Zee David Z, Harris T David
Department of Chemistry , Northwestern University , 2145 Sheridan Road , Evanston , Illinois 60208 , USA.
Department of Chemistry , University of California, Berkeley , Berkeley , California 94720 , USA . Email:
Chem Sci. 2020 May 7;11(21):5447-5452. doi: 10.1039/d0sc01796e. eCollection 2020 Jun 7.
Catalytic heme active sites of enzymes are sequestered by the protein superstructure and are regulated by precisely defined outer coordination spheres. Here, we emulate these protective functions in the porphyrinic metal-organic framework PCN-224 by post-synthetic acetylation and subsequent hydroxylation of the Zr nodes. A suite of physical methods demonstrates that both transformations preserve framework structure, crystallinity, and porosity without modifying the inner coordination spheres of the iron sites. Single-crystal X-ray analyses establish that acetylation replaces the mixture of formate, benzoate, aqua, and terminal hydroxo ligands at the Zr nodes with acetate ligands, and hydroxylation affords nodes with seven-coordinate, hydroxo-terminated Zr ions. The chemical influence of these reactions is probed with heme-catalyzed cyclohexane hydroxylation as a model reaction. By virtue of passivated reactive sites at the Zr nodes, the acetylated framework oxidizes cyclohexane with a yield of 68(8)%, 2.6-fold higher than in the hydroxylated framework, and an alcohol/ketone ratio of 5.6(3).
酶的催化血红素活性位点被蛋白质超结构隔离，并由精确界定的外配位层调控。在此，我们通过对PCN-224卟啉金属有机框架进行后合成乙酰化以及随后对Zr节点进行羟基化，来模拟这些保护功能。一系列物理方法表明，这两种转变均保留了框架结构、结晶度和孔隙率，而未改变铁位点的内配位层。单晶X射线分析表明，乙酰化用乙酸根配体取代了Zr节点处的甲酸根、苯甲酸根、水和末端羟基配体的混合物，羟基化则使节点带有七配位、羟基封端的Zr离子。以血红素催化的环己烷羟基化为模型反应，探究了这些反应的化学影响。由于Zr节点处的活性位点被钝化，乙酰化框架氧化环己烷的产率为68(8)%，比羟基化框架高2.6倍，醇/酮比为5.6(3)。
