Eringathodi Suresh

Ratiometric Detection of Cr3+ and Hg2+ by a Naphthalimide-Rhodamine Based Fluorescent Probe

Newly synthesized rhodamine derivatives, L(1) and L(2), are found to bind specifically to Hg(2+) or Cr(3+) in presence of large excess of other competing ions with associated changes in their optical and fluorescence spectral behavior. These spectral changes are significant enough in the visible region of the spectrum and thus, allow the visual detection. For L(1), the detection limit is even lower than the permissible [Cr(3+)] or [Hg(2+)] in drinking water as per standard U.S. EPA norms; while the receptor, L2 could be used as a ratiometric sensor for detection of Cr(3+) and Hg(2+) based on the resonance energy transfer (RET) process involving the donor naphthalimide and the acceptor Cr(3+)/Hg(2+)-bound xanthene fragment. Studies reveal that these two reagents could be used for recognition and sensing of Hg(2+)/Cr(3+). Further, confocal laser microscopic studies confirmed that the reagent L(2) could also be used as an imaging probe for detection of uptake of these ions in A431 cells.

Resonance energy transfer approach and a new ratiometric probe for Hg2+ in aqueous media and living organism.

Resonance energy transfer from dansyl to the rhodamine moiety in a newly synthesized chemosensor L(2) has been utilized successfully for detection of Hg(2+) in aqueous solution and living cells such as Pseudomonas putida.

Specific Recognition and Sensing of CN− in Sodium Cyanide Solution

Specific recognition of CN(-) in sodium cyanide solution was achieved using two imidazole-based receptors (A and B). Visually detectable color changes were associated with the formation of hydrogen bonded adducts, A.CN(-) and B.CN(-). Ratiometric fluorescence response was achieved for receptor A on binding to CN(-), and this reagent was used for imaging bacterial cells pre-exposed to 1.42 microM CN(-) solution.

Recognition of Hg2+ and Cr3+ in Physiological Conditions by a Rhodamine Derivative and Its Application as a Reagent for Cell-Imaging Studies

A new rhodamine-based receptor, derivatized with an additional fluorophore (quinoline), was synthesized for selective recognition of Hg(2+) and Cr(3+) in an acetonitrile/HEPES buffer medium of pH 7.3. This reagent could be used as a dual probe and allowed detection of these two ions by monitoring changes in absorption and the fluorescence spectral pattern. In both instances, the extent of the changes was significant enough to allow visual detection. More importantly, the receptor molecule could be used as an imaging reagent for detection of Hg(2+) and Cr(3+) uptake in live human cancer cells (MCF7) using laser confocal microscopic studies. Unlike Hg(ClO(4))(2) or Hg(NO(3))(2) salts, HgCl(2) or HgI(2) failed to induce any visually detectable change in color or fluorescence upon interaction with L(1) under identical experimental conditions. Presumably, the higher covalent nature of Hg(II) in HgCl(2) or HgI(2) accounts for its lower acidity and its inability to open up the spirolactam ring of the reagent L(1). The issue has been addressed on the basis of the single-crystal X-ray structures of L(1)·HgX(2) (X(-) = Cl(-) or I(-)) and results from other spectral studies.

Azine-based receptor for recognition of Hg2+ ion: crystallographic evidence and imaging application in live cells.

A newly synthesized azine-based receptor (L) is found to show remarkable specificity toward the Hg(2+) ion in aqueous media over other metal ions. Coordination of L to Hg(2+) induces a detectable change in color and a turn-on fluorescence response. Restricted C=N isomerization of the azine moieties in the excited state as well as the Photoinduced Electron Transfer (PET) involving the lone pair of electrons of N(1)/N(2) on coordination of L to the Hg(2+) ion account for the turn-on fluorescence response. This reagent could be used for imaging the accumulation of Hg(2+) ions in Epithelial cell line KB 31 cells.

