Maninder Singh Hundal

New tripodal and dipodal colorimetric sensors for anions based on tris/bis-urea/thiourea moieties

Seven neutral tripodal and dipodal receptors having mesitylene/triethylbenzene as core moiety, urea/thiourea as binding groups and p-nitrobenzene as signalling unit have been reported. The receptors act as selective colorimetric, naked eye sensors for small and spherical F− ion with some interference from tetrahedral ions. Thiourea derivatives form stable 1:1 H-bonded complexes with F− anion and to some extent with anions, whereas for urea derivatives, the recognition is simply based on acid–base reaction between ureidic protons and basic F− ions and is a completely reversible phenomenon. The pre-organisation of thiourea derivatives coupled with their high-intrinsic acidity is supposed to help them in the formation of strong H-bonded complexes with F− anion. The urea-based receptors do not respond at lower concentrations of the anion, but at higher concentrations, they undergo completely reversible deprotonation concomitant with a colorimetric change, with the production of stable [HF2]− anion.

A cell permeable Cr3+ selective chemosensor and its application in living cell imaging

An efficient fluorescent Cr3+ receptor, 2-(5,6-dihydro-benzo-[4,5]imidazo[1,2-c]quinazolin-6-yl)-quinolin-8-ol (H2L1) was synthesized and characterized by physico–chemico and spectroscopic tools along with single crystal X-ray crystallography. This probe (H2L1) behaves as a highly selective fluorescent sensor for Cr3+ ions at biological pH in ethanol–water (1 : 5, v/v) HEPES buffer (0.1 M, pH 7.4) at 27 °C. Metal ions, viz. alkali (Na+, K+), alkaline earth (Mg2+, Ca2+), and transition-metal ions ((Mn2+, Fe3+, Co3+, Ni2+, Cu2+, Zn2+) and Pb2+, Ag+ did not interfere. The lowest detection limit for Cr3+ was calculated to be 3.6 × 10−7 mol L−1 within a very short responsive time (15–20 s) in ethanol–water (1 : 5, v/v) HEPES buffer (0.1 M, pH 7.4) at 27 °C. The sensor is efficient for detection of Cr3+ in vitro, developing a good image of the biological organelles.

Copper(II)-Catalyzed Disulfide Scission—Stepwise Aerobic Oxidative Cleavage to Sulfinate and Sulfonate and Reductive Anaerobic Cleavage to Thiols

The Cu(II)-catalyzed oxidative and reductive cleavage of the disulfide bond of N-(2-(2-(2-picolinamido)phenyl)disulfanyl)phenyl)picolinamide, L, is reported for the first time. Aerobic oxidation with Cu(II) gives complete oxidation of S-S bond to sulfonates, whereas Ag(I) gives only partial oxidation up to sulfinates, in the absence of any other oxidizing agent, in tetrahydrofuran/water solution. The in situ generated sulfonate product forms a thermally stable, two-dimensional H-bonded polymeric complex with Cu(II) ions in two polymorphic forms. L in the presence of Cu(II), in an inert atmosphere, results in a reductive cleavage of the disulfide bond and an in situ formation of a new C-S bond. The latter forms a unique tetranuclear complex with Cu(II) employing deprotonated amide groups and bridging thiol and chloride atoms. The disulfide precursor and the products were characterized by X-ray crystallography and spectroscopic techniques.

Development of a cell permeable ratiometric chemosensor and biomarker for hydrogen sulphate ions in aqueous solution

A newly designed organic moiety, 5H-5,7a,12-triaza-dibenzo[a,e]azulen-6-one (L) containing a seven membered ring behaves as a hydrogen sulphate ion selective ratiometric chemosensor. The formulation and detailed structural characterisation of L have been established using physico-chemical, spectroscopic tools and single crystal X-ray diffraction study. On additions of hydrogen sulphate ions to the solution of L in HEPES buffer (1 mM; water : ethanol (v/v), 98 : 2) at 25 °C at biological pH, a new fluorescence peak generated at 483 nm was increased with concomitant decrease of the weak fluorescence of L at 430 nm through an isoemissive point at 449 nm due to the selective binding of HSO4− ions with L in a 1 : 1 ratio with a binding constant (K) of 4.13 × 106 M−1, and detects HSO4− ions as low as 5.5 × 10−7 M. The ratiometric enhancement of the fluorescence is based on intermolecular hydrogen bonding assisted chelation enhanced fluorescence (CHEF) process which has been evidenced by 1HNMR titration and supported by theoretical (DFT) calculations. The probe (L) having no cytotoxic effect is also useful for the detection of intracellular HSO4− ion concentrations under a fluorescence microscope.

Fixation of CO2 in air: Synthesis and crystal structure of a μ3-CO3-bridged tricopper(II) compound

A novel trinuclear copper(II) compound [{(L3)Cu(OClO3)}3(μ3-OCO2)][ClO4] has been synthesised using an N-tridentate symmetrical pyridylalkylamine ligand, N-methyl-N,N-bis(2-pyridylmethyl) amine (L3). The structure of the complex has been determined by X-ray crystallography; it is found to crystallise in the hexagonal space group P63/m with a = 13·936(2), b = 13·936(2), c = 14·895(3) Å, α = β = 90°, γ = 120°. The complex possesses a 6̅ symmetry axis passing through the carbon atom of the triply bridging carbonate ion, with the three symmetry related copper ions connected to one another through the oxygen atoms from the bridging carbonato group, giving an equilateral triangular array of copper centres. Each copper ion has distorted square pyramidal environment with the basal plane formed by three nitrogen atoms of the ligand L3 and the oxygen atom of the bridging carbonato group. The apical position at each copper is provided by the weak oxygen coordination from the perchlorate ion.

