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A simple method for the cleavage of methoxymethyl (MOM)-ether and ester derivatives using bismuth trichloride (BiCl3) is described. The alkyl, alkenyl, alkynyl, benzyl and anthracene MOM ether derivatives, as well as MOM esters of both aliphatic and aromatic carboxylic acids, were deprotected in good yields. To better understand the molecular roles of BiCl3 and water for MOM cleavage, two possible binding pathways were investigated using the density functional theory (DFT) method. The theoretical results indicate the differential initial binding site preferences of phenolic and alcoholic MOM substrates to the Bi atom and suggest that water plays a key role in facilitating the cleavage of the MOM group.

A new photoredox-catalyzed decarboxylative radical addition approach to functionalized cyclobutanes is described. The reaction involves an unprecedented formal Giese-type addition of C(sp3 )-centered radicals to highly strained bicyclo[1.1.0]butanes. The mild photoredox conditions, which make use of a readily available and bench stable phenyl sulfonyl bicyclo[1.1.0]butane, proved to be amenable to a diverse range of α-amino and α-oxy carboxylic acids, providing a concise route to 1,3-disubstituted cyclobutanes. Furthermore, kinetic studies and DFT calculations unveiled mechanistic details on bicyclo[1.1.0]butane reactivity relative to the corresponding olefin system.

A microhydration study of sulfur mustard (SM) was carried out using M06-2X, B3LYP, B3LYP-D3, and MP2 levels of theory with the 6-311++G(2d,2p) basis set. The changes in energetics, structural parameters and vibrational wavenumbers following the addition of up to three discrete water molecules to SM were analyzed. We observed slight changes in the geometry of SM upon microhydration. The stability of hydrated clusters is due to weak C–H···O–H hydrogen bonds. The free energy change for the formation of the clusters is positive at room temperature and becomes exergonic when the temperature decreases. The infrared stretchings of C–Cl of SM and O–H of water are redshifted upon the addition of water molecules. The findings from this work add to the literature of hydrated SM and can be useful in its detection and subsequent destruction.

The current research used a virtual screening method to study 57 isolated phytochemicals (alkaloids, phytosterols, and flavonoids) against the SARS-CoV-2 main protease (Mpro). The absorption, distribution, metabolism, excretion, and toxicity (ADMET) of the selected compounds were analysed using admetSAR tool while SwissADME and Molinspiration chemoinformatics tools were used to examine the oral bioavailability and drug-likeness properties. Parameters such as physicochemical properties, activity spectra for substances (PASS) prediction, bioactivity, binding mode, and molecular interactions were also analysed. Our results favoured Lupeol (–8.6 kcal/mol), Lupenone (–7.7 kcal/mol), Hesperetin (–7.4 kcal/mol), Apigenin (–7.3 kcal/mol) and Castasterone (–7.3 kcal/mol) as probable inhibitors of SARS-CoV-2. This is because of their good binding affinities, bioactivities, drug-likeness, ADMET properties, PASS properties, oral bioavailability, binding mode and their interactions with the active site of the target receptor compared to Remdesivir and Azithromycin. Therefore, these compounds could be explored towards the development of new therapeutic agents against SARS-CoV-2., Graphical Abstract

Herein, we describe the synthesis, characterization and computational studies of novel 4-substituted phthalonitriles: (1) 4-(4-((benzothiazole)methyleneamino)phenoxy)phthalonitrile, (2) 4-(4-(3-phenylallylideneamino)phenoxy)phthalonitrile and (3) 4-(4-(4-isopropylbenzylideneamino)phenoxy)phthalonitrile. Compound 1 was obtained from the equimolar condensation reaction of 4-(4-aminophenoxy)phthalonitrile with benzothiazole-2-carboxaldehyde while compounds 2 and 3 were isolated from the reactions of 4-aminophenol with either cinnamaldehyde or cuminaldehyde followed by the nucleophilic substitution reactions of their respective Schiff bases and 4-nitrophthalonitrile. The spectral characterization of 1–3 was done using 1H NMR, IR and UV–Vis spectroscopy, while structural confirmation could be affirmed from single TOF mass spectrometry and single crystal X-ray crystallography (for 1 and 2). Molecular geometry optimizations were conducted using the DFT method and the simulated IR frequencies data concurred well with the experimental data and the respective vibrational assignments. Similarly, TD-DFT studies provided an interesting perspective on the nature of the intra-ligand electronic transitions found within the experimental electronic spectra of the respective Schiff base phthalonitriles. Compound 3 showed the highest Human African sleeping sickness trypanocidal potency.

A selective and sensitive solvent extraction and spectrophotometric study of the ruthenium(III)–p-methylphenyl thiourea (PMPT) system is presented. The optimum conditions were determined by...

A new pyrazole based ‘NNO’ tridentate ligand, 5-methylpyrazole-3yl-N-(2-hydroxyphenylamine)methyleneimine, (MPzOAP) was synthesized and characterized by elemental analyses, mass, IR, 1H NMR spectral parameters. The versatile coordination mode of the ligand was established by the synthesis of Co(III), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) metal ion complexes. These complexes were characterized by elemental analyses, conductance and magnetic susceptibility measurements, UV–Vis, IR, 1H NMR spectroscopy, PXRD and thermal analysis. The structures of the ligand and complexes were also investigated using the DFT method. The ligand structure contains the coordination function of the tertiary nitrogen atom of pyrazole ring, the azomethine nitrogen and the phenolic oxygen atom, suitably spaced for chelation with a metal ion and acting as a ‘NNO’ tridentate donor ligand. In vitro antimicrobial activity of the reported ligand and the metal ion complexes were screened and the mode of action was also studied by scanning electron microscopy (SEM) against some pathogenic bacteria.

