Exchange Of Oxygen Atoms Research Articles

Modular Synthesis of α-Aryl Acrylamido Carboxylic Acids by Triple C-F Bond Cleavage of (Trifluoromethyl)alkenes with Unprotected Amino Acids.

A straightforward and efficient strategy for the construction of tertiary and secondary α-aryl acrylamido carboxylic acids is reported. This N-acrylation protocol of unprotected amino acids is achieved by triple C-F bond cleavage of (trifluoromethyl)alkenes. This method features mild conditions, is operationally simple, is free of transition metals and racemization, can be used on a gram scale, and is compatible with various functional moieties. Mechanistic studies indicate that oxygen atom exchange happens among H2O, NaOH, and amino acids, and the oxygen atom of the amide moiety of the product is incorporated by the ipso-defluorooxylation of (trifluoromethyl)alkene.

Resin acid δ13C and δ18O as indicators of intra-seasonal physiological and environmental variability.

Understanding the dynamics of δ13C and δ18O in modern resin is crucial for interpreting (sub)fossilized resin records and resin production dynamics. We measured the δ13C and δ18O offsets between resin acids and their precursor molecules in the top-canopy twigs and breast-height stems of mature Pinus sylvestris trees. We also investigated the physiological and environmental signals imprinted in resin δ13C and δ18O at an intra-seasonal scale. Resin δ13C was c. 2‰ lower than sucrose δ13C, in both twigs and stems, likely due to the loss of 13C-enriched C-1 atoms of pyruvate during isoprene formation and kinetic isotope effects during diterpene synthesis. Resin δ18O was c. 20‰ higher than xylem water δ18O and c. 20‰ lower than δ18O of water-soluble carbohydrates, possibly caused by discrimination against 18O during O2-based diterpene oxidation and 35%-50% oxygen atom exchange with water. Resin δ13C and δ18O recorded a strong signal of soil water potential; however, their overall capacity to infer intraseasonal environmental changes was limited by their temporal, within-tree and among-tree variations. Future studies should validate the potential isotope fractionation mechanisms associated with resin synthesis and explore the use of resin δ13C and δ18O as a long-term proxy for physiological and environmental changes.

Dynamics of Coordinated Phosphonate Group Directly Observed by 17O-NMR in Lanthanide(iii) Complexes of a Mono(ethyl phosphonate) DOTA Analogue.

Biological phosphates can coordinate metal ions and their complexes are common in living systems. Dynamics of mutual oxygen atom exchange in the tetrahedral group in complexes has not been investigated. Here, we present a direct experimental proof of exchange ("phosphonate rotation") in model Ln(III) complexes of monophosphonate H4dota analogue which alters phosphorus atom chirality of coordinated phosphonate monoester. Combination of macrocycle-based isomerism with P-based chirality leads to several diastereoisomers. (Non)-coordinated oxygen atoms were distinguished through 17O-labelled phosphonate group and their mutual exchange was followed by various NMR techniques and DFT calculations. The process is sterically demanding and occurs through bulky bidentate (κ2-PO2)- coordination and was observed only in twisted-square antiprism (TSA) diastereoisomer of large Ln(III) ions. Its energy demands increase for smaller Ln(III) ions (298ΔG≠(exp./DFT)=51.8/52.1 and 61.0/71.5 kJ mol-1 for La(III) and Eu(III), respectively). These results are helpful in design of such complexes as MRI CA and for protein paramagnetic NMR probes. It demonstrates usefulness of 17O NMR to study solution dynamics in complexes involving phosphorus acid derivatives and it may inspire use of this method to study dynamics of phosphoric acid derivatives (as e. g. phosphorus acid-based inhibitors of metalloenzymes) in different areas of chemistry.

Influence of Electrode Potential on Oxygen Mobility Probed by Polarized Isotopic Exchange in Solid Oxide Electrolyser Cells: Insights for Electro‐Assisted Oxidation Reactions

AbstractOxygen mobility was studied by oxygen isotopic exchange on three electrodes used in Solid Oxide Electrolyser Cells under polarization (La0.8Sr0.2MnO3 (LSM), La0.6Sr0.4Co0.2Fe0.8O3‐δ (LSCF) and La2NiO4+δ (LNO)). The rate of the surface and the bulk mechanisms for oxygen mobility is depending on the type of conductivity (electronic conduction or mixed ionic and electronic conductivity). It is shown that a one oxygen atom exchange is dominant for the surface path whereas a two oxygen atoms mechanism dominates for the bulk path. The rate constant for the bulk path is much higher than the one for the surface path by two orders of magnitude. Additionally, polarized oxygen isotopic exchange revealed that electrode overvoltage increases significantly the rate constant for the surface path, whereas its impact on the bulk path is negligible.

