Self-assembling properties of mono and dirhamnolipids and their interactions with model membranes

La mia tesi riporta un studio biofisico sui mono-ramnolipidi e i di-ramnolipidi, i principali gruppi di molecole di ramnolipidi (RL), una classe di tensioattivi biologici. Comprendere le differenze nelle proprietà chimiche e fisiche dei mono-RL e di-RL è importante per lo sviluppo delle loro potenziali applicazioni, ad esempio come agenti emulsionanti e disperdenti nei processi di biorisanamento. Ho svolto la separazione di mono e di-RL da una miscela commerciale di RL mediante cromatografia su colonna di gel di silice. Ho eseguito misure della tensione superficiale per determinare la CMC dei due componenti. La caratterizzazione strutturale è stata condotta a partire da misure di diffrazione dei raggi X (XRD) su campioni di mono e di-RL in soluzioni acquose concentrate, tra il 10 e il 45 w/w%. Questa tecnica consente di determinare il caratteristico polimorfismo liotropico a risoluzione spaziale di pochi Å. Per derivare le proprietà strutturali in soluzioni diluite, campioni di mono e di-RL sono stati studiati mediante misure di diffusione a piccolo angolo dei raggi X (SAXS), condotte presso il sincrotrone Diamond. I risultati hanno permesso di caratterizzare le strutture micellari formate dai due componenti. Ho studiato le interazioni tra membrane modello con mono e di-RL, mostrando come sia possibile, assumendo un modello cinetico, derivare parametri fisici rilevanti da immagini di microscopia ottica. Ho eseguito esperimenti di microscopia a contrasto di fase e a fluorescenza su vescicole unilamellari giganti (GUV) composte dal lipide POPC e ternarie DOPC:SM:CHOL, in differenti rapporti, molari con mono o di-RL in concentrazioni di 0.06, 0.12 e 0.25 mM. Ho sviluppato e applicato metodi originali per interpretare le immagini di microscopia, i quali hanno consentito la determinazione dell'area e del volume di GUV asimmetriche e la descrizione dell'interazione GUV-RL in termini di due meccanismi cinetici, l’inserimento nel foglietto lipidico e la formazione dei pori.My thesis reports an extensive biophysical study of the two categories of molecules that compose biosurfactant rhamnolipid (RL): mono and di-rhamnolipids. Understanding the differences in chemical and physical properties of mono and di-RL is important because their applications as emulsifying and dispersing agents in bioremediation processes and other biotechnological sectors. My work started with the chemical separation of mono and di-RL from the commercial mixture (RLs) using silica gel column chromatography, confirmed by electrospray mass spectroscopy. I performed surface tension measurements to determinate the CMC of each of them. The physical chemical characterization started using X-ray diffraction on samples of mono and di-RL in concentrated water solutions ranging from 10 to 45 w/w%. This technique allows to determine the characteristic lyotropic polymorphism, as well as the molecular packing and properties at a few Å. To derive the structural properties in dilute solutions, mono or di-RL samples dissolved from 10 to 100 mM in water were analyzed by SAXS at the Diamond synchrotron. Results allowed to characterize different micellar structures formed by mono and di-RL. I studied the interactions between model membranes with mono and di-RL, showing how it is possible, by assuming a kinetic model, to derive relevant physical parameters from optical microscopy images. I performed phase contrast and fluorescence microscopy experiments on plasma membrane models represented by Giant Unilamellar Vesicles (GUVs), composed of single lipid POPC and ternary GUVs DOPC:SM:CHOL in molar ratios 1:1:1, 3:5:2 and 5:3:2. The experiments were performed with GUVs in the presence of mono- or di-RL in 0.06, 0.12 and 0.25 mM concentrations. Novel methods have been developed and applied to microscopy images allowing to determine area and volume of GUVs with asymmetrical shape and the description of the GUV-RL interaction by two kinetic mechanisms, RL-insertion and pore formation

