Gibbs Free Energy Research Articles

Thermodynamics of AdS-Schwarzschild-like black hole in loop quantum gravity

AbstractWe obtained the metric of the Schwarzschild-like black hole with loop quantum gravity (LQG) corrections in anti-de Sitter (AdS) space-time, under the assumption that the cosmological constant is decoupled in LQG. We investigated its thermodynamics, including the equation of state, criticality, heat capacity, and Gibbs free energy. The $$P-v$$ P - v graph was plotted, and the critical behavior was calculated. It was found that, due to the LQG effect, the quantum-corrected Schwarzschild-AdS black hole exhibits a critical point and a critical ratio of 7/18, which differs from the Reissner–Nordstr$$\ddot{\textrm{o}}$$ o ¨ m-AdS black hole’s ratio of 3/8 (the same as that of the Van der Waals system) slightly. However, there are still some similarities compared to the Van der Waals system, such as the same critical exponents and a similar $$P-v$$ P - v graph. Moreover, it is concluded that the energy-momentum tensor related to the black hole’s mass could violate the conventional first law of thermodynamics. This modified first law may violate the conservation of Gibbs free energy during the small black hole-large black hole phase transitions, potentially indicating the occurrence of the zeroth-order phase transition. The Joule–Thomson expansion was also studied. Interestingly, compared to the Schwarzschild-AdS black hole, the LQG effect leads to inversion points. The inversion curve divides the $$\left( P,T\right) $$ P , T coordinate system into two regions: a heating region and a cooling region, as shown in detail by the inversion curves and isenthalpic curves. The results indicated that there is a minimum inversion mass, below which any black hole will not possess an inversion point.

Gibbs Energy of the Transfer of Cryptand[2.2.2] from Water to a Water–Ethanol Solvent

Gibbs Energy of the Transfer of Cryptand[2.2.2] from Water to a Water–Ethanol Solvent

ZnCl2-Based Deep Eutectic Solvent as Solvent-Catalyst in the Michael Addition Reaction of Pyrrole to Maleimide

The use of deep eutectic solvents (DESs) as catalysts presents indisputable advantages, for example, their simplicity of preparation, high biodegradability, and recyclability, as well as zero toxicity and their effectiveness as environmentally friendly reaction media. However, aspects related to their reactivity and catalytic activity are still unclear. In this work, we explore the versatility of ChCl/ZnCl2 DES in the formation of C-C bonds through the Michael-type addition of pyrrole to maleimide, where ChCl/ZnCl2 DES leads to catalysis and chelation of the substrates, thus describing a recommended method for the construction of C-C bonds with high atomic economy. We describe experimental and theoretical aspects that explain the ability of ChCl/ZnCl2 DES in the presence of water to act as a catalyst in the formation of C-C bonds between pyrrole and maleimide. The potential energy surface showed that the ChCl and the zinc-zincate species 2ZnCl2·3H2O, formed by the interaction between zinc chloride and water, decrease the relative free Gibbs energy values for all the species involved in the reaction mechanism (TSs, intermediates, product), favoring the kinetics and thermodynamics of the Michael addition.

The ribosome comes to life.

The ribosome, together with its tRNA substrates, links genotype to phenotype by translating the genetic information carried by mRNA into protein. During the past half-century, the structure and mechanisms of action of the ribosome have emerged from mystery and confusion. It is now evident that the ribosome is an ancient RNA-based molecular machine of staggering structural complexity and that it is fundamentally similar in all living organisms. The three central functions of protein synthesis-decoding, catalysis of peptide bond formation, and translocation of mRNA and tRNA-are based on elegant mechanisms that evolved from the properties of RNA, the founding macromolecule of life. Moreover, all three of these functions (and even life itself) seem to proceed in defiance of entropy. Protein synthesis thus appears to exploit both the energy of GTP hydrolysis and peptide bond formation to constrain the directionality and accuracy of events taking place on the ribosome.

Transition Metals Doped into g-C3N4 via N,O Coordination as Efficient Electrocatalysts for the Carbon Dioxide Reduction Reaction.

