Synthesis of Flavin-Calix[4]arene Conjugate Derivatives

Novel An Efficient Fluorescent Probe Based on Calix[4]triazacrown-5 With Naphthalimide Group for Co2+, Cd2+ and Dopamine Detection

A novel naphthalimide-substituted calix[4]triazacrown-5 (Nap-Calix) at cone conformation was designed and synthesized to employ as a fluorescent probe, which enables the simultaneously detection of Co2+ and Cd2+ metal ions as well as dopamine (DA). 1H-NMR, 13C-NMR, ESI-MS and elemental analysis techniques were carried out to characterize its structure. Cation binding property of Nap-Calix against various metal ions such as Ba2+, Co2+, Ni2+, Pb2+, Zn2+, and Cd2+ exhibited that the sensor selectively binds to Co2+ and Cd2+ metal ions with a remarkable affinity. Introduction of Co2+ and Cd2+ metal ions to a solution of Nap-Calix in DMF/water (1:1, v/v) resulted with a new emission band at 370 nm when excited at 283 nm. In addition, the fluorescence sensing affinity of the probe Nap-Calix against a catecholamine neurotransmitter (dopamine) was investigated in a wide range of concentration of DA (0-0.1 mmol L-1) in 50% DMF/PBS (pH = 5.0). The fluorescence intensity of Nap-Calix, with excitation/emission peaks at 283/327 nm, is highly enhanced by DA. It was also observed that Nap-Calix exhibits excellent fluorescence behavior towards DA with a very low detection limit as 0.21 µmol L-1.

A highly selective and sensitive fluorescence probe for dopamine determination based on a bisquinoline-substituted calix[4]arene carboxylic acid derivative

Dopamine (DA) at normal levels in the human body exhibits a high potential for maintaining a proper neuron network. However, their abnormalities in humans can bring out aggressive disorders such as Schizophrenia, hypertension, Tourette's syndrome, Alzheimer's disease, bipolar depression, Parkinson's disease, drug addiction and attention-deficit hyperactivity diseases. Hence, in this study, a bis-quinoline-substituted calix[4] arene carboxylic acid derivative (Quin-Calix-CO2H) at cone conformation was developed as an effective fluorescent sensor for the detection of a catecholamine neurotransmitter (dopamine). The structure of Quin-Calix-CO2H was confirmed using 1H-NMR, 13C-NMR, ESI-MS and elemental analysis techniques. The calixarene-based fluorescent sensor (Quin-Calix-CO2H) has shown fluorescence emission at 404 nm under the excitation of 270 nm. Further, biomolecules binding property of Quin-Calix-CO2H against various biomolecules such as L-cysteine (L-Cys), α-D-glucose (D-Glu), (+)-sodium-L-ascorbate (SAA), urea (UR), L-alanine (L-Ala) and dopamine (DA) exhibited that the fluorescent sensor enables selectively and sensitively detection for DA with a remarkable affinity. The probe Quin-Calix-CO2H has shown fluorescence quenching towards DA concentration ranging from 0 to 4.0 µM with a very low limit of detection (LOD) of 88.5 nmol L-1. In addition, the binding constant and stoichiometry as well as the mechanism of quenching have been also determined from the fluorescence data.Communicated by Ramaswamy H. Sarma.

Synthesis and electronic properties of π-extended flavins

Flavin derivatives with an extended π-conjugation were synthesized in moderate to good yields from aryl bromides via a Buchwald-Hartwig palladium catalyzed amination protocol, followed by condensation of the corresponding aromatic amines with violuric acid. The electronic properties of the new compounds were investigated by absorption and emission spectroscopy, cyclic voltammetry, density functional theory (DFT) and time dependent density functional theory (TDDFT). The compounds absorb up to 550 nm and show strong luminescence. The photoluminescence quantum yields ϕPL measured in dichloromethane reach 80% and in PMMA (poly(methyl methacrylate)) 77%, respectively, at ambient temperature. The electrochemical redox behaviour of π-extended flavins follows the mechanism previously described for the parent flavin.

Calixarene assembly with enhanced photocurrents using P(SNS-NH2)/CdS nanoparticle structure modified Au electrode systems

Two novel calix[n]arene-adorned gold electrodes producing high photocurrent intensities were successfully constructed.

Enhanced catalysis and enantioselective resolution of racemic naproxen methyl ester by lipase encapsulated within iron oxide nanoparticles coated with calix[8]arene valeric acid complexes

In this study, two types of nanoparticles have been used as additives for the encapsulation of Candida rugosa lipase via the sol–gel method.