Role of the stratosphere in the global mercury cycle.

Mercury (Hg) is a global pollutant with substantial risks to human and ecosystem health. By upward transport in tropical regions, mercury enters into the stratosphere, but the contribution of the stratosphere to global mercury dispersion and deposition remains unknown. We find that between 5 and 50% (passing through the 400-kelvin isentropic surface and tropopause, respectively) of the mercury mass deposited on Earth's surface is chemically processed in the lower stratosphere.

Understanding the fragmentation of glucose in mass spectrometry.

The fragmentation mechanism of D-glucose was investigated in detail by two different fragmentation techniques, namely, collision-induced dissociation (CID) and infrared multiphoton dissociation (IRMPD) using all six C-labeled isotopomers and H-labeled isotopomers. For both CID and IRMPD energy-resolved measurements were carried out. Individual fragmentation pathways were studied at MS and MS levels.

Reply to the 'Comment on "Theoretical study of the NO radical reaction with CHClBr, CHICl, CHBrI, CHClBr, and CHClBr"' by C. J. Nielsen and Y. Tang, , 2022, , DOI: 10.1039/D2CP03013F.

In this Reply, we answer the main argument raised in the Comment about the energy of the NO radical and its influence in the reaction profiles of the reaction of the NO radical with CHClBr, CHICl, CHBrI, CHClBr, and CHClBr by C. J. Nielsen and Y.

The Chemistry of Mercury in the Stratosphere.

Mercury, a global contaminant, enters the stratosphere through convective uplift, but its chemical cycling in the stratosphere is unknown. We report the first model of stratospheric mercury chemistry based on a novel photosensitized oxidation mechanism. We find two very distinct Hg chemical regimes in the stratosphere: in the upper stratosphere, above the ozone maximum concentration, Hg oxidation is initiated by photosensitized reactions, followed by second-step chlorine chemistry.

Theoretical study of the NO radical reaction with CHClBr, CHICl, CHBrI, CHClBr, and CHClBr.

The potential reaction of the nitrate radical (NO), the main nighttime atmospheric oxidant, with five alkyl halides, halons (CHClBr, CHICl, CHBrI, CHClBr, and CHClBr) has been studied theoretically. The most favorable reaction corresponds to a hydrogen atom transfer. The stationary points on the potential energy surfaces of these reactions have been characterized.

Photochemistry of oxidized Hg(I) and Hg(II) species suggests missing mercury oxidation in the troposphere.

Mercury (Hg), a global contaminant, is emitted mainly in its elemental form Hg to the atmosphere where it is oxidized to reactive Hg compounds, which efficiently deposit to surface ecosystems. Therefore, the chemical cycling between the elemental and oxidized Hg forms in the atmosphere determines the scale and geographical pattern of global Hg deposition. Recent advances in the photochemistry of gas-phase oxidized Hg and Hg species postulate their photodissociation back to Hg as a crucial step in the atmospheric Hg redox cycle.

Photodissociation Mechanisms of Major Mercury(II) Species in the Atmospheric Chemical Cycle of Mercury.

Mercury is a contaminant of global concern that is transported throughout the atmosphere as elemental mercury Hg and its oxidized forms Hg and Hg . The efficient gas-phase photolysis of Hg and Hg has recently been reported. However, whether the photolysis of Hg leads to other stable Hg species, to Hg , or to Hg and its competition with thermal reactivity remain unknown.

Gas-Phase Photolysis of Hg(I) Radical Species: A New Atmospheric Mercury Reduction Process.

The efficient gas-phase photoreduction of Hg(II) has recently been shown to change mercury cycling significantly in the atmosphere and its deposition to the Earth's surface. However, the photolysis of key Hg(I) species within that cycle is currently not considered. Here we present ultraviolet-visible absorption spectra and cross-sections of HgCl, HgBr, HgI, and HgOH radicals, computed by high-level quantum-chemical methods, and show for the first time that gas-phase Hg(I) photoreduction can occur at time scales that eventually would influence the mercury chemistry in the atmosphere.

