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The effect of the amylopectin molecular structures on the helical, crystalline and the crystalline-amorphous lamellar properties of native starch
No full textStarch is the primary mechanism of energy storage in plants, is the single most important source of human food energy and is commonly used as an animal feed. It also has many significant industrial uses in adhesives, packaging materials, pharmaceutical excipients and in the production of textiles and papers. Due to its ubiquity, both as a food and as a food additive, starch structure has been examined in relation to its physical and nutritional properties extensively. There has also been significant success in understanding the biochemical/biosynthetic pathways of aspects of its production and how these affect individual starch structures. The various structural features of starch can be divided into several structural levels, the first four of which are most relevant to this research. Level 1 starch structure is the chain length distribution of starch. Level 2 structure relates to the whole individual molecule, such as whole molecule size and branching pattern. Level 3 structure is the aggregated structures of the molecules such as double helices, crystallites and crystalline-amorphous lamellae. Level 4 starch structures relate to the compartmentalisation of the granule into the hilum and semi-crystalline and amorphous growth rings. This project aims to increase understanding of the influence of the molecular structures (levels 1 and 2) of starch upon the larger scale aggregated structures (level 3) that are present in native starch. The crystalline structure as well as the crystalline-amorphous (C-A) lamellae are known to be produced by the amylopectin molecule while the amylose molecules modifies the size and stability of these structures. Thus, waxy starches (those without amylose) can be used to explore the influence of molecular properties of amylopectin on native starch structure. These results can be used to give an indication about which native starch structures are influenced by the underlying molecular structures and which are mediated by biological changes during synthesis that do not affect the molecular structure. The chain length distribution (CLD) of the amylopectin is observed via debranching followed by size characterization, and parameterised by two different techniques to describe the changes in the branch pattern of the different waxy starches. One technique is the empirically based division iii of chains, the other is based upon biosynthetic modelling. Enzymatic techniques are used to probe the assembly of the branches that produce the whole amylopectin molecule. The enzymes degrade the exterior starch chains allowing the observation of the core of the amylopectin molecule which contains all of the branching. These molecular parameters are then to be compared to the aggregated native structures of starch which are most likely to be related to the molecular structure parameters. The first of these aggregated structures are the crystalline properties of the starches, with an observation of the proportion of crystallinity, the proportion of double helices which make up these crystallites as well as the thermal stability of both the double helices and crystallites. The majority of the eleven waxy starches used, which are from a variety of botanical sources, are A-type starches with a single B-type starch which is used to observe whether B-type starches follow the same trends as A-type starches.
The results showed that there was a strong correlation between the molecular parameters of amylopectin, the aggregated starch parameters and the crystalline-amorphous lamellae of native starch. The amylopectin molecule chains that were branched were more likely to be the shoulder length chains in the CLD; increases in these branched shoulder length chains increased the size of the C-A lamellae. No other branch parameters of amylopectin correlated with the CLD of the amylopectin. This indicates that the commonly held belief, that A-chains are more likely to have a lower degree of polymerisation (DP) than B-chains, is questionable. The increase in lamellar size was linked to an increase in the amorphous region of the lamellae which contains the majority of the branch points. The crystalline region of the lamellae increased in size with an increase in the number of longer chains in the first, approximately linear, region of the CLD. The number of longer chains in the linear region increases the likelihood that the starch may produce longer helices, which leads to an increase the crystalline region of the lamellae. Increasing proportions of DP 13-24 and DP 25-36 chains were observed to correlate with an increase in the size of the lamellae while the DP 6-12 chains correlated with a decrease. The DP 13-24 and DP 25-36 chains are likely related to the approximately linear crystalline regions, as iv above, while the DP 6-12 chains decrease the lamellar size by making the production of longer helices unlikely. An increase in the degree of branching of starch was linked to an increase in the number of crystalline defects within starch that is removed with annealing. This was related to the smaller size of the internal chains of the amylopectin molecule which decrease the mobility of the helices during synthesis preventing their correct alignment, which is ameliorated by the annealing process.
Speculation about the biosynthesis of starch in light of these discoveries is given with a focus upon starch branching enzyme 1 and the role of the rate of starch synthesis. Starch branching enzyme 1 seems to be the enzyme that specifically produces the shoulder length CLD chains. This results in an increase in the proportion of the B-chains and the placement of these chains in the amorphous lamellar region. There is an apparent lack of difference in the amylopectin molecules in different areas of the granule. The role of the changing rate of starch synthesis in the production of the amorphous and semi-crystalline growth rings is suggested as a reason for the similarity in molecular structure despite the large differences in granular structure
Structural ensembles reveal intrinsic disorder for the multi-stimuli responsive bio-mimetic protein Rec1-resilin.