Herein, a colorimetric sensor (L) based on a naphthyl derivative bearing hydrazone receptors was synthesized via a one-step reaction process, and its recognition properties towards biologically important anions in an acetonitrile-water mixture were investigated by naked-eye observation and UV-Vis and 1H NMR spectroscopy. The molar addition of anions, such as TBAF-, TBAOH-, TBACN- and TBAAcO-, induced a significant red shift in the charge transfer band (Δλ = 73 nm, from 337 nm to 410 nm), in agreement with visible "naked eye" detectable colorimetric activities; in addition, soaked-in-L paper strips were prepared, which could significantly discriminate cyanide (KCN) and hydroxide (NaOH) ions dissolved in tap water via the litmus test method. This study was complemented by density functional theory computations to gain more insight into the interaction between L and anions.

In this study, two new t-butyl substituted salicyladimines, N,N′-bis(5-t-butylsalicylidene) diphenyl disulphide-2,2′-diamine and N,N′-bis(3-t-butylsalicylidene) diphenyl disulphide-2,2′-diamine were synthesized and characterized by spectroscopy and X-ray diffractometry. The effect of the t-butyl group on the keto-enol tautomerism in solution and solid state was investigated. According to X-ray and spectroscopic data (UV–Vis), both salicyladimines were found to be mainly in the enol-tautomeric form. Density functional theory (DFT) method was used to complement this research work. The theoretical results are in good agreement with those obtained experimentally. The anti-oxidant and anti-bacterial activities of the substituted salicyladimines were compared to the parent Schiff base, N,N′-bis(salicylidene) diphenyl disulphide-2,2′-diamine. The t-butyl derivatives show enhanced activity which can be related to the enol form of the Schiff bases and possibly due to the increase in dipole and quadrupole moments in addition to increase in hydrophobicity and decrease solubility in water.

Extensively conjugated donor-π-acceptor-donor (D-π-A-π-D) type fluorescent styryl dyes bearing imidazo[1,2-a]pyridine units have been investigated for their nonlinear optical properties (NLO). Enhanced Stokes shift (2486–2843 cm−1) brought about by replacing methoxy group by diethyl, dimethyl, cyclohexylamino substituents at C-2 and C-7 positions of imidazo[1,2-a]pyridine core in styryl dyes have been understood in elucidating the electronic structures. The position of methoxy group acting as auxiliary donor largely influences the nonlinear optical (NLO) properties of imidazo[1,2-a]pyridine derivatives. Polarizabilities and hyperpolarizabilies were estimated by solvatochromic and DFT method using BHandHLYP and CAM-B3LYP functionals with the 6-311 + G(d,p) basis set. Imidazo[1,2-a]pyridine derivatives showed minimum ten-fold higher NLO parameters compared to reminiscent of charge transfer contribution of donor groups. The dyes have two-photon cross-section values 66–189 GM and comparable with commercial two photon absorbing styryl dyes.

2,4-Dimorpholino-4-yl-6-(4-nitrophenoxy)-[1,3,5]-triazine (DMNT) was synthesized and the molecular structure and vibrational frequencies were studied by density functional theory (DFT) method. The functional used was Becke’s three parameter exchange functional combined with the Lee-Yang-Parr correlation (B3LYP) and the standard basis set was 6-31G(d) for all atoms. The Fourier Transform-Infra Red (FT-IR) and FT-Raman spectra of DMNT were recorded and complete assignments of the observed vibrational frequencies are done. The assignments were confirmed by isotopic labelling. The structural parameters, harmonic vibrational frequencies, IR intensities and Raman intensities of DMNT in the ground-state were also computed. Non-linear optical behaviour of DMNT was analysed by examining the properties like electric dipole moment, polarizability and hyperpolarizability. Molecular properties such as ionization potential, electro-negativity, chemical potential and chemical hardness were obtained from molecular orbital analysis. Hyper conjugative interaction and charge delocalization taking place in DMNT was confirmed by Natural bond analysis studies. UV-Vis spectrum of DMNT was also recorded to understand the electronic properties. Graphical Abstract

The proposed SN2 reactions of a hindered organophosphorus reactant with aliphatic and aromatic nucleophiles [Ye et al., Org. Lett. 19, 5384–5387 (2017)] were studied theoretically in order to explain the observed stereochemistry of the products. Our computations indicate that the reaction with the aliphatic nucleophile occurs through a backside SN2@P pathway while the reaction with the aromatic nucleophile proceeds through a novel SN2@Cl mechanism, followed by a frontside SN2@C mechanism. To the best of our knowledge, this is the first time that a SN2@Cl mechanism is reported. We also found that on reducing the bulkiness of substituents around the phosphorus atom, the backside SN2@P mechanism is preferred. The conclusions made from investigating the steric effect should help experimentalists to decide for the organophosphorus reactant to achieve the products of desired stereochemistry.

The properties of the hydrogen-bonded complexes of chloroform and bromoform with ammonia, water, hydrogen fluoride, phosphine, hydrogen sulphide and hydrogen chloride were studied by means of ab initio calculations. The properties of interest were the molecular structures, the interaction energies, the vibrational spectra and the nature of the orbital interactions involved in the formation of the complexes. Of particular interest was the determination of whether the various interactions exhibited red-shifted or blue-shifted hydrogen bond behaviour. The complexes optimized in three distinct structural models, singly bonded, cyclic and cage. The interaction energies, in the main, varied systematically with changes of the haloform and of the partner molecules. Changes of the CH or YH (Y = N, O, F, P, S and Cl) bond lengths correlated in most cases with the interaction energies, subject to some inconsistencies, with opposite behaviour being shown by the two sets. Similarly, the CH and YH stretching wavenumber shifts also displayed a dependence on the interaction energies, tracking with the bond length changes. Based on the diagnostic utility of these structural and spectroscopic properties, the complexes were found to be almost exclusively red-shifted, for binding through both the CH and YH groups. The orbital interactions responsible for the stability of the complexes were determined to be donation from a Y atom lone pair orbital of the partner molecule to a CH σ antibonding orbital and from a X lone pair orbital (X = Cl and Br) of the haloform to a YH σ antibonding orbital.

