Highlight Publications 2019

Molecular Hydrophobicity at a Marcoscopically Hydrophilic Surface
Jenée D. Cyran, Michael A. Donovan, Doris Vollmer, Flavio Siro Brigiano, Simone Pezzotti, Daria R. Galimberti, Marie-Pierre Gaigeot, Mischa Bonn and Ellen H.G. Backus
Molecular Hydrophobicity at a Marcoscopically Hydrophilic Surface
Chemical and physical interactions between water and silicates are ubiquitous and relevant for geochemistry and industrial processes, including chromatography, oil extraction and coatings. Characterizing the silica/water interface is important to not only understand the fundamental properties for natural occurring processes but also to improve existing technologies, such as silica coatings, which rely on wettability and thermal-resistant properties to remain effective. At the silica/water interface, we compare the microscopic water organization, from both surface sensitive vibrational sum frequency generation experiments and molecular dynamics simulations, to macroscopic information about the hydrophobicity obtained from contact angle measurements. At the microscopic level, weakly hydrogen-bonded OH groups, typical for hydrophobic interfaces, are observed that originate from water molecules interacting with hydrophobic sites of the silica surface. An increased density of these molecular hydrophobic sites, evident from an increase in weakly hydrogen bonded water OH groups, correlates with an increased macroscopic contact angle.
© MPI-P (2019)
Utilizing macroscopic and microscopic techniques to unveil hydrophobic water at a hydrophilic interface
Non-covalent interactions across organic and biological subsets of chemical space: Physics-based potentials parametrized from machine learning
Tristan Bereau, Robert A. DiStasio Jr., Alexandre Tkatchenko, and O. Anatole von Lilienfeld
Non-covalent interactions across organic and biological subsets of chemical space: Physics-based potentials parametrized from machine learning
Classical intermolecular potentials typically require an extensive parametrization procedure for any new compound considered. To do away with prior parametrization, we propose a combination of physics-based potentials with machine learning (ML), coined IPML, which is transferable across small neutral organic and biologically relevant molecules. ML models provide on-the-fly predictions for environment-dependent local atomic properties: electrostatic multipole coefficients (significant error reduction compared to previously reported), the population and decay rate of valence atomic densities, and polarizabilities across conformations and chemical compositions of H, C, N, and O atoms. These parameters enable accurate calculations of intermolecular contributions—electrostatics, charge penetration, repulsion, induction/polarization, and many-body dispersion. Unlike other potentials, this model is transferable in its ability to handle new molecules and conformations without explicit prior parametrization: All local atomic properties are predicted from ML, leaving only eight global parameters—optimized once and for all across compounds. We validate IPML on various gas-phase dimers at and away from equilibrium separation, where we obtain mean absolute errors between 0.4 and 0.7 kcal/mol for several chemically and conformationally diverse datasets representative of non-covalent interactions in biologically relevant molecules. We further focus on hydrogen-bonded complexes—essential but challenging due to their directional nature—where datasets of DNA base pairs and amino acids yield an extremely encouraging 1.4 kcal/mol error. Finally, and as a first look, we consider IPML for denser systems: water clusters, supramolecular host-guest complexes, and the benzene crystal.
© MPI-P / AIP (2019)
Correlation plots for the total intermolecular energy between reference and present calculations
Monitoring drug nanocarriers in human blood by near-infrared fluorescence correlation spectroscopy
Inka Negwer, Andreas Best, Meike Schinnerer, Olga Schäfer, Leon Capeloa, Manfred Wagner, Manfred Schmidt, Volker Mailänder, Mark Helm, Matthias Barz, Hans-Jürgen Butt & Kaloian Koynov
Monitoring drug nanocarriers in human blood by near-infrared fluorescence correlation spectroscopy
Nanocarrier-based drug delivery is a promising therapeutic approach that offers unique possibilities for the treatment of various diseases. However, inside the blood stream, nanocarriers’ properties may change significantly due to interactions with proteins, aggregation, decomposition or premature loss of cargo. Thus, a method for precise, in situ characterization of drug nanocarriers in blood is needed. Here we show how the fluorescence correlation spectroscopy that is a well-established method for measuring the size, loading efficiency and stability of drug nanocarriers in aqueous solutions can be used to directly characterize drug nanocarriers in flowing blood. As the blood is not transparent for visible light and densely crowded with cells, we label the nanocarriers or their cargo with near-infrared fluorescent dyes and fit the experimental autocorrelation functions with an analytical model accounting for the presence of blood cells. The developed methodology contributes towards quantitative understanding of the in vivo behavior of nanocarrier-based therapeutics.
© MPI-P / Springer Nature (2019)
Schematic of the NIR-FCS experiments in flowing blood.
Comparative Adsorption of Acetone on Water and Ice Surfaces
J.D. Cyran, E.H.G. Backus, M.J. van Zadel, and M. Bonn
Comparative Adsorption of Acetone on Water and Ice Surfaces
Interactions of trace gases with ice and water surfaces play a major role in atmospheric chemistry. The chemical and photochemical processes of trace gases absorbed on ice surfaces are relevant for ozone depletion and alter the chemical composition of the atmosphere. Specifically, small-oxygenated organic molecules, such as acetone, are a critical contributor to the formation of HOx radicals. Here, we combine surface-specific vibrational spectroscopy and a controllable flow cell apparatus to investigate the molecular adsorption of acetone onto the basal plane of single crystalline Ih ice with large surface area. By comparing the adsorption of acetone on the ice/air with the water/air interface, we find two different types of acetone adsorption, as apparent from the different responses of both the free O-H and the hydrogen-bonded network vibrations for ice and liquid water. Adsorption on ice occurs preferentially through interactions with the free OH group, while the interaction of acetone with the surface of liquid water appears less specific.
© MPI-P (2019)
Acetone adsorption on water and ice surfaces unraveled by interfacial spectroscopy
Well-defined metal-polymer nanocomposites: The interplay of structure, thermoplasmonics, and elastic mechanical properties
David Saleta Reig, Patrick Hummel, Zuyuan Wang, Sabine Rosenfeldt, Bartlomiej Graczykowski, Markus Retsch, and George Fytas
Well-defined metal-polymer nanocomposites: The interplay of structure, thermoplasmonics, and elastic mechanical properties
Brillouin light spectroscopy (BLS) is a reliable technique for probing sound velocities in materials. The sound velocity and its temperature and power dependencies further allow determination of thermomechanical properties like elastic moduli and the glass transition temperature. Whereas non-metallic particle-brush systems (e.g., SiO2-PS) typically show linearly dependent sound velocity on temperature and power, thus giving a segmental linear relation between the laser spot temperature and the laser power, their metallic counterparts could display strong non-linearity, as demonstrated here by using Ag-PS nanocomposite films. This non-linearity is due to the plasmonic heating in the Ag nanoparticles induced by the incident laser, and it increases as the PS chain length decreases due to the increasing Ag volume fraction. Additional annealing of the nanocomposite films also increases the non-linearity through the annealing-time-dependent aggregation of Ag nanoparticles. This work reveals the combined effects of composition and (reversible) aggregation on the mechanical and thermoplasmonic properties of metal-polymer nanocomposites. It not only deepens our understanding of the interplay of structure, thermoplasmonics, and elastic properties in metal-polymer nanocomposites but also provides a guide for customizing Ag-PS nanocomposites for potential applications.
© MPI-P (2019)
Schematic laser heating in a Ag-PS (particle-brush) film and the dependence of the laser spot temperature on the laser power.
 
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