Effects of changing ions on the crystal design, non-covalent interactions, antimicrobial activity, and molecular docking of Cu(II) complexes with a pyridoxal-hydrazone ligand.

The present work reports the influence of the presence of different ions (Cl-, Br-, NO3 -, or SO4 2-) on the formation and proprieties of Cu(II) complexes with pyridoxal-benzoylhydrazone (PLBHZ). Four new complexes were successfully synthesized, [CuCl2(PLBHZ)] (1), [CuBr2(PLBHZ)] (2), [CuCl(PLBHZ)H2O]⋅NO3⋅H2O (3), and [CuSO4(PLBHZ)H2O]⋅3H2O (4), and characterized by spectroscopic and physicochemical methods. A single-crystal X-ray study reveals the Schiff base coordinated to the metal center tridentate by the ONS-donor system, resulting in distorted square pyramidal coordination geometries. Noncovalent interactions were investigated by 3D Hirshfeld surface analysis by the d norm function, 2D fingerprint plots, and full interaction maps. The ion exchange is important in forming three-dimensional networks with π⋅⋅⋅π stacking interactions and intermolecular hydrogen bonds. The in vitro biological activity of the free ligand and metal complexes was evaluated against Gram-positive and Gram-negative bacterial strains and the free pyridoxal-hydrazone ligand showed higher activity than their Cu(II) complexes. Molecular docking was used to predict the inhibitory activity of the ligand and complexes against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria.

CO2 and CO Capture on the ZnO Surface: A GCMC and Electronic Structure Study.

The amount of polluting gases released into the atmosphere has grown drastically. Among them, it is possible to cite the release of CO2 and CO gases on a large scale as one of the products of the complete and incomplete combustion of petroleum-derived fuels. It is worth noting that the production of energy by burning fossil fuels supplies the energy demand but causes environmental damage, and several studies have addressed the reduction. One of them is using materials with the potential to capture these gases. The experimental and theoretical studies have significant contributions that promote advances in this area. Among the materials investigated, ZnO has emerged, demonstrating the considerable potential for capturing various gases, including CO2 and CO. This work used density functional theory (DFT) and Grand Canonical Monte Carlo Method (GCMC) to investigate the adsorption of CO2 and CO on the surface of Zinc oxide (ZnO) to obtain adsorption isotherms and interaction energy and the interaction nature. The results suggest that CO2 adsorption slightly changed the angle of the O-C-O to values less than 180°. For the CO, its carbon atom interacts simultaneously with Zn and O of the ZnO surface. However, CO interactions have an ionic character with a lower binding energy value than the CO2 interaction. The energies calculated using the PM6 and DFT methods generated results compatible with the experimental values. In applications involving a mixture of these two gases, the adsorption of CO2 should be favored, and there may be inhibition of the adsorption of CO for high CO2 concentrations.

Electron binding energies of SO2 at the surface of a water cluster.

The electronic properties of SO2 at the surface of a water cluster were investigated by employing a combination of Born-Oppenheimer molecular dynamics and electron propagator theory (EPT). In our work, we utilized a revised version of the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional, which incorporates empirical corrections for dispersion interactions in line with a recent study of the air-water interface conducted by Ohto et al. [J. Phys. Chem. Lett. 10(17), 4914-4919 (2019)]. Polarization effects induce a significant broadening of the electron binding energy distribution, as predicted by EPT. This broadening can result in a substantial increase in electron affinity, impacting the chemical reactivity of SO2 at the air-water interface, a topic of significant and recent research interest. We discuss the relationship between electron binding energies (EBEs) and the specific connections of SO2 to water. The results indicate that configurations involving an OS⋯H bond tend to yield higher electron affinities compared to complex formation through S⋯OW bonds. Surprisingly, SO2 molecules not bound to water molecules according to a specific criterion may also exhibit higher electron affinities. This feature can be explained by the role played by the polarization field from water molecules. Our best estimate for the HOMO-LUMO (H-L) gap of SO2 at the surface of a water cluster is 11.6 eV. Very similar H-L gaps are predicted for isolated and micro-solvated SO2. Fukui functions for the gas phase, and the micro-solvated SO2-H2O complex supports the view that the LUMO is predominantly localized on the SO2 moiety.

Docking and Electronic Structure of Rutin, Myricetin, and Baicalein Targeting 3CLpro.

