[POSTECH University Professor Series ①]
From Dedication to Renown: How Researching Cucurbituril Elevated Him to a World-Renowned Scholar in Supramolecular Chemistry

“Concluding a 36-Year Research Journey at POSTECH”

The usually lively campus of POSTECH is unusually quiet, with vacation underway. Walking past the Chemistry and Life Sciences Buildings, to the Research Building I, a poster for the “POSTECH Retirement Lecture” catches the eye. Though the event was on May 24, it feels as though time has stood still. The lecture was delivered by Professor Kimoon Kim from the Department of Chemistry, who is set to retire on August 31, 2024.

In his presentation titled “My Voyage”, delivered at his retirement lecture, Professor Kim reflected on his extensive research career spanning several decades. Admitted to Seoul National University’s Department of Chemistry in 1972, he was expelled after taking part in a protest against the Park Chung-hee administration’s authoritarian regime, the Yushin order. Few would have predicted that this expelled undergraduate would go on to become a world-renowned authority in supramolecular chemistry. He earned his master’s degree from KAIST, his Ph.D. from Stanford University, and pursued X-ray crystallography at Northwestern University. In 1988, while continuing his research in the United States, his next destination was POSTECH. The school, only three years old at the time, captured his interest due to its philosophy and the persuasion of its first president, Hogil Kim. Thus, his research journey at POSTECH began.

This year, Professor Kimoon Kim celebrated his 70th birthday. Unlike many of his peers, he retired at 70 because he was honored as a “University Professor,” a program POSTECH introduced in 2017. The University Professor program, originally established at institutions such as Harvard University in the 1930s, is designed to offer world-class scholars an exceptional research environment alongside the prestigious title. POSTECH was the first private university in Korea to extend the retirement age for professors to 70 by introducing this program. In its inaugural year, the university appointed Professor Kimoon Kim from the Department of Chemistry and Professor Kilwon Cho from the Department of Chemical Engineering as the program’s first recipients. Currently, there are five University Professors at POSTECH, including Kim, making it one of the institution’s most esteemed titles. As Professor Kim’s distinguished 36-year career at POSTECH draws to a close, but it is said that the end is the starting point of a new beginning. We had the opportunity to speak with him about his research journey and future plans.

― Is there a particular teacher who inspired you to become the researcher you are today?
There are many, but the first is my advisor at Stanford, Dr. James Collman. He constantly encouraged me to pursue ambitious goals that could make a difference in the world. Dr. Collman wasn’t just a brilliant scholar. He also mentored some of the most successful students including two Nobel Prize winners, K. Barry Sharpless and Robert H. Grubbs. Sharpless won the Nobel Prize in 2001 and again in 2022. His words inspired me to think, “I want to hit a home run like that.”

― If there’s an iconic study that epitomizes Kimoon Kim’s research, what would it be?
That would definitely be “cucurbituril.” This distinctive molecule, shaped like a “hollow” pumpkin and composed of six linked glycoluril units, has been a focus of our research. Since I joined POSTECH, we have been a global leader in synthesizing cucurbituril homologues and derivatives, conducting both basic and applied research on them for over 30 years. Cucurbituril has become emblematic of our work.

― How did you begin your research on cucurbiturils?
When I joined POSTECH in 1988 as a young professor, I transitioned from my research in the U.S. to a burgeoning field known as “supramolecular chemistry,” which was attracting global interest. Unlike traditional chemistry, which studies strong bonds between atoms, supramolecular chemistry examines weaker interactions between molecules. To study this field, you need a platform molecule that effectively utilizes these weak forces. In the early 1990s, while perusing academic journals in the library, I encountered cucurbiturils. Originally synthesized by Robert Behrend in Germany in 1905, cucurbituril’s structure and identity were initially unknown. It was largely forgotten until 1980 when Professor William Mock at the University of Illinois reconstructed its synthesis and, using modern analytical techniques, determined its identity and structure. The moment I saw the molecular structure and its functional groups, I knew I had found something remarkable.

