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Browsing by Author "Bryant, G"

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Biochemical interaction of few layer black phosphorus with microbial cells using synchrotron macro-ATR-FTIR
(Materials Australian and The Australian Ceramic Society, 2022-06-01) Shaw, ZL; Cheeseman, S; Huang, LZY; Penman, R; Ahmed, T; Bryant, SJ; Bryant, G; Christofferson, AJ; Orwell-Twigg, R; Dekiwadia, C; Truong, VK; Vongsvivut, JP; Walia, S; Elbourne, A
In the fight against drug-resistant pathogenic microbial cells, low dimensional materials are emerging as a promising alternative treatment. Specifically, few-layer black phosphorus (BP) has demonstrated its effectiveness against a wide range of pathogenic microbial cells with studies suggesting low cytotoxicity towards healthy mammalian cells. However, the antimicrobial mechanism of action of BP is not well understood and further in-depth investigations are required. In this work, the complex biochemical interaction between BP and a series of microbial cells is investigated using advanced, high-resolution microscopy techniques to provide a greater understanding of the antimicrobial mechanism. Synchrotron macro-attenuated total reflection–Fourier transform infrared (ATR-FTIR) micro-spectroscopy is used to elucidate the chemical changes occurring outside and within the cell of interest after exposure to BP nanoflakes. The ATR-FTIR data, coupled with microscopy, reveals chemical changes to the cellular phospholipids, proteins, structural polysaccharides and nucleic acids when compared to untreated cells. These changes can be attributed to the physical interaction combined with the oxidative stress induced by the degradation of the BP nanoflakes. This study provides an insight into the biochemical interaction of BP nanoflakes with microbial cells, allowing for a better understanding of the antimicrobial mechanism of action.
Effects of sugars on lipid bilayers during dehydration - SAXS/WAXS measurements and quantitative model
(American Chemical Society, 2009-02-26) Lenné, T; Garvey, CJ; Koster, KL; Bryant, G
We present an X-ray scattering study of the effects of dehydration on the bilayer and chain-chain repeat spacings of dipalmitoylphosphatidylcholine bilayers in the presence of sugars. The presence of sugars has no effect on the average spacing between the phospholipid chains in either the fluid or gel phase. Using this finding, we establish that for low sugar concentrations only a small amount of sugar exclusion occurs. Under these conditions, the effects of sugars on the membrane transition temperatures can be explained quantitatively by the reduction in hydration repulsion between bilayers due to the presence of the sugars. Specific bonding of sugars to lipid headgroups is not required to explain this effect. © 2009, American Chemical Society
Flow assurance in a model crude oil: a structural and rheometric study.
(Australian Nuclear Science and Technology Organisation, 2008-04) Drabarek, E; Muzny, C; Bryant, G; Hanley, HJM
This report investigates how the technique of small angle neutron scattering (SANS) helps elucidate the phenomenon of wax deposition in a petroleum crude oil. Specifically, we report SANS data, supplemented by results from dynamic light scattering (DLS), obtained from a synthetic petroleum crude oil: a mixture of commercial paraffin wax dissolved in an octane/cyclohexane solvent. The system is a gel below the cloud point. The onset and growth of this waxy gel, and changes in its nanostructure, are recorded here as a function of temperature over the range 10 ≤ T/°C ≤ 65. SANS indicates that the wax has a definite characteristic length of about 100 Å (10 nm) which can be observed at temperatures as high as 57°C, but DLS indicates that the wax also contains very large structures - of the order of a micrometer - over the temperature range 30° - 50°C. The structural studies are supplemented by corresponding sets of viscosity and stress data taken from the gelling wax when subjected to an applied shear. We observe that the stress will increase as the temperature falls - i.e. as the system gels - but, in general, will then reach a maximum and tend to decline. The wax results are compared with those from an equivalent system consisting of a major component of the wax: n-docosane, C22. Significant differences between the behavior of the wax and the pure component in the solvents are noted. The SANS patterns to 20°C from docosane do not give any indication of the nanoscale structure observed from the wax; the DLS patterns for docosane indicate that a solidification occurs over a very narrow temperature range between 10°C and 12°C, accompanied by a dramatic slowing of the dynamics; the large scale structure seen in the wax mixtures is not evident; and the rheological behavior of the two systems is markedly different. The paper also compares and contrasts the rheological behavior of the wax gel with that observed from defined system, gelled colloidal silica. Strong similarities are apparent.
