Percorrer por autor "Da Silva, José Paulo"
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- 2-Hydroxychalcone−β-Cyclodextrin Conjugate with pH-Modulated Photoresponsive Binding PropertiesPublication . Paulino, Micael; Pérez-Juste, Ignacio; Cid, María Magdalena; Da Silva, José Paulo; Pereira, M. Manuela A.; Basílio, NunoStimuli-responsive supramolecular receptors are important building blocks for the construction of self-assembled functional materials. We report the design and synthesis of a pH and light-responsive 2-hydroxychalcone-beta-cyclodextrin conjugate (1-Ct) and its characterization by spectroscopic and computational methods. 1-Ct follows the typical reaction network of trans-chalcone-flavylium photoswitches. Upon light irradiation, 1-Ct can be photochemically converted into the cis-chalcone/hemiketal forms (1-Cc/1-B) under neutral pH conditions or to the flavylium cation (1-AH+) at acidic pH values. This stimuli-responsive beta-cyclodextrin host, 1Ct, was found to form stronger intramolecular self-inclusion complexes (Kintra = 14) than 1-AH+ (Kintra = 3) and weaker than 1-Cc/1-B (overall Kintra = 179), allowing control over their stability and binding properties by combinations of pH and light stimuli.
- A comparative study of the photophysics and photochemistry of 4-chlorophenol adsorbed on silicalite and beta-cyclodextrinPublication . Da Silva, José Paulo; Ferreira, Luís F. Vieira; Silva, Abílio M. da; Oliveira, A. S.The photochemistry and photophysics of 4-chlorophenol (4-CP) were studied onto two model solid supports, silicalite and beta-cyclodextrin (beta-Cl)), using time resolved diffuse reflectance techniques and product degradation analysis. The results have shown that the photochemistry and photophysics of 4-CP are different from solution and depend on the solid. Ground state diffuse reflectance and time resolved luminescence demonstrated the inclusion of the probe in both substrates. 4-CP exhibits room temperature luminescence in both hosts, being structured and much more intense in beta-CD. The emission was assigned to phosphorescence of the inclusion complex. Transient absorption demonstrated the formation of the unsubstituted phenoxyl radical and of 4-chlorophenoxyl radical in beta-CD. In silicalite only the later was detected. The studies of the photodegradation products indicate that phenol is the main photoproduct in beta-CD. In silicalite the chromatographic analysis indicates the presence of products that involve the ring cleavage. (C) 2002 Elsevier Science B.V. All rights reserved.
- A visible-near-infrared light-responsive host-guest pair with nanomolar affinity in waterPublication . Ferreira, Pedro; Ventura, Barbara; Barbieri, Andrea; Da Silva, José Paulo; Laia, Cesar A. T.; Jorge Parola, A.; Basilie, NunoThe discovery of stimuli-responsive high affinity host-guest pairs with potential applications under biologically relevant conditions is a challenging goal. This work reports a high-affinity 1:1 complex formed between cucurbit[8]uril and a water-soluble photochromic diarylethene derivative. It was found that, by confining the open isomer within the cavity of the receptor, a redshift in the absorption spectrum and an enhancement of the photocyclization quantum yield from phi=0.04 to phi=0.32 were induced. This improvement in the photochemical performance enables quantitative photocyclization with visible light that, together with the near-infrared light-induced ring-opening reaction and the 100-fold selectivity for the closed isomer, confirms this as an outstanding light-responsive affinity pair.
- Bile acids as putative social signals in Mozambique tilapia (Oreochromis mossambicus)Publication . Ashouri, Samyar; Da Silva, José Paulo; Canario, Adelino; Hubbard, PeterChemical cues provide potential mates with information about reproductive status and resource-holding potential. In the Mozambique tilapia (Oreochromis mossambicus), males can distinguish female reproductive status through chemical cues, and accessibility of males to females depends on their position in the hierarchy, determined in part by chemical cues. Here, we hypothesized that tilapia faecal cues are attractive to conspecifics once released into the water. C18 solid-phase extracts of faeces from dominant males and pre-ovulatory females evoked stronger olfactory epithelium electrical responses (EOG) than, respectively, subordinate males and postspawning females. Mass spectrometry of the reverse-phase C18 high-performance liquid chromatography fractions of these extracts with highest EOG, identified by amino acids and bile acids. Faeces from pre-ovulatory females contain significantly higher concentrations of cholic acid (CA) and taurocholic acid (TCH) than both post-spawning females and males. A pool of amino acids had no effect on aggression or attraction in males. However, males were attracted to the scent of pre-ovulatory female faeces, as well as CA and TCH, when applied separately. This attraction was accompanied by increased digging behaviour compared to the odour of postspawning females. CA and TCH exert their action through separate receptor mechanisms. These findings are consistent with a role for faeces - and bile acids therein - in chemical communication in this species, acting as an attractant for males to reproductive females.
