Reinhard Zellner | University of Duisburg-Essen (original) (raw)

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Papers by Reinhard Zellner

The conversion of SO_2 into SO_3 (H_2SO_4) in the jet regime of a B-747 airliner has been modelle... more The conversion of SO_2 into SO_3 (H_2SO_4) in the jet regime of a B-747 airliner has been modelled by means of the BOAT code. The gas phase reaction scheme previously developed in our work group has been updated by novel rate constants obtained from ab initio quantum-chemical calculations on the reaction SO_2 + OH rightarrow HSO_3. As a striking feature these rate constants predict the efficiency of SO_2 to SO_3/H_2SO_4 conversion to be lower by a factor of about three. From these findings we conclude that the well-known conversion ratio of about 1-2% confirmed by numerous air-borne experiments can be reproduced only assuming sufficient amounts of both SO_3 and H_2SO_4 to be formed already inside the engine. In addition, we have performed sensitivity calculations in order to quantify the impact of uncertainties in EI(NO_x) as well as of organics on the sulphur conversion ratio.

Physical Chemistry Chemical Physics, 2009

The deliquescence behaviour of ternary aerosols composed of ammonium sulfate (AS) and water, inte... more The deliquescence behaviour of ternary aerosols composed of ammonium sulfate (AS) and water, internally mixed with malonic acid (MOA), maleic acid (MEA) and glutaric acid (GAA), has been studied using a new surface aerosol microscope setup (SAM) as well as an electrodynamic balance (EDB). In each of the systems studied the addition of the organic acids to ammonium sulfate leads to a decrease of the deliquescence relative humidities (DRH). However, the observed behaviour of the DRH values over a large range of acid concentrations is complex and indicates a eutectic behaviour. Moreover, the ternary AS/MOA/water aerosols show a two step deliquescence process whose magnitude and concentration dependence have been quantitatively investigated for the first time. The results suggest that previous DRH interpretations underestimate the strength and the atmospheric implications of the MOA influence. In addition to the deliquescence behaviour, effloresced ternary aerosols were studied with respect to their morphology and crystal behaviour using environmental scanning electron microscopy (ESEM) and Raman microscopy (RM), respectively. It is found that in each case crystalline mixtures consisting of the pure AS and pure organic acid are formed. However, the crystalline appearances of the solids formed are different from those of the effloresced pure acids. Moreover, a maximum size of the single crystallites formed during the efflorescence of these complex ternary aerosols has been assigned.

Since chemical and radiative effects of atmospheric aerosols are size and phase related, they are... more Since chemical and radiative effects of atmospheric aerosols are size and phase related, they are strongly influenced by the ambient relative humidity (RH) due to water absorbing hygroscopic components, changing both particle diameter and wavelength dependent refractive indices. Therefore, the assessment of the net effect on chemistry and/or climate for a given atmospheric particle load will critically depend on the

Faraday Discussions, 2008

The deliquescence relative humidities (DRH) of ammonium sulfate as well as ammonium sulfate/dicar... more The deliquescence relative humidities (DRH) of ammonium sulfate as well as ammonium sulfate/dicarboxylic acid (glutaric, maleic and tartaric) mixtures as a function of temperature and relative composition have been studied using an electrodynamic balance (EDB) in connection with optical microscopy and Mie scattering. The absolute DRH values for pure ammonium sulfate as well as their temperature dependence are consistent with literature data and with the AIM model of Clegg et al. The addition of either glutaric or maleic acid to ammonium sulfate leads to a decrease of the DRH value, with the temperature dependence either remaining constant (glutaric acid) or increasing (maleic acid) with increasing acid concentration. This difference is attributed to the higher acidity of maleic acid, which generates stronger ionic interactions with the ammonium sulfate system. In the case of tartaric acid, the deliquescence behaviour of ammonium sulfate is substantially influenced by the formation of insoluble ammonium tartrate.

Beilstein journal of nanotechnology, 2014

The interfacing of colloidal nanoparticles with mammalian cells is now well into its second decad... more The interfacing of colloidal nanoparticles with mammalian cells is now well into its second decade. In this review our goal is to highlight the more generally accepted concepts that we have gleaned from nearly twenty years of research. While details of these complex interactions strongly depend, amongst others, upon the specific properties of the nanoparticles used, the cell type, and their environmental conditions, a number of fundamental principles exist, which are outlined in this review.

Physical Chemistry Chemical Physics, 2005

The quantum yield of CO in the laser pulse photolysis of acetone at 248 nm and at 298 K in the pr... more The quantum yield of CO in the laser pulse photolysis of acetone at 248 nm and at 298 K in the pressure range 20-900 mbar (N2) has been measured directly using quantitative infrared diode laser absorption of CO. It is found that the quantum yield of CO shows a significant dependence on total pressure with Phi(CO) decreasing with pressure from around 0.45 at 20 mbar to approximately 0.25 at 900 mbar. From a combination of ab initio quantum chemical calculations on the molecular properties of the acetyl (CH3CO) radical and its unimolecular fragmentation as well as the application of statistical (RRKM) and dynamical calculations we show that CO production results from prompt secondary fragmentation (via(2a)) of the internally excited primary CH3CO* photolysis product with an excess energy of approximately 62.8 kJ mol(-1). Hence, our findings are consistent with a consecutive photochemically induced decomposition model, viz. step (1): CH3COCH3+hv--> CH3CO*+ CH3, step (2a): CH3CO*--> CH3+ CO or step (2b) CH3CO*-(+M)--> CH3CO. Formation of CO via a direct and/or concerted channel CH3COCH3+hv--> 2CH(3)+ CO (1') is considered to be unimportant.

