Small-angle X-ray Scattering Data Research Articles

Guinier peak analysis for visual and automated inspection of small-angle X-ray scattering data.

The Guinier region in small-angle X-ray scattering (SAXS) defines the radius of gyration, Rg, and the forward scattering intensity, I(0). In Guinier peak analysis (GPA), the plot of qI(q) versus q2 transforms the Guinier region into a characteristic peak for visual and automated inspection of data. Deviations of the peak position from the theoretical position in dimensionless GPA plots can suggest parameter errors, problematic low-resolution data, some kinds of intermolecular interactions or elongated scatters. To facilitate automated analysis by GPA, the elongation ratio (ER), which is the ratio of the areas in the pair-distribution function P(r) after and before the P(r) maximum, was characterized; symmetric samples have ER values around 1, and samples with ER values greater than 5 tend to be outliers in GPA analysis. Use of GPA+ER can be a helpful addition to SAXS data analysis pipelines.

Development of nano-channel single crystals and verification of their structures by small angle X-ray scattering

Nano-channel single crystals were developed via consecutive growth of various polymer single-crystal channels comprising homo and block copolymers by self-seeding method. Poly(ethylene glycol)-b-polystyrene (PEG-b-PS) and poly(ethylene glycol)-b-poly(methyl methacrylate) (PEG-b-PMMA) block copolymers were synthesized by atom transfer radical polymerization. Self-seeding temperature, concentration, and crystallization time affected the width of the channels. This might provide a new way to investigate directional absorption, diffusion, and immobilization of biomacromolecules on the surface. The crystalline blocks of PEG-b-PS and PEG-b-PMMA diblock copolymers were similar, therefore, the continuity of channel-wire growth was guaranteed. Development of complete square channels next to the channels covered with high molecular weight brushes was infeasible. It was ascribed to a higher hindrance of primarily existing tethered chains on the single-crystal channel. Finally, the consecutive channel-wire single crystals were compared with single-step-grown pyramidal and conic structures. These multilayer crystals grew spirally and formed non-flat channels. The structure and morphology of different crystalline channels were detected by atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). In this work, for the first time, the SAXS data of channel-wire single crystals were reported and they were compared by non-flat channel-like crystals. A profound investigation of PEG-b-PS, PEG-b-PMMA copolymers and PEG homopolymer channel-wire single crystals by SAXS and their comparison with AFM data was a novel work in the field of single-crystal engineering.

Conformational Changes and Flexibility of DNA Devices Observed by Small-Angle X-ray Scattering.

Self-assembled DNA origami nanostructures enable the creation of precisely defined shapes at the molecular scale. Dynamic DNA devices that are capable of switching between defined conformations could afford completely novel functionalities for diagnostic, therapeutic, or engineering applications. Developing such objects benefits strongly from experimental feedback about conformational changes and 3D structures, ideally in solution, free of potential biases from surface attachment or labeling. Here, we demonstrate that small-angle X-ray scattering (SAXS) can quantitatively resolve the conformational changes of a DNA origami two-state switch device as a function of the ionic strength of the solution. In addition, we show how SAXS data allow for refinement of the predicted idealized three-dimensional structure of the DNA object using a normal mode approach based on an elastic network model. The results reveal deviations from the idealized design geometries that are otherwise difficult to resolve. Our results establish SAXS as a powerful tool to investigate conformational changes and solution structures of DNA origami and we anticipate our methodology to be broadly applicable to increasingly complex DNA and RNA devices.

Protein encapsulation in SBA-15 with expanded pores

This work reports the encapsulation of proteins with different molecular weights into SBA-15 ordered mesoporous silica, a potential immunological adjuvant. The Human Gammaglobulin G (HGG) and Bovine Serum Albumin (BSA) proteins were incorporated into the mesoporous silica with expanded pores. A structure swelling agent, triisopropylbenzene (TIPB), was used in the synthesis process, promoting an increase of the average pore diameter and a more disordered pore network, as revealed by nitrogen adsorption isotherm (NAI) and small angle X-ray scattering (SAXS) data. SAXS measurements were also performed to obtain the overall size of the studied proteins. The results showed that both proteins have dimensions that would allow their encapsulation inside the pores of SBA-15. The HGG and BSA proteins were dissolved in phosphate buffered saline (PBS) solutions before encapsulation. It was evidenced the filling of the micropores by the PBS solution and a larger variation in pore volume and surface area for the material with higher mean pore diameter, which was also confirmed by the modeling of SAXS data. It was not observed any significant difference in the SAXS and NAI results of both proteins, indicating that the immunogens could be encapsulated in the silica macroporosity, obstructing the mesopore entrances.

