Ellen H G Backus

Max Planck Institute for Polymer Research, Mayence, Rheinland-Pfalz, Germany

Are you Ellen H G Backus?

Claim your profile

Publications (46)231.63 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: GALA is a 30 amino acid synthetic peptide consisting of a Glu-Ala-Leu-Ala repeat and is known to undergo a reversible structural transition from a disordered to an α-helical structure when changing the pH from basic to acidic values. In its helical state GALA can insert into and disintegrate lipid membranes. This effect has generated much interest in GALA as a candidate for pH triggered, targeted drug delivery. GALA also serves as a well-defined model system to understand cell penetration mechanisms and protein folding triggered by external stimuli. Structural transitions of GALA in solution have been studied extensively. However, cell penetration is an interfacial effect and potential biomedical applications of GALA would involve a variety of surfaces, e.g., nanoparticles, lipid membranes, tubing, and liquid-gas interfaces. Despite the apparent importance of interfaces in the functioning of GALA, the effect of surfaces on the reversible folding of GALA has not yet been studied. Here, we use sum frequency generation vibrational spectroscopy (SFG) to probe the structural response of GALA at the air-water interface and IR spectroscopy to follow GALA folding in bulk solution. We combine the SFG data with molecular dynamics simulations to obtain a molecular-level picture of the interaction of GALA with the air-water interface. Surprisingly, while the fully reversible structural transition was observed in solution, at the water-air interface, a large fraction of the GALA population remained helical at high pH. This “stickiness” of the air-water interface can be explained by the stabilizing interactions of hydrophobic leucine and alanine side chains with the water surface.
    The Journal of Chemical Physics 10/2014; 141:22D517.1-9. · 3.12 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The UV-induced cross-linking of methacryloxypropyl-terminated poly(dimethylsiloxane) oligomers was studied at the air-water-interface either in pure PDMS Langmuir monolayers or in mixed films containing cellulose acetate butyrate. Surface pressure-area isotherms, area measurement at constant surface pressure, Brewster angle microscopy observations and infrared-visible sum frequency generation (SFG) spectroscopy were combined to follow the evolution of the monolayers upon in-situ UV photoirradiation. For both systems, the mean area per repeat unit decreases with irradiation time reflecting the monolayer contraction. In addition, SFG measurements evidence the conversion of the methacrylate groups into unconjugated poly(methacrylate) ones. These results demonstrate PDMS cross-linking, leading to the formation of either a single PDMS network or a PDMS network entrapped in a CAB matrix. The network formation is accompanied by morphology changes as shown by Atomic Force Microscopy on the transferred monolayer. Indeed, filamentous structures appear on both pure and mixed preirradiated monolayers.
    Langmuir : the ACS journal of surfaces and colloids. 09/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Wassermoleküle wechselwirken stark miteinander durch Wasserstoffbrücken. Diese effiziente intermolekulare Kopplung verursacht eine starke Delokalisierung der Molekülschwingungen im Inneren des Wassers. Wir untersuchen die intermolekulare Kopplung der Schwingungen an der Luft/Wasser-Grenzfläche und beobachten, dass die intermolekulare Kopplung 1) signifikant reduziert ist und 2) für verschiedene Wassermoleküle an der Grenzfläche stark variiert – während im Inneren des Wassers die Kopplung homogen ist. Für stark Wasserstoffbrücken-gebundene O-H-Gruppen ist die Kopplung etwa zweimal geringer als im Inneren des Wassers, aufgrund der geringeren Dichte in der grenzflächennahen Region. Für schwach Wasserstoffbrücken-gebundene O-H-Gruppen, die bei 3500 cm−1 absorbieren, ist diese Kopplung um einen weiteren Faktor ≈2 reduziert. Diese O-H-Gruppen werden den äußersten, jedoch Wasserstoffbrücken-gebundenen Wassermolekülen zugeordnet, deren andere O-H-Gruppe zur Gasphase zeigt. Trotz der geringen strukturellen Einschränkungen durch die umgebenden Wasserstoffbrücken auf diese Wassermoleküle ist – bemerkenswerterweise – deren Strukturrelaxation langsam und die intermolekulare Kopplung schwach.
