Gas-phase C60Hn+q (n = 0-4, q = 0,1) fullerenes and fulleranes: spectroscopic simulations shed light on cosmic molecular structures.

The discovery of C60, C60+, and C70 in the interstellar medium has ignited a profound interest in the astrochemistry of fullerene and related systems. In particular, the presence of diffuse interstellar bands and their association with C60+ has led to the hypothesis that hydrogenated derivatives, known as fulleranes, may also exist in the interstellar medium and contribute to these bands. In this study, we systematically investigated the structural and spectroscopic properties of C60Hn+q (n = 0-4, q = 0,1) using an automated global minimum search and density functional theory calculations. Our results revealed novel global minimum structures for C60H2 and C60H4, distinct from previous reports. Notably, all hydrogenated fullerenes exhibited lower ionization potentials and higher proton affinities compared to C60. From an astrochemical perspective, our results exposed the challenges in establishing definitive spectroscopic criteria for detecting fulleranes using mid-infrared and UV-Vis spectroscopies. However, we successfully identified distinct electronic transitions in the near-infrared range that serve as distinctive signatures of cationic fulleranes. We strongly advocate for further high-resolution experimental studies to fully explore the potential of these transitions for the interstellar detection of fulleranes.

Low Energy Isomers and Infrared Spectra Simulations of C4H3N, C4H4N, and C4H5N and Related Ions.

The relative stability of pyrrole derivatives were investigated by applying a global minimum (GM) search for the low-lying energy structures of C4HnN (n = 3-5) clusters at neutral, anionic, and cationic states. Several low-energy structures, previously not reported, were identified. The present results reveal a preference for cyclic and conjugated systems for the C4H5N and C4H4N compounds. In particular, the structures of the cationic and neutral C4H3N species are different from the anionic ones. For the neutrals and cations, cumulenic carbon chains were found, while for the anions, conjugated open chains were obtained. Of particular relevance, the GM candidates C4H4N+ and C4H4N are different from those reported previously. For the most stable structures, infrared spectra were simulated and the main vibrational bands were assigned. Also, a comparison with available laboratory data was done aiming to corroborate with experimental detection.

Revisiting the Spectrum of Co(CN)63-: The Role of Correlation, Solvation, and Vibronic and Spin-Orbit Couplings.

In the present work, we revisit the spectrum of the hexacyanocobaltate(III) ion, [Co(CN)6]3-, which has been considered a prototype complex in the coordination chemistry, with modern quantum chemistry methods. The main features have been describing by revealing the role of different effects, such as vibronic coupling, solvation and spin-orbit coupling. The UV-vis spectrum is composed by two bands (1A1g → 1T1g and 1A1g → 1T2g), characterized by singlet-singlet metal-centered transitions, and a more intense third one, characterized by charge transfer transition. There is also a small band shoulder. The first two are symmetry-forbidden transitions in the Oh group. Their intensity can only be explained by a vibronic coupling mechanism. For the band shoulder, additional to vibronic coupling, spin-orbit coupling is also necessary, since the transition is characterized as singlet to triplet, 1A1g → 3T1g.

Automated Search For The Low-Lying Energy Isomers of Rhamnolipids and Related Organometallic Complexes.

Rhamnolipids (RMLs) are a widely studied biosurfactant due to their high biodegradability and environmentally friendly production. However, the knowledge of the structure-property relationship of RMLs is imperative for the design of highly efficient applications. Aiming to a better understanding of it at a molecular level, we performed an automated search for low energy structures of the most abundant RMLs, namely, Rha-C10 , Rha-C10 -C10 , Rha-Rha-C10 and Rha-Rha-C10 -C10 and their respective C2 -congeners. Besides that, selected neutral metal complexes were also considered. We found that several low-energy congeners have internal hydrogen bonds. Moreover, geometries in "closed" conformation were always more stable than "open" ones. Finally, the energy diferences between open and closed conformations of K+ , Ni2+ , Cu2+ and Zn2+ complexes were found to be 23.5 kcal mol-1 , 62.8 kcal mol-1 , 24.3 kcal mol-1 and 41.6 kcal mol-1 , respectively, indicating a huge structural reorganization after the complex formation.

