Multiple Scale Reorganization of Electrostatic Complexes of PolyStyrene Sulfonate and Lysozyme

We report on a SANS investigation into the potential for these structural reorganization of complexes composed of lysozyme and small PSS chains of opposite charge if the physicochemical conditions of the solutions are changed after their formation. Mixtures of solutions of lysozyme and PSS with high matter content and with an introduced charge ratio [-]/[+]intro close to the electrostatic stoichiometry, lead to suspensions that are macroscopically stable. They are composed at local scale of dense globular primary complexes of radius ~ 100 {\AA}; at a higher scale they are organized fractally with a dimension 2.1. We first show that the dilution of the solution of complexes, all other physicochemical parameters remaining constant, induces a macroscopic destabilization of the solutions but does not modify the structure of the complexes at submicronic scales. This suggests that the colloidal stability of the complexes can be explained by the interlocking of the fractal aggregates in a network at high concentration: dilution does not break the local aggregate structure but it does destroy the network. We show, secondly, that the addition of salt does not change the almost frozen inner structure of the cores of the primary complexes, although it does encourage growth of the complexes; these coalesce into larger complexes as salt has partially screened the electrostatic repulsions between two primary complexes. These larger primary complexes remain aggregated with a fractal dimension of 2.1. Thirdly, we show that the addition of PSS chains up to [-]/[+]intro ~ 20, after the formation of the primary complex with a [-]/[+]intro close to 1, only slightly changes the inner structure of the primary complexes. Moreover, in contrast to the synthesis achieved in the one-step mixing procedure where the proteins are unfolded for a range of [-]/[+]intro, the native conformation of the proteins is preserved inside the frozen core

DIMBOA levels in hexaploid Brazilian wheat are not associated with antibiosis against the cereal aphids Rhopalosiphum padi and Sitobion avenae.

The objective of this study was to evaluate the natural levels of the plant defence compound DIMBOA in young leaves of eight hexaploid Brazilian wheat genotypes and the impact of the genotypes upon development of cereal aphids, Rhopalosiphum padi and Sitobion avenae. HPLC Analysis revealed that the DIMBOA levels varied from 5.376 (in BRS Guabiju) to 30.651 mmol/kgFW (in BRS Timbaúva) with two genotypes outperforming Solstice, a UK variety used as reference. Bioassays were conducted to evaluate the development and fecundity of both aphids when grown on the wheat genotypes. Although BRS Guabiju and BRS Timbaúva were among the genotypes showing the highest and lowest susceptibility respectively, against both aphids, no correlation could be found between DIMBOA levels and antibiosis effects. The cultivar BRS 327 that was among the genotypes showing lower intrinsic rate of population increase for the two aphid species. Elucidating the role of secondary metabolites in plant resistance to aphids and the characterisation of the genotypes that allowed reduced aphid development are important steps to achieve a better natural resistance in hexaploid Brazilian wheat

Shear-Thinning Nanocomposite Hydrogels for the Treatment of Hemorrhage

Internal hemorrhaging is a leading cause of death after traumatic injury on the battlefield. Although several surgical approaches such as the use of fibrin glue and tissue adhesive have been commercialized to achieve hemostasis, these approaches are difficult to employ on the battlefield and cannot be used for incompressible wounds. Here, we present shear-thinning nanocomposite hydrogels composed of synthetic silicate nanoplatelets and gelatin as injectable hemostatic agents. These materials are demonstrated to decrease in vitro blood clotting times by 77%, and to form stable clot-gel systems. In vivo tests indicated that the nanocomposites are biocompatible and capable of promoting hemostasis in an otherwise lethal liver laceration. The combination of injectability, rapid mechanical recovery, physiological stability, and the ability to promote coagulation result in a hemostat for treating incompressible wounds in out-of-hospital, emergency conditions.United States. Army Research Office (Contract W911NF-13-D-0001)National Institutes of Health (U.S.) (Interdepartmental Biotechnology Training Program NIH/NIGMS 5T32GM008334

