Browsing by Subject "IONS"

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  • Juusola, Liisa; Pfau-Kempf, Yann; Ganse, Urs; Battarbee, Markus; Brito, Thiago; Grandin, Maxime; Turc, Lucile; Palmroth, Minna (2018)
    The origin of the flapping motions of the current sheet in the Earth's magnetotail is one of the most interesting questions of magnetospheric dynamics yet to be solved. We have used a polar plane simulation from the global hybrid-Vlasov model Vlasiator to study the characteristics and source of current sheet flapping in the center of the magnetotail. The characteristics of the simulated signatures agree with observations reported in the literature. The flapping is initiated by a hemispherically asymmetric magnetopause perturbation, created by subsolar magnetopause reconnection, that is capable of displacing the tail current sheet from its nominal position. The current sheet displacement propagates downtail at the same pace as the driving magnetopause perturbation. The initial current sheet displacement launches a standing magnetosonic wave within the tail resonance cavity. The travel time of the wave within the local cavity determines the period of the subsequent flapping signatures. Compression of the tail lobes due to added flux affects the cross-sectional width of the resonance cavity as well as the magnetosonic speed within the cavity. These in turn modify the wave travel time and flapping period. The compression of the resonance cavity may also provide additional energy to the standing wave, which may lead to strengthening of the flapping signature. It may be possible that the suggested mechanism could act as a source of kink-like waves that have been observed to be emitted from the center of the tail and to propagate toward the dawn and dusk flanks.
  • Feil, Christoph M.; Hettich, Thomas D.; Beyer, Katharina; Sondermann, Christina; Schlindwein, Simon H.; Nieger, Martin; Gudat, Dietrich (2019)
    N-Heterocyclic phosphenium (NHP) and nitro-sonium (NO+) ligands are often viewed as isolobal analogues that share the capability to switch between different charge states and thus display redox "noninnocent" behavior. We report here on mixed complexes [(NHP)M(CO)(n)(NO)] (M = Fe, Cr; n = 2, 3), which permit evaluating the donor/acceptor properties of both types of ligands and their interplay in a single complex. The crystalline target compounds were obtained from reactions of N-heterocyclic phosphenium triflates with PPN[Fe(CO)(3)(NO)] or PPN[Cr(CO)(4)-(NO)], respectively, and fully characterized (PPN = nitride-bistriphenylphosphonium cation). The structural and spectroscopic (IR, UV-vis) data support the presence of carbene-analogue NHP ligands with an overall positive charge state and pi-acceptor character. Even if the structural features of the M-NO unit were in all but one product blurred by crystallographic CO/NO disorder, spectroscopic studies and the structural data of the remaining compound suggest that the NO units exhibit nitroxide (NO-) character. This assignment was validated by computational studies, which reveal also that the electronic structure of iron NHP/ NO complexes is closely akin to that of the Hieber anion, [Fe(CO)(3)(NO)](-). The electrophilic character of the NHP units is further reflected in the chemical behavior of the mixed complexes. Cyclic voltammetry and IR-SEC studies revealed that complex [(NHP)Fe(CO)(2) (NO)] (4) undergoes chemically reversible one-electron reduction. Computational studies indicate that the NHP unit in the resulting product carries significant radical character, and the reduction may thus be classified as predominantly ligand-centered. Reaction of 4 with sodium azide proceeded likewise under nucleophilic attack at phosphorus and decomplexation, while super hydride and methyl lithium reacted with all chromium and iron complexes via transfer of a hydride or methyl anion to the NHP unit to afford anionic phosphine complexes. Some of these species were isolated after cation exchange or trapped with electrophiles (H+, SnPh3(+)) to afford neutral complexes representing the products of a formal hydrogenation or hydrostannylation of the original M=P double bond.
