C Atoms Research Articles

Atmospheric Chemistry of Chloroprene Initiated by OH Radicals: Combined Ab Initio/DFT Calculations and Kinetics Analysis.

Chloroprene (CP; CH2═C(Cl)-CH═CH2) is a significant toxic airborne pollutant, often originating from anthropogenic activities. However, the environmental fate of CP is incompletely understood. High level CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ calculations combined with kinetic modeling were employed here to glean new insight into the reaction mechanism, energies, and kinetics of the reaction of CP with OH radical (•OH). We report the energies of four different addition pathways and six different abstraction pathways. The •OH attack on the terminal C1 atom of the =CH2 group (which is directly attached to the =CCl moiety), leading to the formation of HOCH2-•C(Cl)-CH═CH2, was found to be a major path. The barrier height for the formation of the corresponding transition state was found to be -1.9 kcal mol-1 below that of the starting CP + •OH reactants. Rate coefficients were calculated for addition and abstraction pathways involving the CP + •OH reaction under pre-equilibrium approximation conditions, employing a combination of canonical variational transition state theory and small curvature tunneling. The overall rate coefficient for the reaction of CP + •OH at 298 K was found to be 1.4 × 10-10 cm3 molecule-1 s-1. The thermochemistry of the possible channels and atmospheric implications are provided. In addition, the fate of HOCH2-•C(Cl)-CH═CH2 in the presence of 3O2 was investigated. We found the reaction of the CP-derived peroxy radical adduct with HO2 and NO to make contributions to the formation of products such as formaldehyde, HO2 radical, Cl atom, HOCH2C(OOH)(Cl)CH═CH2, HOCH2C(O)Cl, ClC(O)CH═CH2, HOCH2C(O)CH═CH2, and HC(O) radical.

Molecular modelling of luciferyl adenylate deprotonation in the active site of Photinus pyralis luciferase

Firefly bioluminescence is a product of chemical reactions that involve luciferin chromophore oxidation in the active site of luciferase proteins. We perform a series of classical molecular dynamic simulations and combined quantum and molecular mechanics (QM/MM) calculations to expose the molecular mechanism of C4 carbon atom deprotonation in luciferyl adenylate molecule. QM/MM calculations confirm that ND-protonated His245 residue is a suitable proton acceptor in the wild-type Photinus pyralis luciferase. Classical molecular dynamic simulations reveal oxygen-binding cavities inside the protein including the one located close to the C4 atom of luciferin. In mutant forms that lack direct interactions with the His245 side chain, a proton wire comprising water molecules stimulates either protonation of the phosphate group of the luciferyl adenylate forming an unstable intermediate or keto–enol tautomerisation of luciferin. The comparison of the ionisation potentials of molecular systems with the ‘deprotonated’ C4 carbon atom revealed that the ionisation energy for the enol tautomeric form is close to the system with the His245 proton acceptor. Thus, the existence of the keto–enol tautomerisation channel might explain bioluminescence in case of the absence of the amino acid proton acceptor.

Mechanism insights into the upgrading of xylose to furfural over the carbon-based catalysts in aqueous media

Exploring low-cost and high-efficient solid acid catalysts and elucidating complete reaction mechanisms are critically important for the sustainable transformation of biomass-derived molecules to bio-fuels and high-value chemicals. Here, we design a renewable strategy to construct carbon-supported solid acid catalysts (M@FRC, M=Sn, Al, Fe, Zn, and Mg) by using biomass waste resources (furfural residue, FR) as the carbon source and tested for dehydration of xylose to furfural (FAL) in the aqueous medium. Kinetic studies revealed the relationship between the main reaction (target product FAL) and the side reaction (other by-products) in the dehydration of xylose under different catalysts. Deuterium-labeling reactions and density functional theory calculations elucidate that the aldehyde carbon of FAL was derived from the C1 of xylose. Furthermore, the C1 of xylose could be broken to form formic acid. While the C1 atom from xylose was converted into formic acid, other carbon atoms could be transformed to tetra-, tri-, di- and mono-carbon compounds. This study offers a prospect for the sustainable catalytic upgrading of biomass by the development of renewable catalytic materials from waste lignocellulosic biomass and an in-depth understanding of the xylose conversion mechanism to develop tailored processes.

