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Lunar Surface

Researchers found clues about the presence of precious metals under Moon’s surface

Presently we have very less information regarding the type of minerals that might be found inside the Moon. But a group of researchers from Canada and the US has used this hint to understand that a treasure is lying beneath the surface.

By getting more information about the chemistry of the moon, scientists would be able to settle a confusion regarding the apparent lack of precious elements constituting the mantle of Moon. Nearly fifty years ago, astronauts brought back a large quantity of lunar material which gave the first hints about the elements that might be present below the surface. James Brenan, Earth scientist from Dalhousie University, Canada said that nearly 400 kilograms of the sample was brought in the Apollo and lunar missions. So to find about the Moon’s interior, scientists have to go through reverse-engineering of the composition of lavas on the surface.

Through retro-engineering the basalts which were brought from the Apollo 15 and 17 missions, researchers estimated the amount of siderophile elements which make up the mantle of Moon. Some of these might have come from the rain of leftover materials in the finishing stages of the Solar System’s construction, so it can tell the assault endured by the Moon after its formation was complete. The work appears in Nature Geoscience journal.

The measurements were lower by 10 to 100 times than what was expected. Even by adjusting the model to accommodate the event of erosion of Moon by the meteorites, the numbers did not add up which left a plethora of questions. Researchers often begin by assuming the geochemistry of Moon to be similar to Earth and this is where the gaps in the measurement start. Although several theories suggest that Moon was made from Earth’s components there are some notable differences.

Hence researchers used the experiment results on sulfur solubility with the models on pressure and the thermodynamics of magma cooling down to get accurate constraints on the composition of the lunar mantle. Brenan said that the results tell that sulfur in the volcanic rocks of Moon indicates the presence of iron sulfide in the Moon’s rocky interior. This is the place where the metals might have been during the formation of lavas.

The results make it clear that we cannot depend on the existing rock samples for any clear conclusion as no accurate estimation of metal composition cannot be found. Whether it would be justified for mining these metals would depend on future missions and economics. But this makes the return to Moon quite exciting.

Research Paper: Abundance of highly siderophile elements in lunar basalts controlled by iron sulfide melt

Researchers develop catalytic reactor for converting greenhouse gas into pure liquid fuel

Researchers develop catalytic reactor for converting greenhouse gas into pure liquid fuel

Rice University has come up with an invention that converts carbon dioxide into valuable fuels. Carbon Dioxide was turned to liquid fuel in an environment-friendly manner by using an electrolyzer and renewable energy. The catalytic reactor was developed by Haotian Wang, a chemical and biomolecular engineer at Rice University.

It uses carbon dioxide as feedstock and the latest prototype produces highly purified concentrated formic acid. Traditional ways of producing formic acid are costly and require energy-intensive purification steps. The direct production of pure formic acid will help in promoting commercial carbon dioxide conversion technologies. The work appears in Nature Energy journal.

Wang and his group pursue all those technologies that convert greenhouse gases into useful products. In experiments, the electrocatalyst reached an energy conversion efficiency of nearly 42%. So almost half the electrical energy can be stored as liquid fuel in the formic acid. Formic acid an energy carrier and a fuel cell that can generate electricity and emit carbon dioxide which can be recycled again. It is a fundamental unit in chemical engineering as a feedstock for other chemicals and also a storage material for hydrogen that can hold 1000 times the energy of the same amount of hydrogen gas, which is also difficult to compress.

Chuan Xia, postdoc researcher at Rice said that this was possible due to two advancements. The first being the development of robust, two-dimensional bismuth catalysts and the second, a solid-state electrolyte which eliminates the need for salt in the reaction. Bismuth is a heavy atom with lower mobility and stabilizes the catalyst. The structure of the reactor prevents contact of water from the catalyst. Currently, catalysts are produced on a milligram or gram scale but Xia and his team have developed a way to produce them in the kilograms thus scaling up the industry.

The polymer-based electrolyte is coated with sulphonic acid ligands to conduct positive charge or amino functional groups for negative ions. Carbon dioxide is usually reduced in a liquid electrode using salty water and for the conduction of electricity, pure water is too resistant. Salts like sodium chloride or potassium bicarbonate have to be added so that ions can move freely.

