Issue 6, 2002

Synthesis and DNA binding properties of bioorganometallic (η5-pentamethylcyclopentadienyl)iridium(iii) complexes of the type [(η5-C5Me5)Ir(Aa)(dppz)]n+ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine, n = 1–3), with S-coordinated amino acids (Aa) or peptides

Abstract

The DNA binding of cationic complexes of the type [(η5-C5Me5)Ir(Aa)(dppz)](CF3SO3)n (dppz = dipyrido[3,2-a:2′,3′-c]phenazine; n = 1, Aa = AccysOH 7; n = 2, Aa = AcmetOMe 4, H2cysOMe 8; n = 3, Aa = H2metOMe 5) containing S-coordinated amino acids (HmetOH = methionine, HcysOH = cysteine) has been studied by UV-vis titration, 2D-NOESY and gel electrophoresis. The observed steady decrease in absorbance at maxima between 350 and 400 nm on UV-vis titration with CT DNA and the bathochromic shifts of these absorption maxima are consistent with stable intercalative DNA binding for these complexes. An increase in the binding constant Kb from 8.80(6) × 104 for the monocation of 7 through 2.30(4) × 105 and 7.04(5) × 105 for the dications of 8 and 4 to 2.62(3) × 106 M−1 for the 3+ cation of 5 clearly reflects the strengthening of the electrostatic interaction with the negatively charged phosphodiester backbone of DNA with increasing cation charge. Analogous values of 2.81(7) × 105 and 1.26(5) × 106 M−1 were obtained for the (η5-C5Me5)RhIII complexes 14 (n = 2, Aa = H2cysOMe) and 13 (n = 3, Aa = H2metOMe). Binding site sizes for the organometallic IrIII and RhIII complexes on CT DNA lie in the range 1.5–2.1 base pairs. NOE cross peaks for the 1 ∶ 1 complex formed between 5 and d(GTCGAC)2 are consistent with intercalation adjacent to T2 from the major groove. Complexes 4, 5 and [(η5-C5Me5)Ir(HglyglymetOH)(dppz)](CF3SO3)26 (HglyOH = glycine) cleave the supercoiled plasmid pBluescript II KS+, on irradiation for 30–180 s with a high pressure Hg lamp, to afford nicked circular and linear DNA forms. X-Ray structural analyses are reported for [(η5-C5Me5)IrCl(dppz)](CF3SO3) 3 and [(η5-C5Me5)Ir(9-Etgua)(phen)] (CF3SO3)216 (9-Etgua = 9-ethylguanine).

Graphical abstract: Synthesis and DNA binding properties of bioorganometallic (η5-pentamethylcyclopentadienyl)iridium(iii) complexes of the type [(η5-C5Me5)Ir(Aa)(dppz)]+ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine, n = 1–3), with S-coordinated amino acids (Aa) or peptides

Supplementary files

Article information

Article type
Paper
Submitted
23 Aug 2001
Accepted
12 Dec 2001
First published
21 Feb 2002

J. Chem. Soc., Dalton Trans., 2002, 966-974

Synthesis and DNA binding properties of bioorganometallic (η5-pentamethylcyclopentadienyl)iridium(III) complexes of the type [(η5-C5Me5)Ir(Aa)(dppz)]n+ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine, n = 1–3), with S-coordinated amino acids (Aa) or peptides

D. Herebian and W. S. Sheldrick, J. Chem. Soc., Dalton Trans., 2002, 966 DOI: 10.1039/B107656F

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