Researchers at the Division of Chemistry and Biological Chemistry are engaged in a variety of exciting research projects. This page lists a sample of their research interests and recent achievements.
Puzzle of the Colour of Red Bird’s Nest Solved
Edible bird’s nest, or 燕窝 (yàn wo), is one of the most expensive Asian food delicacies today, retailing for about S$5,000 per kg. It has been prescribed in traditional Chinese medicine for over a thousand years, and forms a multi-billion dollar annual trade. It is usually white in colour, but there also exists a red version, called “blood nest” (血燕, xuĕ yàn), which is significantly more expensive and believed to have more medicinal value. The reason for the red colour has been a puzzle for centuries. Contrary to popular beliefs, red bird’s nest does not contain haemoglobin, the protein responsible for the red colour in blood.
The colouration of red bird’s nest has now been explained by Professor Lee Soo Ying, a chemist at NTU’s School of Physical and Mathematical Sciences, and his PhD student Eric Shim. In a forthcoming paper in the Journal of Agricultural and Food Chemistry, published by the American Chemical Society, the researchers report that the red colour is caused by the vapour of reactive nitrogen species, in the atmosphere of the bird house or cave, reacting with the initially formed white bird nest. The bird nest also absorbs nitrite and nitrate, which are potentially carcinogenic (cancer-causing), from the vapour; this may mean that non-white bird’s nest is harmful to human health.
Professor Lee Soo Ying and Eric Shim, with samples of white and coloured bird’s nests. Credit: Janis Zhang.
Edible bird’s nest consists mainly of a substance called glycoprotein. By performing biochemical and spectroscopic analysis on white and red bird’s nest, Professor Lee and his student pinpointed the key role played by tyrosine, an amino acid in the glycoprotein. Red bird’s nest contains tyrosine that has combined with reactive nitrogen species to form a new molecule called 3-Nitrotyrosine. At high concentrations, this molecule produces a rich red colour, while at lower concentrations, it produces the yellow, golden and orange colours seen in other varieties of bird’s nest products.
As Professor Lee explains, the vapour of reactive nitrogen species producing this chemical reaction originates from bird droppings. “Red nests, and generally coloured nests, are produced in poorly-maintained bird houses where there is much bird faeces on the floor,” he says. “The swiftlet feeds on tiny flying insects, and so the bird faeces are protein or nitrogen rich. Bacteria decomposes the bird faeces to produce a vapour of reactive nitrogen species, which rises from the floor and reacts with the tyrosine in the bird’s nest above.”
With this research, the puzzle of the colour of red bird’s nest has been solved, albeit in a manner most did not expect. The research also explains why the red bird’s nest contains a high concentration of nitrite and nitrate which are known to lead to carcinogenic compounds. Conversely, white bird’s nest has the capacity to mop up reactive nitrogen species which is generated when our body has disease-related nitrative stress such as in chronic inflammation, atherosclerosis etc. This could be one of the benefits of consuming white bird’s nest, amongst other possible benefits.
Reference: E. K.-S. Shim and S.-Y. Lee, Nitration of Tyrosine in the Mucin Glycoprotein of Edible Bird’s Nest Changes Its Color from White to Red, Journal of Agricultural and Food Chemistry 66, 5654 (2018).
Converting Nitrogen to Ammonia at Room Temperature
Nitrogen constitutes 78% of the air around us, and is a naturally-abundant raw material that can be used to produce ammonia for fuels and fertilizers. One of the great inventions of 20th century chemistry was the Haber-Bosch process for synthetic “nitrogen fixation” (the conversion of nitrogen to ammonia). The Haber-Bosch process is responsible for about half of the nitrogen found in human bodies today, but because it is performed at very high temperatures and pressures, it consumes as much as 2% of the world's total energy output.
Prof. Ling Xing Yi and her research group have developed a new method for performing efficient nitrogen fixation at room temperature and pressure. Their method is to combine a nitrogen-fixing catalyst with a nanostructure known as a Metal-Organic Framework (MOF). By regulating the access of nitrogen and water molecules to the catalyst surface, the MOF allows the nitrogen-to-ammonia conversion to occur with over 18 times the efficiency of conventional electrochemical methods. This work was published in the journal Science Advances in March 2018.
Schematic of the nitrogen fixing (reducing) system. Credit: Lee Hiang Kwee, Ling Xing Yi, et al.
In the future, this method may be used to directly harvest chemical fuels, or other ammonia-based commodity chemicals, directly from the atmosphere. If successful, such developments could revolutionize current industrial chemical manufacturing methods, which are often unsustainable and polluting. Prof. Ling and her collaborators speculate that the method could even be used to extract greenhouse gases from the atmosphere, in order to mitigate global climate change.
Reference: H. K. Lee, C. S. L. Koh, Y. H. Lee, C. Liu, I. Y. Phang, X. Han, C.-K. Tsung, and X. Y. Ling, Favoring the unfavored: Selective electrochemical nitrogen fixation using a reticular chemistry approach, Science Advances 4, eaar3208 (2018).
