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1.
ACS Appl Mater Interfaces ; 12(22): 24531-24543, 2020 Jun 03.
Artigo em Inglês | MEDLINE | ID: mdl-32378873

RESUMO

Polymeric micelles are typically characterized as core-shell structures. The hydrophobic core is considered as a depot for hydrophobic molecules, and the corona-forming block acts as a stabilizing and solubilizing interface between the core and aqueous milieu. Tremendous efforts have been made to tune the hydrophobic block to increase the drug loading and stability of micelles, whereas the role of hydrophilic blocks is rarely investigated in this context, with poly(ethylene glycol) (PEG) being the gold standard of hydrophilic polymers. To better understand the role of the hydrophilic corona, a small library of structurally similar A-B-A-type amphiphiles based on poly(2-oxazoline)s and poly(2-oxazine)s is investigated by varying the hydrophilic block A utilizing poly(2-methyl-2-oxazoline) (pMeOx; A) or poly(2-ethyl-2-oxazoline) (pEtOx; A*). In terms of hydrophilicity, both polymers closely resemble PEG. The more hydrophobic block B bears either a poly(2-oxazoline) and poly(2-oxazine) backbone with C3 (propyl) and C4 (butyl) side chains. Surprisingly, major differences in loading capacities from A-B-A > A*-B-A > A*-B-A* is observed for the formulation with two poorly water-soluble compounds, curcumin and paclitaxel, highlighting the importance of the hydrophilic corona of polymer micelles used for drug formulation. The formulations are also characterized by various nuclear magnetic resonance spectroscopy methods, dynamic light scattering, cryogenic transmission electron microscopy, and (micro) differential scanning calorimetry. Our findings suggest that the interaction between the hydrophilic block and the guest molecule should be considered an important, but previously largely ignored, factor for the rational design of polymeric micelles.

2.
Int J Biol Macromol ; 121: 536-545, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30312700

RESUMO

Stabilization of the enzymes under stress conditions is of special interest for modern biochemistry, bioengineering, as well as for formulation and target delivery of protein-based drugs. Aiming to achieve an efficient stabilization at elevated temperature with no influence on the enzyme under normal conditions, we studied chaperone-like activity of thermoresponsive polymers based on poly(dimethylaminoethyl methacrylate) (PDMAEMA) toward two different proteins, glyceraldehyde-3-phosphate dehydrogenase and chicken egg lysozyme. The polymers has been shown to do not interact with the folded protein at room temperature but form a complex upon heating to either protein unfolding or polymer phase transition temperature. A PDMAEMA-PEO block copolymer with a dodecyl end-group (d-PDMAEMA-PEO) as well as PDMAEMA-PEO without the dodecyl groups protected the denatured protein against aggregation in contrast to PDMAEMA homopolymer. No effect of the polymers on the enzymatic activity of the client protein was observed at room temperature. The polymers also partially protected the enzyme against inactivation at high temperature. The results provide a platform for creation of artificial chaperones with unfolded protein recognition which is a major feature of natural chaperones.


Assuntos
Gliceraldeído-3-Fosfato Desidrogenases/química , Metacrilatos/farmacologia , Muramidase/química , Nylons/farmacologia , Desdobramento de Proteína , Temperatura , Animais , Estabilidade Enzimática/efeitos dos fármacos
3.
Anal Bioanal Chem ; 409(20): 4811-4817, 2017 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-28577073

RESUMO

Hydroxypropyl xylans with varying degrees of substitution were characterized by size-exclusion chromatography. Molar masses of the samples were determined using two approaches: by conventional calibration with molar mass standards and by a multi-detection method that utilizes the combination of static light scattering, viscometry, and differential refractive index detection. The molar mass results obtained by the multi-detection method were accurate, but required the determination of separate refractive index increments for each structurally different sample. The column calibration approach with standard pullulan samples gave biased results due to the differences in hydrodynamic volumes between pullulans and hydroxypropyl xylans with similar molar masses. The degree of hydroxypropylation affected the chain conformation and compactness of the polymer chains. Mark-Houwink parameters and persistence length values suggested that the hydroxypropyl substituents reduced the flexibility of the xylan chain and made the polymer chain more extended.