Study of the Molecular Structure, Spectroscopic Analysis, Electronic Structures and Thermodynamic Properties of Niacin Molecule Using First-principles

This work describes the different properties of Niacin's molecule using the density functional theory (DFT) B3LYP/6-311++G (d, p) basis set. The optimized energy for the Niacin molecule is -436.987 Hartree. The peak values from FT-IR spectra show the C=C, C-C vibrations, C-H stretching vibrations, C-H in-plane bending vibration, C-H out-of-plane bending vibration, C-O stretching vibration, C-N vibration and O-H vibration. The MEP and ESP analyses indicate that the oxygen and nitrogen atoms exhibit nucleophilic regions, while the hydrogen atoms exhibit electrophilic regions. The energy gap of the Niacin molecule is found to be 5.398 eV through HOMO-LUMO analysis. The electronegativity value of 4.847 eV signifies the molecules ability to attract electron and the calculated value of chemical hardness is 2.7 eV which reflects the molecular stability. The softness value of 0.370 eV-1 denotes the molecule polarizability. Also the chemical potential value is -4.847 eV which represent the ability to donate or accept electron. Similarly, electrophilic index with value 4.351 eV shows the electrophilic behavior that signifies its capacity to accept electron. Because of the larger energy gap, the molecule becomes hard and hardness is greater than softness. In this molecule, the C2 atoms have the highest positive charge along with C3 and all the hydrogen atoms, while C1 has the highest negative charge together with some negative charge on C4, C5, N6, C11, O12 and O13 atoms. When the temperature rises, the thermodynamic parameters such as heat capacity at constant volume and pressure, internal energy, enthalpy, and entropy increase, but Gibbs free energy decreases.

Insights on the efficiency and contribution of single active species in photocatalytic degradation of tetracycline: Priority attack active sites, intermediate products and their toxicity evaluation

Photocatalysis has been proven to be an excellent technology for treating antibiotic wastewater, but the impact of each active species involved in the process on antibiotic degradation is still unclear. Therefore, the S-scheme heterojunction photocatalyst Ti3C2/g-C3N4/TiO2 was successfully synthesized using melamine and Ti3C2 as precursors by a one-step calcination method using mechanical stirring and ultrasound assistance. Its formation mechanism was studied in detail through multiple characterizations and work function calculations. The heterojunction photocatalyst not only enabled it to retain active species with strong oxidation and reduction abilities, but also significantly promoted the separation and transfer of photo-generated carriers, exhibiting an excellent degradation efficiency of 94.19 % for tetracycline (TC) within 120 min. Importantly, the priority attack sites, degradation pathways, degradation intermediates and their ecological toxicity of TC under the action of each single active species (·O2−, h+, ·OH) were first positively explored and evaluated through design experiments, Fukui function theory calculations, HPLC-MS, Escherichia coli toxicity experiments, and ECOSAR program. The results indicated that the preferred attack sites of ·O2− on TC were O20, C7, C11, O21, and N25 atoms with high f+ value. The toxicity of intermediates produced by ·O2− was also lower than those produced by h+ and ·OH.

How Do the Position and Number of Methyl Substituents Affect the Photochemical Process of Criegee Intermediate? Trajectory Surface-Hopping Dynamics of Four-Carbon CIs.

Electronic-structure calculations combined with nonadiabatic trajectory surface-hopping (TSH) dynamic simulations were carried out on two alkenyl-substituted Criegee intermediates (CIs), i.e., propenyl-substituted CI (PCI) and 1-methyl-propenyl substituted CI (MPCI), in order to investigate the influence of the position and number of substituents on the photochemical process of CI in S1 states. It is found that they play critical roles in the reactivity, dominant product channel, and mechanism of the CIs. More specifically, introducing a methyl group on either C1 (α-C) or C3 (γ-C) position of a vinyl-substituted CI (VCI) skeleton facilitates the rotation of the C1═O1 bond and leads to the formation of a three-membered dioxirane ring; meanwhile, it evidently enhances the reactively of the S1-state molecule. Meanwhile, methyl substitution on the vinyl moiety [i.e., C2 (β-C) and C3 (γ-C) positions] is beneficial for the rotation of the C2═C3 bond and thus facilitates the formation of the five-membered 1,2-dioxole ring, and the substitution on C2 site decreases the reactivity. The cosubstitution of C2 and C3 atoms by methyl groups well balances the features of VCI in the sense of high reactivity, consistently predominant channel, and possible dioxole side-product. The findings here not only deepen the knowledge on the photochemical processes of the CI but also inspire the rethinking of the "old" concept of substitution effect.

