The syntheses of a new 1,4,7,10-tetraazacyclododecane (cyclen) derivative bearing a picolinate pendant arm (HL1), and its 1,4,8,11-tetraazacyclotetradecane (cyclam) analogue HL2, were achieved by using two different selective-protection methods involving the preparation of cyclen-bisaminal or phosphoryl cyclam derivatives. The acid-base properties of both compounds were investigated as well as their coordination chemistry, especially with Cu(2+), in aqueous solution and in solid state. The copper(II) complexes were synthesized, and the single crystal X-ray diffraction structures of compounds of formula [Cu(HL)](ClO(4))(2)·H(2)O (L = L1 or L2), [CuL1](ClO(4)) and [CuL2]Cl·2H(2)O, were determined. These studies revealed that protonation of the complexes occurs on the carboxylate group of the picolinate moiety. Stability constants of the complexes were determined at 25.0 °C and ionic strength 0.10 M in KNO(3) using potentiometric titrations. Both ligands form complexes with Cu(2+) that are thermodynamically very stable. Additionally, both HL1 and HL2 exhibit an important selectivity for Cu(2+) over Zn(2+). The kinetic inertness in acidic medium of both complexes of Cu(2+) was evaluated by spectrophotometry revealing that [CuL2](+) is much more inert than [CuL1](+). The determined half-life values also demonstrate the very high kinetic inertness of [CuL2](+) when compared to a list of copper(II) complexes of other macrocyclic ligands. The coordination geometry of the copper center in the complexes was established in aqueous solution from UV-visible and electron paramagnetic resonance (EPR) spectroscopy, showing that the solution structures of both complexes are in excellent agreement with those of crystallographic data. Cyclic voltammetry experiments point to a good stability of the complexes with respect to metal ion dissociation upon reduction of the metal ion to Cu(+) at about neutral pH. Our results revealed that the cyclam-based ligand HL2 is a very attractive receptor for copper(II), presenting a fast complexation process, a high kinetic inertness, and important thermodynamic and electrochemical stability.

Single crystal X-ray diffraction show that Zr(IV) forms an octa-coordinated complex with 4 bidentate hydroxamates whose solution structures were investigated utilizing density functional theory at the level of B3LYP/DGDZVP. Stability constants obtained by potentiometry were in accordance with the tendency observed when radiolabeling with 89Zr.

The water exchange process was accelerated for nine-coordinate, monohydrated macrocyclic GdIII complexes by inducing steric compression around the water binding site; the increased steric crowding was achieved by replacing an ethylene bridge of DOTA4- by a propylene bridge; in addition to the optimal water exchange rate, the stability of [Gd(TRITA)(H2O)]- is sufficiently high to ensure safe medical use which makes it a potential synthon for the development of high relaxivity, macromolecular MRI contrast agents.

The synthesis of a new cross-bridged 1,4,8,11-tetraazacyclotetradecane (cb-cyclam) derivative bearing a picolinate arm (Hcb-te1pa) was achieved by taking advantage of the proton sponge properties of the starting constrained macrocycle. The structure of the reinforced ligand as well as its acid-base properties and coordination properties with Cu(2+) and Zn(2+) was investigated. The X-ray structure of the free ligand showed a completely preorganized conformation that lead to very fast copper(II) complexation under mild conditions (instantaneous at pH 7.4) or even in acidic pH (3 min at pH 5) at room temperature and that demonstrated high thermodynamic stability, which was measured by potentiometry (at 25 °C and 0.10 M in KNO3). The results also revealed that the complex exists as a monopositive copper(II) species in the intermediate pH range. A comparative study highlighted the important selectivity for Cu(2+) over Zn(2+). The copper(II) complex was synthesized and investigated in solution using different spectroscopic techniques and DFT calculations. The kinetic inertness of the copper(II) complex in acidic medium was evaluated by spectrophotometry, revealing the very slow dissociation of the complex. The half-life of 96 days, in 5 M HClO4, and 465 min, in 5 M HCl at 25 °C, show the high kinetic stability of the copper(II) chelate compared to that of the corresponding complexes of other macrocyclic ligands. Additionally, cyclic voltammetry experiments underlined the perfect electrochemical inertness of the complex as well as the quasi-reversible Cu(2+)/Cu(+) redox system. The coordination geometry of the copper center in the complex was established in aqueous solution from UV-vis and EPR spectroscopies.

The synthesis and characterization of Hno1pa2py, a new tacn-based ligand, is reported. The complexation process with Cu(2+) was proved to be very fast even in acidic medium. Potentiometric titrations allowed us to establish that Hno1pa2py exhibits an overall low basicity as well as a high selectivity for Cu(2+) over Zn(2+) cations. The copper(II) complex was synthesized and characterized using UV-vis and EPR spectroscopies and density functional theory (DFT) calculations. The studies clearly showed that the [Cu(no1pa2py)](+) complex is present in solution as a mixture of two isomers in which the ligand is coordinated to the metal center using a N5O donor set with the metal center in a distorted octahedral geometry. The very high kinetic inertness of the [Cu(no1pa2py)](+) complex was demonstrated by using acid-assisted dissociation assays as well as cyclic voltammetry. Preliminary investigations of (64)Cu complexation were performed to validate the potential use of such chelating agent for further application in nuclear medicine. The X-ray crystal structures of copper(II) complexes of L1, the ester derivative of Hno1pa2py, have been determined.