Cholesterol-dependent thermotropic behavior and organization of neuronal membranes

The composition of neuronal membranes is unique with diverse lipid composition due to evolutionary requirement. The organization and dynamics of neuronal membranes are crucial for efficient functioning of neuronal receptors. We have previously established hippocampal membranes as a convenient natural source for exploring lipid-protein interactions, and organization of neuronal receptors. Keeping in mind the pathophysiological role of neuronal cholesterol, in this work, we used differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS) to explore thermotropic phase behavior and organization (thickness) of hippocampal membranes under conditions of varying cholesterol content. Our results show that the apparent phase transition temperature of hippocampal membranes displays characteristic linear dependence on membrane cholesterol content. These results are in contrast to earlier results with binary lipid mixtures containing cholesterol where phase transition temperature was found to be not significantly dependent on cholesterol concentration. Interestingly, SAXS data showed that hippocampal membrane thickness remained more or less invariant, irrespective of cholesterol content. We believe that these results constitute one of the early reports on the thermotropic phase behavior and organizational characterization of hippocampal membranes under varying cholesterol content. These results could have implications in the functioning of neuronal receptors in healthy and diseased states.

Identification of BECN1 and ATG14 Coiled-Coil Interface Residues That Are Important for Starvation-Induced Autophagy.

Autophagy, an essential eukaryotic homeostasis pathway, allows the sequestration of unwanted, damaged, or harmful cytoplasmic components in vesicles called autophagosomes, permitting subsequent lysosomal degradation and nutrient recycling. Autophagosome nucleation is mediated by class III phosphatidylinositol-3-kinase complexes that include two key autophagy proteins, BECN1/Beclin 1 and ATG14/BARKOR, which form parallel heterodimers via their coiled-coil domains (CCDs). Here we present the 1.46 Å X-ray crystal structure of the antiparallel, human BECN1 CCD homodimer, which represents BECN1 oligomerization outside the autophagosome nucleation complex. We use circular dichroism and small-angle X-ray scattering (SAXS) to show that the ATG14 CCD is significantly disordered but becomes more helical in the BECN1:ATG14 heterodimer, although it is less well-folded than the BECN1 CCD homodimer. SAXS also indicates that the BECN1:ATG14 heterodimer is more curved than other BECN1-containing CCD dimers, which has important implications for the structure of the autophagosome nucleation complex. A model of the BECN1:ATG14 CCD heterodimer that agrees well with the SAXS data shows that BECN1 residues at the homodimer interface are also responsible for heterodimerization, allowing us to identify ATG14 interface residues. Finally, we verify the role of BECN1 and ATG14 interface residues in binding by assessing the impact of point mutations of these residues on co-immunoprecipitation of the partner and demonstrate that these mutations abrogate starvation-induced upregulation of autophagy but do not impact basal autophagy. Thus, this research provides insights into structures of the BECN1 CCD homodimer and the BECN1:ATG14 CCD heterodimer and identifies interface residues that are important for BECN1:ATG14 heterodimerization and for autophagy.

SAXS Data Alone can Generate High-Quality Models of Protein-Protein Complexes

Modeling driven by small-angle X-ray scattering (SAXS) combines low-resolution data with computational modeling to predict the structure of biomolecular assemblies. A new protocol, ATTRACT-SAXS, has been developed and tested on a large protein-protein docking benchmark with simulated SAXS data. For 88% of cases, high-quality solutions were generated using SAXS data alone without a physiochemical force field (interface-RMSD ≦ 2Å or ligand-RMSD ≦ 5Å; and more than 30% native contacts). ATTRACT-SAXS gave significant improvements compared with previous approaches that filter by SAXS a posteriori. When combining SAXS and interface properties for scoring, the protocol placed high-quality models in 70% of cases among the top-ranked 100 clusters. ATTRACT-SAXS also gave good results when tested on experimental data if the native complex structure was compatible with the SAXS profile. Our results show that, in principle, SAXS on its own can contain enough information to generate high-quality models of protein-protein complexes.

