130,544 research outputs found
Prediction Method for the Surface Damage in Splined Couplings
No full textThe primary purpose of my PhD thesis was to develop design criteria and to verify procedures about fretting wear, that are applicable to crowned spline couplings of a power transmission system of the aeroengines. Fretting is a very complex phenomenon being influenced by many factors, the most important being the presence or absence of lubrication, the load distribution (contact pressure) and the sliding between the bodies. Therefore, the study of fretting needs a deep knowledge of these three main aspects. The first aspect of the problem was based on models and experimental tests considering specify specimens (crowned spline couplings) and imposed movements, so as to uniquely identify the working conditions (load and sliding), in order to facilitate the comparison between the experimental tests and the analytical models. The analytical models have been validated with numerical simulations and by comparison with experimental data, that have been obtained by means of a dedicated test bench that has been designed and built. Thanks to the test rig was possible to determinate the real contact pressure of two engaging teeth; in fact, it is one of the most important parameters affecting the fretting phenomenon, but it is very difficult to evaluate in a quantitative way, especially when considering components with complex geometries. The second phase of this thesis was the development of a predictive model for crowned splined couplings. This model is based on the Ruiz first parameter. The aim of my thesis is to demonstrate how this parameter may be correctly applied to a complex component as the crowned spline coupling, taking into account experimental and FEM validation
Preparation of 1,6-di-deoxy-D-galacto and 1,6-di-deoxy-L-altro nojirimycin derivatives by aminocyclization of a 1,5-dicarbonyl derivative
No full textIminosugars are known glycosidase inhibitors which are the subject of drug development efforts against several diseases. The access to structurally-related families of iminosugars is of primary importance for running structure-activity relationship studies. In this work, the double reductive amination (aminocyclization) reaction of a dicarbonyl derivative of the L-arabino series, in turn obtained from lactose, is reported. Different ratios of 1,6-di-deoxy-D-galacto and 1,6-di-deoxy-L-altro nojirimycin derivatives were obtained depending on the amine employed in this transformation which provided an insight into the effects of their structure on the outcome of the reaction. Of particular interest were the results obtained when two enantiomeric amino acids (D-Phe-OMe and L-Phe-OMe) were used, which resulted in the inversion of the reaction stereoselectivity
An overview of carbohydrate-based carbonic anhydrase inhibitors
No full textCarbonic anhydrases (CAs) are metalloenzymes responsible for the reversible hydration of carbon dioxide to bicarbonate, a fundamental reaction involved in various physiological and pathological processes. In the last decades, CAs have been considered as important drug targets for different pathologies such as glaucoma, epilepsy and cancer. The design of potent and selective inhibitors has been an outstanding goal leading to the discovery of new drugs. Among the different strategies developed to date, the design of carbohydrate-based CA inhibitors (CAIs) has emerged as a versatile tool in order to selectively target CAs. The insertion of a glycosyl moiety as a hydrophilic tail in sulfonamide, sulfenamide, sulfamate or coumarin scaffolds allowed the discovery of many different series of sugar-based CAIs, with relevant inhibitory results. This review will focus on carbohydrate-based CAIs developed so far, classifying them in glycosidic and glycoconjugated inhibitors based on the conjugation chemistry adopted
Dietary Bioactive Compounds: Implications for Oxidative Stress and Inflammation
No full text: Nowadays, it has been amply demonstrated how an appropriate diet and lifestyle are essential for preserving wellbeing and preventing illnesses [...]
Developments in carbohydrate-based metzincin inhibitors
No full textMatrix metalloproteinases (MMPs) and A disintegrin and Metalloproteinase (ADAMs) are zinc-dependent endopeptidases belonging to the metzincin superfamily. Upregulation of metzincin activity is a major feature in many serious pathologies such as cancer, inflammations, and infections. In the last decades, many classes of small molecules have been developed directed to inhibit these enzymes. The principal shortcomings that have hindered clinical development of metzincin inhibitors are low selectivity for the target enzyme, poor water solubility, and long-term toxicity. Over the last 15 years, a novel approach to improve solubility and bioavailability of metzincin inhibitors has been the synthesis of carbohydrate-based compounds. This strategy consists of linking a hydrophilic sugar moiety to an aromatic lipophilic scaffold. This review aims to describe the development of sugar-based and azasugar-based derivatives as metzincin inhibitors and their activity in several pathological models
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