Formic acid generated in this manner mixes with salts. But for most of the applications, salts have to eliminated from the end product which consumes energy and cost. Instead, solid electrolytes made up of insoluble polymers, inorganic compounds were used thus cancelling the need for salts.

The rate of water flow through the chamber determines the concentration of the solution. Researchers have expectations to achieve higher concentration from next-generation reactors accepting gas flow to generate pure formic acid.

The Rice lab worked with Brookhaven National Laboratory to view the process in progress. “X-ray absorption spectroscopy, a powerful technique available at the Inner Shell Spectroscopy (ISS) beamline at Brookhaven Lab’s National Synchrotron Light Source II. It enables us to probe the electronic structure of electrocatalysts during the actual chemical process.

They followed the bismuth’s oxidation states at different potentials and were able to identify the catalyst’s active state during the reduction process of carbon dioxide. The reactor can generate formic acid for 100 hours without any degradation of its components. Carbon dioxide reduction is a big step towards the effect of global warming and with renewable energy, we can make a loop that turns carbon dioxide to useful products without emitting it.

Journal Reference: Nature Energy

listerine mouthwash

Using mouthwash after exercise can lead to a strange thing

It is often shown in television advertisements that when people use mouthwash, immediately all the unpleasant bacteria in their mouths is removed assuring them of their dental hygiene. But the important questions are what actually takes place, when a cap of antibacterial chemical is used and what it really does in the body? What is its effect in other kinds of microorganisms that are beneficial to health?

In an experiment conducted by researchers from the UK and Spain, they found that using mouthwash after exercising can minimize one benefit of exercising: lowering blood pressure. The work appears in Free Radical Biology and Medicine journal.

Our blood vessels open in response to the production of nitric oxide during exercise, increasing the diameter of blood vessels. It increases blood flow circulation to active muscles and this process is called vasodilation. Researchers believed that circulation stays high (blood pressure is lowered) only during exercise for a long time but recently, facts have shown that it takes place even after exercise because of interaction with nitrate, which forms when nitric oxide degrades.

Raul Bescos, physiology specialist from Plymouth University explained that research has shown that nitrate can be absorbed in the salivary glands and excreted with saliva. He also added that nitrite molecule which is produced by a species of bacteria in the mouth using nitrate can strengthen the production of nitric oxide in the body. Nitrite gets absorbed into the blood circulation and reduces back to nitric oxide, once produced and swallowed with saliva. It keeps blood vessels wide and lowers blood pressure.

This biological mechanism can be substantially disrupted if anti-bacterial mouthwash gets added into the post-exercise mix according to this study. 23 participants ran on a treadmill for 30 minutes. They were asked to wash their mouth with either an antibacterial mouthwash or a mint-flavoured placebo, immediately after the exercise and also after an interval of 30,60 and 90 minutes. Their blood pressure was taken during the exercise and after their rest period.

The conclusions showed that the average reduction in systolic blood pressure in the placebo group was –5.2 mmHg (millimetres of mercury) at one hour after the treadmill session. The mouthwash-using group showed an average of -2.0 mmHg at the same time, meaning the use of the antibacterial mouthwash (0.2 percent chlorhexidine) had lowered the systolic blood pressure reduction by more than 60 percent. The mouthwash group showed no sign of reduction in the blood pressure, two hours after the treadmill session whereas the placebo group still showed a significant reduction compared to the pre-exercise values.

The authors explained in their paper that this is the first evidence demonstrating the nitrate-reducing operation of oral bacteria is significant for inducing an acute cardiovascular response to exercise during the period of recovery. Consuming antibacterial chemicals that randomly eliminate the microbes in the mouth could obstruct important biological processes necessary for good health and this study reminds that not all bacteria are necessarily bad for us.

Craig Cutler one of the team nutritionists said that these results show that nitrite synthesis by oral bacteria is very important in reactivating how our bodies react to exercise over the first period of recovery, promoting lower blood pressure and greater muscle oxygenation. He also added that nitrite can’t be produced and vessels will remain in their current state if the oral bacteria will be removed.

Journal Reference: Free Radical Biology and Medicine journal

wedderburn meteorite

Researchers confirm existence of mineral in meteorite never found before in nature

An exclusive mineral has been discovered roadside in a remote gold rush town of Australia, Wedderburn which is 214 kilometers north of Victoria’s capital city, Melbourne. Earlier, it was a hotspot for the researchers and miners and it still is, although occasionally but nobody there had ever seen a lump like this.

