Thermodynamic study of complex formation of benzo-18-crown-6 with K+, Tl+, and Pb2+ in water

H ⁰ and S ⁰ values of the complex formation in water of benzo-18-crown-6 (B18C6) with K⁺, Tl⁺, and Pb²⁺ were determined and compared with those of 18-crown-6. The H⁰ values of B18C6 are negative. The stability in water of the B18C6-metal ion complex at 25°C is governed largely by the magnitude of the H ⁰ value. The B18C6-metal ion complex is less stable in water than the corresponding 18C6-metal ion complex. This is due largely to a less favorable enthalpic contribution of the B18C6-metal ion complex compared with the corresponding 18C6-metal ion complex. The two aromatic ether oxygen atoms of B18C6 are responsible for the larger H ⁰ value of the B18C6-metal ion complex compared with the corresponding 18C6-metal ion complex.     

Trifluoromethylated amino alcohols as chiral ligands for highly enantioselective Reformatsky reaction

The enantioselective Reformatsky reaction of PhCHO was achieved by the use of trifluoromethylated amino alcohols as chiral ligands to afford the corresponding optically active β-hydroxy ester with up to 90% ee.     

Gas Chromatographic Separation of Carbonyl Compounds as Their 2,4-dinitrophenylhydrazones Using Glass Capillary Columns

The gas chromatographic separation of 22 carbonyl compounds as their 2,4-dinitrophenylhydrazones was investigated using glass capillary columns. Complete separation of the 2,4-dinitrophenylhydrazones of ten aliphatic aldehydes, eight aliphatic ketones and four aromatic aldehydes was obtained, except for the derivatives of n-valeraldehyde and isobutyl methyl ketone, whose peaks overlapped, and the o- and m-tolualdehyde derivatives, which were poorly separated. The optimum conditions were as follows: stationary phase, SF-96; column size, 20 m × 0.25 mm I.D. ; column temperature, 200-240°; injection and detector temperatures, 280-290°; carrier gas flow-rate, helium 1.0-1.2 ml/min or nitrogen 1.1-1.2 ml/min. The method was applied to the analysis of aliphatic carbonyl compounds in car exhaust fumes and cigarette smoke.     

Solid sampling technique for direct detection of condensed tannins in bark by matrix-assisted laser desorption/ionization mass spectrometry

A novel method for the direct analysis of condensed tannin components in bark was developed on the basis of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) combined with a simple solid sampling technique. The MALDI mass spectra obtained from the wood (bark) powder sample clearly showed a series of peaks corresponding to the sodium ion adducts of condensed tannin oligomers up to around m/z 3000. The results indicate that the condensed tannins in the bark sample used in this work mostly consist of combinations of flavan-3-ol units such as profisetinidin (PF), prorobinetinidin (PR) and prodelphinidin (PD), at least up to 10-mers (m/z approximately 3000).     

Reaction of tetraazathiapentalene and thiadiazolopyrimidine derivatives with heterocumulenes: Cycloaddition and elimination reactions via hypervalent sulfur intermediates

Tetraazathiapentalene derivative 1 reacts with heterocumulenes such as diphenylketene (2) and 2‐pyridylisothiocyanate (5) to give heterocycles 3, 6 and 7 with elimination of methylisothiocyanate. The reactions of thiadiazolopyrimidine derivatives 8a‐b with ethoxycarbonyl isothiocyanate (9) and carbon disulfide (11) gives heterocycles 10 and 12 via thermal decomposition of 1:1 cycloadducts C and D which have a hypervalent sulfur. The mechanistic and reactivity features of these reactions are described.     