A new organic-inorganic hybrid compound (1) based on 4-(dimethylamino)pyridine and manganese(II), MnCl4(C7H11N2)2, has been synthesized and its structure determined by single-crystal X-ray diffraction, infrared and Raman spectroscopy, Hirshfeld and thermal analysis. At room temperature, 1 crystallizes in the centrosymmetric space group P-1. The structure is built up on isolated [MnCl4]2- anions and 4-(dimethylamino)pyridinium (C7H11N2)+ cations connected by a network of N–H···Cl, C–H···Cl, and π-π supramolecular interactions. The 3 D Hirshfeld surface calculations were performed to investigate the quantitatively relative contribution of these interactions in the crystal packing. The thermal behavior of 1 was characterized by TGA/DTA analysis and Density Functional Theory (DFT); there is a good comparison between the experimental and computed results.

Hydantoin exhibits tautomerism and the interconversion among the tautomers was studied using theoretical methods in the gas phase and solvents (water or ethanol). The implicit solvation as well as one explicit solvent molecule with water or ethanol were investigated. The functional used was B3LYP-D3(BJ) and the basis set for all atoms was aug-cc-pVTZ. The results indicate that the electronic energy barriers in the gas phase and implicit solvation are in the range 50-90 kcal mol-1. However, explicit water is found to have a catalytic effect as the electronic energy barriers are lowered to 18-30 kcal mol-1. Explicit ethanol lowers the electronic energy barriers further by about 2 kcal mol-1. This study should be beneficial for the rational design and experiments involving hydantoin and water or ethanol as solvents.

Linear and nonlinear optical (NLO) properties of triphenyl fused rhodamine analogues were estimated by spectroscopic based mathematical calculations and compared with computed values using density functional theory (DFT) calculations. Various Global hybrids (GHs) and range separated hybrids (RSHs) were utilized for reliable estimations of NLO properties. Spectroscopic based mathematical calculations of polarizability (αCT), first order hyperpolarizability (βCT) and second order hyperpolarizability (γ) were performed in varying polarity solvents. Spectroscopic based mathematical calculted αCT, βCT and γ values are found to have much closer agreement with the DFT computed values obtained by using RSHs. Comparative analysis of αCT, βCT and γ values suggested that these values increases with the increase of triphenylamine substitutions. Moreover, αCT, βCT and γ values increase with decreasing HOMO-LUMO band gap for all the dyes. N-[9-(isobenzofuran-1(3H)-one)-6-(dipnenylamino)-xanthene]-N-diphenyl amine having bis-triphenylamine substituent showed the largest NLO response among all analogues dyes.

The properties of a number of hydrogen-bonded complexes of methyl fluoride and difluoromethane with a range of hydrides of the first two rows of the periodic table have been computed using ab initi...

A novel Pd–ZnO-expanded graphite (EG) photoelectrode was constructed from a Pd–ZnO-EG nanocomposite synthesised by a hydrothermal method and characterised using various techniques such as X-ray diffractometry (XRD), Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy, nitrogen adsorption–desorption analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Cyclic voltammetry and photocurrent response measurements were also carried out on the electrode. The Pd–ZnO-EG electrode was employed in the photoelectrocatalytic removal of 4-nitrophenol as a target water pollutant at a neutral pH and with a current density of 7 mA cm−2. Optical studies revealed that the Pd–ZnO-EG absorbed strongly in the visible light region. The Pd–ZnO-EG electrode showed improved photoelectrocatalytic activity in relation to ZnO-EG and EG electrodes for the removal of the 4-nitrophenol. The photocurrent responses showed that the Pd–ZnO-EG nanocomposite electrode could be employed as a good photoelectrode for photoelectrocatalytic processes and environmental remediation such as treatment of industrial waste waters. Density functional theory method was used to model the oxidative degradation of 4-nitrophenol by the hydroxyl radical which generates hydroquinone, benzoquinone, 4-nitrocatechol, 4-nitroresorcinol and the opening of the 4-nitrophenol ring. Furthermore, the hydroxyl radical is regenerated and can further oxidise the ring structure and initiate a new degradation process.

The Schiff base 3-{( E )-[(2-hydroxyphenyl)imino]methyl}benzene-1,2-diol was synthesized by the condensation of 2,3-dihydroxybenzaldehyde and 2-aminophenol in water at room temperature. The crystal was grown using two solvents (dry methanol and 60% methanol). The compound was characterized using elemental microanalysis, IR, NMR, UV spectroscopies and single-crystal X-ray diffraction crystallography. The X-ray structure reveals that the Schiff base crystallizes as a methanol solvate in dry methanol with triclinic crystal system, space group P-1 and Z = 2 in the unit cell and as a non-methanol solvate in 60% methanol with triclinic crystal system, space group P-1 and Z = 4 in the unit cell. The compound showed absorption bands at 272, 389, 473 and 602 nm in DMSO. These bands were assigned as π → π ∗ , n → π ∗ and n-σ ∗ transitions. The 473 and 602 nm bands in DMSO reveal that the compound exists in tautomeric forms. The presence of N-H, C-O and C N stretching vibrations in the IR spectrum indicates that the compound is zwitterionic in the solid state. This study was supplemented using density functional theory method.

The static first and second hyperpolarizability and their related properties were calculated for triphenylamine-based “push-pull” dyes using the B3LYP, CAM-B3LYP and BHHLYP functionals in conjunction with the 6-311+G(d,p) basis set. The electronic coupling for the electron transfer reaction of the dyes were calculated with the generalized Mulliken-Hush method. The results obtained were correlated with the polarizability parameter α C T , first hyperpolarizability parameter β CT , and the solvatochromic descriptor of 〈 γ 〉 SD obtained by the solvatochromic method. The dyes studied show a high total first order hyperpolarizability (70–238 times) and second order hyperpolarizability (412–778 times) compared to urea. Among the three functionals, the CAM-B3LYP and BHHLYP functionals show hyperpolarizability values closer to experimental values. Experimental absorption and emission wavelengths measured for all the synthesized dyes are in good agreement with those predicted using the time-dependent density functional theory. The theoretical examination on non-linear optical properties was performed on the key parameters of polarizability and hyperpolarizability. A remarkable increase in non-linear optical response is observed on insertion of benzothiazole unit compared to benzimidazole unit.

