Thomas G. Barclay

Observation of the keto tautomer of d-fructose in D2O using 1H NMR spectroscopy

D-Fructose was analysed by NMR spectroscopy and previously unidentified (1)H NMR resonances were assigned to the keto and α-pyranose tautomers. The full assignment of shifts for the various fructose tautomers enabled the use of (1)H NMR spectroscopy in studies of the mutarotation (5-25°C) and tautomeric composition at equilibrium (5-50°C). The mutarotation of β-pyranose to furanose tautomers in D(2)O at a concentration of 0.18 M was found to have an activation energy of 62.6 kJmol(-1). At tautomeric equilibrium (20°C in D(2)O) the distribution of the β-pyranose, β-furanose, α-furanose, α-pyranose and the keto tautomers was found to be 68.23%, 22.35%, 6.24%, 2.67% and 0.50%, respectively. This tautomeric composition was not significantly affected by varying concentrations between 0.089 and 0.36 M or acidification to pH 3. Upon equilibrating at 6 temperatures between 5 and 50°C there was a linear relationship between the change in concentration and temperature for all forms.

Fine-Tuning the Surface of Forward Osmosis Membranes via Grafting Graphene Oxide: Performance Patterns and Biofouling Propensity

Graphene oxide (GO) nanosheets were attached to the polyamide selective layer of thin film composite (TFC) forward osmosis (FO) membranes through a poly L-Lysine (PLL) intermediary using either layer-by-layer or hybrid (H) grafting strategies. Fourier transform infrared spectroscopy, zeta potential, and thermogravimetric analysis confirmed the successful attachment of GO/PLL, the surface modification enhancing both the hydrophilicity and smoothness of the membranes surface demonstrated by water contact angle, atomic force microscopy, and transmission electron microscopy. The biofouling resistance of the FO membranes determined using an adenosine triphosphate bioluminescence test showed a 99% reduction in surviving bacteria for GO/PLL-H modified membranes compared to pristine membrane. This antibiofouling property of the GO/PLL-H modified membrane was reflected in reduced flux decline compared to all other samples when filtering brackish water under biofouling conditions. Further, the high density and tightly bound GO nanosheets using the hybrid modification reduced the reverse solute flux compared to the pristine, which reflects improved membrane selectivity. These results illustrate that the GO/PLL-H modification is a valuable addition to improve the performance of FO TFC membranes.

Analysis of the hydrolysis of inulin using real time 1H NMR spectroscopy

The hydrolysis of various carbohydrates was investigated under acidic conditions in real time by (1)H NMR spectroscopy, with a focus on the polysaccharide inulin. Sucrose was used as a model compound to illustrate the applicability of this technique. The hydrolysis of sucrose was shown to follow pseudo first order kinetics and have an activation energy of 107.0 kJ mol(-1) (SD 1.7 kJ mol(-1)). Inulin, pullulan and glycogen also all followed pseudo first order kinetics, but had an initiation phase at least partially generated by the protonation of the glycosidic bonds. It was also demonstrated that polysaccharide chain length has an effect on the hydrolysis of inulin. For short chain inulin (DPn 18, SD 0.70) the activation energy calculated for the hydrolytic cleavage of glucose was similar to sucrose at 108.5 kJ mol(-1) (SD 0.60). For long chain inulin (DPn 30, SD 1.3) the activation energy for the hydrolytic cleavage of glucose was reduced to 80.5 kJ mol(-1) (SD 2.3 kJ mol(-1)). This anomaly has been attributed to varied conformations for the two different lengths of inulin chain in solution.

Single-Step Assembly of Multifunctional Poly(tannic acid)–Graphene Oxide Coating To Reduce Biofouling of Forward Osmosis Membranes

Graphene oxide (GO) nanosheets have antibacterial properties that have been exploited as a biocidal agent used on desalination membrane surfaces in recent research. Nonetheless, improved strategies for efficient and stable attachment of GO nanosheets onto the membrane surface are still required for this idea to be commercially viable. To address this challenge, we adopted a novel, single-step surface modification approach using tannic acid cross-linked with polyethylene imine as a versatile platform to immobilize GO nanosheets to the surface of polyamide thin film composite forward osmosis (FO) membranes. An experimental design based on Taguchis statistical method was applied to optimize the FO processing conditions in terms of water and reverse solute fluxes. Modified membranes were analyzed using water contact angle, adenosine triphosphate bioluminescence, total organic carbon, Fourier transform infrared spectroscopy, ζ potential, X-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy. These results show that membranes were modified with a nanoscale (<10 nm), smooth, hydrophilic coating that, compared to pristine membranes, improved filtration and significantly mitigated biofouling by 33% due to its extraordinary, synergistic antibacterial properties (99.9%).

