Light-scattering Experiments Research Articles

Rescaled mode-coupling scheme for the quantitative description of experimentally observed colloid dynamics.

We describe experimentally observed collective dynamics in colloidal suspensions of model hard-sphere particles using a modified mode coupling theory (MCT). This rescaled MCT is capable of describing quantitatively the wave-vector and time-dependent diffusion in these systems. Intermediate scattering functions of liquidlike structured dispersions are determined by means of static and dynamic light-scattering experiments. The structure and short-time dynamics of the systems can be described quantitatively employing a multicomponent Percus-Yevick ansatz for the partial structure factors and an effective, one-component description of hydrodynamic interactions based on the semianalytical δγ expansion. Combined with a recently proposed empirical modification of MCT in which memory functions are calculated using effective structure factors at rescaled number densities, the scheme is able to model the collective dynamics over the entire accessible time and wave-vector range and predicts the volume-fraction-dependence of long-time self-diffusion coefficients and the zero-shear viscosity quantitatively. This highlights the potential of MCT as a practical tool for the quantitative analysis and prediction of experimental observations.

Supramolecular systems based on chitosan and chemically functionalized nanocelluloses as protective and reinforcing fillers of paper structure

Supramolecular systems based on chitosan and cellulose nanofibers (CNFs) with a different surface modification (TEMPO-oxidation and carboxymethylation) were investigated and utilized for the functional consolidation of paper. Prior to the paper consolidation, the interactions between chitosan and CNFs dispersed in aqueous solvent were studied. It was detected that the peculiar surface functionalization of nanocellulose is crucial to control the chitosan/CNFs electrostatic attractions and, consequently, the entropic/enthalpic contributions and the stoichiometry of the biopolymer adsorption onto the cellulose nanofibers. Dynamic Light Scattering and rheological experiments revealed that the presence of biopolymeric chains on the CNFs surface favors the entanglement and the aggregation between the nanofibers reinforcing their network. It was observed that chitosan and nanocellulose exhibit synergetic effects on the paper consolidation in terms of reinforcing action, surface hydrophobization and enhancement of the fire-resistance. In conclusion, this paper demonstrates that the electrostatic interactions between chitosan and functionalized nanocellulose drive the formation of hybrid fillers suitable for paper consolidation. Chitosan coated CNFs possess an improved capacity to penetrate the paper structure causing an enhancement of the mechanical resistance and surface hydrophobization. Moreover, chitosan/CNFs create a protective barrier for heat transfer that prevents the paper combustion.

Characterization of nanodisc-forming peptides for membrane protein studies

Lipid-bilayer nanodiscs provide a stable, native-like membrane environment for the functional and structural studies of membrane proteins and other membrane-binding molecules. Peptide-based nanodiscs having unique properties are developed for membrane protein studies and other biological applications. While the self-assembly process rendering the formation of peptide-nanodiscs is attractive, it is important to understand the stability and suitability of these nanodisc systems for membrane protein studies. In this study, we investigated the nanodiscs formation by the anti-inflammatory and tumor-suppressing peptide AEM28. AEM28 is a chimeric peptide containing a cationic-rich heparan sulfate proteoglycan- (HSPG)-binding domain from human apolipoprotein E (hapoE) (141–150) followed by the 18A peptide’s amino acid sequence. AEM28-based nanodiscs made with different types of lipids were characterized using various biophysical techniques and compared with the nanodiscs formed using 2F or 4F peptides. Variable temperature dynamic light-scattering and 31P NMR experiments indicated the fusion and size heterogeneity of nanodiscs at high temperatures. The suitability of AEM28 and Ac-18A-NH2- (2F-) based nanodiscs for studying membrane proteins is demonstrated by reconstituting and characterizing a drug-metabolizing enzyme, cytochrome-P450 (CYP450), or the redox complex CYP450-CYP450 reductase. AEM28 and 2F were also tested for their efficacies in solubilizing E. coli membranes to understand the possibility of using them for detergent-free membrane protein isolation. Our experimental results suggest that AEM28 nanodiscs are suitable for studying membrane proteins with a net positive charge, whereas 2F-based nanodiscs are compatible with any membrane proteins and their complexes irrespective of their charge. Furthermore, both peptides solubilized E. coli cell membranes, indicating their use in membrane protein isolation and other applications related to membrane solubilization.

