A new approach for proficiency test exercise data evaluation

In this paper, a new data evaluation method for proficiency test exercises consisting of a combination of a z-test, a zeta test and an uncertainty outlier test is presented. This new method is compared with eight other evaluation methods (both measurement uncertainty using and measurement uncertainty ignoring) in common use and/or recommended by ISO 13528. The data set used to test the evaluation methods is real data and consists of the ⁹⁵Nb results of the National Physical Laboratory Environmental Radioactivity Proficiency Test Exercise 2007. The evaluation of 14 out of 32 results were affected by the choice of method.     

Die Kristallstrukturen der Phosphanimin‐Komplexe [NaI(HNPPh3)3] und [SrI2(HNPPh3)2(THF)2] sowie des Natrium‐triphenylphosphaniminats [NaNPPh3]6

Crystal Structures of the Phosphaneimine Complexes [NaI(HNPPh₃)₃] and [SrI₂(HNPPh₃)₂(THF)₂], as well as of Sodium Triphenylphosphoraneiminate [NaNPPh₃]₆ [NaI(HNPPh₃)₃] ( 1 ) has been obtained as yellow, moisture sensitive crystals as an intermediate product of the synthesis of sodium triphenylphosphoraneiminate, [NaNPPh₃]₆ ( 2 ) from Ph₃PI₂ and sodium amide in liquid ammonia. Correspondingly, colourless crystals of [SrI₂(HNPPh₃)₂(THF)₂] ( 3 ) are formed from strontium amide and Ph₃PI₂ in liquid ammonia and subsequent recrystallisation of the primary product [SrI₂(HNPPh₃)₄] from thf solution. The complexes 1 – 3 are mainly characterized by crystal structure determinations. 1 · 0,5 thf: space group P3c1, Z = 4, lattice dimensions at 193 K: a = b = 1533.2(1); c = 2545.6(1) pm, R = 0.0417. 1 has a molecular structure in which the sodium atom is tetrahedrally coordinated by the iodine atom with a distance of 315.9 pm and by the nitrogen atoms of the three HNPPh₃ molecules with a distance of 238.9 pm. 2 · C₇H₈: space group P1, Z = 1, lattice dimensions at 213 K: a = 1457.1(1), b = 1484.9(1), c = 1502.7(1) pm; α = 116.32(1)°, β = 115.358(10)°, γ = 93.585(14)°; R = 0.0520. 2 has a molecular structure in which the six sodium atoms and the six nitrogen atoms of the (NPPh₃^–) groups form a hexagonal prism with approximate D_3d symmetry. 3 · 2 thf: space group P1, Z = 2, lattice dimensions at 193 K: a = 1042.9(1), b = 1337.4(1), c = 2095.1(1) pm; α = 90.130(8)°, β = 96.310(8)°, γ = 111.985(8)°; R = 0.0310. 3 has a molecular structure in which the strontium atom is octahedrally coordinated by the iodine atoms, by the nitrogen atoms of the HNPPh₃ molecules and by the oxygen atoms of the thf molecules, all ligands being in trans‐position to one another.     

Total synthesis of lodopyridone

A convergent total synthesis of the structurally unprecedented alkaloid lodopyridone was achieved using a cross-coupling of an iodopyridone fragment with a quinolinethiazolylstannane. Key features of the syntheses of the pentasubstituted 4-pyridone were a regioselective bromination of a 4-pyridone derived from kojic acid, a subsequent Cu-mediated introduction of the thioether, and a directed lithiation/iodination step. A chemoselective Negishi cross-coupling of a dibromothiazole and a quinolinylzinc reagent was used to assemble the chloroquinolinethiazol moiety.     

N‐Heterocyclic Olefin–Carbon Dioxide and –Sulfur Dioxide Adducts: Structures and Interesting Reactivity Patterns

Depending on the amount of methanol present in solution, CO₂ adducts of N‐heterocyclic carbenes (NHCs) and N‐heterocyclic olefins (NHOs) have been found to be in fully reversible equilibrium with the corresponding methyl carbonate salts [EMIm][OCO₂Me] and [EMMIm][OCO₂Me]. The reactivity pattern of representative 1‐ethyl‐3‐methyl‐NHO–CO₂ adduct 4 has been investigated and compared with the corresponding NHC–CO₂ zwitterion: The protonation of 4 with HX led to the imidazolium salts [NHO–CO₂H][X], which underwent decarboxylation to [EMMIm][X] in the presence of nucleophilic catalysts. NHO–CO₂ zwitterion 4 can act as an efficient carboxylating agent towards CH acids such as acetonitrile. The [EMMIm] cyanoacetate and [EMMIm]₂ cyanomalonate salts formed exemplify the first C?C bond‐forming carboxylation reactions with NHO‐activated CO₂. The reaction of the free NHO with dimethyl carbonate selectively led to methoxycarbonylated NHO, which is a perfect precursor for the synthesis of functionalized ILs [NHO–CO₂Me][X]. The first NHO‐SO₂ adduct was synthesized and structurally characterized; it showed a similar reactivity pattern, which allowed the synthesis of imidazolium methyl sulfites upon reaction with methanol.     

Enantioselective photochemical reactions of 2-pyridones in solution

[reaction: see text] Two key photochemical reactions of prochiral 2-pyridones were studied in the presence of a chiral host. The [4 + 4]-photocycloaddition with cyclopentadiene (CpH) proceeded smoothly and with high enantioselectivity (84-87% ee). The absolute configuration of the endo-diastereoisomer was established by X-ray crystallography. The electrocyclic [4pi]-ring closure to 3-oxo-2-azabicyclo[2.2.0]-5-hexenes occurred with lower enantioselectivity (20-23% ee at -20 degrees C). The velocity of the latter reaction slowed significantly with decreasing temperature.     

The challenges in reliable determination of degradation rates and lifetime in polymer electrolyte membrane fuel cells

The durability of polymer electrolyte membrane fuel cells (PEMFCs) needs to be further improved to cope with application requirements and economic competitiveness. This article highlights the challenges in the reliable determination of degradation rates and lifetime. The reliable evaluation of performance degradation rates is fundamental to quantify and benchmark durability and to allow comparisons between PEMFC durability tests performed using different materials or in different laboratories. The use of efficient recovery procedures enables the discrimination of reversible and irreversible voltage losses and facilitates the understanding of recovery mechanisms. In the end, recent contributions about lifetime diagnoses and prediction are presented, which are promising to be implemented in PEMFC applications.