Small-angle X-ray scattering as a useful supplementary technique to determine molecular masses of polyelectrolytes in solution.

ABSTRACTDetermination of molecular masses of charged polymers is often nontrivial and most methods have their drawbacks. For polyelectrolytes, a new possibility for the determination of number‐average molecular masses is represented by small‐angle X‐ray scattering (SAXS) which allows fast determinations with a 10% accuracy. This is done by relating the mass to the position of a characteristic peak feature which arises in SAXS due to the local ordering caused by charge‐repulsions between polyelectrolytes. Advantages of the technique are the simplicity of data analysis, the independency from polymer architecture, and the low sample and time consumption. The method was tested on polyelectrolytes of various structures and chemical compositions, and the results were compared with those obtained from more conventional techniques, such as asymmetric flow field‐flow fractionation, gel permeation chromatography, and classical SAXS data analysis, showing that the accuracy of the suggested method is similar to that of the other techniques. © 2016 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1913–1917

Elucidating the Significance of Segmental Mixing in Determining the Gas Transport Properties of Polyurethanes

Segmental mixing has been speculated to affect the gas transport properties of phase-separated polyurethanes. However, in most of the studies in this field the effect of this factor has not been independently evaluated. Therefore, in this study, varying the solution casting temperature was utilized to induce changes in the final morphology of the prepared films with similar molecular compositions, and the relevance of changes in segmental mixing within the domains to the changes in gas transport properties were investigated. The films were characterized using small-angle X-ray scattering (SAXS) and ATR-FTIR to observe the changes in segmental mixing and hydrogen bonding, respectively. A new mathematical treatment was developed based on the analysis of invariant in conjunction with one-dimensional correlation function calculated from the SAXS data. This method allows for the comparison of the purity of both hard and soft domains among the prepared samples. The effects produced by varying the casting temperature on the purity of the domains were discussed in detail. Also, gas diffusivity and solubility were found to be significantly affected by the purity of soft domains.

Self-Assembling Behavior of Polyglyceryl-Modified Silicone Surfactant in Aqueous Solution

We report interesting self-assembly behavior of a polyglyceryl-modified silicone surfactant in the aqueous solution; the sample has been characterized through measurements of surface tension, transmission electron microscopy (TEM), dynamic light scattering (DLS), and small-angle x-ray scattering (SAXS). Aqueous solutions of this surfactant had a low critical aggregation concentration (CAC) and surface tension (21.5 mN · m−1), substantially lower than those reported for polyether-modified silicone surfactants with a similar molecular architecture. DLS and TEM revealed self-assembled spherical micelles with a narrow size distribution. At higher concentrations (10 wt%), linear packing of micelles was observed, while the micelle size distribution remained similar (50–90 nm). SAXS data could be fitted through the use of a core–shell model and implied that the core radius remained roughly 4.3–6.0 nm for all solutions of the surfactant analyzed. The origin of its curious aggregates behavior is attributed to hydrogen bonding, steric effects, and the directionality of bond angle from the polyglyceryl block of this novel class of silicone surfactant. This type of surfactant coupling lipophilic segments assembles the cores of the micelles in water which may find positive factors for potential applications such as microreaction compartmentalization.

Elastic constants of lamellar and interlamellar regions in α and mesomorphic isotactic polypropylene by AFM indentation

ABSTRACTA study of the nanoscale mechanical properties of isotactic mesomorphic and semi‐crystalline polypropylene (iPP) is presented. Two iPPs produced with metallocene and Ziegler‐Natta catalyst polymerization are used. The resulting fibers are characterized by wide angle X‐ray scattering, small‐angle X‐ray scattering (SAXS), and Raman spectroscopy. The spatial variability of the percentage crystallinity is evaluated based on the SAXS data. AFM indentation is performed to measure the elastic modulus of the fibers in the direction perpendicular and parallel to the fiber axis. Since the AFM probing is performed on a scale larger than the lamellar thickness, a statistical analysis of the AFM and SAXS data is necessary to infer the elastic moduli of the α crystals and of the inter‐lamellar regions. The elastic modulus of the crystalline lamellae in the direction perpendicular to the c‐axis of the α crystal probed in compression is estimated at approximately 3.3 GPa, while the effective modulus of the interlamellar regions ranges from 1.5 to 2.2 GPa. The method proposed can be applied to other material systems with similar layered structure to measure elastic moduli or hardness on length scales smaller than the resolution of the indentation test. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43649.

