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• An Approximate Method for Exploring Nonradiative Decay Pathways From Highly Excited States of Lanthanide Complexes: Application to Luminescent Cerium Complexes

  Ikuta S., Inagaki T., Hatanaka M.

  Journal of Computational Chemistry 47 ( 5 )  2026.02

  ISSN  01928651

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  The exploration of minimum energy crossing points (MEXs) between potential energy surfaces (PESs) is essential for understanding nonradiative decay mechanisms and plays a key role in the design of photofunctional materials. In lanthanide (Ln³⁺) complexes, however, the presence of open-shell 4f^N electrons leads to quasi-degenerate electronic states, making MEX searches particularly challenging. To describe the PESs of 4f-5d or charge-transfer excited states (i.e., 4f^N−1X excited states) of Ln³⁺ complexes, we propose a new approximation, the ion energy shift (IES) method. In this approach, the 4f^N−1X excited state is represented using density functional theory (DFT) with the large-core relativistic effective core potential (RECP) for Ln⁴⁺, which has a higher formal charge than the actual ion (Ln³⁺), and the PES is shifted to reproduce the target excitation energy. In this study, we validate the IES method against the multiconfigurational wavefunction results and apply it to elucidate the origin of the different excited-state lifetimes of hydrated Ce³⁺ complexes with and without coordination of a carboxylate ligand.

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• Mechanistic origin of C- over O-glycosylation in glycosyltransferase GgCGT: a QM/MM study

  Terada D., Inagaki T., Hatanaka M.

  Bulletin of the Chemical Society of Japan 99 ( 2 )  2026.02

  ISSN  00092673

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  C-glycosylation catalyzed by C-glycosyltransferases affords chemically robust C-glycosides, yet the mechanistic origin of the remarkable selectivity for C- over O-glycosylation remains poorly understood. In this study, we present a comprehensive QM/MM investigation of the GgCGT-catalyzed mono-C-glycosylation of phloretin using UDP-glucose, extending our previous cluster-model analysis to explicitly include the full enzymatic environment. The calculated pathway involves an initial proton transfer from phloretin to UDP-glucose, followed by an S<inf>N</inf>2-type C-glycoside bond forming step accompanied by dissociation of UDP. The activation barrier of the rate-determining S<inf>N</inf>2 step is in good agreement with the experimental estimates. Although the alternative O-glycosylation pathway exhibits a lower activation barrier, it is thermodynamically disfavored due to the instability of the O-glycosylated intermediate, which readily undergoes the reverse reaction. In contrast, the C-glycosylated intermediate is strongly stabilized, rendering C-glycosylation effectively irreversible. Structural and natural bond orbital analyses reveal that this stability originates from preservation of a planar His27-Asp122 dyad and a favorable hydrogen-bonding network involving the phosphate group. Furthermore, the C6-OH group of glucose directly stabilizes the key transition state, explaining the reduced reactivity observed experimentally with UDP-xylose. These results establish a dual catalytic strategy in C-glycosyltransferases, combining thermodynamic control for C-selectivity with transition-state stabilization for rate acceleration.

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• Comprehensive Molecular-Level Understanding of MgO Hydration through Computational Chemistry

  Inagaki T., Hatanaka M.

  Journal of Physical Chemistry C 130 ( 3 ) 1312 - 1326 2026.01

  ISSN  19327447

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  The hydration of magnesium oxide (MgO) to magnesium hydroxide (Mg(OH)<inf>2</inf>) is a fundamental solid-surface chemical reaction with significant implications for materials science. Yet its molecular-level mechanism from water adsorption to Mg(OH)<inf>2</inf> nucleation and growth remains elusive due to its complex and multistep nature. Here, we elucidate the molecular process of MgO hydration based on structures of the MgO/water interface obtained by a combined computational chemistry approach of potential-scaling molecular dynamics simulations and first-principles calculations without any a priori assumptions about reaction pathways. The result shows that the Mg²⁺ dissolution follows the dissociative water adsorption. We find that this initial dissolution can proceed exothermically even from the defect-free surface with an average activation barrier of ∼12 kcal/mol. This exothermicity depends crucially on the stabilization of the resulting surface vacancy, achieved by proton adsorption onto neighboring surface oxygen atoms. Further Mg²⁺ dissolution then occurs in correlation with proton penetration into the solid. Moreover, we find that the Mg(OH)<inf>2</inf> nucleation and growth proceeds according to the dissolution–precipitation mechanism, rather than a solid-state reaction mechanism involving a direct topotactic transformation. In this process, Mg²⁺ ions migrate away from the surface and form amorphous Mg–OH chains as precursors for Mg(OH)<inf>2</inf> nucleation. We also demonstrate that sufficient water facilitates the formation of more ordered crystalline nuclei. This computational study provides a comprehensive molecular-level understanding of MgO hydration, representing a foundational step toward elucidating the mechanisms of this class of complex and multistep solid-surface chemical reactions.

