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Hydrodynamic Diameter (hydrodynamic + diameter)
Selected AbstractsDelivery of Nucleic Acids through the Controlled Disassembly of Multifunctional NanocomplexesADVANCED FUNCTIONAL MATERIALS, Issue 24 2009Mahmoud Elsabahy Abstract In this study, novel pH-responsive polyion complex micelles (PICMs) were developed for the efficient delivery of nucleic acid drugs, such as antisense oligonucleotide (AON) and short interfering RNA (siRNA). The PICMs consisted of a poly(amidoamine) (PAMAM) dendrimer,nucleic acid core and a detachable poly(ethylene glycol)- block -poly(propyl methacrylate- co -methacrylic acid) (PEG- b -P(PrMA- co -MAA)) shell. The micelles displayed a mean hydrodynamic diameter ranging from 50 to 70,nm, a narrow size distribution, and a nearly neutral surface charge. They could be lyophilized without any additives and stored in dried form. Upon redispersion in water, no change in complexation efficiency or colloidal properties was observed. Entry of the micelles into cancers cells was mediated by a monoclonal antibody fragment positioned at the extremity of the PEG segment via a disulfide linkage. Upon cellular uptake and protonation of the MAA units in the acidic endosomal environment, the micelles lost their corona, thereby exposing their positively charged endosomolytic PAMAM/nucleic acid core. When these pH-responsive targeted PICMs were loaded with AON or siRNAs that targeted the oncoprotein Bcl-2, they exhibited a greater transfection activity than nontargeted PICMs or commercial PAMAM dendrimers. Moreover, their nonspecific cytotoxicity was lower than that of PAMAM. The pH-responsive PICMs reported here appear as promising carriers for the delivery of nucleic acids. [source] Generic Strategy of Preparing Fluorescent Conjugated-Polymer-Loaded Poly(DL -lactide- co -Glycolide) Nanoparticles for Targeted Cell ImagingADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Kai Li Abstract A general strategy for the preparation of highly fluorescent poly(DL-lactide- co -glycolide) (PLGA) nanoparticles (NPs) loaded with conjugated polymers (CPs) is reported. The process involves encapsulation of organic-soluble CPs with PLGA using a modified solvent extraction/evaporation technique. The obtained NPs are stable in aqueous media with biocompatible and functionalizable surfaces. In addition, fluorescent properties of the CP-loaded PLGA NPs (CPL NPs) could be fine-tuned by loading different types of CPs into the PLGA matrix. Four types of CPL NPs are prepared with a volume-average hydrodynamic diameter ranging from 243 to 272,nm. The application of CPL NPs for bio-imaging is demonstrated through incubation with MCF-7 breast cancer cells. Confocal laser scanning microscopy studies reveal that the CPL NPs are internalized in cytoplasm around the nuclei with intense fluorescence. After conjugation with folic acid, cellular uptake of the surface-functionalized CPL NPs is greatly enhanced via receptor-mediated endocytosis by MCF-7 breast cancer cells, as compared to that for NIH/3T3 fibroblast cells, which indicates a selective targeting effect of the folate-functionalized CPL NPs in cellular imaging. The merits of CPL NPs, such as low cytotoxicity, high fluorescence, good photostability, and feasible surface functionalization, will inspire extensive study of CPL NPs as a new generation of probes for specific biological imaging and detection. [source] Superparamagnetic Hyperbranched Polyglycerol-Grafted Fe3O4 Nanoparticles as a Novel Magnetic Resonance Imaging Contrast Agent: An In Vitro AssessmentADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Liang Wang Abstract Hyperbranched polyglycerol-grafted, magnetic Fe3O4 nanoparticles (HPG-grafted MNPs) are successfully synthesized by surface-initiated ring-opening multibranching polymerization of glycidol. Reactive hydroxyl groups are immobilized on the surface of 6,9,nm Fe3O4 nanoparticles via effective ligand exchange of oleic acid with 6-hydroxy caproic acid. The surface hydroxyl groups are treated with aluminum isopropoxide to form the nanosized macroinitiators. The successful grafting of HPG onto the nanoparticles is confirmed by infrared and X-ray photoelectron spectroscopy. The HPG-grafted MNPs have a uniform hydrodynamic diameter of (24.0,±,3.0) nm, and are very stable in aqueous solution, as well as in cell culture medium, for months. These nanoparticles have great potential for application as a new magnetic resonance imaging contrast agent, as evidenced by their lack of cytotoxicity towards mammalian cells, low uptake by macrophages, excellent stability in aqueous medium and magnetic fields, and favorable magnetic properties. Furthermore, the possibility of functionalizing the hydroxyl end-groups of the HPG with cell-specific targeting ligands will