Lídia Pinheiro

Biodegradation of acrylic based resins: A review

OBJECTIVES The development of different types of materials with application in dentistry is an area of intense growth and research, due to its importance in oral health. Among the different materials there are the acrylic based resins that have been extensively used either in restorations or in dentures. The objective of this manuscript was to review the acrylic based resins biodegradation phenomena. Specific attention was given to the causes and consequences of materials degradation under the oral environment. DATA AND SOURCES Information from scientific full papers, reviews or abstracts published from 1963 to date were included in the review. Published material was searched in dental literature using general and specialist databases, like the PubMED database. STUDY SELECTION Published studies regarding the description of biodegradation mechanisms, in vitro and in vivo release experiments and cell based studies conducted on acrylic based resins or their components were evaluated. Studies related to the effect of biodegradation on the physical and mechanical properties of the materials were also analyzed. CONCLUSIONS Different factors such as saliva characteristics, chewing or thermal and chemical dietary changes may be responsible for the biodegradation of acrylic based resins. Release of potential toxic compounds from the material and change on their physical and mechanical properties are the major consequences of biodegradation. Increasing concern arises from potential toxic effects of biodegradation products under clinical application thus justifying an intensive research in this area.

Shape effects in the partial molar volume of tetraethylphosphonium and ammonium iodides in six nonaqueous solvents

AbstractDensities of dilute solutions of the electrolytes tetraethylphosphonium iodide and tetraethylammonium iodide in the nonaqueous solvents methanol, ethanol, 1-propanol, 1-butanol, acetonitrile, and 2-propanone were measured at 25°C. Using published values for the Debye-Hückel limiting slopes AV, apparent molar volume data were fitted to the Pitzer equation yielding infinite-dilution partial molar volumes

Lipoamino acid-based micelles as promising delivery vehicles for monomeric amphotericin B

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Solubilization power of an amino acid-based gemini surfactant towards the hydrophobic drug amphotericin B

and deviation parameters BV. It is found that the variation in the van der Waals volume of the cationic central atoms is about one half the experimental volume change in 2-propanone solutions, but twice that value in the other five solvents. This finding is interpreted in terms of openness of solute structure and solvent penetration. Parameter BV for each salt is shown to be solvent dependent. An interesting approximate linear variation between AV and BV parameters is suggested by the data. This empirical relationship would entail correlation of short- and long-range interionic interactions in solution.

Densities and refractive indices for the ternary mixture methanol/propan-1-ol/acetonitrile

Accurate second-order rate constants were measured at 5 K intervals in the temperature range 298.15-328.15 K for the quaternisation reaction of triethylphosphine with iodoethane in methanol, ethanol, propan-1-ol and butan-1-ol. These data are complemented previously reported rate constants for the quaternisation reaction of triethylamine with iodoethane in the same solvents and at similar temperatures. Each of these two reaction series is analysed in terms of the isokinetic relationship (IKR) with respect to solvent variation and of the isosolvent relationship (ISoR) with respect to temperature variation, using in the latter case five different empirical solvent scales. Statistically validated IKR and ISoR have been found for both reaction series. The resulting isokinetic temperatures of 347 K (phosphine series) and of 730 K (amine series) are discussed in terms of Linerts theory of the isokinetic relationship. The best ISoR correlation is obtained using the Dimroth-Reichardt E(T)(N) solvent scale for the phosphine series and the Kamlet-Taft alpha(KT) solvent scale for the amine series. It is demonstrated that no real solvent can be envisaged as having the characteristics of an isokinetic solvent. The selectivity of the nucleophiles triethylphosphine and triethylamine in the attack on iodoethane is examined by treating together both reaction series in terms of the isoselective relationship (ISeR). The isoselective temperature with respect to solvent is found to be 289 K, which is close to the value of 302 K predicted by Exner and Gieses formula on the basis of the individual isokinetic temperatures. A novel ISeR analysis with respect to temperature is performed. It reveals that the alpha(KT) scale is the most appropriate solvent scale for describing this selectivity series, and that it is feasible to find an isoselective solvent. A new equation is developed for predicting the isoselective solvent parameter from individual isosolvent parameters and is shown to yield realistic values. The present similarity analysis shows that there are significant differences between the courses of these quaternisation reactions. On the basis of the experimentally determined isoparameter values, in liquid alcohols as solvent it is proposed that the reaction between triethylphosphine and iodoethane follows a classic bimolecular nucleophilic substitution pathway, whereas the desolvation of triethylamine molecules has to be taken into account to describe the mechanism of the original Menshutkin reaction.

Amino acid-based cationic gemini surfactant–protein interactions

Lipoamino acid-based micelles have been developed as delivery vehicles for the hydrophobic drug amphotericin B (AmB). The micellar solubilisation of AmB by a gemini lipoamino acid (LAA) derived from cysteine and its equimolar mixtures with the bile salts sodium cholate (NaC) and sodium deoxycholate (NaDC), as well as the aggregation sate of the drug in the micellar systems, was studied under biomimetic conditions (phosphate buffered-saline, pH 7.4) using UV-vis spectroscopy. Pure surfactant systems and equimolar mixtures were characterized by tensiometry and important parameters were determined, such as critical micelle concentration (CMC), surface tension at the CMC (γCMC), maximum surface excess concentration (Γmax), and minimum area occupied per molecule at the water/air interface (Amin). Rheological behaviour from viscosity measurements at different shear rates was also addressed. Solubilisation capacity was quantified in terms of molar solubilisation ratio (χ), micelle-water partition coefficient (KM) and Gibbs energy of solubilisation (ΔGs°). Formulations of AmB in micellar media were compared in terms of drug loading, encapsulation efficiency, aggregation state of AmB and in vitro antifungal activity against Candida albicans. The LAA-containing micellar systems solubilise AmB in its monomeric and less toxic form and exhibit in vitro antifungal activity comparable to that of the commercial formulation Fungizone.

Preferential solvation and solvatochromic behaviour of quinoline in binary alkan-1-ol/N,N-dimethylformamide solvent mixtures

The growing demand for surfactants worldwide has a profound impact on the environment and public health. The quest for environmentally friendly “green” surfactants has driven research toward bio-based surfactants from renewable sources with improved performances and low toxicity. Amino acid-based surfactants (AAS) are a promising class of biocompatible and biodegradable surfactants for biomedical applications due to their improved safety profiles that meet the requirements of both physiological and ecological compatibility. Natural amino acids are chiral compounds and important raw materials for production of AAS. The amino acid pool allows the synthesis of multifunctional surfactants with chiral properties that can be tailored for specific technological and/or biomedical applications. The nature of the amino acid residue, the chirality, and the ability for hydrogen bond formation strongly influences the surface active properties and self-assembly behavior of AAS. This review summarizes recent developments in AAS structure-property relationships providing valuable information for modulation of the surface active and biological properties of AAS to meet specific biomedical applications. The interaction of AAS with biointerfaces and biological molecules is also addressed concerning cellular toxicity and potential therapeutic applications of AAS as antimicrobial agents, drug delivery vehicles, and a promising alternative to viral vectors in gene therapy.