No full textRec1-resilin is the first recombinant resilin-mimetic protein polymer, synthesized from exon-1 of the Drosophila melanogaster gene CG15920 that has demonstrated unusual multi-stimuli responsiveness in aqueous solution. Crosslinked hydrogels of Rec1-resilin have also displayed remarkable mechanical properties including near-perfect rubber-like elasticity. The structural basis of these extraordinary properties is not clearly understood. Here we combine a computational and experimental investigation to examine structural ensembles of Rec1-resilin in aqueous solution. The structure of Rec1-resilin in aqueous solutions is investigated experimentally using circular dichroism (CD) spectroscopy and small angle X-ray scattering (SAXS). Both bench-top and synchrotron SAXS are employed to extract structural data sets of Rec1-resilin and to confirm their validity. Computational approaches have been applied to these experimental data sets in order to extract quantitative information about structural ensembles including radius of gyration, pair-distance distribution function, and the fractal dimension. The present work confirms that Rec1-resilin is an intrinsically disordered protein (IDP) that displays equilibrium structural qualities between those of a structured globular protein and a denatured protein. The ensemble optimization method (EOM) analysis reveals a single conformational population with partial compactness. This work provides new insight into the structural ensembles of Rec1-resilin in solution. © 2017 Macmillan Publishers Limited, part of Springer Natur
Retention and damage in 3C-β SiC irradiated with He and H ions
No full text3C-β SiC was implanted with He and H ions using plasma immersion ion implantation (PIII). Regions of damage were created at various depths by applying a sample stage bias of 5 kV, 10 kV, 20 kV or 30 kV. Raman spectroscopy results indicate that He irradiation leads to more damage compared to H irradiation, as observed via increased disordered C and Si signals, as well as broadening of the SiC peaks. X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) results indicate significant change to the SiC structure and that surface oxidation has occurred following irradiation, with the degree of change varying dependent on impinging He fluence. The distributions of implanted species were measured using elastic recoil detection analysis. Despite the varying degree and depth of damage created in the SiC by the He ion irradiations, the retained H distribution was observed to not be affected by preceding He implantation. © 2015, Elsevier B.V
Trace metal content in inhalable particulate matter (PM10 and PM2.5 collected from historical mine waste deposits using a laboratory-based approach
No full textMine wastes and tailings are considered hazardous to human health because of their potential to generate large quantities of highly toxic emissions of particulate matter (PM). Human exposure to As and other trace metals in PM may occur via inhalation of airborne particulates or through ingestion of contaminated dust. This study describes a laboratory-based method for extracting PM2.5–10 (coarse) and PM2.5 (fine) particles from As-rich mine waste samples collected from an historical gold mining region in regional, Victoria, Australia. We also report on the trace metal and metalloid content of the coarse and fine fraction, with an emphasis on As as an element of potential concern. Laser diffraction analysis showed that the proportions of coarse and fine particles in the bulk samples ranged between 3.4–26.6 and 0.6–7.6 %, respectively. Arsenic concentrations were greater in the fine fraction (1680–26,100 mg kg−1) compared with the coarse fraction (1210–22,000 mg kg−1), and Co, Fe, Mn, Ni, Sb and Zn were found to be present in the fine fraction at levels around twice those occurring in the coarse. These results are of particular concern given that fine particles can accumulate in the human respiratory system. Our study demonstrates that mine wastes may be an important source of metal-enriched PM for mining communities.© 2016, Springer Science+Business Media Dordrecht
A low temperature reduction of CCl4 to solid and hollow carbon nanospheres using metallic sodium.
No full textCarbon nanospheres are obtained by reacting metallic sodium at 100 °C with tetrachloromethane under a flow of N2 gas at ambient pressure. The product consisted of both hollowed and solid carbon spheres, ranging between 20 and 300 nm in size and comprised of concentrically oriented, disordered graphitic fragments. The maximum surface area recorded for this nanostructured carbon is 830 m2 g−1. Morphological, structural, and chemical analysis of the product is carried out with HR-TEM, BET surface area, XPS, XRD, and Raman spectroscopy. The formation of the spherical shape of the carbon nanoparticles is discussed based on direct observations of the reaction at the interfacial phase boundary.Copyright © 2017 Elsevier B.V
Holocene Environmental Change in Northern New Zealand: the view through the lens of Lake Spectacle
No full textDuring 30th anniversary Australasian Quaternary Association (AQUA)
Biennial Conference Professor Jim Bowler and Professor Roger Jones delivered
public lectures to a full house at the Grand Ball Room, Mildura. This event was
introduced by Glenn Milne, Mayor, Mildura rural city council, and conducted
by Dr. Jessica Reeves, former president of AQUA.
