Ubiquitous Radical Research Articles

Transformation of Graphitic Carbon Nitride by Reactive Chlorine Species: "Weak" Oxidants Are the Main Players.

Graphitic carbon nitride (g-C3N4) nanomaterials hold great promise in diverse applications; however, their stability in engineering systems and transformation in nature are largely underexplored. We evaluated the stability, aging, and environmental impact of g-C3N4 nanosheets under the attack of free chlorine and reactive chlorine species (RCS), a widely used oxidant/disinfectant and a class of ubiquitous radical species, respectively. g-C3N4 nanosheets were slowly oxidized by free chlorine even at a high concentration of 200-1200 mg L-1, but they decomposed rapidly when ClO· and/or Cl2•- were the key oxidants. Though Cl2•- and ClO· are considered weaker oxidants in previous studies due to their lower reduction potentials and slower reaction kinetics than ·OH and Cl·, our study highlighted that their electrophilic attack efficacy on g-C3N4 nanosheets was on par with ·OH and much higher than Cl·. A trace level of covalently bonded Cl (0.28-0.55 at%) was introduced to g-C3N4 nanosheets after free chlorine and RCS oxidation. Our study elucidates the environmental fate and transformation of g-C3N4 nanosheets, particularly under the oxidation of chlorine-containing species, and it also provides guidelines for designing reactive, robust, and safe nanomaterials for engineering applications.

On the crystal chemistry of sulfur-rich lazurite, ideally Na7Ca(Al6Si6O24)(SO4)(S3)–·nH2O

AbstractDark blue lazurite from the Malo-Bystrinskoe lazurite deposit, Baikal Lake area, Eastern Siberian region, Russia, was analyzed by electron microprobe and revealed an unusually high content of total sulfur corresponding to 8.3 wt% S. The relative content of sulfur in sulfate and sulfur in sulfide form was determined by wet chemical analysis. The H2O content was measured by means of differential thermal analysis in combination with mass spectrometry and infrared (IR) spectroscopy. The charge-balanced empirical formula of lazurite calculated on the basis of 12 (Al+Si) atoms per formula unit was (Na6.97Ca0.88K0.10)Σ7.96[(Al5.96Si6.04)Σ12O24](SO4)1.092−(S3−)0.55S0.052− Cl0.04·0.72H2O. The presence of H2O molecules and (S3)– and (SO4)2– groups was confirmed by the combination of IR, Raman, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) methods. The idealized formula of lazurite is Na7Ca[Al6Si6O24](SO4)2–(S3)–·H2O, and it is believed that extra-framework cations and anions are grouped into clusters of [Na3Ca·SO4]3+ and [Na4(S3)–]3+. The types of isomorphous substitutions in nosean and haüyne are discussed. Lazurite is a clathrate-type mineral, which may be an effective (S3)– sensor due to the stability of the trisulfur radical anion in isolated cages of the crystal structure. This specific feature makes it possible to study the behavior of this ubiquitous radical anion over larger T and P ranges as compared to free species. This kind of lazurite, with oxidized and reduced sulfur species, seems to be appropriate for the estimation of the fugacity of SO2 and O2 in metasomatic systems forming lazurite-containing rocks. The systematic presence of incommensurate modulations is a unique structural feature of Baikal lazurite and may be an important marker indicating provenance of the mineral.

Role of hydrogen migrations in carbonyl peroxy radicals in the atmosphere

Carbonyl peroxy radicals (RC(O)O2) are the ubiquitous radical intermediates in the atmospheric oxidation of volatile organic compounds. In this work, theoretical studies are carried out to explore the role of the unimolecular H-migration in the carbonyl peroxy radicals by using quantum chemistry and kinetics calculations. The results showed that H-migration could be significant in the atmosphere at least in CH3CH2CH2C(O)O2 and (CH3)2CHCH2C(O)O2 with rates of ~0.012 and ~0.58 s−1 at 298 K. Subsequent reactions of CH3CHCH2C(O)OOH would lead to the products with multi-functional groups, which might affect the aerosol formation process; while (CH3)2CCH2C(O)OOH would transform to formaldehyde and acetone in a few steps. These processes would be important for the atmospheric modelling of volatile organic compounds under low-NOx conditions.