Impact of light polarization on angle-resolved light scattering from gloss scale

The gloss scale is a set of coated paper samples with different surface roughness allowing for appearance variation from high gloss to mat. Nowadays, the gloss scale is widely used as a reference on visual appearance of glossy and mat surfaces. This work provides for angle resolved analysis of light scattering from gloss scales as well as the analysis of the surface topography parameters relevant for the analysis of light-scattering experiments: RMS-roughness σ, auto-correlation function and power spectrum density, correlation length ℓ c and surface slopes. The angle–resolved measurements of light scattered in reflection within the half–space are performed at 4 angles of incidence, while measurements within the incidence plane are made at 17 angles of incidence and under non–polarized, s–and p–polarized illumination. The polarization of incident light has a significant impact on both the specular and the diffused components of scattered light. Brewster scattering angle is especially well observed for black mat surfaces. Qualitative and quantitative analysis of measured scattered light is made with Rayleigh-Rice and Kirchhoff models applied to statistically representative analysis of surface topography.

Structure and interaction of therapeutic proteins in solution: a combined simulation and experimental study

The aggregation of therapeutic proteins in solution has attracted significant interest, driving efforts to understand the relationship between microscopic structural changes and protein-protein interactions determining aggregation processes in solution. Additionally, there is substantial interest in being able to predict aggregation based on protein structure as part of molecular developability assessments. Molecular Dynamics provides theoretical tools to complement experimental studies and to interrogate and identify the microscopic mechanisms determining aggregation. Here we perform all-atom MD simulations to study the structure and inter-protein interaction of the Fab and Fc fragments of the monoclonal antibody (mAb) COE3. We unravel the role of ion-protein interactions in building the ionic double layer and determining effective inter-protein interaction. Further, we demonstrate, using various state-of-the-art force fields (charmm, gromos, amber, opls/aa), that the protein solvation, ionic structure and protein-protein interaction depend significantly on the force field parameters. We perform SANS and Static Light Scattering experiments to assess the accuracy of the different forcefields. Comparison of the simulated and experimental results reveal significant differences in the forcefields' performance, particularly in their ability to predict the protein size in solution and inter-protein interactions quantified through the second virial coefficients. In addition, the performance of the forcefields is correlated with the protein hydration structure.

Synergism and molecular mismatch in rhamnolipid/CTAC catanionic surfactant mixtures

Rhamnolipids represent a promising class of biosurfactants, whose industrial exploitation could potentially reduce the ecological impact of surfactant-based formulations. In this direction, the rational design of rhamnolipid mixtures with other surfactants constitutes a strategic field of research.In this work, we combine mono-rhamnolipid (mRha) with the cationic surfactant cetyltrimethylammonium chloride (CTAC). The study is conducted at pH = 7.1, so that the mRha carboxylic group is dissociated and catanionic mRha-CTAC mixtures form. The system is investigated across the entire composition range by surface tension and conductivity measurements, which show a strong synergism between the two surfactants in forming mixed aggregates, specifically in mRha-rich mixtures. No coacervation or precipitation is observed, due to the strong asymmetry between the surfactant molecular architectures, with mRha presenting a bulky headgroup and two relatively short tails compared to the single long tail of CTAC. Dynamic Light Scattering (DLS) and Small Angle Neutron Scattering (SANS) experiments show that, while the single surfactants predominantly form small micelles, their mixing results in the spontaneous formation of vesicles. Within the vesicle bilayer, the termini of the longer surfactant tails fold, assuming disordered conformations, as probed by Electron Paramagnetic Resonance (EPR) measurements.These results point to the rational design of rhamnolipid-based catanionic mixtures as a suitable tool to optimize their structural properties, constituting a solid basis for their practical applications.

