Landé g J factor measurements in the 6snd 1,3 D 2 sequences of Yb I

The Landé g _J factors in the 6snd ^1,3 D ₂ sequences as well as states from the perturbing configurations of neutral Ytterbium have been measured by timeresolved fluorescence spectroscopy. Strong singlet-triplet mixing effects were observed. The g _J factors were measured using the Zeeman quantum-beat technique following step-wise laser excitation. The experiment provided new data for checking the Multi-channel Quantum Defect Theory (MQDT) used in energy-level and lifetime analysis.     

Recent development in HPLC enantioseparation — a selected review

Summary Recent developments in the field of separating optical isomers by HPLC are discussed in this brief review. In particular it is focussed on various techniques for direct enantioseparation, the interpretation of possible enantioselective separation mechanisms, and the advantages and limitations of the diverse methods. This goal is supported by representative and selected examples of chiral separations.     

Physical,chemical and immunological characteristics of continuous-density lipoproteins isolated by single-spin gradient ultracentrifugation

The isolation of various lipoproteins of very low, intermediate, low and high density from 5 ml of serum was obtained by single-step ultracentrifugation in a potassium bromide density gradient obtained by smoothing a discontinuous gradient during the run (120 000g, 48 h, 4°C; Beckman SW27 rotor). The density profiles were reproducible. The lipoproteins were characterized by electron microscopy, fluorescence polarization, polyacrylamide gel electrophoresis and complete chemical assays. The composition of the entire lipoprotein spectrum was in accordance with previous results. The lipoprotein molecular mass, particle size distribution, Apo AI/AII ratio and microviscosity varied according to the density range.     

An unusual synthetic way to 2-methyl-3-alkyl-6-ethoxy-heptan-2-ols from 2-ethoxy-5-alkyl-3,4-dihydro-2H-pyrans

A simple and swift preparation of 2-methyl-3-alkyl-6-ethoxyheptan-2-ols may be accomplished in two steps starting from 2-ethoxy-5-alkyl-3-,4-dihydro-2H-pyrans via chlorination of the heterocyclic compounds and subsequent reaction with MeMgBr.     

Regioselective ortho lithiation of halopyridines

Regioselective ortho lithiation of 2-, 3-, and 4-halopyridines is achieved with lithium diisopropylamide (?78°, tetrahydrofuran) to afford, upon quenching with electrophilic reagents, 2,3- and 3,4-disubstituted pyridines in good to excellent yield.     

Withasteroids ofPhysalis. IV. 28-Hydrowithaphysanolide.13C NMR spectrum of 14-α-hydroxywithasteroids

A new withasteroid has been isolated fromPhysalis viscosa L. — 28-hydroxywithaphysanolide, with mp 234°C, composition C₂₈H₃₈O₈. The¹³C NMR spectra of a number of withasteroids have been investigated. For 28-hydroxywithaphysanolide we propose the structure 4,14,17,20R,28-pentahydroxy-l-oxo-22R-witha-2,5,24-trienolide. The corresponding corrections have been made in the structural formulas of withaphysanolide and physalactone.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 197–207, March–April, 1984.     

Comparative studies of reactions of commercial polymers with molecular oxygen,singlet oxygen,atomic oxygen and ozone—I. Reactions with cis-1,4-polybutadiene

The oxidation of cis-1,4-polybutadiene by molecular oxygen, singlet oxygen, atomic oxygen and ozone has been studied using u.v. and i.r. spectroscopic methods. Some possible implications of the results of oxidation in the presence of singlet oxygen (parallel free radical oxidation) and atomic oxygen (formation of NO₂ and its reaction with polymer) are discussed. Chain scission was observed during all types of oxidation. A new mechanism involving opening of double bonds and formation of biradicals has been considered in detail.     

Cellular logic with orthogonal ribosomes

The creation and use of unnatural molecules to control cellular function is a long standing goal of the chemical community, but in general, these efforts have been directed at finding molecules to inhibit or activate a particular molecular target or function, or to elicit a particular phenotype. Here we show that multiple unnatural molecules (orthogonal ribosomes) can be used combinatorially, in a single cell, to program Boolean logic functions. These experiments show how attention to the molecular specificity of noncovalent interactions between unnatural macromolecules allows the synthesis of complex function from the "bottom-up" in living matter.     

Different chemical dynamics for different conformers of biological molecules: photoionization of glycine

Single-photon ionization dynamics of two conformers of glycine is studied by classical trajectory simulations using the semiempirical PM3 potential surface in "on the fly" calculations. Initial conditions for the trajectories are weighted according to the Wigner distribution function computed for the initial vibrational ground state. Vertical ionization in the spirit of the classical Franck-Condon principle is assumed. The dynamics of the two conformers are compared during the first 10 ps. The comparison shows very different dynamical behavior for the two conformers. In particular, the chemical fragmentation pathways differ in part. Also, one of the conformers gives much higher rates of conformational transitions, while the other conformer gives larger chemical fragmentation yields. The example shows significantly different chemical dynamics for two conformers close in energy and separated by a low barrier.