Conductor-like Polarizable Continuum Model Research Articles

Hybrid Cluster-Continuum Method for Single-Ion Solvation Free Energy in Acetonitrile Solvent.

A new hybrid discrete-continuum approach named the cluster-continuum static approximation (CCSA) has been proposed for acetonitrile solvent. The continuum part uses the conductor-like polarizable continuum model for electrostatic and a surface area-dependent term for nonelectrostatic solvation. The CCSA includes only one explicit acetonitrile solvent molecule and a damping function, which makes the CCSA method reduce to pure continuum solvation in the case of weaker potential of mean force for solute-solvent interaction. The performance of the model was tested for 22 anions and 22 cations, including challenge species that cannot be adequately described by pure continuum solvation. A comparison was done with the widely used solvent model density (SMD) model. For anions, the CCSA reduces to pure continuum solvation and the method has the same performance as the SMD model, with a standard deviation of the mean signed error (SD-MSE) of 2.7 kcal mol-1 for both models. However, the CCSA method for cations considerably outperforms the SMD model, with an SD-MSE of 3.3 kcal mol-1 for the former and 8.4 kcal mol-1 for the latter. The method can be automated, and the present study suggests that continuum solvation models could be parameterized taking into account the explicit solvation as proposed in this work.

Enhancing Bioactivity through the Transfer of the 2-(Hydroxymethoxy)Vinyl Moiety: Application in the Modification of Tyrosol and Hinokitiol.

Utilizing Density Functional Theory (DFT) calculations at the B3LYP/QZVP level and incorporating the Conductor-like Polarizable Continuum Model (C-PCM) for solvation, the thermodynamic and chemical activity properties of 21-(hydroxymethoxy)henicosadecaenal, identified in cultured freshwater pearls from the mollusk Hyriopsis cumingii, have been elucidated. The study demonstrates that this compound releases formaldehyde, a potent antimicrobial agent, through dehydrogenation and deprotonation processes in both hydrophilic and lipophilic environments. Moreover, this polyenal exhibits strong anti-reductant properties, effectively scavenging free radicals. These critical properties classify the pearl-derived ingredient as a natural multi-functional compound, serving as a coloring, antiradical, and antimicrobial agent. The 2-(hydroxymethoxy)vinyl (HMV) moiety responsible for the formaldehyde release can be transferred to other compounds, thereby enhancing their biological activity. For instance, tyrosol (4-(2-hydroxyethyl)phenol) can be modified by substituting the less active 2-hydroxyethyl group with the active HMV one, and hinokitiol (4-isopropylotropolone) can be functionalized by attaching this moiety to the tropolone ring. A new type of meso-carrier, structurally modeled on pearls, with active substances loaded both in the layers and the mineral part, has been proposed.

Ab initio investigation of the geometrical behavior in solution and electronic structure of the anion complexes [bis(1,3-dithiole-2-thione-4,5-dithiolate)M], for M = Bi(III), Sb(III), and Zn(II).

