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Argentivorous molecules with mono, di, tri, tetra, and penta-oxyethylene chains in aromatic side-arms were prepared (L1-L5). Titration experiments using proton nuclear magnetic resonance and cold electrospray ionization (cold-spray ionization, CSI) mass spectrometry showed that silver ions were trapped in the cyclen moiety and the arranged oxyethylene chains of the side-arms when two equivalents of silver ions were added. The silver complexes formed by adding one equivalent of silver ion to L2-L5 bind alkali metal ions using the oxyethylene chains; alkali metal ion-induced CSI mass spectral changes of L2-L5 were measured in the absence and presence of silver ions to compare the binding properties of the ligand for Li+, Na+, and K+ ions. As a result, the intensity ratios of [L + H + M]2+/[L + H]+ in L1-L3 were almost zero or very low. L4 and L5, which have tetra(oxyethylene) and penta(oxyethylene) chains, respectively, bind a larger size of alkali metal ions. On the other hand, in the presence of silver ions, the ratio for [L + Ag + M]2+/[L + H]+ (M = Li, Na, K) in L2-L5 was increased. The highest [L + Ag + M]2+/[L + H]+ ratios for K+ were observed in L4 and L5, while selectivity for Na+ was observed in the case of L2 and L3. These results indicate that the increased binding ability and selectivity by L2-L5 are due to the arrangement of oxyethylene chains by the conformational change of the aromatic side-arms. The Ag+-induced carbon-13 nuclear magnetic resonance spectral changes suggested that the second and third oxyethylene units, close to the benzene, are involved in the coordination of the second metal ion.

The Cu2+ complexes formed by a series of cyclen derivatives bearing sulfur pendant arms, 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO4S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO3S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-10-acetamido-1,4,7,10-tetraazacyclododecane (DO3SAm), and 1,7-bis[2-(methylsulfanyl)ethyl]-4,10-diacetic acid-1,4,7,10-tetraazacyclododecane (DO2A2S), were studied in aqueous solution at 25 °C from thermodynamic and structural points of view to evaluate their potential as chelators for copper radioisotopes. UV–vis spectrophotometric out-of-cell titrations under strongly acidic conditions, direct in-cell UV–vis titrations, potentiometric measurements at pH >4, and spectrophotometric Ag+–Cu2+ competition experiments were performed to evaluate the stoichiometry and stability constants of the Cu2+ complexes. A highly stable 1:1 metal-to-ligand complex (CuL) was found in solution at all pH values for all chelators, and for DO2A2S, protonated species were also detected under acidic conditions. The structures of the Cu2+ complexes in aqueous solution were investigated by UV–vis and electron paramagnetic resonance (EPR), and the results were supported by relativistic density functional theory (DFT) calculations. Isomers were detected that differed from their coordination modes. Crystals of [Cu(DO4S)(NO3)]·NO3 and [Cu(DO2A2S)] suitable for X-ray diffraction were obtained. Cyclic voltammetry (CV) experiments highlighted the remarkable stability of the copper complexes with reference to dissociation upon reduction from Cu2+ to Cu+ on the CV time scale. The Cu+ complexes were generated in situ by electrolysis and examined by NMR spectroscopy. DFT calculations gave further structural insights. These results demonstrate that the investigated sulfur-containing chelators are promising candidates for application in copper-based radiopharmaceuticals. In this connection, the high stability of both Cu2+ and Cu+ complexes can represent a key parameter for avoiding in vivo demetalation after bioinduced reduction to Cu+, often observed for other well-known chelators that can stabilize only Cu2+., A series of cyclen derivatives bearing sulfur- or mixed-sulfur-carboxylated pendant arms were considered as chelators for copper radioisotopes in radiopharmaceuticals. Stability and structure of their Cu2+ and Cu+ complexes were studied in aqueous solution using a multimethodological approach. The stability of both Cu2+ and Cu+ complexes should prevent the reductive-based copper demetallation observed in vivo for other copper chelators.

International audience; Tetraazamacrocycle such as 1,4,7,10-tetraazacyclododecane “cyclen” are known for efficient complexation of metallic ions and were used as an ionic recognition agents in chemical sensors in aqueous medium.The aim of this paper is to examine in more detail the oxidation mechanism of amines in cyclen before copper complexation and after copper complexation. Gold electrodes modified with mono-N-MNCyclen(mono methyl-naphtyl-cyclen) and tetra-N-MNCyclen thin films were obtained by deposition of mono-N-MNCyclen and the tetra-N-MNCyclensynthesized respectively by bisaminal route in three steps (protection, N-mono-alkylation and deprotection) and direct route. The comparative study of the electrochemical oxidation of amines in both cyclens allowed the identification of the tertiary and of the secondary amines. From the potential-pH relation and the variation of the intensities of the oxidation peaks, the redox mechanisms of both types of amines was proposed. The electrochemical redox behaviour of the amines in the copper-mono-N-MNCyclen complex was studied. From the potential-pH relation and the variation of the intensities of the oxidation peaks, the redox mechanisms of amines and the structure of the copper-mono-N-MNCyclen complex were proposed. The intensities of the oxidation peaks of the amines vary linearly with the copper concentration, in the range 10−12 M to 10–6 M, leading to a detection limit of of 1 pM of Cu2+.

A tetra-armed cyclen (L) with two substituted 3,5-difluorobenzyl and two substituted pyridine-4-yl methyl groups at the 1,4- and 7,10-positions of the cyclen ring as side arms was synthesized. When L was reacted with 1 equiv of the silver(I), dimetallo[3.3]paracyclophane-like 2:2 cyclic dimer, [Ag2(L)2](PF6)2, was obtained. The reaction of L with 2 equiv of silver(I) gave a 3:6 cyclic trimer, [Ag6(L)3(CH3CN)3](OTf)6·3CH3CN. Furthermore, reversible complexation between the 2:2 cyclic dimer and 3:6 cyclic trimer was confirmed by 1H NMR and the CSI mass in the addition of silver(I) or the [2.2.2]cryptand.

The mechanism responsible for peptide bond hydrolysis by Co(III) and Cu(II) complexes with (oxa)cyclen ligands has been revisited by means of computational tools. We propose that the mechanism starts by substrate coordination and an outer-sphere attack on the amide C atom of a solvent water molecule assisted by the metal hydroxo moiety as a general base, which occurs through six-membered ring transition states. This new mechanism represents a more likely scenario than the previously proposed mechanisms that involved an inner-sphere nucleophilic attack through more strained four-membered rings transition states. The corresponding computed overall free-energy barrier of 25.2 kcal mol-1 for hydrolysis of the peptide bond in Phe-Ala by a cobalt(III) oxacyclen catalyst (1) is consistent with the experimental values obtained from rate constants. Also, we assessed the influence of the nature of the ligand throughout a systematic replacement of N by O atoms in the (oxa)cyclen ligand. Increasing the number of coordinating O atoms accelerates the reaction by increasing the Lewis acidity of the metal ion. On the other hand, the higher reactivity observed for the copper(II) oxacyclen catalyst with respect to the analogous Co(III) complex can be attributed to the larger Bronsted basicity of the copper(II) hydroxo ligand. Ultimately, the detailed understanding of the ligand and metal nature effects allowed us to identify the double role of the metal hydroxo complexes as Lewis acids and Bronsted bases and to rationalize the observed reactivity trends.

