Solvent effects on Diels-Alder reaction in ionic liquids:A reaction density functional study

Extensive experimental studies have been performed on the Diels-Alder(DA)reactions in ionic liquids(ILs),which demonstrate that the IL environment can significantly influence the reaction rates and selectivity.However,the underlying microscopic mechanism remains ambiguous.In this work,the multiscale reaction density functional theory is applied to explore the effect of 1-butyl-3-methylimidazolium hexafluorophosphate([BMIM][PF_(6)])solvent on the reaction of cyclopentadiene(CP)with acrolein,methyl acrylate,or acrylonitrile.By analyzing the free energy landscape during the reaction,it is found that the polarization effect has a relatively small influence,while the solvation effect makes both the activation free energy and reaction free energy decrease.In addition,the rearrangement of local solvent structure shows that the cation spatial distribution responds more evidently to the reaction than the anion,and this indicates that the cation plays a dominant role in the solvation effect and so as to affect the reaction rates and selectivity of the DA reactions.

Shock-induced reaction behaviors of functionally graded reactive material

In this paper,the ballistic impact experiments,including impact test chamber and impact double-spaced plates,were conducted to study the reaction behaviors of a novel functionally graded reactive material(FGRM),which was composed of polytetrafluoroethylene/aluminum(PTFE/Al)and PTFE/Al/bismuth trioxide(Bi_(2)O_(3)).The experiments showed that the impact direction of the FGRM had a significant effect on the reaction.With the same impact velocity,when the first impact material was PTFE/Al/Bi_(2)O_(3),compared with first impact material PTFE/Al,the FGRM induced higher overpressure in the test chamber and larger damaged area of double-spaced plates.The theoretical model,which considered the shock wave generation and propagation,the effect of the shock wave on reaction efficiency,and penetration behaviors,was developed to analyze the reaction behaviors of the FGRM.The model predicted first impact material of the FGRM with a higher shock impedance was conducive to the reaction of reactive materials.The conclusion of this study provides significant information about the design and application of reactive materials.

Oxygen Atom Transfer Reaction of Manganese-oxo Corrole toward Dimethyl Sulfide: a Density Functional Study

The effects of axial ligand on the oxygen atom transfer(OAT)reaction from 5,10,15-tris(pentafluorophenyl)corrole((tpfc)MnVO)to dimethyl sulfide(DMS)have been investigated by density functional theory(DFT)calculations.Imidazole(Im),4-methylimidazole(4-MI)and pyridine(Py)were selected as the axial ligands.The results revealed that the axial ligand can form coordinate bond with(tpfc)MnVO in the transition state(TS)of the OAT reaction.The axial coordination favored charge transferring from(tpfc)MnVO to DMS,and weakened the Mn≡O bond in both singlet and triplet states.Furthermore,axial coordination can reduce the energy barrier of neutral(tpfc)MnVO from 23.62 kJ·mol^-1 to less than 3 kJ·mol^-1 in the triplet state,which is significantly lower than in the singlet state.This makes(tpfc)MnVO tend to direct the OAT reaction via triplet state pathway.On the other hand,the energy barriers of[(tpfc)MnVIO]+species from disproportionation pathway increased from 1.26 to 33.95 kJ·mol^-1 in a doublet state.This suggests axial ligands were conducive for direct(tpfc)MnVO OAT reaction pathway.

Addition Reaction of Fe(CO)_n (n = 3～5) on Fullerene C_(50), C_(60), and C_(70): A Density Functional Theory Study

The electronic structure and reactivities of Fe（CO）n （n = 3~5） addition to different fullerenes have been investigated through the first-principles calculations, and the results indicate that Fe（CO）3 and Fe（CO）4 can be adsorbed to the outside network of fullerene via hollow and bridge sites, respectively. Both of them have larger binding energy, but when Fe（CO）5 is adsorbed via the top site, the binding energy is relatively smaller. According to the directional curvature theory, the reactivities of Fe（CO）3 addition to the fullerenes are determined by KM of the ring center, and those of Fe（CO）4 addition by KD of the C–C bond curvature; while for Fe（CO）5, it presents weak reactivities in the addition reaction because of the larger volume effect. No matter whether the addition reaction takes place on the hollow or bridge site, the binding energies show a linear relationship with KD. This work further enriched the directional curvature theory and applied the isolobel analogy theory in the fullerene addition reactions.

