Mixed-metal supramolecular complexes that couple ruthenium or osmium based light absorbers to a c... more Mixed-metal supramolecular complexes that couple ruthenium or osmium based light absorbers to a central rhodium(III) core have been designed which photocleave DNA upon irradiation with visible light. The complexes [[(bpy)(2)Ru(dpp)](2)RhCl(2)](PF(6))(5), [[(bpy)(2)Os(dpp)](2)RhCl(2)](PF(6))(5), and [[(tpy)RuCl(dpp)](2)RhCl(2)](PF(6))(3), where bpy = 2,2'-bipyridine, tpy = 2,2':6',2' '-terpyridine, and dpp = 2,3-bis(2-pyridyl)pyrazine, all exhibit intense metal to ligand charge transfer (MLCT) based transitions in the visible but possess lower lying metal to metal charge transfer (MMCT) excited states. These supramolecular complexes with low lying MMCT states photocleave DNA when excited into their intense MLCT transitions. Structurally similar complexes without this low lying MMCT state do not exhibit DNA photocleavage, establishing the role of this MMCT state in the DNA photocleavage event. Design considerations necessary to produce functional DNA photocleavage agents are presented herein.
ABSTRACT The title compound, C14H12N2O2, was isolated from the reaction between 4-methylphenyldia... more ABSTRACT The title compound, C14H12N2O2, was isolated from the reaction between 4-methylphenyldiazonium nitrite and salicylaldehyde in sodium hydroxide. Structural analysis revealed a nearly planar molecule with the aromatic rings in trans positions about the azo group. The molecular packing shows interdigitated stacks of 12-membered hydrogen-bonded dimers.
The synthesis, X-ray crystallography, spectroscopic, and electrochemical properties of the title ... more The synthesis, X-ray crystallography, spectroscopic, and electrochemical properties of the title compound, [Hdpa][Cr(dipic)2]·3H2O, 1, are reported. Compound 1 crystallized in the triclinic space group P-1 with a = 7.1057(11) Å, b = 12.965(2) Å, c = 14.269(2) Å, α = 80.306(3)°, β = 82.101(2)°, γ = 83.799(2)°, and V = 1278.6(4) Å3 with Z = 2. The distorted octahedral chromium anions are part of an elaborate network of hydrogen bonding formed by the waters of solvation, the anion, and cation as well as π-stacking interactions.
A detailed investigation of the oxidation of L-ascorbic acid (H2A) by the title complex has been ... more A detailed investigation of the oxidation of L-ascorbic acid (H2A) by the title complex has been carried out using conventional spectrophotometry at 510 nm, over the ranges: 0.010 ≤ [ascorbate]T ≤ 0.045 mol dm−3, 3.62 ≤ pH ≤ 5.34, and 12.0 ≤ θ ≤ 30.0 °C, 0.50 ≤ I ≤ 1.00 mol dm−3, and at ionic strength 0.60 mol dm−3 (NaClO4). The main reaction products are the bis(pyridine-2,6-dicarboxylate)cobaltate(II) ion and l-dehydroascorbic acid. The reaction rate is dependent on pH and the total ascorbate concentration in a complex manner, i.e., k obs = (k 1K 1)[ascorbate]T /(K 1 + [H+]). The second order rate constant, k 1 [rate constant for the reaction of the cobalt(III) complex and HA−] at 25.0 °C is 2.31 ± 0.13 mol−1 dm3 s−1. ΔH ‡ = 30 ± 4 kJ mol−1 and ΔS ‡ = −138 ± 13 J mol−1 K−1. K 1, the dissociation constant for H2A, was determined as 1.58 × 10−4 mol dm−3 at an ionic strength of 0.60 mol dm−3, while the self exchange rate constant, k 11 for the title complex, was determined as 1.28 × 10−5 dm3 mol−1 s−1. An outer-sphere electron transfer mechanism has been proposed.
