Strong Uranium(VI) Binding onto Bovine Milk Proteins, Selected Protein Sequences, and Model Peptides.

Hexavalent uranium is ubiquitous in the environment. In view of the chemical and radiochemical toxicity of uranium(VI), a good knowledge of its possible interactions in the environment is crucial. The aim of this work was to identify typical binding and sorption characteristics of uranium(VI) with both the pure bovine milk protein ß-casein and diverse related protein mixtures (caseins, whey proteins). For comparison, selected model peptides representing the amino acid sequence 13-16 of ß-casein and dephosphorylated ß-casein were also studied. Complexation studies using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy revealed that the phosphoryl-containing proteins form uranium(VI) complexes of higher stability than the structure-analog phosphoryl-free proteins. That is in agreement with the sorption experiments showing a significantly higher affinity of caseins toward uranium(VI) in comparison to whey proteins. On the other hand, the total sorption capacity of caseins is lower than that of whey proteins. The discussed binding behavior of milk proteins to uranium(VI) might open up interesting perspectives for sustainable techniques of uranium(VI) removal from aqueous solutions. This was further demonstrated by batch experiments on the removal of uranium(VI) from mineral water samples.

Self-assembly of an imidazolate-bridged Fe(III)/Cu(II) heterometallic cage.

A rare, discrete, mixed-valent, heterometallic Fe(III)/Cu(II) cage, [Cu6Fe8L8](ClO4)12·χsolvent (H3L = tris{[2-{(imidazole-4-yl)methylidene}amino]ethyl}amine), was designed and synthesized via metal-ion-directed self-assembly with neutral tripodal metalloligands. The formation of this coordination cage was demonstrated by X-ray crystallography, ESI mass spectrometry, FT-IR, and UV-vis-NIR spectroscopy.

Molecular structure, UV/vis spectra, and cyclic voltammograms of Mn(II), Co(II), and Zn(II) 5,10,15,20-tetraphenyl-21-oxaporphyrins.

The 5,10,15,20-tetraphenyl-21-oxaporphyrin complexes of Mn(II), Co(II), and Zn(II) have been crystallized and studied by X-ray diffraction, NMR and UV/vis spectroscopy, and mass spectrometry as well as cyclic voltammetry. The X-ray structure of the earlier described Cu(II) complex is also reported. All complex structures possess a five-coordinate, approximately square-pyramidal geometry with a slight deviation of the heteroaromatic moieties from planarity. The packing structures are characterized by parallel strands of complex molecules interacting by weak hydrogen bonds. In the case of Zn(II) an octahedral complex has also been isolated using a side-chain hydroxy functionalized oxaporphyrin ligand; the structure was verified by NMR and EXAFS spectroscopy. Cyclic voltammetry studies reveal that the reduction of the complex bound Mn(II), Co(II), and Zn(II) ions is a ligand-centered process whereas the first oxidation step depends on the metal ion present.

Complexation, computational, magnetic, and structural studies of the Maillard reaction product isomaltol including investigation of an uncommon π interaction with copper(II).

The metal complexation properties of the naturally occurring Maillard reaction product isomaltol HL(2) are investigated by measurement of its stability constants with copper(II), zinc(II), and iron(III) using potentiometric pH titrations in water, by structural and magnetic characterization of its crystalline complex, [Cu(L(2))(2)]·8H(2)O, and by density functional theory calculations. Strong complexation is observed to form the bis(isomaltolato)copper(II) complex incorporating copper in a typical (pseudo-)square-planar geometry. In the solid state, extensive intra- and intermolecular hydrogen bonding involving all three oxygen functions per ligand assembles the complexes into ribbons that interact to form two-dimensional arrays; further hydrogen bonds and π interactions between the furan moiety of the anionic ligands and adjacent copper(II) centers connect the complexes in the third dimension, leading to a compact polymeric three-dimensional (3D) arrangement. The latter interactions involving copper(II), which represent an underappreciated aspect of copper(II) chemistry, are compared to similar interactions present in other copper(II) 3D structures showing interactions with benzene molecules; the results indicate that dispersion forces dominate in the π system to chelated copper(II) ion interactions.

