Gaurav Bhargava

Perylene Diimide Appended with 8-Hydroxyquinoline for Ratiometric Detection of Cu2+ Ions and Metal Displacement Driven “Turn on” Cyanide Sensing

AbstractPerylene diimide (PDI) 3 and 4 appended with 8-hydroxyquinoline derivatives have been synthesized and their photophysical and spectroscopic properties have been experimentally determined. Moreover, PDIs 3 and 4 show ratiometric behavior to detect Cu2+ colorimetrically with visible color change from coral red to light pink, whereas 3 and 4 show “turn-off” behavior in fluorescence with lowest limit of detection 5 × 10−7 M. The PDI 3 could be further utilized for ratiometric CN− detection colorimetrically and as “turn-on” sensor for CN− detection fluorometrically with lowest limit of detection 8 × 10−6 M. The comparison of spectroscopic properties of PDI 1-4 highlights the importance of linking 8-hydroxyquinoline units on the PDI core at bay position for achieving Cu2+ recognition event into ratiometric signal. FigurePDI 3 shows ratiometric behavior colorimetrically and “turn-off” behavior in fluorescence towards Cu2+ (lowest limit 5 × 10−7 M). The PDI 3-Cu2+ shows ratiometric CN− detection colorimetrically and “turn-on” sensor for CN− detection fluorometrically (lowest limit 8 × 10−6 M).

Triple-signaling mechanisms-based three-in-one multi-channel chemosensor for discriminating Cu2+, acetate and ion pair mimicking AND, NOR, INH and IMP logic functions

Chemosensor 1 shows three different responses towards Cu2+, acetate and Cu(OAc)2 ion pair at different wavelengths independently in its absorption and fluorescence behaviour following a triple-signaling mechanism, namely, internal charge transfer (ICT), CN rotation and excited state intramolecular proton transfer (ESIPT). Chemosensor 1 shows a blue shift of the absorption band from 337 nm to 308 nm in the presence of Cu2+ ions (ICT). It exhibits a fluorescence ‘turn-off’ response at λem 458 nm in the presence of 1 equivalent of Cu2+ ions. The further addition of Cu2+ (6 equivalents) results in ∼24 times enhancement in the emission intensity at λem 427 nm, mimicking an ‘ON–OFF–ON’ molecular switch (ESIPT and CN rotation). The addition of acetate ions to a solution of 1 results in a red shift of the absorption band from 337 to 360 nm (ICT) and ∼4 times enhancement of the emission intensity at λem 458 nm (ESIPT). On the addition of a Cu(OAc)2 ion pair, 1 shows the apparent effect of Cu2+ (blue shift, 337 to 308 nm) and acetate (red shift, 337 to 380 nm), which indicates the synergistic effect of both Cu2+ and AcO− on each others binding. The potential application of chemosensor 1 for the construction of INHIBIT (INH), IMPLICATION (IMP), AND, NOR, YES and NOT logic gates using Cu2+ and acetate as the inputs and absorbance/emission as the outputs is elaborated.

Self-assembled vesicle and rod-like aggregates of functionalized perylene diimide: reaction-based near-IR intracellular fluorescent probe for selective detection of palladium

