RESUMEN
Ternary oil-water-surfactant systems can give rise to an O/W microemulsion in equilibrium with excess oil, a W/O microemulsion in equilibrium with excess water, or a bicontinuous microemulsion in equilibrium with excess oil and water. This type of phase behavior has been known for a long time and the three systems are often referred to as Winsor I, Winsor II and Winsor III, respectively after the British scientist P. A. Winsor who pioneered the area. The Winsor systems are technically important and well understood today. It was later found that addition of a polymer to the oil-water-surfactant system can influence the phase behavior considerably. While a hydrophilic polymer will be incorporated in the water phase and a hydrophobic polymer in the oil phase, an amphiphilic polymer with the right hydrophilic-lipophilic balance may expand the middle phase microemulsion in a Winsor III system. Expansion of the middle phase of such a system will lead to a reduction of the oil/microemulsion and the microemulsion/water interfacial tensions. This can be practically important, and the effect is currently of considerable interest for so-called surfactant flooding for enhanced oil recovery (EOR). Boosting the middle phase of the Winsor III system by addition of a polymer to the surfactant system is still not an established procedure and not so well understood from a scientific point of view. In this review we summarize the work done in the field and we demonstrate that the role of the polymer is intimately linked to its interactions with the three other components in the system: the oil, the water, and the surfactant(s).
RESUMEN
Desoxyribosenucleic acid, DNA, and cellulose molecules self-assemble in aqueous systems. This aggregation is the basis of the important functions of these biological macromolecules. Both DNA and cellulose have significant polar and nonpolar parts and there is a delicate balance between hydrophilic and hydrophobic interactions. The hydrophilic interactions related to net charges have been thoroughly studied and are well understood. On the other hand, the detailed roles of hydrogen bonding and hydrophobic interactions have remained controversial. It is found that the contributions of hydrophobic interactions in driving important processes, like the double-helix formation of DNA and the aqueous dissolution of cellulose, are dominating whereas the net contribution from hydrogen bonding is small. In reviewing the roles of different interactions for DNA and cellulose it is useful to compare with the self-assembly features of surfactants, the simplest case of amphiphilic molecules. Pertinent information on the amphiphilic character of cellulose and DNA can be obtained from the association with surfactants, as well as on modifying the hydrophobic interactions by additives.
Asunto(s)
Celulosa , ADN , Enlace de Hidrógeno , Interacciones Hidrofóbicas e Hidrofílicas , TensoactivosRESUMEN
Double-chain amphiphilic compounds, including surfactants and lipids, have broad significance in applications like personal care and biology. A study on the phase structures and their transitions focusing on dioctadecyldimethylammonium chloride (DODAC), used inter alia in hair conditioners, is presented. The phase behaviour is dominated by two bilayer lamellar phases, Lß and Lα, with "solid" and "melted" alkyl chains, respectively. In particular, the study is focused on the effect of additives of different polarity on the phase transitions and structures. The main techniques used for investigation were differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering (SAXS and WAXS). From the WAXS reflections, the distance between the alkyl chains in the bilayers was obtained, and from SAXS, the thicknesses of the surfactant and water layers. The Lα phase was found to have a bilayer structure, generally found for most surfactants; a Lß phase made up of bilayers with considerable chain tilting and interdigitation was also identified. Depending mainly on the polarity of the additives, their effects on the phase stabilities and structure vary. Compounds like urea have no significant effect, while fatty acids and fatty alcohols have significant effects, but which are quite different depending on the nonpolar part. In most cases, Lß and Lα phases exist over wide composition ranges; certain additives induce transitions to other phases, which include cubic, reversed hexagonal liquid crystals and bicontinuous liquid phases. For a system containing additives, which induce a significant lowering of the Lß-Lα transition, we identified the possibility of a triggered phase transition via dilution with water.
