Physico-Chemistry of Dinitrosyl Iron Complexes as a Determinant of Their Biological Activity

In this article we minutely discuss the so-called “oxidative” mechanism of mononuclear form of dinitrosyl iron complexes (M-DNICs) formations proposed by the author. M-DNICs are proposed to be formed from their building material—neutral NO molecules, Fe2+ ions and anionic non-thiol (L−) and thiol (RS−) ligands based on the disproportionation reaction of NO molecules binding with divalent ion irons in pairs. Then a protonated form of nitroxyl anion (NO−) appearing in the reaction is released from this group and a neutral NO molecule is included instead. As a result, M-DNICs are produced. Their resonance structure is described as [(L−)2Fe2+(NO)(NO+)], in which nitrosyl ligands are represented by NO molecules and nitrosonium cations in equal proportions. Binding of hydroxyl ions with the latter causes conversion of these cations into nitrite anions at neutral pH values and therefore transformation of DNICs into the corresponding high-spin mononitrosyl iron complexes (MNICs) with the resonance structure described as [(L−)2Fe2+(NO)]. In case of replacing L− by thiol-containing ligands, which are characterized by high π-donor activity, electron density transferred from sulfur atoms to iron-dinitrosyl groups neutralizes the positive charge on nitrosonium cations, which prevents their hydrolysis, ensuring relatively a high stability of the corresponding M-DNICs with the resonance structure [(RS−)2Fe2+ (NO, NO+)]. Therefore, M-DNICs with thiol-containing ligands, as well as their binuclear analogs (B-DNICs, respective resonance structure [(RS−)2Fe2+2 (NO, NO+)2]), can serve donors of both NO and NO+. Experiments with solutions of B-DNICs with glutathione or N-acetyl-L-cysteine (B-DNIC-GSH or B-DNIC-NAC) showed that these complexes release both NO and NO+ in case of decomposition in the presence of acid or after oxidation of thiol-containing ligands in them. The level of released NO was measured via optical absorption intensity of NO in the gaseous phase, while the number of released nitrosonium cations was determined based on their inclusion in S-nitrosothiols or their conversion into nitrite anions. Biomedical research showed the ability of DNICs with thiol-containing ligands to be donors of NO and NO+ and produce various biological effects on living organisms. At the same time, NO molecules released from DNICs usually have a positive and regulatory effect on organisms, while nitrosonium cations have a negative and cytotoxic effect.

Relationship between Antioxidant Activity and Ligand Basicity in the Dipicolinate Series of Oxovanadium(IV) and Dioxovanadium(V) Complexes

Oxidative stress plays an important role in the pathogenesis of many serious diseases, including cancer, atherosclerosis, coronary artery disease, Parkinson’s disease, Alzheimer’s disease, stroke and myocardial infarction. In the body’s natural biochemical processes, harmful free radicals are formed, which can be removed with the help of appropriate enzymes, a balanced diet or the supply of synthetic antioxidant substances such as flavonoids, vitamins or anthocyanins to the body. Due to the growing demand for antioxidant substances, new complex compounds of transition metal ions with potential antioxidant activity are constantly being sought. In this study, four oxovanadium(IV) and dioxovanadium(V) dipicolinate (dipic) complexes with 1,10-phenanthroline (phen), 2,2′-bipyridyl (bipy) and the protonated form of 2-phenylpyridine (2-phephyH): (1) [VO(dipic)(H2O)2] · 2 H2O, (2) [VO(dipic)(phen)] · 3 H2O, (3) [VO(dipic)(bipy)] · H2O and (4) [VOO(dipic)](2-phepyH) · H2O were synthesized including one new complex, so far unknown and not described in the literature, i.e., [VOO(dipic)](2-phepyH) · H2O. The oxovanadium(IV) dipicolinate complexes with 1,10-phenanthroline and 2,2′-bipyridyl have been characterized by several physicochemical methods: NMR, MALDI-TOF-MS, IR, but new complex [VOO(dipic)](2-phepyH) · H2O has been examined by XRD to confirm its structure. The antioxidant activities of four complexes have been examined by the nitrotetrazolium blue (NBT) method towards superoxide anion. All complexes exhibit high reactivity with superoxide anion and [VOO(dipic)](2-phepyH) · H2O has higher antioxidant activity than L-ascorbic acid. Our studies confirmed that high basicity of the auxiliary ligand increases the reactivity of the complex with the superoxide radical.

