Tuning the Properties of Rigidified Acyclic DEDPA Derivatives for Application in PET Using Copper-64.

We present a detailed investigation of the coordination chemistry toward [Cu/Cu]copper of a series of HDEDPA derivatives (HDEDPA = 6,6'-((ethane-1,2-diylbis(azanediyl))bis(methylene))dipicolinic acid) containing cyclohexyl (HCHXDEDPA), cyclopentyl (HCpDEDPA) or cyclobutyl (HCBuDEDPA) spacers. Furthermore, we also developed a strategy that allowed the synthesis of a HCBuDEDPA analogue containing an additional NHBoc group at the cyclobutyl ring, which can be used for conjugation to targeting units. The X-ray structures of the Cu(II) complexes evidence distorted octahedral coordination around the metal ion in all cases.

Incorporation of Carboxylate Pendant Arms into 18-Membered Macrocycles: Effects on [Pb]Pb(II) Complexation.

We present a detailed investigation on the coordination chemistry of [Pb]Pb(II) with chelators HPYTA and HCHX-PYTA. These chelators belong to the family of ligands derived from the 18-membered macrocyclic backbone PYAN and present varying degrees of rigidity due to the presence of either ethyl or cyclohexyl spacers. A complete study of the stable Pb(II) complexes is carried out via NMR, X-Ray crystallography, stability constant determination and computational studies.

Rigid versions of PDTA incorporating a 1,3-diaminocyclobutyl spacer for Mn complexation: stability, water exchange dynamics and relaxivity.

Rigid derivatives of the acyclic ligand PDTA4- (HPDTA = propylenediamine-,,','-tetraacetic acid) were prepared by functionalization of a 1,3-diaminocyclobutyl spacer. The new ligands contain either four acetate groups attached to the central scaffold (H4L1) or incorporate pyridyl (H2L2) or propylamide (H2L3) units replacing two of the carboxylate groups. The ligand protonation constants and the stability constants of their Mn complexes were determined using potentiometric and spectrophotometric titrations.

Mn Complexes Containing Sulfonamide Groups with pH-Responsive Relaxivity.

We present two ligands containing a -ethyl-4-(trifluoromethyl)benzenesulfonamide group attached to either a 6,6'-(azanediylbis(methylene))dipicolinic acid unit (HDPASAm) or a 2,2'-(1,4,7-triazonane-1,4-diyl)diacetic acid macrocyclic platform (HNO2ASAm). These ligands were designed to provide a pH-dependent relaxivity response upon complexation with Mn in aqueous solution. The protonation constants of the ligands and the stability constants of the Mn complexes were determined using potentiometric titrations complemented by spectrophotometric experiments.

Axial Ligation in Ytterbium(III) DOTAM Complexes Rationalized with Multireference and Ligand-Field ab Initio Calculations.

The nature of the axial ligand coordinated to the Yb ion in [Yb(DOTAM)] has profound consequences in the magnetic anisotropy and optical properties of the complex, as evidenced by H NMR and UV-vis spectroscopies. The pseudocontact shifts of H nuclei and the F ← F absorption band were found to be very sensitive to the nature of the axial ligand (MeOH, HO, MeOH, or F). The energy levels of the F and F manifolds in [Yb(DOTAM)(X)] (X = MeOH, HO, or dimethyl sulfoxide (DMSO)) and [Yb(DOTAM)F] complexes were assigned from the analysis of the optical spectra and ab initio calculations based on CASSCF wave functions that considered dynamic correlation through perturbation theory (NEVPT2) and spin-orbit coupling effects.

pH-Dependent Hydration Change in a Gd-Based MRI Contrast Agent with a Phosphonated Ligand.

The heptadentate ligand L was shown to form an extremely stable Gd complex at neutral pH with a pGd value of 18.4 at pH 7.4.

Reinforced Ni(ii)-cyclam derivatives as dual H/F MRI probes.

Reinforced cross-bridged Ni2+-cyclam complexes were functionalised with pendant arms containing both amide protons and CF3 groups that lead to a dual 1H/19F response. The resulting complexes possess very high inertness favourable for MRI applications. The paramagnetism of the Ni2+ ion shifts the amide resonance 56 ppm away from bulk water favouring the chemical exchange saturation transfer (CEST) effect and shortening the acquisition times in 19F magnetic resonance imaging (MRI) experiments, thus enhancing the signal-to-noise ratios compared to the fluorinated diamagnetic reference.

A pentadentate member of the picolinate family for Mn(ii) complexation and an amphiphilic derivative.

We report a pentadentate ligand containing a 2,2'-azanediyldiacetic acid moiety functionalized with a picolinate group at the nitrogen atom (H3paada), as well as a lipophylic derivative functionalized with a dodecyloxy group at position 4 of the pyridyl ring (H3C12Opaada). The protonation constants of the paada3- ligand and the stability constant of the Mn(ii) complex were determined using a combination of potentiometric and spectrophotometric titrations (25 °C, 0.15 M NaCl).

On the consequences of the stereochemical activity of the Bi(iii) 6s lone pair in cyclen-based complexes. The [Bi(DO3A)] case.

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.

Toward inert paramagnetic Ni(ii)-based chemical exchange saturation transfer MRI agents.

The Ni complexes with hexadentate ligands containing two 6-methylpicolinamide groups linked by ethane-1,2-diamine (dedpam) or cyclohexane-1,2-diamine (chxdedpam) spacers were investigated as potential contrast agents in magnetic resonance imaging (MRI). The properties of the complexes were compared to that of the analogues containing 6-methylpicolinate units (dedpa and chxdedpa). The X-ray structure of the [Ni(dedpam)] complex reveals a six-coordinated metal ion with a distorted octahedral environment.

A further study of acetylacetone nitrosation.

The nitrosation of acetylacetone (AcAc) has been revised in an aqueous acid medium of perchloric acid and buffers of mono-, di-, or tri-chloroacetic acid. The results show that in the presence of buffers, under conditions of [nit] ≪ [AcAc] (nit = sodium nitrite) the reaction cannot be studied by UV-Vis spectroscopy, contrary to the recently published paper by García-Rio et al. (J.

Iron(III) complexation by Vanchrobactin, a siderophore of the bacterial fish pathogen Vibrio anguillarum.

The bacterial fish pathogen Vibrio anguillarum serotype O2 strain RV22 produces the mono catecholate siderophore Vanchrobactin (Vb) under conditions of iron deficiency. Vb contains two potential bidentate coordination sites: catecholate and salicylate groups. The iron(III) coordination properties of Vb is investigated in aqueous solutions using spectrophotometric and potentiometric methods.

Ester hydrolysis and nitrosative deamination of novocaine in aqueous solutions.

In aqueous solutions, the kinetic features of both the hydrolysis reaction of the ester function of novocaine in alkaline medium and the nitrosation reaction of the primary amine group of novocaine in mild acid medium were investigated by UV/vis spectroscopy. The ester hydrolysis shows first-order kinetics with respect to both the drug and the nucleophile, OH-, concentrations, thus following a typical S(N)2 (Ac) mechanism. The rate of the reaction decreases strongly with the polarity of the reaction media, analyzed for both dioxane-water and Me2SO-water mixtures.