Understanding the role of 3CLpro protease for SARS-CoV-2 replication and knowing the potential of flavonoid molecules like rutin, myricetin, and baicalein against 3CLpro justify an investigation into their inhibition. This study investigates possible bonds and reactivity descriptors of rutin, myricetin, and baicalein through conformational and electronic properties. Density functional theory was used to determine possible interactions. Analyses were carried out through the molecular electrostatic potential, electron localization function, Fukui function descriptors based on frontier orbitals, and non-covalent interactions. A docking study was performed using a resolution of 1.55 Å for 3CLpro to analyze the interactions of rutin, myricetin, and baicalein. Scores of structures showed that rutin is the best ligand, followed by myricetin and baicalein. Docking studies showed that baicalein and rutin can establish effective interactions with residues of the catalytic dyad (Cys145 and His41), but just rutin forms a hydrogen bond. Myricetin, in turn, could not establish an effective interaction with Cys145. Baicalein interaction arose with active residues such as Arg188, Val186, Gln189, and Gln192. Interactions of rutin and myricetin with Arg188 and Gln189 were also found. A critical interaction was observed only for rutin with the hydroxyls of ring A with His41, and also for Cys145 with rings B and C, which is probably related to the highest score of rutin.

Ab Initio Approach to the Structure, Vibrational Properties, and Electron Binding Energies of H2S∙∙∙SO2.

The present study employs high-level ab initio calculations to investigate the structure, vibrational frequencies, and electronic properties of H2S∙∙∙SO2. The analysis of vibrational frequencies reveals an intramolecular vibrational energy transfer phenomenon, where energy from the stretching modes of H2S is transferred to the ν1s mode of SO2. At the CCSD(T)/aug-cc-pVQZ level, the interaction energy between H2S and SO2 is predicted to be 2.78 kcal/mol. Electron propagator theory calculations yield a HOMO-LUMO gap of 8.24 eV for H2S∙∙∙SO2. Furthermore, by utilizing ab initio results for the adiabatic ionization energy and electron affinity, the electrophilicity of H2S∙∙∙SO2 is estimated to be 2.01 eV. This value is similar to the electrophilicity of SO2, suggesting comparable reactivity and chemical behavior. The non-covalent interaction (NCI) analysis of the H2S∙∙∙SO2 complex emphasizes the significant contribution of non-covalent van der Waals interactions in its energetic stabilization.

Crystal Design, Antitumor Activity and Molecular Docking of Novel Palladium(II) and Gold(III) Complexes with a Thiosemicarbazone Ligand.

The current research describes the synthesis and characterization of 2-acetylpyridine N(4)-cyclohexyl-thiosemicarbazone ligand (HL) and their two metal complexes, [Au(L)Cl][AuCl2] (1) and [Pd(L)Cl]·DMF (2). The molecular structures of the compounds were determined by physicochemical and spectroscopic methods. Single crystal X-ray diffraction was employed in the structural elucidation of the new complexes. The complexes showed a square planar geometry to the metal center Au(III) and Pd(II), coordinated with a thiosemicarbazone molecule by the NNS-donor system and a chloride ion. Complex (1) also shows the [AuCl2]- counter-ion in the asymmetric unit, and complex (2) has one DMF solvent molecule. These molecules play a key role in the formation of supramolecular structures due to different interactions. Noncovalent interactions were investigated through the 3D Hirshfeld surface by the dnorm function and the 2D fingerprint plots. The biological activity of the compounds was evaluated in vitro against the human glioma U251 cells. The cytotoxicity results revealed great antitumor activity in complex (1) compared with complex (2) and the free ligand. Molecular docking simulations were used to predict interactions and properties with selected proteins and DNA of the synthesized compounds.

Comparative analysis of the reactivity of anthocyanidins, leucoanthocyanidins, and flavonols using a quantum chemistry approach.

