In this study, small-angle
X-ray scattering (SAXS) is successfully
employed to investigate the structure of the DPPC/diC7PC disc-shaped
bicelles incorporated with different amounts of C16-PEG2000-Ceramide
lipids. The incorporation of the C16-PEG2000-Ceramide lipids could
provide an antifouling capability to the bicelle for biomedical applications.
However, traditionally it is believed that most of the incorporated
PEGlylated lipids should lie in the rim of the disc-shaped bicelle.
In this study, high sensitivity SAXS reveals the distribution of the
added C16-PEG2000-Ceramide lipids in both the planar region and in
the rim of the bicelle. The PEG brushes of C16-PEG2000-Ceramide lipids
form a second shell outside the lipid headgroup shell of the bicelle.
A double shell disc bicelle model is used in analyzing the SAXS data.
The lipid density of C16-PEG2000-Ceramide in the rim is found to be
about 1.7 times the C16-PEG2000-Ceramide lipid density in the planar
region for all three C16-PEG2000-Ceramide concentrations, 1, 2, and
3 mM. Moreover, the bicelle core radius can be predicted well using
the actual molecular ratio of lipids in the planar region to the lipids
in the rim of the bicelles in the model calculation.
Liposome development is of great interest owing to increasing requirements for efficient drug carriers. The structural features and thermal stability of such liposomes are crucial in drug transport and delivery. Reported here are the results of the structural characterization of PEGylated liposomes via small- and wide-angle X-ray scattering and an asymmetric flow field-flow fractionation (AF4) system coupled with differential refractive-index detection, multi-angle light scattering (MALS) and dynamic light scattering. This integrated analysis of the exemplar PEGylated liposome formed from hydrogenated soy phosphatidylcholine (HSPC) with the addition of cholesterol reveals an average hydrodynamic radius (R
h) of 52 nm with 10% polydispersity, a comparable radius of gyration (R
g) and a major liposome particle mass of 118 kDa. The local bilayer structure of the liposome is found to have asymmetric electronic density profiles in the inner and outer leaflets, sandwiched by two PEGylated outer layers ca 5 nm thick. Cholesterol was found to effectively intervene in lipid chain packing, resulting in the thickening of the liposome bilayer, an increase in the area per lipid and an increase in liposome size, especially in the fluid phase of the liposome. These cholesterol effects show signs of saturation at cholesterol concentrations above ca 1:5 cholesterol:lipid molar ratio.
Understanding the dynamic behavior of hydrogel formation induced by a temperature ramp is essential for the design of gel-based injectable formulation as drugdelivery vehicles. In this study, the dynamic behavior of the hydrogel formation of Pluronic F108 aqueous solutions within different heating rates was explored in both macroscopic and microscopic views. It was discovered that when the heating rate is increased, the gelation temperature window (hard gel region) shrinks and the mechanical strength of the hydrogel decreases. A given system at different heating rates would lead to different crystalline structural evolutions. The time-resolved small-angle X-ray scattering (SAXS) experiments at a heating rate of 10 °C/min disclose that the crystalline structure of micelle packing in the hydrogel exhibits a series of transitions: hexagonal close-packed (HCP) to face-centered cubic (FCC) and body-centered cubic (BCC) structures coexisting and then to the BCC structure along with the increasing temperature. For the system at equilibrium, the BCC structure exclusively dominates the system. Furthermore, the addition of a hydrophobic model drug (ibuprofen) to the F108 aqueous solution promotes hard gel formation at even lower temperatures and concentrations of F108. The SAXS results for the system with ibuprofen at a heating rate of 10 °C/min demonstrate a mixture of FCC and BCC structures coexisting over the whole gelation window compared to the BCC structure that exclusively dominates the system at equilibrium. The addition of ibuprofen would alter the structural evolution to change the delivery path of the encapsulated drug, which is significantly related to the performance of drug release.
A cataract is a common disease for the aged people and has a very high chance to lead blindness. Instead of the surgery of replacing the clouding eye lens with an artificial one, it's important to develop a non-surgical therapy. But it's difficult to be carried out due to the lack of understanding on mechanism of cataract.In the vertebrate eye lens, alpha-crystallin(α-crystallin) is the major structural protein and consists of two subunits, αA and αB, which are used to maintain lens transparency throughout life. As a member of the small heat shock protein family (sHsp), α-crystallin exhibits chaperone-like activity to prevent misfolding as well as aggregation of key proteins in the lens associated with cataract diseases. The previous studies reported that binding capacity of α-crystallin to lens lipids increases with age [1], and high molecular complex, comprising α-crystallin and misfolding protein, showed higher association with membrane [2]. Recent evidences showed that sterols compounds can improve lens transparency [3]. Due to the strong interaction between sterols with membranes, we proposed a model based on the membrane-mediated sterol-crystallin interaction.In this study, we used αA and αB crystallin proteins, ergosterol and membranes as a model system to study the interactions between proteins, sterol molecules, and membranes. First, the influence of membrane on chaperone-like activity of αA and αB were checked by the assays of insulin, lysozyme and alcohol dehydrogenase (ADH). Circular dichroism (CD) was used to monitor the secondary structure changes of crystallin proteins induced by binding to membranes. Lamellar X-ray diffraction (LXD) was used to probe crystallin-induced structural change of membranes. Furthermore, small-angle X-ray scattering (SAXS) was used to probe structural changes of membranes with and without ergosterol induced by protein binding. The effects of ergosterol on the interaction between crystallin proteins and membranes will be discussed.
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