PPO Chain Research Articles

Multiscale molecular modeling of bulk amorphous structure of poly(propylene oxide)

An efficient method of multiscale molecular modeling to generate the bulk amorphous structures of coarse-grained (CG) and fully atomistic poly(propylene oxide), PPO, models was developed. The intramolecular short-range interaction of PPO chains was described by the Rotational Isomeric State (RIS) model and the non-bonded intermolecular interaction was represented by the discretized version of Lennard-Jones (LJ) potential energy. Monte Carlo (MC) simulation was implemented to effectively generate and equilibrate the CG models of amorphous structures at the bulk density of PPO, CH3(OCH(CH3)CH2)29OCH3 with the molecular weight of 1728 g/mol, on the second nearest diamond (2nnd) lattice. The reverse mapping of CG models was done to generate the fully atomistic PPO model followed by energy minimization to obtain the relaxed structures. To validate this atomistic PPO model, some molecular and material properties were compared to experimental data with reasonable agreement including chain dimension, conformational statistics, solubility parameter, and X-ray/neutron scatterings.

Synthesis of Poly(propylene oxide)-Poly(N,N'-dimethylacrylamide) Diblock Copolymer Nanoparticles via Reverse Sequence Polymerization-Induced Self-Assembly in Aqueous Solution.

Sterically-stabilized diblock copolymer nanoparticles comprising poly(propylene oxide) (PPO) cores are prepared via reverse sequence polymerization-induced self-assembly (PISA) in aqueous solution. N,N'-Dimethylacrylamide (DMAC) acts as a cosolvent for the weakly hydrophobic trithiocarbonate-capped PPO precursor. Reversible addition-fragmentation chain transfer (RAFT) polymerization of DMAC is initially conducted at 80% w/w solids with deoxygenated water. At 30-60% DMAC conversion, the reaction mixture is diluted to 5-25% w/w solids. The PPO chains become less solvated as the DMAC monomer is consumed, which drives in situ self-assembly to form aqueous dispersions of PPO-core nanoparticles of 120-190 nm diameter at 20 °C. Such RAFT polymerizations are well-controlled (Mw/Mn ≤ 1.31), and more than 99% DMAC conversion is achieved. The resulting nanoparticles exhibit thermoresponsive character: dynamic light scattering and transmission electron microscopy studies indicate the formation of more compact spherical nanoparticles of approximately 33 nm diameter on heating to 70 °C. Furthermore, 15-25% w/w aqueous dispersions of such nanoparticles formed micellar gels that undergo thermoreversible (de)gelation on cooling to 5 °C.

Single-Molecular Poly(propylene oxide) (PPO) Nucleus-Guided Assembly for Hydrophobicity-Dependent Molecular Transport in the Nanopore.

By combining DNA nanotechnology and solid-phase nanopore technology, the aggregation behavior of polymer guided by a single-molecular poly(propylene) (PPO) nucleus in a 3D DNA network has been studied. At low temperature, the PPO chain is evenly dispersed in the rigid 3D DNA network; at higher temperature, the PPO chain self-collapses to a single-molecular nucleus; and upon addition of amphiphilic block copolymers below the critical micelle concentration (CMC), the chains tend to aggregate on the isolated hydrophobic nucleus through intermolecular hydrophobic interactions. The process has been characterized by a rheological test and an electrochemical test. This study not only provides a preliminary understanding of the nucleation and growth process of block copolymers but also offers a theoretical basis for the study of protein self-folding and aggregation in the future. On this basis, utilizing this nucleation and growth event, a novel smart nanopore has been developed for hydrophobicity-dependent molecular transport.

Dynamic Light Scattering Based Microrheology of End-Functionalised Triblock Copolymer Solutions.

