Crests Low-Dimensional Chemistry

Towards biologically inspired design

sample header image

Picture gallery

DragonGFP

There be dragons!

DragonThis dragon, less than half the width of a human hair, was drawn by tracing a tiny light source across a film, one molecule thick, composed of a photo-sensitive molecule. The light source consisted of a hollow pyramid with a hole approximately 150 nm in diameter at its tip, into which a highly focussed beam of light was directed. The pyramid acts as a screen, preventing the light from reaching the surface, except at its very tip, where the small hole is formed.

The ability to write tiny molecular structures is central to the aims of our project, because we want to reassemble the components of a bacterial photosythetic mechanism on a chip. As you can see from the image of the vesicle below, the components used by bacteria to carry out photosynthesis are very small indeed, so we need molecular-scale tools for positioning the components.

Chromatophore vesicle

In the bacterium Rhodobacter sphaeroides, the complete photosynthetic apparatus is contained in a vesicle some 60 nm in diameter. There are many such vesicles in each cell. To give you an idea of scale, 60 nm is only slightly larger than the gate-length of a state-of the art transistor, the gate length being the distance between two of the electrical contacts that form the basis of the component. So an entire biochemical mechanism operates in a volume much smaller than that of a single transistor capable of storing a single bit of information. Nature has already mastered nanotechnology! It did so billions of years ago.

The green doughnuts in the diagram represent light-harvesting complex 2, which collects sunlight and transmits the energy to light-harvesting complex 1 (red rings), which funnels it into the blue blob at its centre (the "reaction centre") where electron transfer to a quinone molecule occurs. The quinone travels through the membrane to a protein called cytochrome bc1, which collects the electron, pumping protons across the vesicle membrane as it does so. Finally, at the end of the cycle, ATPsynthase pumps protons back in the opposite direction creating ATP (adenosine triphosphate) as it does so. ATP is the fuel that drives all biochemical processes.

Image reproduced with permission from Şener, M., Strümpfer, J., Timney, J.A., Freiberg, A., Hunter, C.N. and Schulten, K. (2010) Photosynthetic Vesicle Architecture and Constraints on Efficient Energy Harvesting. Biophys. J. 99, 67-75.

Proteins that glow

GFPGreen fluorescent protein (GFP) was discovered to occur naturally in the jellyfish Aequorea victori. It emits bright green light (fluorescence) when light is shone on it. This image shows lines that are only 70 nm wide (just a few protein molecules wide). They look a little wider than this because the image has been collected with an optical microscope, and conventional microscopes cannot accurately resolve (show the precise dimensions of) structures this small.

The pattern was formed by coating a tiny sharp pyramidal probe (a bit like the one used to draw the dragon above) with titanium dioxide. This is the same material that is used in self-cleaning windows: when UV light shines on it, a process is triggered that breaks down organic (carbon-based) molecules. In this case, a glass slide was coated with non-stick protein-resistant material, which was then carefully removed using the titania probe in selected regions, onto which the GFP could be attached.

Polythene

Polyethylene, also known as polythene, is part of our everyday lives. Although its a very familiar material, we are still learning about its structure.

Polyethylene is known to contain crystalline material, and quite a lot has been discovered about the structures of these crystals, but until recently, there had never been any direct evidence for the organisation of the polymer molecules in the crystal. Now, a member of the Low-Dimensional Chemistry consortium, Nic Mullin, has provided the first direct images of polyethylene molecules in a crystal. the strands can be seen packed close together in the image, acquired with a special kind of atomic force microscope built by Nic in Sheffield.

Images reproduced by permission from N. Mullin and J. K. Hobbs "Direct Imaging of Polyethylene Films at Single-Chain Resolution with Torsional Tapping Atomic Force Microscopy" Phys. Rev. Lett. 2011, 107, 197801.

 

 

 

Polymer nanoparticles

LaticesPolymers are giant molecules, chains that consist of lots of smaller molecules joined together. Block copolymers are chains formed by joining together two or more different molecules, in which the molecules of different types are grouped together. Amphiphilic block copolymers contain a water-loving “hydrophilic” segment and a water-hating “hydrophobic” segment. When they are placed in water, these molecules can organise themselves in such a way that the hydrophobic segments are concealed as effectively as possible – for example in a spherical structure in which the hydrophobic components are on the inside and the hydrophilic components are on the outside, as shown in this micrograph. Similar processes are involved in the action of detergents, for example in laundry systems, where the dirt, which is typically greasy and hydrophobic, is encapsulated in the interior of spherical particles and lifted off the fabric.

In the micrograph here a poly(glycerol monomethacrylate) (PGMA) macromolecular chain transfer agent has been utilized to polymerize benzyl methacrylate (BzMA) in an aqueous emulsion polymerization reaction.

Image reproduced by permission of Vicki Cunningham.

Protein pumps

Bacteriorhodopsin is molecule, found in bacteria, that pumps protons across cell membranes when irradiated with light. We are interested in using it as a component in highly miniaturised molecular systems.

The protein can also be crystallised, to form beautiful, regular arrays of close-packed molecules, as can be seen in this image, which was acquired by Nic Mullin as part of the Low-Dimensional Chemistry project.

Image reprodiced by permission of Nic Mullin.

 

Protein crystals

This micrograph shows crystals of light harvesting complex 1 (LH1) from the photosynthetic bacterium rhodobacter sphaeroides. Each doughnut-shaped complex containts within it a reaction centre, where light energy, funnelled in by LH1, drives an electron transfer process. Two complexes (marked by asterisks) have missing reaction centres.

Image reproduced with permission from Fotiadis, D., Qian, P., Philippsen, A., Bullough, P.A., Engel, A. and Hunter, C.N. (2004) Structural analysis of the RC-LH1 photosynthetic core complex of Rhodospirillum rubrum using atomic force microscopy. J. Biol. Chem. 279, 2063-2068.