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1.
Biomacromolecules ; 24(3): 1318-1328, 2023 03 13.
Artigo em Inglês | MEDLINE | ID: mdl-36749901

RESUMO

Phosphorylation of cellulose nanocrystals (CNCs) has remained a marginal activity despite the undisputed application potential in flame-retardant materials, sustainable high-capacity ion-exchange materials, or substrates for biomineralization among others. This is largely due to strenuous extraction methods prone to a combination of poor reproducibility, low degrees of substitution, disappointing yields, and impractical reaction sequences. Here, we demonstrate an improved methodology relying on the modification routines for phosphorylated cellulose nanofibers and hydrolysis by gaseous HCl to isolate CNCs. This allows us to overcome the aforementioned shortcomings and to reliably and reproducibly extract phosphorylated CNCs with exceptionally high surface charge (∼2000 mmol/kg) in a straightforward routine that minimizes water consumption and maximizes yields. The CNCs were characterized by NMR, ζpotential, conductometric titration, thermogravimetry, elemental analysis, wide-angle X-ray scattering, transmission electron microscopy, and atomic force microscopy.


Assuntos
Nanofibras , Nanopartículas , Celulose/química , Reprodutibilidade dos Testes , Nanopartículas/química , Nanofibras/química , Microscopia Eletrônica de Transmissão
2.
Chemphyschem ; 23(7): e202100635, 2022 04 05.
Artigo em Inglês | MEDLINE | ID: mdl-35130371

RESUMO

We have identified cellulose solvents, comprised of binary mixtures of molecular solvents and ionic liquids that rapidly dissolve cellulose to high concentration and show upper-critical solution temperature (UCST)-like thermodynamic behaviour - upon cooling and micro phase-separation to roughly spherical microparticle particle-gel mixtures. This is a result of an entropy-dominant process, controllable by changing temperature, with an overall exothermic regeneration step. However, the initial dissolution of cellulose in this system, from the majority cellulose I allomorph upon increasing temperature, is also exothermic. The mixtures essentially act as 'thermo-switchable' gels. Upon initial dissolution and cooling, micro-scaled spherical particles are formed, the formation onset and size of which are dependent on the presence of traces of water. Wide-angle X-ray scattering (WAXS) and 13 C cross-polarisation magic-angle spinning (CP-MAS) NMR spectroscopy have identified that the cellulose micro phase-separates with no remaining cellulose I allomorph and eventually forms a proportion of the cellulose II allomorph after water washing and drying. The rheological properties of these solutions demonstrate the possibility of a new type of cellulose processing, whereby morphology can be influenced by changing temperature.


Assuntos
Celulose , Líquidos Iônicos , Acetatos , Celulose/química , Dimetil Sulfóxido/química , Imidazóis/química , Líquidos Iônicos/química , Lactonas
3.
Langmuir ; 38(17): 5197-5208, 2022 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-34879650

RESUMO

Poly(aminoethyl methacrylate) (PAEMA), poly(ethylene oxide)-block-(aminoethyl methacrylate) (PEO-PAEMA), and their guanidinylated derivates, poly(guanidine ethyl methacrylate) (PGEMA) and poly(ethylene oxide)-block-(guanidine ethyl methacrylate) (PEO-PGEMA), were prepared to study their capabilities for CO2 adsorption and release. The polymers of different forms or degree of guanidinylation were thoroughly characterized, and their interaction with CO2 was studied by NMR and calorimetry. The extent and kinetics of adsorption and desorption of N2 and CO2 were investigated by thermogravimetry under controlled gas atmospheres. The materials did not adsorb N2, whereas CO2 could be reversibly adsorbed at room temperature and released by an elevated temperature. The most promising polymer was PGEMA with a guanidinylation degree of 7% showing a CO2 adsorption capacity of 2.4 mmol/g at room temperature and a desorption temperature of 72 °C. The study also revealed relations between the polymer chemical composition and CO2 adsorption and release characteristics that are useful in future formulations for CO2 adsorbent polymer materials.

