Determination of the purity of acidimetric standards by constant-current coulometry, and the intercomparison between CRMs

The accuracy and uncertainty of the coulometric measurement results of reference materials for acidimetric titration were examined in this study. The results for amidosulfuric acid and potassium hydrogen phthalate are presented. The uncertainty was investigated by examining the dependency on the sample size and on the electrolysis current. Changes in the titration parameters did not result in any significant effects on the titration results. Acidimetric standards with the certified value linked to the SI were developed. In addition, the intercomparison of acidimetric standards was carried out by gravimetric titration, and the relationship between our coulometric results was determined. Furthermore, due to recent internationalization, not only the traceability to the SI but also the relationship and consistency of their analytical data have gained increasing importance. Our results were validated using certified reference materials (CRMs) obtained from different National Metrology Institutes (NMIs), and their relationships are presented. Presented at -- “BERM-10” -- April 2006, Charleston, SC, USA.     

Synthesis,structure, and chemical property of the first fluorine-containing porphycene

[structure: see text] A pyrrolic macrocycle, beta-tetrakis(trifluoromethyl)porphycene, is the first example of a fluorine-containing porphycene. Four electron-withdrawing CF(3) substituents provide a highly distorted structure and an attractive electron-deficient nature for the porphycene framework. From the electrochemical study, it is found that the LUMO energy level for the beta-trifluoromethylporphycene is 1.24 V more stabilized compared to that for etioporphyrin. Moreover, the deprotonation of the inner N[bond]H proton in the porphycene was observed upon the addition of DBU.     

Diastereomixture and racemate of myo-inositol derivatives, stronger organogelators than the corresponding homochiral isomers

Contrary to the usually accepted phenomena, an optically heterogeneous 1:1 diastereomixture of DS and LS and a racemate of LS and DR obtained, respectively, from a racemic myo-inositol derivative and (S)- and racemic O-acetylmandelic acid formed stronger organogels, especially with aromatic fluids, than those formed from homochiral isomers, DS and LS. One of the plausible reasons for the formation of the stronger diastereomeric gel is shown to be the complementary interaction of two diastereomers.     

Total synthesis, elucidation of absolute stereochemistry, and adjuvant activity of trihydroxy fatty acids

Pinellic acid from the tuber of Pinellia ternate, an active herbal component of the traditional Japanese herbal (Kampo) medicine Sho-seiryu-to, is a C18 trihydroxy fatty acid whose absolute stereochemistry has now been determined. All stereoisomers of pinellic acid were synthesized via regioselective asymmetric dihydroxylation, regioselective inversion, and stereoselective reduction in order to determine their absolute stereochemistries and adjuvant activities. Among this series of isomers, the (9S,12S,13S)-compound, which is a natural product, exhibited the most potent adjuvant activity. Spectral data for all of the stereoisomers of the 1,2-allylic diols were compared and related to their stereochemistries.     

Harmonization of methods for analysis of cholesterol oxides in foods--the first portion of a long road toward standardization: interlaboratory study

A compilation of literature data on the content of cholesterol oxidation products (COP) in various food products and in blood demonstrates a large variation in content in products or tissues of very similar nature when analyzed in different laboratories according to a large number of methods. The lack of validated, internationally recognized methodology with published accuracy and precision has so far hindered such assessments. Hence an interlaboratory comparision of methodologies of COP analysis was undertaken on egg yolk powders (EYP), whole milk powders (WMP), skim milk powders (SMP), and lard (L). Each product type had one fresh sample (low) and one aged (high) in COP contents. A total of 17 sets of results on WMP, 15 on SMP and EYP, and 13 on L were compared. Overall results (mg/kg sample) varied extensively: Fresh EYP 0.72-265, aged EYP 2.51-361; fresh WMP 0.02-18.1, aged WMP 0.02-26.9; fresh SMP 0.02-6.51, aged SMP <0.01-6.51; fresh L 0.18-97, aged L 4.15-452. Some results were questioned, viz., those from laboratories not indicating substantial differences between samples "low" and "high" in total COP. Others were excluded because of lack of verification of identity of gas chromatographic peaks by mass spectrometry. Then a more narrow range of core results (mg/kg sample) was observed: Fresh EYP 5.69-29.5 sample, aged EYP 11.8-79.0; fresh WMP 0.12-1.76, aged WMP 1.17-13.7; fresh SMP <0.30-<1.21, aged SMP 0.30-2.26; fresh L 0.18-5.07, aged L 94.4-231. At a workshop discussing the results, numerous recommendations were made toward more reliable methodology for determination of COP in foods.     

