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We report the synthesis and characterization of the macrocyclic ligand 2,2'-((2-(3,9-bis(carboxymethyl)-3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-6-yl)ethyl)azanediyl)diacetic acid (H4L) and several of its complexes with lanthanide ions. The structure of the free ligand was determined using X-ray diffraction measurements. Two N atoms of the pyclen moiety in the trans position are protonated in the solid state, together with the exocyclic N atom and one of the carboxylate groups of the ligand. The relaxivity of the Gd3+ complex was found to increase from 6.7 mM-1 s-1 at pH 8.6 to 8.5 mM-1 s-1 below pH ≈ 6.0. Luminescence lifetime measurements recorded from H2O and D2O solutions of the Eu3+ complex evidence the presence of a single complex species in solution at low pH (∼5.0) that contains two inner-sphere water molecules. DFT calculations suggest that the coordination environment of the Ln3+ ion is fulfilled by the four N atoms of the pyclen unit, two oxygen atoms of the macrocyclic acetate groups, and an oxygen atom of an exocyclic carboxylate group. The two inner-sphere water molecules complete coordination number nine around the metal ion. At high pH (∼9.3), the lifetime of the excited 5D0 level of Eu3+ displays a biexponential behavior that can be attributed to the presence of two species in solution with hydration numbers of q = 0 and q = 1. The 1H NMR and DOSY spectra recorded from solutions of the Eu3+ and Y3+ complexes reveal a structural change triggered by pH and the formation of small aggregates at high pH values.

Three new [1 + 1] macrocycles formed by the reaction of 1H-3,5-bis(chloromethyl)pyrazole with the tosylated amines 1,4,7,10-tetraazadecane (L1), 1,4,8,11-tetraazaundecane (L2) and 1,5,10,14-tetraazatetradecane (L3) are described. Potentiometric studies and HR-ESI-Mass spectrometry show the formation of dimeric binuclear Cu2+ complexes whose organization depends on the type of hydrocarbon chains connecting the amine groups. Furthermore, trinuclear or/and tetranuclear complexes are formed depending also on the length of the polyaminic bridge and on the sequence of the hydrocarbon chains. The crystal structures of the [2 + 2] [Cu2(H(H−1L2))2](ClO4)4·4H2O (1) and [Cu2(H−1L2)2](ClO4)2 (2) complexes show in both of them two macrocycles self-assembled by the metal ions which interconnect their pyrazolate fragments that behave as bis(monodentate) ligands. While in 1 one central amine of each macrocycle binds to the axial position of a distorted square-pyramid and the other ones remain protonated, in 2 all the amine groups are involved in the coordination giving rise to a strongly distorted octahedral geometry. Paramagnetic 1H NMR measurements support that these structures also form in solution. Interestingly, tetranuclear complexes [Cu4(H−1L4)2(OH)2.08](ClO4)2.92Br0.54Cl0.46 (3) and [Pd2.39Cu1.61(H−1L4)2(OH)2](ClO4)2Cl1.33Br0.67·2.87H2O (4) have been isolated for the macrocycle containing the 1,5,9,13-tetraamine chain (L4). 3 has two binucleating units, one of them formed by the pyrazolate moieties and their neighbouring secondary amines and the other by the two central amines of both macrocycles. This latter Cu2+ coordination site is completed by two hydroxide anions as bridging ligands. 4 was obtained from a solution prepared to achieve full formation of the dimeric cage [Cu2(H−1(HL4))2]4+ by addition of K2PdCl4. The Pd2+ ion due to its softer acidic characteristics displaces the Cu2+ ions from the pyrazolate site. UV-vis spectroscopy suggests that the exchange is completed at room temperature after one hour.

The affinity and the binding mode of two benzo[g]phthalazine compounds, functionalized with one or two 2-(imidazole-4-yl)-ethylamine groups, to DNA and RNA models have been evaluated by means of UV-Vis, fluorescence and circular dichroism (CD) spectroscopies in combination with viscometry and molecular dynamics. Both organic molecules bind strongly to all nucleic acid models via the intercalation mode in the duplex structure, especially compound 1. Intriguingly, 1 exhibits different emission responses depending on the base composition of duplex DNA/RNAs, which points out the possibility of using it as a base selective nucleic acid probe. Moreover, the acid-base behaviour of both compounds has been studied by pH-metric titrations and UV-Vis and emission fluorescence techniques to investigate the unexplored basicity of this type of compound. 1 behaves as a triprotic base whilst 2 is a diprotic base with the protonation of the benzo[g]phthalazine moiety occurring in the physiological pH range., Financial support by the Spanish MINECO and FEDER funds from the European Union (Projects CONSOLIDER-INGENIO SUPRAMED CSD 2010-00065, CTQ2016-78499-C6-1-R and Unidad de Excelencia Marı´a de Maeztu MDM-15-0538) and Generalitat Valenciana (PROMETEO II 2015-002) is gratefully acknowledged. One of us, A. M.-C., wants to thank the Spanish Ministry of Science Culture and Sport for the PhD grant FPU14/05098. J. G.-G. is indebted to the University of Bordeaux for an IDex postdoctoral fellowship

Two binucleating hezaaza macrocycles containing a pyridinol spacer have been prepared and characterised. Protonation studies indicate the deprotonation of the phenol group at relatively low pH values with the concomitant occurrence of a keto-enolic equilibrium. These ligands readily form binuclear Cu2+ and Zn2+ complexes as denoted by potentiometric and spectroscopic studies. The binding of the metals yields to the ready deprotonation of the phenol with the stabilisation of the keto form that results in complexes of greater stabilities than the analogous ones containing pyridine as spacer instead of pyridine. Mixed Cu2+–Zn2+-complexes were also detected in aqueous solutions containing equimolar amounts of Cu2+, Zn2+ and ligands. The binuclear Cu2+ complexes show significant SOD activity as proved by the McCord–Fridovich assays. The binuclear Cu2+ complexes of the ligands grafted to boehmite nanoparticles (BNPs) show a remarkable increase in SOD activity, which reaches 8-fold in one of the systems. The observed increase can be ascribed to the positive ζ-potential of the BNPs since the same complexes anchored to silica nanoparticles with negative ζ-potential do not show any apparent increase in activity. This behaviour is reminiscent of the positively charged funnel found in CuZnSOD, which has the electroactive copper ion at its end.