  • Kulig, Waldemar; Korolainen, Hanna; Zatorska, Maria; Kwolek, Urszula; Wydro, Pawel; Kepczynski, Mariusz; Rog, Tomasz (2019)
    Phosphatidic acids (PAs) have many biological functions in biomembranes, e.g., they are involved in the proliferation, differentiation, and transformation of cells. Despite decades of research, the molecular understanding of how PAs affect the properties of biomembranes remains elusive. In this study, we explored the properties of lipid bilayers and monolayers composed of PAs and phosphatidylcholines (PCs) with various acyl chains. For this purpose, the Langmuir monolayer technique and atomistic molecular dynamics (MD) simulations were used to study the miscibility of PA and PC lipids and the molecular organization of mixed bilayers. The monolayer experiments demonstrated that the miscibility of membrane components strongly depends on the structure of the hydrocarbon chains and thus on the overall lipid shape. Interactions between PA and PC molecules vary from repulsive, for systems containing lipids with saturated and unsaturated acyl tails (strongly positive values of the excess free energy of mixing), to attractive, for systems in which all lipid tails are saturated (negative values of the excess free energy of mixing). The MD simulations provided atomistic insight into polar interactions (formation of hydrogen bonds and charge pairs) in PC-PA systems. H-bonding between PA monoanions and PCs in mixed bilayers is infrequent, and the lipid molecules interact mainly via electrostatic interactions. However, the number of charge pairs significantly decreases with the number of unsaturated lipid chains in the PA-PC system. The PA dianions weakly interact with the zwitterionic lipids, but their headgroups are more hydrated as compared to the monoanionic form. The acyl chains in all PC-PA bilayers are more ordered compared to single-component PC systems. In addition, depending on the combination of lipids, we observed a deeper location of the PA phosphate groups compared to the PC phosphate groups, which can alter the presentation of PAs for the peripheral membrane proteins, affecting their accessibility for binding.
  • Blum, Markus; Gebhardt, Jacqueline; Papendick, Marius; Schlindwein, Simon H.; Nieger, Martin; Gudat, Dietrich (2018)
    Two N-heterocyclic phosphines with exocyclic SCN substituents were synthesised via metathesis of chlorophosphine precursors with KSCN and fully characterised. The crystallographic studies reveal that the products exhibit pronounced structural differences. The thiocyanato unit binds in one case via the nitrogen atom to yield a molecular structure with a slightly elongated P-N single bond and, in the other case, via the sulfur atom to form a structure that is best described as an ion pair and forms a one-dimensional coordination polymer in the crystal. DFT calculations suggest that the P-N and P center dot center dot center dot S interactions can be described as covalent and dative bonds, respectively, and that the structural differences correlate with the different cation stabilities of the individual phosphenium cation fragments.
  • He, Xu-Cheng; Iyer, Siddharth; Sipila, Mikko; Ylisirniö, Arttu; Peltola, Maija; Kontkanen, Jenni; Baalbaki, Rima; Simon, Mario; Kuerten, Andreas; Tham, Yee Jun; Pesonen, Janne; Ahonen, Lauri R.; Amanatidis, Stavros; Amorim, Antonio; Baccarini, Andrea; Beck, Lisa; Bianchi, Federico; Brilke, Sophia; Chen, Dexian; Chiu, Randall; Curtius, Joachim; Dada, Lubna; Dias, Antonio; Dommen, Josef; Donahue, Neil M.; Duplissy, Jonathan; El Haddad, Imad; Finkenzeller, Henning; Fischer, Lukas; Heinritzi, Martin; Hofbauer, Victoria; Kangasluoma, Juha; Kim, Changhyuk; Koenig, Theodore K.; Kubecka, Jakub; Kvashnin, Aleksandr; Lamkaddam, Houssni; Lee, Chuan Ping; Leiminger, Markus; Li, Zijun; Makhmutov, Vladimir; Xiao, Mao; Marten, Ruby; Nie, Wei; Onnela, Antti; Partoll, Eva; Petäjä, Tuukka; Salo, Vili-Taneli; Schuchmann, Simone; Steiner, Gerhard; Stolzenburg, Dominik; Stozhkov, Yuri; Tauber, Christian; Tome, Antonio; Vaisanen, Olli; Vazquez-Pufleau, Miguel; Volkamer, Rainer; Wagner, Andrea C.; Wang, Mingyi; Wang, Yonghong; Wimmer, Daniela; Winkler, Paul M.; Worsnop, Douglas R.; Wu, Yusheng; Yan, Chao; Ye, Qing; Lehtinen, Kari; Nieminen, Tuomo; Manninen, Hanna E.; Rissanen, Matti; Schobesberger, Siegfried; Lehtipalo, Katrianne; Baltensperger, Urs; Hansel, Armin; Kerminen, Veli-Matti; Flagan, Richard C.; Kirkby, Jasper; Kurten, Theo; Kulmala, Markku (2021)
