Funded PIER Projects 2015

Mechanistic studies on cation exchange reactions in nanocrystals via in-situ optical and synchrotron X-ray structural characterization

Cristina Palencia Ramirez, Martin Trebbin

Cation exchange reactions have emerged as a powerful chemical tool to obtain nanocrystal shapes, compositions or structures not accessible by other methods. This opens up tremendous expectations to modify the electronic and thus optical properties of nanocrystals, but also to controllably tune their stoichiometry. Different exchange systems have been studied with special attention to the main thermodynamic parameters affecting the exchange reaction. However, a reliable accepted mechanism has not been established yet and furthermore there is not a single kinetic model universally applicable to such processes.

Based on the lack of this information, this project aims to study the kinetics and thermodynamics governing cation exchange reactions. The present partnership meets the pairless combination of an extraordinary versatile continuous-flow device with the high intensity synchrotron X-ray radiation produced in PETRA III in DESY. The key idea is to use a continuous-flow device equipped with optic and X-ray flow cells to enable in-situ optical and synchrotron structural characterization of the staring materials, intermediate and final products of the exchange reactions. Nanocrystals size, shape and concentration will be calculated from optical characterization. Moreover, highly-resolved X-ray scattering analysis of the samples will provide information about their size, crystal structure and composition. This advanced characterization will be complemented with positron annihilation spectroscopy to further study the influence of vacancies and/or interstitials in the exchange mechanism. We expect the results of these experiments to reveal solid details about the exchange mechanism.

Mass spectrometry of chemical reactions at surfaces

Giuseppe Mercurio, Franz X. Kärtner

Following a chemical reaction on a metal surface at each step, from the excitation of the reactants to the desorption of the products, has not yet been achieved. We propose to cover this gap and combine time-resolved photoemission experiments with fast externally triggered mass spectrometry. Pump-probe photoemission data, with optical pump laser and EUV/X-ray probes, will provide snapshots of the electronic structure of the reactants and transient species as the reaction occurs. At the same time, the reaction yield, that is the amount of products resulting from the reaction, will be measured by means of a quadrupole mass spectrometer triggered by the pump laser and able to acquire mass spectra of ionic and neutral species up to 300 amu with a time resolution of ~ 100 ns. Fast externally triggered mass spectroscopy in combination with time resolved pump-probe techniques will provide an unprecedented complete picture of chemical reactions at metal surfaces including the electronic structure of the reactants and the corresponding reaction yield. Moreover, a number of additional ex-periments based on the fast detection of the product desorption yield, upon absorption of pump laser pulses by the substrate, will provide complementary knowledge on the excitation mechanism of ad-sorbates leading to a comprehensive understanding of elemental reactions relevant for heteroge-neous catalysis.

Hidden title

Hendrik Jansen, Peter Schleper, Alexandra Junkes, Eckhart Fretwurst, Georg Steinbrueck, Doris Eckstein, Günter Eckerlin, Jan Klug, Pawel Kaminski, Jaakko Härkönen, Prof. Hansen

No further information is available due to patent matters.

Multi-scale analysis of human bone’s hierarchical structure:
How the nano-scale stipulates tissue level properties in health and disease

Björn Busse, Dmitri Svergun, Manfred Rößle, Michael Amling

Human bone is a rigid organ that has a variety of functions which include protecting vital organs and enabling movement among others. When analyzed as a material, bone displays a unique set of features which generate strength and toughness resulting in remarkable fracture resistance. These inherent mechanical properties rely on a hierarchical structure ranging from macromolecules (nano-meter range) to the macroscopic scale and also on the exceptional characteristic of bone being able to repair itself. Common bone diseases such as Osteoporosis and Paget’s disease of bone as well as less frequent diseases like Osteopetrosis can compromise the integrity of bone’s complex structure and lead to an increase in fracture risk. Since the bone remodeling process is carried out by several bone cells, the onset of any disease associated alterations of the bone matrix can only be observed on the smallest length-scale with a suite of high-resolution techniques. Establishing a spatial correlation between both the bone composition and the mechanical properties observed on nano- and microscopic-scales will enable us to not only timely recognize fracture risk but also provide future avenues for therapeutic intervention to ensure skeletal integrity.

Microfluidic crystallization and in situ diffraction of challenging protein targets

Michael Heymann, Jörg Labahn, Arwen Pearson, Markus Perbandt

The transformation of a protein solution to a crystal is governed by two non-equilibrium processes: nucleation and growth. Consequently, supersaturation kinetics are essential in crystallization and the optimal crystallization strategy should screen kinetic trajectories involving variables such as depth and duration of supersaturation, and sample volume.

We developed a suite of microfluidic crystallization platforms capable of in situ diffraction that allows for the systematic and reversible kinetic control of the crystallization trajectory. This entails finding conditions on-chip for which one crystal is grown per drop and then isolating hundreds of drops stored on an X-ray transparent microfluidic chip. Single, non-cryoprotected crystals are too small to collect a complete diffraction set, but a full data set can be obtained by combining many single diffraction patterns.

With this research project we will validate our microfluidic technology using challenging protein systems. We will perform proof-of-principle experiments to demonstrate on-chip crystallization and diffraction for membrane proteins. We will also investigate on chip crystal soaking and co-crystallization with caged compounds en route to time-resolved X-ray crystallography.