A team of chemists at the University of Cambridge has developed a metal-free way to convert symmetrical diols selectively into one of two mirror-image isomers. In their paper published in the journal Science, the group took advantage of the ability of chiral versions of quinuclidine—which were derived from Cinchona alkaloids—to catalyze the dememorization of meso-diols under a blue light in conjunction with a photocatalyst and extract hydrogen atoms from symmetrical molecules.
Noting that transferring hydrogen atoms between molecules is a fundamental chore in modern chemistry, the research team looked to make the process more selective by adding enantioselective hydrogen atom transfer, where one of the enantiomers of a chiral product is preferentially produced during a chemical reaction.
Their work involved the development of a new method for enantioselective hydrogen atom abstraction—one that allowed for the introduction of chirality into the process. Through their use of catalysts derived from the Cinchona alkaloid family, they were able to exploit the resulting chiral amine structure to selectively remove a hydrogen atom from a specific carbon center in a meso-diol.
They did this by focusing on the use of chiral quinuclidine compounds from Cinchona alkaloids, which allowed them to catalyze the desymmetrization of meso-diols with blue light and a photocatalyst.
The method used by the team allowed for selective epimerization, which is where one stereoisomer was transformed into another—by replacing a hydrogen atom with a thiol. At the outset, the catalyst, which was made through the direct hydrogenation of a Cinchona alkaloid, was not very reactive or as selective as hoped.
Further work, however, showed that changing the hydroxyl group to a protected amine and reversing the stereocenter could improve the catalyst's performance significantly.
The researchers point out that their work is a proof of principle, noting that parts of their technique allow for swapping out the quinuclidine and using the chiral version instead. They also note that the catalyst could be used for site-selective chemistry if appropriate. They conclude by suggesting their work could have important implications for pharmaceutical applications, and possibly in other research efforts.
Analytical Chemistry Excellence, Scientific Innovation Awards, Analytical Method Development, Instrumental Analysis Innovation, Cutting-Edge Analytical Techniques, Chemistry Research Achievements, Analytical Science Recognition, Advanced Analytical Tools, Chemical Analysis Awards, Global Chemistry Awards
Analytical Chemistry Excellence Scientific Innovation Awards Analytical Method Development Instrumental Analysis Innovation Cutting-Edge Analytical Techniques Chemistry Research Achievements Analytical Science Recognition Advanced Analytical Tools Chemical Analysis Awards Global Chemistry Awards
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A new study examines acid-base equilibria at the liquid-vapor interface, revealing how sulfur dioxide reacts differently there, impacting air pollution and atmospheric chemistry.
An international study examines the differences in complex acid-base equilibria—specifically, the balance between acidic and basic components—both within the bulk of a solution and at the interface between the solution and the surrounding vapor.
While it is straightforward to measure acid-base equilibria in the bulk of a solution using state-of-the-art methods, determining these equilibria at the boundary between a solution and the surrounding gas phase is challenging. Even though this boundary layer is about one hundred thousand times narrower than a human hair, it plays a very important role in processes that influence air pollution and climate change.
Examining the chemistry of the solution-vapor boundary on a molecular scale thus helps to develop improved models for our understanding of the fate of aerosols in the atmosphere and their influence on the global climate.
Key Findings:
Complex acid-base equilibria determined: The researchers used complementary spectroscopic methods to unravel the complex acid-base equilibria that result when the pollutant sulfur dioxide (SO2) is dissolved in water.
Unique behavior at the liquid-vapor interface: Under acidic conditions, the tautomeric equilibrium between bisulfite and sulfonate is strongly shifted towards the sulfonate species.
Stabilization at the interface: Molecular dynamic simulations revealed that the sulfonate ion and its acid (sulfonic acid) are stabilized at the interface due to ion pairing and higher dehydration barriers, respectively. This explains why the tautomeric equilibria are shifted at the interface.
Implications for Air Pollution:
The findings highlight the contrasting behaviors of chemicals at the interface versus the bulk environment. This difference significantly impacts how sulfur dioxide is absorbed and reacts with other pollutants like nitrogen oxides (NOx) and hydrogen peroxide (H2O2) in the atmosphere.