Anion complexes of the cryptand built with the tripodal amine tris(2-aminoethyl)amine, known as tren, with water and several oxoanions of biological and environmental interest (nitrate, sulfate, phosphate, perchlorate and arsenate) have been crystallized from aqueous solution and resolved with single-crystal X-ray diffraction. All crystals show guest species encapsulated in the interior of the cavity as well as, in some cases, sitting in the grooves defined by the arms of the macrocycle. Hydrogen bonding and electrostatic interactions play a major role in anion binding to the host. The macrocycle is able to encapsulate anions in a wide range of protonation degrees. Solution studies have been carried out to show that those interactions happen also in solution in addition to the solid state. The results show that the receptor binds consistently to the ligand in a wide range protonation degrees., Financial support by the Spanish Ministerio de Economía y Competitividad (projects CTQ2016-78499-C6-1-R, Unidad de Excelencia MDM 2015-0038 and CTQ2017-90852-REDC) and Generalitat Valenciana (Project PROMETEOII2015-002) is gratefully acknowledged. S. B. thanks MINECO for a Juan de la Cierva postdoctoral grant.

A new tetraaza-pyridinophane macrocycle (L1) N-alkylated with two isopropyl and one methyl groups symmetrically disposed has been prepared and its behavior compared with those of the unsubstituted pyridinophane (L3) and the related compound with three methyl groups (L2). The protonation studies show that, first, a proton binds to the central methylated amine group of L1, while, second protonation leads to a reorganization of the protons that are at this stage attached to the lateral isopropylated amines. The X-ray structure of [HL1]+ agrees with the UV–vis and NMR studies as well as with the results of DFT calculations. The stability of the Cu2+ complexes decreases on increasing the bulkiness of the alkyl substituents of the amine groups. The crystal structures of [CuL1Cl](ClO4) and [CuL1(H2O)](ClO4)2·H2O show square pyramidal coordination geometries with the ligands disposed in a bent L-shaped conformation. Kinetic studies indicate that the rates of both complexation and ligand dissociation decrease with...

Polyiodide chemistry is among the first historically reported examples of supramolecular forces at work. To date, owing to the increasingly recognized role of halogen bonding and the incorporation of iodine-based components in several devices, it remains an active field of theoretical and applied research. Herein we re-examine azacyclophanes as a class of ligands for the stabilization of iodine-dense three-dimensional networks, showing how we devised novel possible strategies starting from literature material. The new set of azacyclophane ligands affords novel crystal structures possessing intriguing properties, which develop on a double layer. At a macroscopic level, the obtained networks possess a very high iodine packing density (less than 2 times more diluted than crystalline I2): a simple parameter, IN, is also introduced to quickly measure and compare iodine packing density in different crystals. On the microscopic level, the present study provides evidence about the ability of one of the ligands to act as a three-dimensional supramolecular mold for the template synthesis of the rarely observed heptaiodide (I7&minus, ) anion. Therefore, we believe our approach and strategy might be relevant for crystal engineering purposes.

The novel ligand H3L designed to spontaneously adsorb onto MWCNT via electron-deficient pyrimidine residues and bind metal cations is used to prepare an oxygen reduction reaction (ORR) cathode catalyst based on supported Pd(II) complexes. Herein we report the synthesis of the ligand, its solution behaviour (protonation constants, binding constants for the test cation Cu(II), UV evidence of Cu(II) and Pd(II) complexes formation) and ORR performances together with XPS and STEM characterization. Tripodal nature of the H3L ligand frame it in-between previously studied macrocyclic and linear open chain ligands, allowing to draw meaningful comparisons.

A cyclopeptide-based anion receptor containing alternating 6-aminopicolinic acid and substituted (4R)-4-aminoproline subunits with appended β-alanine residues binds sulfate anions in water. Importantly, appreciable sulfate binding is even observed in phosphate buffer, hence in the presence of anions of similar structure but with a different degree of protonation. The cause for the high selectivity of this receptor is related to the mode of action of the sulfate-binding protein.

The preparation, X-ray structure, and variable temperature magnetic study of the new compound {Ba(H2O)3/2[Cr(pyim)(C2O4)2]2}n·9/2nH2O (1) [pyim = 2-(2′-pyridyl)imidazole and C2O42− = dianion of oxalic acid], together with the potentiometric and spectrophotometric studies of the protonation/deprotonation equilibria of the pyim ligand and the ternary complex [Cr(pyim)(C2O4)2]−, are reported herein. The crystal structure of 1 consists of neutral chains, with diamond-shaped units sharing barium(II), with the two other corners occupied by chromium(III). The two metal centers are connected through bis(bidentate) oxalate. Very weak antiferromagnetic interactions between the chromium(III) ions occur in 1. The values of the protonation constants of the imidazole and pyridyl fragments of pyim as well as the acidity constant of the coordinated pyim in [Cr(pyim)(C2O4)2]− are determined for the first time by potentiometry and UV–Vis spectroscopy in aqueous solution (25 °C and 0.15 M NaNO3 as ionic strength).

The synthesis, acid-base behavior, and Cu(2+) coordination chemistry of a new ligand (L1) consisting of an azamacrocyclic core appended with a lateral chain containing a 3-hydroxy-2-methyl-4(1H)-pyridinone group have been studied by potentiometry, cyclic voltammetry, and NMR and UV-vis spectroscopy. UV-vis and NMR studies showed that phenolate group was protonated at the highest pH values [log K = 9.72(1)]. Potentiometric studies point out the formation of Cu(2+) complexes of 1:2, 2:2, 4:3, 1:1, and 2:1 Cu(2+)/L1 stoichiometries. UV-vis analysis and electrochemical studies evidence the implication of the pyridinone moieties in the metal coordination of the 1:2 Cu(2+)/L1 complexes. L1 shows a stronger chelating ability than the reference chelating ligand deferiprone. While L1 shows no cytotoxicity in HeLa and ARPE-19 human cell lines (3.1-25.0 μg/mL), it has significant antioxidant activity, as denoted by TEAC assays at physiological pH. The addition of Cu(2+) diminishes the antioxidant activity because of its coordination to the pyridinone moiety phenolic group.