Taming the Antiferromagnetic Beast: Computational Design of Ultrashort Mn-Mn Bonds Stabilized by N-Heterocyclic Carbenes.

The development of complexes featuring low-valent, multiply bonded metal centers is an exciting field with several potential applications. In this work, we describe the design principles and extensive computational investigation of new organometallic platforms featuring the elusive manganese-manganese bond stabilized by experimentally realized N-heterocyclic carbenes (NHCs). By using DFT computations benchmarked against multireference calculations, as well as MO- and VB-based bonding analyses, we could disentangle the various electronic and structural effects contributing to the thermodynamic and kinetic stability, as well as the experimental feasibility, of the systems. In particular, we explored the nature of the metal-carbene interaction and the role of the ancillary η6 coordination to the generation of Mn2 systems featuring ultrashort metal-metal bonds, closed-shell singlet multiplicities, and positive adiabatic singlet-triplet gaps. Our analysis identifies two distinct classes of viable synthetic targets, whose electrostructural properties are thoroughly investigated.

Effect of lysed and non-lysed sickle red cells on the activation of NLRP3 inflammasome and LTB4 production by mononuclear cells.

OBJECTIVE AND DESIGN: This study tested the hypothesis that sickle red blood cell (SS-RBC) can induce inflammasome NLRP3 components gene expression in peripheral blood mononuclear cells (PBMCs) as well as interleukin-1ß (IL-1ß) and leukotriene B4 (LTB4) production. Additionally, we investigated the effect of hydroxyurea (HU) treatment in these inflammatory markers. METHODS: PBMCs from healthy donors (AA-PBMC) were challenged with intact and lysed RBCs from SCA patients (SS-RBC) and from healthy volunteers (AA-RBC). NLRP3, IL-1ß, IL-18 and Caspase-1 gene expression levels were assessed by quantitative PCR (qPCR). IL-1ß protein levels and LTB4 were measured by ELISA. RESULTS: We observed that lysed SS-RBC induced the expression of inflammasome NLRP3 components, but this increase was more prominent for CASP1 and IL18 expression levels. Moreover, we observed that intact SS-RBC induced higher production of IL-1ß and LTB4 than lysed SS-RBC. Although SCA patients treated with HU have a reduction in NLRP3 gene expression and LTB4 production, this treatment did not modulate the expression of other inflammasome components or IL-1ß production. CONCLUSIONS: Thus, our data suggest that caspase-1, IL-1ß and IL-18 may contribute to the inflammatory status observed in SCA and that HU treatment may not interfere in this inflammatory pathway.

Production of Long-Lived Benzene Dications from Electron Impact in the 20-2000 eV Energy Range Combined with the Search for Global Minimum Structures.

In this work, we report a systematic search of metastable C6Hn2+ (n = 1-6) dications from electron impact time-of-flight measurements of several benzene derivatives in combination with global minimum search based on the genetic algorithm. Our theoretical calculations reveal that the C6Hn2+ (n < 6) global minimum structures are completely different from that of the benzene dication, featuring linear carbon chains and/or cyclopropenylium moieties. Experimentally, the doubly charged species were investigated for a wide range of electron impact energies, from 20 to 2000 eV, for benzene and several monosubstituted compounds containing either electron-withdrawing or -donating groups. Furthermore, the C6Hn2+ production, evaluated from the yields of the dications with respect to that of the parent ion (or parent dication), was compared to those obtained from charge exchange in the doubly charged 2E spectra and electron impact experiments available in the literature. The yields of the long-lived benzene dications were contrasted to those analogues formed in chlorobenzene. Moreover, the formation of C6Hn2+ species is strongly dependent on the nature of substituent groups, with electron-withdrawing ones favoring the dication formation.

Structure, Stability, and Spectroscopic Properties of Small Acetonitrile Cation Clusters.