Interaction of mixed-donor macrocycles containing the 1,10-phenanthroline subunit with selected transition and post-transition metal ions: metal ion recognition in competitive liquid-liquid solvent extraction of Cu(II), Zn(II), Pb(II), Cd(II), Ag(I), and Hg(II).

Two new mixed aza-thia crowns 5-aza-2,8-dithia[9]-(2,9)-1,10-phenanthrolinophane (L(4)) and 2,8-diaza-5-thia[9]-(2,9)-1,10-phenanthrolinophane (L(7)) have been synthesized and characterized. The coordination behavior of L(4) and L(7) toward the metal ions Cu(II), Zn(II), Pb(II), Cd(II), Hg(II), and Ag(I) was studied in aqueous solution by potentiometric methods, in CD3CN/D2O 4:1 (v/v) by (1)H NMR titrations and in the solid state. The data obtained were compared with those available for the coordination behavior toward the same metal ions of structurally analogous mixed donor macrocyclic ligands L(1)-L(3), L(5), L(6): all these contain a phenanthroline subunit but have only S/O/N(aromatic) donor groups in the remaining portion of the ring and are, therefore, less water-soluble than L(4) and L(7). The complexes [Cd(NO3)2(L(5))], [Pb(L(7))](ClO4)2 x 1/2MeCN, [Pb(L(4))](ClO4)2 x MeCN, and [Cu(L(7))](ClO4)2 x 3/2MeNO2 were characterized by X-ray crystallography. The efficacy of L(1)-L(7) in competitive liquid-liquid metal ion extraction of Cu(II), Zn(II), Cd(II), Pb(II), Ag(I), and Hg(II) was assessed. In the absence of Hg(II), a clear extraction selectivity for Ag(I) was observed in all systems investigated.

Metal complexation by the peptide-bound maillard reaction products N(epsilon)-fructoselysine and N(epsilon)-carboxymethyllysine.

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.

Bis(triethanolamine-O,O')nickel(II) diacetate.

The title compound, [Ni{N(CH(2)CH(2)OH)(3)}(2)](CH(3)COO)(2), was prepared and the structure determined. It is isostructural with the copper(II) analogue.

Self-assembly of neutral hexanuclear circular copper(II) meso-helicates: topological control by sulfate ions.

Bis-pyridylimine ligands with different linking elements are capable of forming unique hexanuclear circular Cu(II) meso-helicates; the self-assembly is controlled by coordination of sulfate ions to the metal centres.

Interaction of an extended series of N-substituted di(2-picolyl)amine derivatives with copper(II). Synthetic, structural, magnetic and solution studies.