Liquid organic hydrogen carrier (LOHC) systems have gained serious traction of late due to their potential application in the envisaged hydrogen economy. This is mainly because LOHCs can undergo reversible dehydrogenation in the presence of a catalyst. Using density functional theory calculations with van der Waals corrections, the role of chalcogens (S, Se and Te) as surface additives, in boosting the catalytic activity of Pt (1 1 1) surface, was investigated for the dehydrogenation of the LOHC system, octahydroindole to indole. The calculated adsorption energies indicate that octahydroindole (the hydrogen rich form (LOHC+)) and indole (the hydrogen lean form (LOHC−)) stably adsorbs on the Pt (1 1 1) surface(s) in the presence of chalcogen surface additives. The S and Se atoms were found to be better catalytic activity boosters in lowering the calculated reaction energy for dehydrogenating octahydroindole to indole than the Te atom. For all the considered chalcogen surface additive species, the calculated reaction energies indicate that the dehydrogenation of octahydroindole to indole can proceed either with or without indoline as a reaction intermediate.

Anticancer activities of ruthenium Schiff base metal complexes have been closely correlated to their steric factors and physicochemical properties. The core objectives of our research study were to synthesize and characterize new ruthenium Schiff base compounds derived from cinnamaldehyde, cuminaldehyde or 4-aminoantipyrine. In addition, the stereo-electronic features of the aforementioned metal compounds and two selected previously reported ruthenium Schiff base compounds were related to their antioxidant and biomolecular interaction capabilities. Therefore, we demonstrated the formation of novel mononuclear ruthenium(III) compounds with chelating N-donor ligands: fac-[RuCl3(PPh3)(ap)] (1) (ap = 4-aminoantipyrine), trans-P-[Ru(PPh3)2(cinap)2](PF6) (2) (cinap = 1,5-dimethyl-2-phenyl-4-{[3-phenylprop-2-en-1-ylidene]amino}-1,2-dihydro-3H-pyrazol-3-one) and cis-Cl, trans-P-[RuCl2(PPh3)2(cumbh)] (3) (cumbh = N'-(4-isopropylbenzylidene)benzohydrazide). Structural confirmations were conducted primarily by spectroscopic techniques while the single crystal X-ray analysis revealed the distorted octahedrons of the respective metal compounds. Voltammetry experiments of 1–3 illustrated one-electron quasi-reversible redox waves which are attributed to metal oxidation state interconversions. CT-DNA binding affinities and modes of the novel metal complexes 1–3 as well as the formerly published ruthenium Schiff base compounds, trans-P, cis-Cl-[Ru(pch)Cl2(PPh3)2] (4) (pch = 4-((pyridine-2yl-imino)methylene)-chromone) and cis-[RuCl2(bpap)(PPh3)] (5) (bpap = 2,6-bis-((antipyrine-imino)methylene)pyridine) were experimentally and computationally investigated. The paramagnetism of 1–4 and the proton-donor abilities of all the metal compounds promoted significantly higher NO and DPPH radical scavenging activities than the natural antioxidant, vitamin C. Experimental electronic BSA titrations revealed that the metal compounds are ideal binders which preferentially bind to site IIA. The X-ray and spectroscopic data were supported by the computed data which was simulated using the density functional theory method.

Density functional theory and time-dependent density functional theory computations were used to understand the electronic and photophysical parameters of NIR β-thiophene-fused BF2-azadipyrromethene dyes. The computed data are in good agreement with those obtained experimentally and they provide insights into the origin of red shifted optical spectra compared to the parent aza-BODIPY, low Stokes shift, non-linear optical responses and quantitative description of the singlet–triplet energy gap. The resultant decrease in the HOMO − LUMO energy gap is responsible for the red shift. The possible use as non-linear optical materials is supported by large enhancement in the non-linear optical properties. On the basis of vertical triplet energies, their possible potential therapeutic use as a photosensitizer in photodynamic therapy is proposed. The singlet–triplet energetic gaps suggest that the β-thiophene-fused BF2-azadipyrromethene dyes can act as a sensitizer to produce an efficient generation of singlet oxygen. Their optimal use as an efficient singlet fission materials has been proposed on the basis of excitation energies in the ground, lowest singlet and triplet excited states.

Formation of pyrazolo[5,1-c]-1,2,4-triazoles by means of Cu(I)-catalysed [3+2] cycloaddition (32CA) reactions of C,N-cyclic azomethine imines with phenylacetylene, experimentally reported by Katritzky et al. (JOC 2012, 77, 5813), was studied using the density functional theory (DFT) method. Comparison with the uncatalysed 32CA reaction indicates that the Cu(I) catalyst provides new reaction pathways with lower electronic energy barriers in dichloromethane as solvent. The mechanism proposed by Katritzky for the Cu(I) catalysed reaction is compared with that proposed by Sharpless et al. (JACS 127, 2005, 210). The major difference between these two mechanisms lies in the coordination of the Cu(I) acetylide to the C,N-cyclic azomethine imine moiety. DFT calculations suggest that the mechanism proposed by Katritzky is kinetically favoured over that of CuAAC-type. ELF topological analysis of the electron density of the stationary points involved in the most favourable reaction pathway associated with the Cu(I)-catalysed 32CA reactions explains the bond formation. This study also reveals the requirement of C,N-cyclic azomethine imines rather than acyclic azomethine imines to favour the mechanism proposed by Katritzky.