Cutting Off Functional Loops from Homodimeric Enzyme Superoxide Dismutase 1 (SOD1) Leaves Monomeric β-Barrels

Demetallation of the homodimeric enzyme Cu/Zn-superoxide dismutase (SOD1) is known to unleash pronounced dynamic motions in the long active-site loops that comprise almost a third of the folded structure. The resulting apo species, which shows increased propensity to aggregate, stands out as the prime disease precursor in amyotrophic lateral sclerosis (ALS). Even so, the detailed structural properties of the apoSOD1 framework have remained elusive and controversial. In this study, we examine the structural interplay between the central apoSOD1 barrel and the active-site loops by simply cutting them off; loops IV and VII were substituted with short Gly-Ala-Gly linkers. The results show that loop removal breaks the dimer interface and leads to soluble, monomeric β-barrels with high structural integrity. NMR-detected nuclear Overhauser effects are found between all of the constituent β-strands, confirming ordered interactions across the whole barrel. Moreover, the breathing motions of the SOD1 barrel are overall insensitive to loop removal and yield hydrogen/deuterium protection factors typical for cooperatively folded proteins (i.e. the active-site loops act as a "bolt-on" domain with little dynamic influence on its structural foundation). The sole exceptions are the relatively low protection factors in β-strand 5 and the turn around Gly-93, a hot spot for ALS-provoking mutations, which decrease even further upon loop removal. Taken together, these data suggest that the cytotoxic function of apoSOD1 does not emerge from its folded ground state but from a high energy intermediate or even from the denatured ensemble.

High energy radiation femtochemistry of water molecules: early electron-radical pairs processes

The damages triggered by ionizing radiation on chemical and biological targets depend on the survival probability of radicals produced in clusters of ionization-excitation events. In this paper, we report on femtolysis (FEMTOsecond radioLYSIS) of pure liquid water using an innovative laser produced high-energy, ultra-short electron bunches in the 2.5-15 MeV range and high energy radiation femtochemistry (HERF) measurements. The short-time monitoring of a primary reducing radical, hydrated electron e $^{-}_{aq}$ , has been performed in confined ionization spaces (nascent spurs). The calculated yield of hydrated electrons at early time, $G({\rm e}^{-}_{aq})_{ET}$ , is estimated to be 6.5 ± 0.5 (number/100 eV) at t ~ 5 ps after the ultrafast energy deposition. This estimated value is high compare to (i) the available data of previous works that used scavenging techniques; (ii) the predictions of stochastic water radiolysis modelling for which the initial behaviour of hydrated electron is investigated in the framework of a classical diffusion regime of independent pairs. The HERF developments give new insights into the early ubiquitous radical escape probability in nascent aqueous spurs and emphasize the importance of short-lived solvent bridged electron-radical complexes [ ${\rm H}_{3}{\rm O}^{+...}$ ${\rm e}_{aq}^{-}$ .. ${\rm OH}]_{n{\rm H}_2{\rm O}}$ (non-independent pairs). A complete understanding of the G( ${\rm e}^{-}_{aq})_{ET}$ value needs to account for quantum aspects of 1s-like trapped electron ground state and neoformed prototropic radicals that govern ultra-fast recombination processes within these non-independent pair configurations. Femtolysis data emphasize that within a time-dependent non-diffusion regime, spatio-temporal correlations between hydrated electron and nearest neighbours OH radical or hydrated proton ( ${\rm H}_{3}{\rm O}^{+}$ ) would assist ultrafast anisotropic 1D recombination within solvent bridged electron-radical complexes. The emerging HERF domain would provide guidance for understanding of ultrashort-lived sub-structure of tracks and stimulate future semi-quantum simulations on prethermal radical reactions.

Two-dimensional fluorescence spectroscopy for the identification of discharge intermediates

A protocol is developed for the identification of discharge intermediates from complex electronic spectra. The protocol involves resonant ionisation mass spectrometry to determine the mass of the unknown carrier followed by a two-dimensional fluorescence spectrum which is used as a "map" to guide higher resolution techniques. High resolution dispersed fluorescence provides accurate ground electronic state vibrational frequencies which are then compared with theoretical calculations of frequencies and structures of a range of isomers consistent with the observed mass. The protocol is demonstrated in the first identification of the cis and trans-1-vinylpropargyl radicals as a ubiquitous radical in hydrocarbon discharges.

