Density Functional Theory Level Research Articles

Synthesis, characterization and sensing mechanism of a novel fluorescence probe for Fe(III) in semi-aqueous solution based on a Schiff base hexadentate receptor

A new acyclic Schiff base chemosensor L was synthesized by the one pot condensation reaction of 2-[3-(formyl phenoxy)2-hydroxypropoxy]benzaldehyde and 2-aminophenol in a 1:2 molar ratio and was characterized by elemental analysis, FTIR, 1H- and 13C NMR, and fluorescence spectroscopies. These studies were complemented with a thorough conformational study at the molecular mechanics and density functional theory (DFT) levels of theory to further elucidate the structure of the compound in solution. The chemosensor L displays high sensitivity and selectivity for Fe3+ in semi-aqueous (H2O-DMF, 1:1) solution, except in the presence of a significant amount of Ni2+, with the presence of Fe3+ being signaled through the total fluorescence quenching of the fluorophore when Fe3+ binds to the recognition unit. The synthesized ligand also shows high selectivity for Fe3+ compared to the metal ions Cu2+, Zn2+, Mg2+, Mn2+, Pb2+, Hg2+, Na+, Ba2+ and Cd2+, and reasonable selectivity in the presence of Ag+, Co2+ and Cr3+. The stoichiometry and structure of the complex formed between Fe3+ and the probe L were determined from a Job’s plot and DFT calculations, respectively. The complex was characterized as a high-spin 1:1 octahedral species, in which the ligand coordinates to the metal through the two ether oxygen atoms, two nitrogen atoms and two terminal hydroxyl groups. Time dependent (TD-DFT) calculations were performed to provide information on the type of mechanism causing the quenching of the fluorescence in the presence of Fe3+.

On the aromaticity and stability of benzynes in the ground and lowest-lying triplet excited states.

In this work, we have revisited the aromaticity of benzyne isomers at the unrestricted density functional theory level (UDFT) using the energetic, magnetic, and delocalization criteria. In addition, this last criterion has also been analyzed employing complete active space (CASSCF) calculations. The results show conservation of aromaticity in these monocycles. Additionally it is observed that this trend is maintained in polycyclic aromatic hydrocarbon derivatives such as biradical didehydrophenanthrenes. Do these results imply a violation of Baird's rule? The answer is No, because this conservation in aromaticity is due to the loss of hydrogen atoms affects only the electronic σ skeleton and exerts a minor influence on the π cloud. Additionally, we have analyzed the relative stability of benzyne isomers and their relationship with experimental ΔES-T values. According to the literature, the stability of the benzynes in the singlet state is due to an effective interaction between the electrons of the biradical centers; however, this effect is completely reversed in the triplet state, which explains why the para isomer has the lowest ΔES-T gap.

Current-Density Calculations on Zn-Porphyrin40 Nanorings.

Two porphyrinoid nanorings have been studied computationally. They were built by linking 40 Zn-porphyrin units with butadiyne bridges. The molecular structures belonging to the D40h point group were fully optimized with the Turbomole program at the density functional theory (DFT) level using the B3LYP functional and the def2-SVP basis sets. The aromatic character was studied at the DFT level by calculating the magnetically induced current-density (MICD) susceptibility using the GIMIC program. The neutral molecules are globally non-aromatic with aromatic Zn-porphyrin units. Charged nanorings could not be studied because almost degenerate frontier orbitals led to vanishing optical gaps for the cations. Since DFT calculations of the MICD are computationally expensive, we also calculated the MICD using three pseudo-π models. Appropriate pseudo-π models were constructed by removing the outer hydrogen atoms and replacing all carbon and nitrogen atoms with hydrogen atoms. The central Zn atom was either replaced with a beryllium atom or with two inner hydrogen atoms. Calculations with the computationally inexpensive pseudo-π models yielded qualitatively the same magnetic response as obtained in the all-electron calculations.

