Schiff's Bases and Crown Ethers as Supramolecular Sensing Materials in the Construction of Potentiometric Membrane Sensors

Anion recognition by simple chromogenic and chromo-fluorogenic salicylidene Schiff base or reduced-Schiff base receptors

This review contains extensive application of anion sensing ability of salicylidene type Schiff bases and their reduced forms having various substituents with respect to phenolic OH group. Some of these molecular systems behave as receptor for recognition or sensing of various anions in organic or aqueous-organic binary solvent mixture as well as in the solid supported test kits. Development of Schiff base or reduced Schiff base receptors for anion recognition event is commonly based on the theory of hydrogen bonding interaction or deprotonation of phenolic -OH group. The process of charge transfer (CT) or inhibition of excited proton transfer (ESIPT) or followed by photo-induced electron transfer (PET) lead to naked-eye color change, UV-vis spectral change, chemical shift in the NMR spectra and fluorescence spectral modifications. In this review we have tried to discuss about the anion sensing properties of Schiff base or reduced Schiff base receptors.

Design and Synthesis of a Pyridine Based Chemosensor: Highly Selective Fluorescent Probe For Pb2+

A pyridine based imine-linked chemosensor has been synthesized and evaluated its binding affinity with library of transition metal ions. It has prominent selectivity towards Pb2+ among other metal ions in DMF/H2O (9:1, v/v) solvent system. The 1:1 stoichiometric was confirmed by job's plot and has a binding constant (Ka) = 5.142 × 103 M-1 on fluorescence. A B3LYP/6-31G and B3LYP/LanL2DZ basis sets were employed for optimization of 3 and 3.Pb2+.

2-{[3-Chloro-4-(4-chloro-phen-oxy)phen-yl]imino-meth-yl}-4-nitro-phenol

In the title compound, C₁₉H₁₂Cl₂N₂O₄, the imine bond length of 1.257 (6) Å is typical of a double bond. The dihedral angle between the para-nitro benzene ring and the central benzene ring is 12.06 (3)° and that between the central benzene and the para-chloro benzene ring is 73.81 (2)°. An intra­molecular O—H⋯N hydrogen bond generates an S(6) ring motif. In the crystal, mol­ecules are linked together by two pairs of C—H⋯O interactions (to the same O atom acceptor), forming inversion dimers. A short Cl⋯Cl contact [3.232 (4) Å] is observed.

Development and applications of paper-based electrospray ionization-mass spectrometry for monitoring of sequentially generated droplets

In this work, sub-microlitre droplets were generated by gravity and electrostatic attraction using a capillary tube. The parameters affecting the sizes and frequency of the droplets were investigated. The volume of droplets could be controlled in the range from 0.7 μL to 2.4 μL and the time interval from 15 s to 60 s with appropriate parameters. Combining the droplets with on-line mass spectrometry (MS) via paper-based electrospray ionization (ESI), a steady flow of solvent was delivered by the capillary tube to the base-side of the paper, which maintained the consistent state of the electrospray. With this approach, each droplet produced a peak in the ion chromatogram. Relative standard deviations (RSDs) not higher than 9% for both the intensities and the time intervals were achieved when using rhodamine 6G and l-phenylalanine as model analytes. The present method was utilized for the monitoring of the amine-aldehyde condensation reaction of butylamine and benzaldehyde. Direct analysis and distribution of molecules in fruits were also performed, which demonstrated the potential application of this approach.

4-Chloro-2-[(4-chloro-benzyl-idene)amino]-phenol

In the title Schiff base compound, C(13)H(9)Cl(2)NO, the mol-ecule displays an E conformation about the imine C=N double bond, with a dihedral angle of 8.09 (11)° between the two benzene rings. In the crystal, mol-ecules are linked by a single O-H⋯O hydrogen bond, giving one-dimensional chains which extend along (100).

Molecularly imprinted polymers for (90)Sr urine bioassay

A molecularly imprinted polymer (MIP) comprising dicyclohexano-18-crown-6 (DCH18C6) was synthesized as a Sr-selective sorbent for urine bioassay purposes. MIP particles (326 ± 2 nm diameter) were formed using acetone and acetonitrile (1:3 v/v) as the porogen, methacrylic acid (MAA) as the functional monomer and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. The DCH18C6-MIP particles were impregnated with additional DCH18C6 and treated further with NaOH to attain better binding affinity for Sr(2+). The effects of pH, ionic strength and amount of particles were evaluated for optimal extraction of (90)Sr(2+) from urine samples, as measured by liquid scintillation analysis (LSA). After up to 94% of (90)Y was removed by precipitation with TiO(2), DCH18C6-MIP particles were applied for selective SPE of (90)Sr remaining in the urine matrix for final LSA.