Polyacrylate glue protein analogs of the glue secreted by Phragmatopoma californica, a marine po synthesized with phosphate, primary amine, and catechol sidechains with molar ratios similar to th proteins. Aqueous mixtures of the mimetic polyelectrolytes condensed into liquid complex coacerv neutral pH. Wet cortical bone specimens bonded with the coacervates, oxidatively crosslinked thro sidechains, had bond strengths nearly 40% of the strength of a commercial cyanoacrylate. The uniq properties of complex coacervates may be ideal for development of clinically useful adhesives and biomaterials.

A brief overview of the principles and associated instrumentation used to monitor polymerization reactions by automatic continuous online monitoring of polymerization reactions (ACOMP) is presented. ACOMP can be used as an analytical method in R&D, as a tool for reaction optimization at the bench and pilot plant level and, eventually, for feedback control of full-scale reactors. ACOMP measures in a model-independent fashion the evolution of average molar mass and intrinsic viscosity, monomer conversion kinetics and, in the case of copolymers, also the average composition drift and distribution. A summary of areas of ACOMP application is given, which include free radical and controlled radical homo- and copolymerization, polyelectrolyte synthesis, heterogeneous phase reactions, including emulsion polymerization, adaptation to batch and continuous reactors, and modifications of polymers. Finally, a brief sketch of two novel complementary methods is given: automatic continuous mixing (ACM) and simultaneous multiple sample light scattering (SMSLS). Copyright ? 2007 Society of Chemical Industry

Unstable biopolymer solutions inevitably lead to mis-characterization of macromolecular properties and irreproducible results. Even under stable or quasi-stable conditions, persistent aggregates can hamper reliable characterization, especially using light scattering methods. Various pitfalls in characterizing biopolymers were worked through, including determination of solution stability zones, dissolution kinetics, estimation of fraction of aggregate populations, and the relationship between batch and fractionation methods. Chitosans, polyampholytic biopolymers with isoelectric point around pH = 6.0, with varying degrees of carboxymethylation were studied. Instability was determined vs. pH and ionic strength using a high throughput screening method, simultaneous multiple sample light scattering (SMSLS). With stable solution conditions determined, equilibrium batch and multi-detector GPC characterization of molecular weight, intrinsic viscosity, and polyelectrolyte properties was made. Finally, a first attempt at continuous online monitoring of the modification reaction itself was made and compared to FTIR analysis of carboxymethylation on discrete aliquots. Given the range of possible characterization problems, multiple approaches with independent instruments may be required for reliable natural product characterization. Online monitoring of modification reactions may lead to rapid advances in understanding and preparation of natural products.

Using automatic, continuous online monitoring of polymerization reactions (ACOMP) the final, divergent growth phase (FDGP) of the condensation polymerization of dimethylamine, epichlorohydrin, and ethylenediamine was monitored, which produced a highly ramified, polyelectrolytic polyamine. The weight average mass, Mw, increased exponentially during the FDGP, whereas weight averaged intrinsic viscosity [η]w increased slowly, reaching a plateau. Multi-detector gel permeation chromatography (GPC) revealed that polymers of mass 20?000 to 106 are branched and self-similar, but above this mass, [η] increases less strongly with M. This appears to be due to higher order ramification, a precursor to gelation. The ACOMP trends in Mw and [η]w provide direct online evidence of this process. It is shown computationally that a mere increase in polydispersity cannot explain this behavior. GPC showed the mass distribution becomes highly asymmetric as conversion increases. A plausible kinetic model for the distribution asymmetry is introduced, and a complementary model for the effects of higher order ramification on [η]w.