Display Omitted Tautomers of 2,4-ditellurouracil and 5-fluorotellurouracil were studied using DFT method.The keto-enol tautomerism was studied in the gas phase.The diketo form is the most stable tautomer.Substitution of hydrogen by fluorine causes a decrease in the interconversion barriers.The ADME parameters of the most stable diketo and dienol tautomers were predicted. 2,4-Ditellurouracil exhibits keto-enol tautomerism via different pathways resulting in seven tautomers. These pathways were studied in the gas phase using density functional theory method. The functionals used were BLYP, B3LYP and BHLYP and the basis sets were 6311++G(d,p) for all atoms except that LanL2DZ ECP was used for tellurium atom only. The results indicate that the diketo form is more stable as observed for uracil and its sulfur and selenium analogues. The effect of introducing fluorine at position 5 was also investigated and the energy difference between the diketo and dienol forms is reduced. 2,4-Ditellurouracil and its 5-fluoro analogue are expected to exist exclusively as the diketo form due to the high interconversion energy barrier. We extended the investigation to predict ADME parameters of the most stable diketo and dienol tautomers in view of understanding their biological properties. This research enlightens keto-enol tautomerism of 2,4-ditellurouracil and its 5-fluoro derivative with additional insights to biological functions.

Density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations of two excited state intramolecular proton transfer (ESIPT) molecules [2,5-bis(2-benzothiazolyl)hydroquinone and 2,5-bis(benzo[d]thiazol-2-yl)-4-methoxyphenol] were performed to study their structural and photo-physical behavior upon excitation. The most stable structure was established by optimizing all possible rotamers. The vertical excitation and emission wavelengths obtained by using TD-DFT show very good correlation with the experimental values. A correlation has been established based on the absorption values to determine the contribution of stable rotamers.

The electronic structures and spectroscopic properties of triphenylamine-based monostyryl and bis(styryl) dyes were studied using quantum chemical methods. The ground-state geometries of these dyes were optimized using the density functional theory (DFT) method. The lowest singlet excited state was optimized using time-dependent density functional theory (TD-DFT). The absorption was also calculated using the ground-state geometries. All the calculations were carried out in the gas phase and in solvent. The results indicate that the absorption maxima calculated using the TD-DFT are in good agreement with those obtained experimentally. These dyes possess a large second-order non-linear property and this is mainly due to the strong donor-π-acceptor conjugation which is attributed to the excited state intramolecular charge transfer (ICT). There is a relationship between the hardness and first hyperpolarizability and second hyperpolarizability of mono- and bis(styryl) dyes. The efficiency of the intersystem crossing process can be improved by reducing the energy gap between the singlet and triplet excited states.

Metal-cyclen complexes have a number of important applications. However, the coordination chemistry between metal ions and cyclen-based macrocycles is much less well studied compared to their metal ion-crown ether analogues. This work, which makes a contribution to address this imbalance by studying complex ions of the type [M(Me4cyclen)(L)]+, was initiated by results of an experimental study which prepared some Group 1 metal cyclen complexes, namely [Li(Me4cyclen)(H2O)][BArF] and [Na(Me4cyclen)(THF)][BArF] and obtained their X-ray crystal structures [J. M. Dyke, W. Levason, M. E. Light, D. Pugh, G. Reid, H. Bhakhoa, P. Ramasami, and L. Rhyman, Dalton Trans., 2015, 44, 13853]. The lowest [M(Me4cyclen)(L)]+ minimum energy structures (M = Li, Na, K, and L = H2O, THF, DEE, MeOH, DCM) are studied using density functional theory (DFT) calculations. The geometry of each [M(Me4cyclen)(L)]+ structure and, in particular, the conformation of L are found to be mainly governed by steric hindrance which decreases as the size of the ionic radius increases from Li+ → Na+ → K+. Good agreement of computed geometrical parameters of [Li(Me4cyclen)(H2O)]+ and [Na(Me4cyclen)(THF)]+ with the corresponding geometrical parameters derived from the crystal structures [Li(Me4cyclen)(H2O)]+[BArF]− and [Na(Me4cyclen)(THF)]+[BArF]− is obtained. Bonding analysis indicates that the stability of the [M(Me4cyclen)(L)]+ structures originates mainly from ionic interaction between the Me4cyclen/L ligands and the M+ centres. The experimental observation that [M(Me4cyclen)(L)]+[BArF]− complexes could be prepared in crystalline form for M+ = Li+ and Na+, but that experiments aimed at synthesising the corresponding K+, Rb+, and Cs+ complexes failed resulting in formation of [Me4cyclenH][BArF] is investigated using DFT and explicitly correlated calculations, and explained by considering production of [Me4cyclenH]+ by a hydrolysis reaction, involving traces of water, which competes with [M(Me4cyclen)(L)]+ formation. [Me4cyclenH]+ formation dominates for M+ = K+, Rb+, and Cs+ whereas formation of [M(Me4cyclen)(L)]+ is energetically favoured for M+ = Li+ and Na+. The results indicate that the number and type of ligands, play a key role in stabilising the [M(Me4cyclen)]+ complexes and it is hoped that this work will encourage experimentalists to prepare and characterise other [M(Me4cyclen)(L)]+ complexes.

The local and global reactivity descriptors of substituted dinitroaniline analogues were investigated using M06-2X/6-31 + G(d,p) method. It was observed that NH2 (m = 3.53 eV; p = 3.70 eV) substituent conveyed the highest nucleophilic character on the benzene ring system than the other groups under study. For the substrates 4-substituted-1-chloro-2,6-dinitrobenzenes, the condensed to atom electrophilicity ( $$ {\omega}_k^{+} $$) increases in the order COOCH3 > NO2 > F > SO3H > CN > Cl > Br. The para substituted groups with the halogens follow the order of increasing electronegativity, F > Cl > Br. However, the nucleophilicity of the halo substituents of the products increases in the order, F > Br > Cl. Molecular docking simulations using the homology model with the crystallographic structure of zinc-induced bovine tubulin heterodimer (1JFF) as one of the templates reveal that the interactions between the tubulins of Plasmodium falciparum and dinitroaniline analogues are due to H-bonding. In general, the binding interaction is with the following residues: Met137, ARG64, Lys60, Glu183, Val4, His28, Cys171, Tyr224, Asn206, 228, Ile235, and Leu238. The pKas of the residue decrease as the ring activating power of the substituents increases from strongly activating to weakly activating groups. There is no evidence of intra or intermolecular H-bonding between Arg64 and Cys171. Electronegativity (χ) gives a better generic description of the dinitroanilines than any other parameters considered. Short-range hydrophobic interaction contributes to reduced binding affinities of the ligands.

