Rate Of Decarboxylation Research Articles

Comparison of decarboxylation rates of acidic cannabinoids between secretory cavity contents and air-dried inflorescence extracts in Cannabis sativa cv. ‘Cherry Wine’

Studies with secretory cavity contents and air-dried inflorescence extracts of the CBD-rich hemp strain, Cannabis sativa cv. ‘Cherry Wine’, were conducted to compare the decarboxylation rates of acidic cannabinoids between two groups. The secretory cavity contents acquired from the capitate-stalked glandular trichomes by glass microcapillaries, and inflorescence samples air-dried for 15 days of storage in darkness at room temperature were analysed by high-pressure liquid chromatography. The ratio of acidic cannabinoids to the total cannabinoids was ranging from 0.5% to 2.4% lower in the air-dried inflorescence samples compared to the secretory cavity samples as follows. In the secretory cavity content, the percentage of acidic cannabinoids to the total cannabinoids was measured as 86.4% cannabidiolic acid (CBDA), 6.5% tetrahydrocannabinolic acid (THCA), 4.3% cannabichromenic acid (CBCA), 1.4% cannabigerolic acid (CBGA), and 0.6% cannabidivarinic acid (CBDVA), respectively. In the air-dried inflorescence, however, the acidic cannabinoids were detected with 84% CBDA, 4.8% THCA, 3.3% CBCA, 0.8% CBGA, and 0.3% Δ9-tetrahydrocannabivarinic acid (Δ9-THCVA), respectively. The ratio of cannabidiol (CBD) to cannabidiolic acid (CBDA) was close to 1:99 (w/w) in secretory cavity contents, however, it was roughly 1:20 (w/w) in the air-dried inflorescence. In addition, Δ9-tetrahydrocannabivarin (Δ9-THCV) and Δ9-tetrahydrocannabivarinic acid (Δ9-THCVA) were only detected in the air-dried inflorescence sample, and the ratio of Δ9-THCV to Δ9-THCVA was about 1:20 (w/w). Besides, cannabidivarinic acid (CBDVA) was only observed in the secretory cavity content.

Effect of short-term storage on cannabinoid content of dried floral hemp (Cannabis sativa L) inflorescence

Floral hemp, a plant rich in cannabinoids, has gained attention for its potential therapeutic properties. It is crucial to have proper storage conditions that will maintain the cannabinoid content. To the best of our knowledge, very little has been done on the storage conditions of dried floral hemp. Hence, this study investigated the effect of storage conditions like moisture content, temperature, storage time, light exposure, and packaging materials, on cannabinoid stability in dried floral hemp. The cultivar ‘Quick Spectrum’ at two moisture levels (8.5 and 4.5 %) was stored over a 6-month storage period. Results indicated that a higher amount of cannabinoids samples was retained at 8.5 ± 1 % moisture compared to samples at 4.5 ± 0.5 %, even though total CBD, total ∆9-THC, and total CBDV content remained statistically the same throughout the storage period, and was not affected by temperature, lighting, and packaging material. In contrast, certain individual cannabinoids, such as CBDVA, CBD, ∆9-THCA, and ∆9-THC were significantly affected by temperature and lighting. Notably, higher storage temperatures (22 °C) and light exposure (F15T8/F5 fluorescent light) increased the degradation and decarboxylation rate of cannabinoids. These findings showed the importance of optimized storage conditions for floral hemp, especially long-term storage. This will help provide standardized storage protocols to aid producers, testing laboratories, distributors, and consumers in making informed decisions about storage practices and advancing quality control in the hemp industry.

Interlaboratory validation and one-year retrospective review of hemp and marijuana decision-point assays