― Did you encounter any difficulties in your research?
Initially, the research faced challenges. Cucurbituril could not be dissolved, and since solubility is crucial for most chemical processes conducted in solution, this was a significant obstacle. After 4-5 years of struggling with no progress, I was on the verge of giving up when a “serendipitous” discovery changed everything. We found that cucurbituril is soluble in salt (Na₂SO₄) water, which opened up new possibilities for research on cucurbiturils.

― The discovery of solubility in salt water opened up new possibilities. What happened next?
Once we discovered how to dissolve cucurbiturils, progress came more easily. We first demonstrated that we could trap and release small molecules inside cucurbituril, creating what we termed a “molecular barrel.” This breakthrough was published in the October 1996 issue of the Journal of the American Chemical Society (JACS) and also featured in Chemical & Engineering News (C&EN), a weekly publication of the American Chemical Society. It marked the first time research from Korea was highlighted in the magazine. Beyond this, we have explored creating structurally interesting supramolecular structures such as “polyrotaxane” and “molecular necklace” by stringing cucurbituril molecules together. This work aligns with the concept of the development of “molecular machines,” which was recognized with the 2016 Nobel Prize in Chemistry.

― Could you tell us more about cucurbituril homologues and derivatives?
One of the intriguing questions in our research on cucurbiturils was why the reaction initially only produced those with six glycoluril units. After extensive experimentation, we discovered that, in addition to the original cucurbituril with six glycoluril units (CB[6]), varying synthesis conditions could yield cucurbituril homologues with anywhere from five to eleven glycoluril units. Through considerable effort, we successfully isolated and characterized the structures of CB[5], CB[7], and CB[8] (see Figure 1). While CB[6] was previously referred to as a “molecular barrel,” our research has expanded to include a range of barrels of different sizes, each capable of accommodating molecules of varying sizes. Findings of this study, with Jaheon Kim -now a professor at Soongsil University- as a lead author, were published in the JACS and earned a material patent in the U.S., marking a significant milestone in supramolecular chemistry.
Another crucial aspect of our work involves synthesizing cucurbituril derivatives. We have developed methods to attach various chemical functional groups to the flanks of cucurbituril. This advancement has greatly propelled our research, enabling us to link cucurbituril to specific molecules or substances.

<Figure 1. Pumpkin and Cucurbituril Homologues.>

― Could you tell us about the international conference you established and your publications?
The redefinition of cucurbituril chemistry through our series of studies has significantly advanced the field, leading to the establishment of an international conference. The first conference was held at POSTECH in 2009 and has been convened every two years since.
I have also authored two books on cucurbiturils. The first, a textbook titled “Cucurbiturils: Chemistry, Supramolecular Chemistry and Applications,” was commissioned and published by Imperial College Press in London in 2018. It was incredibly gratifying to see the field I pioneered since my return to Korea in 1988 reach a level of authority that warranted a textbook. Later, the Royal Society of Chemistry commissioned me to write and edit another book, resulting in the publication of “Cucurbiturils and Related Macrocycles” in November 2019. This book highlights the latest advances in cucurbituril research.

― We learn you’ve done a lot of research in addition to your work on cucurbiturils…
Another significant area of our research is “molecular architecture” using self-assembly, a phenomenon where molecules come together to form supramolecular structures. By connecting metal ions with organic molecules, we create metal-organic porous materials with a regular arrangement of microscopic holes, which possess a high surface area and can be widely used as adsorbents and catalysts.
One of the metal-organic porous materials I studied, POST-1, was published in Nature in 2000 and named after POSTECH. What set POST-1 apart was its chiral pores. Chirality is a property where a structure, like left and right hands, has symmetry but cannot be superimposed on its mirror image. Molecules with this property are known as chiral compounds, which have isomers—molecules with the same components but different chemical properties. For instance, one isomer of the neuroleptic drug thalidomide caused severe birth defects, highlighting the critical importance of selecting the correct isomer when developing new drugs. POST-1 was the first chiral porous crystalline material capable of selectively synthesizing these isomers. The paper has been cited over 3,700 times, and Nature recognized it as one of the 35 most significant studies from 1950 to 2000.