Probing oxygen exchange between UiO-66(Zr) MOF and water using 17 O solid-state NMR.

The Zr-based Metal Organic Framework (MOF) UiO-66(Zr) is widely employed owing to its good thermal and chemical stabilities. Although the long-range structure of this MOF is preserved in the presence of water during several days, little is known about the formation of defects, which cannot be detected using diffraction techniques. We apply here 17 O solid-state NMR spectroscopy at 18.8 T to investigate the reactivity of UiO-66, through the exchange of oxygen atoms between the different sites of the MOF and water. For that purpose, we have selectively enriched in 17 O isotope the carboxylate groups of UiO-66(Zr) by using it with 17 O-labeled terephthalic acid prepared using mechanochemistry. In the presence of water at 50 °C and a following dehydration at 150 °C, we observe an overall exchange of O atoms between COO- and μ3 -O2- sites. Furthermore, we demonstrate that the three distinct oxygen sites, μ3 -OH, μ3 -O2- and COO- , of UiO-66(Zr) MOF can be enriched in 17 O isotope by post-synthetic hydrothermal treatment in the presence of 17 O-enriched water. These results demonstrate the lability of Zr-O bonds and the reactivity of UiO-66(Zr) with water.

Water co-catalysis in aerobic olefin epoxidation mediated by ruthenium oxo complexes.

We report the development of a versatile Ru-porphyrin catalyst system which performs the aerobic epoxidation of aromatic and aliphatic (internal) alkenes under mild conditions, with product yields of up to 95% and turnover numbers (TON) up to 300. Water is shown to play a crucial role in the reaction, significantly increasing catalyst efficiency and substrate scope. Detailed mechanistic investigations employing both computational studies and a range of experimental techniques revealed that water activates the RuVI di-oxo complex for alkene epoxidation via hydrogen bonding, stabilises the RuIV mono-oxo intermediate, and is involved in the regeneration of the RuVI di-oxo complex leading to oxygen atom exchange. Distinct kinetics are obtained in the presence of water, and side reactions involved in catalyst deactivation have been identified.

Nanoscopic decoration of multivalent vanadium oxide on Laser-Induced graphene fibers via atomic layer deposition for flexible gel supercapacitors

Composite materials for high energy/power density supercapacitors are of very high importance. The precise well-defined nanoarchitectonics approach is a key element in the construction of high-performance devices. Surface redox reactions that frequently involve the exchange of oxygen atoms are fundamental to pseudocapacitive reactions mostly mediated by transition metal oxides (TMO). This process often changes the surface stoichiometry and atomic rearrangement in case of uncontrolled growth of TMO. Atomic layer deposition (ALD) has proven to be a facile process for smooth and uniform decoration of TMO on the electrochemically active carbon material to form a binder-free flexible composite material for supercapacitor (SC) applications. Although active carbon materials can be fabricated using various printing and lithographic techniques, continued improvement of cost and scalability, and low dimensional matrix are required to realize their full potential. Here, we demonstrate the scalable fabrication of laser-induced graphene fibers (LIGF) followed by ALD of multivalent vanadium oxide (VOx) films on the LIGF network (VOx-LIGF). The resultant VOx-LIGF shows a specific areal capacitance as high as 99 mF cm−2 at 1 mA cm−2 (aqueous solution, three-electrode cell) and 2 mF cm−2 at 0.25 mA cm−2 (gel electrolyte, two electrode cell). Moreover, the miniaturized supercapacitor device delivers a power density of 244 mW cm−3 as well as long-term cycling stability (93 % capacitance retention after 11,500 cycles) which is among the highest values achieved for any SC. Despite mechanical stress, these flexible supercapacitors maintain excellent electrochemical aspects and thus hold promise for high-power flexible and wearable electronics. Such a general, precise, well-defined, and low-cost route for atomic layer deposition-laser pulse-enhanced supercapacitor materials should find widespread applications.