4.
Small ; 17(27): e2005205, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-33491913

RESUMO

Because of their lightweight structure, flexibility, and immunity to electromagnetic interference, polymer optical fibers (POFs) are used in numerous short-distance applications. Notably, the incorporation of luminescent nanomaterials in POFs offers optical amplification and sensing for advanced nanophotonics. However, conventional POFs suffer from nonsustainable components and processes. Furthermore, the traditionally used luminescent nanomaterials undergo photobleaching, oxidation, and they can be cytotoxic. Therefore, biopolymer-based optical fibers containing nontoxic luminescent nanomaterials are needed, with efficient and environmentally acceptable extrusion methods. Here, such an approach for fibers wet-spun from aqueous methylcellulose (MC) dispersions under ambient conditions is demonstrated. Further, the addition of either luminescent gold nanoclusters, rod-like cellulose nanocrystals or gold nanocluster-cellulose nanocrystal hybrids into the MC matrix furnishes strong and ductile composite fibers. Using cutback attenuation measurement, it is shown that the resulting fibers can act as short-distance optical fibers with a propagation loss as low as 1.47 dB cm-1 . The optical performance is on par with or even better than some of the previously reported biopolymeric optical fibers. The combination of excellent mechanical properties (Young's modulus and maximum strain values up to 8.4 GPa and 52%, respectively), low attenuation coefficient, and high photostability makes the MC-based composite fibers excellent candidates for multifunctional optical fibers and sensors.


Assuntos
Ouro , Metilcelulose , Celulose , Módulo de Elasticidade , Fibras Ópticas
5.
Langmuir ; 37(8): 2639-2648, 2021 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-33594889

RESUMO

Poly(N-acryloyl glycinamide) is a well-known thermoresponsive polymer possessing an upper critical solution temperature (UCST) in water. By copolymerizing N-acryloyl glycinamide (NAGA) with methacrylic acid (MAA) in the presence of a crosslinker, poly(N-acryloyl glycinamide-co-methacrylic acid) [P(NAGA-MAA)] copolymer microgels with an MAA molar fraction of 10-70 mol % were obtained. The polymerization kinetics suggests that the copolymer microgels have a random structure. The size of the microgels was between 60 and 120 nm in the non-aggregated swollen state in aqueous medium and depending on the solvent conditions, they show reversible swelling and shrinking upon temperature change. Their phase transition behavior was studied by a combination of methods to understand the process of the UCST-type behavior and interactions between NAGA and MAA. P(NAGA-MAA) microgels were loaded with silver nanoparticles (AgNPs) by the reduction of AgNO3 under UV light. Compared with the chemical reduction of AgNO3, the photoreduction results in smaller AgNPs and the amount and size of the AgNPs are dependent on the comonomer ratio. The catalytic activity of the AgNP-loaded microgels in 4-nitrophenol reduction was tested.

6.
Biomacromolecules ; 21(2): 830-838, 2020 02 10.
Artigo em Inglês | MEDLINE | ID: mdl-31940433

RESUMO

We show ionically cross-linked, temperature-responsive reversible or irreversible hydrogels of anionic cellulose nanocrystals (CNCs) and methacrylate terpolymers by mixing them homogeneously in the initially charge-neutral state of the polymer, which was subsequently switched to be cationic by cleaving side groups by UV irradiation. The polymer is a random terpolymer poly(di(ethylene glycol) methyl ether methacrylate)-rnd-poly(oligo(ethylene glycol) methyl ether methacrylate)-rnd-poly(2-((2-nitrobenzyl)oxycarbonyl)aminoethyl methacrylate), that is, PDEGMA-rnd-POEGMA-rnd-PNBOCAEMA. The PDEGMA and POEGMA repeating units lead to a lower critical solution temperature (LCST) behavior. Initially, homogeneous aqueous mixtures are obtained with CNCs, and no gelation is observed even upon heating to 60 °C. However, upon UV irradiation, the NBOCAEMAs are transformed to cationic 2-aminoethyl methacrylate (AEMA) groups, as 2-nitrobenzaldehyde moieties are cleaved. The resulting mixtures of anionic CNC and cationic PDEGMA-rnd-POEGMA-rnd-PAEMA show gelation for sufficiently high polymer fractions upon heating to 60 °C due to the interplay of ionic interactions and LCST. For short heating times, the gelation is thermoreversible, whereas for long enough heating times, irreversible gels can be obtained, indicating importance of kinetic aspects. The ionic nature of the cross-linking is directly shown by adding NaCl, which leads to gel melting. In conclusion, the optical triggering of the polymer ionic interactions in combination with its LCST phase behavior allows a new way for ionic nanocellulose hydrogel assemblies.


