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Yoav Eichen

Publications and source records attributed to Yoav Eichen.

9 recordsLinked to original sources
PubMed2007

Anion-binding properties of the tripyrrolemethane group: a combined experimental and theoretical study.

Tripyrrolemethane- and bistripyrrolemethane-containing systems were recently reported to be efficient and selective hosts for anions. Nevertheless, the basic intrinsic properties of tripyrrolemethane as a ligand for anions have not yet been explored. Here we report the study of the anion-binding properties of the tripyrrolemethane group. We applied a combined experimental and theoretical approach to determine the affinity of the tripyrrolemethane system for different anions in the gas phase, in solution and in the crystalline state. In the crystal, the tripyrrolemethane group forms a number of different complexes with the bromide ion, some involving the participation of more than one ligand species. Despite the very similar basicity of fluoride and dihydrogen phosphate, the tripyrrolemethane ligand exhibits a clear preference for the fluoride anion in solution, which indicates an anion-binding system and not merely deprotonation. Although the affinity of the tripyrrolemethane ligand for other ions was negligible in solution, gas-phase studies show that complexation with larger halide ions is favoured over complexation with fluoride.

Journal Article↗
PubMed2006

Sensitive and selective PET-based diimidazole luminophore for Zn(II) ions: a structure-activity correlation.

3-(3-Ethoxymethyl-1H-imidazol-2-yl)-3-(1-ethoxymethyl-1H-imidazol-2-yl)-3H-benzo[de]isochromen-1-one, 4, is a novel photoinduced electron transfer (PET) chemosensor that becomes fluorescent upon binding metal ions and shows a strong preference toward Zn(II) ions. The new bisimidazol PET sensor and its zinc complex were prepared and characterized in terms of their crystal structures, absorption and emission spectra, and orbital energy diagrams. Free 4 is a weakly luminescent species. On the basis of detailed DFT calculations, we suggest that the poor luminescence yield of free 4 originates from its orbital structure in which two pi-orbitals of the two imidazole rings, HOMO and HOMO-1, are situated between two pi-orbitals of the isochromene-one system, HOMO-2 and LUMO. The absorption and emission processes occur between the two pi-orbitals of the isochromene-one system, HOMO-2 and LUMO, and the two pi-imidazole orbitals serve as quenchers for the excited state of the molecule through nonradiative processes. Upon binding Zn(II) ions, 4 becomes a highly luminescent species having a luminescence maximum peaking at 375 nm (lambda(ex) = 329 nm). The significant 900-fold enhancement in luminescence upon binding of the Zn(II) ions is attributed to the stabilization of the pi-orbitals of the imidazole rings upon their engagement in new bonds with the zinc ion. The affinity of 4 to zinc ions in acetonitrile is found to be very high, Ka > 3 x 10(6) M(-1), while with other metals ions, the association constants are considerably weaker.

Benzopyrans↗
PubMed2006

Sensitive and selective photoinduced-electron-transfer-based sensing of alkylating agents.

Photoinduced-electron-transfer (PET)-based chemosensing is a very elegant way of reporting the presence of a guest species in solution. This method was successfully applied for the detection of different ionic species, such as cations, anions, and protons. Herein, we report on the application of the PET chemosensing concept for the efficient and selective detection of different alkylating agents. 2-(2-Dimethylaminoethyl)benzo[de]isoquinoline-1,3-dione (1) was found to be a highly selective and effective PET chemosensor that turns luminescent upon reacting with different alkylating agents. This PET-based system detected even rather weak alkylating agents, such as dichloromethane. A PET-based sensor that consists of 1 as the active component could detect rather low concentrations of alkylating agents in solution and in the gas phase.

Journal Article↗
PubMed2006

Directed DNA metallization.

Genes of interest can be selectively metallized via the incorporation of modified triphosphates. These triphosphates bear functions that can be further derivatized with aldehyde groups via the use of click chemistry. Treatment of the aldehyde-labeled gene mixture with the Tollens reagent, followed by a development process, results in the selective metallization of the gene of interest in the presence of natural DNA strands.

DNA, Complementary↗
PubMed2005

The construction of DNA molecules of figure-eight structure.

Using DNA molecules to construct a structural scaffold for nanotechnology is largely accepted. In this article, we report on two methods for constructing a figure-eight structure of DNA molecules having a relatively high yield that could be used further as a scaffold for nanotechnology applications. In the first method, two plasmids were constructed that, on digestion with a restriction endonuclease producing nicks in the corresponding sites and after heating, produced complementary single-stranded sequences, enabling the plasmids to hybridize to each other and forming a figure-eight structure. The formation of the figure-eight structure was analyzed by restriction analysis and gel electrophoresis as well as by atomic force microscopy. The second method makes use of the bacteriophage M13 that is obtained as either a single- or double-stranded circular DNA molecule. Two M13 molecules harboring complementary sequences were constructed and produced a figure-eight structure on hybridization. The methods described here could be used further for the construction of nanoelectronic devices.

Bacteriophage M13↗
PubMed2005

Reversible and persistent electrical bistability in single crystals of a self-assembled pi-conjugated tetraaryl system: a submicrometer scale electrical characterization.

A new pi-conjugated electroactive 4,4'-bipyridinium that bears two pyridazone self-complementary units was prepared and characterized. The new system readily assembles and forms at least two stable charge-transfer crystalline structures having a thermal population of unpaired electrons. The crystals of one phase exhibit electrical bistability, displaying either high (ON) and low (OFF) conductivity, at the same applied bias, depending on the electrical history of the system. The relation between the supramolecular structure of the crystals and their electrical properties is also discussed.

Journal Article↗
PubMed2004

Enol-enamine tautomerism in crystals of 1,3-bis(pyridin-2-yl) propan-2-one: a combined crystallographic and quantum-chemical investigation of the effect of packing on tautomerization processes.

The enolpyridine, OH-ketoenamime, NH equilibrium in crystals of 1,3-bis(pyridin-2-yl)propan-2-one was studied using temperature-dependent single-crystal X-ray diffraction. The relative population of the different tautomers was found to be sensitive to the temperature in the range of 100-300 K, illustrating the small thermodynamic difference between these two tautomers. This energy resemblance is partially attributed to the molecular packing in the crystal, where the molecules are arranged in the form of dimers. Ab initio electronic energy calculations (HF/6-31G** and MP2/6-31G**) reveal the effect of dimerization in the crystal on the electronic energy levels. Several tautomeric states were identified in the dimer of 1,3-bis(pyridin-2-yl)propan-2-one. A model is proposed in which four of these dimer states are populated in the crystal at ambient temperatures. The crystallographic data were treated according to this four-state dimer model, suggesting that the free energy of the OH-NH dimers is higher than that of the OH-OH dimers by 120 +/- 10 cal mol(-1) and that the NH-NH dimers are yet higher in free energy by 50 +/- 10 cal mol(-1).

Journal Article↗