Reactivity of dissolving pulps modified by TEMPO-mediated oxidation

The reactivity of dissolving pulps towards derivatization or dissolution is a crucial quality parameter and is mainly determined by the accessibility of the hydroxyl groups. When dissolving pulps are produced from paper-grade pulps by cold caustic extraction (CCE), their reactivity is often inferior as compared to commercial prehydrolysis kraft dissolving pulps. It was hypothesized that pulp reactivity can be enhanced by the introduction of small amounts of substituents to facilitate interchain accessibility. In this study, CCE-treated Eucalyptus globulus kraft paper pulp was subjected to TEMPO-mediated oxidation to initiate partial oxidation of the C₆-hydroxyl groups to carboxyl groups. The effect of this pulp modification on the reactivity towards xanthation and the subsequent dissolution in diluted aqueous alkali solution (viscose process) as well as the dissolution in complexing and non-complexing solvents, respectively, was thoroughly examined. The results revealed that the oxidized pulps rich in C₆-carboxylate groups impeded the xanthation reaction obviously because of the reduced availability of hydroxyl groups. When N-methylmorpholine-N-oxide monohydrate was used as a direct solvent, a very high content of C₆-carboxylate groups was found to reduce the solubility of the pulp fibers as less hydrogen bonds can be formed with NMMO·H₂O. In the case of dissolution in the complexing solvent cupriethylenediamine, the dissolution mechanism of cellulose was not deteriorated by the high content of C₆-carboxylate groups. Instead, the oxidation procedure increased the hydrophilic character and the swelling capacity of the outer cell wall layers allowed homogeneous dissolution.     

Water‐Developable Poly(2‐oxazoline)‐Based Negative Photoresists

Copoly(2‐oxazoline)‐based photoresists are prepared from pEtOx₈₀Bu⁼Ox₂₀ and pPhOx₈₀Dc⁼Ox₂₀ , respectively, a tetrathiol, and a photosensitive initiator. It is possible to prepare copoly(2‐oxazoline)s bearing unsaturated side chains in a microwave reactor on a decagram scale in reaction times of 100 min or shorter. UV irradiation of dried polymer films through a quartz mask induces the thiol‐ene reaction in the illuminated areas. Subsequent development of the polymer films in halogen‐free solvents reproduces the negative pattern of the mask with a resolution of 2 μm. The pEtOx₈₀Bu⁼Ox₂₀ ‐derived photoresists can also be developed in water.     

Hybrid large neighborhood search for the bus rapid transit route design problem

Due to an increasing demand for public transportation and intra-urban mobility, an efficient organization of public transportation has gained significant importance in the last decades. In this paper we present a model formulation for the bus rapid transit route design problem, given a fixed number of routes to be offered. The problem can be tackled using a decomposition strategy, where route design and the determination of frequencies and passenger flows will be dealt with separately. We propose a hybrid metaheuristic based on a combination of Large Neighborhood Search (LNS) and Linear Programming (LP). The algorithm as such is iterative. Decision upon the design of routes will be handled using LNS. The resulting passenger flows and frequencies will be determined by solving a LP. The solution obtained may then be used to guide the exploration of new route designs in the following iterations within LNS. Several problem specific operators are suggested and have been tested. The proposed algorithm compares extremely favorable and is able to obtain high quality solutions within short computational times.     

Synthesis of highly functionalized biaryls by condensation of 2-fluoro-1,3-bis(silyloxy) 1,3-dienes with 3-cyanochromones and subsequent domino "retro-Michael/aldol/fragmentation"

The Me(3)SiOTf-mediated condensation of 1-ethoxy-2-fluoro-1,3-bis(trimethylsilyloxy) 1,3-dienes with 3-cyanochromones afforded 3-cyano-2-(4-ethoxy-3-fluoro-2,4-dioxobutyl)chroman-4-ones. Their reaction with triethylamine afforded fluorinated azaxanthones or biaryls. The product distribution depends on the structure of the diene. The formation of the biaryls can be explained by an unprecedented domino "retro-Michael/aldol/fragmentation" reaction.     

