Sanchita Goswami

A new pyridoxal based fluorescence chemo-sensor for detection of Zn(II) and its application in bio imaging

This paper describes the activity of a Schiff base ligand, derived from pyridoxal, as a promising fluorescence probe for biologically important Zn(II) ion sensing. A physiologically compatible pyridoxal based chemosensor PydDmen was synthesized and evaluated for its fluorescent response towards metal ions. Chemosensor PydDmen exhibits a selective turn-on type response in the presence of Zn2+ in ethanol–water mixture. The addition of EDTA quenches the fluorescence of receptor PydDmen-Zn2+, making the chemosensor PydDmen reversible. The response is specific for Zn(II) ions, and remains almost unaffected by the presence of alkali and alkaline earth metals but is suppressed to varying degrees by transition metal ions. The selectivity mechanism of PydDmen for Zn2+ is the combined effects of proton transfer between the prevailing tautomeric forms, CN isomerization and CHEF. The DFT optimized structure of the complex is compatible with elemental analysis, mass spectrometry, FT-IR, electronic and NMR spectra. The experimental and theoretical support in terms of NMR spectroscopy and DFT are provided to establish the existence of Zn2+ induced transformation of PydDmen to a 3-pyridone tautomeric form.

Heterometallic CuII–DyIII Clusters of Different Nuclearities with Slow Magnetic Relaxation

The synthesis, structures, and magnetic properties of two heterometallic Cu(II)-Dy(III) clusters are reported. The first structural motif displays a pentanuclear Cu(II)4Dy(III) core, while the second one reveals a nonanuclear Cu(II)6Dy(III)3 core. We employed o-vanillin-based Schiff base ligands combining o-vanillin with 3-amino-1-propanol, H2vap, (2-[(3-hydroxy-propylimino)-methyl]-6-methoxy-phenol), and 2-aminoethanol, H2vae, (2-[(3-hydroxy-ethylimino)-methyl]-6-methoxy-phenol). The differing nuclearities of the two clusters stem from the choice of imino alcohol arm in the Schiff bases, H2vap and H2vae. This work is aimed at broadening the diversity of Cu(II)-Dy(III) clusters and to perceive the consequence of changing the length of the alcohol arm on the nuclearity of the cluster, providing valuable insight into promising future synthetic directions. The underlying topological entity of the pentanuclear Cu4Dy cluster is reported for the first time. The investigation of magnetic behaviors of 1 and 2 below 2 K reveals slow magnetic relaxation with a significant influence coming from the variation of the alcohol arm affecting the nature of magnetic interactions.

Syntheses, crystal structures, spectral studies, and DFT calculations of two new square planar Ni(II) complexes derived from pyridoxal-based Schiff base ligands

Two new complexes based on a Schiff base derived from pyridoxal N,N-dimethylethylenediamine (HL1) and N,N-diethylethylenediamine (HL2), [Ni(L1)SCN] (1) and [Ni(L2)SCN] (2), have been synthesized and structurally characterized by single-crystal X-ray diffraction along with other physical techniques, including elemental analyses, IR spectra, cyclic voltammetry, UV–vis, and luminescence studies. X-ray studies suggest that in both the complexes nickel lies in a slightly distorted square planar environment occupied by the tridentate ONN ligand and an isothiocyanate moiety. Density functional theory computations have been carried out to characterize the complexes. Two new square planar Ni(II) complexes, [Ni(L1)SCN] (1) and [Ni(L2)SCN] (2) are synthesized from pyridoxal-based Schiff base ligands and structurally characterized. DFT calculations are also done to establish their optimized electronic structures.

CoII4, CoII7, and a Series of CoII2LnIII (LnIII = NdIII, SmIII, GdIII, TbIII, DyIII) Coordination Clusters: Search for Single Molecule Magnets

