Solubilization of Phenols by Intramolecular Micelles Formed by Copolymers of Maleic Acid and Olefins

Conformational Changes of Poly(Maleic Anhydride-alt-styrene) Modified with Amino Acids in an Aqueous Medium and Their Effect on Cytocompatibility and Hemolytic Response

The conformational changes of poly(maleic anhydride-alt-styrene) (PSMA) modified with different amino acids (PSMA-Aa) were studied in an aqueous medium as a function of ionic strength and pH. The specific viscosity of PSMA-Aa decreased with increasing salt concentration due to a more compact conformation. There was a decrease in surface tension with increasing concentrations of the modified polyelectrolyte having a greater effect for the PSMA modified with l-phenylalanine at pH 7.0, demonstrating a greater surface-active character. The conformational changes were also confirmed by molecular dynamics studies, indicating that PSMA-Aa exhibits a compact structure at pH 4.0 and a more extended structure at pH 7.0. On the other hand, the conformational changes of PSMA-Aa were related to its biological response, where the higher surface-active character of the PSMA modified with l-phenylalanine correlates very well with the higher hemolytic activity observed in red blood cells, in which the surface-active capacity supports lytic potency in erythrocytes. The cytocompatibility assays indicated that there were no significant cytotoxic effects of the PSMA-Aa. Additionally, in solvent-accessible surface area studies, it was shown that the carboxylate groups of the PSMA modified with l-phenylalanine are more exposed to the solvent at pH 7.0 and high salt concentrations, which correlates with lower fluorescence intensity, reflecting a loss of mitochondrial membrane potential. It is concluded that the study of the conformational changes in PE modified with amino acids is essential for their use as biomaterials and relevant to understanding the possible effects of PE modified with amino acids in biological systems.

Exogenous Application of Brassinosteroid 24-Norcholane 22(S)-23-Dihydroxy Type Analogs to Enhance Water Deficit Stress Tolerance in Arabidopsis thaliana

Brassinosteroids (BRs) are plant hormones that play an essential role in plant development and have the ability to protect plants against various environmental stresses, such as low and high temperature, drought, heat, salinity, heavy metal toxicity, and pesticides. Mitigation of stress effects are produced through independent mechanisms or by interaction with other important phytohormones. However, there are few studies in which this property has been reported for BRs analogs. Thus, in this work, the enhancement of drought stress tolerance of A. thaliana was assessed for a series of 2-deoxybrassinosteroid analogs. In addition, the growth-promoting activity in the Rice Lamina Inclination Test (RLIT) was also evaluated. The results show that analog 1 exhibits similar growth activity as brassinolide (BL; used as positive control) in the RLIT bioassay. Interestingly, both compounds increase their activities by a factor of 1.2–1.5 when they are incorporated to polymer micelles formed by Pluronic F-127. On the other hand, tolerance to water deficit stress of Arabidopsis thaliana seedlings was evaluated by determining survival rate and dry weight of seedlings after the recovery period. In both cases, the effect of analog 1 is higher than that exhibited by BL. Additionally, the expression of a subset of drought stress marker genes was evaluated in presence and absence of exogenous applied BRs. Results obtained by qRT-PCR analysis, indicate that transcriptional changes of AtDREBD2A and AtNCED3 genes were more significant in A. thaliana treated with analog 1 in homogeneous solution than in that treated with BL. These changes suggest the activation of alternative pathway in response to water stress deficit. Thus, exogenous application of BRs synthetic analogs could be a potential tool for improvement of crop production under stress conditions.