The interaction of Cu(II) with the following secondary N-substituted derivatives of di(2-picolyl)amine () are reported: N-cyclohexylmethyl-di(2-picolyl)amine (), N-benzyl-di(2-picolyl)amine (), N-(4-pyridylmethyl)-di(2-picolyl)amine (), N-(4-carboxymethylbenzyl)-di(2-picolyl)amine (), N-(9-anthracen-8-ylmethyl)-di(2-picolyl)amine (), 1,3-bis[di(2-picolyl)aminomethyl]benzene (), 1,4-bis[di(2-picolyl)aminomethyl]benzene () and 2,4,6-tris[di(2-picolyl)amino]triazine (). The solid complexes [Cu()(micro-Cl)](2)(PF(6))(2), [Cu()(micro-Cl)](2)(PF(6))(2).0.5CH(2)Cl(2), Cu()(ClO(4))(2), Cu()(2)(ClO(4))(2), [Cu()(ClO(4))(2)(H(2)O)].0.5H(2)O, Cu(2)()(ClO(4))(4), [Cu(2)()(Cl)(4)] and [Cu(2)(+H)(micro-OCH(3))(2)(H(2)O)](ClO(4))(3).C(4)H(10)O were isolated and X-ray structures of [Cu()(micro-Cl)](2)(PF(6))(2), [Cu()(micro-Cl)](2)(PF(6))(2).0.5CH(2)Cl(2,) [Cu()(2)(ClO(4))(2)(H(2)O)].0.5H(2)O, [Cu(2)()Cl(4)] and [Cu(2)(+H)(micro-OCH(3))(2)(H(2)O)](ClO(4))(3).C(4)H(10)O were obtained. The series is characterised by a varied range of coordination geometries and lattice architectures which in the case of [Cu()(ClO(4))(2)(H(2)O)].0.5H(2)O includes a chain-like structure formed by unusual intermolecular pi-interactions between metal bound perchlorate anions and the aromatic rings of adjacent anthracenyl groups. Variable temperature magnetic susceptibility measurements have been performed for [Cu()(micro-Cl)](2)(PF(6))(2) and [Cu()(micro-Cl)](2)(PF(6))(2).0.5H(2)O over the range 2-300 K. Both compounds show Curie-Weiss behaviour, with the data indicating weak antiferromagnetic interaction between the pairs of copper ions in each complex. Liquid-liquid (H(2)O/CHCl(3)) extraction experiments involving and as extractants showed that, relative to the parent (unsubstituted) dipic ligand , substitution at the secondary amine site in each case resulted in an increase in extraction efficiency towards Cu(II) (as its perchlorate salt); at least in part, this increase may be attributed to the enhanced lipophilicities of the N-substituted derivatives.

Assembly of a trinuclear metallo-capsule from a tripodal tris(beta-diketone) derivative and copper(II).

A new metallo-capsule has been synthesised that consists of three copper(II) ions and two molecules of a tris-deprotonated tripodal ligand in which three 2,4-pentanedione groups are linked via their gamma-carbons through thioether spacers to the 1,3,5-positions of a triazine core.

Synthetic, structural, electrochemical and solvent extraction studies of neutral trinuclear Co(II), Ni(II), Cu(II) and Zn(II) metallocycles and tetrahedral tetranuclear Fe(III) species incorporating 1,4-aryl-linked bis-beta-diketonato ligands.

Uncharged complexes, formulated as trimeric metallocycles of type [M3(L(1))3(Py)6] (where M = cobalt(II), nickel(II) and zinc(II) and L(1) is the doubly deprotonated form of a 1,4-phenylene linked bis-beta-diketone ligand of type 1,4-bis(RC(O)CH2C(O))C6H4 (R = t-Bu)) have been synthesised, adding to related, previously reported complexes of these metals with L(1) (R = Ph) and copper(ii) with L(1) (R = Me, Et, Pr, t-Bu, Ph). New lipophilic ligand derivatives with R = hexyl, octyl or nonyl were also prepared for use in solvent extraction experiments. The X-ray structures of H2L(1) (R = t-Bu) and of its trinuclear (triangular) nickel(II) complex [Ni3(L(1))3(Py)6].3.5Py (R = t-Bu) are also presented. Electrochemical studies of H2L(1), [Co3(L(1))3(Py)6], [Ni3(L(1))3(Py)6], [Cu3(L(1))3], [Zn3(L(1))3(Py)6] and [Fe4(L(1))6] (all with R = t-Bu) show that oxidative processes for the complexes are predominantly irreversible, but several examples of quasireversible behaviour also occur and support the assignment of an anodic process, seen between +1.0 and +1.6 V, as involving metal-centred oxidations. The reduction behaviour for the respective metal complexes is not simple, being irreversible in most cases. Solvent extraction studies (water/chloroform) involving the systematic variation of the metal, bis-beta-diketone and heterocyclic base concentrations have been performed for cobalt(II) and zinc(II) using a radiotracer technique in order to probe the stoichiometries of the respective extracted species. Significant extraction synergism was observed when 4-ethylpyridine was also present with the bis-beta-diketone ligand in the chloroform phase. Competitive extraction studies demonstrated a clear uptake preference for copper(II) over cobalt(II), nickel(II), zinc(II) and cadmium(II).