The electrochemical carbon dioxide reduction reaction (CO2RR) is a potential and efficient method that can directly convert CO2 into high-value-added chemicals under mild conditions. Owing to the exceptionally high activation barriers of CO2, catalysts play a pivotal role in CO2RR. In this study, the transition metal (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) is doped into g-C3N4 with a unique N,O-coordination environment, namely, TM-N1O2/g-C3N4. Herein, the catalytic performance and reaction mechanism for the CO2RR on TM-N1O2/g-C3N4 are systematically investigated by density functional theory methods. Especially, through the calculation of ΔG*H and ΔG*COOH/ΔG*OCHO, the catalysts with preference for the CO2RR over the hydrogen evolution reaction (HER) are selected for further study. Furthermore, Gibbs free energy computation results of each elementary step for the CO2RR on these catalysts indicate that Ti-N1O2/g-C3N4 has significant catalytic activity and selectivity for reducing CO2 to methanol (CH3OH) with the limiting potential (UL) of -0.55 V. Finally, through frontier molecular orbital theory and charge transfer analyses, the introduction of the O atoms illustrates that it is instrumental in regulating the electron distribution of the catalytic active site, thereby improving the catalytic performance. This work provides insight into the design of single-atom catalysts with unique coordination structures for the CO2RR.

Prolonging Charge Carrier lifetime via Intraband Defect Levels in S-scheme Heterojunctions for Artificial Photosynthesis.

S-scheme heterostructure photocatalysts, distinguished by unique charge-transfer pathways and exceptional catalytic redox capabilities, have found widespread applications in addressing challenging chemical processes, including the photocatalytic reduction of CO2 with a high reaction barrier. Nevertheless, the influence of intraband defect levels within S-scheme heterojunctions on charge separation, carrier lifetime, and surface catalytic reactions has, for the most part, been overlooked. Herein, we develop a tunable defect-level-assisted strategy to construct an electron reservoir, effectively prolonging the lifetime of charge carriers through the rapid capture and gradual release of photoelectrons within WO3-x/In2S3 S-scheme heterojunctions, as authenticated by femtosecond transient absorption spectroscopy and theoretical simulations. The surface photoredox mechanism, unraveled by Gibbs free energy calculations, demonstrates that oxygen-vacancy-induced defect states in WO3-x/In2S3 heterojunctions unlock the rate-determining H2O oxidation into free oxygen molecules by forming metastable oxygen intermediates, contributing to the facilitation of H2O photooxidation. This distinct role, combined with the extended carrier lifetime, results in boosted CO2 photoreduction with nearly 100% CO selectivity in the absence of any photosensitizer or scavenger. Our work sheds light on the role of controllable defect levels in governing charge transfer dynamics within S-scheme heterojunctions, thereby inspiring the development of more advanced photocatalysts for artificial photosynthesis.

Cellulase immobilization on nano-chitosan/chromium metal-organic framework hybrid matrix for efficient conversion of lignocellulosic biomass to glucose

In the current work, cellulase from Aspergillus niger was successfully immobilized on a novel epoxy-affixed chromium metal-organic framework/chitosan (Cr@-MIL-101/CS) support via covalent method using glutaraldehyde as a crosslinker. The bare and cellulase-bound support was characterized by using various microscopic and spectroscopic techniques. Immobilized cellulase exhibited a high immobilization yield of 0.7 ± 0.01 mg/cm2, retaining 87.5 ± 0.04% of its specific activity and displaying enhanced catalytic performance. The immobilized enzyme was maximally active at pH 5.0, temperature 65 °C and 0.9 × 10–2 mg/ml saturating substrate concentration and the half-lives of free and immobilized cellulases were approximately 9 and 19 days, respectively. The decrease in activation energy, enthalpy change, and Gibbs free energy change, coupled with an increase in entropy change upon immobilization, indicated that the enzyme’s efficiency, stability, and spontaneity in catalyzing the reaction were enhanced by immobilization. Additionally, the immobilized cellulase efficiently converted rice husk cellulose to glucose, with a quantification limit of 0.05%, linear measurement ranging from 0.1 to 0.9%, and 8.5% conversion efficiency. The present method exhibited a strong correlation (R2 = 0.998) with the DNS method, validating its reliability. Notably, the epoxy/Cr@-MIL-101/CS-bound cellulase demonstrated impressive thermal and pH stabilities, retaining 50% of its activity at 75 °C and over 96% at pH levels of 4.5 and 5.0 after 12 h. Furthermore, it showed excellent reusability, preserving 80% of its activity after 15 cycles and maintaining 50% of its activity even after 20 days of storage. These results suggest that epoxy/Cr@-MIL-101/CS/cellulase composites could be very effective for large-scale cellulose hydrolysis applications.