Tethering metal complexes, like [Ru(bpy)2Cl2] (bpy = 2,2′-bipyridine), which are redox-active at low reduction potentials and have the ability to transfer electrons to another complex, to a [Ni(cyclen)]2+ electrocatalyst enhanced the reduction of CO2 to CO at low overpotentials. The [Ni(cyclen)]2+ electrocatalyst was modified by tethering redox-active metal complexes via 4-methylpyridyl linkers. The redox-active metal complexes were reduced after CO2 bound to the active site. In controlled potential electrolysis (CPE) experiments in 95 : 5 (v/v) CH3CN/H2O, [{([Ru]pic)4cyclen}NiCl]5+ ([Ru]+ = {Ru(bpy)2Cl}+; pic = 4-methylpyridyl) could be used to reduce CO2 into CO at a turnover frequency (TOF) of 708 s−1 with a faradaic efficiency (FE) of 80% at an onset potential of −1.60 V vs. NHE. At the same time, this electrocatalyst was active at an onset potential of −1.25 V vs. NHE, which is the reduction potential of one of the bpy ligands of the [Ru]+ moieties, with FE = 84% and TOF = 178 s−1. When the electrocatalysis was performed using [bn4cyclenNiCl]Cl (bn = benzyl) without tethered redox-active metal complexes, the TOF value was determined to be 8 s−1 with FE = 77% at an onset potential of −1.45 V vs. NHE. The results show that tethering redox-active metal complexes significantly improves the electrocatalytic activities by lowering the potential needed to reduce CO2.

The proton signals at the 2′- and 6′-positions of the aromatic side arms of a silver(I) complex with a chiral tetra-armed cyclen ((S)-L2) are assigned by comparison with 1H NMR spectra and X-ray st...

The synthesis of a tetra-armed cyclen (L) with two benzyl groups at the 1- and 7-positions and two pyridin-4-ylmethyl groups at the 4- and 10-positions as side arms and the solvent- and/or molar-ratio-dependent coordination modes in the formation of silver(I) complexes are reported. 1H NMR and cold-spray-ionization mass spectrometry studies suggest that a silver(I) complex with L gives different species depending on the molar ratio of silver ions used as the reactant. Furthermore, the conformation of cyclen in the one-dimensional (1D) coordination polymers, obtained using 2 equiv of silver(I), changes depending on the presence or absence of acetonitrile. When L was reacted with 1 and 2 equiv of silver(I) triflate in a mixed solvent system (CH2Cl2/CH3OH/CH3CN), a dimetallo[3.3]paracyclophane-like discrete cyclic dimer, [Ag2L2](OTf)2 (1), and a 1D coordination polymer, [Ag2L(OTf)2(CH3CN)]n (2), respectively, were obtained as single crystals. In the absence of acetonitrile, a zigzag 1D coordination polymer, {[Ag2L(OTf)]OTf·3CH2Cl2}n (3), was obtained when 2 equiv of silver(I) was used. Molar-ratio-dependent structural changes were not observed when L was reacted with AgBF4 or AgPF6 in the CH2Cl2/CH3OH/CH3CN mixed-solvent system. The solvent effect on the coordination modes can be explained by the coordination ability of the solvents toward the metal cation affecting the conformation of the cyclen.

Synthesis of tetra-armed cyclens (2a-2e), with substituted styrylmethyl groups as side-arms, and their Ag+ complexes is reported. The Ag+ complex with a tetra styrylmethyl-armed cyclen (2a) incorporates alkyl nitriles in a pseudo-cavity formed by the four styrylmethyl side-arms. This prompted us to apply this system to the determination of the absolute configurations of chiral nitriles with low [α]D and low circular dichroism (CD) intensity. In the CD spectra of the 2a/Ag+ complex, (S)- and (R)-G1 did not show a specific Cotton effect, while when chiral nitriles were added to the 2a/Ag+ complex, drastic spectral changes were observed. The (S)-G1@2a/Ag+ system exhibited first a negative and then a positive Cotton effect, whereas the (R)-G1@2a/Ag+ system showed the mirror image of the Cotton effect of (S)-G1@2a/Ag+. We have, therefore, demonstrated a new technique for determining the absolute configurations of weak optical rotation molecules using the Ag+ complex with 2a.

A variant of 1,4,7,10-tetraazacyclododecane (cyclen) bearing two semicarbazone pendant groups has been prepared. The octadentate ligand forms complexes with Bi3+ and Pb2+. X-ray crystallography showed that the neutral ligand provides an eight-coordinate environment for both metal ions and intermolecular hydrogen bond interactions have influenced the coordination environments of both complexes in the solid state. NMR spectroscopy revealed a fluxional environment for both complexes. The ligand was radiolabeled with the α-emitting radioactive isotope 213Bi3+, which is used in systemic targeted radiotherapy. The resulting complex was stable in serum for at least 90 min (two decay half-lives). The Pb2+ complex has reasonably fast kinetics of formation (t1/2 = 20 min) at 25 °C and pH 7.4. The Bi3+ and Pb2+ complexes show kinetic stability in 1.2 M HCl (half-lives of 214 min and 47 min, respectively). This is the first description of a macrocycle bearing semicarbazone pendant groups and its utility in coordinating main group metals, specifically those with radiotherapeutic potential.

The catalase family of enzymes, which include a variety with a binuclear manganese active site, mitigate the risk from reactive oxygen species by facilitating the disproportionation of hydrogen peroxide into molecular oxygen and water. In this work, hydrogen peroxide disproportionation using complexes formed between manganese and cyclen or pyclen were investigated due to the spectroscopic similarities with the native MnCAT enzyme. Potentiometric titrations were used to construct speciation diagrams that identify the manganese complex compositions at different pH values. Each complex behaves as a functional mimic of catalase enzymes. UV-visible spectroscopic investigations of the H(2)O(2) decomposition reaction yielded information about the structure of the initial catalyst and intermediates that include monomeric and dimeric species. The results indicate that rigidity imparted by the pyridine ring of pyclen is a key factor in increased TON and TOF values measured compared to cyclen.

