Browsing by Author "Ramamurthy, Vaidhyanathan"
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- 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.
- Photochemical oxidation of polyethylene terephthalate microplastics adsorbed on sand and silica surfacesPublication . Q. V. da Costa, Camila; Nobahar, Amir; Egea-Corbacho, Agata; Jockusch, Steffen; Power, Deborah Mary; Ramamurthy, Vaidhyanathan; Silva, José Paulo daThe environmental contamination by plastics, microplastics, and related compounds is a major concern. While the detection and release of micro- and nanoparticles from these materials have been widely studied, the formation and release of molecules resulting from their degradation in the environment have been overlooked. This work presents a study of the products released from poly(ethylene terephthalate) (PET) irradiated as pure particles and adsorbed on silica and sand surfaces under different irradiation conditions. The role of oxygen was also evaluated. The products were identified by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-high resolution mass spectrometry (LC-HRMS). The main released molecules can be accounted for by considering the cleavage of alpha- and beta-bonds next to the ester moiety of the polymer chain. Volatile products such as benzene as well as monomer units of the polymer and related products were identified. In the presence of oxygen, acetic acid and products resulting from hydroxylation at the benzenic ring or at the ethyl moiety were detected. Adsorption on silica and sand has little effect on the photoproduct distributions. The irradiation at 360 nm leads to distributions similar to the ones observed at 257 nm, but the reaction rate is lower. The identified product ethylene terephthalate is a marker of PET plastics and particles and can therefore be used to evaluate the environmental contamination by this polymer material.
- A supramolecular approach towards the photorelease of encapsulated caged acids in water: 7-diethylaminothio-4-coumarinyl molecules as triggersPublication . Ghosh, Sujit Kumar; Chatterjee, Shreya; Boruah, Paras Pratim; Mandal, Satyajit; Silva, José Paulo da; Srinivasan, Varadharajan; Ramamurthy, VaidhyanathanHerein, we establish the release of aliphatic acids in water upon excitation of 7-diethylaminothio-4-coumarinyl derivatives encapsulated within the organic host octa acid (OA). The 7-diethylaminothio-4-coumarinyl skeleton, employed here as the trigger, photoreleases caged molecules from the excited triplet state, in contrast to its carbonyl analogue, where the same reaction is known to occur from the excited singlet state. Encapsulation in OA solubilizes molecules in water that are otherwise water-insoluble, and retains the used trigger within itself following the release of the aliphatic acid. Such supramolecular characteristics usher in new features to the photorelease methodology. The thiocarbonyl chromophore extends the absorption of coumarinyl trigger to visible range while enhancing the intersystem crossing (ISC) to the triplet state, making it the reactive state. Despite the non-polar environment within the OA capsules the photocleavage occurs in a heterolytic fashion to release the conjugate base and the used trigger as triplet carbocation in an adiabatic process. Interestingly, the triplet carbocation crosses to the ground singlet surface (closed shell singlet carbocation) with the help of water molecules, possibly aided by C = S chromophore. Utilizing the known excited state dynamics of related thiocoumarinyl and coumarinyl systems, we have identified a few of the important mechanistic features of the photorelease process of 7-diethylaminothio-4-coumarinyl derivatives. Ultrafast excited state dynamic studies and quantum chemical calculations planned should help us better understand the photorelease process so as to effectively exploit the proposed system for potential applications.
- 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.