Browsing by Author "Garamus, VM"

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    Analysis of monoPEGylated human galectin-2 by small-angle x-ray and neutron scattering: concentration dependence of PEG conformation in the conjugate
    (American Chemical Society, 2010-12-01) He, LH; Wang, H; Garamus, VM; Hanley, TL; Lensch, M; Gabius, HJ; Fee, CJ; Middelberg, APJ
    Protein conjugation with polyethylene glycol (PEG) is a valuable means for improving stability, solubility, and bioavailability of pharmaceutical proteins. Using human galectin-2 (hGal-2) and 5 kDa PEG as a model system we first produced a PEG-hGal-2 conjugate exclusively at the Cys75 residue, resulting in two monosubstituted subunits per hGal-2 homodimer. Small angle X-ray and neutron scattering (SAXS and SANS) were combined to provide complementary structural information about the PEG-hGal-2 conjugate, wherein signal generation in SAXS depends mainly on the protein while SANS data presents signals from both the protein and PEG moieties. SAXS data gave a constant radius of gyration (Rg = 21.5 Å) for the conjugate at different concentrations and provided no evidence for an alteration of homodimeric structure or hGal-2 ellipsoidal shape upon PEGylation. In contrast, SANS data revealed a concentration dependence of Rg for the conjugate, with the value decreasing from 31.5 Å at 2 mg/mL to 26 Å at 14 mg/mL (based on hGal-2 concentration). Scattering data have been successfully described by the model of the ellipsoidal homogeneous core (hGal-2) attached with polymer chains (PEG) at the surface. Evidently, the PEG conformation of the conjugate strongly depends on conjugate concentration and PEG’s radius of gyration decreases from 24.5 to 15 Å. An excluded volume effect, arising from steric clashes between PEG molecules at high concentration, was quantified by estimating the second virial coefficient, A2, of PEGylated hGal-2 from the SANS data. A positive value of A2 (6.0 ± 0.4 × 10−4 cm3 mol g−2) indicates repulsive interactions between molecules, which are expected to protect the PEGylated protein against aggregation. © 2010 American Chemical Society
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    Elucidation of density profile of self-assembled sitosterol plus oryzanol tubules with small-angle neutron scattering
    (Royal Society of Chenistry, 2012-01-01) Bot, A; Gilbert, EP; Bouwman, WG; Sawalha, H; den Adel, R; Garamus, VM; Venema, P; van der Linden, E; Floter, E
    Small-angle neutron scattering (SANS) experiments have been performed on self-assembled tubules of sitosterol and oryzanol in triglyceride oils to investigate details of their structure. Alternative organic phases (deuterated and non-deuterated decane, limonene, castor oil and eugenol) were used to both vary the contrast with respect to the tubules and investigate the influence of solvent chemistry. The tubules were found to be composed of an inner and an outer shell containing the androsterol group of sitosterol or oryzanol and the ferulic acid moieties in the oryzanol molecule, respectively. While the inner shell has previously been detected in SAXS experiments, the outer shell was not discernible due to similar scattering length density with respect to the surrounding solvent for X-rays. By performing contrast variation SANS experiments, both for the solvent and structurant, a far more detailed description of the self-assembled system is obtainable. A model is introduced to fit the SANS data; we find that the dimensions of the inner shell agree quantitatively with the analysis performed in earlier SAXS data (radius of 39.4 +/- 5.6 angstrom for core and inner shell together, wall thickness of 15.1 +/- 5.5 angstrom). However, the newly revealed outer shell was found to be thinner than the inner shell (wall thickness 8.0 +/- 6.5 angstrom). The changes in the scattering patterns may be explained in terms of the contrast between the structurant and the organic phase and does not require any subtle indirect effects caused by the presence of water, other than water promoting the formation of sitosterol monohydrate in emulsions with aqueous phases with high water activity. © 2012, Royal Society of Chemistry.
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    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
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    Phenylene bolaamphiphiles: Influence of the substitution pattern on the aggregation behavior and the miscibility with classical phospholipids
    (Wiley Online Library, 2014-07-22) Drescher, S; Meister, A; Garamus, VM; Hause, G; Garvey, CJ; Dobner, B; Blume, A
    The synthesis of two symmetric single-chain phenylene-modified bolaamphiphiles with meta and ortho phenyl substitution pattern is described. The aggregation behavior of both bolaamphiphiles in aqueous suspension was investigated by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), Fourier-transform IR (FTIR) spectroscopy, and small angle neutron scattering (SANS). We could show that a change in the substitution pattern from para to meta or ortho leads to a change in the aggregation behavior so that small micelles instead of nanofibers are formed. Furthermore, the mixing behavior of these bolaamphiphiles with classical bilayer forming phospholipids, such as 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) was studied by means of DSC, TEM, cryo-TEM, and small angle X-ray scattering (SAXS). The aim was to stabilize bilayer membranes formed by classical phospholipids by incorporation of bolaamphiphiles to obtain liposomes with improved stability suitable for drug delivery purposes. We could show that the phenylene-modified bolaamphiphiles are indeed miscible with DPPC and DSPC; however, closed vesicles as observed for pure DPPC and DSPC were not found. Instead, small disk-like aggregates are formed. In the case of mixtures of phenylene-modified bolaamphiphiles with DPPC, these bilayer disks have a higher DSC transition temperature compared to pure DPPC indicating an increased stability of the ordered gel phase inside the disks.© 2014 Wiley-VCH Verlag.
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    Small angle neutron scattering study of the interface between ethylcellulose/polyhydroxybutyrate blends during annealing
    (Australian Institute of Physics, 2009-02-05) Garvey, CJ; Russell, RA; Garamus, VM; Boué, F; Foster, LJR; Holden, PJ
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