A molecular NiFe complex (Cyclen@Ni0.5Fe0.5) was incorporated into the framework of COF (NH4@COF-SO3) by a one-pot post-synthesis method. The use of cyclen that can strongly chelate metal ions enables the formation of completely isolated metal sits uniformly distributed on the framework of COF. The resulting single-site heterogeneous catalyst ((Cyclen@Ni0.5Fe0.5)@COF-SO3) exhibits outstanding oxygen evolution reaction (OER) activity because of the maximum atom-utilization efficiency and significant bimetallic synergy effect. The TOF value at the overpotential of 300 mV reaches as high as 0.69 s−1, which is superior to most of the recently reported efficient OER electrocatalysts. Moreover, the catalyst is stable and reusable without the loss of current density during a 25 h long-term test. The combination of advantages of molecular catalysts (metal complex) similar to homogeneous catalysts and solid COF materials for the fabrication of single-site heterogeneous catalysts first reported in this work can bring new avenues to develop highly efficient and stable COF-based catalysts in different catalytic fields.

Luminescent Eu(iii) and Tb(iii) complexes were synthesised from octadentate ligands carrying various carbostyril sensitizing antennae and two bidentate picolinate donors. Antennae were connected to the metal binding site via tertiary amide linkers. Antennae and donors were assembled on a 1,4,7-triazacyclononane (tacn) platform. Solution- and solid-state structures were comparable to those of previously reported complexes with tacn architectures, with nine-coordinate distorted tricapped trigonal prismatic Ln(iii) centres, and distinct from those based on 1,4,7,10-tetraazacyclododecane (cyclen) macrocycles. In contrast, the photophysical properties of these tertiary amide tacn-based complexes were more comparable to those of previously reported systems with cyclen ligands, showing efficient Eu(iii) and Tb(iii) luminescence. This represents an improvement over secondary amide-linked analogues, and is due to a greatly increased sensitization efficiency in the tertiary amide-linked complexes. Tertiary amide-linked Eu(iii) and Tb(iii) emitters were more photostable than their secondary amide-linked analogues due to the suppression of photoinduced electron transfer and back energy transfer.

Bis-argentivorous molecules (La and Lb), which have phenyl and 4,4'-biphenyl groups as linkers, have been prepared. The structures of Ag+ complexes with the new ligands (La and Lb) were investigated in solution and the solid state. The CSI-MS and 1H NMR titration of La and Lb with Ag+ show 1:1 and 1:2 complexes depending on the [Ag+]:[L] ratios. In the solid-state structures, single crystals of La and Lb with 2 equiv of Ag+ were prepared. X-ray crystallography of the silver(I) complexes with La and Lb showed that an intramolecular racemic structure (Δ(δδδδ)Λ(λλλλ) form) and a racemic mixture of Δ(δδδδ)Δ(δδδδ) and Λ(λλλλ)Λ(λλλλ) forms were formed, respectively. The dynamic 1H NMR studies suggest the following: (i) the activation entropies (ΔS⧧) of the side arm rotations in the Ag+ complex with La were all negative, indicating restricted rotation of the side arms due to their shortness, and (ii) the ΔS⧧ values of the Ag+ complexes with Lb were negative only when the side arms of both cyclens rotated simultaneously, and the ΔS⧧ values for the 1:1 and 1:2 complexes were positive when one cyclen side arm was rotated. These values of ΔS⧧ indicate that the biphenyl side arms between the two cyclens are not long enough to rotate the ring freely.

Magnetic coupling resulted by an orbital angular momentum L of a photoexcited cyclic π-conjugated system and total angular momentum J of a localized 4f electronic system in [Dy(TPP)(cyclen)]Cl (TPP = 5,10,15,20-tetraphenylporphyrinato; cyclen = 1,4,7,10-tetraazacyclododecane) has been identified using magnetic circular dichroism (MCD). The MCD A-term patterns of the compound show a negative increment in the intensity by decreasing temperature and nonproportionality to the magnetic field. This phenomenon is experimentally observed for the first time in porphyrin-based lanthanide complexes and indicates the presence of the J-L interaction, with the preferred orientation being antiparallel. A theoretical model in which J and L are assumed to couple antiferromagnetically yielded a quantitative agreement to the experimental data of varied-temperature and varied-magnetic-field MCD spectral measurements. The ab initio calculations were performed, revealing the relationship between two orbital angular momenta, i.e., L(π) and L(f), which result from the delocalized π system and the localized 4f system, respectively.

Lithium amide [(Me 3 TACD)Li] 2 derived from the NNNN macrocycle (Me 3 TACD)H ((Me 3 TACD)H = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane) reacted with DIBAL(H) to give the lithium hydridoaluminate [(Me 3 TACD·AlH i Bu 2 )Li(THF)] ( 1 - THF ). With HBPin, the lithium hydridoborate [(Me 3 TACD·HBPin)Li] ( 2 ) was obtained. Both compounds have been characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction. The monomeric structure contains a five-coordinate lithium and does not show any interaction between the lithium center and the hydride.

We present a detailed study of the lanthanide(III) complexes with cyclen-based ligands containing phenylacetamide pendants that incorporate CF3 group(s) at different distances from the metal ion. The complexes exhibit square-antiprismatic coordination in solution, as demonstrated by analysis of the Yb3+-induced paramagnetic shifts and the X-ray structure of the [YbL3] complex. Luminescence lifetime measurements and a detailed 1H and 17O relaxometric characterization confirmed the presence of an inner-sphere H2O molecule. The Tm3+ complexes provide chemical-exchange saturation-transfer response upon saturation at the frequency of the amide protons. A 19F relaxation study provided accurate estimates of the Ln···F distances that were used to rationalize the efficiency of the complexes as 19F magnetic resonance imaging (MRI) probes, which was tested in vitro using MRI phantom studies.

A total of 44 bis-aryl-monocyclic polyamines, monoaryl-monocyclic polyamines and their transition metal complexes were prepared, chemically characterized, and screened in vitro against the Leishmania donovani promastigotes, axenic amastigotes and intracellular amastigotes in THP1 cells. The IC(50) and/or IC(90) values showed that 10 compounds were similarly active at about 2-fold less potent than known drug pentamidine against promastigotes. The most potent compound had an IC(50) of 2.82 μM (compared to 2.93 μM for pentamidine). Nine compounds were 1.1–13.6-fold more potent than pentamidine against axenic amastigotes, the most potent one being about 2-fold less potent than amphotericin B. Fourteen compounds were about 2–10 fold more potent than pentamidine, the most potent one is about 2-fold less potent than amphotericin B against intracellular amastigotes in THP1 cells. The 2 most promising compounds (FeL7Cl(2) and MnL7Cl(2)), with strong activity against both promastigotes and amastigotes and no observable toxicity against the THP1 cells are the Fe(2+)- and Mn(2+)- complexes of a dibenzyl cyclen derivative. Only 2 of the 44 compounds showed observable cytotoxicity against THP1 cells. Tetraazamacrocyclic monocyclic polyamines represent a new class of antileishmanial lead structures that warrant follow up studies.