Effects of conical singularity and Wu-Yang magnetic monopole on thermodynamic properties of harmonic oscillator interacting with potential

Abstract This paper investigates the thermodynamic properties of the harmonic oscillator system in a conical singularities background. Moreover, we incorporate a Wu-Yang magnetic monopole (WYMM) and inverse square potential into the quantum system and analyze the resulting effects. Using analytical methods, we derive the energy eigenvalues and study the thermodynamic properties, such as the partition function, Helmholtz free energy, Gibbs's free energy and specific heat capacity at finite temperature $T \neq 0$. Our findings demonstrate that these physical parameters are influenced by the topological parameter, strength of WYMM and potential parameters. These results provide valuable insights into the interplay between thermodynamic properties of a quantum mechanical problem and the gravitational effects.

Thermodynamic Aspects of Higher-Dimensional Black Holes in Einstein Gauss-Bonnet Gravity Through Exponential Entropy

Abstract We assume exponential corrections to the entropy of $5D$ charged AdS
black hole solutions, which are derived within the framework of
Einstein Gauss-Bonnet gravity and nonlinear electrodynamics.
Additionally, we consider two distinct versions of $5D$ charged AdS
black holes by setting the parameters $q\rightarrow0$ and
$k\rightarrow0$ (where $q$ represents charge, $k$ is the non-linear
parameter). We investigate these black holes in the extended phase
space, where the cosmological constant is interpreted as pressure,
and demonstrate the first law of black hole thermodynamics. The
focus extends to understanding the thermal stability or instability,
as well as identifying first and second-order phase transitions.
This exploration is carried out through the analysis of various
thermodynamic quantities, including heat capacity at constant
pressure, Gibbs free energy, Helmholtz free energy, and the trace of
the Hessian matrix. In order to visualize phase transitions,
identify critical points, analyzing stability and provide
comprehensive analysis, we have made the contour plot of the
mentioned thermodynamic quantities and observed that our results are
very much consistent. These investigations are conducted within the
context of exponentially corrected entropies, providing valuable
insights into the intricate thermodynamic behavior of these $5D$
charged AdS black holes under different parameter limits.

Potassium and Boron Co-Doping of g-C3N4 Tuned CO2 Reduction Mechanism for Enhanced Photocatalytic Performance: A First-Principles Investigation

Graphitic phase carbon nitride (g-C3N4, abbreviated as CN) can be used as a photocatalyst to reduce the concentration of atmospheric carbon dioxide. However, there is still potential for improvement in the small band gap and carrier migration properties of intrinsic materials. K-B co-doped CN (KBCN) was investigated as a promising photocatalyst for carbon dioxide reduction via the Density Functional Theory (DFT) method. The electronic and optical properties of CN and KBCN indicate that doping K and B can improve the catalytic performance of CN by promoting charge migration and separation. In terms of the Gibbs free energy change, the CO2 reduction reaction catalysed by KBCN results in CH3OH, and its optimal pathway is CO2 → *CO2 → *COOH → CO → *OCH → HCHO → *OCH3 → CH3OH. Compared with CN, the doping elements K and B shift the rate-determining step from CO2 → *CO2 to *CO2 → *COOH. The K and B elements co-doping tuned the charge distribution between the catalyst and the adsorbate and reduced the Gibbs free energy of the rate-determining step from 1.571 to 0.861 eV, suggesting that the CO2 reduction activity of KBCN is superior to that of CN. Our work provides useful insights for the design of metallic–nonmetallic co-doped CN for photocatalytic CO2 reduction (CO2PR) reactions.

Deciphering supramolecular arrangements, micellization patterns, and antimicrobial potential of bacterial rhamnolipids under extreme treatments of temperature and electrolyte

