Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

Lipases (glycerol ester hydrolases, E.C. 3.1.1.3) are enzymes of great industrial interest due to their ability to catalyze a broad range of hydrolytic and synthetic reactions. They find applications in the synthesis of compounds used in clinical, nutritional, environmental, pharmaceutical and chemical fields. For example, lipases are used to catalyze key intermediate steps in the synthesis of biologically active compounds such as Naproxen, Ibuprofen and Atenolol [1]. Depending on the application, lipases may need to be purified and characterized biochemically before they can be used. However, the purification of microbial lipases is often made difficult by the presence of high molecular weight aggregates. These aggregates can form due to the presence, in the fermentation medium, of lipids used to induce the production of the enzyme by the microorganism or simply due to hydrophobic interactions amongst the enzyme molecules themselves [2]. In previous work, we characterized a new lipase produced by Bacillus megaterium CCOC P2637. The enzyme eluted in the void volume during gel filtration chromatography, indicating that it was present in the form of a high molecular weight aggregate. This aggregate was dispersed when a gradient of 60% (v/v) isopropanol was used, but formed again when the enzyme was injected in a gel filtration column for further purification, even when the elution buffer contained 20% (v/v) isopropanol. Further, when the enzyme was diluted in buffer (phosphate pH 7.0 20 mM) containing 30% isopropanol, its specific activity was double the activity obtained by diluting in buffer without isopropanol [3].

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Pollens appear like a fine to coarse powder that is liberated by the microsporangia of Gimnosperms and Angiosperms. The pollen grain wall, the sporoderm, envelopes the microgametophytes (male gametophytes), which produce the male gametes of seed plants. Pollen grains are interesting from the material science point of view since the native polymer, the sporopollenin, found in the sporoderm outer layer (exine), is one of the toughest known materials which is degraded by oxidation but is resistant to reduction. This property permits the sporopollenin persistence as an unaltered polymer in sediments of great age, e.g the Ordovician period, 400 million years ago. Sporopollenin is a mixture of fatty acids, phenyl-derivatives as p-coumaric acid, and carotenes [1]. Its nanostructure is not yet completed revealed. Therefore, more studies must be performed. A number of models have been proposed for the sporopollenin nanostructure of spores and pollen grains [2]. Rowley et al. [3-4] interpret exine structure as being formed by helical subunits, based on transmission and scanning electron microscope (TEM and SEM) studies. The atomic force microscopy (AFM) is the ideal method to study the sporopollenin nanostructure [5] since the arrangement of components is not visualized easily through other microscope techniques (e.g. TEM and SEM). In the present work, we used AFM to study the sporopollenin nanostructure of the Ilex paraguariensis A.St.Hil. exine, an Angiosperm (Aquifoliaceae).

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Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

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Diamond-like carbon (DLC) films have been intensively studied with a view to improving orthopaedic implants. Studies have indicated smoothness of the surface, low friction, high wear resistance, corrosion resistance and biocompatibility [1-4]. DLC coatings can be deposited using various techniques, such as plasma assisted chemical vapour deposition (PACVD), magnetron sputtering, laser ablation, and others [5]. However it has proved difficult to obtain films which exhibit good adhesion. The plasma immersion process, unlike the conventional techniques, allows the deposition of DLC on three-dimensional workpieces, even without moving the sample, without an intermediate layer, and with high adhesion [6], an important aspect for orthopaedic articulations. In our previous work, DLC coatings were deposited on silicon and Ti-13Nb-13Zr alloy substrates using the plasma immersion process for the characterization of microstructure, mechanical properties and corrosion behaviour [7-9]. Hardness, measured by a nanoindenter, ranged from 16.4-17.6 GPa, the pull test results indicate the good adhesion of DLC coatings to Ti-13Nb-13Zr, and electrochemical assays (polarization test and electrochemical impedance spectroscopy) indicate that DLC coatings produced by plasma immersion can improve the corrosion resistance [9].

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

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While investigating isolated or agglomerates of treated Vaccinia virus intracellular mature (IMV) particles in atomic force microscopy (AFM) equipment we noticed that in some occasions the enveloped particles had been totally disrupted, with the interior being spread around. We have also observed in these samples what appear to be some rather intriguing viral surface interactions. Instead of showing a clear division between individual virions the particles seem to be continuous at the interfaces that show coalescence. In order to understand what was happening we focused our attention on the analysis of the images of the interface between virions particles, trying to find out what was the explanation for such type of particle surface interaction and in which conditions it would take place.

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

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Atomic force microscopy (AFM) is a powerful tool for direct visualization of supported biological membranes [1]. Moreover, in-situ AFM measurements permit investigations of biological phenomena in real time and in physiological environments. In a previous work, we have studied the morphology and stability of supported phospholipid layers prepared by solution spreading (casting) on mica [2]. The images were acquired in the contact or contact-intermittent modes and the samples analyzed ex-situ just after solvent evaporation and after a hydration step, and in-situ with immersion in a buffer solution. Contact-mode imaging is less suitable for soft or weakly attached materials, since the tip can often scrape or drag the membranes during scanning, a disadvantage that can be overcome by applying intermittent methods. However, studies have also demonstrated that by adjusting the operative force it is possible to use contact-mode to obtain AFM images of soft phospholipids layers [3]. In the present work, we applied successfully in-situ AFM contact-mode to characterize phospholipid layers of 1,2-dimyristoyl-sn-glycero-3-phosphatitidylcholine (DMPC) and 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC), as well as a binary mixture of these phospholipids. The supported membranes were prepared on mica substrates by vesicle fusion method.

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

The adsorption of polysaccharides onto solid substrates provides an environment for the immobilization of biomolecules [1] giving rise to conditions for the development of biosensors [2] and kits for immunoassays. One can find in the literature reports about the adhesion of proteins on cellulose ester membranes [3]. However, studies about the formation of cellulose ester ultrathin films have been seldom reported. Cellulose esters are nontoxic materials largely used as coating layers, fibers, inks and films.

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In the last decades several investigations have been conducted with the objective of studying the microstructural characteristics and mechanical properties in low carbon microalloyed steel [1,2]. These steels contain a polyphase microstructure, with complex mixture of bainite, MA constituent (martensite-austenite residual), pearlite, ferrite and martensite. They are often used in the automobile industry, in the production pipelines for the transport of gas and oil in areas of sub-zero temperature and in the naval ship construction, because they possess high strength, high toughness at low temperature and good weldability.