Measurements of cluster ions using a nano radial DMA and a particle size magnifier in CLOUD

We built a new instrumental setup for measuring ion distributions in the size range [1.3-6] nm. The implementation of an high transmission inlet increased the total transmission efficiency to more than 6% at 1.47 nm mobility equivalent diameter, allowing the detection of ions at atmospheric concentrations. The size resolution of our measurements is as high as 6. We characterized the instrument in the laboratory and carried out measurements during the CLOUD7 campaign. We compared the results obtained with the Neutral cluster and Air Ion spectrometer finding very good agreement

Evolution of α-Pinene Oxidation Products in the Presence of Varying Oxidizers: Negative APi-TOF Point of View

Laboratory experiments conducted in the frame of the CLOUD project at CERN investigated the oxidation of α-pinene oxidation products in a carefully controlled environment and with different oxidation conditions: 1) pure ozonolysis (with the use of an hydroxyl radical (⋅OH) scavenger), 2) ozonolysis without use of a scavenger, and 3) pure ⋅OH oxidation using nitrous acid (HONO) to produce ⋅OH. The anions and negatively charged clusters present in the chamber were analyzed and their chemical composition compared for the different oxidation pathways

Measuring Composition & Growth of Ion Clusters of Sulfuric Acid, Ammonia, Amines & Oxidized Organics as First Steps of Nucleation in the CLOUD Experiment

The mechanisms behind the nucleation of vapors forming new particles in the atmosphere had been proven difficult to establish. One main aim of the CLOUD experiment was to explore in detail these first steps of atmospheric new particle formation by performing extremely well controlled laboratory experiments. We examined nucleation and growth in the presence of different mixtures of vapors, including sulfuric acid, ammonia, dimethylamine, and oxidation products of pinanediol or α-pinene. Among the employed state-of-the-art instrumentation, a high-resolution mass spectrometer that directly sampled negatively charged ions and clusters proved particularly useful. We were able to resolve most of the chemical compositions found for charged sub-2nm clusters and to observe their growth in time. These compositions reflected the mixture of condensable vapors in the chamber and the role of each individual vapor in forming sub-2nm clusters could be explored. By inter-comparing between individual experiments and ambient observations, we try to establish which vapors participate in nucleation in the actual atmosphere, and how

The Parkinson’s-disease-associated receptor GPR37 undergoes metalloproteinase-mediated N-terminal cleavage and ectodomain shedding

Abstract The G-protein-coupled receptor 37 ( GPR37) has been implicated in the juvenile form of Parkinson’s disease, in dopamine signalling and in the survival of dopaminergic cells in animal models. The structure and function of the receptor, however, have remained enigmatic. Here, we demonstrate that although GPR37 matures and is exported from the endoplasmic reticulum in a normal manner upon heterologous expression in HEK293 and SH-SY5Y cells, its long extracellular N-terminus is subject to metalloproteinase-mediated limited proteolysis between E167 and Q168. The proteolytic processing is a rapid and efficient process that occurs constitutively. Moreover, the GPR37 ectodomain is released from cells by shedding, a phenomenon rarely described for GPCRs. Immunofluorescence microscopy further established that although full-length receptors are present in the secretory pathway until the trans-Golgi network, GPR37 is expressed at the cell surface predominantly in the N-terminally truncated form. This notion was verified by flow cytometry and cell surface biotinylation assays. These new findings on the GPR37 N-terminal limited proteolysis may help us to understand the role of this GPCR in the pathophysiology of Parkinson’s disease and in neuronal function in general

Gas-Phase Ozonolysis of Selected Olefins: The Yield of Stabilized Criegee Intermediate and the Reactivity toward SO₂

The gas-phase reaction of ozone with olefins represents an important path for the conversion of unsaturated hydrocarbons in the atmosphere. The current interest is focused on the formation of stabilized Criegee intermediates (sCI) and possible further reactions of sCI. We report results from the ozonolysis of 2,3-dimethyl-2-butene (TME), trans-2-butene and 1-methyl-cyclohexene (MCH) carried out in an atmospheric pressure flow tube at 293 ± 0.5 K and RH = 50% using chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometry to detect H₂SO₄ produced from SO₂ oxidation by sCI. The yields of sCI were found to be in good agreement with recently observed data: 0.62 ± 0.28 (TME), 0.53 ± 0.24 (trans-2-butene) and 0.16 ± 0.07 (MCH). The rate coefficients for sCI + SO₂ from our experiment, (0.9–7.7) × 10^–13 cm³ molecule^–1 s^–1, are within the range of recommendations from indirect determinations as given so far in the literature. Our study helps to assess the importance of sCI in atmospheric chemistry, especially for the oxidation of SO₂ to H₂SO₄