After the passage of the Agriculture Improvement Act of 2018 (Farm Bill) that defined hemp as Cannabis sativa L. if it contained ≤0.3 % Δ9-THC on a dry weight basis, forensic laboratories were faced with the challenge of distinguishing marijuana from hemp in seized drug samples. This study reports the results of an interlaboratory validation of a previously developed qualitative decision-point assay for the differentiation of illegal marijuana from legal hemp, utilizing gas chromatography-mass spectrometry (GC–MS) with a 1 % Δ9-THC threshold. The method was validated in terms of selectivity, linearity, carryover, precision, accuracy, extract stability, dilution integrity, and measurement uncertainty. Other elements such as decarboxylation rate and potential for CBD interference were also evaluated. Specificity and positive predictive value were both 100 % using known cannabis reference materials. A total of 8 false negative results were observed among the 280 analyses, resulting in an overall assay sensitivity of 94 % and a negative predictive value of 95 %. The small number of false negative results near the 1 % threshold were attributed to decarboxylation inefficiency in some laboratories. While qualitative in nature, the measurement uncertainty of the assay at the 0.3 % Δ9-THC cutoff (legal threshold) using a 95.45 % confidence interval (k = 2) ranged from 12.2 % to 21.8 % among laboratories (equivalent to 0.3 % ± 0.04 % to 0.07 % Δ9-THC by weight). A one-year retrospective study across three agencies and fifteen laboratories was undertaken. Among the three agencies participating in the original study, 93–96 % of all suspected cannabis seizures yielded results above the administrative threshold of 1 % Δ9-THC (n = 3,288). The interlaboratory method development highlighted differences in performance between sites, ultimately improving the overall robustness of the method. Observations highlight the need for site-specific validation and vigilance. While multi-agency collaborations and interlaboratory validations are valuable, they do not replace the necessity for full, independent, and rigorous validation.

Computational study of the solvation effect of supercritical water on o-phthalic acid decarboxylation by varying the solvent dielectric constant

This study investigates the solvation effect on the decarboxylation of o-phthalic acid using quantum calculations with a continuum solvation model with varying dielectric constants. Two mechanisms were considered: with and without a catalytic water molecule. The latter had a lower reaction barrier. Increasing the dielectric constant facilitates the hydrogen transfer but impedes C–C bond breaking in both mechanisms. The change in the free energies due to solvation of the transition state is generally greater than the reactant. The reaction barrier predominantly increased with the dielectric constant in both mechanisms. The Kirkwood slope estimated by plotting estimated rate constants against the Kirkwood polarity parameter, (ε−1)/(2ε+1), was close to the experimental value (only for the assisted mechanism). The simulations indicate that the solvation effect on the decarboxylation rate can be elucidated by considering the effect of dielectric constant of supercritical water.

Computational insights into the binding modes, keto-enol tautomerization and stereo-electronically controlled decarboxylation of oxaloacetate in the active site of macrophomate synthase.

Oxaloacetic acid (OAA) is a β-ketocarboxylic acid, which plays an important role as an intermediate in some metabolic pathways, including the tricarboxylic acid cycle, gluconeogenesis and fatty acid biosynthesis. Animal studies have indicated that supplementing oxaloacetic acid shows an increase of lifespan and other substantial health benefits including mitochondrial DNA protection, and protection of retinal, neural and pancreatic tissues. Most of the chemical transformations of OAA in the metabolic pathways have been extensively studied; however, the understanding of decarboxylation of OAA at the atomic level is relatively lacking. Here, we carried out MD simulations and combined quantum mechanical/molecular mechanical (QM/MM) calculations as an example to systematically elucidate the binding modes, keto-enol tautomerization and decarboxylation of OAA in the active site of macrophomate synthase (MPS), which is a Mg(II)-dependent bifunctional enzyme that catalyzes both the decarboxylation of OAA and [4+2] cycloaddition of 2-pyrone with the decarboxylated intermediate of OAA (pyruvate enolate). On the basis of our calculations, it was found that the Mg2+-coordinated oxaloacetate may exist in enol forms and keto forms. The four keto forms can be transformed into each other by simply rotating the C2-C3 single bond, nevertheless, the keto-enol tautomerization strictly requires the assistance of pocket water molecules. In addition, the decarboxylation is stereo-electronically controlled, i.e., it is the relative orientation of the terminal carboxyl anion that determines the rate of decarboxylation. As such, the chemistry of oxaloacetate in the active site of MPS is complex. On one hand, the most stable binding mode (K-I) may undergo enol-keto tautomerization to isomerize to the enol form, which may further react with the second substrate; on the other hand, K-I may isomerize to another binding mode K-II to proceed decarboxylation to generate pyruvate enolate and CO2. Starting from K-I, the enol-keto tautomerization corresponds to a barrier of 16.2 kcal mol-1, whereas the decarboxylation is associated with an overall barrier of 19.7 kcal mol-1. These findings may provide useful information for understanding the chemistry of OAA and the catalysis of related enzymes, and they are basically in agreement with the available experimental kinetic data.