    Ions enhance the formation rate of atmospheric aerosol particles, which play an important role in Earth's radiative balance. Ion-induced nucleation involves the stepwise accretion of neutral monomers onto a molecular cluster containing an ion, which helps to stabilize the cluster against evaporation. Although theoretical frameworks exist to calculate the collision rate coefficients between neutral molecules and ions, they need to be experimentally confirmed, ideally under atmospherically relevant conditions of around 1000 ion pairs cm(-3). Here, in experiments performed under atmospheric conditions in the CERN CLOUD chamber, we have measured the collision rate coefficients between neutral iodic acid (HIO3) monomers and charged iodic acid molecular clusters containing up to 11 iodine atoms. Three methods were analytically derived to calculate ion-polar molecule collision rate coefficients. After evaluation with a kinetic model, the 50% appearance time method is found to be the most robust. The measured collision rate coefficient, averaged over all iodine clusters, is (2.4 +/- 0.8)x10(-9 )cm(3) s(-1), which is close to the expectation from the surface charge capture theory.
  • Ahonen, L. R.; Kangasluoma, J.; Lammi, J.; Lehtipalo, K.; Hämeri, K.; Petäjä, T.; Kulmala, M. (2017)
    This study was conducted to observe a potential formation and/or release of aerosol particles related to manufacturing processes inside a cleanroom. We introduce a novel technique to monitor airborne sub 2nm particles in the cleanroom and present results from a measurement campaign during which the total particle number concentration (>1nm and >7 nm) and the size resolved concentration in the 1 to 2nm size range were measured. Measurements were carried out in locations where atomic layer deposition (ALD), sputtering, and lithography processes were conducted, with a wide variety of starting materials. During our campaign in the clean room, we observed several time periods when the particle number concentration was 10(5) cm(-3) in the sub 2nm size range and 10(4) cm(-3) in the size class larger than 7nm in one of the sampling locations. The highest concentrations were related to the maintenance processes of the manufacturing machines, which were conducted regularly in that specific location. Our measurements show that around 500cm(-3) sub 2nm particles or clusters were in practice always present in this specific cleanroom, while the concentration of particles larger than 2nm was less than 2cm(-3). During active processes, the concentrations of sub 2nm particles could rise to over 10(5) cm(-3) due to an active new particle formation. The new particle formation was most likely induced by a combination of the supersaturated vapors, released from the machines, and the very low existing condensation sink, leading to pretty high formation rates J(1.4 nm) = (9 4) cm(-3) s(-1) and growth rates of particles (GR(1.1-1.3 nm) = (6 +/- 3) nm/h and GR(1.3-1.8 nm) = (14 +/- 3) nm/h).Copyright (c) 2017 American Association for Aerosol Research
  • Wijsen, N.; Aran, A.; Pomoell, J.; Poedts, S. (2019)
    Aims. We study how a fast solar wind stream embedded in a slow solar wind influences the spread of solar energetic protons in interplanetary space. In particular, we aim at understanding how the particle intensity and anisotropy vary along interplanetary magnetic field (IMF) lines that encounter changing solar wind conditions such as the shock waves bounding a corotating interaction region (CIR). Moreover, we study how the intensities and anisotropies vary as a function of the longitudinal and latitudinal coordinate, and how the width of the particle intensities evolves with the heliographic radial distance. Furthermore, we study how cross-field diffusion may alter these spatial profiles. Methods. To model the energetic protons, we used a recently developed particle transport code that computes particle distributions in the heliosphere by solving the focused transport equation (RTE) in a stochastic manner. The particles are propagated in a solar wind containing a CIR, which was generated by the heliospheric model, EUHFORIA. We study four cases in which we assume a delta injection of 4 MeV protons spread uniformly over different regions at the inner boundary of the model. These source regions have the same size and shape, yet are shifted in longitude from each other, and are therefore magnetically connected to different solar wind conditions. Results. The intensity and anisotropy profiles along selected IMF lines vary strongly according to the different solar wind conditions encountered along the field line. The IMF lines crossing the shocks bounding the CIR show the formation of accelerated particle populations, with the reverse shock wave being a more efficient accelerator than the forward shock wave. The longitudinal intensity profiles near the CIR are highly asymmetric in contrast to the profiles obtained in a nominal solar wind. For the injection regions that do not cross the transition zone between the fast and slow solar wind, we observe a steep intensity drop of several orders of magnitude near the stream interface (SI) inside the CIR. Moreover, we demonstrate that the longitudinal width of the particle intensity distribution can increase, decrease, or remain constant with heliographic radial distance, reflecting the underlying IMF structure. Finally, we show how the deflection of the IMF at the shock waves and the compression of the IMF in the CIR deforms the three-dimensional shape of the particle distribution in such a way that the original shape of the injection profile is lost.
