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41.
Liliana C. Tomé Susana C. M. Fernandes Denilson Silva Perez Patrizia Sadocco Armando J. D. Silvestre Carlos Pascoal Neto Isabel M. Marrucho Carmen S. R. Freire 《Cellulose (London, England)》2013,20(4):1807-1818
Thin nanocomposite films of thermoplastic starch, chitosan and cellulose nanofibers (bacterial cellulose or nanofibrillated cellulose) were prepared for the first time by solvent casting of water based suspensions of the three polysaccharides. The role of the different bioploymers on the final properties (thermal stability, transparency, mechanical performance and antimicrobial activity) of the films was related with their intrinsic features, contents and synergic effects resulting from the establishment of interactions between them. Thermoplastic starch displays an important role on the thermal stability of the films because it is the most stable polysaccharide; however it has a negative impact on the mechanical performance and transparency of the films. The addition of chitosan improves considerably the transparency (up to 50 % transmittance for 50 % of chitosan, in respect to the amount of starch), mechanical performance and antimicrobial properties (at least 25 % of chitosan and no more than 10 % of cellulose nanofibers are required to observe bacteriostatic or bactericidal activity) but decrease their thermal stability. The incorporation of cellulose nanofibers had the strongest positive impact on the mechanical properties of the materials (increments of up to 15 and 30 MPa on the Young′s modulus and Tensile strength, respectively, for films with 20 % of BC or NFC). Nonetheless, the impact in thermal stability and mechanical performance of the films, promoted by the addition of chitosan and cellulose nanofibres, respectively, was higher than the expected considering their percentage contents certainly because of the establishment of strong and complex interactions between the three polysaccharides. 相似文献
42.
Carlota Leonardo-Sousa Andreia Neves Carvalho Romina A. Guedes Pedro M. P. Fernandes Natlia Aniceto Jorge A. R. Salvador Maria Joo Gama Rita C. Guedes 《Molecules (Basel, Switzerland)》2022,27(7)
Proteasome inhibitors have shown relevant clinical activity in several hematological malignancies, namely in multiple myeloma and mantle cell lymphoma, improving patient outcomes such as survival and quality of life, when compared with other therapies. However, initial response to the therapy is a challenge as most patients show an innate resistance to proteasome inhibitors, and those that respond to the therapy usually develop late relapses suggesting the development of acquired resistance. The mechanisms of resistance to proteasome inhibition are still controversial and scarce in the literature. In this review, we discuss the development of proteasome inhibitors and the mechanisms of innate and acquired resistance to their activity—a major challenge in preclinical and clinical therapeutics. An improved understanding of these mechanisms is crucial to guiding the design of new and more effective drugs to tackle these devastating diseases. In addition, we provide a comprehensive overview of proteasome inhibitors used in combination with other chemotherapeutic agents, as this is a key strategy to combat resistance. 相似文献
43.
We report numerical results on the existence of periodic structures embedded in chaotic and hyperchaotic regions on the Lyapunov exponent diagrams of a 4-dimensional Chua system. The model was obtained from the 3-dimensional Chua system by the introduction of a feedback controller. Both the largest and the second largest Lyapunov exponents were considered in our colorful Lyapunov exponent diagrams, and allowed us to characterize periodic structures and regions of chaos and hyperchaos. The shrimp-shaped periodic structures appear to be malformed on some of Lyapunov exponent diagrams, and they present two different bifurcation scenarios to chaos when passing the boundaries of itself, namely via period-doubling and crisis. Hyperchaos-chaos transition can also be observed on the Lyapunov exponent diagrams for the second largest exponent. 相似文献
44.
Sousa DM Fernandes PA Marques GD Ribeiro AC Sebastião PJ 《Solid state nuclear magnetic resonance》2004,25(1-3):160-166
In this paper, we outline the operating principles of a pulsed switched power supply for a fast field-cycling nuclear magnetic resonance spectrometer. The power supply uses a variant of a four-quadrant chopper with a duty cycle that defines the average output current. With this topology only two semiconductors are necessary to drive hundreds of amperes with an output power of several kilowatts. The output current ripple has a well-defined shape that can be reduced to acceptable values by a careful design of the semiconductors' controlling circuits and drivers. A power supply prototype was tested with a home build air-core magnet operating with fields between 0 and 0.21 T. The system is computer controlled using pulse generator and data acquisition PC cards, and specific user-friendly home-developed software. A comparative proton relaxometry study in two well-known liquid crystal compounds 5CB and MBBA was performed to check the reproducibility of the T1 measurements. 相似文献
45.
