Cyano- and isocyanotris(trifluoromethyl)borates: syntheses, spectroscopic properties, and solid state structures of K[(CF3)3BCN] and K[(CF3)3BNC

A two step synthesis to the isocyanotris(trifluoromethyl)borate anion, [(CF3)3BNC]-, and its isomerization to the cyanotris(trifluoromethyl)borate anion, [(CF3)3BCN]-, at temperatures above 150 degrees C are presented. In the first step (CF3)3BNCH was obtained by reacting (CF3)3BCO with hydrogen cyanide followed by deprotonation of the HCN adduct with Li[N(SiMe3)2] in toluene. The thermal behavior of K[(CF3)3BNC] and K[(CF3)3BCN] were investigated by differential scanning calorimetry (DSC), and K[BF4] was identified as a major solid decomposition product. The enthalpy of the isocyanide-cyanide rearrangement, deltaH(iso) = -35 +/- 4 kJ mol(-1), was obtained from DSC measurements, and the activation energy, E(a) = 180 +/- 20 kJ mol(-1), from kinetic measurements. The isomerization was modeled as an intramolecular reaction employing DFT calculations at the B3LYP/6-311+G(d) level of theory yielding a reaction enthalpy of deltaH(iso) = -36.1 kJ mol(-1) and an activation energy of E(a) = 155.7 kJ mol(-1). The solid-state structures of K[(CF3)3BNC] and K[(CF3)3BCN] were determined by single-crystal X-ray diffraction. Both salts are isostructural and crystallize in the orthorhombic space group Pnma (no. 62). In the crystals the borate anions possess C(s) symmetry, while for the energetic minimum C3 symmetry is predicted by DFT calculations. The borate anions have been characterized by IR and Raman spectroscopy as well as by NMR spectroscopy. The assignment of the IR and Raman bands is supported by their calculated wavenumbers and intensities. The spectroscopic and structural properties of both borate anions are compared to the properties of the isoelectronic borane carbonyl (CF3)3BCO and the [B(CF3)4]- anion as well as to those of other related species.     

Covalent and selective immobilization of fusion proteins

A general method for the covalent immobilization of fusion proteins is presented. The approach is based on the unusual mechanism of the human O6-alkylguanine-DNA alkyltransferase, which irreversibly transfers the alkyl group from its substrate, alkylated or benzylated guanine, to a reactive cysteine residue. By attaching the benzyl group to a surface, hAGT fusion proteins immobilize themselves in a specific and covalent manner. The specificity of the reaction of hAGT with its substrate even allows the specific immobilization of hAGT fusion proteins directly out of cell extracts, making the approach an attractive alternative to currently used immobilization procedures.     

Stereocontrolled Syntheses of Seven‐Membered Carbocycles by Tandem Allene Aziridination/[4+3] Reaction

A tandem allene aziridination/[4+3]/reduction sequence converts simple homoallenic sulfamates into densely functionalized aminated cycloheptenes, where the relative stereochemistry at five contiguous asymmetric centers can be controlled through the choice of the solvent and the reductant. The products resulting from this chemistry can be readily transformed into complex molecular scaffolds which contain up to seven contiguous stereocenters.     

In-tube extraction for enrichment of volatile organic hydrocarbons from aqueous samples

In-tube extraction (ITEX) is a novel solventless extraction technique in which a headspace syringe with a needle body filled with a sorbent (here: Tenax TA) is used. The analytes are extracted from sample headspace by dynamic extraction. The needle body is surrounded by a separate heater, which is used for thermal desorption of analytes into the injection port of a GC system. We report here for the first time the optimization and evaluation of a fully automated analytical method based on ITEX. As target analytes, 19 common groundwater contaminants such as halogenated volatiles and monoaromatic compounds have been chosen. Method related parameters such as extraction temperature, number of extraction cycles, extraction and desorption volume as well as extraction and desorption flow rates were investigated in detail. The linear dynamic range of the ITEX method ranged over six orders of magnitude between 0.028 microg/L and 1218 microg/L with linear correlation coefficients between 0.990 and 0.998 for the investigated compounds. Method detection limits for monoaromatic compounds were between 28 ng/L (ethylbenzene) and 68 ng/L (1,2,4-trimethylbenzene). For halogenated volatile organic compounds, method detection limits between 48 ng/L (chloroform) and 799 ng/L (dichloromethane) were obtained. The precision of the method with external calibration was between 3.1% (chloroform ethylbenzene) and 7.4% (1,2,3-trimethylbenzene).     