Physical Chemistry Chemical Physics, 2006

In the presented work an optical levitation technique performed by means of a focused laser beam,... more In the presented work an optical levitation technique performed by means of a focused laser beam, Mie and Raman spectroscopy have been utilized for measuring hygroscopic growth curves and composition of laboratory generated single ammonium sulfate (AS) and internally mixed ammonium sulfate-glutaric acid (GA) droplets in the micrometer range. The generated particles have been found to immediately supersaturate (above 45wt% for AS) at 297 K after capturing in the laser beam. Further increase of the relative humidity (RH) up to 85% does not dilute the droplets under the saturation point. A spontaneous hygroscopic growth takes place at 73.5-78% RH for pure AS. The particle grows with an average factor of 1.62 at the deliquescence relative humidity (DRH). Efflorescence of AS occurs at 43% RH with a corresponding concentration of more than 85wt%. Independent of the mixing ratios in ranges 25/75, 50/50, 75/25% AS/GA mixed particles don't exist as a metastable supersaturated solution droplets in the 35-85% RH range. Instead of growing with increasing relative humidity internally mixed particles build up a solid crystalline layer on the surface. This crystalline phase is not further influenced by ambient relative humidities.

Journal of Materials Chemistry, 2010

Spherical silver nanoparticles with a diameter of 50 AE 20 nm and stabilized with either poly(N-v... more Spherical silver nanoparticles with a diameter of 50 AE 20 nm and stabilized with either poly(N-vinylpyrrolidone) (PVP) or citrate were dispersed in different cell culture media: (i) pure RPMI, (ii) RPMI containing up to 10% of bovine serum albumin (BSA), and (iii) RPMI containing up to 10% of fetal calf serum (FCS). The agglomeration behavior of the nanoparticles was studied with dynamic light scattering and optical microscopy of individually tracked single particles. Whereas strong agglomeration was observed in pure RPMI and in the RPMI-BSA mixture within a few hours, the particles remained well dispersed in RPMI-FCS. In addition, the biological effect of PVP-stabilized silver nanoparticles and of silver ions on human mesenchymal stem cells (hMSCs) was studied in pure RPMI and also in RPMI-BSA and RPMI-FCS mixtures, respectively. Both proteins considerably increased the cell viability in the presence of silver ions and as well as silver nanoparticles, indicating a binding of silver by these proteins.

Zeitschrift für Physikalische Chemie, 2009

ABSTRACT A number of current techniques are presented by which the chemistry of interaction of se... more ABSTRACT A number of current techniques are presented by which the chemistry of interaction of selected gas phase species with atmospheric surfaces as well as the microphysical behaviour of such surfaces can be investigated. The techniques discussed include (i) the coated wall flow tube reactor, (ii) the Knudsen-cell / DRIFT spectroscopy, (iii) the surface aerosol microscopy and (iv) the molecular beam scattering technique. In each of these methods specific and robust information is deduced on the kinetics and thermodynamics of gas adsorption and reaction on Specific examples include the adsorption of acetone on ice surfaces, the adsorption and reaction of SO2 on iron oxides, the hygroscopic and phase behaviour of binary and ternary salt solution droplets (ammonium sulphate and ammonium sulphate / dicarboxylic acids solutions) as well as on the dynamics of inelastic collisions of noble gases on super-cooled sulphuric acid surfaces. In addition we also show how quantum chemistry can be utilized to assist in interpreting absorption energies on structurally different ice surfaces. Whilst each example represents different aspects of heterogenous atmospheric interactions, they jointly represent significant progress in laboratory investigations of multi-phase atmospheric chemistry With substantial potential for application to other systems and/or problems.

ACS Nano, 2011

In biological fluids, proteins associate with nanoparticles, leading to a protein "corona" defini... more In biological fluids, proteins associate with nanoparticles, leading to a protein "corona" defining the biological identity of the particle. However, a comprehensive knowledge of particle-guided protein fingerprints and their dependence on nanomaterial properties is incomplete. We studied the longlived ("hard") blood plasma derived corona on monodispersed amorphous silica nanoparticles differing in size (20, 30, and 100 nm). Employing label-free liquid chromatography mass spectrometry, one-and twodimensional gel electrophoresis, and immunoblotting the composition of the protein corona was analyzed not only qualitatively but also quantitatively. Detected proteins were bioinformatically classified according to their physicochemical and biological properties. Binding of the 125 identified proteins did not simply reflect their relative abundance in the plasma but revealed an enrichment of specific lipoproteins as well as proteins involved in coagulation and the complement pathway. In contrast, immunoglobulins and acute phase response proteins displayed a lower affinity for the particles. Protein decoration of the negatively charged particles did not correlate with protein size or charge, demonstrating that electrostatic effects alone are not the major driving force regulating the nanoparticleÀprotein interaction. Remarkably, even differences in particle size of only 10 nm significantly determined the nanoparticle corona, although no clear correlation with particle surface volume, protein size, or charge was evident. Particle size quantitatively influenced the particle's decoration with 37% of all identified proteins, including (patho)biologically relevant candidates. We demonstrate the complexity of the plasma corona and its still unresolved physicochemical regulation, which need to be considered in nanobioscience in the future.

Beilstein Journal of Nanotechnology, 2014