Hard sphere-like glass transition in eye lens α-crystallin solutions.

We study the equilibrium liquid structure and dynamics of dilute and concentrated bovine eye lens α-crystallin solutions, using small-angle X-ray scattering, static and dynamic light scattering, viscometry, molecular dynamics simulations, and mode-coupling theory. We find that a polydisperse Percus-Yevick hard-sphere liquid-structure model accurately reproduces both static light scattering data and small-angle X-ray scattering liquid structure data from α-crystallin solutions over an extended range of protein concentrations up to 290 mg/mL or 49% vol fraction and up to ca. 330 mg/mL for static light scattering. The measured dynamic light scattering and viscosity properties are also consistent with those of hard-sphere colloids and show power laws characteristic of an approach toward a glass transition at α-crystallin volume fractions near 58%. Dynamic light scattering at a volume fraction beyond the glass transition indicates formation of an arrested state. We further perform event-driven molecular dynamics simulations of polydisperse hard-sphere systems and use mode-coupling theory to compare the measured dynamic power laws with those of hard-sphere models. The static and dynamic data, simulations, and analysis show that aqueous eye lens α-crystallin solutions exhibit a glass transition at high concentrations that is similar to those found in hard-sphere colloidal systems. The α-crystallin glass transition could have implications for the molecular basis of presbyopia and the kinetics of molecular change during cataractogenesis.

Anatomical variations of flexor hallucis longus tendon increase safety in hindfoot endoscopy.

PURPOSE: The flexor hallucis longus (FHL) tendon is the main anatomical landmark during hindfoot endoscopy, and anatomical variations related to the FHL can pose a risk to the tibial nerve and posterior tibial vessels during hindfoot endoscopy. The aim of this study was to determine the distance between the FHL tendon and the tibial neurovascular bundle in the posterior ankle joint when an anatomical variant of the FHL is present. The hypothesis was that the shortest distance between the tibial neurovascular bundle and the FHL tendon in the working area of the hindfoot endoscopy is increased when an anatomical variant of the FHL is present. METHODS: A retrospective review was performed using consecutive ankle magnetic resonance imaging (MRI) scans obtained during 1 year. All scans with anatomical variations related to the FHL were included in the study. A control group including scans without anatomical variations was obtained for comparison. The shortest distance between the FHL tendon and the neurovascular tibial bundle was measured in both groups. RESULTS: Three-hundred and fifty-five ankle MRIs were reviewed. 35 scans with anatomical variants of the FHL (9.8%) were found and comprised the study group that was compared to 35 scans without variants (control group). The mean distance from FHL to the neurovascular tibial bundle in the control group was 0.9 mm. The study group consisted of 18 cases with distal muscle belly insertion (5.1%), and 17 cases with an accessory tendon corresponding to a flexor digitorum accessorius longus (4.5%). In these subgroups, the mean distance from FHL to the neurovascular tibial bundle was 1.1 and 1.5 mm respectively. Overall this distance was found to be higher in the group with anatomical variants (1.3 mm) when compared to the control group (0.9 mm) (p < 0.05). CONCLUSION: During hindfoot endoscopy, the presence of an anatomical variant related to the FHL tendon has proven safer anatomically than in its absence, due to the increased distance between the FHL tendon and the tibial neurovascular bundle in the working area. However, the minimal difference observed in safety distances still poses a major risk of injury during hindfoot endoscopic procedures in all cases.

Structure of heat-induced beta-lactoglobulin aggregates and their complexes with sodium-dodecyl sulfate.

We report on the conformation of heat-induced bovine beta-lactoglobulin (betalg) aggregates prepared at different pH conditions, and their complexes with model anionic surfactants such as sodium dodecyl sulfate (SDS). The investigation was carried out by combining a wide range of techniques such as ultra small angle light scattering, static and dynamic light scattering, small angle neutron scattering, small-angle X-ray scattering, electrophoretic mobility, isothermal titration calorimetry (ITC) and transmission electron microscopy. Three types of aggregates were generated upon heating betalg aqueous dispersions at increasing pH from 2.0 to 5.8 to 7.0: rod-like aggregates, spherical aggregates, and worm-like primary aggregates, respectively. These aggregates were shown not only to differ for their sizes and morphologies, but also for their internal structures and fractal dimensions. The main differences between aggregates are discussed in terms of the ionic charge and conformational changes arising for betalg at different pHs. The formation of complexes between SDS and the various protein aggregates at pH 3.0 was shown to occur by two main mechanisms: at low concentration of SDS, the complex formation occurs essentially by ionic binding between the positive residues of the protein and the negative sulfate heads of the surfactant. At complete neutralization of charges, precipitation of the complexes is observed. Upon further increase in SDS concentration, complex formation of SDS and the protein aggregates occurs primarily by hydrophobic interactions, leading to (i) the formation of an SDS double layer around the protein aggregates, (ii) the inversion of the total ionic charge of each individual protein aggregate, and (iii) the complete redispersion of the protein aggregate-SDS complexes in water. Remarkably, the SDS double layer around the protein aggregates provides an efficient protective shield, preventing precipitation of the aggregates at any possible pH values, including those values corresponding to the isoelectric pH of the aggregates.

Structure of artificial cytoskeleton containing liposomes in aqueous solution studied by static and dynamic light scattering.

The structure of three types of liposomes (egg yolk phosphatidylcholine (EPC) without modification and EPC vesicles containing cross-linked N-isopropylacrylamide (NIPAM) networks of low and a high concentration inside the vesicles) were analyzed by static and dynamic light scattering. Upon polymerization the network was assumed to become attached to the membrane by reactive anchoring monomers. For the sample of high poly(NIPAM) content the polymer network was assumed to fill the whole space in the vesicles. The issue of the present study was to examine hard and hollow sphere behavior of the liposomes with networks of high and low poly(NIPAM) content. The theoretical scattering curves differ markedly for uniform hard and uniform hollow spheres by the presence of specific peaks. However, polydispersity washed out the peaks and led to smoothed asymptotes with fractal dimensions of df = 2 for hollow and df = 4 for hard spheres. The experimental data could efficiently be fitted with weakly polydisperse hollow spheres. No clear conclusion could be drawn from the angular dependence alone for the liposome of high poly(NIPAM) content. The two wavelengths from the HeNe and Ar lasers proved to be too long for the studied liposomes of about 100 nm in radius. However, evidence for hollow sphere behavior was found for fractionated liposomes from the ratio rho = Rg/Rh = 1.04 +/- 0.02 (theory rho = 1.00 for hollow spheres). Finally, from the molar mass and the sphere radius, an apparent density was determined. The analysis gave the expected density for the pure EPC lecithin vesicles and a poly(NIPAM) network density of 0.244 g/mL. For the liposome of low poly(NIPAM) content the network appeared to be attached to the inner surface of the lecithin shell to form a layer of about 18 nm thickness.