Light scattering investigations in the system methyl ethyl ketone + water + secondary butyl alcohol with traces of potassium thiocyanate

The effect of trace amounts of potassium thiocyanate (KSCN) at weight fractions XKSCN = 0.0300, 0.0319 and 0.0320 – the weight fractions at which no particular structural peculiarities exist in the phase diagram of MEK + W + sBA + KSCN; presence of critical endpoints (CEPs) are detected and coexistence domes with minimal separation between the vertices containing double critical points (DCPs) are formed in the phase diagram, respectively [Naseer A. P. et. al., J. mol. Liq. 296 (2019)] – on the critical behaviour of the system methyl ethyl ketone (MEK) + water(W) + secondary butyl alcohol (sBA) are investigated through thelight scattering technique. For MEK weight fractions (x) in the range of 0.1000 ≤ x ≤ 0.1800 at constant XKSCN = 0.0300 near Ising-type behavior is observed for experimental paths approaching both TL from below and TU from the above, while in the range of 0.2000 ≤ x ≤ 0.2100 the samples show a clear mean-field type of behavior both at the TL as well as TU. Investigations near the DCPs corresponding to the minimum approach of the two coexistence domes (i.e., at x = 0.1419 and 0.1608 at XKSCN = 0.0320) do not result in the well-established, doubling of critical exponents γ and ν due to inherent chemical complexities in the system MEK + W + sBA + KSCN. FTIR and LC-HRMS studies establish that the formation of the isothiocyanate-isomer of α-thiocyanated methyl-ethyl-ketone resulting from prolonged exposure to elevated temperatures during the course of the light-scattering experiments, is responsible for the results.

Finite-momentum instability of a dynamical axion insulator

Due to the chiral anomaly, Weyl semimetals can exhibit a signature topological magnetoelectric response known as an axion term which is determined by the microscopic band structure. In the presence of strong interactions Weyl fermions may form a chiral condensate, with the intrinsic dynamics and fluctuations of the associated condensate phase producing a dynamical contribution to the axion response. Here we show that an imbalance in the density of right- and left-handed electrons drives an instability of the chiral condensate towards finite momentum and leads to strong fluctuations in the axion response. We derive a long-wavelength theory of Lifschitz type governing the dynamics of the Goldstone mode and use this to characterize its associated spatial fluctuations, which manifest as an inhomogeneous anomalous Hall effect. We show that these fluctuations produce signatures in inelastic light-scattering experiments across a broad spectrum of frequencies, and can be used to determine the structure factor for the axionic collective mode.

Trehalose counteracts the dissociation of tetrameric rabbit lactate dehydrogenase induced by acidic pH conditions

The lactate dehydrogenase from rabbit skeletal muscle (rbLDH) is a tetrameric enzyme, known to undergo dissociation when exposed to acidic pH conditions. Moreover, it should be mentioned that this dissociation translates into a pronounced loss of enzyme activity. Notably, among the compounds able to stabilize proteins and enzymes, the disaccharide trehalose represents an outperformer. In particular, trehalose was shown to efficiently counteract quite a number of physical and chemical agents inducing protein denaturation. However, no information is available on the effect, if any, exerted by trehalose against the dissociation of protein oligomers. Accordingly, we thought it of interest to investigate whether this disaccharide is competent in preventing the dissociation of rbLDH induced by acidic pH conditions. Further, we compared the action of trehalose with the effects triggered by maltose and cellobiose. Surprisingly, both these disaccharides enhanced the dissociation of rbLDH, with maltose being responsible for a major effect when compared to cellobiose. On the contrary, trehalose was effective in preventing enzyme dissociation, as revealed by activity assays and by Dynamic Light Scattering (DLS) experiments. Moreover, we detected a significant decrease of both K0.5 and Vmax when the rbLDH activity was tested (at pH 7.5 and 6.5) as a function of pyruvate concentration in the presence of trehalose. Further, we found that trehalose induces a remarkable increase of Vmax when the enzyme is exposed to pH 5. Overall, our observations suggest that trehalose triggers conformational rearrangements of tetrameric rbLDH mirrored by resistance to dissociation and peculiar catalytic features.