In the first lecture Jim engaged us with his passionate talk on “Journey to
Discover, Who are we”, where he focussed on his lifelong research at Lake
Mungo. Jim reminded us about the six decades of scientific research at Mungo,
including a vivid description of the day he discovered Mungo Man’s skeleton
in the dunes at Joulni, which was to go on to change our understanding of
Aboriginal occupation of Australia. However, his emphasis then moved onto
the challenges for future research. This included the key role that the current
traditional owners have in managing and facilitating science, their potential
role in researching their history, and the need to establish a keeping place onsite
at Mungo to repatriate the archaeological finds, both past and future. Jim
finished by encouraging young researchers to engage with the site, particularly
given the continued erosion of the dunes and destruction of cultural and
natural heritage, especially given the world heritage listing.
In the second lecture Roger focused on our future world in the face of climate
change, and how we will experience it. Roger began by highlighting the
dominance of uniformitarianism over catastrophism in scientific thinking
during the past few centuries. He described how this trend in thought has
shaped our perspective, and narratives on trends in present and future
climates, highlighting the overall gradual increases in temperature with
time. Roger contended that this is only part of the story, and that we miss the
importance of non-linearity in the climate system – or alternatively stochastic
variation along with a gradual change. He described the importance of this
variability in influencing the lived experience and response of people to
climate change, with particular focus on how we feel an abrupt shift given
the step changes in the nature of extreme events. I think this fact should be
communicated properly to make people concerned about possible future
abrupt change for proper adaptation and better management.
Along with all the conference attendees, many non-scientists, indigenous
people and local electronic and print media reporters attended the public
lecture. People were engaged by the lectures and posed some interesting
questions. Both lecturers were happy to answer questions and share their
practical and research experience. The public lecture got media attention and
huge public interest. I think it was a great idea to arrange a public lecture
during the AQUA conference as it is the best way to engage some of the
community and let them know our scientific findings. I hope it will continue
at all AQUA events in future. © 2014, AQUA Biennial Meeting Mildura
Performance of a new compact ERC Ion source for stable isotope mass spectrometry
No full textWe have developed a mass spectrometry system, known as the IRMS++, for
measurement of isotope ratios of the light elements carbon, nitrogen and oxygen,
for applications in earth and environmental sciences. By generating multiplycharged
atomic ions from molecular gaseous species, such as water vapour or
carbon dioxide gas, isotopes can be measured free from molecular interferences
[1]. The IRMS++ uses an ECR ion source specially designed for this purpose [2].
The new ECRIS design incorporates improvements to the microwave system,
with special attention to generation of the cavity mode which is expected to couple
most effectively to electrons in the ECR resonance zone. Also this design has an
improved magnetic field structure to optimise performance at 7GHz. In this paper we will report initial performance tests of the new ion source. © 2014, Proceedings of the 20th International Workshop on ECR Ion Sources
Cemented in time: formation of the 20 000 year old Willandra fossil trackway
No full textThe Willandra Lakes system of southwestern NSW is situated within the Murray Basin, and consists of 19 interconnected relict lake basins. In general, the lake sediments within the Willandra Lakes system consist of wellsorted quartz sands (with typical lacustrine shelly fauna), associated with deeper water clays and sandy clays. In
2003, the region was found to host the largest known in-situ tract of Pleistocene human footprints in the world, with
the site located on the shoreline of a small, relict lake basin between Lakes Garnpung and Leaghur. Optically Stimulated Luminescence dating revealed that the sediments were deposited between 19 000 and 20 000 years ago.
The area is of great cultural value to the local Aboriginal communities (the traditional tribal groups Paakantyi, Mutthi
Mutthi and Ngiyampaa), as well as to both the national and international scientific communities. Detailed
mineralogical (quantitative XRD), geochemical (XRF, ICP-MS, stable isotopes) and textural (petrography, SEM)
analyses of the sediments were undertaken to help determine their origin and provide a basis for their future
conservation.
The footprints themselves are impressed into a hardpan unit, surrounded by low sand dunes. Approximately 820 m2
of the hardpan has been excavated and explored. The footprint-bearing sediments are composed of a series of thin
laminae totalling 150 mm thick, accumulated over repeated cycles of wetting and drying. These sediments are
largely composed of pelloids and intraclasts of authigenic clay-sized particles (<2–8 μm) of ferroan magnesite (or
hydromagnesite/palygorskite), eolian-derived fractured quartz grains and minor (<10 wt%) kaolinite/illite. There is a
large lateral and vertical variation in the modal mineralogy; the NE corner contains 90.5 wt% ferroan magnesite (and
minor smithsonite) while the SW and W parts contain 49 wt% ferroan magnesite. The other sediments are largely
composed of eolian quartz (up to 85 wt%), kaolinite, illite, rutile, albite, microcline, hematite, goethite and rare
dolomite. In terms of stable isotopes, the ferroan magnesite carbonate has a δ13C of –2.5‰ while the
hydromagnesite has δ13C of 0.4‰. The magnesite, hydromagnesite and palygorskite appear to have been derived through precipitation within the lake.