Nano-sized particles functionalised with short single-stranded (ss)DNAs can act as detectors of complementary DNA strands. Here we consider tri-block-copolymer-based, self-assembling DNA-coated nanoparticles. The copolymers are chemically linked to the DNA strands via azide (N3) groups. The micelles aggregate when they are linked with complementary ssDNA. The advantage of such block-copolymer-based systems is that they are easy to make. Here we show that DNA functionalisation results in inter-micellar attraction, but that N3-groups that have not reacted with the DNA detector strands also change the phase behaviour of the tri-block polymer solution. We studied the triblock copolymer, Pluronic® F108, which forms spherical micelles in aqueous solutions upon heating. We find that the triblock chains ending with either an N3 or N3-DNA complex show a dramatic change in phase behaviour. In particular, the N3-functionalisation causes the chain ends to cluster below the critical micelle temperature (CMT) of pure F108, forming flower-micelles with the N3-groups at the core, while the PPO groups are exposed to the solvent. Above the CMT, we see an inversion with the PPO chains forming the micellar core, while the N3-groups are now aggregating on the periphery, inducing an attraction between the micelles. Our results demonstrate that, due to the two competing self-assembling mechanisms, the system can form transient hydrogels.

Polymeric Surfactant P84/Polyoxometalate α-PW12O403−—A Model System to Investigate the Interplay between Chaotropic and Hydrophobic Effects

Low charge density nanometric ions were recently shown to bind strongly to neutral hydrated matter in aqueous solution. This phenomenon, called the (super-)chaotropic effect, arises from the partial dehydration of both the nano-ion and the solute, leading to a significant gain in enthalpy. Here, we investigate the chaotropic effect of the polyoxometalate α-PW12O403− on the triblock copolymer P84: (EO)19(PO)43(EO)19 with (EO)19 the polyethoxylated and (PO)43 the polypropoxylated chains. The combination of phase diagrams, spectroscopic (nuclear magnetic resonance) and scattering (small angle neutron/X-ray scattering) techniques revealed that: (i) below the micellization temperature of P84, PW12O403− exclusively binds to the propylene oxide moiety of P84 unimers; and (ii) above the micellization temperature, PW12O403− mostly adsorbs on the ethylene oxide micellar corona. The preferential binding of the PW12O403− to the PPO chain over the PEO chains suggests that the binding is driven by the chaotropic effect and is reinforced by the hydrophobic effect. At higher temperatures, copolymer micellization leads to the displacement of PW12O403− from the PPO chain to the PEO chains. This study deepens our understanding of the subtle interplay between the chaotropic and hydrophobic effects in complex salt-organic matter solutions.

Structural Investigation of Diol and Triol Poly(oxypropylene)‐Poly(oxyethylene) Block Copolymers Micelles: Composition Dependence, Temperature Response and Clouding Behavior

AbstractSolution behavior of two commercially used polyether glycols with poly(oxyethylene) (PEO)‐poly(oxypropylene) (PPO)‐poly(oxyethylene) (PEO) triblock composition—Diol (linear) and Triol (star‐like)—was studied, concerning the concentration and temperature effects until the cloud point (CP). 2‐(2‐butoxyetoxy) ethanol (DB) increased their miscibility with water. The structural study was performed with 25% DB in water, which produced isotropic solutions at room temperature at all polymer concentrations. Micelle's formation was only observed above 40% of polymer, when reversed micelles were formed. The solvent nuclei of the reversed micelles increased with increasing polymer concentrations, caused by dehydration of the PPO chains, then decreased at further higher concentrations, with completely dehydrated hydrophobic chains. When CP is reached, the solvent nuclei are separated by large polymer domains, without phase separation. Neither ordered nor gel phase was formed, probably due to a combination of high miscibility and short hydrophobic segments. The study was performed by Small‐Angle X‐ray scattering (SAXS) and complemented by Fourier‐transformed infrared spectroscopy (FTIR) and dynamic light scattering (DLS). The main contribution of this work is based on the fact that the knowledge of the solubility behavior of Diol and Triol, by changing the solvent or temperature, opens up new possibilities of their use to phase separation processes in industrial applications and delivery systems. Moreover, the elucidation of mechanisms of solubility allows for the design of novel polyether glycols with tailored solution behavior for efficient performance in its target use. All applications rely on their solution behavior and can be benefited from the present results.

