DFT calculations have been used to investigate the conformational landscape of a library of 1,3-bis[oxo/thioxo-thiazolinyl] aromatic compounds with two stereogenic Csp2-Nsp2 axes (63 compounds). The good correlation between the experimental and DFT-calculated rotational barriers for five of these compounds allowed the use of DFT as a predictive tool for the entire library. The library was generated by systematically varying the position and number of methyl substituents on the central aromatic ring and on the two oxo/thioxo-thiazoline rings. The predicted rotational barriers span from 3 to 58 kcal/mol at 298.15 K, placing these structures across all three categories defined by LaPlante's classification of rotational stereoisomers. DFT calculations unveiled the preferred rotational pathways, highlighting the main factors influencing the energetic cost of the rotation: intramolecular donor-acceptor interactions, ring distortions, and the nature of the exocyclic heteroatom of the thiazoline rings. The structure-rotational barrier relationship obtained for these molecules with two C-N stereogenic axes represents reference values for the design of atropisomers with aryl-thiazoline scaffolds for various applications, such as chiral bioactive compounds. Also, 15N NMR data are reported for some of the synthesized compounds.

As there are scarce studies on the effect of TiO2 hydroxylated surfaces on the OER, this study provides a systematic investigation using density functional theory (DFT) calculations for the six degrees of hydroxylation and the oxygen coverage on each anatase (100) and (101) surface. Possible changes in mechanisms and active sites when transitioning from one degree of hydroxylation/oxygen coverage to the other were investigated using the thermodynamic model. The associative mechanisms were predicted on highly hydroxylated surfaces (TiO2(100) and TiO2(101): 100% and 86%, respectively), while the associative mechanism was competing with the binuclear one on moderately hydroxylated surfaces (TiO2(100) and TiO2(101): 71% and 57%, respectively). On the least hydroxylated surfaces, an associative mechanism occurred with the aid of bridging oxygen (TiO2(100) and TiO2(101): 43% and 29%, respectively). The analysis was performed from the perspective of balancing the number of electrons between the electron donor (H*-Ob) and electron acceptor (HO*, O*, and HOO*-Ticus) groups. This relation affected both the position of the Fermi level and the strength of adsorption of the OER intermediates. The data were also integrated into the scaling relationship regimes, with the trendlines of O* adsorption energies on titanium sites being very close either to the HOO* trendlines or to the HO* trendlines. The adsorption on the three-coordinated surface oxygen atom (O3c) shifted the intercept closer to the mid of HO* and HOO* intercepts. This imprinted lower theoretical overpotentials. The donor-acceptor electron balance influenced the adsorption energies to a much larger extent than the coverage regimes, which had a negligible effect.

New secondary alcohols of type Ar-CHOH-hetaryl and MeCHOH-hetaryl, the radical hetaryl being a pyrroloazine, were investigated in solid state by X-ray single-crystal diffraction analysis, Hirshfeld analysis and DFT methods to assess their crystallographic features. One of the most important features is the presence of the hydroxyl group bonded to an asymmetric carbon atom which was involved in strong hydrogen bonds. The driving force of crystal packing is H-bond with the O-H···O=C/N≡C bonds being considered as strong comparative to carboxylic acids. These structural properties and binding affinity might lead to enhanced bioavailability of these particular pyrrolo-azines

Raman spectroscopy can provide highly sensitive and detailed information about the structural fingerprint of molecules, enabling their identification. In this study, our aim is to understand the enhanced intensity observed in experimental Raman measurements. Five azobenzene derivatives were selected, each substituted with different functional groups, for both experimental and theoretical investigations. To reproduce the experimental trend, we employed various levels of theory using the QM-DFT approach. Theoretical results were compared to experimental data through both qualitative and quantitative analyses. A good correlation between theoretical and experimental results was achieved when considering electronic transitions to predict the theoretical Raman spectra and interpret the experimental data. Our theoretical results indicate that even dark (nπ*) transitions, which are forbidden and have an oscillator strength close to zero, can have a signature in the Raman spectra due to the resonance effect with incident energy. Additionally, the vibrational modes stimulated by the presence of ππ* bright states, being at the pre-resonance with the incident energy, was clearly separated from the vibrational frequencies of the dark states, which was evinced in the Raman fingerprint. Theoretical Raman spectra of azobenzene derivatives, substituted with push-pull moieties, revealed contributions from the charge transfer transitions (nπ*CT, ππ*CT) as well as back-donation of electron density, observed for the first time in an azobenzene derivative. Our protocol, proposing a quantitative and qualitative overlap between theoretical and experimental data, confirms the presence of combination modes between vibrational levels and electronically excited states.