Assuntos
Celulose/efeitos da radiação , Hidrogéis/efeitos da radiação , Nanopartículas/efeitos da radiação , Raios Ultravioleta , Celulose/química , Cromatografia em Gel/métodos , Difusão Dinâmica da Luz/métodos , Hidrogéis/química , Nanopartículas/química , Temperatura
7.
Biomacromolecules ; 21(2): 955-965, 2020 02 10.
Artigo em Inglês | MEDLINE | ID: mdl-31917581

RESUMO

Soft nanoparticles are interesting materials due to their size, deformability, and ability to host guest molecules. Surface properties play an essential role in determining the fate of the particles in biological medium, and coating of the nanoparticles (and polymers) with carbohydrates has been found to be an efficient strategy for increasing their biocompatibility and fine-tuning other important properties such as aqueous solubility. In this work, soft nanogels of poly(N-vinylcaprolactam), PNVCL, were surface-functionalized with different glucose and maltose ligands, and the colloidal properties of the gels were analyzed. The PNVCL nanogels were first prepared via semibatch precipitation polymerization, where a comonomer, propargyl acrylate (PA), was added after preparticle formation. The aim was to synthesize "clickable" nanogels with alkyne groups on their surfaces. The nanogels were then functionalized with two separate azido-glucosides and azido-maltosides (containing different linkers) through a copper-catalyzed azide-alkyne cycloaddition (CuAAc) click reaction. The glucose and maltose bearing nanogels were thermoresponsive and shrank upon heating. Compared to the PNVCL-PA nanogel, the carbohydrate bearing ones were larger, more hydrophilic, had volume phase transitions at higher temperatures, and were more stable against salt-induced precipitation. In addition to investigating the colloidal properties of the nanogels, the carbohydrate recognition was addressed by studying the interactions with a model lectin, concanavalin A (Con A). The binding efficiency was not affected by the temperature, which indicates that the carbohydrate moieties are located on the gel surfaces, and are capable of interacting with other biomolecules independent of temperature. Thus, the synthesis produces nanogels, which have surface functions capable of biorelevant interactions and a thermoresponsive structure. These types of particles can be used for drug delivery.


Assuntos
Caprolactama/análogos & derivados , Glucose/química , Maltose/química , Nanogéis/química , Polímeros/química , Caprolactama/química , Caprolactama/metabolismo , Coloides/química , Coloides/metabolismo , Corantes Fluorescentes/química , Corantes Fluorescentes/metabolismo , Glucose/metabolismo , Maltose/metabolismo , Polímeros/metabolismo , Propriedades de Superfície , Temperatura
8.
Biomacromolecules ; 20(5): 2105-2114, 2019 05 13.
Artigo em Inglês | MEDLINE | ID: mdl-30983326

RESUMO

Alternatives to petroleum-based plastics are of great significance not only from the point of view of their scientific and practical impact but to reduce the environmental footprint. Inspired by the composition and structure of wood's cell walls, we used phenolic acids to endow cellulosic fibers with new properties. The fiber dissolution and homogeneous modification were performed with a recyclable ionic liquid (IL) (tetrabutylammonium acetate ([N4444][OAc]):dimethyl sulfoxide) to attain different levels of reaction activity for three phenolic acids ( p-hydroxybenzoic acid, vanillic acid, and syringic acid). The successful autocatalytic Fischer esterification reaction was thoroughly investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, elemental analysis, and nuclear magnetic resonance spectroscopy (13C CP-MAS, diffusion-edited 1H NMR and multiplicity-edited heteronuclear single quantum coherence). Control of the properties of cellulose in the dispersed state, welding, and IL plasticization were achieved during casting and recrystallization to the cellulose II crystalline allomorph. Films of cellulose carrying grafted acids were characterized with respect to properties relevant to packaging materials. Most notably, despite the low degree of esterification (DS < 0.25), the films displayed a remarkable strength (3.5 GPa), flexibility (strains up to 35%), optical transparency (>90%), and water resistance (WCA ∼ 90°). Moreover, the measured water vapor barrier was found to be similar to that of poly(lactic acid) composite films. Overall, the results contribute to the development of the next-generation green, renewable, and biodegradable films for packaging applications.


