Series Of Nitroaromatic Compounds Research Articles

Comparison of sensitivity for methods of positive and negative ion mass spectrometry, exemplified by nitrotoluenes

For a model series of nitro aromatic compounds comprising mono-, di- and trinitrotoluenes, and dinitrobenzene, using the same commercial experimental set up consisting of gas chromato-graphy/mass spectrometry (GC/MS) instrument equipped with a quadrupole analyzer, the two types of mass spectra were recorded, of positive ions (in the conventional, standard mode of electron ionization at 70 eV) and of negative ions (NI, generated at low, pre-ionization electron energies by resonant electron capture, REC). The comparative analysis of characteristic fragmentation processes was carried out for molecular ions of both signs. The sensitivity of REC NI MS method was established to enhance upon increasing the number of electron-withdrawing nitro groups, reaching or even outperforming that of the classical method of electron ionization (EI). Thus, the detection limit for trinitrotoluene in a solution was estimated as 5 ppm, which is by an order of magnitude lower as compared to the conventional EI mode of analysis. Comparison of the ion composition of NI mass spectra and of the relative intensities of ion peaks with the corresponding data obtained previously for the studied group of compounds by means of different types of mass spectrometers, has revealed a satisfactory inter-instrumental reproducibility of the NI mass spectra. The results reported herein indicate that the NI generation/registration mode, which can technically be readily available even without modifications of design of commercial GC/MS instrument in their basic configuration, is suitable to be introduced in laboratory practice as the additional tool for increasing the selectivity and reliability in detection/identification of trace amounts of compounds possessing a high electron af nity and for solving extraordinary structural and analytical problems.

An adjustable dual-emission fluorescent metal-organic framework: Effective detection of multiple metal ions, nitro-based molecules and DMA.

A novel multifunctional Pb(II)-based MOF, [Pb1.5(DBPT)]2·(DMA)3(H2O)4 (1), with excellent chemical stability, was successfully assembled by connecting {Pb2O10} unit with a multi-topic polycarboxylate ligand of 3-(3,5-dicarboxylphenyl)-5-(4-carboxylphenyl)-1-H-1,2,4-triazole (H3DBPT). It exhibits dual fluorescence emissions at 380 nm (λex = 280 nm) and 540 nm (λex = 380 nm), respectively. Through the adjustable dual fluorescence emissions, it could act as a turn-off and turn-on switch for detecting N,N-dimethylacetamide (DMA) molecule. Moreover, Fe3+ ions exert luminescence quenching role on compound 1 at both excitation lengths in water, among which the quenching at λex = 280 nm is of high sensitivity (KSV = 1.2 × 105), and the quenching at λex = 380 nm is of wide-range. The sensing for metal ions of In3+, Zr4+, and Al3+ is also effective at λex = 280 nm, with the KSV constants of 1.6 × 105, 1.6 × 105, and 4.3 × 104, respectively. More importantly, a series of nitroaromatic compounds (TNP, 2,4,6-trinitrophenol; 4-NA, 4-nitroaniline; NB, nitrobenzene) and nitro-based drugs (MNZ, metronidazole; DMZ, dimetridazole) could be detected at both excitation lengths, demonstrating the advantage of broad range response of fluorescence sensing. Thanks to the excellent chemical stability and unusual dual emission luminescence properties for chemical detection of various metal ions, nitro-based molecules and DMA solvent, the Pb-based MOF reported in this work is, therefore, a very promising multi-response sensor.

(Invited) Understanding and Predicting Transitions in Proton Coupled Electron Transfer

Proton Coupled Electron Transfer (PCET) mechanisms include all kinds of reactions where concurrent/stepwise processes are involved. Unraveling the distinctive character of a given mechanism is therefore a issue of importance, as concerted mechanisms lead to formation of products, avoiding the formation of high energy intermediates and are important for catalysis, while stepwise steps allow explaining the reactivity where radical species (either neutral or charged), can be invoked. Therefore, studies are not only directed to distinguish between both mechanistic alternatives, but to rationalize their significance in the reactivity of molecules and aggregates. For this purpose, simple trends using model organic compounds have been studied and allow to identify the structural characteristics that a given species must bear to induce any path. Within the workgroup, systematic analysis with series of nitro aromatic compounds [1,2] where Electron Transfer Controlled Hydrogen Bonding (a specific type of PCET process), show the influence of both the basicity of the electrogenerated anion radical and the acidity of the proton donor, describing the trends using descriptors of reactivity derived from changes in the local density of the molecule [3]. Using this approach, we have been able to analyze critical parameters where Hydrogen Bonding can lead to Proton Transfer, thus probably becoming concerted proton transfers. Results are therefore discussed in this work, along with the theoretical analysis described, its own limitations and some recent extensions for multiple-bodies approaches. Also, experimental changed where self-protonation occurs are presented, where we have been able to identify the "non-innocent" character of hydrogen bonding donors within the structures, leading to prior of forward hydrogen bonding interactions. Finally, some results of the influence of hydrogen bonding in the changes in electron transfer entropy are presented. [1] Martínez-González, E.; C. Frontana, J . Org . Chem . 2014, 79, 1131-1137 [2] Martínez-González, E.; Armendáriz-Vidales, G.; Ascenso, J. R.; Marcos, P. M.; Frontana C. J. Org. Chem. 2015, 80, 4581-4589 [3] Gázquez, J. L.; Cedillo, A.; Vela, A. J. Phys Chem. A. 2007, 111, 1966-1970 Figure 1

