Structural Criteria for the Rational Design of Selective Ligands. 3. Quantitative Structure-Stability Relationship for Iron(III) Complexation by Tris-Catecholamide Siderophores

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• 作者：Benjamin P. Hay ; David A. Dixon ; Rubicelia Vargas ; Jorge Garza ; and Kenneth N. Raymond
• 刊名：Inorganic Chemistry
• 出版年：2001
• 出版时间：July 30, 2001
• 年：2001
• 卷：40
• 期：16
• 页码：3922 - 3935
• 全文大小：248K
• 年卷期：v.40,no.16(July 30, 2001)
• ISSN：1520-510X

文摘

We present an extended MM3 model for catecholamide ligands and their Fe³⁺ complexes and the application ofthis model to understand how ligand architecture effects Fe³⁺ binding affinity. Force field parameters were fit togeometries and energies from electronic structure calculations, and to crystal structure data. Optimized geometriesare reported for phenol, acetamide, the phenol-phenol dimer, the acetamide-phenol dimer, and N-methylsalicylamide (HMSA) at the BLYP/DZVP2/A2 level of theory. Optimized geometries and relative energies are reportedfor the pseudo-octahedral ground state and the trigonal planar transition state of [Fe(CAT)₃]^3- at the VWN/DZVP2/A1 level of theory. The MM3 model is validated by comparison of calculated structures with crystalstructures containing 1,2-dihydroxybenzene (H₂CAT) and 2,3-dihydroxy-N-methylbenzamide (H₂MBA) fragments,crystal structures of [Fe(CAT)₃]^3- and tris-catecholamide Fe³⁺ complexes, and comparison of MM3 (6.8 kcal/mol) and VWN (5.9 kcal/mol) barriers for intramolecular octahedral inversion in [Fe(CAT)₃]^3-. The MM3 modelalso rationalizes the higher inversion barrier (14 to 18 kcal/mol) reported for [Ga(N,N-diisopropylterephthalamide)₃]^3-([Ga(DIPTA)₃]^3-). Conformational searches were performed on enterobactin (H₆ENT), 1,3,5-tris(2,3-dihydroxybenzamidomethyl)-2,4,6-triethylbenzene (H₆EMECAM), 1,3,5-tris(2,3-dihydroxybenzamidomethyl)-2,4,6-trimethylbenzene (H₆MMECAM), 1,3,5-tris(2,3-dihydroxybenzamidomethyl)benzene (H₆MECAM), and 1,5,9-N,N',N' '-tris(2,3-dihydroxybenzoyl)cyclotriazatridecane (H₆-3,3,4-CYCAM) and Fe³⁺ complexes with each of theseligands. A conformational search also was done on the Fe³⁺ complex with the 2,2',2' '-tris(2,3-dihydroxybenzamido)triethylammonium cation (H₇TRENCAM⁺). The relationship between calculated steric energies and measuredthermodynamic quantities is discussed, and linear correlations between formation constants and steric energydifferences are reported. Extrapolation to zero strain predicts formation constants 8 ± 5 orders of magnitudehigher than that exhibited by ENT (10⁴⁹) are possible. This prediction is supported by a formation constant of10⁶³ estimated from the formation constant of [Fe(2,3-dihydroxy-N,N-dimethylbenzamide)₃]^3- ([Fe(DMBA)₃]^3-)by considering the entropic consequences of connecting three DMBA ligands to a rigid backbone. Structuralcriteria for the identification of improved tris-catecholate ligand architectures are presented.