1,3-Dithiole-2-thione-4,5-dithiolate (dmit) ligands are known for their conductive and optical properties. Dmit compounds have been assessed for use in sensor devices, information storage, spintronics, and optical material applications. Associations with various metallic centers endow dmit complexes with magnetic, optical, conductive, and antioxidant properties. Optical doping can facilitate the fabrication of magnetic conductor materials from ground-state nonmagnetic cations. While most studied complexes involve transition-metal centers due to their diverse chemistry, compounds with representative elements are less explored in the literature. This study investigated the structural and electronic properties of bisdmit complexes with representative Bi(III), Sb(III), and Zn(II) cations. AIMD calculations revealed two new geometries for Bi(III) and Zn(II) complexes, diverging from the isolated geometry typically used in quantum chemical calculations. The coordination of acetonitrile molecules to the cationic centers of the complexes resulted in unstable structures, while the dimerization of the complexes was stable. SA-CASSCF/NEVPT2 calculations were applied to the structures of the isolated complexes and stable dimers, confirming the multireference character of the electronic structure of the three systems and the multiconfigurational character of the Bi(III) complex. The electronic spectra simulated by the STEOM-DLPNO-CCSD calculations accurately reproduced the experimental UV‒Vis spectra indicating the participation of the isolated Bi(III) dmit complex and its dimeric form in solution. AIMD calculations of the dmit salts were conducted using the GFN2-xTB method with 60 explicit acetonitrile molecules as the solvent at 300K for a total simulation time of 50.0ps, with printing intervals of 0.5fs. The final geometries were optimized employing the PBEh-3c compound method, incorporating implicit conductor-like polarizable continuum model (CPCM) solvation for acetonitrile. Local energy decomposition (LED) analysis at the DLPNO-CCSD(T)/Def2-TZVP level of theory was utilized to investigate the stability of the complex geometries identified by AIMD. The electronic structures of the complexes were assessed using the SA-CASSCF/NEVPT2/Def2-TZVP method to confirm the multiconfigurational and multireference nature of their electronic structures. Electronic spectra were analyzed using the STEOM-DLPNO-CCSD/Def2-TZVP method, with CPCM used to simulate an acetonitrile medium.

Harnessing synergistic effects in GQD@Pt(II) nanocomposites for enhanced photovoltaic performance: a computational study.

The development of efficient solar energy conversion technologies is crucial for addressing global energy challenges and reducing reliance on fossil fuels. Platinum(II) complexes are promising materials for photovoltaic applications due to their strong light absorption and long-lived excited states. However, their narrow absorption in the visible spectrum and stability issues limit their performance. Combining platinum(II) complexes with graphene quantum dots (GQDs) can enhance photovoltaic performance by leveraging the complementary light harvesting and charge transfer characteristics of the two components. This study utilizes density functional theory (DFT) calculations to explore their electronic structures, charge transfer dynamics, and photoelectric performance. Specifically, it investigates the effects of incorporating different substituents, either electron-donating or electron-withdrawing, onto the fluorene motif of the Pt(II) complex. The findings reveal that combining GQDs with Pt(II) complexes extends light absorption into the UV range, enabling comprehensive solar utilization. Upon photoexcitation, electrons migrate between the GQD conduction band and the Pt(II) complex, stabilizing charges and enhancing extraction. Substituents significantly influence charge transfer dynamics: electron-withdrawing groups promote transfer to the GQD, while electron-donating groups encourage charge separation and delocalization. Nanocomposites featuring electron-donating substituents achieve the highest energy conversion efficiencies, with GQD@Pt(II)-NPh2 reaching 24.6%. This is attributed to improved light harvesting, efficient charge injection, and reduced recombination. These insights guide the rational design of GQD-Pt(II) nanocomposites, optimizing charge separation and transfer processes for enhanced photovoltaic performance. The computational approach employed here provides a robust tool for developing advanced materials in renewable energy technologies. The computational studies reported in this work were performed using the DFT approach, specifically employing the hybrid functional PBE0. The PBE0 functional's accuracy in describing electronic structures and excited-state properties is essential for understanding charge transfer processes, photoabsorption, and emission characteristics in metal-organic complexes. Geometry optimizations and time-dependent DFT (TD-DFT) calculations were carried out to investigate the properties of the nanocomposites. The effects of solvents were replicated using the conductor-like polarizable continuum model (CPCM). The charge transfer length (ΔL) and interfragment charge transfer (ΔQ) were calculated using the Multiwfn software package, and all calculations were performed using the BDF software package.

Two-photon absorption in bioactive C4-substituted Coumarin derivatives: Impact of electron-withdrawing and donating groups in different environment