Ionization and fragmentation pathways induced by ionizing agents are key to understanding the formation of complex molecules in astrophysical environments. Acetonitrile (CH3CN), the simplest organic nitrile, is an important molecule present in the interstellar medium. In this work, DFT and MP2 calculations were performed in order to obtain the low energy structures of the most relevant cations formed from electron-stimulated ion desorption of CH3CN ices. Selected reaction pathways and spectroscopic properties were also calculated. Our results indicate that the most stable acetonitrile cation structure is CH2CNH+ and that hydrogenation can occur successively without isomerization steps until its complete saturation. Moreover, the stability of distinct cluster families formed from the interaction of acetonitrile with small fragments, such as CHn+, C2Hn+, and CHnCNH+, is discussed in terms of their respective binding energies. Some of these molecular clusters are stabilized by hydrogen bonds, leading to species whose infrared features are characterized by a strong redshift of the N-H stretching mode. Finally, the rotational spectra of CH3CN and protonated acetonitrile, CH3CNH+, were simulated using distinct computational protocols based on DFT, MP2, and CCSD(T) considering centrifugal distortion, vibrational-rotational coupling, and vibrational anharmonicity corrections. By adopting an empirical scaling procedure for calculating spectroscopic parameters, we were able to estimate the rotational frequencies of CH3CNH+ with an expected average error below 1 MHz for J values up to 10.

Mechanistic Insights into the Formation of Lithium Fluoride Nanotubes.

Born-Oppenheimer molecular dynamics (BOMD) and periodic density functional theory (DFT) calculations have been applied for describing the mechanism of formation of lithium fluoride (LiF) nanotubes with cubic, hexagonal, octagonal, decagonal, dodecagonal, and tetradecagonal cross-sections. It has been shown that high energy structures, such as nanowires, nanorings, nanosheets, and nanopolyhedra are transient species for the formation of stable nanotubes. Unprecedented (LiF)n clusters (n≤12) were also identified, some of them lying less than 10 kcal mol-[1] above their respective global minima. Such findings indicate that stochastic synthetic techniques, such as laser ablation and chemical vapor deposition, should be combined with a template-driven procedure in order to generate the nanotubes with adequate efficiency. Apart from the stepwise growth of LiF units, the formation of nanotubes was also studied by rolling up a planar square sheet monolayer, which could be hypothetically produced from the exfoliation of the FCC crystal structure. It was shown that both pathways could lead to the formation of alkali halide nanotubes, a still unprecedented set of one-dimensional materials.

Diboryne Nanostructures Stabilized by Multitopic N-Heterocyclic Carbenes: A Computational Study.

Different families of nanomaterials produced from the stabilization of diboryne (B≡B) units by multitopic N-heterocyclic carbenes (NHCs), such as nanowires, nanorings, and nanotents, were studied by computational methods. Density functional theory calculations with and without periodic boundary conditions were applied to estimate the dependence of the electronic and thermochemical properties of different diboryne macromolecules with respect to the nature of the bridging ligand. Our results show that all diboryne nanostructures studied herein are viable candidates for synthesis. The Janus-type multitopic naphthobis(imidazolylidene) (5), anthrobis(imidazolylidene) (10), and pyracenetetrakis(imidazolylidene) (16) compounds are the best candidates for generating diboryne nanowires. A path to covalent organic frameworks, nanocages, and nanotubes from the optimized diboryne nanostructures is also described. Rather than just scientific curiosity, diboryne nanostructures emerge as interesting targets for the synthesis of main-group nanomaterials.

Fragment and cluster ions from gaseous and condensed pyridine produced under electron impact.

