Identification of an impurity in synthetically prepared GAZT: 4″,5″-dehydro-GAZT

A minor impurity was recorded by hplc during the final purification of synthetically prepared samples of the 5′-0-glucuronide of azidothymidine (GAZT). Following isolation of a small quantity of this impurity by hplc, elucidation of the structure was undertaken. A combination of two-dimensional nmr methods in conjunction with infrared spectroscopy and mass spectrometry were utilized to unequivocally identify the impurity as the 4″,5″-dehydro-5′-O-glucuronide of AZT (DGAZT).     

Preparation of 2- and 4-arylmethyl N-substituted and N,N-disubstituted anilines via a "green", multicomponent reaction

[reaction: see text] A new, green, regioselective, one-step, multicomponent reaction of an aldehyde possessing a nonenolizable carbonyl function, cyclohex-2-enone (or a derivative thereof), and primary or secondary amines afforded 2-N-substituted arylmethyl anilines or 4-N,N-disubstituted arylmethyl anilines, respectively. Yields and regioselectivities were good. Evidence for a pathway involving imine and iminium intermediates is presented along with examples demonstrating amenability of the process to combinatorial chemistry.     

Synthesis and proposed crystal structure of a disordered cadmium arsenate apatite Cd5(AsO4)3Cl(1-2x-y)O(x)[symbol: see text](x)OH(y)

During a study into the synthesis of minerals composed of mining wastes aimed at improving their immobilisation, a cadmium arsenate apatite has been prepared by hydrothermal methods. The structure of this apatite was analysed by single crystal X-ray diffraction, and was found to consist of a standard apatite framework based on Cd(5)(AsO(4))(3)X, where X represents an anion resident on the (0,0,0.25) site. The framework is hexagonal with the space group P6(3)/m(no 176), a= 9.9709(8), c= 6.4916(4)[Angstrom]. The X ion site is predominantly occupied by Cl(-) ions; however due to significant shortening of the c axis exhibited by all cadmium containing apatite phases, a pure chlorapatite is not possible without a significant cation deficiency. No evidence of the necessary deficiency was found in the crystal structure. For larger bromo- and iodo-apatites significant modulations along the c-axis are required to accommodate the halide. This paper examines a number of compensation mechanisms and proposes that a minor disorder of chloride, oxide and hydroxide located on the X ion site provides the required charge compensation mechanism. This is contrary to previous complex modulations proposed in the literature. The proposed chemical formula is Cd(5)(AsO(4))(3)Cl(1-2x-y)O(x)[symbol:see text](x)OH(y) where [symbol: see text] represents a vacancy.     

Horning-crown macrocycles: novel hybrids of calixarenes and crown ethers

[reaction: see text] Novel macrocycles possessing ether linkages and 2,6-disubstituted phenolics were produced in one step and with 100% atom economy by isoaromatization of chameleon macrocyclic precursors possessing 2,6-diarylidenecyclohexanone moieties. Intramolecular hydrogen bonding of the phenolic hydrogen atoms influenced the shape of the macrocycles and dictated host-guest behavior.     

Basis set and correlation effects on computed lithium ion affinities of some oxygen and nitrogen bases

Basis set expansion and correlation effects on computed lithium cation affinities have been evaluated for the oxygen and nitrogen bases CH₃OH, H₂CO, CO, CH₃NH₂, CH₂NH, and HCN. The presence of diffuse functions on nonhydrogen atoms is found to be the most important single enhancement of double- and triple-split valence plus polarization basis sets. With the triple-split basis, enhancement effects are nearly additive. Correlation usually decreases computed lithium ion affinities, with the second order Møller-Plesset correlation term being the dominant term.     

Kinetics and nitro-products of the gas-phase OH and NO3 radical-initiated reactions of naphthalene-d8, Fluoranthene-d10, and pyrene

The kinetics and nitroarene product yields of the gas-phase reactions of naphthalene-d₈, fluoranthene-d₁₀, and pyrene with OH radicals in the presence of NO_x and in N₂O₅? NO₃? NO₂? air mixtures have been investigated at 296 ± 2 K and atmospheric pressure of air. Using a relative rate method, naphthalene-d₈ was shown to react in N₂O₅? NO₃? NO₂? air mixtures a factor of 1.22 ± 0.10 times faster than did naphthalene, with the 1- and 2-nitronaphthalene-d₇ product yields being similar to those of 1- and 2-nitronaphthalene from naphthalene. From the measured PAH concentrations and the nitroarene product yields, formation yields of 2-, 7-, and 8-nitrofluoranthene-d₉ and 2- and 4-nitropyrene of 0.03, 0.01, 0.003, 0.005, and 0.0006, respectively, were determined from the OH radical-initiated reactions. Effective rate constants for the reactions of fluoranthene-d₁₀ and pyrene with N₂O₅ in N₂O₅? ;NO₃? NO₂? air mixtures of ca. 1.8 × 10^?17 cm³ molecule^?1 s^?1 and ca. 5.6 × 10^?17 cm³ molecule^?1 s^?1, respectively, were derived. Formation yields of 2-nitrofluoranthene-d₉ and 4-nitropyrene of ca. 0.24 and ca. 0.0006, respectively, were estimated for these reaction systems. 2-Nitropyrene was also observed to be formed in these N₂O₅? NO₃? NO₂ reactions, but was found to be a function of the NO₂ concentration and, therefore, would be a negligible product under ambient NO₂ concentrations. These product and kinetic data are consistent with ambient air measurements of the nitroarene concentrations.     

A complete classification of the two-point extensions of a multidimensional bernoulli shift

A theorem is proven which gives five characterizations of a multidimensional Bernoulli shift. The two-point extensions of a multidimensional Bernoulli shift are classified completely. If such an extension is weakly mixing then it must be Bernoulli; otherwise, it is isomorphic to one of 2 ⁿ specific trivial extensions. This result is extended to multidimensional Bernoulli flows and Bernoulli shifts of infinite entropy. This work supported in part by N.S.F. Grant DMS-85-04701 and by the University of Maryland Department of Mathematics.