Relationship between the Ionization Degree and the Inter-Polymeric Aggregation of the Poly(maleic acid-alt-octadecene) Salts Regarding Time

Alternating amphiphilic copolymers are macromolecular systems with a polarity duality in their structure, since they are generally formed by alternating segments corresponding to a potential electrolyte group and an alkyl (aliphatic or aromatic) group. These systems, depending on the ionization degree, as well as the time, may form different types of intra and interpolymeric aggregates in aqueous media. Therefore, this study, which in fact is the continuation of a previously reported work, is focused on establishing how the ionization degree of the sodium and potassium salts of the poly(maleic acid-alt-octadecene) affect zeta potential, pH, electrical conductivity, particle size, polydispersity index, and surface tension over time. The results showed that polymeric salts with a high ionization degree in aqueous media formed homogeneous systems with bimodal sizes and high zeta potential values, which tended to quickly become less negative, lowering the pH and slightly increasing the electrical conductivity; while systems with low ionization degree lead to the opposite, forming heterodispersed systems with several populations of particle sizes, high polydispersity, low zeta potential values, neutral and invariable pH values, and high electrical conductivity values. Consequently, these results suggest that the values of particle size, polydispersity index, zeta potential, pH, and electrical conductivity change regarding the polymeric ionization degree, as well as the time. Therefore, such variables should be considered and controlled when working with this kind of polymeric materials.

Application of Nanoparticle Technology to Reduce the Anti-Microbial Resistance through β-Lactam Antibiotic-Polymer Inclusion Nano-Complex

Biocompatible polymeric materials with potential to form functional structures in association with different therapeutic molecules have a high potential for biological, medical and pharmaceutical applications. Therefore, the capability of the inclusion of nano-Complex formed between the sodium salt of poly(maleic acid-alt-octadecene) and a β-lactam drug (ampicillin trihydrate) to avoid the chemical and enzymatic degradation and enhance the biological activity were evaluated. PAM-18Na was produced and characterized, as reported previously. The formation of polymeric hydrophobic aggregates in aqueous solution was determined, using pyrene as a fluorescent probe. Furthermore, the formation of polymer-drug nano-complexes was characterized by Differential Scanning Calorimetry-DSC, viscometric, ultrafiltration/centrifugation assays, zeta potential and size measurements were determined by dynamic light scattering-DLS. The PAM-18Na capacity to avoid the chemical degradation was studied through stress stability tests. The enzymatic degradation was evaluated from a pure β-lactamase, while the biological degradation was determined by different β-lactamase producing Staphylococcus aureus strains. When ampicillin was associated with PAM-18Na, the half-life time in acidic conditions increased, whereas both the enzymatic degradation and the minimum inhibitory concentration decreased to a 90 and 75%, respectively. These results suggest a promissory capability of this polymer to protect the β-lactam drugs against chemical, enzymatic and biological degradation.

Relationship between the Polymeric Ionization Degree and Powder and Surface Properties in Materials Derived from Poly(maleic anhydride-alt-octadecene)

Polymeric materials derived from poly(maleic anhydride-alt-octadecene)-here referred as PAM-18-have shown interesting properties that make them potential pharmaceutical excipients. In this work, eight polymers derived from PAM-18 were obtained using NaOH and KOH at 1:1; 1:0.75, 1:0.5, and 1:0.25 molar ratios. The resulting products were labeled as PAM-18Na and PAM-18K, respectively. Each polymer was purified by ultrafiltration/lyophilization, and the ionization degree was determined by potentiometric studies, which was related to the zeta potential. The structural characterization was performed using the Fourier transform infrared (FT-IR) espectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) techniques. The physical characterization was carried out by SEM, particle analysis, and humidity loss and gain studies; the surface studies were performed by the sessile drop method. PAM-18Na had ionization degrees of 95%, 63%, 39% and 22%, whereas those for PAM-18K were 99%, 52%, 35% and 20%, respectively. The results also showed that for higher inorganic base amounts used, the polymeric materials obtained possess high ionization degrees, which could form polymeric solutions or hetero-dispersed systems. Likewise, it was observed that for higher proportions of carboxylate groups in the polymeric structure, the capability to retain water is increased and, only can be eliminated by drying at temperatures greater than 160 °C. On the other hand, the modification of PAM-18 to its ionized forms led to the formation of powder materials with low flowability and surfaces that ranged from very hydrophobic to slightly wettable.