Hydrogenation of S6-C60(CF3)12

The first results of the hydrogenation of S6-symmetric trifluoromethylfullerene C60(CF3)12 in two types of reactions were reported: (1) high-temperature radical hydrogenation with 9,10-dihydroanthracene and (2) nucleophilic hydrogenation with sodium tetraborohydride under mild conditions. The high-temperature radical hydrogenation of S6-C60(CF3)12 is accompanied by partial elimination of CF3 groups and leads to the formation of a complex mixture of products of a composition C60(CF3)8–12H18–22. During the hydrogenation of NaBH4 under mild conditions, selective formation of the hydride C60(CF3)12H12 was recorded by mass spectroscopy. A kinetic analysis of the sequential nucleophilic hydrogenation of S6-C60(CF3)12 was performed, using quantum-chemical modeling at the level of density functional theory, under the assumption of linear correlation between the activation energy and the enthalpy of elementary steps of the same type. The isomeric composition was predicted for the series of anionic intermediates C60(CF3)12H−2n−12−1− and their protonation products C60(CF3)12H2n, where n = 1–6. The hydrogenation of S6-C60(CF3)12 should lead to the formation of the thermodynamically and kinetically most stable product ortho-S6-C60(CF3)12H12, in which all hydrogen atoms are located in neighboring positions near the CF3 groups, forming together with them a near-equatorial belt of 24 addends while retaining the triphenylene fragments at two opposite poles. The average bond dissociation energy BDE(C–H) in ortho-S6-C60(CF3)12H12 is 298 kJ mol–1, which is approximately 20 kJ mol–1 higher than the BDE(C–H) of known fullerene hydrides C60H18 and C60H36 (PBE0/def2-SVP).

Investigation of the Effect of Solvents on the Synthesis of Aza-flavanone from Aminochalcone Facilitated by Halogen Bonding.

It has been recognized that CBr4 can give rise to a noncovalent interaction known as halogen bond (XB). CBr4 was found to catalyze, in terms of XB formation, the transformation of 2'-aminochalcone to aza-flavanone through an intramolecular Michael addition reaction. The impact of XB and the resulting yield of aza-flavanone exhibited a pronounced dependence on the characteristics of the solvent. Notably, yields of 88% in ethanol and 33% in DMSO were achieved, while merely a trace amount of the product was detected in benzene. In this work, we use a computational modeling study to understand this variance in yield. The reaction is modeled at the level of density functional theory (based on the M06-2X exchange-correlation functional) with all-electron basis sets of triple-ζ quality. Grimme's dispersion correction is incorporated to account for the noncovalent interactions accurately. Harmonic frequency calculations are carried out to establish the character of the optimized structures (minimum or saddle point). Our calculations confirm the formation of an XB between CBr4 and the reacting species and its role in lowering the activation energy barrier. Stronger orbital interactions and significant lowering of the steric repulsion were found to be important in lowering the activation barrier. The negligible yield in the nonpolar solvent benzene may be attributed to the high activation energy as well as the inadequate stabilization of the zwitterionic intermediate. In ethanol, a protic solvent, additional H-bonding contributes to further lowering of the activation barrier and better stabilization of the zwitterionic intermediate. The combined effects of solvent polarity, XB, and H-bond are likely to give rise to an excellent yield of aza-flavanone in ethanol.

Thermodynamic Overview of Bioconjugation Reactions Pertinent to Lysine and Cysteine Peptide and Protein Residues

Bioconjugation reactions are critical to the modification of peptides and proteins, permitting the introduction of biophysical probes onto proteins as well as drugs for use in antibody-targeted medicines. A diverse set of chemical reagents can be employed in these circumstances to covalently label protein side chains, such as the amine moiety in the side chain of lysine and the thiol functionality in cysteine residues, two of the more frequently employed sites for modification. To provide researchers with a thermodynamic survey of the reaction of these residues with frequently employed chemical modification reagents as well as reactive cellular intermediates also known to modify proteins non-enzymatically, a theoretical investigation of the overall thermodynamics of models of these reactions was undertaken at the T1 and G3(MP2) thermochemical recipe levels (gas phase), the M06-2X/6-311+G(2df,2p)/B3LYP/6-31G(d) (gas and water phase), and the M06-2X/cc-PVTZ(-f)++ density functional levels of theory (water phase). Discussions of the relationship between the reagent structure and the overall thermodynamics of amine or thiol modification are presented. Of additional interest are the observations that routine cellular intermediates such as certain thioesters, acyl phosphates, and acetyl-L-carnitine can contribute to non-enzymatic protein modifications. These reactions and representative click chemistry reactions were also investigated. The computational survey presented herein (>320 reaction computations were undertaken) should serve as a valuable resource for researchers undertaking protein bioconjugation. A concluding section addresses the ability of computation to provide predictions as to the potential for protein modification by new chemical entities, with a cautionary note on protein modification side reactions that may occur when employing synthetic substrates to measure enzyme kinetic activities.