We report on direct measurement of all major ion-fragments and cluster-ions formed during high-energy electron impact of 2 keV on gaseous and condensed-phase pyridine. The ion-fragments of the parent pyridine cation are discussed in groups according to the number of atoms from the aromatic ring. The ion yield distributions within these groups show significant shifts towards higher masses for condensed pyridine compared to gaseous pyridine due to hydrogen migration. A wide spectrum of desorbed hydrogenated fragment-ions and ionic clusters with masses up to 320 u are observed for pyridine. The ion yields for the protonated parent molecule (C5H5NH+), the dehydrogenated dimer (C10H9N2+) and the dehydrogenated trimer (C15H12N3+) depend on the mass of the desorbing ionic clusters. The strongest cluster signals are assigned to binding between the parent cation and subunits of the pyridine molecule. Quantum-chemical calculations reveal that the formation of a bond between the pyridine molecules and a carbenium ion is crucial for the stability of selected cluster ions.

The role of ST2 and ST2 genetic variants in schistosomiasis.

BACKGROUND: Chronic schistosomiasis and its severe complication, periportal fibrosis, are characterized by a predominant Th2 response. To date, specific single nucleotide polymorphisms in ST2 have been some of the most consistently associated genetic variants for asthma. OBJECTIVE: We investigated the role of ST2 (a receptor for the Th2 cytokine IL-33) in chronic and late-stage schistosomiasis caused by Schistosoma japonicum and the potential effect of ST2 genetic variants on stage of disease and ST2 expression. METHODS: We recruited 947 adult participants (339 with end-stage schistosomiasis and liver cirrhosis, 307 with chronic infections without liver fibrosis, and 301 health controls) from a S japonicum-endemic area (Hubei, China). Six ST2 single nucleotide polymorphisms were genotyped. Serum soluble ST2 (sST2) was measured by ELISA, and ST2 expression in normal liver tissues, Hepatitis B virus-induced fibrotic liver tissues, and S japonicum-induced fibrotic liver tissues was measured by immunohistochemistry. RESULTS: We found sST2 levels were significantly higher in the end-stage group (36.04 [95% CI, 33.85-38.37]) compared with chronic cases and controls (22.7 [95% CI, 22.0-23.4], P < 1E-10). In addition, S japonicum-induced fibrotic liver tissues showed increased ST2 staining compared with normal liver tissues (P = .0001). Markers rs12712135, rs1420101, and rs6543119 were strongly associated with sST2 levels (P = 2E-10, 5E-05, and 6E-05, respectively), and these results were replicated in an independent cohort from Brazil living in a S mansoni endemic region. CONCLUSIONS: We demonstrate for the first time that end-stage schistosomiasis is associated with elevated sST2 levels and show that ST2 genetic variants are associated with sST2 levels in patients with schistosomiasis.

Sickle red cells as danger signals on proinflammatory gene expression, leukotriene B4 and interleukin-1 beta production in peripheral blood mononuclear cell.

This study tested the hypothesis that sickle red blood cell (SS-RBC) induce Toll-like receptors (TLR) and Nod-like receptor family, pyrin domain containing 3 (NLRP3)- inflammasome expression in peripheral blood mononuclear cells (PBMC). TLR and NLRP3 inflammasome could contribute to the maintenance of the inflammatory status in sickle cell anemia (SCA) patients, since SS-RBC act as danger signals activating these pathways. In this study, first, we evaluated TLR (2, 4, 5 and 9), NLRP3, Caspase-1, interleukin (IL)-1ß and IL-18 expression in PBMC freshly isolated from SCA patients (SS-PBMC) in comparison with PBMC from healthy individuals (AA-PBMC). In the second moment, we investigated whether SS-RBC could interfere with the expression of these molecules in PBMC from healthy donor, in the absence or presence of hydroxyurea (HU) in vitro. TLRs and NLRP3 inflammasome expression were investigated by qPCR. IL-1ß, Leukotriene-B4 (LTB4) and nitrite production were measured in PBMC (from healthy donor) culture supernatants. TLR2, TLR4, TLR5, NLRP3 and IL-1ß were highly expressed in SS-PBMC when compared to AA-PBMC. Additionally, SS-RBC induced TLR9, NLRP3, Caspase-1, IL-1ß and IL-18 expression and induced IL-1ß, LTB4 and nitrite production in PBMC cultures. HU did not prevent TLR and NLRP3 inflammasome expression, but increased TLR2 and IL-18 expression and reduced nitrite production. In conclusion, our data suggest that TLR and inflammasome complexes may be key inducers of inflammation in SCA patients, probably through SS-RBC; also, HU does not prevent NLRP3 inflammasome- and TLR-dependent inflammation, indicating the need to develop new therapeutic strategies to SCA patients that act with different mechanisms of those observed for HU.

