Synthesis and Characterization of 1,10-Phenanthroline-mono-N-oxides

Abstract

N-oxides of N-heteroaromatic compounds find widespread applications in various fields of chemistry. Although the strictly planar aromatic structure of 1,10-phenanthroline (phen) is expected to induce unique features of the corresponding N-oxides, so far the potential of these compounds has not been explored. In fact, appropriate procedure has not been reported for synthesizing these derivatives of phen. Now, we provide a straightforward method for the synthesis of a series of mono-N-oxides of 1,10-phenanthrolines. The parent compounds were oxidized by a green oxidant, peroxomonosulfate ion in acidic aqueous solution. The products were obtained in high quality and at good to excellent yields. A systematic study reveals a clear-cut correlation between the basicity of the compounds and the electronic effects of the substituents on the aromatic ring. The UV spectra of these compounds were predicted by DFT calculations at the TD-DFT/TPSSh/ def2-TZVP level of theory.

In Vitro and In Vivo Biological Activities of Dipicolinate Oxovanadium(IV) Complexes

“…The spectrum of complex 6 shows peaks at 270 and 280, and a small peak at 310 nm, while the spectrum of complex 8 presents peaks at 265 and 330 nm (Figure S18). According to the literature, − π → π* transitions of the aromatic rings of the 1,10-phenanthroline ligand can also originate peaks at 260–280 nm. Both complexes ( 6 and 8 ) showed no spectral changes over time, meaning that no structural changes occurred.…”

“…Before going more deeply into the biological data regarding these complexes, 5 , 6 , and 8 , their stability in the RPMI culture medium was analyzed at three different time points: 0, 24, and 48 h (Figure S18). The electronic spectra (Figure S18) show an intense band at 230 nm, which may correspond to transitions between π→π* orbitals in the aromatic rings of the 1,10-phenanthroline ligand, present in all three complexes. − In the spectrum corresponding to complex 5 , peaks are observed at 260, 300, 310, and 340 nm, with an overall conservation of the maximum peak absorbance over 48 h, meaning that no structural changes of the complex occurred over time (Figure S18). The spectrum of complex 6 shows peaks at 270 and 280, and a small peak at 310 nm, while the spectrum of complex 8 presents peaks at 265 and 330 nm (Figure S18).…”

Complexes of 1,10-Phenanthroline-Mono-N-Oxides with Copper(Ii) and Nickel(Ii) in Aqueous Solution and Solid Phase

“…phenO, DMPO and TMPO were synthetized using the corresponding phenanthroline derivates and (peroxomonosulphate-ion (HSO 5 -) under acidic condition and were identified by their 1 H NMR and mass spectra as described earlier. [6,10] Details of the synthesis are provided in the Supporting Information (SI). Potassium peroxomonosulfate (PMS) is available as a stable triple salt, brand named Oxone (2KHSO 5 ⋅KHSO 4 ⋅K 2 SO 4 , Merck) and the solid was added directly to the reaction mixtures during the synthesis.…”

“…The acid dissociation constants of phenO and its derivatives obtained by pH-potentiometry are in excellent agreement with previously determined data. [10] Now, we focus on the fluorescence of these ligands. Since the phenanthroline backbone exhibits characteristic strongly pH dependent emission properties, the same scenario is expected for the Noxides.…”

“…Although the ligands were used at μM concentration level in the fluorescent experiments, the results are in excellent agreement with those obtained by pH-potentiometry earlier at considerably higher ligand concentrations. [10].…”