Synthesis of Novel 3-Deoxy-3-thio Derivatives of d-Glucosamine and Their Application as Ligands for the Enantioselective Addition of Diethylzinc to Benzaldehyde.

A series of novel thio-derivatives of d-glucosamine has been synthesized using double inversion procedures at the C3 atom. New compounds were applied as ligands for the diethylzinc addition to benzaldehyde and the products of the addition were obtained with a low to good enantiomeric ratio. The direction and the level of the asymmetric induction were highly dependent on the type of protecting groups on the nitrogen and sulfur atoms.

The Use of Spectroscopic Methods to Study Organic Matter in Virgin and Arable Soils: A Scoping Review

The use of modern spectroscopic methods of analysis, which provide extensive information on the chemical nature of substances, significantly expands our understanding of the molecular composition and properties of soil organic matter (SOM) and its transformation and stabilization processes in various ecosystems and geochemical conditions. The aim of this review is to identify and analyze studies related to the application of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy techniques to study the molecular composition and transformation of organic matter in virgin and arable soils. This article is mainly based on three research questions: (1) Which NMR spectroscopy techniques are used to study SOM, and what are their disadvantages and advantages? (2) How is the NMR spectroscopy technique used to study the molecular structure of different pools of SOM? (3) How is ESR spectroscopy used in SOM chemistry, and what are its advantages and limitations? Relevant studies published between 1996 and 2024 were searched in four databases: eLIBRARY, MDPI, ScienceDirect and Springer. We excluded non-English-language articles, review articles, non-peer-reviewed articles and other non-article publications, as well as publications that were not available according to the search protocols. Exclusion criteria for articles were studies that used NMR and EPR techniques to study non-SOM and where these techniques were not the primary methods. Our scoping review found that both solid-state and solution-state NMR spectroscopy are commonly used to study the structure of soil organic matter (SOM). Solution-phase NMR is particularly useful for studying soluble SOM components of a low molecular weight, whereas solid-phase NMR offers advantages such as higher 13C atom concentration for stronger signals and faster analysis time. However, solution-phase NMR has limitations including sample insolubility, potential signal aggregation and reduced sensitivity and resolution. Solid-state NMR is better at detecting non-protonated carbon atoms and identifying heterogeneous regions within structures. EPR spectroscopy, on the other hand, offers significant advantages in experimental biochemistry due to its high sensitivity and ability to provide detailed information about substances containing free radicals (FRs), aiding in the assessment of their reactivity and transformations. Understanding the FR structure in biopolymers can help to study the formation and transformation of SOM. The integration of two- and three-dimensional NMR spectroscopy with other analytical methods, such as chromatography, mass spectrometry, etc., provides a more comprehensive approach to deciphering the complex composition of SOM than one-dimensional techniques alone.

An innovative form of the essential trace element copper for fortification of dairy products

Microelementosis is a disease associated with a deficiency of certain vital microelements. Today, there are ways to combat the lack of essential micronutrients. In this article, the mechanochemical synthesis of a triple copper-containing complex with ascorbic acid and L-isoleucine, an essential amino acid, was carried out. Examination of the sample by X-ray diffractometry showed that the sample has a trigonal crystal structure with space group P31c. As a result of computer quantum chemical modeling, the values of the difference in total energy, chemical hardness, energy of the highest occupied molecular orbital and the lowest unoccupied molecular orbital were determined. We determined the optimal option for the interaction of copper with vitamin C and L-isoleucine, where the binding occurs through hydroxyl groups attached to the C2 and C3 atoms of ascorbic acid, and through the carboxyl group and α-amino group of isoleucine. The sample was examined by IR spectroscopy and confirmed by computer modeling data. The stability of the resulting complex was studied depending on the technological parameters — pH, temperature and exposure time. Using the Greco-Latin square method, a matrix for planning a multifactorial experiment was compiled. An analysis of the dependence of the change in optical density (∆ D) on pH, temperature and exposure time showed that the pH of the medium and the temperature of the solution have a significant effect on ∆ D: an increase in the pH of the medium and the temperature of the solution leads to an increase in ∆ D. Exposure time does not have a significant effect to change the optical density value (∆ D). The parameters at which sample stability is observed correspond to the lowest values of ∆ D: pH = 3–8, t = 25–70, τ = 5–15. The effect of the concentration of a copper-containing complex on the physicochemical parameters of milk was studied. It has been established that the optimal concentration of copper ascorbate isoleucinate for fortifying dairy products is 0.005 mol/l or less. Next, an organoleptic assessment of the indicators of milk enriched with copper ascorbate isoleucinate was carried out. The analysis of the results showed that the organoleptic parameters (smell and taste) of milk enriched with ascorbate-isoleucinate of copper are 0.1 points higher than those of milk enriched with the inorganic form of the essential trace element copper and 0.3 points lower than that of the control milk sample.