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• Mechanistic elucidation of enzymatic C-glycosylation: facilitation by proton transfer to UDP-glucose

  Terada D., Inagaki T., Hatanaka M.

  Rsc Advances 15 ( 35 ) 28592 - 28600 2025.08

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  C-Glycosyltransferases have garnered attention owing to their ability to synthesize C-glycosides with high conversion and selectivity in one-pot reactions. Their potential in rational enzyme engineering makes them valuable for the synthesis of diverse C-glycosides. However, the detailed reaction mechanism remains unclear. To address this, we investigated the C-glycosylation of phloretin catalyzed by the glycosyltransferase GgCGT in the presence of the coenzyme UDP-glucose. Using density functional theory (DFT) calculations on a cluster model, we identified the most favorable pathway for C-glycosylation. The reaction proceeds via an initial proton transfer from phloretin to UDP-glucose, followed by the nucleophilic attack of phloretin on the glucose moiety and subsequent dissociation of UDP in an S<inf>N</inf>2-like manner. The S<inf>N</inf>2 step yields a non-aromatic intermediate, which can be rapidly converted to C-glycoside even without an enzymatic environment. The key residue that facilitates the rate-determining S<inf>N</inf>2 step is His-27, which stabilizes phloretin via hydrogen bonding. Additionally, to clarify why alternative products such as O-glycosides are not formed, we also investigated the O-glycosylation pathway. Our calculations revealed that O-glycosylation was promoted by proton transfer from UDP-glucose, like C-glycosylation, but was suppressed by structural fixation due to hydrogen bonding among phloretin, glucose, and GgCGT.

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• Exploration of the Global Minimum and Conical Intersection with Bayesian Optimization

  Somaki R., Inagaki T., Hatanaka M.

  Molecular Informatics 44 ( 2 )  2025.02

  ISSN  18681743

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  Conventional molecular geometry searches on a potential energy surface (PES) utilize energy gradients from quantum chemical calculations. However, replacing energy calculations with noisy quantum computer measurements generates errors in the energies, which makes geometry optimization using the energy gradient difficult. One gradient-free optimization method that can potentially solve this problem is Bayesian optimization (BO). To use BO in geometry search, an acquisition function (AF), which involves an objective variable, must be defined suitably. In this study, we propose a strategy for geometry searches using BO and examine the appropriate AFs to explore two critical structures: the global minimum (GM) on the singlet ground state (S<inf>0</inf>) and the most stable conical intersection (CI) point between S<inf>0</inf> and the singlet excited state. We applied our strategy to two molecules and located the GM and the most stable CI geometries with high accuracy for both molecules. We also succeeded in the geometry searches even when artificial random noises were added to the energies to simulate geometry optimization using noisy quantum computer measurements.

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Papers, etc., Registered in KOARA 【 Display / hide 】

Papers, etc., Registered in KOARA 【 Display / hide 】

• Theoretical elucidation of molecular collective structures triggering water autoionization

  Inagaki, Taichi

  学事振興資金研究成果実績報告書 (慶應義塾大学)  2021

• Theoretical elucidation of molecular collective structures triggering water autoionization.

  Inagaki, Taichi

  学事振興資金研究成果実績報告書 (慶應義塾大学)  2020

Research Projects of Competitive Funds, etc. 【 Display / hide 】

Research Projects of Competitive Funds, etc. 【 Display / hide 】

• 溶媒和と揺らぎに着目した空気-水界面の化学反応加速機構の理論的解明

  2025.04

  -

  2029.03

  基盤研究(C), Principal investigator

• 分子シミュレーションで探る化学蓄熱の分子論的な律速過程と反応性向上への道

  2021.04

  -

  2025.03

  MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Early-Career Scientists , Principal investigator

Courses Taught 【 Display / hide 】

Courses Taught 【 Display / hide 】

• LABORATORIES IN BASIC CHEMISTRY

  2026

• LABORATORIES IN CHEMISTRY 1

  2026

• PHYSICAL CHEMISTRY EXERCISE 2

  2026

• PHYSICAL CHEMISTRY EXERCISE 1

  2026

• PHYSICAL CHEMISTRY EXERCISE 2

  2025

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