RESUMEN
Cellulose is the most abundant polymer and a very important renewable resource. Since cellulose cannot be shaped by melting, a major route for its use for novel materials, new chemical compounds and renewable energy must go via the solution state. Investigations during several decades have led to the identification of several solvents of notably different character. The mechanisms of dissolution in terms of intermolecular interactions have been discussed from early work but, even on fundamental aspects, conflicting and opposite views appear. In view of this, strategies for developing new solvent systems for various applications have remained obscure. There is for example a strong need for using forest products for higher value materials and for environmental and cost reasons to use water-based solvents. Several new water-based solvents have been developed recently but there is no consensus regarding the underlying mechanisms. Here we wish to address the most important mechanisms described in the literature and confront them with experimental observations. A broadened view is helpful for improving the current picture and thus cellulose derivatives and phenomena such as fiber dissolution, swelling, regeneration, plasticization and dispersion are considered. In addition to the matter of hydrogen bonding versus hydrophobic interactions, the role of ionization as well as some applications of new knowledge gained are highlighted.
RESUMEN
Neutron and X-ray reflection measurements have been used to study the structure of the adsorbed layer of a chelating surfactant at the air/liquid interface. The chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (C12-DTPA) has a large headgroup containing eight donor atoms that can participate in the coordination of metal ions. The donor atoms are also titrating, resulting in an amphoteric surfactant that can adopt a number of differently charged species depending on the pH. Very strong coordination complexes are formed with metal ions, where the metal ion can be considered as part of the surfactant structure, in contrast to monovalent cations that act as regular counterions to the negative net charge. Adsorption was investigated over a large concentration interval, from well below the critical micelle concentration (cmc) to five times the cmc. The most striking result is the maximum in the surface excess found around the cmc, which is consistent with previous indications from surface tension measurements. Adding divalent metal ions has a limited effect on the adsorption at the air/liquid interface. The reason is the coordination of the metal ion, resulting in compensating deprotonation of the complex. Small variations in the headgroup area of different metal complexes are found, correlating to the conditional stability constants. Adding sodium chloride has a significant effect on the adsorption behavior, and the results indicate that the protonation equilibrium is more important than the ionic strength effects. From combined fits of the neutron and X-ray data, a model that consists of a thick headgroup region and a relatively thin dehydrated tail region is found, and it indicates that the tails are not fully extended and that the limiting area per molecule is determined by the bulky headgroup.
RESUMEN
Dodecyltrimethylammonium triflate (DTATf) micelles possess lower degree of counterion dissociation (α), lower hydration, and higher packing of monomers than other micelles of similar structure. Addition of sodium triflate ([NaTf] > 0.05 M) to DTATf solutions promotes phase separation. This phenomenon is commonly observed in oppositely charged surfactant mixtures, but it is rare for ionic surfactants and relatively simple counterions. While the properties of DTATf have already been reported, the driving forces for the observed phase separation with added salt remain unclear. Thus, we propose an interpretation for the observed phase separation in cationic surfactant solutions. Addition of up to 0.03 M NaTf to micellar DTATf solutions led to a limited increase of the aggregation number, to interface dehydration, and to a progressive decrease in α. The viscosity of DTATf solutions of higher concentration ([DTATf] ≥ 0.06 M) reached a maximum with increasing [NaTf], though the aggregation number slightly increased, and no shape change occurred. We hypothesize that this maximum results from a decrease in interaggregate repulsion, as a consequence of increased ion binding. This reduction in micellar repulsion without simultaneous infinite micellar growth is, probably, the major driving force for phase separation at higher [NaTf].
RESUMEN
Compartmentalized systems produced via the layer-by-layer (LbL) self-assembly method have been produced by alternatively depositing alginate and chitosan layers onto cores of liposomes. The combination of dynamic light scattering (DLS), ζ potential, and transmission electron microscopy (TEM) techniques provides detailed information on the stability, dimensions, charge, and wall thickness of these polyelectrolyte globules. TEM microphotographs demonstrate the presence of nanocapsules with an average diameter of below 300 nm and with a polyelectrolyte wall thickness of about 20 nm. The possibility of encapsulating and releasing molecules from this type of nanocapsule was demonstrated by loading FITC-dextrans of different molecular weights in the liposome system. The release of the loaded molecules from the nanocapsule was demonstrated after liposome core dissolution. Even at low molecular weight (20 kDa), the nanocapsules appear to be appropriate for prolonged molecule compartmentalization and protection. By means of the Ritger-Peppas model, non-Fickian transport behavior was detected for the diffusion of dextran through the polyelectrolyte wall. Values of the diffusion coefficient were calculated and yield useful information regarding chitosan/alginate hollow nanocapsules as drug-delivery systems. The influence of the pH on the release properties was also considered. The results indicate that vesicle-templated hollow polyelectrolyte nanocapsules show great potential as novel controllable drug-delivery devices for biomedical and biotechnological applications.
