N. S. Emel’yanova

Synthesis, structure, NO donor activity of iron–sulfur nitrosyl complex with 2-aminophenol-2-yl and its antiproliferative activity against human cancer cells

A new tetranitrosyl binuclear iron complex, [Fe2(SC6H6N)2(NO)4] (1), has been synthesized by two methods. Molecular and crystalline structure of 1 were determined by X-ray analysis; the complex is binuclear of “μ-S” type with ~2.7052(4) Å between the irons. The compound crystallizes in monoclinic, space group P21/n, Z = 2; parameters of the unit cell: a = 6.6257(2) Å, b = 7.9337(2) Å, c = 16.7858(4) Å, β = 96.742(2)°, V = 876.26(4) Å3. Parameters of Mössbauer spectrum for 1 are: isomer shift δFe = 0.096(1) mm/s, quadrupole splitting ΔEQ = 1.122(1) mm/s, line width 0.264(1) mm/s at 293 K. As follows from the electrochemical analysis of aqueous solutions of 1, it generates NO in protonic media without additional activation. NO amount and the rate of its activation are much higher in acidic solutions than in neutral and alkali ones. The constants of hydrolytic decomposition of 1 were calculated. The geometry and electronic structure of isolated 1 were studied using the density functional theory. Differential sensitivity of four lines of human tumor cells of various genesis to 1 has been determined (ovarian carcinoma (SCOV3), large intestine cancer (LS174T), mammary gland carcinoma (MCF7), and non-small cell carcinoma of lung (A549)); dependence of tumor cells amount on the complex concentration has been studied in order to use the complex as a promising antitumor agent for trials in vivo.

Quantum chemical modeling of the stability of reduced forms of Roussin’s red esters. Effect of the nature of the ligand

The reduced forms of Roussin’s red esters [Fe2(μ-RS)2(NO)4]n− (n = 1, 2; R = Ph, Pr) and their possible decomposition products were studied by quantum chemical calculations. The energy diagram of the processes that occur in a dichloromethane solution was constructed. According to this diagram, the monoanions are much more stable than the corresponding dianions. Possible dissociation paths of the dianions in solution were proposed. The anions with the propyl ligand are more stable than the anions with the phenyl ligand.

Experimental and theoretical study of the effect of the substituent nature on the luminescent properties of scandium complexes with substituted 8-hydroxyquinolines

The luminescent properties of homoleptic scandium complexes with 2-substituted 8-hydroquinolines bearing the substituent groups H (1), CH3 (2), CN (3), and NH2 (4) were studied for use as emission layers in organic light-emitting diodes. It was found that the introduction of a substituent into the 2-position makes its possible to effectively shift the emission maximum to the blue or red region: to 530 nm (yellow-green) by 1 and 2, 615 nm (orange) by 3, and 495 nm (blue-green) by 4. The structure and the optical properties of the complexes were determined by density-functional-theory quantum-chemical calculations. The theoretical spectra agree well with the experimental photoluminescence spectra.

On the mechanism of air nitrogen fixation on activated carbon surface in water

High-performance liquid chromatography and gas chromatography were used to reveal formation of hydroxyl radicals in air-saturated water containing activated carbon. Probable mechanisms of OH· formation are considered. The role of OH· radicals in the formation of carbene centers on the activated carbon surface is discussed. For interpreting the experimental data on atmospheric nitrogen fixation on activated carbon surface, probable mechanisms of nitrogen activation are explored by quantum-chemical methods. Highly reactive OH· radicals are unable to react with molecular nitrogen under mild conditions. A high reactivity of singlet and triplet carbenes of different nature on activated carbon surface with respect to N2 molecules was revealed by density functional theory methods.

Topological analysis of transition states of the concerted molecular decomposition of haloalkanes and alcohols with HHal and HOH elimination

The quantum chemical modeling and topological analysis of transition states of the concerted molecular decomposition of haloalkanes and alcohols with the elimination of HHal and HOH were performed for the ten compounds. The possibility of formation of two types of transition states was mentioned, and their electronic structures were studied. The influence of the alkyl substituent at the C atoms on the binding energy and the nature of the transition state was shown. The decomposition activation energies were calculated using the method of density functional theory (DFT/B3LYP/6-311++G**) and the intersecting parabolas method. The calculated results were compared, and their agreement was shown.