New insight into kinetics behavor of the structural formation process in Agar gelation

A time-resolved experimental study on the kinetics and relaxation of the structural formation process in gelling Agar-water solutions was carried out using our custom-built torsion resonator. The study was based on measurements of three naturally cooled solutions with agar concentrations of 0.75%, 1.0% and 2.0% w/w. It was found that the natural-cooling agar gelation process could be divided into three stages, sol stage (Stage I), gelation zone (Stage II) and gel stage (Stage III), based on the time/temperature evolutions of the structural development rate (SDR). An interesting fluctuant decaying behavior of SDR was observed in Stage II and III, indicative of a sum of multiple relaxation processes and well described by a multiple-order Gaussisn-like equation: . More interestingly, the temperature dependences of the fitted values of Wn in Stage II and Stage III were found to follow the different Arrhenius laws, with different activation energies of EaII= 39-74 KJ/mol and EaIII~7.0 KJ/mol. The two different Arrhenius-like behaviors respectively suggest that dispersions in Stage II be attributed to the relaxation of the self-assembly of agar molecules or the growth of junction zones en route to gelation, in which the formation or fission of hydrogen bonding interactions plays an important role; and that dispersions in Stage III be attributed to the relaxation dynamics of water released from various size domains close to the domain of the viscous flow of water during the syneresis process.Comment: 24 pages, 4 figures, 1 tabl

Internal pressure fluctuations in coacervates and syneresis

Syneresis exhibited by a heterogeneous polyampholyte coacervate (polymer-rich phase) is discussed through non-equilibrium statistical thermodynamics. It has been shown that the coacervate phase is associated with fluctuating excess internal pressure that gives rise to syneresis. It is proposed that energy is dissipated to the environment only by the surface of coacervate, whereas in the bulk, gelatin chains only exchange energy with each other with negligible or no dissipation. Consequently, the internal pressure inside the coacervate follows a damped oscillatory behaviour that relaxes slowly with time, independently of amplitude. We connect the volume of the supernatant released with time (exponential relaxation behavior) with the presence of long-lived nonlinear localized modes (the existence of breathers)

Interaction of soot derived multi-carbon nanoparticles with lung surfactants and their possible internalization inside alveolar cavity

1037-1042A systematic investigation of interaction of multi-carbon nanoparticles, obtained from soot, with dipalmitoyl phosphatidylcholine (DPPC), a clinical pulmonary phospholipid surfactant, sold under trade name “Survanta”, was undertaken to establish a model for internalization of these nanoparticles inside alveolar cavity. In vitro experiments were carried out to establish the phospholipid assisted dispersion mechanism of carbon nanoclusters (size 150 nm, zeta potential -15 mV) in water. Results obtained from an array of experimental methods, like dynamic laser light scattering, electrophoresis, UV-absorption spectroscopy, surface tension studies and transmission electron microscopy, revealed that the carbon nanoparticles interacted with DPPC predominantly via hydrophobic interactions. Selective surface adsorption of DPPC molecules on nanoparticle surface was found to be strongly dependent on the concentration of the phospholipid. DPPC, a gemini surfactant, formed a rigid monolayer around the carbon nanocluster even at nanomolar concentration and provided excellent stability to the dispersion. Based on the experimental data it is proposed that the free-energy gain involved in the hydrophobic interactions will facilitate the internalization of these nanoparticles on the inner wall of the alveolar cavity

Universal Charge Quenching and Stability of Proteins in 1‑Methyl-3-alkyl (Hexyl/Octyl) Imidazolium Chloride Ionic Liquid Solutions