Factors influencing the in situ formation of Δ9-THC from cannabidiol during GC-MS analysis.

Gas chromatography-mass spectrometry (GC-MS) is widely used for the identification of cannabinoids in seized plant material. Conditions used for instrumental analysis should maximize decarboxylation, while minimizing the in situ production of Δ9-THC inside the GC inlet. In this study, decarboxylation of the acidic Δ9-THC precursor and in situ degradation of cannabidiol (CBD) were investigated using seven commercial GC liners with different deactivation chemistries and geometries. While the inlet temperature was previously optimized at 250°C in a previously validated assay, we systematically examined the temperature-dependent decarboxylation of tetrahydrocannabinolic acid-A (Δ9-THCA-A) and cyclization of CBD between 230°C and 310°C using different liners using favorable and unfavorable conditions. Significant differences in decarboxylation rate and CBD cyclization were observed between different liner types. While no temperature-dependent differences in decarboxylation rate were observed within liner type, liner-dependent differences were observed (α =0.05), particularly between those with different geometry. In contrast, temperature and liner-dependent differences were observed for in situ formation of Δ9-THC (α =0.05). This was influenced by liner geometry and to a smaller extent by surface deactivation. Effects were exacerbated with liner usage. While significant differences were observed using new and used GC liners, differences between liners of the same type but different lot numbers were not observed. Inter-instrument differences using the same liner were also evaluated and had minimal effect. Liner- and temperature-dependent effects were also confirmed using more than 20 cannabis plant extracts. Careful selection of liner, inlet conditions, and regular preventive maintenance can mitigate the risks associated with in situ formation Δ9-THC from CBD.

Palladium hydride promotion by KHCO3 enhances the decarboxylation rate

Direct conversion of carboxylic acids to alkanes by decarboxylation on PdHx is an effective way to defunctionalize biomass-derived feedstocks. This catalytic decarboxylation generally suffers from low activity and selectivity loss by competing hydrogenation routes. Anchoring the carboxylate group with K+ on PdHx/C increases the rate of decarboxylation by more than one order of magnitude. Temperature-programmed desorption of CO2 shows that the modification increases the surface basicity. In turn, this induces dissociative adsorption of the acid carboxylic group. The resulting adsorption as carboxylate facilitates the C–C bond cleavage by weakening the bond adjacent to the carboxyl group.

Impact of sunlight irradiation on CvFAP photodecarboxylation

A visible-light-driven photocatalytic decarboxylation of palmitic acid and related fatty acids is described in this study. Remarkable decarboxylation rates have been observed with full conversion in less than 20 min. In this study, we have demonstrated that sunlight irradiation, even on cloudy days, can deliver similar results to traditional LED lamps while using much less energy and minimizing environmental impact. The findings indicate that the process of enzymatic decarboxylation could be useful for the production of different biofuels in the future.

Stepwise generation of spin-polarized radicals and their reactions in the photolysis of an oxime ester compound as studied by pulsed EPR spectroscopy

To generate spin-polarized free radicals, the photolysis of 1,2-octane-dione, 1-[4-(phenylthio)-2-(o-benzoyloxime)] (OXE01) was investigated using time-resolved electron paramagnetic resonance (TR-EPR) and pulsed EPR. This photolysis proceeds through α-cleavage of the N-O bond of OXE01 to yield iminyl and benzoyloxy radicals, the latter of which is converted to a phenyl radical by decarboxylation. The phenyl radical promptly abstracts hydrogen atoms from the surrounding solvent molecules to produce a solvent dehydrogenated radical (solvent radical). The spin polarization created in the initial OXE01 triplet excited state was preserved during these series of reactions, which enhanced EPR sensitivity. This enabled us to observe the TR-EPR spectra of the intermediate free radicals, except phenyl. The decarboxylation rate of the benzoyloxy radical was measured in various solvents by probing the free induction decay signal of the product solvent radicals using pulsed EPR. This new method for preparing free radicals with spin-polarization was applied to determine the addition reaction rate constants of the cyclohexyl radical, a solvent radical, to olefins using pulsed EPR monitoring of the electron spin echo signals of the radical.