A quantum chemical based toxicity study of estimated reduction potential and hydrophobicity in series of nitroaromatic compounds

Nitroaromatic compounds and the products of their degradation are toxic to bacteria, cells and animals. Various studies have been carried out to better understand the mechanism of toxicity of aromatic nitrocompounds and their relationship to humans and the environment. Recent data relate cytotoxicity of nitroaromatic compounds to their single- or two-electron enzymatic reduction. However, mechanisms of animal toxicity could be more complex. This work investigates the estimated reduction and oxidation potentials of 34 nitroaromatic compounds using quantum chemical approaches. All geometries were optimized with density functional theory (DFT) using the solvation model based on density (SMD) and polarizable continuum model (PCM) solvent model protocols. Quantitative structure–activity/property (QSAR/QSPR) models were developed using descriptors obtained from quantum chemical optimizations as well as the DRAGON software program. The QSAR/QSPR equations developed consist of two to four descriptors. Correlations have been identified between electron affinity (ELUMO) and hydrophobicity (log P).

On the development of QSPR models for regulatory frameworks: The heat of decomposition of nitroaromatics as a test case

Many regulatory frameworks, e.g. related to the Transport of Dangerous Goods, the Registration, Evaluation, Authorisation and restriction of chemicals (REACH) or the Classification, Labelling and Packaging of substances and mixtures (CLP), require the characterization of the hazards of chemicals, which could be complex. In particular, the REACH regulation involves an extensive quantity of works, to gather toxicological, eco-toxicological and physico-chemical properties for a large number of compounds. So, the full characterization by experimental way is time-consuming and cost-expensive. Alternative methods are therefore encouraged to complement experimental tests. The Quantitative Structure–Property Relationships (QSPR) approach is one of the recommended methods, provided that they are developed within the rigorous guidelines proposed by the Organization for Economic Co-operation and Development (OECD). In this context, a series of nitroaromatic compounds has been analyzed to achieve new QSPR models for the prediction of their heat of decomposition respecting the requirements for application in regulatory frameworks.Three multilinear models were obtained upon the set of descriptors considered for their development (constitutional, topological or both) that do not need any preliminary time expensive quantum chemical calculations. They were tested by internal and external validation tests. Good performances for the two ones including constitutional descriptors were obtained in particular in terms of predictive power in a well defined applicability domain (RIN2 = 0.81–0.87). They are easier to apply than our previous quantum chemical based model, since they do not need any preliminary calculations.

Synthesis and evaluation of the anti parasitic activity of aromatic nitro compounds

A series of nitroaromatic compounds was synthesized and evaluated as potential antileishmanial and trypanocidal agents. Five compounds exerted significant anti-leishmanial activity in vitro against promastigotes forms of Leishmania (L.) amazonensis, with IC50 in the range of 23–59 μmol L−1, but none were active against amastigotes intracellular forms of Trypanosoma cruzi. In vitro cytotoxicity on the proliferation of human peripheral blood mononuclear cells (PBMC) stimulated with phytohemaglutinin (PHA) was also evaluated. Two compounds, 6 and 7, were found to present a promising anti-leishmanial activity with IC50 values of 59.5 and 50.6 μM, respectively, without affecting the lymphocyte proliferation in PBMCs (selectivity index of 16.1 and 21.7, respectively), indicating low toxicity to human cells.