Total absorption spectrum of benzene aggregates obtained from two different approaches.

CONTEXT: The study of molecular aggregation effects on the electronic spectrum is essential for the development of optoelectronic devices. However, investigating the entire valence absorption spectrum of aggregates using quantum mechanical methods is a challenging task. In this work, we perform systematic simulations of the absorption spectrum of benzene molecular clusters up to 35 eV applying two approaches based on time-dependent density functional theory. The results show that depending on the dimer packing, different energy shifts occur for the symmetry allowed [Formula: see text] transition, in comparison to the monomer. The transition intensity increases for the band around 6 eV for larger aggregates from the monomer to dimers and tetramer, indicating the occurrence of the symmetry forbidden (in [Formula: see text] point group) [Formula: see text] [Formula: see text] transition. The benzene crystal exhibits a large redshift following the experimental spectrum. Also, the continuum regions of all spectra show a good agreement with the experiments both in gas and solid phases. METHODS: Geometry optimization of the monomer was carried out with Gaussian 09 software using the PBE0/def2-TZVP level of theory. We used dimers and tetramer molecular geometries extracted from the experimental crystal structure. The absorption spectra were directly obtained by the Liouville-Lanczos TDDFT approach with plane waves basis set or indirectly by TDDFT pseudo-spectra calculated in a [Formula: see text] basis followed by analytic continuation procedure to obtain complex polarizability. The former is available at Quantum ESPRESSO, and the latter was calculated using Gaussian 09 with the post-processing performed with a code previously developed in our group.

Higher Bifidobacterium spp. fecal abundance is associated with a lower prevalence of hyperglycemia and cardiovascular risk markers among schoolchildren from Bahia, Brazil.

The gut microbiome has recently been the subject of considerable scientific interest due to its essential bodily functions. Several factors can change the composition and function of the gut microbiome, and dietary habits are one of the most important contributors. Despite the recognition of the probiotic effects related to the genus Bifidobacterium spp. (BIF) studies aiming to assess its relationship with metabolic outcomes show conflicting results, particularly in the child population. This cross-sectional study aimed to evaluate the fecal abundance of BIF in a group of schoolchildren from public schools in Bahia, Brazil, and to investigate their relationship with food consumption and laboratory and anthropometric characteristics. A sample of 190 subjects aged 5 to 19y was randomly selected for dietary, laboratory, and anthropometric assessment. Fecal BIF abundance assessment was performed using the Real-Time Polymerase Chain Reaction assay. Fecal BIF abundance was higher among subjects who had lower intakes of meat. The abundance of BIF was also higher among subjects with lower Waist Circumference and Waist-to-Height Ratio (WHtR). Low BIF abundance was associated with a higher prevalence of hyperglycemia (PR 1.04, 95%CI 1.02-1.07, p = 0.001) and high WHtR (PR 1.04, 95%CI 1.01-1, 08, p = 0.015). These findings allow us to conclude that BIF fecal abundance is related to dietary and anthropometric parameters in schoolchildren, and its increase is associated with positive metabolic outcomes.

Comparison among several vibronic coupling methods.

