HOMO-LUMO Orbitals Research Articles

Backing of 2-(diethylamino)-N-(2, 6-dimethylphenyl)-acetamide with molecular, electronic and docking studies

In this study, the anaesthetic compound 2-(diethylamino)-N-(2, 6-dimethylphenyl)-acetamide (DEAL) was optimized with the B3LYP-6-311+G (d, p) density functional theory method. Hyper conjugative interactions revealed the bioactivity of the molecule by natural bond orbital analysis. The current–potential curves were noted at well-defined scan rates by cyclic voltammetry. The solvation free energy was calculated by applying the solvation model on density. Molecular docking simulations were carried out to understand the pharmacokinetic behaviour of the drug. Besides, total energy levels of HOMO-LUMO orbitals, Mulliken atomic charges, natural population analysis and polarizability properties of the molecule were calculated. We found that the secondary amide increases the stability of this molecule. The π→π∗ interactions increase the biological activity of the compound, leading to a very high stabilization.

Combined Experimental and Computational Investigation of 2-(2-Hydroxyphenylimino) Phenolic Derivatives: Synthesis, Molecular Structure and NLO Studies

A series of substituted 2-(2-hydroxyphenylimino) phenolic (salen) derivatives (1-4) have been synthesized and their structures of obtained compound were characterized by analytical, FT-IR, UV-Vis and 13C{1H}-NMR experimentally. The geometry structure optimization, frequencies (IR), NMR, electronic character, frontier molecular orbital (HOMO-LUMO) and first static hyperpolarizability (βtot) studies of reported compounds were calculated using DFT with B3LYP/6-311G(d,p) level of theory. The calculated HOMO and LUMO energies showed that charge transfer occurs within the molecule and from the MEP, the molecular stability and bond strength have been explained. In addition to that influence of energy gap (?Egap) between the HOMO-LUMO orbitals on the first static hyperpolarizability (βtot), we calculated the ?Egap for all the salen compounds. These results reveals that the smaller HOMO-LUMO ?Egap is, larger the βtot is.

Effect of Constituent Units, Type of Interflavan Bond, and Conformation on the Antioxidant Properties of Procyanidin Dimers: A Computational Outlook

Procyanidin (PC) dimers are powerful antioxidants, abundant in plant tissues, and also bioavailable. However, the role of the molecular structure of PCs on their antioxidant properties is still a controversial and not fully understood issue that needs to be addressed in a more specific way. The objective of this study was to analyze the effect of the constituent units, type of interflavan bond, and conformation on the antioxidant properties of PC dimers including PB3, PB4, PB5, PB6, PB7, and PB8, using the density functional theory (DFT) computational method. The analysis was performed in function of parameters that allow determining the ability of the molecules to transfer or to capture electrons, among which the chemical potential, bond dissociation enthalpy (BDE), gap energy, Fukui indices, and charge distribution of HOMO-LUMO orbitals. The factors that showed the most notable effects on the antioxidant properties of the PC dimers were the type of interflavan bond and the conformation. The antioxidant ability of the dimers PB3 and PB4 containing the interflavan bond C4–C8, in their Compact conformation, was very similar to each other but greater than those of dimers PB5, PB6, PB7, and PB8 containing the C4–C6 interflavan bond. PB8 showed the lowest antioxidant ability.

Unsymmetrical pyrazole-based new semiconductor oligomer: synthesis and optical properties

Poly(p-phenylene-1-(2,5-dimethylphenyl)-5-phenyl-1H-pyrazole-3,4-dicarboxy amide) (poly(PDPPD)) was synthesized from reactions of p-phenylene-diamine and 1-(2,5-dimethylphenyl)-5-phenyl-1H-pyrazole-3,4-dicarbonyl dichloride (monomer) by heating under solvent. This newly synthesized poly(PDPPD) was characterized by 1H, 13C-NMR, FT-IR, gel permeation chromatography (GPC). In addition, we investigated optical properties of the poly(PDPPD) containing the substituted pyrazole ring at different molarities. The average transmittance (T avg) values of the poly(PDPPD) in the visible (V) region were higher than the T avg values in the near-ultraviolet (NU) region. The T avg values of the poly(PDPPD) in the NU and visible (V) region decreased with increasing molarity. The absorption band edge (Absbe) value of the poly(PDPPD) decreased with increasing molarity. It was observed that the optical band gap (E g) of the poly(PDPPD) value decreased more with increasing molarity. The refractive index of the poly(PDPPD) decreased with increasing wavelength and decreasing molarity. The structure of the poly(PDPPD) in the lowest energy was optimized by DFT calculation and its HOMO–LUMO orbitals were plotted.

