Naoya Kumagai: Creating the Invisible

2025/06/16

I specialize in organic chemistry—the "chemistry of molecules" where carbon, the primary building block of living organisms, plays the leading role. Molecules are small, so naturally, they are invisible. Various molecules are formed at a scale about one-billionth the size of the things around us. A molecule is a structure in which atoms take on a specific bonding pattern in three-dimensional space; it can be described as the smallest unit that exhibits unique properties and functions. Organic molecules that form life are usually composed of a limited set of atoms such as hydrogen, carbon, nitrogen, oxygen, phosphorus, and sulfur. However, there are over 100 million registered types alone, and it is said that the variations of what can theoretically be created reach astronomical numbers.

By the way, according to Mehrabian's Rule, the degree to which humans are influenced in communication follows a hierarchy: 7% verbal information, 38% auditory information, and 55% visual information. Now, molecules, of course, do not speak. While it is possible to represent three-dimensional molecular structures as linguistic data that computers can recognize, to a human, it is merely a string of symbols that evokes no feeling. Consequently, we fortunately recognize molecular objects through visual information alone, which is the most dominant; however, can we really say that the molecular structures we see with our eyes are "correct"? As organic chemists, we spend our time staring intently at molecular structures, so various molecules become like conversation partners to us. Even though only visual information mediates this communication, a nagging doubt begins to stir: "Are you really who you appear to be?" For example, some of you may have seen so-called molecular structures where element symbols are connected by sticks to represent "bonds," but in reality, there are no sticks between atoms. Nor are there labels for the elements. These are fictions. In reality, the differences between molecules lie only in the probability of the existence of nuclei and electrons, and furthermore, the differences between atoms lie only in the number of protons in the nucleus. While architects can materialize the buildings they envision before their eyes, the molecular structures we envision in our minds are ultimately far from their actual images—they are entities that cannot be perceived through sight. Organic chemistry is a free discipline where one can freely create nearly infinite molecular structures—that is, instead of unearthing treasure, one can create it oneself. What do the molecules we believe we have created actually look like? We pursue molecules every day with a feeling akin to a yearning for something that remains forever out of reach.