminal N-N-N geometry. Such sequence specificity demonstrated in the reaction of the aliphatic tripeptide complexes is interpreted by the interligand interaction between the side chain of the C-terminal amino acid residue and terpy. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
