Showing: 10 from total: 1718 publications
411. Solvente eutéctico profundo
Santos, L ; CIQUP/ Universidade do Porto,
in Revista de Ciência Elementar , 2017, ISSN: 2183-9697,  Volume: 5, 
Article,  Indexed in: crossref 

412. Effect of Confined Hindrance in Polyphenylbenzenes
Lima, CFRAC ; Rodrigues, ASMC ; Santos, LMNBF
in JOURNAL OF PHYSICAL CHEMISTRY A, 2017, ISSN: 1089-5639,  Volume: 121, 
Article,  Indexed in: crossref, scopus, wos 
Abstract A comprehensive thermodynamic study of the whole ortho-polyphenylbenzenes series from biphenyl (n = 1) to hexaphenylbenzene (n = 6) is presented. Combustion calorimetry and phase equilibria measurements for 1,2,3,4-tetraphenylbenzene (n = 4) and pentaphenylbenzene (n = 5) together with literature data were used to understand and quantify the constraint effect of ortho-substitution on the molecular energetics and phase stability of polyaromatic compounds. All of the derived thermodynamic properties (enthalpy of sublimation, entropy of sublimation, and gas phase molecular energetics) show a marked trend shift at n = 4 to 5, which is related to the change of the degree of molecular flexibility after 1,2,3,4-tetraphenylbenzene (n = 4). The greater intramolecular constraint in the more crowded members of the series (n = 5 and 6) leads to a significant change in the molecular properties and cohesive energy. The trend shift in the molecular properties is related with the decrease in molecular flexibility, which leads to lower molecular entropy and destabilization of the intramolecular interaction potential due to the increased hindrance in a confined molecular space.

413. A Computational Investigation of the Equilibrium Constants for the Fluorescent and Chemiluminescent States of Coelenteramide
Min, CG ; da Silva, LP ; Esteves da Silva, JCGE ; Yang, XK ; Huang, SJ ; Ren, AM ; Zhu, YQ
in CHEMPHYSCHEM, 2017, ISSN: 1439-4235,  Volume: 18, 
Article,  Indexed in: crossref, scopus, wos 
Abstract In spite of recent advances in understanding the mechanism of coelenterate bioluminescence, there is no consensus about which coelenteramide specie and/or state are the light emitter. In this study, a systematic investigation of the geometries and spectra of all possible light emitters has been performed at the TD omega B97XD/6-31+ G(d) level of theory, including various fluorescent and chemiluminescent states in vacuum, in a hydrophobic environment and in aqueous solution. To deduce the most probable form of the fluorescent and chemiluminescent coelenteramide emitter, the equilibrium constants for the fluorescent and chemiluminescent states connecting the various species have been calculated. wB97XD gives a qualitatively good description of fluorescent and chemiluminescent structures. Coelenteramide is formed in a "dark" chemiluminescent state and must evolve to a bright fluorescent state. Moreover, the photoacidity of the phenol group is significantly higher in the fluorescent state than in the chemiluminescent state, which allows the formation of phenolate coelenteramide and clarifies its role as the bioluminescent emitter.

414. Vaporization of protic ionic liquids derived from organic superbases and short carboxylic acids
Ribeiro, FMS ; Lima, CFRAC ; Vaz, ICM ; Rodrigues, ASMC ; Sapei, E ; Melo, A ; Silva, AMS ; Santos, LMNBF
in PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 2017, ISSN: 1463-9076,  Volume: 19, 
Article,  Indexed in: crossref, scopus, wos 
Abstract This work presents a comprehensive evaluation of the phase behaviour and cohesive enthalpy of protic ionic liquids (PILs) composed of 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) or 1,8-diazabicyclo[5.4.0] undec-7- ene (DBU) organic superbases with short-chain length (acetic, propionic and butyric) carboxylic acids. Glass transition temperatures, T-g, and enthalpies of vaporization, Delta H-vap, were measured for six [BH][A] (1 : 1) PILs (B = DBN, DBU; A = MeCOO, EtCOO, nPrCOO), revealing more significant changes upon increasing the number of -CH2- groups in the base than in the acid. The magnitude of Delta H-vap evidences that liquid PILs have a high proportion of ions, although the results also indicate that in DBN PILs the concentration of neutral species is not negligible. In the gas phase, these PILs exist as a distribution of ion pairs and isolated neutral species, with speciation being dependent on the temperature and pressure conditions at high temperatures and low pressures the separated neutral species dominate. The higher T-g and Delta H-vap of the DBU PILs are explained by the stronger basicity of DBU (as supported by NMR and computational calculations), which increases the extent of proton exchange and the ionic character of the corresponding PILs, resulting in stronger intermolecular interactions in condensed phases.