  • Palmroth, Minna; Hietala, Heli; Plaschke, Ferdinand; Archer, Martin; Karlsson, Tomas; Blanco-Cano, Xochitl; Sibeck, David; Kajdic, Primoz; Ganse, Urs; Pfau-Kempf, Yann; Battarbee, Markus; Turc, Lucile (2018)
    We use a global hybrid-Vlasov simulation for the magnetosphere, Vlasiator, to investigate magnetosheath high-speed jets. Unlike many other hybrid-kinetic simulations, Vlasiator includes an unscaled geomagnetic dipole, indicating that the simulation spatial and temporal dimensions can be given in SI units without scaling. Thus, for the first time, this allows investigating the magnetosheath jet properties and comparing them directly with the observed jets within the Earth's magnetosheath. In the run shown in this paper, the interplanetary magnetic field (IMF) cone angle is 30 degrees, and a foreshock develops upstream of the quasi-parallel magnetosheath. We visually detect a structure with high dynamic pressure propagating from the bow shock through the magnetosheath. The structure is confirmed as a jet using three different criteria, which have been adopted in previous observational studies. We compare these criteria against the simulation results. We find that the magnetosheath jet is an elongated structure extending earthward from the bow shock by similar to 2.6 R-E, while its size perpendicular to the direction of propagation is similar to 0.5 R-E. We also investigate the jet evolution and find that the jet originates due to the interaction of the bow shock with a high-dynamic-pressure structure that reproduces observational features associated with a short, large-amplitude magnetic structure (SLAMS). The simulation shows that magnetosheath jets can develop also under steady IMF, as inferred by observational studies. To our knowledge, this paper therefore shows the first global kinetic simulation of a magnetosheath jet, which is in accordance with three observational jet criteria and is caused by a SLAMS advecting towards the bow shock.
  • Sipilä, O.; Caselli, P.; Harju, J. (2019)
    We constructed two new models for deuterium and spin-state chemistry for the purpose of modeling the low-temperature environment prevailing in starless and pre-stellar cores. The fundamental difference between the two models is in the treatment of ion-molecule proton-donation reactions of the form XH+ + Y -> X + YH+, which are allowed to proceed either via full scrambling or via direct proton hop, that is, disregarding proton exchange. The choice of the reaction mechanism affects both deuterium and spin-state chemistry, and in this work our main interest is on the effect on deuterated ammonia. We applied the new models to the starless core H-MM1, where several deuterated forms of ammonia have been observed. Our investigation slightly favors the proton hop mechanism over full scrambling because the ammonia D/H ratios are better fit by the former model, although neither model can reproduce the observed NH2D ortho-to-para ratio of 3 (the models predict a value of similar to 2). Extending the proton hop scenario to hydrogen atom abstraction reactions yields a good agreement for the spin-state abundance ratios, but greatly overestimates the deuterium fractions of ammonia. However, one can find a reasonably good agreement with the observations with this model by increasing the cosmic-ray ionization rate over the commonly adopted value of similar to 10(-17) s(-1). We also find that the deuterium fractions of several other species, such as H2CO, H2O, and CH3, are sensitive to the adopted proton-donation reaction mechanism. Whether the full scrambling or proton hop mechanism dominates may be dependent on the reacting system, and new laboratory and theoretical studies for various reacting systems are needed to constrain chemical models.