A small 210-gram piece of weird-looking stone was found just north-east of the Wedderburn town in 1951. Named as the Wedderburn, researchers have been trying to solve its mysteries and they just decoded another. Scientists examined the Wedderburn meteorite and confirmed the first natural occurrence of the mineral called ‘edscottite‘ which is a unique form of an iron-carbide mineral which has never been found in nature. The work appears in the American Mineralogist journal.

The unique black-and-red rock has been investigated to the extent that only one-third of the original specimen remains intact within the geological collection at Museums Victoria, Australia since the Wedderburn meteorite’s spacey origins were first detected. The rest of the rock was taken away to investigate the substances the meteorite is made of. Those investigations have shown traces of gold and iron, along with uncommon minerals such as kamacite, schreibersite, taenite, and troilite and now edscottite can be added to the list.

The discovery is named in honor of Edward Scott – meteorite expert and cosmochemist from the University of Hawaii. It is important because this specific atomic formulation of iron carbide mineral was never before confirmed to occur naturally. For official recognition by the International Mineralogical Association (IMA), this confirmation is important as it is an essential requirement for minerals.

An artificial kind of the iron carbide mineral produced during iron smelting has been well-known about for years. Edscottite is now an official element of the exclusive IMA’s mineral club and it is due to the research by Chi Ma and UCLA geophysicist Alan Rubin. Stuart Mills, Museums Victoria senior curator of geosciences who wasn’t engaged with the new study, said that they have discovered 500,000 to 600,000 minerals in the research lab out of which only 6,000 were identified as naturally occurring minerals.

In regard to how this sliver of natural edscottite was found outside of rural Wedderburn is not yet clear but the mineral could have formed in the heated, pressurized core of an ancient planet according to planetary scientist Geoffrey Bonning from Australian National University, who wasn’t involved with the study. Bonning said that some kind of colossal cosmic collision could have occurred a long time ago involving this unfortunate edscottite-producing planet and another planet, or a moon, or an asteroid and been exploded apart, with the fragmented parts of this wrecked world being hurled across time and space. It is believed that one such part landed just outside Wedderburn after millions of years which has enriched our knowledge of the Universe.

Research Paper: Edscottite, Fe5C2, a new iron carbide mineral from the Ni-rich Wedderburn IAB iron meteorite

clean drop of water liquid

Scientists discover spontaneous production of hydrogen peroxide from water

Water is a strange molecule and even after centuries of research, irrespective of the number of strange things discovered about it, there are still unexpected results waiting to be unearthed. In a new case study, researchers in the United States have discovered that under the proper circumstances, water can spontaneously produce hydrogen peroxide which is a strange aspect of fundamental chemistry that was hiding in plain sight, unnoticed till now.  The work appears in PNAS journal.

Richard Zare, a chemist at Stanford University says that since water is one of the most commonly found elements which has been studied for several years, it is normally expected that there is nothing else to learn about it.

Scientists observed the phenomena with pure water, and just any form of water will not do. According to the team, hydrogen peroxide can be produced when water is atomized into microdroplets which measure between 1 micrometer to 20 micrometers in diameter. One micrometer is one-thousandth of a millimeter, hence it is understood that the droplets are very small in size. At this infinitesimal scale, hydrogen peroxide is formed spontaneously even when there is nothing else present apart from water.

For this process, there is no necessity of chemical reagent, catalyst, electrical potential or radiation. The only requirement is pure water in microdroplet form. This phenomenon was discovered accidentally in previous research while investigating how gold nanoparticles and nanowires can be produced using water droplets. Those experiments revealed that water microdroplets besides accelerating the synthesis of the gold nanostructures also results in their spontaneous formation.

Zare’s team conducted several tests such as spraying pure water microdroplets on a test strip which turned blue if hydrogen peroxide was present. The yield of hydrogen peroxide production was inversely proportional to the size of microdroplet. Researchers think that the spontaneous oxidation of water takes place due to the presence of strong intrinsic electric field between water and air microdroplets, where hydroxyl radicals combine to form hydrogen peroxide in the presence of an electric field.

