Photophysics and photochemistry of sterically strained α-haloanthraquinones: The bromo and/or chloro substituted compounds

The steric hindrance between the oxygen and halogen atoms results in the structural deformation of α-haloanthraquinones and their lowest excited triplet (T₁) states are of mixed nπ ^*-ππ ^* or ππ ^* character with unusually short lifetimes. Moreover, the rates of hydrogen-atom abstraction from ethanol by the T₁ states decrease with their increasing ππ ^* character, and the proximity of the halogen atom to the hydroxy group causes the photochemical intramolecular elimination of hydrogen halide from the initial photoproducts (α-haloanthrahydroquinones) yielding α-haloanthraquinones (or anthraquinone) with one less halogen atom than the original molecule; the final product is anthrahydroquinone. The remarkably large structural deformation of 1,8-dihaloanthrasemiquinone radicals which gives rise to the simultaneous formation of 1,8-dihaloanthrahydroquinones and the original anthraquinones. Of particular interest is observation of the absorption band(s) attributable to the second excited triplet (T₂) states of 1,8-dihaloanthraquinones. However, the electron transfer from triethylamine (TEA) to these T₂ states generating the radical anions is observed only in acetonitrile, while that to the T₁ states generating their exciplexes with TEA is observed not only in acetonitrile but also in toluene and ethanol.     

S-4-methylphenyl-o,o-bis[1-benzotriazolyl] phosphorothioate: a versatile phosphorylating agent

The phosphorylating agent obtained by treatment of S-4-methylphenyl phosphorodichloridothioate with 1-hydroxybenzotriazole can not only be applied for the introduction of polyphosphate functions at the terminal ends of nucleic acids, but also for the formation of 3′-5′-phosphotriester linkages.     

Analogs of pyrimidine nucleosides

α-(1-Cytosinyl)-γ-butyrolactone was obtained by condensation of bis(trimethylsilyl)cytosine with α-bromobutyrolactone. The reduction of α-(1-cytosinyl)-γ-butyrolactone with sodium borohydride gave N₁-(1,4-dihydroxy-2-butyl)cytosine, the acylation of which with benzoyl chloride and subsequent partial hydrolysis gave N₁-(1,4-dihydroxy-2-butyl)-N₄-benzoylcytosine.     

Rapid analysis of small glass fragments by atomic-absorption spectroscopy

A rapid method is described for the determination of magnesium, iron and manganese in small glass fragments (250-500 mug). The speed of the analytical procedure is made possible by the use of a convenient cold digestion stage allied to a discrete sampling method which permits the three elements of interest to be determined by flame atomic-absorption spectrophotometry.     

Crystal and molecular structure of 1-aza-6′-(3′-oxo-5′, 5′-dimethyl-δ1′-pyrrolin-3′-yl)methylidene-2,2,7,7-tetramethyl-4-hydroxybicyclo-[2.2.21azaoctane

An x-ray structural study has shown that 6-(3-oxo-5,5-dimethyl-¹-pyrrolin-3-yl)methylidene-2,2,7, 7-tetramethyl-4-hydroxybicyclo[2.2.2]azaoctane is formed as a low-molecular-weight byproduct of the solid-phase polymerization of 1,4-bis(2,2,6,6-tetramethyl-4-hydroxy-4-piperidyl)butadiyne.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 585–587, March, 1990.     

Dioxane analogs of flavylium salts

The synthesis of benzodioxane derivatives of 1-benzopyrilium salts is reported and their reaction with nucleophiles is investigated.Taros Shevchenko University, Kiev 252017. Translated from Khimiya Geterotsiklicheskikb Soedinenii, No. 3, pp. 322–324, March, 1995. Original article submitted February 6, 1995.     

Arsenic speciation by capillary gas-liquid chromatography

Specific environmentally significant arsenic compounds are determined by capillary gas-liquid chromatography. Inorganic (arsenite, arsenate) and organic (monomethylarsonate, dimethylarsinate) arsenicals are measured as the corresponding methylthioglycolate derivatives, which are simultaneously separated on wide-bore borosilicate glass and fused-silica columns under conditions of temperature programming. Inorganic arsenate and arsenite cannot be differentiated by the derivatization technique. Flame-ionization and electron-capture detection are evaluated. A simple and rapid sample preparation procedure is used for water, urine, blood, and tissue.     

Convenient method for preparation of esters of N-carbonyl-α-amino acids

Conclusions A convenient method was proposed for obtaining the esters of N-carbonyl--amino acids, which is based on the reaction of the esters of N-trimethylsilyl--amino acids with phosgene in the presence of a tertiary amine.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1682–1684, July, 1977.     

Internal molecular disorder in the nematic and smectic phases of thermotropic liquid crystals studied by NMR SPDE experiments

The recently developed NMR SPDE experiment is shown to provide a new and particularly convenient technique for probing the conformational dynamics of mesogens in thermotropic liquid crystals. Measurements have been made in the nematic and smectic phases of the 4,4′-di-n-alkoxyazoxybenzenes. It is shown for the first time that the internal disorder of the alkyl end chains is intimately related to the molecular organization of these mesophases.     

Radiometric titration based on colloidal and slow precipitate formation

Fluoride ions and, in about 0.005M concentration, tungstate ions form gelatinous precipitates, poorly soluble in water, with calcium ions. The radiometric determinations of the above ions are based on these reactions. Accurate radiometric determination can be carried out only if the gelatinous precipitate formed during titration can be properly separated from the solution. It has been found that in the case of fluoride ions the application of crystalline, easily filtrable Ca(COO)₂·H₂O or CaCO₃, and in the case of tungstate ions the application of CaWO₄ precipitate improves the filtration properties of⁴⁵CaF₂ and⁴⁵CaWO₄, respectively, formed during titration, whereby the radiometric determinations of the above ions become possible. Titrations were carried out with 0.05M and 0.005M CaCl₂ solutions, labelled with⁴⁵Ca.