Bis (thiourea) strontium chloride as promising NLO material: An experimental and theoretical study

Single crystals of pure bis (thiourea) strontium chloride (BTSC) have been grown from aqueous solution by slow evaporation method. The results from single crystal X-ray diffraction studies indicated the orthorhombic structure and Pna21 space group of the crystals. 77% transmittance measured by the Ultra violet transmittance studies and a band gap of 4.7 eV indicated the high optical transparency. From Kurtz and Perry powder method, the second Harmonic Generation (SHG) efficiency of the BTSC has been found to be 1.54 times as that of KDP and the phase matching nature of the crystal has been confirmed. Hyper polarizability studies showed that the synthesized BTSC crystal has higher polarisability and dipole values and hence can be used as potential NLO material. The frontier orbital HOMO-LUMO gap has been determined to understand the chemical reactivity and kinetic stability of the title crystal. The values of various global chemical molecular reactivity descriptors like chemical hardness (η) and electrophilicity index (ω) have been calculated. Natural bond orbital (NBO) analysis has been carried out to study the charge distribution and to understand various donor–acceptor interactions taking place in the BTSC crystal.

Design of Assembled Systems Based on Conjugated Polyphenylene Derivatives and Carbon Nanohorns.

Promising materials have been designed and fully characterised by an effective interaction between versatile platforms such as carbon nanohorns (CNHs) and conjugated molecules based on thiophene derivatives. Easy and non-aggressive methods have been described for the synthesis and purification of the final systems. Oligothiophenephenylvinylene (OTP) systems with different geometries and electron density are coupled to the CNHs. A wide range of characterization techniques have been used to confirm the effective interaction between the donor (OTP) and the acceptor (CNH) systems. These hybrid materials show potential for integration into solar cell devices. Importantly, surface-enhanced Raman spectroscopy (SERS) effects are observed without the presence of any metal surface in the system. Theoretical calculations have been performed to study the optimised geometries of the noncovalent interaction between the surface and the organic molecule. The calculations allow information on the monoelectronic energies of HOMO-LUMO orbitals and band gap of different donor systems to be extracted.

Crystal structure, spectroscopic investigations and quantum chemical calculation studies of (3aR,6S,7aR)-7a-bromo-6-methyl-2-[(4-methylphenyl)sulfonyl]-1,2,3,6,7,7a-hexahydro-3a,6-epoxyisoindole: A combined experimental and theoretical studies

The crystal structure and spectroscopic properties of (3aR,6S,7aR)-7a-bromo-6-methyl-2-[(4-methylphenyl)sulfonyl]-1,2,3,6,7,7a-hexahydro-3a,6-epoxyisoindole were determined by X-ray diffraction, IR and 13CNMR and 1H NMR spectroscopy techniques. We investigate molecular and crystal structure of the new sulfonamide, which was derived from an environmental friendly cyclization reaction in water. This work allow to the development of a stereo-selective tandem allylamine isomerization/Diels Alder cyclo-addition sequence led to rapid assembly of complex nitrogen containing heterocycles. The molecular geometry from X-ray determination, vibrational frequencies and NMR shifts values of the title compound in the ground state have been calculated by using CAM-B3LYP and B3LYP methods with 6-311++G(d,p) basis sets. The calculated results show that the optimized geometry can well regenerate the crystal structure and theoretical vibrational frequencies and chemical shift data are in good agreement with experimental data. Besides, it is examined nonlinear optic properties, molecular electrostatic potential map and HOMO-LUMO orbitals of the molecule.