Gold nanoparticle adsorption alters the cell stiffness and cell wall bio-chemical landscape of Candida albicans fungal cells
(Elsevier, 2024-01-15) Penman, R; Kariuki, R; Shaw, ZL; Dekiwadia, C; Christofferson, AJ; Bryant, G; Vongsvivut, JP; Bryant, SJ; Elbourne, A
Hypothesis Nanomaterials have been extensively investigated for a wide range of biomedical applications, including as antimicrobial agents, drug delivery vehicles, and diagnostic devices. The commonality between these biomedical applications is the necessity for the nanoparticle to interact with or pass through the cellular wall and membrane. Cell-nanomaterial interactions/uptake can occur in various ways, including adhering to the cell wall, forming aggregates on the surface, becoming absorbed within the cell wall itself, or transversing into the cell cytoplasm. These interactions are common to mammalian cells, bacteria, and yeast cells. This variety of interactions can cause changes to the integrity of the cell wall and the cell overall, but the precise mechanisms underpinning such interactions remain poorly understood. Here, we investigate the interaction between commonly investigated gold nanoparticles (AuNPs) and the cell wall/membrane of a model fungal cell to explore the general effects of interaction and uptake. Experiments The interactions between 100 nm citrate-capped AuNPs and the cell wall of Candida albicans fungal cells were studied using a range of advanced microscopy techniques, including atomic force microscopy, confocal laser scanning microscopy, scanning electron microscopy, transmission electron microscopy, and synchrotron-FTIR micro-spectroscopy. Findings In most cases, particles adhered on the cell surface, although instances of particles being up-taken into the cell cytoplasm and localised within the cell wall and membrane were also observed. There was a measurable increase in the stiffness of the fungal cell after AuNPs were introduced. Analysis of the synchrotron-FTIR data showed significant changes in spectral features associated with phospholipids and proteins after exposure to AuNPs. © 2023 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license.
Grazing incidence neutron scattering investigations of lateral phase separation in oriented mixed lipid bilayers
(Saha Institue of Nuclear Physics, 2012-07-25) Kent, B; Bryant, G; Hunt, T; Kruezer, M; Stroble, M; Garvey, CJ
Since they were first proposed more than a decade ago, lipid rafts have been shown to carry out essential roles within plasma membranes. At a fundamental level, lipid rafts represent a demixing or phase separation of different components within the membrane. Mixtures of saturated and unsaturated lipids are thought to undergo phase separation due to energetic cost of hydrophobic packing, and that the addition of a hybrid lipid containing both saturated and unsaturated tails may stabilise domains in well defined sizes by lowering the interfacial free energy between the unsaturated and saturated phases (Figure 1). By selectively deuterating lipid species, surface heterogeneity of scattering length densities due to the presence of lipids domains can be probed with off-specular grazing incidence neutron scattering. We examined mixed lipid systems of deuterated saturated lipid (DPPC), hydrogenated hybrid lipid (POPC) and a hydrogenated unsaturated lipid (DOPC) using grazing incidence neutron scattering measurements on the BIOREF reflectometer (Helmholtz-Zentrum Berlin fur Materialien und Energie GmbH, Berlin, Germany). Simultaneous in situ infrared spectroscopy was employed to study phase transitions and phase separation of the lipids. Specular and off-specular scattering was recorded using a two-dimensional area detector and time-of—flight data. Repeat spacings of the lipid bilayers from specular scattering showed distinct phase separation behavior of these systems at 30 °C when compared to 55 °C. These changes are correlated to changes in the smectic length scale of the lipid bilayer and the characteristic height-height correlation function determined from the Fourier transform of the decay of the integrated intensity of the Bragg sheets as a function of qll3.