415. Combined experimental and theoretical study of the photochemistry of 4-and 3-hydroxycoumarin
da Silva, LP ; Simkovitch, R ; Huppert, D ; Esteves da Silva, JCGE
in JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 2017, ISSN: 1010-6030,  Volume: 338, 
Article,  Indexed in: crossref, scopus, wos 
Abstract Steady-state and time-resolved optical spectroscopy techniques were employed to study the photo physics and photochemistry of 4- (4HC) and 3-hydroxycoumarin (3HC). We found that the p K-a of 4HC in aqueous solutions is about 7.5 and the p K-a* is only 4.5. We also found that the nonradiative rate of 4-hydroxycoumarin is high and the excited state proton transfer (ESPT) rate to water is rather slow and so an ESPT process is not observed. Quantum mechanical calculations confirm that the ESPT rate should be slow and the intersystem crossing rate St -> 4 T is large. An ESPT process was also not observed for 3HC, but it might still take place and not being observed as the fluorescence quantum yield of the anion is two orders of magnitude smaller than that of the protonated form. The nonradiative decay of protonated 3HC is explained with an H-atom abstraction mechanism, leading to the formation of a radical species.

416. Theoretical modulation of singlet/triplet chemiexcitation of chemiluminescent imidazopyrazinone dioxetanone via C-8-substitution
Pinto da Silva, LP ; Magalhaes, CM ; Crista, DMA ; Esteves da Silva, JCGE
in PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES, 2017, ISSN: 1474-905X,  Volume: 16, 
Article,  Indexed in: crossref, scopus, wos 
Abstract Coelenterazine, a member of the imidazopyrazinone class of chemiluminescent substrates, presents significant potential as a dynamic probe of reactive oxygen species in a biological environment, such as a superoxide anion, in which these species are important in cellular biology and pathology. The objective of the current study was to understand in what way the efficiency of singlet and triplet chemiexcitation could be modulated, towards a more efficient use of imidazopyrazinone-based compounds as dynamic chemiluminescent probes. To this end the thermolysis of imidazopyrazinone dioxetanone, substituted at the C-8-position with electron-donating or electron-withdrawing groups, was characterized with a theoretical approach based on density functional theory. Substituents with different electron-donating/withdrawing characters have only a limited effect on the singlet chemiexcitation of anionic dioxetanone. For neutral dioxetanone, both electron-withdrawing and weak electron-donating substituents increase singlet chemiexcitation, to the contrary of strong electron-donating groups. During their thermolysis reaction, all molecules presented regions of degeneracy with triplet states, thereby indicating the possibility of triplet chemiexcitation.

417. Thermo-responsive microgels based on encapsulated carbon quantum dots
Campos, BB ; Mutavdzic, D ; Stankovic, M ; Radotic, K ; Lazaro Martinez, JM ; Esteves da Silva, JCGE ; Contreras Caceres, R ; Soledad Pino Gonzalez, MS ; Rodriguez Castellon, E ; Algarra, M
in NEW JOURNAL OF CHEMISTRY, 2017, ISSN: 1144-0546,  Volume: 41, 
Article,  Indexed in: crossref, scopus, wos 
Abstract In this work carbon quantum dot (CQD) nanoparticles are synthesized from D-lactose using a hydrothermal method and then they are coated with polyethylene glycol (CQDs@PEG). These particles exhibit a monodisperse spherical morphology with an average particle size of similar to 4 nm. Nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy showed the presence of the hydroxyl groups from the ethylene glycol molecules grafted onto the CQDs' surfaces, which confirms that PEG was covalently attached to the nanoparticles' surfaces. Fluorescence analysis demonstrates a shift in the emission at 495 nm after PEG coating. Modified carbon dots were introduced into thermo-responsive pNIPAM microgels. The resultant pNIPAM-CQDs@PEG hybrid system exhibits interesting fluorescence properties. Transmission electron microscopy (TEM), fluorescence microscopy, and energy-dispersive X-ray (EDX) spectroscopy confirm the incorporation of CQD particles into the microgels. Finally, dynamic light scattering (DLS) analysis confirms that further hybrid microgels based on pNIPAM are thermo-responsive, with a transition temperature similar to that of a system with an ionic component.

418. Cationic gemini surfactant as a dual linker for a cholic acid-modified polysaccharide in aqueous solution: thermodynamics of interaction and phase behavior
Bai, GY ; Wu, H ; Lou, PX ; Wang, YJ ; Nichifor, M ; Zhuo, K ; Wang, JJ ; Bastos, M
in PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 2017, ISSN: 1463-9076,  Volume: 19, 
Article,  Indexed in: crossref, scopus, wos 
Abstract Understanding the thermodynamics of formation of biocompatible aggregates is a key factor in the bottom up approach to the development of novel types of drug carriers and their structural tuning using small amphiphilic molecules. We chose an anionic amphiphilic and biocompatible polymer that consists of a dextran and grafted cholic acid pendants, randomly distributed along the dextran backbone, with a degree of substitution (DS) of 15 mol% (designated Dex-15CACOONa). The thermodynamics of interaction and phase behavior of mixtures of this polyelectrolyte and a cationic gemini surfactant hexanediyl-alpha, omega-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) or its monomer surfactant dodecyltrimethylammonium bromide (DTAB) in aqueous solution were characterized by isothermal titration calorimetry (ITC) and turbidity, together with cryogenic transmission electron microscopy (Cryo-TEM). The various critical concentrations and the enthalpy changes of the corresponding phase transitions for the oppositely charged system were obtained from the plots of the observed enthalpy change (DHobs) and turbidity measurements as a function of gemini concentration. The morphologies of the aggregates in various phases were observed by Cryo-TEM. Altogether these results suggest the critical role of gemini as a dual linker. At the concentrations where the crosslink between the pendant aggregates happens, the free gemini concentration is proximately zero and the aggregate retains its negative charge. The analysis of various factors involved in the interaction allowed a rationalization of the driving forces for mixed aggregate formation, which will contribute to a subsequent rational design of drug delivery systems based on this polymer/surfactant system.

