Dual Gold Catalysis: σ,π‐Propyne Acetylide and Hydroxyl‐Bridged Digold Complexes as Easy‐To‐Prepare and Easy‐To‐Handle Precatalysts

A series of dinuclear gold σ,π‐propyne acetylide complexes were prepared and tested for their catalytic ability in dual gold catalysis that was based on the reaction of an electrophilic π‐complex of gold with a gold acetylide. The air‐stable and storable catalysts can be isolated as silver‐free catalysts in their activated form. These dual catalysts allow a fast initiation phase for the dual catalytic cycles without the need for additional additives for acetylide formation. Because propyne serves as a throw‐away ligand, no traces of the precatalyst are generated. Based on the fast initiation process, side products are minimized and reaction rates are higher for these catalysts. A series of test reactions were used to demonstrate the general applicability of these catalysts. Lower catalyst loadings, faster reaction rates, and better selectivity, combined with the practicability of these catalysts, make them ideal catalysts for dual gold catalysis.     

Cellulose chiral induction during the synthesis of cellulose N-phthaloyl-amino acid esters

Cellulose was acylated by N-phthaloyl amino acid chlorides in the presence of pyridine to prepare an original library of cellulose N-phthaloyl-amino acid esters as chiral solid supports for enantioselective adsorption of racemates. Cellulose esters derived from N-phthaloyl glycine, alanine, valine, leucine, phenylalanine, phenylglycine and isoleucine were isolated in high yields and with degrees of substitution approaching 3. Interestingly, the use of an optically pure (d or l) or a rac-amino acid led to the same cellulose ester according to (1) the measured optical rotation, (2) the enantiomeric excesses of the amino acids resulting from a non-racemising and total hydrolysis and (3) the enantioselective adsorptions of rac-benzoin, rac-Pirkle’s alcohol and rac-Tröger’s base. This suggests that either the formation of a prochiral ketene intermediate which was diastereoselectively attacked by the cellulose alcohols or, alternatively (or concomitantly), the occurrence of a chiral induction in the formed triesters during prolonged contact with the pyridine base in the reaction medium. Enantiomeric excesses in favour of the (S) form ranged from 8 % to 50 % depending on the N-phthaloyl amino acid. The memory of the chirality of the starting material was lost and new chirality was imprinted by the cellulose backbone on the amino acid residues.     

Experimental and computational studies of molecules with close,non-bonded hydrogen–hydrogen contacts: common computational methods grossly overestimate some ‘through-space’ NMR scalar coupling constants

The NMR spin–spin scalar coupling constants (J_HH's) of closely contacting, but non-bonded hydrogen atoms in a series of highly strained molecules (including a new in,in-cyclophane made specifically for this study) have been examined both experimentally and computationally. The experimental J_HH's are invariably quite small (0.1–0.6 Hz), but common DFT methods with modest basis sets nearly always overestimate these values, by factors of 10–30, and even with quite large basis sets (up to cc-pVQZ) the J_HH's of two of the molecules are overestimated by a factor of 10 or more. Possible reasons for these discrepancies are discussed.     

Development of a compact alpha and beta camera for dismantlement applications

Journal of Radioanalytical and Nuclear Chemistry - A new method has been developed to image surface contamination on-site by short range radiation emitters (such as alpha or beta particle...     

On-surface synthesis of porous graphene nanoribbons containing nonplanar [14]annulene pores

The precise introduction of nonplanar pores in the backbone of graphene nanoribbon represents a great challenge. Here, we explore a synthetic strategy toward the preparation of nonplanar porous graphene nanoribbon from a predesigned dibromohexabenzotetracene monomer bearing four cove-edges. Successive thermal annealing steps of the monomers indicate that the dehalogenative aryl-aryl homocoupling yields a twisted polymer precursor on a gold surface and the subsequent cyclodehydrogenation leads to a defective porous graphene nanoribbon containing nonplanar [14]annulene pores and five-membered rings as characterized by scanning tunneling microscopy and noncontact atomic force microscopy. Although the C–C bonds producing [14]annulene pores are not achieved with high yield, our results provide new synthetic perspectives for the on-surface growth of nonplanar porous graphene nanoribbons.     

