Philosophical Society of Washington

Minutes of the 2294th Meeting

President John Ingersoll called the 2,294th meeting to order at 8:37 pm January 6, 2012 in the Powell Auditorium of the Cosmos Club. Mr. Ingersoll announced the order of business and thanked Millen, White, Zelano & Branigan, PC for their sponsorship of the meeting's lecture.

The minutes of the 2,293rd meeting and the 2011 Annual Meeting were read and approved.

Mr. Ingersoll then introduced the speaker, Mr. J. Fraser Stoddart of Northwestern University. Mr. Stoddart spoke on "The Beauty and Promise of Molecular Nanotechnology."

Mr. Stoddart began by discussing his lifelong interest in the field of chemistry, which he believes, amongst all the sciences, appeals most to human creativity and offers the greatest opportunity to dabble in art. He continued by describing Platonic solids and the chemical aesthetics of pigments and crystals. Molecular nanotechnology brings a new style of beauty to chemistry in the form of miniaturization, he said.

He then described two molecular structures known as mechanically interlocked molecules (MIM). A Catenane consists of two or more interlocked ring-like macrocycles and a Rotaxane is a dumbbell-shaped component threaded through one or more macrocycles. This interlocking is called a "mechanical bond," since no direct covalent bond exists between components.

He continued by describing more topologically complex structures like the trefoil knot and the Borromean Link. The Borromean Link consists of three interlocking rings and is named after the Borromeo family, due to its presence on their family crest. Mr. Stoddart illustrated that similar interlocking structures can be found in art and design across many cultures and throughout history.

Mr. Stoddart then explained how difficult it is to construct molecular Borromean rings by adding each ring in series. He described how, using an eighteen component self-assembly process including six metal ions, the entire structure could be created at once. Mr. Stoddart also described how a change of solvent can cause the self-assembly process to instead create a two-ring structure called a Solomon Knot, which is also widely found in historical and modern art.

Mr. Stoddart demonstrated how a bistable Catenane could be used as a molecular switch. This development led to a more sophisticated switch using a Rotaxane that produced better distinction between states. When deposited on an addressable grid, these switches could be used a molecular memory and Mr. Stoddart noted that a 160 Kbit prototype device would fit inside a single white blood cell.

Mr. Stoddart discussed various applications for molecular switches, such as encasing anti-tumor drugs in a selective delivery vehicle. This mechanized silica nanoparticle (MSNP) would enable treatments to target only the tumor and avoid exposing nearby healthy tissue. This technology is currently under development, but true artificial molecular machines are still a grand challenge, he said.

He concluded by discussing how cyclodextrin can be used as a molecular container. A surprisingly simple chemical process involving mainly sugar, salt, and alcohol can produce a cage of interlocked cyclodextrins called a metal organic framework (MOF). This food-grade MOF is safe, cheap, easily made, and could be applied to problems such as detecting and preventing food spoilage, delivering chemicals in personal care products such as toothpastes and deodorants, or in home care products such as air fresheners and HVAC filtration.

After the question and answer period, Mr. Ingersoll thanked the speaker, made the usual housekeeping announcements, and invited guests to apply for membership. At 10:17 pm, President John Ingersoll adjourned the 2,294th meeting to the social hour.

Attendance: 83
The weather: Clear
The temperature: 13°C

Respectfully submitted,

Justin Stimatze,
Recording secretary

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