No abstract

ABSTRACT:A rare discrete mixed-valent heterometallic Fe(III)/Cu(II) cage, [Cu 6 Fe 8 L 8 ](ClO4)12·χsolvent (H 3 L = tris{[2-{(imidazole-4-yl)methylidene}amino]ethyl}amine), was designed and synthesized via metal-ion directed selfassembly with neutral tripodal metalloligands. The formation of this coordination cage was demonstrated by Xray crystallography, ESI mass spectrometry, FT-IR and UV-vis-NIR spectroscopy.The self-assembly of coordination cages has continued to receive considerable attention over the past decade, 1 because of their many potential applications in gas adsorption, 2 drug delivery, 3 catalysis, 4 magnetic materials, 5 host-guest phenomena 6 and synthetic membranes for ion channels. 7 Although a number of coordination cage types have been developed, the design and successful construction of these systems, particularly those with heteronuclear coordination motifs, still represents a significant challenge. 5d,5e,8 Three synthetic procedures have been successfully exploited for the construction of discrete heteronuclear coordination architectures: 1) exploitation of the inherent coordination properties between ligands and different metal ions for the metal-directed assembly of discrete metallosupramolecular architectures; 9 2) formation of discrete metallo-assemblies preorganised for binding a second metal ion, or ions, to yield discrete heterometallic architectures; 10 3) employing preformed metalloligands functionalised for use as building blocks reacting with additional metal ions and sometimes extra ligands. 2b,5c,5e,8b,11 In a recent review, 12 we discussed the employment of planar di-, tri-and oligonuclear platforms, including both homo-and heteronuclear systems, as structural elements for the formation of both discrete and polymeric metallosupramolecular assemblies. As part of our continuing efforts to prepare heterometallic coordination architectures, we reported the synthesis of predesigned hexanuclear Cu II /Ni II metallocycles featuring unprecedented six-node metallocoronand structural motifs 10b and the preparation of a discrete heteronuclear metallomacrocycle (Ag I 3 /Fe II ) by metalion directed self-assembly via a Fe II template. 10aHerein we report an extension of the above studies leading to the construction of a new discrete coordination heterometallic nanocage 1 [Cu 6 Fe 8 L 8 ] (ClO4)12·χsolvent (H 3 L = tris{[2-{(imidazole-4-yl)methylidene}amino]ethyl}amine) enclosing a void space of 277Å 3 . 13 Thus, we have employed a suitable metalloligand together with an additional metal ion (Cu II ) that was anticipated to favour structure-specific selfassembly. A key feature of our design was to employ short organic components that would bridge the different metal ions in a way that would give the potential for magnetic exchange between metal centers. In addition, we have employed a cooperative effect to build a robust metalloligand which can react with additional metal ions to yield a heterometallic cage. To this end we demonstrated that a heterometallic polyhedral cage can be ...

Concave hydrocarbons, such as 1 (C36H36), 4 5 (C54H48), and 6 (C,,H 52), represent three-dimensionally clamped analogues of x-prismands. They encapsulate small metal ions and accomplish metal-ion extraction from aqueous solution. Their remarkable selectivity allows applications such as incorporation in ion-selective electrodes. The synthetic route is based on well-established cyclophane methodology and, thus, offers a general approach to a whole family of concave hydrocarbons.

Neutral dimeric metallocyclic complexes of type [M 2 (L 1 ) 2 B n ] (where M = cobalt(II), nickel(II) and zinc(II), L 1 is the doubly deprotonated form of a 1,3-aryl linked bis-b-diketone ligand of type 1,3-bis(RC(O)CH 2 C(O))C 6 H 4 (R = Me, n-Pr, t-Bu) and B is pyridine (Py) or 4-ethylpyridine (EtPy)) have been synthesised, adding to similar complexes already reported for copper(II). New lipophilic ligand derivatives with R = octyl or nonyl were also prepared for use in solvent extraction experiments. Structural, electrochemical and solvent extraction investigations of selected metal complex systems from the above series are reported, with the X-ray ] has been examined. Oxidative processes for the complexes are dominantly irreversible, but several examples of quasireversible behaviour were observed and support the assignment of an anodic process, seen between +1.0 and +1.6 V, as a metal-centred oxidation. The reduction processes for the respective metal complexes are not simple, and irreversible in most cases. Solvent extraction studies (water/chloroform) involving variable concentrations of metal, bis-b-diketone and heterocyclic base have been performed for cobalt(II) and zinc(II) using a radiotracer technique to probe the stoichiometries of the extracted species in each case. Synergism was observed when 4-ethylpyridine was added to the bis-b-diketone ligand in the chloroform phase. Competitive extraction studies show a clear uptake preference for copper(II) over cobalt(II), nickel(II), zinc(II) and cadmium(II).

No abstract

The structure of [4-(phenylazo)phenoxy]hexane-1-thiol (AzoC 6 ) self-assembled monolayers (SAMs) on Au(111) has been investigated with scanning tunneling microscopy (STM) and Fourier transform infraredreflection absorption spectroscopy (FTIR-RAS). The FTIR-RAS results yield a tilt angle of the molecules close to 0°, which significantly differs from the 30°tilt angle of linear n-alkanethiols. In STM images two types of domains are observed that have equal unit cell dimensions and two molecules per unit cell but show different tunneling contrasts, which is attributed to a different arrangement of the molecules within the unit cell. The relationship of the molecular lattice to the substrate lattice is found to be commensurate.

Although the Maillard reaction between proteins and carbohydrates is of central importance for food processing and in vivo processes, only little is known about changes of the metal-binding properties induced by protein glycation. The purpose of this study was to examine the complex formation of the quantitatively important peptide-bound Maillard reaction products (MRPs) N(epsilon)-fructoselysine and N(epsilon)-carboxymethyllysine with the biologically relevant metal ions copper(II) and zinc(II). The MRPs were synthesized as the N(alpha)-hippuryllysine derivatives in order to block the coordination function of the alpha-amino group. Stability constant measurements were performed in aqueous solution using pH potentiometry. N(alpha)-Hippuryl-N(epsilon)-fructoselysine forms moderate Cu(II) complexes (Log(10) K(1) = 5.8; Log(10) K(2) = 4.0) but fails to form any complexes with Zn(II). N(alpha)-Hippuryl-N(epsilon)-carboxymethyllysine gives slightly stronger complexes with Cu(II) (Log(10) K(1) = 7.3; Log(10) K(2) = 6.3), but again no complexation with Zn(II) was observed. These results show that post-translational modification of proteins by carbohydrates leads to the formation of new coordination centers for metal ions within a protein chain. Further studies are necessary to clarify the consequences of this phenomenon in terms of protein quality and physiological processes.

A novel molecular host 5 for amino acid zwitterions is described. The covalent connection of a chiral bicyclic guanidinium salt as an anchor function for the carboxylate and a triaza-crown ether as an ammonium binding moiety in combination with a strongly hydrophobic silyl ether serves to complex and transfer amino acids from water into dichloromethane with unprecedented efficiency. Quantitation of the extraction process by radiometry revealed a clean 1:1 stoichiometry and gives evidence for the zwitterion as the species undergoing phase transfer. Even small hydrophilic (Ser, Gly) but no charged amino acids were extracted better by factors up to 3000-fold than by a previously reported host of similar design (Galán, A.; Andreu, D.; Echavarren, A. M.; Prados, P.; de Mendoza, J. J. Am. Chem. Soc. 1992, 114, 1511−1512). Some enantioselection in the transfer of phenylalanine was observed (40% ee).