Minimum Free Energy Pathways of Reactive Processes with Nudged Elastic Bands.

The determination of minimum free energy pathways (MFEP) is one of the most widely used strategies to study reactive processes. For chemical reactions in complex environments, the combination of quantum mechanics (QM) with a molecular mechanics (MM) representation is usually necessary in a hybrid QM/MM framework. However, even within the QM/MM approximation, the affordable sampling of the phase space is, in general, quite restricted. To reduce drastically the computational cost of the simulations, several methods such as umbrella sampling require performing a priori a selection of a reaction coordinate. The quality of the computed results, in an affordable computational time, is intimately related to the reaction coordinate election which is, in general, a nontrivial task. In this work, we provide an approach to model reactive processes in complex environments that does not require the a priori selection of a reaction coordinate. The proposed methodology combines QM/MM simulations with an extrapolation of the nudged elastic bands (NEB) method to the free energy surface (FENEB). We present and apply our own FENEB scheme to optimize MFEP in different reactive processes, using QM/MM frameworks at semiempirical and density functional theory levels. Our implementation is based on performing the FENEB optimization by uncoupling the optimization of the band in a perpendicular and tangential direction. In each step, a full optimization with the spring force is performed, which guarantees that the images remain evenly distributed. The robustness of the method and the influence of sampling on the quality of the optimized MFEP and its associated free energy barrier are studied. We show that the FENEB method provides a good estimation of the reaction barrier even with relatively short simulation times, supporting that its combination with QM/MM frameworks provides an adequate tool to study chemical processes in complex environments.

Shedding Light on the Hidden Roles of Lithium in the Nickel-Catalyzed Cross-Coupling of Aryl Ethers.

The Ni-catalyzed cross-coupling of aryl ethers is a powerful synthetic tool to transform widely available phenol derivatives into functionalized aromatic molecules. Recent theoretical and experimental mechanistic studies have identified the involvement of heterobimetallic nickelates as key intermediates that facilitate the challenging transformation under mild conditions and often without the need for external ligands or additives. In this work, based on calculations performed at the density functional theory (DFT) level and by comparison with spectroscopic and kinetic data, we investigate the mechanism of the Ni(COD)2-catalyzed cross-coupling of 2-methoxynaphthalene with PhLi and assess the speciation of lithium nickelate intermediates. The crucial role of solvent on the reaction is explained, and the multiple roles played by lithium are unveiled. Experimental studies have identified key lithium nickelate species which support and help to evolve the calculated reaction mechanism and ultimately complete the catalytic cycle. Based on this new mechanistic knowledge, a well-known experimental challenge of these transformations, the so-called "naphthalene problem" which restricts the use of electrophilic coupling partners to π-extended systems, can be addressed to enable the cross-coupling of unbiased aryl ethers under mild conditions.

Enriching the electronic populations of D-π-A type ON-OFF solar switches with sp2 hybridization: A TD-DFT possibility to create pull-push effect

The ability of specific molecular acceptors in photovoltaic devices is determined by their structure and chemical composition. Multiscale computations are important to protect investigation design; hence, efforts and money could be saved. Using Density Functional Theory (DFT), the effect of sp2 hybridized nitrogen substitutions (Ns) at the specific positions of a solar cell dye, 2,2′-((4-heptyl-4,9,9-trihexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(methanylylidene)bis(3-oxo-2,3-dihydro-1H-indene-1-yl-2-ylidene)dimalononitrile (IDIC), is explored. The N-incorporated dyes (IDIC1-IDIC5) were optimized at their ground energy minima at the B3LYP level of DFT with 6-31G+(d,p) basis sets. From these optimized geometries, their UV–visible analysis was executed at the DFT functional of CAM-B3LYP/6-31G+(d,p) selected as a result of benchmarking their λmax values with experimental values of IDIC. The computed value was found to be 528 nm which was very near to its experimental value (540 nm). Interestingly, for all the new dyes, λmax had blue-shifted values of (502–513 nm) for IDIC1, IDIC2 and IDIC5 and red-shifted values (557–779 nm) for IDIC3 and IDIC4 as compared to IDIC. The highest second-order Non-Linear Optical (NLO) response of 1054 e.s.u was noted for IDIC4 and IDIC5 which had the lowest energy gaps. It was found that incorporating Ns has significantly decreased the energy gap of electron rearrangement.