expand the range of applications of these MNPs. [source] Kinetics of Formation and Physicochemical Characterization of Thermally-Induced ,-Lactoglobulin AggregatesJOURNAL OF FOOD SCIENCE, Issue 5 2010R.N. Zúñiga Abstract:, The kinetics of heat denaturation and aggregation for ,-lactoglobulin dispersions (5% w/v) were studied at 3 pHs (6, 6.4, and 6.8) and at a heating temperature of 80 °C. Protein aggregates were characterized for hydrodynamic diameter, microstructure, and molecular weight by means of dynamic light scattering, transmission electron microscopy, and polyacrylamide gel electrophoresis, respectively. Concentration of native ,-lactoglobulin decreased with holding time and with a decrease in the pH. Apparent rate constants were calculated for ,-lactoglobulin denaturation applying the general kinetic equation solved for a reaction order of 1.5. Values of the apparent reaction rate constant,k,= 7.5, 6.3 and 5.6 × 10,3 s,1 were found for pH 6, 6.4, and 6.8, respectively. Decreasing the pH of the dispersions produced higher aggregate sizes. After a holding time of 900 s, average hydrodynamic diameters for ,-lactoglobulin aggregates at pH 6, 6.4, and 6.8 were 96, 49, and 42 nm, respectively. These results were confirmed by transmission electron microscopy images, where a shift in the size and morphology of aggregates was found, from large and spherical at pH 6 to smaller and linear aggregates at pH 6.8. ,-Lactoglobulin formed disulfide-linked intermediates (dimers, trimers, tetramers) and so on) which then formed high molecular weight aggregates. From the results obtained by DLS, TEM, and SDS-PAGE a mechanism for ,-lactoglobulin aggregation was proposed. This study shows that heat treatment can be used to produce protein aggregates with different sizes and morphologies to be utilized as ingredients in foods. [source] A hyperbranched, rotaxane-type mechanically interlocked polymerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2010Shijun Li Abstract Based on the dibenzo-24-crown-8/1,2-bis(pyridinium)ethane recognition motif, a hyperbranched mechanically interlocked polymer was prepared by polyesterification of an easily available dynamic trifunctional AB2 pseudorotaxane monomer. It was characterized by various techniques including 1H NMR, COSY, NOESY, GPC, viscosity, TGA, dynamic laser light scattering, AFM, and SEM. Its GPC Mn was determined to be 191 kDa with polydispersity 1.7 and its hydrodynamic diameter in a dilute solution in acetone was about 70 nm. This measured Mn value corresponds to about 93 repeating units. The study reported here presents not only a new polymer topology but also a novel and convenient way to prepare mechanically interlocked polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4067,4073, 2010 [source] Self-assembly of well-defined amphiphilic polymeric miktoarm stars, dendrons, and dendrimers in water: The effect of architectureJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2009Daria E. Lonsdale Abstract Five polymeric architectures with a systematic increase in architectural complexity were synthesized by "click" reactions from a toolbox of functional linear polymers and small molecule linkers. The amphiphilic architectures ranged from a simple 3-miktoarm star block copolymer to the more complex third generation dendrimer-like block copolymer, consisting of polystyrene (PSTY) and polyacrylic acid (PAA). Micellization of these architectures in water at a pH of 7 under identical ionic strength gave spherical micelles ranging in size from 9 to 30 nm. Subsequent calculations of the PSTY core density, average surface area per PAA arm on the corona-core interface, and the relative stretching of the PAA arms provided insights into the effect of architecture on the self-assembly processes. A particular trend was observed that with increased architectural complexity the hydrodynamic diameter, radius of the core in the dry state and the aggregation number also increased with the exception of the third generation dendrimer. On the basis of these observations, we postulate that thermodynamic factors controlling self-assembly were the entropic penalty of forming PSTY loops in the core counterbalanced by the reduction in repulsive forces through chain stretching. This results in a greater number of aggregating unimers and consequently larger micelle sizes. The junction points within the architecture also play an important role in controlling the self-assembly process. The G3 dendrimer showed results contradictory to the aforementioned trend. We believe that the self-assembly process of this architecture was dominated by the increased attractive forces due to stretching of the PSTY core chains to form a more compact core. