Monolithic octadecylsilyl-silica gel column for the high-speed ion chromatographic determination of acidity

A monolithic ODS-silica gel column modified by saturating it with lithium dodecylsulfate (Li-DS) was used to demonstrate the high-speed separation of H+ from other mono- and divalent cations, such as Na+, NH4+, K+, Mg2+ and Ca2+ using ion chromatography (IC). Using a 5 mM EDTA-2K solution containing 0.10 mM Li-DS (pH 4.80) as eluent, H+ was eluted with a sharp and symmetrical peak within 1.0 min before other cations at a flow-rate of 1.5 ml min(-1). The rapid elution of H+ and its conductimetric detection could be attributed to the presence of EDTA (HY2-), which can convert H+ ions as anions. i.e. H(+) + H2Y(2-) --> H3Y(-). The acidity of rainwater and deionized water samples was determined using this IC system with satisfactory results.     

Stepwise and dramatic enhancement of anion recognition with a triple-site receptor based on the calix[4]arene framework using two different cationic effectors

Synthesis and binding behavior of a novel multi-responsive host 1, in which two esters, two polyether moieties, two urea sites, and two bipyridine units as ion binding sites are arranged on the calix[4]arene skeleton, is reported. 1 recognizes Na(+) and Ag(+) simultaneously and quantitatively and captures an anionic guest. The ability of 1 to recognize anions, including CF(3)SO(3)(-) and BF(4)(-), remarkably increases in a stepwise manner using Na(+) and Ag(+) as effectors. The enhancement of the K(a) eventually reaches factors of 1500 and 2000 for NO(3)(-) and CF(3)SO(3)(-), respectively, in the presence of both Na(+) and Ag(+), compared to the free 1. The regulation of binding of multiple ligands may be applicable to multistep cascade systems for the amplification of molecular events, and further studies in this field could provide insight applicable to more advanced molecular devices.     

Semi-micro size-exclusion chromatography of polymers : Calibration of columns and comparison with conventional columns

Stainless-steel tubes having inside diameters of 1.5 mm and 1.8 mm were packed with polystyrene gels of particle diameter 10 ± 2 μm. Two 50 cm × 1.8 mm I.D. packed columns, connected in series, were calibrated and molecular-weight averages of polystyrene NBS 706 were measured, the results coinciding with the data of the National Bureau of Standards. The peak widths of polystyrenes of narrow molecular-weight distributions in both semi-micro column (four 25 cm × 1.5 mm I.D.) and conventional column (two 50 cm × 8 mm I.D.; packed by the manufacturer) systems were determined at different mobile-phase velocities, and the minimum peak width in the latter system was obtained at the velocity of 0.2 mm/sec, which was higher than that for the semi-micro system. The interstitial volume was higher and the inner volume was lower for the semi-micro column system (1.8 mm I.D.) than those for the conventional one, which means that semi-micro columns were packed less densely, resulting in a steep calibration curve. The peak height of a solute was proportional to the cell length of an ultraviolet detector if the sample load was proportional to the cross-sectional areas of columns having the same column efficiency. Although conventional size-exclusion chromatography has many advantages in respect of velocity, calibration curtve and sample peak height, semi-micro size-exclusion chromatography still holds some merits such as low consumption of gels and of mobile-phase solvents.     

Synthesis of the ABCD ring of gambierol

A fully functionalized ABCD ring moiety of gambierol, a marine polycyclic ether toxin, was synthesized by the use of the oxiranyl anion strategy and reductive cycloetherification of a beta,delta-dihydroxy ketone.     

Synthesis of trans-fused polycyclic ethers with angular methyl groups using sulfonyl-stabilized oxiranyl anions

An efficient method has been developed for the synthesis of trans-fused tetrahydropyrans with angular methyl groups adjacent to the ring oxygen. The procedure involves the coupling reaction of a sulfonyl-stabilized oxiranyl anion with an appropriate triflate followed by 6-endo cyclization, and is effective for the construction of 6/6- and 6/7/6-cyclic ether ring systems with sterically congested 1,3-diaxial methyl groups.     

Iterative synthesis of the ABCDEF-ring system of yessotoxin and adriatoxin

A stereocontrolled linear synthesis of the ABCDEF-ring system of yessotoxin and adriatoxin, diarrhetic shellfish toxins, is described. Iterative application of a tetrahydropyran synthesis by reaction of the alkylation of a sulfonyl-stabilized oxiranyl anion followed by 6-endo cyclization of a 4,5-epoxy alcohol led to the synthesis of the trans-fused hexacyclic ether system, and the seven-membered E ring was constructed by ring expansion reaction.     

Synthesis of optically active pheromones with an epoxy ring, (+)-disparlure and the saltmarsh caterpillar moth pheromone [(Z,Z)-3,6-cis-1-9,10-epoxyheneicosadiene]

(+)-Disparlure $\text{2}$, and the saltmarsh caterpillar moth pheromone enantiomers $\text{1}$ were synthesized and the stereochemistry of the naturally occurring $\text{1}$ was shown to be 9$\text{S}$, 1O$\text{R}$.     

Highly sensitive spectrophotometric determination of osmium(VIII) with pyrogallolphthalein and hydrogen peroxide in the presence of Brij 35

Summary A highly sensitive determination of osmium(VIII) is based on the decolouring reaction with pyrogallolphthalein (gallein) and hydrogen peroxide in the presence of Brij 35. Beer's law was obeyed in the range of 0–0.5 ng of osmium(VIII) per 10 ml and the apparent decomposed absorption coefficient was 2.5×10⁹ l mol^–1 cm^–1 at 535 nm.Application of xanthene derivatives in analytical chemistry. Part XCIII. Part XCII see ref. [1]