C,C‐ and N,C‐Coupled Dimers of 2‐Aminotetraphenylporphyrins: Regiocontrolled Synthesis,Spectroscopic Properties,and Quantum‐Chemical Calculations

β,β′‐Bisporphyrins are intrinsically chiral porphyrin dimers with fascinating properties. The configurational stability at their axes can be directed by variation of the central metal atoms. Herein, we present a regioselective functionalization of the monomeric 2‐amino‐tetraphenyl‐porphyrin as a versatile substrate for dimerization by oxidative coupling. By simple variation of the reaction conditions (solvent and oxidant), the oxidation selectively gave either the axially chiral C,C‐coupled diaminobisporphyrin in high yields or, under Ullmann conditions, the twofold N,C‐linked achiral dimer, also in good yields. A generalized mechanism for the coupling reaction is proposed based on DFT calculations. The axially chiral β,β′‐coupled porphyrin dimers were isolated as racemic mixtures, but can be resolved by HPLC on a chiral phase. TDDFT and coupled‐cluster calculations were used to explain the spectroscopic properties of the aminoporphyrins and their dimers and to elucidate the absolute configurations of the C,C‐coupled bisporphyrins.     

Hierarchical self-assembly of aminopyrazole peptides into nanorosettes in water

Self-association of aminopyrazole peptide hybrid 1 leads to stacked nanorosettes. This remarkable, well-ordered structure obeys the laws of nucleic acid self-assembly. In a strictly hierarchical process, formation of aminopyrazole "base" triplets via a hydrogen bond network is accompanied by pi-stacking with a second rosette and final dimerization of two double rosettes to a four-layer superstructure, stabilized by a six-fold half-crown alkylammonium lock. The final complex is soluble in organic as well as in aqueous solution. It was characterized in the solid state by X-ray crystallography, in water by NMR spectroscopy, and in silico by quantum chemical shift calculation. All these methods provide strong evidence for the same hexameric complex geometry. Its structural features bear striking similarity to nucleic acid architectures and their peptidic counterparts, especially alanyl-PNA. The whole self-assembly process is highly solvent- and temperature-dependent and occurs with a high degree of cooperativity--no intermediates are observed. Formation and dissociation of the nanorosette, however, are kinetically slow. The limitation to a hexameric aggregate can be explained by six sterically demanding valine residues, whose replacement by alanines may result in formation of infinite fibers.     

Regioselective Arene Functionalization: Simple Substitution of Carboxylate by Alkyl Groups

Arenes with various alkyl side‐chains were synthesized in high yields and excellent regioselectivities. Starting from toluic and naphthoic acids, the carboxylate group was conveniently substituted by alkyl halides by Birch reduction and subsequent decarbonylation. The method is characterized by inexpensive starting materials and reagents, and methylation of arenes was realized. Besides simple alkyl substituents, the scope of arene functionalization was extended by benzyl, fluoro, amino, and ester groups. We were able to control the alkylation of 1‐naphthoic acid during Birch reduction by the addition of tert‐butanol. This allowed the regioselective synthesis of mono and bis‐substituted naphthalenes from the same starting material.     

Two types of limit cycles of a resonant converter modelled by a three-dimensional system

In this paper, the long-run dynamics of a resonant converter is studied. The modelling of the resonant converter can be done using various approximations and the long-run dynamics of the two dimensional cases were earlier analysed. In this paper, we discuss results that can be extended to the three dimensional case. It seems that limit cycles describe the long-run dynamics in important situations in the three dimensional case, too. Our objective is to relate the limit cycles found previously in the two-dimensional case to those found now in the three dimensional approximation.     

Synthesis of rigid photoswitchable hemithioindigo ω-amino acids

The synthesis of novel N-Boc- and N-Fmoc protected hemithioindigo-based ω-amino acids is described. An approach to modulate the thermal stability of a hemithioindigo subunit is presented. Placing the amino-group in the stilbene part from the para- to meta-position leads to an increase of the half-life of the thermally labile E-form from 19 h to 47 h.     

