Betty L. López

Preparation of mesoporous silica particles with controlled morphology from sodium silicate solutions and a non-ionic surfactant at pH values between 2 and 6

Abstract Isometric particles of mesoporous silica could be synthesized between 25°C and 45°C from reaction mixtures containing silicic acids, sodium chloride and a non-ionic surfactant (Triton X100). The size decreases from some tens of micrometers to less than 1 μm when the pH increases from 1.85 to 6. At pH lower than 3.5, glassy material forms a cement between the particles. The particle size distribution narrows at higher pH and at long reaction times (several days). A spheroidal shape is favored by low pH and high temperature, and a more polyhedral shape appears at high pH whatever the temperature. This behavior could be related to the polycondensation rate of the silicic acids, to the lifetime and disorder of the micelles and to the micelles–silicic acid interactions.

Interplay between structure and dynamics in chitosan films investigated with solid-state NMR, dynamic mechanical analysis, and X-ray diffraction.

Modern solid-state NMR techniques, combined with X-ray diffraction, revealed the molecular origin of the difference in mechanical properties of self-associated chitosan films. Films cast from acidic aqueous solutions were compared before and after neutralization, and the role of the counterion (acetate vs Cl−) was investigated. There is a competition between local structure and long-range order. Hydrogen bonding gives good mechanical strength to neutralized films, which lack long-range organization. The long-range structure is better defined in films cast from acidic solutions in which strong electrostatic interactions cause rotational distortion around the chitosan chains. Plasticization by acetate counterions enhances long-range molecular organization and film flexibility. In contrast, Cl− counterions act as a defect and impair the long-range organization by immobilizing hydration water. Molecular motion and proton exchange are restricted, resulting in brittle films despite the high moisture content.

PEG-g-chitosan nanoparticles functionalized with the monoclonal antibody OX26 for brain drug targeting

AIM Drug targeting to the CNS is challenging due to the presence of blood-brain barrier. We investigated chitosan (Cs) nanoparticles (NPs) as drug transporter system across the blood-brain barrier, based on mAb OX26 modified Cs. MATERIALS & METHODS Cs NPs functionalized with PEG, modified and unmodified with OX26 (Cs-PEG-OX26) were prepared and chemico-physically characterized. These NPs were administered (intraperitoneal) in mice to define their ability to reach the brain. RESULTS Brain uptake of OX26-conjugated NPs is much higher than of unmodified NPs, because: long-circulating abilities (conferred by PEG), interaction between cationic Cs and brain endothelium negative charges and OX26 TfR receptor affinity. CONCLUSION Cs-PEG-OX26 NPs are promising drug delivery system to the CNS.

Poly(methyl acrylate) plus Mesoporous Silica Nanohybrids: Mechanical and Thermophysical Properties

Abstract A mesoporous silica MCM-48 is used as a reinforcement agent for poly(methyl acrylate) (PMA). Methyl acrylate is introduced into the mesoporous silica that has an interconnected porous structure, allowing monomer diffusion into the pores before the polymerization reaction. In order to improve the silica plus polymer adhesion and to decrease the silica agglomeration, the silanol groups of the silica are functionalized with methyl groups without decreasing significantly the pore size. The silica is characterized by nitrogen adsorption, scanning electronic microscopy (SEM) and infrared (IR) spectroscopy. The nanohybrids so obtained are analyzed by tensile testing, thermogravimetry (TGA), differential scanning calorimetry (DSC) and dynamical mechanical analysis (DMA). The highest improvement of mechanical and thermophysical properties is achieved for nanohybrids containing 5 wt. % mesoporous silica. At 10 % silica, agglomeration of the filler takes place and the dispersed phase is less effective in reinforcing the polymer matrix.

Characterization of hydroxylated hyperbranched polyesters of fourth and fifth generation

Abstract Hydroxylated hyperbranched polyester (HBPs) of fourth and fifth generation were obtained by three methods; one step (HBP4, HBP5), step by step (HBP4P, HBP5P) and combinations of one step and step by step (HBP1-4, HBP1- 5). The HBPs were synthesized in bulk from 2,2-bis(hydroxymethyl)propionic acid (DMPA) and pentaerythritol (PE) using acid catalysis (p-toluenesulfonic acid) and characterized by infrared analysis, 1H and 13C nuclear magnetic resonance, gel permeation chromatography, vapor pressure osmometry, electro spray ionizationmass spectrometry, dynamic light scattering, refractive index, thermogravimetric and differential scanning calorimetric analysis. The refractive index of HBPs were low, the infrared and nuclear magnetic resonance analysis showed evidence of the occurrence of reaction between from 2,2-bis(hydroxymethyl) propionic acid (DMPA) and pentaerythritol (PE). The molar mass values of the HBPs determined by gel permeation chromatography were different to vapor pressure osmometry measurements due to small hydrodynamic volume of the HBPs. The mass spectrometry analysis showed different acyclic and cyclic units in the HBPs. The distributions of HBPs studied by dynamic light scattering were monomodal in number and volume and bimodal in intensity. The thermal stability of the fifth generation HBPs was higher than that the fourth generation. All HBPs presented amorphous behavior