Initiation and modulation of Tau protein phase separation by the drug suramin

Tau is an intrinsically disordered neuronal protein in the central nervous system. Aggregated Tau is the main component of neurofibrillary tangles observed in Alzheimer’s disease. In vitro, Tau aggregation can be triggered by polyanionic co-factors, like RNA or heparin. At different concentration ratios, the same polyanions can induce Tau condensates via liquid–liquid phase separation (LLPS), which over time develop pathological aggregation seeding potential. Data obtained by time resolved Dynamic Light Scattering experiments (trDLS), light and electron microscopy show that intermolecular electrostatic interactions between Tau and the negatively charged drug suramin induce Tau condensation and compete with the interactions driving and stabilizing the formation of Tau:heparin and Tau:RNA coacervates, thus, reducing their potential to induce cellular Tau aggregation. Tau:suramin condensates do not seed Tau aggregation in a HEK cell model for Tau aggregation, even after extended incubation. These observations indicate that electrostatically driven Tau condensation can occur without pathological aggregation when initiated by small anionic molecules. Our results provide a novel avenue for therapeutic intervention of aberrant Tau phase separation, utilizing small anionic compounds.

Comparative Insights into the Fundamental Steps Underlying Gelation of Plant and Algal Ionic Polysaccharides: Pectate and Alginate.

Pectate and alginate are among the most important biopolymers able to give rise to ionotropic gelation upon the addition of di- or multivalent counterions. The two ionic polysaccharides exhibit several common aspects of the gelation mechanism with calcium ions, the physiologically and commercially most relevant counterion type. The first one pertains to the role that specific Ca2+/polyion interactions play in the establishment of the ion-mediated chain/chain cross-links. Such interactions include both a specific affinity of the territorially condensed Ca2+ counterions for the polyuronate(s) and the formation of long-lasting chemical bonding (inner ion-sphere complex) of specific interchain sites accompanied by high conformational ordering. As to the first mechanism, it is dominated by the strong desolvation of the interacting ionic species, with concomitant positive variations in both enthalpy and entropy, the contribution of the latter prevailing over the former due to the favorable liberation of a very large number of water molecules of hydration. Both dilatometric and microcalorimetric data point to the higher affinity of Ca2+ for pectate than for alginate. The selective accumulation of calcium ions close to the polyanion(s) favors the onset of the second-chemical bonding-mode, which is associated with charge neutralization at the bonding site. This mode coincides with the largely accepted "egg-box" model for the calcium-mediated interchain junction of pectate and alginate. A new approach was devised for the calculation of the fraction of chemically bound divalent ions; it was based on the available circular dichroism data (further supported by scattering and viscosity results) and successfully tested by comparison with an independently determined fraction in the case of pectate. In detail, the strong bonding mode manifests in two sequential bonding modes. The first one (at low concentrations of added Ca2+ ions) entails a cross-link in which only one calcium ions is bracketed in a "twisted" egg-box between two chains; upon further counterion addition, a series of nearest-neighboring "perfect" egg-box structures develops. Both dilatometric and microcalorimetric changes associated with the latter chemical bonding modes are quantitatively larger for pectate than for alginate; clearly the latter polyuronate suffers from the relevant presence of the weakly calcium-binding mannuronic acid repeating units. Light-scattering experiments provided a clear-cut demonstration of the intermolecular bonding of calcium ions from the very beginning of the linker addition.

The antimicrobial peptide Magainin-2 interacts with BamA impairing folding of E. coli membrane proteins.

Antimicrobial peptides (AMPs) are a unique and diverse group of molecules endowed with a broad spectrum of antibiotics properties that are being considered as new alternative therapeutic agents. Most of these peptides are membrane-active molecules, killing bacteria by membrane disruption. However, recently an increasing number of AMPs was shown to enter bacterial cells and target intracellular processes fundamental for bacterial life. In this paper we investigated the mechanism of action of Maganin-2 (Mag-2), a well-known antimicrobial peptide isolated from the African clawed frog Xenopus laevis, by functional proteomic approaches. Several proteins belonging to E. coli macromolecular membrane complexes were identified as Mag-2 putative interactors. Among these, we focused our attention on BamA a membrane protein belonging to the BAM complex responsible for the folding and insertion of nascent β-barrel Outer Membrane Proteins (OMPs) in the outer membrane. In silico predictions by molecular modelling, in vitro fluorescence binding and Light Scattering experiments carried out using a recombinant form of BamA confirmed the formation of a stable Mag-2/BamA complex and indicated a high affinity of the peptide for BamA. Functional implications of this interactions were investigated by two alternative and complementary approaches. The amount of outer membrane proteins OmpA and OmpF produced in E. coli following Mag-2 incubation were evaluated by both western blot analysis and quantitative tandem mass spectrometry in Multiple Reaction Monitoring scan mode. In both experiments a gradual decrease in outer membrane proteins production with time was observed as a consequence of Mag-2 treatment. These results suggested BamA as a possible good target for the rational design of new antibiotics since this protein is responsible for a crucial biological event of bacterial life and is absent in humans.