Selective Cross‐Ketonization of Carboxylic Acids Enabled by Metallaphotoredox Catalysis

AbstractCarboxylic acids are attractive building blocks for synthetic chemistry because they are chemically stable, abundant, and commercially available with substantial structural diversity. The process of combining two carboxylic acids to furnish a ketone is termed ketonization. This is a potentially valuable transformation that has been underutilized in organic synthesis due to the harsh reaction conditions generally required and the lack of selectivity obtained when coupling two distinct carboxylic acids. We report herein a metallaphotoredox strategy that selectively generates unsymmetrical ketones via cross‐ketonization of two structurally dissimilar carboxylic acids. Cross‐selectivity is achieved by exploiting divergent reactivity of differentially substituted acids towards critical one‐ and two‐electron processes in the proposed coupling mechanism. This method is broadly applicable to a variety of functionalized carboxylic acids. It can also be applied to acids of similar steric profile by exploiting differences in their relative rates of decarboxylation.

Selective Cross-Ketonization of Carboxylic Acids Enabled by Metallaphotoredox Catalysis.

Carboxylic acids are attractive building blocks for synthetic chemistry because they are chemically stable, abundant, and commercially available with substantial structural diversity. The process of combining two carboxylic acids to furnish a ketone is termed ketonization. This is a potentially valuable transformation that has been underutilized in organic synthesis due to the harsh reaction conditions generally required and the lack of selectivity obtained when coupling two distinct carboxylic acids. We report herein a metallaphotoredox strategy that selectively generates unsymmetrical ketones via cross-ketonization of two structurally dissimilar carboxylic acids. Cross-selectivity is achieved by exploiting divergent reactivity of differentially substituted acids towards critical one- and two-electron processes in the proposed coupling mechanism. This method is broadly applicable to a variety of functionalized carboxylic acids. It can also be applied to acids of similar steric profile by exploiting differences in their relative rates of decarboxylation.

Fuel properties and combustion performance of hydrochars prepared by hydrothermal carbonization of different recycling paper mill wastes

AbstractThe incineration of high‐moisture solid residues generated at the recycling paper mills represents an energetically unfavourable method of resource utilization. Alternatively, hydrothermal pre‐treatment is considered. In this study, low‐value paper sludges from three different recycling streams were hydrothermally carbonized at 205, 225, and 245°C for 3 h. The raw feedstocks and derived hydrochars were analyzed for energy properties, chemical characteristics, surface morphology, functional groups, and combustion performance employing energy densification and mass yield quantification, scanning electron microscopy, elemental analyzer, Fourier‐transform infrared spectroscopy, and thermogravimetry. The increase in reaction temperature was reported to cause a decrease in mass yield and an increase in energy densification and calorific values corresponding to 5.98%–49.35% and 10.10%–58.51% for raw fibre rejects and final sludge‐derived hydrochar, respectively. Hydrothermal carbonization (HTC) had a non‐significant influence on the energy densification of primary clarifier sludge‐derived hydrochar. Higher reaction temperatures favoured the rate of dehydration and decarboxylation, leading to hydrochars with lower H/C and O/C ratios, thereby enhancing the overall fuel properties. The low‐nitrogen and low‐sulphur fuels obtained validated the effectiveness of HTC treatment to produce high‐quality cleaner solid fuel. The burnout temperature was mostly reduced with an increase in HTC temperature. At HTC‐205 and 225°C, the ignition temperature and the combustion performance increased as a result of the HTC reaction mechanisms. HTC effectively recovered hydrochar with increased carbon content, improved energy densification, and good combustion adequacy. Hydrochar derived from recycling mills may play a role in the energy sector as a substitute for coal or in co‐combustion at coal‐fired power plants.

