Quantum Chemical Calculations Research Articles

Molecular structure of 3-cyano-4-azido-1,2,5-oxadiazole 2-oxide studied by means of gas electron diffraction and quantum chemical calculations

Molecular structure of 3-cyano-4-azido-1,2,5-oxadiazole 2-oxide studied by means of gas electron diffraction and quantum chemical calculations

A supramolecular approach towards the photorelease of encapsulated caged acids in water: 7-diethylaminothio-4-coumarinyl molecules as triggers.

Herein, we establish the release of aliphatic acids in water upon excitation of 7-diethylaminothio-4-coumarinyl derivatives encapsulated within the organic host octa acid (OA). The 7-diethylaminothio-4-coumarinyl skeleton, employed here as the trigger, photoreleases caged molecules from the excited triplet state, in contrast to its carbonyl analogue, where the same reaction is known to occur from the excited singlet state. Encapsulation in OA solubilizes molecules in water that are otherwise water-insoluble, and retains the used trigger within itself following the release of the aliphatic acid. Such supramolecular characteristics usher in new features to the photorelease methodology. The thiocarbonyl chromophore extends the absorption of coumarinyl trigger to visible range while enhancing the intersystem crossing (ISC) to the triplet state, making it the reactive state. Despite the non-polar environment within the OA capsules the photocleavage occurs in a heterolytic fashion to release the conjugate base and the used trigger as triplet carbocation in an adiabatic process. Interestingly, the triplet carbocation crosses to the ground singlet surface (closed shell singlet carbocation) with the help of water molecules, possibly aided by C = S chromophore. Utilizing the known excited state dynamics of related thiocoumarinyl and coumarinyl systems, we have identified a few of the important mechanistic features of the photorelease process of 7-diethylaminothio-4-coumarinyl derivatives. Ultrafast excited state dynamic studies and quantum chemical calculations planned should help us better understand the photorelease process so as to effectively exploit the proposed system for potential applications.

Vibronic coherent quantum beat in four-layer platinum carbonyl cluster.

Vibronic coherence has been studied for years, but direct comparisons between the rich experimental features and theory remain rare. In this work, we investigate the vibronic coherent quantum beat of a four-layer platinum carbonyl cluster [Pt3(CO)6]42- in a solution utilizing femtosecond vis-pump/vis-probe transient absorption spectroscopy. By varying the excitational wavelength, quantum beats coupled to either the electronic ground state or the excited state are selectively prepared. A 41cm-1 beat at the ground state with a phase flip at 615nm and a 28cm-1 beat at the excited state with a phase node at 735nm are observed. The beat amplitudes are asymmetric, stronger on the red side for ground state beats but weaker for excited state beats. Quantum chemistry calculations suggest that these beats result from coupling between the [Pt3(CO)6] layer motions and the electronic excitation. Theoretical model calculations for quantum beats at both electronic states are performed following the doorway-window approach. The calculations explain the oscillation frequency difference, the node positions, and the asymmetry. The beats with different frequencies result from vibronic coupling with different electronic states with the Herzberg-Teller (ground) or Franck-Condon term (excited) involved. The theoretical nodes occur at absorption and fluorescence centers, respectively, although experimental results show a slight blueshift. Quantum window operator calculations link the beat amplitude asymmetry to the Franck-Condon factor matrix imbalances, with the number of nodes dependent on the electronic dephasing rate. The theoretical insights for quantum beats are expected to be general, potentially helpful for the interpretation of observations in other systems.

Substituent Effects in Scholl-Type Reactions of 1,2-Terphenyls to Triphenylenes.

A series of 3,3''- and 4,4''-dimethoxy terphenyls with different second substituents on their ortho-positions have been synthesized and investigated upon the possibility to be oxidatively cyclodehydrogenated to the corresponding triphenylenes under Scholl-type conditions. The experimentally obtained selectivities were supported and explained by quantum chemical calculations and conclusions on the involved mechanisms (acid catalyzed arenium-ion mechanism (AIM) vs radical cation mechanism) were drawn.

Theoretical Insights into Ultrafast Separation of Photogenerated Charges in a Push-Pull Polarized Molecular Triad.