4.
Nanoscale Res Lett ; 12(1): 74, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-28124301

RESUMO

Silicon-based mesoporous nanoparticles have been extensively studied to meet the challenges in the drug delivery. Functionality of these nanoparticles depends on their properties which are often changing as a function of particle size and surrounding medium. Widely used characterization methods, dynamic light scattering (DLS), and transmission electron microscope (TEM) have both their weaknesses. We hypothesize that conventional light scattering (LS) methods can be used for a rigorous characterization of medium sensitive nanoparticles' properties, like size, stability, and porosity. Two fundamentally different silicon-based nanoparticles were made: porous silicon (PSi) from crystalline silicon and silica nanoparticles (SN) through sol-gel process. We studied the properties of these mesoporous nanoparticles with two different multiangle LS techniques, DLS and static light scattering (SLS), and compared the results to dry-state techniques, TEM, and nitrogen sorption. Comparison of particle radius from TEM and DLS revealed significant overestimation of the DLS result. Regarding to silica nanoparticles, the overestimation was attributed to agglomeration by analyzing radius of gyration and hydrodynamic radius. In case of PSi nanoparticles, strong correlation between LS result and specific surface area was found. Our results suggest that the multiangle LS methods could be used for the size, stability, and structure characterization of mesoporous nanoparticles.

5.
Polymers (Basel) ; 8(3)2016 Mar 22.
Artigo em Inglês | MEDLINE | ID: mdl-30979191

RESUMO

The present work describes the acid-triggered condensation of silicic acid, Si(OH)4, as directed by selected polycations in aqueous solution in the pH range of 6.5⁻8.0 at room temperature, without the use of additional solvents or surfactants. This process results in the formation of silica-polyelectrolyte (S-PE) nanocomposites in the form of precipitate or water-dispersible particles. The mean hydrodynamic diameter (dh) of size distributions of the prepared water-dispersible S-PE composites is presented as a function of the solution pH at which the composite formation was achieved. Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and block copolymers of DMAEMA and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) were used as weak polyelectrolytes in S-PE composite formation. The activity of the strong polyelectrolytes poly(methacryloxyethyl trimethylammonium iodide) (PMOTAI) and PMOTAI-b-POEGMA in S-PE formation is also examined. The effect of polyelectrolyte strength and the OEGMA block on the formation of the S-PE composites is assessed with respect to the S-PE composites prepared using the PDMAEMA homopolymer. In the presence of the PDMAEMA60 homopolymer (Mw = 9400 g/mol), the size of the dispersible S-PE composites increases with solution pH in the range pH 6.6⁻8.1, from dh = 30 nm to dh = 800 nm. S-PDMAEMA60 prepared at pH 7.8 contained 66% silica by mass (TGA). The increase in dispersible S-PE particle size is diminished when directed by PDMAEMA300 (Mw = 47,000 g/mol), reaching a maximum of dh = 75 nm. S-PE composites formed using PDMAEMA-b-POEGMA remain in the range dh = 20⁻30 nm across this same pH regime. Precipitated S-PE composites were obtained as spheres of up to 200 nm in diameter (SEM) and up to 65% mass content of silica (TGA). The conditions of pH for the preparation of dispersible and precipitate S-PE nanocomposites, as directed by the five selected polyelectrolytes PDMAEMA60, PDMAEMA300, PMOTAI60, PDMAEMA60-b-POEGMA38 and PMOTAI60-b-POEGMA38 is summarized.

6.
Biomacromolecules ; 16(9): 2750-6, 2015 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-26207325

RESUMO

Thermally responsive hydrogel nanoparticles composed of self-assembled polystyrene-b-poly(N-isopropylacrylamide)-b-polystyrene block copolymers and fluorescent probe 1-anilinonaphthalene-8-sulfonic acid have been prepared by aerosol flow reactor method. We aimed exploring the relationship of intraparticle morphologies, that were, PS spheres and gyroids embedded in PNIPAm matrix, as well PS-PNIPAm lamellar structure, to probe release in aqueous solution below and above the cloud point temperature (CPT) of PNIPAm. The release was detected by fluorescence emission given by the probe binding to bovine serum albumin. Also, the colloidal behavior of hydrogel nanoparticles at varying temperatures were examined by scattering method. The probe release was faster below than above the CPT from all the morphologies of which gyroidal morphology showed the highest release. Colloidal behavior varied from single to moderately aggregated particles in order spheres-gyroids-lamellar. Hydrogel nanoparticles with tunable intra particle self-assembled morphologies can be utilized designing carrier systems for drug delivery and diagnostics.