A Theoretical Study on the Structure-Radical Scavenging Activity of Some Hydroxyphenols

Antioxidants are made for the struggle and reconstruction of the damaged cells, because of their ability in destroying the free radicals. On account of their importance, a theoretical procedure was applied for the study of the molecular structure and radical scavenging activity of six hydroxyphenols which have been introduced as antioxidant compounds. All geometry structures were optimized by M06-2X, MPWB1K with 6-311++G (d, p) basis in the gas phase and solvent using the CPCM model. Three probable mechanisms for the antioxidant activities have been presented and analyzed. According to bond dissociation enthalpy (BDE) and ionization potential (IP) values, hydrogen atom transfer (HAT) mechanism is a more reasonable path for antioxidant activity. The contribution of the HOMO-LUMO orbitals and spin density distribution have been calculated for evaluating of the previous data. Finally, based on the comparison of the experimental and the calculated data, BDE mechanism showed the best agreement.

Photochromic properties of the molecule Azure A chloride in polyvinyl alcohol matrix

In the present work, isomerization, photophysical properties and heat conductivity of the substance Azure A chloride (AZAC): 3-amino-7-(dimethlamino)phenothiazin-5-ium chloride under the action of UV radiation in the presence of polyvinyl alcohol (PVA) matrix was studied using the Hartree-Fock (HF) and Density Functional Theory (DFT) methods. The electronic absorption spectra of AZAC in dimethylformamide (DMF) solution and in aqueous medium before and after UV radiation were calculated. The nature of absorption bands of AZAC and its tautomeric prototropic form with the transfer of the electron (AZAC1) in the visible and near UV spectral regions was interpreted. The solvent effect on the absorption spectrum of the AZAC has established. The comparison of measured FTIR, UV–Visible data allowed assignments of major special features of title molecules. The frontier molecular orbital HOMO-LUMO have been also presented that shows the charge transfer interactions taking place within these molecules. The excitation energies for both molecules AZAC and AZAC1 have also been calculated. The experimental as well as theoretical investigations of azure molecule have a close agreement and it gives other important clues about the properties of the system. Anisotropy of thermal conductivity in PVA-films containing AZAC and AZAC1 were also measured.

Implicit and explicit solvent effects on the selectivity of the cycloaddition reaction of cyclopentadiene and methyl acrylate; a theoretical study

The product selectivity of the Diels–Alder reaction between cyclopentadiene and methyl acrylate has been studied through a solvent effect analysis by implicit and explicit solvent models. Two paths for this reaction have been proposed and thermodynamic and kinetic parameters for each path were calculated by the B3LYP functional with 6-311++G(d,p) basis set at 298.15 K. In the explicit solvent model, hydrogen bonds were investigated by the QM/MM method. According to the results, the proportion of the exo product in the gas phase is more than for the endo one, which is in contrast to the solvent phase. HOMO–LUMO analyses in the gas phase and different solvents have been done and solvent effects on the energies of the HOMO–LUMO orbitals were investigated. According to the results, the band gap of the TSs was increased in the presence of the solvents. Finally, natural population analysis has been performed to calculate the electronic charges of some atoms that are involved in the centre of the reaction. The data obtained showed that different solvents, including polar and nonpolar solvents, have different effects on the electronic charges of the atoms. Topological analysis of the structures during the reaction by the quantum theory of atoms in molecules (QTAIM) method in the gas phase and different solvents confirmed a cyclic structure for the transition state.

Combination multinitrogen with good oxygen balance: molecule and synthesis design of polynitro-substituted tetrazolotriazine-based energetic compounds.

