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At least 199 records · Page 11Linked to original sources
PubMed2006

Phosphorus-nitrogen compounds. Part 13. Syntheses, crystal structures, spectroscopic, stereogenic, and anisochronic properties of novel spiro-ansa-spiro-, spiro-bino-spiro-, and spiro-crypta phosphazene derivatives.

The condensation reactions of N2Ox (x = 2, 3) donor-type aminopodand (4) and dibenzo-diaza-crown ethers (5, 6, and 9) with hexachlorocyclotriphosphazatriene, N3P3Cl6, produce two kinds of partially substituted novel phosphazene derivatives, namely, spiro-bino-spiro- (19) and spiro-crypta (21, 22, and 25) phosphazenes. The partially substituted spiro-ansa-spiro-phosphazene (11) reacted with pyrrolidine and 1,4-dioxa-8-azaspiro[4,5]decane (DASD) give the corresponding new fully substituted phosphazenes (14 and 16). Unexpectedly, the reactions of 23 and 24 with pyrrolidine result in only geminal crypta phosphazenes (26 and 27). The solid-state structures of 16 and 22 have been determined by X-ray diffraction techniques. The relative inner hole-size of the macrocycle in the radii of 22 is 1.27 A. The relationship between the exocyclic NPN (alpha') and endocyclic (alpha) bond angles for spiro-crypta phosphazenes and exocyclic OPN (alpha') bond angles for spiro-ansa-spiro- and spiro-bino-spiro-phosphazenes with 31P NMR chemical shifts of NPN and OPN phosphorus atoms, respectively, have been investigated. The structures of 10, 14, 16, 19, 21, 22, and 25-27 have also been examined by FTIR, 1H, 13C, and 31P NMR, HETCOR, MS, and elemental analyses. The 31P NMR spectra of 10, 21, 22, and 25 indicate that the compounds have anisochrony. In compounds 16 and 22, the spirocyclic nitrogen atoms have pyramidal geometries resulting in stereogenic properties.

Journal Article↗
PubMed2004

Somatic embryogenesis in pumpkin (Cucurbita pepo L.): control of somatic embryo development by nitrogen compounds.

Embryogenic cultures of pumpkin (Cucurbita pepo L.) were initiated from mechanically wounded mature zygotic embryos on 2,4-D-containing MS medium, and on hormone-free, semisolid modified MS medium containing NH4Cl as the sole source of nitrogen. The habituated line was derived from the embryogenic tissue induced with 2,4-D and maintained on medium without growth regulators. Sustained subculturing of the three embryogenic lines on a medium with NH4Cl as the sole source of nitrogen enabled the establishment of highly uniform cultures in which no further development into mature embryo stages occurred. The tissue consisting of proembryogenic globules or globular stage embryos was maintained, without decline, for over six years. Globular embryos proceeded to maturity when a combination of reduced (NH4) and unreduced (NO3) forms of nitrogen was provided in the medium. Different nitrogen sources in the medium caused changes of medium pH during subculture in the pH range of 4.0-6.5. The tissue growth and embryo development were blocked on medium with pH adjusted and stabilized at 4.0 or at 3.2.

Cell Culture Techniques↗
PubMed1996

An evaluation of neuronal nicotinic acetylcholine receptor activation by quaternary nitrogen compounds indicates that choline is selective for the alpha 7 subtype.

The agonist properties of acetylcholine (ACh), tetramethylammonium, ethyl-trimethylammonium and choline were evaluated for muscle and neuronal nicotinic receptors in Xenopus oocytes. The only essential feature for a neuronal receptor agonist appears to be the charged nitrogen. For specific receptor subtypes, other structural elements appear permissive (neither increasing nor decreasing activity) or non-permissive (decreasing activity). Choline was a full agonist for alpha 7, but a hydroxyl group was strongly non-permissive for other receptor subtypes (alpha 1 beta 1 gamma delta, alpha 3 beta 4, alpha 3 beta 2, and alpha 4 beta 2). The binding of these ligands to brain membranes is consistent with the electrophysiological results. Physiological concentrations of choline desensitize alpha 7 receptors to ACh suggesting that, in vivo, choline may regulate both the activation and inactivation of this receptor.

Acetylcholine↗