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Spectral and Structural Characterization of 5,6-Chrysenequinone Diimine Complexes of Rhodium(III): Evidence for a pH-Dependent Ligand Conformational Switch

Jackson, Brian A. and Henling, Lawrence M. and Barton, Jacqueline K. (1999) Spectral and Structural Characterization of 5,6-Chrysenequinone Diimine Complexes of Rhodium(III): Evidence for a pH-Dependent Ligand Conformational Switch. Inorganic Chemistry, 38 (26). pp. 6218-6224. ISSN 0020-1669. doi:10.1021/ic990824l.

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Rhodium(III) complexes containing 9,10-phenanthrenequinone diimine (phi) ligands have been broadly applied for the construction of DNA binding and recognition molecules, and more recently, derivatives containing the 5,6-chrysenequinone diimine (chrysi) ligand have been shown specifically to recognize base mismatches in DNA. Here the structural properties of [Rh(bpy)_2(chrysi)]Cl_3 and spectroscopic properties of derivatives are examined and compared to those of phi complexes of rhodium. Although similar in many respects, phi and chrysi complexes display distinctly different protonation behavior. The pK_a values of chrysi complexes are as much as 1 unit lower than analogous phi compounds, and visible spectra of the chrysi complexes differ markedly from the phi counterparts in acidic but not basic solution. This protonation behavior is traced to the presence of a steric clash between a proton on the aromatic ring of the chrysi ligand and the acidic immino proton of the metal complex. In avoidance of this steric clash, a significant disruption in the planarity of the chrysi ligand is evident crystallographically in the structure of [Rh(bpy)_2(chrysi)]Cl_3·3CH_3CN·2H_2O (triclinic crystal system, space group P1̄ (No. 2), Z = 2, a = 9.079(3) Å, b = 10.970(3) Å, c = 21.192(8) Å, α = 86.71(3)°, β = 89.21(3)°, γ = 78.58(3)°, V = 2065.4(12) Å^3). Phi complexes, lacking the additional aromatic ring, require no similar distortion from ligand planarity. NMR spectra support this pH-dependent structural distortion for the chrysi complex. Rhodium complexes of chrysenequinone diimine, therefore, not only represent new DNA binding molecules targeted to mismatches but also provide an illustration of a pH “gated” ligand conformational switch.

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URLURL TypeDescription ItemSupporting Information
Barton, Jacqueline K.0000-0001-9883-1600
Additional Information:© 1999 American Chemical Society. Received July 12, 1999. Publication Date (Web): December 3, 1999. We gratefully acknowledge the financial support of the National Institutes of Health (Grant GM33309). B.A.J. acknowledges the NSF and the Parsons Foundation for predoctoral fellowships.
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NSF Predoctoral FellowshipUNSPECIFIED
Ralph M. Parsons FoundationUNSPECIFIED
Issue or Number:26
Record Number:CaltechAUTHORS:20160412-081002999
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Official Citation:Spectral and Structural Characterization of 5,6-Chrysenequinone Diimine Complexes of Rhodium(III):  Evidence for a pH-Dependent Ligand Conformational Switch Brian A. Jackson,Lawrence M. Henling, and, and Jacqueline K. Barton* Inorganic Chemistry 1999 38 (26), 6218-6224 DOI: 10.1021/ic990824l
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:66068
Deposited By: Ruth Sustaita
Deposited On:12 Apr 2016 17:57
Last Modified:10 Nov 2021 23:53

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