― You have also distinguished yourself as a research leader.
Through dedicated work and the support of many colleagues, I’ve had the privilege of leading several pioneering research initiatives funded by the government. In 1997, I was appointed to lead the National Creative Research Initiative Center for Smart Supramolecules. In 2009, took on research responsibilities for the newly established Division of Advanced Materials Science, funded by the World Class Research University (WCU) project. In 2012, I was honored to serve as the director of Center for Self-assembly and Complexity at the Institute of Basic Sciences (IBS). Additionally, I have been instrumental in organizing the International Conference on Cucurbituril, which is held every two years. I’ve also had the opportunity to present as a keynote or invited speaker at prestigious international conferences, including ISMSC, the leading conference in supramolecular chemistry, as well as the Gordon Research Conference and the Solvay Conference. These contributions have helped raise the status of Korean science.

― Among the numerous awards you’ve received, which one stands out to you?
I’ve received a lot of praise that I feel is undeserved. Domestically, I’ve won most of the major awards given to scientists, including the Korea Science Award (2002), the Ho-Am Prize (2006), and the Top Scientist and Technologist Award of Korea (2008). Among these, the most memorable is the Ho-Am Prize. It is particularly prestigious because it is open to anyone with Korean heritage, whether in Korea or abroad. Being awarded this prize among such a distinguished group of Koreans is a significant honor. Internationally, I was honored as the first Korean recipient of The World Academy of Sciences (TWAS) Award in 2002. In 2012, I was named an honorary professor by the Russian Academy of Sciences. However, the Izatt-Christensen Award I received in 2012 stands out as particularly memorable. This award has been given to two Nobel Prize winners and two Wolf Prize winners, and it is often referred to as a “pre-Nobel Prize” because approximately 30% of its recipients have subsequently won the Nobel Prize.

― What was your experience as a research director at the IBS?
In 2011, for the Year of Chemistry, I, along with Professor Ryong Ryoo from KAIST and Professor Taeghwan Hyeon from Seoul National University, was recognized as one of the “Top 100 Chemists in the World by Impact Factor” by Clarivate in the U.K. When the IBS was established in 2012, all three of us were appointed as research directors. I was tasked with leading the “Center for Self-assembly and Complexity.” My goal was to explore “molecular recognition” and “self-assembly” within complex systems, particularly in biological contexts. Building on our foundational research on cucurbiturils, we focused on creating new tools for biological applications. For example, we utilized the strong binding between CB[7] and adamantane molecules to develop a method for purifying protein-based drugs and for isolating and identifying proteins involved in cellular communication. Additionally, we ventured into synthesizing two-dimensional polymers using our expertise in self-assembly. By controlling molecular design and reactions, we successfully created thin-film polymers at the single-molecule level in solution without the need for a mold. We further enhanced their properties by doping them to exhibit semiconducting behavior. Our related paper, published in Chem this year, has attracted attention from both academic circles and industry including inquiries from Samsung Electronics.

― With the extended retirement age, you had extra five years for research compared to most. How did you make the most of this time?
Given the additional opportunities, I made sure to make the most of them and committed to giving my best effort until the very end. With my extended tenure, I aimed to undertake something groundbreaking and audacious, which led me to explore the use of sound waves to control chemical reactions. Although sound covers a broad frequency range with diverse applications, audible sound has had limited use in chemistry due to its low energy. In contrast, physics has a long history of exploring these phenomena. The German physicist and musician Ernst Chladni, for example, found that sprinkling sand on a thin sheet of iron and then scratching it with a violin bow produces intriguing patterns. Similarly, the renowned British physicist Michael Faraday discovered that vibrating the surface of water also creates these patterns known as “Faraday waves.” Inspired by the work of these physicists who lived two centuries ago, I discovered that sound could be harnessed to manipulate chemical reactions both spatially and temporally. These findings, published in Nature Chemistry in 2020, garnered significant global attention. The findings were also featured in Forbes magazine—an uncommon honor for basic research. This recognition was one of my proudest moments during my tenure at the IBS. Additionally, this study brought me personal joy beyond research, as I won the grand prize at the “5th Art in Science Contest” for my work titled “Painting with a Sound Brush,” which showcased aesthetic patterns created through the interaction of chemical reactions and sound (see Figure 2).
This achievement was particularly special to me due to my interest in photography and art. Overall, starting with this study, pioneering this new field of using sound to control chemical reactions has been a major focus of my research over last five years. These accomplishments highlight that the extended retirement age allowed me to explore and achieve new and challenging milestones that might not have been possible otherwise.