Chiral self-assembly of designed amphiphiles: influences on aggregate morphology.

A series of novel amphiphiles were designed for self-assembly into chiral morphologies, the amphiphiles consisting of a glutamic acid (Glu) headgroup connected through an 11-carbon alkoxy chain to a diphenyldiazenyl (Azo) group and terminated with a variable length alkyl chain (R-Azo-11-Glu, where R denotes the number of carbons in the distal chain). TEM imaging of amphiphile aggregates self-assembled from heated, methanolic, aqueous solution showed that chiral order, expressed as twisted ribbons, helical ribbons, and helically based nanotubes, increased progressively up to a distal chain length containing eight carbons, and then decreased with further increases in distal chain length. TEM and CD showed that the chiral aggregations of single enantiomers were influenced by the molecular chirality of the headgroup. However, the assembly of D,L-10-Azo-11-Glu into nanotubes demonstrated that chiral symmetry breaking effected by the azo group was also relevant to the chiral organization of the amphiphiles. The chiral order of aggregate morphologies was additionally affected by the temperature and solvent composition of assembly in a manner correlated to the mechanism driving assembly; i.e., D,L-10-Azo-11-Glu was sensitive to the temperature of assembly but less so to solvent composition, while L-14-Azo-11-Glu was sensitive to solvent composition and not to temperature. FTIR and UV-vis spectroscopic investigations into the organization of the head and azo groups, in chiral and achiral structures, illustrated that a balance of the influences of the hydrophilic and hydrophobic components on self-assembly was required for the optimization of the chiral organization of the self-assembled structures.

Physical characterization and in silico modeling of inulin polymer conformation during vaccine adjuvant particle formation

This study combined physical data from synchrotron SAXS, FTIR and microscopy with in-silico molecular structure predictions and mathematical modeling to examine inulin adjuvant particle formation and structure. The results show that inulin polymer chains adopt swollen random coil in solution. As precipitation occurs from solution, interactions between the glucose end group of one chain and a fructose group of an adjacent chain help drive organized assembly, initially forming inulin ribbons with helical organization of the chains orthogonal to the long-axis of the ribbon. Subsequent aggregation of the ribbons results in the layered semicrystalline particles previously shown to act as potent vaccine adjuvants. γ-Inulin adjuvant particles consist of crystalline layers 8.5 nm thick comprising helically organized inulin chains orthogonal to the plane of the layer. These crystalline layers alternate with amorphous layers 2.4 nm thick, to give overall particle crystallinity of 78%.

A versatile approach to grafting biofouling resistant coatings from polymeric membrane surfaces using an adhesive macroinitiator

Biofouling is a serious problem for any wetted structure, having a negative influence on applications as diverse as marine transport, implanted medical devices and water treatment. Here, we address this issue by creating a polydopamine-based coating on desalination reverse osmosis membranes incorporating a bromo-macroinitiator for subsequent polymerisation of sulfobetaine monomers into anti-biofouling polymer brushes. Surface characterisation using attenuated total reflectance-Fourier transform infrared spectroscopy and the water contact angle demonstrated the attachment of the polysulfobetaine brushes and that the hydrophilicity increased for the coated membranes. Using a macroinitiator formation time of ten minutes followed by polyzwitterion coating of one hour resulted in a 17% increase in water flux without significant effect on the salt rejection performance. These membranes also exhibited substantial suppression of protein and bacterial attachment of 69% and 88% respectively compared to unmodified membranes.

Gamma ray sterilization of delta inulin adjuvant particles (Advax™) makes minor, partly reversible structural changes without affecting adjuvant activity.

