Cross-Talks Between Sulfane Sulfur and Thiol at a Zinc(II) Site

Transformations of sulfane sulfur compounds (e. g. organic polysulfides (R−S_n−R, n>2) and elemental sulfur (S₈)) play pivotal roles in the biochemical landscape of sulfur, and thus supports signaling activities of H₂S. Although a number of previous reports illustrate amine mediated reactions of S₈ and thiol (RSH) yielding R−S_n−R, this report illustrates that a tripodal [Zn^II] complex [( Bn₃Tren )Zn^II−OH₂](ClO₄)₂ ( 1 ) facilitates the reactions of sulfane sulfur and thiol (RSH), thereby offering an amine-free biologically relevant complementary route. UV-vis monitoring of the reactions and a set of control experiments underline the definitive role of [Zn^II] coordination motif in the reactions of sulfane sulfur (e. g. S₈ and R−S_n−R) with RSH. Detailed investigations (UV-vis, NMR, ESI-MS, intermediate trapping, and TEMPO radical interference experiments) disclose the key differences in the [Zn^II] versus previously known amine mediated routes. Moreover, the persulfide (RSS⁻) trapping experiments using 1-fluoro-2,4-dinitrobenzene (F-DNB) reveal the intermediacy of RSS⁻ species in the [Zn^II] mediated reactions of sulfane sulfur and thiol, thereby demonstrating [Zn^II] assisted persulfidation of thiol in the presence of sulfane sulfur species. Of broader impact, this study underscores the feasible influence of biologically relevant [Zn^II] coordination motifs (e. g. carbonic anhydrase) on the sulfane sulfur chemistry in biology.     

Towards a New Family of Photoluminescent Organozinc 8‐Hydroxyquinolinates with a High Propensity to Form Noncovalent Porous Materials

We report on investigations of reactions of tBu₂Zn with 8‐hydroxyquinoline (q‐H) and the influence of water on the composition and structure of the final product. A new synthetic approach to photoluminescent zinc complexes with quinolinate ligands was developed that allowed the isolation of a series of structurally diverse and novel alkylzinc 8‐hydroxyquinolate complexes: the trinuclear alkylzinc aggregate [tBuZn(q)]₃ ( 1₃ ), the pentanuclear oxo cluster [(tBu)₃Zn₅(μ₄‐O)(q)₅] ( 2 ), and the tetranuclear hydroxo cluster [Zn(q)₂]₂[tBuZn(OH)]₂ ( 3 ). All compounds were characterized in solution by ¹H NMR, IR, UV/Vis, and photoluminescence (PL) spectroscopy, and in the solid state by X‐ray diffraction, TGA, and PL studies. Density functional theory calculations were also carried out for these new Zn^II complexes to rationalize their luminescence behavior. A detailed analysis of the supramolecular structures of 2 and 3 shows that the unique shape of the corresponding single molecules leads to the formation of extended 3D networks with 1D open channels. Varying the stoichiometry, shape, and supramolecular structure of the resulting complexes leads to changes in their spectroscopic properties. The close‐packed crystal structure of 1₃ shows a redshifted emission maximum in comparison to the porous crystal structure of 2 and the THF‐solvated structure of 3 .     

Enantioselective Reaction of 2H-Azirines with Phosphite Using Chiral Bis(imidazoline)/Zinc(II) Catalysts

The first highly enantioselective nucleophilic addition reaction of phosphites with 2H-azirines has been developed. The reaction was applied to various 3-substituted 2H-azirines using novel chiral bis(imidazoline)/Zn^II catalysts to afford products in good yield with high enantioselectivity. The transformation of the obtained optically active aziridines showed that 2H-azirines act as either α,β- or β,β-dicarbocationic amine synthons.     

Rapid and convenient conversion of nitroarenes to anilines under microwave conditions using nonprecious metals in mildly acidic medium

Nitroarenes are reduced to the corresponding aniline derivatives using iron or zinc under mild conditions under microwave heating conditions. Mild acidity is provided by ammonium chloride in an aqueous methanol medium. The conditions are tolerant to other functional groups, with the exception of bromoalkyl derivatives, which yield complex reaction mixtures; otherwise, yields are generally quite high (80–99%).     

