Magnetic shielding constants for an isolated fullerene C60, cucurbituril CB[9], and the host-guest complex C60@CB[9] were calculated as a function of separation of the monomers. Our results in the gas phase and water indicate a significant variation of the magnetic properties for all atoms of the monomers in the complex and after liberation of fullerene C60 from the interior of the CB[9] cavity. The interaction between the two monomers results in a charge transfer that collaborates with a redistribution of electron density to deshield the monomers.
We report first-principles calculations carried out to analyze the adsorption of calcium on the outer surface of the fullerene C60, yielding [C60?+?mCa]. Geometric optimization (GO) and molecular dynamics (MD) simulation were performed using the plane-wave pseudopotential method within the framework of density functional theory (DFT) and time-dependent DFT (TD-DFT) to investigate the configurations, the associated energies in the ground state, and the stabilities of fullerenes and endofullerenes doped with radioactive sodium iodide when they interact with calcium atoms on the outer fullerene surface (i.e., [nNa131I@C60?+?mCa]). The reason for investigating these calcium-functionalized (endo)fullerene systems was to gauge their potential stability when used as vectors to deliver radioiodine to cancerous tissue in the human body. In the simulations, we found that the geometric limit on the number of calcium atoms that can be physisorbed on the outer surface of an empty fullerene while maintaining its structural stability is 28 calcium atoms, which also takes into account the proportional expansion of the fullerene as the number of absorbed calcium atoms increases. However, the stability of a fullerene system during calcium adsorption also strongly depends on whether any atoms or molecules are being encapsulated by the fullerene, as these encapsulated atoms/molecules can also interact with the fullerene and influence its stability. A Mulliken electronegativity analysis revealed that, when atoms inside and/or outside the fullerene donate charge (electrons) to the fullerene, the fullerene expands. The excess charge on the carbon atoms of the fullerene weakens some of the carbon–carbon bonds, potentially causing them to break, in which case the fullerene loses its ability to encapsulate molecules and releases them.
Graphical Abstract DFT simulation of a endo fullerene doped with radioactive sodium iodide interacting with 28 calcium atoms in a geometric arrangement
The interaction of external water molecules with hydrated pyrrole-2-carboxaldehyde PCL/(H2O)n complexes was investigated. The work was supported by both theoretical [DFT/TD-DFT methods using 6-311G++(d,p) basis set in the ground (S0) and excited (S1, S2, S3)states] and experimental [UV-Vis, FTIR and Raman] verification. The focus of the present work was on the weak intermolecular O–H?O, N–H?O–H hydrogen bonded interaction (IerHB) between PCL and external water molecules, and the influence of increasing the number of water molecules to form hydrated PCL/(H2O)n complexes. Effects were observed on different vibrational normal modes and on electronic transition levels. A hydrogen-bonded network of water induces a shift to higher energy in certain normal modes of PCL to form stable PCL/(H2O)n complexes by lowering the barrier energy. Potential energy distribution (PED) analysis indicates a significant charge transfer from PCL to water by creating a water bridge. Hydrogen bonding effects account for the substantial red shift and broadness in νNH, νCO vibrational modes. Water rearrangement turns out to be the main driving force for hydrated complex formation.
The dual role of the ionic liquid 1-butyl-3-methyl-imidazolium trifluoroacetic acid ([C4mim]TFA) as an extractant for thiophene (TH) and a catalyst for the oxidation of TH was explored at the molecular level by performing density functional theory (DFT) calculations. The calculated interaction energies demonstrated why [C4mim]TFA is a better extractant for thiophene sulfone (THO2) than for TH. Two pathways were proposed for the oxidation of TH to THO2 with [C4mim]TFA acting as a catalyst. In the dominant pathway, a peracid is formed which then oxidizes TH to the sulfoxide and sulfones. The presence of [C4mim]TFA was found to greatly reduce the barrier to the oxidative desulfurization (ODS) of TH using H2O2 as an oxidant.