Assuntos
Portadores de Fármacos/química , Portadores de Fármacos/síntese química , Hidrogéis/química , Hidrogéis/síntese química , Nanopartículas/química , Animais , Bovinos , Tamanho da Partícula , Soroalbumina Bovina/química
7.
J Colloid Interface Sci ; 446: 1-10, 2015 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-25646785

RESUMO

Polymeric amines have been intensively studied for application in smart systems and as matrices for the design of composite materials, including bioinspired substances. A new thermo- and pH-responsive polymer was obtained by radical polymerization of N-(3-(diethylamino)propyl)-N-methylacrylamide. Upon heating, the polymer precipitated from aqueous solutions above pH 9; the observed cloud point was dependent on the polymer concentration and decreased from 95°C at pH 9 to 40°C at pH 11. The basicity of the polymer decreased at elevated temperatures owing to an increase in the hydrophobicity-driven compaction of the macromolecules. Dynamic light scattering analysis demonstrated that the formation of large multimolecular associates with radius 1000-2000 nm was initiated from 1 to 2°C below the cloud point. The new polymer is demonstrated to be an effective matrix for various siliceous composite structures, including 200-300 nm solid spherical raspberry-like particles and hollow hemispherical particles of more than 1000 nm diameter. Condensation of silicic acid in the presence of polymeric amines is a model reaction in biosilicification studies, and the obtained data are also discussed from the perspective of the matrix hypothesis for biosilica formation.


Assuntos
Aminas/química , Substâncias Macromoleculares/química , Nanocompostos/química , Polímeros/química , Dióxido de Silício/química , Água/química , Concentração de Íons de Hidrogênio , Tamanho da Partícula , Propriedades de Superfície , Temperatura
8.
Soft Matter ; 10(39): 7712-22, 2014 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-25137480

RESUMO

A comparative light-scattering study of isotactic and atactic poly(methacrylic acid), iPMA and aPMA, respectively, in aqueous solutions with added alkali chlorides, XCl (X = Li, Na, Cs), at 25 °C and XCl concentration of 0.1 mol L(-1), demonstrates that both PMA isomers are strongly associated at low degrees of neutralization, αN (= 0 for aPMA and 0.25 for iPMA), in the presence of all XCls. The shape parameter ρ and the scattering functions suggest that aggregates have the characteristics of microgel particles, with a dense core surrounded by a less dense shell. The extent of aggregation depends on the stereoregular structure of the polymer and on the type of the added cation. Li(+) and Na(+) ions support aggregation better than Cs(+) ions. Besides, iPMA chains are more strongly aggregated than aPMA chains and form particles with a denser core. A model of the aggregation process is suggested for iPMA. At high αN, a slow diffusive process (so-called extraordinary or anomalous mode in diffusion of polyelectrolytes), arising from electrostatic interactions between charged chains, is observed for both PMAs. Results suggest that under the same experimental conditions iPMA is effectively more charged than aPMA. The role of ions in the slow-mode phenomenon is less pronounced than in aggregation.

9.
J Am Chem Soc ; 136(3): 866-9, 2014 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-24380366

RESUMO

Cellulose nanocrystals (CNCs) are high aspect ratio colloidal rods with nanoscale dimensions, attracting considerable interest recently due to their high mechanical properties, chirality, sustainability, and availability. In order to exploit them for advanced functions in new materials, novel supracolloidal concepts are needed to manipulate their self-assemblies. We report on exploring multivalent interactions to CNC surface and show that dendronized polymers (DenPols) with maltose-based sugar groups on the periphery of lysine dendrons and poly(ethylene-alt-maleimide) polymer backbone interact with CNCs. The interactions can be manipulated by the dendron generation suggesting multivalent interactions. The complexation of the third generation DenPol (G3) with CNCs allows aqueous colloidal stability and shows wrapping around CNCs, as directly visualized by cryo high-resolution transmission electron microscopy and electron tomography. More generally, as the dimensions of G3 are in the colloidal range due to their ~6 nm lateral size and mesoscale length, the concept also suggests supracolloidal multivalent interactions between other colloidal objects mediated by sugar-functionalized dendrons giving rise to novel colloidal level assemblies.