Intrinsically disordered stress protein COR15A resides at the membrane surface during dehydration
(Biophysical Society, 2017-08-08) Bremer, A; Kent, B; Hauß, T; Thalhammer, A; Yepuri, NR; Darwish, TA; Garvey, CJ; Bryant, G; Hincha, DK
Plants from temperate climate zones are able to increase their freezing tolerance during exposure to low, above-zero temperatures in a process termed cold acclimation. During this process, several cold-regulated (COR) proteins are accumulated in the cells. One of them is COR15A, a small, intrinsically disordered protein that contributes to leaf freezing tolerance by stabilizing cellular membranes. The isolated protein folds into amphipathic α-helices in response to increased crowding conditions, such as high concentrations of glycerol. Although there is evidence for direct COR15A-membrane interactions, the orientation and depth of protein insertion were unknown. In addition, although folding due to high osmolyte concentrations had been established, the folding response of the protein under conditions of gradual dehydration had not been investigated. Here we show, using Fourier transform infrared spectroscopy, that COR15A starts to fold into α-helices already under mild dehydration conditions (97% relative humidity (RH), corresponding to freezing at −3°C) and that folding gradually increases with decreasing RH. Neutron diffraction experiments at 97 and 75% RH established that the presence of COR15A had no significant influence on the structure of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes. However, using deuterated POPC we could clearly establish that COR15A interacts with the membranes and penetrates below the headgroup region into the upper part of the fatty acyl chain region. This localization is in agreement with our hypothesis that COR15A-membrane interaction is at least, in part, driven by a hydrophobic interaction between the lipids and the hydrophobic face of the amphipathic protein α-helix. © 2017 Biophysical Society - Open access
Inverse hexagonal - inverse ribbon - lamellar gel phase transition sequence in low hydration DOPC:DOPE phospholipid mixtures
(Elsevier, 2009-01) Kent, B; Garvey, CJ; Cookson, DJ; Bryant, G
The inverse hexagonal to inverse ribbon phase transition in a mixed phosphatidylcholine-phosphatidylethanolamine system at low hydration is studied using small and wide angle X-ray scattering. It is found that the structural parameters of the inverse hexagonal phase are independent of temperature. By contrast the length of each ribbon of the inverse ribbon phase increases continuously with decreasing temperature over a range of 50 C. At low temperatures the inverse ribbon phase is observed to have a transition to a gel lamellar phase, with no intermediate fluid lamellar phase. This phase transition is confirmed by differential scanning calorimetry. © 2008, Elsevier Ltd.
Kinetics of the lamellar gel-fluid transition in phosphatidylcholine membranes in the presence of sugars
(Elsevier, 2010-02) Lenné, T; Garvey, CJ; Koster, KL; Bryant, G
Phase diagrams are presented for dipalmitoylphosphatidylcholine (DPPC) in the presence of sugars (sucrose) over a wide range of relative humidities (RHs). The phase information presented here, determined by small angle X-ray scattering (SAXS), is shown to be consistent with previous results achieved by differential scanning calorimetry (DSC). Both techniques show a significant effect of sucrose concentration on the phase behaviour of this phospholipid bilayer. An experimental investigation into the effect of sugars on the kinetic behaviour of the gel to fluid transition is also presented showing that increasing the sugar content appears to slightly increase the rate at which the transition occurs. © 2010, Elsevier Ltd.
Location of sugars in multilamellar membranes at low hydration
(Elsevier, 2006-11-15) Lenné, T; Bryant, G; Garvey, CJ; Kelderling, U; Koster, KL
Severe dehydration is lethal for most biological species. However, there are a number of organisms which have evolved mechanisms to avoid damage during dehydration. One of these mechanisms is the accumulation of small solutes (e.g. sugars), which have been shown to preserve membranes by inhibiting deleterious phase changes at low hydration. Specifically, sugars reduce the gel to fluid phase transition temperatures of model lipid/water mixtures. However, there is a debate about the precise mechanism, the resolution of which hinges on the location of the sugars. In excess water, it has been observed using contrast variation SANS that the sugar concentration in the excess phase is higher than in the interlamellar region [Deme and Zemb, J. Appl. Crystallog. 33 (2000) 569]. This raises two questions regarding the location of the sugars at low hydrations: first, does the system phase separate to give a sugar/water phase in equilibrium with a lipid/water/sugar lamellar region (with different sugar concentrations); and second, is the sugar in the interlamellar region uniformly distributed, or does it concentrate preferentially either in close proximity to the lipids, or towards the center of the interbilayer region. In this paper we present the preliminary results of measurements using contrast variation SANS to determine the location of sugars in lipid/water mixtures. © 2006, Elsevier Ltd.