Photoreduction of gaseous oxidized mercury changes global atmospheric mercury speciation, transport and deposition.

Anthropogenic mercury (Hg(0)) emissions oxidize to gaseous Hg(II) compounds, before deposition to Earth surface ecosystems. Atmospheric reduction of Hg(II) competes with deposition, thereby modifying the magnitude and pattern of Hg deposition. Global Hg models have postulated that Hg(II) reduction in the atmosphere occurs through aqueous-phase photoreduction that may take place in clouds.

Chemical modification of alginate with cysteine and its application for the removal of Pb(II) from aqueous solutions.

It has been synthesized, characterized and tested a new biomaterial AlgS (sodium alginate functionalized with cysteine) to remove Pb(II) in aqueous media. The maximum Pb(II)-sorption capacity of AlgS (Q = 770 mg·g) is between almost two and nine times higher than other alginate-materials reported in the literature. Techniques, such as TGA/DSC, SEM/EDS, BET, FTIR, UV-Vis, XRD and C solid state-NMR have been used to study the chemical-modification of alginate at oxidation and aminofication stages.

Chemical modification of sodium alginate with thiosemicarbazide for the removal of Pb(II) and Cd(II) from aqueous solutions.

A new material (Alg-TSC), based on alginate (Alg) chemically modified with thiosemicarbazide (TSC), has been synthesized and tested as an effective biomaterial to remove Pb(II) and Cd(II) ions in aqueous solutions. The synthesis was carried out by controlling the following steps, i/partial oxidation process of alginate in NaIO to obtain AlgOx, ii/reacting of AlgOx, at 40-45 °C, with TSC in NaBH. Alg-TSC has been characterized by Field Emission Scanning Electron Microscopy (FESEM/EDS), Fourier Transform Infrared Spectroscopy (ATR-IR), solid state C NMR spectroscopy and Point of Zero Charge (pH) measuremenmts.

Energy resolved mass spectrometry of chlorogenic acids and its application to isomer quantification by direct infusion tandem mass spectrometry.

Introduction: With the advent of high-perfomance liquid chromatography (HPLC)-tandem mass spectrometry (MS) using ion trap mass analysers it is possible to acquire unambigious structural information in particular with respect to aspects of regiochemistry and stereochemistry of organic compounds present in complex mixtures such as coffee extracts. However, HPLC-MS methods are resource extensive, laborious and lacking user friendliness.

Objective: To introduce a simple parameter - the energy threshhold for fragmentation - determined using energy resolved MS and demonstrate its value for the complete structural characterisation and even relative quantification of individual isomeric chlrogenic acids in direct infusion experiments.

Energetic and Structural Properties of Two Phenolic Antioxidants: Tyrosol and Hydroxytyrosol.

Theoretical and experimental studies on the energetic, structural and some other relevant physicochemical properties of the antioxidant tyrosol (1), hydroxytyrosol (1OH) molecules and the corresponding radicals 1 and 1O are reported in this work. The experimental values of the gas-phase enthalpy of formation, Δ H(g), in kJ·mol, of 1 (-302.4 ± 3.

Gas-Phase Acidities and Basicities of Alanines and N-Benzylalanines by the Extended Kinetic Method.

This paper reports an experimental determination of the gas-phase acidities and basicities of N-benzylalanines, in both their α and β forms, by means of the extended kinetic method (EKM). The experimental gas-phase acidity of β-alanine was also determined. Standard ab initio molecular orbital calculations at the G3 level were performed for alanines, and at the G3(MP2)//B3LYP level for N-benzylalanines.

Binary twinned-icosahedral [BH] interacts with cyclodextrins as a precedent for its complexation with other organic motifs.

