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Hydrogenated and hydroxylated nanodiamonds (NDs) are modeled by putting emphasis on the most common paramagnetic impurities—dangling bonds as well as single substitutional nitrogen atoms—and their interaction with water. It is shown that, despite its overall hydrophobicity, hydrogenated ND can become locally hydrophilic due to the introduced defects; therefore, water molecules may be attracted to the particular sites at its surface. To assess the direct influence of water on the magnetic behavior of NDs, the solvent-induced shift of the g-tensor was employed, indicating that for the same types of impurities, the impact the water has strongly depends on their positions in ND. In addition, water molecules at the locally hydrophilic sites of hydrogenated ND may influence the magnetic behavior of defects to the same extent as it may be influenced in the case of hydroxylated ND. Moreover, the overall hydrophilic nature of the latter does not necessarily guarantee that water, although being strongly attracted to the vicinity of impurity, will form a hydrogen bond network with a substantial impact on the local environment of the unpaired electron. The obtained data imply that in the context of the Overhauser effect, for which the solvent-induced shift of the g-tensor is proposed as a tool to reveal whether some NDs are more favorable for it to occur compared to the others, hydrogenated NDs should perform no worse than hydroxylated ones, despite only the local hydrophilicity of the former. [ABSTRACT FROM AUTHOR]

The electronic g-tensor dependence on the size, shape, and surface functionalization of nanodiamonds (NDs) is theoretically investigated by selecting dangling bonds and single substitutional nitrogen atoms as a main source of the unpaired electrons. The performed g-tensor calculations reveal that aforementioned paramagnetic impurities introduced into octahedrally shaped ND of C84H64 size behave in a very similar manner as those embedded into a smaller octahedral model of C35H36 size. Since cubic and tetrahedral NDs—C54H48 and C51H52—demonstrate a wider range of g-shift values than octahedral systems, the g-tensor dependence on different shapes can be considered as more pronounced. However, a different surface functionalization scheme, namely, fluorination, results in a much larger variation of the g-shifts, pointing to a significant impact the F atoms have on the local environment of the unpaired electrons in C35F36. A partial surface functionalization of C35H36 with benzoic acid and aniline groups indicates that, in some special cases, these linkers might induce a noticeable spin density redistribution which in turn substantially modifies the g-shift values of the system. Additional infrared (IR) spectra calculations show that some of paramagnetic defects in C35H36 and C35F36 possess clearly expressed signatures which could be useful while analyzing the experimental IR spectra of NDs. [ABSTRACT FROM AUTHOR]

The electronic g-tensor calculations are carried out for various paramagnetic defects introduced into hydrogenated diamond nanocrystal C35H36, showing that such a system can be successfully used to model magnetic properties of nanodiamonds (NDs) with paramagnetic centers containing no vacancies. In addition, it is revealed that, depending on the geometric positions in ND, paramagnetic centers of the same type produce noticeable variations of the g-tensor values. A side-by-side comparison of the performance of effective nuclear charge and spin-orbit mean field (SOMF) approaches indicates that the latter is more sensitive to the quality of basis sets, especially concerning diffuse functions, the inclusion of which is found to be nonbeneficial. What is more, the SOMF method also exhibits a much more pronounced gauge-origin dependence. Compared to electronic charge centroid, spin centers (SCs) demonstrate a superior suitability as gauge origins, providing a better agreement with diamagnetic and paramagnetic contributions of g-tensor obtained employing gauge-including atomic orbitals (GIAOs). Therefore, SCs can be recommended for the g-tensor calculations of NDs whenever GIAOs are not available. [ABSTRACT FROM AUTHOR]

New data on the valine molecule (C5H11NO2) fragmentation under the low-energy electron-impact are presented. These data are related to the formation of ionized products due to the ionizing radiation influence on the above amino acid molecule. A series of the fragments produced are identified by applying an extensive DFT-theory approach. The results obtained allowed the principal pathways of the valine molecule fragmentation to be found. The absolute appearance energies of some fragments are both measured experimentally and calculated theoretically. The experimental and theoretical data are compared and analysed. [ABSTRACT FROM AUTHOR]

The present study describes the fragmentation of the amino acid L-threonine (C4H9NO3) with and without the inclusion of water influence. The fragmentation of the L-threonine molecule was theoretically studied using the Becke’s three-parameter hybrid functional method by applying the non-local correlation provided by Lee, Yang and Parr (B3LYP) with the correlation consistent triple zeta basis (cc-pVTZ). The polarizable continuum model (PCM) was used to evaluate the influence of water. Fragments were selected based on data from mass spectrometry experiments. The chemical compositions of fragments were identified, and the appearance energy was calculated. Based on the obtained results, we can conclude that water affects the appearance energy, the fragment structure and the fragment formation processes.

