Loading...
11 results
Search Results
Now showing 1 - 10 of 11
- 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.
- 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
- 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.
- Capsular complexes of nonpolar guests with octa amine host detected in the gas phasePublication . Silva, José P. da; Kulasekharan, Revathy; Cordeiro, Carlos; Jockusch, Steffen; Turro, Nicholas J.; Ramamurthy, V.Nanocapsules, made up of the deep cavitand octa amine and several guests, were prepared in aqueous acidic solution and were found to be stable in the gas phase as detected by electrospray ionization mass spectrometry (ESI-MS). The observed gas phase host-guest complexes contained five positive charges and were associated with several acid molecules (HCI or HBr).
- Self aggregation of supramolecules of nitroxides@cucurbit[8]uril revealed by EPR spectraPublication . Jayaraj, Nithyanandhan; Porel, M; Ottaviani, MF; Maddipatla, MVSN; Modelli, A; Silva, José P. da; Bhogala, BR; Captain, B; Jockusch, Steffen; Turro, NJ; Ramamurthy, V.Supramolecular complexation behavior of cucurbiturils with paramagnetic nitroxide spin probes was examined by H-1 NMR, X-ray diffraction studies of crystals, computation, and EPR. Both cucurbit[7]uril (CB7) and cucurbit(S]uril (CB8) form a 1:1 complex with 4-(N,N,N-trimethylammonium)-2,2,6,6-tetramethylpiperidinyl-N-oxy bromide (CAT 1). The structure of the complex in the solid state was inferred by X-ray diffraction studies and in the gas phase by computation (B3LYP/6-31G(d)). Whereas ESI-MS data provided evidence for the existence of the complex in solution, indirect evidence was obtained through H-1 NMR studies with a structural diamagnetic analogue, 4-(N,N,N-trimethylammonium)-2,2,6,6- tetramethyl-N-methylpiperidine iodide (DCAT1). The EPR spectrum of the CAT1@CB7 complex consisting of three lines suggested that probe CATI is associated with host CB7 such that the nitroxide part is exposed to water. The spectral pattern was independent of the concentration of the complex and the presence of salt such as NaCl. The most interesting observation was made with CB8 as the host. In this case, in addition to the expected three-line spectrum, an additional spectrum consisting of seven lines was recorded. The contribution of the seven-line spectrum to the total spectrum was dependent on the concentration of the complex and added salt (NaCl) to the aqueous solution. The coupling constant for the seven-line spectrum for N-14-substituted CATI is 5 G, and that for the four-line spectrum for N-15-substituted CATI is 7.15 G. The only manner by which we could reproduce the observed spectra by simulation for both N-14- and N-15-substituted CAT1@CB8 was by assuming a spin exchange among three nitroxide radicals. To account for this observation, we hypothesize that three CAT1 molecules included within CB8 interact in such a way that there is an association of three supramolecules Of CAT1@CB8 (i.e., [CAT1@CB8](3)) in 11 triangular geometry that leads to spin exchange between the three radical centers. We have established, with the help of 13 additional examples, that this is it general phenomenon. We are in the process of understanding this unusual phenomenon.
- Probing the photoreactivity of aryl chlorides with oxygenPublication . Silva, José P. da; Jockusch, Steffen; Turro, Nicholas J.Molecular oxygen was used to probe the mechanism of the phototransformation of chlorobenzene and 4-chloroanisole in organic solvents. Laser. ash photolysis, electron paramagnetic resonance and product distribution studies clarified the reaction mechanisms of these compounds under a wide range of conditions. The main primary photochemical reaction step is the homolytic cleavage of the C-Cl bond to produce a triplet radical pair in the solvent cage. In non-polar solvents hydrogen abstraction, after radical diffusion, leads to reduction. In polar solvents, in addition to H-abstraction, electron transfer within the caged radical pair occurs and leads to an ion pair (phenyl cation and Cl(-)). In the presence of oxygen, phenyl radicals can form phenylperoxyl radicals which have a bathochromically shifted absorption, thus making the homolytic cleavage visible by. ash photolysis. The peroxyl radicals can couple, leading to more polar compounds, or undergo back reaction to the phenyl radical. For concentrations of the aryl chlorides of higher than 10(-3) M, dimerization becomes an important transformation process and occurs after reaction of the transients with ground state molecules. In addition, excimer formation is postulated to be involved in the dimerization process.
- 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.
- Photochemistry of 4-chlorophenol and 4-chloroanisole adsorbed on MFI zeolites: supramolecular control of chemoselectivity and reactive intermediate dynamicsPublication . Silva, José P. da; Jockusch, Steffen; Martinho, José M. G.; Ottaviani, M. Francesca; Turro, Nicholas J.The phototransformation of aryl chlorides adsorbed on MFI zeolites is markedly different from that observed in solution and other solid surfaces such as silica. The formation of radical cations and the constraints imposed by the channels shift the reactivity from the C-CI bond to the O-R bond. Irradiation generates kinetically stabilized intermediates that can be characterized using conventional steady-state spectroscopic techniques, and these intermediates can be used as ordinary chemical reagents.
- Supramolecular photocatalysis: insights into cucurbit[8]uril catalyzed photodimerization of 6-methylcoumarinPublication . Pemberton, Barry C.; Singh, Raushan K.; Johnson, Alexander C.; Jockusch, Steffen; Silva, José P. da; Ugrinov, Angel; Turro, Nicholas J.; Srivastava, D. K.; Sivaguru, J.Guest induced shape change of the cucurbit[8]uril cavity is likely rate limiting in the supramolecular photocatalytic cycle for CB8 mediated photodimerization of 6-methylcoumarin.