Nitrogen-Sulfur Polymers Break New Ground

In a set of chemical firsts, University of Iowa researchers have created three polymers that incorporate nitrogen-sulfur groups: sulfenamides (–R₂NSR–), diaminosulfides (–R₂NSNR₂–), and diaminodisulfides (–R₂NSSNR₂–). The members of this new family of polymers fall apart in aqueous solution and appear to be nontoxic—ideal properties for using them as biodegradable drug delivery materials. The three nitrogen-sulfur functional groups are found in a modest number of small organic molecules, but they haven’t appeared in macromolecules until now, noted Iowa’s Ned B. Bowden, whose group carried out the research in collaboration with the group of Iowa colleague Aliasger K. Salem. Bowden’s team prepared the polymers by reacting secondary amines with sulfur reagents (Macromolecules, DOI: 10.1021/ma300190b and 10.1021/ma2023167). For example, the researchers made poly(diaminosulfide)s by reacting secondary amines with bis(N-dialkyl) sulfides. They made microparticles out of the polymers and showed in lab tests that, similar to polyester drug delivery materials, the particles are absorbed by human embryonic cells and exhibit no measurable toxicity. Once they enter cells’ mildly acidic environment, the polymers degrade rapidly, Bowden explained. He is intrigued by the degradation products, which include sulfur monoxide, hydrogen sulfide, and the antioxidant allicin. The release of these by-products could possibly be controlled for additional therapeutic effects beyond those of a delivered drug, he suggested.