In situ near infrared (NIR) spectroscopy is performed simultaneously with automatic continuous online monitoring of polymerization reactions (ACOMP) during methyl methacrylate polymerization. ACOMP is an absolute technique that furnishes weight average molecular mass Mw, intrinsic viscosity, monomer conversion, and other characteristics, whereas NIR furnishes monomer conversion data via an empirical calibration. An advantage of in situ NIR is that it furnishes immediate information on the conversion in the reactor, whereas ACOMP relies on continuous withdrawal and dilution of a small stream of reactor fluid, so that there is a lag time of several minutes between what ACOMP reports and what is occurring in the reactor. Simultaneous monomer conversion data from in situ NIR and ACOMP, the latter derived from both refractive index and UV absorption, are compared and found to be in good agreement. The evolution of conversion kinetics and Mw generally conform to the predictions of the Quasi-Steady State Approximation. Having established the agreement between the methods, the path is now open for combining NIR with ACOMP to characterize increasingly complex systems, such as copolymerization with two or more monomeric species, that are not feasible by either technique separately.

ACOMP allows comprehensive, model-independent, near realtime monitoring of many different types of polymerization reactions. It provides conversion kinetics, and the evolution of average molar mass, intrinsic viscosity and average composition distributions (for copolymers). Here, recent advances in ACOMP will be summarized, dealing with continuous reactors, copolymerization, ‘living’ type reactions (NMP, RAFT, ATRP, ROMP), polyelectrolytes, heterogeneous phase reactions, including free radical reactions in emulsions, and predictive control. In the case of emulsion polymerization, a new approach will be presented in which the evolution of the characteristics of both the soluble phase – monomer conversion, polymer molar mass and intrinsic viscosity- and the dispersed phase – particle size – are simultaneously monitored. NSF CBET 0623531, BoR ITRS 019B, NASA NCC3-946, TIMES, PolyRMC (Tulane Center for Polymer Reaction Monitoring and Characterization).

This paper investigates the feasibility of arsenate removal by aggregated metal oxide nanoparticle media in packed bed columns. Batch experiments conducted with 16 commercial nanopowders in four water matrices were used to select a metal oxide nanoparticle that both amply removes arsenate and can be aggregated using an inert binder. TiO2, Fe2O3, ZrO2 and NiO nanopowders, which exhibited the highest arsenate removal in all water matrices, were characterized with fitted Freundlich adsorption isotherm (View the MathML source) parameters. In 10 mM NaHCO3 buffered nanopure water and at both pH ≈ 6.7 and 8.4, K ranged from 1.3 to 12.09 (mg As/g(media)) (L/mg As)1/n, and 1/n ranged from 0.21 to 0.52. Under these conditions, the fitted Freundlich isotherm parameters for TiO2 nanoparticles aggregated with inorganic and organic binders (K of 4.75–28.45 (mg As/g(media)) (L/mg As)1/n and 1/n of 0.37–0.97) suggested favorable arsenate adsorption. To demonstrate that aggregated nanoparticle media would allow rapid mass transport of arsenate in a fixed bed adsorber setting, short bed adsorber (SBA) tests were conducted on TiO2 nanoparticle aggregates at empty bed contact times (EBCT) of 0.1–0.5 min and Re × Sc = 1000 and 2000. These SBA tests suggested that the binder has a negligible role in adsorbing arsenic and that mass transport is controlled by rapid intraparticle diffusion rather than external film diffusion.

A series of new aggregation-induced emission enhancement derivatives from bis(triphenylethylene) with strong blue-light-emitting properties and high thermal stability have been synthesized. Their maximum fluorescence emission wavelengths range between 464–468 nm, with fluorescence quantum yields of 0.58–0.88. Their glass transition temperatures range from 125 °C to 178 °C. The obtained experimental results demonstrate the different aggregation-induced emission enhancement phenomena caused by the effect of solvent and formation of both H- and J- aggregation states. An emitting device was fabricated using a bis(triphenylene) derivative in the emitting layer which exhibited a luminance efficiency of up to 2 cd/A with a maximum brightness of 548 cd/m2.

