Similarities between polyelectrolyte gels and biopolymer solutions

Small angle neutron scattering (SANS) measurements and osmotic swelling pressure measurements are reported for polyelectrolyte gels and solutions under nearly physiological conditions. A synthetic polymer (sodium-polyacrylate) and three biopolymers (DNA, hyaluronic acid, and polyaspartic acid) are studied. The neutron scattering response of these anionic polyelectrolytes is closely similar, indicating that at larger length scales the organization of the polymer molecules is not significantly affected by the fine details of the molecular architecture (e.g., size and chemical structure of the monomer unit, type of polymer backbone). The results suggest that specific interactions between the polyelectrolyte chains and the surrounding monovalent cations are negligible. It is found that the osmotic compression modulus of these biopolymer solutions determined from the analysis of the SANS response decreases with increasing chain persistence length. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3679–3686, 2006     

Rheology and sensory texture of biopolymer gels

Sensory texture perception is based on food structure and the mastication process. Real-time observations of crack growth and rheological measurements have shown different patterns of microstructural fracture. This has allowed for a reductive approach in consolidating a range of gels into characteristic microstructures and fracture patterns that can be linked to sensory texture.     

Specific thermosensitive volume change of biopolymer gels derived from propylated poly(γ-glutamate)s

Thermosensitive biopolymers with an amphipathic structure were synthesized through the propyl esterification of the carboxyl groups of poly(γ-glutamic acid) (γ-PGA). The clouding temperature on heating was controlled by the addition of different amounts of NaCl and by the degree of esterification. The clearing temperature on cooling was independent of the aqueous milieu, presumably because of the strong multiple hydrogen bonds between the polymer chains formed in the collapsed state. The hydrogel of γ-PGA propylate crosslinked by a chemical reaction with hexamethylene diisocyanate also showed pH-responsive and thermoresponsive shrinking, but the volume recovery was incomplete during the cooling process. A Fourier transform infrared/attenuated total reflection study showed that the incomplete volume recovery might be associated with the amide hydrogen bonding being strengthened by the chemical crosslinkage. The addition of urea made the volume change complete. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4492–4501, 2004     

Preparation of amidoxime-functionalized biopolymer/graphene oxide gels and their application in selective adsorption separation of U(VI) from aqueous solution

Journal of Radioanalytical and Nuclear Chemistry - The amidoxime-functionalized biopolymer/graphene oxide gels were prepared and their performance in the application of the adsorption separation of...     

Field-flow fractionation in biopolymer analysis

Field-flow fractionation is a new separation method convenient for the analysis of biopolymers within a wide range of molecular weights, and of particles of biological origin. It is similar to chromatography, but in principle exhibits many advantages over alternative separation methods.     

Adsorption of protein-coated lipid droplets to mixed biopolymer hydrogel surfaces: role of biopolymer diffusion

The adsorption of charged particles to hydrogel surfaces is important in a number of natural and industrial processes. In this study, the adsorption of cationic lipid droplets to the surfaces of anionic hydrogels was examined. An oil-in-water emulsion containing cationic beta-lactoglobulin-coated lipid droplets was prepared (d32=0.24 microm, zeta=+74 mV, pH 3.0). An anionic hydrogel containing 0.1 wt % beet pectin and 1.5 wt % agar (pH 3.0) was prepared. Emulsions containing different lipid droplet concentrations (0.3-5 wt %) were brought into contact with the hydrogel surfaces for different times (0-24 h). The adsorption of lipid droplets to the hydrogel surfaces could not be explained by a typical adsorption isotherm. We found that the electrical charge on the nonadsorbed lipid droplets became less positive or even became negative in the presence of the hydrogel and that extensive droplet aggregation occurred, which was attributed to the ability of pectin molecules to diffuse through the hydrogels and interact with the lipid droplets. These results may have important consequences for understanding certain industrial and biological processes, as well as for the design of controlled or triggered release systems.     