10.
Macromolecules ; 45(20): 8401-8411, 2012 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-23150721

RESUMO

This work describes properties of thermo-sensitive submicron sized particles having the same chemical composition but different morphologies. These particles have been prepared with an aerosol technique using dimethylformamide solutions of linear polystyrene-block-poly(N-isopropylacrylamide-block-polystyrene, PS-b-PNIPAM-b-PS. The particles were characterized by cryo-electron microscopy, microcalorimetry, and light scattering. Block-copolymers self-assembled within the particles forming onion-like, gyroid-like, and spherical morphologies having poly(N-isopropylacrylamide) matrix and physically cross-linking polystyrene domains. The particles were dispersed in aqueous media and their behavior in water was studied both below and above the lower critical solution temperature of poly(N-isopropylacrylamide). We found out that the particles with spherical and gyroid-like morphologies swell considerably in water at 20 °C, whereas at 40 °C the particles resemble more of those studied without water treatment. Light scattering experiments showed that the particles gradually aggregate and precipitate with time at 40 °C. Microcalorimetric studies revealed for all three studied morphologies that PNIPAM undergoes a two-step transition due to the different hydration levels of PNIPAM inside and outside the particles. Thicknesses of the PS and PNIPAM layers within the onion-like particles were analyzed using the TEM micrographs by fitting a model of electron density to the integrated electron intensity data. The surface layer of the particles was found out to be PNIPAM, which was supported by light scattering and microcalorimetry. It was also found out from the TEM micrograph analysis that the width of the outmost PS layer is considerably thinner than the one in the dry state prior to immersion in water, and a degradation scheme is proposed to explain these results.

11.
Carbohydr Res ; 352: 151-8, 2012 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-22370176

RESUMO

Norway spruce O-acetyl-galactoglucomannans (GGM) are water-soluble hemicelluloses that have potential to be produced in large scale as a side product of the mechanical pulping industry or by hot-water extraction of wood. Chemical modification is often needed to tailor such water-soluble polysaccharides into industrially valuable compounds. In this work, treatment of GGM with butyric and benzoic anhydride in pyridine/dimethylformamide rendered GGM derivatives, which were hydrophobic and partially soluble in organic solvents. The degree of substitution can be adjusted by varying the quantity of the reagent and reaction temperature. The dn/dc value for the benzoyl ester of GGM was determined in 0.05 M LiBr DMSO in order to obtain accurate molar mass analysis with SEC-MALLS-RI. Novel substances with adjusted hydrophobicity can thus be prepared on one step synthesis from natural hemicelluloses, which then showed a slight increase in the molar mass upon esterification.


Assuntos
Interações Hidrofóbicas e Hidrofílicas , Mananas/química , Papel , Temperatura de Transição , Benzoatos/química , Butiratos/química , Cor , Peso Molecular , Solubilidade , Solventes/química
12.
Biomacromolecules ; 12(9): 3213-22, 2011 Sep 12.
Artigo em Inglês | MEDLINE | ID: mdl-21761847

RESUMO

A series of amphiphilic star and linear block copolymers were synthesized using ATRP. The core consisted of either polystyrene (PS) or poly(n-butyl acrylate) (PBuA), having different glass-transition (T(g)) values. These polymers were used as macroinitiators in the polymerization of the cationic 2-(dimethylamino)ethyl methacrylate (DMAEMA). The polymers were used to study the effects of polymer architecture and flexibility on the self-assembling properties, DNA complexation, and transfection. All polymers formed core-shell micelles in aqueous solutions and condensed plasmid DNA. Linear PDMAEMA-PBuA-PDMAEMA has transfection efficiency comparable to PEI25K in ARPE19 cell line. Glassy state of the micellar core and star-shaped architecture decreased the DNA transfection compared with the rubbery and linear polymer structures. The polymers showed low cellular toxicity at low nitrogen/phosphate (n/p) ratios.