Sol?gel materials are often reinforced through the addition of particulate fillers to improve their mechanical properties, such as toughness or stiffness. Related studies of filled polymeric materials suggest that the effectiveness of added reinforcements may depend sensitively on the state of particulate aggregation in the composites. In some systems and situations, aggregates are found to enhance properties, while in others they are deleterious. The objective of the present study was to determine the effect of state of aggregation of alumina nanoparticle fillers on the mechanical properties of a GPS sol?gel hybrid composite. Aggregates of different sizes were produced at loadings of 3.6, 7.5, and 16.8 volume percent in the GPS sol?gel monoliths by inducing aggregation through the addition of varying amounts of tetrasodium pyrophospate (TSPP). The small amounts of TSPP required to induce varying states of aggregation did not affect the properties of the gel in the absence of the particles. Unaggregated particles or small aggregates were found to impart significant improvements in the mechanical properties of the gel, but at a particular critical aggregate size and beyond, the cured material cracked and crumbled. The critical size was found to correspond roughly to an effective aggregate volume fraction of 0.64 in the final composite, suggestive of a randomly close-packed aggregate structure.

Oxygen-transfer enhancement has been observed in the presence of colloidal dispersions of magnetite (Fe3O4) nanoparticles coated with oleic acid and a polymerizable surfactant. These fluids improve gas?liquid oxygen mass transfer up to 6-fold (600%) at nanoparticle volume fractions below 1% in an agitated, sparged reactor and show remarkable stability in high-ionic strength media over a wide pH range. Through a combination of experiments using physical and chemical methods to characterize mass transfer, it is shown that (i) both the mass transfer coefficient (kL) and the gas?liquid interfacial area (a) are enhanced in the presence of nanoparticles, the latter accounting for a large fraction of the total enhancement (80% or more), (ii) the enhancement in kL measured by physical and chemical methods is similar and ranges from 20 to 60% approximately, (iii) the enhancement in kL levels off at a nanoparticle volume fraction of approximately 1% v/v, and (iv) the enhancement in kLa shows a strong temperature dependence. These results are relevant to a wide range of processes limited by the mass transfer of a solute between a gas phase and a liquid phase, such as fermentation, waste treatment, and hydrogenation reactions.

Targeted delivery of therapeutics possesses the potential to localize therapeutic agents to a specific tissue as a mechanism to enhance treatment efficacy and abrogate side effects. Antibodies have been used clinically as therapeutic agents and are currently being explored for targeting drug-loaded nanoparticles. Peptides such as RGD peptides are also being developed as an inexpensive and stable alternative to antibodies. In this study, cyclo(1,12)PenITDGEATDSGC (cLABL) peptide was used to target nanoparticles to human umbilical cord vascular endothelial cell (HUVEC) monolayers that have upregulated intercellular cell-adhesion molecule-1 (ICAM-1) expression. The cLABL peptide has been previously demonstrated to possess high avidity for ICAM-1 receptors on the cell surface. Poly(dl-lactic-coglycolic acid) nanoparticles conjugated with polyethylene glycol and cLABL demonstrated rapid binding to HUVEC with upregulated ICAM-1, which was induced by treating cells with the proinflammatory cytokine, interferon-γ. Binding of the nanoparticles could be efficiently blocked by preincubating cells with free peptide suggesting that the binding of the nanoparticles is specifically mediated by surface peptide binding to ICAM-1 on HUVEC. The targeted nanoparticles were rapidly endocytosed and trafficked to lysosomes to a greater extent than the untargeted PLGA-PEG nanoparticles. Verification of peptide-mediated nanoparticle targeting to ICAM-1 may ultimately lead to targeting therapeutic agents to inflammatory sites expressing upregulated ICAM-1.

Oxygen-transfer enhancement has been observed in the presence of colloidal dispersions of magnetite (Fe3O4) nanoparticles coated with oleic acid and a polymerizable surfactant. These fluids improve gas-liquid oxygen mass transfer up to 6-fold (600%) at nanoparticle volume fractions below 1% in an agitated, sparged reactor and show remarkable stability in high-ionic strength media over a wide pH range. Through a combination of experiments using physical and chemical methods to characterize mass transfer, it is shown that (i) both the mass transfer coefficient (kL) and the gas-liquid interfacial area (a) are enhanced in the presence of nanoparticles, the latter accounting for a large fraction of the total enhancement (80% or more), (ii) the enhancement in kL measured by physical and chemical methods is similar and ranges from 20 to 60% approximately, (iii) the enhancement in kL levels off at a nanoparticle volume fraction of approximately 1% v/v, and (iv) the enhancement in kLa shows a strong temperature dependence. These results are relevant to a wide range of processes limited by the mass transfer of a solute between a gas phase and a liquid phase, such as fermentation, waste treatment, and hydrogenation reactions.

