Laser flash photolysis and quantum chemical studies of UV degradation of pharmaceutical drug chloramphenicol: Short-lived intermediates, quantum yields and mechanism of photolysis.

Using methods of time-resolved and stationary photolysis, HPLC-MS and quantum-chemical calculations by the DFT method, the mechanism of direct UV photolysis of the antibiotic chloramphenicol (CAP) was established. For the first time, short-lived intermediates formed during photolysis were detected. The primary photoprocess is the cleavage of the ß-C-C bond relative to the aromatic system with the formation of 4-nitrobenzylalcohol radical and residual aliphatic radical. The first radical in deoxygenated solutions predominantly transforms into para-nitrobenzaldehyde and its secondary photolysis products. In the presence of oxygen, the aromatic radical and para-nitrobenzaldehyde are transformed into para-nitrosobenzoic and para-nitrobenzoic acids as a result of reaction with reactive oxygen species (ROS). Formation of ROS is provoked by reactions of aliphatic radical with dissolved oxygen, so this radical is very important for CAP degradation. The quantum yield of direct photolysis of CAP is ∼3% and does not depend on the presence of dissolved oxygen and on the change of the excitation wavelength in the range of 254-308 nm. Obtained data are important for further understanding of the transformation pathways of CAP and similar PPCP in natural and wastewaters under the action of sunlight and artificial UV radiation.

New Ruthenium Nitrosyl Complexes Combining Potentially Photoactive Nitrosyl Group with the Magnetic Nitroxide Radicals as Ligands.

Two ruthenium nitrosyl complexes of Na[RuNOCl4L] with nitronyl nitroxide radicals coordinated to ruthenium with N-donor pyridine rings were prepared and described. The crystal structure of both complexes is 1D or 2D polymeric, due to the additional coordination of sodium cation by bridging the chloride ligands or oxygen atoms of nitroxides. Partially, the oligomeric forms remain in the solutions of the complexes in acetonitrile. The magnetic measurements in the solid state demonstrate the presence of antiferromagnetic interactions through the exchange channels, with the distance between paramagnetic centers equal to 3.1-3.9 Å. The electrochemical behavior of the prepared complexes was investigated in acetonitrile solutions.

Praseodymium Metallacrown-Based NMR Probe for Enantioselective Discrimination of Mandelate Anions in Water.

Recently, the enhanced interest in water-soluble aminohydroximate Ln(III)-Cu(II) metallacrowns (MC) is largely due to their fascinating structural chemistry, diverse properties and ease of synthesis. We examined the water-soluble praseodymium(III) alaninehydroximate complex Pr(H2O)4[15-MCCu(II)Alaha-5]·3Cl (1) as a highly effective chiral lanthanide shift reagent for NMR analysis of the biologically relevant (R/S)-mandelate (MA) anions in aqueous media. The R-MA and S-MA enantiomers can be easily discriminated in the presence of small (1.2-6.2 mol %) amounts of MC 1 by the 1H NMR signals of multiple protons exhibiting an enantiomeric shift difference (ΔΔδ) of 0.06 ppm up to 0.31 ppm. Additionally, a possibility of coordination of MA to the metallacrown was investigated by the ESI-MS technique and a Density Functional Theory modeling of the molecular electrostatic potential and noncovalent interactions.

Photolysis by UVA-Visible Light of TNT in Ethanolic, Aqueous-Ethanolic, and Aqueous Solutions According to Electrospray and Aerodynamic Thermal Breakup Droplet Ionization Mass Spectrometry.

The mechanism of photolytic degradation of 2-4-6-trinitrotoluene (TNT) by UVA−visible light (>320 nm) in ethanolic, aqueous-ethanolic, and aqueous solutions was investigated by electrospray and aerodynamic thermal breakup droplet ionization mass-spectrometric analyses. For the photolysis, a DRK-120 mercury-quartz lamp was used. Products of the photolysis reaction were compared with known products of TNT transformation in the environment. Because the photochemistry of some compounds in alcohols (in contrast to aqueous solutions) features a transfer of electrons from the solvent to the light-excited compound, we believe that the efficiency of photolysis (polymerization) of TNT in ethanol and aqueous-ethanolic solutions is based on this mechanism.

Highly Active Visible Light-Promoted Ir/g-C3N4 Photocatalysts for the Water Oxidation Reaction Prepared from a Halogen-Free Iridium Precursor.

