Comparative time-course study of aminoacyl- and dipeptidyl-resin hydrolysis

The classic hydrolysis procedure for quantification of resin-bound aminoacyl and peptidyl groups with 12 N HCl: propionic acid was recvaluated by studying the influence of the nature of the resin and the resin-bound group. Their stability during acid hydrolysis was dependent on the C-terminal amino acid, and the order of acid stability was Phe > Val > Gly. Otherwise, the dipeptides Ala-Gly, Ala-Val, and Ala-Phe displayed enhanced rates of hydrolysis of the resin if compared with their parent aminoacyl groups. Amongthe resins assayed, the order of acid stability was: benzhydrylamine-resin > p-methylbenzhydrylamine-resin ≅4-(oxymethyl)-phenylacetamidomethyl-resin > chloromethyl-copolymer of styrene-1%-divinylbenzene. Important for peptide synthesis method, the findings demonstrate that longer hydrolysis times than previously recommended in the literature (1 h at 130°C and 15 min at 160°C for peptides attached to the chloromethyl-copolymer of styrene-1%-divinylbenzene) are necessary for the quantitative acid-catalyzed cleavage of some resin-bound groups. The observed broad range of hydrolysis time varied from less than 1 h to about 100 h.

Rheological properties of tin oxide suspensions

The rheological properties of tin oxide slurries were studied experimentally and theoretically. The deflocculants used were ammonium polyacrilate (PAA) and the copolymer poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVB-PVA-PVAc), in water and ethanol, respectively. The amount of deflocculant was optimized for different solid contents by means of viscosity measurements. In spite of the high stability of PVB-dispersed slurries, a high solid concentration was not obtained. On the other hand, a slurry with a 56.4 vol.% of solids was attained when PAA was used. A theoretical study of the adsorption of PAA in its dissociated (basic solution) and non-dissociated (acidic solution) forms on SnO 2 (110) is presented. This analysis was made by means of the PM3 method using a large cluster Sn 15O 28 for the surface model. The calculated adsorption energy is larger for the ionized PAA than for the non-ionized form, indicating that alkaline slurries favor PAA adsorption on the SnO 2 surface. © 2002 Elsevier Science Ltd. All rights reserved.

Morphological, mechanical and rheological properties of nylon 6/acrylonitrile-butadiene-styrene blends compatibilized with MMA/MA copolymers

The morphological, mechanical and rheological properties of nylon 6/acrylonitrile-butadiene-styrene blends compatibilized with MMA-MA [poly(methyl methacrylate-comaleic anhydride)] copolymers were studied. A twin screw extruder was used for melt-blended the polymers and the injection moulding process was used to mold the samples. The main focus was on nylon 6/ ABS blends compatibilized with one MMA-MA copolymer. This copolymer has PMMA segments that appear to be miscible with the styrene-acrylonitrile (SAN) phase of ABS and the anhydride groups can react with amine end groups of the nylon 6 (Ny6) to form graft copolymers at the interface between Ny6 and ABS rich phases. Tensile and impact and morphological properties were enhanced by the incorporation of this copolymer. Transmission electron microscopy (TEM) observations revealed that the ABS domains are finely dispersed in nylon 6 matrix and led to the lowest ductile-brittle transition temperatures and highest impact properties. It can be concluded that the MMA-MA copolymer is an efficient alternative for the reactive compatibilization and can be used as a compatibilizer for nylon 6/ABS blends.© 2003 Kluwer Academic Publishers.

Effect of compatibilizer in acrylonitrile-butadiene-styrene toughened nylon 6 blends: Ductile-brittle transition temperature

The ductile-brittle transition temperatures were determined for compatibilized nylon 6/acrylonitrile-butadiene-styrene (PA6/ABS) copolymer blends. The compatibilizers used for those blends were methyl methacrylate-co-maleic anhydride (MMA-MAH) and MMA-co-glycidyl methacrylate (MMA-GMA). The ductile-brittle transition temperatures were found to be lower for blends compatibilized through maleate modified acrylic polymers. At room temperature, the PA6/ABS binary blend was essentially brittle whereas the ternary blends with MMA-MAH compatibilizer were supertough and showed a ductile-brittle transition temperature at -10°C. The blends compatibilized with maleated copolymer exhibited impact strengths of up to 800 J/m. However, the blends compatibilized with MMA-GMA showed poor toughness at room temperature and failed in a brittle manner at subambient temperatures.