Combined Surface Light Scattering and Pendant-Drop Experiments for the Determination of Viscosity and Surface Tension of High-Viscosity Fluids Demonstrated for Ionic Liquids

The present study provides a strategy for the determination of the viscosity and surface tension of high-viscosity fluids in the form of ionic liquids (ILs) at equilibrium conditions by combining surface light scattering (SLS) and the pendant-drop (PD) method within one experimental setup. Through the study of the same sample under identical conditions by both methods inside a closed system, the surface tension determined via the PD method can be directly used to evaluate the dynamics of surface fluctuations of ILs with an overdamped behavior probed by SLS for accessing their viscosity. In connection with the SLS experiments, variations in the applied detection geometries in reflection and transmission direction and in the probed wave vectors down to relatively small values were also addressed. The reliability and self-consistency of SLS and the PD method applied within the same sample cell has been proven by investigating the reference fluids tris(2-ethylhexyl) trimellitate (TOTM) and n-dodecane featuring relatively high and low viscosities. For the two studied model ILs of opaque to non-transparent color, i.e., the hydrophobic 1-methyl-3-octylimidazolium hexafluorophosphate ([OMIM][PF6]) and the hydrophilic 1,3-bis(2-(2-methoxyethoxy)ethyl)imidazolium iodide ([(mPEG2)2Im]I), the combination of PD measurements and SLS experiments in reflection direction performed at ambient pressure between (303 and 373) K allowed access to the viscosity and surface tension with typical relative expanded uncertainties of (4 and 2) %. These results agree well with own viscosity data from capillary viscometry and experimental data in the literature, demonstrating the performance of the novel approach for the contactless in-situ measurement of viscosity and surface tension of fluids with relatively high-viscosity such as ILs.

Hydrodynamic and Polyelectrolyte Properties of Actin Filaments: Theory and Experiments.

Actin filament’s polyelectrolyte and hydrodynamic properties, their interactions with the biological environment, and external force fields play an essential role in their biological activities in eukaryotic cellular processes. In this article, we introduce a unique approach that combines dynamics and electrophoresis light-scattering experiments, an extended semiflexible worm-like chain model, and an asymmetric polymer length distribution theory to characterize the polyelectrolyte and hydrodynamic properties of actin filaments in aqueous electrolyte solutions. A fitting approach was used to optimize the theories and filament models for hydrodynamic conditions. We used the same sample and experimental conditions and considered several g-actin and polymerization buffers to elucidate the impact of their chemical composition, reducing agents, pH values, and ionic strengths on the filament translational diffusion coefficient, electrophoretic mobility, structure factor, asymmetric length distribution, effective filament diameter, electric charge, zeta potential, and semiflexibility. Compared to those values obtained from molecular structure models, our results revealed a lower value of the effective G-actin charge and a more significant value of the effective filament diameter due to the formation of the double layer of the electrolyte surrounding the filaments. Contrary to the data usually reported from electron micrographs, the lower values of our results for the persistence length and average contour filament length agree with the significant difference in the association rates at the filament ends that shift to sub-micro lengths, which is the maximum of the length distribution.

Chiral ruthenium(II) complexes as stabilizers for an RNA triplex: In contrast to Λ-enantiomer, Δ-enantiomer stabilizes the Watson-Crick duplex and the Hoogsteen strand without significant preference

