Open Access

Show Abstract ▼

Abstract: Pseudanabaena dominates cyanobacterial blooms in the First-Generation Magnox Storage Pond (FGMSP) at a UK nuclear site. The fission product Cs is a radiologically significant radionuclide in the pond, and understanding the interactions between Cs and Pseudanabaena spp. is therefore important for determining facility management strategies, as well as improving understanding of microbiological responses to this non-essential chemical analogue of K. This study evaluated the fate of Cs following interactions with Pseudanabaena catenata, a laboratory strain most closely related to that dominating FGMSP blooms. Experiments showed that Cs (1 mM) exposure did not affect the growth of P. catenata, while a high concentration of K (5 mM) caused a significant reduction in cell yield. Scanning transmission X-ray microscopy elemental mapping identified Cs accumulation to discrete cytoplasmic locations within P. catenata cells, indicating a potential bioremediation option for Cs. Proteins related to stress responses and nutrient limitation (K, P) were stimulated by Cs treatment. Furthermore, selected K+ transport proteins were mis-regulated by Cs dosing, which indicates the importance of the K+ transport system for Cs accumulation. These findings enhance understanding of Cs fate and biological responses within Pseudanabaena blooms, and indicate that K exposure might provide a microbial bloom control strategy.

Show Abstract ▼

Abstract: The correlation between size of nanoparticles and structure and shape of mesogenic ligands and the ensuing assembly behaviour is not really understood and closer inspection shows very surprising features. Here 2 and 4 nm gold nanoparticles (NP) were synthesized, grafted with a forked ligand containing two rod-like mesogens in its two branches: one with cholesterol and the other with azobenzene. The 4 nm NPs also contained n-hexylthiol as co-ligand. They were found to form an FCC cubic superlattice, while the 2 nm NPs form hexagonal HCP with weak birefringence, hence with partially oriented ligands. The structures were compared with those of related systems containing a range of different azobenzene-to-cholesterol ratios, all giving body-centered tetragonal superlattices with various degrees of anisotropy. Geometric analysis is presented in terms of asphericity of NP surrounding, requirement for space-filling and structural anisotropy. Some general rules are derived to help design the soft corona around the NPs in order to obtain superlattices with desired structure and anisotropy.

Show Abstract ▼

Abstract: Although the concept of the Luttinger liquid (LL) describing a one-dimensional (1D) interacting fermion system1,2 collapses at higher dimensions, it has been proposed to be relevant to enigmatic problems in condensed matter physics including the normal state of cuprate superconductors3,4,5, unconventional metals6,7 and quantum criticality8,9. Here we investigate the electronic structure of quasi-2D η-Mo4O11, a charge-density wave material, using high-resolution angle-resolved photoemission spectroscopy and ab initio calculations. We show a prototypical LL behaviour originating from the crossed quasi-1D chain arrays hidden in the quasi-2D crystal structure. Our results suggest that η-Mo4O11 materializes the crossed LL phase10,11,12 in its normal state, where the orthogonal orbital components substantially reduce the coupling between intersecting quasi-1D chains and therefore maintain the essential properties of the LL. Our finding not only presents a realization of a 2D LL, but also provides a new angle to understand non-Fermi liquid behaviour in other 2D and 3D quantum materials.

Open Access

Show Abstract ▼

Abstract: The chemistries that can be incorporated within melt-quenched zeolitic imidazolate framework (ZIF) glasses are currently limited. Here we describe the preparation of a previously unknown purine-containing ZIF which we name ZIF-UC-7. We find that it melts and forms a glass at one of the lowest temperatures reported for 3D hybrid frameworks.

Show Abstract ▼

Abstract: This doctoral thesis reports an extensive biophysical study concerning the two major categories of molecules that compose a biological surfactant called rhamnolipid, which are mono- and di-rhamnolipids. Understanding the differences in chemical and physical properties of mono-rhamnolipids and di-rhamnolipids is important in view of their potential applications as emulsifying and dispersing agents in bioremediation processes and in other biotechnological sectors, such as in the cosmetics industry. Also, although there are a few studies concerning the molecular properties of mono- and di-rhamnolipids, information is scarce regarding the mechanisms by which each of the two components interacts with cell membranes. In order to be able to study the chemical and physical properties of the two components, my thesis work started from the chemical separation of the mono and the di-rhamnolipids from the commercial mixture (RLs), performed by using a silica gel column chromatography. After separation and purification, electrospray mass spectroscopy was used to confirm the quality of the process. Then, I performed surface tension measurements to determinate the CMC (Critical Micelle Concentration) of each of them. The physical chemical characterization started using X-ray diffraction (XRD) techniques, conducted in our biophysics laboratory on samples of mono and di-RLs dissolved in concentrated water solutions ranging from 10 to 45 w/w %. This technique allows to determine the characteristic lyotropic polymorphism, as well as the molecular packing and properties at a few Angstrom resolutions. To derive the structural properties in dilute solutions, mono or di-RL samples dissolved at concentration from 10 to 100 mM in water were then analysed by performing Synchrotron Small Angle X-ray Scattering (SAXS) experiments at the Diamond Light Source synchrotron (Didcot, UK). Results allowed to characterize the different micellar structures formed by mono-RL and di-RL in water. Finally, I extensively studied the interactions between model membranes with mono- and di-RLs, showing how it is possible, by assuming a kinetic model, to derive relevant physical parameters from optical microscopy images. I performed phase contrast and fluorescence microscopy experiments on plasma membrane models represented by Giant Unilamellar Vesicles (GUVs), composed of single lipid POPC and ternary GUVs containing DOPC:SM:CHOL in three molar ratios, 1:1:1, 3:5:2 and 5:3:2. The experiments were performed with GUVs in the presence of either mono-RL or di-RL in 0.06, 0.12 and 0.25 mM concentrations. Novel methods have been developed and applied to microscopy images allowing the determination the area and the volume of GUVs with asymmetrical shape and the description of the GUV-RL interaction in terms of two kinetic mechanisms, RL-insertion and pore formation.