Asunto(s)
Alginatos/química , Quitosano/química , Liposomas/química , Nanocápsulas/química , Tomografía con Microscopio Electrónico , Ácido Glucurónico/química , Ácidos Hexurónicos/química , Concentración de Iones de Hidrógeno , Liposomas/ultraestructura , Nanocápsulas/ultraestructura , Tamaño de la PartículaRESUMEN
DNA is a highly charged polyelectrolyte and is prone to associative phase separation driven by the presence of multivalent cations, charged surfactants, proteins, polymers and colloids. The process of DNA phase separation induced by positively charged species is often called DNA condensation. Generally, it refers to either intramolecular DNA compaction (coil-globule transition) or intermolecular DNA aggregation with macroscopic phase separation, but the formation of a DNA liquid crystalline system is also displayed. This has traditionally been described by polyelectrolyte theory and qualitative (Flory-Huggins-based) polymer theory approaches. DNA in the cell nucleus is packed into chromatin wound around the histone octamer (a protein complex comprising two copies each of the four histone proteins H2A, H2B, H3 and H4) to form nucleosomes separated by linker DNA. During the last decade, the phenomenon of the formation of biomolecular condensates (dynamic droplets) by liquid-liquid phase separation (LLPS) has emerged as a generally important mechanism for the formation of membraneless organelles from proteins, nucleic acids and their complexes. DNA and chromatin droplet formation through LLPS has recently received much attention by in vitro as well as in vivo studies that established the importance of this for compartmentalisation in the cell nucleus. Here, we review DNA and chromatin LLPS from a general colloid physical chemistry perspective. We start with a general discussion of colloidal phase separation in aqueous solutions and review the original (pre-LLPS era) work on DNA (macroscopic) phase separation for simpler systems with DNA in the presence of multivalent cations and well-defined surfactants and colloids. Following that, we discuss and illustrate the similarities of such macroscopic phase separation with the general behaviour of LLPS droplet formation by associative phase separation for DNA-protein systems, including chromatin; we also note cases of segregative association. The review ends with a discussion of chromatin LLPS in vivo and its physiological significance.
Asunto(s)
Cromatina , Histonas , Histonas/metabolismo , Polielectrolitos , Separación de Fases , ADN , Polímeros/metabolismo , Química Física , Coloides , Cationes/metabolismo , TensoactivosRESUMEN
Calcium alginate beads, which are biodegradable and biocompatible, have been widely employed as delivery matrices for biomacromolecules. In the present work, the feasibility of encapsulation of DNA (which is used as a model biomacromolecule) in calcium alginate nanobeads (sub-200 nm size), prepared using a recently developed protocol based on the phase inversion temperature (PIT) emulsification method [Machado et al. Langmuir 2012, 28, 4131-4141], was assessed. The properties of the nanobeads were compared to those of the corresponding macroscopic (millimeter sized) calcium alginate beads. It was found that DNA, representing a relatively stiff and highly charged polyanion (thus like-charged to alginate), could be efficiently encapsulated in both nanosized and macroscopic beads, with encapsulation yields in the range of 77-99%. Complete release of DNA from the beads could be accomplished on dissolution of the gel by addition of a calcium-chelating agent. Importantly, the DNA was not denatured or fragmented during the preparation and collection of the nanobeads, which are good indicators of the mildness of the preparation protocol used. The calcium alginate nanobeads prepared by the herein utilized protocol thus show good potential to be used as carriers of sensitive biomacromolecules.