We earlier identified a developmental series of seven isoforms/polymorphs of microparticulate inulin by comparing non-covalent bonding strengths. Their pharmaceutical utility lies in the modulation of cellular immunity, exploited as vaccine adjuvants (Advax™) especially for delta inulin (DI). As such particles cannot be sterilized by filtration we explore the effect of (60)Co gamma radiation (GR) on inulin isoforms, particularly DI. Its adjuvant activity and overt physical properties were unaffected by normal GR sterilizing doses (up to 25kGy). Heating irradiated isoform suspensions near their critical dissolution temperature revealed increased solubility deduced to reflect a single lethal event in one component of a multi-component structure. Local oxidative effects of GR on DI were not found. The observed DI loss was almost halved by re-annealing at the critical temperature: surviving inulin chains apparently reassemble into smaller amounts of the original type of structure. Colorimetric tetrazolium assay revealed increases in reducing activity after GR of raw inulin powder, which yielded DI with normal physical properties but only 25% normal recovery yet 4× normal reducing ability, implying final retention of some GR-changed inulin chains. These findings suggest minimal inulin chain cleavage and confirm that GR may be a viable strategy for terminal sterilization of microparticulate inulin adjuvants.

Investigation of the biodistribution, breakdown and excretion of delta inulin adjuvant

Insoluble, nanostructured delta inulin particles enhance the immunogenicity of co-administered protein antigens and consequently are used as a vaccine adjuvant (Advax™). To better understand their immunomodulatory properties, the in vitro hydrolysis and in vivo distribution of delta inulin particles were investigated. Delta inulin particle hydrolysis under bio-relevant acidic conditions resulted in no observable change to the bulk morphology using SEM, and HPLC results showed that only 6.1% of the inulin was hydrolysed over 21days. However, 65% of the terminal glucose groups were released, showing that acid hydrolysis relatively rapidly releases surface bound chemistries. This was used to explain in vivo biodistribution results in which delta inulin particles surface-labelled with fluorescein-5-thiosemicabizide were administered to mice using intramuscular (I.M.) or subcutaneous (S.C.) routes. Comparison analysis of the fluorescence of soluble inulin in the supernatants of homogenised tissues maintained at room temperature or heated to 100°C to solubilise particulate inulin was used to distinguish between fluorescent probe on soluble inulin and probe bound to inulin within particles. Following both I.M. and S.C. injection delta inulin exhibited a depot behaviour with local injection site residence for several weeks. Over this time, as injection site inulin reduced, there was measurable transport of intact delta inulin particles by macrophages to secondary lymphoid organs and the liver. Ultimately, the injected delta inulin became solubilised resulting in its detection in the plasma and in the urine. Thus injected delta inulin particles are initially taken up by macrophages at the site of injection, trafficked to secondary lymphoid tissue and the liver, and hydrolysed resulting in their becoming soluble and diffusing into the blood stream, from whence they are glomerularly filtered and excreted into the urine. These results provide important insights into the biodistribution of I.M. or S.C. injected delta inulin particles when used as vaccine adjuvants and their method of excretion.

A Novel Fabrication Approach for Multifunctional Graphene-based Thin Film Nano-composite Membranes with Enhanced Desalination and Antibacterial Characteristics

A practical fabrication technique is presented to tackle the trade-off between the water flux and salt rejection of thin film composite (TFC) reverse osmosis (RO) membranes through controlled creation of a thinner active selective polyamide (PA) layer. The new thin film nano-composite (TFNC) RO membranes were synthesized with multifunctional poly tannic acid-functionalized graphene oxide nanosheets (pTA-f-GO) embedded in its PA thin active layer, which is produced through interfacial polymerization. The incorporation of pTA-f-GOL into the fabricated TFNC membranes resulted in a thinner PA layer with lower roughness and higher hydrophilicity compared to pristine membrane. These properties enhanced both the membrane water flux (improved by 40%) and salt rejection (increased by 8%) of the TFNC membrane. Furthermore, the incorporation of biocidal pTA-f-GO nanosheets into the PA active layer contributed to improving the antibacterial properties by 80%, compared to pristine membrane. The fabrication of the pTA-f-GO nanosheets embedded in the PA layer presented in this study is a very practical, scalable and generic process that can potentially be applied in different types of separation membranes resulting in less energy consumption, increased cost-efficiency and improved performance.