Hydration behavior of alkyl amines and their corresponding protonated forms. 1. Ammonia and methylamine.

The structure and dynamics of hydration of ammonia/ammonium and methylamine/methylammonium systems have been studied by Car-Parrinello molecular dynamics simulation. While methylamine interacts weakly with the aqueous environment, the interaction of ammonia is found to be much stronger than expected. Both protonated species show a highly structured first solvation sphere. The solvent exchange mechanisms for all species were also investigated, along with the geometry of the hydration spheres. Comparison of these exchange mechanisms with that published for the ammonium ion shows only a minor difference. Analysis of the respective distribution functions has allowed insight into the thermodynamics of solvation for both systems. The calculated pKa values (9.23/10.65) correspond very closely with the published experimental values of 9.25 and 10.65.

Neutral (bis-beta-diketonato) iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) metallocycles: structural, electrochemical and solvent extraction studies.

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-beta-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 structures of [Co(2)(L(1))(2)(Py)(4)] x 2.25CHCl(3) x 0.5H(2)O (R=Pr), [Co(2)(L(1))(2)(EtPy)(4)] (R=t-Bu), [Ni(2)(L(1))(2)(EtPy)(4)] (R=t-Bu), [Zn(2)(L(1))(2)(EtPy)(2)] (R=Me) and [Zn(2)(L(1))(2)(EtPy)(4)] (R=t-Bu) being presented. The electrochemistry of H(2)L(1) (R=t-Bu) and of [Fe(2)(L(1))(3)], [Co(2)(L(1))(2)(Py)(4)], [Ni(2)(L(1))(2)(Py)(4)], [Cu(2)(L(1))(2)] and [Zn(2)(L(1))(2)(Py)(2)] 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-beta-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-beta-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).

Silver(I) complexation of linked 2,2'-dipyridylamine derivatives. Synthetic, solvent extraction, membrane transport and X-ray structural studies.

Synthesis of the 2,2'-dipyridylamine derivatives di-2-pyridylaminomethylbenzene 1, 1,2-bis(di-2-pyridylaminomethyl)benzene 2, 1,3-bis(di-2-pyridylaminomethyl)benzene 3, 2,6-bis(di-2-pyridylaminomethyl)pyridine 4, 1,4-bis(di-2-pyridylaminomethyl)benzene 5, and 1,3,5-tris(di-2-pyridylaminomethyl)benzene 6 are reported together with the single-crystal X-ray structures of 2, 3, and 5. Reaction of individual salts of the type AgX (where X = NO(3)(-), PF(6)(-), ClO(4)(-), or BF(4)(-)) with the above ligands has led to the isolation of thirteen Ag(I) complexes, nine of which have also been characterised by X-ray diffraction. In part, the inherent flexibility of the respective ligands has resulted in the adoption of a range of coordination arrangements. A series of liquid-liquid (H(2)O/CHCl(3)) extraction experiments of Ag(I) with varying concentrations of 1-6 in the organic phase have been undertaken, with the counter ion in the aqueous phase being respectively picrate, perchlorate and nitrate. In general, extraction efficiencies for a given ionophore followed the Hofmeister order of picrate > perchlorate > nitrate; in each case the tris-dpa derivative 6 acting as the most efficient extractant of the six systems investigated. Competitive seven-metal bulk membrane transport experiments (H(2)O/CHCl(3)/H(2)O) employing the above ligands as the ionophore in the organic phase and equimolar concentrations of Co(II), Ni(II), Zn(II), Cu(II), Cd(II), Pb(II) and Ag(I) in the aqueous source phase were also undertaken, with transport occurring against a pH gradient. Under the conditions employed 1 and 5 yielded negligible transport of any of the metals present in the source phase while sole transport selectivity for Ag(I) was observed for 2-4 and 6.