Assuntos
DNA/farmacologia , Portadores de Fármacos/síntese química , Células Epiteliais/efeitos dos fármacos , Fibroblastos/efeitos dos fármacos , Técnicas de Transferência de Genes , Metacrilatos/síntese química , beta-Galactosidase/farmacologia , Acrilatos/química , Animais , Cátions/química , Linhagem Celular , Sobrevivência Celular/efeitos dos fármacos , Microscopia Crioeletrônica , DNA/genética , DNA/metabolismo , Portadores de Fármacos/metabolismo , Células Epiteliais/citologia , Células Epiteliais/metabolismo , Fibroblastos/citologia , Fibroblastos/metabolismo , Expressão Gênica , Haplorrinos , Humanos , Metacrilatos/metabolismo , Micelas , Plasmídeos , Polietilenoglicóis/química , Polímeros/química , Poliestirenos/química , Soluções , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz , Transfecção , beta-Galactosidase/genética , beta-Galactosidase/metabolismo
13.
Biomacromolecules ; 12(8): 2997-3006, 2011 Aug 08.
Artigo em Inglês | MEDLINE | ID: mdl-21740051

RESUMO

Herein we report the synthesis of cellulose nanocrystals (CNCs) grafted with poly(acrylic acid) (PAA) chains of different lengths using Cu-mediated surface initiated-controlled radical polymerization (SI-CRP). First, poly(tert-butylacrylate) (PtBA) brushes were synthesized; then, subsequent acid hydrolysis was used to furnish PAA brushes tethered onto the CNC surfaces. The CNCs were chemically modified to create initiator moieties on the CNC surfaces using chemical vapor deposition (CVD) and continued in solvent phase in DMF. A density of initiator groups of 4.6 bromine ester groups/nm(2) on the CNC surface was reached, suggesting a dense functionalization and a promising starting point for the controlled/living radical polymerization. The SI-CRP of tert-butylacrylate proceeded in a well-controlled manner with the aid of added sacrificial initiator, yielding polymer brushes with polydispersity values typically well below 1.12. We calculated the polymer brush grafting density to almost 0.3 chains/nm(2), corresponding to high grafting densities and dense polymer brush formation on the nanocrystals. Successful rapid acid hydrolysis to remove the tert-butyl groups yielded pH-responsive PAA-polyelectrolyte brushes bound to the CNC surface. Individually dispersed rod-like nanoparticles with brushes of PtBA or PAA were clearly visualized by AFM and TEM imaging.


Assuntos
Celulose/química , Cobre/química , Eletrólitos/química , Nanopartículas , Polímeros/química , Cromatografia em Gel , Esterificação , Hidrólise , Espectroscopia de Ressonância Magnética , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz , Propriedades de Superfície
14.
J Gene Med ; 13(7-8): 402-9, 2011 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-21721076

RESUMO

BACKGROUND: Polyethylenimine (PEI) polyplexes mediate efficient gene transfer only at high +/- charge ratios at which free noncomplexed PEI is present. The excess of PEI gives polyplexes a positive surface charge that plays a role in polyplex binding on the cell membrane. Although positively charged PEI polyplexes are known to interact with anionic cell-surface glycosaminoglycans (GAGs), the exact role of free PEI in such interactions is unclear. METHODS: Chinese hamster ovary wild-type cells and mutants lacking cell-surface GAGs were transfected with marker genes using PEI polyplexes with and without free PEI. The total amount of cell-associated plasmid DNA (pDNA) delivered by polyplexes was determined by quantitative real-time PCR and transgene expression was determined using ß-galactosidase and luciferase assays. RESULTS: Transfection activity of polyplexes without free PEI in cells expressing cell-surface GAGs was low even though pDNA was delivered to cells. In the absence of cell-surface GAGs, polyplexes without free PEI had high transfection efficacy. This indicates that the cell-surface GAGs inhibit transfection by purified polyplexes. PEI polyplexes with free carrier mediated transfection in both normal and GAG-deficient cells because free PEI overcomes the inhibitory effect of cell-surface GAGs on transfection. The intracellular elimination of pDNA was faster in the presence of GAGs and, despite improved transfection, free PEI reduced pDNA association with the cells. CONCLUSIONS: Free PEI is essential for minimizing the undesirable binding of polyplexes to cell-surface GAGs that have a negative impact on transfection. The same mechanism may be important in transfections with other polyplexes that require high charge ratios for transfection.