Assuntos
Plásticos Biodegradáveis/síntese química , Celulose/análogos & derivados , Líquidos Iônicos/química , Esterificação , Fenóis/química , Embalagem de Produtos/métodos , Resistência à Tração
9.
Chemistry ; 24(11): 2669-2680, 2018 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-29265502

RESUMO

This study aims at extending the understanding of the toxicity mechanism of ionic liquids (ILs) using various analytical methods and cytotoxicity assays. The cytotoxicity of eight ILs and one zwitterionic compound was determined using mammalian and bacterial cells. The time dependency of the IL toxicity was assessed using human corneal epithelial cells. Hemolysis was performed using human red blood cells and the results were compared with destabilization data of synthetic liposomes upon addition of ILs. The effect of the ILs on the size and zeta potential of liposomes revealed information on changes in the lipid bilayer. Differential scanning calorimetry was used to study the penetration of the ILs into the lipid bilayer. Pulsed field gradient nuclear magnetic resonance spectroscopy was used to determine whether the ILs occurred as unimers, micelles, or if they were bound to liposomes. The results show that the investigated ILs can be divided into three groups based on the cytotoxicity mechanism: cell wall disrupting ILs, ILs exerting toxicity through both cell wall penetration and metabolic alteration, and ILs affecting solely on cell metabolism.


Assuntos
Líquidos Iônicos/química , Lipossomos/química , Aliivibrio fischeri/efeitos dos fármacos , Varredura Diferencial de Calorimetria , Linhagem Celular , Difusão Dinâmica da Luz , Epitélio Corneano/citologia , Epitélio Corneano/efeitos dos fármacos , Epitélio Corneano/metabolismo , Eritrócitos/citologia , Eritrócitos/efeitos dos fármacos , Eritrócitos/metabolismo , Hemólise/efeitos dos fármacos , Humanos , Líquidos Iônicos/toxicidade , Espectroscopia de Ressonância Magnética
10.
Biomacromolecules ; 19(7): 2795-2804, 2018 07 09.
Artigo em Inglês | MEDLINE | ID: mdl-29733648

RESUMO

We show that composite hydrogels comprising methyl cellulose (MC) and cellulose nanocrystal (CNC) colloidal rods display a reversible and enhanced rheological storage modulus and optical birefringence upon heating, i.e., inverse thermoreversibility. Dynamic rheology, quantitative polarized optical microscopy, isothermal titration calorimetry (ITC), circular dichroism (CD), and scanning and transmission electron microscopy (SEM and TEM) were used for characterization. The concentration of CNCs in aqueous media was varied up to 3.5 wt % (i.e, keeping the concentration below the critical aq concentration) while maintaining the MC aq concentration at 1.0 wt %. At 20 °C, MC/CNC underwent gelation upon passing the CNC concentration of 1.5 wt %. At this point, the storage modulus ( G') reached a plateau, and the birefringence underwent a stepwise increase, thus suggesting a percolative phenomenon. The storage modulus ( G') of the composite gels was an order of magnitude higher at 60 °C compared to that at 20 °C. ITC results suggested that, at 60 °C, the CNC rods were entropically driven to interact with MC chains, which according to recent studies collapse at this temperature into ring-like, colloidal-scale persistent fibrils with hollow cross-sections. Consequently, the tendency of the MC to form more persistent aggregates promotes the interactions between the CNC chiral aggregates towards enhanced storage modulus and birefringence. At room temperature, ITC shows enthalpic binding between CNCs and MC with the latter comprising aqueous, molecularly dispersed polymer chains that lead to looser and less birefringent material. TEM, SEM, and CD indicate CNC chiral fragments within a MC/CNC composite gel. Thus, MC/CNC hybrid networks offer materials with tunable rheological properties and access to liquid crystalline properties at low CNC concentrations.


Assuntos
Hidrogéis/química , Metilcelulose/química , Nanopartículas/química , Birrefringência , Elasticidade
11.
Biomacromolecules ; 18(4): 1293-1301, 2017 04 10.
Artigo em Inglês | MEDLINE | ID: mdl-28262019

RESUMO

Fiber spinning of anionic TEMPO-oxidized cellulose (TOCN) nanofibrils with polycations by interfacial polyelectrolyte complexation is demonstrated. The formed fibers were mostly composed of cellulose nanofibrils and the polycations were a minor constituent, leading to yield and ultimate strengths of ca. 100 MPa and ca. 200 MPa, and Young's modulus of ca. 15 GPa. Stretching of the as-formed wet filaments of TOCN/polycation by 20% increased the Young's modulus, yield strength, and ultimate tensile strength by approximately 45, 36, and 26%, respectively. Importantly, feasibility of compartmentalized wound bicomponent fibers by simultaneous spinning of two fibers of different compositions and entwining them together was shown. This possibility was further exploited to demonstrate reversible shape change of a bicomponent fiber directly by humidity change, and indirectly by temperature changes based on thermally dependent humidity absorption. The demonstrated route for TOCN-based fiber preparation is expected to open up new avenues in the application of nanocelluloses in advanced fibrous materials, crimping, and responsive smart textiles.