Mixed-metal supramolecular complexes that couple ruthenium or osmium based light absorbers to a c... more Mixed-metal supramolecular complexes that couple ruthenium or osmium based light absorbers to a central rhodium(III) core have been designed which photocleave DNA upon irradiation with visible light. The complexes [[(bpy)(2)Ru(dpp)](2)RhCl(2)](PF(6))(5), [[(bpy)(2)Os(dpp)](2)RhCl(2)](PF(6))(5), and [[(tpy)RuCl(dpp)](2)RhCl(2)](PF(6))(3), where bpy = 2,2'-bipyridine, tpy = 2,2':6',2' '-terpyridine, and dpp = 2,3-bis(2-pyridyl)pyrazine, all exhibit intense metal to ligand charge transfer (MLCT) based transitions in the visible but possess lower lying metal to metal charge transfer (MMCT) excited states. These supramolecular complexes with low lying MMCT states photocleave DNA when excited into their intense MLCT transitions. Structurally similar complexes without this low lying MMCT state do not exhibit DNA photocleavage, establishing the role of this MMCT state in the DNA photocleavage event. Design considerations necessary to produce functional DNA photocleavage agents are presented herein.
ABSTRACT The title compound, C14H12N2O2, was isolated from the reaction between 4-methylphenyldia... more ABSTRACT The title compound, C14H12N2O2, was isolated from the reaction between 4-methylphenyldiazonium nitrite and salicylaldehyde in sodium hydroxide. Structural analysis revealed a nearly planar molecule with the aromatic rings in trans positions about the azo group. The molecular packing shows interdigitated stacks of 12-membered hydrogen-bonded dimers.
The synthesis, X-ray crystallography, spectroscopic, and electrochemical properties of the title ... more The synthesis, X-ray crystallography, spectroscopic, and electrochemical properties of the title compound, [Hdpa][Cr(dipic)2]·3H2O, 1, are reported. Compound 1 crystallized in the triclinic space group P-1 with a = 7.1057(11) Å, b = 12.965(2) Å, c = 14.269(2) Å, α = 80.306(3)°, β = 82.101(2)°, γ = 83.799(2)°, and V = 1278.6(4) Å3 with Z = 2. The distorted octahedral chromium anions are part of an elaborate network of hydrogen bonding formed by the waters of solvation, the anion, and cation as well as π-stacking interactions.
A detailed investigation of the oxidation of L-ascorbic acid (H2A) by the title complex has been ... more A detailed investigation of the oxidation of L-ascorbic acid (H2A) by the title complex has been carried out using conventional spectrophotometry at 510 nm, over the ranges: 0.010 ≤ [ascorbate]T ≤ 0.045 mol dm−3, 3.62 ≤ pH ≤ 5.34, and 12.0 ≤ θ ≤ 30.0 °C, 0.50 ≤ I ≤ 1.00 mol dm−3, and at ionic strength 0.60 mol dm−3 (NaClO4). The main reaction products are the bis(pyridine-2,6-dicarboxylate)cobaltate(II) ion and l-dehydroascorbic acid. The reaction rate is dependent on pH and the total ascorbate concentration in a complex manner, i.e., k obs = (k 1K 1)[ascorbate]T /(K 1 + [H+]). The second order rate constant, k 1 [rate constant for the reaction of the cobalt(III) complex and HA−] at 25.0 °C is 2.31 ± 0.13 mol−1 dm3 s−1. ΔH ‡ = 30 ± 4 kJ mol−1 and ΔS ‡ = −138 ± 13 J mol−1 K−1. K 1, the dissociation constant for H2A, was determined as 1.58 × 10−4 mol dm−3 at an ionic strength of 0.60 mol dm−3, while the self exchange rate constant, k 11 for the title complex, was determined as 1.28 × 10−5 dm3 mol−1 s−1. An outer-sphere electron transfer mechanism has been proposed.
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Papers by Alvin Holder