ABSTRACT In this review we discuss about the immobilization of enzymes in Langmuir-Blodgett films in order to determine the catalytic properties of these biomacromolecules when adsorbed on solid supports. Usually, the conformation of enzymes depends on the environmental conditions imposed to them, including the chemical composition of the matrix, and the morphology and thickness of the film. In this review, we show an outline of manuscripts that report the immobilization of enzymes as LB films since the 1980’s, and also some examples of how the surface properties of the floating monolayer prepared previously to the transfer to the solid support are important to determine the efficiency of the resulting device.

Films were deposited from aluminum acetylacetonate (Al(acac)3) using a methodology involving reactive sputtering and low energy ion bombardment. The plasma was generated by the application of radiofrequency power to the powder containing electrode and simultaneously, negative pulses were supplied to the electrode where the substrates were attached. It was investigated the effect of the duty cycle of the pulses (Δ) on the properties of the coatings. Association of ion bombardment to the deposition process increased film thickness, structure reticulation and organic content. Ions from the deposition environment were implanted at the film-air interface or underneath it. Morphology and topography were altered depending on Δ. Considering the enhancement of Δ, it affected the flux of ions reaching the depositing interface and then the deposition rate, H content, crosslinking degree and surface microstructure. Alumina groups were detected in the infrared spectra, whereas the precipitation of amorphous alumina was confirmed by X-ray diffraction.

Alumina films were deposited from a new plasma method using aluminum acetylacetonate (AAA) powder as precursor. The AAA was sputtered in argon and oxygen plasma mixtures. It was investigated the effect of the oxygen proportion (O2%) on the properties of the coatings. Deposition rate was derived from the layer height measured by profilometry. The elemental composition and molecular structure of the films were determined by Rutherford backscattering and infrared spectroscopies, respectively. Grazing incidence X-ray diffraction was used to investigate the microstructure of the films while hardness was determined by nanoindentation technique. Inspections on the surface morphology and on the film composition were conducted associating scanning electron microscopy and energy dispersive spectroscopy. Incorporation of oxygen affects the plasma kinetics and consequently the properties of the coatings. As moderated concentrations of oxygen (< 25%) are added, the structure is predominantly organic containing stoichiometric amorphous alumina. On the other hand, as high O2% (> 25%) are incorporated, the structure become rich in metallic aluminum with carbon rising at low proportions. The deposited layer is not homogeneous in thickness once the chemical composition of the precursor is changed by the action of the reactive oxygen plasma. Oxygen ablation on the film surface also contributes to the lack of homogeneity of the structure, especially as high oxygen proportions are imposed. Hardness data (0.5-2.0 GPa) corroborated the idea of an amorphous structure. Based on the results presented here it was possible to identify the oxygen concentration in the plasma atmosphere which mostly removed organics while preserving the stoichiometric alumina precipitation, subject of great relevance as one considers the reduction in the energy necessary for the creation of fully oxide coatings.

During the extraction of aluminum from bauxite, a waste of oxides containing traces of heavy metals in a highly alkaline matrix, called Red Mud (RM), is produced. In this study RM is characterized and the feasibility of using it as a precursor for the production of thin films by Plasma Sputtering and by Plasma Immersion Ion Implantation and Deposition (PIIID) is demonstrated. The chemical structure and composition, surface morphology, topography, and wettability of the films prepared using such methodologies were investigated. The films consist mainly of the elements aluminum, silicon, iron and carbon. Infrared spectroscopic analyses reveal the presence of C=O, C-H2, Fe(OH), Al-O and Si-C functionalities. RF Sputtering produced films with smoother surfaces, whereas PIIID produced granular surface structures. Surface contact angle measurements showed that despite the presence of oxides and hydroxides, the films are hydrophobic, thus exhibiting an interesting link between the physical and thermodynamical properties.

Este trabalho apresenta aspectos de equilíbrio e dinâmicos da adsorção na interface ar/líquido de duas formas de fosfatase alcalina de placa óssea de ratos: DSAP, solubilizada com tensoativo não-iônico (C12E9), contendo uma âncora de glicosilfosfatidilinositol (GPI), e PLSAP, com a porção hidrofóbica da âncora clivada por fosfolipase-C. A tensão superficial dinâmica, gamadyn, e o módulo de elasticidade superficial dilatacional, épsilon, foram determinados para soluções de PLSAP, DSAP e C12E9 pelo método de oscilação harmônica e análise do formato da gota eixo-simétrica. Cinéticas de adsorção revelaram que DSAP adsorve trinta vezes mais rapidamente que PLSAP, apresentando um mínimo, e, para PLSAP, a tensão superficial cai continuamente. Para o sistema DSAP/C12E9, épsilon atinge um máximo na concentração crítica de agregação (CAC), mas para PLSAP, épsilon diminui continuamente com a concentração. Soluções de C12E9 apresentam épsilonmais elevados, decrescentes com a concentração. Um modelo, baseado na influência da âncora GPI, é proposto para explicar os resultados obtidos.

This work presents equilibrium and dynamic aspects for the adsorption at the air/liquid interface of two rat osseous plate alkaline phosphatase forms: DSAP, solubilized by a surfactant, C12E9, and containing a glycosylphosphatidylinositol (GPI) anchor; and PLSAP, resulting from phospholipase-C cleavage of the hydrophobic portion of the GPI anchor. Dynamic surface tension, gammadyn, and surface elasticity modulus, epsilon, were determined for PLSAP, DSAP and pure C12E9 solutions using harmonic oscillation and axisymmetric drop shape analysis Adsorption kinetics studies revealed that DSAP adsorbs thirty times faster than PLSAP, presenting a minimum in the curve. For DSAP/ C12E9 mixed system, e increases with concentration and a maximum appears at the critical aggregation concentration (CAC). For PLSAP, a continuous decreasing with concentration for gammadyn and epsilon was observed. For pure C12E9 solution, the elasticity modulus increases with concentration and epsilon values are higher when compared to the mixed system. A model based on the influence of the GPI anchor is proposed.