The reaction of N-Boc triprotected cyclam with bis(chloromethyl)biphenyl followed by the corresponding deprotection of the nitrogen atoms allows the preparation of receptor 3 containing an azonia spiro subunit. This receptor shows slightly increased basicity than cyclam, in particular for the formation of the appropriate triply charged species as a consequence of the reduced capacity of the structure present in 3 to stabilize the species with lower protonation degrees through the formation of intramolecular hydrogen bonds. The properties of 3 as a receptor for Cu2+ and Zn2+ and the anions derived from PO 4 3 − ( Pi ) , P 2 O 7 4 − ( PPi ) , P 3 O 10 5 − ( TPP ) and ATP have been studied by pH-metric titrations carried out in aqueous solution. While Cu2+ forms a CuL2+ complex and two hydroxylated species of moderate stability, Zn2+ forms only hydroxylated complexes. The association constants obtained for the 1:1 A:L anion complexes denote significant stability for Pi, PPi and ATP; the stability of the H5LA complex found in the case of TPP being lower. 1H NMR spectra for the ATP:L carried out at pD=5.8 show features attributable to the occurrence of intermolecular π–π stacking between the biphenyl unit of 3 and the adenine ring of the nucleotide. DFT calculations have been carried out to rationalize some of the results found, in particular the remarkable different basicity between receptor 3 and cyclam.

The synthesis of two new ligands constituted of a tris(2-aminoethyl)amine moiety linked to the 2,6 positions of a pyridine spacer through methylene groups in which the hanging arm is further functionalized with a 2-pycolyl (L1) or 3-pycolyl (L2) group is presented. The protonation of L1 and L2 and formation of Cu(2+) complexes have been studied using potentiometric, NMR, X-ray, and kinetic experiments. The results provide new information about the relevance of molecular movements in the chemistry of this kind of so-called scorpiand ligand. The comparison between these two ligands that only differ in the position of the substituent at the arm reveals important differences in both thermodynamic and kinetic properties. The Cu(2+) complex with L1 is several orders of magnitude more stable than that with L2, surely because in the latter case the pyridine nitrogen at the pendant arm is unable to coordinate to the metal ion with the ligand acting as hexadentate, a possibility that occurs in the case of [CuL1](2+), as demonstrated by its crystal structure. Significant differences are also found between both ligands in the kinetic studies of complex formation and decomposition. For L1, those processes occur in a single kinetic step, whereas for L2 they occur with the formation of a detectable reaction intermediate whose structure corresponds to that resulting from the movement typical of scorpiands. Another interesting conclusion derived from kinetic studies on complex formation is that the reactive form of the ligand is H(3)L(3+) for L1 and H(2)L(2+) for L2. DFT calculations are also reported, and they allow a rationalization of the kinetic results relative to the reactive forms of the ligands in the process of complex formation. In addition, they provide a full picture of the mechanistic pathway leading to the formation of the first Cu-N bond, including outer-sphere complexation, water dissociation, and reorganization of the outer-sphere complex.

Interaction of nitrate anions with a cyclophane (L) containing two pyridine units connected to two diethylenetriamine bridges through methylene positions is reported both in pure water and in the solid state. The crystal structure of [H4L](NO3)4 shows that one of the nitrate anions resides in the macrocyclic cavity forming two sets of bifurcated hydrogen bonds with the four protonated amino groups of the macrocycle. This anion is symmetrically placed in the middle of the pyridine rings with distances between its nitrogen atom and the centroids of the ring of 3.58 A. Despite this location, calculations by theoretical analysis were carried out to confirm whether the stabilizing effect is due to anion−π interactions.

The synthesis, protonation, and Cu(2+) coordination chemistry of a tripodal heptaamine ligand (L(1)) functionalized with 2-pyridine fragments at the ends of its three branches are reported. L(1) presents six relatively high protonation constants followed by much more reduced constant that as indicated by the UV-vis and NMR data, occur on the pyridine fragments. p[H]-metric, ESI/MS(+), EPR and UV-vis data show that L(1) is able to form mono-, di-, and trinuclear Cu(2+) complexes. Slippage movements and molecular reorganizations have been observed to occur as a function of p[H] in the 1:1 Cu(2+) complexes. The kinetic studies showed that the complex formation is fast and proceeds through a dissociative Eigen-Wilkins mechanism. The decomposition of CuL(1) upon addition of acid excess occurs with two separate kinetic steps; the rate constant for the fast process does not vary with respect to the H(+) concentration whereas a linear dependence on H(+) is observed for the slow step.

A ligand (L1) (bis(aminoethyl)[2-(4-quinolylmethyl)aminoethyl]amine) containing a 4-quinolylmethyl group attached to one of the terminal amino groups of tris(2-aminoethyl)amine (tren) has been prepared, and its protonation constants and stability constants for the formation of Cu(2+) complexes have been determined. Kinetic studies on the formation of Cu(2+) complexes in slightly acidic solutions and on the acid-promoted complex decomposition strongly suggest that the Cu(2+)-L1 complex exists in solution as a mixture of two species, one of them showing a trigonal bipyramidal (tbp) coordination environment with an absorption maximum at 890 nm in the electronic spectrum, and the other one being square pyramidal (sp) with a maximum at 660 nm. In acidic solution only a species with tbp geometry is formed, whereas in neutral and basic solutions a mixture of species with tbp and sp geometries is formed. The results of density functional theory (DFT) calculations indicate that these results can be rationalized by invoking the existence of an equilibrium of hydrolysis of the Cu-N bond with the amino group supporting the quinoline ring so that CuL1(2+) would be actually a mixture of tbp [CuL1(H(2)O)](2+) and sp [CuL1(H(2)O)(2)](2+). As there are many Cu(2+)-polyamine complexes with electronic spectra that show two overlapping bands at wavelengths close to those observed for the Cu(2+)-L1 complex, the existence of this kind of equilibrium between species with two different geometries can be quite common in the chemistry of these compounds. A correlation found between the position of the absorption maximum and the tau parameter measuring the distortion from the idealized tbp and sp geometries can be used to estimate the actual geometry in solution of this kind of complex.

