Rational design of biologically important chemosensors: a novel receptor for selective recognition of acetylcholine over ammonium cations

An Indole-based Chromofluorogenic Probe for Detection of Trivalent Al3+, Ga3+, In3+ and Fe3+ Ions

An easily synthesizable indole-derived chromofluorogenic probe InNS has been demonstrated for recognition of trivalent metal ions (i. e., Al3+, Ga3+, In3+ and Fe3+). Both UV-Vis and emission spectral studies have been employed to assess the cation sensing ability of InNS in semi-aqueous medium. This probe exhibited a chromogenic response for these metal ions, and the related change was accompanied with the appearance of a new absorption near 376 nm. An obvious color change from pale yellow to dark yellow could also be noticed upon addition of the aforementioned metal ions to the probe's solution. Distinctively from the UV-Vis analysis, the fluorescence behavior of InNS was completely different; it displayed a 'turn-on' fluorescence response for only Al3+ among all the studied cations. The detection limit and the association constant (Ka) for Al3+ were determined to be 12.5 nM and 6.85×106 M-1, respectively. A potential 1 : 1 binding mode of Al3+-InNS has been established based on Job's plot, 1H NMR and DFT analyses. The reversibility experiment was conducted using strongly chelating EDTA ion, and a corresponding logic gate has been devised. In terms of practical applications, the InNS has been utilized to detect Al3+ in human breast carcinoma (MCF-7) cell lines displaying promising 'turn-on' bioimaging experiments.

A novel pyrazole bearing imidazole frame as ratiometric fluorescent chemosensor for Al3+/Fe3+ ions and its application in HeLa cell imaging

New pyrazole bearing imidazole derivative was successfully synthesized and thoroughly characterized by various spectroanalytical techniques. The sensor DIBI shows a highly selective and sensitive fluorescent response with the addition of Al³⁺/Fe³⁺ ions in acetonitrile-water mixture. The strong fluorescent molecule exhibits a notable ratiometric emissions at 462 nm and 470 nm for Al³⁺ and Fe³⁺ ions, respectively (λ_ex = 280 nm). Job's plot studies conclude that the coordination between DIBI with Al³⁺/Fe³⁺ was 1:1 binding stoichiometry. The limit of detection of DIBI with Al³⁺/Fe³⁺ was calculated as 2.12 × 10^-7 M and 1.73 × 10^-6 M, respectively. The TD-DFT calculations further supported the photonics performances of the free probe and its complexes. The reversibility and reusability of the sensor molecule are studied using EDTA. The probe was used to track Al³⁺/Fe³⁺ in cancer cells via fluorescence microscopy.

A highly selective and sensitive fluorescent turn-on Al3+ chemosensor in aqueous media and living cells: experimental and theoretical studies

A highly selective and sensitive fluorescent chemosensor exhibited enhanced fluorescence in the presence of Al³⁺ and in living cells.

Estimating the binding ability of onium ions with CO2 and π systems: a computational investigation

The impact of increasing methyl substitution on onium ions in their complexes with CO₂ and aromatic systems has been analyzed using DFT calculations.

Selective deprotonation of oxazole and photoelectron imaging of the oxazolide anion

A photoelectron imaging study of the oxazolide anion obtained by selective deprotonation of oxazole at the C2 position is reported. The photodetachment transitions observed at 355, 392, and 532 nm are assigned to the ground state of the neutral oxazolyl σ radical. A Franck-Condon analysis of this transition aids in the first determination of the adiabatic electron affinity of oxazolyl, EA = 2.21 ± 0.02 eV. A vibrational progression with a frequency of 890 ± 80 cm(-1) is observed, corresponding to an in-plane ring distortion mode. The photoelectron angular distributions are analyzed using the mixed s-p model, shedding light on the hybrid character of the anion HOMO.