The versatile applications of coumarin derivatives in materials processing, fluorescence imaging, data storage, and photodynamic therapy have sparked considerable interest in scientific community. In this research paper, we explore the UV–vis spectra, IR spectra, and two photon absorption (TPA) characteristics of biological active coumarin derivatives under the influence of electron withdrawing (specifically X = CONH2, CHO, and NO2) and electron donating (X= -CH3, -OH, -NH2) functional groups at C-4 position. To delve into the absorption spectra, we employ time-dependent density functional theory calculations. Results revealed that acceptor functional groups (specifically R = CONH2, CHO, and NO2) not only lower the energy of the lowest two photon active state but also increase the corresponding TPA cross-section. Furthermore, using the Conductor-like Polarizable Continuum Model (CPCM), the influence of solvent polarity on C-4 substituted coumarin derivative was also investigated. Our findings effectively capture how substitutions and solvents impact the nonlinear optical response in coumarins, as evidenced by the measurement of the two-photon absorption cross-section (σTPA). This study offers valuable insights for identifying and designing novel coumarin derivatives with C4 substitutions, unlocking new and intriguing possibilities for their practical applications.

Insight on relationship between crystallinity and band gap energies of polyhydroxyalkanoates polymers

This study explores the electronic properties of polyhydroxyalkanoates (PHAs), a class of biodegradable polymers. The focus lies in examining the relationship between crystallinity and band gap energies in PHAs. A notable discovery is the identification of a band gap plateau, suggesting a threshold in electronic properties with increasing polymer chain length. DFT calculations were employed to model the complexities of PHA polymers, with the conductor-like polarizable continuum model (CPCM) offering insights into solvent effects. The results demonstrate a strong negative correlation between crystallinity and band gap in both vacuum and CPCM environments. This study underscores the significance of structural order in shaping the electronic properties of PHAs, paving the way for the development of sustainable polymeric materials for various applications.

Theoretical Evaluation of Fluorinated Resazurin Derivatives for In Vivo Applications.

Primarily owing to the pronounced fluorescence exhibited by its reduced form, resazurin (also known as alamarBlue®) is widely employed as a redox sensor to assess cell viability in in vitrostudies. In an effort to broaden its applicability for in vivo studies, molecular adjustments are necessary to align optical properties with the near-infrared imaging window while preserving redox properties. This study delves into the theoretical characterisation of a set of fluorinated resazurin derivatives proposed by Kachur et al., 2015 examining the influence of fluorination on structural and electrochemical properties. Assuming that the conductor-like polarisable continuum model mimics the solvent effect, the density functional level of theory combining M06-2X/6-311G* was used to calculate the redox potentials. Furthermore, (TD-)DFT calculations were performed with PBE0/def2-TZVP to evaluate nucleophilic characteristics, transition states for fluorination, relative energies, and fluorescence spectra. With the aim of exploring the potential of resazurin fluorinated derivatives as redox sensors tailored for in vivo applications, acid-base properties and partition coefficients were calculated. The theoretical characterisation has demonstrated its potential for designing novel molecules based on fundamental principles.

A theoretical approach to the corrosion inhibition of iron in acidic solution by a green formulation derived from Nigella sativa L seeds oil

A theoretical approach combining density functional theory (DFT) computation, Monte Carlo (MC) methods, and molecular dynamics (MD) simulations was used to investigate and validate the iron corrosion inhibition performances in the acidic medium of a green formulation based on the oil extracted from Nigella sativa L. DFT calculations allowed to determine the energetic, global, and local chemical reactivity parameters. The most stable adsorption configuration of the fatty acids components of the Nigella sativa L. formulation was determined by the Monte Carlo methods with the adsorption locator module and by molecular dynamics simulations. Results indicated that all the compounds are absorbed with a totally flat orientation on the first layer of the metal surface.The active sites of molecules were effectively established by using DFT through the analysis of frontier molecular orbitals (FMO), the Hirshfeld population analysis (HPA), the electrostatic potential (ESP), molecular electron density analysis (MED), and Fukui indices (FI). The solvent effect was investigated by using the conductor-like polarizable continuum model (CPCM). Protonation effects were also analysed through the protonation energy (PE), the proton affinity (PA), and the absolute gas phase basicity (GB). The formation of a coating on the iron surface validated the good protective action of the green formulation derived from Nigella sativa L.The computational and theoretical approaches substantiate our experimental electrochemical and spectroscopic studies [1].

Computational-based investigation of antioxidative potential polyphenolic compounds of Salvia officinalis L.: combined DFT and molecular docking approaches.