A combination of the exceptional stability of fac-[Ir(H2O)3(NO2)3] together with thermolability of nitro and aqua ligands and high solubility in various solvents makes it promising as a brand-new chlorine-free precursor of iridium for the preparation of heterogeneous catalysts. In the current work, a new technique of fac-[Ir(H2O)3(NO2)3] preparation based on hydrothermal treatment of (NH4)3[Ir(NO2)6] was developed. For this purpose, the influence of reaction parameters such as the reaction time, temperature, and pH of the solution on the process of hexanitroiridate salt hydrolysis was investigated. The synthesized fac-[Ir(H2O)3(NO2)3] solution in this optimized way was used for the preparation of the series of Ir/g-C3N4 catalysts, which were evaluated in the water oxidation reaction with NaIO4 utilized as a sacrificial reagent. A 20-fold enhancement of the oxygen evolution reaction (OER) activity was found to take place under visible light (λ = 411 nm) illumination of the systems. The highest rate of the photoinduced OER per iridium center was achieved by the Ir0.005/g-C3N4 (air, 400°C) catalyst with an exceptional turnover frequency value of 967 min-1 approaching the activity of known homogeneous iridium OER catalysts. The leaching experiments have shown that aquated Ir species are generated in a solution after prolonged functioning of the catalysts. Despite this, in the closed system the photodriven OER activity persists at a steady-state level evidencing an equilibrium achieved between dissolved and anchored Ir species forming catalytic tandem with the g-C3N4.

Hydrolysis of [PtCl6]2- in Concentrated NaOH Solutions.

The transformations of Pt complex species in concentrated NaOH solutions (1-12 M) of Na2[PtCl6] were studied with a combination of methods, including 195Pt nuclear magnetic resonance, ultraviolet-visible, and Raman spectroscopy. The two-step process was observed under the following conditions: (1) formation of the [Pt(OH)5Cl]2- anion that proceeds relatively fast even at room temperature and (2) further slow substitution of the last chlorido ligand with the formation of the [Pt(OH)6]2- anion. Overall, it was determined that the [PtCl6]2- to [Pt(OH)6]2- transformation (especially the first stage) is greatly accelerated under blue light (455 nm) irradiation. The structures of [Pt(OH)Cl5]2- and [Pt(OH)5Cl]2- were determined using the single-crystal X-ray diffraction data of the corresponding salts isolated for the first time. Analysis of the [Pt(OH)Cl5]2- reactivity showed that under analogous conditions, its hydrolysis proceeds 2 orders of magnitude slower than that of [PtCl6]2-, indicating that the formation of [Pt(OH)5Cl]2- from [PtCl6]2- (stage 1) does not follow a simple sequential substitution pattern. A model for [Pt(OH)5Cl]2- anion formation that includes the competing reaction of direct Cl ligand substitution and the self-catalyzed second-order reaction caused by a redox process is proposed. The influence of Pt speciation in alkaline solutions on the reductive behavior is shown, illustrating its impact on the preparation of Pt nanoparticles.

Acceleration of the thermal degradation of PETN in the microdroplets flow reactor.

Thermal degradation of pentaerythritol tetranitrate (PETN) was investigated in microdroplets within a heated capillary used as a flow reactor. The thermal degradation was monitored by aerodynamic thermal breakup droplet ionization mass spectrometry. It was shown that the PETN degradation in microdroplets occurs much faster than the bulk reaction (by 4-5 orders of magnitude). The effect of the capillary material [stainless steel (Fe, Cr), copper (Cu), or fused quartz (SiO2)] on the thermal PETN degradation in microdroplets of water or acetonitrile was studied next. The capillary material affected the rate of thermal PETN degradation much more weakly than did the use of microdroplets (pure Cu was most conducive to the degradation). Kinetic parameters (activation energy and the frequency factor) of the PETN degradation for all the studied materials of the flow-through reactor and the solvents were estimated under the assumption that the thermal degradation is a first-order reaction. Implications of the acceleration of PETN degradation in microdroplets are discussed.

Rh(III) hydroxocomplexes speciation using HPLC-ESI-MS.

A mixture of rhodium(iii) hydroxocomplexes formed during the polycondensation process in alkaline media has been fully characterized by the hyphenated high performance liquid chromatography with electrospray ionization mass spectrometry (HPLC-ESI-MS). The baseline separation was achieved using reverse phase ion-pair chromatography (RP-IP-HPLC) in gradient elution mode. When using SDS as the ion pair, the formation of all types of its associates with the molecules of acetonitrile, as well as oligomers of rhodium aquahydroxocomplexes, etc. was taken into consideration. As a result, it was shown that the test mixture is presented by [Rh(H2O)6]3+, [Rh2(µ-OH)2(H2O)8]4+, [Rh3(µ-OH)4(H2O)10]5+, [Rh4(µ-OH)6(H2O)12]6+.

Aerodynamic Thermal Breakup Droplet Ionization in Mass Spectrometric Drug Analysis.

Aerodynamic thermal breakup droplet ionization (ATBDI) in mass spectrometric drug analysis is considered. Cocaine, heroin, and the main alkaloids of opium (morphine, codeine, papaverine) were chosen as the test compounds. The principles of ATBDI ionization are discussed. The dependences of the intensities of the peaks of the target compounds on temperature during ATBDI ionization are also considered. In some cases, a comparison of ATBDI ionization with electrospray ionization (ESI) was performed. In addition, a comparison of methods is demonstrated by the analysis of confiscated opium that was provided by the local police department. Five major alkaloids are found in opium: morphine, codeine, thebaine, papaverine, and narcotine.

Analysis of trinitrotoluene in solutions using Aerodynamic Thermal Breakup Droplet Ionization (ATBDI) mass spectrometry.

