Cooler than squares – molecular triangles exhibit ultrafast light harvesting

Molecular triangles

We’ve seen a whole range of molecular shapes over the years, from spheres to squares and from spirals and grids. Well, now we’ve also got triangles and they’re not just a gimmick – they are able to harvest light and undergo ultrafast charge separation, thanks to the close proximity of the chromophores within them.

In an article published in the Journal of the American Chemical Society last month, a team of researchers from the University of Würzburg, Germany, describe their synthesis of triangular molecules assembled from perylene diimide units, or PDIs. These highly aromatic systems are well known for their photochemical properties, but it would appear that is not only the electronic structure of these molecules which enhances their photophysical performance, but their spacial arrangements with each other as well.

The stacking of the PDIs in a triangular arrangement actually limits their pi-pi interactions with each other, allowing them to compete as separate chromophores, allowing up to six charge-separated states to exist within the molecule. Furthermore, EPR spectroscopy shows that electronic communication does exist between the three PDI units, as a single unpaired electron is able to be shared by all three.

The research is still in its infancy in regards to how it may be applied in the future, but this presents a new and interesting form of light-harvesting molecule which may find use in solar cell technology or organic electronics, due to its remarkable number of charge separated states. It’s early days, but watch this space!

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Chemistry Nobel Prize 2015 – the lowdown

DNA

Undoubtedly, many of you will have heard last week’s announcement that the 2015 Nobel Prize for Chemistry was awarded to Thomas Lindahl, Paul Modrich and Aziz Sancar for their work into “mechanistic studies of DNA repair“. However, for a lot of us, this work is outside of our field of research, so what exactly did these men achieve, and what does it mean?

Firstly, let’s talk about DNA repair. Why is this needed? The DNA in our cells is damaged every single day through a variety of natural and external processes, Natural sources of damage can include attack by reactive metabolic byproducts within the body, or errors in the initial replication of the DNA. Cells can also become damaged by harmful chemicals and toxins, radiation damage, thermal damage or attacks by viruses. When this DNA becomes damaged, cells can’t function correctly, as the information contained within them is now corrupted and inaccessible. It is therefore vital that your body is able to spot damage to DNA and consequently repair it.

Real pioneering work into this began with Thomas Lindahl in the 1960s, when he questioned the apparently stability of DNA. Indeed, he discovered that DNA did undergo degradation, and the idea of DNA repair was born. Lindahl put together the idea of base excision repair (see below), where an enzyme called glycosylase cuts out a mismatched base so that it can be replaced and the DNA can be fixed.

Base excision repair

Aziz Sancar worked particularly in the area of repairing UV damage. He put forward the theory of nucleotide excision repair, where a whole section of the DNA strand is removed to get rid of a faulty nucleotide caused by UV damage. DNA polymerase fills in the resulting gap, allowing the DNA to function correctly.

Paul Modrich worked on understanding how the body repairs damages caused during cell division. He devised a mechanism by which the body rectifies mismatched nucleotides formed during cell replication, cuts out this faulty strand, and fills in the gap. This is known as mismatch repair. It’s an amazing phenomenon, and 99.9% of such errors are repaired in this way.

Not only did the outstanding work carried out by these three men develop the understanding of how DNA is replicated, modified and repaired, discovering these repair pathways has opening the doors for researchers to try and reverse the process and cause damage to unwanted DNA present in the body – such as those found in cancer cells. If the repair of unwanted cells can be ‘switched off’, their efficient replication may be halted and the disease could be stopped in its tracks. Some treatments are already in use which have this mode of action, an example being Olaparib – a drug which inhibits the growth of some hereditary cancers.

This year’s Nobel prize in Chemistry not only honours work which has greatly expanded knowledge of the field, but which has had tremendous implications on the way we understand our own bodies, and how we can preserve them and keep them healthy. There’s still a great deal of scope for this field, but thanks to Lindahl, Sancar and Modrich there is solid ground to be built on for the future.

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VW Emission Scandal – the Chemistry Behind the Headlines

It’s been all over the news this week – Volkswagen have admitted to cheating emissions tests and have recalled millions of cars around the world. Exactly how they have achieved this remains unclear, but stock prices in the company have plummeted and its reputation may never recover from this scandal.

But what emissions have VW been illegally controlling, and what is there to worry about?

Well, this article on the Chemistry World website explains everything.

It would seem that VW have been using sophisticated software to control NOx emissions during testing – leading to up to 40 times more NOx being released outside of testing. NOx nitrogen oxide and nitrogen dioxide – are extremely hazardous to health, and have been linked to many respiratory issues. It can also cause smog and ground-level ozone to be produced, further risking public health.

The production of nitrogen oxides is difficult to avoid – at the high temperatures found within car engines, nitrogen and oxygen in the atmosphere will inevitably react. They must instead by cleaned up post-combustion, which is achieved through the ‘lean NOx trap’, or selective catalytic reduction (SCL). The NOx trap involves using alkali earth oxides to convert the NOx emissions into nitrates, whilst SCL injects urea into the exhaust, which evaporates and reacts with the NOx gases in a zeolite catalyst to form nitrogen and water. Neither method is perfect, as the NOx trap continually uses fuel to keep itself clear, and SCL can fail when cars are stuck in traffic, as the exhaust temperature isn’t high enough for the required reactions to take place.

The unfortunate reality for car manufacturers is that lower NOx emissions generally means lower fuel economy, greater wear and tear on engine parts or higher cost for the consumer, all of which they want to avoid. There’s a real worry amongst experts and customers alike that this will lead to manufacturers building engines specifically to pass lab tests, which might not perform nearly as well on real road situations. This could prove catastrophic for the environment, and will diminish trust completely in the sector, and is unfortunately what appears to have happened in VW’s case.

Obviously, there’s a real need for improved technology in this area, so that the challenge of lowering NOx emissions whilst maintaining a high-quality car can be conquered once and for all.

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