Study on the thermal stability of a chiral stationary phase coated on capillaries for GC

A chiral stationary phase prepared by bonding L -valine-t-butylamide to XE-60 has been coated on glass and metal capillaries. The performances of the chiral glass and metal columns were equivalent to those of commercial fused silica capillary columns. The thermal stability of the glass column was examined up to 280°C. It was found that no appreciable change in separation factor (α value) was observed up to 230°C. The α values gradually decreased between 240 and 260°C, and enantiomer separation was no longer achieved at 280°C. It was concluded that the allowable upper limit temperature of the chiral stationary phase is between 230 and 240°C in the isothermal mode, and ca 260°C in temperature-programmed mode.     

Ionic conductivity of superionic conducting glasses in the pseudobinary system AgIAg2MoO4

The ionic conductivity was measured in the temperature range 250–300 K as a function of composition of superionic conducting glasses in the pseudobinary system AgIAg₂MoO₄. The conductivity, ranging from 10^?2 to 10^?4 Ω^?1 cm^?1 at room temperature, increases linearly in logarithmic scale with increasing AgI content, while the total silver ion concentration remains nearly constant in the whole glass-forming region of the present system. Such a composition dependence of conductivity is considered to be evidence that only a fraction of the silver ions in glass contributes to the ionic conduction. The conductivity and the activation energy for conduction differ slightly between bulk glasses and pressed pellets of pulverized glasses. The close agreement in bulk glasses and pellets suggests that bulk rather than grain boundary or surface diffusion dominates the conduction process in the present glasses.     

Isolation and crystal structure of a water-soluble iridium hydride: a robust and highly active catalyst for acid-catalyzed transfer hydrogenations of carbonyl compounds in acidic media

This paper reports the isolation and structural determination of a water-soluble hydride complex [Cp*Ir(III)(bpy)H](+) (1, Cp* = eta(5)-C(5)Me(5), bpy = 2,2'-bipyridine) that serves as a robust and highly active catalyst for acid-catalyzed transfer hydrogenations of carbonyl compounds at pH 2.0-3.0 at 70 degrees C. The catalyst 1 was synthesized from the reaction of a precatalyst [Cp*Ir(III)(bpy)(OH(2))](2+) (2) with hydrogen donors HCOOX (X = H or Na) in H(2)O under controlled conditions (2.0 < pH < 6.0, 25 degrees C) which avoid protonation of the hydrido ligand of 1 below pH ca. 1.0 and deprotonation of the aqua ligand of 2 above pH ca. 6.0 (pK(a) value of 2 = 6.6). X-ray analysis shows that complex 1 adopts a distorted octahedral geometry with the Ir atom coordinated by one eta(5)-Cp*, one bidentate bpy, and one terminal hydrido ligand that occupies a bond position. The isolation of 1 allowed us to investigate the robust ability of 1 in acidic media and reducing ability of 1 in the reaction with carbonyl compounds under both stoichiometric and catalytic conditions. The rate of the acid-catalyzed transfer hydrogenation is drastically dependent on pH of the solution, reaction temperature, and concentration of HCOOH. The effect of pH on the rate of the transfer hydrogenation is rationalized by the pH-dependent formation of 1 and activation process of the carbonyl compounds by protons. High turnover frequencies of the acid-catalyzed transfer hydrogenations at pH 2.0-3.0 are ascribed not only to nucleophilicity of 1 toward the carbonyl groups activated by protons but also to a protonic character of the hydrido ligand of 1 that inhibits the protonation of the hydrido ligand.     

Model Construction for the A–B–C Ring System of Lysergic Acid via Vilsmeier–Haack‐Type Cyclization of 1H‐Indole‐4‐propanoic Acid Derivatives

Vilsmeier–Haack‐type cyclization of 1H‐indole‐4‐propanoic acid derivatives was examined as model construction for the A–B–C ring system of lysergic acid ( 1 ). Smooth cyclization from the 4 position of 1H‐indole to the 3 position was achieved by Vilsmeier–Haack reaction in the presence of K₂CO₃ in MeCN, and the best substrate was found to be the N,N‐dimethylcarboxamide 9 (Table 1). The modified method can be successfully applied to an α‐amino acid derivative protected with an N‐acetyl function, i.e., to 27 (Table 2); however, loss of optical purity was observed in the cyclization when a chiral substrate (S)‐ 27 was used (Scheme 5). On the other hand, the intramolecular Pummerer reaction of the corresponding sulfoxide 20 afforded an S‐containing tricyclic system 22 , which was formed by a cyclization to the 5 position (Scheme 3).     