The synthesis and coordination chemistry of two novel ligands, 2,6,9,12,16-pentaaza[17]metacyclophane (L1) and 2,6,9,12,16-pentaaza[17]paracyclophane (L2), is described. Potentiometric studies indicate that L1 and L2 form a variety of mononuclear complexes the stability constants of which reveal a change in the denticity of the ligand when moving from L1 to L2, a behaviour that can be qualitatively explained by the inability of the paracyclophanes to simultaneously use both benzylic nitrogen atoms for coordination to a single metal centre. In contrast, the formation of dinuclear hydroxylated complexes is more favoured for the paraL2 ligand. DFT calculations have been carried out to compare the geometries and relative energies of isomeric forms of the [CuL]2+ complexes of L1 and L2 in which the cyclophane acts either as tri- or tetradentate. The results indicate that the energy cost associated with a change in the coordination mode of the cyclophane from tri- to tetradentate is moderate for both ligands so that the actual coordination mode can be determined not only by the characteristics of the first coordination sphere but also by the specific interactions with additional nearby water molecules. The kinetics of the acid promoted decomposition of the mono- and dinuclear CuII complexes of both cyclophanes have also been studied. For both ligands, dinuclear complexes convert rapidly to mononuclear species upon addition of excess acid, the release of the first metal ion occurring within the mixing time of the stopped-flow instrument. Decomposition of the mononuclear [CuL2]2+ and [CuHL2]3+ species occurs with the same kinetics, thus showing that protonation of [CuL2]2+ occurs at an uncoordinated amine group. In contrast, the [CuL1]2+ and [CuHL1]3+ species show different decomposition kinetics indicating the existence of significant structural reorganisation upon protonation of the [CuL1]2+ species. The interaction of AMP with the protonated forms of the cyclophanes and the formation of mixed complexes in the systems Cu–L1-AMP, Cu–L2-AMP, and Cu–L3-AMP, where L3 is the related pyridinophane containing the same polyamine chain and 2,6-dimethylpyridine as a spacer, is also reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The o-B232, m-B232 and p-B232 cyclophanes result from attaching the terminal amine groups of 1,4,8,11-tetraazaundecane (232) to the benzylic carbons of the corresponding o-, m- or p-xylanes. The cavity size of these cyclophanes changes moderately as a consequence of the substitution at the aromatic ring. The effects caused by these changes on the equilibrium constants for protonation and CuII complex formation of the cyclophanes are analyzed and compared with those of the noncyclic 232 polyamine. All three cyclophanes form mononuclear complexes, but only o-B232 is able to coordinate to CuII through the four amine groups simultaneously, whereas m-B232 and p-B232 can only use three nitrogen donors. The larger cavity and higher flexibility of the latter two cyclophanes allow them to form stable dinuclear CuII complexes. The kinetics of the acid-promoted dissociation of CuII from its mono- and dinuclear complexes has also been studied and the results indicate the existence of large differences in the kinetic properties for the complexes with these three closely related ligands. Whereas the mononuclear m-B232 and p-B232 complexes decompose with very similar kinetic behaviour to that of the Cu(232)2+ complex, the lability of the Cu–N bonds is largely reduced in the Cu(o-B232)2+ complex, and this leads to slower decomposition and even to a different rate law for this complex. The dinuclear complexes are not formed with o-B232, and very different decomposition kinetics is observed for the complexes formed by m-B232 and p-B232. In the case of m-B232, the two metal ions are situated very close to each other, which causes a rapid release of one of them upon reaction with acid. In contrast, the larger size of p-B232 allows it to accommodate two metal ions without important electrostatic or steric interactions so that they are released with statistically controlled kinetics.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The synthesis of the open-chain and cyclic polyamines, 1,5,8,12,15,19-hexaazaheptadecane (L1) and 2,6,9,13,16,20-hexaaza[21]-(2,6)-pyridinophane (L2), are described. The protonation constants and interaction constants with Cu(II) have been determined by potentiometric measurements carried out at 298.1 K in 0.15 mol dm −3 NaClO 4 . The values obtained are discussed as a function of the open-chain or cyclic nature of the ligands and compared with analogous polyamines containing different sets of hydrocarbon chains between the nitrogen donors. Kinetic studies on the acid-promoted dissociation of the Cu(II) complexes indicate that the mono and binuclear complexes of L1 decompose with different kinetics, a behavior unprecedented for open-chain polyamines. In contrast, the dissociation of the first metal ion is accelerated in the binuclear complexes of L2 and so, all the mono and binuclear complexes of L2 decompose with the same kinetics. The voltammetric response of Cu(II)–L1 and Cu(II)–L2 complexes has been studied in order to correlate electrochemical and structural data.

The synthesis, characterization, Cu2+ coordination and interaction with AMP of three tripodal polyamines are reported. The polyamines are based on the structure of the tetraamine (tren) which has been enlarged with three propylamino functionalities (TAL), with a further anthrylmethyl fragment at one of its terminal primary nitrogens (ATAL) or with naphthylmethyl fragments at its three ends (N3TAL). The protonation constants of all three polyamines show that at pH 6, all six primary and secondary nitrogen atoms in the arms are protonated. The interaction with Cu2+ and AMP (adenosine-5′-monophosphate) has been studied by potentiometric, UV-Vis, ESI-MS spectroscopy and NMR techniques. pH-Metric, NMR and ESI/MS techniques indicate that TAL and ATAL form with AMP adducts of 1 : 1, 2 : 1 and 3 : 1 AMP : L stoichiometries in water. This is one of the first examples for the formation of such complexes in aqueous solution. Formation of ternary complexes between TAL, ATAL, N3TAL, Cu2+ and AMP is observed. Paramagnetic NMR techniques have been used to obtain structural information on the binding mode of AMP to the Cu2+–TAL binuclear complexes.

A new fluorescent macrocyclic structure (L1) bearing two naphthalene units at both ends of a cyclic polyaminic chain containing two phenanthroline units was investigated with potentiometric and fluorescence (steady-state and time-resolved) techniques. The fluorescence emission spectra show the simultaneous presence of three bands: a short wavelength emission band (naphthalene monomer), a middle emission band (phenanthroline emission), and a long-wavelength band. All three bands were found to be dependent on the protonation state of the macrocyclic unit (including the polyaminic and phenanthroline structures). The existence of the long-wavelength emission band is discussed and is shown to imply that a bending movement involving the two phenanthroline units leads to excimer formation. This is determined by comparison with the excimer emission formed by intermolecular association of 1,10-phenanthroline. With ligand L1, excimer formation occurs only at pH values above 4. At very acidic pH values, the protonation of the polyamine bridges is extensive leading to a rigidity of the system that precludes the bending movement. The interaction with metal cations Zn(II) and Cu(II) was also investigated. Excimer formation is, in these situations, increased with Zn(II) and decreased with Cu(II). The long-emission band is shown to present a different wavelength maximum, depending on the metal, which can be considered as a characteristic to validate the use of ligand L1 as a sensor for a given metal.