We investigated 5,8-dinitro-5,6,7,8-tetrahydrotetrazolo[1,5-b][1,2,4]triazine (short for DNTzTr (1)) using various ab initio quantum chemistry methods. We proposed an additional three novel polynitro-substituted tetrazolotriazine-based compounds with exceptional performance, including 5,8-dinitro-5,6-dioxotetrazolo[1,5-b][1,2,4]triazine, DNOTzTr (2), 4,5,9,10-tetranitro[1,2,4,5]tetrazolo[3,4-b][1,2,4,5]tetrazolo[3',4':5,6]triazino[2,3-e]triazine, TNTzTr (3), and 4,5,6,10,11,12-hexanitro-bis[1,2,4,5]tetrazolo[3',4':5,6]triazino[2,3-b:2',3'-e]triazine, HNBTzTr (4). The optimized structure, electronic density, natural bond orbital (NBO) charges and HOMO-LUMO orbitals, electrostatic potential on surface of molecule, IR- and NMR-predicted spectra, as well as thermochemical parameters were calculated with the B3LYP/6-311+G(2d) level of theory. Critical parameters such as density, enthalpy of formation (EOF), and detonation performance have also been predicted. Characters with positive EOF (1386.00 and 1625.31 kJ/mol), high density (over 2.00 g/cm(3)), outstanding detonation properties (D = 9.82 km/s, P = 45.45 GPa; D = 9.94 km/s, P = 47.30 GPa), the perfect oxygen balance set to zero, and acceptable impact sensitivity led novel compounds 3 and 4 to be very promising energetic materials. This work provides the theoretical molecule design and a reasonable synthesis path for further experimental synthesis and testing.

The Pseudo‐Michael Reaction of 2‐Hydrazinylidene‐1‐Arylimidazolidines with Diethyl Ethoxymethylenemalonate

The pseudo‐Michael reaction of 2‐hydrazinylidene‐1‐arylimidazolidines with diethyl ethoxymethylenemalonate (DEEM) was investigated. The reaction yields the chain adduct, namely diethyl{[2‐(1‐arylimidazolidin‐2‐ylidene)hydrazinyl]methylidene}propanedioates. This is contrary to the pseudo‐Michael reaction of DEEM with 1‐aryl‐4,5‐dihydro‐1H‐imidazol‐2‐amines that does not allow isolation of chain derivatives and leads to cyclic imidazo[1,2‐a]pyrimidine derivatives while even at thermodynamic control. At first cyclization of diethyl{[2‐(1‐arylimidazolidin‐2‐ylidene)hydrazinyl]methylidene}propanedioates leads to ethyl 1‐aryl‐5(1H,8H)oxo‐2,3‐dihydro‐imidazo[2,1‐c][1,2,4]triazepine‐6‐carboxylates. 1,5‐Sigmatropic shift, following the cyclization, caused isomerization of 5(1H,8H)oxo‐2,3‐dihydro‐imidazo[2,1‐c][1,2,4]triazepine‐6‐carboxylates to ethyl 1‐aryl‐5(1H)hydroxy‐2,3‐dihydroimidazo[2,1‐c][1,2,4]triazepine‐6‐carboxylates. Presence of both isomers in the reaction product was detected in the NMR spectra. The structure of all the compounds was confirmed with spectroscopic studies (1H NMR and MS). The structure of diethyl{[2‐(1‐phenylimidazolidin‐2‐ylidene)hydrazinyl]methylidene}propanedioate was also confirmed by X‐ray crystallography. In the addition reaction, thermodynamics and HOMO–LUMO orbitals of the reactants were studied by using quantum chemical calculations.

Fukui Function Analysis and Optical, Electronic, and Vibrational Properties of Tetrahydrofuran and Its Derivatives: A Complete Quantum Chemical Study

The spectroscopic, optical, and electronic properties of tetrahydrofuran and its derivatives were investigated by FTIR techniques. We have done a comparative study of tetrahydrofuran and its derivatives with B3LYP with 6-311 G (d, p) as the basis set. Here we have done a relative study of their structures, vibrational assignments, and thermal, electronic, and optical properties of ttetrahydrofuran and its derivatives. We have plotted frontier orbital HOMO-LUMO surfaces and molecular electrostatic potential surfaces to explain the reactive nature of tetrahydrofuran and its derivatives.