- Competing pathways for photoremovable protecting groups: the effects of solvent, oxygen and encapsulationPublication . Field, Thomas; Peterson, Julie; Ma, Chicheng; Jagadesan, Pradeepkumar; Da Silva, José Paulo; Rubina, Marina; Ramamurthy, V.; Givens, Richard S.Extending the applications of Photoremovable Protecting Groups (PPGs) to "cage" phenols has generally met with unusually complex PPG byproducts. In this study, we demonstrate that thep-hydroxyphenacyl (pHP) cage for both simple and complex phenolics, including tyrosine, dispenses free phenols. With the simpler unsubstituted phenols, the reaction is governed by their Bronsted Leaving Group ability. On the other hand, the byproducts of the cage vary with these phenols. For the more acidic phenols the cage byproduct follows the Favorskii rearrangement to formp-hydroxyphenylacetic acid whereas for the weaker phenols other reactions such as reduction and hydrolysis begin to emerge. When the photolysis is conducted in octa acid (OA) containers, non-Favorskii, unrearranged fragments of the cage and other byproducts arise.
- Effects of foliar application of organic acids on strawberry plantsPublication . Saavedra, Teresa; Gama, Florinda; Rodrigues, Maria Joao; Abadía, Javier; de Varennes, Amarilis; Pestana, Maribela; Da Silva, José Paulo; Correia, Pedro JoséThe large economic costs and environmental impacts of iron-chelate treatments has led to the search for alter-native methods and compounds to control iron (Fe) deficiency chlorosis. Strawberry plants (Fragaria x ananassa) were grown in Hoagland's nutrient solution in a greenhouse with two levels of Fe: 0 and 10 mu M Fe(III)-EDDHA. After 20 days, plants growing without Fe showed typical symptoms of Fe deficiency chlorosis in young leaves. Then, the adaxial and abaxial sides of one mature or one young leaf in each plant were brushed with 10 mM malic (MA), citric (CA) or succinic (SA) acids. Eight applications were done over a two-week period. At the end of the experiment, the newly emerged (therefore untreated), young and mature leaves were sampled for nutritional and metabolomic analysis, to assess the effectiveness of treatments. Leaf regreening was monitored using a SPAD-502 apparatus, and the activity of the ferric chelate-reductase activity (FCR) was measured using root tips. Iron deficiency negatively affected biomass and leaf chlorophyll but did not increase FCR activity. Application of succinic acid alleviated the decrease in chlorophyll observed in other treatments, and the overall nutritional balance in the plant was also changed. The concentrations of two quinic acid derivatives increased under Fe deficiency and decreased in plants treated with succinic acid, and thus they are proposed as Fe stress markers. Data suggest that foliage treatments with carboxylates may be, in some cases, environmentally friendly alter-natives to Fe(III)-chelates. The importance of Fe mobilization pathways in the formulation of new fertilizers is also discussed.
- ESI-MS of Cucurbituril Complexes Under Negative PolarityPublication . Rodrigues, Maria A. A.; Mendes, Debora C.; Ramamurthy, Vaidhyanathan; Da Silva, José PauloElectrospray ionization mass spectrometry (ESI-MS) is a powerful tool to study host-guest supramolecular interactions. ESI-MS can be used for detailed gas-phase reactivity studies, to clarify the structure, or simply to verify the formation of complexes. Depending on the structure of the host and of the guest, negative and/or positive ESI are used. Here we report the unexpected formation of host-guest complexes between cucurbit[n]urils (n = 7, 8, CB[n]) and amine, styryl pyridine, and styryl pyridine dimer cations, under negative ESI. Non-complexed CB[n] form double charged halide (Br-, Cl-, F-) adducts. Under negative ESI, halide ions interact with CB[n] outer surface hydrogen atoms. One to one host-guest complexes (1:1) of CB[n] with positive charged guests were also observed as single and double charged ions under negative ESI. The positive charge of guests is neutralized by ion-pairing with halide anions. Depending on the number of positive charges guests retain in the gas phase, one or two additional halide ions are required for neutralization. Complexes 1:2 of CB[8] with styryl pyridines retain two halide ions in the gas phase, one per guest. Styryl pyridine dimers form 1:1 complexes possessing a single extra halide ion and therefore a single positive charge. Negative ESI is sensitive to small structural differences between complexes, distinguishing between 1:2 complexes of styryl pyridine-CB[8] and corresponding 1:1 complexes with the dimer. Negative ESI gives simpler spectra than positive ESI and allows the determination of guest charge state of CB[n] complexes in the gas phase.