Growth Mechanism of Polymer Membranes Obtained by H-Bonding Across Immiscible Liquid Interfaces.

Complexation of polymers at liquid interfaces is an emerging technique to produce all-liquid printable and self-healing devices and membranes. It is crucial to control the assembly process, but the mechanisms at play remain unclear. Using two different reflectometric methods, we investigate the spontaneous growth of H-bonded PPO-PMAA (polypropylene oxide-polymetacrylic acid) membranes at a flat liquid-liquid interface. We find that the membrane thickness h grows with time t as h ∼ t1/2, which is reminiscent of a diffusion-limited process. However, counterintuitively, we observe that this process is faster as the PPO molar mass increases. We are able to rationalize these results with a model which considers the diffusion of the PPO chains within the growing membrane. The architecture of the latter is described as a gel-like porous network, with a pore size much smaller than the radius of the diffusing PPO chains, thus inducing entropic barriers that hinder the diffusion process. From the comparison between the experimental data and the result of the model, we extract some key piece of information about the microscopic structure of the membrane. This study opens the route toward the rational design of self-assembled membranes and capsules with optimal properties.

N-Heterocyclic carbene/Lewis acid-mediated ring-opening polymerization of propylene oxide. Part 2: Toward dihydroxytelechelic polyethers using triethylborane

Propylene oxide (PO) is polymerized by metal-free ring-opening polymerization (ROP) at 25 °C using N-heterocyclic carbenes (NHCs) and triethylborane (Et3B) as a bicomponent catalytic system. Poly(propylene oxide)s with predictable molar mass up to 60 000 g·mol−1 and low dispersity (Ð < 1.10) were obtained without the occurrence of undesirable transfer reaction to the monomer. In presence of an alcohol as the initiator, the ROP of PO follows an anionic mechanism assisted by monomer activation improving the efficiency of NHCs for the polymerization of substituted epoxides. Et3B is involved both in the formation of a complexed active center and in the activation of PO. Interestingly, dihydroxytelechelic PPOs can be readily synthesized not only using 1,4-benzenedimethanol but also water, both serving as difunctional initiators. Block copolyethers are also prepared by PPO chain extension experiments. All (co)polyethers have been thoroughly characterized by 1H NMR spectroscopy, SEC and MALDI-TOF mass spectrometry as means to elucidate the reaction mechanisms involved in this chemistry.

N-Heterocyclic carbene/Lewis acid-mediated ring-opening polymerization of propylene oxide. Part 1: Triisobutylaluminum as an efficient controlling agent

Ring-opening polymerization (ROP) of propylene oxide (PO) is achieved at 25 °C either in bulk or in solution, using N-heterocyclic carbenes (NHCs) and triisobutylaluminum (i-Bu3Al) as a bicomponent catalytic system. Transfer to monomer was not observed and poly(propylene oxide)s with predictable molar masses up to 60 000 g·mol−1 and low dispersities were obtained. In presence/absence of an alcohol as the initiator, the polymerization of PO follows anionic or zwitterionic ROP mechanisms, respectively. The addition of the Lewis acid strongly improves the efficiency of NHCs for the polymerization of substituted epoxides. It is established that i-Bu3Al is involved both in the formation of an initiating/propagating complex of moderate basicity/nucleophilicity and in the coordination of PO, enabling the activation of the monomer towards the complexed nucleophilic active species. Block copolyethers are also prepared by PPO chain extension experiments. All (co)polyethers were thoroughly characterized by 1H NMR spectroscopy, SEC and MALDI-TOF mass spectrometry as means to prove the control and benefit of this NHC approach for epoxides ROP.

Exploring NIR Aza-BODIPY-Based Polarity Sensitive Probes with ON-and-OFF Fluorescence Switching in Pluronic Nanoparticles.

