A zinc (II) complex comprising an aminoethyl-nitropyridine-derived N,N,O-donor Schiff base ligand serves as an efficient ON-OFF probe for Cu(II).

A new fluorescent zinc (II) complex-based probe 1 encompassing a Schiff's base (E)-2-methoxy-6-((2-[5-nitropyridin-2-ylamino]ethylimino)methyl)phenol (HL) was designed, synthesized, and used for the highly selective detection of Cu2+ . Ligand HL and complex 1 were characterized using various spectroscopic techniques such as 1 H, 13 C-NMR, and FTIR spectroscopy, high-resolution mass spectronomy (HRMS), UV/visible light spectroscopy, and fluorescence studies. Ligand HL did not exhibit any considerable change in fluorescence in the presence of various cations. Notably, its Zn(II) complex 1 exhibited highly selective 'TURN-OFF' fluorescence signalling towards Cu2+ that remained uninterrupted with competing analytes. Probe 1 interacted with Cu2+ in 1:2 (1:Cu2+ ) stoichiometry as estimated through a Job's plot. Moreover, the selectivity of 1 was further confirmed through the interaction of the 1 + Cu2+ complex with some possible interfering metal ions inducing an insignificant response. Additionally, the association and quenching constant were determined to be 3.30 × 104 M-1 and 0.21 × 105 M-1 through the Benesi-Hildebrand method and Stern-Volmer plot, respectively.

Synthesis and Spectral Studies of Some Homo Dinuclear Lanthanide(III) Complexes of a Mesogenic Schiff Base.

A mesogenic Schiff base, N,N'-di(4-decyloxysalicylidene)-1',8'-diamino-3',6'-dioxaoctane (H2L) and a series of homo dinuclear lanthanide(III) complexes of the type [Ln2(LH2)3(NO3)4](NO3)2, (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho) were synthesized and characterized by elemental analysis, mass spectrometry, FTIR, and NMR spectral techniques. The IR and NMR spectral evidences imply bonding of a neutral bidentate H2L species through two phenolate oxygen atoms in its zwitterionic form to LnIII, rendering the overall geometry of the complexes as a seven-coordinate polyhedron - possibly distorted mono-capped octahedron. Differential scanning calorimetry (DSC) and polarizing optical microscopic (POM) studies reveal mesogenic properties (smectic-X, smectic-A and nematic mesophases) in the ligand over a wide range of temperature but none mesomorphism in the LnIII complexes synthesized under this study. Luminescence studies exhibit emissions of H2L and TbIII complex.

Occurrence, profile and spatial distribution of organochlorines pesticides in soil of Nepal: Implication for source apportionment and health risk assessment.

Nepal is a landlocked country located between world's two most populous countries-India and China where high level of organochlorines pesticides has been reported from multi-environmental matrices. In this study, we investigated the occurrence, distributions and profile of selected OCP chemicals in surface soil samples (N=72) from four major cities of Nepal. Overall, the sum of total OCPs in soil ranged from 20 to 250ng/g with Biratnagar being the most polluted site in Nepal. DDTs and endosulfans were the most abundant OCP chemicals in soil samples. The concentration of DDTs ranged from 8 to 230ng/g, 8-56ng/g, 8-63ng/g, and 8-27ng/g in surface soil, while endosulfans were in the range of 2.9-3.3ng/g, 2.8-8.7ng/g, 2.8-3.4ng/g, 2.8-3.2ng/g in Biratnagar, Kathmandu, Pokhara and Birgunj, respectively. The isomeric ratio of DDT and their metabolites suggested the ongoing usages of technical DDT as well as dicofol in this region. Lower ratio of α/ß-endosulfan indicated past application of endosulfans in Nepal. HCHs were less detected OCPs in soil sample accounting only 4-9% of ∑OCPs. The isomeric ratio of α-/γ-HCH indicated that the HCHs may be originated from mixed source of technical HCH as well as lindane use. Scattered plot of TOC and BC showed they were weakly and positively related with concentration of OCPs in soil. Health risk assessment modeling study of OCPs in soil suggested moderate cancer risk with ingestion being the most potential pathway of OCPs exposure.

Synthesis and characterization of lanthanide(III) complexes with a mesogenic Schiff-base, N,N'-di-(4-decyloxysalicylidene)-2',6'-diaminopyridine.

A mesogenic Schiff-base, N,N'-di-(4-decyloxysalicylidene)-2',6'-diaminopyridine, H2ddsdp (abbreviated as H2L3) that exhibits nematic mesophase, was synthesized and its structure studied by elemental analysis, mass spectrometry, NMR & IR spectral techniques. The Schiff-base, H2L3, upon condensation with hydrated lanthanide(III) nitrates, yields LnIII complexes of the general composition [Ln2(L3H2)3(NO3)4](NO3)2, where Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Ho. Among the metal complexes, only that of HoIII is found to be mesogenic with smectic-X and nematic phases. The IR and NMR spectral data imply a bi-dentate bonding of the Schiff-base in its zwitterionic form (as L3H2) to the LnIII ions through two phenolate oxygens, rendering the overall geometry of the complexes to seven-coordinated polyhedron, possibly distorted mono-capped octahedron.

Homo dinuclear lanthanide(III) complexes of a mesogenic Schiff-base, N,N'-di-(4-decyloxysalicylidene)-1',6'-diaminohexane: synthesis and characterization.

A mesogenic Schiff-base, N,N'-di-(4-decyloxysalicylidene)-1',6'-diaminohexane, H2ddsdh (abbreviated as H2L2) that exhibits smectic-B (SmB) mesophase, was synthesized and its structure studied by elemental analysis, mass spectrometry, NMR & IR spectral techniques. The Schiff-base, H2L2, upon condensation with hydrated lanthanide(III) nitrates, yields LnIII complexes of the general composition [Ln2(L2H2)3(NO3)4](NO3)2, where Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Ho. IR and NMR spectral data imply a bi-dentate bonding of the Schiff-base in its zwitterionic form (as L2H2) to the LnIII ions through two phenolate oxygens. The POM and DSC studies reveal that none of the LnIII complexes exhibits mesomorphism. Fluorescence studies show that the TbIII complex displays characteristic metal-centered fluorescence (solution state).