Background Gene delivery vectors that restrict the expression of a therapeutic gene to a particular type of cells are critical to gene therapy in a complex structure, such as the central nervous system. We constructed a nonviral vector for targeted gene transfer to cells expressing nerve growth factor (NGF) receptor TrkA. Methods and results The vector was a synthetic chimeric peptide composed of a targeting moiety derived from NGF loop 4 and a DNA-binding moiety of 10 lysine residues. The peptide activated signal transduction pathways of the NGF receptor TrkA in PC12 cells and supported the survival of the cells after serum deprivation. After forming complexes with plasmid DNA, the peptide dose-dependently increased reporter gene expression in PC12 cells, which could be inhibited by excess NGF. The peptide-mediated gene expression was not affected in PC12 cells by co-incubation with a blocking antibody against the low-affinity NGF receptor p75 and was significantly enhanced in NIH3T3 cells stably transfected with TrkA cDNA, suggesting the involvement of the high-affinity NGF receptor TrkA without the participation of p75. Moreover, the peptide did not assist gene transfer in TrkA-poor, but TrkB- and/or TrkC-positive primary cerebellar granule neurons and primary cortical glial cells. Conclusions The chimeric peptide reported will be useful in gene delivery to and gene therapy of the nervous system and other tissues/organs with cells expressing TrkA.

The zeta-potentials of the self-assembled surface ionic surfactants (sodium dodecyl sulfate—SDS and hexadecyltrimethyl ammonium bromide—CTAB) on graphite surfaces were determined both from streaming potential and electrophoretic mobility measurements. The adsorption of the surfactants at graphite–liquid interfaces has been studied using atomic force microscopy (AFM) soft-contact imaging which shows the formation of linear, parallel hemicylinders with headgroups oriented towards the solution. The magnitude of the zeta-potential increased with an increase in surfactant concentration, reaching a constant value at a concentration corresponding to the point of surface micelle formation as confirmed from AFM imaging. The streaming potential and electrophoretic mobility measurements showed that the zeta-potentials of SDS and CTAB surface micelles adsorbed at the graphite surface were about ?75 and +70 mV, respectively, well in agreement with the values reported for bulk phase micelles in the literature.

To optimize 19F MR tracking of stem cells, we compared cellular internalization of cationic and anionic perfluoro-15-crown-5-ether (PFCE) nanoparticles using cell culture plates with different surface coatings. The viability and proliferation of anionic and cationic PFCE-labeled neural stem cells (NSCs) did not differ from unlabeled cells. Cationic PFCE nanoparticles (19F T1/T2= 580/536 ms at 9.4T) were superior to anionic particles for intracellular fluorination. Best results were obtained with modified polystyrene culture dishes coated with both carboxylic and amino groups rather than conventional carboxyl-coated dishes. After injecting PFCE-labeled NSCs into the striatum of mouse brain, cells were readily identified in vivo by 19F MRI without changes in signal or viability over a 2-week period post-grafting. These results demonstrate that neural stem cells can be efficiently fluorinated with cationic PFCE nanoparticles without using transfection agents and visualized in vivo over prolonged periods with an MR sensitivity of approximately 140 pmol of PFCE/cell.

