Tuttle Robert R, Folkman Scott J, Rubin Heather N, Finke Richard G, Reynolds Melissa M
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States.
School of Biomedical Engineering, Colorado State University, Fort Collins, Colorado 80523, United States.
ACS Appl Mater Interfaces. 2020 Sep 2;12(35):39043-39055. doi: 10.1021/acsami.0c08961. Epub 2020 Aug 25.
The metal-organic framework (MOF) H[(CuCl)-(BTTri), HBTTri = 1,3,5-tris(H-1,2,3-triazol-5-yl)benzene] (CuBTTri) is a precatalyst for biomedically relevant nitric oxide (NO) release from nitrosoglutathione (GSNO). The questions of the number and nature of the catalytically most active, kinetically dominant sites are addressed. Also addressed is whether or not the well-defined structural geometry of MOFs (as solid-state analogues of molecular compounds) can be used to generate specific, testable hypotheses about, for example, if intrapore vs exterior surface metal sites are more catalytically active. Studies of the initial catalytic rate vs CuBTTri particle external surface area to interior volume ratio show that intrapore copper sites are inactive within the experimental error (≤1.7 × 10 of the observed catalytic activity)-restated, the traditional MOF intrapore metal site catalysis hypothesis is disproven for the current system. All observed catalysis occurs at exterior surface Cu sites, within the experimental error. Fourier transform infrared (FT-IR) analysis of CN-poisoned CuBTTri reveals just two detectable Cu sites at a ca. ≥0.5% detection limit, those that bind three or one CN ("Cu(CN)" and "CuCN"), corresponding to the CN binding expected for exterior surface, 3-coordinate (Cu) and intrapore, 5-coordinate (Cu) sites predicted by the idealized, metal-terminated crystal structure. Two-coordinate Cu defect sites are ruled out at the ≥0.5% FT-IR detection limit as such defect sites would have been detectable by the FT-IR studies of the CN-poisoned catalyst. Size-selective poisoning studies of CuBTTri exterior surface sites reveal that 1.3 (±0.4)% of total copper in 0.6 ± 0.4 μm particles is active. That counting of active sites yields a normalized turnover frequency (TOF), TOF = (4.9 ± 1.2) × 10 mol NO (mol Cu) s (in water, at 20 min, 25 °C, 1 mM GSNO, 30% loss of GSNO, and 1.3 ± 0.4 mol % Cu)-a value ∼100× higher than the TOF calculated without active site counting. Overall, Ockham's razor interpretation of the data is that exterior surface, Cu sites are the catalytically most active sites present at a 1.3 (±0.4)% level of total Cu.
金属有机框架（MOF）H[(CuCl)-(BTTri)]，HBTTri = 1,3,5-三（H-1,2,3-三唑-5-基）苯（CuBTTri）是一种用于从亚硝基谷胱甘肽（GSNO）生物医学相关释放一氧化氮（NO）的预催化剂。研究了催化活性最高、动力学上占主导地位的位点的数量和性质问题。还探讨了MOF明确的结构几何形状（作为分子化合物的固态类似物）是否可用于生成关于例如孔内与外表面金属位点是否更具催化活性的特定、可测试的假设。对初始催化速率与CuBTTri颗粒外表面面积与内部体积比的研究表明，在实验误差范围内（≤观察到的催化活性的1.7×10），孔内铜位点是无活性的——也就是说，传统的MOF孔内金属位点催化假设在当前体系中被证伪。在实验误差范围内，所有观察到的催化作用都发生在外表面的铜位点上。对氰化物中毒的CuBTTri进行傅里叶变换红外（FT-IR）分析，在约≥0.5%的检测限下仅发现两个可检测到的铜位点，即那些结合三个或一个氰化物的位点（“Cu(CN)”和“CuCN”），这与理想化的金属端接晶体结构预测的外表面三配位（Cu）和孔内五配位（Cu）位点的氰化物结合情况相对应。在≥0.5%的FT-IR检测限下排除了二配位铜缺陷位点，因为此类缺陷位点在氰化物中毒催化剂的FT-IR研究中本应可检测到。对CuBTTri外表面位点的尺寸选择性中毒研究表明，0.6±0.4μm颗粒中总铜的1.3（±0.4）%是有活性的。对活性位点的计数得出归一化周转频率（TOF），TOF = (4.9 ± 1.2) × 10 mol NO (mol Cu) s（在水中，20分钟，25°C，1 mM GSNO，GSNO损失30%，以及1.3 ± 0.4 mol% Cu）——该值比未进行活性位点计数时计算的TOF高约100倍。总体而言，对数据的奥卡姆剃刀式解释是，外表面的铜位点是总铜中1.3（±0.4）%水平上存在的催化活性最高的位点。
