Theoretical Analyses on Phosphorescent Processes in Pt(thpy)₂ and Its Derivatives

Theoretical estimation of the peak wavelengths of phosphorescence was performed at the MCSCF+SOCI/SBKJC+p level of theory for several typical platinum complexes in the research field of organic-light-emitting-diodes (OLEDs), where MCSCF+SOCI is the abbreviation of multiconfiguration self-consistent field calculations followed by second-order configuration interaction calculations. The spin–orbit coupling (SOC) integrals among low-lying electronic states of different spin multiplicities were explicitly calculated within the <i>Z</i>_eff approximation. By using these computational methods, the experimental results for peak wavelengths of phosphorescence were reasonably explained for <i>cis</i>-bis­[2-(2′-thienyl)­pyridinato-N,C_3′]­platinum­(II) and its derivatives. The replacement of one of the 2-(2′-thienyl)­pyridinate (<i>thpy</i>) ligands by a 2,4-pentanedionate (<i>acac</i>) ligand causes a blue shift of the phosphorescent peak by about 10 nm. The use of a 1,3-bis­(phenyl)­propane-1,3-dionate (<i>bpp</i>), 1,3-bis­(<i>n</i>-methoxyphenyl)­propane-1,3-dionate (<i>bmp</i>), or 1,3-bis­(3,4-methoxyphenyl)­propane-1,3-dionate (<i>bdmp</i>) ligand, instead of an <i>acac</i> ligand, has almost no effect on the peak wavelength of phosphorescence. When a benzene ring is fused to a <i>thpy</i> ligand, the peak wavelength is estimated to be 613 or 651 nm for [2,2′-(4′,5′-benzo)­thienyl)­pyridinato-N,C_3′]­[1,3-bis­(3,4-dibutoxyphenyl)­propane-1,3-dionato-O,O]­platinum­(II) [<i>btp</i>Pt­(bdbp)] and [1-(2′-thienyl)­isoquinolyl-N,C_3′]­[1,3-bis­(3,4-dibutoxyphenyl)­propane-1,3-dionato-O,O]­platinum­(II) [<i>1tiq</i>Pt­(bdbp)], respectively, after correction of the present computational underestimation. These theoretical estimations are in good agreement with the corresponding observations

Bacterial Production of the Tunicate-Derived Antitumor Cyclic Depsipeptide Didemnin B

Natural products obtained from marine invertebrates such as sponges and tunicates are attractive sources of drugs. However, a critical obstacle in the development of these compounds is the problem of supply. In most cases, neither chemical synthesis nor mariculture of invertebrates is economically feasible. Due to structural similarities, many marine natural products are suspected to be produced by associated microorganisms. A favorable strategy for the production of such compounds is to use culturable microorganisms. Here we report that didemnin B, a tunicate-derived depsipeptide, has been isolated from a culturable bacterium, <i>Tistrella mobilis</i> YIT 12409