The antioxidant properties of the three polyphenolic compounds (carnosol, cirsiliol, and luteolin) of Salvia officinalis L. were investigated employing the density functional theory (DFT) calculations at the B3LYP of basis set at 6-311 + + G (d, p) in order to evaluate their antioxidant activity. The enthalpies of reactions associated with the SET-PT, SPLET, and HAT mechanisms were analyzed in gas and in different solvents using the CPCM (conductor-like polarizable continuum) model. For all possible hydrogen donor sites, the corresponding parameters (BDE, AIP, PDE, PA, ETE, HOMOs, and LUMOs) and reactivity indices (IPE, EA, Χ, η, S, and ω) were also evaluated. The calculated results showed that derivatives 12-OH, 11-OH, 4'-OH, and 3'-OH had the lowest antioxidant activity. The results showed as well that carnosol, cirsiliol, and luteolin have higher reactivity compared to ascorbic acid and could be considered better antioxidants. According to research, the catechol group is crucial in influencing the studied compounds antioxidant activity. The theoretically predicted order of antioxidant efficiencies in this work agrees well with the QSAR (quantitative structure-activity relationship) data. The findings show that in the vacuum as well as benzene media. HAT would be the most effective mechanism; in contrast, the thermodynamic equilibrium approach in polar media is the SPLET mechanism. Likewise, the outcomes of the docking modeling confirm that the selected molecules have high inhibitory activity to glutathione-S-transferases (GSTs) receptors. Moreover, they have very important pharmacokinetic, chemical, and biological profiles. Finally, all the results show that the three natural molecules have good pharmacokinetic profiles, particularly the bioavailability and permeability toward biological membranes. The software packages used in this investigation are Gaussian 16, Discovery studio Visualizer, and AutoDock vina. The three compounds (carnosol, cirsiliol, and luteolin) of Salvia officinalis L. were optimized with DFT/B3LYP of basis set at 6-311 + + G (d, p). The optimized structures were established via vibrational analysis (i.e., no imaginary frequencies in the frequency set). All enthalpies were zero-point (ZPE) corrected. Vibrational frequency calculations were performed at 298.15K and 1 atmosphere pressure to determine the thermodynamic characteristics of the investigated reactions. The descriptors were associated with the antioxidant mechanisms for investigated molecules in vacuum and in various solvents. The molecular docking was used by AutoDock vina to estimate and evaluate the title compounds compatibility as potential antioxidant drugs utilizing appropriate receptor proteins. The solvation effect in the medium of benzene (ɛ = 2.27) and water (ɛ = 78.39) was taken into account. Furthermore, a methanol solvent (ɛ = 32.61) was also taken into consideration to compare with the empirical data.

Low-cost quantum mechanical descriptors for data efficient skin sensitization QSAR models

Quantitative Structure Activity Relationship modelling methodologies need to incorporate relevant mechanistic information to have high predictive performance and validity. Electrophilic reactivity is a common mechanistic feature of skin sensitization endpoints which could be concisely characterized with electronic descriptors which is key to enabling the modelling of small datasets in this domain. However, quantum mechanical methodologies have previously featured high computational costs which would exclude the use of large datasets. Consequently, we investigate the use of electronic descriptors calculated using the Hartree Fock with 3 corrections (Hf-3c) method, a low-cost ab initio methodology that has higher chemical accuracy than previous semiempirical methodologies for modelling in vitro skin sensitization assay outcomes. We also model the Ames assay as a surrogate for determining skin sensitization outcomes. The quantum chemical descriptors calculated using the Hf-3c method with conductor-like polarizable continuum model (CPCM) implicit solvation found improved QSAR model performance for the in vitro Ames (n = 6049, 0.770 AUC), KeratinoSens (n = 164, 0.763 AUC), and Direct Peptide Reactivity Assay (n = 122, 0.750 AUC) datasets, with their combination producing high predictive performance for unseen in vivo Local Lymph Node Assay (n = 86, 0.789 AUC) and Human Repeated Insult Patch Test (n = 86, 0.791 AUC) assay toxicant outcomes.