The weakly coordinating binary macropolyhedral anion closo,closo-[BH] (B21; D symmetry) has been synthesized using a simplified strategy compared to that in the literature. While gas-phase complexes of B21 with β- and γ-cyclodextrin (CD) were detected using ESI FT-ICR spectrometric measurements, α-CD did not bind to the B21 guest. This spectroscopic evidence has been interpreted using quantum-chemical computations, showing that β- and γ-CD are able to interact with B21 due to their larger cavities, in contrast to the smaller α-CD.

Ab initio quantum-chemical computations of the electronic states in HgBr and IBr: Molecules of interest on the Earth's atmosphere.

The electronic states of atmospheric relevant molecules IBr and HgBr are reported, within the UV-Vis spectrum range (170nm≤λ≤600 nm) by means of the complete-active-space self-consistent field/multi-state complete-active-space second-order perturbation theory/spin-orbit restricted-active-space state-interaction (CASSCF/MS-CASPT2/SO-RASSI) quantum-chemical approach and atomic-natural-orbital relativistic-correlation-consistent (ANO-RCC) basis sets. Several analyses of the methodology were carried out in order to reach converged results and therefore to establish a highly accurate level of theory. Good agreement is found with the experimental data with errors not higher than around 0.

Phase transition thermodynamics of bisphenols.

Herein we have studied, presented, and analyzed the phase equilibria thermodynamics of a bisphenols (BP-A, BP-E, BP-F, BP-AP, and BP-S) series. In particular, the heat capacities, melting temperatures, and vapor pressures at different temperatures as well as the standard enthalpies, entropies, and Gibbs energies of phase transition (fusion and sublimation) were experimentally determined. Also, we have presented the phase diagrams of each bisphenol derivative and investigated the key parameters related to the thermodynamic stability of the condensed phases.

Static and dynamic properties of 1,1'-bi-2-naphthol and its conjugated acids and bases.

Several convergent techniques were used to characterize 1,1'-bi-2-naphthol (BINOL) and some of its properties. Its acidity in the gas-phase, from neutral species to monoanion, was measured by mass spectrometry. The conformation and structure of BINOL in the gas phase was determined by microwave rotational spectroscopy.

Energetic and structural study of bisphenols.

We have studied thermochemical, thermophysical and structural properties of bisphenols A, E, F, and AP. In particular, the standard enthalpies of sublimation and the standard enthalpies of formation in the gas phase at 298.15 K for all these species were experimentally determined.

Acidities of closo-1-COOH-1,7-C2B10H11 and amino acids based on icosahedral carbaboranes.

Carborane clusters are not found in Nature and are exclusively man-made. In this work we study, both experimentally and computationally, the gas-phase acidity (measured GA = 1325 kJ·mol(-1), computed GA = 1321 kJ·mol(-1)) and liquid-phase acidity (measured pKa = 2.00, computed pKa = 1.

Investigating the thermal decomposition of starch and cellulose in model systems and toasted bread using domino tandem mass spectrometry.

Many dietary products containing polysaccharides, mostly starch and cellulose, are processed by thermal treatment. Similarly to the formation of caramel from mono- and disaccharides, the chemical structure of the carbohydrates is dramatically altered by heat treatment. This contribution investigates the products of thermal decomposition of pure starch and cellulose as model systems followed by an investigation of bread obtained at comparable conditions using a combination of modern mass spectrometry techniques.

Can an amine be a stronger acid than a carboxylic acid? The surprisingly high acidity of amine-borane complexes.

The gas-phase acidity of a series of amine-borane complexes has been investigated through the use of electrospray mass spectrometry (ESI-MS), with the application of the extended Cooks kinetic method, and high-level G4 ab initio calculations. The most significant finding is that typical nitrogen bases, such as aniline, react with BH(3) to give amine-borane complexes, which, in the gas phase, have acidities as high as those of either phosphoric, oxalic, or salicylic acid; their acidity is higher than many carboxylic acids, such as formic, acetic, and propanoic acid. Indeed the complexation of different amines with BH(3) leads to a substantial increase (from 167 to 195 kJ mol(-1)) in the intrinsic acidity of the system; in terms of ionization constants, this increase implies an increase as large as fifteen orders of magnitude.