Reactions occurring at mineral–fluid interfaces are important in all geochemical processes and essential for the cycling of elements within the Earth. Understanding the mechanism of the transformation of one solid phase to another and the role of fluids is fundamental to many natural and industrial processes. Problems such as the interaction of minerals with CO2-saturated water, the durability of nuclear waste materials, the remediation of polluted water, and mineral reactions that can destroy our stone-based cultural heritage, are related by the common feature that a mineral assemblage in contact with a fluid may be replaced by a more stable assemblage.

Coupled dissolution and precipitation at mineral-fluid interfaces

Two decades after the introduction of matrix assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI), soft ionization mass spectrometry represents a powerful toolset for the structural investigation of synthetic polymers. The present review highlights the current state-of-the-art, covering the latest developments of novel techniques, enabling instrumentation as well as the important applications of soft ionization MS from the beginning of 2008. Special attention is paid to the role that soft ionization MS has played in the mechanistic investigation of radical polymerization processes since 2005. © 2010 The Royal Society of Chemistry.

Mass spectrometry in polymer chemistry: A state-of-the-art up-date

Formation of cirrus clouds depends on the availability of ice nuclei to begin condensation of atmospheric water vapor. Although it is known that only a small fraction of atmospheric aerosols are efficient ice nuclei, the critical ingredients that make those aerosols so effective have not been established. We have determined in situ the composition of the residual particles within cirrus crystals after the ice was sublimated. Our results demonstrate that mineral dust and metallic particles are the dominant source of residual particles, whereas sulfate and organic particles are underrepresented, and elemental carbon and biological materials are essentially absent. Further, composition analysis combined with relative humidity measurements suggests that heterogeneous freezing was the dominant formation mechanism of these clouds.

Clarifying the Dominant Sources and Mechanisms of Cirrus Cloud Formation

Our understanding of crystal nucleation is a limiting factor in many fields, not least in the atmospheric sciences. It was recently found that feldspar, a component of airborne desert dust, plays a dominant role in triggering ice formation in clouds, but the origin of this effect was unclear. By investigating the structure/property relationships of a wide range of feldspars, we demonstrate that alkali feldspars with certain microtextures, related to phase separation into Na and K-rich regions, show exceptional icenucleating abilities in supercooled water. We found no correlation between ice-nucleating efficiency and the crystal structures or the chemical compositions of these active feldspars, which suggests that specific topographical features associated with these microtextures are key in the activity of these feldspars. That topography likely acts to promote ice nucleation, improves our understanding of ice formation in clouds, and may also enable the design and manufacture of bespoke nucleating materials for uses such as cloud seeding and cryopreservation.

Dataset associated with ‘The role of phase-separation and related topography in the exceptional ice-nucleating ability of alkali feldspars’

Abstract. Ice-nucleating particles (INPs) are known to affect the amount of ice in mixed-phase clouds, thereby influencing many of their properties. The atmospheric INP concentration changes by orders of magnitude from terrestrial to marine environments, which typically contain much lower concentrations. Many modelling studies use parameterizations for heterogeneous ice nucleation and cloud ice processes that do not account for this difference because they were developed based on INP measurements made predominantly in terrestrial environments without considering the aerosol composition. Errors in the assumed INP concentration will influence the simulated amount of ice in mixed-phase clouds, leading to errors in top-of-atmosphere radiative flux and ultimately the climate sensitivity of the model. Here we develop a global model of INP concentrations relevant for mixed-phase clouds based on laboratory and field measurements of ice nucleation by K-feldspar (an ice-active component of desert dust) and marine organic aerosols (from sea spray). The simulated global distribution of INP concentrations based on these two species agrees much better with currently available ambient measurements than when INP concentrations are assumed to depend only on temperature or particle size. Underestimation of INP concentrations in some terrestrial locations may be due to the neglect of INPs from other terrestrial sources. Our model indicates that, on a monthly average basis, desert dusts dominate the contribution to the INP population over much of the world, but marine organics become increasingly important over remote oceans and they dominate over the Southern Ocean. However, day-to-day variability is important. Because desert dust aerosol tends to be sporadic, marine organic aerosols dominate the INP population on many days per month over much of the mid- and high-latitude Northern Hemisphere. This study advances our understanding of which aerosol species need to be included in order to adequately describe the global and regional distribution of INPs in models, which will guide ice nucleation researchers on where to focus future laboratory and field work.

