Reference

Possible role of singlet molecular oxygen in the control of the phototactic reaction sign of Anabaena variabilis

Possible role of singlet molecular oxygen in the control of the phototactic reaction sign of Anabaena variabilis. Schuchart, Hartwig; Nultsch, Wilhelm (Fachbereich Biol., Phillipps-Univ. Marburg, Marburg D-3550/1, Fed. Rep. Ger.). J. Photochem., 25(2-4), 317-25 (English) 1984. CODEN: JPCMAE. ISSN: 0047-2670. DOCUMENT TYPE: Journal CA Section: 10 (Microbial Biochemistry) In A. variabilis, the phototactic reaction sign at high photon fluence rates is reversed from neg. to pos. by the addn. of 10-3M NaN3. This effect has been interpreted to indicate that a hypothetical phototactic reaction sign reversal generator in the sensory transduction chain is controlled by the level of singlet O which is quenched by N3-. To confirm this hypothesis, expts. with other quenching agents, at various pH values, as well as in N and O atmospheres, were carried out. Expts. with a phosphate buffer at various pH values show that the transition point from pos. to neg. phototaxis is shifted from 5.7 W m-2 at pH 7 to ~15 W m-2 at pH 6. At pH 5.5, only pos. responses occur even at 120 W m-2. At lower pH values, movement ceases. However, at alk. pH (8.0), the transition point is shifted to lower fluence rates (4.5 W m-2). When imidazole buffer (pH 6) is used, the reaction sign reversal is even more pronounced. L-Histidine, a 1O2 quencher, decreases neg. phototaxis at 13.5 W m-2 with increasing concn., but does not reverse the reaction sign. 1,4-Diazabicyclo[2.2.2]octane reverses the reaction sign at 13.5 W m-2 from neg. to slightly pos., but is cytotoxic at higher concns. When the Petri dishes are gassed with N and O, only pos. reactions are obsd. up to 54 W m-2. Apparently, in Anabaena, the phototactic reaction sign is controlled by the 1O2 concn. via a reaction sign reversal generator. This mechanism enables the Anabaena filaments to escape dangerous light conditions. 2 ′ 10-2 M KI inhibits both pos. and neg. phototaxis.

Chromone studies

Chromone studies. Part 14. Unprecedented dimerization of chromone-3-carbaldehyde-derived Baylis-Hillman adducts. Kaye, Perry T.; Nchinda, Aloysius T.; Sabbagh, Liezel V.; Bacsa, John ( Dept. of Chem., Rhodes Univ., Grahmstown 6140, S. Afr.). Journal of Chemical Research, Synopses, (3), 111-113 (English) 2003 Science Reviews. CODEN: JRPSDC. ISSN: 0308-2342. DOCUMENT TYPE: Journal CA Section: 27 (Heterocyclic Compounds (One Hetero Atom)) Section cross-reference(s): 22, 75 1,4-Diazabicyclo[2. 49619-59-2 and 705-15-7 are also in the experiment.2.2]octane (DABCO)-catalyzed Baylis-Hillman reactions of selected chromone-3-carboxaldehydes with Me acrylate were shown to afford mixts. of the expected Baylis-Hillman products and unprecedented dimeric derivs. The Baylis-Hillman products, on heating at 80°C in the presence of DABCO, are converted to the corresponding dimers, the structures of which have been unambiguously established by NMR and X-ray.crystallog. anal. Electron-impact and electrospray MS data for the dimeric systems are discussed. .