Iridium complexes peptides

Other oxidizing agents which can convert Cu(II)G4 to Cu(III)G4 include S2082- and IrCle2". The IrC 2" reaction is quantitative under suitable conditions and was used to help prove that Cu(III)-peptide complexes could be formed and characterized in aqueous solutions (9). Electrochemical oxidation is more efficient and avoids the need to remove the iridium complexes. The Cu(III)-peptide complexes have now been characterized by ... 

The bioconjugation of iridium complexes remains currently under intense exploration. For example, two new, cyclometalated iridium(III) and rhodium(III) bis(pyridylbenzaldehyde) complexes were designed by Lo et al. in 2010 both with and without biotin tags, with their uptake followed in HeLa cells.Furthermore, cell-penetrating peptides conjugated to Ir(III)... 

One of the standard methods for preparing enantiomerically pure compounds is the enantioselective hydrogenation of olefins, a,/3-unsaturated amino acids (esters, amides), a,/3-unsaturated carboxylic acid esters, enol esters, enamides, /3- and y-keto esters etc. catalyzed by chiral cationic rhodium, ruthenium and iridium complexes ". In isotope chemistry, it has only been exploited for the synthesis of e.p. natural and nonnatural H-, C-, C-, and F-labeled a-amino acids and small peptides from TV-protected a-(acylamino)acrylates or cinnamates and unsaturated peptides, respectively (Figure 11.9). This methodology has seen only hmited use, perhaps because of perceived radiation safety issues with the use of hydrogenation procedures on radioactive substrates. Also, versatile alternatives are available, including enantioselective metal hydride/tritide reductions, chiral auxiliary-controlled and biochemical procedures (see this chapter. Sections 11.2.2 and 11.3 and Chapter 12). 

Iridium can be removed from Cu(III)—peptide solutions by passing them through anion exchange columns. The resulting Cuin(H 3G4) is much slower to decompose in acid than is the Cun(H 3G4)2" complex. In neutral solutions at 25° the half-life of Cum(H 3G4) is about 1 hr. The decomposition rate increases in base as well as in acid. The substitution kinetics of the Cu(III) (ds) complexes are clearly much slower than the corresponding Cu(II) complexes. This fact was used in choosing Chelex ion exchange resin to remove Cu(II) from Cu(III) in order to determine the molar absorptivity of Cum(H 3G4). This value of 7200 d= 300 M"1 cm"1 at 365 nm was checked by several other methods (9). 

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