Assuntos
Celulose Oxidada/química , Óxidos N-Cíclicos/química , Nanofibras/química , Polieletrólitos/química , Polietilenos/química , Compostos de Amônio Quaternário/química , Módulo de Elasticidade , Fenômenos Mecânicos , Microscopia de Força Atômica , Microscopia Eletrônica de Varredura , Nanofibras/ultraestrutura , Reologia , Propriedades de Superfície , Resistência à Tração
12.
Biomacromolecules ; 16(3): 1062-71, 2015 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-25665073

RESUMO

One of the major, but often overlooked, challenges toward high end applications of nanocelluloses is to maintain their high mechanical properties under hydrated or even fully wet conditions. As such, permanent covalent cross-linking or surface hydrophobization are viable approaches, however, the former may hamper processability and the latter may have adverse effect on interfibrillar bonding and resulting material strength. Here we show a concept based on physical cross-linking of cellulose nanofibers (CNF, also denoted as microfibrillated cellulose, MFC, and, nanofibrillated cellulose, NFC) with chitosan for the aqueous preparation of films showing high mechanical strength in the wet state. Also, transparency (∼70-90% in the range 400-800 nm) is achieved by suppressing aggregation and carefully controlling the mixing conditions: Chitosan dissolves in aqueous medium at low pH and under these conditions the CNF/chitosan mixtures form easily processable hydrogels. A simple change in the environmental conditions (i.e., an increase of pH) reduces hydration of chitosan promoting multivalent physical interactions between CNF and chitosan over those with water, resulting effectively in cross-linking. Wet water-soaked films of CNF/chitosan 80/20 w/w show excellent mechanical properties, with an ultimate wet strength of 100 MPa (with corresponding maximum strain of 28%) and a tensile modulus of 4 and 14 GPa at low (0.5%) and large (16%) strains, respectively. More dry films of similar composition display strength of 200 MPa with maximum strain of 8% at 50% air relative humidity. We expect that the proposed, simple concept opens new pathways toward CNF-based material utilization in wet or humid conditions, which has still remained a challenge.


Assuntos
Quitosana/química , Nanofibras/química , Papel , Celulose/química , Concentração de Íons de Hidrogênio , Interações Hidrofóbicas e Hidrofílicas , Fenômenos Ópticos , Resistência à Tração , Água/química
13.
Carbohydr Polym ; 339: 122242, 2024 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-38823911

RESUMO

Glucuronoxylans (GX), particularly crude fractions obtained by pressurized hot water extraction of birch wood, act as potent emulsifiers and stabilizers against physical separation and lipid oxidation. Herein, we studied the adsorption of GX on hydrophobic interfaces to correlate their multicomponent character towards the formation of interfacial layers in emulsions. Dynamic interfacial tension (DIFT) and quartz crystal microgravimetry with dissipation monitoring (QCM-D) were applied to various GX fractions and the results compared with those from cellulose-based emulsifiers. The roles of residual lignin and polysaccharides are discussed considering the formation of interfacial layers during emulsification. The DIFT of the different GXs reached quasi-equilibrium faster as the lignin concentration increased, implying a correlation between the rate of adsorption and the residual lignin content. The effect of NaCl addition was more pronounced in polysaccharide-rich fractions, indicating that the polysaccharide fraction modulated the effect of ionic strength. QCM-D showed that despite the fast adsorption exhibited by the lignin-rich GX extract in the DIFT curves, the adsorbed materials were lightweight, suggesting that the polysaccharide fraction built the bulk of the interfacial layer. These results provide a foundation towards understanding the role of GX in interfacial stabilization beyond traditional plant-based counterparts.

14.
Chemistry ; 19(39): 12978-81, 2013 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-24038302

RESUMO

1-2-3 gel! Subcomponent self-assembly is introduced as a new design route towards multistimuli-responsive metallogels. It offers a rapid and facile access to supramolecular gels and allows to design smart materials with diverse functional and structural properties by simply exchanging one (or more) of the components. Herein, the exchange of the metal ions is emphasized (see scheme).