Herein, we propose a purely-organic donor-acceptor (D-A) molecular triad, with a light-absorbing polarized molecular wire (PMW) used as a central linkage, as a proof of concept for the possible future applications of the D-PMW-A arrangement in molecular photovoltaics. This work builds upon our earlier study on the PMW unit itself, which proved to be highly promising for the ultrafast photogeneration of free charge carriers. Quantum-chemical calculations performed for the D-PMW-A triad at a semi-empirical level of theory reveal a large electric dipole moment of the system, and show strong charge-transfer (CT) character of its lowest-energy excited electronic states, including the S1, which favours efficient dissociation of an exciton initially formed upon the absorption of light. The confirmation for this effect was found with nonadiabatic molecular dynamics simulations, revealing an ultrafast relaxation from higher, bright excited states to S1, completed on a subpicosecond timescale. The architecture of the proposed molecular triad enables its electronic coupling to the surrounding environment through chemical bonds, or noncovalent stacking interactions, which might open way for synthesis of a new class of D-PMW-A efficient molecular organic photovoltaic materials.

Influence of flue gas components on SO2 adsorption by activated carbon at low temperature

Activated carbon can adsorb SO2 in flue gas, whose performance is significantly enhanced when lowering the adsorption temperature; however, the characteristics and mechanism of SO2 adsorption under the action of complex flue gas components at low temperatures remain unclear. In this study, adsorption experiments were conducted to investigate the characteristics of SO2 adsorption on activated carbon and the impact of O2, H2O, and NO within −20 to 20 °C. The saturated adsorption of SO2 showed a 2.21-fold increase when the temperature was lowered from 20 °C to −20 °C. Within this temperature range, physical adsorption was dominant, accounting for 73.7–91.0 %. O2 and H2O inhibited the physical adsorption of SO2 and promoted its chemical adsorption. As the temperature was lowered, the promoting effect of O2 increased, while the influence of H2O shifted from promotion to inhibition. NO affects SO2 adsorption only when co-existing with O2. As the temperature decreased, the promoting effect of NO on both physical and chemical adsorption strengthened and was significantly higher than that of O2 and H2O. Based on desorption experiments and quantum chemical calculations, the mechanisms by which H2O and NO affect SO2 adsorption were proposed·H2O and SO2 share the same physical adsorption sites, with H2O being more strongly adsorbed, thus significantly inhibiting the SO2 physical adsorption. When NO coexists with O2, gaseous SO2 reacts with the NOx adsorption configurations to form C-SO3 and C-HSO3. Active atoms near C-SO3 and C-HSO3 can adsorb NO2, forming a co-adsorption configuration, which in turn enhances the nearby physical adsorption of SO2. Enhancing the catalytic oxidation and adsorption of NO through surface modification of activated carbon can improve the low-temperature adsorption performance of SO2.

Energy-efficient CO2 capture using novel low-viscosity water-lean aromatic amine solvent MBA/BDMA/EG/H2O: Performance, mechanism and thermodynamics

To address the challenges of high regeneration energy and corrosion in traditional mixed amine absorbents, as well as the increased viscosity issues in water-lean absorbents post-saturation, this study introduces the co-solvent ethylene glycol (EG) to replace part of the water in the high stability N-methylbenzylamine (MBA) and N, N-dimethylbenzylamine (BDMA) systems, resulting in a novel water-lean aromatic amine solvent, MBA/BDMA/EG/H2O, is proposed as an alternative solution. The addition of the tertiary amine BDMA significantly enhanced the regeneration efficiency of the absorbent. When the mass ratio of MBA/BDMA/EG/H2O is set at 1.5:1.5:3.5:3.5, the CO2 loading reaches 0.36 mol/mol, while the viscosity is only 10.82 mPa⋅s at room temperature. The CO2 capture mechanism of this absorbent was elucidated using 13C NMR and quantum chemical calculations. Initially, CO2 reacts with MBA to form MBACOO-/MBAH+. Subsequently, MBA+COO– undergoes deprotonation to produce MBAH+ and BDMAH+. As the concentration of free MBA decreases to a certain level, BDMA undergoes hydrolysis, resulting in the formation of HCO3–. In the later stages of absorption, some of the carbamate products convert to unstable alkyl carbonates by reaction with EG. Notably, the regeneration energy of MBEH is reduced by 21.1 % (estimate), compared to 30 wt% MEA aqueous solution. The corrosion rate of 30 wt% MEA (after absorption) on carbon steel is 3.6 times higher than that of MBEH (after absorption). Therefore, the proposed MBEH solution presents a promising absorbent with excellent desorption performance, low viscosity, reduced regeneration energy, and low corrosion rate.