Conformational Flexibility Enables Function of a BECN1 Region Essential for Starvation‐Mediated Autophagy

BECN1 is essential for autophagy, a critical eukaryotic cellular homeostasis pathway. Here we delineate a highly conserved BECN1 domain (residues 141–171), located between the previously characterized BH3 and coiled‐coil domains, and elucidate its structure and role in autophagy. The 2.0 Å Sulfur‐Single Wavelength Anomalous Diffraction crystal structure of this domain demonstrates that its N‐terminal half is unstructured, while its C‐terminal half is helical, hence we name it the Flexible Helical Domain (FHD). Circular dichroism, Double‐Electron‐Electron Resonance‐Electron Paramagnetic Resonance and Small Angle X‐ray Scattering (SAXS) analyses confirm that this domain is partially disordered even in the context of adjacent BECN1 domains. Molecular dynamic simulations fitted to SAXS data indicate that the FHD transiently samples more helical conformations in solution. Strikingly, the FHD is predicted to fold upon binding, and we find it becomes more helical in the presence 2,2,2‐trifluoroethanol, indicating it may undergo a disorder‐to‐helix conformational change upon binding to a partner. A completely helical conformation would place highly conserved FHD residues on the same face of the helix, suggesting that these residues may be involved in binding. Lastly, cellular studies show that highly conserved FHD residues are essential for the starvation‐induced up‐regulation of autophagy, the first BECN1 region shown to be critical for starvation‐induced autophagy rather than basal autophagy. Thus, our combined data suggest that the FHD likely undergoes a disorder‐to‐helix transition upon binding to appropriate partners, and conserved residues critical for this interaction are essential for starvation‐induced up‐regulation of autophagy.Support or Funding InformationThis work was supported by National Institutes of Health grants RO3 NS090939 (S.S.) and R15 GM113227 (C.C.); a National Science Foundation grant MCB‐1413525 (S.S.); North Dakota EPSCoR doctoral dissertation award for Y.M. (S.S.). AR was supported by a ORNL Laboratory Director's Research and Development SEED proposal 7278.

Thermal stability of extracellular hemoglobin of Rhinodrilus alatus (HbRa): DLS and SAXS studies.

Oxy-HbRa thermal stability was evaluated by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) at pH 5.0, 7.0, 8.0, and 9.0. DLS results show that oxy-HbRa, at pH 7.0 and 5.0, remains stable up to 56°C, undergoing denaturation/aggregation in acidic media above 60°C, followed by partial sedimentation of aggregates. At alkaline pH values 8.0 and 9.0, oxy-HbRa oligomeric dissociation is observed above 30°C, before denaturation. SAXS data show that oxy-HbRa, at 20°C, is in its native form, displaying radius of gyration (R g) and particle maximum dimension (D max) of 108±1 and 300±10Å, respectively. Oxy-HbRa, at pH 7.0, undergoes denaturation/aggregation at 60°C. At pH 5.0-6.0, HbRa thermal denaturation/aggregation start earlier, at 50°C, accompanied by an increase of R g and D max values. However, an overlap of oligomeric dissociation and denaturation in the system is observed upon temperature increase, with an increase in R g and D max. Analysis of experimental p(r) curves as a linear combination of theoretical curves obtained for HbGp fragments from the crystal structure shows an increasing contribution of dodecamer (abcd)3 and tetramer (abcd) in solution, as a function of pH values (8.0 and 9.0) and temperature. Finally, our data show, for the first time, that oxy-HbRa, in neutral and acidic media, does not undergo oligomeric dissociation before denaturation, while in alkaline media the oligomeric dissociation process is an important step in the thermal denaturation.