A comparison of four approaches to account the vibronic coupling in photoabsorption is performed. The methods considered are nuclear ensemble (NE), direct vibronic coupling (DVC), adiabatic Hessian (AH), and vertical gradient (VG). The case study is the symmetry-forbidden [Formula: see text] [Formula: see text]A[Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text]A[Formula: see text] (n [Formula: see text] [Formula: see text]) transition in formaldehyde. Being forbidden in the equilibrium geometry, this transition is entirely induced by vibronic coupling and constitutes an appropriate case to study the performance of different methods. From DVC, it is found that mode 1 (C=O out-of-plane bending) is the most inducing, followed by mode 6 (in-plane C-H asymmetric stretching) and finally by mode 2 (in-plane C-H asymmetric bending). We were able to correlate 17 out of 20 structures obtained from NE with these modes, showing that these two methods, although different in principle, give comparable results. The simulated spectra were obtained for all methods and compared, and each one has its own advantage. In what concerns the transition studied, NE gives the best description of the spectrum, DVC is the only one that easily gives an absolute value for OOS, and AH and VG are the computationally less expensive methods. From the latter two, VG is the less demanding on computational grounds, since it does not require the excited state Hessian.

Bond strength of two universal adhesive systems to human dentin using different strategies.

The objective of this study was to evaluate the microtensile bond strength (µTBS) to dentin of two universal adhesive systems: Single Bond Universal (SBU) and Ambar Universal (AU), used in different adhesion strategies. MATERIALS AND METHOD: Thirty-six human teeth were prepared (n=6) and treated following different adhesive strategies: G1: SBU-etch-and-rinse, applied on dry dentin; G2: SBUetch- and-rinse, applied on moist dentin; G3: SBU-self-etching; G4: AU-etch-and-rinse, applied on dry dentin; G5: AU-etch-and-rinse, applied on moist dentin; G6: AU-self-etching. The specimens were submitted to µTBS test, failure analysis, and scanning electron microscopy (SEM). Data were analyzed with ANOVA and Tukey's tests (p<0.05). RESULTS: Microtensile bond strength was significantly lower in G1 than G2 and G3. AU adhesive performed worse than the SBU system, except in G5. Cohesive and mixed failures predominated in G1 and G2, while adhesive failures predominated in G3 and G5. CONCLUSIONS: Universal adhesives are an interesting innovation, but there are still doubts about their performance, mainly regarding the different protocols provided by the manufacturers. The conventional adhesive strategy on moist dentin demonstrated higher µTBS for both adhesives. The use of the selfetching strategy with the SBU showed promising results.

O objetivo deste estudo foi avaliar a resistência de união à microtração (µTBS) de dois sistemas adesivos universais: Single Bond Universal (SBU) e Ambar Universal (AU), utilizados em diferentes estratégias de adesão. Materiais e método: 36 dentes humanos foram preparados (n=6) e tratados seguindo diferentes estratégias adesivas: G1: SBU-condicionamento e enxágue, aplicado sobre dentina seca; G2: SBU-condicionamento e enxágue, aplicado sobre dentina úmida; G3: SBU-autocondicionante; G4: AU-condicionamento e enxágue, aplicado em dentina seca; G5: AU-condicionamento e enxágue, aplicado sobre dentina úmida; G6: AU-autocondicionante. Os espécimes foram submetidos ao teste de µTBS, análise de falhas e microscopia eletrônica de varredura (SEM). Os dados foram analisados com os testes ANOVA e Tukey (p<0,05). Resultados: A resistência de união à microtração de G1 foi significativamente menor que G2 e G3. O adesivo AU teve um desempenho pior que o sistema SBU, com exceção do G5. Falhas coesivas e mistas predominaram em G1 e G2 enquanto G3 e G5 apresentaram predominância de falhas adesivas. Conclusões: Os adesivos universais representam uma inovação interessante, mas ainda há dúvidas sobre seu desempenho, principalmente em relação aos diferentes protocolos fornecidos pelos fabricantes. A estratégia adesiva convencional em dentina úmida demonstrou maior µTBS para ambos os adesivos. O uso da estratégia autocondicionante com a SBU apresentou resultados promissores.

An Environmental and Nutritional Evaluation of School Food Menus in Bahia, Brazil That Contribute to Local Public Policy to Promote Sustainability.