Understanding these processes is crucial for developing strategies to reduce air pollution and its harmful effects on health and the environment.
Reference:
“Direct observation of the complex S(IV) equilibria at the liquid-vapor interface” by Tillmann Buttersack, Ivan Gladich, Shirin Gholami, Clemens Richter, Rémi Dupuy, Christophe Nicolas, Florian Trinter, Annette Trunschke, Daniel Delgado, Pablo Corral Arroyo, Evelyne A. Parmentier, Bernd Winter, Lucia Iezzi, Antoine Roose, Anthony Boucly, Luca Artiglia, Markus Ammann, Ruth Signorell and Hendrik Bluhm, 18 October 2024, Nature Communications.
Climate models Solution-vapor interface Atmospheric chemistry Surface reactions Interface dynamics Aerosols Chemical kinetics Greenhouse gases Climate change Microphysics Environmental impact Energy transfer Surface tension Emission modeling Photochemical reactions Climate science innovations Computational chemistry Water vapor interactions Reaction mechanisms Atmospheric interfaces
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Two lawsuits aim to stop US federal regulators and industry from “illegally” hiding basic information about toxic chemicals used in consumer products that are potentially polluting the environment and endangering public health.
Companies often claim that toxic chemicals’ health and safety data, and even their names, are “confidential business information” (CBI) because making the data public could damage their bottom line.
The US Environmental Protection Agency frequently allows industry to use the tactic, which makes it virtually impossible for public health researchers to quickly learn about dangerous chemicals. It also bars most EPA staff and state regulators from accessing the information and criminal charges could be brought against those who do.
That leaves regulators attempting to protect the public without essential information for some chemicals and in effect creates a “shadow regulatory government” in the EPA, said Tim Whitehouse, a former EPA attorney who is now director of Public Employees for Environmental Responsibility (Peer), a plaintiff inone of the suits.
“It makes it impossible to have proper chemical oversight because much of the information that the EPA is evaluating is withheld from other regulators within the EPA, the states and the public,” he said.
He pointed to the EPA’s approval of hundreds of types of PFAS, or “forever chemicals”, which are a class of compounds known to generally be toxic, accumulate in humans and not fully break down in the environment. The chemical class is thought to be contaminating drinking water for tens of millions of people.
A 2016 EPA new chemicals database for about 200 PFAS approved for commercial use by the agency shows more than 3,500 pieces of information on the chemicals concealed from the public.
“When dangerous chemicals like that get on the market there can be significant health and financial consequences,” Whitehouse said.
The tactic continues to be widely used despite that Congress’s 2016 revision of the Toxic Substances Act included provisions designed to increase transparency around chemicals. But when the EPA implemented the legislation and developed rules, it weakened the law, said Samantha Liskow, an attorney with the Environmental Defense Fund nonprofit, which has sued over the EPA’s rules.
Before the law’s 2016 revision, businesses could make proprietary claims with virtually no review from the EPA. The revision put in place a process for EPA review, but public health advocates say the agency rubber-stamps virtually every proprietary claim.
Among other charges, the EDF suit alleges the EPA has narrowed Congress’s definitions of what should be made public, given itself more discretion over whether information should be made public than the law allows and conceals identifying information that should be publicly available.
That can include chemical names, chemical structures, where the substance is made and which company makes it. The information is critical because it informs the public about who could be exposed, which workers will handle dangerous chemicals, which communities sit near a factory that will produce the chemicals, and which consumer products will contain the substances, Liskow said.
The EPA is also withholding chemical safety test results that show health risks to the public or environment.
“Even when companies say, ‘I don’t want this out there,’ Congress says ‘No, the public should have this,’” Liskow said.
Separately, Peer is suing the EPA for hiding health and safety data for chemicals made by Inhance Technologies, which produces plastic containers found to leach dangerous levels of PFOA, a highly toxic compound, into the containers’ contents.
