24 Aug 2017: Chang-Joon Lee

Thu 24 Aug 2017 3:30pm (Murdoch University, Senate Room 121.1.002)

Dude, where’s my oxygen? – A computational study of factors that predispose the kidney to hypoxia

Chang-Joon Lee

School of Engineering and IT, Murdoch University & Faculty of Engineering and Mathematical Sciences, The University of Western Australia

great interest due to the perplexing fact that the kidney is highly susceptible to hypoxia despite being well-supplied with oxygenated blood and having the lowest oxygen extraction ratio of the major organs. One leading hypothesis for this paradox is that a fraction of the oxygen delivered to the kidney never reaches renal tissue, but instead diffuses from arterial to venous segments of the cortical vasculature. However the biological significance of arterial-to-venous (AV) oxygen shunting in the renal cortex remains a matter of controversy.

To assess the physiological significance of AV oxygen shunting and identify other potential factors that may play a major role in renal hypoxia, we generated a new pseudo-three-dimensional computational model of renal cortex based on the cortical vasculature in the rat kidney. The model provides estimates of oxygen tension (PO2) in the renal tissue and how it changes for given combinations of renal oxygen delivery and/or consumption, as well as the magnitude of oxygen shunted from the arterial to venous segments.

While a number of lines of evidence suggest AV shunting is significant, most importantly our computational model predicts AV shunting is small under normal physiological conditions (~0.9% of total renal oxygen delivery), but increases under pathologic states (up to ~3.0% of total renal oxygen delivery). We conclude that AV oxygen shunting normally has only a small impact on renal oxygenation, but may exacerbate renal hypoxia during certain pathologic states. We further conclude that, among other factors that may predispose the kidney to renal hypoxia, renal hypoxia is most likely to be initiated by drastic reduction in the surface area of peritubular capillaries.

25 May 2017: Rob Atkins

Thu 25 May 2017 3:30pm (Murdoch University, ECL Postgraduate Suite, 460.2.031)

Structure, Solutes and Surfaces in Ionic Liquids

Rob Atkin

School of Molecular Sciences, The University of Western Australia, WA 6009, Australia

Ionic Liquids (ILs) are a subset of molten salts, distinguished by having melting points below 100 °C. Their low melting points are brought about by weakening electrostatic interactions between the ions and hindering their packing into a crystal lattice. Electrostatic forces are reduced by engineering their molecular structure so that at least one of the ions is large and organic, which increases the distance between neighbouring charged centres, and by delocalising the ionic charge over a large molecular volume. Ionic liquids have some unusual and remarkable properties, including pronounced nanostructures, which is one of their unique, yet unifying, characteristicss.

Neutron diffraction measurements modelled with reverse Monte Carlo simulations will be used to show that ILs have a sponge-like (bicontinuous) nanostructure; IL cation alkyl chains and ionic groups are segregated into domains that percolate throughout the bulk liquid.1-3 A snapshot of the simulation box for ethylammonium nitrate (EAN, a protic IL) is shown in Figure 1 (left). Varying the structure of the ions changes way inter-ionic forces are expressed, which leads to changes in nanostructure. The effect of dissolved water, glycerol and octanol on bulk IL nanostructure will be examined.4,5

High resolution amplitude modulated atomic force microscope images (c.f. Figure 1) will be used to demonstrate how IL nanostructure changes at a solid surface with the ion structure, and the effect of dissolved solutes.6-8 A 20 nm × 20 nm topographic AM-AFM images of the 1-Ethyl-3-methylimidazolium bis(trifluoromethyl- sulfonyl) imide – graphite Stern layer is shown in Figure 1 (middle), with the position of the ions shown in the magnified area in Figure 1 (right). The effect of applying a potential to a conducting solid surface on the IL interfacial nanostructure will also be discussed, and recent results for the spontaneous exfoliation of graphene into an ionic liquid will be described.9

Figure 1. (left) Snap shot of simulation box used to fit neutron diffraction data for EAN. (middle and right) AM-AFM image of the 1-Ethyl-3-methylimidazolium bis(trifluoromethyl- sulfonyl) imide – graphite Stern layer.

References

(1) Atkin, R.; Warr, G. G. J. Phys. Chem. B 2008, 112, 4164.

(2) Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. Physical Chemistry Chemical Physics 2011, 13, 3237.

(3) Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. Angewandte Chemie International Edition 2013, 52, 4623.

(4) Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. Angewandte Chemie International Edition 2012, 51, 7468.

(5) Murphy, T.; Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. Physical Chemistry Chemical Physics 2014, 16, 13182.

(6) Elbourne, A.; Voitchovsky, K.; Warr, G. G.; Atkin, R. Chemical Science 2015, 6, 527.

(7) Page, A. J.; Elbourne, A.; Stefanovic, R.; Addicoat, M. A.; Warr, G. G.; Voitchovsky, K.; Atkin, R. Nanoscale 2014, 6, 8100.

(8) Elbourne, A.; McDonald, S.; Voïchovsky, K.; Endres, F.; Warr, G. G.; Atkin, R. ACS Nano 2015, 9, 7608.

(9) Elnourne, A.; Mclean, B. D.; Voïchovsky, K.; Warr, G. G.; Atkin, R J. Phys. Chem. Lett., 2016, 7, 3118

 

Rob Atkin is a Professor of Chemistry at the University of Western Australia. Rob obtained his PhD from the University of Newcastle (Australia) in 2003 under the supervision of Prof Simon Biggs, then joined the group of Prof. Brian Vincent at Bristol University as a postdoctoral fellow, working on polymer microencapsulation. In 2005 he was awarded an Australian Research Council (ARC) Postdoctoral Fellowship to study surfactant self-assembly in ionic liquids at the University of Sydney in collaboration with Prof Greg Warr. He returned to Newcastle in 2007 as a University of Newcastle Research Fellow, was awarded an ARC Future Fellowship in 2012, and promoted to Professor in 2015. In March 2017 Rob moved to his current position at the University of Western Australia. Rob has published 6 book chapters and 130 journal articles and collaborates with groups in Australia and in the UK, Sweden, Germany, the USA, Japan and France.

