Field-Desorption Mass Spectra of Fern Phloroglucinols Containing Three to Six Ring Constituents

It has been previously shown that the structural analysis of the title compounds by electron-impact ionization (EI)mass spectrometry is complicated by extensive, if not complete, thermal rottlerone-type rearrangement and/or fragmentation reactions. The use of a ‘softer’ ionization technique such as field desorption (FD) is, therefore, required in order that these compounds may be characterized in terms of their molecular size and composition. In this report, the FD mass spectra of typical representatives of this class of compounds are described along with the attempted suppression of undesirable thermal reactions by the optimization of the emitter temperatures.     

Carbon-13 spectral analysis,tautomeric structures and conformations of four two-ring methylene-bridged phloroglucinol derivatives

The ¹³C NMR spectra of phloropyron BB, desaspidin BB, albaspidin BB and margaspidin BB were recorded and the structures of the compounds investigated with the aid of chemical shifts and CH coupling constants. The filicinic acid ring of the first three compounds appeared to have a monoketonic structure with the carbonyl group in position 2 (acyl group in position 3). The pyronone ring of phloropyron BB also has a monoketonic structure, with the carbonyl function adjacent to the ring oxygen. The two rings of the first three compounds attain a conformation where a stabilizing hydrogen bond(s) is (are) formed between the two rings, as shown by the observed CH couplings to some of the hydroxyl protons. The spectrum of margaspidin BB, whichconsists of two aromatic acyl phloroglucinol rings, indicates less inter-ring hydrogen bonding interactions.     

Visible light-mediated atom transfer radical addition via oxidative and reductive quenching of photocatalysts

Herein, the development of visible light-mediated atom transfer radical addition (ATRA) of haloalkanes onto alkenes and alkynes using the reductive and oxidative quenching of [Ir{dF(CF(3))ppy}(2)(dtbbpy)]PF(6) and [Ru(bpy)(3)]Cl(2) is presented. Initial investigations indicated that the oxidative quenching of photocatalysts could effectively be utilized for ATRA, and since that report, the protocol has been expanded by broadening the scope of the reaction in terms of the photocatalysts, substrates, and solvents. In addition, further modifications of the reaction conditions allowed for the efficient ATRA of perfluoroalkyl iodides onto alkenes and alkynes utilizing the reductive quenching cycle of [Ru(bpy)(3)]Cl(2) with sodium ascorbate as the sacrificial electron donor. These results signify the complementary nature of the oxidative and reductive quenching pathways of photocatalysts and the ability to predictably direct reaction outcome through modification of the reaction conditions.     

Fast-Atom-Bombardment Mass Spectra of Phloroglucinols from Dryopteris Ferns

Fast-atom-bombardment mass spectra of ten phloroglucinol derivatives containing two to six ring units were recorded. The mass spectral behavior of the compounds was quite similar under these conditions. Molecular-weight information was readily available as well as sequential structural data due to extensive fragmentation. Sequential alterations due to the rottlerone change or other analogous decomposition reactions proved to be almost lacking in fast-atom-bombardment mass spectrometry. The negative-ion spectra in general showed better signal-to-noise ratios and more distinct fragment ions.     

Molecular conformations in a phospholipid bilayer extracted from dipolar couplings: a computer simulation study

This paper describes an analysis of NMR dipolar couplings in a bilayer formed by dimyristoylphosphatidylcholine (DMPC). The couplings are calculated from a trajectory generated in a molecular dynamics (MD) simulation based on a realistic atom-atom interaction potential. The analysis is carried out employing a recently developed approach that focuses on the construction of the conformational distribution function. This approach is a combination of two models, the additive potential (AP) model and the maximum entropy (ME) method, and is therefore called APME. In contrast to the AP model, the APME procedure does not require an intuition-based choice of the functional form of the torsional potential and is, unlike the ME method, applicable to weakly ordered systems. The conformational distribution function for the glycerol moiety of the DMPC molecule derived from the APME analysis of the dipolar couplings is in reasonable agreement with the "true" distributions calculated from the trajectory. Analyses of dipolar couplings derived from MD trajectories can, in general, serve as guidelines for experimental investigations of bilayers and other complex biological systems.