Charge-Transfer Interactions Between Antibiotics and Small Organic Acids: Spectroscopic Characterization and Computational Investigation

Six new charge-transfer complexes using ofloxacin (OFL) and sulfamethazine (SMR) as electron donors and coumaric acid (COA), cinnamic acid (CNA), and salicylic acid (SAA) as acceptors via equimolar mixture have been synthesized. The experiment used UV-vis spectroscopy to determine the formation of the complex in methanol through the presence of a new broad absorption band with a maximum wavelength in the 200-400 nm range. The molecular composition of the charge-transfer complexes was determined by the spectrophotometric titration method and found to be 1:1 (donor: acceptor). These complexes have been characterized by infrared (FTIR) and scanning electron microscopy (SEM). In the FTIR spectra, the CT complexes showed a wavelength shift compared to the reactants. The complexes exhibited various morphologies by SEM, including spherical particles, short rods, and flattened shapes. Additionally, quantum chemical calculations at the DFT/B3LYP level of theory investigated the complexes' steady-state structures, energies, and charge densities. The intermolecular binding energies was negative, indicating that the reactions of the six complexes proceeded spontaneously. There was strong van der Waals forces and hydrogen bonds between the donor and acceptor, which contributed to the complexes' strong molecular stability. The C-N and N-H groups in the donor molecule, and the -COOH group in the acceptor molecule, played key roles in the complexation process. DFT calculation results were appropriate to support our experimental results. This study highlights the molecular mechanisms of donor and acceptor action in charge-transfer interactions, providing a theoretical basis for the synthesis of antibiotic complexes and the removal of antibiotics.

Screening and evaluation of phase change absorbents by molecular polarity index: Experimental and quantum chemical calculation studies

Phase change absorbents have recently received increasing attention due to their potential to reduce the energy penalty of CO2 capture. However, its complex composition makes the prediction of phase separation performance difficult. Phase separation behavior and phase separation rate have been investigated for the amine-aqueous 5.0 M amine blends by experimental and quantum chemical calculations (including MPI, hydrogen bonds and Gibbs free energy). The different phase behaviors upon CO2 absorption were discussed and well explained by the polarity change of components and the reaction products. A defined MPI value of tertiary amines was recommended to predict the immiscible type (MPI > 10.55 Kcal/mol), phase separation type (9.00 Kcal/mol < MPI < 10.08 Kcal/mol), and miscible type (MPI < 6.74 Kcal/mol). The electron density at the critical point of hydrogen bonds and interaction region indicators were employed to visually evaluate the influence of intramolecular and intermolecular hydrogen bonds on phase separation behaviors. The results show that the presence of excessive hydrogen bonds decreased the phase separation capacity. Furthermore, the relationship between the MPI, the Gibbs free energy of the proton transfer process and the phase separation time were explored. The increase of MPI caused by the tertiary amines can enhance the stability of the final product, delay the appearance of the phase separation peak and reach a maximum phase separation time of 230 min. Therefore, this study is significant for the screening and evaluation of efficient phase change absorbents with good potential for industrial applications in CO2 capture.

COSMO-RS prediction, experimental investigation, and mechanism analysis: A new approach to separating the n-hexane–tert-butanol azeotropic system via liquid-liquid extraction with ionic liquids