Electronic structure and molecular properties of nitisinone and mesotrione in water

ContextNitisinone is a medium-sized organic molecule that is used in treating hereditary tyrosinemia type 1 (HT-1). The structurally analogous mesotrione, however, is used as a pesticide/herbicide. What molecular properties are responsible for the similarity/dissimilarity of these molecules is investigated here. The solvent effect reduces the electron affinity to rather negative values and causes the negative electron affinity which manifests itself in a very high positive absolute reduction potential.MethodsB3LYP method was utilized for a geometry optimization of nitisinone and mesotrione in their neural and ionized (L0, L+, L−) forms of 6 structures. The calculations were conducted in water as a solvent using conductor-like polarizable continuum model (CPCM), nitisinone also in vacuo. The complete vibrational analysis at the true energy minimum allows evaluating the thermodynamic functions with focus to the zero-point energy and overall entropic term. The change of the Gibbs energy on reductions and/or oxidation facilitates evaluating the absolute reduction and absolute oxidation potentials. Also, DLPNO-CCSD(T) method that involves the major part of the correlation energy has been applied to nitisinone and mesotrione and their molecular ions.

Structure of 2-nitro-2’-hydroxy-5’-methylazobenzene: Theoretical and spectroscopic study

Objectives. 2-Hydroxy-nitroazobenzenes comprise reagents for the synthesis of heteroaromatic compounds, in the molecules of which the benzene and azole cycles are annulated. These reagents are widely used in the production of chemical products for various industries. In particular, 2-2’-hydroxy-5’-methylphenylbenzotriazole is used as an effective photo stabilizer for polystyrene and polyethylene. A promising method for its preparation is the liquid-phase catalytic hydrogenation of 2-nitro-2'-hydroxy-5'-methylazobenzene (2NAB). The aim of the present study was to establish the structure of 2NAB in solutions of different composition.Methods. Theoretical calculations were carried out within the framework of the density functional theory at a temperature of 298.15 K for the gas phase at B3LYP/6-311++G(d, p) and M06-2X/6-311++G(d, p) levels; for hexane, 2-propanol, toluene at B3LYP/6-311++G(d, p) level using the conductor-like polarizable continuum model. An experimental study to determine the probable isomeric structure of 2NAB in various solvents, including sodium hydroxide (NaOH) and acetic acid (CH3COOH) additives, was carried out using infrared (IR) and ultraviolet (UV) spectroscopy.Results. The most probable structure of 2NAB isomers for the gas phase and a number of solvents was determined. Experimental and theoretical IR and UV spectra were obtained. The thermodynamic characteristics of the reaction of intramolecular proton transfer from –OH to –N=N– group in the gas phase were calculated.Conclusions. A comparison of the experimental and calculated results supports the conclusion that the cis-isomer should be considered most probable for the gas phase. For the studied solutions, a trans-isomer of 2NAB with hydrogen bonds formed between the hydroxyl group hydrogen and the β-nitrogen atom of the azo group of dye molecule should be considered as the most likely structure. In the studied individual and binary solvents, prototropic equilibrium is shifted towards the azo form of the dye, while intramolecular proton transfer is possible only in aqueous diethylamine and dimethylformamide solutions with additions of NaOH.

Structure of 2-nitro-2’-hydroxy-5’-methylazobenzene: Theoretical and spectroscopic study