Transition‐metal‐atom‐pairs deposited on g‐CN monolayer for nitrogen reduction reaction:Density functional theory calculations

The development of highly active DFT catalysts for an electrocatalytic N_(2)reduction reaction(NRR)under mild conditions is a difficult challenge.In this study,a series of atom‐pair catalysts(APCs)for an NRR were fabricated using transition‐metal(TM)atoms(TM=Sc−Zn)doped into g‐CN monolayers.The electrochemical mechanism of APCs for an NRR has been reported by well‐defined density functional theory calculations.The calculated limiting potentials were−0.47 and−0.78 V for the Fe_(2)@CN and Co_(2)@CN catalysts,respectively.Owing to its high suppression of hydrogen evolution reactions,Co_(2)@CN is a superior electrocatalytic material for a N_(2)fixation.Stable Fe_(2)@CN may be a strongly attractive material for an NRR with a relatively low overpotential after an improvement in the selectivity.The two‐way charge transfer affirmed the donation‐acceptance procedure between N_(2)and Fe_(2)@CN or Co_(2)@CN,which play a crucial role in the activation of inert N≡N bonds.This study provides an in‐depth investigation into atom‐pair catalysts and will open up new avenues for highly efficient g‐CN‐based nanostructures for an NRR.

Thermal kinetic analysis of a complex process from a solid-state reaction by deconvolution procedure from a new calculation method and related thermodynamic functions of Mn_(0.90)Co_(0.05)Mg_(0.05)HPO_4?3H_2O

Three individual peaks of thermal solid-state reaction processes of the synthesized Mn0.90Co0.05Mg0.05HPO4?3H2O were observed corresponding to dehydration I,dehydration II and polycondensation processes.An alternative method for the calculation of the extent of conversion was proposed from the peak area of the individual DTG peak after applying the best fitting deconvolution function(Frazer–Suzuki function).An iterative integral isoconversional equation was used to compute the values of the apparent activation energy Eαand they were found to be 65.87,78.16 and 119.32 kJ/mol for three peaks,respectively.Each individual peak was guaranteed to be a single-step kinetic system with its unique kinetic parameters.The reaction mechanism functions were selected by the comparison between experimental and model plots.The results show that the first,second and final individual peaks were two-dimensional diffusion of spherical symmetry(D2),three-dimensional diffusion of spherical symmetry(D3)and contracting cylinder(cylindrical symmetry,R2)mechanisms.Pre-exponential factor values of 3.91×106,1.35×107 and 2.15×107 s?1 were calculated from the Eαvalues and reaction mechanisms.The corresponded standard thermodynamic functions of the transition-state(activated)complexes were determined and found to agree well with the experimental data.

A reaction density functional theory study of solvent effect in the nucleophilic addition reactions in aqueous solution

Whereas the proper choice of reaction solvent constitutes the cornerstone of the green solvent concept,solvent effects on chemical reactions are not mechanistically well understood due to the lack of feasible molecular models.Herein,by taking the case study of nucleophilic addition reaction in aqueous solution,we extend the proposed multiscale reaction density functional theory(RxDFT)method to investigate the intrinsic free energy profile and total free energy profile,and study the solvent effect on the activation and reaction free energy for the nucleophilic addition reactions of hydroxide anion with methanal and carbon dioxide in aqueous solution.The predictions of the free energy profile in aqueous solution for these two nucleophilic addition reactions from RxDFT have a satisfactory agreement with the results from the RISM and MD-FEP simulation.Meanwhile,the solvent effect is successfully addressed by examining the difference of the free energy profile between the gas phase and aqueous phase.In addition,we investigate the solvent effect on the reactions occurred near solid-liquid interfaces.It is shown that the activation free energy is significantly depressed when reaction takes place in the region within 10A distance to the substrate surface owing to the decrease of hydration free energy at the solid-liquid interface.

