Lowest optical excitations in molecular crystals: bound excitons versus free electron-hole pairs in anthracene

By solving the Bethe-Salpeter equation for the electron-hole Green function for crystalline anthracene we find the lowest absorption peak generated by strongly bound excitons or by a free electron-hole pair, depending on the polarization direction being parallel to the short or the long molecular axis, respectively. Both excitations are shifted to lower energies by pressure. The physical difference of these excitations is apparent from the electron-hole wave functions. Our findings are a major contribution to solve the long-standing puzzle about the nature of the lowest optical excitations in organic materials.     

Organic azides: an exploding diversity of a unique class of compounds

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aubé rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.     

A New Acyclic α‐Hydrogen Bearing Nitroxide and its Corresponding Alkoxyamine for Stable Free Radical Polymerization

Summary: The synthesis of the new α‐hydrogen bearing nitroxide, 2,2,5‐trimethyl‐4‐(isopropyl)‐3‐azahexane‐3‐oxyl (BIPNO) ( 4 ), and its corresponding alkoxyamine, N‐tert‐butyl‐N‐(1‐isopropyl‐2‐methyl‐propyl)‐O‐(1‐phenyl‐ethyl)‐hydroxylamine (PhEt‐BIPNO) ( 7 ), are described in this paper. Reaction of styrene with the new nitroxide in the presence of a Jacobsen‐like manganese catalyst, Mn(salen)Cl, at ambient atmosphere afforded the alkoxyamine in 96% yield. Styrene and n‐butyl acrylate were polymerized in bulk in the presence of the new alkoxyamine. The alkoxyamine turned out to be a suitable “initiator” for controlled radical polymerization.

Structure of α‐hydrogen bearing nitroxide and its corresponding alkoxyamine.     

Interconversion of cis‐ and trans‐Fused Oxabicyclo[5.2.0]nonan‐2‐ones

On irradiation (350 nm) in the presence of alkenes (2,3‐dimethylbut‐2‐ene, 1,1‐dimethoxyethene, and 2,4,4‐trimethylpent‐1‐ene), benzoxepinone 1 and dioxepinone 2 are converted into mixtures of cis‐ and trans‐fused oxabicyclo[5.2.0]nonan‐2‐ones. Their relative thermodynamic stabilities (as reflected by the observed diastereoisomer ratios after equilibration with basic alumina) depend on the substitution pattern of the alkene moiety.     

Synthesis and bio-functionalization of magnetic nanoparticles for medical diagnosis and treatment

The synthesis of multifunctional magnetic nanoparticles (NPs) is a highly active area of current research located at the interface between materials science, biotechnology and medicine. By virtue of their unique physical properties magnetic nanoparticles are emerging as a new class of diagnostic probes for multimodal tracking and as contrast agents for MRI. Furthermore, they show great potential as carriers for targeted drug and gene delivery, since reactive agents, such as drug molecules or large biomolecules (including genes and antibodies), can easily be attached to their surface. On the other hand, the fate of the nanoparticles inside the body is mainly determined by the interactions with its local environment. These interactions strongly depend upon the size of the magnetic NPs but also on the individual surface characteristics, like charge, morphology and surface chemistry. This review not only summarizes the most common synthetic approaches for the generation of magnetic NPs, it also focuses on different surface modification strategies that are used today to enhance the biocompatibility of these NPs. Finally, key considerations for the application of magnetic NPs in biomedicine, as well as various examples for the utilization in multimodal imaging and targeted gene delivery are presented.     

Facile, fast, and inexpensive synthesis of monodisperse amorphous nickel-phosphide nanoparticles of predefined size

Monodisperse, size-controlled Ni-P nanoparticles were synthesised in a single step process using triphenyl-phosphane (TPP), oleylamine (OA), and Ni(II)acetyl-acetonate. The nanoparticles were amorphous, contained ~30 at% P and their size was controlled between 7-21 nm simply by varying the amount of TPP. They are catalytically active for tailored carbon nanotube growth.     

Effective and selective extraction of noble metal nanoparticles from environmental water through a noncovalent reversible reaction on an ionic exchange resin

Capable of preserving the size and shape of nanoparticles, a novel method to effectively and selectively extract noble metal nanoparticles even at the 80 ng L(-1) level from real environmental water was designed and performed using a noncovalent reversible adsorption onto an ionic exchange resin.     

Thermoelektrik

Thermoelectrics is already used in niche applications, when reliability or comfort are more important than costs. In future the potential of this technology is higher for waste heat. Main areas will be in the automotive industry and industrial waste heat. For a huge market entry, there are several challenges: materials for higher efficiency, improved module technology and the integration of thermoelectric devices into systems are the main focus of interest. This article reflects these actual challenges from an industrial point of view.     

Isoleucine-catalyzed direct asymmetric aldol addition of enolizable aldehydes

Isoleucine-catalyzed direct enantioselective aldol additions between enolizable aldehydes are reported. Intermediate acetal structures dictate the configurative outcome and were supported by a hydrogen bond. This direct isoleucine-catalyzed aldol addition represents a welcome complement to both proline- and histidine-catalyzed aldol additions of enolizable aldehydes.     

Oligonuclear molecular models of intermetallic phases: a case study on [Pd2Zn6Ga2(Cp*)5(CH3)3

The synthesis, characterization, and theoretical investigation by means of quantum-chemical calculations of an oligonuclear metal-rich compound are presented. The reaction of homoleptic dinuclear palladium compound [Pd(2)(μ-GaCp*)(3)(GaCp*)(2)] with ZnMe(2) resulted in the formation of unprecedented ternary Pd/Ga/Zn compound [Pd(2)Zn(6)Ga(2)(Cp*)(5)(CH(3))(3)] (1), which was analyzed by (1)H and (13)C?NMR spectroscopy, MS, elemental analysis, and single-crystal X-ray diffraction. Compound 1 consisted of two C(s)-symmetric molecular isomers, as revealed by NMR spectroscopy, at which distinct site-preferences related to the Ga and Zn positions were observed by quantum-chemical calculations. Structural characterization of compound 1 showed significantly different coordination environments for both palladium centers. Whilst one Pd atom sat in the central of a bi-capped trigonal prism, thereby resulting in a formal 18-valence electron fragment, {Pd(ZnMe)(2)(ZnCp*)(4)(GaMe)}, the other Pd atom occupied one capping unit, thereby resulting in a highly unsaturated 12-valence electron fragment, {Pd(GaCp*)}. The bonding situation, as determined by atoms-in-molecules analysis (AIM), NBO partial charges, and molecular orbital (MO) analysis, pointed out that significant Pd-Pd interactions had a large stake in the stabilization of this unusual molecule. The characterization and quantum-chemical calculations of compound 1 revealed distinct similarities to related M/Zn/Ga Hume-Rothery intermetallic solid-state compounds, such as Ga/Zn-exchange reactions, the site-preferences of the Zn/Ga positions, and direct M-M bonding, which contributes to the overall stability of the metal-rich compound.