This article presents an extensive Cambridge Structural Database (CSD) analysis on the presence and the role of the halogen bonds in the 5-chlorinated pyrazole motif. The study involved eighty CSD structures (83 .cif) and two new crystals of 1-aryl-5-chloropyrazoles obtained by us with the aim to establish the role of the chlorine atom attached at C-5 of the pyrazole ring both as donor and acceptor of the halogen bond. Different types of halogen contacts appear in 50 % of the investigated molecules. Chlorine atom in the 5-chloropyrazoles structures is involved in Cl & sdot;& sdot;& sdot;Cl, & sdot;& sdot;& sdot; Cl, Cl & sdot;& sdot;& sdot;Y & sdot;& sdot;& sdot; Y (Y: O, N, etc.), and Cl & sdot;& sdot;& sdot;pi & sdot;& sdot;& sdot; pi halogen contacts. The most numerous contacts found were of type Cl & sdot;& sdot;& sdot;Y & sdot;& sdot;& sdot; Y (Y: O, N, etc.). The two new 1-aryl-5-chloropyrazole structures reported herein present Cl & sdot;& sdot;& sdot;O & sdot;& sdot;& sdot; O contacts at the sum of the vdW distance. The Cl & sdot;& sdot;& sdot;O & sdot;& sdot;& sdot; O contacts were evaluated also through DFT methods compared with other bonds acting on the same direction.

Across the last years, substantial efforts were done to understand the limitations of the oxygen evolution reaction (OER) catalysts and to develop robust ones such as to solve the efficiency problem in water splitting. Fundamental understanding represents a pathway towards designing superior catalysts. In this direction, several descriptors (eta(TD), ESSI, G(max)(eta)) have been derived based on the adsorption energies of the OER intermediate moieties (Delta E-HO*/Delta E-O*/Delta E-HOO*) for faster screening of the materials. A universal scaling between the adsorption energies of HO* and HOO* was established for a wide range of materials and in many cases was shown to govern the minimum theoretical overpotential. On the other hand, the scaling between the adsorption energies of HO* and O* fragments have a large scattering along the trendline. In this work we derive five trends for the O* adsorption energies based on theoretical overpotential intervals, using data collected from the published studies employing DFT calculations for OER. It is shown that the best materials have an adsorption energy for HO* placed within a limited interval, yet sufficiently large for a pool of promising catalysts (-0.5,1.5 eV), and that the adsorption energies of O* scales with that of HO* at a slope of one and an intercept of 1.81 eV. Furthermore, a decrease of the intercept for the scaling between HOO* and HO* from 3.14 (valid for all data analyzed) to 3.03 eV is found. For three of the other four trends, the slope of the adsorption energies of O*/HO*scaling is one with intercepts closer either to HOO* (2.2/2.78) or to HO*(1.43/0.78) adsorption energies. For each set of data, the scaling between HOO* and HO* adsorption energies varies from 3 to 3.37 eV. Separately, the trends for O* adsorption energies were analyzed for the TiO2(110) semiconducting rutile surface when doped with transition metals and modified (i) with HO* or H* co-adsorbed fragments that act as charge donor/acceptor moieties or (ii) when the surface was provided with an excess or a lack of electrons. The analysis was performed using the data collected from the published literature, supplemented by additional calculations. Clear trends based on the amount of charge were obtained when standard GGA functionals were used. An understanding for the origin of the large variation of the oxygen adsorption energies for the systems that have similar adsorption energies for the HO*/HOO* is provided. However, when the Hubbard corrected GGA functional is used, some trends change. Clearly, it is still a challenge describing accurately and in a cost-effective manner the adsorption of OER moieties on the undoped or doped transition metal oxides, especially for O*. A strategy to get further insight into the origin of large variations of oxygen adsorption energies for the materials that have similar adsorption energies of HO* and HOO* is discussed.