Further research is needed to test this hypothesis, although there is no ambiguity regarding the generation of hydrogen peroxide itself. This could lead to more eco-friendly ways of producing hydrogen peroxide. Research like this opens doors to innovative opportunities such as green and affordable production of hydrogen peroxide, environment-friendly synthesis of chemicals, safe cleaning and food processing. This is a surprising discovery even to someone such as Zare who himself holds 11 honorary doctorates and considers it to be one of the most significant discoveries.

Research Paper: Spontaneous generation of hydrogen peroxide from aqueous microdroplets

Researchers find explanations behind the mystery of North Pacific gyre

Researchers find explanations behind the mystery of North Pacific gyre

The center of oceans of the Earth are covered with an enormous arrangement of rotating currents known as subtropical gyres, which occupy 40% of the Earth’s surface. They have been considered as stable biological deserts with little deviation in chemical composition or the nutrients needed to sustain life.

The region in the North Pacific Subtropical Gyre ecosystem that occupies the Pacific Ocean between China and the United States has confused scientists over the years by its strange abnormality in chemistry that changes periodically. There is a remarkable variation in the levels of phosphorus and iron which affects the entire nutrient composition and eventually biological productivity.

The research team has found out the explanation behind the variations in the North Pacific Subtropical Gyre ecosystem. It includes Matthew Church, a microbial ecologist with the University of Montana’s Flathead Lake Biological Station, Ricardo Letelier from Oregon State University and David Karl from the University of Hawaii. The work appears in the Proceedings of the National Academy of Sciences.

Church said that the variations in the ocean climate arise to basically control ocean nutrient concentrations by regulating iron supply and altering the kinds of plankton growing in these waters. He also said that after constant, long-term observations on the role of plankton in controlling ocean nutrient availability, their team has finally confirmed that tightly linked plankton supplies nutrients, particularly iron, delivered from the atmosphere.

With the help of three decades of observational data from Station ALOHA, a six-mile area in the Pacific Ocean, the researchers discovered that the periodic shift in the level of iron is due to iron input from Asian dust, accounting for the chemical variances and varying amounts of nutrients to sustain life.

The ocean-atmosphere relationship known as The Pacific Decadal Oscillation varies between weak and strong stages of atmospheric pressure in the northeast Pacific Ocean which is the major factor of the variance. The winds from Asia become stronger and move in a more southern direction in years when the low pressure weakens in the northeast Pacific bringing more dust from Asia and fertilizing the ocean around ALOHA. The opposite occurs when the pressure strengthens.

Phosphorous and iron are the essential components of life and the supply of nutrients is a fundamental controller of ocean productivity. The process of fertilizing the ocean’s upper water level by mixing nutrient-rich water from the bottom is challenging in the North Pacific Subtropical Gyre ecosystem because the waters are very layered and very less mixing takes place. The creatures are allowed to grow and use phosphorus in the upper layers of the ocean when strong Asian winds bring in substantial quantity of iron while they are forced to return to a bottom-water-mixing nutrient delivery system when the Asian winds weaken and iron quantity is reduced creating the periodic ebb and flow of iron and phosphorus levels in the North Pacific Gyre.

Church said that the results from the study highlight the crucial need to include both atmospheric and ocean circulation variability for forecasting the climate change impact on ocean ecosystems. He also added that it confirms the necessity to think about the biology of tightly connected plankton to changes in climate as well as land use which can directly impact dust supply to the ocean.

Researchers hope to see long-term changes in wind patterns across the North Pacific as Earth’s temperature continues to increase. The sources and quantity of iron and other nutrients carried by the wind across the ocean will get affected by the evolution of land use and pollution caused by human activity in Asia.

To know the impact of the changes on ecosystems around the ocean region as well as others around the world, more research is needed.

Journal Reference: Proceedings of the National Academy of Sciences.

Synthesis of cyclocarbon

Researchers for the first time create a stable ring of only carbon atoms

Carbon atoms can be organized in numerous arrangements. Every carbon atom, when bonded to three other carbon atoms, the resultant element, soft graphite, is formed. Addition of one more bond in graphite results in diamond which is the hardest known substance. Buckyballs are obtained by projecting 60 carbon atoms together in a football shape. But the best efforts of researchers of forming a ring of carbon atoms, where each atom is bonded to just two others results in gaseous carbon ring which dissipates rapidly.

