Ferrocene receptor

Debroy, P., Banerjee, M., Prasad, M., Moulik, S. R, Roy, S., Binding of amino acids into a novel multiresponsive ferrocene receptor having an ene backbone. Org. Lett. 2005, 7, 403-406. 

Recently, Miyaji and coworkers [52] reported the chromogenic molecular switch 65 as a new ditopic ferrocene receptor for anions in the presence of cations. Upon addition of F to a solution of 65 in CH3CN, a new absorbance appeared at 472 nm (Ka=9,340 M"1). Addition of K+ to the solution of 65-F" caused a reverse behavior and the solution turned colorless. This implied that the color change was controlled by F switches on and K+ switches off . This result was... 

We also prepared an acyclic mixed-ruthenium(II) bpy-ferrocene receptor 135 (257). The emission of the ruthenium center in the free receptor is quenched by the ferrocene units. However, on addition of dihydrogen phosphate anion the emission increases 20-fold, being switched on by the presence of the anion... 

Beer and co-workers have devised a system that can simultaneously detect two different cations. In the presence of and Ba + in CH3CN solution, the ditopic aza-crown receptor 10 produces three new peaks in the voltammo-gram. These correspond to the 10 2Ba +, 10 2Mg +, and 10 Ba +Mg + complexes with anodic shifts (compared to 10 alone) of 150, 395, and 275 mV, respectively. Ferrocene receptor 11, of Martinez-Manez and co-workers, is monofunctionalized with a smaller aza-oxa crown. In this case the binding unit is Hg selective. Electrochemical results in CH3CN solution show that at pH 5 the receptor is selective for Hg over Pb +, Cu +, Cd +, or... 

The novel series of ferrocene receptors 64-68, which incorporate thiobar-biturate anion binding/chromophore groups, have been shown to operate as UV-vis anion sensors in acetonitrile solution. Addition of basic anions such as cyanide, acetate and benzoate causes the attenuation of the absorption maximum at around 440 nm (due to a charge transfer transition between the amine and the thiobarbiturate group), with the simultaneous occurrence of a new band at 370 nm. In cases where the titration data could be fitted, 1 2 receptor anion binding stoichiometries were found [47]. 

Fig. 2 Ferrocene receptors for transition metal and soft metal cations.

The boronic acid 20 reported by Shinkai is a rare example of an enantiopme chiral redox-active receptor." It was found to bind linear and cyclic sugars in aqueous solution at neutral pH due to the reversible reaction between the boronic acid moiety of the protonated ferrocene receptor and the sugar to form a boronate ester. Electrochemical studies revealed that complexation imparted cathodic (ca. - 50 mV) shifts in the Fc /Fc redox couple. Interestingly, moderate enantioselectivity was observed in that (+ ) — 1 bound the linear saccharide D-sorbitol more strongly than L-sorbitol (ATd/AIl = 1-4). However, differences in the electrochemical response to the binding of these enantiomers by 20 were not apparent. 

Collinson, S.R. Gelbrich, T. Hursthouse, M.B. Tucker, J.H.R. Novel ferrocene receptors for barbiturates and ureas. Chem. Commun. 2001, 555-556. 

An acyclic [Ru(bpy)3] -ferrocene receptor 25 was prepared (Fig. The ferrocene units quench the... 

Scheme 2 Binding of dicarboxylic acid to the ferrocene receptor 41...

The ferrocene 44 bearing only one tetrapeptide chain (-Gly-Gly-L-Tyr-L-Arg-OH) is designed to bind to papain [147]. The ferrocene 44 acts as an efficient competitive papain inhibitor for AT-benzoylarginine ethyl ester hydrolysis, with an inhibition constant Ki of 9 xM at pH 6.2. Binding of papain to the ferrocene receptor 44 causes an electrochemical response, resulting in a small cathodic shift of the redox potential of the ferrocene moiety of 44. 

Figure 1 Ferrocene receptors for s-block metal cations.

Figure 2 Ferrocene receptors for d-block metal cations.

Figure 4 Ferrocene receptors for neutral molecules and charge-neutral species.

Scheme 3 Chiral sensing of (/ )- and (5)-Binol by ferrocene receptor 27.

Figure 9.8.1. The principle of bonding of a difunctional molecule to the ferrocene receptor. The active conformation of the receptor is induced by the substrate (reproduced by permission from the Wiley-VCH, STM-Copyright Licenses).

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