Identification of extracellular polymeric substances layer barrier in chloroquine phosphate-disturbed anammox consortia and mechanism dissection on cytotoxic behavior by computational chemistry

The over-dosing use of chloroquine phosphate (CQ) poses severe threats to human beings and ecosystem due to the high persistence and biotoxicity. The discharge of CQ into wastewater would affect the biomass activity and process stability during the biological processes, e.g., anammox. However, the response mechanism of anammox consortia to CQ remain unknown. In this study, the accurate role of extracellular polymeric substances barrier in attenuating the negative effects of CQ, and the mechanism on cytotoxic behavior were dissected by molecular spectroscopy and computational chemistry. Low concentrations (≤6.0 mg/L) of CQ hardly affected the nitrogen removal performance due to the adaptive evolution of EPS barrier and anammox bacteria. Compact protein of EPS barrier can bind more CQ (0.24 mg) by hydrogen bond and van der Waals force, among which O-H and amide II region respond CQ binding preferentially. Importantly, EPS contributes to the microbiota reshape with selectively enriching Candidatus_Kuenenia for self-protection. Furthermore, the macroscopical cytotoxic behavior was dissected at a molecular level by CQ fate/distribution and computational chemistry, suggesting that the toxicity was ascribed to attack of CQ on functional proteins of anammox bacteria with atom N17 (f–=0.1209) and C2 (f+=0.1034) as the most active electrophilic and nucleophilic sites. This work would shed the light on the fate and risk of non-antibiotics in anammox process.

A trapped covalent intermediate as a key catalytic element in the hydrolysis of a GH3 β-glucosidase: An X-ray crystallographic and biochemical study

Glycoside hydrolases (GHs) are industrially important enzymes that hydrolyze glycosidic bonds in glycoconjugates. In this study, we found a GH3 β-glucosidase (CcBgl3B) from Cellulosimicrobium cellulans sp. 21 was able to selectively hydrolyze the β-1,6-glucosidic bond linked glucose of ginsenosides. X-ray crystallographic studies of the ligand complex ginsenoside-specific β-glucosidase provided a novel finding that support the catalytic mechanism of GH3. The substrate was clearly identified within the catalytic center of wild-type CcBgl3B, revealing that the C1 atom of the glucose was covalently bound to the Oδ1 group of the conserved catalytic nucleophile Asp264 as an enzyme–glycosyl intermediate. The glycosylated Asp264 could be identified by mass spectrometry. Through site-directed mutagenesis studies with Asp264, it was found that the covalent intermediate state formed by Asp264 and the substrate was critical for catalysis. In addition, Glu525 variants (E525A, E525Q and E525D) showed no or marginal activity against pNPβGlc; thus, this residue could supply a proton for the reaction. Overall, our study provides an insight into the catalytic mechanism of the GH3 enzyme CcBgl3B.

Iron Ascorbate Threonine (II) as a New Chelated Form of Essential Iron for Food Fortification