Adsorption behaviors of heavy metal ions by different hydrazone-modified sodium alginate in aqueous medium: Experimental and DFT studies

Herein the hydrazone-modified sodium alginate, being prepared with aldimine condensation through dihydrazide and dialdehydes sodium alginate, possessed extremely effective and selective removal of Pb2+, Cd2+, and Cu2+. Equilibrium adsorption data of biphthalate dihydrazidemodified sodium alginate was obeyed the Freundlich isotherm and pseudo-second-order kinetics models, which reflected that the adsorption process was mainly via the chemisorption, and the maximum adsorption capacities for Pb2+, Cd2+, and Cu2+ were found to be 668.42, 472.37, and 200.10 mg g−1, respectively. The thermodynamic parameter for the sorption demonstrated the process was endothermic and spontaneous. Fourier Transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses revealed combination of chelation interactions coordination and ion exchange of nitrogen and oxygen atoms with heavy metal ions, and the density functional theory (DFT) calculations confirmed that heavy metal ions formed a stable five membered ring coordination structure with the nitrogen and oxygen atoms in hydrazone groups. Moreover, the adsorption efficiency was not significantly reduced after 10 adsorption–desorption recycles. To sum up, this study provides a new strategy for the removal of heavy metal ions by hydrazone-modified sodium alginate with great potential for wastewater treatment.

A Silicon-Stereogenic Silanol - 18 O-Isotope Labeling and Stereogenic Probe Reveals Hidden Stereospecific Water Exchange Reaction.

A silicon-stereogenic aminosilanol was isolated in excellent diastereomeric ratio and the absolute configuration was determined. The silanol is configurative and condensation stable in solution and shows stereoselective transformations with a clean stereospecific pathway in follow-up reactions, which leads to the isolation of a silicon-stereogenic zinc complex and siloxane compounds. Investigations with 18 O-labelled water and mass spectrometry analysis revealed an otherwise hidden exchange of oxygen atoms of silanol and water in solution that proceeds with retention of the configuration at the silicon center. This novel combination of a stereochemical probe and isotopic labeling in a silicon-stereogenic compound opens new analytic possibilities to study stereochemical courses of reactions with the aid of chiral silanols mechanistically.

Properties of Oxygen and their relationship to Einstein's Special Relativity Theory

Oxygen has been shown able to be released from aqueous water when the water flows through magnetic fields. Such a production process is called magneto synthesis and it is successful when the principle of induced current took place. Oxygen produced from this newly discovered process possessed properties differently when compared to the photosynthesis process. This study can be made when the magneto synthesis process was carried out closed to the saturation point of oxygen dissolution equilibrium in aqueous water. At the saturation point, the exchange of oxygen atoms or molecules between these two processes has happened. This interchange state allowed a unique single steep-drop characteristic to be observed. The single steep-drop characteristic of the magneto synthesis process provides two pieces of evidence on the properties of oxygen; they are heavier by mass and higher by oxidative power. The unique properties as discovered are supported by Einstein’s Special Relativity Theory. In this matter, gamma-ray flashes are thought to produce when the hydrogen-electron pairs are formed. A mechanism where gamma-ray flashes could be produced was proposed and sufficient evidence for gamma-ray flashes to occur was outlined. The gamma-ray flashes are the clue in the inter-permutable between the mass and energy. This is the clue to let the special relativity theory take a place.

PROPERTIES OF OXYGEN AND THEIR RELATIONSHIP TO EINSTEIN'S SPECIAL RELATIVITY THEORY

Oxygen has been shown able to be released from aqueous water when the water flows through magnetic fields. Such a production process is called magneto synthesis and it is successful when the principle of induced current took place. Oxygen produced from this newly discovered process possessed properties differently when compared to the photosynthesis process. This study can be made when the magneto synthesis process was carried out closed to the saturation point of oxygen dissolution equilibrium in aqueous water. At the saturation point, the exchange of oxygen atoms or molecules between these two processes has happened. This interchange state allowed a unique single steep-drop characteristic to be observed. The single steep-drop characteristic of the magneto synthesis process provides two pieces of evidence on the properties of oxygen; they are heavier by mass and higher by oxidative power. The unique properties as discovered are supported by Einstein’s Special Relativity Theory. In this matter, gamma-ray flashes are thought to produce when the hydrogen-electron pairs are formed. A mechanism where gamma-ray flashes could be produced was proposed and sufficient evidence for gamma-ray flashes to occur was outlined. The gamma-ray flashes are the clue in the inter-permutable between the mass and energy. This is the clue to let the special relativity theory take a place.

