Organometallurgy: Xie Zuowei builds new molecules

9 September 2016

As a boy attending a modest rural high school in southern China during the Cultural Revolution, Professor Xie Zuowei, a professor of chemistry and associate dean at the Chinese University of Hong Kong, had his first exposure to the subject which would become the focus of his working life.

“Of course, the subject was officially called ‘agricultural science’ but the teacher included a lot of chemistry,” remembers Xie, who says he was initially attracted to the colourful practical experiments about fertilisers and chemical reactions and wanted to learn more.

An international experience

Leaving school at the age of 14, Xie failed to pass the national university entrance examinations and, faced with the prospect of working as a farmer, took extra part-time classes to prepare for the following year’s exam while working in a transformer workshop.

He passed the second time around at the age of fifteen and found himself one of the youngest students at Hangzhou University, studying chemistry.

“The oldest student in my class was 29 years old,” says Xie and he was subsequently selected to study for his Masters degree at the prestigious Shanghai Institute of Organic Chemistry, the Chinese Academy of Sciences.

While studying in Shanghai, a chance meeting with a visiting German scientist, the late Herbert Schumann, Professor of inorganic chemistry at the Technical University of Berlin, led to him undertaking part of his PhD work in the German city and becoming one of the earliest mainland Chinese academics to study in Europe after the Cultural Revolution.

It was after the first year of his PhD that Xie first became interested in organometallic chemistry, the study of compounds containing at least one bond between a metal and the carbon atom of an organic compound. It is now a field routinely used stoichiometrically both in research and industrial chemical reactions, but at that time it was quite new.

“It’s a kind of overlap between organic and inorganic chemistry and it was not a traditional research field so there was lots of new stuff,” says Xie. Later, during his time as a postdoctoral researcher at the University of Southern California, he was given more time and freedom to pursue research, which led to his first major published breakthrough.

Fickle molecules

“We were making super unstable molecules and studying why they were unstable and getting them to stabilise so they could be observed for the first time in a condensed medium,” he says.

Working with his post-doctoral supervisor, Professor Christopher Reed, he synthesised the Tricoordinate Silylium Ion. This ion is a reactive, silyl-containing cation with three, rather than the usual four, bonds to other atoms found in conventional silicon compounds. It had never before been observed or created in the condensed phase because of its very reactive nature and had only ever been observed in a gas phase.

“It was a very big moment in my career,” admits Xie but despite the impact of his work he did not consider continuing his work in North America.

“After USC, I was looking for a Chinese community with academic freedom and strong funding support so Hong Kong was my first choice,” he says and joined CUHK as assistant Professor in 1995.

“I wanted to initiate a new research programme at CUHK,” he says and decided to focus on carboranes: clusters composed of boron, carbon, and hydrogen atoms. Like many of the related boranes, these clusters are polyhedra and can be made in a slightly different way for neutral or anionic structural forms. 

Neutron Capture Therapy

A very stable inert carborane can be part of a catalyst used in the manufacturing process of polymers or plastic materials. Carboranes have been explored as a source of boron, with important medical applications including neutron capture therapy (NCT).

NCT is a non-invasive therapeutic modality for treating locally invasive malignant tumours and, when utilising the non-radioactive isotope boron-10, is known as ‘boron neutron capture therapy’ (BNCT).

Xie explains that a boron-10 can be excited by neutrons to create nuclear fission, which generates alpha particles with very high energy levels that can kill cancer cells. 

Ball-and-Stick model of carborane

If the carborane can be delivered to the cancer cell effectively, it can eliminate it. 

The larger the cluster, the more boron atoms present, and the more efficient its cancer killing properties.

In 2003 a Senior Croucher Fellowship award allowed Xie to further focus on research into carboranes and in 2005 his team synthesised the largest closed-cage carborane known to date, containing 14 vertices. It was another seminal piece of research.

Xie’s current research is also looking at multi-tasking drugs; inserting anti-cancer materials inside a carborane cage and then delivering the cage to cancer cells. However, researchers still need to locate a suitable vector.

“We now need to develop a method to functionalise the cage,” says Xie and this remains a research priority for his team of eight postgraduate and postdoctoral chemists.

His numerous findings also encompass the discovery of the highest hapticity of arachno-carboranes, the first example of 1,3-dehydro-o-carborane, and the development of a novel class of organic-inorganic hybrid versatile ligands.

Professor Xie Zuowei is Choh-Ming Li Professor of Chemistry and Associate Dean (Research) at The Chinese University of Hong Kong. Professor Xie is an internationally renowned research chemist with expertise in organometallic chemistry. He graduated from the Hangzhou University in 1983 and was awarded his MSc from the Shanghai Institute of Organic Chemistry in 1986 before undertaking his PhD studies at the Technical University of Berlin in Germany which were completed at the Shanghai Institute of Organic Chemistry in 1990. He was a post-doctoral fellow under the supervision of Professor Christopher Reed at the University of Southern California (1991-95) before joining CUHK as assistant professor. He was appointed Professor of Chemistry in 2006 and his work has been highlighted in Chemical & Engineering News several times. Professor Xie has received several prestigious awards including the State Natural Science Awards in 2008 and 1997, the Chinese Chemical Society Yao-Zeng Huang Award in Organometallic Chemistry in 2010, and the Croucher Senior Research Fellowship in 2003.

To view Professor Xie’s personal Croucher profile, please click here.