n-Hexane and tert-Butanol (TBA) are frequently utilized to refine the conditions for Grignard, Wittig, and Friedel-Crafts alkylation reactions. During the synthesis of loratadine, the formation of azeotropic mixtures n-hexane and TBA, which are challenging to separate through conventional distillation, is inevitable. This study utilizes the COSMO-RS model to identify suitable ionic liquids (ILs) for the separation of the n-hexane–TBA azeotropic system. Based on solvent capacity and selectivity, 1-ethyl-3-methylimidazolium trifluoroacetate ([EMIM][TFA]), 1-butyl-3-methylimidazolium trifluoroacetate ([BMIM][TFA]), and 1-hexyl-3-methylimidazolium trifluoroacetate ([HMIM][TFA]) were selected as extractants. The liquid–liquid equilibrium (LLE) data for the n-hexane–TBA – ILs ternary system were measured at 303.15 K and atmospheric pressure. Distribution coefficients and selectivity were calculated to evaluate the performance of the extractants, with the NRTL model used to correlate the experimental LLE data. The consistency of the NRTL model parameters was corroborated through topological analysis associated with the Gibbs tangent principle. Quantum chemical calculations, including interaction energy, ESP analysis, IGMH analysis, and QTAIM topological analysis, were performed to explore the separation mechanism at the molecular level. The results indicated that the interaction energies between the ILs and TBA were higher than those between the ILs and n-hexane, indicating a stronger attraction of ILs to TBA. Consequently, the ILs effectively separated TBA from the n-hexane–TBA azeotropic system, with extraction capacities ranked as [EMIM][TFA] > [BMIM][TFA] > [HMIM][TFA]. The quantum chemical calculations successfully explained the experimental results, aligning with COSMO-RS model predictions and confirming their reliability. IGMH and QTAIM topological analyses systematically explored the types and strengths of interactions, revealing that hydrogen bonds are predominant between the ILs and TBA, with additional contributions from van der Waals forces. Furthermore, the hydrogen bond strengths between TBA and the anions and cations of the ILs are classified as strong and moderate, respectively. This work provides valuable insights into the separation of azeotropic systems using ILs, elucidating the underlying mechanisms behind this process.

New nor-ent-halimane and nor-clerodane diterpenes from Callicarpa integerrima with anti-MRSA activity

Two new nor-ent-halimane diterpenes and three previously unreported nor-clerodane diterpenes, designated callicaintides A−E (1−5), were isolated from Callicarpa integerrima. Compounds 1 and 2 feature a distinctive 5/6-membered ring system, while compounds 3−5 are characterized by progressively truncated carbon skeletons, containing 18, 17, and 16 carbons, respectively. In addition, four known compounds 6−9 were also identified. Their structures were elucidated using advanced spectroscopic techniques, including nuclear magnetic resonance (NMR), high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), ultraviolet (UV), infrared radiation (IR), optical rotatory dispersion (ORD), DP4+ analysis and electronic circular dichroism (ECD), supported by quantum chemical calculations. Compounds 1−9 were evaluated for their anti-MRSA activity. Among them, compound 6 demonstrated significant anti-MRSA activity, with a minimum inhibitory concentration (MIC) of 16 μg·mL−1.

Efficient membrane separation of SO2 by choline chloride-based natural deep eutectic solvents: The role of hydrogen bonding sites

Natural deep eutectic solvents (NDESs) are recognized as promising membrane materials for sustainable SO2 separation. Evaluating their separation performances is necessary, as well as understanding of the role that each hydrogen bonding site (including anion and functional groups in NDESs) plays in SO2 separation. Herein, three choline chloride (ChCl)-based NDESs bearing different number and type of functional groups were firstly incorporated into Pebax matrix to fabricate blended membranes for removing SO2 from CO2 and N2. The Pebax/NDES membranes show SO2 permeability up to 10502 Barrer (0.20 bar and 40 °C), with excellent SO2/N2 and SO2/CO2 selectivity of 1808 and 62.5 obtained, respectively, which are enhanced by 156 %, 61.5 % and 56.1 % compared with those in neat Pebax membrane. By means of gas solubility and diffusivity measurements, quantum chemical calculations and spectral characterizations, the highly-reversible multi-site interactions between SO2 and hydrogen bonding sites in NDESs (Cl−···SO2, carbonyl O···SO2 and hydroxyl O···SO2) were revealed. Meanwhile, the strength of hydrogen bonding network inside the NDESs, which is governed by the hydrogen bonding sites, is found to significantly influence the gas diffusion. More importantly, SO2/CO2/N2 (2.5/15/82.5 mol%) mixed gas separation experiment also displays the superior separation performance and long-term stability of Pebax/NDES membrane.