This paper inquires the C60 capabilities to contain radio-iodide (131I2) molecules. The encapsulation conditions are investigated applying first principles method to simulate with geometric optimizations and molecular dynamics at 310 K and atmospheric pressure. We find that the n131I2@C60 system, where n?=?1, 2, 3…, is stable if the content does not exceed three molecules of radio-iodide. The application of density functional theory allows us to determine that, the nanocapsules content limit is related with the amount of charge that is transferred from the iodine 131I2 molecules to the carbon atoms in the fullerene surface. The Mulliken population analysis reveals that the excess of charge increases the repulsive forces between atoms and the bond length average in the C60 structure. The weakened bonds easily break and will critically damage the encapsulation properties. Additionally, we test the interaction nanocapsules with different amounts of radioactive iodine diatomic molecules content with calcium atoms, and find that only the fullerene containing one radioactive iodine diatomic molecule was able to interact with up to nine atoms of calcium without disrupting or cracking. Other fullerenes with two and three radio iodine diatomic molecules cannot resist the interaction with a single calcium atom without cracking or being broken.
Catalytic fields illustrate topology of the optimal charge distribution of a molecular environment reducing the activation energy for any process involving barrier crossing, like chemical reaction, bond rotation etc. Until now, this technique has been successfully applied to predict catalytic effects resulting from intermolecular interactions with individual water molecules constituting the first hydration shell, aminoacid mutations in enzymes or Si→Al substitutions in zeolites. In this contribution, hydrogen to fluorine (H→F) substitution effects for two model reactions have been examined indicating qualitative applicability of the catalytic field concept in the case of systems involving intramolecular interactions.
Utilizing first-principles calculations, we studied the electronic and optical properties of C24, C12X6Y6, and X12Y12 fullerenes (X?=?B, Al; Y?=?N, P). These fullerenes are energetically stable, as demonstrated by their negative cohesive energies. The energy gap of C24 may be tuned by doping, and the B12N12 fullerene was found to have the largest energy gap. All of the fullerenes had finite optical gaps, suggesting that they are optical semiconductors, and they strongly absorb UV radiation, so they could be used in UV light protection devices. They could also be used in solar cells and LEDs due to their low reflectivities.
A sphere-in-contact model is presented that is used to build physical models of carbon materials such as graphite, graphene, carbon nanotubes and fullerene. Unlike other molecular models, these models have correct scale and proportions because the carbon atoms are represented by their atomic radius, in contrast to the more commonly used space-fill models, where carbon atoms are represented by their van der Waals radii. Based on a survey taken among 65 undergraduate chemistry students and 28 PhD/postdoctoral students with a background in molecular modeling, we found misconceptions arising from incorrect visualization of the size and location of the electron density located in carbon materials. Based on analysis of the survey and on a conceptual basis we show that the sphere-in-contact model provides an improved molecular representation of the electron density of carbon materials compared to other molecular models commonly used in science textbooks (i.e., wire-frame, ball-and-stick, space-fill). We therefore suggest that its use in chemistry textbooks along with the ball-and-stick model would significantly enhance the visualization of molecular structures according to their electron density.
Detailed density functional theory (DFT) calculations on the structure and harmonic frequencies of model all-trans and all-cis polyenes were undertaken. For the first time, we report on the convergence of selected B3LYP/6-311++G** and BLYP/6-311++G** calculated structural parameters resulting from a systematic increase in polyene size (chains containing 2 to 14 C?=?C units). The limiting values of the structural parameters for very long chains were estimated using simple three-parameter empirical formulae. BLYP/6-311++G** calculated ν(C?=?C) and ν(C–C) frequencies for all-trans and all-cis polyenes containing up to 14 carbon–carbon double bonds were used to estimate these values for very long chains. Correction of raw, unscaled vibrational data was performed by comparing theoretical and experimental wavenumbers for polyenes chains containing 3 to 12 conjugated C?=?C units with both ends substituted by tert-butyl groups. The corrected ν(C?=?C) and ν(C–C) wavenumbers for all-trans molecules were used to estimate the presence of 9 – 12 C?=?C units in all-trans polyene pigment in red coral.
Graphical abstract Detailed density functional theory (DFT) calculations on the structure and harmonic frequencies of model all-trans and all-cis polyenes were undertaken. For the first time, we report on the convergence of selected B3LYP/6-311++G** and BLYP/6-311++G** calculated structural parameters resulting from a systematic increase in polyene size (chains containing 2 to 14 C=C units). The limiting values of the structural parameters for very long chains were estimated using simple three-parameter empirical formulae.