Surfactant-based gels

This article reviews known approaches to generating viscoelastic and gel-like surfactant systems focusing on how the formation of these viscous phases are often sensitive to a variety of chemical and physio-chemical factors. An understanding of this sensitivity is essential for generating high viscosity surfactant phases in more challenging solvent environments. The initial focus is on the generation of worm-like and reverse worm-like micelles. In addition, other approaches for using surfactant self-assembly for viscosity enhancement have been examined, namely gelatin microemulsion based organogels and the addition of substituted phenols to AOT reverse micelles.     

Mixed biopolymer systems based on starch

A binary mixture of starch-starch or starch with other biopolymers such as protein and non-starch polysaccharides could provide a new approach in producing starch-based food products. In the context of food processing, a specific adjustment in the rheological properties plays an important role in regulating production processing and optimizing the applicability, stability, and sensory of the final food products. This review examines various biopolymer mixtures based on starch and the influence of their interaction on physicochemical and rheological properties of the starch-based foods. It is evident that the physicochemical and rheological characteristics of the biopolymers mixture are highly dependent on the type of starch and other biopolymers that make them up mixing ratios, mixing procedure and presence of other food ingredients in the mixture. Understanding these properties will lead to improve the formulation of starch-based foods and minimize the need to resort to chemically modified starch.     

Positron annihilation lifetime measurements in collagen biopolymer

Lifetime measurement in Positron Annihilation Spectroscopy (PAS) is applied to the study of free-volume collagen characteristics as a function of concentration. The lifetimes of positrons were measured by a conventional fast-fast coincidence system. All lifetime data are fitted in three components by using the computer program POSITRON-FIT and resolved. For each concentration, lifetime distributions were analyzed in order to obtain the different components, thus we have observed three components of which one long component τ₃. This long lived component can be associated with a pick-off annihilation of ortho-positronium (o-Ps) trapped in free volumes of amorphous region. This investigation shows the potential of positron annihilation spectroscopy in the study of biopolymer microstructures.     

Development and characterization of on-chip biopolymer membranes

In lab-on-a-chip applications, filtration is currently performed prior to sample loading or through pre-cast membranes adhered to the substrate. These membranes cannot be patterned to micrometer resolution, and their adhesion may be incompatible with the fabrication process or may introduce contaminants. We have developed an on-chip separation process using a biocompatible polymer that can be patterned and has controllable molecular rejection properties. We spun cast cellulose acetate (CA) membranes directly onto silicon wafers. Characterization of the molecular flux across the membrane showed that molecular weight and charge are major factors contributing to the membranes' rejection characteristics. Altering casting conditions such as polymer concentration in the casting solution and the quenching-bath composition and/or temperature allowed control of the molecular weight cut-off (MWCO). Three MWCOs; 300, 350, and 700 Da have been achieved for non-linear molecules. Molecular shape is also very important as much higher molecular weight single-stranded DNA was electrophoresed across the membranes while heme with a similar negative charge density was rejected. This was due to DNA's small molecular cross section. This is an important result because heme inhibits polymerase chain reactions (PCR) reducing the detection and characterization of DNA from blood samples.     

Continuous flow structuring of anisotropic biopolymer particles

We review concepts and provide examples for the controlled structuring of biopolymer particles in hydrodynamic flow fields. The structuring concepts are grouped by the physical mechanisms governing drop deformation and shaping: (i) capillary structuring, (ii) shear and elongational structuring and (iii) confined flow methods. Non-spherical drops can be permanently structured if a solidification process, such as gelation or glass formation in the bulk or at the interface, is superimposed to the flow field. The physical and engineering properties of these processes critically depend on an elaborate balance between capillary phenomena, rheology, gel or glass formation kinetics, and bulk heat, mass and momentum transfer in multiphase fluids. This overview is motivated by the potential of non-spherical suspension particles, in particular those formed from ‘natural’ and ‘sustainable’ biopolymers, as rheology modifiers in food materials, consumer products, cosmetics or pharmaceuticals.     