To further determine the factors governing the triplex stabilization by chiral ruthium(II) polypyridyl complexes, two new dppz-beased binding reagents, Δ-[Ru(bpy)2(6-NO2-dppz)]2+ (Δ-1; bpy = 2,2′-bipyridine; 6-NO2-dppz = 6-nitro-dipyrido-3,2-a,2′,3′-c]phenazine) and Λ-[Ru(bpy)2(6-NO2-dppz)]2+ (Λ-1), have been synthesized and characterized in this work. Binding properties of the two enantiomers Δ-1 and Λ-1 with the RNA poly(U)•poly(A)*poly(U) triplex have been studied by spectroscopic technologies and viscosity measurements as well as melting measurements. Spectral titrations and viscosity experiments as well as light-scattering experiments show that although the two enantiomers bind to the triplex through an intercalative mode, the binding affinity of Δ-1 toward the triplex is slightly higer than that of Λ-1. Moreover, melting measurements show that the two enantiomers exhibit different stabilization effects on the triplex under the same conditions. The enantiomer Δ-1 stabilizes the triplex without significant preference, thereby almost equally stabilizing the Watson-Crick base-paired duplex (the template duplex) and the Hoogsteen base-paired strand (third-strand) of the triplex. In contrast to Δ-1, Λ-1 shows preference for stabilizing the template duplex rather than third-strand to a large extent. This suggests that the racemic complex [Ru(bpy)2(6-NO2-dppz)]2+ is similar as a non-specific metallointercalator for the triplex investigated in this study. The results obtained in this work show that in addition to chiralities of Ru(II) polypyridyl complexes, substituent effects of the main ligands also play important roles in altering the ability and selectivity of the metal complex enantiomers to stabilize the triplex.

Flexible Organic Framework-Based Anthracycline Prodrugs for Enhanced Tumor Growth Inhibition.

A water-soluble flexible organic framework FOF-hz of low cytotoxicity has been synthesized from a pyridinium-derived tetracationic tetraaldehyde and a citric acid-derived tritopic acylhydrazine (1:2) through the formation of a hydrazone bond. Dynamic light-scattering experiments reveal that FOF-hz has a hydrodynamic diameter of 79 nm at 0.1 mM concentration of the tetrahedral precursor. Dialysis experiments show that the free acylhydrazine units of FOF-hz can react with the C-13 ketone units of anthracycle drugs, including doxorubicin (DOX), daunorubicin, epirubicin, and pirarubicin, at pH = 3.0 to conjugate the drugs in 78-85% yields. The resulting FOF-prodrugs exhibit remarkable acid-responsive deconjugation of the conjugated active agents. Laser confocal scanning microscopy and flow cytometric analysis support that FOF-hz displays enhanced permeability and retention effect, which helps to overcome the multidrug resistance of MCF-7/ADR tumor cells and leads to enhanced cytotoxicity for MCF-7/ADR cells. In vivo studies reveal a considerable improvement of the efficacy of the prodrug FOF-DOX for the inhibition of the growth of the MCF-7/ADR tumor.

Structural Characterization of Biomaterials by Means of Small Angle X-rays and Neutron Scattering (SAXS and SANS), and Light Scattering Experiments.

Scattering techniques represent non-invasive experimental approaches and powerful tools for the investigation of structure and conformation of biomaterial systems in a wide range of distances, ranging from the nanometric to micrometric scale. More specifically, small-angle X-rays and neutron scattering and light scattering techniques represent well-established experimental techniques for the investigation of the structural properties of biomaterials and, through the use of suitable models, they allow to study and mimic various biological systems under physiologically relevant conditions. They provide the ensemble averaged (and then statistically relevant) information under in situ and operando conditions, and represent useful tools complementary to the various traditional imaging techniques that, on the contrary, reveal more local structural information. Together with the classical structure characterization approaches, we introduce the basic concepts that make it possible to examine inter-particles interactions, and to study the growth processes and conformational changes in nanostructures, which have become increasingly relevant for an accurate understanding and prediction of various mechanisms in the fields of biotechnology and nanotechnology. The upgrade of the various scattering techniques, such as the contrast variation or time resolved experiments, offers unique opportunities to study the nano- and mesoscopic structure and their evolution with time in a way not accessible by other techniques. For this reason, highly performant instruments are installed at most of the facility research centers worldwide. These new insights allow to largely ameliorate the control of (chemico-physical and biologic) processes of complex (bio-)materials at the molecular length scales, and open a full potential for the development and engineering of a variety of nano-scale biomaterials for advanced applications.