The new transition-metal oxothiostannate [Ni(cyclen)(H2O)2]4[Sn10S20O4]·∼13H2O (1) was prepared under hydrothermal conditions using Na4SnS4·14H2O as the precursor in the presence of [Ni(cyclen)(H2O)2](ClO4)2·H2O. Compound 1 comprises the [Sn10S20O4]8– anion constructed by the T3-type supertetrahedron [Sn10S20] and the [Sn10O4] anti-T2 cluster. Channels host the H2O molecules, and the sample can be reversibly dehydrated and rehydrated without significantly affecting the crystallinity of the material. 119Sn NMR spectroscopy of an aqueous solution of Na4SnS4·14H2O evidences that between 25 and 120 °C only [SnS4]4– and [Sn2S6]4– anions are present. In further experiments, hints were found that the formation of tin oxosulfide ions depends on the Ni2+-centered complexes. Compound 1 exhibits promising photocatalytic properties for the visible-light-driven hydrogen evolution reaction, with 18.7 mmol·g–1 H2 being evolved after 3 h.

The pyridinophane molecule L2 (3,6,9,15-tetraazabicyclo[9.3.1]penta-deca-1(15),11,13-trien-13-ol) has shown promise as a therapuetic for neurodegenerative diseases involving oxidative stress and metal ion misregulation. Protonation and metal binding stability constants with Mg(2+), Ca(2+), Cu(2+), and Zn(2+) ions were determined to further explore the therapeutic and pharmacological potential of this water soluble small molecule. These studies show that incorporation of an –OH group in position 4 of the pyridine ring decreases the pI values compared to cyclen and L1 (3,6,9,15-tetraazabicyclo[9.3.1]penta-deca-1(15),11,13-triene). Furthermore, this approach tunes the basicity of the tetra-aza macrocyclic ligand through the enhanced resonance stabilization of the –OH in position 4 and rigidity of the pyridine ring such that L2 has increased basicity compared to previously reported tetra-aza macrocycles. A metal binding preference for Cu(2+), a redox cycling agent known to produce oxidative stress, indicates that this would be the in vivo metal target of L2. However, the binding constant of L2 with Cu(2+) is moderated compared to cyclen due to the rigidity of the ligand and shows how ligand design can be used to tune metal selectivity. An IC(50)=298.0 µM in HT-22 neuronal cells was observed. Low metabolic liability was determined in both Phase I and II in vitro models. Throughout these studies other metal binding systems were used for comparison and as appropriate controls. The reactivity reported to date and pharmacological features described herein warrant further studies in vivo and the pursuit of L2 congeners using the knowledge that pyridine substitution in a pyridinophane can be used to tune the structure of the ligand and retain the positive therapeutic outcomes.

We reported a set of water-soluble transition metal complexes that can serve as both 19F and PARACEST magnetic resonance imaging agents. The high number of equivalent fluorine atoms and the paramagnetic effect of metals offer these complexes high 19F sensitivity as demonstrated by in vitro19F MRI experiments. The complexes contain carboxamide groups appended onto a cyclen macrocycle, which provide 1H CEST peaks well differentiated from bulk water. The Co(ii) agent displays two CEST peaks that can be utilized for ratiometric pH determination and the concept of combining 19F MR and PARACEST as complementary imaging techniques was demonstrated with the Fe(ii) complex.

A series of water-soluble chiral cyclen-based chelators with chemical handles for selective targeting have been synthesized (cyclen = 1,4,7,10-Tetraazacyclododecane). Optical studies, relaxivity measurements, and competitive titrations were performed to show the versatility of these chiral chelators. The complexations of L3, L4, and L5 with Lu3+, Y3+, Sc3+, and Cu2+ were successfully demonstrated in around 90% to 100% yields. Efficient and rapid radiolabeling of L5 with 177Lu was achieved under mild conditions with 96% yield. The chelators exhibit near quantitative labeling efficiencies with a wide range of radiometal ions, which are promising for the development of targeting specific radiopharmaceutical and molecular magnetic resonance imaging contrast agents.

Intramolecular magnetic interaction between a localized open-shell 4f-electronic system and a photoexcited macrocyclic π-conjugate system in terbium-phthalocyaninnato (Tb-Pc) 1:1 complex was investigated using variable-temperature variable-field magnetic circular dichroism (VTVH MCD) spectroscopy. The 1:1 complex [Tb(Pc)(cyclen)]Cl (Pc2- = phthalocyaninato dianion, cyclen = 1,4,7,10-tetraazacyclododecane) with the capping ligand providing an exact fourfold symmetry showed a significant temperature dependence and a nonlinear field dependence in the MCD intensity of the Pc-centered highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) π-π* transition, while a diamagnetic congener [Y(Pc)(cyclen)]Cl showed a temperature-independent MCD with a linear-field dependence. This indicates that the (4f)8 system of the Tb ion with a total angular momentum J and the photoexcited π-system of the Pc macrocycle with an orbital angular momentum L are magnetically coupled. By numerical simulation using a model where ground doublet state |Jz⟩ = |±6⟩ and excited quartet state |Jz, Lz⟩ = |±6, ±|Lz|⟩ are included, the J-L interaction magnitude ΔJL and the Pc-centered orbital angular momentum |Lz|ℏ were determined to be 1.1 cm-1 and 2.0 ℏ, respectively. From ab initio restricted active space self-consistent field (RASSCF)-restricted active space state interaction (RASSI) calculations on the π-π* excited states of the Tb complex, the magnitude of the J-L interaction was estimated. The comparison between the calculations on the Y and Tb complexes revealed that the ferromagnetic-type coupling occurs between the orbital component in the J of Tb and the L on Pc, supporting the model that we employed for the analysis of the experimental data.

The amyloid cascade is central for the neurodegeneration disease pathology, including Alzheimer’s and Parkinson’s, and remains the focus of much current research. S100A9 protein drives the amyloid-neuroinflammatory cascade in these diseases. DOPA and cyclen-based compounds were used as amyloid modifiers and inhibitors previously, and DOPA is also used as a precursor of dopamine in Parkinson’s treatment. Here, by using fluorescence titration experiments we showed that five selected ligands: DOPA-D-H-DOPA, DOPA-H-H-DOPA, DOPA-D-H, DOPA-cyclen, and H-E-cyclen, bind to S100A9 with apparent Kd in the sub-micromolar range. Ligand docking and molecular dynamic simulation showed that all compounds bind to S100A9 in more than one binding site and with different ligand mobility and H-bonds involved in each site, which all together is consistent with the apparent binding determined in fluorescence experiments. By using amyloid kinetic analysis, monitored by thioflavin-T fluorescence, and AFM imaging, we found that S100A9 co-aggregation with these compounds does not hinder amyloid formation but leads to morphological changes in the amyloid fibrils, manifested in fibril thickening. Thicker fibrils were not observed upon fibrillation of S100A9 alone and may influence the amyloid tissue propagation and modulate S100A9 amyloid assembly as part of the amyloid-neuroinflammatory cascade in neurodegenerative diseases.