Synthesis,Structure, and Physico‐optical Properties of Manganate(II)‐Based Ionic Liquids

Several ionic liquids (ILs) based on complex manganate(II) anions with chloro, bromo, and bis(trifluoromethanesulfonyl)amido (Tf₂N) ligands have been synthesized. As counterions, n‐alkyl‐methylimidazolium (C_nmim) cations of different chain length (alkyl=ethyl (C₂), propyl (C₃), butyl (C₄), hexyl (C₆)) were chosen. Except for the 1‐hexyl‐3‐methylimidazolium ILs, all of the prepared compounds could be obtained in a crystalline state at room temperature. However, each of the compounds displayed a strong tendency to form a supercooled liquid. Generally, solidification via a glass transition took place below ?40 °C. Consequently, all of these compounds can be regarded as ionic liquids. Depending on the local coordination environment of Mn²⁺, green (tetrahedrally coordinated Mn²⁺) or red (octahedrally coordinated Mn²⁺) luminescence emission from the ⁴T(G) level is observed. 1 The local coordination of the luminescent Mn²⁺ centre has been unequivocally established by UV/Vis as well as Raman and IR vibrational spectroscopies. Emission decay times measured at room temperature in the solid state (crystalline or powder) were generally a few ms, although, depending on the ligand, values of up to 25 ms were obtained. For the bromo compounds, the luminescence decay times proved to be almost independent of the physical state and the temperature. However, for the chloro‐ and bis(trifluoromethanesulfonyl)amido ILs, the emission decay times were found to be dependent on the temperature even in the solid state, indicating that the measured values are strongly influenced by nuclear motion and the vibration of the atoms. In the liquid state, the luminescence of tetrahedrally coordinated Mn²⁺ could only be observed when the tetrachloromanganate ILs were diluted with the respective halide ILs. However, for [C₃mim][Mn(Tf₂N)₃], in which Mn²⁺ is in an octahedral coordination environment, a weak red emission from the pure compound was found even in the liquid state at elevated temperatures.     

Localization of noncovalent complexes in MALDI-preparations by CLSM

The unambiguous detection of noncovalent complexes (NCCs) by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is still a far cry from being routine. For protein NCCs such as their quaternary structure it has been reported that signals of the intact complex are only obtained for the first or at most the first few laser exposures of a given sample area. This observation was called the first-shot phenomenon. In the present study, this first-shot phenomenon has been investigated for the hexameric protein complex allophycocyanine (APC) by two independent methods, MALDI-MS with a (nearly) pH-neutral matrix 6-aza-2-thiothymine (6-ATT) and by imaging the fluorescence of the complex in APC-6-ATT preparations by confocal laser scan microscopy (CLSM). The intact APC heterohexamer loses its visible fluorescence upon dissociation into its subunits. Both methods consistently show that intact APC complexes are precipitated at the matrix crystal surface, but dissociate upon incorporation into the matrix crystals.     

Terminal Alkenes as Versatile Chemical Reporter Groups for Metabolic Oligosaccharide Engineering

The Diels–Alder reaction with inverse electron demand (DAinv reaction) of 1,2,4,5‐tetrazines with electron rich or strained alkenes was proven to be a bioorthogonal ligation reaction that proceeds fast and with high yields. An important application of the DAinv reaction is metabolic oligosaccharide engineering (MOE) which allows the visualization of glycoconjugates in living cells. In this approach, a sugar derivative bearing a chemical reporter group is metabolically incorporated into cellular glycoconjugates and subsequently derivatized with a probe by means of a bioorthogonal ligation reaction. Here, we investigated a series of new mannosamine and glucosamine derivatives with carbamate‐linked side chains of varying length terminated by alkene groups and their suitability for labeling cell‐surface glycans. Kinetic investigations showed that the reactivity of the alkenes in DAinv reactions increases with growing chain length. When applied to MOE, one of the compounds, peracetylated N‐butenyloxycarbonylmannosamine, was especially well suited for labeling cell‐surface glycans. Obviously, the length of its side chain represents the optimal balance between incorporation efficiency and speed of the labeling reaction. Sialidase treatment of the cells before the bioorthogonal labeling reaction showed that this sugar derivative is attached to the glycans in form of the corresponding sialic acid derivative and not epimerized to another hexosamine derivative to a considerable extent.     

Benzo‐Annulated Steroids: Synthesis of Octahydro‐indeno‐phenanthrenes by Formal [3+3] Cyclocondensation Reaction with 1,3‐Bis[(trimethylsilyl)oxy]buta‐1,3‐dienes

Octahydro‐indeno‐phenanthrenes, benzo‐annulated steroids, were prepared by formal [3+3] cyclocondensation reaction of 1,3‐bis[(trimethylsilyl)oxy]buta‐1,3‐dienes with the silyl enol ether of 16‐formylestrone methyl ether.