The micellization properties of rhamnolipids (RLs) in extreme electrolyte concentrations and temperatures have gained considerable attention due to their broad industrial applications. In this study, the aggregation behavior, specifically the micellization pattern (critical micelle concentration (CMC)) of RLs produced from a newly isolated thermophilic strain of Pseudomonas aeruginosa from a harsh environment of an oil field, was investigated by a spectrophotometric method at various temperatures (293–393 K) and electrolyte concentrations (NaCl: 2–20%). The result indicated that the CMC values (0.267–0.140 mM⋅dm−3) were both electrolyte- and temperature-dependent exhibiting a U-shaped trend as temperature and NaCl concentration increased. Variations in NaCl concentration and temperature also affected the standard Gibbs free energy (ΔGomic), enthalpy (ΔHomic), and entropy (ΔSomic) of micellization. The molecule also showed stability at a broad range of temperatures, pH, and NaCl concentrations. Thin-layer chromatography (TLC) and Fourier-transform infrared (FTIR) analysis confirmed the similarity in composition between the crude extract and the commercial RL with Rf values of 0.72 for mono-rhamnolipids and 0.28 for di-rhamnolipids. FTIR analysis confirmed the chemical nature particularly key aliphatic functional groups present in the fatty acid tail of RLs and the -COC- bond in the structure of the rhamnose moiety. Additionally, LC-ESI-QTOF analysis confirmed corresponding ionic fragments of mono- and di-rhamnolipids congeners. Furthermore, the antimicrobial potential was determined against different human pathogens in the absence and presence of NaCl by measuring zones of inhibition. The result revealed enhanced inhibitory effects against Gram-positive pathogens (S. aureus, S. epidermidis, and L. monocytogene), with zones of inhibition of 26, 30, and 20 mm in the presence of NaCl. These findings underline the role of NaCl in the micellization of RL molecules and highlight their importance in environmental applications, pharmaceuticals, and various life science sectors.

A Target to Combat Antibiotic Resistance: Biochemical and Biophysical Characterization of 3-Dehydroquinate Dehydratase from Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is associated with the acquisition of nosocomial infections, community-acquired infections, and infections related to livestock animals. In the pursuit of molecular targets in the development process of antibacterial drugs, enzymes within the shikimate pathway, such as 3-dehydroquinate dehydratase (DHQD), are regarded as promising targets. Therefore, through biochemical and biophysical techniques, in the present work, the characterization of DHQD from MRSA (SaDHQD) was performed. The kinetic results showed that the enzyme had a Vmax of 107 μmol/min/mg, a Km of 54 μM, a kcat of 48 s−1, and a catalytic efficiency of 0.9 μM−1 s−1. Within the biochemical parameters, the enzyme presented an optimal temperature of 55 °C and was thermostable at temperatures from 10 to 20 °C, being completely inactivated at 60 °C in 10 min. Furthermore, SaDHQD showed an optimal pH of 8.0 and was inactivated at pH 4.0 and 12.0. Moreover, the activity of the enzyme was affected by the presence of ions, surfactants, and chelating agents. The thermodynamic data showed that the rate of inactivation of the enzyme was a temperature-dependent process. Furthermore, the enthalpy change, entropy change, and Gibbs free energy change of inactivation were positive and practically constant, which suggested that the inactivation of SaDHQD by temperature was driven principally by enthalpic contributions. These results provide, for the first time, valuable information that contributes to the knowledge of this enzyme and will be useful in the search of SaDHQD inhibitors that can serve as leads to design a new drug against MRSA to combat antibiotic resistance.

Adsorption Structure-Activity Correlation in the Photocatalytic Chemistry of Methanol and Water on TiO2(110).

