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DNA binding studies of a new dicationic porphyrin. Insights into interligand interactions
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Shelton, Alexander H., Rodger, Alison and McMillin, David R. (2007) DNA binding studies of a new dicationic porphyrin. Insights into interligand interactions. Biochemistry, Vol.46 (No.31). pp. 9143-9154. doi:10.1021/bi700293g ISSN 0006-2960.
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Official URL: http://dx.doi.org/10.1021/bi700293g
Abstract
Cationic porphyrins have an affinity for DNA and potential for applications in the fields of photodynamic therapy and cellular imaging. This report describes a new dicationic porphyrin, 5,15-dimethyl-10,20-di(N-methylpyridinium-4-yl)porphyrin, abbreviated H(2)tMe(2)D4. Although tetrasubstituted, H(2)tMe(2)D4 presents modest steric requirements and forms in reasonable yield by a '' 2+2 '' synthetic method. Accordingly, studies of the zinc(II)- and copper(II)-containing derivatives, Zn(tMe(2)D4) and Cu(tMe(2)D4), have also been possible. Methods used to characterize DNA-binding motifs include absorption, emission, linear, and circular dichroism spectroscopies, as well as viscometry. An unusually detailed picture of porphyrin uptake emerges. As the ratio of DNA to porphyrin increases during a typical titration, H(2)tMe(2)D4 or Cu(tMe(2)D4) initially aggregates on the host and then shifts to intercalative binding at close quarters before finally dispersing into non-interacting intercalation sites of the host. Emission studies of the copper(II) porphyrin have been very valuable. The existence of a measurable signal is diagnostic of intercalative binding, and the saturation behavior establishes that internalization typically monopolizes approximately three base pairs. In the moderate loading regime, emission data are most telling because dipole-dipole interactions between near-neighbor porphyrins tend to confuse other spectroscopic assays. The third ligand, Zn(tMe(2)D4), behaves differently in that the uptake is a strictly cooperative process. The mode of binding also varies with the base content of the DNA host. When the DNA is rich in A=T base pairs, the porphyrin remains five-coordinate and binds externally; however, Zn(tMe(2)D4) loses its axial ligand and binds by intercalation if the host contains only G equivalent to C base pairs.
Item Type: | Journal Article | ||||
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Subjects: | Q Science > QD Chemistry | ||||
Divisions: | Faculty of Science, Engineering and Medicine > Research Centres > Molecular Organisation and Assembly in Cells (MOAC) | ||||
Journal or Publication Title: | Biochemistry | ||||
Publisher: | American Chemical Society | ||||
ISSN: | 0006-2960 | ||||
Official Date: | 7 August 2007 | ||||
Dates: |
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Volume: | Vol.46 | ||||
Number: | No.31 | ||||
Number of Pages: | 12 | ||||
Page Range: | pp. 9143-9154 | ||||
DOI: | 10.1021/bi700293g | ||||
Status: | Peer Reviewed | ||||
Publication Status: | Published | ||||
Access rights to Published version: | Restricted or Subscription Access |
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