Spherical Clay Conglomerates: A Novel Stationary Phase for Solid-Phase Extraction and “Reversed-Phase” Liquid Chromatography

A new solid phase is presented to be used for the solid-phase extraction (SPE) of organic compounds from aqueous solutions and as a stationary phase for the separation of organic compounds in "reversed-phase" HPLC. The material consists of spherical clay conglomerates (SCCs) in the size ranges of 2-5, 5-10, and 10-20 μm. SCCs are especially well suited for the extraction and separation of aromatic compounds with electron-withdrawing substituents, because of the formation of specific electron donor-acceptor (EDA) complexes of such compounds with natural clay minerals. A series of nitroaromatic compounds (NACs), e.g., nitrophenols, and nitrotoluenes, served as probe substances for the characterization of the SPE with SCCs online coupled to a C18-HPLC-DAD system. Breakthrough volumes were > 1 L and method detection limits (MDLs) < 100 ng/L for compounds with moderate to high affinity towards clay minerals. The performance of the material is hardly affected by matrix effects and because of its excellent physical properties, i.e., regenerability and pressure-resistance, it meets the requirements for fully automated routine trace analysis of several primary pollutants, such as 6-methyl-2,4-dinitrophenol (DNOC) or 2,4,6-trinitrotoluene (TNT), in various natural waters. Offline SPE with SCCs was superior or equivalent to commercial SPE products for analysis of such compounds. Finally, SCCs are shown to be well suited as a stationary phase in reversed-phase HPLC. This opens a wide range of applications, e.g., as an easy and fast separation technique that is orthogonal to C18 reversed-phase HPLC.

Electron-transfer quenching vs. exciplex-mediated quenching of the low-lying excited states in phthalocyanines

Oxidative electron-transfer quenching of the lowest ligand-centered /sup 3/..pi pi..* of ruthenium (RU) phthalocyanines (pc)L/sub 2/, L = dimethylformamide (dmf) or pyridine (py), by a series of nitroaromatic compounds, viologen salts, and metal complexes has been investigated by laser and conventional flash photolysis. The quenching rate constants, treated according to Marcus-Hush and Rehm-Weller equations, gave self-exchange rate constants, k/sub exch/ approx. 10/sup 7/ M/sup -1/ s/sup -1/, for the electron exchange between the /sup 3/..pi pi..* and the ruthenium(II) ligand radical. The excited states of a number of phthalocyanines, e.g. Ru(pc)(dimethyl sulfoxide(Me/sub 2/SO)/sub 2/), Ru(pc)(dmf)CO, Ru(pc)(py)CO, and Rh(pc)(methanol(CH/sub 3/OH)chloride), undergo quenching mediated by exciplex formation. The formation of exciplexes is discussed in terms of the related exciplexes of the porphyrins.

Intramolecular electron transfer and dehalogenation of nitroaromatic anion radicals

A series of nitroaromatic compounds, containing Cl, Br, or tosyl groups at various positions, were synthesized and studied by pulse radiolysis in aqueous alcohol solutions. One-electron reduction of the compounds produces the anion radicals which then undergo an intramolecular electron transfer and eliminate X/sup -/ (Cl/sup -/, Br/sup -/, or TsO/sup -/). The rates of X/sup -/ elimination vary over six orders of magnitude and are affected by the C-X bond dissociation energies, the size and nature of the group bridging the X with the ..pi.. system, and the relative positions of these groups. Intramolecular electron transfer through space is also demonstrated.

Identification of nitroaromatics in diesel exhaust particulate using gas chromatography/negative ion chemical ionization mass spectrometry and other techniques

A series of nitroaromatic compounds were identified in diesel exhaust particulate extract. Isomers of nitroanthracene (and/or nitrophenanthrene) and nitropyrene (and/or nitrofluoranthene) were unequivocally identified. Alkyl homologues of nitroanthracene through C/sub 3/-alkyl-nitroanthracene were tentatively identified. In addition, a C/sub 18/H/sub 11/NO/sub 2/ isomer was tentatively identified. The nitro-substituted polynuclear aromatic hydrocarbons (PAHs) were found in two fractions of diesel exhaust particulate extract collected from a low-pressure liquid chromatography (LPLC) column. One of the two fractions containing nitroaromatic constitutents accounted for a large percentage of the mutagenicity of the crude particulate extract. Initial identification were made by using high-resolution gas chromatography/electron impact mass spectrometry/computer (GC/EIMS) and negative ion chemical ionization mass specrometry/computer (GC/NICIMS). These identifications were confirmed by direct probe high-resolution mass spectrometry (HRMS) and gas chromatography/Fourier transform infrared spectrometry (GC/FT IR). The relative merit of each analytical technique for the determination of nitroaromatics is discussed with emphasis on the usefulness of GC/NICIMS as a means of analyzing for nitro-substituted PAHs.