We developed a novel method to fabricate nanocomposite monodisperse SiO2 spheres (～100 nm) containing homogeneously dispersed Ag quantum dots (2～5 nm). The inclusion morphology is controlled through the timing of the photochemical reduction of silver ions during hydrolysis of tetraethoxysilane in a microemulsion. Depending on the timing, Ag quantum dots can be directed to different annuli within the SiO2 spheres, as well as onto the SiO2 sphere surfaces. The embedded Ag quantum dots show a plasmon resonance absorption band at 438 nm. These Ag@SiO2 particles have significant surface charge and readily self-assemble into crystalline colloidal array (CCA) photonic crystals which Bragg-diffract light in the visible region. The magnitude of the plasmon resonance absorption depends on the CCA Bragg diffraction condition. The negative dielectric constant of the silver nanoparticles may be decreasing the silica?silver nanodot composite refractive index below that of the water medium. We may be observing an analogue of the Borrmann effect previously observed in X-ray scattering, where the incident and diffracted electric field standing wave becomes localized in regions of small CCA crystal absorption.

The expansion of various rice starches in solution was studied using dynamic light scattering (DLS) in order to provide information on their microstructure. Hydrodynamic diameters of starch molecules were found to change with solvent conditions. The component starches in the rice varieties studied had similar sizes in pure water (between 125 and 235 nm), but showed different expansion behaviour with changes in salt concentration, with addition of urea (which disrupts hydrogen bonding) and with the addition of 1-butanol (which reduces solvent polarity). Some starches showed a gradually increasing size with increasing [NaCl], while others showed an initial steep increase followed by more gradual behaviour. The size distributions from DLS indicated two (and possibly three) components at about 100 and 1000 nm. The larger component was largely responsible for the expansion with added salt, an effect which is ascribed to the greater ability of larger chains to expand. Chain length distributions (CLD) of debranched starch from the same samples were examined by capillary electrophoresis (CE) for correlation with the expansion behaviour obtained by DLS. The ratio of shorter to longer chains partly correlated with the classes of expansion behaviour. The data suggest that the expansion behaviour is sensitive to the branching structure (connectivity) as well as to the distribution of the lengths of the branches.

It has been shown that starch can effectively stabilize nanoscale magnetite particles, and starch-stabilized magnetite nanoparticles (SMNP) are promising for in situ remediation of arsenic-contaminated soils. However, a molecular level understanding has been lacking. Here, we carried out XAFS studies to bridge this knowledge gap. Fe K-edge XAFS spectra indicated that the Fe–O and Fe–Fe coordination numbers of SMNP were lower than those for bare magnetite particles, and these coordination numbers decreased with increasing starch concentration. The decrease in the average coordination number at elevated stabilizer concentration was attributed to the increase in the surface-to-volume ratio. Arsenic K-edge XAFS spectra indicated that adsorbed arsenate on SMNP consisted primarily of binuclear bidentate (BB) complexes and monodentate mononuclear (MM) complexes. More BB complexes (energetically more favorable) were observed at higher starch concentrations, indicating that SMNP not only offered greater adsorption surface area, but also stronger adsorption affinity toward arsenate.

Effects of 360-kHz ultrasound on aqueous solutions of chitosan and starch were studied. This treatment is an efficient procedure for reduction of molecular weight of both polysaccharides. It has been demonstrated that at the applied ultrasound frequency degradation is caused both by OH radicals and mechanochemical effects. In Ar-saturated 2×10?2 mol dm?3 chitosan solutions, pH 3, at an ultrasound dose rate of 170 W kg?1, the average sonochemical chain scission yield in the sonication time range of 0–90 min is ca. 8×10?11 mol J?1. This yield has been shown to depend on polymer concentration, ultrasound power and gas used to saturate the solution. Scission is accompanied by side reactions leading to the formation of carbonyl groups. Ultrasound-induced chain scission of starch proceeds with lower yield, one of the reasons being probably the different chain conformation when compared with rod-like chitosan macromolecules.