Measurement of glucose exclusion from the fully hydrated DOPE inverse hexagonal phase
(Royal Society of Chemistry, 2010-03-21) Kent, B; Garvey, CJ; Lenné, T; Porcar, L; Garamus, VM; Bryant, G
The degree of exclusion of glucose from the inverse hexagonal HII phase of fully hydrated DOPE is determined using contrast variation small angle neutron scattering and small angle X-ray scattering. The presence of glucose is found to favour the formation of the non-lamellar HII phase over the fluid lamellar phase, over a wide range of temperatures, while having no significant effect on the structure of the HII phase. Glucose is preferentially excluded from the lipid–water interface resulting in a glucose concentration in the HII phase of less than half that in the coexisting aqueous phase. The degree of exclusion is quantified and the results are consistent with a hydration layer of pure water adjacent to the lipid head groups from which glucose is excluded. The osmotic gradient created by the difference in glucose concentration is determined and the influence of glucose on the phase behaviour of non-lamellar phase forming lipid systems is discussed. © 2010, Royal Society of Chemistry
A multilayered approach to polyfluorene water-based organic photovoltaics
(Elsevier Science BV, 2012-07-01) Stapleton, A; Vaughan, B; Xue, BF; Sesa, E; Burke, K; Zhou, XJ; Bryant, G; Werzer, O; Nelson, A; Kilcoyne, ALD; Thomsen, L; Wanless, E; Belcher, W; Dastoor, P
Water-based polymer nanoparticle dispersions offer the prospect of addressing two of the main challenges associated with printing large area organic photovoltaic (OPV) devices; namely how to control the nanoscale architecture of the active layer and eliminate the need for hazardous organic solvents during device fabrication. However, to date, the efficiencies of nanoparticulate-based devices have been inferior to that of the corresponding bulk-heterojunction devices. Here we present an approach for producing optimised OPV devices from polymer nanoparticles via the fabrication of multilayered device architectures. We show that by controlling both nanoparticle morphology and inter-particle interactions it is now possible to build polyfluorene OPV devices from aqueous dispersions of nanoparticles that are more efficient than the corresponding bulk heterojunction devices. In particular we show that: (1) the polyfluorene nanoparticle morphology is suited to effective charge separation, (2) thermal treatment of the deposited layers results in improved interparticle connectivity and effective charge transport, and (3) the optimal device thickness is a delicate balance between the repair of layer defects and the creation of stress cracking in the nanoparticulate film. As such, this work offers insights for the development of printable photovoltaic devices based on water-dispersed nanoparticulate formulations. © 2012, Elsevier Ltd.
New insights into colloidal phase transitions using neutron scattering techniques
(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Chea, K; Bryant, G; Garvey, CJ; Van Megan, B
The fundamentals of crystallisation and glass formation in atomic systems are not yet fully understood. Hardsphere colloidal nanoparticles have been shown to be promising model systems for understanding crystallisation and glass formation in atomic systems: As colloidal motion is Brownian, rather than ballistic, kinetics and dynamics are orders of magnitude slower than in atomic systems and can be studied in real-time. However, despite previous work, key elements are still missing from our understanding of phase transition in colloidal suspensions especially regarding metastability, supercooling and the glass transition. In particular, there is still no clear understanding of the effects of polydispersity: although studies of both polydisperse and binary mixtures of hard sphere colloids have been performed, a systematic study of the effects of polydispersity on structure, crystallisation kinetics and particle dynamics is still lacking. One of the reasons for this is the relatively limited types of suspensions which have be studied - most particles used for such studies need to be suspended in mixed solvents for refractive index matching for light scattering studies, which introduces potential problems such as selective solvation and evaporation. In this work we explore the possibility of using ionic liquids (ILs) and deep eutectic solvents (DESs) as the suspending solvent, as these can be tuned to match the refractive index of the particles, and don’t suffer from evaporation. We will then develop suitable binary colloidal suspensions consisting of deuterated & non-deuterated nanoparticles suspended in the solvent. With a combination of lab techniques and beam time allocations at the Australian Synchrotron, ANSTO and overseas neutron facilities, we will expansively investigate the nature of metastability, crystallisation and the glass transition, and provide a significant advance on our current understanding of these processes.
