Ponnaboina Thirupathi

Selective and sensitive ratiometric detection of Hg(II) ions using a simple amino acid based sensor.

Synthesis of a novel pyrene derivative sensor (Py-Met) based on amino acid and its fluorescent behavior for Hg(II) in water was investigated. Upon Hg(II) binding, the Py-Met-bearing sulfonamide group exhibited a considerable excimer emission at 480 nm along with a decrease of monomer emission at 383 nm. Py-Met allows a selective and sensitive ratiometric detection of Hg(II) without any interference from other metal ions.

Friedel−Crafts Arylation Reactions of N-Sulfonyl Aldimines or Sulfonamidesulfones with Electron-Rich Arenes Catalyzed by FeCl3·6H2O: Synthesis of Triarylmethanes and Bis-heteroarylarylmethanes

The FeCl(3) x 6H(2)O-catalyzed Friedel-Crafts arylation reactions of N-sulfonyl aldimines or sulfonamidesulfones with electron-rich arenes and heteroarenes, which lead to the formation of triarylmethanes and bis-heteroarylarylmethanes, are developed. The use of mild reaction conditions, low catalytic loading, high yield, and single step synthesis are the advantages of the present procedure.

Highly selectively monitoring heavy and transition metal ions by a fluorescent sensor based on dipeptide

Fluorescent sensor (DMH) based on dipeptide was efficiently synthesized in solid phase synthesis. The dipeptide sensor shows sensitive response to Ag(I), Hg(II), and Cu(II) among 14 metal ions in 100% aqueous solution. The fluorescent sensor differentiates three heavy metal ions by response type; turn on response to Ag(I), ratiometric response to Hg(II), and turn off detection of Cu(II). The detection limits of the sensor for Ag(I) and Cu(II) were much lower than the EPAs drinking water maximum contaminant levels (MCL). Specially, DMH penetrated live cells and detected intracellular Ag(+) by turn on response. We described the fluorescent change, binding affinity, detection limit for the metal ions. The study of a heavy metal-responsive sensor based on dipeptide demonstrates its potential utility in the environment field.

InBr3: a versatile catalyst for the different types of Friedel-Crafts reactions.

Mild and efficient InBr(3)-catalyzed Friedel-Crafts alkylation of heteroaromatic or electron-rich aromatic compounds with alpha-amido sulfones at room temperature in CH(2)Cl(2) has been developed. The products undergo further Friedel-Crafts alkylation with heteroaromatic or electron-rich aromatic compounds leading to unsymmetrical or bis-symmetrical triaryl methanes in good yield. Alpha-amido sulfones are employed for the synthesis of the unsymmetrical and bis-symmetrical triaryl methanes. The use of mild reaction condition, low catalytic loading, and high yield are the advantages of the present procedures.

Pyrene Excimer-Based Peptidyl Chemosensors for the Sensitive Detection of Low Levels of Heparin in 100% Aqueous Solutions and Serum Samples

Fluorescent chemosensors (1 and 2, Py-(Arg)nGlyGlyGly(Arg)nLys(Py)-NH2, n = 2 and 3) bearing two pyrene (Py) labeled heparin-binding peptides were synthesized for the sensitive ratiometric detection of heparin. The peptidyl chemosensors (1 and 2) sensitively detected nanomolar concentrations of heparin in aqueous solutions and in serum samples via a ratiometric response. In 100% aqueous solutions at pH 7.4, both chemosensors exhibited significant excimer emission at 486 nm as well as weak monomer emission in the absence of heparin. Upon the addition of heparin into the solution, excimer emission increased with a blue shift (10 nm) and monomer emission at 376 nm decreased. The chemosensors showed a similar sensitive ratiometric response to heparin independent of the concentration of the chemosensors. The peptidyl chemosensors were applied to the ratiometric detection of heparin over a wide range of pH (1.5-11.5) using the excimer/momomer emission changes. In the presence of serum, 1 and 2 displayed significant monomer emission at 376 nm with relatively weak excimer emission and the addition of heparin induced a significant increase in excimer emission at 480 nm and a concomitant decrease in monomer emission. The enhanced ratiometric response to heparin in the serum sample was due to the interactions between the peptidyl chemosensors and serum albumin in the serum sample. The detection limits of 2 for heparin were less than 1 nM in 100% aqueous solutions and serum samples. The peptidyl chemosensors bearing two heparin-binding sites are a suitable tool for the sensitive ratiometric detection of nanomolar concentrations of heparin in 100% aqueous solutions and serum samples.

