Allyl complexes of scandium: synthesis and structure of neutral, cationic and anionic derivatives

Neutral, cationic and anionic allyl compounds of scandium contain highly fluxional allyl ligands in solution, whilst in the solid state both η(1)- and η(3)-binding modes are detected.     

CycloPs: generating virtual libraries of cyclized and constrained peptides including nonnatural amino acids

We introduce CycloPs, software for the generation of virtual libraries of constrained peptides including natural and nonnatural commercially available amino acids. The software is written in the cross-platform Python programming language, and features include generating virtual libraries in one-dimensional SMILES and three-dimensional SDF formats, suitable for virtual screening. The stand-alone software is capable of filtering the virtual libraries using empirical measurements, including peptide synthesizability by standard peptide synthesis techniques, stability, and the druglike properties of the peptide. The software and accompanying Web interface is designed to enable the rapid generation of large, structurally diverse, synthesizable virtual libraries of constrained peptides quickly and conveniently, for use in virtual screening experiments. The stand-alone software, and the Web interface for evaluating these empirical properties of a single peptide, are available at http://bioware.ucd.ie .     

Interleaved Distance-of-Flight Mass Spectrometry: A Simple Method to Improve the Instrument Duty Factor

Distance-of-flight mass spectrometry (DOFMS) is a velocity-based, spatially dispersive MS technique in which ions are detected simultaneously along the plane of a spatially selective detector. In DOFMS, ions fly though the instrument and mass separate over a set period of time. The single flight time at which all ions are measured defines the specific m/z values that are detectable; the range of m/z values is dictated by the length of the spatially selective detector. However, because each packet of ions is detected at a single flight time, multiple groups of ions can fly through the instrument concurrently and be detected at a single detector. In this way, DOFMS experiments can be interleaved to perform several mass separation experiments within a single DOF repetition period. Interleaved operation allows the orthogonal acceleration region to be operated at a repetition rate higher than the reciprocal of the flight time, which improves the duty factor of the technique. In this paper, we consider the fundamental parameters of interleaved DOFMS and report first results.

Supported oxorhenate catalysts prepared by thermal spreading of metal Re for methanol conversion to methylal

TiO₂-anatase and SiO₂ supported oxorhenate catalysts were prepared by an original and simple technique based on the oxidative dispersion of metallic rhenium under dry conditions. The dispersion process of the supported oxorhenate phase as a function of the rhenium coverage and the support properties are discussed on the base of in situ characterization. The structures of the as prepared catalysts were found to be comparable to those of materials prepared using the incipient wetness impregnation technique. The absence of water in the preparation technique has made it possible to highlight the role of the hydration level on the rhenium oxide volatilization. The as-prepared Re/TiO₂ catalysts were found to be effective for the direct conversion of methanol to methylal.     

Rare-earth metal allyl and hydrido complexes supported by an (NNNN)-type macrocyclic ligand: synthesis, structure, and reactivity toward biomass-derived furanics

The preparation and characterization of a series of neutral rare‐earth metal complexes [Ln(Me₃TACD)(η³‐C₃H₅)₂] (Ln=Y, La, Ce, Pr, Nd, Sm) supported by the 1,4,7‐trimethyl‐1,4,7,10‐tetraazacyclododecane anion (Me₃TACD^?) are reported. Upon treatment of the neutral allyl complexes [Ln(Me₃TACD)(η³‐C₃H₅)₂] with Brønsted acids, monocationic allyl complexes [Ln(Me₃TACD)(η³‐C₃H₅)(thf)₂][B(C₆X₅)₄] (Ln=La, Ce, Nd, X=H, F) were isolated and characterized. Hydrogenolysis gave the hydride complexes [Ln(Me₃TACD)H₂]_n (Ln=Y, n=3; La, n=4; Sm). X‐ray crystallography showed the lanthanum hydride to be tetranuclear. Reactivity studies of [Ln(Me₃TACD)R₂]_n (R=η³‐C₃H₅, n=0; R=H, n=3,4) towards furan derivatives includes hydrosilylation and deoxygenation under ring‐opening conditions.     

