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- 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.
- 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.
- 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.
- 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.
- Melding caged compounds with supramolecular containers: photogeneration and miscreant behavior of the coumarylmethyl carbocationPublication . Kamatham, Nareshbabu; Da Silva, José Paulo; Givens, Richard S.; Ramamurthy, V.By merging well-established concepts of supramolecular chemistry, protecting group strategy, and photochemistry, we have solubilized in water hydrophobic organic molecules consisting of a photoactive protecting group and masked carboxylic acids, released the desired acid, and confined a reactive carbocation intermediate within a capsule. Confinement of the photogenerated carbo cation brought out the latent radical-like behavior. This observation is consistent with the recent theoretical prediction of the 7-(diethylamino)coumarinyl-4-methyl carbocation having a triplet diradical ground-state electronic contribution.
- Photorelease of incarcerated guests in aqueous solution with phenacyl esters as the triggerPublication . Jagadesan, Pradeepkumar; Silva, José P. da; Givens, Richard S.; Ramamurthy, V.We report the clean, efficient photorelease of a series of carboxylic acids embedded in octa acid (OA) host and protected by a p-hydroxyphenacyl cage. A key role is played by the cage by providing hydrophobicity for entry into the OA enclosure and yet readily removable as a photoactivated protecting group for release from the host. The rapid photo-Favorskii rearrangement of the departing chromophore does not react with the host OA but diminishes hydrophobicity of the OA contents, leading to their facile release into the solvent.
- 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.
- Photorelease of incarcerated caged acids from hydrophobic coumaryl esters into aqueous solutionPublication . Kamatham, Nareshbabu; Mendes, Débora C.; Silva, José P. da; Givens, Richard S.; Ramamurthy, V.Photolysis of aqueous solutions of carboxylic acid esters of 7-(methoxycoumaryl)-4-methanol included within the capsule made up of two molecules of octaacid released the acids in water. The trigger 7-(methoxycoumaryl)-4-methyl chromophore remains within octaacid either as the alcohol or as an adduct with the host octaacid through a hydrogen abstraction process. The method established here offers a procedure to release hydrophobic acid molecules in water at will in a timely manner with light. In addition, the system offers an unanticipated opportunity to probe the mechanistic dichotomy of a diradicaloid intermediate expressing both radical and ionic behavior when generated by coumarylmethyl ester photolysis in a hydrophobic environment.
- 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.