Geminal Diol Formation from the Interaction of a Ketone with Water in the Gas Phase: Structure and Reactivity of Cyclooctanone-(H2O)1,2 Clusters.

The hydration of ketones is known to occur in condensed phases, but it is not considered to be favorable in the gas phase due to restricted water content. We report the first evidence of geminal diol formation upon ketone hydration in the gas phase, obtained through the investigation of the interactions of cyclooctanone with water using broadband rotational spectroscopy. Oxygen-atom exchange between water and cyclooctanone was observed for two isomers of cyclooctanone-H2O and two isomers of cyclooctanone-(H2O)2. All complexes were unambiguously identified from the analysis of the rotational spectrum of the parent species and all their 13C and 18O isotopologues, and their heavy-atom substitution and effective structures were determined as well as their binding interactions. The production of gem-diols from gas-phase hydration of ketones has implications for atmospheric chemistry and opens a new channel for secondary aerosol formation.

Influence of sample volume on nitrate N and O isotope ratio analyses with the denitrifier method.

Analyses of the isotope ratios of nitrogen (15 N/14 N) and oxygen (18 O/16 O) in nitrate (NO3 - ) with the denitrifier method require relatively high sample volumes at low concentrations (≤1 μM) to afford sufficient analyte for mass spectrometry, resulting in isotopic offsets compared to more concentrated samples of the same isotopic composition. To uncover the origins of isotopic offsets, we analyzed the N and O isotope ratios of NO3 - reference materials spanning concentrations of 0.5-20 μM. We substantiated the incidence of volume-dependent isotopic offsets, then investigated whether they resulted from (a) incomplete sample recovery during N2 O sparging, (b) blanks - bacterial, atmospheric, or in reference material solutions - and (c) oxygen atom exchange with water during the bacterial conversion of NO3 - to N2 O. Larger sample volumes resulted in modest offsets in δ15 N, but substantial offsets in δ18 O. N2 O recovery from sparging was less complete at higher volumes, resulting in decreases in δ15 N and δ18 O due to associated isotope fractionation. Blanks increased detectably with volume, whereas oxygen atom exchange with water remained constant within batch analyses, being sensitive to neither sample volume nor salinity. The sizeable offsets in δ18 O with volume are only partially explained by the factors considered in our analysis. Our observations argue for bracketing of NO3 - samples with reference materials that emulate sample volumes (concentrations) to achieve improved measurement accuracy and foster inter-comparability.

Carbon Dioxide under Earth Mantle Conditions: From a Molecular Liquid through a Reactive Fluid to Polymeric Regimes.

In both its gaseous and condensed forms, carbon dioxide has an ever-increasing impact on Earth's chemistry and human life and activities. However, many aspects of its high-pressure phase diagram remain unclear. In this work, we present a complete structural characterization of carbon dioxide fluids under geological conditions using extensive ab initio molecular dynamics simulations throughout a wide pressure and temperature range, corresponding to Earth's lower mantle. We identify and describe four different disordered regimes, including two polymeric forms and two molecular ones, all within the geothermal conditions of the lower mantle. At pressures below 40 GPa, we find that the molecular liquid becomes very reactive above 2000 K: the C-O double bond routinely breaks, resulting in small and transient chains composed of CO2 units and frequently leading to an exchange of oxygen atoms between molecules. At higher pressures, in addition to the polymeric fluid previously reported at 3000 K, we find a polymeric system with glass-like behavior at lower temperatures, suggesting a complex interplay between kinetics and stability.

The C(3P) + O2(3Σg-) → CO2 ↔ CO(1Σ+) + O(1D)/O(3P) reaction: thermal and vibrational relaxation rates from 15 K to 20 000 K.