Objectives. 2-Hydroxy-nitroazobenzenes comprise reagents for the synthesis of heteroaromatic compounds, in the molecules of which the benzene and azole cycles are annulated. These reagents are widely used in the production of chemical products for various industries. In particular, 2-2’-hydroxy-5’-methylphenylbenzotriazole is used as an effective photo stabilizer for polystyrene and polyethylene. A promising method for its preparation is the liquid-phase catalytic hydrogenation of 2-nitro-2'-hydroxy-5'-methylazobenzene (2NAB). The aim of the present study was to establish the structure of 2NAB in solutions of different composition.Methods. Theoretical calculations were carried out within the framework of the density functional theory at a temperature of 298.15 K for the gas phase at B3LYP/6-311++G(d, p) and M06-2X/6-311++G(d, p) levels; for hexane, 2-propanol, toluene at B3LYP/6-311++G(d, p) level using the conductor-like polarizable continuum model. An experimental study to determine the probable isomeric structure of 2NAB in various solvents, including sodium hydroxide (NaOH) and acetic acid (CH3COOH) additives, was carried out using infrared (IR) and ultraviolet (UV) spectroscopy.Results. The most probable structure of 2NAB isomers for the gas phase and a number of solvents was determined. Experimental and theoretical IR and UV spectra were obtained. The thermodynamic characteristics of the reaction of intramolecular proton transfer from –OH to –N=N– group in the gas phase were calculated.Conclusions. A comparison of the experimental and calculated results supports the conclusion that the cis-isomer should be considered most probable for the gas phase. For the studied solutions, a trans-isomer of 2NAB with hydrogen bonds formed between the hydroxyl group hydrogen and the β-nitrogen atom of the azo group of dye molecule should be considered as the most likely structure. In the studied individual and binary solvents, prototropic equilibrium is shifted towards the azo form of the dye, while intramolecular proton transfer is possible only in aqueous diethylamine and dimethylformamide solutions with additions of NaOH.

Rational design of co-ordination compounds in combination of bipyridine type of ligands and group 7 metal (M = Mn, Re) for photoCORM: a DFT study.

A large number of manganese and rhenium tricarbonyl complexes are known in literature along with various applications in different fields. CO-releasing molecules (CORMs) got recent research attention because CO can act as a prodrug for different diseases. CORMs offer the promising prospect of a safe and controllable amount of CO release. In this research work, we have explored the electronic properties of compounds such as bipyridine-related [Mn(CO)3] and [Re(CO)3] and we have compared the electronic properties of both manganese and rhenium tricarbonyl complexes in the light of carbon monoxide releasing tendency. The chosen Mn and Re metals have enough possibility to vary or play with ligands and design a new and novel CORM molecule. In this context, we have taken a range of 4,4'-disubstituted 2,2' bipyridyl ligands (Rbpy, where R = NH2, tBu, OCH3, H, CF3, CN, NO2) to investigate CO's liberation ability to identify and study such molecules. The calculated absorbance of designed complexes (1-14) shows visible/near-IR region (350-850 nm). The HOMO-LUMO energy gap of 7 (ΔE=2.40 eV) complex and for complex 14 (ΔE=2.28 eV) which is lesser in all complexes but the MLCT percentage is greater in Mn tricarbonyl complexes in comparison to Re tricarbonyl complexes. The calculated results of the FMO approach revealed that complex 7 and 14 have the lowest energy gap which is also in good agreement with DOSs and TDM results. The theoretically calculated results revealed that the both Mn and Re tricarbonyl complexes have a tendency for labialization of CO, but Mn tricarbonyl complexes are more prone to CO release because they have higher MLCT percentage. In this research work, we have performed density functional theory (DFT) calculations to explore the physical properties of compounds such as bipyridine-related [Mn(CO)3] and [Re(CO)3] and we have compared the physical properties of both manganese and rhenium tricarbonyl complexes in the light of carbon monoxide releasing tendency. DFT-based calculations were performed by using B3LYP/LANL2DZ basis set followed by acetonitrile solvent using the conductor-like polarizable continuum model (CPCM) for different calculations. Various geometrical calculations were performed using the Gaussian16 suite of programs and the output results obtained from Gaussian16 were visualized using GaussView 5.0.16. The same level of theory was used for various calculations, including frontier molecular orbital (FMO) analysis, metal to ligand charge transfer (MLCT), density of state (DOS) calculations, and transition density of matrix (TDM) calculations. For specific calculations, GaussSum 2.2 software package was used to calculate the density of states, and the Multiwfn 3.8 program was used to analyze the transition density matrix, which is presented using heat maps for both electrons and holes.

