Monika Mukherjee

A New Half-Condensed Schiff Base Compound: Highly Selective and Sensitive pH-Responsive Fluorescent Sensor

A new probe, 3-[(3-benzyloxypyridin-2-ylimino)methyl]-2-hydroxy-5-methylbenzaldehyde (1-H) behaves as a highly selective fluorescent pH sensor in a Britton-Robinson buffer at 25 °C. The pH titrations show a 250-fold increase in fluorescence intensity within the pH range of 4.2 to 8.3 with a pK(a) value of 6.63 which is valuable for studying many of the biological organelles.

A highly selective fluorescent chemosensor for zinc ion and imaging application in living cells.

A new 2,6-bis(5,6-dihydrobenzo[4,5]imidazo[1,2-c]quinazolin-6-yl)-4-methylphenol (1) serves as a highly selective and sensitive fluorescent probe for Zn(2+) in a HEPES buffer (50 mM, DMSO:water = 1:9 (v/v), pH = 7.2) at 25 °C. The increase in fluorescence in the presence of Zn(2+) is accounted for by the formation of dinuclear Zn(2+) complex [Zn(2)(C(35)H(25)N(6)O)(OH)(NO(3))(2)(H(2)O)] (2), characterized by X-ray crystallography. The fluorescence quantum yield of the chemosensor 1 is only 0.019, and it increases more than 12-fold (0.237) in the presence of 2 equiv of the zinc ion. Interestingly, the introduction of other metal ions causes the fluorescence intensity to be either unchanged or weakened. By incubation of cultured living cells (A375 and HT-29) with the chemosensor 1, intracellular Zn(2+) concentrations could be monitored through selective fluorescence chemosensing.

Synthesis of Selenoxo Peptides and Oligoselenoxo Peptides Employing LiAlHSeH

Synthesis of selenoxo peptides by the treatment of N(α)-protected peptide esters with a combination of PCl(5) and LiAlHSeH is delineated. The method is simple, high-yielding, and free from racemization. Thus obtained selenoxo peptides are used as units for N-terminal chain extension through N(α)-deprotection/coupling to yield peptide-selenoxo peptide hybrids. Multiple selenation is demonstrated by conversion of two peptide bonds of tripeptides into selenoxo peptide bonds. Amino acid derived arylamides are also converted into aryl selenoamides. C(6)H(5)-CSeNH-Val-OMe 8f is obtained as single crystal, and its structure was determined through X-ray diffraction study.

Synthesis, chemical characterization, structural data and solid state behaviour of N, N′-diethyl-1, 2-ethanediamine complexes of nickel(II) thiocyanate

Abstract [NiL 2 (NCS) 2 ]·H 2 O ( 1 ) and [NiL 2 (NCS) 2 ] ( 2 ) (L = N, N′-diethyl-1, 2-ethanediamine) have been synthesized from solution. The species 1 on deaquation transforms to [NiL 2 (NCS) 2 ] ( 1a ) which subsequently undergoes an irreversible exothermic phase transition (118–142°C; Δ H = −3.8kJ mol −1 ) accompanied by a pinkish-blue to blue thermochromism producing an isomer [NiL 2 (NCS) 2 ] ( 1b ). The pinkish-blue species 2 on heating shows an endotherm (82–120°C; Δ H =kJ mol −1 ) yielding the species 1b . Single crystal X-ray structure analyses of 1 and 2 have been carried out. The metal atoms in both the complexes, lying at crystallographic inversion centres, display distored octahedral geometries with four amine nitrogen atoms defining the equatorial plane and two isothiocyanato groups in trans axial positions.

Thermochromism in copper(II) complexes: thermal, spectroscopic, solid-state broadline 1H NMR and room-temperature single-crystal x-ray analysis of bis(N,N′-dimethyl-1,2-ethanediamine)copper(II) dinitrate

Abstract The complex bis(N,N′-dimethyl-1,2-ethanediamine)copper(II) dinitrate, Cu (NN′-dmen)2(NO3)2, undergoes a first-order thermochromic phase transition at ca 148°C, changing from blue-violet to blue. The low-temperature phase has been characterized by X-ray crystallography. The copper ion possesses distorted (4+2) octahedral geometry with two five-membered chelate rings, in the δλ conformation, forming the CuN4 plane [CuN = 2.000(6) and 2.033(7) A] and oxygens from the two nitrate groups weakly coordinated in the two axial coordination sites [CuO = 2.506(8) A]. The broad-line 1H NMR indicates the onset of a dynamic disorder of diamine chelate rings at the phase transition temperature region. The electronic spectrum broadens on phase transition.

MACROCYCLIC DIMERIC VANADIUM(IV) AND HETERODINUCLEAR VANADIUM(IV)-NICKEL(II) COMPLEXES. STRUCTURE, MAGNETIC, ELECTRONIC AND REDOX PROPERTIES