Magnetism and structure of nanocomposites made from magnetite and vegetable oil based polymeric matrices

The aim of this work is to study the influence of the polymeric matrix composition on particle aggregation, magnetic interparticle interactions and nanoparticle surface effects, which affect the magnetic and structural properties of different ultra-diluted magnetite nanocomposites (MNCPs). Bio-based matrices were selected as a possible response to the increasing demand for renewable materials. To investigate the influence of different bio-based polymeric matrices on the magnetic behavior, three different bio-based polymers were used to prepare MNCPs with 1 wt.% of magnetite nanoparticles (MNPs). One of them was prepared using a tung oil (TO)/styrene (St) weight ratio of 70/30, a second one was prepared by replacing the styrene with methylester (green comonomer obtained from tung oil, ME, 70TO/30ME) and a third one that incorporated a green modifier, acrylated epoxidized soybean oil (AESO), using a tung oil/AESO weight ratio of 90/10. Structural features as nanoparticle aggregation state, nanoparticle and cluster sizes, and fractal dimension were studied and determined from small-angle X-ray Scattering (SAXS). The experimental SAXS data were analyzed by means of fractal aggregate model. Results indicate differences in nanoparticle arrangement depending of the containing matrix. The magnetic characterization of these materials indicates that the matrix strongly affects the physical and chemical properties of the MNCPs. All samples display superparamagnetic behavior at room temperature, but the blocking temperature varies from 75 K (tung oil/styrene with 1 wt.% MNPs) to 126 K (tung oil/AESO 1 wt.% MNPs). Furthermore, the temperature dependence of the coercive field changes for all samples, suggesting a strong influence of the polymer properties on the magnetic properties of the MNCPs.

Conformational Flexibility Enables the Function of a BECN1 Region Essential for Starvation-Mediated Autophagy.

BECN1 is essential for autophagy, a critical eukaryotic cellular homeostasis pathway. Here we delineate a highly conserved BECN1 domain located between previously characterized BH3 and coiled-coil domains and elucidate its structure and role in autophagy. The 2.0 Å sulfur-single-wavelength anomalous dispersion X-ray crystal structure of this domain demonstrates that its N-terminal half is unstructured while its C-terminal half is helical; hence, we name it the flexible helical domain (FHD). Circular dichroism spectroscopy, double electron-electron resonance-electron paramagnetic resonance, and small-angle X-ray scattering (SAXS) analyses confirm that the FHD is partially disordered, even in the context of adjacent BECN1 domains. Molecular dynamic simulations fitted to SAXS data indicate that the FHD transiently samples more helical conformations. FHD helicity increases in 2,2,2-trifluoroethanol, suggesting it may become more helical upon binding. Lastly, cellular studies show that conserved FHD residues are required for starvation-induced autophagy. Thus, the FHD likely undergoes a binding-associated disorder-to-helix transition, and conserved residues critical for this interaction are essential for starvation-induced autophagy.

Facilitating model reconstruction for single-particle scattering using small-angle X-ray scattering methods.

X-ray free-electron lasers generate intense femtosecond X-ray pulses, so that high-resolution structure determination becomes feasible from noncrystalline samples, such as single particles or single molecules. At the moment, the orientation of sample particles cannot be precisely controlled, and consequently the unknown orientation needs to be recovered using computational algorithms. This delays the model reconstruction until all the scattering patterns have been re-oriented, which often entails a long elapse of time and until the completion of the experiment. The scattering patterns from single particles or multiple particles can be summed to form a virtual powder diffraction pattern, and the low-resolution region, corresponding to the small-angle X-ray scattering (SAXS) regime, can be analysed using existing SAXS methods. This work presents a pipeline that converts single-particle data sets into SAXS data, from which real-time model reconstruction is achieved using the model retrieval approach implemented in the software package SASTBX [Liu, Hexemer & Zwart (2012). J. Appl. Cryst.45, 587-593]. To illustrate the applications, two case studies are presented with real experimental data sets collected at the Linac Coherent Light Source.

A review of multi-domain and flexible molecular chaperones studies by small-angle X-ray scattering.

Intrinsic flexibility is closely related to protein function, and a plethora of important regulatory proteins have been found to be flexible, multi-domain or even intrinsically disordered. On the one hand, understanding such systems depends on how these proteins behave in solution. On the other, small-angle X-ray scattering (SAXS) is a technique that fulfills the requirements to study protein structure and dynamics relatively quickly with few experimental limitations. Molecular chaperones from Hsp70 and Hsp90 families are multi-domain proteins containing flexible and/or disordered regions that play central roles in cellular proteostasis. Here, we review the structure and function of these proteins by SAXS. Our general approach includes the use of SAXS data to determine size and shape parameters, as well as protein shape reconstruction and their validation by using accessory biophysical tools. Some remarkable examples are presented that exemplify the potential of the SAXS technique. Protein structure can be determined in solution even at limiting protein concentrations (for example, human mortalin, a mitochondrial Hsp70 chaperone). The protein organization, flexibility and function (for example, the J-protein co-chaperones), oligomeric status, domain organization, and flexibility (for the Hsp90 chaperone and the Hip and Hep1 co-chaperones) may also be determined. Lastly, the shape, structural conservation, and protein dynamics (for the Hsp90 chaperone and both p23 and Aha1 co-chaperones) may be studied by SAXS. We believe this review will enhance the application of the SAXS technique to the study of the molecular chaperones.

