A quick and regioselective access of spirooxindole-oxazoline by reaction of isatin and isocyanoacetate “on water”

A greener, rapid and regioselective “on water” synthesis of spirooxindole-oxazoline by the reaction of isatin and isocyanoacetate at room temperature is described. The developed protocol has the advantage of being atom-economical, eco-friendly, and benign reaction conditions. Broader substrate scope, experimentally simple procedures, and easy purification of products with high yield further make this method attractive. The synthesized compounds have been fully characterized with spectral analysis.     

Conformational Dynamics of Monomer‐ versus Dimer‐like Features in a Naphthalenediimide‐Based Conjugated Cyclophane

The design and synthesis of an enantiomeric pair of 1,8‐diethynylanthracene‐bridged naphthalenediimide (NDI)‐based cyclophanes ( Cyclo‐NDI s) are reported. Each enantiomer of Cyclo‐NDI exhibits a circularly polarized luminescence signal with a relatively large luminescence dissymmetry factor (g_lum=±8×10^?3). We have further investigated the modulation of through‐space electronic communication between co‐facially oriented NDIs in a discrete Cyclo‐NDI with changes in the temperature. Tuning of the electronic communication results from the conformational transformation of monomer‐ versus dimer‐like features of Cyclo‐NDI , as confirmed by UV/Vis, fluorescence, circular dichroic, and NMR spectroscopic analysis. The temperature‐dependent optical response in the Cyclo‐NDI through the conformational transformation could be utilized as a highly sensitive and reversible optical thermometer in a wide temperature range (100 to ?80 °C).     

Synthesis and characterization of LSMO manganite-based biocomposite

In this paper we study the structural, morphological and magnetic properties of La_0.67Sr_0.33MnO₃ (LSMO) manganite nanoparticles (NPs) and its biocomposite, obtained by mixing NPs of hydroxyapatite (HA). From the studies of X-ray diffraction and Fourier transmission of infrared spectroscopy it is evident that in the biocomposite sample both the individual phases are distinguishable from each other. The measurements of direct current (DC) magnetization and hysteresis loops reveal that the basic magnetic behaviour of LSMO–HA is similar to that of LSMO; however, the admixture of HA makes the sample magnetically softer. From the investigation of transmission electron microscopy it is observed that such a biocomposite is composed of the NPs of LSMO surrounded by HA particles, which can be found suitable for biomedical applications.     

Discrete π Stack of a Tweezer-Shaped Naphthalenediimide–Anthracene Conjugate

The design and synthesis of a tweezer-shaped naphthalenediimide (NDI)–anthracene conjugate ( 2NDI ) are reported. In the structure of the closed form (π_NDI ⋅⋅⋅ π_NDI stack) of 2NDI , which was elucidated by single-crystal XRD, the existence of C−H ⋅⋅⋅ O hydrogen bonding involving the nearest carbonyl oxygen atom of an NDI unit was suggested. The tunability of π_NDI ⋅⋅⋅ π_NDI interactions was studied by means of UV/Vis absorption, fluorescence and NMR spectroscopy and molecular modelling. This revealed that the π_NDI ⋅⋅⋅ π_NDI interactions in 2NDI affect the absorption and emission properties depending on the temperature. Furthermore, in polar solvents, 2NDI prefers the stronger π_NDI ⋅⋅⋅ π_NDI stack, whereas the π_NDI ⋅⋅⋅ π_NDI interaction is diminished in nonpolar solvents. Importantly, the conformational variations of 2NDI can be reversibly switched by variation in temperature, and this suggests potential application for fluorogenic molecular switches upon temperature changes.     

Studies of thermodynamic fluctuations of thermoelectric power of Tl2Ba2Ca0.8Y0.2Cu2O8+y superconductor

Excess thermoelectric power (TEP) of Tl₂Ba₂Ca_0.8Y_0.2Cu₂O_8+y ceramic superconductor has been studied. Variation of excess TEP with temperature has been found to follow an equation similar to that of Aslamazov and Larkin derived for the variation of excess conductivity with temperature. The superconducting behaviour of the sample, as determined from excess TEP, has been found to be 2-dimensional in nature.     