Finkelstein Reaction in Functionalized Crown-ether Ionic Liquids

Functional crown-ether ionic liquids were used as catalytic green solvents of Finkelstein reaction of 1-bromooctane and iodide. The rate and yield of the reaction were obvious improved compared with that using crown ether in water. No free crown ether loss was observed after reaction.

Spreading Speed for a Periodic Reaction-diffusion Model with Nonmonotone Birth Function

A reaction-diffusion model for a single species with age structure and nonlocal reaction for periodic time t is derived. Some results about the model with monotone birth function are firstly introduced, and then by constructing two auxiliary equations and squeezing method, the spreading speed for the system with nonmonotone birth function is obtained.

Adsorption and Reaction of CN +O→OCN on Cu(100) Surface: A Density Functional Theory Study

The adsorption and reaction of O ＋ CN → OCN on Cu（100） are studied by using density functional theory and cluster model. Cu14 cluster model is used to simulate the surface. The calculated results show that the OCN species with the molecule perpendicular to the surface via N atom （N-down） is more favorable than other adsorption models, and the N-down at the bridge site is the most favorable. For N-down, calculated OCN symmetric and asymmetric stretching frequencies are all blue-shifted compared with the calculated values of free and in good agreement with the experiments. The charge transfer from the surface to the OCN species leads to that the bonding of OCN to the metal surface is largely ionic. The present studies also show that CN with the molecule perpendicular to the surface via C atom （NC-down） at the top site is the most stable. Except NC-down at the top site, the calculated CN stretching frequencies are all red-shifted. With O coadsorbed at the hollow site, the adsorption of NC-down at the next nearest bridge or top site is energetically more favorable than that at the adjacent hollow site. The reaction of O ＋ CN → OCN on Cu（100） has no energy barrier via both Eley-Rideal and Langmuir-Hinshelwood processes.

Evaluation of Excitation Functions of Reactions Used in Production of Some Medical Radioisotopes

In this work, reaction cross-sections were calculated and Excitation Functions were evaluated for productions of 208Bi, 212,211,210At, 211,210Po isotopes using EXIFON code in the energy range from 0 MeV to 30 MeV. The code is based on an analytical model for statistical multistep direct and multistep compound reactions (SMD/SMC model). This work also investigates the shell structure effect on the reaction cross-section, the results obtained show that the cross-sections of (a, na) reaction for both with shell correction and without shell correction are zeros at energies range considered, this shows that the energy of the incident particle is below the threshold of this reaction due to the present of coulomb repulsive force between the projectile and target nucleus.

Hydrogen evolution reaction between small-sized Zr_(n)(n=2–5)clusters and water based on density functional theory

Density functional theory(DFT)is used to calculate the most stable structures of Zr_(n)(n=2-5)clusters as well as the adsorption energy values of Zr_(n)(n=2-5)clusters after adsorbing single water molecule.The results reveal that there is a significant linear relationship between the adsorption energy values and the energy gaps of the Zr_(n)(n=2-5)clusters.Furthermore,the calculations of the reaction paths between Zr_(n)(n=2-5)and single water molecule show that water molecule can react with Zr_(n)(n=2-5)clusters to dissociate,producing hydrogen,and O atoms mix with the clusters to generate Zr_(n)O(n=2-5),all of which are exothermic reactions.According to the released energy,the Zr4 cluster is the most efficient in Zr_(n)(n=2-5)clusters reacting with single water molecule.The natural population analysis(NPA)and density of states(DOS)demonstrate the production of hydrogen and orbital properties in different energy ranges,respectively,jointly forecasting that Zr_(n)O(n=2-5)will probably continue to react with more water molecules.Our findings contribute to better understanding of Zr's chemical reactivity,which can conduce to the development of effective Zr-based catalysts and hydrogen-production methods.

