Synthesis, Structure, and DNA Cleavage Properties of Copper(II) Complexes of 1,4,7-Triazacyclononane Ligands Featuring Pairs of Guanidine Pendants
| Autor: | Bimbil Graham, Tanmaya Joshi, Linda Tjioe, Leone Spiccia, Joël Brugger |
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| Rok vydání: | 2010 |
| Předmět: |
Stereochemistry
chemistry.chemical_element Crystal structure Crystallography X-Ray Ligands Phosphates Nitrophenols Inorganic Chemistry chemistry.chemical_compound Deprotonation Heterocyclic Compounds Spectroscopy Fourier Transform Infrared Polymer chemistry Anaerobiosis DNA Cleavage Physical and Theoretical Chemistry Guanidine Hydrogen bond Esters Hydrogen Bonding Free Radical Scavengers Hydrogen-Ion Concentration Copper Solutions Kinetics Trigonal bipyramidal molecular geometry chemistry Indicators and Reagents Spectrophotometry Ultraviolet Titration Amine gas treating Reactive Oxygen Species Plasmids |
| Zdroj: | Inorganic Chemistry. 50:621-635 |
| ISSN: | 1520-510X 0020-1669 |
| DOI: | 10.1021/ic1018136 |
| Popis: | Two new ligands, L(1) and L(2), have been prepared via N-functionalization of 1,4,7-triazacyclononane (tacn) with pairs of ethyl- or propyl-guanidine pendants, respectively. The X-ray crystal structure of [CuL(1)](ClO4)2 (C1) isolated from basic solution (pH 9) indicates that a secondary amine nitrogen from each guanidine pendants coordinates to the copper(II) center in addition to the nitrogen atoms in the tacn macrocycle, resulting in a five-coordinate complex with intermediate square-pyramidal/trigonal bipyramidal geometry. The guanidines adopt an unusual coordination mode in that their amine nitrogen nearest to the tacn macrocycle binds to the copper(II) center, forming very stable five-membered chelate rings. A spectrophotometric pH titration established the pK(app) for the deprotonation and coordination of each guanidine group to be 3.98 and 5.72, and revealed that [CuL(1)](2+) is the only detectable species present in solution above pH ∼ 8. The solution speciation of the CuL(2) complex (C2) is more complex, with at least 5 deprotonation steps over the pH range 4-12.5, and mononuclear and binuclear complexes coexisting. Analysis of the spectrophotometric data provided apparent deprotonation constants, and suggests that solutions at pH ∼ 7.5 contain the maximum proportion of polynuclear complexes. Complex C1 exhibits virtually no cleavage activity toward the model phosphate diesters, bis(p-nitrophenyl)phosphate (BNPP) and 2-hydroxypropyl-p-nitrophenyl phosphate (HPNPP), while C2 exhibits moderate activity. For C2, the respective kobs values measured at pH 7.0 (7.24 (± 0.08) × 10(-5) s(-1) (BNPP at 50 °C) and 3.2 (± 0.3) × 10(-5) s(-1) (HPNPP at 25 °C)) are 40- and 10-times faster than [Cu(tacn)(OH2)2](2+) complex. Both complexes cleave supercoiled pBR 322 plasmid DNA, indicating that the guanidine pendants of [CuL(1)](2+) may have been displaced from the copper coordination sphere to allow for DNA binding and subsequent cleavage. The rate of DNA cleavage by C2 is twice that measured for [Cu(tacn)(OH2)2](2+), suggesting some degree of cooperativity between the copper center and guanidinium pendants in the hydrolysis of the phosphate ester linkages of DNA. A predominantly hydrolytic cleavage mechanism was confirmed through experiments performed either in the presence of various radical scavengers or under anaerobic conditions. |
| Databáze: | OpenAIRE |
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