Asunto(s)
Alginatos/química , ADN/química , Nanopartículas/química , Cápsulas , Estudios de Factibilidad , Geles , Ácido Glucurónico/química , Ácidos Hexurónicos/química , Temperatura , Agua/químicaRESUMEN
The macroscopic phase behavior and other physicochemical properties of dilute aqueous mixtures of DNA and the cationic surfactant hexadecyltrimethylammounium bromide (CTAB), DNA and the polyamine spermine, or DNA, CTAB, and (2-hydroxypropyl)-ß-cyclodextrin (2HPßCD) were investigated. When DNA is mixed with CTAB we found, with increasing surfactant concentration, (1) free DNA coexisting with surfactant unimers, (2) free DNA coexisting with aggregates of condensed DNA and CTAB, (3) a miscibility gap where macroscopic phase separation is observed, and (4) positively overcharged aggregates of condensed DNA and CTAB. The presence of a clear solution beyond the miscibility gap cannot be ascribed to self-screening by the charges from the DNA and/or the surfactant; instead, hydrophobic interactions among the surfactants are instrumental for the observed behavior. It is difficult to judge whether the overcharged mixed aggregates represent an equilibrium situation or not. If the excess surfactant was not initially present, but added to a preformed precipitate, redissolution was, in consistency with previous reports, not observed; thus, kinetic effects have major influence on the behavior. Mixtures of DNA and spermine also displayed a miscibility gap; however, positively overcharged aggregates were not identified, and redissolution with excess spermine can be explained by electrostatics. When 2HPßCD was added to a DNA-CTAB precipitate, redissolution was observed, and when it was added to the overcharged aggregates, the behavior was essentially a reversal of that of the DNA-CTAB system. This is attributed to an effectively quantitative formation of 1:1 2HPßCD-surfactant inclusion complexes, which results in a gradual decrease in the concentration of effectively available surfactant with increasing 2HPßCD concentration.
Asunto(s)
Compuestos de Cetrimonio/química , Ciclodextrinas/química , ADN/química , Espermina/química , Tensoactivos/química , Cationes/química , Cetrimonio , Dicroismo Circular , Luz , Dispersión de Radiación , Espectrofotometría UltravioletaRESUMEN
Complex salts of double-stranded DNA with amphiphilic counterions offer novel opportunities for studies of DNA-lipid interactions. Here the effect of the hydrophobicity of the amphiphilic counterion is in focus. For this purpose, double stranded DNA with didodecyldimethylammonium ions as counterions, DDADNA, is prepared and investigated with respect to microstructure. In particular, in order to monitor the interactions with phospholipids, the phase diagram of the DDADNA/lecithin/water system is determined and compared with the previously determined phase diagram with single alkyl chain counterions, dodecyltrimethylammonium, DTA. In both systems, there is a formation of lamellar and reverse hexagonal phases, where hydrated DNA is sandwiched between bilayers or forms the core of reverse cylindrical micelles, respectively. However, whereas the lecithin lamellar phase can incorporate large amounts of DDADNA, there is in the case of the single chain surfactant, DTADNA, a transition to a bicontinuous cubic phase at higher DTADNA concentrations. The general appearance of the phase diagrams, and in particular the role of counterion hydrophobicity, can be rationalized in a simple geometric model.