Pure rotational spectroscopic measurements on a uranium-containing polyatomic compound: SUO2

Ground-state rotational constants were determined from the rotational spectra of two isotopologues (S-32 and S-34) of SUO2. For 32SUO2 it was determined that A0= 5150.34(17) MHz, B0= 2950.302(12) MHz, and C0= 1872.933(13) MHz. The SUO2 molecules were produced using a laser ablation nozzle inside of a chirped pulse Fourier transform microwave spectrometer operating between 8 GHz and 18 GHz. The obtained rotational constants and Kraitchman substitution coordinates for sulfur are in very good agreement with those obtained from quantum chemical calculations.

Synthesis of polyaniline tannate-modified carbon nanotubes by oxidative copolymerization as highly efficient corrosion inhibitors for mild steel in HCl solution

Corrosion is a prevalent issue in industrial production, directly impacting the production process and causing severe damages. To mitigate this problem, corrosion inhibitors are highly desired. Herein, a novel type of nano corrosion inhibitor, referred to as PTCNT, was synthesized through an oxidative copolymerization method utilizing aniline, ammonium persulfate (APS), and tannic acid (TA)-modified multiwalled carbon nanotubes (MWCNTs). The results demonstrated that the PTCNT effectively inhibited the corrosion of mild steel in 1 M HCl solution, achieving the corrosion inhibition efficiency of 90.6 % at the concentration of 75 mg/L. Characterization results implied that the PTCNT adsorbed onto the surface of the mild steel, forming a protective shielding layer. Potentiodynamic polarization measurements proved that the PTCNT functioned as the hybrid corrosion inhibitor. Furthermore, the adsorption of PTCNT on the mild steel surface was investigated using adsorption isotherm and adsorption kinetic modeling. Quantum chemical calculations were used to elucidate the adsorption mechanism of PTCNT. These findings raise new avenues for the development of highly efficient corrosion inhibitors for the mild steel in HCl solutions.

Electron Properties of Baicalein and its Derivatives via Quantum Chemistry Calculation: The Effect of Hydroxyl-substitution at A and C Rings

Abstract: The electron properties of baicalein-family are of great importance in influencing its properties and corresponding bioactivities. In this work, we conducted comprehensive quantum chemistry calculations on pristine baicalein, and its two hydroxyl-substituted derivatives where the hydroxylsubstitution respectively occur at A and C rings. By contrasting with each other, the effects of the hydroxyl-substitution on the electron properties were studied from the aspects of the density of states, molecular orbital, electronic excitation, electrostatic potential, and electron delocalization. According to our computation, the hydroxyl-substitution results in variations in geometry and the consequent electron properties among the discussed molecules. Certainly, this research can contribute to the development of the research on the electron involved properties and the structure-property-activity relationship for the baicalein-family.

Design of heterostructure photocatalysts based on layered perovskite-like bismuth silicate

Heterostructure photocatalysts attract a lot of attention of researchers thanks to their enhanced photocatalytic performance. Herein, we focus on the formation of the p-n type heterojunction based on bismuth metasilicate Bi2SiO5 and β-Bi2O3. To date, there are some publications dedicated to these objects, however, the monitoring of the phase composition in the Bi2O3-Bi2SiO5 system and strong evidence of the heterostructure formation in the composite material have not been provided together. At first, we show with quantum-chemical calculations that such interface is possible to design. After that, using XRD in situ we clearly show the pathway of formation of Bi2SiO5 by consuming β-Bi2O3 phase with increasing of temperature. Such results allow monitoring the phase content of the composite material. Finally, we choose two calcination modes to prepare the samples. Based on the results of HRTEM, DRS, XRD, IR and Raman data we clearly show the difference between the mechanical mixture of the semiconductors and generated heterostructure material. Photocatalytic properties of the samples are tested in photodegradation of Rhodamine B under different wavelength of LEDS. Under visible light (470 nm) the heterostructure demonstrates better catalytic activity. Additionally, using air flow and trapping agents it is demonstrated that the holes h+ mainly take part in deethylation of the dye.

Resolution and Absolute Configuration of Fargesin Enantiomers.