A novel citric acid (CA)–glycerol co-plasticized thermoplastic starch (CGTPS) was prepared by melt blending. The CA content varies from 10% to 40 wt%. Result from Fourier Transform Infrared spectroscopy (FTIR) show that partial esterification occurred during blending. The degrees of substitution and esterification increased as the CA content increased. Results from intrinsic viscosity measurement, laser light scattering (LLS), and FTIR demonstrate the molecular weight of starch decreased as the CA percentage increased. The weight average molecular weight (Mw) of CGTPS with 20 wt% CA was only one-tenth of that without CA under the same processing conditions. Crystal type and crystallinity changes as a function of CA were recorded by X-ray diffraction (XRD). Thermal stability and the glass transition temperature (Tg) were detected by thermogravimetric (TG) and differential scanning calorimeter (DSC). Compared to the traditional GTPS, the novel CGTPS exhibits the special characters of partial esterification, low molecular weight and stronger interaction between starch and plasticizers. These new properties can be expected to prevent retrogradation, promote compatibility with polyesters, improve the processing ability, and adjust the degradation properties.

Novel cationic hydroxyethyl cellulose (HEC) polymers with different molecular weights (1.1 × 105 to 1.7 × 106 g/mol) and ethylene oxide (EO) side chain lengths (1.5?2.9 EO units) were mixed with sodium dodecyl sulfate (SDS) in aqueous solutions. The phase diagrams of cationic HEC?SDS complexes were determined in the dilute polymer concentration regime (<0.5 wt %) with gradual addition of SDS molecules. The viscosity and structures of the complexes during the phase evolution were studied using rheometry and dynamic light scattering. The gradual addition of SDS first induced interchain associations with the bound SDS aggregates serving as cross-linkers to form an open network structure, producing a very broad size distribution and high viscosities of the complex solutions, and then condensed the network and induced a structure reorganization, resulting in globular aggregates with narrow size distributions. The growth of these globular aggregates in size eventually led to macroscopic sedimentation near charge neutralization. Further addition of SDS randomly broke the sedimentary aggregates into small particles and SDS micelles with low solution viscosities. The effects of molecular weight and EO side chain length of polymers on the phase boundary, viscosity, and structure of cationic HEC?SDS complexes were discussed.

It has been shown that starch can effectively stabilize nanoscale magnetite particles, and starch-stabilized magnetite nanoparticles (SMNP) are promising for in situ remediation of arsenic-contaminated soils. However, a molecular level understanding has been lacking. Here, we carried out XAFS studies to bridge this knowledge gap. Fe K-edge XAFS spectra indicated that the FeeO and FeeFe coordination numbers of SMNP were lower than those for bare magnetite particles, and these coordination numbers decreased with increasing starch concentration. The decrease in the average coordination number at elevated stabilizer concentration was attributed to the increase in the surface-to-volume ratio. Arsenic K-edge XAFS spectra indicated that adsorbed arsenate on SMNP consisted primarily of binuclear bidentate (BB) complexes and monodentate mononuclear (MM) complexes. More BB complexes (energetically more favorable) were observed at higher starch concentrations, indicating that SMNP not only offered greater adsorption surface area, but also stronger adsorption affinity toward arsenate.

ABSTRACT: Amphiphilic diblock copolymers were synthesized based on poly(2-ethyl-2-oxazoline) (PEtOz) as a hydrophilic block and aliphatic polyesters such as poly(L-lactide) (PLA) or poly(-caprolactone) (PCL) as a hydrophobic block. Their micellar characteristics in an aqueous phase were investigated by using dynamic light scattering and fluorescence techniques. The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (cmcs) in the range of 1.0-8.1 mg/L. The cmc values become lower upon increasing the length of the hydrophobic block. The mean diameters of the micelles were in the range of 108-192 nm, with a narrow distribution. In general, the micelle size increased as the hydrophobic PLA or PCL block became larger. The partition equilibrium constants, Kv, of pyrene in the micellar solutions of the block copolymers were from 1.79  105 to 5.88  105. For each block copolymer system of PEtOz-PLA or PEtOz-PCL, the Kv value increased as the length of the hydrophobic block increased. The steady-state fluorescence anisotropy values (r) of 1,6-diphenyl-1,3,5-hexatriene (DPH) were 0.265-0.284 in PEtOz-PLA solution and 0.189-0.196 in PEtOz-PCL solution. The anisotropy values of PEtOz-PLAs were higher than those of PEtOz-PCLs. The anisotropy values were independent of the length of the hydrophobic block when the chemical structures of the hydrophobic blocks were identical. The micelles underwent hydrogen bonding at pH <3.5 with poly(acrylic acid), which produced polymer complex precipitates that could be reversibly dispersed as micelles at pH >3.8.

