RESUMEN

Pyridoxal and pyridoxal 5'-phosphate are aldehyde forms of B6 vitamin that can easily be transformed into each other in the living organism. The presence of a phosphate group, however, provides the related compounds (e.g., hydrazones) with better solubility in water. In addition, the phosphate group may sometimes act as a binding center for metal ions. In particular, a phosphate group can be a strong ligand for a gold(III) ion, which is of interest for researchers for the anti-tumor and antimicrobial potential of gold(III). This paper aims to answer whether the phosphate group is involved in the complex formation between gold(III) and hydrazones derived from pyridoxal 5'-phosphate. The answer is negative, since the comparison of the stability constants determined for the gold(III) complexes with pyridoxal- and pyridoxal 5'-phosphate-derived hydrazones showed a negligible difference. In addition, quantum chemical calculations confirmed that the preferential coordination of two series of phosphorylated and non-phosphorylated hydrazones to gold(III) ion is similar. The preferential protonation modes for the gold(III) complexes were also determined using experimental and calculated data.

Asunto(s)

Oro , Hidrazonas , Piridoxal , Hidrazonas/química , Oro/química , Piridoxal/química , Fosfato de Piridoxal/química , Complejos de Coordinación/química , Espectrofotometría Ultravioleta , Estructura Molecular

RESUMEN

Gold(III) complexes with different ligands can provide researchers with a measure against pathogenic microorganisms with antibiotic resistance. We reported in our previous paper that the UV-Vis spectra of different protonated species of complexes formed by gold(III) and five hydrazones derived from pyridoxal 5'-phosphate are similar to each other and to the spectra of free protonated hydrazones. The present paper focuses on the reasons of the noted similarity in electron absorption spectra. The geometry of different protonated species of complexes of gold(III) and hydrazones (15 structures in total) was optimized using the density functional theory (DFT). The coordination polyhedron of gold(III) bond critical points were further studied to identify the symmetry of the gold coordination sphere and the type of interactions that hold the complex together. The UV-Vis spectra were calculated using TD DFT methods. The molecular orbitals were analyzed to interpret the calculated spectra.

Asunto(s)

Oro , Hidrazonas , Hidrazonas/química , Fosfatos , Piridoxal

RESUMEN

Lanthanides such as cerium(III), europium(III), and gadolinium(III) are widely used for designing fluorescent probes or magnetic resonance imaging contrasting agents for biological systems. The synthesis and study of lanthanide complexes in buffer solutions imitating biological fluids are often complicated because of a lack of data on the lanthanide interactions with buffer solution components. Therefore, Ln(III) [where Ln(III) = La(III), Ce(III), Gd(III), Eu(III)] complexation with a widely used buffer agent, tris(hydroxymethyl)aminomethane (Tris), in aqueous solution is studied using potentiometry, spectrofluorimetry, and 139La NMR spectroscopy. The stoichiometric composition of complexes is determined using mass spectrometry. The thermodynamic stability constants of Ln(III)-Tris complexes are calculated from potentiometric and spectral data; the difficulties in the study of these systems, reliability, and accuracy of the obtained constants are discussed. The possible structures of free Tris and its complexes with lanthanides(III) are optimized on the density functional theory/PBE0 level; the peculiarities of metal-ligand bonds were studied by Quantum Theory Atoms in Molecules analysis.

RESUMEN

We have designed and constructed a combined experimental setup for synchronous measurements of electron diffraction patterns and mass-spectra of gas samples. Test measurements have been performed for acetic acid at two temperatures, 296 K and 457 K. Electron diffraction data have been analyzed taking into account mass spectra measured in the same experiments. From the diffraction intensities, molecular structures and mole fractions of the acetic acid monomer and dimer have been refined. The obtained results demonstrate the importance of measuring mass spectra in gas electron diffraction experiments. In particular, it is possible to detect the sample decomposition, which can be used for the optimization of experimental conditions and for the data interpretation. The length of the hydrogen bond in the acetic acid dimer determined in this work, re(O⋯H) = 1.657(9) Å, is in good agreement with modern theoretical predictions. We recommend measuring the diffraction patterns of acetic acid for the calibration of the sample pressure in the diffraction volume.

RESUMEN

The molecular structure of 4-nitropyridine N-oxide, 4-NO2-PyO, has been determined by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and by quantum chemical calculations (DFT and MP2). Comparison of these results with those for non-substituted pyridine N-oxide and 4-methylpyridine N-oxide CH3-PyO, demonstrate strong substitution effects on structural parameters and electron density distribution. The presence of the electron-withdrawing -NO2 group in para-position of 4-NO2-PyO results in an increase of the ipso-angle and a decrease of the semipolar bond length r(N→O) in comparison to the non-substituted PyO. The presence of the electron-donating -CH3 group in 4-CH3-PyO leads to opposite structural changes. Electron density distribution in pyridine-N-oxide and its two substituted compounds are discussed in terms of natural bond orbitals (NBO) and quantum theory atoms in molecule (QTAIM).