International audience; We report a detailed study of the thermodynamic stability and dissociation kinetics of lanthanide complexes with two ligands containing a cyclen unit, a methyl group, a picolinate arm, and two acetate pendant arms linked to two nitrogen atoms of the macrocycle in either cis (1,4-H3DO2APA) or trans (1,7-H3DO2APA) positions. The stability constants of the Gd3+ complexes with these two ligands are very similar, with log KGdL values of 16.98 and 16.33 for the complexes of 1,4-H3DO2APA and 1,7-H3DO2APA, respectively. The stability constants of complexes with 1,4-H3DO2APA follow the usual trend, increasing from log KLaL = 15.96 to log KLuL = 19.21. However, the stability of [Ln(1,7-DO2APA)] complexes decreases from log K = 16.33 for Gd3+ to 14.24 for Lu3+. The acid-catalyzed dissociation rates of the Gd3+ complexes differ by a factor of ∼15, with rate constants (k1) of 1.42 and 23.5 M–1 s–1 for [Gd(1,4-DO2APA)] and [Gd(1,7-DO2APA)], respectively. This difference is magnified across the lanthanide series to reach a 5 orders of magnitude higher k1 for [Yb(1,7-DO2APA)] (1475 M–1 s–1) than for [Yb(1,4-DO2APA)] (5.79 × 10–3 M–1 s–1). The acid-catalyzed mechanism involves the protonation of a carboxylate group, followed by a cascade of proton-transfer events that result in the protonation of a nitrogen atom of the cyclen unit. Density functional theory calculations suggest a correlation between the strength of the Ln–Ocarboxylate bonds and the kinetic inertness of the complex, with stronger bonds providing more inert complexes. The 1H NMR resonance of the coordinated water molecule in the [Yb(1,7-DO2APA)] complex at 176 ppm provides a sizable chemical exchange saturation transfer effect thanks to a slow water exchange rate of (15.9 ± 1.6) × 103 s–1.; L'arrangement des atomes donneurs de ligand autour de l'ion lanthanide provoque des différences dramatiques dans les stabilités thermodynamiques et la cinétique de dissociation des complexes de lanthanides, comme le démontre l'étude des complexes avec deux ligands à base de régioisomères du cyclen, contenant un bras picolinate et deux bras acétate soit en position 1,7 ou 1,4 de la structure macrocyclique.

International audience; We report the synthesis of an original ligand scaffold and the corresponding yttrium(III), europium(III) and ytterbium(III) complexes. All three compounds show reversible photochromism with high photo-conversions. Photoluminescence experiments demonstrate that this design is adapted for both europium and ytterbium emission switching. The OFF/ON luminescence ratio are excellent in the case of europium (4 to 8 %) and still quite good in the case of ytterbium (around 13 %); Nous présentons la synthèse d'un ligand original et ses complexes d'yttrium (III), d'europium (III) et d'ytterbium (III). Les trois composés présentent un photochromisme réversible avec des photo-conversions élevées. Les expériences de photoluminescence démontrent que le conception est adapté tant pour la commutation de l’émission de l'europium et de l'ytterbium. Le rapport de luminescence OFF/ON est excellent dans le cas de l'europium (4 à 8%) et encore assez bon dans le cas de l'ytterbium (environ 13%)

With a half-life of 7.45 days, silver-111 (βmax 1.04 MeV, Eγ 245.4 keV [Iγ 1.24%], Eγ 342.1 keV [Iγ 6.7%]) is a promising candidate for targeted cancer therapy with β– emitters as well as for associated SPECT imaging. For its clinical use, the development of suitable ligands that form sufficiently stable Ag+-complexes in vivo is required. In this work, the following sulfur-containing derivatives of tetraazacyclododecane (cyclen) have been considered as potential chelators for silver-111: 1,4,7,10-tetrakis(2-(methylsulfanyl)ethyl)-1,4,7,10-tetraazacyclododecane (DO4S), (2S,5S,8S,11S)-2,5,8,11-tetramethyl-1,4,7,10-tetrakis(2-(methylsulfanyl)ethyl)-1,4,7,10-tetraazacyclododecane (DO4S4Me), 1,4,7-tris(2-(methylsulfanyl)ethyl)-1,4,7,10-tetraazacyclododecane (DO3S), 1,4,7-tris(2-(methylsulfanyl)ethyl)-10-acetamido-1,4,7,10-tetraazacyclododecane (DO3SAm), and 1,7-bis(2-(methylsulfanyl)ethyl)-4,10,diacetic acid-1,4,7,10-tetraazacyclododecane (DO2A2S). Natural Ag+ was used in pH/Ag-potentiometric and UV–vis spectrophotometric studies to determine the metal speciation existing in aqueous NaNO3 0.15 M at 25 °C and the equilibrium constants of the complexes, whereas NMR and DFT calculations gave structural insights. Overall results indicated that sulfide pendant arms coordinate Ag+ allowing the formation of very stable complexes, both at acidic and physiological pH. Furthermore, radiolabeling, stability in saline phosphate buffer, and metal-competition experiments using the two ligands forming the strongest complexes, DO4S and DO4S4Me, were carried out with [111Ag]Ag+ and promising results were obtained., Five cyclen derivatives bearing sulfide pendant arms were considered, and their Ag+ complex formation was studied in aqueous solution by potentiometry, UV−vis, NMR, radiolabeling experiments with 111Ag, and DFT calculations. Overall results indicated that sulfide pendant arms coordinate Ag+ allowing the formation of very stable complexes, both at acidic and physiological pH. These ligands might be of interest for the setup of 111Ag labeled radiopharmaceuticals.

We report here the synthesis, characterization and kinetic studies of [RuL2(mac)]n+ complexes [mac = 1,4,8,11-tetraazacyclotetradecane (cyclam) or 1,4,7,10-tetraazacyclododecane (cyclen); and L = Cl−, OH−, OH2]. The dichloride complexes release one Cl− producing [RuCl(L)(mac)]n+ or two Cl− producing [Ru(L)2(mac)]n+ (L = OH2, OH−) in aqueous solution within pH 1–7. The product of these reactions were characterized by ultraviolet–visible (UV–Vis) spectroscopy. The chloride affinity of Ru(III) depends on the macrocyclic ring size and geometric structure. The k1 and thermodynamic activation parameters (at pH 4.4, T = 25 °C) of cis-[RuCl2(cyclen)]+ complex are k1 = 3.6 × 10−3 s−1 (25 °C); ΔH# = 40.2 kJ mol−1 and ΔS# = − 138 J K mol−1; under similar conditions, for cis-[RuCl2(cyclam)]+ these values are 2.4 × 10−3 s−1, ΔH# = 50.8 kJ mol−1 and ΔS# = − 119 J K mol−1. The rate of chloride aquation reactions for cis-[RuCl2(cyclen)]+ is about 1.5 times faster than for the cyclam complex. The reactivity difference could be due to a combination of the σ-trans effect, the nephelauxetic effect and the effect of solvation.