Mechanisms of Tebuconazole Adsorption in Profiles of Mineral Soils

The study attempted to identify the soil components and the principal adsorption mechanisms that bind tebuconazole in mineral soils. The KF values of the Freundlich isotherm determined in 18 soils from six soil profiles in batch experiments after 96 h of shaking ranged from 1.11 to 16.85 μg1–1/n (mL)1/n g–1, and the exponent 1/n values from 0.74 to 1.04. The adsorption of tebuconazole was inversely correlated with the soil pH. Both neutral and protonated forms of this organic base were adsorbed mainly on the fraction of humins. The adsorption of the protonated form increased in the presence of hydrogen cations adsorbed in the soil sorption sites. Fourier transform infrared spectroscopy coupled with the molecular modeling studies and partial least squares regression analysis indicated that the tebuconazole molecule is bound in the organic matter through the formation of hydrogen bonds as well as hydrophobic and π–π interactions. Ion exchange was one of the adsorption mechanisms of the protonated form of this fungicide. The created mathematical model, assuming that both forms of tebuconazole are adsorbed on the organic matter and adsorption of the protonated form is affected by the potential acidity, described its adsorption in soils well.

Protonated Forms of Layered Perovskite-Like Titanate NaNdTiO4: Neutron and X-ray Diffraction Structural Analysis

Structures of partially and completely protonated Ruddlesden–Popper phases, H0.7Na0.3NdTiO4·0.3H2O and HNdTiO4, have been established by means of neutron and X-ray diffraction analysis and compared among themselves as well as with that of the initial titanate NaNdTiO4. It was shown that while interlayer sodium cations in the partially protonated form are coordinated by nine oxygen atoms, including one related to intercalated water, in the fully protonated compound the ninth oxygen proves to be an axial anion belonging to the opposite slab of titanium-oxygen octahedra. Moreover, the partially protonated titanate was found to significantly differ from the other two in the octahedron distortion pattern. It is characterized by a weakly pronounced elongation of the octahedra towards the Nd-containing interlayer space making Ti4+ cations practically equidistant from both axial oxygen atoms, which is accompanied by a low-frequency shift of the bands relating to the asymmetric stretching mode of axial Ti–O bonds observed in the Raman spectra.

Static vs. Dynamic Electrostatic Repulsion Reversed Phase Liquid Chromatography: Solutions for Pharmaceutical and Biopharmaceutical Basic Compounds

Many efforts have been made to separate basic compounds, which are challenging to resolve in reversed phase liquid chromatography. In this process, they are strongly retained and the peak shape undergoes significant distortion. The principal origin of this has been identified with the non-negligible interaction with residual deprotonated silanols. Consequently, all solutions that efficiently shield silanols are being sought. This review is an upgrade on the use of the electrostatic repulsion reversed phase (ERRP) approach: retention of bases, in protonated form, can be achieved by modulating the charge repulsion caused by the presence of positive charges in the chromatographic system. This study successfully (i) introduced fixed positive charges in the structure of stationary phases, (ii) used cationic and hydrophobic additives in the mobile phase, and (iii) used the ERRP-like approach employed at the preparative level for peptide purification.

Erdmann’s Anion—An Inexpensive and Useful Species for the Crystallization of Illicit Drugs after Street Confiscations