Because of their deep penetration capability in tissue, red or near infrared (NIR) fluorophores attract much attention in bio-optical imaging. Among these fluorophores, the ones that respond to the immediate microenvironment (i.e., temperature, polarity, pH, viscosity, hypoxia, etc.) are highly desirable. We studied the response of six NIR aza-BODIPY-based and structurally similar fluorophores to polarity and viscosity for incorporation inside Pluronic nanoparticles as switchable fluorescent probes (SFPs). Based on our results, all of these fluorophores were moderately to strongly sensitive to the polarity of the microenvironment. We concluded that attaching amine groups to the fluorophore is not necessary for having strong polarity sensitive probes. We further studied the response of the fluorophores when embedded inside Pluronic nanoparticles and found that four of them qualified as SFPs. We also found that the switching ratio of the fluorophore-encapsulated Pluronic nanoparticles (ION-to-IOFF) is related to the length of the hydrophobic chain of the Pluronic tri-block copolymers. As such, the highest switching ratio pertained to F-68 with the lowest hydrophobic block poly (propylene oxide) (PPO chain of only 30 units).

Adherence behavior of 1-poly(propylene oxide)-2-(1-pyrenyl)benzimidazoles on graphene oxide surface

1-Poly(propylene oxide)-2-(1-pyrenyl)benzimidazole (PyrBI-PPO(n), n denotes the degree of polymerization (DP) of poly(propylene oxide) (PPO)) was synthesized by the ring-opening polymerization of propylene oxide (PO) with NH-deprotonated 2-(1-pyrenyl)benzimidazole (PyrBI). The DP of the PPO chain depended on the feed ratio of PO/(NH-deprotonated PyrBI). The solubility of PyrBI-PPO(n) in water depended on the PPO chain length. The reaction of water-soluble PyrBI-PPO(n) (n = 26, 46, and 125) with graphene oxide (GO) in water at various feed ratios of GO/PyrBI-PPO(n) caused the adherence of the pyrenyl group on the GO surface and produced water-soluble composites, namely, PyrBI-PPO(n)-GO. The adherence behavior of PyrBI-PPO(n) on the GO surface was investigated by UV–vis and photoluminescence spectroscopy analyses.

Effects of polymer concentration and type on the interactions between 1-methyl-3-tetradecylimidazolium bromide and polymers in aqueous solution

The interactions between the long-chain ionic liquid of 1-methyl-3-tetradecylimidazolium bromide (C14mimBr) and five polymers have been studied in detail using surface tension, electric conductivity, isothermal titration microcalorimetry (ITC), and steady-state fluorescence methods. The polymers used include neutral polymers of polyethylene glycol (PEG) and polyvinyl alcohol (PVA), triblock copolymers of PEO13PPO30PEO13 (L64) and PEO79PPO30PEO79 (F68), and polyelectrolyte of sodium carboxymethylcellulose (NaCMC). This paper focuses on the effects of polymer concentration and type on the surfactant-polymer interactions. The curves in the absence and in the presence of the polymer have more or less differences, exhibiting the cooperative interaction of the surfactant and five polymers. Although the effects of each polymer addition on the surfactant aggregates can be proved by various techniques, for one system, the inflection points on the curves from different method are difficult to unify and an attempt to show the concurrence of the data is only diluting the essence of this area. It is concluded that the interacting intensity between C14mimBr and the polymer has the order of NaCMC > L64 >F68 >PVA > PEG, which is determined by the strong electrostatic attraction, relatively strong hydrophobic interaction, and/or weak ion-dipole interaction relating to the polymer structure. Due to the precipitation formation of NaCMC and cationic surfactant aqueous solution, copolymers especially the existence of PPO chain not only has a good synergistic effect with surfactant, but also can adjust the viscosity of the system.

