Scientists discover new properties of imidazolium salts

Dec 1 2008

Scientists at Singapore's Institute of Bioengineering and Nanotechnology (IBN) have uncovered new properties of imidazolium salts (IMSs), which suggest that they could play a vital role in disease prevention and treatment.

The report on the redox properties of IMSs was published in the Journal of the American Chemical Society .

In a separate study published in Angewandte Chemie International Edition , IBN researchers reported the first use of these salts to convert carbohydrates into versatile chemical compounds for biofuel production.

IBN researchers successfully used IMS to develop a new catalyst system for converting sugars into 5-hydroxymethylfurfural (HMF), a key compound used in biofuel chemistry and the petroleum industry.

In the Journal of the American Chemical Society, the IBN researchers described how they used IMSs to synthesize successfully uniform gold nanoparticles within seconds at room temperature. The ultrafine (1-2 nm) nanoparticles remained stable for up to 6 months at 4°C.

Unlike conventional synthesis techniques using borane or borohydride reduction processes, IBN's method does not require a strong reducing reagent yet is able to produce gold nanoparticles under very mild reaction condition with remarkable efficiency.

IBN's new synthesis protocol could easily be scaled up for industrial applications.

Commonly used as solvents for various organic reactions, IMSs are room-temperature ionic liquids that are chemically stable and have low vapor pressure. While IMSs' physical properties have been widely studied, their biochemical properties and medical applications have seldom been mentioned in the scientific literature.

IBN Principal Research Scientist Yugen Zhang, Ph.D., said, "Our successful use of IMSs as a reducing agent led us to believe that we might also be able to use this compound as a radical scavenger antioxidant to counter the damage caused by reactive oxygen species in the body."

Environmental stress triggered by an unhealthy lifestyle, such as excessive alcohol consumption, exposure to toxins and drugs, smoking and lack of sleep, may lead the body to produce superoxide radicals known as reactive oxygen species (ROS) that could cause cell damage through oxidation.

Oxidative stress from ROS is implicated in most diseases including cancer, heart disease, liver fibrosis, neurodegenerative diseases, autoimmune disorders and aging. Radical scavenger antioxidants help to trap free radicals in the body's cellular system, thus attenuating the effects of ROS.

IMS is a precursor for N-heterocyclic carbenes (NHC). A naturally occurring form of NHC is thiamine or vitamin B, which plays a very important biological role. Vitamin B deficiency has been linked to oxidative stress. While natural antioxidants such as epigallocatechin gallate (EGCG), a green tea extract, have been known to slow down or prevent the oxidative process, they also exhibit low potencies and a rapid turnover in the body's metabolism.

IBN Principal Research Scientist Lang Zhuo, Ph.D., said, "Our investigations with hepatic stellate cells show that IMSs have more powerful antioxidant properties than EGCG, yet are remarkably less cytotoxic. They significantly decreased ROS levels in liver cells by 11% more than EGCG. In addition, IMSs are simple and inexpensive to produce. Therefore, they show great promise as a new type of antioxidant with potential biomedical applications."

In a separate study published in Angewandte Chemie International Edition, IBN researchers successfully used IMS to develop a new catalyst system for converting sugars into 5-hydroxymethylfurfural (HMF), a key compound used in biofuel chemistry and the petroleum industry.

Diminishing fossil fuel reserves and global warming effects have made the search for sustainable, renewable alternative energy sources a critical global concern. Biofuels are currently the only sustainable source of liquid fuels available, but the lack of highly efficient methods to convert carbohydrates into chemical compounds for biofuel production has impeded the replacement of petroleum feedstock by biomass.

HMF and its 2,5-disubstituted furan derivatives can replace key petroleum-based building blocks, and there are several known catalysts that are active in the dehydration of sugars to form HMF.

However, most of them also produce side reactions that form undesired byproducts, and rehydrate HMF to form acid. Therefore, the use of these catalysts has often been constrained to simple sugar feedstock such as fructose. They have not been able to efficiently convert glucose, a more abundant and stable sugar source.

With IMSs as the starting point, IBN researchers developed NHC-metal complexes as catalysts to transform sugars into HMF. These offer a great deal of flexibility as the catalytic activity may be modified by changing specific properties of the NHC. The researchers were able to extract HMF easily as the sole product. IBN's new catalyst achieved the highest reported yields of HMF so far, for both fructose and glucose feedstocks.

Dr. Zhang said, "Our HMF yields were as high as 96% for fructose and 81% for glucose. As both the catalyst and the ionic liquid can be recycled, our technology is more environmentally friendly and would potentially lead to cost savings in the biofuel manufacturing process."

IBN Executive Director Professor Jackie Y. Ying added, "We are excited by the tremendous potential of these novel compounds to make an impact on medicine and alternative energy. Our discovery paves the way for more effective treatment of various degenerative diseases, as well as the conversion of biofuels, helping to alleviate some of the pressing concerns facing our global community."