Erdmann’s anion [1,6-diammino tetranitrocobaltate(III)] is useful in the isolation and crystallization of recently confiscated street drugs needing to be identified and catalogued. The protonated form of such drugs forms excellent crystals with that anion; moreover, Erdmann’s salts are considerably less expensive than the classically used AuCl4− anion to isolate them, while preparation of high-quality crystals is equally easy in both cases. We describe the preparation and structures of the K+CoH6N6O8− and NH4+CoH6N7O8−, salts of Erdmann’s. In addition, herein are described the preparations of this anion’s salts with cocaine (C17H28CoN7O12), with methamphetamine (C10H22CoN7O8), and with methylone (C22H34CoN8O14), whose preparation and stereochemistry had been characterized by the old AuCl4− salts methodology. For all species in this report, the space groups and cell constants were determined at 296 and 100 K, looking for possible thermally induced polymorphism—none was found. Since the structures were essentially identical at the two temperatures studied, we discuss only the 100 K results. Complete spheres of data accessible to a Bruker ApexII diffractometer with Cu–Kα radiation, λ = 1.54178 Å, were recorded and used in the refinements. Using the refined single crystal structural data for the street drugs, we computed their X-ray powder diffraction patterns, which are beneficial as quick identification standards in law enforcement work.

Potential of Nb2O5 nanofibers in photocatalytic response for organic pollutants remediation

Due to the pollution caused by different organic pollutants, various photocatalytic nanomaterials for environmental remediation have been promoted. In this study, Nb2O5 nanofibers were obtained by electrospinning technique, presenting controlled crystallinity and high specific surface area to improve the photoactivity response. The structural characterization indicated Nb2O5 nanofibres with orthorhombic phase formation, and the photoluminescence measurements showed different energy levels contributing to the electronic transition events. The nanofibers with a bandgap up to 3.6 eV were applied to photocatalysis of dyes [Rhodamine B (RhB) or Methylene Blue (MB)], and Prozac®, listed as an emergent pollutant. In the optimized condition (pH = 9), the RhB and MB photocatalysis was 59% and 93% more efficient than photolysis due to ζ = − 50 ± 5 mV for EtOH_550 sample that increased the interaction with MB (cationic) compared to RhB unprotonated (pKa = 3.7). Therefore, Prozac® (pKa = 10.7) was selected due to protonated form at pH = 9 and showed 68% ±1 adsorption in 30 min for EtOH_550. The Prozac® photocatalytic degradation under UV light irradiation was up to 17% higher than the photolytic degradation. The formation of hydroxyl radicals in the photocatalytic system (EtOH_550) was proven by the Coumarine probe assay, corroborating with the greater amount of α-[2-(Methylamino)ethyl]benzylalcohol (MAEB), a by-product obtained after Prozac® oxidation. Additionally, the material achieved specific catalytic activity for the different organic compounds (RhB, MB, or Prozac®), showing that only using dyes may not be ideal to conclude the great material applicability in environmental remediation studies. Therefore, Nb2O5 nanofibers were efficient for the degradation of three different pollutants under UV light, proving to be a viable alternative for environmental remediation.

Crystal Structure Determination of 4-[(Di-p-tolyl-amino)-benzylidene]-(5-pyridin-4-yl-[1,3,4]thiadiazol-2-yl)-imine along with Selected Properties of Imine in Neutral and Protonated Form with Camforosulphonic Acid: Theoretical and Experimental Studies

The crystal structure was determined for the first time for 4-[(di-p-tolyl-amino)benzylidene]-(5-pyridin-4-yl-[1,3,4]thiadiazol-2-yl)-imine (trans-PPL9) by X-ray diffraction. The imine crystallized in the monoclinic P21/n space group with a = 18.9567(7) Å, b = 6.18597(17) Å, c = 22.5897(7) Å, and β = 114.009(4)°. Intermolecular interactions in the PPL9 crystal were only weak C−H∙∙∙N hydrogen bonds investigated using the Hirshfeld surface. The electronic and geometric structure of the imine were investigated by the density functional theory and the time-dependent density-functional theory. The properties of the imine in neutral and protonated form with camforosulphonic acid (CSA) were investigated using cyclic voltammetry, UV–vis and 1H NMR spectroscopy. Theoretical and experimental studies showed that for the 1:1 molar ratio the protonation occured on nitrogen in pyridine in the PPL9 structure, as an effect of Brönsted acid–base interactions. Thermographic camera was used to defined defects in constructed simple devices with ITO/PPL9 (or PPL9:CSA)/Ag/ITO architecture. In conclusion, a thermally stable imine was synthesized in crystalline form and by CSA doping, a modification of absorption spectra together with reduction of overheating process was observed, suggesting its potential application in optoelectronics.