We report herein the syntheses and investigation of the magnetic properties of a CoII4 compound, a series of trinuclear CoII2LnIII (LnIII = NdIII, SmIII, GdIII, TbIII, DyIII) complexes, and a CoII7 complex. The homometallic CoII4 core was obtained from the reaction of Ln(NO3)3·xH2O/Co(NO3)2·6H2O/H2vab/Et3N in a 0.5:0.5:1:2 ratio in methanol. Variation in synthetic conditions was necessary to get the desired CoII-LnIII complexes. The CoII-LnIII assembly was synthesized from Ln(NO3)3·xH2O/Co(OAc)2·4H2O/H2vab/NaOMe in a 0.4:0.5:1:1 ratio in methanol. The isostructural CoII2LnIII complexes have a core structure with the general formula [Co2Ln(Hvab)4(NO3)](NO3)2·MeOH·H2O, (where H2vab = 2-[(2-hydroxymethyl-phenylimino)-methyl]-6-methoxy-phenol) with simultaneous crystallization of CoII7 complex in each reaction. The magnetic investigation of these complexes reveals that both homometallic complexes and four CoII-LnIII complexes (except CoII-NdIII) display behavior characteristic of single molecule magnets.

A highly selective “ON–OFF” probe for colorimetric and fluorometric sensing of Cu2+ in water

We present herein a diformyl phenol based probe, 3-({3-[2,3-dihydroxy-propylimino-methyl]-2-hydroxy-5-methyl-benzylidene}-amino)-propane-1,2-diol (H5dpm), as a colorimetric and fluorometric chemosensor for selective detection of Cu2+ in aqueous solution under physiological conditions. This simple system produces a colorimetric change enabling naked eye detection as well as on–off fluorescence response towards Cu2+ in an aqueous medium with a detection limit of 11.2 nM. To further demonstrate the utility of H5dpm, we next explored the application of H5dpm for imaging Cu2+ in Vero cells. The attractive imaging properties of the H5dpm probe will open up avenues for molecular imaging and biomedical applications.

A new fluorescence turn-on chemosensor for nanomolar detection of Al3+ constructed from a pyridine–pyrazole system

Herein, a new probe, 5-methyl-1-pyridin-2-yl-1H-pyrazole-3-carboxylic acid (1-pyridin-2-yl-ethylidene)-hydrazide (Hmppc), bearing a pyridine–pyrazole moiety, was synthesized, which offered potential for chemical sensing of Al3+. Investigations of the fluorescence behaviour of Hmppc in DMSO/H2O (2 : 8, v/v) solution under biologically relevant conditions in HEPES buffer (pH = 7.4) displayed a dramatic switch-on response to Al3+ as a result of chelation-induced enhanced fluorescence (CHEF). Detailed experimental studies reveal that Hmppc can detect Al3+ in solution with high sensitivity and selectivity, having a detection limit of 1.2 nM. Furthermore, to demonstrate the analytical potential of Hmppc, we validated our sensing system as a naked eye detector for Al3+. Interestingly, bioimaging studies on HepG2 cells demonstrated that Hmppc responded selectively towards Al3+, allowing real time detection of Al3+ in living cells.

Bis{2-[(5-hy­droxy­pent­yl)imino­meth­yl]phenolato-κ2N,O1}copper(II)

In the title compound, [Cu(C12H16NO2)2], the CuII ion, located on a center of inversion, is coordinated by two singly deprotonated Schiff base ligands derived from condensation of salicyldehyde and 1-aminopentan-5-ol. The imino N and phenol O atoms from both ligands offer a square-planar arrangement around the metal ion. The Cu—N and Cu—O bond lengths are 2.0146 (15) and 1.8870 (12) Å, respectively. Since the Cu—O and Cu—N bond lengths are different, it can be concluded that the resulting geometry of the complex is distorted. The aliphatic –OH group of the ligand is not coordinated and points away from the metal coordination zone and actively participates in hydrogen bonding connecting two other units and thus stabilizing the crystal lattice. This results in a two-dimensional extended array parallel to (201).

Diazine based ligand supported CoII3 and CoII4 coordination complexes: role of anions

We report the synthesis and characterisation of a family of three CoII4, two CoII3 complexes from an symmetrical diazine ligand, H2hyda = N,N−bis(3−methoxy salicylidene) hydrazine). The metallic skeletons of all complexes describe a nearly linear arrangement of CoII centers. The present results highlight the profound influence of the anions on the structural outcome of a complex. Furthermore, the distortion imposed by the twisted nature of the diazine based ligand depends on the use of associated anions which results in triple helical CoII4 and double helical CoII3 entities. The CoII ions in complexes 1−3 are antiferromagnetically coupled leading to diamagnetic ground state. In contrast, complexes 4 and 5 exhibit a magnetic ground state, but exhibit different behaviour at low temperatures due to differences in crystal packing and hence intermolecular interactions.