ビス(μ-オキソ)二核ニッケル(3)錯体の酸化反応により誘導される反応中間体の同定と反応機構に関する研究

取得学位：博士(学術)，学位授与番号：博甲第757号，学位授与年月日：平成17年9月30日,学位授与年：200

Challenges of Measuring Soluble Mn(III) Species in Natural Samples

Soluble Mn(III)-L complexes appear to constitute a substantial portion of manganese (Mn) in many environments and serve as critical high-potential species for biogeochemical processes. However, the inherent reactivity and lability of these complexes-the same chemical characteristics that make them uniquely important in biogeochemistry-also make them incredibly difficult to measure. Here we present experimental results demonstrating the limits of common analytical methods used to quantify these complexes. The leucoberbelin-blue method is extremely useful for detecting many high-valent Mn species, but it is incompatible with the subset of Mn(III) complexes that rapidly decompose under low-pH conditions-a methodological requirement for the assay. The Cd-porphyrin method works well for measuring Mn(II) species, but it does not work for measuring Mn(III) species, because additional chemistry occurs that is inconsistent with the proposed reaction mechanism. In both cases, the behavior of Mn(III) species in these methods ultimately stems from inter- and intramolecular redox chemistry that curtails the use of these approaches as a reflection of ligand-binding strength. With growing appreciation for the importance of high-valent Mn species and their cycling in the environment, these results underscore the need for additional method development to enable quantifying such species rapidly and accurately in nature

Helicity-driven chiral self-sorting supramolecular polymerization with Ag+: right- and left-helical aggregates

The study of chiral self-sorting is extremely important for understanding biological systems and for developing applications for the biomedical field. In this study, we attempted unprecedented chiral self-sorting supramolecular polymerization accompanying helical inversion with Ag+ in one enantiomeric component. Bola-type terpyridine-based ligands (R-L-1 and S-L-1) comprising R- or S-alanine analogs were synthesized. First, R-L-1 dissolved in DMSO/H2O (1 : 1, v/v) forms right-handed helical fibers (aggregate I) via supramolecular polymerization. However, after the addition of AgNO3 (0.2-1.1 equiv.) to the R-L-1 ligand, in particular, it was found that aggregate II with left-handed helicity is generated from the [R-L-1(AgNO3)(2)] complex through the [R-(LAg)-Ag-1](+) complex via the dissociation of aggregate I by a multistep with an off pathway, thus demonstrating interesting self-sorting properties driven by helicity and shape discrimination. In addition, the [R-L-1(AgNO3)(2)] complex, which acted as a building block to generate aggregate III with a spherical structure, existed as a metastable product during the formation of aggregate II in the presence of 1.2-1.5 equiv. of AgNO3. Furthermore, the AFM and CD results of two samples prepared using aggregates I and III with different volume ratios were similar to those obtained upon the addition of AgNO3 to free R-L-1. These findings suggest that homochiral self-sorting in a mixture system occurred by the generation of aggregate II composed of the [R-(LAg)-Ag-1](+) complex via the rearrangement of both, aggregates I and III. This is a unique example of helicity- and shape-driven chiral self-sorting supramolecular polymerization induced by Ag+ starting from one enantiomeric component. This research will improve understanding of homochirality in complex biological models and contribute to the development of new chiral materials and catalysts for asymmetric synthesis

Nanozyme Based on Porphyrinic Metal-Organic Framework for Electrocatalytic CO2 Reduction

Mimicry of natural enzyme systems is an important approach for catalyst design. To create an enzyme-inspired catalyst, it is essential to mimic both the active center and the second coordination sphere. Metal-organic frameworks (MOFs), an emerging class of porous materials, are ideal candidates for heterogeneous catalysts because their versatile building blocks confer a high level of structural tunability, and the chemical environment surrounding the active center can be controlled at the molecular level. Herein, a new 2D porphyrinic MOF, PPF-100, constructed from a nonplanar saddle-distorted porphyrin linker and a Cu paddle-wheel metal node is reported. The strategic introduction of ethyl substituents allows not only to mimic the active center and second coordination sphere but also to increase the catalytic selectivity while completely inhibiting H-2 generation in the CO2 reduction reaction