The new tetrakis[methyl(diphenylphosphorylated)] cyclen derivative DOTMPPh2 was synthesized and its complexation with cobalt(II), nickel(II), copper(II), and zinc(II) perchlorates was studied. According to the X-ray diffraction data, isostructural compounds [Zn(DOTMPPh2)](ClO4)2·2.66CH3CN·0.34H2O and [Co(DOTMPPh2)](ClO4)2·2.72CH3CN·0.28H2O provide the first examples of octacoordinate Zn2+ and Co2+ complexes with cyclen molecules. The coordination polyhedra of M2+ atoms are distorted Archimedean antiprisms formed by four cyclen N atoms and four phosphoryl O atoms. In [Cu(DOTMPPh2)](ClO4)2 the polyhedron of the copper atom is a slightly distorted tetragonal pyramid with four nitrogen atoms at the base and the O atom of a phosphoryl group at the apical vertex. The IR spectral data suggest that in the solid state Ni2+ complex with DOTMPPh2 has an octahedral structure, and it was confirmed by the high-spin magnetic moment of the complex. According to the UV–vis data, the structures of Cu2+, Ni2+, and Co2+ complexes in solution are close to those in the solid state. The stability constants of Cu2+, Ni2+, and Co2+ complexes with DOTMPPh2 in ethanol and acetonitrile have been estimated from UV–vis spectrophotometric data. The log K values for the M2+ + L = M2+L reaction in acetonitrile increase in the Co2+L

Herein we describe the synthesis, characterization, and role of three dichloric iron(III) complexes, [L1Fe(III)(Cl)2]ClO4 (L1Fe), [L2Fe(III)(Cl)2]ClO4 (L2Fe), and [L3Fe(III)(Cl)2]ClO4 (L3Fe) [L1 (Pyclen) = 1,4,7,10-tetra-aza-2,6-pyridinophane; L2 = 1,4,7,10-tetra-aza-2,6-pyridinophane-14-ol; L3 = 1,4,7,10-tetra-aza-2,6-pyridinophane-13-ol, in the coupling of pyrrole and phenylboronic acid to form 2-phenylpyrrole. The oxidation- and spin state of the iron complexes were characterized using X-ray crystallography, UV–vis absorbance spectroscopy, electron paramagnetic resonance spectroscopy, cyclic voltammetry, and mass spectrometry. Electrochemistry results rank ligand L1–L3 as moderate tetra-azamacrocycle donors to iron between cyclen and Me2EBC-12. Characterization of the iron(III) complexes and subsequent catalytic testing indicates that the complexes enter the C–C coupling catalytic cycle in the high-spin iron(III) oxidation state. Furthermore, the results indicate that the iron(III) complexes are essential for catalytic and regioselective production of the 2-phenylpyrrole product.

International audience; The triethylbenzene-bis-cyclen (cyclen = 1,4,7,10-tetraazacyclododecane) compound (tbmce) was designed with an imposed structural rigidity at the m-xylyl spacer to be compared to a less restrained and known parent compound (bmce). The framework of both compounds differs only in the substituents of the m-xylyl spacer. The study was centered in the differences observed in the acid–base reactions of both compounds, their copper(II) and zinc(II) complexation behaviors, as well as in the uptake of phosphate and polyphosphate anions (HPPi3–, ATP4–, ADP3–, AMP2–, PhPO42–, and HPO42–). On the one hand, the acid–base reactions showed lower values for the third and fourth protonation constants of tbmce than for bmce, suggesting that the ethyl groups of the spacer in tbmce force the two cyclen units to more conformational restricted positions. On the other hand, the stability constant values for copper(II) and zinc(II) complexes revealed that bmce is a better chelator than tbmce pointing out to additional conformational restraints imposed by the triethylbenzene spacer. The binding studies of phosphates by the dinuclear copper(II) and zinc(II) complexes showed much smaller effective association constants for the dicopper complexes. Single-crystal X-ray and computational (density functional theory) studies suggest that anion binding promotes the formation of tetranuclear entities in which anions are bridging the metal centers. Our studies also revealed the dinuclear zinc(II) complex of bmce as a promising receptor for phosphate anions, with the largest effective association constant of 5.94 log units being observed for the formation of [Zn2bmce(HPPi)]+. Accordingly, a colorimetric study via an indicator displacement assay to detect phosphates in aqueous solution found that the [Zn2bmce]4+ complex acts as the best receptor for pyrophosphate displaying a detection limit of 2.5 nM by changes visible to naked eye.

Many drugs that are applied in anticancer therapy such as the anthracycline doxorubicin contain DNA-intercalating 9,10-anthraquinone (AQ) moieties. When Cu(II) cyclen complexes were functionalized with up to three (2-anthraquinonyl)methyl substituents, they efficiently inhibited DNA and RNA synthesis resulting in high cytotoxicity (selective for cancer cells) accompanied by DNA condensation/aggregation phenomena. Molecular modeling suggests an unusual bisintercalation mode with only one base pair between the two AQ moieties and the metal complex as a linker. A regioisomer, in which the AQ moieties point in directions unfavorable for such an interaction, had a much weaker biological activity. The ligands alone and corresponding Zn(II) complexes (used as redox inert control compounds) also exhibited lower activity.

The C7-Gd and C8-Gd tags are compact hydrophilic cyclen-based lanthanide tags for conjugation to cysteine residues in proteins. The tags are enantiomers, which differ in the configuration of the 2-hydroxylpropyl pendant arms coordinating the lanthanide ion. Here, we report the electron paramagnetic resonance (EPR) performance of the C7-Gd ( S configuration) and C8-Gd ( R configuration) tags loaded with Gd(III) on two mutants of the homodimeric ERp29 protein. The W-band EPR spectra were found to differ between the tags in the free state and after conjugation to the protein. In addition, the spectra were sensitive to the labeling position, which may originate from an environment-dependent charge density on the Gd(III)-coordinating oxygens. This is in agreement with previous NMR experiments with different lanthanide ions, which suggested sensitivity to H-bonding. W-band 1H-ENDOR (electron-electron double resonance) experiments detected effects from orientation selection in the central transition, due to a relatively narrow distribution in the ZFS parameters as indicated by simulations. In contrast, the distance distributions derived from DEER (double electron-electron resonance) measurements were insensitive to the R or S configuration of the tags and did not exhibit any orientation selection effects. The DEER measurements faithfully reflected the different widths of the distance distributions at the different protein sites in agreement with previous DEER measurements using other Gd(III) tags. Due to their small size, short tether to the protein, and a broad central EPR transition, the C7-Gd and C8-Gd tags are attractive Gd(III) tags for measurements of relatively short (

Single crystals of two novel uranyl sulfates and two novel uranyl selenates with protonated cyclen and 3-aminotropane molecules, ((C8H24N4)[(UO2)3(SO4)5](H2O)3 (I), (C8H24N4)(H5O2)(H3O)[(UO2)4(SeO4)7(H2O)](H2O)6.6 (II), (C8H18N2)(H5O2)(H3O)[(UO2)3(SO4)5(H2O)](H2O)0.5 (III), and (C8H18N2)(H5O2)(H3O)[(UO2)3(SeO4)5 (H2O)](H2O)2 (IV) have been prepared by isothermal evaporation from aqueous solutions and structurally characterized. Uranyl-containing 2D units have been investigated using topological approach and information-based complexity measures demonstrating that complex topologies form more rare than their simplest counterparts, which is a response of the crystal structure to changes of chemical conditions within the system.