The interaction in aqueous solution of adenosine 5′-triphosphate (ATP) with a series of open-chain polyamines linked at one or both ends to anthrylmethyl or naphthylmethyl fragments was followed by potentiometric titration, 1H-, 13C-, and 31P-NMR spectroscopy, and by steady-state fluorescence measurements. The results revealed greater stabilities for the compounds containing one anthracene moiety than for those with one naphthalene moiety, the stabilities of the compounds with both ends N-substituted with naphthylmethyl groups being close to those containing just one anthrylmethyl unit. The 1H-NMR spectra showed that in all systems, there is involvement of π-π stacking interactions in the stabilization of the adduct species. The competitive effect of the anions afforded by the supporting electrolyte was checked in some of the studied systems working at two different ionic strenghts (0.15M and 1.0M NaCl). The joint analysis of the spectrofluorimetric titrations and pH-metric species-distribution curves showed that for all the ATPreceptor systems, a quenching of the fluorescence occurred upon protonation of the adenine N(1)atom. Steady-state fluorescence and time-correlated single-photon-counting analysis of a system made up of ATP and a bis-chromophoric polyamine receptor containing anthracene and naphthalene fluorophores established that the energy-transfer process between the naphthalene and anthracene moieties is still operative despite the presence of ATP.

The fluorescence emission properties of a series of chemosensors containing a polyamine receptor bearing an anthracene signaling unit were studied. The fluorescence emission intensity is dependent on the protonation degree of the receptor, the fully protonated form exhibiting the highest emission intensity. By removing protons from the nitrogens a quenching effect can be observed, due to an electron-transfer from the amine to the excited fluorophore. The rate constant of the quenching process is exponentially dependent on the distance of the nitrogen from which the electron is transferred (β=0.6 A−1). The ability of the chemosensors for signaling anions was tested through the model anion hexacyanocobaltate(III). The temperature dependence of the association constants shows that at least for this compound, the change in solvation entropy is probably the controlling parameter to account for the binding.

The synthesis and coordination chemistry of the novel pyridine-functionalized ligand 2,6,9,12,16-pentaaza[17]-(2,6)pyridinophane (L1) is described. The compound behaves as a hexaprotic base in aqueous solution. NMR studies indicate a protonation pattern in which the sp2 pyridine nitrogen (N(py)) does not undergo a net protonation although it is involved in formation of hydrogen bonds. L1 forms mono and binuclear hydroxylated complexes. The crystal structure of [CuL1](ClO4)2 shows a square planar coordination for Cu2+ with the pyridine and the three central nitrogens of the chain forming the vertices of the square. The benzylic nitrogens could be occupying the axial positions of a strongly axially asymmetrically elongated octahedron. The kinetic data show that decomposition of the [Cu(HL1)]3+, [Cu(L1)]2+ and [Cu2(L1)(OH)]3+ complexes takes place in two steps the slower one being ascribed to the dissociation of the Cu–N(py) bond.

We report a novel 1-D helical coordination polymer formed by protonated polyamine 1H-pyrazole cryptands interconnected by Cu2+ metal ions that are able to encapsulate anionic species behaving as a multianion receptor. Switching from a monomeric receptor to a polymeric receptor is activated by metal ions and pH.

The formation of copper(II) complexes with symmetrical dinucleating macrocyclic ligands containing two either monomethylated (L1) or trimethylated (L2) diethylenetriamine (Medien or Me3dien) subunits linked by pyridine spacers has been studied by potentiometry. Potentiometric studies show that L1 has larger basicity than L2 as well as higher stability of its mono- and binuclear complexes. The crystal structures of L1·6HCl (1), [Cu2(L1)Cl2](CF3SO3)2 (2), [Cu2(L1)(OH)](ClO4)3·3H2O (3) and [Cu(L1)](ClO4)2 (4) show that L1 adopts different coordination modes when bound to copper(II). Whereas in 2, each copper(II) is bound to one Medien subunit and to one pyridine group, in 3 each metal center is coordinated to one 2,6-di(aminomethyl) pyridine moiety (damp) and to one aminomethyl group. The mononuclear complex 4 shows pseudo-octahedral coordination with two weakly coordinated axial nitrogens. Kinetic studies indicate that complex decomposition is strongly dependent on the coordination mode of L1. Upon addition of an acid excess, all the species except [Cu2(L1)]4+ convert very rapidly to an intermediate that decomposes more slowly to copper(II) and a protonated ligand. In contrast, [Cu2(L1)]4+ decomposes directly without the formation of any detectable intermediate. These results can be rationalized by considering that the crystal structures are maintained in solution and that the weakest Cu–N bonds are broken first, thus indicating that kinetic measurements on complex decomposition can be used to provide information about structural reorganizations in the complexes. In any case, complete decomposition of the L1 complexes takes place in a maximum of two kinetically resolvable steps. However, minor changes in the structure of the complexes can lead to drastic changes in the kinetics of decomposition and the L2 complexes decompose with polyphasic kinetics in which up to four different steps associated with the successive breaking of the different Cu–N bonds can be resolved.

Cu(2+) and Zn(2+) coordination chemistry of a new member of the family of scorpiand-like macrocyclic ligands derived from tris(2-aminoethyl)amine (tren) is reported. The new ligand (L1) contains in its pendant arm not only the amine group derived from tren but also a 6-indazole ring. Potentiometric studies allow the determination of four protonation constants. UV-vis and fluorescence data support that the last protonation step occurs on the indazole group. Equilibrium measurements in the presence of Cu(2+) and Zn(2+) reveal the formation of stable [ML1](2+), [MHL1](3+), and [ML1(OH)](+) complexes. Kinetic studies on the acid-promoted decomposition of the metal complexes were carried out using both absorbance and fluorescence detection. For Zn(2+), both types of detection led to the same results. The experiments suggest that [ZnL1](2+) protonates upon addition of an acid excess to form [ZnHL1](3+) within the mixing time of the stopped-flow instrument, which then decomposes with a first-order dependence on the acid concentration. The kinetic behavior is more complex in the case of Cu(2+). Both [CuL1](2+) and [CuHL1](3+) show similar absorption spectra and convert within the mixing time to a new intermediate species with a band at 750 nm, the process being reverted by addition of base. The intermediate then decomposes with a second-order dependence on the acid concentration. However, kinetic experiments with fluorescence detection showed the existence of an additional faster step. With the help of DFT calculations, an interpretation is proposed in which protonation of [CuL1](2+) to form [CuHL1](3+) would involve dissociation of the tren-based NH group in the pendant arm and coordination of a 2H-indazole group. Further protonation would lead to dissociation of coordinated indazole, which then will convert to the more stable 1H tautomer in a process signaled by fluorescence changes that would not be affecting to the d-d spectrum of the complex.

The interaction of the polyamines 4,7,10,13-tetraazahexadecane-1,16-diamine (L1) and 4,7,10-triazatridecane-1,13-diamine (L2) with H + , Cu 2+ , Zn 2+ , Co 2+ and the nucleotides ATP, ADP and AMP has been followed by NMR and potentiometric studies performed at 298.1 K in 0.15 mol dm −3 NaClO 4 . The influence of the different sequences of hydrocarbon chains and chelate rings present in the ligands on the values of the protonation constants, the stability of the metal ion complexes as well as in the co-ordination to nucleotides is analysed. The formation of mixed complexes has been investigated for the system Cu 2+ –L1–AMP.