The characteristic fragment ions and visualization of cationic starches on pulp fiber using ToF‐SIMS

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to investigate the distribution of cationic starch on pulp fiber. To identify the characteristic fragment ions of the cationic starches, deuterium‐labeled cationic starches were prepared and analyzed using ToF‐SIMS. The starch 2‐hydroxypropyltrimethylammonium chloride derivative generated characteristic fragments at m/z 58 and 59, which were identified as [H₂C?N(CH₃)₂]⁺ and [N(CH₃)₃]^+·, respectively. The fragmentation patterns were also suggested. From the imaging analysis, the adsorption of the cationic starch on fibers was uneven on individual fibers, as well as between fibers. This may have been on account of fiber morphology and structure. On examining scanning electron microscope (SEM) images, the quaternary ammonium starch derivative (QS) did not penetrate the fiber. No migration of cationic starch was observed under various drying conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

A novel separation technique of diastereomeric esters of pyridylethanols by extraction: formal total synthesis of PNU-142721, HIV-1 reverse transcriptase inhibitor

The separation of diastereomeric esters derived from (±)-pyridylethanols and 3β-acetoxyetienic acid were achieved by an extraction technique using diethyl ether and aqueous hydrochloric acid. A formal total synthesis of PNU-142721 was effectively carried out to prepare the chiral, non-racemic synthon 1-furo[2,3-c]pyridin-5-yl-ethanol (1) by means of this technique. The structure optimized using MOPAC calculations on each diastereomer suggested the presence of intramolecular CH/π interaction in only the (S)-isomer of the diastereomers.     

Decomposition analyses of the intermolecular interaction energies in two π?π stacking complexes: Quinhydrone and N,N,N′, N′-tetramethyl-P-diaminobenzene-chloranil complex

Although there is a similarity in the orbital interaction scheme between quinhydrone and N,N,N′,N′-tetramethyl-p-diaminobenzene-chloranil complex, the stacking conformations are different from each other. The former prefers the half-stacked conformation, whereas the latter prefers the completely stacked conformation. We have done ab initio molecular orbital calculations and decomposition analyses of the intermolecular interaction energies to clarify the origin of the different stacking conformations. It was concluded that the main origin is the difference in the steric part of the interaction energies. © 1994 by John Wiley & Sons, Inc.     

Enantioselective total synthesis of (−)-pseudophrynaminol through tandem olefination, isomerization and asymmetric Claisen rearrangement

A new and efficient total synthesis of (−)-pseudophrynaminol, the pyrrolo[2,3-b]indole alkaloid bearing the allylic moiety at the 3a-position, has been achieved by a sequence involving 3-allylindol-2-one 8 as a key intermediate. The enantioselective construction of the quaternary carbon in 8 was performed through a tandem cascade reaction of 2-allyloxyindolin-3-one 4, olefination, isomerization, and asymmetric Claisen rearrangement.     

Tertiary amine-mediated synthesis of microporous carbon membranes

Microporous carbon membranes were prepared on an -alumina support by a pyrolysis of cationic tertiary amine/anionic polymer composites. The precursor solutions contain a thermosetting resorcinol/formaldehyde (RF) polymer and a cationic tertiary amine. Three types of cationic tertiary amines with different chain lengths were used, such as tetramethlammonium bromide (TMAB), tetrapropylammonium bromide (TPAB) and cetyltrimethylammonium bromide (CTAB). A porous structure was produced by a decomposition of the amine and the resulting pores assisted the further gasification of the RF polymer at high temperature. The carbon/alumina membranes have thin and continuous carbon top layers with a thickness of 1 μm. Gas permeation tests were performed using single gases of CO₂, O₂, N₂, CF₄, n-C₄H₁₀ and i-C₄H₁₀, as well as binary mixtures of CH₄/n-C₄H₁₀ and N₂/CF₄ at different temperatures between 23 and 150 °C. The carbon membrane prepared using TMAB showed separation factors higher than 650 for the CH₄/n-C₄H₁₀ mixtures and higher than 8100 for the N₂/CF₄ mixture. From the permeation of pure gases with different molecular sizes, the pore sizes of the carbon membrane prepared using TMAB, TPAB and CTAB are estimated to be 4.0, 5.0 and larger than 5.5 Å, respectively, indicating that the micropore size of the carbon membranes is controllable by using different amines.