Novichoks are the suspected nerve agents in the March 2018 Skripal poisoning. In this context, the novichok agent A234 (chemical structure proposed by Mirzayanov) was studied using computational methods to shed light on its molecular, electronic, spectroscopic, thermodynamic and toxicity parameters as well as on potential thermal and hydrolysis degradation pathways. The poisoning action and antidote of A234 were also investigated. Some of these parameters were compared to three common G- and V-series nerve agents, namely GB, VR and VX. The research findings should be useful towards the detection, development of antidotes and destruction of A234.

A number of properties of the homodimers of the three families of molecules MH3X, where M is Si, Ge, and Sn and X is F, Cl, Br, and I are computed. The results are compared with those of a similar study of the homodimers of the methyl halides containing the same four halogen atoms, and some notable differences are observed among related sets of monomer species. The interaction energies, the primary intermolecular geometrical parameters, the changes in the intramolecular bond lengths, and the vibrational data (wavenumber shifts and dimer/monomer infrared intensity ratios) of some of the modes most closely associated with the site of interaction show, for the most part, regular variations as the central atom and the halogen atom are systematically varied. The results are interpreted in terms of the changes in the bonding properties of the monomer molecules as they undergo dimerization.

Dege, Necmi/0000-0003-0660-4721; Rhyman, Lydia/0000-0002-8624-8431; Ayogu, Jude/0000-0002-1301-3172 WOS: 000464988000010 Two novel Schiff bases, 3-{(E)-[(2-hydroxy-5-methylphenyl)iminolmethyllbenzene-1,2-diol (SBPC) and 3-{(E)-[(3-hydroxyphenyl)iminolmethyllbenzene-1,2-diol (SB3A), were synthesized by the condensation of 2,3-dihydroxybenzaldehyde with 2-amino-4-methylphenol and 3-aminophenol, respectively. The Schiff bases were characterized using elemental microanalysis, NMR, IR, and UV-visible spectroscopy, and single crystal X-ray diffraction analysis (XRD). Density functional theory method was used for computing molecular parameters and some of these were compared with experimental data. The X-ray diffraction data reveal that SBPC crystallized in the orthorhombic space group P2(1)2(1)2(1) with Z=4, while SB3A crystallized in the monoclinic space group C2/c with Z = 8. The C-O and C-N interatomic distances in both compounds lie between single and double bond, which confirm their existence in zwitterionic form. Docking studies identified SB3A and SBPC as potential inhibitors of four essential antibacterial targets. (C) 2019 Elsevier B.V. All rights reserved. Tertiary Education Trust Fund (TETFund), Nigeria [TETFUND/DESS/UNI/NSUKKA/2017/RP/VOL.I] LNO is grateful to Tertiary Education Trust Fund (TETFund), Nigeria for sponsoring this research through the research project no. TETFUND/DESS/UNI/NSUKKA/2017/RP/VOL.I. AI appreciates Dr Ntie-Kang F. of Chemical and Bioactive Information Centre, University of Buea, Cameroun for computational support.

WOS: 000399466200011, Conformers of N-methacryloyl-(L)-glutamic acid (MAGA, C9H13NO5) in the gas phase, benzene or methanol environment were searched by the density functional theory (DFT) and time-dependent DFT. Selected conformational isomers based on potential energy surface analysis were studied by considering the structural and electronic properties. B3LYP functional, and HF and MP2 levels were used with the 6-31+G(d,p), 6-311+G(3df,p) and aug-cc-pVDZ basis sets. We explored the effect of medium on the conformational preferences, UV spectra and frontier molecular orbitals of the conformers. The outcomes of this research will be useful for future studies including moieties analogous to MAGA.

The Schiff base, 4-[3-(4-methoxy-phenyl)-allylideneamino]-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-one (TPMC/AAP) was synthesized by the condensation of 4-aminoantipyrine (4-amino-1,5-dimethyl-2-phenylpyrazole-3-one) and trans-para-methoxycinnamaldehyde (trans-3,4-methoxyphenyl-2-propenal) in dry methanol at 75 °C. The compound was characterized using elemental microanalysis, IR, NMR, UV spectroscopies and single-crystal X-ray crystallography. The X-ray structure determination shows that the Schiff base, (TPMC/AAP) is orthorhombic with the Pbca space group. The anti-microbial screening of the compound was carried out with Escherichia coli, Bacillus subtillis, Staphylococcus aureus, Pseudemonas aeruginosa, Candida albicans and Aspergillus niger using agar well diffusion method. The Schiff base possesses significant antimicrobial activity. The minimum inhibitory concentration (MIC) of the compound was also determined and the activity was compared with that of conventional drugs ciprofloxacin and ketoconazole. The compound (TPMC/AAP) showed varying activity against the cultured bacteria and fungi used. To complement the experimental data, density functional theory (DFT) was used to have deeper understanding into the molecular parameters and infrared spectra of the compound.

