A single Cu(II) catalyst for the three-component coupling of diverse nitrogen sources with aldehydes and alkynes

A single Cu(II) catalyst without the addition of ligand or base couples a diverse range of nitrogen sources with alkynes and aldehydes bearing alkyl, halogenated, silyl, aryl, and heteroaryl groups. The first example of a copper-catalyzed alkynylation involving p-toluenesulfonamide provides high yields of N-Ts-protected propargylamines. The superior activity of copper(II) triflate also allows this three-component alkynylation to incorporate a ketone.     

Electrochemiluminescent peptide nucleic acid-like monomers containing Ru(II)-dipyridoquinoxaline and Ru(II)-dipyridophenazine complexes

A series of Ru(II)-peptide nucleic acid (PNA)-like monomers, [Ru(bpy)(2)(dpq-L-PNA-OH)](2+) (M1), [Ru(phen)(2)(dpq-L-PNA-OH)](2+) (M2), [Ru(bpy)(2)(dppz-L-PNA-OH)](2+) (M3), and [Ru(phen)(2)(dppz-L-PNA-OH)](2+) (M4) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, dpq-L-PNA-OH = 2-(N-(2-(((9H-fluoren-9-yl)methoxy)carbonylamino)ethyl)-6-(dipyrido[3,2-a:2',3'-c]phenazine-11-carboxamido)hexanamido)acetic acid, dppz-L-PNA-OH = 2-(N-(2-(((9H-fluoren-9-yl) methoxy)carbonylamino)ethyl)-6-(dipyrido[3,2-f:2',3'-h]quinoxaline-2-carboxamido)acetic acid) have been synthesized and characterized by IR and (1)H NMR spectroscopy, mass spectrometry, and elemental analysis. As is typical for Ru(II)-tris(diimine) complexes, acetonitrile solutions of these complexes (M1-M4) show MLCT transitions in the 443-455 nm region and emission maxima at 618, 613, 658, and 660 nm, respectively, upon photoexcitation at 450 nm. Changes in the ligand environment around the Ru(II) center are reflected in the luminescence and electrochemical response obtained from these monomers. The emission intensity and quantum yield for M1 and M2 were found to be higher than for M3 and M4. Electrochemical studies in acetonitrile show the Ru(II)-PNA monomers to undergo a one-electron redox process associated with Ru(II) to Ru(III) oxidation. A positive shift was observed in the reversible redox potentials for M1-M4 (962, 951, 936, and 938 mV, respectively, vs Fc(0/+) (Fc = ferrocene)) in comparison with [Ru(bpy)(3)](2+) (888 mV vs Fc(0/+)). The ability of the Ru(II)-PNA monomers to generate electrochemiluminescence (ECL) was assessed in acetonitrile solutions containing tripropylamine (TPA) as a coreactant. Intense ECL signals were observed with emission maxima for M1-M4 at 622, 616, 673, and 675 nm, respectively. At an applied potential sufficiently positive to oxidize the ruthenium center, the integrated intensity for ECL from the PNA monomers was found to vary in the order M1 (62%) > M3 (60%) > M4 (46%) > M2 (44%) with respect to [Ru(bpy)(3)](2+) (100%). These findings indicate that such Ru(II)-PNA bioconjugates could be investigated as multimodal labels for biosensing applications.     

Predicting cyclic peptide chemical shifts using quantum mechanical calculations

A hybrid sequential molecular mechanics and quantum mechanical approach to modeling cyclic peptides has led to an effective method for predicting their ¹H and ¹³C NMR chemical shift values. The method was first developed to predict chemical shifts in chloroform before being adapted to a more peptide friendly solvent, DMSO. Finally the effectiveness of this method was tested in a blind fashion and excellent agreement with the experimental NMR chemical shifts was observed.     