Rydberg-type electronic excited state dynamics in small sodium–water clusters

Equilibrium geometries and thermodynamic potentials of the neutral and ionised species of the Na ⋯ ( H 2 O ) n ( n = 1 , . . , 8 ) mixed clusters were computed at MN15/def2-TZVPD level of density functional theory (DFT). The vertical and adiabatic ionisation energies and enthalpies were computed and their cluster size dependence was discussed. Laser-induced ionisation involves electronic excitation through Rydberg-type excited states, which have been characterised using the TDDFT method, including the ωB2PLYP double-hybrid exchange-correlation functional. Ab initio molecular dynamics calculations were performed on a time scale of 20 picoseconds. Fluctuations of the charge and the sodium–oxygen atomic distances predict that, the 3 s 1 electron of the sodium atom are transferred from the delocalised Rydberg orbitals to the Rydberg orbitals around the water molecules and the sodium atom becomes positively charged with around 0.6e after the first 10 ps . On the other hand, some of the water molecules can move away up to 5 Å from the sodium with a significant negative charge on them. It has been shown that non-radiative relaxation cannot be excluded, they can mostly occur for cases n ⩾ 4 . The results confirm that the adiabatic photo-ionisation can occur on the basis of cluster disintegration.

Automated potential development workflow: Application to BaZrO3

We present a Python workflow, Automated Potential Development (APD), for automating the development of interatomic potentials, including calculation of density functional theory (DFT) fitting data, optimization of potentials, and potential-driven molecular dynamics (MD) simulations. The workflow currently supports CASTEP and VASP DFT codes and the MEAMfit potential optimization code for optimization of reference-free modified embedded atom method (RF-MEAM) potentials. The LAMMPS software is supported for calculating the relaxed geometry, elastic constants, phonon dispersion, thermal expansion and radial distribution functions using the optimized potentials. These same properties are also computed at the DFT level and APD automatically generates plots and tables of these data. Query-by-committee active learning is supported, using multiple fitted potentials to evaluate the energies of atomic configurations generated from LAMMPS MD runs. The workflow is demonstrated on BaZrO3, an oxide-based perovskite material, with RF-MEAM results found in good agreement with DFT. Program summaryProgram title: Automated potential development (APD) workflowCPC Library link to program files:https://doi.org/10.17632/pd9gbxyy8d.1Developer's repository link:https://gitlab.com/AndyDuff123/meamfitLicensing provisions: BSD 3-clauseProgramming language: Python, BashNature of problem: Development of new interatomic potentials is a time-consuming process and requires expertise in density functional theory (DFT), potential optimization, and molecular dynamics (and statics) simulations using the optimized potential. Furthermore repeated cycles are usually required to fix numerical issues and improve the potential, requiring further DFT calculations and potential reoptimization. There are also many tedious steps including setting up inputs, submitting jobs (including continuation jobs where jobs terminated prematurely), analyzing outputs, and validating predictions of the interatomic potential. The latter requires multiple calculations of properties computed at both the DFT and potential level.Solution method: The APD workflow provides a black-box solution to fully automate the generation of interatomic potentials. The workflow takes as input a Materials Project id and temperature range of interest. All DFT, potential optimization, and potential molecular dynamics simulations are automatically set-up, submitted and analyzed. Active-learning is incorporated, and properties are computed both at the DFT and potential-level for validation purposes, with tables and graphs for relaxed geometry, elastic constants, phonon dispersion, partial radial distribution functions, and thermal expansion automatically generated.Additional comments including restrictions and unusual features: A full guide to installation, including setting up an environment with all relevant packages and libraries, are included in the distribution. The APD workflow is currently restricted to RF-MEAM potentials and the properties listed above. Some materials which are particularly challenging at the DFT level, e.g. complex magnetic structures, may require intervention in tuning DFT input parameters.