Experimental IR and Raman Spectroscopy and DFT Methods Based Material Characterization and Data Analysis of 2- Nitrophenol

Vibrational characteristics of 2- nitrophenol have been investigated using experimental IR and Raman data and computational data using DFT method employing the 6-311++G** basis set available on Gaussian-09 software for the most stableconformer C-1. Complete vibrational assignments of the experimental IR and Raman bands have been proposed in light of the results obtained from the DFT computations and the PEDs computed using GAR2PED software. The optimized geometrical parameters suggest that the overall symmetry of the most stablemolecule is Cs. The molecule is expected to have three conformers. In the present article all the characterizations and the analyses of the lowest energy conformer of 2-NP have been studied. The charge transfer occurring in the molecule has been shown by HOMO–LUMO energy orbitals the energy gap of HOMO LUMO orbitals have been found 4.03eV. The mappings of electron density iso-surface with the electrostatic potential (ESP), has been carried out to get the information about the size, shape, charge density distribution and site of chemical reactivity of 2-NP. Current density and magnetic shielding of C-1 have been investigated. Some essential thermo molecular characteristics, namely, enthalpy, Gibb’s free energy, thermal energy, entropy, heat capacity, internal energy and the partition functions of the molecule have also been analyzed.

Insight into the acidic behavior of oxazolidin-2-one, its thione and selone analogs through computational techniques

Deprotonation thermochemistry of Oxazolidin-2-one (OXA), Oxazolidine-2-thione (OXA-S), and Oxazolidine-2-selone (OXA-Se) has been studied in order to find the most acidic site and relative acidities of these heterocyclics at various sites. The deprotonation enthalpies at MP2/6-311++G**//MP2/6-31+G* and B3LYP/6-31+G* levels, while the free energies for deprotonation process and pKa values at B3LYP/6-31+G* level both in gas and aqueous phase (using PCM continuum model) of the anions of the three heterocyclics have been computed at 298 K. Calculated aqueous phase pKa values of OXA vary by ~6–7 units from the experimental aqueous phase pKa values of OXA and its derivatives. The deprotonation at the nitrogen is favored in OXA over the carbon atoms in contrast to the OXA-S and OXA-Se where in the deprotonation at the carbon attached to the nitrogen is most preferred. Deprotonation at this carbon induces an important C–O bond rupture in OXA-S and OXA-Se promoting an energetically favored ring-opening process. The finding offers a rare case when C–H acidity is able to dominate over the N–H acidity. In order to explain the relative stabilities, relative acidities and deprotonation enthalpies various characteristics of these molecules as well as their anions such as molecular electrostatic potential surface (MEP), frontier molecular orbital (FMO) features, chemical hardness, softness have been governed. The three dimensional MEP maps and HOMO–LUMO orbitals encompassing these molecules yield a reliable relative stability and reactivity (in terms of acidity) map displaying the most probable regions for deprotonation. The differential distribution of the electrostatic potential over the neutral and anionic species of OXA, OXA-S, and OXA-Se molecules is authentically reflected by HOMO–LUMO orbitals and NBO charge distribution analysis. The lone pair occupancies, second order delocalization energies for orbital interactions and the distribution of atomic charges over the entire molecular framework as obtained from natural bond orbital (NBO) analysis are found to faithfully replicate the predictions from the MEP maps and HOMO–LUMO band gaps in respect of explaining the relative stabilities and acidities in most of the cases. Good linear correlations have been obtained between HOMO–LUMO gap and pKa values in the aqueous phase for OXA and OXA-S molecules.

Investigating the adsorption of H 2O on ZnO nanoclusters by first principle calculations

The interaction of a single H 2O molecule on selected ZnO nanoclusters is investigated by carrying out calculations based on the density-functional theory at the hybrid-GGA (B97-2) level. These clusters have ring, drum, tube and bubble shapes and their physical properties like the binding energy and the band gap energy depend strongly on the shape and size of the cluster. Depending on the stability of the cluster, H 2O show both chemisorption and dissociation on the surfaces of the clusters. We analyzed the effect of H 2O adsorption on the properties of clusters of size n = 12 via the density of state, HOMO–LUMO orbitals and the changes in the IR frequencies.