Topological surface states of Bi2Te2Se are robust against surface chemical modification

The robustness of the Dirac‐like electronic states on the surfaces of topological insulators (TIs) during materials process‐ing is a prerequisite for their eventual device application. Here, the (001) cleavage surfaces of crystals of the topological insulator Bi₂Te₂Se (BTS) were subjected to several surface chemical modification procedures that are common for electronic materials. Through measurement of Shubnikov–de Hass (SdH) oscillations, which are the most sensitive measure of their quality, the surface states of the treated surfaces were compared to those of pristine BTS that had been exposed to ambient conditions. In each case – surface oxidation, deposition of thin layers of Ti or Zr oxides, or chemical modification of the surface oxides – the robustness of the topological surface electronic states was demonstrated by noting only very small changes in the frequency and amplitude of the SdH oscillations. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Control of Excitation and Quenching in Multi‐colour Electrogenerated Chemiluminescence Systems through Choice of Co‐reactant

We demonstrate a new approach to manipulate the selective emission in mixed electrogenerated chemiluminescence (ECL) systems, where subtle changes in co‐reactant properties are exploited to control the relative electron‐transfer processes of excitation and quenching. Two closely related tertiary‐amine co‐reactants, tri‐n‐propylamine and N,N‐diisopropylethylamine, generate remarkably different emission profiles: one provides distinct green and red ECL from [Ir(ppy)₃] (ppy=2‐phenylpyridinato‐C2,N) and a [Ru(bpy)₃]²⁺ (bpy=2,2′‐bipyridine) derivative at different applied potentials, whereas the other generates both emissions simultaneously across a wide potential range. These phenomena can be rationalized through the relative exergonicities of electron‐transfer quenching of the excited states, in conjunction with the change in concentration of the quenchers over the applied potential range.     

Click‐Assembled,Oxygen‐Sensing Nanoconjugates for Depth‐Resolved,Near‐Infrared Imaging in a 3 D Cancer Model

Hypoxia is an important contributing factor to the development of drug‐resistant cancer, yet few nonperturbative tools exist for studying oxygenation in tissues. While progress has been made in the development of chemical probes for optical oxygen mapping, penetration of such molecules into poorly perfused or avascular tumor regions remains problematic. A click‐assembled oxygen‐sensing (CAOS) nanoconjugate is reported and its properties demonstrated in an in vitro 3D spheroid cancer model. The synthesis relies on the sequential click‐based ligation of poly(amidoamine)‐like subunits for rapid assembly. Near‐infrared confocal phosphorescence microscopy was used to demonstrate the ability of the CAOS nanoconjugates to penetrate hundreds of micrometers into spheroids within hours and to show their sensitivity to oxygen changes throughout the nodule. This proof‐of‐concept study demonstrates a modular approach that is readily extensible to a wide variety of oxygen and cellular sensors for depth‐resolved imaging in tissue and tissue models.     

Solid polymers doped with rare earth metal salts. I. Complex formation and morphology in the neodymium chloride–poly(ethylene oxide) system

The complex formation and morphology of the NdCl₃?PEO system have been investigated. Peak shifts, peak broadening, and the appearance of new peaks in the 800–1200 cm^?1 range of the infrared (IR) spectra, by comparison with what is observed with pure PEO, unequivocally demonstrates complex formation. Although the NdCl₃?PEO complex is found to be highly hygroscopic, residual moisture can be removed reversibly, thereby permitting the role of water in affecting the morphology of the solid film to be examined. As elucidated with infrared, differential scanning calorimetry, thermogravimetric analysis, and hot-stage polarized optical microscopy, under anhydrous conditions the resultant complex is amorphous at an EO/NdCl₃ ratio approximately less than ca. 8; but above this critical value the PEO in excess of the stoichiometric ratio required for complexation tends to form a separate crystalline phase. Furthermore, water was found to compete with the ethylene oxide unit for complexation with Nd³⁺, resulting in phase-separated PEO with a tendency toward crystallinity. The glass transition temperature of the complex is found to increase sigmoidally with the NdCl₃ content, an observation further substantiating complexation between NdCl₃ and PEO.