Research Guides

My general field of research is host-guest supramolecular chemistry, which covers a broad area of interests.

With a view to increasing the understanding of molecular recognition processes in biological systems and producing new molecular sensors, switches and devices, my research is focused on the synthesis of novel macrocyclic and interlocked host molecules that contain redox- or photo-active reporter groups. These systems have been designed to complex and sense cationic, anionic or neutral inorganic or organic guest species via electrochemical and optical methods. Selective binding of a particular guest species is of paramount importance for commercial applications such as potential prototypes of new molecular sensory devices, molecular switches and extraction agents for cleansing the environment of toxic materials.

Specific research topics of current interest include:

• Rotaxane and Catenane Host Systems: The synthesis of novel interlocked molecular architectures using anionic species as templating motifs is a key area of our research. Using this methodology, we have constructed a range of novel pseudo-rotaxanes, rotaxanes and catenanes, wherein a halide anion directs the interpenetration process. The crystal structure below, for example, displays a [2]catenane in which the templating chloride anion remains encapsulated within the interlocked motif. After halide anion template removal, these interlocked host systems have the potential, by virtue of their unique topological cavities, to exhibit unprecedented anion recognition, sensing and molecular machine-like properties, whereby anion binding controls molecular movement of the rotaxane/catenane constituent parts.

• Sensors for Anionic Guest Species: The synthesis of novel anion sensors is achieved through the attachment of redox- and photo-active reporter groups to selective anion receptors. Careful design enables these sensor molecules to optically or electrochemically detect anionic guest species of particular biological and environmental importance, such as phosphates, nitrates, halides and carboxylates. The topology of the host cavity is designed to complement the target anion and results in the desired selectivity.

• Surface and Nanoparticle Based Anion Sensors: There has been an explosion of interest in the area of surface and nanoparticle chemistry in recent years, due to the singular optical and electrochemical properties of nanoparticles and their applications in catalysis, biomedical imaging and materials. In collaboration with Dr Jason Davis' group, our research in this area focuses on exploiting the remarkable surface enhancement of anion recognition to fabricate highly sensitive and selective anion detection devices. For example the surface assembled redox-active rotaxane displayed below selectively senses chloride ions electrochemically.
 

 • Ion Pair Recognition: This exciting area of coordination chemistry is concerned with the syntheses of host molecules that contain binding sites for both anionic and cationic guest species. These host systems are designed to be selective for target metal salts and zwitterionic guests such as amino acids. The simultaneous binding of toxic/radioactive ion-pair species could make these systems novel extraction reagents for the purification of industrial effluent, soil water and radioactive waste steams.
 

• Transition Metal Directed Self-Assembly of Molecular Hosts: We are interested in the metal directed self-assembly of nano-sized hosts as molecular receptors or containers, in which large or multiple substrate molecules can be bound, stored, transported or even reacted upon. We have had particular success using the dithiocarbamate ligand for this purpose, synthesizing a variety of macrocycles, cryptands and catenanes that complex anions, cations and neutral guests such as C60, as shown below.

• Halogen bonding: Of the non-covalent interactions employed in supramolecular chemistry, halogen bonding is largely underexploited, with the majority of reported cases in the solid state. However, we have recently reported the first examples of interpenetrated and interlocked molecular systems to be constructed through halogen bonding, for example the iodotriazolium rotaxane whose crystal structure is displayed below. Integrating halogen atoms into molecular host frameworks influences greatly the host’s recognition behaviour. Research is currently underway to extend the scope of solution phase halogen bonding in supramolecular chemistry.

Evans, Nicholas H.; Rahman, Habibur; Leontiev, Alexandre V.; Greenham, Neil D.; Orlowski, Grzegorz A.; Zeng, Qiang; Jacobs, Robert M. J.; Serpell, Christopher J.; Kilah, Nathan L.; Davis, Jason J.; Beer, Paul D.
Solution and surface-confined chloride anion templated redox-active ferrocene catenanes
Chemical Science (2012), 3(4), 1080-1089.

Caballero, Antonio; Zapata, Fabiola; White, Nicholas G.; Costa, Paulo J.; Felix, Vitor; Beer, Paul D.
A Halogen-Bonding Catenane for Anion Recognition and Sensing
Angewandte Chemie, International Edition (2012), 51(8), 1876-1880.

Serpell, Christopher J.; Cookson, James; Ozkaya, Dogan; Beer, Paul D.
Core@shell bimetallic nanoparticle synthesis via anion coordination
Nature Chemistry (2011), 3(6), 478-483.

Evans, Nicholas H.; Serpell, Christopher J.; Beer, Paul D.
Chloride Anion Templated Synthesis and Crystal Structure of a Handcuff Catenane
Angewandte Chemie, International Edition (2011), 50(11), 2507-2510.

Kilah, Nathan L.; Wise, Matthew D.; Serpell, Christopher J.; Thompson, Amber L., White, Nicholas G.; Christensen, Kirsten E.; Beer, Paul D.
Enhancement of Anion Recognition Exhibited by a Halogen-Bonding Rotaxane Host System
Journal of the American Chemical Society (2010), 132(34), 11893-11895.

Vickers, Matthew S.; Beer, Paul D.
Anion templated assembly of mechanically interlocked structures
Chemical Society Reviews (2007), 36(2), 211-225.