Do Young Ra

Calix[4]arenes bridged with two different crown ether loops: Influence of crown size on metal ion recognition

A series of calix[4]arene-bis-crownethers were synthesized in a fixed 1,3-alternateconformation with good yields by the reaction of amonocyclic calixcrown ether with multi-ethyleneglycoldi-p-toluenesulfonate in the presence of cesiumcarbonate. In the preparation of the monocycliccalixcrown ethers (1 and 2), the use ofpotassium carbonate as a base provided the best yieldregardless of the template concept. In two phaseextraction and competitive transport experiments forligand-metal complexation, calix[4]arene biscrown(5) provided the best selectivity for potassiumion. When a calixbiscrown ether (4) bearingdifferent sized crown ether loops coordinates to K+and Cs+, respectively, the changes of peak splittingpatterns and chemical shift on 1H NMR spectra aredependent on the complexed metal ion species.

Calix[4]arene dibenzocrown ethers as caesium selective extractants

A series of 1,3-dialkyloxycalix[4]arene dibenzocrown ethers were synthesized in the fixed 1,3-alternate conformation with good yields by the reaction of 1,3-dialkyloxycalix[4]arenes with dibenzodimesylate in the presence of caesium carbonate. The three dimensional 1,3-alternate conformation was confirmed by X-ray crystal structure. Upon two phase extraction, NMR studies on the ligand–metal complex, single ion and competitive ion transport experiments through a bulk liquid membrane, 1,3-dipropyloxycalix[4]arene dibenzocrown-6, in which two benzo groups are symmetrically attached to the crown-6 linkage, gave one of the most efficient and selective extractabilities for caesium ion over other alkali metal ions. From supported liquid membrane experiments using 1 and 3 as organic carriers, permeation coefficients of the caesium ion were estimated to be 0.42 and 0.27 cm h–1, respectively. The selectivity of caesium over sodium ion was observed to increase with permeation time.

Novel Calix[4]arene Azacrown Ether

Abstract 1,3-diproyloxycalix[4]arene azacrown ether was successfully synthesized in the fixed 1,3-alternate conformation which was confirmed by a solid state structure.

Synthetic and tautomeric studies of 5-amino-2,3-dihydro-1,2,4-oxadiazol-3-one

5-Amino-2,3-dihydro-1,2,4-oxadiazol-3-one 2 was synthesized as an analogue of cytosine. Among the possible four tautomers it was established by spectroscopic methods and ab initio calculations that it exists as a lactam form 2b like cytosine. The NH is more acidic than NH2, thus it could be regioselectively mesylated and acetylated under basic conditions.

MASS SPECTROMETRIC STUDIES OF 3-SUBSTITUTED-5-AMINO-1,3,4- THIADIAZOLIN-2-ONES

Abstract Fragment pathways of 3-alkyl and acyl-5-amino-1,3,4-thiadiazolin-2-ones were completely assigned by mass analyzed kinetic energy spectra (MIKE), collisional activated dissociation (CAD) spectra and high resolution mass spectra. [NH2CS]+ and [S[dbnd]C[dbnd]O]+ ions were directly formed from molecular ion of the 3-alkyl compounds and from 5-amino-3H−1,3,4 -thiadiazolin-2-one ion ( 1 ) which was produced by McLafferty rearrangement from molecular ion of 3-acyl compounds. A loss of neutral SCO was only detected from 3-alkyl substituted molecular ions.