Anthocyanidins, leucoanthocyanidins, and flavonols are natural compounds mainly known due to their reported biological activities, such as antiviral, antifungal, anti-inflammatory activities, and antioxidant activity. In the present study, we performed a comparative structural, conformational, electronic, and nuclear magnetic resonance analysis of the reactivity of the chemical structure of primary anthocyanidins, leucoanthocyanidins, and flavonoids. We focused our analysis on the following molecular questions: (i) differences in cyanidin catechols ( +)-catechin, leucocyanidin, and quercetin; (ii) the loss of hydroxyl presents in the R1 radical of leucoanthocyanidin in the functional groups linked to C4 (ring C); and (iii) the electron affinity of the 3-hydroxyl group (R7) in the flavonoids delphinidin, pelargonidin, cyanidin, quercetin, and kaempferol. We show unprecedented results for bond critical point (BCP) of leucopelargonidin and leucodelphirinidin. The BCP formed between hydroxyl hydrogen (R2) and ketone oxygen (R1) of kaempferol has the same degrees of covalence of quercetin. Kaempferol and quercetin exhibited localized electron densities between hydroxyl hydrogen (R2) and ketone oxygen (R1). Global molecular descriptors showed quercetin and leucocyanidin are the most reactive flavonoids in electrophilic reactions. Complementary, anthocyanidins are the most reactive in nucleophilic reactions, while the smallest gap occurs in delphinidin. Local descriptors indicate that anthocyanidins and flavonols are more prone to electrophilic attacks, while in leucoanthocyanidins, the most susceptible to attack are localized in the ring A. The ring C of anthocyanidins is more aromatic than the same found in flavonols and leucoanthocyanidins. METHODS: For the analysis of the molecular properties, we used the DFT to evaluate the formation of the covalent bonds and intermolecular forces. CAM-B3LYP functional with the def2TZV basis set was used for the geometry optimization. A broad analysis of quantum properties was performed using the assessment of the molecular electrostatic potential surface, electron localization function, Fukui functions, descriptors constructed from frontier orbitals, and nucleus independent chemical shift.

Dithiocarbazate ligands and their Ni(II) complexes with potential biological activity: Structural, antitumor and molecular docking study.

In the search for new metal complexes with antitumor potential, two dithiocarbazate ligands derived from 1,1,1-trifluoro-2,4-pentanedione (H2L1) and (H2L2) and four Ni(II) complexes, [Ni(L1)PPh3] (1), [Ni(L1)Py] (2), [Ni(L2)PPh3] (3), and [Ni(L2)Py] (4), were successfully synthesized and investigated by physical-chemistry and spectroscopic methods. The crystal structure of the H2L1 and the Ni(II) complexes has been elucidated by single-crystal X-ray diffraction. The obtained structure from H2L1 confirms the cyclization reaction and formation of the pyrazoline derivative. The results showed square planar geometry to the metal centers, in which dithiocarbazates coordinated by the ONS donor system and a triphenylphosphine or pyridine molecule complete the coordination sphere. Hirshfeld surface analysis by d norm function was investigated and showed π-π stacking interactions upon the molecular packing of H2L1 and non-classical hydrogen bonds for all compounds. Fingerprint plots showed the main interactions attributed to H⋅H C⋅H, O⋅H, Br⋅H, and F⋅H, with contacts contributing between 1.9% and 38.2%. The mass spectrometry data indicated the presence of molecular ions [M + H]+ and characteristic fragmentations of the compounds, which indicated the same behavior of the compounds in solution and solid state. Molecular docking simulations were studied to evaluate the properties and interactions of the free dithiocarbazates and their Ni(II) complexes with selected proteins and DNA. These results were supported by in vitro cytotoxicity assays against four cancer cell lines, showing that the synthesized metal complexes display promising biological activity.

In silico study of tacrine and acetylcholine binding profile with human acetylcholinesterase: docking and electronic structure.

Alzheimer disease (AD) is a neurodegenerative process, one of the most common and incident dementia in the population over 60 years. AD manifests the presence of complex biochemical processes involved in neuronal degeneration, such as the formation of senile plaques containing amyloid-ß peptides, the development of intracellular neurofibrillary tangles, and the suppression of the acetylcholine neurotransmitter. In this way, we performed a set of theoretical tests of tacrine ligand and acetylcholine neurotransmitter against the human acetylcholinesterase enzyme. Molecular docking was used to understand the most important interactions of these molecules with the enzyme. Computational chemistry calculation was carried out using MP2, DFT, and semi-empirical methods, starting from molecular docking structures. We have also performed studies regarding the non-covalent interactions, electron localization function, molecular electrostatic potential and explicit water molecule influence. For Trp86 residue, we show two main interactions in accordance to the results of the literature for TcAChE. First, intermolecular interactions of the cation-π and sigma-π type were found. Second, close stacking interactions were stablished between THA+ and Trp86 residue on one side and with Tyr337 residue on the other side.