A team of researchers from Oxford University and IBM Research has done an excellent and challenging job by creating a stable carbon ring. The smallest cyclocarbon, it is a ring-shaped carbon compound made from 18 carbon atoms is expected to be thermodynamically stable and its image has been obtained from the modern microscopy methods. The paper has been published in Science journal.

Cyclocarbon seems to act as semiconductor and has possible use in electronics according to the research on its structure. Its high reactivity could be used to develop other carbon allotropes and carbon-abundant elements, surprisingly the property that made cyclocarbons tough to separate in the first place. Scientists started synthesizing triangular cyclocarbon oxide C24O6  which is 18 carbon atoms, bonded to six carbon monoxide molecules, two grouped at each of the three corners of the triangle to achieve this feat.

To ensure an inert surface that keeps the structure stable, the compound was moved to a layer of sodium chloride on a copper plate, cooled in a vacuum chamber to just above absolute zero. After that, the team pulled out the carbon monoxide (CO) molecules off the structure, leaving just the ring of carbon atoms behind using the top of an atomic force microscope. The scientists couldn’t always pull all the CO off without falling the ring structure and they instead produced molecules such as C22O4 and C20O2. The scientists wrote in their paper that they detached all six CO moieties from C24O6, with 13 percent yield, generally resulting in circular molecules.

It is interesting to know that the atoms in the cyclocarbon formed a polyynic structure, with an alternating triple and single bonds answering the question whether one-dimensional carbon or a cumulenic structure, with repeated double bonds, would produce this. This reciprocating structure is expected to produce semiconductivity and also suggests that carbon chains would also be semiconductive. One ring structure can be built at a time. So, Researchers are searching for ways to build multiple cyclocarbons at once and refining the process to produce a more reliable yield.

Researchers can initiate experimenting with applications after the formation of stable cyclocarbons – understanding how the semiconductivity can be used for exploring cyclocarbon properties as a basic building block for even more complex molecules. The researchers wrote that their outcomes ensure direct experimental understandings into the structure of a cyclocarbon and clear the way to form other unachievable carbon-rich molecules by atom management.

Research Paper: https://science.sciencemag.org/content/early/2019/08/14/science.aay1914

Scientists create the world's thinnest gold

Scientists create the world’s thinnest gold

Scientists at the University of Leeds have created a new form of gold which is just two atoms thick – the thinnest unsupported gold ever created.

The researchers measured the thickness of the gold to be 0.47 nanometres – one million times thinner than a human fingernail.

The material is regarded as 2D because it comprises just two layers of atoms sitting on top of one another. All atoms are surface atoms, there are no ‘bulk’ atoms hidden beneath the surface.

It could have wide-scale applications in the medical device and electronics industries, and also as a catalyst to speed up chemical reactions in a range of industrial processes.

Laboratory tests show that the ultra-thin gold is 10 times more efficient as a catalytic substrate than the larger gold nanoparticles currently used in industry.

‘Landmark achievement’

Scientists believe the new material could also form the basis of artificial enzymes for potential use in rapid, point-of-care medical diagnostic tests and in water purification systems.

The announcement that the ultra-thin metal had been successfully synthesised was made in Advanced Science. The journal paper’s lead author, Dr Sunjie Ye, from Leeds’ Molecular and Nanoscale Physics Group and the Leeds Institute of Medical Research, said: “This work amounts to a landmark achievement.
“Not only does it open up the possibility that gold can be used more efficiently in existing technologies, it is providing a route which would allow material scientists to develop other 2D metals.”This method could innovate nanomaterial manufacturing.”

The research team is looking to work with industry on ways of scaling-up the process.

…industry could get the same effect from using a smaller amount of gold, and this has economic advantages…

PROFESSOR STEPHEN EVANS

Synthesising the gold nanosheet takes place in an aqueous solution and starts with chloroauric acid, an inorganic substance that contains gold. It is reduced to its metallic form in the presence of a “confinement agent” – a chemical that encourages the gold to form as a sheet just two atoms thick.

Because of the gold’s nanoscale dimensions, it appears green in water, and given its frond-like shape, the researchers describe it as gold nanoseaweed.

Images taken from an electron microscope reveal the way the gold atoms have formed into a highly organised lattice structure.

Image shows a picture from an electron microscope showing tightly packed atoms

This electron microscope picture shows the gold atoms’ lattice structure(Credit: University of Leeds)

Professor Stephen Evans heads the Leeds’ Molecular and Nanoscale Research Group and supervised the research. He said the considerable gains that could be achieved from using ultra-thin gold sheets were down to their high surface-area-to-volume ratio.

