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- 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.
- Synthetic versus natural receptors: supramolecular control of chemical sensing in fishPublication . Silva, José P. da; Choudhury, Rajib; Porel, Mintu; Pischel, Uwe; Jockusch, Steffen; Hubbard, Peter; Ramamurthy, Vaidhyanathan; Canario, Adelino V. M.The encapsulation of odorants by the synthetic receptor cucurbit[7]uril (CB[7]) reduces the response of olfactory receptors in Mozambique tilapia (Oreochromis mossambicus) in vivo. For example, the olfactory receptor response to the odorant adamantan-1-amine, as measured by electro-olfactography, was suppressed by 92% in the presence of CB[7]. A reduction in olfactory response of 88% was observed for pentane-1,5-diamine (cadaverine), an odorant associated with carrion avoidance in some fish. The results reveal how the association constants and the concentrations of natural and synthetic receptors play a determinant role and show that synthetic receptors can be used to remove bioactive molecules from fish olfaction.
- Release of guests from encapsulated masked hydrophobic precursors by a phototriggerPublication . Jayaraj, Nithyanandhan; Jagadesan, Pradeepkumar; Samanta, Shampa R.; Silva, José P. da; Ramamurthy, V.Examples of release of organic acids from encapsulated p-methoxyphenacyl esters provided here demonstrate the value of a phototrigger strategy to release chemicals of interest in water from hydrophobic precursors. In this study, a photochemical beta-cleavage process centered on the p-methoxyphenacyl group is exploited to release the acid of interest from a water-soluble capsule made up of octa acid.
- 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.
- Aggregates of cucurbituril complexes in the gas phasePublication . Silva, José P. da; Jayaraj, Nithyanandhan; Jockusch, Steffen; Turro, Nicholas J.; Ramamurthy, V.The self-organization of cucurbit[n]uril (n = 7 and 8, CBs) complexes was probed by electrospray mass spectrometry. The self-association of CB complexes is a general phenomenon but shows some dependence on the absence, presence, and type of included guest molecules.
- Benzoin type photoinitiator for free radical polymerizationPublication . Esen, Duygu Sevinc; Arsu, Nergis; Silva, José P. da; Jockusch, Steffen; Turro, Nicholas J.Benzoin, a popular photoinitiator for free radical polymerization of vinyl monomers, was improved by introduction of two methyl thioether substituents. This new benzoin derivative showed an about 50 times higher light absorption in the near-UV spectral region and performed better than the unsubstituted benzoin in polymerization experiments in bulk solutions or films of acrylate monomers when low initiator concentrations are used. Laser flash photolysis, low temperature luminescence experiments and photoproduct studies by mass spectrometry suggest that a slow -cleavage mechanism (k = 2.2 x 105 s1) from the electronic triplet state with a quantum yield of 0.1 is the primary photoreaction to generate the initiating free radicals. (c) 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013, 51, 1865-1871
- Supramolecular photochemistry of encapsulated caged ortho-nitrobenzyl triggersPublication . Kamatham, Nareshbabu; Raj, A. Mohan; Givens, Richard S.; Da Silva, José Paulo; Ramamurthy, V.ortho-Nitrobenzyl (oNB) triggers have been extensively used to release various molecules of interest. However, the toxicity and reactivity of the spent chromophore, o-nitrosobenzaldehyde, remains an unaddressed difficulty. In this study we have applied the well-established supramolecular photochemical concepts to retain the spent trigger o-nitrosobenzaldehyde within the organic capsule after release of water-soluble acids and alcohols. The sequestering power of organic capsules for spent chromophores during photorelease from ortho-nitrobenzyl esters, ethers and alcohols is demonstrated with several examples.