Complete mechanochemical defluorination of perfluorooctanoic acid using Al2O3 and Al powders through matching electron-mediated reduction with decarboxylation

This work reports a mechanochemical (MC) method for complete defluorination of perfluorooctanoic acid (PFOA) by using Al and Al2O3 as milling agents. Both the Al/Al2O3 molar ratio (nAl/nAl2O3) and the pre-thermal treatment of Al2O3 strongly influenced the defluorination of PFOA. When commercial γ-Al2O3 was pre-treated at 1200 °C, the use of Al and heat-treated γ-Al2O3 with nAl/nAl2O3 of 1: 1 led to PFOA defluorination of 100% after ball milling for 26 min at 350 rpm, being much higher than those (8.3%–58.1%) for using singlet milling agents or binary milling agents containing γ-Al2O3 pre-heated at temperatures lower than 700 °C. It was clarified that the carboxylate-mediated adsorption of PFOA on Al2O3 was essential for the MC decarboxylation as a degradation initiation step, and the in-situ generated electron on milled Al consequently caused the reductive dissociation of C–F bonds in the decarboxylation intermediate. A larger nAl/nAl2O3 increased the in-situ electron generation rate (re), and a higher heat-treatment temperature decreased OH−/H2O adsorbed on Al2O3 to low the PFOA decarboxylation rate (rdec). The re/rdec ratio determined defluorination pathways, and the percentage of the defluorination of PFOA in its total degradation including the generation of any degradation intermediates increased linearly with increasing re/rdec.

On the rate of phytoplankton respiration in the light

The rate of algal and cyanobacterial respiration in the light is an important ecophysiological term that remains to be completely characterized and quantified. To address this issue, we exploited process-specific decarboxylation rates from flux balance analysis and isotopically nonstationary metabolic flux analysis. Our study, based on published data, suggested that decarboxylation is about 22% of net CO2 assimilation when the tricarboxylic acid cycle is completely open (characterized by the commitment of alpha ketoglutarate to amino acid synthesis and very low rates of succinate formation). This estimate was supported by calculating the decarboxylation rates required to synthesize the major components of biomass (proteins, lipids, and carbohydrates) at their typical abundance. Of the 22 CO2 molecules produced by decarboxylation (normalized to net assimilation = 100), approximately 13 were from pyruvate and 3 were from isocitrate. The remaining six units of decarboxylation were in the amino acid synthesis pathways outside the tricarboxylic acid cycle. A small additional flux came from photorespiration, decarboxylations of six phosphogluconate in the oxidative pentose phosphate pathway, and decarboxylations in the syntheses of lower-abundance compounds, including pigments and ribonucleic acids. This general approach accounted for the high decarboxylation rates in algae and cyanobacteria compared to terrestrial plants. It prompts a simple speculation for the origin of the Kok effect and helps constrain the photoautotrophic respiration rate, in the light, in the euphotic zone of the ocean and lakes.

Catalase protects against nonenzymatic decarboxylations during photorespiration in Arabidopsis thaliana.

Photorespiration recovers carbon that would be otherwise lost following the oxygenation reaction of rubisco and production of glycolate. Photorespiration is essential in plants and recycles glycolate into usable metabolic products through reactions spanning the chloroplast, mitochondrion, and peroxisome. Catalase in peroxisomes plays an important role in this process by disproportionating H2O2 resulting from glycolate oxidation into O2 and water. We hypothesize that catalase in the peroxisome also protects against nonenzymatic decarboxylations between hydrogen peroxide and photorespiratory intermediates (glyoxylate and/or hydroxypyruvate). We test this hypothesis by detailed gas exchange and biochemical analysis of Arabidopsis thaliana mutants lacking peroxisomal catalase. Our results strongly support this hypothesis, with catalase mutants showing gas exchange evidence for an increased stoichiometry of CO2 release from photorespiration, specifically an increase in the CO2 compensation point, a photorespiratory‐dependent decrease in the quantum efficiency of CO2 assimilation, increase in the 12CO2 released in a 13CO2 background, and an increase in the postillumination CO2 burst. Further metabolic evidence suggests this excess CO2 release occurred via the nonenzymatic decarboxylation of hydroxypyruvate. Specifically, the catalase mutant showed an accumulation of photorespiratory intermediates during a transient increase in rubisco oxygenation consistent with this hypothesis. Additionally, end products of alternative hypotheses explaining this excess release were similar between wild type and catalase mutants. Furthermore, the calculated rate of hydroxypyruvate decarboxylation in catalase mutant is much higher than that of glyoxylate decarboxylation. This work provides evidence that these nonenzymatic decarboxylation reactions, predominately hydroxypyruvate decarboxylation, can occur in vivo when photorespiratory metabolism is genetically disrupted.

