Invited Plenary Lecture 1
Title: Electronic and chemical properties of buried interfaces.
Invited Plenary Lecture 2
Title: Computational imaging with synchrotron light
Recent years witnessed a proliferation of hard x-ray imaging instruments at synchrotron and laboratory-based facilities that can provide spatial resolution down to few tens of nanometers. Imaging of specimens at these fine scales is particularly challenging, because of the reduced photon efficiency, higher radiation doses, and inaccuracies of the stages that lead to noisy and sparse datasets. Besides, these microscopy techniques pose a new level of challenge for imaging applications in terms of data rates, volumes and complexity. In this talk, I will present a review of the current status of techniques and computational x-ray imaging approaches to alleviate these issues in practice. I will also talk about the scalable implementation of these algorithms and their applications at high-throughput imaging beamlines of the Advanced Photon Source.
Invited Plenary Lecture 3
Title: Nanomaterial-Biological System Interaction Studied by X-ray Imaging Techniques
Abstract: Many nanomaterials are useful in biological detection, diagnosis, and therapy for diseases and have shown great potential for biomedical applications. Therefore, the toxicity of nanomaterials becomes an increasing concern. Both in vitro and in vivo studies were applied to evaluate biological consequence of nanomaterials. We summarize our recent progress of probing the nano-bio interaction of nanomedicine, focus on the driving force and redox reaction at nano-bio interface, which have been recognized as the main factors that regulate the functions and toxicities of nanomedicine.
The intrinsic physicochemical properties of nanomaterials have decisive influence on their biological consequences and toxicity. These properties include size, shape, surface charge, chemical composition, surface modification, metal impurities, agglomeration and dispersion, degradation, as well as the formation of “protein corona”. It is important to obtain a better understanding of the uptake, trafficking, pharmacokinetics, clearance, and role of nanomaterials in biological systems, so that their possible undesirable effects can be avoided.
Development of adequate and specific analytical protocols or methodologies for the quantification of NMs/NPs in nanosafety, nanomedicine and biomedical nanotechnology studies have been proposed. Synchrotron radiation, which is highly polarized, tunable, and concentrated over a small area, plays an indispensable role for nanotoxicology studies. As an example, in our study, the combination of ICP-MS, synchrotron-based scanning transmission X-ray microscopy (STXM), microbeam X-ray absorbance near edge structure (μ-XANES) and μ-SR-XRF have simultaneously provided information about the subcellular distribution and chemical species of metal-containing nanomaterials of interest.
Invited Plenary Lecture 4
Title: Principles of RIXS and applications on molecular systems
Abstract: What governs rate and selectivity in chemical processes down to the atomic level is the bearing point of high resolution resonant inelastic X-ray scattering on molecular systems. Here both active moieties and the interacting fluctuating network of the solvent, most notably liquid water, are the constituting entities. RIXS derives excited state dynamics at active sites and determine the ground state potential energy surface in directional cuts spanning from equilibrium geometries to strong distortions along bond coordinates, mapping out the parameter space on which thermal chemistry takes place. Thus, the multitude of potential energy surfaces of hydrogen bridge bonded water molecules in liquid water can be experimentally determined.
Diverging views exist on liquid water, dating back to Wilhelm Conrad Röntgen, postulating distinct phases to coexist in liquid water even under ambient conditions – competing with a single-phase liquid in a fluctuating hydrogen bonding network – the continuous distribution model. Over time, X-ray spectroscopic methods have repeatedly been interpreted in support of Röntgen’s postulate. However, quantitative X-ray spectroscopic analyses show that this is not the case. At room temperature and normal pressure, the X-ray spectroscopic observables can be fully and consistently described with continuous distribution models of near-tetrahedral liquid water at ambient conditions: The water molecules form a fluctuating network with an average of 1.74 ± 2.1% donor and acceptor hydrogen bridge bonds per molecule each, allowing tetrahedral coordination to neighbours. In addition, across the full phase diagram, correlations to e.g. second shell coordination is established and the influence of ultrafast dynamics from X-ray matter interaction is separated and quantified.
Can these X-ray spectroscopic conclusions on water at ambient conditions now also resolve the heavily debated question of the existence of a second critical point in the so-called “no man’s land” of upercooled water? This postulated second critical point is conceptually based on the extension of the established low- and high-density amorphous ice phases into purported low- and high-density liquid phases along a Widom line where the second critical point is found as the extrapolated divergence of stable and supercooled water‘s thermodynamic response functions around -45°C at atmospheric pressure. From the physics of critical fluctuations, it is known, that well above a critical point one should view the state of matter as homogeneous. Incipient and large fluctuations are allowed as one approaches closely the phase boundary and the critical point: How close one has to approach it in energy and on what time scale to sense the divergence is not fully answered, but expectations from observations in solid state physics are that you have to be close to realize the 2-phase effects. Even if the purported second critical point at -45°C and ambient pressure existed, the ambient conditions of liquid water in equilibrium would be by any means far away in temperature. Thus, the fluctuating continuous distribution model of near-tetrahedral liquid water at ambient conditions holds true independent of whether the second critical point of water in the supercooled region exists or not.
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