Stability and degradation of PEO20PPO70PEO20 triblock copolymers in mesostructured silica

Organic−inorganic hybrid mesostructured silicas are prepared, without stirring (at pH = 0.0) and with stirring (at pH = 0.6) to obtain isolated and gyroidal-like attached silica grains with incorporated triblock P123 poly (ethylene oxide)-poly (propylene oxide)–poly (ethylene oxide) copolymers. Selected hybrids are submitted to various thermal and aging treatments for studying hydrolysis and oxidation of PEO and PPO chains. Two complementary spectroscopic techniques are used: near-infrared (NIR) with measurements performed in diffuse reflectance, as well as 1H and 13C liquid- and solid-state nuclear magnetic resonance (NMR) to study the mobility and stability of PEO and PPO chains. With precipitated fresh hybrids, the ratio of PEO over (PEO + PPO) units is lower (30% ± 5%) than in theory. This ratio also decreases depending on temperature when a hydrothermal treatment is applied. An acidic hydrolysis involving both PEO and PPO chains, with generated fragments eliminated by washing with water and/or synthesis liquor, is then demonstrated. For comparison, another hybrid obtained by spray drying via evaporation-induced self assembly mechanism is also studied. Its NMR signals are much more stable than those of the samples prepared by precipitation. Depending on aging time, thermal history, and materials processing, the textural properties and template decomposition inside mesostructured silica are found significantly different. The influence of the hydrolysis and oxidation of the template onto final materials texture is likely to be as important as the processing conditions.

Surfactant selection as a strategy for tailoring the structure and properties of UCT manganese oxides

Mesoporous manganese oxides were synthesized using the UCT inverse micelle templating method with four different Pluronic surfactants to investigate the effects on the morphology, microstructure and desulfurization behavior of these materials. All of the as-synthesized samples exhibited similar hierarchical microstructures, but the size and shape of the primary nanoparticles for each sample was different. The primary nanoparticle sizes for these samples vary between 2.3 and 7.0 nm. Most of the samples are crystalline and are composed of a mixture of Mn3O4 and Mn5O8 phases. The adsorption behavior of these samples was tested using a fixed bed reactor at a temperature of 200 °C. Microstructural analysis of the samples after the desulfurization tests revealed a transformation of the mesoporous manganese oxide to a dense manganese sulfide phase; this involves a volumetric expansion of the crystal, leading to densification and a rapid decay in the sorption capacity after the breakthrough point. The variation in the structure and properties of these materials is related to ratio of the PEO and PPO chain segment lengths in the Pluronic surfactants used. This indicates that the ratio must dictate the volume, shape and assembly of the inverse micelles in the UCT synthesis.

Accelerated ultraviolet aging of structural and luminescent properties of the ureasil-polyether hybrid materials U-PEO:Eu3+ and U-PPO:Eu3+

In this paper, we evaluate the role played by the polyether type and chain length on the complexation of Eu3+ by the urea group of siloxane-polyether organic-inorganic hybrid materials based on polyethylene oxide (U-PEO, mw = 1900 g mol−1) and polypropylene oxide (U-PPO, mw = 230, 2000, and 4000 g mol−1). Investigation was made of the effect of the photooxidation of the PEO and PPO chains, induced by artificially accelerated ultraviolet aging (λ ≥ 300 nm), with the decomplexation of Eu3+ from the urea-polyether array. Fourier transform infrared (FTIR) and photoluminescence (PL) spectra evidenced loss of the ligand-to-metal charge transfer (LMCT) when the Eu3+ cations were unable to disrupt the strong hydrogen-bonded urea/urea aggregates formed using shorter U-PPO chains (230 g mol−1) or semicrystalline U-PEO (1900 g mol−1). FTIR analysis showed that formate was the main photoproduct formed continuously during the artificial ultraviolet aging of U-PEO (1900 g mol−1) and U-PPO (2000 g mol−1), with concomitant decreases of Eu3+ complexed to urea bridges, spatially correlated siloxane nodes, and the Judd-Ofelt parameter Ω2 (R). The kinetics of all these parameters were described by exponential laws with comparable time constants, evidencing the sensitivity of the Eu3+ photoluminescence to the elimination/formation of the hydrogen-bonded urea-polyether array during the photooxidation of PPO chains. In the case of U-PEO:Eu3+, different time constant values were observed, indicating the existence of a faster process governed by the facilitated transport of the oxidative species through the amorphous moieties of the semicrystalline U-PEO. This sensitivity of structural and PL properties arising from the photoinduced degradation of ureasil-polyether films can be exploited in the fabrication of new transparent, flexible, and biocompatible UV dosimeters and sensors.