Graphene nanoclusters (GNCs), part of the graphene family of nanomaterials, are attracting interest as promising Pt free catalysts for the Oxygen Reduction Reaction (ORR) at the cathode of the fuel cells. This investigation focuses on the theoretical prediction of their possible edge activity towards ORR determined by their shape, size and termination type. In this framework, using density functional theory (DFT) we examined the zigzag (zz) and armchair terminated (ac) triangular (T), rhombohedral (R) and hexagonal (H) GNCs of various sizes, ranging from C13 to C114. The theoretical onset overpotential (ηth,onset) indicate that several GNC edges could be active for ORR. The model indicates that the zigzag edges of all triangular GNCs (C13–C46) as well as of the largest investigated rhombohedral shapes (C48, C70) are active for ORR. A correlation between the band gaps, spin densities and p-band centers of the edge carbon atoms and the adsorption energies of the ORR intermediate moieties (HOO*/O*/HO*) are discussed and which are directly related to their activity. One trend is related to the decrease of the adsorption energies with the decrease of the band gap and accordingly an increase of their ORR activities. The case studies, show that the explicit water model developed by using machine learning potentials and combined with DFT, stabilizes the ORR intermediates stronger than the implicit one, thus increasing slightly the onset overpotential. Overall, this computational study enhances our fundamental understanding of the edges of GNC for their potential application in electrocatalysis without doping.

We have investigated the possible activity of the N-doped graphene quantum dots (N-GQD) toward the oxygen reduction reaction (ORR) using density functional theory (DFT) method. The effect of the shape (triangular (N-GQDT), rhombohedral (N-GQDR) and hexagonal (N-GQDH)), connected both with the zigzag (zz) and armchair (ac) edge terminations of the GQD and with the location of the N atom across the sheets are investigated. The activity of part of the studied N-GQDTac, GQDRac, N-GQDHac and N-GQDHzz structures improves significantly compared to the similar pristine structures. On the other hand, no matter on the location of the N in the N-GQDTzz and in the N-GQDRzz, their activity gets worsen, when compared with the activity of the pristine structures or with the activity of the other four investigated structures. N-GQDTac and N-GQDRac are the structures with the most possible locations of N, that generates active sites. CN bond breaking takes place in the triangular shapes (N-GQDTzz and N-GQDTac) when oxygen adsorption takes place. These bonds are less likely to regenerate and new reaction sites are created. The new reaction site created on the N-GQDTzz represents a possible active site compared to the site generated on the N-GQDTac, that is highly inactive.

The role of halogen bonding as a supramolecular directing interaction was investigated in a series of ten 3-halogenocoumarin derivatives using X-ray diffraction analysis. Halogen bonds might not be as strong as classical hydrogen bonds in molecules such as substituted coumarins but are nevertheless expected to play a certain role in the supramolecular assemblies. Hirshfeld surface analysis, full interaction maps and quantum calculations are used to identify halogen interactions such as X···O, X···π or interhalogen contacts of type I and II, where X is a halogen atom. The halogen interactions in this series appear to be in competition with other supramolecular interactions which leads to a larger structural diversity than expected. This might be due to the steric shielding by the ortho substituents of the halogen atom in the 3-position on the lactone ring of the coumarin motif which are themselves strong hydrogen bond acceptors or donors, but also to the relatively abundant presence of π- π interactions between the aromatic coumarin moieties.

Graphene oxide (GO) and N-doped graphene [(N)G] graphenes were submitted to H-2 glow discharge under different discharge regimes, in both the negative glow and positive column plasma regions. The resulted catalysts were fully characterized using several techniques such as Raman, DRIFT and XPS spectroscopy, powder X-ray diffraction, H-2 pulse chemisorption and H-2-, CO2- and NH3-TPD experiments. Density functional theory calculations were performed taking a slab model of graphene sheet with an optimized C-C bond length (1.426 angstrom) and a 16 angstrom vacuum layer between sheets. An overview of these characterizations showed that the O/C atomic ratio of GO is influenced by the plasma regime, indicating the occurrence of O removal, as also predicted by DFT calculations. In the case of (N)G, the plasma treatment also removes pyridinic N with an increase of the C/N ratio. The efficiency of the plasma modification has been checked through catalytic tests in hydroisomerization of 1-octene and hydrogenation of alpha-methyl-styrene. Contrarily to classical thermal activation requiring high temperatures, the generation of the defects by treating with plasma occurs at voltages in the range of 2 5 kV. In consequence, the hydrogenation and isomerization of alkenes resulted with high yields and good selectivities. Graphene prepared from sodium alginate from brown algae was considered as reference in these investigations.