Intramolecular electron (eT) and energy transfer (ET) have shown to occur in a covalently linked donor–acceptor (CLDA) system consisting of a naphthalene donor covalently linked through a polyamine chain connector to an anthracene acceptor; the connector has been chosen in order to switch ON or OFF the energy flux as a function of its protonation state as well as by co-ordination to Zn 2+ . The largest energy transfer efficiency ( η =0.61) occurs for the fully protonated form (pH 9 (eT) from the lone pairs of the nitrogens to the excited fluorophore takes place, leading to complete quenching of the emission. On the other hand at neutral and basic pH values, co-ordination of Zn 2+ prevents the eT quenching allowing the ET process to occur.

The synthesis, protonation behaviour and coordination capabilities towards Cu 2+ , Zn 2+ and towards the nucleotides ATP and ADP of a cyclophane ditopic receptor 2,6,10,23,27,31-hexaaza[11,11](2,2′)biphenylophane containing two 2,2′-biphenylene spacers linked to the ends of 1,5,9-triazanonane chains are presented.

Bis-polyaza pyridinophane scorpiands bind nucleotides in aqueous medium with 10–100 micromolar affinity, predominantly by electrostatic interactions between nucleotide phosphates and protonated aliphatic amines and assisted by aromatic stacking interactions. The pyridine-scorpiand receptor showed rare selectivity toward CMP with respect to other nucleotides, whereby two orders of magnitude affinity difference between CMP and UMP was the most appealing. The phenanthroline-scorpiand receptor revealed at pH 5 strong selectivity toward AMP with respect to other NMPs, based on the protonation of adenine heterocyclic N1. The results stress that the efficient recognition of small biomolecules within scorpiand-like receptors relies mostly on the electrostatic and H-bonding interactions despite the competitive interactions in the bulk solvent, thus supporting further optimisation of this versatile artificial moiety.

The interaction of the cyclophanes 2,6,9,13-tetraaza[14]paracyclophane (L1) and 2,6,9,13-tetraaza[14]metacyclophane (L2) and of their Zn2+ and Cu2+ complexes with CO32− and its protonated forms is described. The actuation of the Cu2+–L2 system as an electrocatalyst for the reduction of CO2 to CO in water is advanced. Copyright © 2001 John Wiley & Sons, Ltd.

Several chemosensors bearing a fluorescent unit at both ends of a linear polyamine chain were synthesised. The protonation as well as the association constants with Cu2+ and Zn2+ were determined by potentiometry in 0.15 mol dm−3 NaCl at 298.1 K. In the case of 1,16-bis(1-naphthylmethyl)-1,4,7,10,13,16-hexaazadecane hexahydrochloride (L1), formation of an excimer emission in aqueous acidic solutions was observed. The system was characterized by steady state fluorescence emission and by time resolved fluorescence. In the ground state the molecule is expected to adopt a more or less linear conformation, while in the excited state a bending movement of the chain must occur in order to allow the excimer emission. The system can be viewed as an elementary machine driven by light.

Interaction of Cu 2+ with the macrocycle 2,6,9,13-tetraaza[14]paracyclophane (L) and ATP has been followed by pH-metric titration, cyclic voltammetry and differential pulse voltammetry (DPV). Mixed adduct species with various degrees of protonation were found to be stable for pH>4. In neutral and alkaline media reduction of mixed complexes occurs in a two-electron quasi-reversible step in contrast with binary Cu 2+ L complexes which display two successive one-electron couples. The potentiometric and voltammetric data suggest that in ternary adducts ATP binds to Cu 2+ ions through the phosphate chain and one N-site of the adenine ring system.

A large number of systems displaying pH controlled multistages of fluorescence emission intensity, have not been recognized from this point of view. In this work we present two paradigmatic cases: (i) polyamine receptors linked to a fluorophore unit, in which the signal is modulated by an intra-molecular pH dependent electron transfer process, (ii) phenols presenting adiabatic excited state proton transfer. In the first example the chemosensors are constituted by a receptor unit containing a polyaza moiety suitable for binding protons (but also metal ions or anions). The receptor is linked to a benzene or naphthalene unit that acts as a fluorophore. The fluorescence signal is dependent on the protonation state of the receptor. In the second example, addition of buffers are used to tune the intensity of the fluorescence emission.

The present article is concerned with proton transfer reactions in aqueous solution of open-chain, macrocyclic and macropolycyclic or cage compounds having nitrogen atoms as protonation sites in the molecular framework, although several compounds with additional different donors will be considered. The main purpose of this review is to collect some significant examples of proton transfer processes in order to show how the electronic properties and molecular topology of polyamines affect the thermodynamic parameters of their protonation equilibria.

The interaction of the open-chain polyamine N-(3-aminopropyl)-N′-[3-(anthrylmethyl)aminopropyl]ethane-1,2-diamine (L) with the relevant anionic forms of adenosine 5′-triphosphate (ATP), adenosine 5′-diphosphate (ADP) and adenosine 5′-monophosphate (AMP) is described. Unambiguous criteria for defining thermodynamic selectivity based on the use of effective stability constants are presented. The interaction of L and several other topologically similar polyammonium receptors with ATP has been shown to occur through electrostatic and π-stacking intermolecular forces. The π-stacking binding mode is modulated by the protonation degree of ATP as indicated by fluorescence emission titrations. Evidence for the use of these receptors as ATP luminescent chemosensors is advanced.

The synthesis of the new thiophenophanes 2,5,8,11-tetraaza[12](2,5)thiophenophane (L1), 2,6,9,13-tetraaza[14](2,5)thiophenophane (L2) and 2,5,8,11,14-pentaaza[15](2,5)thiophenophane (L3) is described. The stepwise protonation constants of the macrocycles are determined by pH-metric titration and their protonation patterns are analysed by means of 1H and 13C NMR spectroscopy. L1 and L2 present first protonation on the thenylic nitrogens while L3 protonates first on the central nitrogens of the polyamine bridge. Molecular orbital calculations are used to locate the atomic orbitals contributing to the HOMO of the free amines. The interaction with Cu2+ shows for L1 and L3 formation of binuclear complexes which readily hydrolyse to give very stable species. Electrochemical studies show for all three Cu2+–receptor systems an important stabilisation of the Cu+ oxidation state towards its disproportionation into Cu2+ and Cu0 oxidation states.