Herein, we report design, synthesis, and self-assembly of perylene diimide (PDI) based near-IR intracellular probe (PS-PDI). PS-PDI molecules undergo aggregation to form self-assembled nanospheres and nanorods morphology in THF : H2O (1 : 1) and DMSO : H2O (1 : 9), respectively. The nanospheres have an open hole on surface reminiscent of vesicle structure (with a diameter of internal void in the range of 20-25 nm) whereas lengths of the nanorods extended up to few μm range. The Pd0 based depropargylation leads to de-aggregation of these PS-PDI aggregates into smaller spherical aggregates as evidenced by DLS, SEM, and TEM studies. Interestingly, these aggregates of PS-PDI in solution show highly sensitive behavior in the presence of Pd0 showing absorbance changes in NIR region (λmax = 710 nm) and quenching of emission at λem 630 nm (DMSO : H2O, 1 : 9) with a limit of detection = 6.6 × 10-9 M or at λem 564 nm (THF : H2O, 1 : 1) with limit of detection = 2.1 × 10-8 M. Time and concentration dependent kinetics profiles of PS-PDI aggregates revealed an impressive rate constant value of 0.4 s-1 and 0.21 s-1 (DMSO : H2O, 1 : 9), respectively in fluorescence and UV-Vis spectroscopy using 2 × 10-5 M concentration of Pd0. PS-PDI undergoes rapid internalization into HeLa cells with low cytotoxicity and was successfully used as an intracellular imaging reagent for Pd0 in live HeLa cells. For practical applications, we exploited these nano-aggregates of PS-PDI for estimation of Pd2+ in the presence of a NaBH4-PPh3 mixture, Pd0 in drug and environmental samples, and Pd2+ in urine samples with excellent selectivity and sensitivity.

Diphenylpyrimidinone–salicylideneamine – new ESIPT based AIEgens with applications in latent fingerprinting

Diphenylpyrimidinone–salicylideneamine DPPS-1 undergoes concentration dependent self-assembly to form aggregates with rods – mimicking a ‘coral reef’ superstructure and a spherical morphology evident from dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). DPPS-1 and DPPS-2 exhibit weak excited state intramolecular proton transfer (ESIPT) based emission in CH3CN and their binary mixtures with water, but in solutions containing >70% water fraction DPPS-1 and DPPS-2 molecules aggregate and ESIPT is facilitated to give a strong green ESIPT emission at 526 nm (ϕ = 0.273, 0.068). The ESIPT process remains active in the solid state and solid DPPS-1 and DPPS-2 appear as fluorescent green under 365 nm light illumination. The AIE-active nature of DPPS-1 and DPPS-2 finds applications in the visualization of latent fingerprints on aluminium, steel and glass surfaces. Even 24 h after the placement of the fingerprints, up to the second level of information viz. core, lake, ridge termination and dots, delta and bifurcation in the fingerprints could be identified.

Self-assembled nanorods of bay functionalized perylenediimide: Cu2+ based ‘turn-on’ response for INH, complementary NOR/OR and TRANSFER logic functions and fluorosolvatochromism

We designed and synthesized the mono bay functionalized perylenediimide (PDI) derivative PDI-DMEA which undergoes self-assembly to form a nanorod morphology. The diameter of these nanorods is in the range of 150–300 nm and the length extended up to the μm range. These nanorods on interaction with Cu2+ ions transformed into spherical aggregates having a diameter of 350–600 nm in accordance with DLS studies. In solution, PDI-DMEA shows a blue shift of the internal charge transfer (ICT) absorption band from 605 to 570 nm along with a hyperchromic effect at 570 nm, in the presence of 0.7 equivalents of Cu2+ ions. The addition of 2 equivalents of Cu2+ ions results in complete disappearance of the ICT band at 570 nm and appearance of a normal absorption band of PDI at 515 nm (a visual colour change from colourless to yellow). On the other hand PDI-DMEA shows a strong fluorescence ‘turn-on’ response at 537 and 573 nm on addition of higher equivalents of Cu2+ ions. Thus, PDI-DMEA represents several examples of molecular switches such as ‘OFF–ON–OFF’ and ‘ON–OFF–ON’ at 570/515 nm (Cu2+, absorbance), and ‘OFF–ON’ at 570 nm (Fe2+, absorbance) and 537 nm (Cu2+, fluorescence) and thus offers the possibility for developing NOR, OR, INH and TRANSFER logic and complimentary logic circuits. Moreover, PDI-DMEA and the PDI-DMEA–Cu2+ complex show fluorosolvatochromism which helps to develop a colour array for differentiating organic solvents. The detailed mechanism of interaction of Cu2+ and Fe2+ with PDI-DMEA, confocal laser scanning microscopic studies, dynamic light scattering, 1H NMR titration and reversibility are discussed.