Restorative treatment in patient with Williams Syndrome: case report

ABSTRACT In Dentistry, any user with one or more limitations, of temporary or permanent mental nature, of physical, sensory, emotional or medical growth, is considered to be a Patient with Special Needs, preventing him from being subjected to a conventional dental situation. These patients form a group which may be considered at high risk for the development of oral diseases, according to the kind of pathogen. Among them, is the Williams-Beuren Syndrome, a rare congenital disease with cardiovascular involvement, mental retardation, dysmorphic face, idiopathic hypercalcemia, musculoskeletal problems, dental and growth anomalies. Familial and sporadic cases are thought to result from deletion of genetic material from adjacent genes located on the long arm of chromosome 7. This article reports a clinical case involving a four-year-old boy with Williams-Beuren Syndrome, referred to the clinic of the Specialization Course for Patients with Special Needs, at the São Leopoldo Mandic Dental Research Center, Campinas (SP). As the patient was resistant to dental care, in order to reduce anxiety and increase collaboration in clinical sessions, the Hixizine® medication was administered. For atraumatic restorative treatment and restorations, the following materials were used: Cleanjoy®, Futurabond DC®, Ionofil Plus® Grandioso®, Grandio® and Profluorid®. As result, it was possible to reach a level of excellence using the indicated materials and specific protocols. Based on this work and the lived experience, it can be observed that these patients can receive welcoming dental care in specialized clinics

Tailoring melanins for bioelectronics: Polycysteinyldopamine as an ion conducting redox-responsive polydopamine variant for pro-oxidant thin films

Polycysteinyldopamine (pCDA), a red hair-inspired polydopamine-like polymer with ionic conductor behavior, can produce smooth and highly adhesive thin films and coatings on quartz, glass and other surfaces, and is shown to markedly accelerate the autoxidation of glutathione at physiological pH via an efficient redox exchange proces

ABS/clay nanocomposites obtained by a solution technique: Influence of clay organic modifiers

Acrylonitrile-butadiene-styrene (ABS) polymer/clay nanocomposites were produced using an intercalation\u2013adsorption technique from polymer in solution: polymer/clay suspensions were subjected to ultrasonic processing to increase the effectiveness of mixing. Several kinds of organically modified layered silicates (OMLS) were used to understand the influence of the surfactant nature on the intercalation\u2013exfoliation mechanism. We show that only imidazolium-treated montmorillonite (DMHDIM-MMT) is stable at the processing temperature of 200 \ub0C, used for hot-pressing, whereas alkyl-ammonium modified clays show significant degradation. The morphology of ABS based polymer nanocomposites prepared in this work was characterized by means of wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Dynamic-mechanical analysis (DMA) was used to determine the storage modulus and damping coefficient as a function of temperature, and to investigate the correlations between mechanical properties and morphology of the nanocomposites. The thermal stability was assessed by means of thermogravimetric analysis (TGA). DMA and TGA show that the nanocomposites based on imidazolium-modified clay out-perform the nanocomposites based on quaternary-ammonium-modified clays in terms of mechanical properties and thermal stability

Imidazolium-modified clay-based ABS nanocomposites: a comparison between melt-blending and solution-sonication processes

Acrylonitrile–butadiene–styrene (ABS) nanocomposites containing imidazolium-modified montmorillonite have been prepared by melt-blending (MB) and solution-sonication in order to study the effects of processing on the morphology and properties of the polymer/clay composites. The structure-property relationships of the prepared composites have been studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), mechanical testing, dynamic-mechanical analyses (DMA), thermal gravimetrical analyses (TGA), fluorescence probe confocal microscopy, and fluorescence spectroscopy (FS). X-Ray and TEM show that both nanocomposites have a mixed intercalated/exfoliated structure. Fluorescence probe confocal microscopy reveals that the sonicated sample has a more homogeneous dispersion: this result is confirmed by the values of elongation at break and flexural elastic modulus measured for the composites. Fluorescence spectroscopy has also been used to investigate the distribution of clay in the composites and results indicate that clay layers in ABS are preferentially located in the styrene-acrylonitrile (SAN) phase, independent of the dispersion process used