Double metal-insulator peaks and effect of Sm substitution on magnetic and transport properties of hole-doped La0.85Ag0.15MnO3

La_0.85−xSm_xAg_0.15MnO₃ (x=0−0.2) ceramics were prepared using the conventional solid-state synthesis method to investigate the effect of Sm³⁺ substitution on magnetic and electrical transport properties. Magnetic susceptibility versus temperature measurements showed all samples exhibit ferromagnetic to paramagnetic transition with Curie temperature, T_c decreasing from 283 K (x=0) to 164 K (x=0.2) with increasing Sm³⁺. The observed slope in susceptibility, χ′ versus temperature curves below T_c indicates the possible presence of FM and AFM phases in the metallic region. In addition, a deviation from the Curie-Weiss law above T_c in 1/χ′ versus T curves indicates the existence of a Griffith's phase in the x=0.05−0.2 samples due to the Sm³⁺ ion substitution. The Griffith temperature, T_G was found to decrease from 295 K (x=0.05) to 229 K (x=0.2). Electrical resistivity measurements of the samples in zero field showed transition from metallic behavior to insulating behavior as the temperature was increased. For x=0, two metal-insulator, MI transition peaks were observed at T_p1=282 K and at T_p2=250 K. Both peaks shifted to lower temperatures with the increase in Sm³⁺. The relative resistivity of the first peak to the second peak decreases with increasing Sm³⁺ for x>0.05 while at x=0.2 the T_p1 peak was strongly suppressed. Magnetoresistance, MR was observed to weaken with Sm³⁺ substitution. The metallic region of the ρ(T) curve of the x=0−0.15 samples was fitted to the model of electron-electron and electron-magnon scattering while the insulating region was fitted to the variable range hopping, VRH model. The resistivity behavior indicated that the substitution of Sm³⁺ weakened the double exchange process and enhanced the Jahn-Teller effect. Our results indicated that the T_p1 peak is strongly related to the double-exchange mechanism while the T_p2 peak is suggested to originate from magnetic inhomogeneity.     

Catalyst-free synthesis of 3-substituted-3-hydroxy-2-oxindoles by reaction of isatin and cyclic enaminone in water

An easy protocol for the synthesis of enaminone attached 3-substituted-3-hydroxy-2-oxindoles has been demonstrated by reaction of isatin and cyclic enaminone in water. The developed catalyst-free reaction has the advantage of being atom-economical, eco-friendly, and benign reaction conditions. The broader substrate scope, experimentally simple procedures, and easy purification of products with high yield further make this method attractive and useful.     

DABCO-catalyzed synthesis of 3-substituted-3-hydroxyindolin-2-ones in aqueous media

An efficient and greener protocol for easy access to 3-susbstituted-3-hydroxy-2-oxindoles by the reaction with various substituted isatins and acetophenones is described. This protocol is widely applicable for a variety of isatins and acetophenones using water as a reaction media and 1,4-diazabicyclo[2.2.2]octane (DABCO) as catalyst with shorter reaction time and good to excellent yield of products.     

Ambient Water-Stable Dianionic Electron Donors: Intramolecular Noncovalent Conduits Assist Charge Delocalization

Electron-rich π-conjugated dianions are known to be ambient unstable and their stabilization in ambient water is yet to be realized. We report the first example of an exceptionally stable naphthalenediimide-based dianion in ambient and hot water, forming one of the most stable redox-active dianion. The half-life (t_1/2) of dianion ( 1 a²⁻ ) is more than four months in ambient water. The dianionic state was confirmed by X-ray crystallography and by various spectroscopic methods. The noncovalent electronic conduits introduced for the first time in dianions, embrace n_O→π*_C≡N interactions and aid in delocalizing the dianionic charge as validated from theoretical studies. The dianions harness strong NIR absorption and electron donor ability to organic acceptors and metal ions, which make them suitable for potential green energy applications.