Relationship between Surface Properties and In Vitro Drug Release from Compressed Matrix Containing Polymeric Materials with Different Hydrophobicity Degrees

This work is the continuation of a study focused on establishing relations between surface thermodynamic properties and in vitro release mechanisms using a model drug (ampicillin trihydrate), besides analyzing the granulometric properties of new polymeric materials and thus establishing the potential to be used in the pharmaceutical field as modified delivery excipients. To do this, we used copolymeric materials derived from maleic anhydride with decreasing polarity corresponding to poly(isobutylene-alt-maleic acid) (hydrophilic), sodium salt of poly(maleic acid-alt-octadecene) (amphiphilic), poly(maleic anhydride-alt-octadecene) (hydrophobic) and the reference polymer hydroxyl-propyl-methyl-cellulose (HPMC). Each material alone and in blends underwent spectroscopic characterization by FTIR, thermal characterization by DSC and granulometric characterization using flow and compaction tests. Each tablet was prepared at different polymer ratios of 0%, 10%, 20%, 30% and 40%, and the surface properties were determined, including the roughness by micro-visualization, contact angle and water absorption rate by the sessile drop method and obtaining Wadh and surface free energy (SFE) using the semi-empirical models of Young-Dupré and  Owens-Wendt-Rabel-Käelbe (OWRK), respectively. Dissolution profiles were determined simulating physiological conditions in vitro, where the kinetic models of order-zero, order-one, Higuchi and Korsmeyer-Peppas were evaluated. The results showed a strong relationship between the proportion and nature of the polymer to the surface thermodynamic properties and kinetic release mechanism.

Relationship between Surface Properties and In Vitro Drug Release from a Compressed Matrix Containing an Amphiphilic Polymer Material

The performance of compressed tablet drug delivery systems made using polymeric materials depend on multiple factors, such as surface properties like contact angle, surface free energy and water absorption rate, besides the release mechanisms driven by the kind of polymer used. Hence, it should be possible to establish a relationship between the surface properties and the drug release kinetics. Compressed tablets with different proportions of poly(maleic acid-alt-octadecene) potassium salt (0%, 10%, 20%, 30% and 40%) were prepared. Blends of a model drug (ampicillin trihydrate) and the polymer material were analyzed by DSC. The surface properties of the tablets were determined by the sessile drop method, while the surface energy was determined using the semi-empirical Young-Dupre, Neumann and OWRK models. The release profiles were determined simulating in vitro conditions (buffer solutions pH 1.2 and pH 7.4 with ionic strength of 1.5 M at 37 °C (310.15 K)). A kinetic analysis of the dissolution profiles using different models (zero order, first order, Higuchi and Korsmeyer-Peppas) was realized. The results showed a significant effect of the proportion of polymer in both the surface properties of the tablets and the dissolution release, indicating a relationship between the kinetic and thermodynamic properties.

Encapsulation of Antioxidant Gallate Derivatives in Biocompatible Poly(ε-caprolactone)-b-Pluronic-b-Poly(ε-caprolactone) Micelles

Formulation of antioxidant agents is still a challenge that limits their application in the biomedical field. Pentablock copolymers obtained through modification of two common PEO-PPO-PEO copolymers (Pluronic F127 and F68) with poly(ε-carprolactone) (PCL) were evaluated regarding their capability to form nanocarriers suitable for gallic acid, methyl gallate, and ethyl gallate. Applying a dialysis method, PCL/F127/PCL and PCL/F68/PCL self-assembled into spherical micelles in 0.9% NaCl aqueous solution but notably differed in critical micellar concentration (CMC), micelle core hydrophobicity, and micelle size, as evidenced by pyrene fluorescence, transmission electron microscopy, and dynamic light scattering. Cytotoxicity studies showed that the copolymers were safe at concentrations well above the CMC. Transfer of gallic acid and derivatives from aqueous medium to the micelle phase was characterized in terms of distribution constant and free energy of transference, which were shown to be strongly dependent on the hydrophobicity of the gallate derivatives and the length of PCL in the pentablock copolymer. Antioxidant activity of gallates was challenged against DPPH previously loaded in PCL/F127/PCL and PCL/F68/PCL micelles. The more the hydrophobicity of the gallate derivative, the greater the capability to enter in the micelle and to consume free radicals. In vitro release studies of gallic acid, methyl gallate, and ethyl gallate from the pentablock copolymer micelles also evidenced the influence of the hydrophobicity of both the gallate derivative and the micelle core on release rate, recording a variety of release patterns. Overall, PCL/F127/PCL and PCL/F68/PCL appear as suitable nanocarriers of potent antioxidant agents in a wide range of polarities, which may be useful for diverse therapeutic applications.