Asunto(s)
ADN/química , Lecitinas/química , Compuestos de Amonio Cuaternario/química , Interacciones Hidrofóbicas e HidrofílicasRESUMEN
Full equilibrium phase diagrams are presented for two ternary systems composed of the cationic surfactant dodecyltrimethylammonium bromide (DTAB), water (D(2)O), and a cyclodextrin, either ß-cyclodextrin (ß-CD) or (2-hydroypropyl)-ß-cyclodextrin (2HPßCD). (2)H NMR, SAXS, WAXS, and visual examination were used to determine the phase boundaries and characterize the nature of the phases formed. Additionally, diffusion (1)H NMR was used to investigate parts of the diagrams. The water solubility of 2HPßCD is 80% (w/w), whereas it is only 1.85% (w/w) for ß-CD. Solubility increases for both species upon complexation with DTAB; while the increase is minute for 2HPßCD, it is dramatic for ß-CD. Both systems displayed an isotropic liquid solution (L(1)) one-phase region, the extension of which differs extensively between the two systems. Additionally, the DTAB:2HPßCD:water system also comprised a normal hexagonal (H(1)) area, which was not found for the DTAB:ß-CD:water system. In the DTAB:ß-CD:water system, on the other hand, we found cocrystallization of DTAB and ß-CD. From this work we conclude that DTAB and CD molecules form 1:1 inclusion complexes with high affinities. Moreover, we observed indications of an association of 2HPßCD to DTAB micelles in the isotropic solution phase, which was not the case for ß-CD and DTAB micelles. This is, to our knowledge, the first complete phase diagrams of surfactant-CD mixtures; as a novel feature it includes the observation of cocrystallization at high concentrations.
Asunto(s)
Ciclodextrinas/química , Compuestos de Amonio Cuaternario/química , Tensoactivos/química , Cristalización , Micelas , Agua/químicaRESUMEN
A procedure for the preparation of calcium alginate nanoparticles in the aqueous phase of water-in-oil (W/O) nanoemulsions was developed. The emulsions were produced from mixtures of the nonionic surfactant tetraethylene glycol monododecyl ether (C(12)E(4)), decane, and aqueous solutions of up to 2 wt % sodium alginate by means of the phase inversion temperature (PIT) emulsification method. This method allows the preparation of finely dispersed emulsions without a large input of mechanical energy. With alginate concentrations of 1-2 wt % in the aqueous phase, emulsions showed good stability against Ostwald ripening and narrow, monomodal distributions of droplets with radii <100 nm. Gelation of the alginate was induced by the addition of aqueous CaCl(2) to the emulsions under stirring, and particles formed were collected using a simple procedure based on extraction of the surfactant on addition of excess oil. The final particles were characterized using cryo-transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS). They were found to be essentially spherical with a homogeneous interior, and their size was similar to that of the initial emulsion droplets. The herein presented "low-energy" method for preparation of biocompatible nanoparticles has the potential to be used in various applications, e.g., for the encapsulation of sensitive biomacromolecules.
Asunto(s)
Alginatos/química , Emulsiones/química , Nanopartículas/química , Aceites/química , Agua/química , Microscopía por Crioelectrón , Óxido de Etileno/química , Ácido Glucurónico/química , Ácidos Hexurónicos/química , Microscopía Electrónica de Transmisión , Nanopartículas/ultraestructura , Tensoactivos/química , TemperaturaRESUMEN
In this work we have investigated the structures of aggregates formed in model systems of dilute aqueous mixtures of "model chromatin" consisting of either recombinant nucleosome core particles (NCPs) or nucleosome arrays consisting of 12 NCPs connected with 30 bp linker DNA, and liposomes made from different mixtures of cationic and zwitterionic lipids, 1,2-dioleoyl-3-trimethylammonium-propane chloride salt (DOTAP) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). The aggregates formed were characterized using different optical microscopy methods and small-angle X-ray scattering (SAXS), and the results are discussed in terms of the competing intermolecular interactions among the components. For a majority of the samples, the presence of lamellar structures could be identified. In samples with high fractions of DOTAP in the liposomes, well-defined lamellar structures very similar to those formed by the corresponding lipid mixtures and DNA alone (i.e., without histone proteins) were observed; in these aggregates, the histones are expelled from the model chromatin. The findings suggest that, with liposomes containing large fractions of cationic lipid, the dominating driving force for aggregation is the increase in translational entropy from the release of counterions, whereas with lower fractions of the cationic lipid, the entropy of mixing of the lipids within the bilayers results in a decreased DNA-lipid attraction.
