Research

Overview
The goal of Biomimetic Materials Laboratory is to clarify the 'Biological Process' in the reactions of metalloenzymes through the biomimetic system and utilize the biomimetic techniques in medical and environmental applications.
○ Design of Model Complexes of Metalloenzymes
○ Characterization and Reactivity Studies for Biomimetic Materials
○ Application for Medical (e.g., Drug Development) and Environmental Materials




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Recent Achievements

Metal-Nitrosyl Complex
Cells use gaseous molecules such as nitric oxide (NO) to transmit both intracellular and intercellular signals. In principle, the endogenous small molecules regulate physiological changes, but it is unclear how randomly diffusive molecules trigger and discriminate signaling programs. Herein, it is shown that gasotransmitters use time‐dependent dynamics to discriminate the endogenous and exogenous inputs. For a real‐time stimulation of cell signaling, we synthesized a photo‐cleavable metal–nitrosyl complex, [CoIII(MDAP)(NO)(CH3CN)]2+ (MDAP=N,N′‐dimethyl‐2,11‐diaza[3,3](2,6)pyridinophane), which can stably deliver and selectively release NO with fine temporal resolution in the cytosol, and used this to study the extracellular signal‐regulated kinases (ERKs), revealing how cells use both exogenous and endogenous NO to disentangle cellular responses. This technique can be to understand how diverse cellular signaling networks are dynamically interconnected and also to control drug delivery systems.
S. Shin
,
 
J. Choe,
 
Y. Park,
 
D. Jeong
H. Song, 
Y. You, 
 
D. Seo, 
 
J. Cho
(‡Equal contribution) "Artificial Control of Cell Signaling Using a Photocleavable Cobalt(III)–Nitrosyl ComplexAngew. Chem. Int. Ed. 58, 30, 10126, 2019. [corresponding author] IF = 12.1


Metal-Iodosylarene
Transition metal−iodosylarene complexes have been proposed to be key intermediates in the catalytic cycles of metal catalysts with iodosylarene. We report the first X-ray crystal structure and spectroscopic characterization of a mononuclear nonheme manganese- (III)−iodosylarene complex with a tetradentate macrocyclic ligand, [MnIII(TBDAP)(OIPh)(OH)]2+. The manganese(III)−iodosylarene complex is capable of conducting various oxidation reactions with organic substrates, such as C−H bond activation, sulfoxidation and epoxidation. Kinetic studies including isotope labeling experiments and Hammett correlation demonstrate the electrophilic character on the Mn−iodosylarene adduct. This novel intermediate would be prominently valuable for expanding the chemistry of transition metal catalysts.
 J. Am. Chem. Soc. 140, 47, 16037, 2018. [corresponding author] IF = 14.4

C-H Bond Activation
Naphthalene oxidation with metal–oxygen intermediates is a difficult reaction in environmental and biological chemistry. We report that a MnIV bis(hydroxo) complex, which was fully characterized by various physicochemical methods, such as ESIMS, UV/Vis, and EPR analysis, Xray diffraction, and XAS, can be employed for the oxidation of naphthalene in the presence of acid to afford 1,4naphthoquinone. Redox titration of the MnIV bis(hydroxo) complex gave a oneelectron reduction potential of 1.09 V, which is the most positive potential for all reported nonheme MnIV bis(hydroxo) species as well as MnIV oxo analogues. Kinetic studies, including kinetic isotope effect analysis, suggest that the naphthalene oxidation occurs through a ratedetermining electron transfer process.
D. Jeong, J. Yan, H. Noh, B. Hedman, K. Hodgson, E. Solomon, J. Cho, "Naphthalene Oxidation of a Manganese(IV)-Bis(Hydroxo) Complex in the Presence of AcidAngew. Chem. Int. Ed. 57, 26, 7764, 2018[corresponding author] IF = 12.1

Nitrile Activation
A mononuclear side-on peroxocobalt(III) complex with a tetradentate macrocyclic ligand, [CoIII(TBDAP)(O2)]+, shows a novel and facile mode of dioxygenase-like reactivity with nitriles (R—C≡N; R = Me, Et, and Ph) to produce the corresponding mononuclear hydroximatocobalt(III) complexes, [CoIII(TBDAP)(R—C(NO)O)]+, in which the nitrile moiety is oxidized by two oxygen atoms of the peroxo group. The overall reaction proceeds in one-pot under ambient conditions (ca. 1 h, 40 °C). 18O-Labeling experiments confirm that both oxygen atoms are derived from the peroxo ligand. The structures of all products, hydroximatocobalt(III) complexes, were confirmed by X-ray crystallography and various spectroscopic techniques. Kinetic studies including the Hammett analysis and isotope labeling experiments suggest that the mechanistic mode of [CoIII(TBDAP)(O2)]+ for activation of nitriles occurs via a concerted mechanism. This novel reaction would be significantly valuable for expanding the chemistry for nitrile activation and utilization.
H. NohD. Jeong, T. Ohta, T. Ogura, J. S. Valentine, J. Cho, "Distinct Reactivity of a Mononuclear Peroxocobalt(III) Species towards Activation of Nitriles
J. Am. Chem. Soc. 139, 32, 10960, 2017[corresponding author] IF = 13.8


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