Potential drug delivery system: study of the association of a model nitroimidazole drug with aggregates of amphiphilic polymers on aqueous solution

This study evaluated the association of N-hexyl-2-methyl-4-nitroimidazol, a model drug, to aggregates formed by anionic polyelectrolytes on aqueous solution. The alternating copolymers of maleic anhydride and N-vinyl-2-pyrrolidone were synthesized and then modified by reaction of the anhydride groups with aliphatic amines and alcohols of varying length of the alkyl chain. The partition of the model drug between water and the hydrophobic microdomains provided by the copolymers was studied using the pseudo-phase model to determinate the distribution coefficient K S, and the standard free energy of transfer ∆µ°t. The results indicate that all copolymers assessed are potential pharmaceutical reservoirs of the model drug. Nevertheless, the solubility of N-hexyl-2-methyl-4-nitroimidazol on the polymeric solutions is independent from the length of the alkyl chain of the copolymer.

Partial molar volume of anionic polyelectrolytes in aqueous solution

In this work the partial molar volumes (V) of different anionic polyelectrolytes and hydrophobically modified polyelectrolytes (PHM) were measured. Polymers like polymaleic acid-co-styrene, polymaleic acid-co-1-olefin, polymaleic acid-co-vinyl-2-pyrrolidone, and polyacrylic acid (abbreviated as MAS-n, PA-n-K2, AMVP, and PAA, respectively) were employed. These materials were investigated by density measurements in highly dilute aqueous solutions. The molar volume results allow us to discuss the effect of the carboxylic groups and the contributions from the comonomeric principal chain. The PAA presents the smaller V, while the largest V value was for AMVP. The V of PHM shows a linear relationship with the number of methylene groups in the lateral chain. It is found that the magnitude of the contribution per methylene group decreases as the hydrophobic character of the environment increases.

Bioengineering Functional Copolymers. IX. Poly[(maleic anhydride-co-hexene-1)-g-poly(ethylene oxide)]

Amphiphilic bioengineering copolymers having a combination of hydrophilic/hydrophobic linkages and polyelectrolyte behavior, along with an ability to interact with biomacromolecules, in particular with the invertase enzyme, have been synthesized by (a) complex-radical copolymerization of maleic anhydride (MA, the acceptor) and hexene-1 (H-1, the donor) monomers with benzoyl peroxide as the initiator in 1,4-dioxane at 65 degrees C under high-conversion conditions and (b) subsequent grafting (polyesterification) of synthesized poly(MA-alt-H-1) with alpha-methoxy-omega-hydroxy-poly(ethylene oxide) (PEO). Copolymerizations were also carried out in the steady state, in order to essentially reduce the effect of copolymer composition drift. The values of the monomer reactivity ratios (r(1) and r(2)) determined by using the known terminal models of Fineman-Ross (FR) and Kelen-Tüdös (KT), as well as by nonlinear regression (NLR) analysis, are: r(1) = 0.16 and r(2) = 0.30 (FR), r(1) = 0.14 and r(2) = 0.27 (KT), and r(1) = 0.15 and r(2) = 0.29 (NLR), respectively. All the copolymers and graft copolymers were characterized by FTIR spectroscopy, (1)H{(13)C} NMR spectroscopy, viscometric measurements, and chemical (acid number), thermal (DSC and TGA), and X-ray diffraction analyses. Unlike poly(MA-alt-H-1)s, PEO macrobranched graft copolymers exhibit expressed polyelectrolyte and swelling behavior in diluted and concentrated dioxane solutions, respectively. The copolymer and its PEO hyperbranched derivatives can be used as carriers for enzyme immobilization.