Electronic and structural study of T315I mutated form in DFG-out conformation of BCR-ABL inhibitors.

In this work, the four main drugs for the treatment of chronic myeloid leukemia were analyzed, being imatinib, dasatinib, nilotinib and ponatinib followed by four derivative molecules of nilotinib and ponatinib. For these derivative molecules, the fluorine atoms were replaced by hydrogen and chlorine atoms in order to shade light to the structural effects on this set of inhibitors. Electronic studies were performed at density functional theory level with the B3LYP functional and 6-311+G(d,p) basis set. The frontier molecular orbitals, gap HOMO-LUMO, and NBO were analyzed and compared to docking studies for mutant T315I tyrosine kinase protein structure code 3IK3, in the DFG-out conformation. Structural similarities were pointed out, such as the presence of groups common to all inhibitors and modifications raised up on new generations of imatinib-based inhibitors. One of them is the trifluoromethyl group present in nilotinib and later included in ponatinib, in addition to the 1-methylpiperazin-1-ium group that is present in imatinib and ponatinib. The frontier molecular orbitals of imatinib and ponatinib are contributing to the same amino acid residues, and the ineffectiveness of imatinib against the T315I mutation was discussed.Communicated by Ramaswamy H. Sarma.

Investigation on the interaction behavior of afatinib, dasatinib, and imatinib docked to the BCR-ABL protein.

Chronic myeloid leukemia (CML) is a pathological condition associated with the uncontrolled proliferation of white blood cells and respective loss of function. Imatinib was the first drug that could effectively treat this condition, but its use is hindered by the development of mutations of the BCR-ABL protein, which are the cause of resistance. Therefore, dasatinib and afatinib present similarities that can be explored to discover new molecules capable of overcoming the effects of imatinib. Afatinib exhibited electronic and docking behavior, indicating that a replacement with some minor modifications could design a new potential inhibitor. The amide group in each candidate is clearly of pharmacophoric importance, and it needs to concentrate a negative region. Sulfur group presents a good pharmacophoric profile, which was shown by dasatinib results, adding to the influence of the Met318 residue in the target protein active site configuration. This behavior suggests that the sulfur atom and other fragments that have an affinity for the methionine sidechain may provide a significant positive effect when present in TKI molecules such as afatinib or dasatinib.

Removal of hydrogen sulfide from a binary mixture with methane gas, using IRMOF-1: a theoretical investigation.

The natural gas is mainly composed by methane, ethane, propane, and contaminants. Among these contaminants, the H2S gas has some specific characteristics such as its toxicity and corrosion, besides reducing the combustion power efficiency of natural gas. In this context, metal-organic frameworks appear as promising materials for purification of natural gas by adsorption, due to their large surface area and pore volume. In this work, Grand Canonical Monte Carlo method was used to study the adsorption and separation of CH4:H2S mixture by IRMOF-1. The adsorption isotherms were computed for the pure components, and at different compositions of binary mixture (90:10, 75:25, 50:50, 25:75, and 10:90). Interaction energy obtained with the semiempirical method confirmed that the inorganic unit is the preferred site for CH4 and H2S adsorption. Moreover, in a gas mixture with 50:50 proportion of CH4:H2S mixture, methane adsorbs preferentially in the inorganic unit only at pressures close to 20 bar. Non-covalent interaction (NCI) analyses indicated that the interactions involving H2S are more effective than that for CH4, due to an electrostatic character in the H2S interaction. The simulations also showed that the separation of gases occurs in all compositions and pressures studied, suggesting that IRMOF-1 has a promising potential for this application.

Analysis of Conformational, Structural, Magnetic, and Electronic Properties Related to Antioxidant Activity: Revisiting Flavan, Anthocyanidin, Flavanone, Flavonol, Isoflavone, Flavone, and Flavan-3-ol.

Understanding the antioxidant activity of flavonoids is important to investigate their biological activities as well as to design novel molecules with low toxicity and high activity. Aromaticity is a chemical property found in cyclic structures that plays an important role in their stability and reactivity, and its investigation can help us to understand the antioxidant activity of some heterocyclic compounds. In the present study, we applied the density functional theory (DFT) to investigate the properties of seven flavonoid structures with well-reported antioxidant activity: flavan, anthocyanidin, flavanone, flavonol, isoflavone, flavone, and flavan-3-ol. Conformational, structural, magnetic, and electronic analyses were performed using nuclear magnetic resonance, ionization potentials, electron affinity, bond dissociation energy, proton affinity, frontier molecular orbitals (highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO)), and aromaticity through nucleus-independent chemical shifts to analyze these seven flavonoid structures. We revised the influence of hydroxyl groups on the properties of flavonoids and also investigated the influence of the aromaticity of these seven flavonoids on the antioxidant activity.