Nonlinear Dynamics - This work explores the role of asymmetrical damping and geometrical nonlinearities in the suspension system of a simplified vehicle model in order to improve comfort. Improving... 相似文献
46.
Zinc is the second most abundant transition element in biology and the only metal known to be represented in enzymes from each one of the six classes established by the International Union of Biochemistry. The flexible coordination geometry, the fast ligand exchange, the lack of redox activity, and its role as Lewis acid are just some of the features that make zinc an invaluable element in biological catalysis. In this study, we have analyzed the importance in mononuclear Zn enzymes of an interesting mechanistic phenomenon known as carboxylate shift, which is characterized by a change in the coordination mode of a carboxylate group (mono to bidentate or vice versa) with both ligand entrance or exit from the metal coordination sphere. Using B3LYP calculations, we were able to unveil in detail patterns relating the intrinsic characteristics of a given Zn coordination sphere with the existence or not of a carboxylate-shift mechanism and the additional energy stabilization arising from it. In particular, a specific Zn coordination sphere containing a carboxylate ligand (Asp or Glu), a cysteine, and a histidine has been shown to have the most favorable combination of amino acid residues that ensures a fast ligand exchange. 相似文献
47.
Alvaro S. de Sousa Zanele Hlam Manuel A. Fernandes Helder M. Marques 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(4):o229-o232
The crystal structure of the title compound, C8H17NO2, consists of (R,R) and (S,S) enantiomeric pairs packed in adjacent double layers which are characterized by centrosymmetric hydrogen‐bonded dimers, generated via N—H...O and O—H...O interactions, respectively. Intermolecular interactions, related to acceptor and donor molecule chirality, link the achiral double layers into tubular columns, which consist of a staggered hydrophilic inner core surrounded by a hydrophobic cycloalkyl outer surface and extend in the [011] direction. 相似文献
48.
Fernandes Joo Lucas Ribeiro e de Souza Altair Lcio de Faria Geraldo Lcio 《Journal of Thermal Analysis and Calorimetry》2022,147(12):6593-6603
Journal of Thermal Analysis and Calorimetry - The hot coil slump is a recurrent problem in the manufacturing process of medium and high equivalent carbon steel plates. Even with the success of the... 相似文献
49.
Dr. Tiago Fernandes Prof. Helena I. S. Nogueira Dr. Carlos O. Amorim Dr. João S. Amaral Dr. Ana L. Daniel-da-Silva Prof. Tito Trindade 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(61):e202202382
Chemical analyses in the field using surface-enhanced Raman scattering (SERS) protocols are expected to be part of several analytical procedures applied to water quality monitoring. To date, these endeavors have been supported by developments in SERS substrate nanofabrication, instrumentation portability, and the internet of things. Here, we report distinct chemical strategies for preparing magneto-plasmonic (Fe3O4 : Au) colloids, which are relevant in the context of trace-level detection of water contaminants due to their inherent multifunctionality. The main objective of this research is to investigate the role of poly(amidoamine) dendrimers (PAMAMs) in the preparation of SERS substrates integrating both functionalities into single nanostructures. Three chemical routes were investigated to design magneto-plasmonic nanostructures that translate into different ways for assessing SERS detection by using distinct interfaces. Hence, a series of magneto-plasmonic colloids have been characterized and then assessed for their SERS activity by using a model pesticide (thiram) dissolved in aqueous samples. 相似文献
50.
In flow injection analysis, several plugs can be injected simultaneously into the same carrier system, in order to achieve overlapped zones. The potentialities of such sequential injections are studied in model systems with spectrophotometric detection; the procedure is shown to give better precision than the use of concentration gradients. The method is used with atomic absorption spectrometry to allow the determination of a wide range of manganese contents in rocks, and to facilitate the use of standard additions for the determination of copper in ethanol. 相似文献