Relation between higher-order structure and crystalline phase transition of oriented isotactic polybutene-1 investigated by temperature-dependent time-resolved simultaneous WAXD/SAXS measurements

Drawing of isotactic polybutene-1 sample near the melting point gives the oriented form II sample with the complicated higher-order structure or the stacked lamellar structure. The small-angle X-ray scattering (SAXS) measurement may give us a useful information about the higher order structure in principle. However, it is almost impossible to detect the higher-order structure from the SAXS data, since the electron density of form II crystal is almost the same as that of the amorphous phase. The 2-dimensional SAXS pattern has started to be detected gradually as the crystalline phase transition from form II to form I was proceeded, since the form I has the higher electron density than the form II and amorphous phase. In this paper, the simultaneous time-resolved measurement of wide-angle and small-angle X-ray scattering data has been performed for the first time to reveal the lamellar stacking structure created in the form II sample by monitoring the phase transition from form II to I crystal. The thus-visualized lamellar stacking structure has been found to be different depending on the preparation condition of the oriented form II sample. The phase transition rate was also found to differ for the various types of samples depending on the temperatures of the experiment: the maximal point was located at around 30 °C. The phenomenological equation of the phase transition behavior, derived by modifying a classical theory of nucleation and growth of crystals, has succeeded to reproduce the observed temperature dependence of the phase transition rate.

SASpy: a PyMOL plugin for manipulation and refinement of hybrid models against small angle X-ray scattering data.

Summary: Complex formation and conformational transitions of biological macromolecules in solution can be effectively studied using the information about overall shape and size provided by small angle X-ray scattering (SAXS). Hybrid modeling is often applied to integrate high-resolution models into SAXS data analysis. To facilitate this task, we present SASpy, a PyMOL plugin that provides an easy-to-use graphical interface for SAXS-based hybrid modeling. Through a few mouse clicks in SASpy, low-resolution models can be superimposed to high-resolution structures, theoretical scattering profiles and fits can be calculated and displayed on-the-fly. Mouse-based manual rearrangements of complexes are conveniently applied to rapidly check and interactively refine tentative models. Interfaces to automated rigid-body and flexible refinement of macromolecular models against the experimental SAXS data are provided.Availability and implementation: SASpy is available as open source at: github.com/emblsaxs/saspy/. Working installations of both PyMOL (www.pymol.org) and ATSAS (www.embl-hamburg.de/biosaxs/download.html) are required.Contact: apanjkovich@embl-hamburg.de or svergun@embl-hamburg.de

Spontaneously Formed Unilamellar Vesicles of Siloxane-Phospholipids

We have synthesized trisiloxane-containing phosphocholines (SiPCs) and characterized their aggregation in aqueous solution. We were interested in examining the spontaneous self-assembly of our SiPCs and with this in mind we prepared SiPC liposomes without using the extrusion techniques commonly used in phospholipid vesicle preparation. Small angle X-ray scattering (SAXS) data exhibited a plain diffuse scattering pattern devoid of any Bragg peaks. This signified that, unlike their diacyl phosphocholine analogs, SiPCs do not self-assemble into multilamellar vesicles in aqueous solution. Instead we were able to analyse SAXS data in terms of unilamellar vesicles. From the SAXS data we determined the area per lipid, membrane thickness, and lipid volume. From dynamic light scattering, liposomal preparations showed two size populations, of which the smaller in size accounts for greater than 80% of the total population; the mode size of the lipid nanoparticles was found to range between 100 and 200 nm. Langmuir isotherms revealed that SiPCs do not exhibit an observable liquid condensed phase prior to the onset of film collapse. We are currently preparing and characterizing new SiPCs, which will be included in our future work examining controlled release profiles of model bioactive agents.