Theoretical evaluation of the performance of IRMOFs and M-MOF-74 in the formation of 5-fluorouracil@MOF.

Drug delivery systems are a viable resource to be used in medical treatments that tend to be very aggressive to patients, increasing the bioavailability. In this context, porous structures such as MOFs emerge as promising for this type of application, in which a specific drug is adsorbed onto the structure for further release. MOFs such as IRMOFs and M-MOF-74 are investigated in many applications, including use as a drug carrier. In this work, the Monte Carlo grand canonical simulation was used for obtaining insights on the behaviour of 5-fluorouracil adsorption on IRMOF-1, IRMOF-8, IRMOF-10, Mg-MOF74, Fe-MOF74, Cu-MOF74 and Zn-MOF74. We have evaluated the influence of the adsorption of changing organic and inorganic units, which resulted in different chemical environments. It was seen that the drug interacts more efficiently with M-MOF-74, where the metallic centre plays an important role. For IRMOFs, a larger pore volume increases the amount of adsorbed molecules. This effect is mainly due to the contribution of the efficient interaction between 5-fluorouracil molecules.

Accurate spectroscopic properties by diffusion quantum Monte Carlo calculations.

The capability of Diffusion Quantum Monte Carlo (DMC) to produce high quality potential energy curve (PEC) was evaluated. H2+, HeH+ and LiH PECs were built by all-electron fixed-node DMC calculations. Trial wave functions were obtained from Hartree-Fock (HF) (H2+), MCSCF and CI (HeH+ and LiH) calculations multiplied by Jastrow factor. The quality of these generated PECs was analyzed throughout equilibrium distance, dissociation energy, vibrational energies and rovibrational spectroscopic constants (ωe, ωexe, ωeye, αe, γe and Be). The Discrete Variable Representation (DVR) and the Dunham approaches were used to determine the rovibrational spectroscopic constants. The PECs and the aforementioned properties were also obtained by the following methods: MCSCF/aug-cc-pV5Z (LiH), CCSD(T)/aug-cc-pV5Z (HeH+ and LiH) and HF (H2+ and HeH+) levels. The results of these DMC computations, specially the DMC-DVR procedure, are the most accurate among others DMC calculations available in the literature for these systems. They suggest that DMC can be used to achieve accurate PECs to produce spectroscopic properties with the same level of accuracy of theoretical benchmarks and experimental data of the literature.

Computational analysis of vibrational frequencies and rovibrational spectroscopic constants of hydrogen sulfide dimer using MP2 and CCSD(T).

Previous studies have shown that the weakly bonded H2S dimer demands high level quantum chemical calculations to reproduce experimental values. We investigated the hydrogen bonding of H2S dimer using MP2 and CCSD(T) levels of theory in combination with aug-cc-pV(D,T,Q)Z basis sets. More precisely, the binding energies, potential energy curves, rovibrational spectroscopic constants, decomposition lifetime, and normal vibrational frequencies were calculated. In addition, we introduced the local mode analysis of Konkoli-Cremer to quantify the hydrogen bonding in the H2S dimer as well as providing for the first time the comprehensive decomposition of normal vibrational modes into local modes contributions, and a decomposition lifetime based on rate constant. The local mode force constant of the H2S dimer hydrogen bond is smaller than that of the water dimer, in accordance with the weaker hydrogen bonding in the H2S dimer.

Modified Density Functional Dispersion Correction for Inorganic Layered MFX Compounds (M = Ca, Sr, Ba, Pb and X = Cl, Br, I).