- Pomegranate liquor preparation and analysisPublication . Galego, Ludovina; Estevinho, Letícia; Silva, José P. daThe pomegranate (Punica granatum L.) liquor has been produced for several centuries in the south of Portugal, mainly in the mountain areas. The “Assaria” variety is the preferred cultivar due to its organoleptic properties and high arils to peel ratio. Wild pomegranates are also widely distributed but, despite the health benefits that have been associated to the fruits, they continue to be unappreciated for consumption. Liquor preparation is a very good alternative for wild pomegranate fruits. We prepared pomegranate liquors by following a maceration procedure using the arils or juice of Assaria and wild pomegranate fruits. Strawberry tree (Arbutus unedo L.) fruit spirits were used to prepare the liquors. At the end of the maceration time 5 day as minimum sugar syrup was added. The maturation period was three months or longer. The obtained liquors showed a very attractive pink colour. The colour and the total polyphenol, as well as the anthocyanin and ellagitannin profiles, were measured at the end of the maceration and maturation times. Wild pomegranates gave rise liquors with more intense pink colour and higher polyphenol contents than the prepared using Assaria fruits. The anthocyanin and ellagitannin profiles also indicated higher contents of polyphenols for liquors prepared using wild pomegranate fruits. When juice is used instead of complete arils during the maceration period punicalin is not present and the consequently total polyphenols is low. The main anthocyanins identified in the liquors were delphinidin-3,5-diglucoside, cyaniding-3,5-diglucoside, delphinidin–3-glucoside, cyaniding–3-glucoside, pelargonidin–3–glucoside; the main ellagitannins were punicalagin and punicalin.
- Quantitative analysis of biogenic polyamines in distilled drinks by direct electrospray ionization tandem mass spectrometry using a nanocontainerPublication . Galego, Ludovina; Rodrigues, Maria A. A.; Mendes, Débora C.; Jockusch, Steffen; Silva, José P. daRATIONALE: Biogenic polyamines in drinks have been implicated in undesirable physiological effects. Methods for their detection and quantification usually involve derivatization, pre-concentration and clean-up. To assist the evaluation of the potential risk of distillates, it was important to develop a simple and fast analytical method, which is described in this study.METHODS: Biogenic polyamines were selectively encapsulated after addition of a nanocontainer, cucurbit[7] uril (50 mu M), to the distilled drink samples, which were acidified with HCl (pH 3) prior addition of the nanocontainer. The quantification of polyamines was achieved by direct infusion electrospray ionization quadrupole ion trap mass spectrometry in the multiple reaction monitoring mode, using encapsulated amantadine as internal standard, and by monitoring signals originating from their host-guest complexes.RESULTS: Six point calibration curves, ranging from 0.5 mu M to 20 mu M of polyamines in water and ethanol/water (50: 50), were used to establish instrument response. The method was validated by analysis of fortified Arbutus spirits. Samples of Arbutus and grape pomace spirits were also analyzed. Linear responses were observed for all polyamines and were similar in water, hydro-alcoholic solutions and fortified Arbutus spirits. Putrescine the simple polyamine was detected only in grape pomace distillate samples.CONCLUSIONS: A quantitative method was developed for rapid and simple analysis of biogenic polyamines in distilled drinks. The detection limits depend on the ionization properties of the samples. Encapsulated amantadine can be used to probe these properties and method application. Copyright (C) 2016 John Wiley & Sons, Ltd.
- Cooperative assembly of discrete stacked aggregates driven by supramolecular host-guest complexationPublication . Basílio, Nuno; Piñeiro, Ángel; Silva, José P. da; García-Río, Luísp-Sulfonatocalix[4]arene (SC4) interacts with the aromatic dye crystal violet (CV) to form complexes with stoichiometries ranging from SC4:CV = 1:1 up to 1:5 both in solution and in the gas phase. While the 1:1 complex is of the inclusion type, as frequently observed for other guests, in the higher-order complexes the CV molecules interact with SC4 in a peripheral manner. The formation of such complexes is driven by ionic interactions established between the dye and the calixarene and by CV-CV stacking interactions. The application of an advanced fitting procedure made possible a quantitative analysis of the UV-vis data and allowed the determination of the stepwise binding constants. This unprecedented approach provides evidence that the formation of the highest-order complexes occurs through a cooperative mechanism. Moreover, the development of a quantitative analytical model enables the possibility of using this type of system for water-soluble sensing assays, as is also exemplified in the present work. © 2013 American Chemical Society.