Nanomolar fluorogenic detection of Al(III) by a series of Schiff bases in an aqueous system and their application in cell imaging

Three positional isomers of a Schiff base containing -OH as end groups have been synthesized and evaluated for selective Al(III) detection due to inhibition of ESIPT, PET and activation of CHEF in 70% aqueous medium. Devoid of any conventional fluorophore, these sensors have nanomolar detection limits with high quantum yields and naked eye sensing of Al(III). Moreover, these probes have been demonstrated to enable the Al(III) detection in live human HeLa cells and rat C6 glioma cells using a confocal microscope.

Tandem sigmatropic shifts in [4 + 2] cycloaddition reactions of 1,3-diazabuta-1,3-dienes with butadienylketene: synthesis of pyrimidinone derivatives

The reactions of 4-dialkylamino substituted 1,3-diazabuta-1,3-dienes 1 with butadienylketene 2, are shown to undergo [4 + 2] cycloadditions to yield 5-(buta-1′,3′-dienyl)pyrimidinone 4 and tandem [1,5]H and [1,5]SCH3 shifts are shown to accompany the [4 + 2] cycloaddition reactions of 4-dialkylamino-4-methylthio substituted 1,3-diazabuta-1,3-dienes 5 with 2. The regioselective reactions of N-arylamino-1,3-diazabuta-1,3-dienes 11 and 14 with butadienylketene 2 are reported to yield 5-(buta-1′,3′-dienyl)-2-dialkylaminopyrimidin-4(3H)-one 13 and a mixture of 5-(buta-1′,3′-dienyl)-2-methylthiopyrimidin-4(3H)-one 17, 2-methylthio-5-[1′-(N-phenylamino)but-2′-enyl]pyrimidin-4(3H)-one 19 and 2-methylthio-5-[3′-(N-phenylamino)but-1′-enyl]pyrimidin-4(3H)-one 20, respectively. Tandem [1,5]H, [1,3]NHPh and [1,5]NHPh shifts are involved in the formation of pyrimidinones 19 and 20. The Diels–Alder reactions of the 5-dienylpyrimidinones with dimethyl acetylenedicarboxylate (DMAD) and 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) yielded corresponding cycloadducts.

Synthesis, crystal structure investigation, DFT analyses and antimicrobial studies of silver(I) complexes with N,N,N′,N′′-tetrakis(2-hydroxyethyl/propyl) ethylenediamine and tris(2-hydroxyethyl)amine

The synthesis, crystal structures, DFT and antimicrobial studies of three novel complexes of silver: [Ag(THEEN)]2(PIC)2 (1), [Ag(THPEN)]2(PIC)2 (2) and [Ag(TEAH3)2](PIC) (3), have been reported in the present work, where THEEN/THPEN (N,N,N′,N′′-tetrakis(2-hydroxyethyl/propyl)ethylenediamine) are tetrapodal ligands and TEAH3 (tris(2-hydroxyethyl)amine) is a tripodal ligand. Complexes (1) and (2) are dinuclear, whereas (3) is mononuclear. Complex (1) adopted a see-saw geometry with coordination number four, whereas (2) and (3) are five coordinated. Complex (2) acquired distorted square-pyramidal geometry, whereas complex (3) acquired distorted trigonal-bipyramidal geometry. Extensive hydrogen bonding interactions have been found in all three complexes. The primary coordination sphere of the newly synthesized silver(I) complexes has been optimized, structural parameters have been calculated and the energy gaps of the frontier orbitals have been predicted with the B3LYP/6-31G/LANL2DZ level of theory. Structural parameters from the crystallographic and DFT studies are in good agreement with each other. The relatively smaller calculated HOMO–LUMO energy gaps (HLG) suggest charge transfer transitions. Antimicrobial studies have been performed with the new silver(I) complexes against gram +ve bacteria (Staphylococcus aureus), gram −ve bacteria (Serratia marcescens, Sphingobium japonicum and Stenotrophomonas maltophilia) and fungal species (Candida albicans, Aspergillus niger and Saccharomyces cerevisiae). Dinuclear complexes (1) and (2) exhibited remarkable results. All the synthesized silver(I) complexes have been proven to be better antibacterial and antifungal agents, even than their standard drugs (ciprofloxacin and fluconazole) and can be used as effective antimicrobial agents and potential drugs in the future.

Bis(triethanolamine)calcium 3,5-Dinitrobenzoate

In the title complex, [Ca(C6H15NO3)2](C7H3N2O6)2, the Ca2+ ion is sandwiched between two triethanolamine ligands, each of them coordinating through all four potential donor sites. The coordination polyhedron is distorted cubic. The 3,5-dinitrobenzoate counter anions do not interact directly with the cation but are hydrogen bonded to the hydroxyl groups of the triethanolamine ligands.

Bis-pyridine-tetramide 18-membered macrocycles. Role of increased preorganisation on selectivity

Abstract Enhanced preorganisation induced by four substituted amide groups in macrocycles 4a and 4b increases the Ag+ extraction efficiency by >30% to 74–81% and Ag + Pb 2+ selectivity by >300% to 245 – 283 times than in 1.