Pyrophosphate selective fluorescent chemosensors: cascade recognition of nuclear stain mimicking DAPI.

A new zinc(ii) complex with a condensed hydroxynaphthyl pyridine (SPHN) as the coordinated ligand has been synthesized for the selective recognition of pyrophosphate (PPi) over other anions including phosphate in a mixed aqueous solution. The fluorescence enhancement of SPHN in association with Zn(2+) ions is quenched in the presence of intracellular pyrophosphate. This phenomenon is utilized in the construction of a logic gate. The binding of SPHN with Zn(2+) and its displacement by PPi have been established by photophysical investigation and supported by the DFT level of studies. The development of blue fluorescence in the {} complex upon binding of zinc with is shown to be useful as a nucleus marker in a cell similar to the commercially available staining compound, DAPI (diamino-2-phenylindole).

Role of caffeine in DNA recognition of a potential food-carcinogen benzo[a]pyrene and UVA induced DNA damage.

Electron transfer (ET) reactions are important for their implications in both oxidative and reductive DNA damages. The current contribution investigates the efficacy of caffeine, a xanthine alkaloid in preventing UVA radiation induced ET from a carcinogen, benzo[a]pyrene (BP) to DNA by forming stable caffeine-BP complexes. While steady-state emission and absorption results emphasize the role of caffeine in hosting BP in aqueous medium, the molecular modeling studies propose the energetically favorable structure of caffeine-BP complex. The picosecond-resolved emission spectroscopic studies precisely explore the caffeine-mediated inhibition of ET from BP to DNA under UVA radiation. The potential therapeutic activity of caffeine in preventing DNA damage has been ensured by agarose gel electrophoresis. Furthermore, time-gated fluorescence microscopy has been used to monitor caffeine-mediated exclusion of BP from various cell lines including squamous epithelial cells, WI-38 (fibroblast), MCF-7 (breast cancer) and HeLa (cervical cancer) cells. Our in vitro and ex vivo experimental results provide imperative evidences about the role of caffeine in modified biomolecular recognition of a model carcinogen BP by DNA resulting dissociation of the carcinogen from various cell lines, implicating its potential medicinal applications in the prevention of other toxic organic molecule induced cellular damages.

Nanomolar detection of hypochlorite by a rhodamine-based chiral hydrazide in absolute aqueous media: application in tap water analysis with live-cell imaging.

By employing the oxidation property of hypochlorite (OCl(-)), a novel rhodamine-based hydrazide of the chiral acid ((S)-(-)-2-pyrrolidone-5-carboxylic acid) (RHHP) was designed and synthesized for detection of OCl(-) absolutely in aqueous medium at nanomolar level. The structure of the chiral sensor was also proved by the X-ray crystallography. The bioactivity and the application of the probe for detection of OCl(-) in natural water system have been demonstrated. A plausible mechanism for oxidation of the sensor followed by hydrolysis is also proposed. The sensibility of the receptor toward OCl(-) was studied in absolute aqueous media, and the detection limit of hypochlorite-mediated oxidation to the receptor in nanomolar level makes this platform (RHHP) an ultrasensitive and unique system for OCl(-) oxidation.

Visual and near IR (NIR) fluorescence detection of Cr3+ in aqueous media via spirobenzopyran ring opening with application in logic gate and bio-imaging.

A new spirobenzopyran derivative (SPNH) was designed and synthesized which was applied in simultaneous colorimetric and NIR fluorescence detections for Cr(3+). This spirobenzopyran receptor is normally colorless in aqueous organic media but the formation of merocyanine occurs by Cr(3+) showing a yellow color. Here the formation of yellow color in UV-vis spectra and strong NIR fluorescence emission at 675 nm makes SPNH a good sensor for Cr(3+) ion. It is also found to be useful in cell imaging and in construction of logic gate. It shows INHIBIT gate in fluorescence and OR gate in absorption. To the best of our knowledge, this is the first report of NIR fluorescence emission of a spirobenzopyran derivative by Cr(3+) and its application to cell-biology and also in the logic gate.

Selective detection and bio-imaging of Pd2+ with novel 'C-CN' bond cleavage of cyano-rhodamine, cyanation with diaminomaleonitrile.

A new rhodamine based chemosensor, cyano-rhodamine, has been designed and synthesized with a green approach which shows a specific 'C-CN' bond breaking with the action of the Pd(2+) ion to produce the specific color and fluorescence of rhodamine 6G itself in solution and in HeLa cells.

The histone acetyl transferase LdHAT1 from Leishmania donovani is regulated by S-phase cell cycle kinase.

Histone acetyl transferases (HATs) are important histone modifiers that affect critical cellular processes like transcription, DNA replication and repairs through highly dynamic chromatin remodelling. Our earlier studies recognized LdHAT1 as a substrate of the S-phase cell cycle kinase LdCyc1-CRK3 from Leishmania donovani. Here, we confirm through site-directed mutagenesis that RXL-like cyclin-binding (Cy) motif dependent interaction of LdHAT1 with LdCyc1 is essential for its phosphorylation at a canonical Cdk target site by the kinase complex. LdHAT1 acetylates K10 residue of a peptide derived from L. donovani histone H4 N-terminal tail. Interestingly, phosphorylation of LdHAT1 by the S-phase kinase inhibits its H4K10 acetylation activity, implicating an important mechanism of periodic regulation of histone acetylation during cell cycle progression.

Identification of substrates of an S-phase cell cycle kinase from Leishmania donovani.

Despite the importance of cyclin-Cdk related kinases (CRK) in regulation of cell and life cycle of kinetoplastida parasites, only limited knowledge about their substrates are presently available. Here, the potential substrates were searched for an S-phase LdCyc1-CRK3 complex from Leishmania donovani based on the presence of Cdk target phosphorylation site together with the cyclin interacting Cy-motif in genome-derived putative protein sequences. Three substrates could be identified with one of them being a unique protein with no known homologues. Another identified substrate is similar to MYST family of histone acetyl transferase and the third one contains Ku-70 related conserved domains. All the substrates interact directly with LdCyc1 and are phosphorylated in a Cy-motif dependent manner suggesting the importance of Cy-motif for their functions.