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Effect of Ring Methylation on the Photophysical, Photochemical and Photobiological Properties of cis ‐Dichlorobis(1,10‐Phenanthroline)Rhodium(III)Chloride †
Author(s) -
Loganathan Devanesan,
Morrison Harry
Publication year - 2006
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/2005-01-19-ra-420
Subject(s) - rhodium , chemistry , phototoxicity , phenanthroline , photochemistry , chloride , covalent bond , chromophore , stereochemistry , medicinal chemistry , crystallography , organic chemistry , catalysis , biochemistry , in vitro
Methylated analogues of cis ‐dichlorobis(1,10‐phenanthroline)‐rhodium(III)chloride (BISPHEN) have been prepared in order to increase the hydrophobicity of the parent compound, and thus create octahedral rhodium (III) complexes suitable for use as anticancer and antiviral agents that can be photo‐activated. The parent complex has been shown in earlier work to be unable to cross through cell membranes. Octamethylation, as in the case of cis ‐dichlorobis(3,4,7,8‐tetramethyl‐1,10‐phenanthroline)rhodium(III)chloride (OCTBP), provides enough hydrophobicity to be taken up by KB tumor cells. It also provides a higher level of ground‐state association with double‐stranded DNA and increases the quantum efficiency of photoaquation by greater than 10‐fold, relative to BISPHEN. OCTBP forms covalent bonds to deoxyguanosine when irradiated with the nucleoside, as has been seen with the parent complex. Irradiation of OCTBP in the presence of the KB or M109 tumor cell lines using narrow‐band UVB (λ= 311 nm) irradiation initiates a considerable amount of phototoxicity. There is evidence that OCTBP acts as a prodrug ( i.e. after passing through the cell membrane the metal complex is photolyzed to cis ‐chloro aquo OCTBP, which may be the active phototoxic agent). OCTBP and the tetramethyl analogue cis ‐dichlorobis(4,7‐dimethyl‐1,10‐phenanthroline)rhodium(III)chloride (47TMBP) also show photoaquation upon excitation with visible light (λ > 500 nm), and indeed, some phototoxicity of KB cells is observed at these wavelengths as well. This is attributed to direct population of photoactive triplet‐excited states. These results, together with our earlier studies of cis ‐dichloro[dipyrido(3,2‐a: 2′,3′‐c)phenazine (1,10‐phenanthroline)rhodium(III)chloride (DPPZPHEN) demonstrate that such octahedral rhodium complexes are viable “photo‐cisplatin” reagents.