Fluorescent sensors for the detection of chemical explosives are in great demand. It is shown herein that the fluorescence of ZnL* (H2L=N,N'-phenylene-bis-(3,5-di-tert-butylsalicylideneimine)) is quenched in solution by nitroaromatics and 2,3-dimethyl-2,3-dinitrobutane (DMNB), chemical signatures of explosives. The relationship between the structure and fluorescence of ZnL is explored, and crystal structures of three forms of ZnL(base), (base=ethanol, tetrahydrofuran, pyridine) are reported, with the base=ethanol structure exhibiting a four-centered hydrogen bonding array. Solution structures are monitored by 1H NMR and molecular weight determination, revealing a dimeric structure in poor donor solvents which converts to a monomeric structure in the presence of good donor solvents or added Lewis bases to form five-coordinate ZnL(base). Fluorescence wavelengths and quantum yields in solution are nearly insensitive to monomer-dimer interconversion, as well as to the identity of the Lewis base; in contrast, the emission wavelength in the solid state varies for different ZnL(base) due to pi-stacking. Nitroaromatics and DMNB are moderately efficient quenchers of ZnL*, with Stern-Volmer constants KSV=2-49 M-1 in acetonitrile solution.
"Recently the P 4 O 7 4− detection has become an important issue for cancer research and for rheumatological disorder that arises due to the accumulation of crystals of calcium pyrophosphate dehydrates in the connective tissues . Knapp et al. has also used a fluorescent Zn (salicylaldimine) sensor array for the discrimination of nitro aromatics and explosives    . "
[Show abstract][Hide abstract] ABSTRACT: A benzothiazole functionalized chemosensor L1, exhibited colorimetric as well as fluorometric response to Zn2+ ion at physiological pH based on CHEF process. Selective naked eye detection of Zn2+ ion over most of the biologically important cations was also demonstrated. Sensing of biologically hazardous cadmium ion was also possible with L1. Further, both the zinc and cadmium ensembles of L1 were found to respond P4O74− and H2PO4− anion among other important biological anions and nucleotides via fluorescence quenching. Chemosensor L1, was also found to be reversible and recyclable toward Zn2+ and pyrophosphate ions over more than six cycles and responds to a INHIBIT logic gate. NMR titration and theoretical calculations were also conducted to understand the sensing behavior of L1.
Sensors and Actuators B Chemical 06/2014; 202:788-794. DOI:10.1016/j.snb.2014.06.012 · 4.10 Impact Factor
"Fig. 2. Normalized fluorescence emission spectra of 1 × 10 − 5 M Zn–salophen in CHCl 3 (dashed line), in POPC liposomes (solid line) and in POPC liposomes after 120 h from LUV preparation (dash dotted line). have been obtained by Knapp and coworkers for several Zn–salophen complexes in acetonitrile . The ability to incorporate hydrophobic and amphiphilic molecules in the monomeric form within the bilayer is one of the typical properties of liposomes as carriers  . "
[Show abstract][Hide abstract] ABSTRACT: A Zn-salophen complex has been incorporated into POPC large unilamellar liposomes (LUV) obtained in phosphate buffer at pH 7.4. Fluorescence optical microscopy and anisotropy measurements show that the complex is located at the liposomal surface, close to the polar headgroups. The interaction of the POPC phosphate group with Zn(2+) slowly leads to demetallation of the complex. The process follows first order kinetics and rate constants have been measured fluorimetrically in pure water and in buffered aqueous solution. The coordination of the phosphate group of monomeric POPC with salophen zinc also occurs in chloroform as detected by ESI-MS measurements. The effect of the Zn-salophen complex on the stability of POPC LUV has been evaluated at 25°C by measuring the rate of release of entrapped 5(6)-carboxyfluorescein (CF) in the presence and in the absence of Triton X-100 as the perturbing agent. It turns out that the inclusion of the complex significantly increases the stability of POPC LUV.
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