Catalytic activity of V_(2)CO_(2) MXene supported transition metal single atoms for oxygen reduction and hydrogen oxidation reactions:A density functional theory calculation study

Two-dimensional(2D)MXene and single-atom(SA)catalysts are two frontier research fields in catalysis.2D materials with unique geometric and electronic structures can modulate the catalytic performance of supported SAs,which,in turn,affect the intrinsic activity of 2D materials.Density functional theory calculations were used to systematically explore the potential of O-terminated V2C MXene(V_(2)CO_(2))-supported transition metal(TM)SAs,including a series of 3d,4d,and 5d metals,as oxygen reduction reaction(ORR)and hydrogen oxidation reaction(HOR)catalysts.The combination of TM SAs and V_(2)CO_(2)changes their electronic structure and enriches the active sites,and consequently regulates the intermediate adsorption energy and catalytic activity for ORR and HOR.Among the investigated TM-V_(2)CO_(2)models,Sc-,Mn-,Rh-,and PtMCCh showed high ORR activity,while Sc-,Ti-,V-,Cr-,and Mn-V_(2)CO_(2)exhibited high HOR activity.Specifically,Mn-and Sc-V_(2)CO_(2)are expected to serve as highly efficient and cost-effective bifunctional catalysts for fuel cells because of their high catalytic activity and stability.This work provides theoretical guidance for the rational design of efficient ORR and HOR bifunctional catalysts.

Branched Polyamines Functionalized with Proposed Reaction Pathways Based on ¹H-NMR, Atomic Absorption and IR Spectroscopies

Three novel branched polyamines N,N,N’,N’-tetrakis-[3((pyridine-2-methyl)-amine) propyl]-1,4- butanediamine (1), N,N,N’,N’-tetrakis-[N-((2-methylpyridine)ethyl)propanamide]ethylenediamine (2) and N,N,N’,N’-tetrakis-[3((2-hidroxibenziliden)-amine)propyl]-1,4-butanediamine (3), were synthesized starting from 2-pyridinecarboxaldeyde with DAB-Am-4 for 1, PAMAM G0 for 2 and from salicylaldehyde with DAB-Am-4 for 3. The pathway reactions have been proposed by 1H-NMR, IR and Atomic Absorption Spectroscopy. The optimal reaction time was set by IR spectroscopy following aldehyde? peak modification. 1 and 2 were obtained as both hydrochlorides and as free amines and 3 only as free imine. These polyamines were characterized by UV-Vis, IR, 1H-NMR and 13C-NMR and Mass Spectrometry.

A reaction density functional theory study of solvent effects on keto-enol tautomerism and isomerization in pyruvic acid

It is important to study the solvent effect on keto-enol tautomerism that has applications in many areas of chemical engineering.In this work,we use a multiscale reaction density functional theory(Rx DFT)to study the keto-enol tautomerism and isomerization of pyruvic acid.The results show that both effects of solvation and water assistance could reduce the reaction barriers.The water molecule participates the reaction as a catalyst to accept/give the protons with forming a hexagonal ring in the transition state.As a result of this temporary and intermediate hexagonal ring,the solute configuration undergoes a small variation during the reaction,giving a diminished contribution to the intrinsic reaction free energy.The solvent distribution shows a local ordering behavior near the solute that also reduces the contribution of solvation effect to the reaction barrier.Water assistance plays a major role in both pre-reaction and postreaction process.In terms of the driving force for the reaction,the effects of both solvation and water assistance are important.

Regulating carbon work function to boost electrocatalytic activity for the oxygen reduction reaction

Electronic regulation of carbon is essential for developing non-platinum electrocatalysts for oxygen reduction reactions(ORRs).In this work,we used Cs to further regulate the electronic structure of nitrogen-doped(N-doped)carbon.The Cs atoms coordinated with the nitrogen atom in the N-doped carbon for injecting electrons into the carbon conjugate structure and reducing the work function of the carbon network.The low-work-function surface improved electron donation,facilitated O_(2) dissociation,and enhanced the adsorption of an OOH^(*) intermediate.Thus,electrocatalytic performance for the ORR was improved.The material shows potential as an ORR electrocatalyst comparable with Pt/C.