AIMD-Chig: Exploring the conformational space of a 166-atom protein Chignolin with ab initio molecular dynamics

Molecular dynamics (MD) simulations have revolutionized the modeling of biomolecular conformations and provided unprecedented insight into molecular interactions. Due to the prohibitive computational overheads of ab initio simulation for large biomolecules, dynamic modeling for proteins is generally constrained on force field with molecular mechanics, which suffers from low accuracy as well as ignores the electronic effects. Here, we report AIMD-Chig, an MD dataset including 2 million conformations of 166-atom protein Chignolin sampled at the density functional theory (DFT) level with 7,763,146 CPU hours. 10,000 conformations were initialized covering the whole conformational space of Chignolin, including folded, unfolded, and metastable states. Ab initio simulations were driven by M06-2X/6-31 G* with a Berendsen thermostat at 340 K. We reported coordinates, energies, and forces for each conformation. AIMD-Chig brings the DFT level conformational space exploration from small organic molecules to real-world proteins. It can serve as the benchmark for developing machine learning potentials for proteins and facilitate the exploration of protein dynamics with ab initio accuracy.

C–H activation of ethane on palladium clusters: a computational study at the dual levels of density functional theory and coupled-cluster theory

C–H activation of ethane on palladium clusters: a computational study at the dual levels of density functional theory and coupled-cluster theory

Quantifying Intramolecular Basis Set Superposition Errors.

We show that medium-sized Gaussian basis sets lead to significant intramolecular basis set superposition errors at Hartree-Fock and density functional levels of theory, with artificial stabilization of compact over extended conformations for a 186 atom deca-peptide. Errors of ∼80 and ∼10 kJ/mol are observed, with polarized double zeta and polarized triple zeta quality basis sets, respectively. Two different procedures for taking the basis set superposition error into account are tested. While both reduce the error, it appears that polarized quadruple zeta basis sets are required to reduce the error below a few kJ/mol. Alternatively, the basis set superposition error can be eliminated using multiresolution methods based on Multiwavelets.

Infrared Ion Spectroscopic Characterization of the Gaseous [Co(15-crown-5)(H2O)]2+ Complex.

We report fingerprint infrared multiple-photon dissociation spectra of the gaseous monohydrated coordination complex of cobalt(II) and the macrocycle 1,4,7,10,13-pentaoxacyclopentadecane (or 15-crown-5), [Co(15-crown-5)(H2O)]2+. The metal-ligand complexes are generated using electrospray ionization, and their IR action spectra are recorded in a quadrupole ion trap mass spectrometer using the free-electron laser FELIX. The electronic structure and chelation motif are derived from spectral comparison with computed vibrational spectra obtained at the density functional theory level. We focus here on the gas-phase structure, addressing the question of doublet versus quartet spin multiplicity and the chelation geometry. We conclude that the gas-phase complex adopts a quartet spin state, excluding contributions of doublet species, and that the chelation geometry is pseudo-octahedral with the six oxygen centers of 15-crown-5 and H2O coordinated to the metal ion. We also address the possible presence of higher-energy conformers based on the IR spectral evidence and calculated thermodynamics.

Mg-Containing Zn3O3 Structures for Detection of CO2: A DFT Study on CHEM Effects of SERS and Electronic Properties.

Surface-enhanced Raman spectra (SERS) and electronic-structure-based properties are important tools for investigation of the molecular sensing ability of nanoparticles. The present computational study is intended to explore the sensing ability of Zn3O3 and Mg-containing Zn3O3 structures for CO2 molecules by CHEM effects of the SERS technique. Geometries of CO2-adsorbed Zn3O3, Zn2MgO3 (Mg as a substitutional impurity), and Zn3O3Mg (Mg as an interstitial impurity) structures are modeled using the B3LYP/6-31G(d,p) level of density functional theory. The Mg site of the Zn2MgO3 and Zn3O3Mg structures is preferential for the adsorption of CO2. The observed energy trends are supported by geometrical analysis, molecular orbital interactions, redshifts in CO2 vibrational modes, and topological properties. Raman activity enhancement of the CO2 symmetric vibrational mode is significant when the molecule is adsorbed at the Mg site of Zn3O3Mg. The observed Raman activity enhancement is supported by SERS spectra obtained from anharmonic calculations carried out on B3LYP/6-31G(d,p) geometries and substantiated by a larger change in the polarizability with energy corresponding to the symmetric vibrational mode of CO2. The TDDFT calculations, frequency-dependent polarizabilities, and charge transfer interactions show that Zn3O3Mg is a good substrate for sensing of CO2, with visible wavelengths, by resonance Raman effect. The trends with adsorption energy, Raman activity, and excited state properties are also substantiated by B3LYP/6-311+G(d,p) calculations.

