Browsing by Author "Heinemann, A"

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    Encapsulation of protein in silica matrices: structural evolution on the molecular and nanoscales.
    (American Chemical Society, 2010-01-19) Gao, Y; Heinemann, A; Knott, RB; Bartlett, JR
    The immobilization of biological species such its proteins and enzymes in sol-gel hosts is currently an area of intense research activity. However, the majority of these studies have been directed toward investigating the biological activity or physicochemical properties of the encapsulated species, with much less attention having been directed toward the effect of proteins on the structural evolution of the sol-gel matrix. This study investigates the structural evolution of sol-gel matrices in the presence of a model protein, bovine serum albumin (BSA). The sol-gel matrices were produced via the NaF-catalyzed hydrolysis of a mixture of tetramethyoxysilane (TMOS) and methyltrimethoxysilane (MTMS), yielding nanohybrid matrices with controlled pore sizes, pore volumes, and surface chemistry. The structural evolution of the matrix was investigated using a complementary suite of techniques, including solid-state Si-29 NMR, FTIR, SANS contrast variation, and N-2 sorption. A novel approach was developed to model the SANS data, to extract key structural parameters. The results indicated that the structural evolution of the matrices was modulated by a series of complex interactions between the enzyme and the evolving sol-gel nanohybrid: On the molecular scale, increasing BSA content led to an associated increase in both the abundance of linear Si-O-Si species (FTIR) and the Qn network connectivity (Si-29 NMR). However, only minor changes in the connectivity of the evolving Tn network were evident with varying BSA content. The selective role of the protein in these systems, where the approach of the methylated monomer to the vicinity of the protein's surface is presumably impeded by the hydrophobicity of the monomer, will be discussed. On the nanoscale, N-2 sorption data were consistent with an initial increase in the mesopore volume and surface area at low BSA loadings, followed by a subsequent monotonic decrease with increasing BSA content. In contrast, no such trends were evident in the in situ SANS data obtained from these samples, suggesting that modulation of the evolving network structure of the silica matrix by BSA during condensation prevents collapse of the nanoscale gel structure during freeze-drying. This latter comparison reflects the important role of in situ techniques such as small angle scattering (which can be used to study both open and closed porosity and probe nanostructure on length scales from similar to 1 nm to > 100 nm) in investigating such complex, multicomponent systems, and techniques for modeling such data in sol-gel systems will be discussed. © 2010, American Chemical Society
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    Structure of organic-inorganic nanohybrids incorporating titanium(IV) oxoalkoxyacylate nanoclusters: a SANS study
    (American Chemical Society, 2008-12-25) Karatchevtseva, I; Heinemann, A; Hartley, V; Knott, RB
    The small angle neutron scattering (SANS) technique was used to investigate the structure of nanohybrids consisting of a poly(methylmethacrylate) (PMMA) and one of two types of titanium(IV) nanoclusters. Cluster 1, [Ti6O4](OC2H5)(8)(CH2=CCH3COO)(8), with polymerizable MMA ligands, formed covalent bonds with the polymer chains during the copolymerization, whereas cluster 2, [Ti6O4](OC2H5)(8)(CH3COO)(8), had no polymerizable linkers and was blended into the polymeric matrix purely as a filler. In this study, SANS with contrast variation was used to investigate the size, shape and aggregation of the clusters in the hybrid materials, and their effect on the structure of the matrix. A polydispersed core-diffusion zone model was employed to explain the scattering contribution from the titanium clusters in both nanohybrid materials. No significant differences between the structures of the two nanohybrids were found. The fitted models suggest that the interface region between the cluster and matrix (the diffusion zone) is heavily occupied by the PMMA chains; however, they do not penetrate into the core region (titanium cluster). © 2008, American Chemical Society
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    Synthesis and characterisation of nanocomposite materials prepared by dispersion of functional TiO2 nanoparticles in PMMA matrix
    (Royal Society of Chemistry, 2011-07-29) Arrachart, G; Karatchevtseva, I; Heinemann, A; Cassidy, DJ; Triani, G
    Composite powders and thin films composed of poly(methyl methacrylate) (PMMA) and functionalised titania nanoparticles are successfully prepared by in situ bulk co-polymerisation using benzoyl peroxide (BPO) as the initiator. The functionalised titania nanoparticles are synthesised by an arrested hydrolysis of Ti(OiPr)4 with either undecylenic (UA) or undecenylphosphonic (UPA) acids used as the organic templates with the long hydrocarbon chains and functional (terminal double bond) groups. Surface-modified TiO2 nanoparticles could be easily dispersed in organic solvent due to the long hydrocarbon chain surrounding the titanium core, and engaged as a co-monomer in polymerisation with the MMA due to the presence of a terminal double bond. TEM and small angle X-ray scattering (SAXS) data presented support the homogeneous and consistent distribution of inorganic phase within the PMMA matrix, with the larger titania nanoparticles detected when the UPA was employed to modify a TiO2 nanoparticle. This is attributed to the UPA greater binding affinity towards the TiO2 surfaces and therefore particles aggregation to some extent. © 2011 Royal Society of Chemistry