Solubilization of p-nitrophenol in aggregates formed by hydrophobically modified polyelectrolytes

The solubilization of p-nitrophenol into the hydrophobic microdomains provided by polyelectrolytes carrying alkyl side chains of different length has been investigated in aqueous solutions of pH 5.0 and 8.0. Under these pH conditions p-nitrophenol is predominantly present in its neutral and ionic forms, respectively. Potassium salts of poly(maleic acid-co-1-olefins), PA-nK2 with n = 12, 14, 16, 18, were synthesized, and the pseudo-phase model was used to determine the distribution coefficient KS, and the standard free energy of transfer Deltamut0 of p-nitrophenol between water and polymer aggregates. The results indicate that at both pH's the solubilization of p-nitrophenol increases with increasing size of the side alkyl chain; i.e., the values of KS follow the order PA-18K2 > PA-16K2 > PA-14K2 > PA-12K2. The free energies, Deltamut0, were plotted as a function of the number of carbon atoms in the side alkyl chain and a linear relation was found. From these plots contributions of -0.324 and -0.676 kJ mol(-1) per methylene group were determined at pH 5.0 and 8.0, respectively. The effect of aggregate size on the solubility of phenol is attributed to the hydrophobic contribution per CH2 group to the free energy of transfer. The hydrophobic nature of the CH2 group is suggested to derive largely from the enthalpic contribution.

Solubilization of phenols in surfactant/polyelectrolyte systems

The properties of the microheterogeneous systems formed by mixtures of cetyltrimethylammonium bromide (CTAB) and an alternating copolymer of maleic acid and styrene, MAS, and their anionic monoesters, MAS-n with n=2, 4, 6, 8, were investigated. The fluorescence of pyrene was used to sense the polarity of the polymer/CTAB aggregates. Measurements of the ratio III/I in pyrene fluorescence spectra indicate that the polymer/CTAB aggregates are more hydrophobic than normal micelles. A series of p-alkyl substituted phenols were employed to probe the solubilization ability of these aggregates. The distribution constant K(S) of phenol, p-methylphenol, p-ethylphenol, and p-propylphenol between water and MAS-n/CTAB aggregates and the corresponding free energy of transfer Deltamicro(0)(t) have been determined using the pseudo-phase model. The results show that the distribution is mainly determined by the phenol structure, and a linear free energy relationship has been found between Deltamicro(0)(t) and the structure of phenols. On the other hand, an increase in the number of methylene groups in the side alkyl chain has no effect on Deltamicro(0)(t). The results are discussed and compared with those obtained for ionic micelles.

Adsorption of hydrophobically modified polyelectrolytes at the -octane/water interface

The interfacial activity of polyelectrolytes carrying alkyl side chains of different length has been studied. Potassium salts of poly(maleic acid-co-1-olefins), PA-n K2 with n=12 , 14, 16, 18, were synthesized, and the interfacial tension at the aqueous solution/n -octane interface was measured as a function of the length of the alkyl side chain. The results show that the interfacial tension lowering, the limiting excess concentration Gamma (m), and the efficiency of adsorption pC (20) depend on the number of methylene groups in the alkyl side chain. According to Rosen the last two parameters define two different contributions to the standard free energy of adsorption: one arises from the distribution of the polymer between the bulk of the solution and the interface Delta G (dist )(0), and another comes from the configuration adopted at the interface Delta G (int )(0). These free energies were plotted as a function of the number of carbon atoms in the alkyl side chain and a linear relation was found for both of them. From these plots contributions of 0.83 and -0.58 per methylene group were determined for Delta G (0)(dist ) and Delta G (0)(int ), respectively. The positive value for the incremental free energy of distribution is attributed to the formation of a polymer micelle which is stabilized by longer alkyl side chains. On the other hand, the negative value for Delta G (0)(int ) indicates that at the interface the polymer adopts a configuration where the hydrocarbon tail is interacting with the octane molecules.