  • Wang, Yang; Kangasluoma, Juha; Attoui, Michel; Fang, Jiaxi; Junninen, Heikki; Kulmala, Markku; Petäjä, Tuukka; Biswas, Pratim (2017)
    While flame aerosol reactor (FLAR) synthesis of nanoparticles is widely used to produce a range of nano-materials, incipient particle formation by nucleation and vapor condensation is not well understood. This gap in our knowledge of incipient particle formation is caused by limitations in instruments, where, during measurements, the high diffusivity of sub 3 nm particles significantly affects resolution and transport loss. This work used a high resolution differential mobility analyzer (DMA) and an atmospheric pressure interface-mass spectrometer (APi-TOF) to observe incipient particle formation during flame synthesis. By tandemly applying these two instruments, differential mobility analysis-mass spectrometry (DMA-MS) measured the size and mass of the incipient particles simultaneously, and the effective density of the sub 3 nm particles was estimated. The APi-TOF further provided the chemical compositions of the detected particles based on highly accurate masses and isotope distributions. This study investigated the incipient particle formation in flames with and without the addition of synthesis precursors. Results from FLAR using two types of precursors including tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TTIP) are presented. The effect of the precursor feed rates on incipient particle growth was also investigated. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.
  • Wijsen, N.; Aran, A.; Scolini, C.; Lario, D.; Afanasiev, A.; Vainio, R.; Sanahuja, B.; Pomoell, J.; Poedts, S. (2022)
    Aims. We model the energetic storm particle (ESP) event of 14 July 2012 using the energetic particle acceleration and transport model named 'PArticle Radiation Asset Directed at Interplanetary Space Exploration' (PARADISE), together with the solar wind and coronal mass ejection (CME) model named 'EUropean Heliospheric FORcasting Information Asset' (EUHFORIA). The simulation results illustrate both the capabilities and limitations of the utilised models. We show that the models capture some essential structural features of the ESP event; however, for some aspects the simulations and observations diverge. We describe and, to some extent, assess the sources of errors in the modelling chain of EUHFORIA and PARADISE and discuss how they may be mitigated in the future. Methods. The PARADISE model computes energetic particle distributions in the heliosphere by solving the focused transport equation in a stochastic manner. This is done using a background solar wind configuration generated by the ideal magnetohydrodynamic module of EUHFORIA. The CME generating the ESP event is simulated by using the spheromak model of EUHFORIA, which approximates the CME's flux rope as a linear force-free spheroidal magnetic field. In addition, a tool was developed to trace CME-driven shock waves in the EUHFORIA simulation domain. This tool is used in PARADISE to (i) inject 50 keV protons continuously at the CME-driven shock and (ii) include a foreshock and a sheath region, in which the energetic particle parallel mean free path, lambda(parallel to), decreases towards the shock wave. The value of lambda(parallel to) at the shock wave is estimated from in situ observations of the ESP event. Results. For energies below similar to 1 MeV, the simulation results agree well with both the upstream and downstream components of the ESP event observed by the Advanced Composition Explorer. This suggests that these low-energy protons are mainly the result of interplanetary particle acceleration. In the downstream region, the sharp drop in the energetic particle intensities is reproduced at the entry into the following magnetic cloud, illustrating the importance of a magnetised CME model.
