Seed gum ofStryphnodendron barbatiman (barbatimão)

Stryphnodendron barbatiman (barbatimão) is a native tree that is found throughout the “Cerrados,” a region of Central Brazil. Plant seeds, on water extraction, furnished 28 g% galactomannan (dryweight basis), the monosaccharide composition of which (galactose to mannose ratio, 1.0:1.5) fits in the legume heteromannan group. This seed gum, after Sevag deproteinization, still retained 6 g% of associated protein and had a molecular weight of about 1.8 MD on gel filtration. A high intrinsic viscosity (1300 cP) was observed for the polysaccharide sample obtained after reflux of the crushed seeds in 80% aqueous methanol.

     

Finite element simulation of wave propagation in an axisymmetric bar

An accurate solution for high-frequency pulse propagation in an axisymmetric elastic bar is obtained using a new finite element technique that yields accurate non-oscillatory solutions for wave propagation problems in solids. The solution of the problem is very important for the understanding of dynamics experiments in the split Hopkinson pressure bar (SHPB). In contrast to known approaches, no additional assumptions are necessary for the accurate solution of the considered problem. The new solution helps to elucidate the complicated distribution of parameters during high-frequency pulse propagation down the bar as well as to estimate the applicability of the traditional dispersion correction used in the literature for the analysis of wave propagation in a finite bar. Due to the dimensionless formulation of the problem, the numerical results obtained depend on Poisson's ratio, the length of the bar and the pulse frequency, and are independent of Young's modulus, the density and the radius of the bar.     

Lectins and/or xyloglucans/alginate layers as supports for immobilization of dengue virus particles

Formation of stable thin films of mixed xyloglucan (XG) and alginate (ALG) onto Si/SiO(2) wafers was achieved under pH 11.6, 50mM CaCl(2), and at 70 degrees C. XG-ALG films presented mean thickness of (16+/-2)nm and globules rich surface, as evidenced by means of ellipsometry and atomic force microscopy (AFM), respectively. The adsorption of two glucose/mannose-binding seed (Canavalia ensiformis and Dioclea altissima) lectins, coded here as ConA and DAlt, onto XG-ALG surfaces took place under pH 5. Under this condition both lectins present positive net charge. ConA and DAlt adsorbed irreversibly onto XG-ALG forming homogenous monolayers approximately (4+/-1)nm thick. Lectins adsorption was mainly driven by electrostatic interaction between lectins positively charged residues and carboxylated (negatively charged) ALG groups. Adhesion of four serotypes of dengue virus, DENV (1-4), particles to XG-ALG surfaces were observed by ellipsometry and AFM. The attachment of dengue particles onto XG-ALG films might be mediated by (i) H bonding between E protein (located at virus particle surface) polar residues and hydroxyl groups present on XG-ALG surfaces and (ii) electrostatic interaction between E protein positively charged residues and ALG carboxylic groups. DENV-4 serotype presented the weakest adsorption onto XG-ALG surfaces, indicating that E protein on DENV-4 surface presents net charge (amino acid sequence) different from E proteins of other serotypes. All four DENV particles serotypes adsorbed similarly onto lectin films adsorbed. Nevertheless, the addition of 0.005mol/L of mannose prevented dengue particles from adsorbing onto lectin films. XG-ALG and lectin layers serve as potential materials for the development of diagnostic methods for dengue.     

Rapid and efficient solid-supported reagent synthesis of fluorine derivatives of phosphorus(V) compounds

Direct conversion of phosphorus(V) chlorides to the corresponding phosphorus(V) fluorides was achieved utilizing a solid-supported reagent. The phosphorus(V) fluorides were straightforwardly synthesized and efficiently isolated in very good yields.     

Characterisation of ultra-thin films of oxidised bacterial cellulose for enhanced anchoring and build-up of polyelectrolyte multilayers

The process of catalytic oxidation of bacterial cellulose (BC) ultra-thin films with 2,2,6,6-tetramethyl-1-piperidinyloxy was investigated along with their capability to adsorb oppositely charged polyelectrolytes of chitosan and alginate. The time-dependent oxidation of BC films was analysed by X-ray photoelectron spectroscopy and quartz crystal microbalance (QCM) experiments. A negatively charged surface was achieved by inserting carboxylic groups, which was augmented by prolonged media exposure (17.9 %), compared with a fast oxidation process (9.1 %). Polyelectrolyte deposition was followed by QCM, which indicated that BC oxidation increased the first layer uptake of chitosan 17-fold (?105.0?±?1.5 Hz) in comparison with unoxidised BC (?6.0?±?0.2 Hz), confirming the capability of oxidised BC surfaces to exhibit strong electrostatic interactions and to support the build-up of a thicker multilayer system. These findings indicate that oxidised BC surfaces are capable of immobilising and detecting several charged species.     

Study of the effect of director fluctuations on liquid-crystalline molecular reorientation

Initial phase of field-induced molecular reorientation in threshold geometry of a liquid-crystalline structure is essentially influenced by thermal orientational fluctuations. Still not quite clear is the way in which the reorientation starts and how it runs over an LC-structure in its initial phase. Fluctuations are stochastic events in time and also in space. This feature suggests, that the reorientation process may be induced by director fluctuations locally in a particular part of the LC-structure. In this work we have studied the impact of fluctuations on the molecular reorientation in nematics involving optical nonlinear interaction. The restricted area of a nematic layer was excited by light beam that amplified director fluctuations locally. By manipulation of optical excitation we were able to affect the dynamics of the effect. Since the threshold-type configuration of nematics is used in a number of optical devices, the obtained results may have practical aspect contributing to a new way of controlling the field-induced transition.     

A novel liquid crystal light modulator

We present a conception of two optical modulators. One of these, which we have called the scattering liquid crystal cell seems to be promising with a view to possible applications. We assumed that the modulator could be used in optical logic as a gate element, but other applications in optoelectronics would appear also to be possible. Some preliminary results of an experimental examination of the modulators are also presented.     

Nanocapsule of cationic liposomes obtained using "in situ" acrylic acid polymerization: stability, surface charge and biocompatibility

In this work, didecyldimethylammonium bromide (DDAB) and 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) (2.5:1) were used to prepare liposomes coated with polyacrylic acid (PAA) using "in situ" polymerization with 2.5, 5 and 25 mM of acrylic acid (AA). The PAA concentrations were chosen to achieve partially to fully covered capsules, and the polymerization reaction was observed with real-time monitoring using dynamic light scattering (NanoDLS). The DDAB:DOPE liposomes showed stability in the tested temperature range (25-70°C), whereas the results confirmed the success of the polymerization according to superficial charge (zeta potential of +66.7±1.2 mV) results and AFM images. For the liposomes that were fully coated with PAA (zeta potential of +0.3±3.9 mV), cytotoxicity was independent of the concentration of albumin. Cationic liposomes and nanocapsules of the stable liposomes coated with PAA were obtained by controlling the surface charge, which was the most important factor related to cytotoxicity. Thus, a potential, safe drug nanocarrier was successfully developed in this work.