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6292,6303, 2009 [source] Superparamagnetic iron oxide particles: contrast media for magnetic resonance imaging,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2004Rüdiger Lawaczeck Abstract The mainstream magnetic iron oxide particles used as contrast media for magnetic resonance (MR) imaging are composed of a magnetic iron oxide core surrounded by a dextran or carboxydextran coat. The core size ranges from 2 nm to less than 10 nm, and the hydrodynamic diameter ranges from 20 nm to about 120 nm. The coat prevents aggregation and sedimentation of the particles in aqueous solutions, achieves high biological tolerance, and prevents toxic side effects. Two kinds of particles are considered: (i) large particles (>30 nm), called superparamagnetic iron oxide particles (SPIOs) for liver imaging; (ii) smaller particles (<30 nm hydrodynamic diameter), called ultrasmall SPIOs (USPIOs), e.g. for MR angiography. To characterize the particles, Mössbauer spectra are presented for the two particle ensembles. These spectra allow insight into the magnetic coupling, the valency of the iron ions and a rough estimate of the core size to be deduced. On the basis of the concentration dependence of the MR signal intensities, two applications are discussed together with two representative clinical examples. Future indications for MR diagnostics, e.g. the labeling and tracking of stem cells during stem-cell therapy control, are outlined. Copyright © 2004 John Wiley & Sons, Ltd. [source] Micellization of casein- graft -dextran copolymer prepared through Maillard reactionBIOPOLYMERS, Issue 1 2006Xiaoyun Pan Abstract Casein is almost insoluble at around pH 4.6, which is its isoelectric point (pI). Grafting copolymer, casein- g -dextran, was prepared through the Amadori rearrangement of the Maillard reaction. The copolymer has a reversible pH sensitive property: micellization at the pI of casein forming a casein core and dextran shell structure and dissociation when pH differs from the pI. The micelles produced at pH 4.6 have a spherical shape and their size is dependent on the Maillard reaction: reaction time, molar ratio of casein to dextran, and molecular weight of dextran used. Typically, the hydrodynamic diameter of the micelles is about 100 nm and the critical micelle concentration is about 10 mg/L. The micelles are very stable in aqueous solution and can be stored as lyophiled powder. The micelles are able to encapsulate hydrophobic compounds such as pyrene. © 2005 Wiley Periodicals, Inc. Biopolymers 81: 29,38, 2006 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Surface-Functionalized Ultrasmall Superparamagnetic Nanoparticles as Magnetic Delivery Vectors for CamptothecinCHEMMEDCHEM, Issue 6 2009Feride Cengelli Abstract Drug,nanoparticle conjugates: The anticancer drug camptothecin (CPT) was covalently linked at the surface of ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) via a linker, allowing drug release by cellular esterases. Nanoparticles were hierarchically built to achieve magnetically-enhanced drug delivery to human cancer cells and antiproliferative activity. The linking of therapeutic drugs to ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) allowing intracellular release of the active drug via cell-specific mechanisms would achieve tumor-selective magnetically-enhanced drug delivery. To validate this concept, we covalently attached the anticancer drug camptothecin (CPT) to biocompatible USPIOs (iron oxide core, 9,10,nm; hydrodynamic diameter, 52,nm) coated with polyvinylalcohol/polyvinylamine (PVA/aminoPVA). A bifunctional, end-differentiated dicarboxylic acid linker allowed the attachment of CPT to the aminoPVA as a biologically labile ester substrate for cellular esterases at one end, and as an amide at the other end. These CPT,USPIO conjugates exhibited antiproliferative activity in,vitro against human melanoma cells. The intracellular localization of CPT,USPIOs was confirmed by transmission electron microscopy (iron oxide core), suggesting localization in lipid vesicles, and by fluorescence microscopy (CPT). An external static magnetic field applied during exposure increased melanoma cell uptake of the CPT,USPIOs. [source] Cover Picture: Synthesis of Gadolinium-Labeled Shell-Crosslinked Nanoparticles for Magnetic Resonance Imaging Applications (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 8 2005Mater. Abstract Robust, amphiphilic core,shell nanoparticles that are selectively labeled with gadolinium in the hydrophilic and water-swollen shell layer are depicted in the cover picture. These well-defined nanostructured materials exhibit high relaxivity, a large loading capacity, and are based upon a biocompatible platform for ultimate function in magnetic resonance imaging (MRI) applications, as reported by Wooley and co-workers on p.,1248. Shell-crosslinked knedel-like nanoparticles (SCKs; "knedel" is a Polish term for dumplings) were derivatized with gadolinium chelates and studied as robust magnetic-resonance-imaging-active structures with hydrodynamic diameters of 40,±,3,nm. SCKs possessing an amphiphilic core,shell morphology were produced from the aqueous assembly of diblock copolymers of poly-(acrylic acid) (PAA) and poly(methyl acrylate) (PMA), PAA52,b,PMA128, and subsequent covalent crosslinking by amidation upon reaction with 2,2,-(ethylenedioxy)bis(ethylamine) throughout the shell layer. The properties of these materials, including non-toxicity towards mammalian cells, non-immunogenicity within mice, and capability for polyvalent targeting, make them ideal candidates for utilization within biological systems. The synthesis of SCKs derivatized with GdIII and designed for potential use as a unique nanometer-scale contrast agent for MRI applications is described herein. Utilization of an amino-functionalized diethylenetriaminepentaacetic acid,Gd analogue allowed for direct covalent conjugation throughout the hydrophilic shell layer of the SCKs and served to increase the rotational correlation lifetime of the Gd. In addition, the highly hydrated nature of the shell layer in which the Gd was located allowed for rapid water exchange; thus, the resulting material demonstrated large ionic relaxivities (39,s,1,mM,1) in an applied magnetic field of 0.47,T at 40,°C and, as a result of the large loading capacity of the material, also demonstrated high molecular relaxivities (20,000,s,1,mM,1). [source] Kinetics of Formation and Physicochemical Characterization of Thermally-Induced ,-Lactoglobulin AggregatesJOURNAL OF FOOD SCIENCE, Issue 5 2010R.N. Zúñiga Abstract:, The kinetics of heat denaturation and aggregation for ,-lactoglobulin dispersions (5% w/v) were studied at 3 pHs (6, 6.4, and 6.8) and at a heating temperature of 80 °C. Protein aggregates were characterized for hydrodynamic diameter, microstructure, and molecular weight by means of dynamic light scattering, transmission electron microscopy, and polyacrylamide gel electrophoresis, respectively. Concentration of native ,-lactoglobulin decreased with holding time and with a decrease in the pH. Apparent rate constants were calculated for ,-lactoglobulin denaturation applying the general kinetic equation solved for a reaction order of 1.5. Values of the apparent reaction rate constant,k,= 7.5, 6.3 and 5.6 × 10,3 s,1 were found for pH 6, 6.4, and 6.8, respectively. Decreasing the pH of the dispersions produced higher aggregate sizes. After a holding time of 900 s, average hydrodynamic diameters for ,-lactoglobulin aggregates at pH 6, 6.4, and 6.8 were 96, 49, and 42 nm, respectively. These results were confirmed by transmission electron microscopy images, where a shift in the size and morphology of aggregates was found, from large and spherical at pH 6 to smaller and linear aggregates at pH 6.8. ,-Lactoglobulin formed disulfide-linked intermediates (dimers, trimers, tetramers) and so on) which then formed high molecular weight aggregates. From the results obtained by DLS, TEM, and SDS-PAGE a mechanism for ,-lactoglobulin aggregation was proposed. This study shows that heat treatment can be used to produce protein aggregates with different sizes and morphologies to be utilized as ingredients in foods. [source] Dissimilar aggregation processes govern precipitation and gelation of human IgM cryoglobulinsJOURNAL OF MOLECULAR RECOGNITION, Issue 2 2007Vicky Vallas Abstract Cryoglobulinemia is associated with a range of diseases including rheumatoid arthritis, B-cell malignancies, and chronic viral infections. This "cold-sensitivity" condition is caused by cryoglobulins that precipitate, gel, or occasionally crystallize in the cold. Clinical manifestations vary widely in severity, depending on many factors, including the type of cryoglobulin (monoclonal or mixed immunoglobulins) and the physical nature of the aggregates (precipitate, gel, or crystal). Dynamic light scattering (DLS) was used to examine the cold-induced precipitation or gelation of two human cryoglobulins, namely, Pot IgM and Yvo IgM. The DLS assay was highly reproducible, sensitive, and had low intra-assay variations for both IgM cryoglobulins. Distinct processes were revealed to contribute to precipitation and gelation of cryoglobulins. The precipitation of Pot IgM displayed a rapid transition from solution to solid phases, with a wide distribution of aggregate sizes. In contrast, the gelation of Yvo IgM progressed gradually across a broad temperature range to produce a relatively uniform gel matrix. Initial cryoglobulin concentrations determined the kinetics and critical temperatures for both precipitation and gelation. Moreover, the Yvo IgM was observed to have a distinct relationship between concentrations and mean hydrodynamic