The interaction of PtCl42− with the new azaparacyclophane 2,5,8,11-tetraaza[12]paracyclophane (L2) has been studied by 1H, 13C and 195Pt NMR spectroscopy. Three different complexes are detected as a function of pH, all of them presenting cis-arrangement of nitrogen donors and chloride anions. In the first one, formed at acidic pH, the central nitrogen atoms of the macrocyclic are coordinating to Pt(II) while the benzylic nitrogens remain protonated. Deprotonation of these nitrogens brings about a reorganisation of the complex, and the platinum is then coordinated by one benzylic nitrogen and the consecutive nitrogen in the macrocycle. This process can be monitored by NMR. Finally, addition of a second mol of PtCl42− for each mole of L2 causes, most likely, the formation of a binuclear complex in which the tetrammine chain behaves as two ethylenediamine subunits. The crystal structure of the adduct [PtBr4]2[H4L1] has been solved by X-ray diffraction analysis (space group P21/c, a = 8.092(2), b = 16.049(2), c = 21.783(3) A, α = 90.00(1), β = 100.34(2), γ = 90.00(1), Z = 4, R1 = 0.0528, wR2 = 0.1612). The compound is held together mainly through coulombic interactions between the charged polyammonium groups of the macrocycle and the PtBr42− anions aswell as through an extensive hydrogen bond network in which participate the bromides of the two PtBr42− anions and a lattice water molecule.

A new polyazamacrocycle (L) containing two 2,2'-bipyridino (bpy) units, where the heteroaromatic nitrogen atoms point outwards from the macrocyclic cavity, was synthesized and characterized by elemental analysis, ESI-MS, (1)H and (13)C NMR, FTIR and TGA. Five protonation constants involving aliphatic nitrogens with log K in the range 9.39-3.07 were determined by potentiometry and NMR and a sixth protonation (log K = 2.2) involving a bipyridine moiety could be detected by UV-Vis and NMR titrations. The interaction of L with the cyanometallate anions [Pt(CN)4](2-) and [Co(CN)6](3-) was studied by potentiometry yielding respectively log K values in the ranges 4.0-6.4 and 5.2-10.5, covering protonation degrees from 1 to 5. Studies on L with [Ru(CN)6](4-) led to early precipitation preventing potentiometry, but crystals of [H4L][Ru(CN)6]·10H2O and also of [H2L](ClO4)2·4H2O suitable for X-ray diffraction could be obtained and the crystalline structures are described. The interaction of L with Zn(2+) was investigated by potentiometry and UV-Vis showing the formation of mono- and dinuclear complexes involving the bipyridines. The macrocycle was used as a bridging ligand for the successful synthesis of a new dinuclear [(Ru(bpy)2)2(L)](PF6)4·4HPF6 complex that was fully characterized. The protonation (log K in the range 9.9-1.6) and coordination features of this compound towards Cu(2+) and Zn(2+) were explored by UV-Vis absorption and emission spectroscopies.

The novel cyclophane receptor 2,6,10,13,17,21-hexaaza[22]metacyclophane (L) has been synthesised and characterised. The acid-base behaviour and interaction with ATP, ADP and AMP have been studied by potentiometry in 0.15 mol dm−3 at 298.1 K and multinuclear NMR. L presents in its protonated forms a molecular organization which enables its multipoint binding with nucleotides. Salt-bridge formation occur between the polyammonium sites of L and the phosphate chain of the nucleotides while π-stacking between the meta-phenylene subunit incorporated in the receptor and the adenine ring of the nucleotides.

The new [n.n]paraazacyclophane 3,7,10,14,21,25,28,32-octaazapentacyclo[32.2.27,10.216,19.225,28]tetratetraconta-1(37),16(41),17,19(40),34(38),35-hexaene (L) has been prepared. Its protonation has been studied by means of potentiometry and direct microcalorimetry in 0.15 mol dm–3 NaClO4 at 298.1 K. A NMR analysis shows that protons bind alternately at both sides of L, the benzylic nitrogens being the first sites to be protonated. From dynamic variable-temperature NMR analysis an activation enthalpy of 61(2) kJ mol–1 has been derived for the chair–chair interconversion of the piperazine ring. The entropy is almost negligible. Compound L forms with Cu2+ in aqueous solution complexes [Cu(H3L)]3+ and [Cu2L]4+ with stability constants log βCuH3L= 33.20(6) and log βCu2L= 16.6(1) in 0.15 mol dm–3 NaClO4 at 298.1 K, respectively. The low stability of the binuclear complex is attributed to the energy loss due to interconversion between the chair and boat conformers of the piperazine moieties. The interaction of Pd2+ with L has been monitored by NMR analysis. The spectral features show formation of strong binuclear complexes with the involvement of all eight nitrogens of the macrocycle.

Reaction of N,N′,N″,N‴-tetrakis (2-aminoethyl)-1,4,8,11-tetraazacyclotetradecane (taec) with ferrocenecarbaldehyde and further reduction with LiAlH4 resulted in the synthesis of the redox-active receptor N,N′,N″,N‴-tetrakis(4-ferrocenyl-3-azabutyl)-1,4,8, 11-tetraazacyclotetradecane (tfabc). The protonation behaviour of tfabc and its complex formation with CuII, ZnII and CdII have been studied in tetrahydrofuran–water (70 : 30 v/v)(0.1 mol dm–3 NBut4ClO4, 25 °C). The potentiometric and electrochemical data indicate the formation of 1 : 1 and 1 : 2 (tfabc: M2+) stoichiometries. The E½ values for tfabc shift as a function of the pH from 389 (pH 10) to 482 mV (pH 2.5) and E½vs. pH curves for the tfabc–H+–M2+ systems (M = Cu, Zn or Cd) show that tfabc electrochemically recognises the presence of copper(II) selectively at pH < 5. The shift of E½ appears to be caused by electrostatic forces and the E½vs. pH curves can be predicted in terms of the distribution diagrams of the tfabc–H+–M2+ systems.