Design, synthesis, and density functional theory studies of a new selective chemosensor for Pb2+

Herein, we have focused on a new colorimetric ligand synthesized from the reaction of 2-hydroxy-5-methylbenzene-1,3-dialdehyde with 2-amino-thiophenol, and investigated its activity as a sensor. In this regard, the sensory activity of the ligand towards different ions (Mn2+, Cu2+, Co2+, Fe2+, Fe3+, Zn2+, Ni2+, Cd2+, Ag+, Na+, Cs+, Mg2+, Al3+, Ba2+, K+, and Pb2+) was studied. The specificity of ion bindings is discussed through UV–Vis analysis. The ligand that was synthesized showed remarkable sensitivity, with a detection limit of 0.001 ppb. Additionally, the presence of Pb2+ ions can be visually detected through a color change from colorless to yellow. In the last part of this work, we seek to predict the available experimental measurements. Density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) are employed to examine the bonding between the ligand and the Pb2+ ion. The effect of water solvent was thoroughly examined for all the steps via the conductor-like Polarizable Continuum Model (CPCM). The theoretical findings revealed that electronic properties, including energy gap, adsorption energy, charge/energy transfer, and optical characteristics, undergo significant changes when Pb2+ cations are present. Hence, it can be inferred that the newly synthesized chemosensor (NC) is highly efficient in detecting Pb2+.

Resonance Raman spectra and excited state properties of methyl viologen and its radical cation from time-dependent density functional theory.

Time-dependent density functional theory (TDDFT) was applied to gain insights into the electronic and vibrational spectroscopic properties of an important electron transport mediator, methyl viologen (MV2+ ). An organic dication, MV2+ has numerous applications in electrochemistry that include energy conversion and storage, environmental remediation, and chemical sensing and electrosynthesis. MV2+ is easily reduced by a single electron transfer to form a radical cation species (MV•+ ), which has an intense UV-visible absorption near 600 nm. The redox properties of the MV2+ /MV•+ couple and light-sensitivity of MV•+ have made the system appealing for photo-electrochemical energy conversion (e.g., solar hydrogen generation from water) and the study of photo-induced charge transfer processes through electronic absorption and resonance Raman spectroscopic measurements. The reported work applies leading TDDFT approaches to investigate the electronic and vibrational spectroscopic properties of MV2+ and MV•+ . Using a conventional hybrid exchange functional (B3-LYP) and a long-range corrected hybrid exchange functional (ωB97X-D3), including with a conductor-like polarizable continuum model to account for solvation, the electronic absorption and resonance Raman spectra predicted are in good agreement with experiment. Also analyzed are the charge transfer character and natural transition orbitals derived from the TDDFT vertical excitations calculated. The findings and models developed further the understanding of the electronic properties of viologens and related organic redox mediators important in renewable energy applications and serve as a reference for guiding the interpretation of electronic absorption and Raman spectra of the ions.

Extended Conductor-like Polarizable Continuum Solvation Model (CPCM-X) for Semiempirical Methods.

We have developed a new method to accurately account for solvation effects in semiempirical quantum mechanics based on a polarizable continuum model (PCM). The extended conductor-like polarizable continuum model (CPCM-X) incorporates a computationally efficient domain decomposition conductor-like screening model (ddCOSMO) for extended tight binding (xTB) methods and uses a post-processing approach based on established solvation models, like the conductor-like screening model for real solvents (COSMO-RS) and the universal solvent model based on solute electron density (SMD). According to various benchmarks, the approach performs well across a broad range of systems and applications, including hydration free energies, non-aqueous solvation free energies, and large supramolecular association reactions of neutral and charged species. Our method for computing solvation free energies is much more accurate than the current methods in the xtb program package. It improves the accuracy of solvation free energies by up to 40% for larger supramolecular association reactions to match even the accuracy of higher-level DFT-based solvation models like COSMO-RS and SMD while being computationally more than 2 orders of magnitude faster. The proposed method and the underlying ddCOSMO model are readily available for a wide variety of solvents and are accessible in xtb for use in various computational applications.