Research Area: Synthetic Chemistry and Catalysis
The field of synthetic chemistry deals with the development of new chemical reactions and the preparation of target molecules with unique properties, such as biologically-active natural products, drugs, polymers and functional materials. Advances in synthetic chemistry research are critical for many areas of modern science and technology, particularly the chemical and pharmaceutical industries. In the Division of Chemistry and Biological Chemistry, our synthetic chemists are performing research on topics such as:
- Catalytic aliphatic C-H bonds functionalisation
- Environmentally benign molecular transformations performed without noble toxic transition metals (involving ubiquitous front-row transition-metal catalysts such as copper, iron, nickel and manganese together with high-performing organocatalysts)
- Synthesis of complex natural products and functional materials
- Biomass conversion
- Methods for biomolecule functionalisation
- In-vivo catalysis
- Integrated synthesis methods for continuous manufacturing
Faculty members working in this area include Loh Teck Peng, Roderick Bates, Robin Chi, Shunsuke Chiba, Jason England, Leung Pak Hing, Liu Xuewei, Sreekumar Pankajakshan, Sumod Pullarkat, Soo Han Sen, Mihaiela Stuparu, Tan Choon Hong, Xing Bengang, Motoki Yamane, Naohiko Yoshikai, Zhao Yanli, and Steve Zhou.
Research Area: Medicinal Chemistry
In the field of medicinal chemistry, researchers aim to develop novel chemical synthesis methods to address medicinal and biomedical challenges. At the Division of Chemistry and Biological Chemistry, research in this important area focuses on the following topics:
- Design and synthesis of novel anticancer and antiviral agents
- Computational modelling and simulation of biomolecules
- Synthesis and study of cell surface-bound carbohydrates, such as sialylpolysaccharides and lipopolysaccharides
- Phage display and peptide chemistry
- Synthesis of biologically interesting natural products
Faculty members working in this area include Roderick Bates, Gang CHEN, Robin Chi, Shunsuke Chiba, Loh Teck Peng, Liu Xuewei, Tan Choon Hong, and Xing Bengang.
Research Area: Imaging and Sensing Technologies
The ability to image biological cells, and their components, is critical for a range of scientific and technological applications, including the study of how proteins function and how drugs work. Researchers at the Division of Chemistry and Biological Chemistry are developing robust imaging methods that improve on current methods based on fluorescent or bioluminescent organic dyes.
White light image and fluorescence image of a salt crystal. Credit: Dr. Liu Fang.
Our researchers are also developing new technologies for sensing chemicals such as pollutants, toxins, pathogens, and explosives. This line of research involves developing new chemical processes so that the presense of the target molecules triggers chemical signals that can be accurately measured using electronic or optical instruments. This involves understanding a range of physical and chemical processes such as solubility, fluorescence quenching, photobleaching, protein-label interactions, label-cell interactions and more.
Specific research topics in the area of imaging and sensing include:
- Developing efficient multiplexing labels
- Understanding the properties of dyes and plasmonic nanostructures
- Studying recognition among biomolecules
- Electrochemical sensing
- Membrane-based biosensing
Faculty members working in this area include Alessandra Bonanni, Chen Gang, Chen Hongyu, Leong Weng Kee, Ling Xing Yi, Loh Zhi Heng, Shao Fangwei, So Cheuk Wai, Tan Howe Siang, Richard Webster, Xing Bengang, Edwin Yeow, and Zhao Yanli.
Research Area: Main Group Chemistry
Of all the blocks of elements in the periodic table, the main group elements (s- and p-block) are the most dissimilar, possessing a much wider range of properties than any other block of elements. Main group elements range from highly reactive non-metallic elements (such as fluorine), and semi-metals (such as silicon) to the highly reactive alkali metals (such as potassium). One of the long-standing challenges of fundamental chemistry is to understand the surprising and sometimes unpredictable nature of main group chemistry. The Division of Chemistry and Biological Chemistry has a strong team involved in carrying out main group research, with a particular focus on the synthesis of compounds containing main group elements, and the investigation of their reactivity patterns with an eye toward possible applications. Research topics include:
- Novel bonding and structural paradigms of main group compounds
- Main group organometallic chemistry and its applications
- Main group elements in catalysis and their applications
- Influence of main group elements in wider contexts (such as heterocyclic chemistry, carbon analogues, low-valent compounds, transition metal clusters and asymmetric synthesis)
- Electronic applications (including molecular materials for optoelectronics, new π-electron systems for electronic devices, main group transition-metal systems for molecular wires and main group magnetic systems)
- Novel materials (such as photocatalyst doping or grapheme doping)
- Energy storage systems (such as molecular wires and main group magnetic systems)
Faculty members working in this area include Felipe García, Rei Kinjo, Leong Weng Kee, Sumod Pullarkat, So Cheuk Wai, and Steve Zhou.
Research Area: Ultrafast and Single-Molecular Chemistry
Experimental measurements of the attosecond (10-18 s) scale transient absorbance of an ion.
Credit: Prof. Loh Zhi-Heng.
Using state-of-the-art spectroscopic techniques, it is now possible to study chemical processes occurring at ultra-short time-scales (ultrafast phenomena), as well as ultra-small length scales (down to the level of individual molecules). Researchers at the Division of Chemistry and Biological Chemistry have developed sensitive techniques for studying fundamental photophysical reactions, which govern the efficiency of devices such as solar cells.
We have also applied single-molecule microscopy to the study of pharmaceutical interactions, in order to improve the design of antibacterial and anticancer treatments. In the area of ultrafast phenomena, our researchers have developed new techniques for performing ultrafast multidimensional spectroscopy, which can be used to observe phenomena that cannot be detected by conventional methods (such as transient absorption/pump probe spectroscopy). These techniques can be used to study the ultrafast energy-transfer processes that occur during photosynthesis, to investigate the ultrafast dynamics of photovoltaic and optoelectronic materials, etc.
Faculty members working in this area include Lee Soo Ying, Loh Zhi Heng, Tan Howe Siang, and Edwin Yeow.