Mo6 cluster-based compounds for energy conversion applications: comparative study of photoluminescence and cathodoluminescence

Abstract

We report the photoluminescence (PL) and cathodoluminescence (CL) properties of face-capped [Mo₆Xⁱ₈L^a₆]^2? (X = Cl, Br, I; L = organic or inorganic ligands) cluster units. We show that the emission of Mo₆ metal atom clusters depends not only on the nature of X and L ligands bound to the cluster and counter-cations, but also on the excitation source. Seven members of the A_xMo₆Xⁱ₈L^a₆ series (A = Cs⁺, (n-C₄H₉)₄N⁺, NH₄⁺) were selected to evaluate the influence of counter-cations and ligands on de-excitation mechanisms responsible for multicomponent emission of cluster units. This study evaluates the ageing of each member of the series, which is crucial for further energy conversion applications (photovoltaic, lighting, water splitting, etc.).     

Acid Active Receptor‐Specific Peptide Ligand for In Vivo Tumor‐Targeted Delivery

Targeting therapy of tumors in their early stages is crucial to increase the survival rate of cancer patients. Currently most drug‐delivery systems target the neoplasia through the tumor‐associated receptors overexpressed on the cancer cell membrane. However, the expression of these receptors on normal cells and tissues is inevitable, which leads to unwanted accumulation and side effects. Characteristics of the tumor microenvironment, such as acidosis, are pervasive in almost all solid tumors and can be easily accessed. It is shown that the different extracellular pH value can be used to activate/inactivate the receptor‐mediated endocytosis on tumor/normal cells. This idea is implemented by conjugating a shielding molecule at the terminus of a receptor‐specific ligand via a pH‐sensitive hydrazone bond. The acid‐activated detachment of the shielding molecule and enhanced tumor/background accumulation ratio are demonstrated. These results suggest that acid active receptor‐specific peptide ligand‐modified tumor‐targeting delivery systems have potential use in the treatment of tumors.     

Solvothermal synthesis of 1D and 2D cobalt(II) and nickel(II) coordination polymers with 2,5-dihydroxy-p-benzenediacetic acid

1D cobalt(II) and nickel(II) coordination polymers {[Co(dba)(H₂O)₄] · H₂O}_n (1) and {[Ni(dba)(H₂O)₄] · H₂O}_n (2) (H₂dba = 2,5-dihydroxy-p-benzenediacetic acid) were synthesized under low temperature solvothermal condition. When 4,4′-bipyridine (bpy) was introduced to the synthetic systems of 1 and 2, respectively, two novel 2D coordination polymers {[Co(dba)(bpy)] · 0.5H₂O}_n (3) and [Ni(dba)(bpy)(H₂O)₂]_n (4) with different structures were obtained. All of the compounds were characterized by elemental analysis, FT-IR, UV–Vis spectra and single crystal X-ray diffraction.     

Identification of trinucleotide repeat ligands with a FRET melting assay

DNA hairpin structures formed within a repeated tract might be a causative factor for triplet expansion observed in several debilitating diseases. We have designed and used a fluorescence resonance energy transfer (FRET) melting assay to screen for ligands that bind specifically to the CNG triplet repeats. Using this assay, we screened a panel of 33 chemicals that were previously designed to bind DNA or RNA secondary structures. Remarkably, we found that macrocyclic compounds, such as acridine dimers and trimers, exhibit interesting affinities and specificities for this motif.     

Synthesis and Biological Studies of Pyrazolyl‐Diamine PtII Complexes Containing Polyaromatic DNA‐Binding Groups