The oxovanadium(IV) complexes [{VO(H2L1)}2(µ-SO4)][NO3]2, [(VO)L1Ni(H2O)2(SO4)]·H2O and [(VO)L1Ni(µ-SO4)(H2O)]·2H2O have been synthesized from the dinucleating tetraaminodiphenol macrocycle H2L1. The crystal structure of the first, in which two unco-ordinated amino nitrogens are protonated, has been determined. The two distorted-octahedral vanadium centres in the complex, separated by 6.741(4)A, are bridged by sulfate and have an anti-oxo configuration. In the solid state the magnetic moment of this complex per vanadium decreases from 1.71 to 1.64 µB on lowering the temperature from 299 to 5 K, indicating very weak intra-/or inter-molecular exchange interactions. Its ESR spectra in fluid solution and glass, however, showed the absence of VO ⋯ VO electron-spin interaction. This complex undergoes stepwise oxidation to produce VOIVVOV and VOVVOV species with E1/2(1)= 0.445 V and E½(2)= 0.60 V vs. Ag–AgCl electrode; the comproportionation constant Kc= 4.2 × 102. The other two complexes have identical composition but differ in their IR and UV/VIS spectra and electrochemistry. In the first the oxovanadium(IV) and nickel(II) centres are revesibly oxidized at 0.436 and 0.756 V, respectively, while in the second irreversible oxidation of both metal centres takes place at 1.05 and 1.25 V. Both behave ferromagnetically and their exchange coupling constants J are 10(1) and 6(1) cm–1, respectively.

Thermally induced phase transition and X-ray crystal structure of bis(N,N'-dimethyl-1,2-ethanediamine)di-isothiocyanatonickel(II)

The complex [Ni(MeNHCH2CH2NHMe)2(NCS)2](1) has been synthesised and characterised by X-ray crystallography. It undergoes an irreversible endothermic phase transition (452.5–468.5 K, ΔH= 13.4 kJ mol–1) to species (2) which reverts to (1) in a humid atmosphere. Complex (1) crystallises in the monoclinic space group C2/c with a= 13.069(2), b= 9.783(3), c= 15.074(4)A, β= 111.40(2)°, and Z= 4. The structure has been solved by Patterson and successive Fourier methods and refined to R= 0.032 for 1 240 independent observed reflections. The co-ordination around the nickel atom, lying on a crystallographic inversion centre, is close to octahedral with the two thiocyanate N atoms in trans position. The chelate rings exist in the δλ conformation. For complex (2), a=b= 8.16(3), c= 7.53(2)A, α=β= 107.0(2), γ= 73.6(3)°, and Z= 1. Crystallographic and i.r. spectroscopic data suggest a non-centrosymmetric structure for (2) with a qualitative change in the conformation of the complex to δδ or λλ.

Topological features and electronic structure of 4-chloro-1H-pyrrolo[2,3-b]pyridine: experimental charge density analysis and DFT studies

The experimental charge density distribution in 4-chloro-1H-pyrrolo[2,3-b]pyridine has been carried out using high resolution X-ray diffraction data collected at 100(2) K. Multipole refinement based on the Hansen–Coppens formalism coupled with an estimation of anisotropic displacement parameters (ADPs) of hydrogen atoms converged to R(F) = 0.0353 for 5700 reflections with I > 3σ(I) and sin θ/λ ≤ 1.08 A−1. The topology of the bonding scheme within the molecule as well as of the intermolecular N–H⋯N and C–H⋯Cl hydrogen bonds has been investigated. The covalent nature of N–C and C–C bonds in the pyrrolopyridine skeleton of the molecule has been established by (3, −1) bond critical points associated with relatively large electron densities [2.07(2)–2.74(3) e A−3] and highly negative Laplacian values [−11.37(4) to −19.20(10) e A−5]. The topological parameters corresponding to H⋯N and H⋯Cl critical points indicate a moderately strong intermolecular N–H⋯N hydrogen bond and a weak C–H⋯Cl closed-shell interaction. The electronic structure of the title compound has been calculated by density functional theory (DFT) at the BLYP level. A large HOMO–LUMO energy gap (3.59 eV; HOMO is the highest occupied molecular orbital and LUMO is the lowest unoccupied molecular orbital) implies a high kinetic stability of the title compound.

Structural study of three o-hydroxyacetophenone derivatives using X-ray powder diffraction: interplay of weak intermolecular interactions

A family of three o-hydroxyacetophenone derivatives, 2-hydroxy-5-methoxy-4-methylacetophenone (1), 5-methoxy-4-methyl-2-(phenylmethoxy)acetophenone (2) and 2-O-(α-methyl carboethoxy)-5-methoxy-4-methyl-acetophenone (3) were synthesized and their crystal structures were solved using laboratory X-ray powder diffraction data along with a detailed analysis of the Hirshfeld surfaces and 2D-fingerprint plots, facilitating a comparison of intermolecular interactions. The DFT optimized molecular geometries in 1 and 3 agree closely with those obtained from the crystallographic studies. In 2, however, the relative orientation of the two planar phenyl rings as established by the X-ray analysis and quantum mechanical calculations differs by 34.9°. The crystal packing in the compounds is stabilized by an interplay of weak hydrogen bonds, such as C–H⋯O, C–H⋯π and π⋯π interactions, forming supramolecular assemblies. The intermolecular C–H⋯O hydrogen bonds in 1–3 generate C11(6) chains and Rmn(X) rings, which are further connected through C–H⋯π hydrogen bonds and π⋯π interactions to produce parallel molecular sheets built by fused R22(24) rings in 1, a three-dimensional architecture with C22(16)[R22(6)][R22(14)] synthons in 2, and a two-dimensional columnar framework in 3.

Intramolecular [2+2] photocycloaddition of 1,6-dienes incorporated in a furanose ring. Unusual formation of cis-syn-cis 6-oxatricyclo[6.2.0.03,7]decanes

Intramolecular [2+2] photocycloaddition of 1,6-dienes incorporated in a furanose ring either in the presence of a copper(I) catalyst or with a sensitiser led to the unusual formation of cis-syn-cis adducts.