    Angewandte Chemie 07/2014; 126(31).
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Water molecules interact strongly with each other through hydrogen bonds. This efficient intermolecular coupling causes strong delocalization of molecular vibrations in bulk water. We study intermolecular coupling at the air/water interface and find intermolecular coupling 1) to be significantly reduced and 2) to vary strongly for different water molecules at the interface-whereas in bulk water the coupling is homogeneous. For strongly hydrogen-bonded OH groups, coupling is roughly half of that of bulk water, due to the lower density in the near-surface region. For weakly hydrogen-bonded OH groups that absorb around 3500 cm(-1) , which are assigned to the outermost, yet hydrogen-bonded OH groups pointing towards the liquid, coupling is further reduced by an additional factor of 2. Remarkably, despite the reduced structural constraints imposed by the interfacial hydrogen-bond environment, the structural relaxation is slow and the intermolecular coupling of these water molecules is weak.
    Angewandte Chemie International Edition in English 06/2014; · 13.45 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In nature, aqueous solutions often move collectively along solid surfaces (for example, raindrops falling on the ground and rivers flowing through riverbeds). However, the influence of such motion on water-surface interfacial chemistry is unclear. In this work, we combine surface-specific sum frequency generation spectroscopy and microfluidics to show that at immersed calcium fluoride and fused silica surfaces, flow leads to a reversible modification of the surface charge and subsequent realignment of the interfacial water molecules. Obtaining equivalent effects under static conditions requires a substantial change in bulk solution pH (up to 2 pH units), demonstrating the coupling between flow and chemistry. These marked flow-induced variations in interfacial chemistry should substantially affect our understanding and modeling of chemical processes at immersed surfaces.
    Science 06/2014; 134(6188):1138-1142. · 31.03 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We introduce an infrared pump-terahertz probe technique to measure the thermalization dynamics of aqueous solutions with a time resolution <200 fs. This technique makes use of the sensitivity of the terahertz absorption to the temperature of the hydrogen bond network. The thermalization dynamics of different aqueous solutions are measured and compared to the dynamics inferred from ultrafast infrared pump-infrared probe measurements on the intramolecular stretch vibration of water. This technique can shed new light on important aspects of energy transfer and heat dynamics and is applicable to a wide range of systems.
    Optics Letters 04/2014; 39(7):1717-20. · 3.39 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We study the properties of water molecules adjacent to a hydrophobic molecular layer with vibrational sum-frequency generation spectroscopy. We find that the water molecules at D2O/hexane, D2O/heptane, and D2O/polydimethylsiloxane interfaces show an enhanced ordering and stronger hydrogen-bond interactions than the water molecules at a D2O/air interface. With increasing temperature (up to 80 °C) the water structure becomes significantly less ordered and the hydrogen bonds become weaker.
    The Journal of Chemical Physics 02/2014; 140(5):054711. · 3.12 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Water possesses an extremely high polarity, making it a unique solvent for salts. Indeed, aqueous electrolyte solutions are ubiquitous in the atmosphere, biology, energy applications and industrial processes. For many processes, chemical reactions at the water surface are rate determining, and the nature and concentration of the surface-bound electrolytes are of paramount importance, as they determine the water structure and thereby surface reactivity. Here we investigate the dynamics of water molecules at the surface of sodium chloride and sodium iodide solutions, using surface-specific femtosecond vibrational spectroscopy. We quantify the interfacial ion density through the reduced energy transfer rates between water molecules resulting from the lowered effective interfacial density of water molecules, as water is displaced by surface active ions. Our results reveal remarkably high surface propensities for halogenic anions, higher for iodide than for chloride ions, corresponding to surface ion concentrations several times that of the bulk.
