Figure - available from: Journal of Inclusion Phenomena and Macrocyclic Chemistry
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The effects of electrolytes on protonation were studied by UV spectrometry on the geometrical isomers of dioxapentaazacyclophanes that were synthesized by 1+1-cyclization of diethylenetriaminepentaacetic (DTPA) dianhydride with aromatic diamine involving 1,3- or 1,4-phenylenebis(methyleneoxy) group. Absorption bands at 245 and 280 nm respond to pH...
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![Figure 3. Crystal structure of Rb 2 [U(NH 2 ) 6 ]. Rb atoms are shown...](publication/340714059/figure/fig3/AS:881330116108288@1587136882817/Crystal-structure-of-Rb-2-UNH-2-6-Rb-atoms-are-shown-in-dark-green-U-atoms-in_Q320.jpg)
The pyrophoric compound Rb2[U(NH2)6] was obtained as a grey to black powder from the reaction of more than three equivalents of RbNH2 with UI3 in anhydrous liquid ammonia. During the process, UIII is oxidized to UIV and ammonia is reduced under evolution of H2. Rb2[U(NH2)6] crystallizes in the cubic crystal system, space group Fm3m, with the lattic...
Citations
... Indeed, DTPA amide cyclophanes derived from aromatic diamines show high selectivity towards metal ions. Regarding the factor of the type of donor atoms, there is a general tendency for oxa-macrocycles to interact more strongly with alkali metals than aza-macrocycles, while nitrogen has a stronger binding capacity towards protons and other metal ions (Soberanes et al. 2018). ...
The development of phosphors for warm white light plays a decisive role in the quest for energy-efficient and environmentally friendly lighting technologies. Lanthanide-based phosphors, especially those containing europium ions (Eu³⁺), offer promising possibilities as they can emit light in the entire visible spectrum. In this study, the luminescence properties of two Eu³⁺ complexes, specifically [Eucy1a] and [Eu2cy2], synthesized with macrocyclic ligands are presented. The macrocyclic ligands (cy1a)H3 and (cy2)H6 provide a stable coordination environment that allows fine-tuning of photophysical properties, which are crucial for warm white phosphors. Synthesis, molecular modeling using density functional theory (DFT) and spectroscopic characterization of the complexes were performed. Notably, the complexes showed an inefficient energy transfer from the ligands to the Eu³⁺ ions, resulting in a broad blue emission spectrum corresponding to the ligand emission and the red 4f–4f transitions of Eu³⁺,which is important for the generation of white light. Photometric evaluation revealed favorable properties, including correlated color temperatures (CCT) indicative of warm white light, high color rendering index (CRI) values and exceptional Luminous Efficacy of Radiation (LER). In addition, the presence of coordinated water molecules influenced the luminescence lifetime and quantum efficiency of the complexes. Overall, the synthesized Eu³⁺ complexes show promising prospects for applications in solid-state lighting, LED designs and emergency technologies that offer high performance and energy efficiency.
Graphical Abstract
... The pD-variable NMR titration method has been examined by application to the complexation of histidine with a DTPA-derived cyclophane shown in Scheme 1. The pD dependence of NMR shifts of the cyclophane shows that the first protonation occurs in a pD range of 8-10 (cf. Figure S3) [7]. In a wide pD range, the major species is the mono-protonated anion abbreviated as cyH 2− , which is expected to form complexes with organic ions through ion-paring and subsequent encapsulation in the cavity, as reported for similar cyclophane acids [8,9]. ...
... The cyclophane was synthesised by the previously reported method [7]. DL-Histidine hydrochloride was used as supplied from Sigma-Aldrich. ...
The complexation of organic electrolytes, like carboxylic acids and amines, is studied usually by spectrometric titration at a constant pH. Obtained stability constants are, however, conditional and dependent on the pH selected, differing from the proper constants. In nuclear magnetic resonance (NMR) titration in D2O, a stability constant determined at a given pD is not directly correlated to other properties observed at a pH in H2O because of difference between acid dissociations in the solvents. To overcome these problems, this report proposes pD-variable NMR spectrometry, which monitors NMR signals of a mixture of the reactants with the variation of pD. This method identifies complexes formed in different pD ranges, and determines the proper stability constants, to yield the species distribution, which can be replotted in pH scale. The usefulness and limitation are examined by simulation of titration curves. An experimental example is presented for complexation of histidine with a cyclophane acid. Excel® files for calculations are available in Supplementary material.
As an effort to search for paramagnetic probing agents toward specific substrates, ¹H NMR studies were carried out on the Dy³⁺ complex of a chelating cyclophane derived from DTPA (diethylenetriaminepentaacetate) and p-xylylenediamine, and the paramagnetic effects were examined on coexisting D-histidine and histamine. The lanthanide metal complex exhibits well-defined paramagnetic shifts of the psuedocontact term, owing to the highly rigid macrocyclic framework. Coexisting histamine and histidine also show sharp NMR peaks with small but significant shifts, in contrast to the spectra in the coexistence of the free metal ion. The metal chelate molecule has a large open space, in which a substrate molecule is captured and exchanged with nearby molecules. Through this exchange process, the spatial paramagnetic effect of the metal chelate extends in a long range so that coexisting substrate molecules can be probed by NMR.