  • Stolzenburg, Dominik; Fischer, Lukas; Vogel, Alexander L.; Heinritzi, Martin; Schervish, Meredith; Simon, Mario; Wagner, Andrea C.; Dada, Lubna; Ahonen, Lauri R.; Amorim, Antonio; Baccarini, Andrea; Bauer, Paulus S.; Baumgartner, Bernhard; Bergen, Anton; Bianchi, Federico; Breitenlechner, Martin; Brilke, Sophia; Mazon, Stephany Buenrostro; Chen, Dexian; Dias, Antnio; Draper, Danielle C.; Duplissy, Jonathan; El Haddad, Imad; Finkenzeller, Henning; Frege, Carla; Fuchs, Claudia; Garmash, Olga; Gordon, Hamish; He, Xucheng; Helm, Johanna; Hofbauer, Victoria; Hoyle, Christopher R.; Kim, Changhyuk; Kirkby, Jasper; Kontkanen, Jenni; Kuerten, Andreas; Lampilahti, Janne; Lawler, Michael; Lehtipalo, Katrianne; Leiminger, Markus; Mai, Huajun; Mathot, Serge; Mentler, Bernhard; Molteni, Ugo; Nie, Wei; Nieminen, Tuomo; Nowak, John B.; Ojdanic, Andrea; Onnela, Antti; Passananti, Monica; Petäjä, Tuukka; Quélever, Lauriane L. J.; Rissanen, Matti P.; Sarnela, Nina; Schallhart, Simon; Tauber, Christian; Tome, Antonio; Wagner, Robert; Wang, Mingyi; Weitz, Lena; Wimmer, Daniela; Xiao, Mao; Yan, Chao; Ye, Penglin; Zha, Qiaozhi; Baltensperger, Urs; Curtius, Joachim; Dommen, Josef; Flagan, Richard C.; Kulmala, Markku; Smith, James N.; Worsnop, Douglas R.; Hansel, Armin; Donahue, Neil M.; Winkler, Paul M. (2018)
    Nucleation and growth of aerosol particles from atmospheric vapors constitutes a major source of global cloud condensation nuclei (CCN). The fraction of newly formed particles that reaches CCN sizes is highly sensitive to particle growth rates, especially for particle sizes <10 nm, where coagulation losses to larger aerosol particles are greatest. Recent results show that some oxidation products from biogenic volatile organic compounds are major contributors to particle formation and initial growth. However, whether oxidized organics contribute to particle growth over the broad span of tropospheric temperatures remains an open question, and quantitative mass balance for organic growth has yet to be demonstrated at any temperature. Here, in experiments performed under atmospheric conditions in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN), we show that rapid growth of organic particles occurs over the range from -25 degrees C to 25 degrees C. The lower extent of autoxidation at reduced temperatures is compensated by the decreased volatility of all oxidized molecules. This is confirmed by particle-phase composition measurements, showing enhanced uptake of relatively less oxygenated products at cold temperatures. We can reproduce the measured growth rates using an aerosol growth model based entirely on the experimentally measured gas-phase spectra of oxidized organic molecules obtained from two complementary mass spectrometers. We show that the growth rates are sensitive to particle curvature, explaining widespread atmospheric observations that particle growth rates increase in the single-digit-nanometer size range. Our results demonstrate that organic vapors can contribute to particle growth over a wide range of tropospheric temperatures from molecular cluster sizes onward.
  • Venäläinen, Salla H.; Hartikainen, Helinä (2018)
    Treatment of acidic mining water (MW) with industrial minerals and alkaline chemicals requires utilisation of unrenewable raw materials and produces disposable inorganic sludges of no further use. We investigated the efficiency of bio-based anionic nanofibrillated cellulose (NFC) to purify authentic MW high in metals and sulphate. In a short-term (10 min) adsorption experiment, highly acidic (pH 3.2) multi-metal process water was treated with anionic NFC gels differing in their consistency (1.1%, 1.4% and 1.8% wow) at three sorbent-to-solution ratios. To unravel the purification efficiency of the NFC gels, MW was treated stepwise with a set of fresh NFC gels in three sequential batches. Each treated solution was filtrated before pH measurement and analysis for the NFC-induced changes in the metal and sulphate concentrations. All NFC gels efficiently co-adsorbed metals and sulphate and decreased the acidity of MW. Depending on the dosage, a triplicated treatment with the NFC gels removed as much as 32-75% of metal cations and 34-75% of sulphate anions. The retention of metals highly exceeded the amount of carboxyl groups in the sorbent Thus, we concluded that, instead of electrostatic adsorption, the retention took place through formation of covalent metal-NFC complexes. The subsequent surplus in positive total charge formed on the NFC-surface, in turn, enabled electrostatic co-adsorption of sulphate anions. The mutual interactions between cellulose nanofibrils in the NFC gel weakened with decreasing consistency, which promoted the accessibility of the sorption sites. This improved the purification efficiency while decreasing the demand for cellulosic raw material. We concluded that anionic NFC could potentially serve as a multifunctional and resource-efficient purification agent in the treatment of acidic process waters of high ionic strength. Ideally, the elements retained could be liberated and recycled elsewhere. (C) 2018 Elsevier Ltd. All rights reserved.