    Nature Communications 01/2014; 5:4083. · 10.74 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Interfaces of liquid water play a critical role in a wide variety of processes that occur in biology, a variety of technologies, and the environment. Many macroscopic observations clarify that the properties of liquid water interfaces significantly differ from those of the bulk liquid. In addition to interfacial molecular structure, knowledge of the rates and mechanisms of the relaxation of excess vibrational energy is indispensable to fully understand physical and chemical processes of water and aqueous solutions, such as chemical reaction rates and pathways, proton transfer, and hydrogen bond dynamics. Here we elucidate the rate and mechanism of vibrational energy dissipation of water molecules at the air-water interface using femtosecond two-color IR-pump/vibrational sum-frequency probe spectroscopy. Vibrational relaxation of nonhydrogen-bonded OH groups occurs at a subpicosecond timescale in a manner fundamentally different from hydrogen-bonded OH groups in bulk, through two competing mechanisms: intramolecular energy transfer and ultrafast reorientational motion that leads to free OH groups becoming hydrogen bonded. Both pathways effectively lead to the transfer of the excited vibrational modes from free to hydrogen-bonded OH groups, from which relaxation readily occurs. Of the overall relaxation rate of interfacial free OH groups at the air-H2O interface, two-thirds are accounted for by intramolecular energy transfer, whereas the remaining one-third is dominated by the reorientational motion. These findings not only shed light on vibrational energy dynamics of interfacial water, but also contribute to our understanding of the impact of structural and vibrational dynamics on the vibrational sum-frequency line shapes of aqueous interfaces.
    Proceedings of the National Academy of Sciences 11/2013; · 9.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Vibrational sum-frequency generation (VSFG) spectra of the amide-I band of proteins can give detailed insight into biomolecular processes near membranes. However, interpreting these spectra in terms of the conformation and orientation of a protein can be difficult, especially in the case of complex proteins. Here we present a formalism to calculate the amide-I infrared (IR), Raman and VSFG spectra based on the protein conformation and orientation distribution. Based on the protein conformation, we set up the amide-I exciton Hamiltonian for the backbone amide modes that generate the linear and nonlinear spectroscopic responses. In this Hamiltonian, we distinguish between nearest-neighbor and non-nearest-neighbor vibrational couplings. To determine nearest-neighbor couplings we use an ab initio 6-31G +(d) B3LYP-calculated map of the coupling as a function of the dihedral angles. The other couplings are estimated using the transition-dipole coupling model. The local-mode frequencies of hydrogen-bonded peptide bonds and of peptide bonds to proline residues are redshifted. To obtain realistic hydrogen-bond shifts we perform a molecular dynamics simulation in which the protein is solvated by water. As a first application, we measure and calculate the amide-I IR, Raman and VSFG spectra of cholera toxin B subunit docked to a model cell membrane. To deduce the orientation of the protein with respect to the membrane from the VSFG spectra, we compare the experimental and calculated spectral shapes of single-polarization results, rather than comparing the relative amplitudes of VSFG spectra recorded for different polarization conditions for infrared, visible and sum-frequency light. We find that the intrinsic uncertainty in the interfacial refractive index - essential to determine the overall amplitude of the VSFG spectra - prohibits a meaningful comparison of the intensities of the different polarization combinations. In contrast, the spectral shape of most of the VSFG spectra is independent of the details of the interfacial refractive index, and provides a reliable way of determining molecular interfacial orientation. Specifically, we find that the symmetry axis of the cholera toxin B subunit is oriented at an angle of 6° ± 17° relative to the surface normal of the lipid monolayer, in agreement with five-fold binding between the toxin's five subunits and the receptor lipids in the membrane.
    The Journal of Physical Chemistry A 04/2013; · 2.77 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Capillary adhesion of microparticles was analytically calculated, modelled by finite element method (FEM) simulations and measured. The effects of elastic deformation and liquid adsorption were analyzed. By means of an atomic force microscope, we measured the force between a silica bead of 2 μm radius and a planar polydimethylsiloxane surface (Young's modulus E = 1 MPa) in the presence of ethanol at different vapor pressures. Results were compared to adhesion forces measured on a silicon wafer. Independent of the sample elastic modulus experiments showed a monotonous decrease of capillary forces with increasing ethanol partial vapor pressure for P/Psat > 0.2, where Psat is the saturation vapor pressure. However, adhesion forces on the soft surface were much stronger than on the rigid silicon wafer. In order to explain the experimental results, a previous developed theory (Soft Matter, 2010, 6, 3930) was extended to take into account vapor adsorption of ethanol. Analytical calculations were compared to results of FEM simulations where the detailed deformation of the elastic support close to the meniscus was explicitly taken into account.