Affinity-Based Functionalization of Biomedically Utilized Micelles Composed of Triblock Copolymers through Polymer-Binding Peptides.

Polymeric micelles and vesicles that are self-assembled from amphiphilic block copolymers are frequently used in biomedical applications. Poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO, so-called Pluronic, is a Food and Drug Administration approved triblock copolymer utilized in biomedical applications. However, the control of drug loading and surface functionalization of micelles remain challenging due to structural limitations. In this study, Pluronic micelles with various structures were rationally functionalized via the PPO-binding peptide, which was previously identified using a biologically constructed peptide library displayed on filamentous phages. The interactions between the peptide and Pluronic micelles were characterized in detail based on fluorescence changes in an extrinsic fluorescence dye, and a sufficient PPO chain length of Pluronic was essential for the interactions. Furthermore, enzymatic degradation of the model substrate-conjugated peptide loaded into Pluronic micelles showed stable loading of the peptide. Importantly, the exposure level of the conjugated molecules to the peptide was dependent on the PEO chain length of Pluronic, suggesting controllable functionalization of polymeric micelles. Anticancer drug-conjugated peptide-loaded Pluronic micelles with suitable polymeric structures were applied in a cell culture assay. The anticancer efficacy of the loaded drugs can be controlled by the molecular design of the binding peptide and polymers. These results demonstrate that an affinity-based functionalization strategy may facilitate polymeric micelles for various biomedical applications.

Coupling Photoluminescence and Ionic Conduction Properties Using the Different Coordination Sites of Ureasil-Polyether Hybrid Materials.

In this article, we demonstrate that each functional group of ureasil organic-inorganic hybrid (OIH) materials can act as a specific coordination site for a given active guest species, hence allowing the possibility of combining different functional properties. To illustrate this concept, the sol-gel process was used to produce diurea cross-linked siloxane-polyethylene oxide (U-PEO) and siloxane-polypropylene oxide (U-PPO) hybrid host frameworks with similar molecular weights (1900 and 2000 g mol-1 for PEO and PPO, respectively), with Li+ and Eu3+ as active guest ions providing ionic conduction and photoluminescence (PL) properties, respectively. Comparison of Fourier transform infrared spectra and small-angle X-ray scattering results for single-doped (using Li+ or Eu3+) and co-doped (using Li+ and Eu3+) U-PEO and U-PPO hosts showed that in every case, there was specific coordination of Eu3+ by the carbonyl group of the urea bridge and of Li+ by ether-type oxygen of the PEO and PPO chains. Optical analyses demonstrated that loading with Li+ did not affect the luminescence properties of the Eu3+-loaded OIH. Although loading with Eu3+ had a small effect on ionic transport, co-doping with Li+ ions ensured macroscopic ion-conduction of the transparent and luminescent hybrid material. The results suggested that the combination of both properties in a transparent elastomeric material could be useful for the development of multifunctional devices. The results suggested that the combination of both properties in a transparent elastomeric material could be useful for the development of multifunctional polyelectrolytes applied in the field of dual luminescent devices such as photoelectrochromic smart windows.

Influence of molecular structure on lubrication of aqueous triblock copolymer lubricants between rutile surfaces: An MD approach

The influence of molecular structure on adsorption and lubrication of aqueous triblock copolymer on TiO 2 surfaces has been investigated using a realistic MD model. Reference data obtained from DFT calculations have been employed to develop an interaction potential between the copolymer and TiO 2 surface. The results show that R Pluronics form an anchor–buoy–anchor structure absorbed on TiO 2 surface and L Pluronic for buoy–anchor–buoy structure. The shear of tribo-system influences slightly on the orientation of copolymers and non-slip behavior has been observed at solid-fluid interfaces due to the strong adhesion strength of copolymer on rutile surface. The shear viscosity increases with copolymer concentration and molecular chain length. L Pluronic has a lower shear stress than the R ones. • A new interacting FF between PEO, PPO and TiO 2 surface results in a better prediction of adsorption of copolymer. • The adsorption of copolymer on TiO 2 surface is physisorption with adsorption energy for PPO block larger than PEO. • The adsorption energy per PPO or PEO chain reduces with an increase of surface coverage and in the presence of water. • R Pluronics form an anchor–buoy–anchor structure on the surface while there is a buoy–anchor–buoy one for L types. • The shear affects the orientation of copolymers, and a non-slip behavior has been observed at solid-fluid interfaces. • The shear viscosity increases with the copolymer concentration and chain length. • L Pluronic has a lower shear stress than the R ones.