Density Function Theory Study on the Reaction Mechanism of Cerium with Oxygen for Ce-bearing Aerosol Particle Formation

We obtained the reaction mechanism of cerium with oxygen by means of density functional theory (DFT) under the explosive or detonation situation. The energy level order of cerium was calculated and the potential energy profile was plotted. The properties of the bonds of all special structures in the reaction path were analyzed using the method of the electron localization function (ELF). The results indicate that the final reaction pathway can be expressed as Ce+O2→ FC→TS→IM→O-Ce-O, and the formation of Ce2O3 has not been found. In addition, the ELF diagram of the final product CeO2 shows that Ce bonds with both O atoms and the bond angles increase significantly.

Direct atomic-level insight into oxygen reduction reaction on size-dependent Pt-based electrocatalysts from density functional theory calculations

Developing novel oxygen reduction reaction(ORR)catalysts with high activity is urgent for proton exchange membrane fuel cells.Herein,we investigated a group of size-dependent Pt-based catalysts as promising ORR catalysts by density functional theory calculations,ranging from single-atom,nanocluster to bulk Pt catalysts.The results showed that the ORR overpotential of these Pt-based catalysts increased when its size enlarged to the nanoparticle scale or reduced to the single-atom scale,and the Pt_(38)cluster had the lowest ORR overpotential(0.46 V)compared with that of Pt_(111)(0.57 V)and single atom Pt(0.7 V).Moreover,we established a volcano curve relationship between the ORR overpotential and binding energy of O*(ΔE_(O*),confirming the intermediate species anchored on Pt38cluster with suitable binding energy located at top of volcano curve.The interaction between intermediate species and Pt-based catalysts were also investigated by the charge distribution and projected density of state and which further confirmed the results of volcano curve.

Changes in brain activation patterns according to cross-training effect in serial reaction time task An functional MRI study

Cross-training is a phenomenon related to motor learning, where motor performance of the untrained limb shows improvement in strength and skill execution following unilateral training of the homologous contralateral limb. We used functional MRI to investigate whether motor performance of the untrained limb could be improved using a serial reaction time task according to motor sequential learning of the trained limb, and whether these skill acquisitions led to changes in brain activation patterns. We recruited 20 right-handed healthy subjects, who were randomly allocated into training and control groups. The training group was trained in performance of a serial reaction time task using their non-dominant left hand, 40 minutes per day, for 10 days, over a period of 2 weeks. The control group did not receive training. Measurements of response time and percentile of response accuracy were performed twice during pre- and post-training, while brain functional MRI was scanned during performance of the serial reaction time task using the untrained right hand. In the training group, prominent changes in response time and percentile of response accuracy were observed in both the untrained right hand and the trained left hand between pre- and post-training. The control group showed no significant changes in the untrained hand between pre- and post-training. In the training group, the activated volume of the cortical areas related to motor function （i.e., primary motor cortex, premotor area, posterior parietal cortex） showed a gradual decrease, and enhanced cerebellar activation of the vermis and the newly activated ipsilateral dentate nucleus were observed during performance of the serial reaction time task using the untrained right hand, accompanied by the cross-motor learning effect. However, no significant changes were observed in the control group. Our findings indicate that motor skills learned over the 2-week training using the trained limb were transferred to the opposite homologous limb, and motor skill acquisition of the untrained limb led to changes in brain activation patterns in the cerebral cortex and cerebellum.

Methylation reactions at dopaminergic nerve endings, serving as biological off-switches in managing dopaminergic functions

The mechanisms for the regulation of synaptic dopamine （DA） include its release from presynaptic vesicles, its interaction with post-synaptic and pre-synaptic DA receptors, the reuptake of DA, via dopamine transporter （DAT）, the diffusion of DA and its metabolism by mono-amine oxidase （MAO） and cate- chol-O-methyl transferase （COMT）. DA controls complex and specialized functions including, movements, behavior, mood, perception, reward, and more recently, neurogenesis （Popolo et al., 2004; Reimer et al., 2013） and neuroregeneration （Hoglinger et al., 2004; Yang et al., 2008）. These functions are varied and of high fidelity. Movement, as an example, requires regulatory mechanisms for initiating, stopping, slowing-down speed- ing-up, changing directions, for governing the relentless urges to move in the young and sedentariness in the old as well as in motor-freezing, catalepsy, tremor and stereotypy.