Nitrogen-doped graphene represents a good alternative and a promising catalytic structure for the oxygen reduction reaction (ORR) in fuel cell applications compared with the more costly Pt-containing catalyst materials. In the present study, using density functional theory calculations, we analyze the effect of the oxygen functional groups (HO*/O*) that are highly probable to be coadsorbed in the vicinity of reaction sites on the undoped and N-doped zigzag graphene nanoribbon edges. These coadsorbates on some of the structures produce local structural changes around the active sites (i.e., the cyclic C-N bond breaking when O* is adsorbed near the most outside graphitic nitrogen.ending in the formation of the pyridine site and of new C active sites, the formation of hydrogen bonds, etc.) and accordingly an electronic modification of the C active sites compared to the structures without coadsorbates (i.e., variation of the p state intensities close to the Fermi level and accordingly of the bond strength that varies proportionally with the distance from the coadsorbate). All these changes are reflected in the final activities of the sites toward the ORR and results in either higher or lower theoretical overpotentials. These overpotentials were patterned into a volcano plot. The most active sites are those from the locally modified structures-when graphitic N was changed in protonated pyridinic site by the presence of O* coadsorbate, the site next to graphitic N when in the vicinity is the coadsorbed HO* fragment and the edge of undoped graphene with no coadsorbate present. In this last case, the coadsorbate worsens the activity. The study was performed in the context of almost nonexistent studies of this type.coadsorbents effects on graphene systems.

Density Functional Theory calculations were performed on N doped graphene sheet to investigate the trends for adsorption energy variation of oxygen reduction reaction intermediates (HOO*, O*, HO*) when the N concentration increases from 0N (0%) to 1N (33%), to 2N (67%) and to 3N (100%) around the C active site. The impact of the distance between the doping N atoms and the C active site is also studied. Last, the impact of additionally co-adsorbed HO*/O* intermediates was probed. For all the studied systems the magnitudes with which varies the adsorption energies are shaped by the HO*/HOO* capability of accommodating less charge than O* (i.e according to octet rule 1e(-) vs. 2e(-)). When N concentration increases, adsorption energy of O* increases with a much higher magnitude than that of HO*/HOO* (i.e with 5 eV vs. 2.7 eV, when going from 0N to 3N). In the presence of the O* co-adsorbate, adsorption energy of intermediates on the investigated active site decrease with a much higher magnitude than when 1HO* is present as co-adsorbate (approximate to 2 eV vs. 1 eV). The theoretical overpotential trends are evaluated using Delta G(HO*)-Delta G(O*) descriptor and are found to be significantly influenced by all these environmental changes around the active site. By applying the water stabilization effects, the activity trends remain the same as when it is not taken into account. These results reveal aspects of ORR activity variations that take place when N is clustering on graphene sheets, structures that can be possible as a function of synthesis procedures that could lead to unevenly distribution of dopants in the matrix.

Multiple strategies to overcome the intrinsic limitations of the oxygen evolution reaction (OER) have been proposed by numerous research groups. Despite the substantial efforts, the driving force required for water oxidation is largely making the reaction inefficient. In the present work, we collected published studies involving DFT calculations for the OER, with the purpose to understand why the progress made so far, for lowering the overpotential of the reaction, is relatively small. The data revealed that the universal scaling relationship between HO* and HOO* intermediates is still present and robust, despite the variety in methods and structures used for calculating the binding energies of the intermediates. On the other hand, the data did not show a clear trend line regarding the O* binding. Our analysis suggested that trends in doped semiconducting oxides behave very differently from those in other oxides. This points towards a computational challenge in describing doped oxides in a realistic manner. We propose a way to overcome these computational challenges, which can be applied to simulations corresponding to doped semiconductors in general.