Temperature and Composition Dependent Optical Properties of CdSe/CdS Dot/Rod-Based Aerogel Networks

Employing nanocrystals (NCs) as building blocks of porous aerogel network structures allows the conversion of NC materials into macroscopic solid structures while conserving their unique nanoscopic properties. Understanding the interplay of the network formation and its influence on these properties like size-dependent emission is a key to apply techniques for the fabrication of novel nanocrystal aerogels. In this work, CdSe/CdS dot/rod NCs possessing two different CdSe core sizes were synthesized and converted into porous aerogel network structures. Temperature-dependent steady-state and time-resolved photoluminescence measurements were performed to expand the understanding of the optical and electronic properties of these network structures generated from these two different building blocks and correlate their optical with the structural properties. These investigations reveal the influence of network formation and aerogel production on the network-forming nanocrystals. Based on the two investigated NC building blocks and their aerogel networks, mixed network structures with various ratios of the two building blocks were produced and likewise optically characterized. Since the different building blocks show diverse optical response, this technique presents a straightforward way to color-tune the resulting networks simply by choosing the building block ratio in connection with their quantum yield.     

Boswellic Acids Show In Vitro Activity against Leishmania donovani

In continuation of our search for leads from medicinal plants against protozoal pathogens, we detected antileishmanial activity in polar fractions of a dichloromethane extract from Boswellia serrata resin. 11-keto-β-boswellic acid (KBA) could be isolated from these fractions and was tested in vitro against Leishmania donovani axenic amastigotes along with five further boswellic acid derivatives. 3-O-acetyl-11-keto-β-boswellic acid (AKBA) showed the strongest activity with an IC₅₀ value of 0.88 µM against axenic amastigotes but was inactive against intracellular amastigotes in murine macrophages     

New Quinoxaline Derivatives as Dual Pim-1/2 Kinase Inhibitors: Design,Synthesis and Biological Evaluation

Proviral integration site for Moloney murine leukemia virus (Pim)-1/2 kinase overexpression has been identified in a variety of hematologic (e.g., multiple myeloma or acute myeloid leukemia (AML)) and solid (e.g., colorectal carcinoma) tumors, playing a key role in cancer progression, metastasis, and drug resistance, and is linked to poor prognosis. These kinases are thus considered interesting targets in oncology. We report herein the design, synthesis, structure–activity relationships (SAR) and in vitro evaluations of new quinoxaline derivatives, acting as dual Pim1/2 inhibitors. Two lead compounds (5c and 5e) were then identified, as potent submicromolar Pim-1 and Pim-2 inhibitors. These molecules were also able to inhibit the growth of the two human cell lines, MV4-11 (AML) and HCT-116 (colorectal carcinoma), expressing high endogenous levels of Pim-1/2 kinases.     

Transparent carbon nanotube-based driving electrodes for liquid crystal dispersion display devices

We report the fabrication of transparent rigid or flexible liquid crystal dispersion displays driven by electrodes prepared from coating inert substrates with stable aqueous suspensions of single-walled carbon nanotubes (SWNTs) or multiple-walled carbon nanotubes (MWNTs). The SWNT-coated electrodes exhibit a dense nanotube network with a sheet resistivity ( 25 k) about one decade lower than that of their MWNT counterparts. The electro-optical performance of the SWNT-based devices is at least equivalent to that of an indium tin oxide-based display, whereas those driven by MWNT electrodes operate at slightly higher threshold and saturation voltages. The novel, flexible display devices can be repeatedly bent without any noticeable loss of physical characteristics. PACS 42.79.Kr; 61.46.+w; 81.07.De