A density functional theory study was performed on the [3+2] cycloaddition (32CA) reaction of 1H-phosphorinium-3-olate and 1-methylphosphorinium-3-olate with methyl acrylate. The thermodynamic and kinetic parameters were analysed by considering the regio- and stereoisomeric pathways in gas phase and solvents. The geometries indicate that the transition states are slightly more advanced and asynchronous in ethanol. Electron localisation function topological analysis of the bonding changes along the most favourable reaction pathway associated with the 32CA reaction of 1H-phosphorinium-3-olate with methyl acrylate indicates that the reaction takes place through a two-stage one-step mechanism. Non-covalent interactions analysis of TS6x-H reveals the existence of weak hydrogen bonding explaining the regioselectivity found in this low-polar zw-type 32CA reaction. On comparing these theoretical findings with the nitrogen analogues of the 32CA reactions, it is found that the regioselectivity is affected and the pathways are kinetically and thermodynamically enhanced. Therefore, a priori, the phosphorus cycloadducts could be synthesised.

The photo-physical behaviour of bis-2,5-(2-benzoxazolyl) hydroquinone and 2,5-bis (benzo[d]oxazol-2-yl)-4-methoxyphenol was studied using the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT). All the possible rotamers were optimized to obtain global minimum optimized structure. The theoretical absorption and emission values of rotamers estimated by using TD-DFT [TD-B3LYP/6-31G(d)] are in good agreement with experimental absorption and emission wavelengths. Based on the absorption values, the contribution of respective rotamer is determined theoretically.

Can cyclen (1,4,7,10-tetraazacyclododecane) bind alkali metal azides? This question is addressed by studying the geometric and electronic structures of the alkali metal azide-cyclen [M(cyclen)N3] complexes using density functional theory (DFT). The effects of adding a second cyclen ring to form the sandwich alkali metal azide-cyclen [M(cyclen)2N3] complexes are also investigated. N3(-) is found to bind to a M(+) (cyclen) template to give both end-on and side-on structures. In the end-on structures, the terminal nitrogen atom of the azide group (N1) bonds to the metal as well as to a hydrogen atom of the cyclen ring through a hydrogen bond in an end-on configuration to the cyclen ring. In the side-on structures, the N3 unit is bonded (in a side-on configuration to the cyclen ring) to the metal through the terminal nitrogen atom of the azide group (N1), and through the other terminal nitrogen atom (N3) of the azide group by a hydrogen bond to a hydrogen atom of the cyclen ring. For all the alkali metals, the N3-side-on structure is lowest in energy. Addition of a second cyclen unit to [M(cyclen)N3] to form the sandwich compounds [M(cyclen)2N3] causes the bond strength between the metal and the N3 unit to decrease. It is hoped that this computational study will be a precursor to the synthesis and experimental study of these new macrocyclic compounds; structural parameters and infrared spectra were computed, which will assist future experimental work.

A series of novel 2-aryl-6-bromo-4-chloro-8-iodoquinazolines were prepared and subjected to sequential two-step (Sonogashira and subsequent one-pot bis-Suzuki) and one-pot three-step Sonogashira cross-coupling reactions to afford unsymmetrical polycarbo-substituted quinazolines. Selectivity in the cross-coupling for these multihalogenated quinazolines was found to depend on both the intrinsic reactivity of the Csp2–halogen bond, which relates to the bond dissociation energy or bond strength and the electronic position of the halogen atom on the electron deficient scaffold (trend: Csp2–I>C(4)–Cl>Csp2–Br). The electronic absorption and emission properties of the prepared polycarbo-substituted quinazolines were evaluated in solution by means of UV–vis and emission spectroscopy in conjunction with density functional theory (DFT) method.

The corrosion inhibition of steel in 1 M HCl in the presence of four synthesized Schiff bases: 3-[(3-Hydroxy-4-methoxy-benzylidene)-amino]-benzoic acid (HMAMB), 3-[(2-Hydroxy-naphthalen-1-ylmethylene)-amino]-benzoic acid (HNCAMB), 3-[3-(4-Methoxy-phenyl)-allylideneamino]-benzoic acid (TMCAMB) and 4-[3-(4-Methoxy-phenyl)-allylideneamino]-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-one (TMCATP) was studied by potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), surface analyses and computational studies. The inhibition efficiency of HMAMB, HNCAMB, TMCAMB and TMCATP obtained at the optimum inhibitor concentration (1.0 mM) from polarization measurement were 87.3%, 89.1%, 96.5% and 97.0% respectively. The values of inhibition efficiencies obtained via the electrochemical analyses for the four inhibitors were comparable. The data from polarization measurement implies the compounds inhibited as mixed-type inhibiting molecules in the tested media but mostly minimized the cathodic reaction. The data obtained experimentally fitted well into Langmuir adsorption isotherm with R2 values and slopes close to unity. The values of Gibbs free energy of adsorption ranged from −33.96 to −37.62 kJ mol−1, suggesting that the molecules adsorbed spontaneously to the surface of the metal by interchange of physical and chemical adsorption mechanisms. The energy dispersive X-ray (EDX) spectra results displayed a decrease in the percentage of oxygen on the surface of the mild steel and scanning electron microscopy (SEM) micrograph also indicated a minimal damage of the metal surface in solutions containing the Schiff bases when likened to the solution without the inhibitors. The results of DFT calculations showed that the molecules had high tendencies in interacting with the steel surface. The values of energy gap (eV) obtained were 4.09, 3.74, 3.69 and 3.58 while the estimated adsorption energy obtained from molecular dynamic simulation studies were − 654.2, −760.8, −741.3 and − 951.9 kJ mol−1 for HMAMB, HNCAMB, TMCAMB and TMCATP, respectively.