    Soft Matter 04/2013; 9(17):4534-4543. · 4.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We study the effects of ions and hydrophobic molecular groups on the orientational dynamics of water using THz dielectric relaxation (THz-DR) and polarization-resolved femtosecond infrared (fs-IR) pump-probe spectroscopy. We measure the dynamics of water in solutions of NaI, NaCl, CsCl, guanidinium chloride (GndCl) and tetramethyl guanidinium chloride (TMGndCl) of different the static dipoles of their surrounding water molecules. With fs-IR we find that concentrations. With THz-DR we observe that strongly hydrated cations align the OD groups that form hydrogen bonds to halide anions reorient with two distinct time constants of 2 +/- 0.3 ps and 9 +/- 1 ps. The fast process is assigned to a wobbling motion of the OD group that keeps the hydrogen bond with the anion intact. The amplitude of this wobbling motion depends on the nature of both the anion and the counter cation. The replacement of four of the six hydrogen atoms of the weakly hydrated cation guanidinium by hydrophobic methyl groups leads to an exceptionally strong slowing down of the water dynamics. Hydrophobic groups thus appear to have a much stronger effect on the dynamics of water than ions. These findings give new insights in the mechanism of protein denaturation by GndCl and TMGndCl.
    Faraday Discussions 01/2013; 160:171-89; discussion 207-24. · 3.82 Impact Factor
  • Source
    Mischa Bonn, Huib J Bakker, Yujin Tong, Ellen H G Backus
    [Show abstract] [Hide abstract]
    ABSTRACT: The surface vibrational spectrum of water at biological interfaces is often interpreted as having 'ice-like' and 'liquid-like' components. Here we show that the vibrational spectrum of water at both water-lipid and water-protein interfaces greatly simplifies upon H/D isotopic dilution, which is inconsistent with the presence of 'ice-like' structures. The changes in the spectra as a function of isotope content can be explained by intramolecular coupling between bend and stretch vibrations of the water molecules.
    Biointerphases 12/2012; 7(1-4):20. · 1.91 Impact Factor
  • Source
    Yuki Nagata, Ruben E Pool, Ellen H G Backus, Mischa Bonn
    [Show abstract] [Hide abstract]
    ABSTRACT: Using combined theoretical and experimental approaches, we demonstrate that the bond orientation of water at the water-vapor interface depends markedly on the water isotope (H-D) composition. While the interfacial water structures of H_{2}O and D_{2}O are indistinguishable, the intramolecular symmetry breaking in HDO is directly reflected at the surface: the OD bonds preferably orient down towards the bulk water, whereas the OH bond tends to orient up into the vapor phase. Path integral molecular dynamics simulations show good agreement with surface-specific sum-frequency generation (SFG) spectroscopy results, revealing that the distinct interfacial bond orientations originate from nuclear quantum effects. The enhanced localization of the heavier D atom leads to stronger hydrogen bonds, giving rise to OD bonds pointing down into the bulk.
    Physical Review Letters 11/2012; 109(22):226101. · 7.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We performed sum-frequency generation (SFG) spectroscopic measurements on water in contact with supported thin metal and metal-oxide films. We employed an internal reflection configuration and varied the angles of incidence of the visible and infrared beams and measured the SFG signals using different polarization combinations. While SFG is a surface-specific vibrational spectroscopy, the shape of the SFG spectra can be fully accounted for by the bulk response of the materials through the frequency-dependent enhancement of the local incident infrared fields at the interface, i.e., Fresnel effects. We find that the dispersion of the refractive index of the bulk water phase leads to a strong enhancement of the electric field at the interface at specific infrared frequencies. These local, frequency-dependent fields act on the frequency-independent, nonresonant SFG response of the electrons at the surfaces of the metal or metal-oxide films. As a result, the measured SFG spectra closely follow this infrared frequency dependence. Hence, we conclude that the nonresonant SFG signal from the electrons in the metal or metal-oxide film strongly dominates over the resonant SFG signal of the interfacial water vibrations. This work demonstrates the importance of Fresnel factors in SFG spectroscopy of metal(-oxide)–liquid interfaces and shows that the spectral dependence and magnitude of the Fresnel factors can be calculated, making corrections to the data in principle possible. Finally, this work provides practical recommendations for the selection of suitable experimental conditions for future SFG studies on metal(-oxide)–liquid interfaces aimed at elucidating interfacial water structures at these interfaces.