This study reports pH dependent stability of protein dispersions of five common proteins, bovine serum albumin (BSA), human serum albumin (HSA), immunoglobulin (IgG), β-lactoglobulin (β-Lg), and gelatin-B (Gel-B), all having isoelectric pH, p<i>I</i> ≈ 5, in room temperature ionic liquid solutions of 1-methyl-3-alkyl (hexyl/octyl) imidazolium chloride (concentration 0–0.2% <i>w</i>/<i>v</i>). Molecular hydrophobicity index, (H-index = hydrophobicity/hydrophilicity) of these molecules spanned the range 0.43–0.87. Electrophoretic characteristics, surface tension data and hydrodynamic size information revealed that IL solutions provide dispersion stability owing to specific protein-IL binding which did not alter their pI values though their surface charge was considerably screened. Change in maximum (ζ_max) and minimum (ζ_min) zeta potential values observed at pH ∼3 (maximum protonated state) and pH ∼8 (maximum deprotonated state) could be described universally as function of IL concentration, <i>c</i> as Δζ_<i>x</i> = [1 – exp­(−<i>ac</i>)] where Δζ_<i>x</i> is either |(ζ_max – ζ_w)|/ζ_w or |(ζ_min – ζ_w)|/ζ_w, and ζ_w is the corresponding value in water. Tensiometry data showed two major stages of protein-IL interactions: (i) for <i>c</i> < cmc of IL, the IL molecules selectively bind with imidazolium cation through electrostatic forces forming protein-IL _complex and (ii) for c> cmc free IL-aggregates begin to form. Similarly, we can define Δγ_<i>x</i> as either |(γ_max – γ_w)|/γ_w at pH 3 or |(γ_min – γ_w)|/γ_w at pH 8. Both Δζ_<i>x</i> and Δγ_<i>x</i> showed linear dependence with <i>c</i>, Δγ_min, max (or Δζ_min, max) = (1 – <i>K</i>_γ (or <i>K</i>_ζ) H-index), where the slopes <i>K</i>_ζ and <i>K</i>_γ defined intermolecular interactions. Hydrodynamic radii data revealed protein stabilization, circular dichroism spectra implied retention of secondary structures, and Raman spectra confirmed a marginal increase in water structure. Results concluded that selective binding of IL molecules to protein surface in the form of bilayer screen protein surface charge, thereby, contributing to its dispersion stability

Effect of Water Structure on Gelation of Agar in Glycerol Solutions and Phase Diagram of Agar Organogels

A comprehensive study of hydration of polyanionic agar molecules in its solution and gel phase in glycerol–water binary solvent is reported. Raman spectroscopy results predict differential water structure arrangement for glycerol–water binary solvent, 0.02% (w/v) agar in glycerol solution and 0.3% (w/v) agar organogel. The 3200 cm^–1 Raman band pertaining to ice-like structure of water was found to increase in gel phase alike in glycerol–water solvent while it decreased in agar solutions with increase in glycerol concentration. In contrast, the partially structured water corresponding to the component 3310 cm^–1 of Raman spectra increased in agar solution, and decreased in gel phase similar to glycerol–water solvent case. We have explained these observations based on a simple model where the available oxygen to hydrogen atom ratio in a given solvent–polymer system uniquely defines hydration in solution and gel phases. The gelation concentration was found to increase from 0.18 (for water) to 0.22% (w/v) (50% v/v glycerol solution) as the glycerol concentration was raised. Correspondingly, the gelation temperature, <i>T</i>_g, showed a decline from 40 to 20 °C, and the gel melting temperature, <i>T</i>_m, revealed a reduction from 81 to 65 °C in the same glycerol concentration regime. Two distinctive features are evident here: (i) presence of glycerol as a cosolvent does not favor the gelation of agar as compared to water and (ii) agar organogels are softer than their hydrogels. A unique 3D phase diagram for the agar organogel is proposed. Circular dichroism data confirmed that the agar molecules retained their biological activity in these solvents. Thus, it is shown that thermo-mechanical properties of these organogels could be systematically tuned and adapted as per application requirement