Effects of alkylamino and bromo substituents on imidazo[1,2-a]pyridines containing donor-π-acceptor type groups were comprehensively investigated for their linear and nonlinear optical properties by solvatochromic and DFT (CAM-B3LYP and BHandHLYP) methods. The difference between the ground and excited dipole moments as well as their ratios obtained by solvatochromic analysis indicate that the excited state is more polar than the ground state for both the bromo and diethyl amino derivative. More than twofold enhancement in the excited state dipole moments was observed as revealed by the difference and ratio of dipole moment upon the introduction of alkylamino donor group and these suggest large intramolecular charge transfer in the dyes. Stabilization energy above 20 kJ/mol was observed for large number of electron donor–acceptor interactions in Natural Bonding Orbital (NBO) analysis. Bond length alternation (BLA) and Bond order alternation (BOA) values tend to zero suggesting a high degree of polarization in the dyes. Enhancement in mean polarizability (α0), first hyperpolarizability (β0) and second static hyperpolarizabilities ( $\bar \gamma$) were observed by the introduction of alkylamino and bromo group in place of chloro in spite of the fact that Hammett constant of chloro and bromo are the same. The dyes have fundamental and intrinsic properties within the Hamiltonian limits. The two-photon absorption cross section value (≈100 GM) is comparable with LDS-698, a commercial TPA dye. This investigation is important for understanding the electronic structure of imidazo[1,2-a]pyridine with active functional groups and extending the potential for optical applications.

The Paternὸ-Buchi reaction of benzene with benzaldehyde and furan with furfural were studied theoretically. The mechanism was investigated using Density Functional Theory (DFT). It was found that the final product of the benzene reaction is oxetane 3, while in the case of furan the oxetane 6 is unstable and goes through oxetane ring opening. The target of this article was to study the reaction mechanism and calculate the thermodynamic parameters of the reactions. The oxetane 3 formed was found to be stable with reaction energy of -120 kcal/mol. However, the oxetane 6 was found to be less stable with reaction energy 21 kcal/mol which tends to produce more stable product 7 through the oxetane ring opening. In addition, the molecular orbitals were calculated and analyzed for all the intermediates, oxetanes and final products.

Houk and co-workers clarified several aspects of the mechanism of the Fischer indole synthesis, showing that the SCS-MP2/6-31G(d)//MP2/6-31G(d) method is suitable for studying the mechanism in water. Fluorine substitution can affect the kinetic and thermodynamic parameters of a reaction, hence the work reported here considers the impact of fluorine substituents located on the ketone component of the starting phenylhydrazone in a Fischer indole synthesis. When one of the nitrogens is protonated, the presence of one fluorine decreases the activation energy of the key [3,3]-sigmatropic rearrangement and increases the thermodynamic stability of the resulting non-aromatic imine; the presence of two fluorines also reduces the activation energy versus the unsubstituted situation, but by a smaller amount. For a non-protonated sequence, although the presence of one fluorine again decreases the activation energy of the key [3,3]-sigmatropic rearrangement, inclusion of two fluorines actually increases the activation energy slightly.

The rhenium(V) complexes [ReCl3(t-BuNC)(L)(PPh3)] (1–3) were isolated by the reaction of trans-[ReIIICl3(t-BuNC)(PPh3)2] (t-BuNC = tert-butyl isocyanide) with the ligands H2L (H2L = aniline (1), o-phenylenediamine (2), anthranilic acid (3)). In all these complexes the dianionic ligands L are coordinated monodentately as the imide. However, unexpectedly, with 2-aminophenol the complexes [ReVCl2(t-BuNC)(L)(PPh3)2](ReO4) (4) and the novel [ReIIICl2(t-BuNC)(ibq)(PPh3)2] (5) (ibq− = 2-iminobenzoquinonate, the two-electron oxidized form of HL−) were identified as the products. These complexes were characterized by single crystal X-ray crystallography, 1H NMR spectrometry, IR and electronic spectroscopy, and cyclic voltammetry. To complement the experimental data, density functional theory (DFT) and time-dependent DFT methods were used to have a deeper understanding into the molecular parameters and infrared and electronic spectra of these complexes.

WOS: 000352668100017, PubMed ID: 25754388, 4-Mercaptophenylboronic acid (4-mpba, C6H7BO2S) was investigated experimentally by vibrational spectroscopy. The molecular structure and spectroscopic parameters were studied by computational methods. The molecular dimer was investigated for intermolecular hydrogen bonding. Potential energy distribution analysis of normal modes was performed to identify characteristic frequencies. The present work provides a simple physical picture of the OH stretch vibrational spectra of 4-mpba and analogues of the compound studied. When the different computational methods are compared, there is a strong evidence of the better performance of the BLYP functional than the popular B3LYP functional to describe hydrogen bonding in the dimer. The findings of this research work should be useful to experimentalists in their quests for functionalised 4-mpba derivatives

The photophysical and electrochemical properties of eleven polycyclic benzimidazole fused organic pigments (four based on phthalic anhydride, four based on naphthalic anhydride and three based naphthalene tetra carboxylic acid dianhydride) were investigated using density functional theory and time dependent density functional theory methods (B3LYP/6-31G(d) and M06/6-31G(d)). The predicted geometries are comparable using both functionals. The electrochemical properties are in good agreement with the experimental results. However, the experimental absorption-emission properties are closer to the values computed using the M06/6-31G(d) method. Both the methods perform equally well in explaining the intramolecular charge transfer characteristics. This work can help to understand the modern age functional materials at molecular level and to design new molecules.

A series of gallium telluride, GamTen (m = 1, 2 and n = 1–4), clusters has been examined using density functional theory (DFT), second-order Moller–Plesset perturbation theory (MP2) and the coupled cluster approach with single and double substitutions and a perturbative treatment of triple excitations [CCSD(T)]. The study unravels the question of whether neutral GaTe2 is isostructural with BO2 as proposed earlier by a previous experiment (Trans. Faraday Soc. 1968, 64, 2998). The results of gallium tellurides are compared with the oxygen, sulfur and selenium analogues. In most cases, the substitution of O/S/Se by Te atoms in the gallium clusters does not drastically affect the structural characteristics. The adiabatic electron affinities (AEAs) of GamTen (m = 1, 2 and n = 1–4) clusters range from 1.33 to 3.46 eV at the CCSD(T)//B3LYP level. The AEAs of gallium tellurides are found to be independent on the electrophilicity of the clusters. Further, the adiabatic ionization potentials (AIPs) of the clusters are in good agreement with available experimental data. This research is expected to provide insight into the structural characteristics and electronic properties of gallium chalcogenides.