Nitrogen-Sulfur Polymers Break New Ground | Chemical & Engineering News
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Web Date: August 21, 2012

Nitrogen-Sulfur Polymers Break New Ground

ACS Meeting News: Polymers bearing nitrogen-sulfur groups have potential applications as biodegradable drug-delivery materials
Department: Science & Technology
News Channels: Materials SCENE, Biological SCENE
Keywords: polymer science, biodegradable, drug delivery, inorganic polymer

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, described at the American Chemical Society national meeting in Philadelphia on Monday, 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 DOI: 10.1021/ma2023167). For example, the researchers made poly(diaminosulfides) 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 allicin—a sulfur antioxidant compound found in garlic. The release of these by-products could possibly be controlled for additional therapeutic effects beyond those of a delivered drug, he suggested. Besides drug delivery, the functional groups might also be incorporated into conducting polymers for electronics applications, Bowden added.

“The ability to incorporate N–S linkages into a polymer backbone brings a wealth of opportunities ranging from biomaterials to microelectronics,” commented polymer expert Craig J. Hawker, a former IBM researcher now at the University of California, Santa Barbara. “It’s not often that a new class of polymers is developed that bears little resemblance to current materials—these polymers are really something unique.”

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Wes M (August 25, 2012 4:21 PM)
Hydrogen sulfide, while naturally occurring, is also highly toxic. I assume sulfur monoxide is as well. These are not the kinds of things I would want being produced in pharmacologic quantitities in vivo.
Ned Bowden (August 29, 2012 10:16 AM)

Very little is known about sulfur monoxide because it is very short lived in the body and not commercially available. It will degrade in seconds to release SO2 and elemental sulfur.

Hydrogen sulfide possesses the smell of rotten eggs and is even more toxic than carbon monoxide, so at first glance the release of H2S is a serious problem. Yet, there is a large and growing body of work in chemistry and medicine that recognizes the importance of hydrogen sulfide. In fact, hydrogen sulfide (which is synthesized by several enzymes in human bodies and is found at roughly micromolar concentrations in blood) is one of few gaseous molecules that is implicated in many physiological functions. Small molecules that release H2S are being studied in medicine for medicinally beneficial applications such as myocardial infarction, cardiopulmonary bypass surgery, thoracoabdominal aortic aneurysm surgery, liver ischemia and reperfusion, organ storage and transplantation, and acute lung injury. (Please see a recent paper by Giuseppe Caliendo, Giuseppe Cirino, Vincenzo Santagada, and John L. Wallace “Synthesis and biological effects of hydrogen sulfide (H2S): Development of H2S-releasing drugs as pharmaceuticals”, J. Med. Chem. 2010, 53, 6275-6286). Also, a recent “News of the Week” feature in C&EN discussed the importance of H2S as a key starting material for the synthesis of HSNO and is implicated in “biological signaling and regulation, linking the effects of nitric oxide and hydrogen sulfide”. (see C&EN page 5, July 9, 2012 and an article in JACS, 2012, I34, 12016-12027). Clearly, H2S is an important but underappreciated molecule in medicine.


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