Lipid-conjugated polysaccharide vesicles in nano- and micro-scale were developed from amphiphilic octadecanol-modified dextrans (OMD) prepared by partial esterification of dextran with activated octadecanol-carbamate imidazole in a well-controlled manner. The critical aggregation concentration (CAC) of OMD adducts in aqueous phase varies, depending mainly on their octadecanol contents. Through supramolecular assembly of the OMD adducts comprising either 17 or 28 mol% octadecanol residues with respect to the anhydroglucopyranose units by the partial solvent displacement technique with the initial water content of DMSO/H2O solutions beyond a critical point, stable nano-scaled OMD assemblies were developed and characterized by the vesicle-like morphology. The dimension of polymersomes can be effectively controlled by the OMD composition as well as the initial water content. On the other hand, micro-scaled OMD polymersomes can be achieved by the double emulsion technique in a water/oil/water (w1/o/w2) manner. Both the contents of NaCl in aqueous solution as the w1 phase and of DMSO in DMSO/CHCl3 co-solvents as the organic phase, in which OMD was dissolved, are of great importance in controlling the polymersome morphology and size. These micro-scaled OMD polymersome walls are characterized by size-selective permeability capable of encapsulating large water-soluble cargoes while allowing transport of small polar species across the membrane, thereby rendering these unique colloidal particles of potential applications in biomedical technologies.

Effects of 360-kHz ultrasound on aqueous solutions of chitosan and starch were studied. This treatment is an efficient procedure for reduction of molecular weight of both polysaccharides. It has been demonstrated that at the applied ultrasound frequency degradation is caused both by OH radicals and mechanochemical effects. In Ar-saturated 2!10K2 mol dmK3 chitosan solutions, pH 3, at an ultrasound dose rate of 170 W kgK1, the average sonochemical chain scission yield in the sonication time range of 0–90 min is ca. 8!10K11 mol JK1. This yield has been shown to depend on polymer concentration, ultrasound power and gas used to saturate the solution. Scission is accompanied by side reactions leading to the formation of carbonyl groups. Ultrasound-induced chain scission of starch proceeds with lower yield, one of the reasons being probably the different chain conformation when compared with rod-like chitosan macromolecules. q 2004 Elsevier Ltd. All rights reserved.

Corn starch of different physical forms (solid and liquid) was irradiated with 60Co gamma rays and electron beam in the dose range of 50 Gy to 100 kGy to investigate the effect of ionizing radiation on its molecular weight (Mw). Degradation was observed for both solid and liquid states upon radiation. However, degradation of the starch in the liquid state was remarkably greater than that in the solid state. The free radicals that formed during water irradiation must be responsible for such degradation in the liquid form. Thermostated viscometer, rheometer and multi-angle static laser light scattering were employed to study the changes in the Mw of corn starch that occurred during irradiation at constant temperature and different concentrations. It was observed that electron beam irradiated corn starch has uniform decreasing in Mw and radius of gyration (Rg) in the range of (4.4
107–2.9
107 g mol21) and (199.3–85.6 nm), respectively. The influence of gas atmosphere on the degradation process during gamma irradiation was studied to find that, theMw and Rg values were in the range of (4.4
107–1.8
107 g mol21) and (199.3–120.4 nm) for the oxygen saturated samples, while, they were (4.4
107–1.05
107 g mol21) and (199.3–85.6 nm) for the argon saturated samples.