    The Journal of Physical Chemistry C. 10/2012; 116(44):23351–23361.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Monolayers of a cellulosic polymer bearing cinnamate groups were characterized at the air-water interface by combining isotherm measurements, Brewster angle microscopy, and infrared-visible sum-frequency generation (SFG) spectroscopy. This spectroscopic technique was used to detect the photochemical behavior of the cinnamate groups upon UV photoirradiation of the monolayers. From the disappearance of the C═C mode and the absence of a change in the C═O mode, it could be concluded that isomerization is the dominant photoreaction for a monolayer of this polymer. This conclusion was corroborated by a comparison of the spectra of the monolayer after irradiation with spectra measured for monolayers spread from preirradiated solutions, for which it is known that isomerization is the main process.
    The Journal of Physical Chemistry B 05/2012; 116(20):6041-9. · 3.61 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report a combined vibrational sum-frequency generation (SFG) spectroscopy, Brewster angle microscopy (BAM), and ellipsometry study of different surfactants on water as a function of surfactant density. Vibrational SFG spectra of surfactants on the water surface in a Langmuir trough have been measured in both the surfactant CH and the water OH stretch regions. At low densities, the SFG signal generated at the surface in the presence of the surfactant is indistinguishable from the SFG signal generated at the clean water-air interface. When the surfactant density increases, i.e., upon compressing the monolayer, a very sudden increase in the SFG signal in both the CH and OH spectral regions is observed. For higher laser fluences, this stepwise increase occurs at increasingly higher surfactant densities. Since BAM shows that surfactant molecules are clearly present at these low densities, we conclude that at low surfactant density the laser beam displaces relatively high-density domains with surfactants in the liquid expanded phase out of the region of the laser focus. This is a consequence of the thermal gradient induced by local heating of the water phase with the monolayer on top due to repetitive laser excitation at 1 kHz. It can be circumvented by using a rotating trough. In this manner, the sampled surface area can be refreshed, allowing artifact-free vibrational SFG spectra to be measured down to the very lowest surfactant densities. In ellipsometry experiments, a similar step can be noticed, which, however, is of a different nature; i.e., it is not related to heating (the laser fluence is very low and the light nonresonant) but to a molecular transition. The occurrence of the step in ellipsometry as a function of area per molecule depends critically on the preparation of the monolayer. By giving the molecules time and space to relax during the preparation of the monolayer, this step could also be eliminated.
    The Journal of Physical Chemistry B 03/2012; 116(9):2703-12. · 3.61 Impact Factor
  • Ruben E Pool, Jan Versluis, Ellen H G Backus, Mischa Bonn
    [Show abstract] [Hide abstract]
    ABSTRACT: As a surface-specific technique, vibrational sum-frequency generation (SFG) is used in a wide range of applications where soft matter or solid interfaces are to be probed on a molecular level through their vibrational modes. In recent years, phase-specific sum-frequency generation (PS-SFG, also known as heterodyne-detected SFG) spectroscopy has been increasingly replacing its predecessor (direct SFG, also known as homodyne SFG) as the experimental technique of choice for characterizing interfacial structure. The technique enables phase sensitive measurements, allowing for the determination of the real and imaginary parts of the interfacial vibrational response function and thereby the unambiguous identification of molecular orientation. This phase-sensitivity requires, however, a complete understanding of the complex optical properties of the sample and of their effect on the signal. These optical properties significantly influence the raw spectral data from which the real and imaginary parts of the second-order susceptibility are retrieved. We show that it is essential to correct the data appropriately to infer the true molecular response. The current study presents a detailed description of the physical contributions to the phase-resolved spectrum, allowing a direct comparison between the phase-resolved spectrum and that obtained using the well-understood direct detection method in a step-by-step data analysis process. In addition to phase sensitivity, PS-SFG has been shown to increase the sensitivity compared to traditional (direct) SFG spectroscopy. We present a quantitative comparison between theoretical limits of the signal-to-noise ratio of both techniques, which shows that for many systems the signal-to-noise ratio is very similar for direct- and phase-specific SFG signals.
