New preparation of 1,2,4,5,7,8-hexaoxonanes

A new versatile procedure was developed for the synthesis of 1,2,4,5,7,8-hexaoxonanes based on the Lewis acid catalyzed reaction of acetals with 1,1'-dihydroperoxydicycloalkyl peroxides. The procedure substantially extends the structural diversity of these compounds and, in most cases, allows the synthesis of these compounds in higher yields (to 96%) and with higher selectivity. Complexation of hexaoxonane with chloroform was documented for the first time. The structures of several triperoxides were established by X-ray diffraction.     

CT-CT annihilation in rigid perylene end-capped pentaphenylenes

The time-dependent spectral properties of a rigid, extended system consisting of three pentaphenylene units end-capped with perylene monoimide were investigated in detail by femtosecond transient absorption and single photon timing measurements. In polar solvents, the molecular system shows the occurrence of photoinduced charge transfer. Upon gradually increasing the excitation power, annihilation involving two states with charge-transfer character has been observed. Quantum-chemical calculations performed on the system consisting of two pentaphenylene units end-capped with perylene monoimide strongly support the experimental data.     

Peptide synthesis in aqueous environments: the role of extreme conditions on amino acid activation

The free energy surfaces and reaction mechanisms underlying the activation of amino acids by COS in bulk water at ambient conditions as well as extreme temperature-pressure thermodynamic conditions were studied using accelerated ab initio molecular dynamics. The results for the reaction sequence leading from glycine to its activated form, a so-called Leuchs anhydride or alpha-amino acid N-carboxyanhydride (NCA), suggest that extreme conditions not far from the critical point of water may favor the formation of this activated species. This is traced back to appropriately affecting relative stabilities of neutral versus charged or zwitterionic molecular species which shifts equilibria, affects relative barriers, and thus modifies reaction rates. Furthermore, it is shown that the N-carboxyanhydride of glycine is not formed from N-thiocarboxyl glycine by its direct cyclization, but instead an indirect mechanism, the so-called isocyanate route, is clearly preferred at both conditions. The work quantitatively underpins the impact of extreme solvent conditions on the investigated organic reactions in aqueous media which implies that the presented results are of relevance to fields such as prebiotic chemistry and green chemistry.     

New Type of Neutral Binuclear Spin-Crossover Complex of Iron(III) with Twist of Two Disulfide Bridges as a Product of Electrochemical Oxidation of [FeIII(5Cl-thsa)2]− Anions

As a result of the electrochemical oxidation process, the [Fe^III(5Cl-thsa)₂]⁻ spin-crossover (SCO) anion with N₂S₂O₂ coordination sphere transforms into N₄O₂-coordinated Fe^III SCO neutral binuclear complex 2 with twist of two disulfide bridges. Each dimeric complex is a binuclear double-stranded helicate with similar chirality of both Fe centers. The crystal structure of the complex 2 ⋅ 3H₂O at 100 K has a monoclinic C2/c space group and contains large cavities (about 21.5 % of the unit cell volume) half-filled by 3 water molecules per one dimer. The N₄O₂ coordination of iron(III) with two oxygen atoms (−O⁻) of phenoxy groups, two imine-type (−N_im=) nitrogen atoms of azomethine groups, one amidrazone-type (=N_amidH) nitrogen atom and one ionized terminal group (−N_ionizH) of nitrogen has not been observed in CCDC so far. The oxidation state of the iron atoms in the dimeric complex was confirmed by ⁵⁷Fe Mössbauer spectroscopy on 90 % enriched ⁵⁷Fe sample. Mössbauer spectra and dc magnetic measurements demonstrated the partial HS-HS→LS-LS SCO in the 185–225 K temperature range. The details of the structure of complex 2 and the features of its magnetic properties were refined by theoretical analysis based on DFT calculations. The B3LYP* functional correctly predicting the energy of the spin-crossover process was revealed.     

Unconditional convergence and error estimates for bounded numerical solutions of the barotropic Navier–Stokes system

We consider a mixed finite‐volume finite‐element method applied to the Navier–Stokes system of equations describing the motion of a compressible, barotropic, viscous fluid. We show convergence as well as error estimates for the family of numerical solutions on condition that: (a) the underlying physical domain as well as the data are smooth; (b) the time step and the parameter of the spatial discretization are proportional, ; and (c) the family of numerical densities remains bounded for . No a priori smoothness is required for the limit (exact) solution. © 2016 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 1208–1223, 2017     

Implementing an image based control algorithm for an optomechanical image derotator

In this paper an image-based control for an optomechanical image derotator is implemented. A derotator is an optical system to support measurements on rotating components by tracking their rotational movement. As a consequence, the position and rotational velocity of the measurement object has to be known continuously. In general this would be accomplished by measuring these variables using a rotary encoder. However, not all measuring objects are equipped for this task. As a solution universally applicable to a wide range of measuring objects, an image-based approach is developed in the scope of this work. The object is captured with a high-speed camera to determine its position and velocity by image processing algorithms. To proof the applicability of this concept, a controller using the data acquired with the camera and a controller using data of the rotary encoder are compared. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of α-CF3- and α-CCl3 substituted nitrogen heterocycles by aza Diels-Alder and cyclocondensation reactions

Convenient synthetic approaches for α-CF₃- and α-CCl₃ substituted pyridines, hydrogenated pyridines, azanorbornenes, 4H-1,2,4-thiadiazine- and 2H-1,2,6-thiadiazine-1,1-dioxides were developed on the basis of cycloaddition and cyclocondensation reactions of trihaloethaneimines and imidoyl chlorides.     

The Low Mach Number Limit for the Full Navier–Stokes–Fourier System

We study the low Mach number asymptotic limit for solutions to the full Navier–Stokes–Fourier system, supplemented with ill-prepared data and considered on an arbitrary time interval. Convergencetowards the incompressible Navier–Stokes equations is shown.     

On the Long-Time Behaviour of Solutions to the Navier–Stokes–Fourier System with a Time-Dependent Driving Force

In this paper, we give a complete characterization of the asymptotic behaviour of solutions to the Navier–Stokes–Fourier system. We show that either the driving force behaves asymptotically as a gradient of a scalar function, in which case any solution tends to a static state, or the total energy goes to infinity with growing time.     

Asymptotically Local Minimax Estimation of Infinitely Smooth Density with Censored Data

The problem of the nonparametric minimax estimation of an infinitely smooth density at a given point, under random censorship, is considered. We establish the exact asymptotics of the local minimax risk and propose the efficient kernel-type estimator based on the well known Kaplan-Meier estimator.