“Gold is a highly effective catalyst. Because the nanosheets are so thin, just about every gold atom plays a part in the catalysis. It means the process is highly efficient.

“Our data suggests that industry could get the same effect from using a smaller amount of gold, and this has economic advantages when you are talking about a precious metal.”

The flakes are also flexible, meaning they could form the basis of electronic components for bendable screens, electronic inks and transparent conducting displays.

Image shows Dr Sunjie Ye and Professor Stephen Evans at a machine that analyses gold particle.

Dr Sunjie Ye and Professor Stephen Evans used x-ray photo electron spectroscopy to confirm the purity of the new form of gold. (Credit: University of Leeds)

Professor Evans thinks there will inevitably be comparisons made between the 2D gold and the first 2D material ever created – graphene, which was fabricated at the University of Manchester in 2004.

He said: “The translation of any new material into working products can take a long time and you can’t force it to do everything you might like to. With graphene, people have thought that it could be good for electronics or for transparent coatings, or as carbon nanotubes that could make an elevator to take us into space because of its super strength.

“I think with 2D gold we have got some very definite ideas about where it could be used, particularly in catalytic reactions and enzymatic reactions. We know it will be more effective than existing technologies – so we have something that we believe people will be interested in developing with us.”

Journal Reference: Advanced Science

Materials provided by the University of Leeds

Aequorea victoria ventral view

Researchers identify fluorescent proteins in the body of jellyfish for the first time

This jellyfish makes glowing proteins which were previously unknown to scientists. Nathan Shaner and his colleagues back in 2017 had found something unusual near Herons land. They were snorkeling through the southern coasts of Australia near the Great Barrier Reef and spotted a strange-looking jellyfish. Scientists took the jellyfish and bought it back to the boat and after having a closer look it came to notice that the translucent body of the fish had shot through luminous lines of blue.

Shaner, an optical probe developer at the University of California collected the animal due to his wish as it was blue and wanted to take it home but the team was not looking primarily for jellies however came across one. The team identified the five fluorescent proteins in the body of the jellyfish which were previously unknown. This may lead to the discovery of newer techniques for exploring how genes are expressed in cells and gain the brightest fluorescent protein tag.

Shaner and his team went back to the lab and prepared a sample for analysis and after sequencing its transcriptome, the genes present in the jelly’s body, he was surprised to find several light-producing proteins similar to green fluorescent protein which was being used by scientists for decades to track cell protein and make glow-in-the-dark cats.

The original protein known as avGEP has led to dozens of bioengineered GFP variants, some of the variants glow in colors like cobalt blue and turquoise. Further analysis revealed that jelly A.australis produces five fluorescent proteins which include two which glow green, two more that are blue and one between yellow and clear when exposed to light. When researchers looked at the original GPF jelly once again, they found genes of previously unknown fluorescent proteins, some had narrow excitation and emission peaks from which they could absorb and emit light at a specified wavelength. It helped in the study of the expression of several genes simultaneously with the help of colors of fluorescent protein tags. AausFP1, the brightest protein was almost five times brighter than GFP, which was enhanced for powerful fluorescence.

Fluorescent proteins have different use depending on what we are trying to study and the brighter the better for everyone as it will hopefully enable people to see things that could not be seen before. AausFP1 is bright and does not lose its glow when exposed to light and can be used for cell imaging for extended amounts of time for continuously up to 2.5 days where normal GFP variant would bleach within few hours.

Joachim Goedhart, a fluorescent protein engineer at the University of Amsterdam says the study is exciting and researchers came back with different variants and that fluorescent protein needs modifications for being useful. Mutations would be required for smaller, brighter and easier manipulations in the cell.

More articles on Fluorescence:

Performing Chemistry in Floating Droplets

Performing Chemistry in Floating Droplets

Could chemists be ready to ditch the venerable test tube, the very symbol of chemistry in the minds of many people? Maybe not quite yet, but Caltech’s Jack Beauchamp is working on it.

Beauchamp is doing work in what he calls “lab-in-a-drop” chemistry, in which chemical reactions are performed within a drop of liquid suspended in midair through acoustic levitation.

