Spectroscopic and electrochemical studies of two distal diethyl ester azocalix[4]arene derivatives

Azocalix[4]arene with three distal ethyl ester residues as a highly selective chromogenic sensor for Ca2+ ions

Three azocalix[4]arenes with distal ethyl ester residues, 5-phenylazo-25,26,27-tris[(ethoxycarbonyl)methoxy]-28-hydroxycalix[4]arene (2), 5-(o-methylphenyl)azo-25,26,27-tris[(ethoxycarbonyl)methoxy]-28-hydroxycalix[4]arene (3), 5-(p-Methylphenyl)azo-25,26,27-tris[(ethoxycarbonyl)methoxy]-28-hydroxycalix[4]arene (4), were synthesized and their binding properties with metal ions were investigated by ultraviolet (UV)/visible spectroscopy. The chromogenic behavior of these compounds upon metal ion complexation indicates a specific selectivity toward Ca2+ ion in the presence of other cations tested. The stoichiometry of 3 to Ca2+ ion in the complex is 1:1 and the stability constant of the complex is 1.28×104m−1.

Spectrophotometric and electrochemical study for metal ion binding of azocalix[4]arene bearing p-ethylester group

The complexation behavior of diazophenylcalix[4]arene bearing para-ethylester group (p-EAC) for alkali, alkaline earth, various heavy and transition metal ions (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Cr³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Pb²⁺) was investigated by spectrophotometric and electrochemical methods in CH₃CN. p-EAC exhibits decreased absorbance at 353nm in the presence of Cr³⁺, Fe²⁺, Pb²⁺, and Cu²⁺. The spectra of p-EAC showed bathochromic shift in absorption maximum on the addition of Cr³⁺, Fe²⁺, or Pb²⁺ with decreasing order of absorbance (Cr³⁺>Fe²⁺>Pb²⁺), and on the other hand, hypsochromic shift on the addition of Cu²⁺. This leads to the selective coloration from light green to orange and colorless for Cr³⁺ and Cu²⁺ that can be detected by the naked eye, respectively. In electrochemistry experiments, p-EAC also showed two different types of voltammetric changes toward Cr³⁺, Fe²⁺, or Pb²⁺, and toward Cu²⁺, whereas no significant changes occurred in the presence of the other metal ions. Nonlinear fitting curve procedure was used to determine a logarithmic value of 5.20, 4.92, 3.54 and 4.80 for the stability constants of the complex of p-EAC with Cr³⁺, Fe²⁺, Pb²⁺, and Cu²⁺, respectively.

Spectroscopic properties of some new azo-azomethine ligands in the presence of Cu(2+), Pb(2+), Hg(2+), Co(2+), Ni(2+), Cd(2+) and Zn(2+) and their antioxidant activity

Due to their potential applicability as selective receptors in optical sensors, two novel azo Schiff-base derivatives I and II are synthesized and characterized with FT-IR, (1)H NMR and elemental analysis techniques. The optical response of azo groups of I and II towards Ni(2+), Co(2+), Cu(2+), Pb(2+), Hg(2+), Zn(2+) and Cd(2+) metal ions is studied in DMSO by UV-vis spectroscopy. The absorption spectra of both compounds with cations show marked changes. In solution, azo Schiff-base I produces a cation induced 95nm blue shift for Cu(2+) ion from 555nm to 460nm with remarkable color change from red to yellow. Whereas no significant color change is observed upon addition of studied metal cations to the solution of ligand II or other metal ions to the solution of ligand I. Furthermore, Job's plot indicate 1:1 binding-stoichiometry for I with Cu(2+) ion and Benesi-Hildebrand plot is used for the determination of its association constant. Therefore receptor I is highly specific for copper ions in DMSO solution. Finally, the study of antioxidant properties of I and II with DPPH method reveals high and significant activities.

Spectrophotometric and voltammetric characterization of a novel selective electroactive chemosensor for Mg2+

A novel azocalix[4]arene derivative, 5,11,17,23-tetrakis[(acetophenone)azo]-25,26,27,28-tetrahydroxycalix[4]arene (APC4), containing acetophenone azo groups at the upper rim was synthesized as a chemosensor. Its binding and sensing properties with alkali and alkaline earth metal ions (Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+) were investigated by UV-vis spectrophotometric and voltammetric techniques. The stoichiometric ratio and the association constant were determined spectrophotometrically as 1:1 and (1.94±0.31)×105 L mol−1 for the complex between Mg2+ and the chemosensor, respectively. Moreover, it was shown that the interaction between Mg2+ and the APC4 occurred by means of the phenol groups at the lower rim by voltammetric methods. The results of spectrophotometric and voltammetric experiments showed that the chromogenic chemosensor has high selectivity towards Mg2+ among the other used metal ions, especially the interfering Ca2+ ion.

Optical spectroscopy studies of the complexation of bis(azophenol)calix[4]arene possessing chromogenic donors with Ni2+, Co2+, Cu2+, Pb2+ and Hg2+

Due to their potential applicability as selective receptors in electrochemical or optical sensors, a bis(azophenol)calix[4]arene derivative H(2)L has been investigated. The complexation properties of this molecule towards Ni(2+) and Co(2+) metal ions has been studied. It is revealed that this ligand exhibits tetradentate with N(2)O(2) core when bound to Ni (II) or Co (II) metal ion. The optical response of azo groups of H(2)L towards Ni(2+), Co(2+), Cu(2+), Pb(2+) and Hg(2+) metal ions has been investigated in DMSO by UV-vis spectroscopy. The absorption spectra of calix[4]arene with cations show marked changes, especially for Co(2+) ion. Furthermore, Job's plot indicate 1:1 binding-stiochiometry for calix[4]arene with Co(2+) ion and Benson-Hilderbrand plot is used for the determination of its association constant. The investigation of UV-vis spectra of chromogenic calix[4]arene in different solvents shows that cis-trans isomerization of azo groups probably depends on kind of solvent. Also the different between the polarity and viscosity of organic solvents used is likely responsible for the changes of the band shape of the spectra.