    The Journal of Physical Chemistry B 11/2011; 115(51):15362-9. · 3.61 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have obtained molecular insights into a monolayer of azobenzene-based photoswitchable lipids self-assembled on water, using the surface sensitive technique vibrational sum-frequency generation spectroscopy in combination with surface pressure measurements. The photolipids can undergo wavelength-dependent, light-triggered cis/trans and trans/cis isomerization, allowing for reversible control of the surface pressure and the molecular ordering of the lipids in the monolayer. If the photoswitchable lipid is embedded in a layer with conventional phospholipids, such as 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), we show that the surface pressure and molecular ordering of DPPC can be influenced by switching the azobenzene-based lipid between its two states. Remarkably, the state with the higher surface pressure (cis-state) is characterized by a lower degree of molecular order. This counterintuitive result can be understood by noting that the azobenzene moiety in the cis state has a higher dipole moment and therefore favors interaction with water. The surface free energy of the system is lowered (increase of surface pressure) by electrostatic interactions with the lipid headgroups at the interface, resulting in a loop formation of the lipid tail with the cis-azobenzene. This disorder in the tail of the photoswitchable lipid perturbs as well the ordering of DPPC.
    The Journal of Physical Chemistry B 02/2011; 115(10):2294-302. · 3.61 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Duramycin is a small tetracyclic peptide which binds specifically to ethanolamine phospholipids (PE). In this study, we used lipid monolayers consisting of 1-palmitoyl-2-oleoyl phosphatidylethanolamine (POPE) and various phosphatidylcholines (PC) to investigate the effect of duramycin on the organization of lipids and its influence on surrounding water molecules, using vibrational sum-frequency generation spectroscopy in conjunction with surface pressure measurements and fluorescence microscopy. The results show that while duramycin has no effect on the PC lipid monolayers, it induces significant disorder of PE molecules and causes an increase of the PE monolayer surface pressure. Duramycin adopts a β-sheet conformation and is well-ordered at the air-water interface as well as after binding to PE. Our results are consistent with duramycin inserting into the PE monolayer via its hydrophobic end, exposing phenylalanine residues to the lipid. Binding of duramycin to PE broadens the hydrogen-bond distribution of lipid-bound water molecules, notably increasing the fraction of the less strongly hydrogen-bonded, possibly undercoordinated, water molecules. Fluorescence microscopy reveals that the interaction of duramycin with PE causes a change in the shape of the liquid-condensed domains of the PE monolayer from circular to horseshoe-like, indicating a reduction of line tension at the boundary of the two lipid phases. These results reveal that the first steps in the disruption of membrane integrity by duramycin consist of a reduction of the line tension, a decrease in the lipid order, and a weakening of the hydrogen bonding network of water around PE.
    Langmuir 10/2010; 26(20):16055-62. · 4.38 Impact Factor

Publication Stats

321 Citations
231.63 Total Impact Points

Institutions

  • 2012–2014
    • Max Planck Institute for Polymer Research
      Mayence, Rheinland-Pfalz, Germany
  • 2011–2013
    • FOM Institute AMOLF
      Amsterdamo, North Holland, Netherlands
  • 2007–2008
    • University of Zurich
      • Institut für Physikalische Chemie
      Zürich, ZH, Switzerland
  • 2004–2007
    • Leiden University
      • Leiden Institute of Chemistry
      Leiden, South Holland, Netherlands