- Exploring Ulva australis Areschoug for possible biotechnological applications: In vitro antioxidant and enzymatic inhibitory properties, and fatty acids contentsPublication . Trentin, Riccardo; Custódio, Luísa; Rodrigues, Maria Joao; Moschin, Emanuela; Sciuto, Katia; Da Silva, José Paulo; Moro, IsabellaUlva australis Areschoug (Ulvales, Chlorophyta) is traditionally used as a foodstuff in Korea and to treat several diseases, such as hyperlipidemia and urinary ailments. It is now considered an invasive species of the Venice Lagoon (Italy). This work explored U. australis as a potential source of bioactive molecules with biotechnological applications. For that purpose, organic and water extracts were prepared from dried biomass of U. australis and evaluated for radical scavenging activity (RSA), metal chelating activities and for in vitro inhibition of enzymes related with several disorders, namely Alzheimer's disease (acetylcholinesterase, butyrylcholinesterase), hyperpigmentation (tyrosinase), obesity (lipase), Type-2 diabetes mellitus (alpha-glucosidase, alpha-amylase) and skin sagging (elastase). Extracts were also evaluated for total contents of phenolics, flavonoids condensed tannins and carbohydrates. Finally, the fatty acids methyl esters profile of the biomass was established by gas chromatography-mass spectrometry. Extracts had low to moderate radical scavenging activity on DPPH, and a higher ability to chelate Fe2+ than Cu2+, and the maximum Fe2+ chelating capacity was observed in the tincture (IC50 = 4.82 mg/mL). Samples had a higher ability to inhibit alpha-amylase and microbial alpha-glucosidase than the other tested enzymes. The biomass of U. australis presented a highly saturated fatty acids profile, enriched in palmitic acid. These data suggest U. australis as a promising source of natural products with anti- diabetic properties and as a desirable species for biodiesel production.
- Fluorescence sensing of microplastics on surfacesPublication . Costa, Camila Q. V.; Cruz, Joana; Martins, Jorge; Teodosio, Maria; Jockusch, Steffen; Ramamurthy, V.; Da Silva, José PauloMicroplastics, nanoplastics and related products have been recently found in marine ecosystems worldwide, calling for new analytical methods for rapid detection and risk assessment. Fluorescence is a sensitive technique that when used with polarity probes can potentially detect low-polarity plastic particles in environments. Here, we evaluated the fuorescence technique to sense polystyrene microparticles directly on salt, silica and sand surfaces, using Nile Red and pyrene as polarity probes. Results show that all probes displayed fuorescence on silica and sand, whereas strong fuorescence quenching was observed on NaCl. Polystyrene particles increase the fuorescence intensity due to probe migration into their nonpolar microenvironment. In the presence of polystyrene, the spectra of Nile Red are shifted to shorter wavelengths, while the ratio of vibronic bands I1/I3 of fuorescence of pyrene decreases to about 1. Pyrene showed similar sensitivity toward surface-modifed carboxyl polystyrene particles. On NaCl, the emission of pyrene increases linearly with polystyrene content for concentrations from 0.5 to 20 µg/g. The detection limit of polystyrene microparticles on natural sea salt using pyrene as probe is about 0.2 µg/g, while on sand, the sensitivity is about one order of magnitude lower. Overall, although being of relatively low selectivity, the fuorescence technique can be used to determine a maximum content of plastic particles of few micrometers size with little sample preparation. Fluorescence, when used in conjunction with pyrene probe, allows for detection and quantifcation of microplastic particles in the sub-ppm range.
- Host−guest complexes of cyclopentadienyl iron dicarbonyl (CpFe(CO)2) CO-releasing molecules with Cucurbit[7]urilPublication . Monteiro, Rodrigo P.; Calhau, Isabel B.; Gomes, Ana C.; Mendes, Ricardo F.; Paz, Filipe A. Almeida; D. Lopes, André; Silva, José Paulo da; Romão, Carlos C.; Gonçalves, Isabel S.; Pillinger, MartynIron(II) cyclopentadienyl carbonyl complexes are promising as CO-releasing molecules (CORMs) for therapeutic applications. In common with other metallodrugs, the practical application of Fe-CORMs may require their conjugation with biocompatible carriers to improve their bioavailability and protect them from premature degradation. Here, we show that the CO-releasing properties of the complexes [CpFe(CO)2Cl] (1) and [CpFe(CO)2CH2CONH2] (2) are retained when noncovalently encapsulated within cucurbit[7]uril (CB7), a well-established drug-enhancing excipient. The inclusion compounds were characterized in the solid-state by single-crystal and powder XRD, ATR-IR spectroscopy, Raman spectroscopy, TGA, and 13C{1H} CP MAS NMR. In the crystal structure of 2@CB7, there are two crystallographically independent [2@CB7] binary complexes that differ in the orientation of the guest molecules inside the CB cavity. High-resolution ESI-MS and 1H NMR studies verified the formation and stability of 1:1 2@CB7 inclusion complexes in an aqueous solution. In a physiological buffer, complex 2 is stable in the dark, but releases ca. 1.4 equiv of CO when irradiated with low-power cold white light, with a half-life (t 1/2) of 19.2 +/- 1.9 min. The photodecarbonylation behavior of the complexes is largely maintained in the inclusion compounds, with t 1/2 of 10.0 +/- 0.6 and 21.1 +/- 1.9 min for encapsulated 1 and 2.
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