15.
Biomater Sci ; 11(14): 4972-4984, 2023 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-37334482

RESUMO

Microfluidic on-chip production of polymeric hydrogel microspheres (MPs) can be designed for the loading of different biologically active cargos and living cells. Among different gelation strategies, ionically crosslinked microspheres generally show limited mechanical properties, meanwhile covalently crosslinked microspheres often require the use of crosslinking agents or initiators with limited biocompatibility. Inverse electron demand Diels Alder (iEDDA) click chemistry is a promising covalent crosslinking method with fast kinetics, high chemoselectivity, high efficiency and no cross-reactivity. Herein, in situ gellable iEDDA-crosslinked polymeric hydrogel microspheres are developed via water-in-oil emulsification (W/O) glass microfluidics. The microspheres are composed of two polyethylene glycol precursors modified with either tetrazine or norbornene as functional moieties. Using a single co-flow glass microfluidic platform, homogenous MPs of sizes 200-600 µm are developed and crosslinked within 2 minutes. The rheological properties of iEDDA crosslinked bulk hydrogels are maintained with a low swelling degree and a slow degradation behaviour under physiological conditions. Moreover, a high-protein loading capacity can be achieved, and the encapsulation of mammalian cells is possible. Overall, this work provides the possibility of developing microfluidics-produced iEDDA-crosslinked MPs as a potential drug vehicle and cell encapsulation system in the biomedical field.


Assuntos
Compostos Heterocíclicos , Hidrogéis , Animais , Hidrogéis/química , Microfluídica , Encapsulamento de Células , Química Click , Elétrons , Microesferas , Norbornanos/química , Mamíferos
16.
Chem Commun (Camb) ; 59(61): 9408-9411, 2023 Jul 27.
Artigo em Inglês | MEDLINE | ID: mdl-37436128

RESUMO

The reaction of reducing end groups in cellulose nanocrystals with dodecylamine was examined. Using a direct-dissolution solution-state NMR protocol, the regioselective formation of glucosylamines was shown. This provides an elegant approach to sustainably functionalize these bio-based nanomaterials, that may not require further reduction to more stable secondary amines.

17.
Nat Protoc ; 18(7): 2084-2123, 2023 07.
Artigo em Inglês | MEDLINE | ID: mdl-37237027

RESUMO

Owing to its high sustainable production capacity, cellulose represents a valuable feedstock for the development of more sustainable alternatives to currently used fossil fuel-based materials. Chemical analysis of cellulose remains challenging, and analytical techniques have not advanced as fast as the development of the proposed materials science applications. Crystalline cellulosic materials are insoluble in most solvents, which restricts direct analytical techniques to lower-resolution solid-state spectroscopy, destructive indirect procedures or to 'old-school' derivatization protocols. While investigating their use for biomass valorization, tetralkylphosphonium ionic liquids (ILs) exhibited advantageous properties for direct solution-state nuclear magnetic resonance (NMR) analysis of crystalline cellulose. After screening and optimization, the IL tetra-n-butylphosphonium acetate [P4444][OAc], diluted with dimethyl sulfoxide-d6, was found to be the most promising partly deuterated solvent system for high-resolution solution-state NMR. The solvent system has been used for the measurement of both 1D and 2D experiments for a wide substrate scope, with excellent spectral quality and signal-to-noise, all with modest collection times. The procedure initially describes the scalable syntheses of an IL, in 24-72 h, of sufficient purity, yielding a stock electrolyte solution. The dissolution of cellulosic materials and preparation of NMR samples is presented, with pretreatment, concentration and dissolution time recommendations for different sample types. Also included is a set of recommended 1D and 2D NMR experiments with parameters optimized for an in-depth structural characterization of cellulosic materials. The time required for full characterization varies between a few hours and several days.