Concerted versus stepwise proton transfer reactions in the [2, 2'-bipyridyl]-3-3'-diol molecule: A static and dynamic ab-initio investigation.

The double proton transfer (PT) reaction has been investigated in the [2,2'-bipyridyl]-3-3'-diol, a complex molecule where the proton movements is coupled to significant rearrangement of the electronic structure. Moreover, the reaction could be concerted, that is the two protons are exchanged simultaneously, or stepwise, where the two protons are transferred sequentially. To this end, a static exploration of the potential energy surface (PES) was carried together with the analysis of the free-energy surface (FES), both surfaces being evaluated at density functional theory level and different exchange-correlation functionals. While the concerted mechanism has been clearly discharged, the characteristics of the stepwise PT significantly depends on the chosen functionals, some suggesting a clear stepwise mechanism characterized by a stable reaction intermediates and two transitions states, whereas other approaches propend for a asynchronous PT, with a single TS. These features appear on both PES and FES, albeit some differences appears due to their different nature.

Developing machine-learned potentials to simultaneously capture the dynamics of excess protons and hydroxide ions in classical and path integral simulations.

The transport of excess protons and hydroxide ions in water underlies numerous important chemical and biological processes. Accurately simulating the associated transport mechanisms ideally requires utilizing abinitio molecular dynamics simulations to model the bond breaking and formation involved in proton transfer and path-integral simulations to model the nuclear quantum effects relevant to light hydrogen atoms. These requirements result in a prohibitive computational cost, especially at the time and length scales needed to converge proton transport properties. Here, we present machine-learned potentials (MLPs) that can model both excess protons and hydroxide ions at the generalized gradient approximation and hybrid density functional theory levels of accuracy and use them to perform multiple nanoseconds of both classical and path-integral proton defect simulations at a fraction of the cost of the corresponding abinitio simulations. We show that the MLPs are able to reproduce abinitio trends and converge properties such as the diffusion coefficients of both excess protons and hydroxide ions. We use our multi-nanosecond simulations, which allow us to monitor large numbers of proton transfer events, to analyze the role of hypercoordination in the transport mechanism of the hydroxide ion and provide further evidence for the asymmetry in diffusion between excess protons and hydroxide ions.

Lithium Promotes Acetylide Formation on MgO During Methane Coupling Under Non-Oxidative Conditions.

A prototypical material for the oxidative coupling of methane (OCM) is Li/MgO, for which Li is known to be essential as a dopant to obtain high C2 selectivities. Herein, Li/MgO is demonstrated to be an effective catalyst for non-oxidative coupling of methane (NOCM). Moreover, the presence of Li is shown to favor the formation of magnesium acetylide (MgC2 ), while pure MgO promotes coke formation as evidenced by solid-state 13 C NMR, thus indicating that Li promotes C-C bond formation. Metadynamic simulations of the carbon mobility in MgC2 and Li2 C2 at the density functional theory (DFT) level show that carbon easily diffuses as a C2 unit at 1000 °C. These insights suggest that the enhanced C2 selectivity for Li-doped MgO is related to the formation of Li and Mg acetylides.

Lithium Promotes Acetylide Formation on MgO During Methane Coupling Under Non‐Oxidative Conditions

AbstractA prototypical material for the oxidative coupling of methane (OCM) is Li/MgO, for which Li is known to be essential as a dopant to obtain high C2 selectivities. Herein, Li/MgO is demonstrated to be an effective catalyst for non‐oxidative coupling of methane (NOCM). Moreover, the presence of Li is shown to favor the formation of magnesium acetylide (MgC2), while pure MgO promotes coke formation as evidenced by solid‐state 13C NMR, thus indicating that Li promotes C−C bond formation. Metadynamic simulations of the carbon mobility in MgC2 and Li2C2 at the density functional theory (DFT) level show that carbon easily diffuses as a C2 unit at 1000 °C. These insights suggest that the enhanced C2 selectivity for Li‐doped MgO is related to the formation of Li and Mg acetylides.