Thermal rates for the C(3P) + O2(3Σg−) ↔ CO(1Σ+)+ O(1D)/O(3P) reaction are investigated over a wide temperature range based on quasi classical trajectory (QCT) simulations on 3-dimensional, reactive potential energy surfaces (PESs) for the 1A′, (2)1A′, 1A′′, 3A′ and 3A′′ states. These five states are the energetically low-lying states of CO2 and their PESs are computed at the MRCISD+Q/aug-cc-pVTZ level of theory using a state-average CASSCF reference wave function. Analysis of the different electronic states for the CO2 → CO + O dissociation channel rationalizes the topography of this region of the PESs. The forward rates from QCT simulations match measurements between 15 K and 295 K whereas the equilibrium constant determined from the forward and reverse rates is consistent with that derived from statistical mechanics at high temperature. Vibrational relaxation, O + CO(ν = 1,2) → O + CO(ν = 0), is found to involve both, non-reactive and reactive processes. The contact time required for vibrational relaxation to take place is τ ≥ 150 fs for non-reacting and τ ≥ 330 fs for reacting (oxygen atom exchange) trajectories and the two processes are shown to probe different parts of the global potential energy surface. In agreement with experiments, low collision energy reactions for the C(3P) + O2(3Σg−, ν = 0) → CO(1Σ+) + O(1D) lead to CO(1Σ+, ν′ = 17) with an onset at Ec ∼ 0.15 eV, dominated by the 1A′ surface with contributions from the 3A′ surface. Finally, the barrier for the COA(1Σ+) + OB(3P) → COB(1Σ+) + OA(3P) atom exchange reaction on the 3A′ PES yields a barrier of ∼7 kcal mol−1 (0.300 eV), consistent with an experimentally reported value of 6.9 kcal mol−1 (0.299 eV).

Surface reducibility, reactivity, and stability induced by noble metal modifications on the γ-Fe2O3 maghemite (001) surfaces

In these last years large research efforts have been devoted to the synthesis and investigation of reducible metal oxide surfaces modified with metal atoms and nanoparticles for improving their performance in a number of advanced applications. Among reducible metal oxides, iron oxides have the advantage to be made up from two of the most common elements on Earth. In this paper we analyze the structural, electronic, and magnetic consequences of the insertion of isolated noble metal atoms (Cu, Ag, Au) on the γ-Fe2O3 (001) surface. We have considered many different configurations for the single atoms: adsorbed, substitutional to iron atoms, or to oxygen atoms, and, using first principles calculations, we have studied how the presence of the noble metal atoms on the surface influences the surface stability, its reducibility, and, therefore, its catalytic activity, and how these properties depend on the kind of noble metal atom and its position. Our results show that noble metal atoms adsorbed on the surface facilitate the adsorption of CO molecules, and, among them, Cu atoms are those that bind best to the surface also providing the strongest adsorption energy for the CO molecule. At ambient temperature and pressure the noble metal atoms prefer to substitute the iron atoms than to just adsorb on the surface, but for Ag atoms the adsorption and substitutional energies are very close. The surfaces with Ag in place of Fe are the most reducible and reactive for exchange of oxygen atoms. Finally, Au is the best noble metal for oxygen substitution. Our results provide useful insights for the researchers designing and synthesizing new noble metal—iron oxides nanostructures for applications in biology, medicine, catalysis, and chemical analysis.

Lattice Oxygen Exchange in Rutile IrO2 during the Oxygen Evolution Reaction.

The development of efficient acidic water electrolyzers relies on understanding dynamic changes of the Ir-based catalytic surfaces during the oxygen evolution reaction (OER). Such changes include degradation, oxidation, and amorphization processes, each of which somehow affects the material’s catalytic performance and durability. Some mechanisms involve the release of oxygen atoms from the oxide’s lattice, the extent of which is determined by the structure of the catalyst. While the stability of hydrous Ir oxides suffers from the active participation of lattice oxygen atoms in the OER, rutile IrO2 is more stable and the lattice oxygen involvement is still under debate due to the insufficient sensitivity of commonly used online electrochemical mass spectrometry. Here, we revisit the case of rutile IrO2 at the atomic scale by a combination of isotope labeling and atom probe tomography and reveal the exchange of oxygen atoms between the oxide lattice and water. Our approach enables direct visualization of the electrochemically active volume of the catalysts and allows for the estimation of an oxygen exchange rate during the OER that is discussed in view of surface restructuring and subsequent degradation. Our work presents an unprecedented opportunity to quantitatively assess the exchange of surface species during an electrochemical reaction, relevant for the optimization of the long-term stability of catalytic systems.