Zirconium-phosphate-fluoride gels

Summary The volume of amorphous zirconium phosphate precipitates formed in acid solutions (pH=0–2) is increased many times by the action of fluoride (hydrofluoric acid). At fluoride concentrations corresponding to a maximum precipitate volume, the particles slowly (during several days) coalesce to form a semi-solid gel.Dedicated to Univ. Prof. Dr.O. Olaj, University of Vienna, on the occasion of his 60^th birthday     

Interaction between components of plant-based biopolymer systems

Proteins and polysaccharides are key elements in formulated foods, cosmetics, and pharmaceuticals. Their interaction behavior mainly determines the organoleptic, optical, textural, and rheological properties of foods. Traditionally, animal-based biopolymers have been widely used because of their excellent techno-functionality; however, plant-based alternatives gained enormous interest among scientists and manufacturers because of sustainable, religious, ethical, and nutritional reasons. The directed complexation of mixed biopolymers entirely originated from plants might be used to stabilize food colloids, modulate interfacial and bulk properties, control the release of bioactives, and mask bitter components. As such, this review highlights the general separation mechanism of mixed biopolymers systems entirely composed of plant-based biopolymers to be used as functional food ingredients. Particularly, ‘traditional’ and ‘novel’ proteins and polysaccharides obtained from different plant sources (e.g. soy, wheat, pea, potato, apple, citrus) are introduced to be assembled to modulate interfacial and bulk properties of food colloids.     

The biopolymer bacteriorhodopsin in optical data processing

Bacteriorhodopsin (BR) from Halobacterium halobium [1] is embedded as a twodimensional crystalline lattice of BR-trimers in the lipid bilayer of the cell membrane [2]. BR consists of a single polypeptide chain of 248 amino acids which is arranged in seven transmembrane α-helices. A retinal molecule bound via a Schiff base to lysine-216 forms the chromophoric group [3]. Under illumination BR creates a proton gradient across the cell membrane which is used by a membrane-bound ATP-ase for ATP synthesis [4].     

Towards an action principle governing biopolymer foldingin vitro

The exploration of conformation space performed by biopolymers is biased towards a confined region. This property is paramount in providing theoretical underpinnings of the time constrained nature of folding. By introducing anaction principle in the space of folding pathways, we show how the folding process is guided expeditiously within realistic time frames.     

Sol‐gel transition of biopolymer dispersions

Sol‐gel transition of dispersions of biopolymers, which are used widely in food, cosmetics, biomedical and related industries, is classified by the temperature dependence of storage shear modulus. Sol‐gel transition of gellan gum solution is described well by a criterion of Winter‐Chambon. Too fast gelation of dispersions of konjac glucomannan in the presence of excessive amount of alkaline coagulant and/or at higher temperatures leads to a formation of gels with lower modulus. A solution of xyloglucan from which a certain amount of galactose residues is removed forms a gel on heating and reverts into a solution on further heating. The lower temperature transition of this xyloglucan solution is induced by hydrophobic interaction.     

Anion-responsive supramolecular gels

Supramolecular gels that change their state or structure in response to anion stimuli have been highlighted. Only a few examples exist of such supramolecular gels, the structures and properties of which can be controlled and modulated by interactions with anions. To form anion-responsive dimensionally-controlled organized structures, the constituent low-molecular-weight gelator molecules must act as anion receptors by possessing one or more of van der Waals interaction units (aliphatic chains), stacking pi planes, hydrogen-bonding sites, and metal-coordination units. This Concept focuses on the gelation and transition behaviors of amide- and urea-based anion-stimulated systems, metal-coordinated systems, and novel acyclic pi-conjugated oligopyrroles that act as "molecular flippers."     

Inhomogeneous triplet absorption in 1,4-dibromonaphthalene

Additional information is obtained on the nature of the inhomogeneously broadened lowest triplet absorption of 1,4-dibromonaphthalene. The presence of different absorptions is demonstrated by measurements on the delayed fluorescence and phosphorescence emission.     

Anisotropic agarose gels

Agarose hydrogels deswell reversibly over a wide range of concentration. Two types of deswelling measurements are considered here, isotropic and uniaxial. We describe some of the properties of the gels observed in the deswollen state. In both the isotropic and uniaxial geometry, the swelling pressure varies approximately as the square of the concentration.