Kinetic resolution of racemic Grignard reagents by nickel-catalyzed asymmetric Grignard cross-coupling

Racemic Grignard reagents, 2-phenylpropylmagnesium chloride and 2-norbornylmagnesium chloride were kinetically resolved by asymmetric cross-coupling with vinyl bromides in the presence of chiral phosphine-nickel catalysts to give optically active coupling products (~37% ee) and carboxylic acids after carbonation with carbon dioxide.     

Carbon-carbon bond-forming enantioselective synthesis of chiral organosilicon compounds by rhodium/chiral diene-catalyzed asymmetric 1,4-addition reaction

[reaction: see text] A new synthetic method for chiral organosilicon compounds through a rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to beta-silyl alpha,beta-unsaturated carbonyl compounds has been developed. By employing (R,R)-Bn-bod* as a ligand, a range of arylboronic acids can be coupled with these substrates in very high enantiomeric excess. The resulting beta-silyl 1,4-adducts can be converted to beta-hydroxy carbonyl compounds or allylsilanes while retaining their stereochemical information.     

Crystal chemistry of the gold (I) trimer,Au(3)(NC(5)H(4))(3): formation of hourglass figures and self-association through aurophilic attraction

X-ray crystallography reveals that individual molecules of Au(3)(NC(5)H(4))(3) self-associate through aurophilic interactions into two distinct structural motifs that involve both extended chains of molecules connected by pairwise Au.Au contacts and individual Au.Au contacts and discrete dimers linked by pairwise Au.Au contacts. The colorless or pale yellow crystals are remarkable for the formation of a distinct hourglass shape within the crystals that develops after months of standing in the atmosphere or after immersion in 4 M hydrochloric acid for a few days. The hourglass figures appear to result from the deposition of gold and are unusual in being formed by a chemical reaction within a crystal rather than as a result of dying the crystal during growth.     

Silver-selective sensor using an electrode-separated piezoelectric quartz crystal modified with a chitosan derivative.

Silver(I) adsorbed selectively onto a quartz plate modified with N-(2-pyridylmethyl)chitosan in an ammonium chloride buffer solution containing EDTA, and the frequency of the quartz plate increased. It was supposed that the increasing frequency was caused by the desorption of adsorbed water on the chitosan derivative, which was induced from the reaction of silver(I) with the chitosan derivative. The concentration of the buffer, pH, temperature, conductivity and eluent affected the frequency shift resulting from the adsorption of silver(I). The frequency decreased at a conductivity lower than 2.2 mS/cm, and increased with increasing conductivity above this value. The frequency shifts caused by the adsorption of silver(I) were proportional to the concentration over the range 10-80 nM of silver(I), and the correlation coefficient was 0.9969. The detection limit and the relative standard deviation at 50 nM for five times were 6 nM and 3.4%, respectively. The proposed method was simple while showing higher sensitivity and selectivity.     

Preparation of optically active allylsilanes by catalytic asymmetric hydrosilylation of 1-arylbutadienes1

Asymmetric hydrosilylation of 1-arylbutadienes with trichlorosilane in the presence of a chiral ferrocenylphosphine-palladium catalyst gave optically active allylsilanes, ($\text{Z}$)-1-aryl-1-silyl-2-butenes and their regioisomers.