Dopaminergic Activity in Antipsychotic-Naïve Patients Assessed With Positron Emission Tomography Before and After Partial Dopamine D2 Receptor Agonist Treatment: Association With Psychotic Symptoms and Treatment Response

BackgroundDopamine activity has been associated with the response to antipsychotic treatment. Our study used a four-parameter model to test the association between the striatal decarboxylation rate of 18F-DOPA to 18F-dopamine (k3) and the effect of treatment on psychotic symptoms in antipsychotic-naïve patients with first-episode psychosis. We further explored the effect of treatment with a partial dopamine D2 receptor agonist (aripiprazole) on k3 and dopamine synthesis capacity (DSC) determined by the four-parameter model and by the conventional tissue reference method. MethodsSixty-two individuals (31 patients and 31 control subjects) underwent 18F-DOPA positron emission tomography at baseline, and 15 patients were re-examined after 6 weeks. Clinical re-examinations were completed after 6 weeks (n = 28) and 6 months (n = 15). Symptoms were evaluated with the Positive and Negative Syndrome Scale. ResultsHigh baseline decarboxylation rates (k3) were associated with more positive symptoms at baseline (p < .001) and with symptom improvement after 6 weeks (p = .006). Subregion analyses showed that baseline k3 for the putamen (p = .003) and nucleus accumbens (p = .013) and DSC values for the nucleus accumbens (p = .003) were associated with psychotic symptoms. The tissue reference method yielded no associations between DSC and symptoms or symptom improvement. Neither method revealed any effects of group or treatment on average magnitudes of k3 or DSC, whereas changes in dopamine synthesis were correlated with higher baseline values, implying a potential effect of treatment. ConclusionsStriatal decarboxylation rate at baseline was associated with psychotic symptoms and treatment response. The strong association between k3 and treatment effect potentially implicate on new treatment strategies.

Pharmacokinetic Modeling of 18F-FDOPA PET in the Human Brain for Early Parkinson's Disease

Objectives:Early detection is essential for the treatment approaches of Parkinson’s disease (PD). Clinical criteria alone may be insufficient to distinguish early PD from other conditions. This study aimed to investigate the transfer rate constants of 6-18F-fluoro-L-dopa (18F-FDOPA) in positron emission tomography (PET) brain images as a sensitive parameter to detect early PD.Methods:Retrospective 18F-FDOPA PET data of five patients with early PD were collected. PET data were acquired for 90 min after intravenous injection of 306-379 MBq 18F-FDOPA, and reconstructed into a series of 18 five-minute frames. Reoriented PET images were coregistered and normalized with the PET brain template on the statistical parametric mapping. The 18F-FDOPA activity concentrations were measured in the striatum, caudate, and putamen on both sides: Contralateral (as PD) and ipsilateral (as control) to the main motor symptoms. The pharmacokinetic model was generated using the SAAM II simulation software. The transfer rate constants across the blood-brain barrier (forward, K1 and reverse, k2) and decarboxylation rate constants (k3) were estimated in these regions.Results:The activity uptakes in the contralateral striatum (0.0323%±0.0091%) and putamen (0.0169%±0.0054%) were significantly lower than the control (0.0353%±0.0086%, 0.0199%±0.0054%, respectively). The K1 and k3 were significantly lower in the contralateral striatum and putamen (p<0.05). There were no significant differences in any transfer rate constants in the caudate.Conclusion:The transfer rate constants (K1 and k3) of 18F-FDOPA on the contralateral striatum and putamen were significantly lower than the control. These biokinetic data could be potential indicators for quantitative detection of early PD diagnosis.

Contributions of acidic-basic sites on hybridized FER@g-C3N4 for liquid-phase decarboxylation of naphthenic acids

The efficient removal method of acidic and corrosive organic naphthenic acids (NAs) in heavy crude oils such as benzoic acid as a model acidic component was investigated for a liquid-phase decarboxylation reaction. A novel hybridized heterogeneous basic graphitic carbon nitride (g-C3N4) coated on the acidic ferrierite (H-FER) zeolite (denoted as FER@CN) was newly proposed as one of the efficient heterogeneous hybridized catalysts. The basic g-C3N4 selectively promoted the absorption of the acidic NAs by acid-base neutralization reaction, and the acidic H-FER effectively enhanced decarboxylation rate by generating CO2. The synergy effects of the hybrid FER@CN were maximized at an optimal g-C3N4/FER weight ratio of 0.5 by enhancing the number of the moderate strength acidic and total basic sites simultaneously. The promoting effects between acidic and basic sites on the FER@CN were mainly attributed to a higher dispersion of g-C3N4 nanoparticles on the H-FER surfaces, which was responsible for a higher decarboxylation activity with larger reduction of total acid number (TAN) with the help of the larger amount of moderate strength acidic and basic sites.