Recent developments in the synthesis of condensed β-lactams

β-Lactams are important heterocycles with diverse pharmacological profiles and have emerged as useful organic synthons. Different variants of β-lactams condensed with carbo-/heterocycles, which have a broad range of antimicrobial activities and other useful pharmacological activities, justify a renewed interest in their synthetic developments. This review embraces an array of different reports on condensed β-lactams dating back to 2000. The aim of this review is to provide practicing and aspiring β-lactam chemists with a survey and flavor of the types of reactions used to prepare nonconventional condensed-β-lactams, and an insight into why certain methodologies are advantageous under particular circumstances.

Perylene diimide-based organic π-motif for differentiating CN− and F− ions by electron-transfer and desilylation mechanisms: applications to complex logic circuits

In this work, we have designed and synthesized a perylene diimide based derivative PDI-SiHQ having an O-silylated-8-hydroxyquinoline group at the bay position. PDI-SiHQ is able to detect and differentiate CN− from F− in the presence of other anions. The electron transfer from cyanide ions to PDI-SiHQ leads to the emergence of panchromatic and NIR absorption bands due to the formation of a PDI-SiHQ˙− radical anion. In contrast, fluoride induced desilylation of PDI-SiHQ coupled with π–π aggregation results in a red-shifted absorption band at 730 nm. 1H NMR and cyclic voltammetry combined with the reversal of the PDI-SiHQ˙− radical anion to the PDI-SiHQ neutral form in the presence of NOBF4 or Cu2+ ions confirm the formation of the radical anion in PDI-SiHQ. Multi-channel UV-Vis-NIR absorption and emission bands and their reversibility with NOBF4/Cu2+ ions offer the possibility for fabrication of complex logic circuits such as complementary IMP/INH logic circuits, magnitude comparators and ‘set–reset’ flip flop memory elements.

A facile and chemoselective synthesis of 1,4-benzodiazepin-2-ones and dienyl thiazolidin-4-ones

An efficient protocol for chemoselective synthesis of previously unknown 1,4-benzodiazepin-2-ones and dienyl thiazolidin-4-one carboxylates in excellent yields by ring transformation reactions of functionally decorated 2-azetidin-3-thiazolidin-4-ones is reported.

Cu(I) mediated Kinugasa reactions of α,β-unsaturated nitrones: a facile, diastereoselective route to 3-(hydroxy/bromo)methyl-1-aryl-4-(-styryl)azetidin-2-ones

The manuscript describes a facile and highly diastereoselective synthesis of cis-3-(hydroxy/bromo)methyl-1-aryl-4-(-styryl)azetidin-2-ones via copper(I) mediated Kinugasa reactions of previously unexplored functionalized α,β-unsaturated nitrones. A variety of functionalized acetylenes and α,β-unsaturated nitrones were studied to yield cis-3-(hydroxy/bromo)methyl-1-aryl-4-(-styryl)azetidin-2-ones in good yields (82%).

1,3,4-Trisubstituted-2-azetidinone Derivatives as Novel Receptors for Bismuth(III) Ion-Selective Electrodes: Application in Pharmaceutical and Glass Samples

Abstract Polymeric membrane electrodes (PMEs) and coated graphite electrodes (CGEs) containing 1,3,4-trisubstituted-2-azetidinone derivatives as ion carriers are reported here for bismuth(III) ion selectivity. These electrodes exhibited Nernstian response for Bi3+ ions over a wide concentration range (5.0 × 10−7 M to 1.0 × 10−1 M for CGE) with a lower detection limit of 3.98 × 10−7 M (for CGE) and wide pH range (1.3–5.0). Compared to polymeric membrane electrode, the coated graphite electrode has shown better selectivity for Bi3+ ions with respect to common metal ions. Proposed electrodes have been used for the estimation of Bi3+ ions in pharmaceutical and glass samples.