Redox properties of [Fe2(SC6H5)2(NO)4]: an experimental study and quantum chemical modeling

Reduction of the complex [Fe2(SC6H5)2(NO)4] in an aprotic solvent was studied by cyclic voltammetry in a wide range of potential scan rates. It was established that transfer of the first electron is reversible and the redox potential of this reaction was determined. Further reduction of the complex is irreversible because the product of attachment of the second electron is unstable and partially decomposes during the characteristic time of potential scan. The molecular and electronic structures of mono- and dianion of the complex as well as its theoretical redox potential value were calculated using the density functional theory methods with the local (BP86) and hybrid (B3LYP) functionals. The former functional better describes the geometry of the complex while the latter gives a better insight into its electronic structure. The extra negative charge is delocalized over NO groups, phenyl ligands, and iron atoms. The calculated redox potentials of one-electron reduction of the complexes are close to the experimental values obtained by analyzing cyclic voltammograms. Attachment of the second electron opens the decomposition channel of the complex, which is also consistent with experimental data.

The energy and geometric characteristics of the transition state in reactions of RO2• with carbonyl compound C-H bonds

The energy and geometry of the transition state in reactions of the ethyl peroxyl radical with ethane, ethanol (its α and β C-H bonds), acetone, butanone-2, and acetaldehyde were calculated by the density functional theory method. In all these reactions (except EtO2/• + ethanol α C-H bond), the C…H…O reaction center has an almost linear configuration (φ = 176° ± 2°); polar interaction only influences the r≠ (C…O) interatomic bond. In the reaction of EtO2/• with the ethanol α C-H bond, it is the O-H…O H-bond formed in the transition state that determines the configuration of the reaction center with the angle φ(C…H…O) = 160°. The results were used to estimate the r≠ (C…H) and r≠ (O…H) interatomic bonds in the transition state by the method of intersecting parabolas and the contribution of polar interaction to the activation energy of reactions between peroxyl radicals and aldehydes and ketones.

Theoretical Analysis of the Alternative Additions of Radicals to Multiple Bonds

The alternative additions of the hydrogen atom and methyl, aminyl, and methoxyl radicals to the double bond of CH2=Y (Y = CHR, CR2, CHCH=CH2, CHPh, NH, O) compounds are theoretically analyzed using the intersecting parabolas method and DFT. The enthalpies, activation energies, and geometric parameters of the transition state in the reactions R· + CH2=Y → RCH2Y· and R· + CH2=Y → RYC·H2 are calculated. The results obtained by the two methods are compared with experimental data. The competing alternative radical additions to the multiple bonds are governed by the enthalpies of the reactions.

Quantum chemical approaches to the study of Fe—S bond in Roussin’s red esters: replacement of functional ligands by glutathione

Density functional quantum chemical calculations of Roussin’s red esters with phenyl [Fe2(SPh)2(NO)4] and ortho-aminophenyl [Fe2(SC6H4NH2)2(NO)4] ligands, as well as products of partial and complete replacement of functional ligands by glutathione were carried out. Main characteristics of the Fe—S bonds in these compounds were estimated within the framework of the NBO approach and the AIM theory. The possibility for ligand substitution reactions to occur was demonstrated. A possible mechanism of these processes is proposed.

Free-radical abstraction reactions with concerted fragmentation and NO formation

The enthalpy and activation energy of reactions involving attack by MeO2• and MeO2• on CH2 groups of 2-butyl nitrite and 2-nitrosobutane have been calculated by quantum chemical methods. The abstraction of a hydrogen atom is accompanied, in the former case, by concerted N–O bond breaking and, in the latter case, by concerted C–N bond breaking, resulting in NO• formation. On the basis of the results obtained, an algorithm has been developed within the intersecting parabolas model for calculating the enthalpies, activation energies, and rate constants of these types of reactions involving alkyl, alkoxyl, aminyl, peroxyl, phenoxyl, thiyl, and hydroxyl radicals.