We report a macrocyclic ligand (H 3 L 6 ) based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform containing three acetate pendant arms and a benzyl group attached to the fourth nitrogen atom of the macrocycle. The X-ray structures of the Y L 6 and Tb L 6 complexes reveal nine coordination of the ligand to the metal ions through the six nitrogen atoms of the macrocycle and three oxygen atoms of the carboxylate pendants. A combination of NMR spectroscopic studies ( 1 H, 13 C, and 89 Y) and DFT calculations indicated that the structure of the Y L 6 complex in the solid state is maintained in an aqueous solution. The detailed study of the emission spectra of the Eu L 6 and Tb L 6 complexes revealed Ln 3+ -centered emission with quantum yields of 7.0 and 60%, respectively. Emission lifetime measurements indicate that the ligand offers good protection of the metal ions from surrounding water molecules, preventing the coordination of water molecules. The Y L 6 complex is remarkably inert with respect to complex dissociation, with a lifetime of 1.7 h in 1 M HCl. On the other hand, complex formation is fast (∼1 min at pH 5.4, 2 × 10 –5 M). Studies using the 90 Y-nuclide confirmed fast radiolabeling since [ 90 Y]Y L 6 is nearly quantitatively formed (radiochemical yield (RCY) > 95) in a short time over a broad range of pH values from ca. 2.4 to 9.0. Challenging experiments in the presence of excess ethylenediaminetetraacetic acid (EDTA) and in human serum revealed good stability of the [ 90 Y]Y L 6 complex. All of these experiments combined suggest the potential application of H 3 L 6 derivatives as Y-based radiopharmaceuticals.
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. The protonation constants of the dedpa and dedpam ligands and the stability constants of their Ni complexes were determined using pH-potentiometry and spectrophotometric titrations (25 °C, 0.15 M NaCl). The [Ni(dedpa)] complex (log K = 20.88(1)) was found to be considerably more stable than the corresponding amide derivative [Ni(dedpam)] (log K = 14.29(2)). However, the amide derivative [Ni(chxdedpam)] was found to be considerably more inert with respect to proton-assisted dissociation than the carboxylate derivative [Ni(chxdedpa)]. A detailed H NMR and DFT study was conducted to assign theH NMR spectra of the [Ni(chxdedpa)] and [Ni(chxdedpam)] complexes. The observed H NMR paramagnetic shifts were found to be dominated by the Fermi contact contribution. The amide resonances of [Ni(chxdedpam)] at 91.5 and 22.2 ppm were found to provide a sizeable chemical exchange saturation transfer effect, paving the way for the development of NiCEST agents based on these rigid non-macrocyclic platforms.
This work analyses the influence of fine concrete fractions (<5 mm) of different natures —calcareous (HcG) and siliceous (HsT)—obtained from construction and demolition waste (C&DW) on the behaviour of blended cement pastes with partial replacements between 5 and 10%. The two C&DW fractions were characterised by different instrumental techniques. Subsequently, their lime-fixing capacity and the physico-mechanical properties of the blended cement pastes were analysed. Lastly, the environmental benefits of reusing these fine wastes in the manufacture of future eco-efficient cement pastes were examined. The results show that HsT and HcG exhibit weak pozzolanic activity, owing to their low reactive silica and alumina content. Despite this, the new cement pastes meet the physical and mechanical requirements of the existing regulations for common cements. It should be highlighted that the blended cement pastes initially showed a coarser pore network, but then they underwent a refinement process between 2 and 28 days, along with a gain in compressive strength, possibly due to the double pozzolanic and filler effect of the wastes. The environmental viability of the blended cements was evaluated in a Life Cycle Assessment (LCA) concluding that the overall environmental impact could be reduced in the same proportion of the replacement rate. This is in line with the Circular Economy goals and the 2030 Agenda for Sustainable Development.
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