Naphthalene derived Schiff base as a reversible fluorogenic chemosensor for aluminium ions detection.

Schiff base (HNPD) was achieved by reacting 2-hydroxy-1-naphthaldehyde with N-phenyl-o-phenylenediamine in enthanol medium. The spectroscopic analyses were done to establish the formation of Schiff base apparently. Further, synthesized Schiff base conjugate was successfully used as a fluorogenic chemosensor to detect aluminium ions (Al3+) with high fluorescence amplification among the other interfering various metal ions. The limit of detection of 0.0248 × 10-6 M and a binding constant of 6.19 × 103 M-1 were obtained by the receptor HNPD for Al3+ detection. A high influence of intramolecular charge transfer kinetics was established to realize the selective responsiveness towards Al3+ ions. Density functional theory approximation formulated the band energy modulation and localization and delocalization of electron density for the HNPD and Al3+ complexation. The developed sensor ultimately inspected on the real soil and water samples and ascertained the practical ability of Al3+ ions detection of HNPD chemosensor.

A lead selective dimeric quinoline based fluorescent chemosensor and its applications in milk and honey samples, smartphone and bio-imaging.

Dimeric quinoline-based Schiff base was developed (DQS) for the specific detection of Pb2+ ion via fluorimetry. DQS coordinates with Pb2+, a variation in fluorescence intensity with enhanced radical blue shift was observed due to the restriction of CN rotation, CN isomerization, and photoinduced electron transfer (PET) mechanisms. In addition, the intramolecular charge transfer (ICT) from electron-donating morpholine to phenylene diamine acceptor linked quinoline bridge is responsible for the blue-shifted fluorescence enhancement in the DQS-Pb2+ complex. The binding stoichiometry of DQS: Pb2+ (1:2) was confirmed by host-guest titration and mass spectrometry. The limit of detection (LOD) of the DQS was found to be 1.3 × 10-7 M for Pb2+ ion. The DQS sensing ability of Pb2+ was further applied into milk and honey samples, smartphone, bio-imaging and to construct of an INHIBIT molecular logic gate.

Conformational study of palindromic tripeptides (GPG, IPI and KPK) in HIV-1 protease--a density functional theory study.

A comparative study has been carried out on three palindromic tripeptides Gly-Pro-Gly, Ile-Pro-Ile and Lys-Pro-Lys which were present in HIV protein along with their analogues applying density functional computation at B3LYP/6-31G* level of theory. Discrepancy from the structural analysis has been noted for all the systems and it was found to be more for amide capped structure at the C terminal of proline. The puckering amplitude A and Phase angle P of the pyrrolidine ring of proline in the chosen palindromic tripeptides and their analogues were calculated from the endocyclic torsion angles. The minimum energy conformers lying well within the prescribed region of proline were obtained for the derived compounds from potential energy surface scan mentioning that no role has been played by its terminal residues. This is further supported by the simulated amide bands identifying the helical structure for all three palindromic tripeptides signifying the importance of proline. The molecular properties such as stabilization energy, chemical hardness along with dipole moment were calculated and interpreted. The values of Calpha-H(s) and the peptide backbone N-Calpha-CO for all the selected conformers specify the three palindromic tripeptides to have a symmetrical achiral structure.