The steady-state fluorescence emission spectra of the azacyclophanes 2,5,8,11-tetraaza[12] paracyclophane (L1), 2,6,9,13-tetraaza[14]paracyclophane (L2), 14,15,17,18-tetramethyl-2,5,8,11-tetraaza[12]paracyclophane (L3) and 16,17,19,20-tetramethyl-2,6,9,13-tetraaza[14]paracyclophane (L4) as a function of pH have been measured. The fully protonated species of each cyclophane gives the highest fluorescence-emission quantum yield. The shapes of the titration curves have been explained by the existence of an electron-transfer quenching effect from a non-protonated amine to the benzene chromophore. This effect is greater for macrocycles in which the first deprotonated amine group is closer to the benzene. The association constants for the interaction of the four fully protonated macrocycles with K3[Co(CN)6] have been measured either by potentiometry or from fluorescence-emission measurements, and increase in the order L3≈ L4 < L1≈ L2. The photoaquation quantum yields of K3[Co(CN)6] have been measured in the presence of the macrocycles L1 and L2, and indicate that three of the CN nitrogens of the complex are involved in adduct formation with the fully protonated macrocycles, as supported by molecular modelling.

Azacycloalkanes and azacyclophanes are among the first macrocyclic ligands developed in the field of supramolecular chemistry. Since they are polyamines, they show dual nature in the coordination of both metal cations, when they are in the free-base form, and anionic species, when they are protonated. As a matter of fact, they played a key role in the birth of macrocyclic chemistry of transition metal complexes and anion coordination chemistry. Furthermore, azacyclophanes fostered also the birth of apolar complexation in aqueous solution, since their aromatic units act as binding sites for apolar substrates. Keywords: azacycloalkanes; azacyclophanes; metal complexes; anion complexes; apolar complexation; binding of neutral molecules; azamacrocycles; polyamines

The interaction of hydrogen ions with the series of macrocyclic receptors 2,5,8-triaza[9]paracyclophane, 2,6,10-triaza [11] paracyclophane, 13,14,16,17-tetramethyl-2,6,10-triaza[11]paracyclophane, 14,15,17,18-tetramethyl-2,5,8,11-tetraaza [12] paracyclophane and 16,17,19,20-tetramethyl-2,6,9,13-tetraaza[14]paracyclophane has been studied by potentiometry at 298.1 ± 0.1 K as well as by direct microcalorimetry and 1H and 13C NMR spectroscopy. Correlations of the basicity with the atomicity of the macrocycle, the type of chains within the bridge and the nature of the aromatic spacer are envisaged.

The new open-chain polyamine 4,8,11,15-tetraazaoctadecane-1,18-diamine has been synthesised and characterized. The acid–base behaviour and the co-ordination abilities towards Cu2+, Ni2+, Co2+, Zn2+, Cd2+ and Pb2+ have been studied by potentiometry at 298.1 K in 0.15 mol dm–3 NaClO4, as well as by 1H and 13C NMR spectroscopy. The protonation pattern shows the effects produced by the presence of primary and secondary nitrogen atoms as well as ethylenic and propylenic hydrocarbon chains within the molecule. The stability and spectroscopic data show that at most four of the six nitrogens present are involved in co-ordination to the different metal ions. The contrast to other hexaamines, this compound is able to form binuclear species with all the metal ions studied. Formation of predominant binuclear hydroxo species has been detected in a number of systems.

The protonation behaviour of the azaparacyclophanes 2, 6, 9, 13-tetraaza[14]paracyclophane (L1), 2, 5, 8, 11-tetraaza[12]paracyclophane (L2) and 2, 5, 8, 11, 14-pentaaza[15]paracyclophane (L3) has been studied at 298.1 K in 0.1 5 mol dm–3 NaClO4 by potentiometry, direct microcalorimetry, and 1H and 13C NMR spectroscopy. The data obtained by the different techniques suggest that first protonation of L1 and L2 occurs mainly on the benzylic nitrogens. All three ligands form mononuclear copper(II) complexes in aqueous solution characterized by an incomplete participation of the nitrogen donors in the co-ordination to the metal ion. The ligands L2 and L3 also form the binuclear species [Cu2L2(OH)2]2+ and [Cu2L3]4+, [Cu2L3(OH)]3+ and [Cu2L3(OH)2]2+ in solution. The crystal structure of the complex [Cu2L2Cl4]·1.5H2O has been solved by X-ray crystal diffraction analysis [space group P21/n, a= 10.625 (3), b= 14.014(3), c= 14.952(7)A, β= 109.55(3)°β= 109.55(3)°, Z = 4, R = 0.066 and R′= 0.06]. Both metal ions show a distorted square-pyramidal co-ordination geometry. The basal plane is defined for each metal centre by a benzylic nitrogen atom, the adjacent nitrogen atom in the chain and two chloride ions. The apical position is occupied by another chloride from a symmetry-related molecule with a much weaker bond than those in the plane. The presence of the para-phenylene subunit imposes enough strain to divide the macrocyclic cavity of L2 into two separate ethylenediamine subunits.

The synthesis of two new methylated ligands 1,10-dimethyl-1,4,7,10,13,16-hexaazacyclooctadecane L and 1,4,7-trimethyl-1,4,7,10,13,16,19-heptaazacyclohenicosane L1 is described. Basicity constants and protonation enthalpies of both ligands have been determined by potentiometric and microcalorimetric measurements in 0.15 mol dm–3 NaClO4 at 298.1 K. The protonated forms of these cyclic polyamines bind ATP in solution. The equilibrium constants of the species formed have been determined (0.15 mol dm–3 NaClO4, 298.1 K). The results presented for L and L1 are compared with those previously obtained for the related ligands 1,4,7,10,13,16-hexaazacyclooctadecane, 1,4,7,10,13,16,19-heptaazacyclohenicosane and 1,4,7,13-tetramethyl-1,4,7,10,13,16-hexaazacyclooctadecane. Among these macrocycles Lis a selective receptor for ATP binding.The crystal structure of the compound (H4L)(ClO4)4[space group P21/c, a= 9.257(4), b= 8.600(2). c= 17.990(10)A, β= 101.74(4)°, V= 1402(1)A3, Z= 2] shows that the four charged ammonium groups point inside the macrocyclic cavity.

The synthesis and characterization of the new azacyclophane, 2,6,9,13-tetraaza[14]paracyclophane, is described. The acid–base behaviour and the metal and anion coordination capabilities of this compound have been studied by potentiometry at 298.15 K in 0.15 mol dm–3 NaClO4, as well as, by 1H and 13C NMR spectroscopy. The protonation patterns show stabilization effects produced by the presence of the aromatic ring. The aromatic spacer prevents simultaneous involvement of all four nitrogens in the coordination to the metal ions Cu2+ and Zn2+. Stable mono-hydroxylated species have been detected for both metal ions. The triprotonated species is the main one over a wide pH range around neutrality making this ligand a good coordinating agent for such anionic species as ATP4–and p2O74–. Formation of complexed anionic species with degrees of protonation varying from three to six has been detected.