Spectrophotometric determination of cobalt(II) with 2-(3′-sulfobenzoyl)pyridine benzoylhydrazone

A simple method has been described for the Spectrophotometric determination of cobalt(II) with 2-(3′-sulfobenzoyl)pyridine benzoylhydrazone (SBPBH). In aqueous solution, cobalt(II) reacts with SBPBH to form a yellow complex, which is not destroyed even by the addition of 3.8 M perchloric acid. The absorption maximum of the complex in 1.5 M perchloric acid medium was found to be 400 nm; the molar absorptivity was 2.17 × 10⁴ liters mol⁻¹ cm⁻¹. The proposed method is fairly selective and has been applied to the determination of cobalt in standard alloy steel samples.     

Cover Picture

The cover picture shows a section of the electron charge density of the first metal carbide endohedral metallofullerene (Sc(2)C(2))@C(84) obtained from a synchrotron X-ray powder diffraction study by the maximum entropy method (MEM). The several density maxima, which correspond to scandium and carbon atoms, are clearly seen inside the C(84) carbon cage. The MEM charge density distribution also reveals that the C(84) cage has D(2d) symmetry (no. 23) and that the C(2) axis is parallel to the <100> face-centered cubic (fcc) direction of the unit cell. As a consequence of the site symmetry being 4mm, the C(2) axis of (Sc(2)C(2))@C(84) is oriented to six equivalent <100> directions and shows a merohedral disorder. The resultant Sc small middle dot small middle dot small middle dotSc distances and C-C bond lengths of the Sc(2)C(2) cluster are 0.429(2) and 0.142(6) nm, respectively. The observed C-C bond length is between that of a typical single and a double bond, and is very close to that of the C-C bond (0.143 nm) combining two pentagons in a C(60) molecule. More about this fascinating structure can be found in the contribution by Shinohara and co-workers on p. 397 ff.     

NMR assignment methods for the aromatic ring resonances of phenylalanine and tyrosine residues in proteins

The unambiguous assignment of the aromatic ring resonances in proteins has been severely hampered by the inherently poor sensitivities of the currently available methodologies developed for uniformly 13C/15N-labeled proteins. Especially, the small chemical shift differences between aromatic ring carbons and protons for phenylalanine residues in proteins have prevented the selective observation and unambiguous assignment of each signal. We have solved all of the difficulties due to the tightly coupled spin systems by preparing regio-/stereoselectively 13C/2H/15N-labeled phenylalanine (Phe) and tyrosine (Tyr) to avoid the presence of directly connected 13C-1H pairs in the aromatic rings. The superiority of the new labeling schemes for the assignment of aromatic ring signals is clearly demonstrated for a 17 kDa calcium binding protein, calmodulin.     

Cyanobenzoylation and hydrocyanation of aldehydes with benzoyl cyanide using no catalyst

[reaction: see text] In the presence of MS 4A in DMSO, cyanobenzoylation of various aldehydes with benzoyl cyanide proceeded very smoothly to give the corresponding cyanohydrin benzoates in high to excellent yields without an acid or a base. On the other hand, reaction of aldehydes with BzCN in DMSO-H(2)O also occurred readily to afford the corresponding free cyanohydrins exclusively.     

Diastereoselective imino-aldol condensation of chiral 3-(p-Tolylsulfinyl)-2-furaldimine and ester enolates

(Ss)-3-(p-Tolylsufinyl)-2-furaldimine was synthesized, and condensation of the chiral furaldimine with lithium ester enolates has been examined. The product distribution of the reaction is dependent upon reaction conditions and on the kind of the substituent placed on the esters. Disubstituted ester enolate resulted in the exclusive formation of (4R)-beta-lactam, while unsubstituted, tert-butyl ester enolate preferentially gave (3R)-beta-amino ester. With the monosubstituted ester enolates, the condensation afforded (4R)-beta-lactams and/or (3R)-beta-amino esters as major products. This method has been applied to an efficient route to chiral furyl beta-lactams.     

Unprecedented double nucleophilic addition of a hydride at a central carbon of an eta3-allyl ligand

Treatment of eta(3)-allyl compound [Cp(2)Mo(eta(3)-C(3)H(5))](+)(1; Cp =eta(5)-C(5)H(5)) with MH (M = Li, Na) resulted in reduction of the allyl ligand to give propane. Deuterium-labeling studies were used to trace the origins and fates of the hydrogen atoms. The mechanism is discussed in light of the HSAB principle. The studies showed that the formation of propane can be explained by 1,2-hydrogen migration from the central to the terminal carbon of the allyl ligand, and the subsequent double nucleophilic addition of the hydride at the central carbon.