Assuntos
DNA/metabolismo , Glicosaminoglicanos/metabolismo , Polietilenoimina/metabolismo , Animais , Células CHO , Cricetinae , Cricetulus , Expressão Gênica , Técnicas de Transferência de Genes , Espaço Intracelular/metabolismo , Plasmídeos/genética , Plasmídeos/metabolismo , Polietilenoimina/química , Polietilenoimina/toxicidade , Transfecção , Transgenes
15.
Biomacromolecules ; 12(5): 1772-80, 2011 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-21469744

RESUMO

The role of polymer (poly(vinylamine)) size (238-11000 units) on silicic acid condensation to yield soluble nanoparticles or composite precipitates has been explored by a combination of light scattering (static and dynamic), laser ablation combined with aerosol spectrometry, IR spectroscopy, and electron microscopy. Soluble nanoparticles or composite precipitates are formed according to the degree of polymerization of the organic polymer and pH. Nanoparticles prepared in the presence of the highest molecular weight polymers have core-shell like structures with dense silica cores. Composite particles formed in the presence of polymers with extent of polymerization below 1000 consist of associates of several polymer-silica nanoparticles. The mechanism of stabilization of the "soluble" silica particles in the tens of nanometer size range involves cooperative interactions with the polymer chains which varies according to chain length and pH. An example of the use of such polymer-poly(silicic acid) nanoparticles in the generation of composite polymeric materials is presented. The results obtained have relevance to the biomimetic design of new composite materials based on silica and polymers and to increasing our understanding of how silica may be manipulated (stored) in the biological environment prior to the formation of stable mineralized structures. We suspect that a similar method of storing silicic acid in an active state is used in silicifying organisms, at least in diatom algae.


Assuntos
Nanopartículas , Polivinil/química , Dióxido de Silício/química , Microscopia Eletrônica de Varredura , Espectrofotometria Infravermelho
16.
J Phys Chem B ; 115(14): 3793-803, 2011 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-21417252

RESUMO

Complexes formed between a cationic surfactant cetylpyridinium chloride, CPC, and an anionic polyelectrolyte sodium poly(styrenesulfonate), NaPSS, in aqueous 0.1 M NaCl solutions were studied by static and dynamic light scattering and by ζ-potential measurements in a broad region of surfactant cation, CP(+), to polyanion, PSS(-), charge ratio, S/P. Two NaPSS samples were used, NaPSS-L with a lower molar mass, M(w) = 1.4 × 10(5) g/mol, and NaPSS-H with a considerably higher M(w) (= 2.6 × 10(6) g/mol), to elucidate the effect of the polyion chain length on the behavior of the aggregates. In the polyelectrolyte-rich regime (S/P < 1), CPPSS complexes are soluble up to rather high S/P values (around 0.72, irrespective of the polyion chain length), which is attributed to a specific interaction between the hydrophobic benzene groups on the polyion and the surfactant micelle, which leads to a less efficient charge screening. The addition of surfactant causes chain contraction. The obtained data suggest a pronounced effect of the NaPSS chain length on the structural properties of the CPPSS complexes. The CPPSS-L complexes are small and dense (the radius of gyration, R(g), is 7.3 nm at S/P = 0.7), and their shape is close to spherical. In contrast, the CPPSS-H complexes (R(g) around 73 nm at S/P = 0.7) have no well-defined structure and reveal a stronger tendency toward intermolecular association when the nominal charge of the complex is reduced, although they remain pretty monodisperse. A model of a temporary network-like association in which surfactant micelles serve as cross-links for polyion chains is proposed to explain the behavior in CPPSS-H solutions. The forces responsible for such labile intermolecular association are weak, in contrast to strong specific interaction involved in the formation of the primary complex. The redissolution of the complex by adding excess surfactant (S/P > 1: the surfactant-rich regime) depends strongly on the polyion chain length and is a slow process, taking several days (CPPSS-L) or even weeks (CPPSS-H). It is achieved only at very high S/P values (around 240 and 2400 in the CPPSS-L and CPPSS-H cases, respectively) by hydrophobic binding of surfactant to the CPPSS complex. The predominating species in these solutions are free surfactant micelles. Similarly, a large excess of NaCl (almost 390 and 690 mol per 1 mol of CPPSS-L and CPPSS-H, respectively) is needed to disintegrate the stoichiometric CPPSS (S/P = 1) complex into free polyion chains and free surfactant micelles.