An engineered protein tag for multiprotein labeling in living cells

The visualization of complex cellular processes involving multiple proteins requires the use of spectroscopically distinguishable fluorescent reporters. We have previously introduced the SNAP-tag as a general tool for the specific labeling of SNAP-tag fusion proteins in living cells. The SNAP-tag is derived from the human DNA repair protein O6-alkylguanine-DNA alkyltransferase (AGT) and can be covalently labeled in living cells using O6-benzylguanine derivatives bearing a chemical probe. Here we report the generation of an AGT-based tag, named CLIP-tag, which reacts specifically with O2-benzylcytosine derivatives. Because SNAP-tag and CLIP-tag possess orthogonal substrate specificities, SNAP and CLIP fusion proteins can be labeled simultaneously and specifically with different molecular probes in living cells. We furthermore show simultaneous pulse-chase experiments to visualize different generations of two different proteins in one sample.     

A comparison of three heuristics on a practical case of sub-daily staff scheduling

Sub-daily personnel planning, which is the focus of our work offers considerable productivity reserves for companies in certain industries, such as logistics, retail and call centres. However, it also creates complex challenges for the planning software. We compare particle swarm optimisation (PSO), the evolution strategy (ES) and a constructive agent-based heuristic on a set of staff scheduling problems derived from a practical case in logistics. All heuristics significantly outperform conventional manual full-day planning, demonstrating the value of sub-daily scheduling heuristics. PSO delivers the best overall results in terms of solution quality and is the method of choice, when CPU-time is not limited. The approach based on artificial agents is competitive with ES and delivers solutions of almost the same quality as PSO, but is vastly quicker. This suggests that agents could be an interesting method for real-time scheduling or re-scheduling tasks.     

Recoverable strain storage capacity of shape memory polyethylene

Shape memory polymers (SMPs) are an important class of smart materials. So far the focus of such polymers was to find suited triggers for various application fields. Thus, the potential of most of these macromolecular networks regarding their maximally storable strain capability was not explored. In this study, the polyethylenes HDPE, LDPE, and ethylene‐1‐octene (EOC) were systematically investigated with respect to their strain storage potential. To achieve maximum strains, the polymers were chemically cross‐linked in such a way that they are at the borderline between thermoplastics and elastomers. All investigated polymers showed higher strain storage than literature reported systems and exhibited excellent shape memory parameters. The highest stored strain was found for networks of EOC with fully recoverable 1400%. Interestingly, this value could not be enlarged by using EOCs with higher molecular weight, which is probably due to increasing content of entanglements as confirmed by Mooney‐Rivlin. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1033–1040     

Silver(I) Clusters Stabilized by the Carba-closo-dodecaboranylethynyl Ligand with O-Donor Coligands and Template Ions

Large silver(I) clusters stabilized by the dianionic carba-closo-dodecaboranylethynyl ligand were obtained. Crystallization of polymeric {Ag₂(12-C≡C-closo-1-CB₁₁H₁₁)}_n from dimethyl sulfoxide afforded [Ag₁₄(12-C≡C-closo-1-CB₁₁H₁₁)₇(DMSO)₁₂] · DMSO that contained an Ag^I₁₀ cage augmented by four Ag^I ions. Crystals of [Ag₁₆(12-C≡C-closo-1-CB₁₁H₁₁)₈(THF)₁₂] · 2THF were obtained from anhydrous THF and {Ag₂(12-C≡C-closo-1-CB₁₁H₁₁)}_n. In the presence of moisture the similar but water-containing complex [Ag₁₆(12-C≡C-closo-1-CB₁₁H₁₁)₈(THF)₁₂(H₂O)₂] · 2.5THF was identified. Both silver(I) clusters are composed of a central octahedral Ag^I₆ unit and ten further silver(I) ions bonded via argentophilic interactions. [Ag₁₄(12-C≡C-closo-1-CB₁₁H₁₁)₇(DMSO)₁₂] · DMSO and [Ag₁₆(12-C≡C-closo-1-CB₁₁H₁₁)₈(THF)₁₂] · 2THF were characterized by elemental analysis and vibrational (IR and Raman) as well as NMR spectroscopy. In addition, the crystal structures of [Ag₂₅(12-C≡C-closo-1-CB₁₁H₁₁)₁₂(CH₃CN)_13.5(OH)] · 0.5CH₃CN and [Ag₂₅(12-C≡C-closo-1-CB₁₁H₁₁)₁₂{(CH₃)₂CO}_13.5(H₂O)Cl] · 15(CH₃)₂CO were determined. Both compounds contain Ag^I₁₄ rhombic dodecahedrons augmented by eleven silver(I) ions. A hydroxide or a chloride template ion is present in the center of the rhombic dodecahedron, respectively.