Hyacintha Rennet Lobo

Ultrasound and deep eutectic solvent (DES): A novel blend of techniques for rapid and energy efficient synthesis of oxazoles

The present work deals with the synthesis of novel oxazole compounds by using effective combination of ultrasound (US) and deep eutectic solvent (DES). The reaction was also conducted by thermal method (NUS) and the comparative studies are provided. It was observed that applying ultrasound not only improved yields and reduced reaction times but also saved more than 85% energy as shown by energy consumption calculations. The advantages of using DES as reaction medium is highlighted from the fact that it is bio-degradable, non-toxic, recyclable and could be easily prepared using inexpensive raw materials. The recyclability for DES was studied wherein it was found that ultrasound has no negative effects on DES even up to four runs. In addition, the present work is the first report on the combinative use of DES and US in organic synthesis.

Deep eutectic solvents and glycerol: a simple, environmentally benign and efficient catalyst/reaction media for synthesis of N-aryl phthalimide derivatives

Abstract Deep eutectic solvents (DES) and glycerol have been successfully employed as efficient catalysts/reaction media in the synthesis of N-aryl phthalimide derivatives from phthalic anhydride and primary aromatic amines. The DES prepared from choline chloride and malonic acid proved to be an efficient catalyst whereas glycerol and the DES of choline chloride and urea played a dual role of catalyst and solvent. These mixtures are biodegradable, nontoxic, and cost-effective thereby providing a good industrial alternative to conventional methods. These methods gave products in moderate to high yields with good recyclability of catalyst/solvent at least up to five consecutive runs.

Comparative material study and synthesis of 4-(4-nitrophenyl)oxazol-2-amine via sonochemical and thermal method.

The present paper deals with the synthesis of aminooxazole derivatives via thermal and ultrasonic methods using deep eutectic solvent as medium. It was observed that ultrasound-assisted method gave 90% yield in just 8min as against 3.5h required to get 69% yield by thermal method. One of the compounds 4-(4-nitrophenyl)-1,3-oxazol-2-amine synthesized by both methods were subjected to material characterization study via XRD, TGA and SEM analysis. It was observed that use of ultrasound not only increased the rate of reaction but also improved the quality of product obtained. The crystallinity of the product from ultrasound method was 21.12% whereas thermal method fetched only 8.33% crystallinity thereby improving crystallinity by almost 60%. In addition, sonochemical synthesis also saved more than 70% energy as depicted by energy calculations.

Extensive Reduction in Back Electron Transfer in Twisted Intramolecular Charge‐Transfer (TICT) Coumarin‐Dye‐Sensitized TiO2 Nanoparticles/Film: A Femtosecond Transient Absorption Study

We report the synthesis, characterization, and optical and electrochemical properties of two structurally similar coumarin dyes (C1 and C2). These dyes have been deployed as sensitizers in TiO2 nanoparticles and thin films, and the effect of molecular structure on interfacial electron-transfer dynamics has been studied. Steady-state optical absorption, emission, and time-resolved emission studies on both C1 and C2, varying the polarity of the solvent and the solution pH, suggest that both photoexcited dyes exist in a locally excited (LE) state in solvents of low polarity. In highly polar solvents, however, C1 exists in an intramolecular charge-transfer (ICT) state, whereas C2 exists in both ICT and twisted intramolecular charge-transfer (TICT) states, their populations depending on the degree of polarity of the solvent and the pH of the solution. We have employed femtosecond transient absorption spectroscopy to monitor the charge-transfer dynamics in C1- and C2-sensitized TiO2 nanoparticles and thin films. Electron injection has been confirmed by direct detection of electrons in the conduction band of TiO2 nanoparticles and of radical cations of the dyes in the visible and near-IR regions of the transient absorption spectra. Electron injection in both the C1/TiO2 and C2/TiO2 systems has been found to be pulse-width limited (<100 fs); however, back-electron-transfer (BET) dynamics has been found to be slower in the C2/TiO2 system than in the C1/TiO2 system. The involvement of TICT states in C2 is solely responsible for the higher electron injection yield as well as the slower BET process compared to those in the C1/TiO2 system. Further pH-dependent experiments on C1- and C2-sensitized TiO2 thin films have corroborated the participation of the TICT state in the slower BET process in the C2/TiO2 system.

Lipase and Deep Eutectic Mixture Catalyzed Efficient Synthesis of Thiazoles in Water at Room Temperature

Lipase bio-catalyst or ammonium based deep eutectic mixture efficiently catalyzed aqueous phase synthesis of methyl-thiazole and amino-thiazole derivatives. The simple ammonium deep eutectic catalyst, easily synthesized from choline chloride and urea, is inexpensive, recyclable and bio-degradable, making it suitable for industrial applications.Graphical AbstractAn efficient and eco-friendly process for methyl and amino-thiazole synthesis in aqueous media involving bio-catalyst or ammonium deep eutectic mixtures as catalysts is described. Both the catalysts are bio-degradable, recyclable and non-toxic.

Restriction of molecular twisting on a gold nanoparticle surface.

To understand the photophysical properties of intramolecular charge transfer (ICT) and twisted intramolecular charge transfer (TICT) states on a gold nanoparticle (Au NP) surface, we have designed and synthesized a new coumarin molecule (C3) that exists both as ICT and TICT states in its excited state in a polar environment. On a Au NP surface, an excited C3 molecule only exists as an ICT state owing to restricted molecular rotation of a diethylamino group; as a result, no conversion from the ICT to TICT state was observed. Selection of the preferential state of a molecule with dual emitting states can be helpful for selected biological applications.