Contribution of Feldspar and Marine Organic aerosols to global ice nucleating particles concentrations

Dust is the major source of iron in atmospheric aerosols but little is known about its role in catalyzing polymerization reactions of organics in particles. Using Arizona Test Dust (AZTD) and hemat...

Dust-Catalyzed Oxidative Polymerization of Catechol and Its Impacts on Ice Nucleation Efficiency and Optical Properties

Mineral dust particles can initiate the freezing of cloud droplets in the atmosphere. The freezing efficiency of these particles can, however, be strongly affected by solutes, such as inorganic aci...

Effects of Inorganic Acids and Organic Solutes on the Ice Nucleating Ability and Surface Properties of Potassium-Rich Feldspar

Ammonia oxidation catalyzed by molecular compounds is of current interest as a carbon free source of dihydrogen. Activation of N-H bonds through coordination to transition metal centers is a key reaction in this process. We report the substantial activation of ammonia via reaction with low valent molybdenum complexes of a diborate pentadentate ligand system. Spontaneous loss of hydrogen atoms from (B 2 Pz 4 Py)Mo(II)-NH 3 at room temperature to produce H 2 and the dinuclear μ-nitrido compound (B 2 Pz 4 Py)Mo-N-Mo(B 2 Pz 4 Py) is observed due to substantial N-H bond weakening upon coordination to Mo. Mechanistic details are supported through the experimental observation/characterization of terminal amido, imido and nitrido complexes and density functional theory computations. The generally under-appreciated role of bridging nitrido intermediates is revealed and discussed, providing guidance for further catalyst development for this process.

Spontaneous Ammonia Activation Through Coordination Induced Bond Weakening in Molybdenum Complexes of a Dianionic Pentadentate Ligand Platform.

Flavin-based photocatalysts such as riboflavin tetraacetate (RFT) serve as a robust platform for light-mediated protein labelling via phenoxy radical-mediated tyrosine–biotin phenol coupling on live cells. To gain insight into this coupling reaction, we conducted detailed mechanistic analysis for RFT-photomediated activation of phenols for tyrosine labelling. Contrary to previously proposed mechanisms, we find that the initial covalent binding step between the tag and tyrosine is not radical addition, but rather radical–radical recombination. The proposed mechanism may also explain the mecha-nism of other reported tyrosine-tagging approaches. Competitive kinetics experiments show that phenoxyl radicals are generated with several reactive intermediates in the proposed mechanism—primarily with the excited riboflavin-photocatalyst or singlet oxygen—and these multiple pathways for phenoxyl radical generation from phenols increase the likelihood of radical–radical recombination.

/pdf/targeted-proximity-labelling-of-protein-tyrosines-via-flavin-13uynf96.pdf

Targeted proximity-labelling of protein tyrosines via flavin-dependent photoredox catalysis with mechanistic evidence for a radical–radical recombination pathway

Nicole Removski

Papers

Dust-Catalyzed Oxidative Polymerization of Catechol and Its Impacts on Ice Nucleation Efficiency and Optical Properties

Effects of Inorganic Acids and Organic Solutes on the Ice Nucleating Ability and Surface Properties of Potassium-Rich Feldspar

Spontaneous Ammonia Activation Through Coordination Induced Bond Weakening in Molybdenum Complexes of a Dianionic Pentadentate Ligand Platform.

Targeted proximity-labelling of protein tyrosines via flavin-dependent photoredox catalysis with mechanistic evidence for a radical–radical recombination pathway