We report a detailed study of the structure of the [Bi(DO3A)] complex both in the solid state and in solution. The X-ray crystal structure of [Bi(DO3A)] evidences the octa-coordination of the Bi(III) ion, which is directly coordinated to the four nitrogen atoms of the cyclen unit and three oxygen atoms of the carboxylate groups. The octa-coordination is completed by an oxygen atom of a neighboring carboxylate group, which bridges Bi(III) ions thanks to μ2–η1:η1 coordination, resulting in the formation of a coordination polymer. The Bi(III) ion presents a twisted-square antiprismatic (TSAP) coordination geometry associated with the Δ(δδδδ)/Λ(λλλλ) enantiomeric pair. A computational DFT study indicates that the 6s2 lone pair of Bi(III) is stereochemically active in [Bi(DO3A)] and most of the cyclen-based complexes reported in the literature. Depending on the spatial arrangement of the donor atoms of the ligand the lone pair points in different directions, so that Bi(III) can easily accommodate different coordination environments. In solution the [Bi(DO3A)] complex exists as a monomeric complex, as demonstrated by DOSY measurements. The stability constant of the [Bi(DO3A)] complex, determined by using batch spectrophotometric titrations, was found to be rather high (log K = 26.85(5)). The complex presents characteristic absorption in the UV spectrum at 299 nm (e = 8770 M−1 cm−1) that was attributed to the Bi(III)-centered 6p ← 6s band on the basis of TDDFT calculations. Spectrophotometric titrations reveal weak binding of different anions to the [Bi(DO3A)] complex, with association constants of K11 = 3.55(8), 3.09(7), 6.2(1) and 2.19(5) for Cl−, Br−, I− and N3−, respectively.

A series of the new monophthalocyaninato lanthanide complexes, [Ln(Pc)(cyclen)]Cl (Ln = Y, Tb, Dy, Ho, Er, Tm, and Yb; Pc = phthalocyaninato; cyclen = 1,4,7,10-tetraazacyclododecane) was synthesized and characterized. The crystallographic study of monophthalocyaninato complexes with a capping macrocyclic ligand having no π-conjugation while keeping the 4-fold symmetry is presented for the first time. All the six complexes were crystallized in a tetragonal structure of the I4mm space group. In addition to this, the Tb complex exhibited a triclinic crystal structure of the P1 space group. All of the complexes are isostructural, where both Pc and cyclen are coordinated to an Ln3+ ion giving an eight-coordinate square-antiprismatic geometry. The skew angle between the Pc and cyclen ligands was 45° in the tetragonal crystals and 41.5° in the triclinic crystal. The metal–nitrogen bond lengths were shorter on the Pc ligand side than cyclen side, presumably due to the difference in the charges of the ligands and...

The magnesium triphenylsilyl complex [(Me3TACD)Mg(SiPh3)] (2) was synthesized from magnesium bis(triphenylsilyl) [Mg(SiPh3)2(THF)2]·THF (1; THF = tetrahydrofuran) and the NNNN-type macrocyclic amidotriamine proligand (Me3TACD)H ((Me3TACD)H = Me3[12]aneN4 = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane). Treating 2 with AlR3 (R = Me, Et) gave the magnesium triphenylsilyl complexes with “blocked” amido function [(Me3TACD·AlR3)Mg(SiPh3)] (3a: R = Me; 3b: R = Et). Instead of forming a Mg–H bond upon reaction with dihydrogen or hydrosilanes, 2 and 3a,b underwent rapid silyl–silane exchange with hydrosilanes. Treating the ethyl complex [(Me3TACD·AlEt3)MgEt] with H3SiPh gave [(Me3TACD·AlEt3)MgH] (4), albeit not in a reproducible manner. The silyl–hydrosilane exchange allows access to other magnesium silyls of the type [(Me3TACD)Mg(SiR′3)] (5a: SiR′3 = SiH2Ph; 5b: SiR′3 = SiHPh2) and [(Me3TACD·AlR3)Mg(SiR′3)] (6a: SiR′3 = SiH2Ph, R = Me; 6b: SiR′3 = SiH2Ph, R = Et; 7a: SiR′3 = SiHPh2, R = Me; 7b: SiR′3 = SiHPh2,...

The Eu3+/2+ redox couple provides a convenient design platform for responsive pO2 sensors for magnetic resonance imaging (MRI). Specifically the Eu2+ ion provides T1w contrast enhancement under hypoxic conditions in tissues, whereas, under normoxia, the Eu3+ ion can produce contrast from chemical exchange saturation transfer in MRI. The oxidative stability of the Eu3+/2+ redox couple for a series of tetraaza macrocyclic complexes was investigated in this work using cyclic voltammetry. A series of Eu-containing cyclen-based macrocyclic complexes revealed positive shifts in the Eu3+/2+ redox potentials with each replacement of a carboxylate coordinating arm of the ligand scaffold with glycinamide pendant arms. The data obtained reveal that the complex containing four glycinamide coordinating pendant arms has the highest oxidative stability of the series investigated.

Invited for the cover of this issue are the groups of Y. Ye from Zhengzhou University, China, A. Angerhofer from the University of Florida, USA, Y. Zhao from Xiamen University, China, and L.-J. Ming from the University of South Florida, USA. The cover image shows the pathways for dinuclear catechol oxidation by CuII complexes of cyclotriphosphazene derivatives with up to six metal-binding sites.

Paramagnetic NMR techniques allow for studying three-dimensional structures of RNA–protein complexes. In particular, paramagnetic relaxation enhancement (PRE) data can provide valuable information about long-range distances between different structural components. For PRE NMR experiments, oligonucleotides are typically spin-labeled using nitroxide reagents. The current work describes an alternative approach involving a Cu(II) cyclen-based probe that can be covalently attached to an RNA strand in the vicinity of the protein’s binding site using “click” chemistry. The approach has been applied to study binding of HIV-1 nucleocapsid protein 7 (NCp7) to a model RNA pentanucleotide, 5′-ACGCU-3′. Coordination of the paramagnetic metal to glutamic acid residue of NCp7 reduced flexibility of the probe, thus simplifying interpretation of the PRE data. NMR experiments showed attenuation of signal intensities from protein residues localized in proximity to the paramagnetic probe as the result of RNA–protein interactions. The extent of the attenuation was related to the probe’s proximity allowing us to construct the protein’s contact surface map.