ConspectusPhotocatalysis, a process involving light absorption (band gap excitation), charge separation, interfacial charge transfer, and surface redox reactions, has attracted intensive attention because of the potential applications in solar to fuel conversion. Despite the great efforts devoted to the design of materials and optimization of charge separation and overall efficiency, the molecular mechanism of photocatalytic reactions, for example, water oxidation, is still unclear, mainly because of the complexity of powder catalysts and the aqueous environment which prevent the direct experimental detection of adsorption sites, surface species, and charge/energy transfer dynamics. Without direct evidence, the charge transfer and elementary reaction steps remain elusive, and misleading conclusions are sometimes drawn. For instance, the positively charged 5-fold coordinated Ti sites (Ti5cs) on TiO2 surfaces are argued to propel holes and therefore cannot be active sites for oxidative reactions, regardless of the demonstration by scanning tunneling microscopy (STM). Direct site-specific measurements are thus highly demanded. Surface science studies, which rely on well-defined single crystals and ultrahigh vacuum based techniques, can identify the active sites and active species at the catalyst surfaces and measure the interfacial electronic structure and energy of desorbing species for charge transfer analysis, providing direct evidence for investigating the photocatalytic reaction mechanism at the molecular level.In this Account, the elementary photocatalytic chemistry of methanol and water on TiO2, which are investigated by surface science techniques such as atom-resolved STM, ensemble-averaged mass spectrometer based temperature-programmed desorption/time-of-flight spectroscopy, and photoelectron spectroscopy in combination with theoretical calculations, will be described. Both methanol and water can be photocatalytically oxidized at Ti5cs, producing adsorbed formaldehyde and gaseous •OH radicals, respectively, under ultraviolet (UV) light irradiation. The photocatalytic activity shows salient adsorption structure including adsorption site (terminal/bridging), adsorption state (molecular/dissociative) and adsorption configuration (monomer/cluster) dependence, which comes from the ability to generate terminal anions which are capable of capturing photogenerated holes and exhibit superior photocatalytic activity over their parent molecules. These studies reveal the origin of the correlation between photocatalytic activity and adsorption structure of CH3OH and H2O on TiO2 surfaces and suggest that the simple criteria widely used to analyze the feasibility of charge transfer, i.e., the relative position of the band edges and the molecular orbitals of adsorbates, should be replaced by the change of Gibbs free energy of the charge trapping reaction from the thermodynamic point of view. These results contribute to the fundamental understanding of photocatalysis. Based on our research, future state-resolved and time-resolved studies can provide deeper insight into the charge and energy transfer and transient intermediate species, which will benefit the depiction of the overall photocatalytic reactions, for example, the photocatalyzed oxygen evolution reaction from water.

Effective Uptake of Cadmium and Chromium from Wastewater Using Carbon-Based Capsicum annuum

Toxic metal ions such as cadmium-Cd(II) and chromium-Cr(VI) are toxic, do not degrade easily in nature, and can cause various disorders and diseases in humans. Removing and monitoring Cd(II) and Cr(VI) ions is necessary for improving water quality. This study aimed to produce an adsorbent from activated carbon of Capsicum annuum and assess its ability to adsorb Cd(II) and Cr(VI) ions from water. The results showed that the adsorbent from C. annuum was porous after its conversion to activated carbon. The pH(PZC) of carbon-based Capsicum annuum was acidic, with a pH of 2.68. The highest capacities for both metal ions were observed at a pH of 1 for Cr(VI) and pH 5 for Cd(II), with capacities of 18.38 and 29.48 mg/g, respectively. The Freundlich sorption model proved to be the most suitable method. The adsorption of Cr(VI) and Cd(II) increased when the initial concentrations were raised from 20 and 60 mg/L; thereafter, a decrease was observed. The data showed that the adsorption of Cd(II) was fast and reached a maximum in 40 min, while Cr(VI) increased with time up to 30 min; thereafter, the rate for Cr(VI) decreased, while equilibrium was reached for Cd(II) ions. The temperature effect showed that the adsorption of Cd(II) and Cr(VI) ions reached a maximum at 55 and 45 °C, respectively. The results of enthalpy change (ΔH°) showed that the uptake process was exothermic, while the change in thermodynamic values of Gibbs energy (ΔG°) indicated that the sorption process was spontaneous and achievable. The greatest adsorption capacities for Cd(II) and Cr(VI) ions were 34.34 and 15.24 mg/g, respectively. The activated carbon from C. annuum proved to be effective for the adsorption of Cd(II) and Cr(VI) from wastewater.

Micellar solubility and co-solubilization of fragrance raw materials in sodium dodecyl sulfate and polysorbate 20 surfactant systems.

The aim of this work was to investigate the solubility and co-solubilization of fragrance raw materials (FRMs) in sodium dodecyl sulfate (SDS) and polysorbate 20 (P20) surfactant micellar systems, which can advance our knowledge of multi-solute micellar solubilization and fragrance olfactory performance from product matrices containing the surfactants. The transfer of individual FRMs and binary FRM mixtures into micellar phases was quantified by UV-VIS differential spectroscopy and evaluated in terms of the standard Gibbs free energy change and micelle-water partition coefficient. Co-solubilization effects were further evaluated by the deviation ratio. Anionic SDS was found overall to be a more efficient solubilizer than nonionic P20. On an individual basis, micellar solubilization generally increased with solute lipophilicity but was additionally impacted by solute rigidity and steric effects. Micellar solubilization was favoured for more rigid structures and less favoured for FRMs that exhibited larger molecular rotation and steric hindrance. For multi-solute systems, three co-solubilization effects were observed: (i) inhibitive effect in which micellar partitioning of both solutes decreased, (ii) an inverse effect where partitioning of one solute increased while the other decreased and (iii) synergistic effect in which partitioning of both solutes increased. During co-solubilization in P20 micelles, many FRMs competed for solubilization between the polyoxyethylene chains in the outer layer of the micelle, thereby resulting in an inhibitory effect for both solutes. Co-solubilization of FRM binary mixtures in SDS micelles often resulted in a synergistic increase in micellar solubility, possibly due to micellar swelling, thereby facilitating partitioning of additional solutes into the micelle. An inverse effect in which the micellar solubility of one solute increased, while the other decreased was observed in both surfactant systems with varying degrees of partitioning depending on the composition of the FRM mixture. The results of this study provide valuable insights into the impact of FRM composition on multi-solute partitioning behaviour and the impact of surfactant type on co-solubilization in micellar solutions.