General electron theory of reduction and oxidation of metals

The significance of the new theory of metal reduction from ores has been demonstrated. It was shown that all the existing versions of the theory are based on atomic-molecular representations of the early 20-th century where reduction is considered as a process of exchange of oxygen atoms between a reducing agent and oxide molecules. These representations do not take into account changes in the crystalline structure of oxides and in the state of a gas medium with change in temperature and pressure. The attention here was drawn to the absence of molecules in oxides, and atoms in metals. Inconsistency of a number of the theory conclusions with practice of reduction during operation of plants was revealed. Based on the assumptions of redox reactions as processes of exchange of reagents by the valence electrons, defective ionic structure of real crystals, changes in the state of the gaseous medium during heating and pressure increase using some statements of quantum mechanics on the distribution of electrons in solids, the authors have developed electron version of the reduction theory. This theory is based on the unity of the anionic sublattice of all crystals of the oxide phase and the collective electronic system of all valence electrons of metal cations in oxide. It is shown that in the reduction plants, due to the thermal ionization of gases and thermionic emission from the surface of the heated bodies, the gas medium is plasma. The presence of charged particles in the plasma ensures their interaction at a considerable distance and the course of chemical processes in the kinetic mode. The gaseous reduction products are removed from the reaction zone with exhaust gases, and the electrons released in the plasma are absorbed by the oxide surface and exist in the oxide together with the anionic vacancies that arise when oxygen is removed. In high-grade ores the vacancies merge and disappear on the oxide surface, and the free electrons of the vacancies combine the nearest cations with a metal bond to form a metal shell which later turns into carbides. The formation of carbide shells blocks the oxide surface and stops reduction. When temperature rises and the shells melt the reduction process resumes. Therefore, the carbon-thermal reduction produces cast iron and high-carbon ferroalloys. In low-grade and complex ores the vacancies are scattered in the oxide volume along the total anionic sublattice forming solution of vacancies and free electrons. The vacancies merge and disappear in places of increased concentration of cations where the Fermi level of atoms is less than the chemical potential of the free electrons. In the formed anionic void the free electrons rearrange metal cations with low Fermi energy and bind them with a metal bond bypassing the stage of atom formation. Crystal growth in an anionic void occurs without resistance from the parent oxide phase.

Mechanism of self-propagating hightemperature synthesis of AlB<sub>2</sub>‒Al<sub>2</sub>O<sub>3</sub>

The mechanism of self-propagating high-temperature synthesis (SHS) of AlB2‒Al2O3 composite powders was studied by means of a combustion front quenching method (CFQM). The results showed that combustion reaction started with the melting of B2O3 and Al particles. As the combustion reaction proceeded, the interpenetration of Al and B2O3 in melts happened. The XRD results of the product revealed the reflections of Al2O3, suggesting there had been an exchange of oxygen atoms between Al and B, and evidencing the reaction, B2O3 (l) + 2Al (l) → 2B (s) + Al2O3 (l). Under higher temperature, some of B2O3 volatilized and reacted with B forming gaseous B2O2, which deposited on the surface of Al to precipitate Al2O3 and B. Then B made available dissolved into Al melt, and reacted with the Al in melt to precipitate AlB12 particles. Finally, AlB12 transforms to AlB2 at the peritectic temperature under high cooling rate. Thus, this combustion reaction can be described by the dissolution-precipitation mechanism. In the final products, besides AlB2 and Al2O3 particles, some of Al was also detected. A model corresponding to the dissolutionprecipitation mechanism was proposed, and the ignition temperature of the combustion reaction was determined to be around 800 °C. Ill. 13. Ref. 47.

Atmospherically relevant acrolein-water complexes: spectroscopic evidence of aldehyde hydration and oxygen atom exchange.

Direct spectroscopic evidence of a reaction occurring between acrolein and water and involving the exchange of an oxygen atom has been obtained by characterizing the non-covalently bound water complexes and their isotopic forms, via rotational spectroscopy. The experimental geometries of the binary and ternary water complexes have been determined, and other stationary points on the reaction path have been characterized using ab initio quantum chemical methods at the MP2/6-311++G(d,p) level. These results can enhance the understanding of the water-mediated atmospherically important reactions involving acrolein.