Structural evidence is reported for C-HCl- hydrogen bonds in solution and in the solid state of HgCl2 complexes with cyclen-based cryptands. These cyclen-based cryptands (1) and (2) are bridged by di- and triethylene glycol units, respectively, between two aromatic rings. The X-ray structure indicates that the 2/HgCl2 complex contains an acetonitrile molecule in the cavity.

The crystal structure of the title salt, [Cu(ClO4)(C8H20N4)]ClO4, is reported. The CuIIion exhibits a square-pyramidal geometry and is coordinated by the four N atoms of the neutral 1,4,7,10-tetraazacyclododecane (cyclen) ligand and an O atom from one perchlorate anion, with the second perchlorate ion hydrogen-bonded to one of the amine N atoms of the cyclen ligand. Additional N—H...O hydrogen bonds between the amine H atoms and the coordinating and non-coordinating perchlorate groups create a three-dimensional network structure. Crystals were grown from a concentrated methanol solution at ambient temperature, resulting in no co-crystallization of solvent.

[Abstract] The ditopic receptor L3 [1-(2-((7-(4-(tert-butyl)benzyl)-1,4,7,10-tetraazacyclododecan-1-yl)methyl)phenyl)-3-(3-nitrophenyl)urea] containing a macrocyclic cyclen unit for Cu(II)-coordination and a urea moiety for anion binding was designed for recognition of metal salts. The X-ray structure of [CuL3(SO4)] shows that the sulfate anion is involved in cooperative binding via coordination to the metal ion and hydrogen-bonding to the urea unit. This behaviour is similar to that observed for the related receptor L1 [1-(2-((bis(pyridin-2-ylmethyl)amino)methyl)phenyl)-3-(3-nitrophenyl)urea], which forms a dimeric [CuL1(μ-SO4)]2 structure in the solid state. In contrast, the single crystal X-ray structure of [ZnL3(NO3)2] contains a 1 : 2 complex (metal : anion) where one anion coordinates to the metal and the other is hydrogen-bonded to the urea group. Spectrophotometric titrations performed for the [CuL3(OSMe2)]2+ complex indicate that this system is able to bind a wide range of anions with an affinity sequence: MeCO2− > Cl− > H2PO4− > Br− > NO2− > HSO4− > NO3−. Lipophilic analogues of L1 and L3 extract CuSO4 and CuCl2 from water into chloroform with high selectivity over the corresponding Co(II), Ni(II) and Zn(II) salts. Xunta de Galicia; EM 2012/088 Xunta de Galicia; CN-2012/011

The interaction of aminomethylphosphonic acid (H2amp) with the Zn(II)–cyclen complex and the formation of ternary complexes was studied by potentiometry and 31P NMR titrations. Data evaluation of each of the methods separately was found to be insufficient. Thus, data obtained from the both methods were simultaneously treated with the computer program OPIUM. The determined stability constants indicated only weak (log K ∼ 3) coordination of aminomethylphosphonic acid through the phosphonate group. The chelating coordination mode with the participation of the amine group was not confirmed. In excess of Zn(II)–cyclen, the formation of dinuclear complexes, in which two Zn(II)–cyclen units are bridged by a phosphonate group, was observed and their presence was confirmed by mass spectrometry. Such a coordination motif is typical for phosphonates in the solid state and also for phosphatases.

Metal-cyclen complexes have a number of important applications. However, the coordination chemistry between metal ions and cyclen-based macrocycles is much less well studied compared to their metal ion-crown ether analogues. This work, which makes a contribution to address this imbalance by studying complex ions of the type [M(Me4cyclen)(L)]+, was initiated by results of an experimental study which prepared some Group 1 metal cyclen complexes, namely [Li(Me4cyclen)(H2O)][BArF] and [Na(Me4cyclen)(THF)][BArF] and obtained their X-ray crystal structures [J. M. Dyke, W. Levason, M. E. Light, D. Pugh, G. Reid, H. Bhakhoa, P. Ramasami, and L. Rhyman, Dalton Trans., 2015, 44, 13853]. The lowest [M(Me4cyclen)(L)]+ minimum energy structures (M = Li, Na, K, and L = H2O, THF, DEE, MeOH, DCM) are studied using density functional theory (DFT) calculations. The geometry of each [M(Me4cyclen)(L)]+ structure and, in particular, the conformation of L are found to be mainly governed by steric hindrance which decreases as the size of the ionic radius increases from Li+ → Na+ → K+. Good agreement of computed geometrical parameters of [Li(Me4cyclen)(H2O)]+ and [Na(Me4cyclen)(THF)]+ with the corresponding geometrical parameters derived from the crystal structures [Li(Me4cyclen)(H2O)]+[BArF]− and [Na(Me4cyclen)(THF)]+[BArF]− is obtained. Bonding analysis indicates that the stability of the [M(Me4cyclen)(L)]+ structures originates mainly from ionic interaction between the Me4cyclen/L ligands and the M+ centres. The experimental observation that [M(Me4cyclen)(L)]+[BArF]− complexes could be prepared in crystalline form for M+ = Li+ and Na+, but that experiments aimed at synthesising the corresponding K+, Rb+, and Cs+ complexes failed resulting in formation of [Me4cyclenH][BArF] is investigated using DFT and explicitly correlated calculations, and explained by considering production of [Me4cyclenH]+ by a hydrolysis reaction, involving traces of water, which competes with [M(Me4cyclen)(L)]+ formation. [Me4cyclenH]+ formation dominates for M+ = K+, Rb+, and Cs+ whereas formation of [M(Me4cyclen)(L)]+ is energetically favoured for M+ = Li+ and Na+. The results indicate that the number and type of ligands, play a key role in stabilising the [M(Me4cyclen)]+ complexes and it is hoped that this work will encourage experimentalists to prepare and characterise other [M(Me4cyclen)(L)]+ complexes.

Herein we present a supramolecular (delayed luminescent) Eu(III)-based pH-responsive probe/sensor with the ability to detect the urease-mediated hydrolysis of urea in aqueous solution. A series of photophysical titrations show this Eu(III) chelate behaves as an ‘on-off’ luminescent switching probe, with its luminescence being quenched upon urea being enzymatically convert- ed into ammonia and carbon dioxide. Calculation of the rate constant (k) and activation energy (Ea) for this hydrolysis reaction are detailed; the results demonstrate a direct observation of enzymatic activity in solution by the sensor. The potential application of this probe in detecting the onset of catheter-associated urinary tract infections (CAUTIs) is also demonstrated by incorporating 1.Eu into water-permeable hydrogels that can be utilized as an alternative coating for catheters.