Anion complexation of a pentafluorophenyl-substituted tripodal urea receptor in solution and the solid state: selectivity toward phosphate

The binding and selectivity of halides (spherical) and oxyanions (tetrahedral) toward a recently reported pentafluorophenyl-substituted tripodal urea-based receptor L(1) are examined thoroughly in the solid state by single-crystal X-ray crystallography as well as in solution by multinuclear NMR techniques. Crystallographic results show proof of a fluoride encapsulation in the cavity of L(1) in complex [L(1)(F)][Bu(4)N], . Fluoride encapsulation inside the C(3v) symmetric cleft is observed via six hydrogen bonds to all six urea protons of the receptor. In case of complex crystallographic results show encapsulation of sulfate ion inside a supramolecular cage formed upon 1 : 2 (guest-host) complex formation between sulfate and L(1). Sulfate encapsulation is observed via fourteen hydrogen bonding interactions from all six urea moieties of two L(1) units. Our effort to isolate single crystal of halides/oxyanions complexes of L(2) always yield single crystals of free L(2) though literature shows anion binding with this receptor in solution. Solution state binding studies of L(1) are carried out by (1)H-NMR titration to calculate binding constants, which show the following anion binding sequence H(2)PO(4)(-) > SO(4)(2-)> CH(3)COO(-) > F(-) > Cl(-) >> Br(-) whereas there is no binding with I(-), NO(3)(-) and ClO(4)(-) guests. Comparison of phosphate and sulfate binding in L(1) and L(2), show higher binding with the pentafluorophenyl substituted receptor, L(1). Further (19)F and (31)P-NMR experiments in solution are also carried out to probe the binding of F(-) and H(2)PO(4)(-) with L(1), respectively. Extensive (1)H-NMR experiments in solution and crystallization in the presence of multiple anions are also undertaken to evaluate the selectivity of H(2)PO(4)(-) over other anions.

A rhodamine-based chemosensor that works in the biological system.

A new rhodamine-based reversible chemosensor (L1 ) is reported, which could bind Hg2+ and Cu2+ in aqueous methanol solution with detectable change in color. Cu2+ and Hg2+ ions responded differently toward the fluorescence output signals on binding to L1.L1 could also be used as a selective probe for monitoring Hg2+ adsorbed on bacteria using an optical microscope.

Synthesis, spectral and X-ray structural characterization of [cis-MoO2(L)(solv)] (L=salicylidene salicyloyl hydrazine) and its use as catalytic oxidant

Abstract The synthesis and characterization of cis-[MoO2(L) (solv)] [L=salicylidene salicyloyl hydrazine and solvent=H2O/MeOH) is described. The tridentate Schiff base ligand was obtained by the condensation of salicylaldehyde and salicylic acid hydrazide in 1:1 ratio. The dioxomolybdenum complex was isolated from 1:1 reaction mixture containing the Schiff base ligand and MoO2(acac)2. The orange colored, non-electrolytic and diamagnetic compound was characterized by elemental analyses, spectroscopic techniques (IR, 1H NMR and UV-Vis), and cyclic voltammetry. The molecular structure was determined using crystals obtained from methanol, confirmed the formula cis-MoO2(L)(CH3OH) with triclinic P-1 space group. The Mo is coordinated by two cis terminal Os, ONO from the ligand and O of methanol. The oxo-transfer reaction from cis-[MoO2(L)(solv)] to PPh3, is reported.

Spontaneous Resolution to Absolute Chiral Induction: Pseudo-Kagomé Type Homochiral Zn(II)/Co(II) Coordination Polymers with Achiral Precursors

It is observed that conglomerate crystallization of achiral precursors yielding racemate metal organic frameworks/coordination polymers (MOFs/CPs) can be driven to absolute homochiral crystallization of the desired enantiomorph by utilizing a suitable chiral induction agent. In a series of crystallization experiments isostructural Zn and Co homochiral CPs (1P, 1M and 2P, 2M) are prepared using the achiral precursors. In the presence of enantiopure camphoric acid, the crystallization process prefers absolute chiral induction over conglomerate formation which is established by single crystal X-ray diffraction and CD spectroscopy.

Stereoselective synthesis of spirocyclopentanones via N-heterocyclic carbene-catalyzed reactions of enals and dienones

Homoenolates generated from enals by nucleophilic heterocyclic carbene (NHC) catalysis undergo a conjugate addition/cyclization sequence with cyclic dienones, culminating in the efficient synthesis of spirocyclopentanones.