Hydrophobic Acceleration of Electron Transfer Processes
摘要:
Electron transfer processes between 1-alpha-naphthyl-3-oxa-alkanes (1-n, n = 1, 8, 12, 16) and 2-alkyl-3,5,6-trichloro-1,4-benzoquinones (2-n, n = 8, 12, 16) facilitated by hydrophobic-lipophilic interactions (HLI) have been investigated by means of fluorescence spectroscopy in dioxane-H2O systems of different psi values, where psi is the volume fraction of the organic component of an aquiorgano mixture. Three lines of evidence, namely, EPR, UV-vis, and fluorescence quenching, indicate that electron transfer between 1-12 and 2-12 has occurred. Furthermore, both UV-vis evidence and the near constancy of the life time tau of 1-12* in the presence of different concentrations of the quencher 2-12 show that the electron transfer is preceded by preassociation, i.e., the quenching process is static. Therefore, the extent of HLI-driven coaggregation (preassociation) between the donors and the accepters may be assessed from the Stern-Volmer slopes (Ksv). The chain-length effect, and possibly also a chain-foldability effect, has been observed. A notable observation is the importance of solvent aggregating power (SAgP) effect, which is indicated by the surge of Ksv values at psi less than or equal to 0.40 (dioxane-H2O) for monomeric 1-12.
Novel Cytotoxic, Alkylated Hydroquinones from <i>Lannea welwitschii</i>
作者:Amiram Groweiss、John H. Cardellina、Lewis K. Pannell、Duangchan Uyakul、Yoel Kashman、Michael R. Boyd
DOI:10.1021/np960435t
日期:1997.2.1
Two novel natural products, lanneaquinol (1) and 2'(R)-hydroxylanneaquinol (2), were isolated from the organic extract of the plant Lannea welwitschii (Hiern) Engl. Their structures were solved by spectroanalytical methods and confirmed by comparison to synthetic models. The absolute configuration of 2 was determined by the modified Mosher method. Both compounds exhibited modest cytotoxicity against