Characterization and evaluation of a tray dryer with change of position: kinetics and thermodynamic properties of the process, preserving the nutraceutical properties in Golden Delicious apple slices.

The drying kinetics in apple slices between 45–55 °C was studied until reach a moisture ratio of 10±2%. 8 thin layer drying models were statistically fitted where the Midilli-Kucuk model presented the best performance, moreover its drying constant increased with the temperature, effective diffusivity was ranged from 68.16 E-10 – 2.28 E-08 m2 s-1, the Arrhenius factor and activation energy were 3.74 E-02 m2 s-1 and 28.11 kJ mol-1, the enthalpy decreased from 25.46–25.38 kJ mol-1, the entropy was ranged between (-0.2728 – -0.2730) kJ mol-1 K-1, and the Gibbs free energy increased from 112.25–114.98 kJ mol-1. The 45 °C treatment preserved the highest phenolic compounds (51.1±1.54 mg EAG 100 g-1), while the initial activity of elimination of radicals was 766.9±91.4 and 973.3±103.4 µg mg-1 according to the DPPH and ABTS methods, the antioxidant activity shows an inverse behavior to the drying temperature. This work will allow to establish the temperature, time, moisture ratio and energy to drying apple slices according to local weather or under controlled conditions.

Two-Dimensional Topological Platinum Telluride Superstructures with Periodic Tellurium Vacancies for Efficient and Robust Catalysis.

Defect engineering in the inherently inert basal planes of transition metal dichalcogenides (TMDs), involving the introduction of chalcogen vacancies, represents a pivotal approach to enhance catalytic activity by exposing high-density catalytic metal single-atom sites. However, achieving a single-atom limit spacing between chalcogen vacancies to form ordered superstructures remains challenging for creating uniformly distributed high-density metal single-atom sites on TMDs comparable to carbon-supported single-atom catalysts (SACs). Here we unveil an efficient TMD-based topological catalyst for hydrogen evolution reaction (HER), featuring high-density single-atom reactive centers on a few-layer (7 × 7)-PtTe2-x superstructure. Compared with pristine Pt(111), PtTe2, and (2 × 2)-PtTe2-x, (7 × 7)-PtTe2-x exhibits superior HER performance owing to its substantially increased density of undercoordinated Pt sites, alongside exceptional catalytic stability when operating at high current densities. First-principles calculations confirm that multiple types of undercoordinated Pt sites on (7 × 7)-PtTe2-x exhibit favorable hydrogen adsorption Gibbs free energies, and remain active upon increasing hydrogen coverage. Furthermore, (7 × 7)-PtTe2-x possesses nontrivial band topologies with robust edge states, suggesting potential enhancements for HER. Our findings are expected to advance TMD-based catalysts and exploration of topological materials in catalysis.

Activation of Alkenes via Chalcogen Bond: Chalcogen⋅⋅⋅π Bond Catalyzed the Diels‐Alder Reaction of 2‐Vinylindoles

