Neutron activation cross-section of zirconium-94

The thermal neutron activation cross-section of⁹⁴Zr was found to be 49.3±0.6 millibarns. It is shown that neutron activation analysis of Zr in silicate samples with a Zr/U ratio<10 has considerable uncertainty due to fission contribution. A correction factor for the fission contribution has been determined experimentally.     

The esterase and peptidase activities of an elastolytic enzyme of Actinomyces rimosus

Summary 1. It has been shown that the values of K_m for the esterase activity of elastase ofActinomyces rimosus and for pancreatic elastase are of the same order of magnitude.2. The elastase ofActinomyces rimosus, unlike the pancreatic enzyme, is capable of hydrolyzing only the methyl ester of N-acetyltrialanine, and not the mono and di derivatives.3. It has been found that in the initial stage of the hydrolysis reaction it is mainly the ester bonds that are cleaved.Institute of Molecular Biology, Academy of Sciences of the USSR, Moscow. N. D. Zelinskii Institute of Organic Chemistry, Academy of Sciences of the USSR, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 693–695, September–October, 1977.     

The influence of seasonal changes in the concentration of trace elements in liver tissue of various wild animals determined by instrumental neutron activation analysis

Levels of some of the most essential minerals in liver tissue of wild animals living in game reserves in South Africa were studied by instrumental thermal neutron activation analysis and a Ge(Li) detector. In addition, some of the most important trace elements were determined by atomic absorption spectrometry. The distribution of the content of the various elements was followed for about two years and attempts have been made to explain the influence of seasonal fluctuations of the micronutrients determined.     

Synthesis of racemic and optically active Δ1- and Δ6-3,4-cis-tetrahydrocannabinols1

Three syntheses of the hitherto unknown (±)-Δ⁶-3,4-cis-THC 4a and the first total synthesis of optically active Δ¹- and Δ⁶-cis-THC's are described. These syntheses utilize a stereospecific intramolecular epoxide opening by phenolate anion; an acid catalyzed equilibration of Δ¹- and Δ⁶-cis-THC acetates; and a kinetically controlled dehydration. The use of HPLC, GLC and NMR for the separation and identification of closely related THC's is discussed.     

Chemistry of thienopyridines. VII. Mechanistic studies on the synthesis of thieno[2,3-c] pyridine by thermolytic cyclization

A study was made of the formation of thieno[2,3-c]pyridine (1) from hydrogen sulfide and 4-vinylpyridine in a flow system at 630°. 2-(4-Pyridyl)ethanethiol and bis-2-(4-pyridyl)ethyl sulfide were found to be likely intermediates. Based on these studies, there was devised a two-step practical preparative method for I (optimum overall yield 58%) which consists of preliminary conversion of 4-vinylpyridine to benzyl 2-(4-pyridyl)ethyl sulfide and subsequent thermolysis (at 605°) of this substance.     

Translational energy disposal in molecular collisions: The transfer of momentum constraint

A Franck—Condon type argument, which requires the least transfer of momenta to the nuclei during a collision is outlined and applied to the analysis of translational energy disposal and its dependence on the initial translational energy. Using the maximal entropy procedure of information theory we are able to proceed directly from the assumed (model) constraint to the product state distribution.     

An investigation of some experimental parameters in atomic fluorescence spectrophotometry

Atomic fluorescence in flames is measured by an adaptation of a commercially available flame spectrophotometer. A study is reported of the effect of background radiation and source scattering on 3 flames, air-propane, air-hydrogen and air-acetylene, and of the effects of variation of fuel gas pressure, zone of measurement in the flame, analysing monochromator slit-width and wavelength of measurement. The air-propane flame appears to offer several advantages. The atomic fluorescence of 10 metals is described; those of Co, Fe and Mn have not been previously reported. Excitation of spectra is achieved by means of an a.c. xenon arc lamp or individual discharge lamps.     

Quantum solvation of phthalocyanine in superfluid helium droplets

We have measured quantum states of the solvent-solute system of phthalocyanine in superfluid helium droplets in a high resolution pump-probe experiment. This provides evidence for the attribution of a splitting effect in the emission spectra of phthalocyanine in helium droplets to the relaxation of the first helium layer upon electronic excitation, measured recently by us. Our experimental results are a strong indication for the first helium layer playing a key roll for the solvation of molecules in helium droplets and, thus, for their spectroscopic features.     

Interfacial electron transfer in FeII(CN)6 4- -sensitized TiO2 nanoparticles: a study of direct charge injection by electroabsorption spectroscopy

Electroabsorption (Stark) spectroscopy has been used to study the dye sensitized interfacial electron transfer in an Fe(II)(CN)(6)(4)(-) donor complex bound to a TiO(2) nanoparticle. The average charge-transfer distance determined from the Stark spectra is 5.3 A. This value is similar to the estimated distance between the Fe(II) center of the complex and the Ti(IV) surface site coordinated to the nitrogen end of a bridging CN ligand in (CN)(5)Fe(II)-CN-Ti(IV)(particle). This finding suggests that the electron injection is to either an individual titanium surface site or a small number of Ti centers localized around the point of ferrocyanide coordination to the particle and not into a conduction band orbital delocalized over the nanoparticle. The polarizability change, Tr(Deltaalpha), between the ground and the excited states of the Fe(II)(CN)(6)(4)(-)-TiO(2)(particle) system is approximately 3 time larger than normally observed in mixed-valence dinuclear metal complexes. It is proposed that the large polarizability of the excited state increases the dipole-moment changes measured by Stark spectroscopy.