Fargesin is an important bioactive furofuran lignan isolated from different plant species. Despite presenting potent biological activities, its stereochemical characterization has relied mostly on empirical correlations of optical rotation, an approach considered risky that commonly leads to misassignments and error propagation. Additionally, the enantiomeric purity of fargesin isolates used for biological assays has not been previously investigated. Herein, we report the enantioresolution of a scalemic mixture of fargesin isolated from Aristolochia warmingii along with the first unambiguous determination of the absolute configuration of each enantiomer by means of optical rotatory dispersion, as well as electronic and vibrational circular dichroism aided by quantum-chemical calculations.

Highly efficient CO2 capture by a non-aqueous amine-based absorbent of 3 aminopropanol/polyethylene glycol 200: Experimental and computational simulation

In the present work, a novel non-aqueous 3-aminopropanol/polyethylene glycol 200 (3AP/PEG200) absorbent for efficient carbon dioxide (CO2) capture was designed using environment-benign and non-toxic polyethylene glycol 200 (PEG200) as an alternative to water. The mechanism, physical, thermodynamic, and kinetic properties of absorption process was investigated through a combination of experimental and multi-scale computational simulation approaches including molecular dynamics (MD) simulation and quantum chemical (QC) calculations. It was found that the addition of PEG200 not only enhanced the thermal stability of the absorbent, but also did not significantly increase the viscosity. In addition, kinetic studies revealed that the absorption process conforms to a pseudo-first-order equation, with the activation energy (Ea) value of 20.40 kJ/mol, significantly lower than that of the benchmark 30 % monoethanolamine (MEA) aqueous solution used in industrial CO2 capture. Furthermore, the enthalpy change (ΔH) and entropy change (ΔS) values were found to be more negative than those of other liquid absorption systems, indicating that the 3AP/PEG200 absorbent is favorable for CO2 absorption even at low partial pressures. Most importantly, the absorption system exhibited good regeneration capability, as demonstrated by five absorption–desorption cycle experiments. In conclusion, the non-aqueous 3AP/PEG200 absorbent exhibits low viscosity, high thermal stability, enhanced absorption capacity, and excellent cyclic performance, positioning it as a promising candidate for CO2 absorption in industrial applications.

Experimental and molecular insights into ionic liquid-based recovery of valuable metals from spent lithium-ion batteries

A new type of collaborative extractants consisting of the ionic liquid (IL) 1-aminoprooyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide, ([APMIM][Tf2N]) and Cyanex 923 (C923) is first applied for selective extraction of valuable metals from spent lithium-ion batteries (LIBs). The one-stage extraction efficiencies of Co2+, Ni2+ and Mn2+ are up to 99.87 %, 97.74 %, 99.98 %, respectively, at the optimal conditions, and the high-purity Li+ was enriched at the raffinate. It is found that the extraction process follows the so-called “cation exchange mechanism”, and the molecular-level mechanism is revealed via quantum chemical (QC) calculations. The findings show that C923 plays the role of coordinating with metal ions, the cation of IL exchanges metal ions from the aqueous to organic phases, and the anion [Tf2N]- of IL can stabilize the complex species of metal ion-[Tf2N]--C923 in organic phase. This work provides new insights for the design of novel IL-based extractants for the recycling of spent LIBs.

Multiscale model for bottom-up prediction of failure parameters of unidirectional carbon-fiber-reinforced composite lamina from the atomic to filament-scales, and its application to failure modeling of open-hole quasi-isotropic composite laminates

A multiscale model is developed to comprehensively predict the failure parameters associated with the elasto-plasticity of a unidirectional carbon-fiber-reinforced composite lamina; the prediction is performed according to the resin-matrix design. The developed model involves quantum-chemical reaction-path calculations, molecular-dynamics simulations, and micromechanical analyses at the filament scale. The presented model is further combined with an advanced numerical approach developed based on an extended finite-element method, to analyze composites at the laminate scale. Using the established four-scale model, the open-hole tension and compression of a quasi-isotropic laminate are simulated, starting from the composition of an epoxy resin. The predicted elasto-plastic properties and strengths of a unidirectional lamina are in good agreement with the previously reported experimental results. Furthermore, the strengths predicted for the open-hole tests are also plausible, as they are similar to the experimental values reported in literature. The established multiscale model is expected to be useful in composite-material development as it facilitates rapid and exhaustive analysis.