Acoustic levitation works by creating areas of high and low pressure in the air through the use of ultrasonic transducers. These transducers act like tiny but powerful speakers that operate at a frequency above what human ears can hear. The sonic energy emitted by these transducers is focused in such a way that the high- and low-pressure zones they create form “traps” that can hold small objects in place in the air. An object placed in one of the low-pressure zones is held there by the high-pressure zones that surround it. An acoustic levitator of this sort can be constructed for about $75 from off-the-shelf parts using 3D-printing techniques.

An animated gif showing a hand place a pellet in the levitator. Graphics showing high- and low-pressure zones are superimposed.

Credit: Caltech

In a new paper, Beauchamp and his colleagues describe the use of the technique to study how a skin-cancer drug works at a chemical level. The research, he says, represents the first successful use of acoustic levitation as a “wall-less” reactor in a detailed study of chemical reactions.

In the work, Beauchamp and his team coated a droplet of water with lipids, biomolecules that make up cell membranes. They then applied an anti-cancer drug to the droplet and used a mass spectrometer to “sniff” the chemical signature given off by the droplet as the drug reacted with the lipid when illuminated with a red laser pointer.

In the experiment, the researchers added a small amount of one of two lipids, cardiolipin and POPG (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1′-rac-glycerol)), to each drop of water. The lipids migrated to the surface of the droplet, where they organized to form a thin film that is similar in composition to the cell membrane of a living cell.

With the membrane established, a chemical called temoporfin was added to the droplet. Temoporfin, a ring-like molecule, is excited by red light. In this state, the temoporfin transfers energy to molecular oxygen, forming an excited electronic state that easily oxidizes molecules it comes into contact with, including those that make up cell membranes. This makes temoporfin useful as a treatment for some skin cancers. A doctor could apply the drug to a cancerous lesion and then illuminate it with red light, which easily shines through tissues. As the compound is illuminated and excited, it oxidizes vital cellular materials, including lipids, proteins, and nucleic acids, triggering cell death.

It was this cancer-killing process that Beauchamp wanted to study. “When you’re doing this chemistry, you’d like to be able to carry out these reactions under conditions where you don’t have any contact of the liquid with surfaces,” he says. “We achieve this goal by performing chemistry in a levitated droplet.”

The acoustic levitator allowed Beauchamp and his team to suspend in midair a 1 millimeter droplet of water containing a mixture of the lipid and temoporfin. The droplet was then illuminated by red laser light, exciting the temoporfin and causing it to oxidize the molecules of the membrane layer.

As this oxidation was occurring, a pair of high-voltage electrodes placed near the droplet pulled minute amounts of material off the droplet and into the sensor of a mass spectrometer, which provided readings that allowed researchers to deduce the molecular structures of compounds within the drop. By continually monitoring these readings, the researchers were able to see how the compounds on the surface became progressively more oxidized. By looking at these reaction products, Beauchamp says the research team could determine how the oxidation processes work.

“As far as I know, we’re the only people doing serious chemistry this way, examining the kinetics and mechanism of the reactions involved” Beauchamp says.

Acoustic levitation could find use in other fields as well, he says. As an example, he cites the research of Caltech’s Joe Parker, an assistant professor of biology and biological engineering who studies the symbiotic relationship between certain species of ants and beetles. Beauchamp says it would be possible to levitate an ant and a beetle in close proximity to one another and then use the apparatus to analyze the pheromones they emit.

The technique could have other applications as well. In collaborative studies with Caltech’s John Seinfeld, Louis E. Nohl Professor of Chemical Engineering, Beauchamp previously revealed details of the complex environmental chemistry that leads to the formation of organic aerosols in the atmosphere in studies using droplets hanging on the end of a capillary. With the new levitation methodology, that capillary would no longer be required.

The paper describing Beauchamp’s research, titled “Mass Spectrometric Study of Acoustically Levitated Droplets Illuminates Molecular-Level Mechanism of Photodynamic Therapy for Cancer Involving Lipid Oxidation,” appears in the April 23 issue of Angewandte Chemie, the flagship journal of the German Chemical Society. Beauchamp’s co-authors include Chaonan Mu, Jie Wang, and Xingxing Zhang of Nankai University, and Kevin J. Barraza, a postdoctoral scholar in chemistry at Caltech.

Materials provided by the California Institute of Technology