Thermal properties of nylon6/ABS polymer blends: Compatibilizer effect

Nylon6/ABS binary blends are incompatible and need to be compatibilized to achieve better performance under impact tests. Poly(methyl methacrylate/maleic anhydride) (MMA-MA) is used in this work to compatibilize in situ nylon6/ABS immiscible blends. The MA functional groups, from MMA-MA copolymers, react with NH2 groups giving as products nylon molecules grafted to MMA-MA molecules. Those molecular species locate in the nylon6/ABS blend interfacial region increasing the local adhesion. MMA-MA segments are completely miscible with the SAN rich phase from the ABS. The aim of this work is to study the effects of ABS and compatibilizing agent on the melting and crystallization of nylon6/ABS blends. This effect has been investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Incorporation of this compatibilizer and ABS showed little effect on the melting behavior of the PA6 crystalline phase, in general. DMTA analysis confirmed the system immiscibility and showed evidence of compatibility between the two phases, nylon6 and ABS, produced by MMA-MA copolymer presence. The nylon6/ABS blend morphology, observed by transmission electron microscopy (TEM), changes significantly by the addition of the MMA-MA compatibilizer. A better dispersion of ABS in the nylon6 phase is observed. © 2004 Kluwer Academic Publishers.

Morphological, mechanical and thermal properties of nylon 6/ABS blends using glycidyl methacrylate-methyl methacrylate copolymers

Nylon6 is an attractive polymer for engineering applications because it has reactive functionality through amine and carboxyl end groups that are capable of reacting. For this reason, it has been used a lot in polymeric blends. Blends of nylon6/ABS (acrylonitrile-butadiene-styrene) were produced using glycidyl methacrylate-methyl methacrylate (GMA-MMA) copolymers as compatibilizer. The binary blends were immiscible and exhibited poor mechanical properties that stemmed from the unfavorable interactions among their molecular segments. This produced an unstable coarse phase morphology and weak interfaces between the phases in the solid state. The presence of the copolymer in the blends clearly led to a more efficient dispersion of the ABS phase and consequently optimized Izod impact properties. However, the compatibilized blend showed poor toughness at room temperature and failed in a brittle manner at subambient temperatures. © 2005 Springer Science + Business Media, Inc.

Ferroelectric switching and dielectric response of P(VDF-TrFE)/PMMA blends

The ferroelectric and the dielectric behaviors of binary blends formed by an equi-molar Poly(vinylidene fluoride trifluoroethylene) copolymer [P(VDF-TrFE)] and Poly(methyl methacrylate) [PMMA] were investigated, for several PMMA compositions. For 40 wt.% or more PMMA contents, the blends are completely amorphous. Below this value, they crystallize in the usual Cm2m polar structure of P(VDF-TrFE). The ferroelectric switching characteristics and the dielectric response of the blends demonstrate the formation of dynamically stable ferroelectric domains. Moreover, the blended films are highly transparent in the optical region. Therefore, thin films of these binary blends are good candidates as host materials for nonlinear optical applications.

Thermoanalytical study of praziquantel-loaded PLGA nanoparticles

Polymeric nanoparticles have received great attention as potential controlled drug delivery systems. Biodegradable polymers has been extensively used in the development of these drug carriers, and the polyesters such as polylactic acid, polyglycolic acid and their copolymers as poly-lactide-co- glycolide are the most used, considering its biocompatibility and biodegradability. Thermal analysis techniques have been used for pharmaceutical substances for more than 30 years and are routine methods for screening drug-excipient interactions. The aim of this work is to use thermal analysis to characterize PLGA nanoparticles containing a hydrophobic drug, praziquantel. The results show that the drug is in an amorphous state or in disordered crystalline phase of molecular dispersion in the PLGA polymeric matrix and that the microencapsulation process did not interfere with the chemical structure of the polymer, mantaining the structural drug integrity.

