KAIST Identifies Molecular Structure Changes in Chemical Reaction Transition States

Domestic researchers have succeeded in measuring molecular structural changes of the photochemical reaction transition state using spectroscopic techniques. Spectroscopic methods enable the determination of quantum mechanical molecular structures through the interaction of light and molecules.

Although it has been possible to observe molecular structural changes occurring during chemical reactions in real time through femtochemistry (pioneered by Nobel Chemistry laureate Ahmed Zewail in 1999), it has been very rare to directly observe molecular structural changes of the transition state according to energy in a strict sense, which gives significance to this study.

(From the top left clockwise) Dr. Kim Jeong-gil, student Kang Min-seok, Dr. Yoon Joon-ho, Professor Kim Sang-gyu. Provided by KAIST

KAIST announced on the 4th that Professor Sangkyu Kim’s research team in the Department of Chemistry succeeded in experimentally revealing the transition state structure of chemical reactions.

The transition state is a core concept established with the development of chemical reaction kinetics. According to transition state theory, the reaction rate, relative yield of products, and energy distribution are determined by the molecular structure and dynamic characteristics of the transition state located between reactants and products.

Transition state theory has been the most universal reaction kinetics theory widely applied over the past century in all environments, including combustion, organic, and biochemical reactions.

However, since the transition state exists only for a time shorter than a femtosecond (10^-15 seconds), directly observing the transition state experimentally has remained a challenge.

The research team’s precise measurement of structural changes observed as molecules approach the transition state using spectroscopic techniques is the world’s first case, adding significance to the research results.

Through the abrupt changes in reaction rates observed in the transition state molecular structures measured by spectroscopy, the team also demonstrated the correlation between molecular structure and chemical reactivity.

This research was conducted with support from the Korea Research Foundation’s Mid-Career Research Program and the Basic Science 4.0 Focus Research Institute (Natural Science Research Institute).

The research results were published last month as a representative achievement in Nature Communications by Dr. Junggil Kim (first author), PhD candidate Minseok Kang, and Dr. Junho Yoon (currently at LG Chem) as co-authors.

Additionally, in an exceptional highlight comment in Nature Communications jointly authored by Robert Field, the world’s leading authority in spectroscopy from MIT, and Professor Baraban from Ben-Gurion University of Israel, the originality, implications, importance, and future impact of this research in experimental physical chemistry were emphasized.

Professor Kim stated, “This is the first case to reveal the rapidly changing molecular structure when approaching the transition state in molecular chemical reactions using spectroscopic and reaction kinetics techniques, and it is expected to promote many theoretical and experimental studies in the future. Above all, the transition state structure will provide the most fundamental information for designing highly efficient catalysts that can selectively accelerate specific chemical reactions.”