17.
Anal Chim Acta ; 675(2): 191-8, 2010 Aug 24.
Artigo em Inglês | MEDLINE | ID: mdl-20800732

RESUMO

The use of asymmetrical flow field-flow fractionation (AsFlFFF) in the study of heat-induced aggregation of proteins is demonstrated with bovine serum albumin (BSA) as a model analyte. The hydrodynamic diameter (d(h)), the molar mass of heat-induced aggregates, and the radius of gyration (R(g)) were calculated in order to get more detailed understanding of the conformational changes of BSA upon heating. The hydrodynamic diameter of native BSA at ambient temperature was approximately 7 nm. The particle size was relatively stable up to 60 degrees C; above 63 degrees C, however, BSA underwent aggregation (growth of hydrodynamic diameter). The hydrodynamic diameters of the aggregated particles, heated to 80 degrees C, ranged from 15 to 149 nm depending on the BSA concentration, duration of incubation, and the ionic strength of the solvent. Heating of BSA in the presence of sodium dodecyl sulfate (1.7 or 17 mM) did not lead to aggregation. The heat-induced aggregates were characterized in terms of their molar mass and particle size together with their respective distributions with a hyphenated technique consisting of an asymmetrical field-flow fractionation device and a multi-angle light scattering detector and a UV-detector. The carrier solution comprised 8.5 mM phosphate and 150 mM sodium chloride at pH 7.4. The weight-average molar mass (M(w)) of native BSA at ambient temperature is 6.6x10(4) g mol(-1). Incubation of solutions with BSA concentrations of 1.0 and 2.5 mg mL(-1) at 80 degrees C for 1 h resulted in aggregates with M(w) 1.2x10(6) and 1.9x10(6) g mol(-1), respectively. The average radius of gyration and the average hydrodynamic radius of the heat-induced aggregate samples were calculated and compared to the values obtained from the size distributions measured by AsFlFFF. For comparison static light scattering measurements were carried out and the corresponding average molar mass distributions of solutions with BSA concentrations of 1.0 and 2.5 mg mL(-1) at 80 degrees C for 1 h gave aggregates with M(w) 1.7x10(6) and 3.5x10(6) g mol(-1), respectively.


Assuntos
Fracionamento por Campo e Fluxo/métodos , Soroalbumina Bovina/química , Animais , Bovinos , Desenho de Equipamento , Fracionamento por Campo e Fluxo/instrumentação , Temperatura Alta , Luz , Peso Molecular , Conformação Proteica , Refratometria , Espalhamento de Radiação , Cloreto de Sódio/química , Dodecilsulfato de Sódio/química , Raios Ultravioleta
18.
J Agric Food Chem ; 56(13): 5069-77, 2008 Jul 09.
Artigo em Inglês | MEDLINE | ID: mdl-18553881

RESUMO

The structures of barley ( Hordeum vulgare) arabinoxylans isolated from two industrial side fractions, barley husks (BH) and barley fiber (BF), were characterized. Arabinoxylans were extracted with saturated barium hydroxide after enzymatic pretreatment. Barium hydroxide was selective toward arabinoxylans, and only a minor amount of glucose-containing material was coextracted. Acid methanolysis followed by gas chromatography, 1H NMR spectroscopy, and specific enzymatic treatments followed by anion exchange chromatography with pulse amperometric detection (HPAEC-PAD) revealed that the chemical structure of barley husk arabinoxylan (BHAX) clearly differed from that of barley fiber arabinoxylan (BFAX). BFAX was more branched, containing more beta-D-xylopyranosyl (beta-D-Xylp) residues carrying alpha-L-arabinofuranosyl (alpha-L-Araf) units at both O-2 and O-3 positions. BHAX, on the other hand, contained more 2-O-beta-D-Xyl p-alpha-L-Ara f substituents than BFAX. BHAX and BFAX also differed with respect to the hydrodynamic properties investigated with multidetector size exclusion chromatography. BFAX had a higher weight-average molar mass and larger hydrodynamic volume, the latter indicating less dense conformation than BHAX. Mn, Mw /Mn, Rh, and the Mark-Houwink a value were also determined for both arabinoxylans.