7 Apr 2017 : Jitendra Mata

Fri 7 Apr 2017 – 3:30pm (Murdoch University, Senate Room)

Nanoscale Characterisation Techniques at ANSTO

Dr Jitendra P. Mata — ANSTO

ACNS, Australian Nuclear Science and Technology Organisation (ANSTO), Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.

E-mail: jitendra.mata@ansto.gov.au

SANS instruments at ACNS

S mall angle X-ray and neutron scattering (SAXS, SANS) are versatile techniques for investigating the nanoscale structure of soft materials such as food, surfactants, polymers, colloids, minerals processing fluids, and emulsions. These techniques have been exceptionally useful for studying complex materials of industrial importance in recent years. The use of small angle scattering (SAS) in combination with traditional techniques offers a unique insight into the structure, size, shape and morphology of the materials. Different processes like aggregation, structural transitions, crystallization and phase separation can be studied using SAS techniques in various conditions. SAS are well-established characterisation techniques for the nano and microstructure (from 1 nm to >1000 nm) investigations in various materials. These techniques are mostly nondestructive, and particularly useful to study systems in complex sample environment, in-situ, and at different kinetic stages. The use of deuterated molecules and partial deuteration has enhanced the applicability of these methods for soft materials (particularly for SANS technique). We discuss the advantages and limitations of these techniques, and provide examples of recent applications in mineral processing, food technology and colloid science in this talk.

Australia is the home of state of the art reactor based SANS instrument known as Quokka (at the ACNS, ANSTO). Combining Quokka with onsite lab based SAXS instrument or with the Australian Synchrotron based SAXS-WAXS instrument provide versatile techniques to study complex soft matter systems. ANSTO is known for its high class neutron scattering based science, outstanding deuteration facility, and exceptional sample environment options to couple with various neutron scattering techniques. A general overview of the institute and techniques available will also be provided.

16 Feb 2017 : Philipp Schönhöfer

Thu 16 Feb 2017 – 3:30 pm (Murdoch University, Senate Conference Room)

Entropic self-assembly of bicontinuous structures : the gyroid … and more?

Mr Philipp Schönhöfer – Murdoch University

Note: Philipp is a PhD candidate in the School of Engineering and IT, and this talk is part of his confirmation of candidature process.

Many biological and synthetical systems  (like lipid/water mixtures [1] and di-block copolymers [2]) form highly complex and symmetric triply-periodic, bicontinous structures by enthalpic self-assembly. Studies by Barmes et al. [3] and Ellison et al. [4] showed that one of these structures, the so called Ia(-3)d double gyroid, can also be generated in equilibrium systems of hard pear-shaped particles with suitable tapering and aspect ratio and consequently systems where entropy is the key factor and no attractive forces are needed.

Performing MD and MC simulations, we  have reproduced the spontaneous formation of the gyroid by hard tapered particles and generated a density-tapering phase diagram. To compare the differences between the enthalpically and entropically driven processes further, we studied the geometrical and morphological properties of the gyroid phase, using scattering functions and Voronoi tessellations. Through this, we show that the formation mechanisms prevalent in this entropy-driven system differ from those found in systems which form Gyroid structures in nature.

Subsequently, hard spheres which shall take up the role of solvent to model mixtures with a solvent are introduced into the simulations. With an explicit solvent the system should be complex enough to model most common phenomena in cubic phases. In this particular case we especially examine a potential stabilizing influence of spheres on the gyroid structure. From a biological point of view this will give information on the formation of other bicontinous structures like the Pn3m double diamond or unbalanced membranes (eg. if the generation of the I4(1)32 gyroid structure is solez entropy driven). Hence, systems with different concentrations and sphere sizes are analysed.

[1] J. M. Seddon and R. H. Tepler, Phil. Trans. R. Soc. A 344(1672), 377–401 (1993).

[2] M. W. Matsen and M. Schick, PRL 72(16), 2660 (1994).

[3] F. Barmes, M. Ricci, C. Zannoni, and D. J. Cleaver, Phys. Rev. E 68, 021708 (2003).

[4] L. J. Ellison, D. J. Michel, F. Barmes, and D. J. Cleaver, Phys. Rev. Lett. 97, 237801 (2006).

24 Nov 2016 : Peter Metaxas

Thu 24 Nov 2016 – 3:30 pm (Murdoch University, Postgrad Suite ECL2.031)

Towards frequency-based electronic bio-detection at the nano-scale

Dr Peter Metaxas — School of Physics, University of Western Australia

Magnetic biosensing exploits chemically functionalised magnetic nanoparticles for labelling and subsequent detection of analytes of interest in biological samples, opening routes to new technologies for point-of-care medical diagnostics [1]. Many solid state nanoparticle detection techniques are voltage-level based. For example, in conventional magnetoresistive sensors, the magnetic configuration within the device is modified by the nanoparticles’ stray magnetic fields, generating a change in the device resistance (and thus the voltage across the device). In contrast, electrically probed, field-dependent magnetisation dynamics in magnetic nanostructures offer a route towards intrinsically frequency-based electronic biosensing. This resonance-based approach potentially offers high speed sensing with nano-scale devices [2] which can operate under very large magnetic field ranges [3]. We demonstrate the potential of this approach first using large area, periodically nanostructured ferromagnets (“magnonic crystals”) [3,4]. These systems enable us to probe the effect of nanoparticles on ferromagnetic resonances that are