419. Lactoferricin Peptides Increase Macrophages' Capacity To Kill Mycobacterium avium
Silva, T ; Moreira, AC ; Nazmi, K ; Moniz, T ; Vale, N ; Rangel, M ; Gomes, P ; Bolscher, JGM ; Rodrigues, PN ; Bastos, M ; Gomes, MS
in MSPHERE, 2017, ISSN: 2379-5042,  Volume: 2, 
Article,  Indexed in: crossref, scopus, wos 
Abstract Mycobacterial infections cause a significant burden of disease and death worldwide. Their treatment is long, toxic, costly, and increasingly prone to failure due to bacterial resistance to currently available antibiotics. New therapeutic options are thus clearly needed. Antimicrobial peptides represent an important source of new antimicrobial molecules, both for their direct activity and for their immunomodulatory potential. We have previously reported that a short version of the bovine antimicrobial peptide lactoferricin with amino acids 17 to 30 (LFcin17-30), along with its variants obtained by specific amino acid substitutions, killed Mycobacterium avium in broth culture. In the present work, those peptides were tested against M. avium living inside its natural host cell, the macrophage. We found that the peptides increased the antimicrobial action of the conventional antibiotic ethambutol inside macrophages. Moreover, the D-enantiomer of the lactoferricin peptide (D-LFcin17-30) was more stable and induced significant killing of intracellular mycobacteria by itself. Interestingly, D-LFcin17-30 did not localize to M. avium-harboring phagosomes but induced the production of proinflammatory cytokines and increased the formation of lysosomes and autophagosome-like vesicles. These results lead us to conclude that D-LFcin17-30 primes macrophages for intracellular microbial digestion through phagosomal maturation and/or autophagy, culminating in mycobacterial killing. IMPORTANCE The genus Mycobacterium comprises several pathogenic species, including M. tuberculosis, M. leprae, M. avium, etc. Infections caused by these bacteria are particularly difficult to treat due to their intrinsic impermeability, low growth rate, and intracellular localization. Antimicrobial peptides are increasingly acknowledged as potential treatment tools, as they have a high spectrum of activity, low tendency to induce bacterial resistance, and immunomodulatory properties. In this study, we show that peptides derived from bovine lactoferricin (LFcin) improve the antimicrobial activity of ethambutol against Mycobacterium avium growing inside macrophages. Moreover, the D-enantiomer of a short version of lactoferricin containing amino acids 17 to 30 (D-LFcin17-30) causes intramacrophagic death of M. avium by increasing the formation of lysosomes and autophagosomes. This work opens the way to the use of lactoferricin-derived peptides to treat infections caused by mycobacteria and highlights important modulatory effects of D-FLcin17-30 on macrophages, which may be useful under other conditions in which macrophage activation is needed.

420. Carbon footprint of the insulation cork board
Tártaro, AS ; Mata, TM ; Martins, AA ; Esteves da Silva, JCG
in Journal of Cleaner Production, 2017, ISSN: 0959-6526,  Volume: 143, 
Article,  Indexed in: scopus 
Abstract This work aims to calculate the carbon footprint of the ICB produced by a Portuguese company and to compare it with other insulation materials available in the market. A Life Cycle Thinking approach and the ISO/TS 14067 (2013) requirements were followed in this work to perform a “cradle-to-gate” life cycle analysis. The inventory analysis mainly uses primary data collected from a Portuguese ICB producing company, complemented with secondary data from commercial life cycle databases and literature concerning respectively, the external transportation of the cork raw-material and the emission factors of electricity and fuel production and use. Results of this study show that ICB has a carbon footprint of −116.229 kg CO2 equivalent per m3 of ICB. It is the only insulation material present in the market with a negative carbon footprint, which is mainly due to the utilization of cork, a renewable raw material, the proximity of its source to the factory, and the use of biomass for generating the steam needed for its production process. To the authors’ knowledge, this is the first study to report the carbon footprint of ICB and to compare it with other building insulation materials. © 2016 Elsevier Ltd