The fragmentation of the alanine (C3H7NO2) molecule due to the low-energy electron impact was studied both experimentally and theoretically using the mass spectroscopic technique combined with the density functional theoretical approach. The main emphasis was given to the mechanisms of initial molecule fragment production. Special attention was paid to the energy characteristics of the ionic fragment yield. The geometrical parameters of initial molecule rearrangement were also analysed. [ABSTRACT FROM AUTHOR]

The midpoint single-electron reduction potential of nitroaromatic compounds in aqueous medium at pH 7.0 (potential of ArNO 2 /ArNO 2 · - couple, E m7 ) frequently determines their therapeutic and/or toxic properties. However, its estimation remains a complex problem. We propose a modified method of E m7 estimation by quantum mechanical calculations, based on the use of the dielectric continuum model together with a certain number of H 2 O molecules at the vicinity of nitro group. The optimal number of H 2 O molecules corresponds to a minimal difference between the experimentally determined and calculated values of E m7 , and/or the most negative value of calculated E m7 . This enabled us to calculate the E m7 values for a number of ArNO 2 ( n =  19) with the average deviation of 0.027 V from the experimentally determined ones. Apart from nitrobenzene derivatives, the application of this approach for the representatives of nitropyridines, nitrofurans, nitrothiophenes, and nitrothiazoles was demonstrated. In this case, nitroimidazole derivatives are an exception, evidently due to a strong proton accepting properties of N 3 atom of their free radicals.

The preparation and properties of a series of novel 1,3-dihydro- 2H -benzimidazol-2-one nitro and nitramino derivatives are described. A detailed crystal structure of one of the obtained compounds, 4,5,6-trinitro-1,3-dihydro- 2H -benzimidazol-2-one (TriNBO), was characterized using low temperature single crystal X-ray diffraction, namely an orthorhombic yellow prism, space group 'P 2 21 21', experimental crystal density 1.767 g/cm 3 (at 173 K). Methyl analog, 5-Me-TriNBO-monoclinic red plates, space group, P 21/c, crystal density 1.82 g/cm 3 . TriNBO contains one activated nitro group at the fifth position, which was used for the nucleophilic substitution in the aminolysis reactions with three monoalkylamines (R=CH 3 , C 2 H 5 , (CH 2 ) 2 CH 3 ) and ethanolamine. The 5-R-aminoderivatives were further nitrated with N 2 O 5 / HNO 3 and resulted in a new group of appropriate nitramines: 1,3-dihydro- 2H -5-R-N(NO 2 )-4,6-dinitrobenzimidazol-2-ones. Thermal analysis (TGA) of three selected representatives was performed. The new compounds possess a high melting point (200-315 °C) and thermal stability and can find a potential application as new thermostable energetic materials. Some calculated preliminary energetic characteristics show that TriNBO, 5-Me-TriNBO, 5-methylnitramino-1,3-dihydro- 2H -4,6-dinitrobenzimidazol-2-one, and 5-nitratoethylnitramino-1,3-dihydro- 2H -4,6-dinitrobenzimidazol-2-one possess increased energetic characteristics in comparison with TNT and tetryl. The proposed nitrocompounds may find potential applications as thermostable high-energy materials.

The therapeutic action of nitroaromatic antiandrogens nilutamide and flutamide may be complicated by their cytotoxicity, whose mechanisms are still incomprehensively understood. In particular this concerns the enzymatic redox cycling of flutamide and its metabolites, and its impact on their cytotoxicity. In this work, we examined the single-electron reduction of nilutamide, flutamide, its metabolites 2-hydroxyflutamide and 4-nitro-3-trifluorormethyl-phenylamine, and a topical antiandrogen (3-amino-2-hydroxy-2-methyl- N -(4-nitro-3-trifluoromethyl)-phenyl) propanamide by NADPH:cytochrome P-450 reductase and adrenodoxin reductase/adrenodoxin. The obtained steady-state bimolecular rate constants of oxidant reduction ( k cat / K m ) enabled to establish single-electron reduction midpoint potentials ( E 1 7 ) of compounds, -0.377 - -0.413 V, which were in line with enthalpies of formation of their free radicals, obtained by quantum mechanical calculations. Using murine hepatoma MH22a cells, the obtained cytotoxicity vs. E 1 7 correlation based on the data of model nitroaromatic compounds shows that redox cycling and oxidative stress could be the main factor of cytotoxicity of nitroaromatic antiandrogens. Other minor cytotoxicity factors could be their redox metabolism involving NAD(P)H:quinone oxidoreductase (NQO1) and cytochromes P-450.

The detailed structure, chemical and spectroscopic properties of the derivatives of the selected 2,5-bis(1-aziridinyl)-benzo-1,4-quinone conformers were studied by applying quantum chemical and experimental methods. The relationship between the structure and chemical activity of the selected 3 bifunctional bioreductive quinonic anticancer agents - aziridinyl benzoquinones (AzBQ compounds) was obtained. The results obtained showed that the position of aziridine rings influenced by the chemical activity of the investigated compound were more significant than the substitutions of the benzene ring of the AzBQ compounds. The solvents influencing this activity were obtained, too., (Copyright © 2017. Published by Elsevier B.V.)