Inhance produces tens of millions of plastic containers used across the economy annually. Peer submitted a Freedom of Information Act request for results of EPA testing on the level at which the chemicals leach into the containers’ contents.
The EPA redacted the results, which Peer said is illegal, citing revised TSCA language.
“They’re hiding behind the cloak of CBI to prevent the release of this very pertinent information,” said Peer attorney Colleen Teubner.
The EDF lawsuit also alleges the agency further carved out CBI exemptions not included in the law. One significant example is allowing an exemption when a lab that conducted health and safety studies is “part of or closely affiliated with” the chemical maker. That creates a situation in which potential conflicts of interest are hidden.
Though the revised law was also supposed to grant better access for state regulators, state agencies say the EPA put in place a process for accessing the chemicals that is so onerous that it in effect continues to bar access. When Minnesota and California regulators tried in 2020 to access chemical information, they gave up because of the difficulty.
Whitehouse said industry is likely behind the EPA’s business-friendly approach to CBI.
“When it comes to chemicals, the EPA views industry as its client, not the American public, unfortunately,” Whitehouse said.
Toxic chemicals Chemical regulation Environmental law US regulators EPA (Environmental Protection Agency) Public health Environmental justice Industrial pollution Chemical disclosure Regulatory transparency Legal accountability Lawsuit Chemical safety Toxic substances Environmental protection
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Diatoms Unlock Nature’s Secret to Massive CO2 Capture
A groundbreaking study reveals a protein shell in diatoms that enhances their CO2 fixation capabilities, offering new avenues for bioengineering to combat climate change by optimizing photosynthesis.
Tiny ocean diatoms are highly efficient at capturing carbon dioxide (CO2) from the environment, accounting for up to 20 percent of the Earth’s CO2 fixation. Researchers at the University of Basel in Switzerland have now discovered a protein shell within these algae that is essential for their ability to fix CO2 so effectively. This significant finding could inspire new bioengineering strategies to help reduce atmospheric CO2 levels.
Diatoms, though invisible to the naked eye, are among the most productive algae in the ocean and play a crucial role in the global carbon cycle. Through photosynthesis, they absorb large amounts of CO2 from the environment and convert it into nutrients that sustain much of ocean life. Despite their significance, how diatoms perform this process so efficiently has remained a mystery.
Now, researchers led by Prof. Ben Engel at the University of Basel’s Biozentrum, along with teams from the University of York, UK, and Kwansei-Gakuin University in Japan, have uncovered a protein shell crucial to diatoms’ CO2 fixation. Using advanced imaging techniques like cryo-electron tomography (cryo-ET), they mapped the molecular structure of the PyShell protein sheath and revealed its function. These findings were recently published in two papers in the journal Cell.
In plants and algae, photosynthesis takes place in chloroplasts. Inside these chloroplasts, energy from sunlight is harvested by thylakoid membranes and then used to help the enzyme Rubisco fix CO2.
However, algae have an advantage: they pack all their Rubisco into small compartments called pyrenoids, where CO2 can be captured more efficiently. “We have now discovered that diatom pyrenoids are encased in a lattice-like protein shell,” says Dr. Manon Demulder, author on both studies. “The PyShell not only gives the pyrenoid its shape, but it helps create a high CO2 concentration in this compartment. This enables Rubisco to efficiently fix CO2 from the ocean and convert it into nutrients.”
When the researchers removed the PyShell from the algae, their ability to fix CO2 was significantly impaired. Photosynthesis and cell growth were reduced. “This showed us how important the PyShell is for efficient carbon capture – a process that is crucial for ocean life and the global climate,” says Manon Demulder.
The discovery of the PyShell could also open promising avenues for biotechnological research aimed at combatting climate change – one of the most pressing challenges of our time. “First of all, we humans must reduce our CO2 emissions to slow the pace of climate change. This requires immediate action,” says Ben Engel.
