Search

The kinetic HH/HD/DH/DD isotope effects of an intramolecular reversible nondegenerate double proton transfer reaction are described. The molecule studied is 8-acetyl-3,13,17-tris(2-(methoxycarbonyl)ethyl]-2,7,12,18-tetramethyl-(21H,23H)-porphyrin (acetylporphyrin, ACP) dissolved in CD 2 Cl 2 . As a thermodynamic and kinetic method we used dynamic 1 H and 13 C NMR spectroscopy of suitably 2 H, 15 N, and 13 C labeled ACP. The 15 N label was introduced at the 21, 23, and 24 positions, the 13 C label at the 6- and 7-methyl positions, and 2 H at the central proton sites, respectively

"Do you know the word Schadenfreude ?" "No" "It's one of those German words, like Gestalt or Weltschmerz, that has a special flavor that doesn't come across in the English equivalent: gloating. Schadenfreude is more subtle and yet meaner. The more impeccable your reputation, and the more significant the work you retract, the greater the Schadenfreude among your peers ." "I can't believe what you're saying," exclaimed Paula. "You scientists, you upholders of the social contract, gloat like other mortals when somebody makes a mistake? Even when he confesses the mistake ?" Cantor let out a sigh. "I'm afraid the answer is yes. I've been guilty of that. I mean gloating," he added quickly. "I've never had to retract any of my published work and I hope to God I won't need to do it this time. Because of the rareness of such events, innocent or otherwise —" "What does 'otherwise' mean?" interjected Paula . "Data manipulation, even outright fraud ..." ...

Sponges are unique in regard to membrane phospholipid composition. Features virtually without parallel in other organisms are the predominance of the C26-C30 polyenoic acids (demospongic acids) in the phosphatidylethanolamines (PE) and the attachment of identical acyl groups to the glycerol moiety. The biosynthesis and disposition of these unusual phospholipids were followed in the marine sponge Microciona prolifera where PE ( delta 5,9-26:2, delta 5,9-26:2) is a major molecular species. Incorporation experiments with radiolabeled fatty acids, bases, and intact phospholipids revealed the de novo biosynthesis of the two major phosphatides, phosphatidylethanolamines (PE) and phosphatidylcholines (PC), via the cytidine pathway as in higher animals, with ethanolamine selectively incorporated into PE( delta 5,9-26:2, delta 5,9-26:2). Methylation of PE and random acyl chain migration across different phospholipid classes were marginal, but the exchange of PC for PE, apparently mediated by the action of phospholipase, was indicated after uptake of the unnatural PC( delta 9-27:1, delta 9-26:1). The present study demonstrates in the most primitive multicellular animals a phospholipid metabolic pattern similar to that in higher organisms, with unique acyl and phosphoethanolamine transferases apparently involved in the biosynthesis of the (demospongic) di-C26-acyl-PE molecular species.

The synthesis and thermotropic properties of 1,2-di-(9Z)-9-tetracosenoylphosphatidylcholine [delta 9-PC(24:1,24:1), 1], 1,2-di-(5Z)-5-tetracosenoylphosphatidylcholine [delta 5-PC(24:1,24:1), 2], and 1,2-di-(15Z)-15- tetracosenoylphosphatidylcholine [delta 15-PC(24:1,24:1), 3] are reported. Liposomes prepared from these phospholipids differ from those of the natural sponge phospholipids, 1,2-di-(5Z,9Z)-5,9-hexacosadienoylphosphatidylcholine (4a) and the corresponding ethanolamine (4b), both of which virtually exclude cholesterol from their bilayers. The behavior of 1 and 2 is similar to that of 1,2-di-(6Z,9Z)-6,9-hexacosadienoylphosphatidylcholine (5), which exhibits a partial molecular interaction with cholesterol. In the case of 3, cholesterol appears to interact with the saturated acyl chain regions of this phospholipid in a manner similar to that of its interaction with DPPC acyl chains. This study delineates the effect of the double-bond location in long fatty acyl chains of phospholipids on their interactions with cholesterol.

The synthesis and chiroptical properties of (2R)-2-deuterio-3-hexanone (8a), (2R)-2-deuterio-4-methylpentanone (8b), (2R)-2-deuteriopentanal (9a), (2R)-2-deuterio-3-methylbutanal (9b), and (3R)-3-deuteriohexanal (13) are described. All exhibit Cotton effects consistent with the preferred eclipsed conformation of the carbonyl/..cap alpha..-alkyl moiety. The ..beta..-deuterio aldehyde 13 shows a sign change in accordance with the proximity rule previously observed in CD studies.

The authors previous MCD and absorption spectral studies of monosubstituted free-base alkylporphyrins found evidence in the sign and magnitude of visible-band MCD for out-of-plane conformers of ..pi.. substituents, as well as effects due to the electronic influence of alkyl groups and the equilibrium of central-proton tautomers. The present study examines the MCD and absorption spectra of a series of acetylheptaalkylporphyrin free bases with various alkyl groups adjacent to the acetyl, as well as a fused-ring ketocyclohexenoporphyrin. Out-of-plane rotation angles of approximately 85, 65, and 35/sup 0/ for the acetyl moiety of the tert-butyl-, isopropyl-, and ethyl-substituted porphyrins, respectively, are deduced from variations in the observed MCD of the Q/sub 0//sup x/ band. INDO calculations of B terms for acetylporphyrin free base are found to reproduce the angle dependence observed for the MCD.