Organometallic ionophore

Other self-assembly approaches have been applied in order to obtain polynuclear metallacycles for potential medical applications, for example, counterion encapsulation [84] or use as organometallic ionophores [85] employing halfsandwich Ru(II), Rh(III), or Ir(III) building blocks. Despite the fact that some of these species have a chiral environment around the metal, studies of comparative cytotoxicity between single homochiral or heterochiral systems have not been carried out as yet. 

Scheme 10.1 Ligands, L1-L3, and organometallic fragments for the synthesis of potential organometallic ionophores.

As shown in Scheme 10.3, [(CgH5C02Et)Ru(Ll)]3 provides an organometalla-macrocycle that is highly selective to Li ions over the more highly concentrated Na ions [12]. The CPK models of this organometallic ionophore, and that of the Li complex (Cl omitted for clarity) are shown in Fig. 10.19. 

Fig. 10.19 Left organometallic ionophore, [(CgHsCOjEQRuILlIjj. Right Li complex.

An ionophore, from the Greek words ion and/ero (carry), is a compound (organic or organometallic) which can selectively and reversibly coordinate to a specific ion and can thus, based on differences in Gibbs energy, transport the ion from the aqueous solution into a membrane. Up-to-date knowledge in the area of ionophores suggests that there are some very important physicochemical characteristics that a compound must have in order to be a candidate for use as an ionophore in ISEs. The most important of these are ... 

The well-developed and highly adaptable synthetic chemistry of ferrocene, together with its accessible ferrocene/ ferrocenium (Fc/Fc ) redox couple has led to its abundant use in redox-active receptors. The first organometallic cation receptors to be studied were the ferrocene-modified crown ethers of Saji 1 and Beer 2-4. The electron-rich crown ethers provide the cation-binding site—they are potent ionophores for group 1 and 2 metal cations. NMR (in methanol/acetone solution) and solid-state X-ray crystal structure studies demonstrated that 2-4 bind Na, K, and Cs. The binding stoichiometry varies depending on the receptor and cation used. Both Na and form 2 1 cation receptor complexes with 3, as does Na with 2. The ability of ferrocene to swivel around the CpFeCp axis also allows the formation of a 1 1 intramolecular sandwich complex, as seen in 2 Na, 2 K, 2 Cs and 3 K. ... 

Synthetic ionophore ligands, mostly based on cyclic and branched polyethers, have been widely used in the last decade to study carrier facilitated cation transport across membranes. It has recently been observed that the organometallic ligand (C H )Co[P0(0C2H )2]2 Iso has... 

Further structural investigations of related complexes and chemical modifications of the organometallic ligand are under way in order to improve the ionophoric properties of this type of molecular hosts. 

---