<Figure 2. Painting with a Sound Brush: Grand Prize Winner at the “5th Art in Science Contest”.>

― As you approach retirement, it must be difficult to transition away from such impactful work.
Indeed, it is. To put it bluntly, it feels like a “sudden death”. While retirement isn’t exactly sudden, it can feel like a “sudden death for a researcher”—no more students, no more research grants, and a complete halt to ongoing research. Fortunately, a company recognized the potential of cucurbiturils and has agreed to provide limited support for two years. This allows me to continue my research on a smaller scale. I plan to dedicate two years to this work after retirement.― There are many researchers approaching retirement just like you.Research achievements are not solely the result of the ideas of young researchers; quite a lot of them also stem from accumulated experience and knowledge. I believe that experienced senior researchers should also be supported if their research demonstrates strong competitiveness through fair competition. One potential solution is to establish a “senior league,” recognizing that junior researchers often find it challenging to work alongside more senior colleagues.

― What are the trends in other countries?
In the U.S., the retirement age for university professors has been abolished, and Europe has followed suit, with only a few exceptions at institutions such as Cambridge and Oxford in the UK. While it’s true that older researchers may face physical challenges compared to their younger counterparts, their extensive experience remains invaluable. They should not be denied opportunities simply because they are older. In Korea, we are dealing with a demographic cliff and a shortage of researchers. It is crucial to explore ways to effectively utilize senior researchers. For instance, some professors at Harvard University continue to lead teams of 70 to 80 researchers well into their later years.

― Despite its outstanding resources and support, POSTECH often remains under the radar due to its distance from the capital city.
It’s true that POSTECH’s potential and promise can be overshadowed by its location away from the metropolitan area. POSTECH was established following the will of the late Chairman Tae-Joon Park of POSCO who envisioned creating a world-class science and technology university in Pohang. I was offered a professorship at Seoul National University twise, but I chose to remain at POSTECH, possibly because I was determined to excel in my research in Pohang. I found that the university’s exceptional professors and talented students fostered an environment conducive to outstanding research. The research infrastructure, including the accelerator, is also excellent, and I think this is one of the reasons why outstanding research results were able to be produced.

― POSTECH alumni are also known for their remarkable sense of community.
On the POSTECH campus, there is an incubator called CHANGeUP Ground, which provides space for startups. A significant percentage of the companies there are founded by POSTECH alumni. There is also an alumni company council. Though the university is under 40 years old and the alumni base is relatively small, there is a collective drive to achieve significant accomplishments.

― I understand you’ve also made personal donations.
I donated the prize money I received from winning the Ho-Am Prize in 2006 to award scholarships to outstanding graduate students in chemistry every year. When I reached retirement age, I also contributed to the development fund to hold lectures by inviting renowned scholars from home and abroad. I will continue to contribute in the future, hoping that this will help POSTECH expand its global reach.

― What message would you like to pass on to future generations of students, Professor Kimoon Kim?
I want future generations of students to achieve the dreams that my generation couldn’t. One guiding principle in my life is the notion of “Here’s where it gets interesting.” When you embark on something, the real challenge begins. Even if you fall short, you must let go of past failures and fully commit yourself, demonstrating your dedication and effort. Additionally, I want to share the advice from my teacher, Professor Collman: “Always think big”. By aiming for significant goals that have the potential to transform the world, you will inevitably achieve many ancillary successes. I am confident that the researchers and students at POSTECH will accomplish great things.