The aggregation kinetics of silver nanoparticles (AgNPs) that were coated with two commonly use agents—citrate and polyvinylpyrrolidone (PVP)—were investigated. Time-resolved dynamic light (DLS) was employed to measure the aggregation kinetics of the AgNPs over a range of monovalen electrolyte concentrations. The aggregation behavior of citrate-coated AgNPs in NaCl was in excel with the predictions based on Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, and the Ham of citrate-coated AgNPs in aqueous solutions was derived to be 3.7 × 10 J. Divalent electrolytes efficient in destabilizing the citrate-coated AgNPs, as indicated by the considerably lower critical c concentrations (2.1 mM CaCl and 2.7 mM MgCl vs. 47.6 mM NaCl). The PVP-coated AgNPs w significantly more stable than citrate-coated AgNPs in both NaCl and CaCl , which is likely due to repulsion imparted by the large, non-charged polymers. The addition of humic acid resulted in the the macromolecules on both citrate- and PVP-coated AgNPs. The adsorption of humic acid induce electrosteric repulsion that elevated the stability of both nanoparticles in suspensions containing Na concentrations of CaCl . Conversely, enhanced aggregation occurred for both nanoparticles at high concentrations due to interparticle bridging by humic acid clusters.

The emulsion droplet solvent evaporation method has been used to prepare nanoclusters of monodisperse magnetite nanoparticles of varying morphologies depending on the temperature and rate of solvent evaporation and on the composition (solvent, presence of polymer, nanoparticle concentration, etc.) of the emulsion droplets. In the absence of a polymer, and with increasing solvent evaporation temperatures, the nanoparticles formed single- or multidomain crystalline superlattices, amorphous spherical aggregates, or toroidal clusters, as determined by the energetics and dynamics of the solvent evaporation process. When polymers that are incompatible with the nanoparticle coatings were included in the emulsion formulation, monolayer- and multilayer-coated polymer beads and partially coated Janus beads were prepared; the nanoparticles were expelled by the polymer as its concentration increased on evaporation of the solvent and accumulated on the surfaces of the beads in a well-ordered structure. The precise number of nanoparticle layers depended on the polymer/magnetic nanoparticle ratio in the oil droplet phase parent emulsion. The magnetic nanoparticle superstructures responded to the application of a modest magnetic field by forming regular chains with alignment of nonuniform structures (e.g., toroids and Janus beads) that are in accord with theoretical predictions and with observations in other systems.

Static light scattering of high amylopectin waxy maize starch gently dispersed in 90% dimethyl sulfoxide–water yielded a weight average molecular weight Mw and radius of gyration Rg of 560×106 g/mol and 342 nm, respectively. To obtain an independent hydrodynamic characterization of these solutions, we measured the sedimentation coefficient for the main component in an analytical ultracentrifuge. The value of s0, the infinite dilution sedimentation coefficient, was 199 S. The translational diffusion coefficient D0 in very dilute solutions was measured by dynamic light scattering at 90° and found to be 2.33×10-9 cm2/s. An effective hydrodynamic radius Rh was calculated from this diffusion constant using the Stokes–Einstein equation and found to be 348 nm. The structure-related parameter ρ=Rg/Rh was calculated to be 0.98. The weight average molecular weight calculated from the Svedberg equation using the values measured for s0 and D0 was 593×106 g/mol. This result is in reasonable agreement with the light scattering results. As light scattering results are subject to experimental errors due to the possibility of dust contamination, the presence of microgel or aggregates, and the questionable applicability of light scattering theory to interpret results for macromolecular sizes approaching the wave length of light used as a source for scattering, it is advisable to have corroborating hydrodynamic data when possible to further validate light scattering results in this very high molecular weight range.

Porous cross-linked enzyme aggregates (p-CLEAs) were prepared by adding starch as a pore-making agent, which facilitates CLEAs in cases where the substrates of enzyme are macromolecules. This novel strategy for preparation of p-CLEAs involves co-precipitation, cross-linking and removal of starch by α-amylase. The resulting papain p-CLEAs were characterized by scanning electron microscope (SEM) images, showing a porous structure. The 95.9% and 90.4% increased catalytic efficiencies of p-CLEAs than conventional CLEAs on bovine serum albumin (BSA) and ovalbumin verified the feasibility of this protocol.