Characterization of chitin and chitosan extracted from shrimp shells by two methods

Abstract Shrimp shells from Penaeus Vannamei species were hydrolyzed for chitin extraction by a chemical and a papain enzymatic method. Composition of shells was analyzed and their microstructure was characterized before and after hydrolysis by microscopy. Chitin fibers arrangement in the tissue was preserved after chemical extraction, but after papain hydrolysis the tissue presented structural disarrangement indicating that papain reacts indistinctly with peptidic and N-acetyl linkages. Although chemical purification is very effective, by-products are not recoverable. Conversely, papain hydrolysis yields partially purified chitosan but permits aminoacids isolation, which is important in food industry. This method has other advantages such as low cost and easy accessibility of papain. Chitin and chitosan were characterized by thermogravimetric analysis, infrared spectrophotometry and capillary electrophoresis. Degree of N-acetylation (DA) was determined by cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS 13CNMR) or potentiometry and crystallinity was measured by X ray diffraction.

Synthesis of micron-sized particles of mesoporous silica from tri-block surfactants in presence of fluoride, usable as stationary phase in HPLC

Abstract The relations between the morphology (particle shape and size) of SBA-15 and SBA-16 mesoporous silica and the synthesis parameters (composition of the reaction mixtures, nature of the triblock surfactant, fluoride anions, synthesis procedure) were established. This allowed defining the conditions for the formation of materials with micro-sized isometric particles suitable for HPLC applications. The presence of fluoride anions favors the formation of spherical shaped particles, with probably higher weak acidic silanol groups content to give higher hydrophobic materials after silylation, which is an advantage for their use as HPLC reverse phases. The different materials were evaluated in HPLC tests (separation of mixtures of aromatic and polynuclear aromatic molecules).

Catalytic conversion of α-pinene by using mesoporous aluminosilicates

Mesoporous aluminosilicates are prepared using CTMABr and sodium silicate and aluminum sulfate as Si and Al source, respectively. The materials are characterized by XRD, elemental analysis, N 2 adsorption, 27 Al NMR and Infrared spectroscopy with pyridine sorption. The results show that the use of aluminum sulfate conducts to mesoporous aluminosilicates where the framework charges are compensated by protons giving acidic Bronsted sites No Lewis acid sites are observed. The Bronsted acidity seems not to be directly related to the number of incorporated tetrahedral Al atoms but to the nature of the Bronsted sites and to the mesoporous organization. Their catalytic activity towards the transformation of α-pinene is due to their Bronsted acidity. A good selectivity at 160°C towards camphene (75%) can be obtained with the catalyst with the lowest Si/Al ratio.

Synthesis and characterization of a pressure-sensitive adhesive based on an isobutyl acrylate / 2-ethylhexyl acrylate copolymer

Abstract A removable pressure-sensitive adhesive was obtained by free-radical emulsion polymerization. The product is a low-viscosity copolymer from different polar and apolar acrylic monomers consisting of microspheres of about 1 μm diameter. 2-Ethylhexyl acrylate and isobutyl acrylate were used as non-polar constituents while acrylic acid and acrylamide provided the more polar constituents to regulate the cohesive force of the adhesive. The amounts of initiator, water and emulsifier (nonylphenol) were varied to obtain the best adhesive properties at the given copolymer composition. The resulting adhesive showed the desired balance of low tack and good adhesive strength in combination with a wide variety of substrates, which made it useful as a removable adhesive for many applications. The product was characterised by viscometry, measurements of tack and peel strength, FTIR, DSC, and microscopy.

Use of mesoporous silica as a reinforcing agent in rubber compounds

Abstract Mesoporous silica is used as filler for styrene-butadiene rubber (SBR); filler-polymer interactions are compared with those exhibited when Ultrasil silica (VN3) is used. A silane coupling agent is added to improve filler dispersion and its influence on the bound-rubber formation is also investigated. The bound-rubber content is higher for the mesoporous silica and increases further for the sample containing silane. The increase is explained by chemical interactions between filler and rubber and penetration of the rubber chains into the mesopores. This is confirmed by 13C solid-state NMR, IR spectroscopy and differential scanning calorimetry. Dynamic mechanical thermal analysis shows higher storage modulus for the rubber filled with mesoporous silica.