Assuntos
Líquidos Iônicos , Líquidos Iônicos/química , Solubilidade , Celulose/química , Solventes/química , Espectroscopia de Ressonância Magnética , Eletrólitos/química
18.
Mol Pharm ; 9(7): 1932-41, 2012 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-22591051

RESUMO

The use of additives in crystallization of pharmaceuticals is known to influence the particulate properties critically affecting downstream processing and the final product performance. Desired functionality can be build into these materials, e.g. via optimized synthesis of a polymeric additive. One such additive is the thermosensitive polymer poly(N-isopropyl acrylamide) (PNIPAM). The use of PNIPAM as a crystallization additive provides a possibility to affect viscosity at separation temperatures and nucleation and growth rates at higher temperatures. In this study, novel PNIPAM derivatives consisting of both isotactic-rich and atactic blocks were used as additives in evaporative crystallization of a model compound, nitrofurantoin (NF). Special attention was paid to possible interactions between NF and PNIPAM and the aggregation state of PNIPAM as a function of temperature and solvent composition. Optical light microscopy and Raman and FTIR spectroscopy were used to investigate the structure of the NF crystals and possible interaction with PNIPAM. A drastic change in the growth mechanism of nitrofurantoin crystals as monohydrate form II (NFMH-II) was observed in the presence of PNIPAM; the morphology of crystals changed from needle to dendritic shape. Additionally, the amphiphilic nature of PNIPAM increased the solubility of nitrofurantoin in water. PNIPAMs with varying molecular weights and stereoregularities resulted in similar changes in the crystal habit of the drug regardless of whether the polymer was aggregated or not. However, with increased additive concentration slower nucleation and growth rates of the crystals were observed. Heating of the crystallization medium resulted in phase separation of the PNIPAM. The phase separation had an influence on the achieved crystal morphology resulting in fewer, visually larger and more irregular dendritic crystals. No proof of hydrogen bond formation between PNIPAM and NF was observed, and the suggested mechanism for the observed dendritic morphology is related to the steric hindrance phenomenon. PNIPAM can be used as a crystallization additive with an obvious effect on the growth of NF crystals.


Assuntos
Resinas Acrílicas/química , Polímeros/química , Cristalização/métodos , Peso Molecular , Nitrofurantoína/química , Solubilidade , Solventes/química , Temperatura , Viscosidade , Água/química
19.
Langmuir ; 28(41): 14792-8, 2012 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-22994542

RESUMO

Aqueous solution and water-air interfacial properties of associative thermally responsive A-B-A stereoblock poly(N-isopropylacryl amide), PNIPAM, polymers were studied and compared to atactic PNIPAM. The A-B-A polymers consist of atactic PNIPAM as a hydrophilic block (either A or B) and a water-insoluble block of isotactic PNIPAM. The surface tensions of aqueous PNIPAM solutions were measured as a function of both temperature and concentration. The isotactic blocks did not have an effect on the surface activity of the solutions. Rheological measurements on the water-air interface showed that the aggregated PNIPAMs containing isotactic blocks increased the elasticity of the surface significantly as compared to the atactic reference upon heating. Two fluorescence probes, pyrene and (4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (4HP), added to the aqueous polymer solutions were concluded to reside in surroundings with lower polarity and increased microviscosity in cases when the polymers contained isotactic blocks, as compared to ordinary atactic polymers.


Assuntos
Acrilamidas/química , Fluorescência , Polímeros/química , Resinas Acrílicas , Modelos Moleculares , Estrutura Molecular , Reologia , Tensão Superficial
20.
Ultrason Sonochem ; 85: 105970, 2022 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-35367736

RESUMO

Lipid-based materials, such as substitutes for saturated fats (oleogels) structurally modified with ultrasonic standing waves (USW), have been developed by our group. To enable their potential application in food products, pharmaceuticals, and cosmetics, practical and economical production methods are needed. Here, we report scale-up of our procedure of structurally modifying oleogels via the use of USW by a factor of 200 compared to our previous microfluidic chamber. To this end, we compared three different USW chamber prototypes through finite element simulations (FEM) and experimental work. Imaging of the internal structure of USW-treated oleogels was used as feedback for successful development of chambers, i.e., the formation of band-like structures was the guiding factor in chamber development. We then studied the bulk mechanical properties by a uniaxial compression test of the sonicated oleogels obtained with the most promising USW chamber, and sampled local mechanical properties using scanning acoustic microscopy. The results were interpreted using a hyperelastic foam model. The stability of the sonicated oleogels was compared to control samples using automated image analysis oil-release tests. This work enabled the effective mechanical-structural manipulation of oleogels in volumes of 10-100 mL, thus paving the way for USW treatments of large-scale lipid-based materials.


Assuntos
Compostos Orgânicos , Ultrassom , Ácidos Graxos/análise , Compostos Orgânicos/química , Ondas Ultrassônicas
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