Transient versus static electron spin relaxation in Mn2+ complexes relevant as MRI contrast agents

[Abstract] The zero-field splitting (ZFS) parameters of the [Mn(EDTA)(H2O)]2–·2H2O and [Mn(MeNO2A)(H2O)]·2H2O systems were estimated by using DFT and ab initio CASSCF/NEVPT2 calculations (EDTA = 2,2′,2″,2‴-(ethane-1,2-diylbis(azanetriyl))tetraacetate; MeNO2A = 2,2′-(7-methyl-1,4,7-triazonane-1,4-diyl)diacetate). Subsequent molecular dynamics calculations performed within the atom-centered density matrix propagation (ADMP) approach provided access to the transient and static ZFS parameters, as well as to the correlation time of the transient ZFS. The calculated ZFS parameters present a reasonable agreement with the experimental values obtained from the analysis of 1H relaxation data. The correlation times calculated for the two systems investigated turned out to be very short (τc ∼ 0.02–0.05 ps), which shows that the transient ZFS is modulated by molecular vibrations. On the contrary, the static ZFS is modulated by the rotation of the complexes in solution, which for the small complexes investigated here is characterized by rotational correlation times of τR ∼ 35–60 ps. As a result, electron spin relaxation in small Mn2+complexes is dominated by the static ZFS.España. Ministerio de Economía y Competitividad; CTQ2013-43243-PEspaña. Ministerio de Economía y Competitividad; CTQ2015-71211-RED

Relationship between microbial activity and microbial community structure in six full-scale anaerobic digesters

High activity levels and balanced anaerobic microbial communities are necessary to attain proper anaerobic digestion performance. Therefore, this work was focused on the kinetic performance and the microbial community structure of six full-scale anaerobic digesters and one lab-scale co-digester. Hydrolytic (0.6-3.5 g COD g(-1) VSS d(-1)) and methanogenic (0.01-0.84 g COD g(-1) VSS d(-1)) activities depended on the type of biomass, whereas no significant differences were observed among the acidogenic activities (1.5-2.2 g COD g(-1) VSS d(-1)). In most cases, the higher the hydrolytic and the methanogenic activity, the higher the Bacteroidetes and Archaea percentages, respectively, in the biomasses. Hydrogenotrophic methanogenic activity was always higher than acetoclastic methanogenic activity, and the highest values were achieved in those biomasses with lower percentages of Methanosaeta. in sum, the combination of molecular tools with activity tests seems to be essential for a better characterization of anaerobic biomasses

Ln2M complexes (M = Ru, Re) derived from a bismacrocyclic ligand containing a 4,4'-dimethyl-2,2'-bipyridyl bridging unit.

Homodinuclear lanthanide complexes derived from a ligand featuring two DO3A chelating sites linked by a 4,4'-dimethyl-2,2'-bipyridyl spacer were prepared and characterized. The bipyridyl coordination site of 1 was used to introduce Ru(Bpy)(2) and Re(CO)(3)Cl moieties, leading to the formation of heterometallic d-f(2) complexes with general formulae [Ln(2)·1·Ru(Bpy)(2)](2+) (Ln = Nd, Eu, Tb, Yb and Lu) and [Ln(2)·1·Re(CO)(3)Cl] (Ln = Nd, Yb and Lu). The luminescence properties of the complexes were investigated by means of absorption spectroscopy and steady-state and time-resolved luminescence spectroscopy covering the visible and NIR regions. Both Ru and Re chromophores were shown to act as efficient sensitizers of the NIR emission of Yb and Nd in aqueous solutions. We also consider the unsaturated coordination spheres of the Ln cations in the Ln(2)·1 complexes, which form ternary complexes with bidentate anions without showing particular synergistic effects for polyanionic species

Gd(3+)-Based Magnetic Resonance Imaging Contrast Agent Responsive to Zn(2.)

[Abstract] We report the heteroditopic ligand H5L, which contains a DO3A unit for Gd3+ complexation connected to an NO2A moiety through a N-propylacetamide linker. The synthesis of the ligand followed a convergent route that involved the preparation of 1,4-bis(tert-butoxycarbonylmethyl)-1,4,7-triazacyclononane following the orthoamide strategy. The luminescence lifetimes of the Tb(5D4) excited state measured for the TbL complex point to the absence of coordinated water molecules. Density functional theory calculations and 1H NMR studies indicate that the EuL complex presents a square antiprismatic coordination in aqueous solution, where eight coordination is provided by the seven donor atoms of the DO3A unit and the amide oxygen atom of the N-propylacetamide linker. Addition of Zn2+ to aqueous solutions of the TbL complex provokes a decrease of the emission intensity as the emission lifetime becomes shorter, which is a consequence of the coordination of a water molecule to the Tb3+ ion upon Zn2+binding to the NO2A moiety. The relaxivity of the GdL complex recorded at 7 T (25 °C) increases by almost 150% in the presence of 1 equiv of Zn2+, while Ca2+ and Mg2+ induced very small relaxivity changes. In vitro magnetic resonance imaging experiments confirmed the ability of GdL to provide response to the presence of Zn2+.Ministerio de Economía y Competitividad; CTQ2013-43243-

Toward Inert Paramagnetic Ni(II)-Based Chemical Exchange Saturation Transfer MRI Agents

The Ni2+ complexes with hexadentate ligands containing two 6 methylpicolinamide groups linked by ethane-1,2 diamine (H2dedpam) or cyclohexane-1,2 diamine (H2chxdedpam) spacers were investigated as potential contrast agents in magnetic resonance imaging (MRI). The properties of the complexes were compared to those of the analogues containing 6 methylpicolinate units (dedpa2 and chxdedpa2 ). The X ray structure of the [Ni(H2dedpam)]2+ complex reveals a six-coordinated metal ion with a distorted octahedral environment. The protonation constants of the dedpa2 and H2dedpam ligands and the stability constants of their Ni2+ complexes were determined using pH-potentiometry and spectrophotometric titrations (25 ºC, 0.15 M NaCl). The [Ni(dedpa)] complex (logKNiL = 20.88(1)) was found to be considerably more stable than the corresponding amide derivative [Ni(H2dedpam)]2+ (logKNiL = 14.29(2)). However, the amide derivative [Ni(H2chxdedpam)]2+ was found to be considerably more inert with respect to proton-assisted dissociation than the carboxylate derivative [Ni(chxdedpa)]. A detailed 1H NMR and DFT study was conducted to assign the 1H NMR spectra of the [Ni(chxdedpa)] and [Ni(H2chxdedpam)]2+ complexes. The observed 1H NMR paramagnetic shifts were found to be dominated by the Fermi contact contribution. The amide resonances of [Ni(H2chxdedpam)]2+ at 91.5 and 22.2 ppm were found to provide sizeable chemical exchange staturation transfer effect, paving the way for the development of NiCEST agents based on these rigid non-macrocyclic platforms

Probing Electrostatic Potential by NMR with the Use of a Paramagnetic Lanthanide(III) Chelate

The paramagnetic complex [Yb­(DOTA)]⁻ forms ion pairs in aqueous solution with cationic species such as <i>N</i>-monoalkyl- and <i>N</i>,<i>N</i>′-dialkyl-4,4′-bipyridinium cations. The magnitude and sign of the induced ¹H NMR pseudocontact shift values can be correlated to the electrostatic potential calculated at the MPWLYP/6-311G** level