LA419, a Novel Nitric Oxide Donor, Prevents Cardiac Remodeling Via the Endothelial Nitric Oxide Synthase Pathway

The discovery of NO as the endothelium-derived relaxing factor unleashed new horizons. NO is a ubiquitous radical exerting both hemodynamic and tissue growth–modifying effects. The vasodilative and antiproliferative properties of NO produced by endothelial NO synthase are considered to act beneficially within the cardiovascular system. However, under certain circumstances, the inducible NO synthase produces large quantities of NO that may be harmful.1 Most NO effects can be attributed to the activation of soluble guanylate cyclase and the subsequent cascade of events including enhanced cGMP concentration, activation of cGMP-dependent kinase-1, and reduced intracellular calcium levels in target cells. NO acts as a principal regulator of vascular function. Venodilatation and arterial relaxation result in a decrease of left ventricular pressure and chamber size, leading to attenuation of oxygen consumption. NO dilates epicardial coronary arteries, enhances collateral flow, and inhibits platelet aggregation. Moreover, NO was shown to inhibit collagen synthesis and to reduce cardiomyocyte growth. NO, thus, represents an opposing force to vasoconstrictors and growth-promoting substances, such as angiotensin II and endothelin. The depression of NO signaling, including downregulated expression and attenuated enzymatic activity of NO synthase and scavenging of NO by oxygen-derived free radicals, seems to be a principal disorder in endothelial dysfunction. NO deficiency is, therefore, related to many cardiovascular pathologies, such as coronary atherosclerosis with myocardial ischemia, arterial hypertension with left ventricular hypertrophy, or heart failure. It is obvious that NO plays an important role in the circulatory physiology. Nevertheless, the impact of therapeutically increased NO bioactivity on cardiovascular morbidity and mortality is unclear. In the Gruppo Italiano per lo Studio della Streptochinasi nell’Inffarto Miocardico 3 and International Study of Infarct Survival 4 trials, nitrates failed to reduce mortality when given after myocardial infarction.2 Although the effect of the combination of isosorbide dinitrate and hydralazine in the Vasodilator-Heart …

Aerobic oxidation of cis-cyclooctene by iron-substituted polyoxotungstates: Evidence for a metal initiated auto-oxidation mechanism

Catalytic aerobic epoxidation is a key process for new sustainable systems in the field of hydrocarbon functionalization. The screening of selected Fe-POM catalysts for the aerobic epoxidation has been performed using cis-cyclooctene as model substrate. Our results support a ubiquitous radical chain epoxidation with selectivity up to 66%, TOF in the range 4–50 h −1 and total turnover number >7000. FT-IR spectroscopy has been used to assess the stability of the various POM-based catalysts with respect to analogue organic porphyrine ligands.

Nitric Oxide in Health and Disease from the Point of View of the Otorhinolaryngologist

Nitric oxide (NO) plays role in a great range of important functions in the organism, such as vasodilatation, relaxation of muscles, neurotransmission, neuromediation, and host defense reactions. In the upper airways, nasal cavities and paranasal sinuses are the main sources of this biological mediator. Although the exact role of NO in nasal physiology remains poorly understood, the functions are thought to be host defense, ciliary motility and improved ventilation-perfusion ratio in the lungs by auto-inhalation. Low NO concentrations were reported in certain diseases such as primary ciliary dyskinesia, cystic fibrosis, and acute and chronic maxillary sinusitis whereas high concentrations were detected in upper airway infection, allergic rhinitis and nasal polyposis. Additionally this ubiquitous radical is being implicated in the regulation of cochlear blood flow, sensorineural hearing loss, middle ear effusions, and outer hair cell and vestibular functions. Solid tumors is another area where NO appears to have both tumor-promoting and tumor-inhibiting effects. The presence of NO with high levels within the nose and paranasal sinuses makes it reasonable to believe that this pluripotent gas is involved in a variety of physiological as well as pathophysiological events in the airways. Although NO has an ever-increasing role in various areas related to the practice of otolaryngology, further research is required to understand fully the role of NO in the upper airways.