Lanthanide(III) complexes of a cross-bridged cyclam derivative containing two picolinate pendant arms are kinetically inert in very harsh conditions such as 2 M HCl, with no dissociation being observed for at least 5 months. Importantly, the [Ln(dota)](-) complexes, which are recognized to be extremely inert, dissociate under these conditions with lifetimes in the range ca. 1 min to 12 h depending upon the Ln(3+) ion. X-ray diffraction studies reveal octadentate binding of the ligand to the metal ion in the [Eu(cb-tedpa)](+) complex, while (1)H and (13)C NMR experiments in D2O point to the presence of a single diastereoisomer in solution with a very rigid structure. The structure of the complexes in the solid state is retained in solution, as demonstrated by the analysis of the Yb(3+)-induced paramagnetic shifts.

Two new macrocyclic ligands, 6,6′-((1,4,7,10-tetraazacyclododecane-1,7-diyl)bis(methylene))dipicolinic acid (H2DODPA) and 6,6′-((4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-diyl)bis(methylene))dipicolinic acid (H2Me-DODPA), designed for complexation of lanthanide ions in aqueous solution, have been synthesized and studied. The X-ray crystal structure of [Yb(DODPA)](PF6)·H2O shows that the metal ion is directly bound to the eight donor atoms of the ligand, which results in a square-antiprismatic coordination around the metal ion. The hydration numbers (q) obtained from luminescence lifetime measurements in aqueous solution of the Eu(III) and Tb(III) complexes indicate that the DODPA complexes contain one inner-sphere water molecule, while those of the methylated analogue H2Me-DODPA are q = 0. The structure of the complexes in solution has been investigated by 1H and 13C NMR spectroscopy, as well as by theoretical calculations performed at the density functional theory (DFT; mPWB95) level. The minimum energy conformation calculated for the Yb(III) complex [Λ(λλλλ)] is in good agreement with the experimental structure in solution, as demonstrated by the analysis of the Yb(III)-induced paramagnetic 1H shifts. The nuclear magnetic relaxation dispersion (NMRD) profiles recorded for [Gd(Me-DODPA)]+ are typical of a complex with q = 0, where the observed relaxivity can be accounted for by the outer-sphere mechanism. However, [Gd(DODPA)]+ shows NMRD profiles consistent with the presence of both inner- and outer-sphere contributions to relaxivity. A simultaneous fitting of the NMRD profiles and variable temperature 17O NMR chemical shifts and transversal relaxation rates provided the parameters governing the relaxivity in [Gd(DODPA)]+. The results show that this system is endowed with a relatively fast water exchange rate k(ex)(298) = 58 × 10(6) s(–1).

Herein, we present a new approach that combines DFT calculations and the analysis of Tb(III)-induced (1)H NMR shifts to quantitatively and accurately account for the contact contribution to the paramagnetic shift in Ln(III) complexes. Geometry optimizations of different Gd(III) complexes with macrocyclic ligands were carried out using the hybrid meta-GGA TPSSh functional and a 46 + 4f(7) effective core potential (ECP) for Gd. The complexes investigated include [Ln(Me-DODPA)](+) (H(2)Me-DODPA = 6,6'-((4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-diyl)bis(methylene))dipicolinic acid, [Ln(DOTA)(H(2)O)](-) (H(4)DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate), [Ln(DOTAM)(H(2)O)](3+) (DOTAM = 1,4,7,10- tetrakis[(carbamoyl)methyl]-1,4,7,10-tetraazacyclododecane), and related systems containing pyridyl units (Ln = Gd, Tb). Subsequent all-electron relativistic calculations based on the DKH2 approximation, or small-core ECP calculations, were used to compute the (1)H hyperfine coupling constants (HFCCs) at the ligand nuclei (A(iso) values). The calculated A(iso) values provided direct access to contact contributions to the (1)H NMR shifts of the corresponding Tb(III) complexes under the assumption that Gd and Tb complexes with a given ligand present similar HFCCs. These contact shifts were used to obtain the pseudocontact shifts, which encode structural information as they depend on the position of the nucleus with respect to the lanthanide ion. An excellent agreement was observed between the experimental and calculated pseudocontact shifts using the DFT-optimized geometries as structural models of the complexes in solution, which demonstrates that the computational approach used provides (i) good structural models for the complexes, (ii) accurate HFCCs at the ligand nuclei. The methodology presented in this work can be classified in the context of model-dependent methods, as it relies on the use of a specific molecular structure obtained from DFT calculations. Our results show that spin polarization effects dominate the (1)H A(iso) values. The X-ray crystal structures of [Ln(Me-DODPA)](PF(6))·2H(2)O (Ln = Eu or Lu) are also reported.