Aimed at improving the quality of school meals, the Sustainable School Program (SSP) implemented low-carbon meals, twice a week, in 155 schools of 4 municipalities, reaching more than 32,000 students. This study evaluated the environmental impact and nutritional viability of this intervention for this population. The 15 most repeated meals from the conventional and sustainable menus were selected, and we considered the school age group and number of meals served per student/day. Nutritional information was calculated using validated food composition tables, nutritional adequacy was assessed using National School Feeding Program (PNAE) requirements, the level of processing was considered using NOVA classification, and greenhouse gas emissions (GHGE) were estimated using food life cycle assessment (LCA) validated data. We found both conventional and sustainable food menus are equivalent, in terms of nutrients, except for calcium, iron, and magnesium. Sustainable food menus were cholesterol-free. However, there was a reduction of up to 17% in GHGE, depending on the school age group analysed. Considering the greater energy efficiency and lower environmental impact of these food menus, the SSP, therefore, demonstrates that a substantial reduction in climate impact is feasible, successful, and can be an inspiration to other regions globally.

Rotational spectrum simulations of asymmetric tops in an astrochemical context.

Rotational spectroscopy plays a major role in the field of observational astrochemistry, enabling the detection of more than 200 species including a plethora of complex organic molecules in different space environments. Those line detections allow correctly determining the sources and physical properties, as well as exploring their morphology, evolutionary stage, and chemical evolution pathways. In this context, quantum chemistry is a powerful tool to the investigation of the molecular inventory of astrophysical environments, guiding laboratory experiments and assisting in both line assignments and extrapolation of the experimental data to unexplored frequency ranges. In the present work, we start by briefly reviewing the rotational model Hamiltonian for asymmetric tops beyond the rigid-rotor approximation, including rotational-vibrational, centrifugal, and anharmonic effects. Then, aiming at further contributing to the recording and analysis of laboratory microwave spectroscopy by means of accessible, less demanding quantum chemical methods, we performed density functional theory (DFT) calculations of the spectroscopic parameters of astrochemically relevant species, followed by their rotational spectrum simulations. Furthermore, dispersion-correction effects combined with different functionals were also investigated. Case studies are the asymmetric tops H2CO, H2CS, c-HCOOH, t-HCOOH, and HNCO. Spectroscopic parameter predictions were overall very close to experiment, with mean percentage errors smaller than 1% for zeroth order and [Formula: see text] for first-order constants. We discuss the implications and impacts of those constants on spectrum simulations, and compare line-frequency predictions at millimeter wavelengths. Moreover, theoretical spectroscopic parameters of c-HCOOH and HNCO are introduced for the first time in this work.

Acrylic acid hydrodeoxygenation reaction mechanism over molybdenum carbide studied by DFT calculations.

Platinum- and palladium-based catalysts are commonly used in hydrogenation reactions, but they present a great disadvantage of being quite expensive. In most cases, they can be substituted by cheaper alternative catalysts formed by transition metal carbides, such as molybdenum carbide (Mo2C). Among the reactions that can be catalyzed by Mo2C, hydrodeoxygenation (HDO) presents a great technological interest, especially in biofuel production. Nonetheless, the selectivity of carbides in HDO reactions of fatty acids is not well understood yet. In the present work, the reaction mechanism of the acrylic acid HDO over Mo2C, a fatty acid model molecule, was studied by density functional theory (DFT), with Perdew-Burke-Ernzerhof (PBE) functional and periodic boundary conditions. A global mechanism is proposed, divided in four steps, from acrylic acid to propane. In the first reaction step, decomposition by C-OH bond cleavage, with 24 kcal mol- 1 of activation energy, dominates over C=C and C=O hydrogenation. This result is in line with the absence of propanoic acid among the products and the formation of acrolein, as shown in an experimental work previously published. The proposed global mechanism is in fair agreement with the experimental findings. The main product is propane, which has the same number of carbon atoms of the reactant. This mechanism can be viewed as a model for HDO of any fatty acid catalyzed by Mo2C, since acrylic acid has the minimal structural features of fatty acids, i.e., a carboxyl group and a C=C double bond. Graphical Abstract HDO over Mo2C provides a product with same carbon atoms number of the reactant.