Author Archives: lyle browning

The end is in sight…or maybe not.

Go into the UBC chemical storeroom, and you will find a range of chemicals. But what you won’t find at UBC, or anywhere else, is the element unquadseptium. And that’s because unquadseptium, with an atomic number of 147, has yet to be proven to exist and, according to some chemists, will never exist.

Since Dimitri Mendeleev developed the periodic table in 1875, chemists have added 55 elements to its rows and periods. While most of the 118 elements we are familiar with today exist naturally, some exist briefly and only after the collision of high-speed particles. These “synthetic” elements include einsteinium (atomic number 99) through organessan (atomic number 118).

Dimitri Mendeleev’s prototype for the periodic table. Source

Creating new elements is an ongoing area of research. The question that divides chemists is whether a limit exists for nuclear mass and, therefore, the number of elements that may exist. Multiple chemists have used Einstein’s theory of relativity to try and determine the limit to the mass of an atom’s nucleus.

The nucleus of an atom exerts a gravitational and magnetic pull on the orbiting electrons. As the mass of the nucleus grows, so does its pull on the electrons, and as modeled by the Bohr equation, orbiting electrons must travel faster to prevent falling inwards. According to Einstein’s theory of relativity, mass increases exponentially with speed. A result of this relationship is that the speed of light presents a universal speed limit for matter.

This universal limit led Richard Feynman and other chemists to propose element 137 as the limit to the periodic table. Feynman argued that beyond element 137, electrons would have to travel faster than the speed of light to remain in orbit and could not exist according to the laws of physics.

Pekka Pyykkö’s proposed 172-element periodic table. Source

However, many chemists argue that the limit for nuclear mass should be much higher. Notably, Pekka Pyykkö from the University of Helsinki published a paper in 2011 that theorized the existence of elements up to atomic number 172. His paper built upon the work of physicists Berndt Muller and Johann Rafelski. The two physicists used the Dirac equation, which considers effects ignored by the Bohr equation, to find the maximum limit for nuclear mass. According to the Dirac equation, orbiting electrons reach the speed of light when the atomic number equals 173 and not 137.

Pushing the limits of the periodic table further still, some chemists and physicists believe that nuclear mass is unlimited. They propose that new quantum behavior of electrons, unknown to present science, allows the orbit of “superheavy” nuclei. Physicist Walter Greiner believes that after element 172, electrons enter a never-ending continuum of negative energy. Greigner believes that the periodic table “will never end!”

In the coming years, chemists and physicists will discover new elements as we develop stronger particle accelerators and detectors with greater sensitivity. However, it remains unknown what the limit to these discoveries will be; only time will tell whether future chemists will see the likes of unquadseptium in their labs.

From catnip to bug spray

Researchers from Iwate University in Japan have published a new paper that explains one aspect of the intriguing response cats have to catnip. The paper, published on June 14th 2022, shows that chewing catnip leaves maximize the release of organic compounds and repels insects. Tamako Miyazaki, who led the research, hopes that the work will pave the way for development of new insect repellants.

A photo of a domesticated cat eliciting a behavioral response to catnip. Source

Catnip is a non-toxic plant in the mint family and it has been long known to elicit several responses in cats. And, it’s not just domesticated cats that are affected, catnip induced behavior has been seen across the feline family including leopards, cougars, tigers, and lions.

Figure 1: Effect of leaf damage on the airborne emission of nepetalactone. Data adapted from Miyazaki et al.

The behavioral response which includes rolling, licking and chewing is seen in two thirds of all felines. The prevalence of these responses led Miyazaki and his team to believe there was a biological importance of the behavior.

Miyazaki and his group have previously identified nepetalactone as the compound responsible for triggering the behaviors.

Nepetalactone is a iridoid compound that is present in high concentration in several plant species including catnip. The group’s previous work, published in 2014, showed that nepetalactone had a strong insect repellant effect. The behavioral response of rolling resulted in the transfer of nepetalactone to the cats fur and provided protection from insect bites.

Following on from this study the team turned there attention to why cats are often seen chewing catnip. Considering that this behavior was also linked to insect repellence the team began by measuring the airborne emission of Nepetalactone from intact and manually damaged leaves. The manual damage was intended to simulate the effects that chewing had on the leaves.

The results, shown in figure 1, was a 20 fold increase in nepetalactone emission in the manually damaged group. When tested on mosquitos, the damaged leaves showed a much greater repellant effect than intact ones. The research group also found that leaf damage affected the cat’s response duration. On average, the studied cats responded to damaged leaves 6 minutes longer than were presented with intact leaves.

The researchers propose that chewing the catnip leaves is an important evolved response that maximizes the amount of airborne nepetalactone. When combined with rolling, the behavior maximizes the protective qualities of catnip and offers a significant benefit to cats.

The paper concludes that there maybe something to be learnt from catnip. Specifically, further studying into the structure and synthesis of nepetalactone may lead to new kinds of insect repellents. While more studies are needed to assess the effectiveness of such a use one thing for sure is that it would have the seal of approval from cats.

A green future for ammonia

Chemists from the University of California, Berkley (UCB) have designed a new material that could reduce the energy requirements of the Haber-Bosch process. The group hopes their research, published January 11th 2023, will conserve energy and lead to a “greener” future for ammonia and fertilizer production.

Current infrastructure needed to maintain the pressure and temperature required for the Haber-Bosch process source

The Haber-Bosch process has been the main method for producing ammonia since its invention over 100 years ago. It is widely considered one of the most important scientific discoveries of the 20^th century. Yet, despite its important role producing ammonia for agricultural fertilizer, its industrial synthesis continues to be energy inefficient.

High temperatures and pressures are needed to produce ammonia which must then be extracted to be used. Conventionally, the reaction mixture is cooled from 500℃ to -20℃. This condenses the synthesized ammonia and separates it from the remaining chemicals. However, cooling the mixture while maintaining the pressure of 300 atmospheres accounts for a large proportion of the processes’ energy loss.

Benjamin Snyder, who leads the UCB research group, said it was this extraction step that his team sought to improve by “finding a material where you can capture and then release very large quantities of ammonia, ideally with a minimal input of energy”.

These requirements led the research group to create a metal-organic framework (MOF) material. The MOF had a crystal structure made from copper atoms linked to cyclohexane dicarboxylate molecules. The crystalline structure gave the material unique properties suited for its use in ammonia extraction.

Structure of the cyclohexane dicarboxylate molecule used to make the MOF source

When exposed to ammonia the material changes its structure from a rigid crystal to a loosely packed and porous polymer. The polymer form can readily store a large amount of ammonia within it which can then be released with cooling. The result is that ammonia can be extracted 195℃ above the temperature required by current methods and at half the pressure.

Not only would the MOF save energy in the extraction process but, interestingly, after releasing the ammonia “the polymer somehow weaves itself back into a three-dimensional framework” says Snyder. This mechanism, which is still being studied, allows the MOF to be used repeatably.

With the Haber-Bosch process using 1% of the world’s energy, the research done by Snyder and his group is an important step in producing a greener future for ammonia.