Asunto(s)
Cationes/química , Ensamble y Desensamble de Cromatina , Cromatina/química , ADN/química , Membrana Dobles de Lípidos/química , Ácidos Grasos Monoinsaturados/metabolismo , Histonas/química , Liposomas/química , Microscopía Confocal , Microscopía Fluorescente , Nanotecnología/métodos , Nucleosomas/química , Fosfatidilcolinas/metabolismo , Compuestos de Amonio Cuaternario/metabolismo , Proteínas Recombinantes/química , Dispersión del Ángulo Pequeño , Rayos XRESUMEN
Effects of the addition of a cationic amino acid-based synthetic amphiphile, arginine N-lauroyl amide dihydrochloride (ALA), to a lipid-based transfection formulation have been investigated. It is shown that the inclusion of ALA results in a substantial enhancement of the transfection capability of lipoplexes prepared with liposomes of 1-palmitoyl-2-oleoyl-sn-glycero-3-ethylphosphocholine and cholesterol, which themselves mediate highly efficient transfection. A possible explanation for the increased biological activity is that ALA adsorbed to the surface of the DNA-lipid complexes is involved in triggering internalization. However, in order to identify possible additional factors underlying the enhanced transfection efficiency, the physical properties of formulations with and without ALA were characterized using cryo-transmission electron microscopy, dynamic light scattering, and an ethidium bromide intercalation assay. ALA seems to have limited influence on the initial internal structure of the complexes and the protection of DNA, but its presence is found to decrease the average effective size of the dispersed particles; this change in size may be important in improving the biological activity. Furthermore, ALA can act to influence the transfection efficiency of the formulation by promoting the release of DNA following internalization in the transfected cells.
Asunto(s)
Arginina/análogos & derivados , ADN/química , Liposomas/química , Transfección/métodos , Animales , Células Cultivadas , Colesterol/química , Microscopía por Crioelectrón , ADN/administración & dosificación , Etidio/química , Femenino , Interacciones Hidrofóbicas e Hidrofílicas , Liposomas/administración & dosificación , Ratones , Ratones Endogámicos BALB C , Fosforilcolina/análogos & derivados , Dispersión de RadiaciónRESUMEN
With amphiphilic properties, cellulose molecules are expected to adsorb at the O/W interface and be capable of stabilizing emulsions. The effect of solvent quality on the formation and stability of cellulose-based O/W emulsions was evaluated in different alkaline systems: NaOH, NaOH-urea and tetrabutylammonium hydroxide (TBAH). The optimal solvency conditions for cellulose adsorption at the O/W interface were found for the alkaline solvent with an intermediate polarity (NaOH-urea), which is in line with the favorable conditions for adsorption of an amphiphilic polymer. A very good solvency (in TBAH) and the interfacial activity of the cation lead to lack of stability because of low cellulose adsorption. However, to achieve long-term stability and prevent oil separation in NaOH-urea systems, further reduction in cellulose's solvency was needed, which was achieved by a change in the pH of the emulsions, inducing the regeneration of cellulose at the surface of the oil droplets (in-situ regeneration).
RESUMEN
Iodine added to iodide-based ionic liquids leads to extraordinarily efficient charge transport, vastly exceeding that expected for such viscous systems. Using terahertz time-domain spectroscopy, in conjunction with dc conductivity, diffusivity and viscosity measurements we unravel the conductivity pathways in 1-methyl-3-propylimidazolium iodide melts. This study presents evidence of the Grotthuss mechanism as a significant contributor to the conductivity, and provides new insights into ion pairing processes as well as the formation of polyiodides. The terahertz and transport results are reunited in a model providing a quantitative description of the conduction by physical diffusion and the Grotthuss bond-exchange process. These novel results are important for the fundamental understanding of conduction in molten salts and for applications where ionic liquids are used as charge-transporting media such as in batteries and dye-sensitized solar cells.