New discrete and polymeric supramolecular architectures derived from dinuclear (bis-beta-diketonato)copper(II) metallocycles.

New examples of adducts between di- (and, in one instance, tetra-) functional nitrogen ligands and planar 'platform-like' dinuclear copper(II) complexes, [Cu2L2], incorporating the 1,3-aryl linked bis-beta-diketonato bridging ligand 1,1'-(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione) (H2L) have been synthesised. The X-ray structures of six adduct species are reported. The interaction of [Cu2(L)2] with the ditopic ligand aminopyrazine (apyz) yielded the sandwich-like tetranuclear species [(Cu2L2(apyz))2]. A variable-temperature magnetochemical investigation of this product indicated weak antiferromagnetic coupling between the (five-coordinate) copper centres, mediated by the 2-aminopyrazine linkers. An analogous structure, [(Cu2L2(dabco))2] (dabco=1,4-diazabicyclo[2.2.2]octane), was generated when dabco was substituted for aminopyrazine while use of 4,4'-dipyridyl sulfide (dps) and 4,4'-(1,3-xylylene)-bis(3,5-dimethylpyrazole) (xbp) as the ditopic 'spacer' ligands resulted in polymeric species of type [Cu2L2(dps)]n and [Cu2L2(xbp)]n, respectively. These latter species exist as one-dimensional chain structures in which copper(II) centres on different dinuclear platforms are linked in a 'zigzag' fashion. In contrast, with 2,2'-dipyridylamine (dpa) a discrete complex of type [Cu2L2(dpa)2] formed in which one potential pyridyl donor from each 2,2'-dipyridylamine ligand remains uncoordinated. The use of the potentially quadruply-bridging hexamethylenetetramine (hmt) ligand as the linker unit was found to give rise to an unusual two-dimensional polymeric motif of type [(Cu2(L2)2)3(hmt)2]n. The product takes the form of a (6,3) network, incorporating triply bridging hexamethylenetetramine units.

Assembly of a tri-silver metallo-capsule incorporating a tripodal tris-pyridyl ligand.

A trinuclear metallo-capsule has been assembled from a new tripodal pyridyl ligand and three silver(I) ions; the X-ray structure shows the presence of a Ag-Ag interaction in the solid state giving rise to a non-symmetric capsule arrangement while NMR evidence indicates that the structure in solution is symmetrical.

Host-guest assembly of ligand systems for metal ion complexation. Synergistic solvent extraction of copper(II) and silver(I) by 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclodecane in combination with carboxylic acids.

Host-guest formation between 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclodecane (1) and lipophilic organic carboxylic acids in chloroform has been investigated and the effect of such ligand assembly on the solvent extraction of copper(II) and silver(I) has been probed. NMR titration experiments in the absence of a metal ion confirm the formation of weak 1:1 and 1:2 (macrocycle:carboxylic acid) assemblies in CDCl(3) between 1 and palmitic (hexadecanoic) acid or 4-tert-butylbenzoic acid while difunctional salicylic acid showed a 1 [ratio] 2 interaction that is somewhat stronger. The interaction between the former two acids and the tetra-N-benzylated macrocycle is significantly less than that reported previously for its non-substituted parent, cyclam; a result that likely reflects the presence of the less-basic, more sterically hindered tertiary nitrogens in 1 relative to the secondary nitrogens present in cyclam. Carboxylic acid-containing assemblies of this type have been used as extractants in a series of solvent extraction (water/chloroform) experiments. From both previous observations as well as from entropy considerations, it was anticipated that the use of a host-guest assembly of the above type for metal-ion complexation might contribute to enhanced metal ion binding (and concomitant enhanced metal ion extraction). Such behaviour is postulated to arise from the components of the coordination sphere being, at least in part, assembled for complex formation. In accord with this, the use of the ligand assembly involving palmitic acid/macrocycle 1 was found to lead to enhanced (synergistic) extraction of copper(II) at a metal ion concentration of 10(-3) mol dm(-3) while, for silver(I), synergism was somewhat marginal at this concentration but was clearly apparent under related conditions when the silver concentration was reduced to 10(-4) mol dm(-3). Similar behaviour towards silver was also observed when 4-tert-butylbenzoic acid was substituted for palmitic acid, while the use of salicylic acid resulted in enhanced (synergistic) extraction at both metal ion concentrations.