Nondestructive three-dimensional analysis of layered polymer structures with chemical imaging

Three-dimensional (3D) chemical information was obtained by means of a combination of two-dimensional attenuated total reflection Fourier transform infrared (ATR-FT-IR) imaging with a focal plane array detector and variable angle depth profiling. Since the penetration depth of the evanescent wave in ATR spectroscopy is not limited by diffraction, it was possible to resolve thin sandwiched polymer layers nondestructively within a stack of polymer layers. Chemical images were obtained from layers of different thickness of the laminate by moving a custom-made aperture to specific positions on the condenser lens of the ATR accessory. Sequences of absorption images detect the successive appearance of thin, buried layers of polybutylmethacrylate (d(PBMA) = 400 nm) and polycarbonate (d(TMPC) = 300 nm) in different depths of the stack of polymer layers. The depth resolution of variable-angle ATR-FT-IR imaging is sufficiently high to detect surface roughness at the interface between different polymer layers. Two different stacks of polymers with reordered sandwich-layers were imaged simultaneously, demonstrating the potential of variable angle ATR-FT-IR for 3D-imaging of a sample with xyz-heterogeneity, which can be a powerful analytical technique for materials science and biomedical research.     

Ordered mesoporous MFe(2)O(4) (M = Co, Cu, Mg, Ni, Zn) thin films with nanocrystalline walls, uniform 16 nm diameter pores and high thermal stability: template-directed synthesis and characterization of redox active trevorite

In this paper, we report on ordered mesoporous NiFe(2)O(4) thin films synthesized via co-assembly of hydrated ferric nitrate and nickel chloride with an amphiphilic diblock copolymer, referred to as KLE. We establish that the NiFe(2)O(4) samples are highly crystalline after calcination at 600 °C, and that the conversion of the amorphous inorganic framework comes at little cost to the ordering of the high quality cubic network of pores averaging 16 nm in diameter. We further show that the synthesis method employed in this work can be readily extended to other ferrites, such as CoFe(2)O(4), CuFe(2)O(4), MgFe(2)O(4), and ZnFe(2)O(4), which could pave the way for innovative device design. While this article focuses on the self-assembly and characterization of these materials using various state-of-the-art techniques, including electron microscopy, grazing incidence small-angle X-ray scattering (GISAXS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS), as well as UV-vis and Raman spectroscopy, we also examine the electrochemical properties and show the benefits of combining a continuous mesoporosity with nanocrystalline films. KLE-templated NiFe(2)O(4) electrodes exhibit reasonable levels of lithium ion storage at short charging times which stem from facile pseudocapacitance.     

Shuangancistrotectorines A–E,Dimeric Naphthylisoquinoline Alkaloids with Three Chiral Biaryl Axes from the Chinese Plant Ancistrocladus tectorius

Five novel dimeric naphthylisoquinoline alkaloids, shuangancistrotectorines A ( 3 a ), B ( 3 b ), C ( 4 ), D ( 5 a ), and E ( 5 b ), have been isolated from the twigs of the Chinese plant Ancistrocladus tectorius. Their absolute stereostructures were determined by spectroscopic and chiroptical methods in combination with quantum chemical CD calculations. In contrast to all other known dimeric naphthylisoquinoline alkaloids, in which the central binaphthalene axis is 6′,6′′‐coupled and thus not rotationally hindered, the dimers described here are linked via the sterically more hindered 3′,3′′‐ or 1′,1′′‐positions of the naphthalene units. They are thus the first such dimers—and even the very first natural products at all—that have three consecutive stereogenic axes. Hence, including the stereogenic centers, they have up to seven stereogenic units in total. Some of the compounds, in particular shuangancistrotectorines A, B, and D ( 3 a , 3 b , and 5 a ) exhibit very good, and specific, antiplasmodial activities.     

Hot-electron-driven enhancement of spin-lattice coupling in Gd and Tb 4f ferromagnets observed by femtosecond x-ray magnetic circular dichroism

Femtosecond x-ray magnetic circular dichroism was used to study the time-dependent magnetic moment of 4f electrons in the ferromagnets Gd and Tb, which are known for their different spin-lattice coupling. We observe a two-step demagnetization with an ultrafast demagnetization time of 750 fs identical for both systems and slower times which differ sizeably with 40 ps for Gd and 8 ps for Tb. We conclude that spin-lattice coupling in the electronically excited state is enhanced up to 50 times compared to equilibrium.     

Scheduling with few changes

In this work we consider scheduling problems where a sequence of assignments from products to machines – or from tasks to operators, or from workers to resources – has to be determined, with the goal of minimizing the costs (=money, manpower, and/or time) that are incurred by the interplay between those assignments. To account for the different practical requirements (e.g. few changes between different products/tasks on the same machine/operator, few production disruptions, or few changes of the same worker between different resources), we employ different objective functions that are all based on elementary combinatorial properties of the schedule matrix. We propose simple and efficient algorithms to solve the corresponding optimization problems, and provide hardness results where such algorithms most likely do not exist.