Effect of Ammonium Salts on the Decarboxylation of Oxaloacetic Acid in Atmospheric Particles

Oxaloacetic acid (OAA) is a 3-oxocarboxylic acid formed from the oxidation of succinic acid. OAA and other 3-oxocarboxylic acids experience a decarboxylation reaction in aqueous solutions, which can be catalyzed by ammonium and amines. This catalysis has not been studied under atmospherically relevant conditions despite previous interest in OAA in the atmosphere. To address this, 1 mM solutions of OAA were prepared with varying concentrations of ammonium sulfate, ammonium bisulfate, ammonium chloride, and sodium sulfate to simulate various atmospheric conditions. The extent of the decarboxylation was monitored using UV–visible absorption spectroscopy. OAA’s uncatalyzed decarboxylation lifetime was around 5 h. Under moderately acidic conditions representative of aerosol particles (pH = 3–4), the decarboxylation rate increased linearly with ammonium concentration up to about 2.7 M, after which additional ammonium had no effect. The effective lifetime of OAA reduced to approximately 1 h under these conditions. Density functional theory calculations support the proposed catalytic mechanism, predicting the free energy barrier height for decarboxylation to be approximately 21 kcal/mol lower after OAA has reacted with ammonium. In more acidic solutions (pH < 1), OAA’s decarboxylation was suppressed, with lifetimes of tens of hours, even in the presence of ammonium. A comparison of the decarboxylation rate with the expected rate of oxidation by OH suggests that decarboxylation will be the dominant loss mechanism for OAA, and presumably other 3-oxocarboxylic acids, in aerosol particles and cloud/fog droplets. This result explains why OAA is hard to detect in field measurements even though it is a known oxidation product of succinic acid.

Modeling the transformation of І and ІІІ types kerogen by the method of entropy maximization

Purpose, methods and research methodology. The aim of the work is to calculate and compare the trends of transformation of organic matter of I-A and III-A type kerogen, which is in contact with organic and inorganic gases in the process of immersion of organ-containing rocks. The calculations were performed for I and III type kerogen and a mixture of organic and inorganic gases within depths of 1-20 km and heat flows from 40 to 100 mW / m2. Results, scientific novelty and practical significance of research. A comparison and analysis of changes in the total entropy of the system was performed for I and III type kerogen, which showed the complex nature of the total entropy functional dependence on depth. It was revealed that the entropy has two reversible sections, the maxima of which are at a depth of 6 and 12 km. The analysis of changes in the Gibbs energy during the immersion of the geochemical system unambiguously indicates the presence of a stability zone for the hydrocarbon component. The maximum of this zone corresponds to the minimum value of the Gibbs energy, depends on the kerogen type and heat flow, is in the range of 4-7 km and indicates the area of stability, or "oil window". The complex nature of the balance between constitutional water and kerogen, depending on the heat flow and depth, has been established. To analyze this equilibrium, a simple dehydration equilibrium constant (Kd) was proposed, which generalizes the transformations of water in the kerogen matrix. Thermodynamic methods were used to calculate and compare the gas-generating capacity of I and III type kerogen for all heat flows, which showed that I type kerogen is the most productive with gas-generating potential, and III type is the least productive. To estimate the proportional composition of hydrocarbon gases in equilibrium with kerogen, the fat content coefficient of the gas generated by I and III type kerogen was calculated. It is shown that with immersion, the fat content coefficient first increases rapidly, which indicates an increase in the proportional content of alkanes heavier than methane. This growth reaches a maximum within 2-3 km for all considered heat flows, after which the fat content coefficient decreases. The equilibrium constant of the Kolbe-Schmitt reaction is calculated, which showed that regardless of the heat flow, the rate of kerosene decarboxylation decreases with increasing depth due to the shift of equilibrium to the left, and the contribution of this reaction to kerogen conversion is insignificant.