Diabetes affects a large population of the globe and is considered as a leading cause of death. Many synthetic and natural inhibitors have been developed for diabetes treatment. Herein, we report the potential antidiabetic activity of two new heterocyclic systems, namely 3.6-dimethyl-5-oxo-pyrido[3,4f][1,2,4]triazepino[2,3-a]benzimidazole (I) and 10-amino-2-methyl-4-oxo pyrimido[1,2-a]benzimidazole (II) against three related enzymes: α-amylase, α-glucosidase and β-galactosidase. Compounds I and II were synthesized by the action of DMF-DMA and dimethyl sulfate in the presence of water on 2-methyl-3H-benzimidazolo[1,2b][1,2,4]triazepin-4(5H)-one, and are characterized by single X-ray diffraction. The binding interaction modes in the active sites of I and II and targeted enzymes (stable complexes ligand-receptor) are emphasized using the molecular docking approach by applying the Lamarckian genetic algorithm method. Furthermore, plausible mechanisms have been proposed explaining their synthesis. Hirshfeld surface analysis reveals the nature of molecular interactions and fingerprint plots provide information about the percentage contribution from each individual molecular contact to the structure surface.
Herein we report a study of the switchable [3]rotaxane reported by Huang et al. (Appl Phys Lett 85(22):5391–5393, 1) that can be mounted to a surface to form a nanomechanical, linear, molecular motor. We demonstrate the application of semiempirical electronic structure theory to predict the average and instantaneous force generated by redox-induced ring shuttling. Detailed analysis of the geometric and electronic structure of the system reveals technical considerations essential to success of the approach. The force is found to be in the 100–200 pN range, consistent with published experimental estimates.
Density functional theory (DFT) was used to study the cobalt(I)-catalyzed enantioselective intramolecular hydroacylation of ketones and alkenes. All intermediates and transition states were fully optimized at the M06/6-31G(d,p) level (LANL2DZ(f) for Co). The results demonstrated that the ketone and alkene present different reactivities in the enantioselective hydroacylation. In ketone hydroacylation catalyzed by the cobalt(I)–(R,R)-Ph-BPE complex, reaction channel “a” to (R)-phthalide was more favorable than channel “b” to (S)-phthalide. Hydrogen migration was both the rate-determining and chirality-limiting step, and this step was endothermic. In alkene hydroacylation catalyzed by the cobalt(I)–(R,R)-BDPP complex, reaction channel “c” leading to the formation of (S)-indanone was the most favorable, both thermodynamically and kinetically. Reductive elimination was the rate-determining step, but the chirality-limiting step was hydrogen migration, which occurred easily. The results also indicated that the alkene hydroacylation leading to (S)-indanone formation was more energetically favorable than the ketone hydroacylation that gave (R)-phthalide, both thermodynamically and kinetically.
Graphical abstract A DFT study demonstrated that the ketone and alkene in the cobalt(I)-catalyzed enantioselective intramolecular hydroacylation showed different reactivities
The characterization of the seleno-sulfide-bromo systems and the isomerization process on the [H, S, Se, Br] potential energy surface were investigated using state-of-the-art theoretical methods. The CCSD(T) and the MP2 levels of theory were employed along with the series of correlation consistent basis sets extrapolated to the complete basis set (CBS) limit in the optimization of the geometrical parameters and computation of electronic energies. The relative stability, in kcal mol?1, at the CCSD(T)/CBS follows the trend: HSSeBr (0) > HSeSBr (9.51) > SSeHBr (24.02) > SeSHBr (25.42). This order was observed in the previous study of the [H, S, Se, Cl] species. The structural parameters and vibrational frequencies of the [H, S, Se, Br] species are reported. This research work should be helpful to experimentalists in order to gain insights into these novel heteroatom molecules.
Graphical abstract Relative energy profile (in kcal mol?1) using the CCSD(T)/CBS and MP2/CBS (in parentheses) method of the stationary states on the [H, S, Se, Br] PES.
