An improved monotone algorithm for scheduling related machines with precedence constraints

We answer an open question posed by Krumke et al. (2008) [6] by showing how to turn the algorithm of Chekuri and Bender for scheduling related machines with precedence constraints into an O(logm)-approximation algorithm that is monotone in expectation. This significantly improves on the previously best known monotone approximation algorithms for this problem, from Krumke et al. [6] and Thielen and Krumke (2008) [8], which have an approximation guarantee of O(m^2/3).     

Aqueous Catalytic Polymerization of Olefins

Catalytic conversions in aqueous environments by transition metal complexes have become a well‐established field over the past two decades. However, the vast majority of investigations have focussed on small‐molecule synthesis. This may appear somewhat surprising as water is a particularly attractive reaction medium, especially for polymerization reactions. For example, aqueous emulsion and suspension polymerization is carried out today on a large scale by noncatalytic free‐radical routes. Polymer latices can be obtained as a product, that is, stable aqueous dispersions of polymer particles in the size range of 50 to 1000 nm. Such latices possess a unique property profile. Amongst other advantages, the use of water as a dispersing medium is particularly environmentally friendly. In comparison to these free‐radical reactions, aqueous catalytic polymerizations of olefinic monomers have received less attention. However, considerable advances and an increased awareness of this field have emerged during the past few years. A variety of high molecular weight polymers ranging from amorphous or semicrystalline polyolefins to polar‐substituted hydrophilic materials have now been prepared by catalytic polymerization of olefinic monomers in water. Polymer latices based on a number of readily available monomers are accessible and catalytic activities as high as 10⁵ turnovers per hour have already been reported. As another example, materials prepared by aqueous catalytic polymerization have been investigated as protein inhibitors. A versatile field spanning colloids, polymer, and coordination chemistry has emerged.     

1-Zirconacyclobuta-2,3-dienes: synthesis of organometallic analogs of elusive 1,2-cyclobutadiene,unprecedented intramolecular C–H activation,and reactivity studies

The structure, bonding, and reactivity of small, highly unsaturated ring systems is of fundamental interest for inorganic and organic chemistry. Four-membered metallacyclobuta-2,3-dienes, also referred to as metallacycloallenes, are among the most exotic examples for ring systems as these represent organometallic analogs of 1,2-cyclobutadiene, the smallest cyclic allene. Herein, the synthesis of the first examples of 1-zirconacyclobuta-2,3-dienes of the type [Cp′₂Zr(Me₃SiC₃SiMe₃)] (Cp′₂ = rac-(ebthi), (ebthi = 1,2-ethylene-1,1′-bis(η⁵-tetrahydroindenyl)) (2a); rac-Me₂Si(thi)₂, thi = (η⁵-tetrahydroindenyl), (2b)) is presented. Both complexes undergo selective thermal C–H activation at the 7-position of the ansa-cyclopentadienyl ligand to produce a new type of “tucked-in” zirconocene system, 3a and 3b, that possesses a η³-propargyl/allenyl ligand. Both types of complexes react with carbonyl compounds, producing enynes in the case of 2a and 2b, as well as η¹-allenyl complexes for 3a and 3b. Computational analysis of the structure and bonding of 2a and 3a reveals significant differences to a previously described related Ti complex. All complexes were fully characterised, including X-ray crystallography and experimental results were supported by DFT analysis.

A detailed study of structure, bonding and reactivity of new 1-zirconacyclobuta-2,3-dienes is presented in comparison to a lighter Ti analog. We found a unique C–H activation at the widely used rac-(ebthi) ligand for that only occurs for Zr.     

Novel Amidoniobium Complexes with a Functional Relationship to the [Cp2ZrR]+ Ion*

Partial abstraction of apical methyl groups is observed in aminopyridinatoniobium alkyne complexes, as exemplified with the synthesis and characterization of 1 . This results in cationic complex fragments, which facilitate the polymerization of ethylene and in the presence of methylalumoxane the selective dimerization of 1-butene.     

Negishi Cross-Coupling in the Preparation of Benzyl Substituted Pyrrolo[2,3-d]pyrimidine Based CSF1R Inhibitors

The colony-stimulating factor 1 receptor (CSF1R) is a protein kinase emerging as an attractive target with clinical relevance in cancer, CNS and inflammatory diseases. Molecular docking experiments followed by synthesis and structure–activity relationship have been used to identify low molecular weight structures as promising hits for lead optimization. These molecules are synthesized from a 4-chloro-6-iodo-pyrrolo[2,3-d]pyrimidine building block using Negishi and Suzuki–Miyaura cross-coupling reactions in high yields. Several inhibitors possessed excellent enzymatic potency, and the parent compound preferably binds to the autoinhibited form of CSF1R. Cellular and in vivo profiling indicate that further tuning of drug structure is needed prior to efficacy studies.     

Linear-temperature programmed pyrolysis of thermoresistant polymers - mass and FTIR spectrometries I. Experimental; aromatic polyethers and polyetherketones

During thermal decomposition, most of the thermo-resistant polymers leave a considerable fraction of the original mass behind, consisting mainly of a carbonaceous material. The gases evolved are, to the largest part, low-molecular (H₂O, CO₂, CO, NH₃, HCN, hydrocarbons); they are formed during polycondensation processes. The rate of heating strongly influences the degradation mechanism and thus the composition of the gaseous pyrolyzate. Rapid heating i.v. to the maximum temperature chosen frequently favors the formation of heavy fragments. These can be identified by field-ionization or low-voltage mass spectrometry; they usually allow conclusions on the composition of the original polymer. Slow, temperature-controlled heating allows rearrangement and polycondensation reactions in the polymer. A study of the processes going on in the residue during temperature-controlled heating is important with regard to the behavior of thermoresistant polymers under real conditions. An elegant method of continuous residue analysis is FTIR spectrometry. A heatable IR cell designed in our institute allows the study of both gaseous pyrolyzate and solid residue in separate experiments. The time needed for the measurement of one spectrum (from 20 scans) was 36 s. This, with a heating rate of 5 K/min, corresponds to a temperature resolution of 3 K/spectrum. Results are given for aromatic polyethers and polyetherketones.