In vitro antimicrobial efficiency of a mouthwash containing triclosan/gantrez and sodium bicarbonate

Several antiseptic substances have been used as adjuncts to routine mechanical procedures of oral hygiene, based on their antimicrobial effects. The objective of this study was to assess in vitro the antimicrobial efficiency of 2 mouthwash containing Triclosan/Gantrez and sodium bicarbonate in comparison to both positive and negative controls. Standard strain samples of Escherichia coli, Pseudomonas aeruginosa, Actinomyces viscosus and Bacillus subtilis were used. Samples of Streptococcus mutans and Gram-negative bacilli were collected from 20 volunteers (10 with a clinically healthy periodontium and 10 presenting biofilm-associated gingivitis). Evaluation of the antimicrobial activity was performed by determining the minimal inhibitory concentration (MIC). The results indicated that the test solution inhibited the growth of both Gram-negative and Gram-positive microorganisms from the volunteers' saliva as well as that of the standard strains at the MIC dilution of 1:20, whereas the MIC dilution of 0.12% chlorhexidine against the same bacteria was 1:80. Thus, even though the tested mouthrinse solution presented an in-vitro antimicrobial activity superior to that of a placebo, it was inferior to that of chlorhexidine.

Development and sensory analysis of shampoo for curly hair

Objective: This study aimed to compare the sensory performance of a shampoo formulation with Polyurethane-14, AMP-acrylates copolymer (PAAC) in relation to control formulation in curly and natural hair tresses. Methods: Curly and natural hair tresses (n = 8) of equal size and weight were pre-treated by washing with a standard shampoo. After the hair tresses were treated with a formulation containing polymer (formulation A) and compared to hair tresses treated with control formulation (Formulation B). Each panelist (n=2) is asked to indicate which tress performs better for each of seven sensory attributes evaluated (quantity and creamy foam, combing, wet touch, frizz formation, curl definition and volume). It was collected images of hair tresses at 0, 1, 2, 4 and 24 hours of washing, comparing the attributes: volume, frizz formation and curl definition. The results were analyzed using table to test of paired assessment, being: SUPERIOR results - 8 and 7 positive evaluations; SIMILAR results - 2 to 6 positive evaluations; INFERIOR results - 1 and 0 positive evaluations. Results: The addition of the PAAC on the shampoo formulation provided definition and modeling of curls, reducing volume and frizz in 24 hours. There was also lower foam formation in the formulation with polymer PAAC. However, it is important to note that this attribute has inversely proportional effect to the creamy foam, since more creamy foam, smaller quantity. Conclusions: It was concluded that the shampoo developed was effective in defining and modeling curl in natural and curly hair.

Estudo das propriedades de fotogeração e transporte de portadores de cargas em dispositivos optoeletrônicos orgânicos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Aplicação do copolímero PLA/PGA adicionado ao fosfato de cálcio ao redor de implantes osseointegráveis instalados sem estabilidade primária em tíbia de coelhos: estudo biomecânico, histométrico e imunoistoquímico

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Avaliação do copolímero de ácido polilático e poliglicólico ao redor de implantes osseointegráveis sem estabilidade primária: análise biomecânica, histométrica e imunoistoquímica em coelhos

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Avaliação do copolímero de ácido polilático e poliglicólico associado ao vidro bioativo no processo de regeneração óssea: análise histomorfométrica e imunoistoquímica em ratos

Pós-graduação em Odontologia - FOA

Ciprofloxacino encapsulado em lipossomas revestidos com ácido poli láctico co-glicólico ou veiculado em gel de copolímero de bloco Pluronic R F127

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)