New [PtCl(pz*NN)]ⁿ⁺ complexes anchored by pyrazolyl‐diamine (pz*NN) ligands incorporating anthracenyl or acridine orange DNA‐binding groups have been synthesized so as to obtain compounds that would display synergistic effects between platination and intercalation of DNA. Study of their interaction with supercoiled DNA indicated that the anthracenyl‐containing complex L²Pt displays a covalent type of binding, whereas the acridine orange counterpart L³Pt shows a combination of intercalative and covalent binding modes with a strong contribution from the former. L²Pt showed a very strong cytotoxic effect on ovarian carcinoma cell lines A2780 and A2780cisR, which are, respectively, sensitive to and resistant to cisplatin. In these cell lines, L²Pt is nine to 27 times more cytotoxic than cisplatin. In the sensitive cell line, L³Pt showed a cytotoxic activity similar to that of cisplatin, but like L²Pt was able significantly to overcome cisplatin cross‐resistance. Cell‐uptake studies showed that L²Pt accumulates preferentially in the cytoplasm, whereas L³Pt reaches the cell nucleus more easily, as clearly visualized by time‐lapse confocal imaging of live A2870 cells. Altogether, these findings seem to indicate that interaction with biological targets other than DNA might be involved in the mechanism of action of L²Pt because this compound, despite having a weaker ability to target the cell nucleus than L³Pt , as well as an inferior DNA affinity, is nevertheless more cytotoxic. Furthermore, ultrastructural studies of A2870 cells exposed to L²Pt and L³Pt revealed that these complexes induce different alterations in cell morphology, thus indicating the involvement of different modes of action in cell death.     

Complexes of Ir(III)-octaethylporphyrin with peptides as probes for sensing cellular O2

Ir(III)-porphyrins are a relatively new group of phosphorescent dyes that have potential for oxygen sensing and labeling of biomolecules. The requirement of two axial ligands for the Ir(III) ion permits simple linkage of biomolecules by a one-step ligand-exchange reaction, for example, using precursor carbonyl chloride complexes and peptides containing histidine residue(s). Using this approach, we produced three complexes of Ir(III)-octaethylporphyrin with cell-penetrating (Ir1 and Ir2) and tumor-targeting (Ir3) peptides and studied their photophysical properties. All of the complexes were stable and possessed bright, long-decay (unquenched lifetimes exceeding 45 μs) phosphorescence at around 650 nm, with moderate sensitivity to oxygen. The Ir1 and Ir2 complexes showed positive staining of a number of mammalian cell types, thus demonstrating localization similar to endoplasmic reticulum and ATP- and temperature-independent intracellular accumulation (direct translocation mechanism). Their low photo- and cytotoxicity allows intracellular oxygen to be probed.     

The Iridium‐Catalyzed Synthesis of Symmetrically and Unsymmetrically Alkylated Diamines under Mild Reaction Conditions

An iridium catalyst – stabilized by an anionic P,N ligand – was used for the symmetrical and unsymmetrical monoalkylation of para‐, meta‐, and ortho‐benzenediamines. Benzyl and aliphatic alcohols were used as alkylating reagents. 28 derivatives were synthesized. 14 of them are new compounds. Furthermore, the alkylation of the pharmacological important diamine Dapson^® (dapsone) is described. 14 dapsone derivatives were synthesized among them 9 new compounds.     

Iron‐Catalyzed Highly Enantioselective Reduction of Aromatic Ketones with Chiral P2N4‐Type Macrocycles

Novel P₂N₄‐donors containing chiral 22‐membered macrocyclic ligands have been synthesized and the structures have been determined by an X‐ray diffraction study. The catalytic systems in situ generated from triiron dodecarbonyl, Fe₃(CO)₁₂, and the chiral macrocyclic ligand exhibited high activity (TOF up to 1940 h⁻¹) and excellent enantioselectivity with up to 99% ee in the asymmetric transfer hydrogenation of various aromatic ketones.     

Asymmetric Counteranion‐Directed Iron Catalysis: A Highly Enantioselective Sulfoxidation

A highly active and enantioselective ion‐pair sulfoxidation catalyst, consisting of an achiral iron(III)‐salen cation and a chiral phosphate counteranion, mediates the oxidization of various sulfides with high yields and enantioselectivities. The enantioselectivities observed, especially for electron‐poor substrates, represent the best results so far in manganese and iron‐salen systems. This work represents the first application of our concept of asymmetric counteranion‐directed catalysis (ACDC) to iron catalysis.     

Synthesis of Aryl Carbamates via Copper‐Catalyzed Coupling of Aryl Halides with Potassium Cyanate

Coupling of aryl halides with potassium cyanate takes place at 100–110 °C in alcohols under the catalysis of CuI (cuprous iodide) and 2‐(2,6‐dimethylphenylamino)‐2‐oxoacetic acid, affording the corresponding aryl carbamates with great diversity.