Using density functional theory (DFT) and molecular dynamics (MD), we studied the interaction of a titanium atom with a half of a C60 fullerene (i.e., C30), formed from the corannulene structure with a pentagonal base. We considered atmospheric pressure and 300 K. We found that the most stable adsorption of the titanium atom on C30 occurs in the concave surface of the molecule. Afterward, we investigated the interaction of the system C30-titanium with carbon monoxide and carbon dioxide molecules, respectively. We found that each of these molecules is chemisorbed, with no dissociation. The value of the adsorption energy for the carbon monoxide molecule varies from ?0.897 to ?1.673 eV, and for the carbon dioxide molecule, it is between ?1.065 and ?1.274 eV. These values depend on the initial orientation of these molecules with respect to TiC30.
A mechanistic investigation using Becke3LYP density functional theory (DFT) was carried out on the palladium-catalyzed amidition of bromobenzene and tBu-isocyanide. The whole catalytic cycle consists of five steps: oxidative addition, migratory insertion, anion exchange, reductive elimination, and hydrogen migration. The rate-determining step is oxidative addition, with a small Gibbs free energy of 14.6 kcal mol?1. In the migratory insertion step, tBu-isocyanide provides an important source of carboxy and amino groups to establish the amide group. For anion exchange, path 1a is suggested as the most favorable pathway with the help of the base, and water provides a source of oxygen which is perfectly in line with experimental observations. Finally, in the hydrogen migration step, we illustrate that the six-membered ring path is energetically favored due to the assisting influence of water. In addition, our calculations indicate that using dimethyl sulfoxide as a solvent does not change the rate-determining step.
In the development of quantum computing and communications, improvements in materials capable of single photon emission are of great importance. Advances in single photon emission have been achieved experimentally by introducing nitrogen-vacancy (N-V) centers on diamond nanostructures. However, theoretical modeling of the anisotropic effects on the electronic properties of these materials is almost nonexistent. In this study, the electronic band structure and density of states of diamond nanowires with N-V defects were analyzed through first principles approach using the density functional theory and the supercell scheme. The nanowires were modeled on two growth directions [001] and [111]. All surface dangling bonds were passivated with hydrogen (H) atoms. The results show that the N-V introduces multiple trap states within the energy band gap of the diamond nanowire. The energy difference between these states is influenced by the growth direction of the nanowires, which could contribute to the emission of photons with different wavelengths. The presence of these trap states could reduce the recombination rate between the conduction and the valence band, thus favoring the single photon emission.
The aldol reaction in the presence of L-proline acting as an organocatalyst is a well-known example of asymmetric synthesis. Many theoretical and experimental studies have been carried out to probe the mechanism of this reaction. In this work, two levels of density functional theory in the gas phase and DMSO were used to elucidate the best pathways for this reaction, with the enamine and enol considered intermediates and L-proline considered either a reactant or a facilitator. The calculations indicated that both intermediates are formed simultaneously in the reaction medium. Interestingly, the formation of the enamine intermediate predominates in DMSO at room temperature, whereas the enol becomes the predominant intermediate upon the addition of water.
New ionic liquids (ILs) involving increasing numbers of organic and inorganic ions are continuously being reported. We recently developed a new force field; in the present work, we applied that force field to investigate the structural properties of a few novel imidazolium-based ILs in aqueous mixtures via molecular dynamics (MD) simulations. Using cluster analysis, radial distribution functions, and spatial distribution functions, we argue that organic ions (imidazolium, deprotonated alanine, deprotonated methionine, deprotonated tryptophan) are well dispersed in aqueous media, irrespective of the IL content. Aqueous dispersions exhibit desirable properties for chemical engineering. The ILs exist as ion pairs in relatively dilute aqueous mixtures (10 mol%), while more concentrated mixtures feature a certain amount of larger ionic aggregates.
For the first time, the structures, stabilities and electronic properties of alkaline-earth metal doped B44 fullerenes were investigated by means of density functional theory calculations. Our results reveal that M@B44 (M = Ca, Sr, Ba) possess endohedral configurations as their lowest energy structures, whereas the exohedral form is favored when metal is Be or Mg. The large binding energies and sizable HOMO–LUMO gap energies of Ca@B44, Sr@B44 and Ba@B44 suggest the considerable possibility to achieve these novel endohedral borofullerenes experimentally. Born-Oppenheimer molecular dynamics (BO-MD) simulations at various temperatures further confirmed the extreme dynamic stabilities of these endohedral complexes. Their bonding patterns were also analyzed in detail. Finally, we simulated their infrared absorption spectra and 11B nuclear magnetic resonance spectra to help future structural characterization.
