Chalcogen–chalcogen-bond activation by an ambiphilic,doubly reduced organoborane

The 9,10-dimethyl-9,10-dihydro-9,10-diboraanthracene dianion salt Li₂[1] instantaneously reacts with the dichalcogens O₂(tBu)₂, S₂Me₂, S₂(pTol)₂, Se₂Ph₂, and Te₂Ph₂ under reductive cleavage of the chalcogen–chalcogen bonds to give lithium chalcogenides and neutral 1. In solution, the products are involved in rapid association/dissociation equilibria. In the crystalline state, 1 and Li[O(tBu)] form a diadduct, whereas Li[SMe] gives a B?B-bridged monoadduct. In the three remaining cases, the crystal lattices contain monoadducts of 1 with one tri- and one tetracoordinate boron atom.     

X-ray crystal structures and conformational analysis of cyclic acetals derived from tartaric acid and rigid spacer units

Three tartaric ester and tartaric acid derivatives (1?C3) with the hydroxy groups being linked via cyclic acetal (1,3-dioxolane) formation to a rigid core, containing phenyl and ethynyl units, have been synthesized. Their crystal structures are reported, emphasizing the molecular geometry, intermolecular interactions, and the resulting packing motifs. All dioxolane rings present in the crystal structures of 1?C3 are analyzed and compared with regard to their conformational behavior. In spite of similar substitution patterns, the dioxolane units adopt different conformations including twist and varying envelope isomers. The crystal structures are dominated by C?CH···O (esters 1 and 2) and O?CH···O (acid 3) hydrogen bonds, leading to different types of packing motifs being characteristic of strand and layer formation.     

Kinetic dehydroxylation of nontronite,estimated from isothermal and nonisothermal thermogravimetry

Dehydroxylation of an American nontronite (Manito) was followed via records of isothermal and dynamic thermogravimetry. Analysis of the isothermal weight-change curves (673-753 K). was performed with the procedure suggested by Hancock and Sharp. A fourteen-kinetic equation procedure was employed for analysis of the non-isothermal weight change in the range 623–1023 K. (A second-order decomposition equation seems to fit the dehydroxylation better under these conditions). The activation energies associated with the isothermal and nonisothermal processes are 118.8 and 136.8 kJ/mol^–1, respectively.

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Zusammenfassung Anhand isothermer und herkömmlicher Thermogravimetrie wurde die Dehydroxylierung eines amerikanischen Nontronites (Manito) verfolgt. Die isothermen TG-Kurven (673–753 K) wurden mittels der von Hancock und Sharp (1972). Ein kinetisches Vierzehngleichungsverfahren wurde zur Analyse der nichtisothermen TG-Kurven im Bereich 623–1023 K angestellt. Einer Dehydroxylierung unter diesen Bedingungen scheint eine Zersetzungsgleichung zweiter Ordnung besser zu entsprechen. Die Aktivierungsenefgie für die isothermen bzw. nichtisothermen Prozesse beträgt 118,8 bzw. 136,8 kJ/mol.

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(). (673–753 ) . , 623–1023, . . , , 118,8 136,8 /.

     

THE USE OF SPIN LABEL OXIMETRY IN THE STUDY OF PHOTODYNAMIC INACTIVATION OF CHINESE HAMSTER OVARY CELLS

Spin label oximetry has been used to study the effects of photosensitizer hematoporphyrin on oxygen consumption in Chinese hamster ovary cells. These measurements demonstrate that, in the presence of the sensitizer, there occurs (i) an increase in total oxygen consumption during irradiation and (ii) a decrease in oxygen consumption following irradiation. These results are attributed to the effects of photosensitized oxygen consumption and decreased cellular respiration due to cell inactivation. Thus the inhibition of oxygen consumption after irradiation was shown to correlate with decreased cell survival measured in cell culture experiments. Possible mechanisms of inactivation and extensions of the oximetric approach are discussed.