Ricardo C. Michel

Concentration Regimes of Biopolymers Xanthan, Tara, and Clairana, Comparing Dynamic Light Scattering and Distribution of Relaxation Time

The aim of this work was to evaluate the utilization of analysis of the distribution of relaxation time (DRT) using a dynamic light back-scattering technique as alternative method for the determination of the concentration regimes in aqueous solutions of biopolymers (xanthan, clairana and tara gums) by an analysis of the overlap (c*) and aggregation (c**) concentrations. The diffusion coefficients were obtained over a range of concentrations for each biopolymer using two methods. The first method analysed the behaviour of the diffusion coefficient as a function of the concentration of the gum solution. This method is based on the analysis of the diffusion coefficient versus the concentration curve. Using the slope of the curves, it was possible to determine the c* and c** for xanthan and tara gum. However, it was not possible to determine the concentration regimes for clairana using this method. The second method was based on an analysis of the DRTs, which showed different numbers of relaxation modes. It was observed that the concentrations at which the number of modes changed corresponded to the c* and c**. Thus, the DRT technique provided an alternative method for the determination of the critical concentrations of biopolymers.

Influence of the relative composition of trace elements and vitamins in physicochemical stability of total parenteral nutrition formulations for neonatal use

ObjectiveThe present study aimed to evaluate the influence of the relative composition of trace elements and vitamins in physicochemical stability of neonatal parenteral nutrition.Material and methodsThree formulations for neonatal administration were selected; the main variable was the presence of trace elements and vitamins. The analyses where carried out immediately after preparation and at 24 h, 48 h, 72 h and 7 days after preparation. Three methods were selected to determine globule size: light obscuration, dynamic light scattering and optical microscopy. Complementary evaluation including visual inspection, determination of pH and osmolarity, peroxide levels and measurements of zeta potential were also performed.ResultsThere was an observable alteration in color and phase separation in the PN stored at 25°C and 40°C. Neither globule size pattern, nor any other physicochemical characteristic evaluated appeared to be considerably altered in any of the analyzed formulations even after 7 days of storage at 5°C. Globule size in all the PN studied was consistent with the established limit, below 500 nm by DLS measurement, and PFAT5 was below 0.05% under all storage temperatures.ConclusionConcomitant presence of trace elements and vitamins in the same neonatal formulation did not alter the evaluated aspects of stability.

Modificação da Fibra de Coco com Polianilina e o seu Uso como Sensor de Pressão

O presente trabalho teve por foco a modificacao de fibras de coco, tornando-as materiais compositos condutores de eletricidade. Para tanto, foi utilizada uma tecnica de polimerizacao in situ, capaz de gerar nanoparticulas de polianilina sobre a superficie de fibras tratadas. As fibras modificadas com polianilina foram caracterizadas por FTIR, UV-Vis, DRX e SAXS. Alem disso, foram submetidas a ensaios eletromecânicos, com a finalidade de indicar quais condicoes de modificacao sao mais eficientes para a obtencao de um material sensivel a esforcos compressivos. Os resultados de sensibilidade a compressao sugerem que os materiais modificados com as menores quantidades de polianilina sao os mais adequados para aplicacoes no campo de sensores de pressao de natureza resistiva, podendo ser utilizados no desenvolvimento de dispositivos inteligentes.

Síntese e caracterização de copolímeros à base de metacrilato de metila e divinilbenzeno com propriedades magnéticas

In this work, copolymers based on methyl methacrylate and divinylbenzene containing iron with magnetic properties were produced using the suspension polymerization method. An investigation was performed of the effect from the concentration of iron added to the polymerization, the MMA/DVB molar ratio in the copolymer formation, type of suspension agent and stirring speed on the synthesis of the copolymers. The copolymers morphology, thermal stability, contents of embedded iron, particle size distribution, magnetic properties, surface area, volume and pore size were evaluated. Polymeric microspheres with magnetic properties were successfully obtained. These materials showed good control of the spherical shape and agglomeration of iron particles under the surface of the microsphere. The analysis of magnetic properties pointed to materials with no hysteresis loops, thus being close to a material with superparamagnetic properties with saturation magnetization between 8.0 and 13.0 emu.g-1.

Hydrophilic cyclodextrin protected Pd nanoclusters: insights into their size control and host–guest behavior

The process of formation of narrow size spherical PdNPs covered by cyclodextrins with an average size of 5.1 nm ± 0.5 nm has been investigated in aqueous solution at room-temperature. Analyses by UV-Vis spectroscopy and dynamic light scattering (DLS) at the beginning of reaction indicated a fast exchange of chloride ions with water molecules within the palladium coordination sphere. This process is followed by reduction of Pd(II) species according to the α-HPCD concentration. The hydrodynamic radii observed from both PdNPs and α-HPCD aqueous solutions suggested that regular CDs assemblies in the order of a few nanometers may direct the homogeneous NPs growth towards uniform aggregates. These scattering measurements are corroborated by 1H DOSY NMR spectroscopy in solution and AFM (atomic force microscopy) analyses which provided evidence of stable hybrid assemblies. Interestingly, by changing the cavity size, structures with distinct hydrodynamic diameters are formed. Further evidence from ECD (electronic circular dichroism) spectra reveals that the primary face of cyclodextrin is most likely associated to the metal surface.

Estudo da dissolução de polieletrólitos em água pura e em meios de força iônica moderada

The dissolution of polielectrolyte powders was monitored by flowing dissolving material through an online filter, a multi-angle light scattering unit, a refractometer and a capillary viscometer. When the polyelectrolytes were dissolved in solutions of moderate ionic strength their dissolution behavior was similar to that of neutral polymers. When dissolved in pure water, however, there was a small population of aggregates that appeared at the beginning of the dissolution process. The conformation of the aggregates seems to evolve from a spherically simmetric gaussian distribution of mass density into structures resembling random coils containing multiple chains, before dissolving completely into well dispersed, stiffened coil polielectrolytes.