Zinc oxide films and nanomaterials for photovoltaic applications

We provide an overview of ZnO applications in solar cells. ZnO (and ZnO‐based materials) can be used as electrodes and/or scattering/light trapping layers, as well as electron transport layers in solar cells based on nanoparticles and organic materials (polymer solar cells, dye‐sensitized solar cells). For each of these applications, we will briefly summarize common research directions, as well as existing problems and unresolved questions. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ternary cadmium zinc sulphide films with high charge mobilities

Cadmium zinc sulphide thin films with high charge mobilities are obtained from acidic chemical baths employing the corresponding metal chlorides, urea and thioacetamide. The films are characterized by powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, inductively coupled plasma mass spectrometry, absorption spectroscopy and charge transport measurements. The compositional control afforded by the technique and the resultant changes in the structural, optical and electronic properties of the films are critically examined. We find good correlation between structure and properties at extremes of the composition range.     

Near‐IR Core‐Substituted Naphthalenediimide Fluorescent Chemosensors for Zinc Ions: Ligand Effects on PET and ICT Channels

Near‐IR (NIR) emission can offer distinct advantages for both in vitro and in vivo biological applications. Two NIR fluorescent turn‐on sensors N,N′‐di‐n‐butyl‐2‐(N‐{2‐[bis(pyridin‐2‐ylmethyl)amino]ethyl})‐6‐(N‐piperidinyl)naphthalene‐1,4,5,8‐tetracarboxylic acid bisimide and N,N′‐di‐ n‐butyl‐2‐[N,N,N′‐tri(pyridin‐2‐ylmethyl)amino]ethyl‐6‐(N‐piperidinyl)naphthalene‐1,4,5,8‐tetracarboxylic acid bisimide (PND and PNT) for Zn²⁺ based on naphthalenediimide fluorophore are reported. Our strategy was to choose core‐substituted naphthalenediimide (NDI) as a novel NIR fluorophore and N,N‐di(pyridin‐2‐ylmethyl)ethane‐1,2‐diamine (DPEA) or N,N,N′‐tri(pyridin‐2‐ylmethyl)ethane‐1,2‐diamine (TPEA) as the receptor, respectively, so as to improve the selectivity to Zn²⁺. In the case of PND, the negligible shift in absorption and emission spectra is strongly suggestive that the secondary nitrogen atom (directly connected to the NDI moiety, N¹) is little disturbed with Zn²⁺. The fluorescence enhancement of PND with Zn²⁺ titration is dominated with a typical photoinduced electron‐transfer (PET) process. In contrast, the N¹ atom for PNT can participate in the coordination of Zn²⁺ ion, diminishing the electron delocalization of the NDI moiety and resulting in intramolecular charge‐transfer (ICT) disturbance. For PNT, the distinct blueshift in both absorbance and fluorescence is indicative of a combination of PET and ICT processes, which unexpectedly decreases the sensitivity to Zn²⁺. Due to the differential binding mode caused by the ligand effect, PND shows excellent selectivity to Zn²⁺ over other metal ions, with a larger fluorescent enhancement centered at 650 nm. Also both PND and PNT were successfully used to image intracellular Zn²⁺ ions in the living KB cells.     

Effect of bridging anions on the structure and stability of phenoxide bridged zinc dipicolylamine coordination complexes

A series of four related phenol derivatives, with 2,2′-dipicolylamine substituents at the ortho positions, were prepared and their Zn²⁺ coordination complexes studied by spectroscopic methods. X-ray crystal diffraction analysis of a dinuclear zinc complex with two bridging acetate anions showed a ternary structure with highly charged interior and lipophilic exterior, which helps explain why this class of water-soluble complexes can effectively diffuse through cell membranes. The stability of the dinuclear zinc complexes in aqueous solution was found to be strongly anion dependent; that is, bridging oxyanions, such as acetate and pyrophosphate, lock the two Zn²⁺ cations to the surrounding ligand and greatly enhance ligand/zinc affinity. Overall, the results provide new insight into the structural and mechanistic factors that control the recognition and chemosensing performance of phenoxide bridged dipicolylamine molecular probes.