Chemical Science Blog

In a recent Edge article, Chemical Science Associate Editor Professor Haw Yang and his group at Princeton University use Brownian motion to transport a two-sided micro-particle to a target, with the help of ‘photon-nudging’ to keep it on track.

The micrometer precision of this simple method of locomotion is notable.  It could potentially be used to deliver drugs and molecules in cells, precisely and in real-time.

Normally, Brownian motion causes micro-particles to move randomly in fluids.  This presents a challenge for the creation of controllable ‘micro-swimmers’.  Yet, with some external direction, this motion can deliver particles to their targets.

The adaptive photon-nudging idea.

Yang and co-workers ‘steer’ a two-sided microsphere in a fluid, as it undergoes Brownian motion.  One side has a gold coating, whilst the other is polystyrene.  When the polystyrene side is facing the target, a laser beam is activated.  The light then moves this ‘Janus’ particle in one of two ways, either by ‘radiation-pressure’ (pushing by photons) or by heat-induced locomotion via the photophoretic effect.  The latter effect forces this particle, when it has a large temperature difference across its two faces, to move in the direction of the cooler side (polystyrene side) (see also Crooke’s radiometer).

The authors do not use ‘photon-nudging’ constantly.  It is used occasionally, just to steer the particle in the right direction. Brownian motion does most of the work transporting the particle to the target– making this a good example of a man-made Brownian motor.

It will be interesting to see how soon researchers can refine this ‘photon-nudging’ method to achieve nanometer or molecular scale accuracy.  Many would welcome that level of control for particles and molecules in cells and chemical solutions.

Read this HOT Chem Sci cover article in full!

Harnessing thermal fluctuations for purposeful activities: the manipulation of single micro-swimmers by adaptive photon nudging
Bian Qian, Daniel Montiel, Andreas Bregulla, Frank Cichos and Haw Yang
Chem. Sci., 2013, 4, 1420-1429
DOI: 10.1039/C2SC21263C

Geoff Nelson is a guest web-writer for Chemical Science.  He currently works as a post-doctoral research associate in Dr David Payne’s research group in the Department of Materials at Imperial College, London.  Geoff’s current research concerns the synthesis and characterization of post-transition metal oxides for use in the energy sector.  His other research interests include carbon-based materials, biophysical chemistry, and surface science.

Scientists in the US have prepared three UiO-68 network topology metal-organic frameworks (MOFs) using phosphorylurea substituted organic ligands and used them as sorbents to extract actinide elements from water and artificial sea water. 

The MOFs were shown to be highly efficient at sorbing uranyl ions, with saturation sorption capacities as high as 217 mg U g^-1 which is equivalent to binding one uranyl ion for every two sorbent groups.

In the future, the technology could be used to extract uranium from seawater for nuclear fuel production and for the removal of radionuclides from waste streams and drains at nuclear power plants.

Read this ‘HOT’ article for free for a limited period:

Highly porous and stable metal-organic frameworks for uranium extraction
Wenbin Lin , Michael Carboni , Carter Abney and Shubin Liu
Chem. Sci., 2013, DOI: 10.1039/C3SC50230A

Resiniferatoxin (1) and daphnetoxin (2) are members of the daphnane diterpenoids—a class of diterpenoid orthoester compounds, many of which exhibit fascinating therapeutic activity. Resiniferatoxin, whose total synthesis has been achieved only once, is a strong analgesic possessing a complex and densely functionalised tetracyclic core. Now, the Inoue research group at the University of Tokyo have used a series of radical reactions to construct the tetracyclic skeleton of the daphnane diterpenoids (3).

The first radical process was a 3-component coupling of a cyclopentanone (4), O,Se-acetal 5 and an allylstannane (6), and proceeded via a bridgehead radical generated from the reactive O,Se-acetal species. This impressive coupling assembled the A and C rings of the cyclic skeleton, forming 5 consecutive stereocentres in one step. These stereocentres were generated with high stereoselectivity with regards to the tertiary centres at C4 and C10, while the reaction was stereospecific for the creation of the tetrasubstituted C9 centre.

Subsequently, the researchers performed a 7-endo radical cyclisation of xanthate 8 in order to construct the 7-membered B ring. The protected daphnane diterpenoid skeleton (9) was produced as a single isomer with the desired stereochemistry at C8.

Tetracyclic skeleton 3 represents a common intermediate which, following functional group manipulations, would allow the synthesis of naturally-occurring daphnane diterpenoids, including resiniferatoxin, in addition to artificial analogues. The approach demonstrated by the Inoue group showcases the power of radical reactions in the formation of highly congested carbon frameworks and reinforces their relevance in the field of total synthesis.

Scientists studying organometallic catalysts attached to DNA have used the technology to perform cyclopropanation reactions in water, and have reported efficient yields and high enantiomeric excesses.

By attaching the catalytically active metal complex to a DNA scaffold, the chirality of the DNA helix can be directed toward the reaction, influencing its outcome.

You can read this article for free for a limited period:

DNA-based asymmetric organometallic catalysis in water
Jens Oelerich and Gerard Roelfes
Chem. Sci., 2013, DOI: 10.1039/C3SC00100H

Chad Mirkin and colleagues have investigated how the flow of block co-polymer inks from the tip of an AFM probe is affected by the ink’s viscosity. The size of the ink features was found to increase with dwell time and decrease with ink viscosity.

The technique, known as dip-pen nanolithography, was originally developed as a molecular patterning technique for printing small alkanethiol molecules onto a gold surface, but it has rapidly become popular method for synthesising all manner of nano structures.

An understanding of how different substances behave as they move between the probe tip and the surface of the substrate is crucial for designing new materials, patterns and processes.

Read the article for free today:

The role of viscosity on polymer ink transport in dip-pen nanolithography
Guoliang Liu , Yu Zhou , Resham S. Banga , Radha Boya , Keith A. Brown , Anthony J. Chipre , SonBinh T. Nguyen and Chad A. Mirkin
Chem. Sci., 2013, DOI: 10.1039/C3SC50423A

A comprehensive study of the mechanism by which electrochemical water splitting occurs on gold surfaces has been carried out by scientists writing in Chemical Science.

The researchers used in-situ surface enhanced Raman spectroscopy (SERS), on-line electrochemical mass spectrometry and density functional theory (DFT) calculations and found that more than one mechanism may be at work, depending on the voltage applied.

The results show that electrocatalytic surfaces for oxygen evolution may undergo dynamic changes as the reaction progresses. The oxygen evolved on a gold electrode at the onset of potential appears to be the product of an oxygen decomposition step.

Electrochemical water splitting by gold: evidence for an oxide decomposition mechanism
Marc T.M. Koper , Oscar Diaz-Morales , Federico Calle-Vallejo and Casper de Munck
Chem. Sci., 2013, DOI: 10.1039/C3SC50301A