Structural insights into the membrane receptor ShuA in DDM micelles and in a model of gram-negative bacteria outer membrane as seen by SAXS and MD simulations

Successful crystallization of membrane proteins in detergent micelles depends on key factors such as conformational stability of the protein in micellar assemblies, the protein-detergent complex (PDC) monodispersity and favorable protein crystal contacts by suitable shielding of the protein hydrophobic surface by the detergent belt. With the aim of studying the influence of amphiphilic environment on membrane protein structure, stability and crystallizability, we combine molecular dynamics (MD) simulations with SEC-MALLS and SEC-SAXS (Size Exclusion Chromatography in line with Multi Angle Laser Light Scattering or Small Angle X-ray Scattering) experiments to describe the protein-detergent interactions that could help to rationalize PDC crystallization. In this context, we compare the protein-detergent interactions of ShuA from Shigella dysenteriae in n-Dodecyl-β-D-Maltopyranoside (DDM) with ShuA inserted in a realistic model of gram-negative bacteria outer membrane (OM) containing a mixture of bacterial lipopolysaccharide and phospholipids. To evaluate the quality of the PDC models, we compute the corresponding SAXS curves from the MD trajectories and compare with the experimental ones. We show that computed SAXS curves obtained from the MD trajectories reproduce better the SAXS obtained from the SEC-SAXS experiments for ShuA surrounded by 268 DDM molecules. The MD results show that the DDM molecules form around ShuA a closed belt whose the hydrophobic thickness appears slightly smaller (~22 Å) than the hydrophobic transmembrane domain of the protein (24.6 Å) suggested by Orientations of Proteins in Membranes (OPM) database. The simulations also show that ShuA transmembrane domain is remarkably stable in all the systems except for the extracellular and periplasmic loops that exhibit larger movements due to specific molecular interactions with lipopolysaccharides (LPS). We finally point out that this detergent behavior may lead to the occlusion of the periplasmic hydrophilic surface and poor crystal contacts leading to difficulties in crystallization of ShuA in DDM.

Enhanced solubilization of an insect juvenile hormone (JH) mimetic (piryproxyfen) using eugenol in water nanoemulsions stabilized by a triblock copolymer of poly(ethylenglycol) and poly(propilenglycol)

The encapsulation of a synthetic insecticide, pyriproxyfen, has been carried out using eugenol in water nanoemulsions, including different weight fractions of oil phase (eugenol), and stabilized by a triblock amphiphilic copolymer, poloxamer 407. Dynamic Light Scattering (DLS) experiments have evidenced the formation of polydisperse nanoemulsions, in both nanoemulsions free of the insecticide and those containing it. These nanoemulsion present a good long-term stability, and only a slight sedimentation of the bigger droplets was found after several months of storage (the aging during 24 months of the nanoemulsions was evaluated). This long-term chemical and physical stability is important for the potential application of these systems in insect pest control, which may also take advantage of the high solubilization efficiency of piryproxyfen evidenced by the nanoemulsions. Therefore, this study combined with an additional evaluation of the efficiency of these formulations, may open many possibilities for the preparation of ready-to-use formulations against different insect pests.

Green-banana biomass consumption by diabetic patients improves plasma low-density lipoprotein particle functionality

The aim of this study was to investigate the effects of 6-months consumption of green-banana biomass on the LDL particle functionality in subjects with type 2 diabetes. Subjects (n = 39, mean age 65 years old) of both sexes with diabetes (HbA1c ≥ 6·5%) were randomized to receive nutritional support plus green-banana biomass (40 g) (n = 21) or diet alone (n = 18) for 6-months. Non-linear optical responses of LDL solutions from these participants were studied by Z-scan technique. UV–visible spectrophotometer was used to measure the absorbance of the LDL samples. Small Angle X-ray Scattering and Dynamic Light Scattering experiments were used to look for any structural changes in LDL samples and to determine their size distribution. The Lipoprint test was used to determine the LDL sub-fractions in terms of distribution and size. Consumption of green-banana biomass, reduced total- (p = 0.010), non-HDL-cholesterol (p = 0.043), glucose (p = 0.028) and HbA1c (p = 0.0007), and also improved the protection of the LDL particle against oxidation, by the increase in carotenoids content in the particles (p = 0.007). This higher protection against modifications may decrease the risk of developing cardiovascular disease. These benefits of the green-banana biomass encourage the use of resistant starches with potential clinical applications in individuals with pre-diabetes and diabetes.