MFX (M = Ca, Ba, Sr, Pb and X = Cl, Br, I) compounds have received considerable attention due to their technological application as X-ray detectors, pressure sensors, and optical data storage materials, when doped with rare-earth ions. MFX compounds belong to the class of layered materials with a tetragonal Matlockite crystal structure, characterized by weakly stacked double-halide layers along the crystallographic c-axis. These layers predominantly determine phase transitions, elastic, and mechanical properties. However, the correct description of the lattice parameter c is a challenge for most standard DFT functionals, which tend to overestimate the lattice parameter c. Because of the weak interactions between the halide layers, dispersion-corrected functionals seem to be a better choice. We investigated 11 different inorganic layered MFX compounds for which experimental data are available, with standard and dispersion-corrected functionals to assess their performance in reproducing the lattice parameter c, structural, and vibrational properties of the MFX compounds. Our results revealed that these functionals do not describe the weak interactions between the halide layers in a balanced way. Therefore, we modified Grimme's popular DFT-D2 dispersion correction scheme in two different ways by (i) replacing the dispersion coefficients and van der Waals radii with those of noble gas atoms or (ii) increasing the van der Waals radii of the MFX atoms up to 40%. Comparison with the available experimental data revealed that the latter approach applied to the PBE (Perdew-Burke-Ernzerhof)-D2 functional with 30% increased van der Waals radii, which we coined PBE-D2* (Srvdw 1.30) is best suited to fine-tune the description of the weak interlayer interactions in MFX compounds, thus significantly improving the description of their structural, vibrational, and mechanical properties. Work is in progress applying this new, computationally inexpensive scheme to other inorganic layered compounds and periodic systems with weakly stacked layers.

DFT analysis, spectroscopic study and biological activity of a newly synthesized benzoylhydrazone binuclear Cu(II) complex.

The current work reports a joint experimental and theoretical study of a novel Cu(II) complex [CuL(µ-CH3COO)]2, based on 2-acetylpyridine-benzoylhydrazone ligand (HL). The two Cu(II) atoms are five-coordinated, consisting of three NNO-donor atoms from the hidrazone ligand connected by acetate bridges. In addition to the structural analysis, the complete characterization includes magnetic susceptibility, elemental analysis, FT-IR and UV-Vis. Two different approaches of Density Functional Theory (DFT) with localized basis set and plane waves were performed. The theoretical calculations were used to optimize the complex geometry of the new structure allowing a better understanding of its spectroscopic properties with insights of most important interactions. Thereunto, we made a comparison between the following functionals: B3LYP, PBE1PBE, B3PW91, ω-B97XD, M06 (hybrids), CAM-B3LYP (long range hybrid), and B97-d (pure), using localized basis set, and for plane waves we used the PW91 functional. Considering the expected antifungal and antibacterial activity of hydrazone derivative ligand, the antimicrobial activity of HL and the complex [CuL(µ-CH3COO)]2 was tested against pathogenic Gram-positive and Gram-negative bacteria and fungi. The synthesized new structure of hydrazone complexed with copper (II) shows antimicrobial activity, and magnetic susceptibility results indicate weak antiferromagnetic coupling between the copper atoms.

Quantitative evaluation of the surface stability and morphological changes of Cu2O particles.

Cu2O low-index surfaces periodic models have been simulated based on density functional theory. The calculated surfaces energies allowed estimating the morphology by means of the Wulff theorem as well as the investigation of possible paths of morphological changes. Therefore, systematic morphology diagrams and change paths according to the energy modulation in relation to the surfaces stabilizations were elaborated. The applicability of this strategy was exemplified by comparing the obtained results with experimental available data from the literature. The morphology diagrams with the quantitative energetic point of view can be used as a guide to support experimental works in order to understand the relation between surface interactions and crystal growth.

Analysis of lowest energy transitions at TD-DFT of pyrene in vacuum and solvent.

Polycyclic aromatic hydrocarbons are present in interstellar medium and trapped in water ice. Among these compounds, pyrene has a controversial theoretical excitation spectrum. We carried out time-dependent density functional theory, including the long-range correction functionals, with the aim to help to understand the inversion of the first two UV bands of lower energies. The pyrene molecule was optimized at TD-DFT functionals with Def2svp basis set. The spectrum of pyrene molecule was calculated using implicit and explicit solvent models. The explicit solvent effect was studied, including a cluster of 51 water molecules. The implicit solvent PCM model was used with water and benzene as solvents. CAM-B3LYP and ωB97XD give correct band positions and the ω parameter was also optimized. NBO and frontier molecular orbitals were used to study the UV band inversion. Graphical abstract Analysis of frontier orbitals involved in the lowest energy transitions at TD-DFT of pyrene.