Determination of association constant of host-guest supramolecular complex (molecular recognition of carbamazepine, antiseizure drug, with calix(4)arene)

A colorimetric and fluorescent sensor for the detection of both fluoride ions and trifluoroacetic acid based on acylhydrazone derivatives

An acylhydrazone-based colorimetric and fluorescent sensor (PAH-8) for the detection of fluoride ions (F-) and trifluoroacetic acid (TFA)/triethylamine (TEA) has been studied. PAH-8 solution and organogel are highly selective and sensitive to F- among various tested anions (F-, Cl-, Br-, AcO-, and H2PO4-) in DMSO. Upon addition of F-, the maximum absorption wavelength of PAH-8 in DMSO solution shows a big red shift from 377 nm to 464 nm with a marked color change from colorless to yellow, and the fluorescence emission also displays a red shift from 438 nm to 532 nm with its fluorescence emission switching from blue to yellow. Both Job's plot and the Benesi-Hildebrand plot confirm a 1 : 1 stoichiometric relationship between PAH-8 and F-. The detection limit of PAH-8 for the analysis of F- can reach 8.31 × 10-7 M. Very interestingly, an expeditious 'naked eye' detection of F- can be realized by the reversible gel-sol transition, along with a color change from slight yellow to bright red and fluorescence quenching. In addition, the cast film of PAH-8 (the solution was developed from the DMSO gel upon the addition of TBAF) can detect water in air by color switching or fluorescence on/off. In both solution and solid states, PAH-8 also exhibits obvious acid-base stimulated fluorescence conversion. The solution of PAH-8 can convert the blue emission into intensive sky blue emission after adding trifluoroacetic acid (TFA), and the solid film exhibits no fluorescence after fuming with TFA vapors, while fuming with triethylamine (TEA) vapors resulted in intensive green emission.

Inclusion of fluorophores in cyclodextrins: a closer look at the fluorometric determination of association constants by linear and nonlinear fitting procedures

The author discusses methods for the fluorometric determination of affinity constants by linear and nonlinear fitting methods. This is outlined in particular for the interaction between cyclodextrins and several anesthetic drugs including benzocaine. Special emphasis is given to the limitations of certain fits, and the impact of such studies on enzyme-substrate interactions are demonstrated. Both the experimental part and methods of analysis are well suited for students in an advanced lab.

New water soluble Hg2+ selective fluorescent calix[4]arenes: Synthesis and application in living cells imaging

The present study demonstrates the synthesis of water-soluble fluorescent calix[4]arenes (6 and 7) and its application in living cell imaging for Hg²⁺ detection at a low level. The synthesized fluorescent ligands 6 and 7 were characterized by ¹H NMR technique. The fluorescent study showed both water soluble ligands were Hg²⁺ selective and follow photo-induced electron transfer (PET) process. From the fluorimeter titration experiment detection limit was calculated as 1.14×10^-5 and 3.42×10^-5 for ligand 6 and 7, respectively. From the Benesi-Hildebrand plot binding constant values were evaluated as 666.7 and 733.3M^-1 for 6 and 7, respectively. The interactions between ligands 6 and 7 and Hg²⁺ were also demonstrated in living cells, SW-620, using Fluorescent Cell Imager. While ligands 6 and 7 alone show fluorescent properties, they loss their action with the presence of Hg²⁺ in SW-620 cells.