Effect of dynamic high pressure microfluidization on structure and stability of pluronic F127 modified liposomes

Pluronics modified liposomes have been prepared and shown to enhance stability of liposomes in our previous reports. In this study, we intended to evaluate the effect of dynamic high pressure microfluidization (DHPM) on the structure and stability of pluronic F127 modified liposomes. The results indicated that the particle size of F127 modified liposomes was decreased from 1180.6 nm to 73.5 nm after DHPM treatment. Meanwhile, the morphology was changed from irregularly multilamellar vesicle to spherically unilamellar structure. Structural characteristics were examined by fourier transformed infrared spectrometer, differential scanning calorimetry and X-ray powder diffraction. The subtle difference of structure might be attributed to the incorporation of PPO chains into the bilayer caused by DHPM treatment. Stability studies indicated that DHPM treatment could enhance the storage and membrane stability of F127 modified liposomes. This study may provide more insight to understand the effect of preparation method on the structure and stability of F127 modified liposomes.

Study of the Protein Bovine Serum Albumin (BSA) and the Triblock Copolymer P103 Interface By Differential Capacitance

Triblock copolymers are considered as non-ionic surfactants due to their self-assembling nature. Triblock copolymers can form structures similar to micelles and larger structures at a certain concentration and temperature. The triblock copolymers used here are biodegradable, water-soluble and are formed by chains of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), which can be arranged as A-B-A or B-A-B; where A are chains of PEO and B chains of PPO. And in this case they are referred by the commercial name Pluronics. The physicochemical properties of these surfactants (Critical micellar temperature (CMT), critical micellar concentration (CMC), density, molecular weight, etc.) depend on their molecular weight, the number of PPO and PEO chains present in the triblock copolymer, on the solvent (polar or no polar) and on the presence of salts in the solution. Applications of triblock copolymers are diverse; for instance, in the field of biotechnology they have been used for the controlled release of drugs, proteins, DNA. However, even when these compounds are already used and applied in several topics, there is a lack in the knowledge concerning to the effect of the interactions of them with other compounds, such as biopolymers. The main interest is to understand the effects of these interactions in the characteristic shape or size of aggregates formed by triblock copolymers. In order to obtain information about this topic, an initial approach is to study the interactions of some triblock copolymer and some well-characterized protein, as bovine serum albumin (BSA). BSA protein is cheap, easy to isolate and purify. In this way, BSA is an excellent option for the interactions study that exist between proteins and triblock copolymers. The objective of this work is to contribute to the knowledge of the interactions of triblock copolymers and proteins through the use of electrochemical techniques to obtain information about the amount of species adsorbed on the electrodes, as well as the size of the interface formed by the interaction of both, protein and triblock copolymers, once they are adsorbed on a metal surface. This information is important in the design of the sensors and is also necessary for the application of drug delibery and other fields of bioengineering and biomedicine. Thus, this investigation is focused on the interaction between BSA and the termosensible triblock copolymer Pluronic® P103 (PEO17-PPO60-PEO17). The interactions are studied by the adsorption of both compounds onto a gold disk electrode immersed in a phosphate buffer solution. Some electrochemical techniques, such as cyclic voltammetry and Differential-capacitance vs. Polarization potential are presented and analyzed in a wide range of temperatures and different P103 and BSA concentration. The thickness of the interface and the effect on the polarization potential are reported.