Assuntos
Indústria Química , Hordeum/química , Xilanos/química , Cromatografia por Troca Iônica , Enzimas/metabolismo , Hordeum/metabolismo , Hidrólise , Espectroscopia de Ressonância Magnética , Extratos Vegetais/química , Extratos Vegetais/isolamento & purificação , Xilanos/isolamento & purificação
19.
Biomacromolecules ; 7(11): 3229-38, 2006 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-17096555

RESUMO

Polyelectrolyte complexes of a synthetic polycation with either a genomic DNA or a synthetic poly(oxyethylene-block-sodium methacrylate), POE-b-PMANa, have been studied in aqueous solutions as a function of cation:anion ratio, the degree of polymerization of the polycation, the ionic strength, and temperature using dynamic light scattering and turbidity measurements. The polycation was a copolymer of methacryl oxyethyl trimethylammonium chloride and poly(oxyethylene) monomethyl ether monomethacrylate with 4-5 oxyethylene repeating units, PMOTAC-g-POE. The molar masses of the polycations in a homological series were 0.3, 0.9, and 2.1 x 10(6) g/ mol. The amount of comonomers with poly(oxyethylene) tails in the copolymers was 15 mol %. The molar mass of the POE-b-PMANa was 75000 g/mol and that of the POE-block was 5000 g/mol. The molar mass of the polycation was shown to have a dramatic effect on the stability and size of the complexes formed by either of the polyanions. An increase in the polycation molar mass shifts the cloud point toward the lower polycation content in the complexes, and a macro phase separation occurs in the solutions with the cation to anion molar ratios much below than 1:1. Increasing the ionic strength has a similar effect. Further addition of salt to turbid and phase-separated solutions results in dissociation of the complexes, and the polyions dissolve as individual macromolecules. The effect of POE on the stability of polyelectrolyte complexes is discussed as well.


Assuntos
DNA/química , Metacrilatos/química , Polietilenoglicóis/química , Cátions , Concentração Osmolar , Temperatura
20.
Biomacromolecules ; 5(5): 1853-61, 2004.
Artigo em Inglês | MEDLINE | ID: mdl-15360298

RESUMO

Intermolecular complexes of genomic polydisperse DNA with synthetic polycations have been studied. Two cationic polymers have been used, a homopolymer poly(methacryl oxyethyl trimethylammonium chloride) (PMOTAC) and its analogue grafted with poly(oxyethylene). The amount of poly(oxyethylene) grafts in the copolymer was 15 mol % and Mw of the graft was 200 g/mol. Salmon DNA (sodium salt) was used. The average molecular weight (Mw) of DNA was 10.4 x 10(6) g/mol. Conductivity, pH, and dynamic light scattering studies were used to characterize the complexes. The size and shape of the polyelectrolyte complex particles have been studied as a function of the cation-to-anion ratio in aqueous solutions of varying ionic strengths. The polyelectrolyte complexes have extremely narrow size distributions taking into account the polydispersity of the polyelectrolytes studied. The poly(oxyethylene) grafts on PMOTAC promote the formation of small colloidally stabile complex particles. Addition of salt shifts the macroscopic phase separation toward lower polycation content; that is, complexes partly phase separate with the mixing ratios far from 1:1. Further addition of salt to the turbid, partly phase separated solution results in the dissociation of complexes and the polycation and DNA dissolve as individual chains.


Assuntos
Cloreto de Amônio/análise , DNA/análise , Polietilenoglicóis/metabolismo , Ácidos Polimetacrílicos/análise , Cloreto de Amônio/metabolismo , DNA/metabolismo , Polietilenoglicóis/análise , Ácidos Polimetacrílicos/metabolismo
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