  • Myllys, Nanna; Kubecka, Jakub; Besel, Vitus; Alfaouri, Dina; Olenius, Tinja; Smith, James Norman; Passananti, Monica (2019)
    In atmospheric sulfuric-acid-driven particle formation, bases are able to stabilize the initial molecular clusters and thus enhance particle formation. The enhancing potential of a stabilizing base is affected by different factors, such as the basicity and abundance. Here we use weak (ammonia), medium strong (dimethylamine) and very strong (guanidine) bases as representative atmospheric base compounds, and we systematically investigate their ability to stabilize sulfuric acid clusters. Using quantum chemistry, we study proton transfer as well as intermolecular interactions and symmetry in clusters, of which the former is directly related to the base strength and the latter to the structural effects. Based on the theoretical cluster stabilities and cluster population kinetics modeling, we provide molecular-level mechanisms of cluster growth and show that in electrically neutral particle formation, guanidine can dominate formation events even at relatively low concentrations. However, when ions are involved, charge effects can also stabilize small clusters for weaker bases. In this case the atmospheric abundance of the bases becomes more important, and thus ammonia is likely to play a key role. The theoretical findings are validated by cluster distribution experiments, as well as comparisons to previously reported particle formation rates, showing a good agreement.
  • Björkenheim, R.; Jämsen, E.; Eriksson, E.; Uppstu, P.; Aalto-Setälä, L.; Hupa, L.; Eklund, K. K.; Ainola, M.; Lindfors, N. C.; Pajarinen, Jukka (2021)
    Bioactive glasses (BAG) are used as bone-graft substitutes in orthopaedic surgery. A specific BAG scaffold was developed by sintering BAG-S53P4 granules. It is hypothesised that this scaffold can be used as a bone substitute to fill bone defects and induce a bioactive membrane (IM) around the defect site. Beyond providing the scaffold increased mechanical strength, that the initial inflammatory reaction and subsequent IM formation can be enhanced by coating the scaffolds with poly(DL-lactide-co-glycolide) (PLGA) is also hypothesised. To study the immunomodulatory effects, BAG-S53P4 (+/- PLGA) scaffolds were placed on monolayers of primary human macrophage cultures and the production of various pro- and anti-inflammatory cytokines was assessed using reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) and ELISA. To study the osteogenic effects, BAG-S53P4 (+/- PLGA) scaffolds were cultured with rabbit mesenchymal stem cells and osteogenic differentiation was evaluated by RT-qPCR and matrix mineralisation assays. The scaffold ion release was quantified and the BAG surface reactivity visualised. Furthermore, the pH of culture media was measured. BAG-S53P4 scaffolds had both anti-inflammatory and osteogenic properties that were likely attributable to alkalinisation of the media and ion release from the scaffold. pH change, ion release, and immunomodulatory properties of the scaffold could be modulated by the PLGA coating. Contrary to the hypothesis, the coating functioned by attenuating the BAG surface reactions and subsequent anti-inflammatory properties, rather than inducing an elevated inflammatory response compared to BAG-S53P4 alone. These results further validated the use of BAG-S53P4 (+/- PLGA) scaffolds as bone substitutes and indicate that scaffold properties can be tailored to a specific clinical need.