Nanostructures of the aragonitic otolith of cod (Gadus morhua)

Topographical relationships between the mineral and organic components are important to understand the process involved in biomineralisation. We examined nanostructural features of cod (Gadus morhua) otoliths using atomic force microscope (AFM). Acicular aragonitic fibres that form primary increments observed in scanning electron or light microscopy were composed of lamellae, themselves being composite arrangements of round granules (diameter<50 nm) surrounded by an organic (?) cortex. The lamellae presented a banding pattern, which might correspond to a growth period of about 15 min. Cod otolith granules were similar in size, shape and arrangement to that previously reported for another fish species. The existence of smallest otolith organization units is suggested since granules are themselves composite. Finally, the intra-daily growth rhythm makes it possible to consider very high-resolution biological and environmental reconstructions in the future.     

Reducing the internal reorganization energy via symmetry controlled π-electron delocalization

The magnitude of the reorganization energy is closely related to the nonradiative relaxation rate, which affects the photoemission quantum efficiency, particularly for the emission with a lower energy gap toward the near IR (NIR) region. In this study, we explore the relationship between the reorganization energy and the molecular geometry, and hence the transition density by computational methods using two popular models of NIR luminescent materials: (1) linearly conjugated cyanine dyes and (2) electron donor–acceptor (D–A) composites with various degrees of charge transfer (CT) character. We find that in some cases, reorganization energies can be significantly reduced to 50% despite slight structural modifications. Detailed analyses indicate that the reflection symmetry plays an important role in linear cyanine systems. As for electron donor–acceptor systems, both the donor strength and the substitution position affect the relative magnitude of reorganization energies. If CT is dominant and creates large spatial separation between HOMO and LUMO density distributions, the reorganization energy is effectively increased due to the large electron density variation between S₀ and S₁ states. Mixing a certain degree of local excitation (LE) with CT in the S₁ state reduces the reorganization energy. The principles proposed in this study are also translated into various pathways of canonically equivalent π-conjugation resonances to represent intramolecular π-delocalization, the concept of which may be applicable, in a facile manner, to improve the emission efficiency especially in the NIR region.

The reorganization energies may be significantly reduced by molecular symmetry effect.     

Photoredox-Catalyzed Labeling of Hydroxyindoles with Chemoselectivity (PhotoCLIC) for Site-Specific Protein Bioconjugation

We have developed a novel visible-light-catalyzed bioconjugation reaction, PhotoCLIC, that enables chemoselective attachment of diverse aromatic amine reagents onto a site-specifically installed 5-hydroxytryptophan residue (5HTP) on full-length proteins of varied complexity. The reaction uses catalytic amounts of methylene blue and blue/red light-emitting diodes (455/650 nm) for rapid site-specific protein bioconjugation. Characterization of the PhotoCLIC product reveals a unique structure formed likely through a singlet oxygen-dependent modification of 5HTP. PhotoCLIC has a wide substrate scope and its compatibility with strain-promoted azide-alkyne click reaction, enables site-specific dual-labeling of a target protein.     

Stereoconvergent Synthesis of Z-1,3-Disubstituted-1,3-Dienes by Uphill Photocatalysis

A variety of 1-aryl-1,3-dienes were isomerized from E to Z isomers by photocatalysis using Ru(bpy)₃[PF₆]₂ and blue LED light. Enrichment of the Z-isomer is thought to occur by selective triplet energy transfer from the photocatalyst to the stereoisomeric mixture. The 1,3-diene starting materials are easily made by catalytic ene-yne metathesis (EYM). To access 1,3-diene Z-stereoisomers directly, a one pot procedure was developed. Additional 1,3-dienes were investigated for both isomerization and Z-enrichment. The combination of cross EYM with photocatalysis allows for the stereoconvergent synthesis of Z-1,3-dienes.