AbstractChalcogen bond catalysis is a promising catalytic strategy, characterized by its environmental friendliness, relatively inexpensive cost, and similar reactivity to transition metal catalysis. Experimental results suggest that the S⋅⋅⋅π and Se⋅⋅⋅π bonds can efficiently drive the vinyl‐indole‐based Diels‐Alder reaction (Angew. Chem. Int. Ed. 2021, 60, 9395–9400). In this work, chalcogen bond catalysis in the Diels‐Alder reaction between 2‐vinylindoles is investigated based on density functional theory. For this reaction, the Te⋅⋅⋅π bond catalysis is as an alternative catalytic strategy. The Diels‐Alder reaction catalyzed by chalcogen bond is stepwise and involves two steps: the carbon–carbon bond formation process and the cyclization process. The cyclization process is the rate‐determining step. From the perspective of energy decomposition analysis, the electrostatic interaction is the main factor to cause Se⋅⋅⋅π bond catalysis, the polarization interaction is the main factor to cause Te⋅⋅⋅π bond catalysis. Additionally, this catalytic reaction involves the endo pathway and exo pathway. The Gibbs free energy barrier values of the endo pathway are lower than those of the exo pathway, which facilitates the formation of the endo product. This study will provide a valuable perspective on the application of chalcogen bond in the activation of alkenes.

Control of hydrogen concentrations by microbial sulfate reduction in two contrasting anoxic coastal sediments

IntroductionMolecular hydrogen is produced by the fermentation of organic matter and consumed by organisms including hydrogenotrophic methanogens and sulfate reducers in anoxic marine sediment. The thermodynamic feasibility of these metabolisms depends strongly on organic matter reactivity and hydrogen concentrations; low organic matter reactivity and high hydrogen concentrations can inhibit fermentation so when organic matter is poor, fermenters might form syntrophies with methanogens and/or sulfate reducers who alleviate thermodynamic stress by keeping hydrogen concentrations low and tightly controlled. However, it is unclear how these metabolisms effect porewater hydrogen concentrations in natural marine sediments of different organic matter reactivities.MethodsWe measured aqueous concentrations of hydrogen, sulfate, methane, dissolved inorganic carbon, and sulfide with high-depth-resolution and 16S rRNA gene assays in sediment cores with low carbon reactivity in White Oak River (WOR) estuary, North Carolina, and those with high carbon reactivity in Cape Lookout Bight (CLB), North Carolina. We calculated the Gibbs energies of sulfate reduction and hydrogenotrophic methanogenesis.ResultsHydrogen concentrations were significantly higher in the sulfate reduction zone at CLB than WOR (mean: 0.716 vs. 0.437 nM H2) with highly contrasting hydrogen profiles. At WOR, hydrogen was extremely low and invariant (range: 0.41–0.52 nM H2) in the upper 15 cm. Deeper than 15 cm, hydrogen became more variable (range: 0.312–2.56 nM H2) and increased until methane production began at ~30 cm. At CLB, hydrogen was highly variable in the upper 15 cm (range: 0.08–2.18 nM H2). Ratios of inorganic carbon production to sulfate consumption show AOM drives sulfate reduction in WOR while degradation of organics drive sulfate reduction in CLB.DiscussionWe conclude more reactive organic matter increases hydrogen concentrations and their variability in anoxic marine sediments. In our AOM-dominated site, WOR, sulfate reducers have tight control on hydrogen via consortia with fermenters which leads to the lower observed variance due to interspecies hydrogen transfer. After sulfate depletion, hydrogen accumulates and becomes variable, supporting methanogenesis. This suggests that CLB’s more reactive organic matter allows fermentation to occur without tight metabolic coupling of fermenters to sulfate reducers, resulting in high and variable porewater hydrogen concentrations that prevent AOM from occurring through reverse hydrogenotrophic methanogenesis.

From germolane to germylenes: a theoretical DFT study of thermal decomposition pathways and reactivity

This study addresses the often-overlooked chemistry of germanium compared to the extensively researched carbon and silicon. Using advanced DFT methods, we investigated the thermal decomposition of germolane (germacyclopentane). The suggested mechanisms include a 1,2-H shift and 1,1-H2 elimination to form a pentacyclic germylene (1λ2-germolane). The other pathway involves a stepwise [3 + 2] cycloreversion to form a diradical followed by ethene and germirane. Under M062X/def2-TZVP level of theory, the activation barriers in terms of Gibbs energy (ΔG ‡ 298) for the 1,2-H shift and 1,1-H2 elimination pathways were 240.9 and 236.3 kJ/mol, respectively. The reaction energies (ΔG° 298) for the initiative steps in the 1,2-H shift and 1,1-H2 elimination mechanisms were 102.9 and 96.2 kJ/mol, indicating a thermodynamic and kinetic competition between the two routes. Temperature dependence analysis from 300 to 1200 K reveals that the 1,1-H2 elimination dominates at higher temperatures and is expected to become spontaneous above 1000 K.