diameters or particle sizes. Concentration-dependent effects on particle sizes were present, but not as pronounced for the Pot IgM. Precipitation and gelation of cryoglobulins were also found to be differentially responsive to changes in the aqueous environment. Our results indicate that DLS is a rapid, reliable, and sensitive method for characterizing the nature of disease-associated cryoglobulins. Copyright © 2007 John Wiley & Sons, Ltd. [source] Poly(,-caprolactone)- b -poly(ethylene glycol)- b -poly(,-caprolactone) triblock copolymers: Synthesis and self-assembly in aqueous solutionsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2007Yaqiong Zhang Abstract Nontoxic and biodegradable poly(,-caprolactone)- b -poly(ethylene glycol)- b -poly(,-caprolactone) triblock copolymers were synthesized by the solution polymerization of ,-caprolactone in the presence of poly(ethylene glycol). The chemical structure of the resulting triblock copolymer was characterized with 1H NMR and gel permeation chromatography. In aqueous solutions of the triblock copolymers, the micellization and sol,gel-transition behaviors were investigated. The experimental results showed that the unimer-to-micelle transition did occur. In a sol,gel-transition phase diagram obtained by the vial-tilting method, the boundary curve shifted to the left, and the gel regions expanded with the increasing molecular weight of the poly(,-caprolactone) block. In addition, the hydrodynamic diameters of the micelles were almost independent of the investigated temperature (25,55 °C). The atomic force microscopy results showed that spherical micelles formed at the copolymer concentration of 2.5 × 10,4 g/mL, whereas necklace-like and worm-like shapes were adopted when the concentration was 0.25 g/mL, which was high enough to form a gel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 605,613, 2007 [source] Microparticle-mediated gene delivery for the enhanced expression of a 19-kDa fragment of merozoite surface protein 1 of Plasmodium falciparumBIOTECHNOLOGY PROGRESS, Issue 1 2010Shan Liu Abstract The 19 kDa carboxyl-terminal fragment of merozoite surface protein 1 (MSP119) is a major component of the invasion-inhibitory response in individual immunity to malaria. A novel ultrasonic atomization approach for the formulation of biodegradable poly(lactic- co -glycolic acid) (PLGA) microparticles of malaria DNA vaccines encoding MSP119 is presented here. After condensing the plasmid DNA (pDNA) molecules with a cationic polymer polyethylenimine (PEI), a 40 kHz ultrasonic atomization frequency was used to formulate PLGA microparticles at a flow rate of 18 mL h,1. High levels of gene expression and moderate cytotoxicity in COS-7 cells were achieved with the condensed pDNA at a nitrogen to phosphate (N/P) ratio of 20, thus demonstrating enhanced cellular uptake and expression of the transgene. The ability of the microparticles to convey pDNA was examined by characterizing the formulated microparticles. The microparticles displayed Z-average hydrodynamic diameters of 1.50,2.10 ,m and zeta potentials of 17.8,23.2 mV. The encapsulation efficiencies were between 78 and 83%, and 76 and 85% of the embedded malaria pDNA molecules were released under physiological conditions in vitro. These results indicate that PLGA-mediated microparticles can be employed as potential gene delivery systems to antigen-presenting cells in the prevention of malaria. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Four Generations of Water-Soluble Dendrimers with 9 to 243 Benzoate Tethers: Synthesis and Dendritic Effects on Their Ion Pairing with Acetylcholine, Benzyltriethylammonium, and Dopamine in WaterCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2008Elodie Boisselier Abstract Water-soluble benzoate-terminated dendrimers of four generations (from G0 with 9 branches to G3 with 243 branches) were synthesized and fully characterized. They form water-soluble assemblies by ion-pairing interactions with three cations of medicinal interest (acetylcoline, benzyltriethylammonium, and dopamine), which were characterized and investigated by 1H,NMR spectroscopy, whereas such interactions do not provoke any significant shift of 1H,NMR signals with the monomeric benzoate anion. The calculated association constants confirm that the dendritic carboxylate termini reversibly form ion pairs and aggregates. Diffusion coefficients and hydrodynamic diameters of the dendrimers, as well as changes thereof on interaction with the cations, were evaluated by DOSY experiments. The lack of increase of dendrimer size on addition of the cations and the upfield shifts of the 1H,NMR signals of the cation indicate encapsulation within the hydrophobic dendrimer interiors together with probable backfolding of the benzoate termini. [source] | |||||||||||||