Microelements are an extremely important part of the diet of any living organism. However, in order to achieve its maximum digestibility, a man has to search for new nutrient forms. Microelements in the chelated complexes composition keep greater digestibility compared to such popular forms as inorganic and organic, therefore, the development of new chelated microelement forms is relevant. The research aimed at developing and studying a biologically active chelate complex of the essential microelement iron with ascorbic acid and the essential amino acid L-threonine (iron ascorbate threonine (II)). The thesis presents a method for obtaining the complex, its stability study, IR spectroscopy of the resulting compound and the antioxidant activity research of milk enriched with iron ascorbate threonine (II) complex. The stability study of the developed complex demonstrated that the developed complex was stable in neutral and acidic environments, unstable in an alcaline environment. The authors revealed that an increase in the mixing time and synthesis temperature led to the iron ascorbate (II) destruction; the complex formation was due to chelating iron through the carboxyl group and the α-amino group of L-threonine and hydroxyl groups attached to the C2 and C3 atoms of ascorbic acid. The final stage of the study concerns the antioxidant activity of milk enriched with a complex of the essential microelement iron with ascorbic acid and the essential amino acid L-threonine. A man found that the developed complex exhibited antioxidant activity at the level of 40 % of the trolox activity; determined that the antioxidant milk activity increased by 42.8 % relative to the control milk sample. The results obtained enables to conclude that the iron ascorbate threonine (II) complex demonstrates antioxidant activity and can be used for the functional food products development.

A chiral zeolite material with improved enantioselective catalytic properties prepared from readily accessible ephedrine alkaloids

Substituted-benzyl-containing N-methyl-ephedrinium derivatives (BMEP), prepared from the highly-accessible (1R,2S)- or (1S,2R)-ephedrine alkaloids, have been found to act as efficient structure-directing agents for the synthesis of chiral zeolite GTM-4 with –ITV framework structure, promoting the enantio-enrichment in one of the chiral crystalline polymorphs as a function of the organic handedness. Results of a systematic variation of substituents in the benzyl ring attached to the ephedrine core (with methyl-, fluoro- or chloro-groups in the different positions of the aromatic ring) revealed that F-containing SDAs brought about an improvement in the structure-directing ability toward the –ITV framework, giving asymmetric zeolite acid-catalysts that yielded notable enantiomeric excesses in the range of 40–45 % for the trans-stilbene oxide ring-opening with 1-butanol. Interestingly, the incorporation of a methyl group in ortho-position (oMBMEP) had a double positive effect: on the one hand, this SDA prevented the crystallization of the competing BEC phase, allowing the crystallization of the -ITV structure at higher temperature and with higher crystallinity, and on the other, it drove to GTM-4 asymmetric catalysts that yielded enantiomeric excesses up to 60 %, resulting in the chiral GTM catalysts with the best enantioselective properties found so far. Remarkably, our catalytic results show the same chiral activity (in terms of zeolite handedness) for GTM-4 materials prepared from benzyl-containing (1S,2S)-N-methyl-pseudoephedrinium (BMPS) and (1S,2R)-N-methyl-ephedrinium (BMEP) derivatives, thus suggesting that the host-guest transfer of chirality during crystallization with these chiral organic aromatic agents is imposed by the absolute configuration of the C1 atom to which the OH group is attached. The relatively high enantiomeric excess of 60 % achieved, combined with the high accessibility of the ephedrine chiral precursors used for the synthesis that enables the production of both crystalline handedness of the –ITV framework, bring these materials closer to a potential application as heterogeneous asymmetric catalysts for the synthesis of chiral compounds of interest.

A multifunctional flavoprotein monooxygenase HspB for hydroxylation and C-C cleavage of 6-hydroxy-3-succinoyl-pyridine.

Flavoprotein monooxygenases catalyze reactions, including hydroxylation and epoxidation, involved in the catabolism, detoxification, and biosynthesis of natural substrates and industrial contaminants. Among them, the 6-hydroxy-3-succinoyl-pyridine (HSP) monooxygenase (HspB) from Pseudomonas putida S16 facilitates the hydroxylation and C-C bond cleavage of the pyridine ring in nicotine. However, the mechanism for biodegradation remains elusive. Here, we refined the crystal structure of HspB and elucidated the detailed mechanism behind the oxidative hydroxylation and C-C cleavage processes. Leveraging structural information about domains for binding the cofactor flavin adenine dinucleotide (FAD) and HSP substrate, we used molecular dynamics simulations and quantum/molecular mechanics calculations to demonstrate that the transfer of an oxygen atom from the reactive FAD peroxide species (C4a-hydroperoxyflavin) to the C3 atom in the HSP substrate constitutes a rate-limiting step, with a calculated reaction barrier of about 20 kcal/mol. Subsequently, the hydrogen atom was rebounded to the FAD cofactor, forming C4a-hydroxyflavin. The residue Cys218 then catalyzed the subsequent hydrolytic process of C-C cleavage. Our findings contribute to a deeper understanding of the versatile functions of flavoproteins in the natural transformation of pyridine and HspB in nicotine degradation.IMPORTANCEPseudomonas putida S16 plays a pivotal role in degrading nicotine, a toxic pyridine derivative that poses significant environmental challenges. This study highlights a key enzyme, HspB (6-hydroxy-3-succinoyl-pyridine monooxygenase), in breaking down nicotine through the pyrrolidine pathway. Utilizing dioxygen and a flavin adenine dinucleotide cofactor, HspB hydroxylates and cleaves the substrate's side chain. Structural analysis of the refined HspB crystal structure, combined with state-of-the-art computations, reveals its distinctive mechanism. The crucial function of Cys218 was never discovered in its homologous enzymes. Our findings not only deepen our understanding of bacterial nicotine degradation but also open avenues for applications in both environmental cleanup and pharmaceutical development.

