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The Father of Dendrimers Recalls Their Roots

by BETHANY HALFORD, C&EN WASHINGTON
June 13, 2005 | A version of this story appeared in Volume 83, Issue 24

 

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Credit: ROBERT BARCLAY/CENTRAL MICHIGAN U
Tomalia (left) and Svenson confer at IDS-4.
Credit: ROBERT BARCLAY/CENTRAL MICHIGAN U
Tomalia (left) and Svenson confer at IDS-4.

COVER STORY

The Father Of Dendrimers Recalls Their Roots

When they want to tease him, Donald A. Tomalia's friends and colleagues call him "Donny Appleseed." It's not hard to understand why. Tomalia can hardly contain his enthusiasm for dendrimer science, spreading seeds of praise for the treelike molecules that he developed more than two decades ago to chemists, biologists, regulators, patent examiners, journalists, and pretty much anyone else who'll listen.

These days, Tomalia can easily find an audience eager to hear his thoughts on the future of dendrimers and dendritic molecular architectures, but that hasn't always been the case. Back when Tomalia first came up with the idea to build a molecule with a system of treelike branches extending out from a central core, it was greeted with skepticism by his colleagues at Dow Chemical. They told him it would never work. Of course, that's how every great success story begins.

In the late 1970s, when Tomalia was working as a synthetic polymer chemist at Dow, the company let employees devote Friday afternoons to their own pet projects. More often than not, Tomalia spent this time trying to build the branching molecules that had taken root in his imagination, but most of these Friday experiments were outright failures.

Tomalia recalls one particular spring day when he and his colleague James Dewald were trying to improve their standard procedure for making linear random-coil polyamidoamine (PAMAM) polymers by employing methanol as a solvent for the reaction. They were using the methanol to make the stirring easier and didn't expect it to affect the chemistry of the reaction.

"Much to everyone's amazement, we did not get the same random-coil polymer we usually made," recalled Tomalia in a 1995 article in Scientific American. "Instead, when we determined the structure of the product from this reaction, we discovered a remarkable arrangement: There were no long strands, only discrete units consisting of two methyl acrylate groups connected to each end of the ethylenediamine."

Tomalia tells C&EN that he could hardly sleep during the days that followed that experiment. He knew he had found a way to build his branching molecules. Tomalia repeated the procedure on the product from that first reaction and made an even more intricate compound. After that it was just a matter of adapting the process so that the chemical building blocks branched out from a central core. Tomalia named the molecules dendrimers based on the Greek word for tree.

While the idea excited and inspired chemists in academic circles--Tomalia notes that, unbeknownst to him, Fritz Vögtle at Germany's University of Bonn was developing branched molecules at about the same time--industry's attitude was decidedly cooler. The macromolecules weren't cheap to make, and by the early 1990s, dendrimer research still hadn't led to any major commercial applications. Dow shuttered its dendrimer research program but let Tomalia take global licensing rights for the scientific applications of dendrimers in exchange for his future royalty rights to the technology.

Fast-forward 15 years. After helping to found two start-up companies based on dendrimers--Dendritech, in Midland, Mich., with which he is no longer associated, and his current company, Dendritic NanoTechnologies, in Mount Pleasant, Mich.--Tomalia finds that dendrimers are finally gaining attention and respect outside of academia, thanks in part to the nanotechnology revolution.

"This is perhaps one of the most exciting times in my life," Tomalia gushed to a crowd of dendrimer scientists and enthusiasts at last month's Fourth International Dendrimer Symposium (IDS-4). In a case of etymological validation, he noted that the word "dendrimer" now appears in the dictionary.

Even after decades of studying dendrimers, Tomalia's excitement for the field shows no signs of flagging. "He absolutely, unequivocally believes that his science is going to change the human condition," remarks Robert I. Berry, Dendritic Nanotechnologies' chief executive officer.

Tomalia tells C&EN that it's gratifying to see how dendrimers have grown into areas that he never even dreamed of. "I was just so riveted by all the new progress," he says, reflecting on the breadth of research presented at IDS-4. Tomalia adds that learning about what's going on at the cutting edge of the blossoming science gave him a new boost of energy.

So how did "Donny Appleseed" spend the weekend after the meeting? Why, he planted seedlings on his 50-acre tree farm in central Michigan, of course.

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