Zinc homeostasis and signaling in health and diseases: Zinc signaling

The essential trace element zinc (Zn) is widely required in cellular functions, and abnormal Zn homeostasis causes a variety of health problems that include growth retardation, immunodeficiency, hypogonadism, and neuronal and sensory dysfunctions. Zn homeostasis is regulated through Zn transporters, permeable channels, and metallothioneins. Recent studies highlight Zn’s dynamic activity and its role as a signaling mediator. Zn acts as an intracellular signaling molecule, capable of communicating between cells, converting extracellular stimuli to intracellular signals, and controlling intracellular events. We have proposed that intracellular Zn signaling falls into two classes, early and late Zn signaling. This review addresses recent findings regarding Zn signaling and its role in physiological processes and pathogenesis

Synthesis and photophysical studies of donor-acceptor substituted tetrahydropyrenes

The tetrahydropyrene derivatives 2-N,N-dimethylamino-7-nitro-4,5,9,10-tetrahydropyrene (1) and 2-N,N-dimethylamino-7-acetyl-4,5,9,10-tetrahydropyrene (2) were synthesized and characterized. Photophysical properties of these molecules were investigated in several solvents. The absorption spectrum of 1 shows a slight red shift with solvent polarity, whereas that of 2 remains more or less unchanged. Fluorescence spectra of these compounds exhibit large, solvent-polarity-dependent Stokes shifts. The Stokes shifts are correlated to E<SUB>T</SUB>(30) and E<SUP>N</SUP><SUB>T</SUB> parameters and were quantitatively analyzed by the Mataga-Liptay equation. Both compounds show low fluorescence quantum yields in cyclohexane. Nanosecond flash photolysis studies suggested that the low quantum yield in cyclohexane is due to intersystem crossing to a triplet state. In the case of 2, the fluorescence quantum yields are high in all other solvents. In the case of 1 fluorescence quantum yields are very low in polar solvents and this is explained by invoking a twisted intramolecular charge transfer state

Photoinduced intramolecular charge transfer in donor-acceptor substituted tetrahydropyrenes

Two novel donor-acceptor-substituted tetrahydropyrene derivatives (1 and 2, Chart 1) were synthesized and photophysical properties investigated in solvents of different polarities. These studies revealed the existence of an intramolecular charge transfer (ICT) excited state in these molecules. The fluorescence lifetime and quantum yield measurements revealed that emission occurs from a planar <SUP>1</SUP>CT state in all the solvents. The solvent-dependent Stokes shift values for 1 and 2 were analyzed by the Lippert-Mataga equation and Liptay's modified equation to obtain the excited-state dipole moment values. The CT nature of the emitting states is further confirmed by studies in acidic medium. Change of pH results in well-separated LE and CT fluorescence and absorption bands. It is suggested that this property can be utilized for ph-sensing applications

Photoinduced Intramolecular Charge Transfer in Donor−Acceptor Substituted Tetrahydropyrenes^†

Two novel donor−acceptor-substituted tetrahydropyrene derivatives (1 and 2, Chart ) were synthesized and photophysical properties investigated in solvents of different polarities. These studies revealed the existence of an intramolecular charge transfer (ICT) excited state in these molecules. The fluorescence lifetime and quantum yield measurements revealed that emission occurs from a planar 1CT state in all the solvents. The solvent-dependent Stokes shift values for 1 and 2 were analyzed by the Lippert−Mataga equation and Liptay's modified equation to obtain the excited-state dipole moment values. The CT nature of the emitting states is further confirmed by studies in acidic medium. Change of pH results in well-separated LE and CT fluorescence and absorption bands. It is suggested that this property can be utilized for pH-sensing applications

Probing Ternary Complex Equilibria of Crown Ether Ligands by Time-Resolved Fluorescence Spectroscopy

Ternary complex formation with solvent molecules and other adventitious ligands may compromise the performance of metal-ion-selective fluorescent probes. As Ca­(II) can accommodate more than 6 donors in the first coordination sphere, commonly used crown ether ligands are prone to ternary complex formation with this cation. The steric strain imposed by auxiliary ligands, however, may result in an ensemble of rapidly equilibrating coordination species with varying degrees of interaction between the cation and the specific donor atoms mediating the fluorescence response, thus diminishing the change in fluorescence properties upon Ca­(II) binding. To explore the influence of ligand architecture on these equilibria, we tethered two structurally distinct aza-15-crown-5 ligands to pyrazoline fluorophores as reporters. Due to ultrafast photoinduced electron-transfer (PET) quenching of the fluorophore by the ligand moiety, the fluorescence decay profile directly reflects the species composition in the ground state. By adjusting the PET driving force through electronic tuning of the pyrazoline fluorophores, we were able to differentiate between species with only subtle variations in PET donor abilities. Concluding from a global analysis of the corresponding fluorescence decay profiles, the coordination species composition was indeed strongly dependent on the ligand architecture. Altogether, the combination of time-resolved fluorescence spectroscopy with selective tuning of the PET driving force represents an effective analytical tool to study dynamic coordination equilibria and thus to optimize ligand architectures for the design of high-contrast cation-responsive fluorescence switches