A new peptidyl fluorescent chemosensors for the selective detection of mercury ions based on tetrapeptide.

A novel peptidyl chemosensor (PySO2-His-Gly-Gly-Lys(PySO2)-NH2, 1) was synthesized by incorporation of two pyrene (Py) fluorophores into the tetrapeptide using sulfonamide group. Compound 1 exhibited selective fluorescence response towards Hg(II) over the other metal ions in aqueous buffered solutions. Furthermore, 1 with the potent binding affinity (Kd=120 nM) for Hg(II) detected Hg(II) without interference of other metal ions such as Ag(I), Cu(II), Cd(II), and Pb(II). The binding mode of 1 with Hg(II) was investigated by UV absorbance spectroscopy, (1)H NMR titration experiment, and pH titration experiment. The addition of Hg(II) induced a significant decrease in both excimer and monomer emissions of the pyrene fluorescence. Hg(II) interacted with the sulfonamide groups and the imidazole group of His in the peptidyl chemosensor and then two pyrene fluorophores were close to each other in the peptide. The decrease of both excimer and monomer emission was mainly due to the excimer/monomer emission change by dimerization of two pyrene fluorophores and a quenching effect of Hg(II).

Fluorescent peptide-based sensors for the ratiometric detection of nanomolar concentration of heparin in aqueous solutions and in serum

New fluorescent peptide-based sensors (1-3) for monitoring heparin in serum sample were synthesized using short peptides (1∼3mer) as a receptor. The peptide-based sensors (2 and 3) showed a sensitive ratiometric response to heparin both in aqueous buffered solution (10 mM HEPES, pH 7.4) and in 2% human serum sample by increase of excimer emission of pyrene at 480 nm and concomitant decrease of monomer emission of pyrene at 376 nm, whereas the peptide-based sensor 1 showed a turn off response only by decrease of monomer emission at 376 nm. 2 and 3 exhibited excellent selectivity toward heparin among various anions and competitors of heparin including chondroitin 4-sulfate (ChS) and hyaluronic acid (HA). Peptide-based sensor 3 showed a more sensitive response to heparin than 2. The detection limit of 3 was determined as 36 pM (R(2) = 0.998) for heparin in aqueous solution and 204 pM (R(2) = 0.999) for heparin in aqueous solutions containing 2% human serum. The peptide-based sensors, 2 and 3 provided a practical and potential tool for the detection and quantification of heparin in real biological samples.

A ratiometric fluorescent detection of Zn(II) in aqueous solutions using pyrene-appended histidine.

A fluorescent chemosensor, Py-His, based on histidine was easily synthesized in solid phase synthesis. Py-His displayed a highly sensitive ratiometric response to Zn(II) with potent binding affinity (Ka = 1.17 × 10(13)M(-2)) in aqueous solutions. The detection limit of Py-His for Zn(II) was calculated as 80.8 nM. Moreover, Py-His distinguished Zn(II) and Hg(II) by different ratiometric response type; the chemosensor showed a more enhanced increase of excimer emission intensity to Zn(II) than Hg(II). Upon addition of Ag(I) and Cu(II), Py-His showed a turn-off response mainly due to the quenching effect of these metal ions. The binding stoichiometry (2:1 or 1:1) of Py-His to target metal ions played a critical role in the fluorescent response type (ratiometric and turn off response) to target metal ions. The role of imidazole group of Py-His for ratiometric detection of Zn(II) was proposed by pH titration experiments.