Amphipathic benzenes are designed inhibitors of the estrogen receptor alpha/steroid receptor coactivator interaction

We report here on the design, synthesis, and evaluation of small molecule inhibitors of the interaction between a steroid receptor coactivator and estrogen receptor alpha. These inhibitors are based upon an amphipathic benzene scaffold whose hydrophobic face mimics the leucine-rich alpha-helical consensus sequence on the steroid receptor coactivators that interacts with a shallow groove on estrogen receptor alpha. Several of these molecules are among the most potent inhibitors of this interaction described to date and are active at low micromolar concentrations in both in vitro models of estrogen receptor action and in cell-based assays of estrogen receptor-mediated coactivator interaction and transcription.

De novo design approach based on nanorecognition toward development of functional molecules/materials and nanosensors/nanodevices

For the design of functional molecules and nanodevices, it is very useful to utilize nanorecognition (which is governed mainly by interaction forces such as hydrogen bonding, ionic interaction, π-H/π-π interactions, and metallic interactions) and nanodynamics (involving capture, transport, and release of electrons, photons, or protons). The manifestation of these interaction forces has led us to the design and realization of diverse ionophores/receptors, organic nanotubes, nanowires, molecular mechanical devices, molecular switches, enzyme mimetics, protein folding/unfolding, etc. In this review, we begin with a brief discussion of the interaction forces, followed by some of our representative applications. We discuss ionophores with chemo-sensing capability for biologically important cations and anions and explain how the understanding of hydrogen bonding and π-interactions has led to the design of self-assembled nanotubes from calix[4]hydroquinone (CHQ). The binding study of neutral and cationic transition metals with the redox system of hydroquinone (HQ) and quinone (Q) predicts what kind of nanostructures would form. Finally, we look into the conformational changes between stacked and edge-to-face conformers in π-benzoquinone-benzene complexes controlled by alternating electrochemical potential. The resulting flapping motion illustrates a promising pathway toward the design of mobile nanomechanical devices.

Phenol vs Water Molecule Interacting with Various Molecules: σ-type, π-type, and χ-type Hydrogen Bonds, Interaction Energies, and Their Energy Components

The nature of interactions of phenol with various molecules (Y = HF, HCl, H2O, H2S, NH3, PH3, MeOH, MeSH) is investigated using ab initio calculations. The optimized geometrical parameters and spectra for the global energy minima of the complexes match the available experimental data. The contribution of attractive (electrostatic, inductive, dispersive) and repulsive (exchange) components to the binding energy is analyzed. HF favors sigma O-type H-bonding, while H2O, NH3, and MeOH favor sigma H-type H-bonding, where sigma O-/sigma H-type is the case when a H-bond forms between the phenolic O/H atom and its interacting molecule. On the other hand, HCl, H2S, and PH3 favor pi-type H-bonding, which are slightly favored over sigma O-, sigma H-, sigma H-type bonding, respectively. MeSH favors chi H-type bonding, which has characteristics of both pi and sigma H. The origin of these conformational preferences depending on the type of molecules is elucidated. Finally, phenol-Y complexes are compared with water-Y complexes. In the water-Y complexes where sigma O/sigma H-type involves the H-bond by the water O/H atom, HF and HCl favor sigma O-type, H2O involves both sigma O-/sigma H-type, and H2S, NH3, PH3, MeOH, and MeSH favor sigma H-type bonding. Except for HF, seven other species have larger binding energies with a phenol molecule than a water molecule.

Efficient Fluoride-Selective Fluorescent Host: Experiment and Theory

A new naphthalene derivative containing a urea group at the 1,8-position of naphthalene was synthesized and showed a unique absorption and fluorescence peak with fluoride ion. Calculations suggested that a new peak was attributed to the increased anionic character of urea nitrogen due to the strongly charged hydrogen bonding between fluoride and amide protons of the urea. The fluoride selectivity among halides (F(-), Cl(-), Br(-)) comes from the fact that the fluoride approaches much closer to the amide protons than other halides and resides in the cavity with fast dynamics. The nature of electronic transitions that were analyzed from the calculations by the collective electronic oscillator method also supports the anionic nature of the complex between host and fluoride.