Asunto(s)
Líquidos Iónicos/química , Conductividad Eléctrica , Oxidación-ReducciónRESUMEN
The adsorption of and conformation adopted by a branched-linear polymer conjugate to the hydrophilic silica-aqueous solution interface have been studied by in situ null ellipsometry and Monte Carlo simulations. The conjugate is a highly branched polyethyleneimine structure with ethyleneoxide chains grafted to its primary and secondary amino groups. In situ null ellipsometry demonstrated that the polymer conjugate adsorbs to the silica surface from water and aqueous solution of 1 mM asymmetric divalent salt (calcium and magnesium chloride to emulate hard water) over a large pH range. The adsorbed amount is hardly affected by pH and large charge reversal on the negatively charged silica surface occurred at pH = 4.0, due to the adsorption of the cationic polyelectrolyte. The Monte Carlo simulations using an appropriate coarse-grained model of the polymer in solution predicted a core-shell structure with no sharp boundary between the ethyleneimine and ethyleneoxide moieties. The structure at the interface is similar to that in solution when the polymer degree of protonation is low or moderate while at high degree of protonation the strong electrostatic attraction between the ethyleneimine core and oppositely charged silica surface distorts the ethyleneoxide shell so that an "anemone"-like configuration is adopted. The adsorption of alkyl benzene sulfonic acid (LAS) to a preadsorbed polymer layer was also investigated by null ellipsometry. The adsorption data brought additional support for the existence of a strong polymer adsorption and showed the presence of a binding which was further enhanced by the decreased solvency of the surfactant in the salt solution and confirmed the surface charge reversal by the polymer adsorption at pH = 4.0.
Asunto(s)
Óxido de Etileno/química , Polietileneimina/química , Polímeros/química , Dióxido de Silicio/química , Adsorción , Interacciones Hidrofóbicas e Hidrofílicas , Estructura Molecular , Método de MontecarloRESUMEN
Assemblies formed by a well-defined quality of DNA (4331 bp T7 DNA) and the small net-cationic protein lysozyme in dilute aqueous solutions have been characterized using cryo-transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS) as the main techniques. In a wide range of different DNA to lysozyme ratios in solutions of low ionic strength, dispersions of aggregates with the same general morphology and a practically constant hydrodynamic size are formed. The basic structure formed in the dispersions is that of rather flexible worm-like assemblies with a diameter of 10-20 nm, which are suggested to be made up by bundles of on the order of 10 DNA chains with an intervening matrix of lysozyme. With increased ionic strength, the worm-like appearance of the assemblies is lost and they adopt a less well-defined shape. The results suggest that the formation of the DNA-lysozyme aggregates is strongly influenced by cooperative assembly of the components and that, in addition to the electrostatic attraction between DNA and lysozyme, attractive interactions between the protein units are important in governing the behavior of the system.
Asunto(s)
ADN/química , Muramidasa/química , Luz , Microscopía Electrónica de Transmisión , Dispersión de Radiación , Agua/químicaRESUMEN
Polymeric multilayer capsules formed by the Layer-by-Layer (LbL) technique are interesting candidates for the purposes of storage, encapsulation, and release of drugs and biomolecules for pharmaceutical and biomedical applications. In the current study, cellulose-based core-shell particles were developed via the LbL technique alternating two cellulose derivatives, anionic carboxymethylcellulose (CMC), and cationic quaternized hydroxyethylcellulose ethoxylate (QHECE), onto a cationic vesicular template made of didodecyldimethylammonium bromide (DDAB). The obtained capsules were characterized by dynamic light scattering (DLS), ζ potential measurements, and high-resolution scanning electron microscopy (HR-SEM). DLS measurements reveal that the size of the particles can be tuned from a hundred nanometers with a low polydispersity index (deposition of 2 layers) up to micrometer scale (deposition of 6 layers). Upon the deposition of each cellulose derivative, the particle charge is reversed, and pH is observed to considerably affect the process thus demonstrating the electrostatic driving force for LbL deposition. The HR-SEM characterization suggests that the shape of the core-shell particles formed is reminiscent of the spherical vesicle template. The development of biobased nano- and micro-containers by the alternating deposition of oppositely charged cellulose derivatives onto a vesicle template offers several advantages, such as simplicity, reproducibility, biocompatibility, low-cost, mild reaction conditions, and high controllability over particle size and composition of the shell.