Threo selective cross aldol condensation with thioamide enolates generated by a michael addition of organometallics to unsaturated thioamides

Crotonothioamide, sorbothioamide, and cinnamothioamide undergo a threo selective aldol condensation via their enolates generated by a Michael addition of organometallics.     

Development of novel polymer-type dehydrocondensing reagents comprised of chlorotriazines

A novel immobilized dehydrocondensing reagent comprised of a triazine-type dehydrocondensing reagent itself in a polymerized form was synthesized by copolymerization between tetra(ethylene glycol) bis(dichlorotriazinyl) ether and tris(2-aminoethyl)amine.     

Successive methyl migrations occurring in the acid treatment of 1-epoxyethyl-1,2,2-trimethyl-cyclopentane derivative

Acid treatment of (IR, 3S,1′S)-1-(1′,2′-Epoxyethyl)-1,2,2-trimethyl-3-acetoxymethyl-cyclopentane $\text{6}$) has been shown to yield three products ($\text{8}$, $\text{9}$, $\text{10}$), among which $\text{8}$ and $\text{9}$ are 1-oxa-bicyclo[3.3.0]octane derivatives formed $\text{via}$ successive methyl migrations followed by an oxorane ring closure.     

Light-harvesting macroring accommodating a tetrapodal ligand based on complementary and cooperative coordinations

A porphyrin macroring, mimicking the light-harvesting complex of photosynthetic purple bacteria, was synthesized by self-assembling trisporphyrinatoZn(II) complexes with imidazolyl substituents at both molecular terminals. Very strong complementary coordination of imidazolyl to Zn(II) afforded exclusively the cyclic trimer of trisporphyrin under dilute conditions at 27 degrees C in CHCl3/MeOH = 9/1 (v/v). 1H NMR spectra of the macroring indicate the existence of two topological isomers, one symmetric and one asymmetric. Use of three noncoordinated porphyrinatoZn(II) sites allows a tetrapodal ligand to be incorporated into the cavity of the macroring. A Job plot and the clear bending behavior on UV-vis titration indicated the formation a 1:1 complex; the heterogeneity of two topological isomers was not observed, and both isomers similarly accommodated the tetrapodal ligand. The association constant obtained by curve fitting analysis was 8 x 108 M-1 in toluene. This large association constant reflects the cooperative nature of three coordination sites.     

A examination of the EDTA titration of manganese(II) taking into consideration formation of 1:1 and 1:2 complexes with Eriochrome Black T indicator

In the EDTA titration of manganese(II) with Eriochrome Black T as indicator, the effect of formation of 1:1 and 1:2 manganese(II)—indicator complexes must be taken into consideration. The titration error can be reduced to less than 0.1%. For comparison purpose the titration of zinc(II) has also been studied.     

Dependence of chiral recognition on the degree of substitution of cellulose benzoate

A series of cellulose benzoates with different degrees of substitution (DS) were prepared by aminolysis under homogeneous conditions. Using them as a stationary phase, the dependence of the chromatographic chiral recognition of cellulose benzoate (CB) on its DS was studied under normal phase conditions. For most enantiomeric pairs, chiral recognition decreased along with the decrease in DS. However, some enantiomeric pairs were resolved only by CBs carrying unsubstituted hydroxyl groups. Many of the compounds were quite strongly retained by cellulose benzoate with a DS of 2.8. A study of the retention behaviors of simple achiral compounds led us to the conclusion that the change in the retention behaviors by introducing free hydroxyl groups into tribenzoate is not caused by hydrogen bonding including the hydroxyl groups, but by a specific unidentified change.     

Purity determination as needed for the realisation of primary standards for elemental determination: status of international comparability

Within the National Metrology Institutes (NMIs) and designated laboratories, an interlaboratory comparison, CCQM-P107, was conducted to verify the degree of international comparability concerning the results of purity analysis. The mass fractions of Ag, Bi, Cd, Cr, Ni, Tl at the lower mg/kg-level in a high purity zinc material were determined, but the real measurand in metrological sense was the sum of the six mass fractions. Homogeneity was investigated by glow discharge mass spectrometry, reference values were obtained using isotope dilution mass spectrometry. Six NMIs participated, contributing eight independent data sets. The agreement amongst the results of the participants, their median and the agreement with the reference values were usually excellent and in almost all cases below the target uncertainty of 30% relative. In this manner, the accuracy of results and the comparability between the participants was demonstrated to be established.     

International comparison of the determination of the mass fraction of cadmium, chromium, mercury and lead in polypropylene: the Comité Consultatif pour la Quantité de Matière pilot study CCQM-P106

The CCQM-P106 pilot study was organized by the inorganic working group of the Comité Consultatif pour la Quantité de Matière (CCQM) as a feasibility comparison to study the applicability of different analysis methods to the polypropylene sample and test the abilities of the participants for measuring the Cd, Cr, Hg and Pb in polypropylene. National Institute of Metrology P.R. China (NIM) acted as the coordinating laboratory of this pilot study. There were 21 laboratories that submitted the final results. The median values of the mass fraction of Cd, Cr, Hg and Pb were 36.12 mg kg^?1 (the median absolute deviation about the median (MADe) = 0.46 mg kg^?1), 252.5 mg kg^?1 (MADe = 3.4 mg kg^?1), 387.0 mg kg^?1 (MADe = 10.1 mg kg^?1) and 466.2 mg kg^?1 (MADe = 8.9 mg kg^?1), respectively. Isotope dilution mass spectrometry (IDMS), inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma-optical emission spectrometry (ICP-OES), atomic absorption spectrometry (AAS), instrumental neutron activation analysis (INAA) and X-ray fluorescence (XRF) measurement methods were used, and microwave digestion was used by the most of the participants. In general, very good agreement of the results was observed. Moreover, compared to the results of other methods, the results of IDMS still showed less spread amongst laboratories and had a smaller uncertainty. In addition, the results of some analytes used by XRF and INAA also got satisfactory agreement with the median value.