Crystal structures, phase transitions, thermodynamics, and molecular dynamics of organic–inorganic hybrid crystal [NH(CH3)3]2ZnCl4

Understanding the physical properties of organic–inorganic hybrid [NH(CH3)3]2ZnCl4 is necessary for its potential application in batteries and fuel cells due to its environmentally-friendly, and highly stable character. Here, we determine its overall properties in detail, such as its orthorhombic crystal structure, and phase transition temperatures associated with five different phases. Structural geometry was studied by the chemical shifts caused by the local field around 1H. No changes were observed for the environment around 1H for CH3, whereas the 1H chemical shifts around NH in the cation were shown due to the change in the hydrogen bond N‒H···Cl. This is related to the change in Cl around Zn in the anion. In addition, the coordination geometry of 14N and 1H around 13C exhibited increased symmetry at high temperatures. Finally, we were able to understand its molecular dynamics by the significant change with temperature observed from the spin–lattice relaxation time T1ρ values, which represent the energy transfer for the 1H and 13C atoms of the cation. The activation energies obtained from the T1ρ results were 3–4 times large at phase I (> 348 K) than at phase V and IV (< 286 K). The relaxations show that the energy barriers in phases IV and V are related to the reorientation of methyl groups around the triple symmetry axis, while the reorientation of methyl groups of the cation in phase I is related to as a whole.

Doubly substituted isotopologues of HCCCN in TMC-1: Detection of D13CCCN, DC13CCN, DCC13CN, DCCC15N, H13C13CCN, H13CC13CN, HC13C13CN, HCC13C15N, and HC13CC15N

We report the first detection in space of a complete sample of nine doubly substituted isotopologues of HCCCN towards the cyanopolyyne peak of TMC-1 using observations of the QUIJOTE1 line survey taken with the Yebes 40 m telescope. We detected D13CCCN, DC13CCN, DCC13CN, DCCC15N, H13C13CCN, H13CC13CN, HC13C13CN, HCC13C15N, and HC13CC15N through their J = 4 − 3 and J = 5 − 4 lines in the 7 mm window. In addition, we present an extensive analysis of the emission of HCCCN and its singly substituted isotopologues through a large velocity gradient model of the lines detected at 7 mm and 3 mm using the Yebes 40 m and the IRAM 30 m telescopes, respectively. The derived column densities for all the isotopologues are consistent in the two spectral bands for an H2 volume density of 1 × 104 cm−3 and a kinetic temperature of 10 K. Whereas we observed a 13C fractionation for HCC13CN and other double isotopologues with a 13C atom adjacent to the nitrogen atom, we derived similar C/13C abundance ratios for the three 13C substituted species of DCCCN. This suggests additional chemical discrimination for deuterated isotopologues of HCCCN. Finally, we present the spatial distribution of the J = 4 − 3 and J = 5 − 4 lines from the singly substituted species observed with the Yebes 40 m telescope. The emission peak of the spatial distribution of DCCCN appears to be displaced by ∼40″ with respect to that of HCCCN and the 13C and 15N isotopologues. In addition to a different formation route for the deuterated species, we could also expect that this differentiation owing to the deuterium fractionation is more efficient at low temperatures, and therefore, that deuterated species trace a colder region of the cloud.

