Optimization of the Lariat Ether Carboxylic Acid Host Structure for Ferrioxamine B: Demonstration of a Second Coordination Shell Chelate Effect

详细信息    查看全文

• 作者：Stephen M. Trzaska ; Myeongseob Kim ; Richard A. Bartsch ; and Alvin L. Crumbliss
• 刊名：Inorganic Chemistry
• 出版年：2001
• 出版时间：November 5, 2001
• 年：2001
• 卷：40
• 期：23
• 页码：5823 - 5828
• 全文大小：76K
• 年卷期：v.40,no.23(November 5, 2001)
• ISSN：1520-510X

文摘

Host-guest supramolecular assembly formation constants involving the second-sphere complexation of thesiderophore ferrioxamine B (FeHDFB⁺) by a lariat ether carboxylic acid host (L_n+2COOH) in wet chloroformwere obtained from liquid-liquid extractions at pH values above and below the host pK_a (~5.3). The host-guestformation constants, K_a, determined at pH = 3.2 for the assemblies {FeHDFB⁺,L_n+2COOH,ClO₄^-} (n = 4, 7,10, 15) in wet chloroform are similar to those of the parent crown ether, benzo-18-crown-6. At pH = 9.3, thelariat ethers are ionized, and this results in a more stable assembly, {FeHDFB⁺,L_n+2COO^-}, as measured by thehost-guest formation constant, K_app. This enhanced stability is shown to be a function of the lariat ether sidearmchain length (n = 4, 7, 10, 15) and is corroborated by molecular modeling calculations. Additionally, molecularmodeling and extraction data demonstrate that there is an optimum lariat ether sidearm chain length with respectto host-guest assembly stability as measured by K_app. We attribute the enhanced stability effect of the ionizedlariat ether in the host-guest assembly {FeHDFB⁺,L_n+2COO^-}, relative to {FeHDFB⁺,L_n+2COOH,ClO₄^-} or to{FeHDFB⁺,B18C6,ClO₄^-}, to a second coordination shell chelate effect.