  • Puhakka, Eini; Li, Xiaodong; Ikonen, Jussi; Siitari-Kauppi, Marja (2019)
    Sorption of Se(IV) and Se(VI) species onto Mg-rich biotite (phlogopite) and calcite surfaces was investigated using molecular modelling techniques. A CASTEP code implemented into Materials Studio was used to calculate the periodic systems, site densities and site types on the phlogopite and calcite surfaces. According to the results, the Se oxyanions attach to both edge and basal surfaces of phlogopite via an oxygen atom. However, calculated sorption energies indicate that surface complexation reactions via hydrogen bonding happen on the edge surfaces of phlogopite while cation exchange reactions happen on the basal surfaces of phlogopite. These reactions occur on the so-called weak sites according to the PHREEQC modelling. On the calcite surface, only cation exchange reactions are possible, and only for neutral Se species which do not occur in low saline groundwater conditions with pH 8–10. Biotite which is an abundant mineral in crystalline rock works fairly well as a sorbent but calcite which often exists on fracture surfaces of bedrock does not act as a sorbent for Se species.
  • Papendick, Marius; Feil, Christoph M.; Nieger, Martin; Gudat, Dietrich (2018)
    Metathesis of Na[Mn(CO)(5)] with N-tBu and N-Mes substituted, electrophilic N-heterocyclic phosphane derivatives afforded in the first case an ionic N-heterocyclic phosphenium (NHP) metalate and in the second case a covalent phosphenium complex. The products were characterized by analytical and spectroscopic data and the NHP complex as well by a single-crystal X-ray diffraction study. A DFT study allows relating the different outcome of the reactions studied with the energetics of the decarbonylation of the appropriate NHP metalates. Closer evaluation reveals steric factors as the key to explaining the observed behavior, and indicates that their impact displays close parallels to NHC chemistry.
  • Madar Johansson, Miralda; Belurier, Eva; Papageorgiou, Anastassios C.; Sundin, Anders P.; Rahkila, Jani; Kallonen, Teemu; Nilsson, Ulf J.; Maatsola, Santeri; Nyholm, Thomas K. M.; Kapyla, Jarmo; Corander, Jukka; Leino, Reko; Finne, Jukka; Teneberg, Susann; Haataja, Sauli (2020)
    Streptococcus suis is part of the pig commensal microbiome but strains can also be pathogenic, causing pneumonia and meningitis in pigs as well as zoonotic meningitis. According to genomic analysis, S. suis is divided into asymptomatic carriage, respiratory and systemic strains with distinct genomic signatures. Because the strategies to target pathogenic S. suis are limited, new therapeutic approaches are needed. The virulence factor S. suis adhesin P (SadP) recognizes the galabiose Gal alpha 1-4Gal-oligosaccharide. Based on its oligosaccharide fine specificity, SadP can be divided into subtypes P-N and P-O. We show here that subtype P-N is distributed in the systemic strains causing meningitis, whereas type P-O is found in asymptomatic carriage and respiratory strains. Both types of SadP are shown to predominantly bind to pig lung globotriaosylceramide (Gb3). However, SadP adhesin from systemic subtype P-N strains also binds to globotetraosylceramide (Gb4). Mutagenesis studies of the galabiose-binding domain of type P-N SadP adhesin showed that the amino acid asparagine 285, which is replaced by an aspartate residue in type P-O SadP, was required for binding to Gb4 and, strikingly, was also required for interaction with the glycomimetic inhibitor phenylurea-galabiose. Molecular dynamics simulations provided insight into the role of Asn-285 for Gb4 and phenylurea-galabiose binding, suggesting additional hydrogen bonding to terminal GalNAc of Gb4 and the urea group. Thus, the Asn-285-mediated molecular mechanism of type P-N SadP binding to Gb4 could be used to selectively target S. suis in systemic disease without interfering with commensal strains, opening up new avenues for interventional strategies against this pathogen.
  • Nazarov, Anton V.; Chernysh, Vladimir S.; Zavilgelsky, Andrey D.; Shemukhin, Andrey A.; Lopez-Cazalilla, Alvaro; Djurabekova, Flyura; Nordlund, Kai (2021)
    The effect of noble gas cluster species on the cluster interaction with solid surfaces was investigated. Processes of Ar, Kr and Xe clusters interaction with Cu and Mo surfaces were studied using molecular dynamics simulations. It is shown that lighter cluster front atoms undergo more backscattering from surface atoms, causing more intense multiple collisions between cluster atoms. This affects cluster penetration, energy exchange between the cluster and surface atoms, and cluster thermalization. The influence of energy per cluster atom on these effects is discussed.