“The CO2 that we emit now will remain in our atmosphere for thousands of years. We hope that discoveries such as the PyShell can help inspire new biotechnology applications that improve photosynthesis and capture more CO2 from the atmosphere. These are long-term goals, but given the irreversibility of CO2 emissions, it is important that we perform basic research now to create more opportunities for future carbon-capture innovations.”
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This approach addresses the limitations of traditional optical techniques, particularly Fourier-transform infrared (FTIR) spectroscopy, which requires large optically active areas to achieve satisfactory signal-to-noise ratios. The authors highlight the potential of this method to miniaturize devices while improving the sensitivity and efficiency of polaritonic measurements.
Polaritons are quasiparticles formed by the coupling of electromagnetic waves with material excitations, such as phonons or plasmons. The study of polaritons in two-dimensional materials, particularly hexagonal boron nitride (hBN) and graphene, has gained attention due to their ability to confine light at subwavelength scales.
The article discusses the significance of different types of hyperbolicity in hBN, specifically type I and type II hyperbolicity, which influence polariton behavior across various spectral ranges. The authors note that the lower reststrahlen band of hBN has been less explored than the upper band, despite its potential for high-quality factors and lateral confinement.
This research aims to investigate the spectral photoresponse of polaritonic nanoresonators and their tunability through electrical gating of graphene.
The study used precise lithographic techniques to fabricate polaritonic nanoresonators from a high-quality heterostructure of hBN and graphene. A silicon wafer was first coated with polymethyl methacrylate (PMMA) to serve as a resist. Electron beam lithography (EBL) was then employed to define the patterns for the metallic nanostructures, which were developed to create templates for the resonators.
After patterning, a thin layer of gold was deposited onto the substrate using thermal evaporation, forming the metallic components of the devices. The hBN layers were mechanically exfoliated from bulk crystals and transferred onto the gold-coated substrate, followed by the placement of a graphene layer. The graphene was doped using a back gate voltage to modulate its carrier concentration, enhancing the interaction with the polaritonic modes.
For optical characterization, a Fourier-transform infrared (FTIR) spectrometer with a nitrogen-cooled mercury-cadmium-telluride (MCT) detector measured the transmission spectra across a wavelength range of 1.54 to 15.4 μm. Photocurrent spectroscopy was conducted using a quantum cascade laser (QCL) with tunable wavelengths from 6.6 to 13.6 μm.
The devices were positioned using a motorized XYZ-stage, and photocurrent was measured with a lock-in amplifier to improve signal detection. This comprehensive approach facilitated a detailed investigation of the polaritonic resonances and their tunability through electrical gating.
The results showed that the electrical spectroscopy method significantly outperformed traditional FTIR techniques in terms of signal-to-noise ratios (SNR). Devices designed for photocurrent measurements exhibited SNR values one to two orders of magnitude higher than those measured by FTIR.
For example, device 2 achieved an SNR of approximately 100, despite its small area, while device 5, measured by FTIR, had an SNR of only 1 due to larger area requirements. This contrast highlights the advantages of electrical spectroscopy for studying polaritonic resonances in devices with limited active areas.
The authors also investigated the tunability of the polaritonic response by varying the gate voltages applied to the graphene channel. Doping the graphene improved device performance and allowed it to function as a partial mirror for polaritons, modifying the hybridized modes and enhancing tuning capabilities. The study found that the highest quality factors and lateral confinement occurred in the lower reststrahlen band, suggesting the potential for practical applications of these modes.
This article introduces an electrical spectroscopy method that significantly enhances sensitivity and efficiency in polaritonic nanoresonators compared to traditional optical techniques. The research emphasizes the unique properties of hBN and graphene, facilitating exploration of the lower reststrahlen band and highlighting the potential for high-quality polaritonic modes. The findings demonstrate the benefits of miniaturized devices for improved signal detection, enabling innovative applications in sensing and imaging technologies. The authors suggest further investigation into the tunability of polaritonic responses through electrical gating, which could advance the development of next-generation photonic devices. Overall, this study provides important insights into the manipulation of polaritons in two-dimensional materials, laying the groundwork for future research and technological advancements in the field.
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