A high-level quantum chemical study of the thermodynamics associated with chlorine transfer between N-chlorinated nucleobases

The relative free energies of the isomers formed upon N-chlorination of each nitrogen atom within the DNA nucleobases (adenine, guanine, and thymine) have been obtained using the high-level G4(MP2) composite ab initio method (the free energies of the N-chlorinated isomers of cytosine have been reported at the same level of theory previously). Having identified the lowest energy N-chlorinated derivatives for each nucleobase, we have computed the free energies associated with chlorine transfer from N-chlorinated nucleobases to other unsubstituted bases. Our results provide quantitative support pertaining to the results of previous experimental studies, which demonstrated that rapid chlorine transfer occurs from N-chlorothymidine to cytidine or adenosine. The results of our calculations in the gas-phase reveal that chlorine transfer from N-chlorothymine to either cytosine, adenine, or guanine proceed via exergonic processes with ΔG o values of −50.3 (cytosine), −28.0 (guanine), and −6.7 (adenine) kJ mol–1. Additionally, we consider the effect of aqueous solvation by augmenting our gas-phase G4(MP2) energies with solvation corrections obtained using the conductor-like polarizable continuum model. In aqueous solution, we obtain the following G4(MP2) free energies associated with chlorine transfer from N-chlorothymine to the three other nucleobases: −58.4 (cytosine), −26.4 (adenine), and −18.7 (guanine) kJ mol–1. Therefore, our calculations, whether in the gas phase or in aqueous solution, clearly indicate that chlorine transfer from any of the N-chlorinated nucleobases to cytosine provides a thermodynamic sink for the active chlorine. This thermodynamic preference for chlorine transfer to cytidine may be particularly deleterious since previous experimental studies have shown that nitrogen-centered radical formation (via N–Cl bond homolysis) is more easily achieved in N-chlorinated cytidine than in other N-chlorinated nucleosides.

C-PCM study on the electronic and optical properties of Fe(CO)4B12N12 complexes

We explored solvent effect on the stability, dipole moment, polarizability and first hyperpolarizability of Fe(CO)4B12N12 complexes at MPW1PW91/6-311G(d,p) level of theory. These complexes were considered in the low spin states. The self-consistent reaction field theory (SCRF) based on conductor-like polarizable continuum model (PCM) was employed to illustration of the solvent influences. The relations between the parameters with solvent polarity functions (McRae and Suppan functions) were given. Also, relations of the wavenumbers values of the stretching of carbonyl ligands with the Kirkwood–Bauer–Magat equation (KBM) were provided.

Analytical derivative couplings within the framework of time-dependent density functional theory coupled with conductor-like polarizable continuum model: Formalism, implementation, and applications.

The nonadiabatic phenomena, which are characterized by a strong coupling between electronic and nuclear motions, are ubiquitous. The nonadiabatic effect of the studied system can be significantly affected by the surrounding environment, such as solvents, in which such nonadiabatic process takes place. It is essential to develop the theoretical models to simulate these processes while accurately modeling the solvent environment. The time-dependent density functional theory (TDDFT) is currently the most efficient approach to describe the electronic structures and dynamics of complex systems, while the polarizable continuum model (PCM) represents one of the most successful examples among continuum solvation models. Here, we formulate the first-order derivative couplings (DCs) between the ground and excited states as well as between two excited states by utilizing time-independent equation of motion formalism within the framework of both linear response and spin flip formulations of TDDFT/CPCM (the conductor-like PCM), and implement the analytical DCs into the Q-CHEM electronic structure software package. The analytic implementation is validated by the comparison of the analytical and finite-difference results, and reproducing geometric phase effect in the protonated formaldimine test case. Taking 4-(N,N-dimethylamino)benzonitrile and uracil in the gas phase and solution as an example, we demonstrate that the solvent effect is essential not only for the excitation energies of the low-lying excited-states but also for the DCs between these states. Finally, we calculate the internal conversion rate of benzophenone in a solvent with DC being used. The current implementation of analytical DCs together with the existing analytical gradient and Hessian of TDDFT/PCM excited states allows one to study the nonadiabatic effects of relatively large systems in solutions with low computational cost.