Although direct precipitation of these phases is rare under surficial conditions, it can occur if there is a high Mg/Ca,
only possible if extensive early precipitation of calcite cements occurred before the waters entered into the lake. As
the lake dried-out, there was an increase in salinity resulting in a decrease in the activity of water in solution,
thereby increasing the hydrated Mg2+ leading to magnesite precipitation
Reconstructing flow patterns from tsunami deposits with no visible sedimentary structure
No full textHigh energy coastal events, such as tsunamis, commonly leave sediment deposits in the landscape that may be preserved in the geological record. A set of anomalous sand and silt layers intercalated between soil units was identified alongside an estuary in Okains Bay, Banks Peninsula, New Zealand. Okains Bay, comprised of a coastal plain of Holocene progradational dune ridges, was flooded by tsunamis in 1868 and 1960. Previous research has assessed the relationship between tsunami flow patterns and sediment deposits for recent events, and we aim to extend this application to older deposits where flow patterns were not recorded and sedimentary structures are not visually apparent. A multi-proxy approach was used to investigate the sediment deposits at twelve sites along a 2 km length of the estuary margin and map inundation patterns. Measurements of Magnetic Fabric (MF: Anisotropy of Magnetic Susceptibility) were used to determine the flow direction during deposition, alongside stratigraphy and particle size analyses to assess wave energy. Flow direction results were overlaid on a digital elevation model of the study site to interpret flow patterns. Deposits became thinner and particle size decreased with distance from the coast, indicating waning flow energy with distance inland. MF results indicate that inundation occurred via the estuary channel, with primary flow directions oriented perpendicular or sub-perpendicular to the channel at each site. On a smaller scale, results showed evidence of current reversal at some sites, with flow directed alternately away from and towards the estuary channel. This is consistent with uprush and backwash patterns observed in tsunami wave sequences. Topographic control of flow patterns is also evident from the data. This research demonstrates a method for investigating older, structurally-degraded deposits and has implications for the reconstruction of paleotsunami inundation from their sedimentary deposits
Marine water from mid-holocene sea level highstand trapped in a coastal aquifer: Evidence from groundwater isotopes, and environmental significance
No full textA multi-layered coastal aquifer in southeast Australia was assessed using environmental isotopes, to identify the origins of salinity and its links to palaeo-environmental setting. Spatial distribution of groundwater salinity (electrical conductivity values ranging from 0.395 to 56.1 mS/cm) was examined along the coastline along with geological, isotopic and chemical data. This allowed assessment of different salinity sources and emplacement mechanisms. Molar chloride/bromide ratios range from 619 to 1070 (621 to 705 in samples with EC > 15 mS/cm), indicating salts are predominantly marine. Two distinct vertical salinity profiles were observed, one with increasing salinity with depth and another with saline shallow water overlying fresh groundwater. The saline shallow groundwater (EC = 45.4 to 55.7 mS/cm) has somewhat marine-like stable isotope ratios (δ18O = − 2.4 to − 1.9 ‰) and radiocarbon activities indicative of middle Holocene emplacement (47.4 to 60.4 pMC). This overlies fresher groundwater with late Pleistocene radiocarbon ages and meteoric stable isotopes (δ18O = − 5.5 to − 4.6‰). The configuration suggests surface inundation of the upper sediments by marine water during the mid-Holocene (c. 2–8 kyr BP), when sea level was 1–2 m above today's level. Profiles of chloride, stable isotopes, and radiocarbon indicate mixing between this pre-modern marine water and fresh meteoric groundwater to varying degrees around the coastline. Mixing calculations using chloride and stable isotopes show that in addition to fresh-marine water mixing, some salinity is derived from transpiration by halophytic vegetation (e.g. mangroves). The δ13C ratios in saline water (− 17.6 to − 18.4‰) also have vegetation/organic matter signatures, consistent with emplacement by surface inundation and extensive interaction between vegetation and recharging groundwater. Saline shallow groundwater is preserved only in areas where low permeability sediments have slowed subsequent downwards propagation. The configuration is unlikely to be stable long-term due to fluid density; this may be exacerbated by pumping the underlying aquifer. © 2015, Elsevier B.V