A new cryptophane receptor featuring three endo-carboxylic acid groups: synthesis, host behavior and structural study.

Examples of a new type of cryptophane molecule incorporating aromatic groups in the bridges (1-4) and, for the first time, being also supplied with three endo-positional ionizable carboxylic acid functions (1) have been synthesized and characterized. The cryptophane triester 2 yielded a solvate (channel inclusion compound) with trichloromethane and water, the X-ray crystal structure of which is reported. The complexation of 1 with low-molecular-weight alcohols in solution was studied, and the liquid-liquid extraction of different metal ions including alkali (Na(+), Cs(+)), alkaline earth (Mg(2+), Ca(2+), Sr(2+), Ba(2+)), and the lanthanide metal ions Eu(3+) and Yb(3+) in an extraction system containing metal nitrate buffer/H(2)O/1/CHCl(3) was examined. Molecular modeling calculations of the cryptophanes 1 and 2, and of the Eu(3+) complex of 1 were carried out contributing to the discussion.

Macrocyclic ligand design. Structure-function relationships involving the interaction of pyridinyl-containing, oxygen-nitrogen donor macrocycles with selected transition and post transition metal ions on progressive N-benzylation of their secondary amines.

Structure-function relationships underlying the interaction of progressively N-benzylated N(4)O(2)-donor macrocycles with cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) have been probed using a range of techniques that include X-ray diffraction, DFT computations, solvent extraction, potentiometric stability constant determinations and competitive membrane transport experiments. Collectively, the results indicate that N-benzylation of the secondary amine donor groups of the parent macrocyclic ring results in an enhanced tendency towards selectivity for silver(I) relative to the other six metals investigated. The observed behaviour serves as additional exemplification of the previously proposed concept of selective 'detuning' as a mechanism for metal ion discrimination.

Metal ion recognition via 'selective detuning'. The interaction of selected transition and post-transition metal ions with a mono-N-benzylated O2N3-donor macrocycle and its xylyl-bridged ring analogue.

The interaction of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) with symmetrical mono-N-benzylated and xylyl-linked macrocyclic ligands derived from the O2N3-macrocycle, 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane, has been investigated. The log K values for the respective 1 : 1 complexes in 95% methanol (I= 0.1; Et4NClO4, 25 degrees C) of the mono-benzylated derivative have been determined potentiometrically and the results compared with the values obtained previously for the parent (non-benzylated) ring system as well as for related di- and tri-benzylated macrocyclic species. Mono-benzylation results in slightly enhanced stability for the 1 : 1 silver(I) complex while the values for the corresponding complexes of the other six ions are in each case decreased even though the highest stability is still maintained for the 1 : 1 copper(II) complex. The log K results are in accord with a previous proposal that N-benzylation of amine-containing macrocyclic rings of the present type will normally have only a minor (positive or negative) influence on the affinity towards silver(I) while the corresponding binding strengths towards the remaining six metal ions are significantly reduced-behaviour we term 'selective detuning'. Competitive seven-metal transport experiments across a bulk chloroform membrane have been performed using both ligand systems as ionophores. In parallel to the log K results, transport selectivity for copper(II) was exhibited by both systems, with similar transport efficiencies being evident when compared on a 'per macrocyclic cavity' basis.