Phospholipid membrane protection by sugar molecules during dehydration-insights into molecular mechanisms using scattering techniques
(MDPI AG, 2013-04-01) Garvey, CJ; Lenné, T; Koster, KL; Kent, B; Bryant, G
Scattering techniques have played a key role in our understanding of the structure and function of phospholipid membranes. These techniques have been applied widely to study how different molecules (e. g., cholesterol) can affect phospholipid membrane structure. However, there has been much less attention paid to the effects of molecules that remain in the aqueous phase. One important example is the role played by small solutes, particularly sugars, in protecting phospholipid membranes during drying or slow freezing. In this paper, we present new results and a general methodology, which illustrate how contrast variation small angle neutron scattering (SANS) and synchrotron-based X-ray scattering (small angle (SAXS) and wide angle (WAXS)) can be used to quantitatively understand the interactions between solutes and phospholipids. Specifically, we show the assignment of lipid phases with synchrotron SAXS and explain how SANS reveals the exclusion of sugars from the aqueous region in the particular example of hexagonal II phases formed by phospholipids.© 2011, MDPI Publishing. © 2013, MDPI Publishing
Small molecule interactions with lipid bilayers by neutron diffraction
(International Conference on Neutron Scattering, 2017-07-12) Garvey, CJ; Kent, B; Hauß, T; Georgii, R; Demé, B; Cristiglio, V; Darwish, TA; Wu, CM; Mancera, RL; Bryant, G
While well established for studying the internal structure of bilayers and orientation of peptides and proteins with respect to bilayers, neutron lamellar diffraction is also a powerful tool for studying the average locus of solubilisation of small molecules in stacks of lipid bilayers. The approach has provided unique insights into important issues in anhydrobiology and cryobiology, where previously only molecular dynamics simulations (MD) had been able to provide molecular scale insights. Currently we use the methodology to understand the interaction of cryo-protectants with bilayers, with the aim of providing important validation of MD parameters to further enhance the utility of the method. Here we discuss the experimental approach, both in terms of the use of contrast variation and the use of selective deuteration to simplify the extraction of scattering length density profiles within the bilayer.
Study of the effect of Penetratin on the gyroid to diamond phase transition in Myverol
(Australian Institute of Physics, 2012-02-01) Goder, JND; Rafi, NAM; Bryant, G; Hunt, T; Kent, B; Garvey, CJ
Cell-penetrating peptides (CPPs), such as penetratin, have aroused a lot of interest in both the academic and applied research areas for their ability to penetrate cell membranes [1]. Even though there has been much work done, mostly on bilayer membranes, we still do not fully understand the mechanisms involved during this phenomenon. In our investigation, we are going to focus on the phase transition of Myverol/Saline system from Gyroid to Diamond cubic phase in the presence of penetratin, to get an understanding of how CPPs work in a more complex system. We use a Myverol/Saline system that exhibits these types of phase behaviors at specific compositions [2]. We plan to use a variety of Small Angle Scattering techniques in an attempt to elucidate the transitional phase behavior of the Myverol/Saline system with varying concentrations of penetratin. From this we hope to develop a model system for investigating the role of a simple peptide in changing the packing of amphiphilic molecules. In this study, we are making the use of 2 complementary techniques, Small Angle X-ray Scattering (SAXS) and small angle neutron scattering (SANS), to investigate the Myverol/Saline system as functions of both temperatures and peptide composition. We also hope to carry out DSC measurements in parallel with the SAXS. We will report on preliminary SAXS experiments carried out at the Australian Synchrotron.
Sugar distribution between and around membranes during dehydration
(Elsevier, 2006-12) Bryant, G; Lenné, T; Koster, KL; Garvey, CJ
It is now well known that small solutes such as sugars can reduce membrane damage during freezing and dehydration. One of the mechanisms for this protection is that small solutes can hinder deleterious phase transitions, thus preserving membrane integrity. The mechanisms for this can be understood in terms of the hydration forces explanation (HFE) [G. Bryant, K.L. Koster, J. Wolfe, Seed Sci. Res. 11 (2001) 17–25]. At low to intermediate hydrations, the presence of small solutes reduces membrane transition temperatures through their (non-specific) volumetric and osmotic properties. If concentrations are sufficiently high that vitrification occurs, then the transition temperatures are depressed even further. In the fully dehydrated state, direct hydrogen bonding between solutes and membranes may become important. Recently [K. Koster, G. Bryant, Eur. Biophys. J. 32 (2003) 96–105], we showed how solutes can be excluded from inter-membrane regions during dehydration if the solutes are too large, explaining why large solutes (eg polymers) cannot inhibit membrane phase transition. This raises two questions: (1) is there partial exclusion of small and intermediate sized solutes? (2) if so, how does this alter the effects of the solutes? and (3) is there a maximum useful concentration of small solutes? Question (3) is answered in an accompanying paper (see Lenné et al., this volume). In this paper we will present the results of Small Angle Neutron Scattering (SANS) and Small angle X-ray scattering (SAXS) experiments designed to answer the first two questions, and discuss the implications for our understanding of the effects of solutes on membranes during dehydration. © 2010, Elsevier Ltd.

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