The experimental evidences show that the nanoplatelets of 20 rim wide and 3 - 4 nm height, deposited on graphene promote Suzuki cross-coupling reactions. In this regard the adsorption and activation of halobenzene (C6H5Cl(Br/I)), of phenylboronic acid (C6H5B(OH)(2)) and the formation of biphenyl (C6H5-C6H5) molecules on surfaces that simulates the facets and edges of the gold nanoplatelets, were investigated by means of DFT calculations. The activation and reaction energies of halobenzene molecules are the lowest on the edge between (111)/(100) facets, but even so for C-Cl is relatively high. On all surfaces the energies decrease with decreasing the C-X bond strengths. Therefore, for C-I bond the dissociation is possible also on (111), (100) and the edge between (111)/(111) facets. The phenylboronic acid dissociates easily on all surfaces in the presence of adsorbed hydroxyl fragments. The C-C coupling between two phenyl (C6H5) fragments is the least sensitive to the type of sites, being the rate determining step, competing with C-Cl dissociation. The strong adsorption energy of KI molecule indicate possible poisoning of the (111)/(100) edge and of the (111) facet. Overall the studies show a probability of the reaction to take place especially on the edge between (111)/(100) microfacets. If some of the reactions steps are straightforward predicted to take place on the nanoplatelets sites, the reaction steps with higher activation energies are expected to be influenced also by other parameters such as interfaces between nanoplatelets and graphene and which are intended to be studied separately.

5-Iodo-1-arylpyrazoles are interesting templates for investigating the halogen bond propensity in small molecules other than the already well-known halogenated molecules such as tetrafluorodiiodobenzene. Herein, we present six compounds with different substitution on the aryl ring attached at position 1 of the pyrazoles and investigate them in the solid state in order to elucidate the halogen bonding significance to the crystallographic landscape of such molecules. The substituents on the aryl ring are generally combinations of halogen atoms (Br, Cl) and various alkyl groups. Observed halogen bonding types spanned by these six 5-iodopyrazoles included a wide variety, namely, C–I⋯O, C–I⋯π, C–I⋯Br, C–I⋯N and C–Br⋯O interactions. By single crystal X-ray diffraction analysis combined with the descriptive Hirshfeld analysis, we discuss the role and influence of the halogen bonds among the intermolecular interactions.

Films of few-layers defective N-doped or undoped graphene (10-15 nm) containing antimony oxide nanoparticles (15-30 nm) have been prepared on quartz by pyrolysis of alginate or chitosan adsorbing Sb(OAc)(3). XPS shows that the prevalent Sb oxidation state is +III, while thermoprogrammed CO2 desorption shows that these films exhibit basic sites. These thin films have used as basic catalysts to promote the Michael addition of active methylene compounds and the Henry condensation. These results have been rationalized by DFT calculations that have shown that undercoordinated or two-fold coordinated oxygen atoms on SbOx clusters can act as basic sites, providing a wide range of basic strength. (c) 2020 Elsevier Inc. All rights reserved.

N-doped defective graphene [(N)G] obtained by pyrolysis at 900 degrees C of chitosan contains about 3.7% of residual N atoms, distributed as pyridinic, pyrrolic and graphitic N atoms. It has been found that (N)G acts as basic catalyst promoting two classical C-C bond forming nucleophilic additions in organic chemistry, such as the Michael and the Henry additions. Computational calculations at DFT level of models corresponding to the various N atoms leads to the conclusion that N atoms are more stable at the periphery of the graphene sheets and that H adsorption on these sites is a suitable descriptor to correlate with the catalytic activity of the various sites. According to these calculations the most active sites are pyridinic N atoms at zig-zag edges of the sheets. In addition, N as dopant changes the reactivity of the neigh. bour C atoms. Water was found a suitable solvent to achieve high conversions in both reactions. In this solvent the initial distribution of N atoms is affected due to the easy protonation of the N-py to N-pyH sites. As an effect, C edge sites adjacent at N-PyH with an appropriate reactivity towards the alpha-C-H bond breaking are formed. The present results show the general activity of N-doped graphene as base catalysts and illustrate the potential of carbocatalysis to promote reactions of general interest in organic synthesis. (C) 2019 Elsevier Inc. All rights reserved.

Halogen bonding as important directional forces in the supramolecular structure of iodinated 1-arylpyrazoles.