Effects of Chemical Complexity on the Autoxidation Mechanisms of Endocyclic Alkene Ozonolysis Products: From Methylcyclohexenes toward Understanding α‑Pinene

Formation of highly oxidized, multifunctional products in the ozonolysis of three endocyclic alkenes, 1- methylcyclohexene, 4-methylcyclohexene, and α-pinene, was investigated using a chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometer with a nitrate ion (NO₃^–) based ionization scheme. The experiments were performed in borosilicate glass flow tube reactors at room temperature (<i>T</i> = 293 ± 3 K) and at ambient pressure. An ensemble of oxidized monomer and dimer products was detected, with elemental compositions obtained from the high-resolution mass spectra. The monomer product distributions have O/C ratios from 0.8 to 1.6 and can be explained with an autocatalytic oxidation mechanism (=autoxidation) where the oxygen-centered peroxy radical (RO₂) intermediates internally rearrange by intramolecular hydrogen shift reactions, enabling more oxygen molecules to attach to the carbon backbone. Dimer distributions are proposed to form by homogeneous peroxy radical recombination and cross combination reactions. These conclusions were supported by experiments where H atoms were exchanged to D atoms by addition of D₂O to the carrier gas flow. Methylcyclohexenes were observed to autoxidize in accordance with our previous work on cyclohexene, whereas in α-pinene ozonolysis different mechanistic steps are needed to explain the products observed

Plasma Membrane Expression of Gonadotropin-Releasing Hormone Receptors: Regulation by Peptide and Nonpeptide Antagonists

Gonadotropin-releasing hormone acts via cell surface receptors but most human (h) GnRH receptors (GnRHRs) are intracellular. A membrane-permeant nonpeptide antagonist [(2S)-2-[5-[2-(2-axabicyclo[2.2.2]oct-2-yl)-1,1-dimethy-2-oxoethyl]-2-(3,5-dimethylphenyl)-1H-indol-3-yl]-N-(2-pyridin-4-ylethyl)propan-1-amine (IN3)] increases hGnRHR expression at the surface, apparently by facilitating its exit from the endoplasmic reticulum. Here we have quantified GnRHR by automated imaging in HeLa cells transduced with adenovirus expressing hemagglutinin-tagged GnRHR. Consistent with an intracellular site of action, IN3 increases cell surface hGnRHR, and this effect is not blocked or mimicked by membrane-impermeant peptide antagonists [Ac-D2Nal-D4Cpa-D3Pal-Ser-Tyr-d-Cit-Leu-Arg-Pro-d-Ala-NH2 (cetrorelix) and antide]. However, when the C-terminal tail of a Xenopus (X) GnRHR was added (h.XGnRHR) to increase expression, both peptides further increased cell surface GnRHR. Cetrorelix also synergized with IN3 to increase expression of hGnRHR and a G-protein coupling-deficient mutant (A261K-hGnRHR). Cetrorelix also increased cell surface expression of hGnRHR, h.XGnRHR, and mouse GnRHR in gonadotrope-lineage LβT2 cells, and in HeLa cells it slowed h.XGnRHR internalization (measured by receptor-mediated antihemagglutinin uptake). Thus cetrorelix has effects other than GnRHR blockade; it acts as an inverse agonist in internalization assays, supporting the potential importance of ligand-biased efficacy at GnRHR. We also developed an imaging assay for GnRH function based on Ca2+-dependent nuclear translocation of a nuclear factor of activated T cells reporter. Using this in HeLa and LβT2 cells, IN3 and cetrorelix behaved as competitive antagonists when coincubated with GnRH, and long-term pretreatment (16 h) with IN3 reduced its effectiveness as an inhibitor whereas pretreatment with cetrorelix increased its inhibitory effect. This distinction between peptide and nonpeptide antagonists may prove important for therapeutic applications of GnRH antagonists