A quantum chemical study on the reaction of 1-aryl-1,2-dihydrophosphinine oxides with dimethyl acetylenedicarboxylate

A β-oxophosphorane/ylide ( 2a) and an oxaphosphete ( 3a), the product and the possible intermediate of an inverse Wittig type reaction of 1-(2,4,6-triisopropylphenyl-)1,2-dihydrophosphinine oxide with dimethyl acetylenedicarboxylate were studied by quantum chemical calculations. The reaction of the title reagents following either a traditional [4 + 2] cycloaddition protocol to afford phosphabicyclo[2.2.2]octadiene 5 or a novel route yielding eventually β-oxophosphorane/ylide 2 was evaluated by energy calculations. The mechanism for the formation of intermediate 3a 2 was refined by HF/6-31G* transition state calculations. Analysis of the HOMO–LUMO orbitals of the reagents justified the reactivity experienced.

Photochemical dimerisation of 2-vinylfuran and 2-vinylthiophene derivatives bearing electron-withdrawing groups

The photochemical dimerisation of 1,3-diheteroaryl-2-propen-1-one derivatives gave a mixture of dimers in agreement with the hypothesis that the reaction is under frontier orbitals control and preferential formation of only the more stable isomers. On the contrary, the reaction of 2-heteroaryl-nitroethylene derivatives were not observed to give cyclobutane dimers but only coupling products with the loss of one nitro group. This behaviour is in agreement with the nature of the HOMO–LUMO orbitals which do not allow the superimposition of the reagents. This result allows to formulate the hypothesis that the photochemical dimerisation of 1-heteroaryl-2-EWG-ethylenes must occur as a concerted reaction. Finally, 2-heteroaryl-1,1-dicyanoethylene derivatives gave the corresponding dimers. Also in this case, we obtained only the head-to-head dimer and the more stable one.

An excitonic mechanism of detonation initiation in explosives

A novel mechanism for detonation initiation in solid explosives is proposed. This is based on electronic excitations induced by an impact wave propagating through the crystal. We illustrate the model by using the RDX (C3H6N6O6) crystal as an example. In our model, a key role belongs to lattice defects, in particular edge dislocations, which promote dramatic changes in the electronic structure, primarily a reduction of the optical gap due to the splitting off of local electronic states from both valence and conduction bands. The pressure inside the impact wavefront further reduces the band gap, making it close to zero. This promotes highest occupied molecular orbital–lowest unoccupied molecular orbital HOMO–LUMO transitions resulting in N–NO2 bond breaking and the creation of favorable conditions for the initiation of a chain reaction. Experimental facts supporting the suggested mechanism are discussed.

A density functional theory study on the reactivity of monosubstituted cycloimmonium ylides

The aim of this study, based on the Density Functional Theory Approach, semi-empirical calculations and confronted with experimental results, developed within the scope of the reactivity of the monosubstituted cycloimmonium ylides, is to elucidate some fundamental and principal features of these compounds. We demonstrate that the resonance interaction phenomenon is less favoured in the case of monosubstituted cycloimmonium ylides than in the case of planar disubstituted cycloimmonium ylides. Besides, using the frontier molecular orbital theory, we could estimate the reactivity of some virtual reaction centers by their absolute values of atomic orbital coefficients corresponding to the frontier HOMO–LUMO orbitals. The monosubstituted cycloimmonium ylides undergo 3+2 dipolar cycloaddition reactions more rapidly than the disubstituted cycloimmonium ylides. The absolute values of atomic orbital coefficients for the ylidic carbon atoms and the α aromatic carbon atoms, corresponding to the frontier HOMO–LUMO orbitals in the case of monosubstituted cycloimmonium ylides, are greater than those of planar disubstituted cycloimmonium ylides. Also, the rotational barriers, for the ylidic bond, in the monosubstituted cycloimmonium ylides are comparable to those of planar disubstituted cycloimmonium ylides. In this way we show a significant difference between monosubstituted and disubstituted cycloimmonium ylides. All these results are in good agreement with those of experiments where the atoms involved in the 3+2 dipolar cycloaddition reactions are those predicted by the frontier molecular orbitals theory: the ylidic carbon atom and the α carbon atoms in the heterocyclic ring.