Elastic and inelastic cross-sections for 12C + CO2 and 13C + CO2 scattering at superthermal energies

ABSTRACT We report elastic and inelastic cross-sections for fast superthermal 12C(3P) and 13C(3P) atoms scattering on 12CO2. The cross-sections were computed using quantum-mechanical rotationally close-coupling formalism with the electronic interaction described by a newly constructed potential energy surface correlating to the lowest energy asymptote of the complex. State-to-state rotational cross-sections, differential cross-sections, and derived transport properties of interest for energy relaxation are also reported. The computed elastic differential cross-sections are found to be strongly anisotropic, show significant energy dependence, and differ by up to 2 percent between the two isotopes of carbon.

Carbon atom insertion into N-heterocyclic carbenes to yield 3,4-dihydroquinoxalin-2(1H)-ones

A molecular editing strategy to construct quinoxalinones from chromones and benzimidazolylidene N-heterocyclic carbenes (NHCs) was developed. The C2 atoms of the chromones were incorporated into the quinoxalinones via ring expansion of the NHCs.

Reducing the formation of asphaltene deposits and increasing the flow rates of oil wells

Purpose. Reducing the formation of asphaltene deposits in the bottom-hole zone of wells and increasing their flow rate. Methodology. The purpose of the work is achieved by conducting theoretical and experimental studies on the formation of asphaltene and paraffin deposits in the bottom-hole zone of the oil reservoir and identifying patterns of their dissolution by pumping heated low-boiling oil components containing carbon atoms C6–C9 in molecules into the well. Findings. The experimental studies conducted under laboratory conditions showed high solubility of asphalt-resin and paraffin compounds in low-boiling oil components. To prevent the deposition of asphaltene deposits in the bottom-hole zone of wells, the turbulent nature of oil movement is necessary, which is achieved by increasing reservoir pressure when water or gas is injected into the oil reservoir. It is also necessary to have a reservoir pressure above the saturation pressure of oil with gas. Effective methods are recommended to reduce the formation of asphaltene deposits in the oil reservoir in the bottom-hole zone and to restore the production rates of producing wells by pumping heated low-boiling oil components containing carbon atoms C6–C9 in molecules into the well. It has been experimentally established that when the temperature of the specified solvent changes from 20 to 800 °C, the time of complete dissolution of the asphalt-resin compound (bitumen) in the form of balls with a diameter of 5 mm is within 0.20–3.0 hours, and in reservoir conditions with a temperature of 60–80 °C – significantly less for 0.2–0.25 hours. This indicates that before pumping low-boiling oil components containing C6–C9 carbon atoms in the molecules, they must be preheated to reservoir temperature. A method is also proposed for treating the bottom-hole zone of an oil reservoir with a complex solution including low-boiling oil components containing carbon atoms C6–C9 in molecules, hydrochloric and fluoric acids. Originality. Effective methods are proposed to reduce the formation of asphaltene and paraffin deposits in the bottom-hole zone of the oil reservoir and to restore the production rates of producing wells by pumping heated low-boiling oil components into the well, as well as a complex solution with the inclusion of acids. Practical value. A technique has been developed to improve technological processes to reduce the formation of asphalt-resin-paraffin deposits and to establish rational parameters of the installation for producing low-boiling oil components containing carbon atoms C6–C9 in industrial conditions. Using the results of research in oil fields allows you to restore the initial permeability and thereby increase the flow rate of oil wells by 20–30 %.

Creating a Defined Chirality in Amino Acids and Cyclic Dipeptides by Photochemical Deracemization

Abstract2,5‐Diketopiperazines are cyclic dipeptides displaying a wide range of applications. Their enantioselective preparation has now been found possible from the respective racemates by a photochemical deracemization (53 examples, 74 % to quantitative yield, 71–99 % ee). A chiral benzophenone catalyst in concert with irradiation at λ=366 nm enables to establish the configuration at the stereogenic carbon atom C6 at will. If other stereogenic centers are present in the diketopiperazines they remain unaffected and a stereochemical editing is possible at a single position. Consecutive reactions, including the conversion into N‐aryl or N‐alkyl amino acids or the reduction to piperazines, occur without compromising the newly created stereogenic center. Transient absorption spectroscopy revealed that the benzophenone catalyst processes one enantiomer of the 2,5‐diketopiperazines preferentially and enables a reversible hydrogen atom transfer that is responsible for the deracemization process. The remarkably long lifetime of the protonated ketyl radical implies a yet unprecedented mode of action.