Polyammonium macrocycles

Figure 11 Stability constants for complexes of polyammonium macrocycles with dicarboxylate substrates 02C(CH2)m-C02-. a = [24]N6 6HC1 (72a) O = [32]N6 6HC1 (72b) - [38]N6 6HC1 (72c)...

Polyammonium macrocycles and macropolycycles have been studied most extensively as anion receptor molecules. They bind a variety of anionic species (inorganic anions, carboxylates, phosphates, etc.) with stabilities and selectivities resulting from both electrostatic and structural effects. 

The electrochemical properties of redox-active substrates are also affected on binding to a receptor molecule. This is the case for the complexation of metal hexacyanides by polyammonium macrocycles where the shift of the redox potential depends on the binding constants and the oxidation or reduction of the substrates leads to pronounced changes in stability (see Chapter 3) [3.21, 3.22]. 

Hosseini, M. W., Lehn, J. M., Anion coreceptor molecules - linear molecular recognition in the selective binding of dicar-boxylate substrates by ditopic polyammonium macrocycles. Helv. Chlm. Acta 1986, 69, 587-603. 

Dietrich, B. Hosseini, M. W. Lehn, J.-M. Sessions, R. B. Anion receptor molecules. Synthesis and anion-binding properties of polyammonium macrocycles, J. Am. Chem. Soc. 1981,103, 1282-1283. 

Clifford, T. Danby, A. Llinares, J. M. Mason, S. Alcock, N. W. Powell, D. Aguilar, J. A. Garcia-Espana, E. K. Bowman-James, K. Anion binding with two polyammonium macrocycles of different dimensionality, Inorg. Chem. 2001, 40, 4710-4720. 

Oxaazamacrocycles are molecules with combined crown ether and amino group properties for example, in dependence on the size of macrocyclic ring and the position of heteroatoms stable complexes with various metals can be formed [32]. Furthermore, when protonated, these compounds are excellent anion binders. In fully protonated polyammonium macrocycles, the coulom-bic attractions and hydrogen bond formation play a dominant role in the anion complexation. The receptors (R,R)-5 and (S,S,S,S)-6 were designed to bind dicarboxylates [33]. 

A method for the preparation of thin films of Fe4[Ru(CN)6]3 ( ruthenium purple ) involving electrochemical reduction of K3[Ru(CN)6] in a solution of Fe2(S04)3 has been developed.28 This ruthenium purple modified electrode is claimed to be one of the best catalysts for evolution of oxygen and chlorine. Electrochemical studies on polyammonium macrocyclic complexes of [Ru(CN)6]4 indicate a 1 1 stoichiometry with a monoelectronic, reversible, oxidation for these complexes this illustrates the control of redox potential of anions by complexation with appropriate receptor molecules.29 The kinetics of oxidation of [Ru(CN)6]4 by [Mn04] in HC104 have been investigated by stopped-flow techniques. It is found that [Ru(CN)6]4" is quantitatively oxidized to [Ru(CN)6]3 in accordance with equation (1) and that two protonated intermediates [RuH(CN)6]3 and [RuH2(CN)6]3 are involved in the oxidation process.30... 

The results of studies for complexes formed between polyammonium macrocycles and transition metal complex anions indicate that cation anion electrostatic attraction is a crucial factor in complexation reactions and serves to regulate the stoichiometry of the complexes formed. Hydrogenbonding, size, and conformational factors also play major roles. Anions can be incorporated in or out of the ring. Two illustrative examples are metal ion complexes with the octaprotonated macrocycle Hg[30]aneNio (46). In the complex with Co(CN)6 , the anion hes outside the macrocycle. The PdCLi complex is a true inclusion situation, however, in which the PdCU is situated along the minor axis of the macrocychc cavity, and the Cl atoms are out of the frame, forming strong hydrogen bonds with the polyammonium... 

Polyaza macrocycles in their protonated form, either full or partial, are able to interact with anionic species, by establishing noncovalent interactions (both electrostatic and hydrogen bonding). Complexation of anions by synthetic polyammonium molecules has been explored over the past two decades, and several examples of selective recognition of different anionic substrates have been reported [14 22], Some polyammonium macrocycles such as [24]aneN6H6 +, 16, and... 

Supercoordination by the polyammonium macrocycle has a thermodynamic effect, as it induces an anodic shift of the Fe /Fe potential it has also a kinetic effect on the photoinduced process, through the formation of the ion-pair with iodide. 

NO3 (nitrate), polyammonium macrocycles [24]Ng02 and [18]N402 Papoyan 1996 Nucleic acids (united-atom) MacKerell 1995 Ornithine, DMSO Mihailescu 1999 Peptides, proteins Momany 1993 Peptide nucleic acids (PNA)... 

Co(CN)g] at 50,600cm has been assigned to a photochemical reactivity of [Co(CN) ] is reported to be controlled by association with polyammonium macrocyclic receptors. Published data suggest that it is... 

Many of the most successful enzyme mimics have involved functionalised cyclodextrins, and the work of Breslow in particular is familiar to anyone who has followed the field. [24] These hosts bind aromatic rings within a hydrophobic cavity. In another seminal contribution Lehn [25,26] has used polyammonium macrocycles to catalyse phosphate transfer reactions of ATP, demonstrating that multiple hydrogen-bonds can also be an effective source of binding between flexible systems in aqueous solution. 

Catalysis can be broken down into a number of areas, depending on the substrate and the catalytic reaction. One of the prime areas of the initial effort in catalysis has been small molecule activation, such as oxygen with a number of transition metal ion macrocycles and carbon dioxide, the latter particularly with cobalt(I) and nickel (I) macrocycles. " Once the polyammonium macrocycles were found to be able to recognize substrates other than metal ions, other catalysis applications evolved. For example, phosphoryl transfer catalysis with simple polyammonium macrocycles has become quite accessible. ... 

Papoyan. G. Gu, K. Wibrkiewicz-Kuczera. J. Kuczera. K. Bowman-James. K. Molecular dynamics simulations of nitrate complexes with polyammonium macrocycles Insight on phosphoryl transfer catalysis. J. Am. Chem. Soc. 1996. 118. 1354- 1364. 

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