The droplets breakup and compounds ionization in the heated capillary were investigated; the ionization method was named Aerodynamic Thermal Breakup Droplet Ionization (ATBDI). The mass spectrometric analysis was performed for solutions of trinitrotoluene (TNT) in water, ethanol, and acetonitrile. Considering the total current and the target analyte peaks, the ionization efficiency in the heated capillary was correlated with the physical properties of the solvents. For aqueous and ethanol solutions of TNT, the limit of detection (LOD) was obtained when using the ATBDI mass spectrometry. It was estimated to be 10-7 g mL-1 and 10-6 g mL-1 for water and ethanol solutions, respectively.

Semi-quantitative analysis of samples in solutions using Aerodynamic Breakup Droplet ionization (ABDI) mass spectrometry.

In Aerodynamic Breakup Droplet ionization (ABDI) mass spectrometry the dimer/monomer (I2/I1) and trimer/dimer (I3/I2) ratios are considered for compounds ionized in various ways. The following test compounds were selected: morphine (gives protonated ion, (M+H)+); hexogen, RDX (forms adducts with anion of chlorine or nitrate ion); and trinitrotoluene, TNT (gives deprotonated ion, (M-H)-). The test compounds were dissolved in water, acetonitrile or ethanol. It is shown that in the ABDI mass spectra of a number of compounds (protonated morphine ions in water and RDX adducts with chlorine in acetonitrile), the ratios I2/I1 and I3/I2 linearly depend on the analyte concentration in the solution. This is evident throughout the range of measured concentrations, when monomers and dimers are simultaneously visible in the mass spectrum. The phenomenon can be roughly explained by the dimerization of analyte molecules in singly charged parent drops during ABDI ionization. The linearity of the I2/I1 and I3/I2 on the concentration can be used for estimation of the analyte concentration in a sample without using an internal or external standard. This can be useful for routine analysis when standards are not commercially available or very expensive.

Using of aerodynamic droplet breakup for mass-spectrometric analysis.

The method of ionization by aerodynamic droplet breakup is considered for applications in mass spectrometric analysis. It is assumed that Aerodynamic Breakup Droplet Ionization (ABDI) occurs in a tube linking the region of atmospheric pressure to the area of weak vacuum. The possibility of ionization of solutions of organic compounds and organometallic complexes is shown. As test compounds were chosen: heroin (as an example of organic compounds) and organometallic complexes of ruthenium and copper, dissolved in water or acetonitrile. The quality of the ABDI spectra depends on the analyte. In general, the analytes ionized by the ABDI method show a great propensity to form dimers and trimers. ABDI system can be easily installed on any mass spectrometer with inlet at atmospheric pressure and used as an additional method. Since compounds prone to degradation in ESI analysis are better suited for ABDI analysis, this seems useful.

Ionization of solutions using mechanical spray in collison nebulizer: a new simple ion source for mass-spectrometric analysis.

Ionization methods for mass-spectrometric analysis based on mechanical liquid spray by a high-speed gas flow (like Sonic Spray Ionization (SSI)) offer some advantages over other ionization methods. Among these one should mention the absence of electric voltage, radioactive sources and heaters. In this paper we suggest using the Collison nebulizer for solution ionization via mechanical spray. Research results into the efficiency of the Collison spray ionization of different solvents used in chemical synthesis are submitted. It is shown that an increase in dipole moment of the solvent molecules leads to increased ionization efficiency for all solvents tested, except water. This seems to result from anomaly high surface tension and vaporization enthalpy for water. High concentrations (>10(-4) g/ml) of both inorganic salts (NaCl, K2SO4) and organic additive (morphine) give a decrease in the total ion current at the Collison nebulizer outlet. This is assumed to be due both to an increased droplet size of aerosol produced upon spraying and a low dipole moment of an ion-solvation shell complex. Mass-spectra of aqueous K2SO4 and morphine (C17H19NO3) were obtained with the Collison nebulizer. These spectra contained non-identified background peaks along with the peaks of K(+) and H(+)C17H19NO3 that were likely to result from the water ionization and presence of uncontrolled impurities. A relationship between the intensity of mass-spectroscopic peaks of the ions of potassium and morphine and the concentration of appropriate aqueous solution was determined. Mass-spectrometric analysis using the Collison spray ionization gave a detection limit for morphine ∼10(-8) g/ml and a linear response range for protonated molecular ion (H(+)C17H19NO3 with m/z=286 from 10(-8) g/ml to 2×10(-7) g/ml.

Ion peak narrowing by applying additional AC voltage (ripple voltage) to FAIMS extractor electrode.

The use of a non-uniform electric field in a high-field asymmetric waveform ion mobility spectrometry (FAIMS) analyzer increases sensitivity but decreases resolution. The application of an additional AC voltage to the extractor electrode ("ripple" voltage, U(ripple)) can overcome this effect, which decreases the FAIMS peak width. In this approach, the diffusion ion loss remains minimal in the non-uniform electric field in the cylindrical part of the device, and all ion losses under U(ripple) occur in a short portion of their path. Application of the ripple voltage to the extractor electrode is twice as efficient as the applying of U(ripple) along the total length of the device.