The mechanistic details of N-heterocyclic olefin-catalyzed formation of cyclic carbonate from CO2 and propargylic alcohols were investigated by DFT calculations. Six mechanisms, four for the formation of five-membered cyclic carbonate (M-A, M-B, M-B’ and M-C), and two for six-membered cyclic carbonate (M-D and M-E), were fully investigated. The energy profiles in dichloromethane showed that M-B is the predominant reaction with the lowest barrier of 31.99 kcal mol?1, while M-C and M-D may be kinetically competitive to M-B. The very high activation energy of 45.37 kcal mol-1, 57.07 kcal mol-1 and 59.61 kcal mol?1 for M-A, M-B’ and M-E, respectively, suggest that they are of lesser importance in the overall mechanism.
Graphical abstract Formations of five-membered ring product and six-membered ring product are kinetically competitive, but five-membered ring product is thermodynamically more preferable.
Recent outbreaks of highly pathogenic influenza strains have highlighted the need to develop new anti-influenza drugs. Here, we report an in silico study of carvone derivatives to analyze their binding modes with neuraminidase (NA) active sites. Two proposed carvone analogues, CV(A) and CV(B), with 36 designed ligands were predicted to inhibit NA (PDB ID: 3TI6) using molecular docking. The design is based on structural resemblance with the commercial inhibitor, oseltamivir (OTV), ligand polarity, and amino acid residues in the NA active sites. Docking simulations revealed that ligand A18 has the lowest energy binding (?Gbind) value of ?8.30 kcal mol-1, comparable to OTV with ?Gbind of ?8.72 kcal mol-1. A18 formed seven hydrogen bonds (H-bonds) at residues Arg292, Arg371, Asp151, Trp178, Glu227, and Tyr406, while eight H-bonds were formed by OTV with amino acids Arg118, Arg292, Arg371, Glu119, Asp151, and Arg152. Molecular dynamics (MD) simulation was conducted to compare the stability between ligand A18 and OTV with NA. Our simulation study showed that the A18-NA complex is as stable as the OTV-NA complex during the MD simulation of 50 ns through the analysis of RMSD, RMSF, total energy, hydrogen bonding, and MM/PBSA free energy calculations. 相似文献
Based on a prototype sensitizer W2, we designed triarylamine-based p-type sensitizers W2-1 to W2-7 that contain modified π-spacers (π'), a π-spacer and two anchors. For W2-1 to W2-4, instead of 2,1,3-benzothiadiazole in W2, thieno[3,4-b]-1,4-dioxin, thiophene, thieno[3,4-c][1,2,5]thiadizole, thiazolo[5,4-d]thiazole are π' and thiophene as π-spacer. For W2-5 to W2-8, π' and π are same, with 2,1,3-benzothiadiazole, thieno[3,4-b]-1,4-dioxin, thieno[3,4-c][1,2,5]thiadiazo, thiazolo[5,4-d]thiazole, respectively, as the π'-spacers. Structure optimization, electronic level and absorption characters were calculated with density functional theory (DFT) and time-dependent DFT (TDDFT) at the CAM-B3LYP/6-311G (d,p). The solvent effect was involved using a polarized continuum model in chloroform. The results showed that the highest occupied molecular orbital and the lowest unoccupied molecular orbital guarantee sufficient hole injection (lower than –0.2 eV), and dye regeneration (lower than –0.2 eV). W2-4 has higher light-harvesting efficiency (LHE) (0.994) and larger overlap with the visible light from 400 nm to 600 nm. Finally, the results suggest that the driving force of hole injection, dye regeneration and charge recombination (ΔGinj, ΔGreg and ΔGCR) of W2-4 are the best, with more negative ΔGinj (–4.33), ΔGreg (–1.74) and more positive ΔGCR (1.92). Replacing 2,1,3-benzothiadiazole with thiazolo[5,4-d]thiazole as π'-spacers is a effective way to improve the performance of the dyes. An introduction of thiazolo[5,4-d]thiazole group can improve the absorption ability and hinder charge recombination.
The formation of silaspiropentane from addition of singlet silacyclopropylidene 1 and silacyclopropylidenoid 8 to ethylene has been investigated separately at the B3LYP, X3LYP, WB97XD, and M05–2X theories using the 6–31+G(d,p) basis set. The silacycloproylidenoid addition follows a stepwise route. In contrast, a concerted mechanism occurs for silacyclopropylidene addition. Moreover, the intramolecular rearrangements of silaspiropentane 9 to methylenesilacyclobutane 11 and 2-silaallene?+?ethylene 12 have been studied extensively. The required energy barrier for the isomerization of 9 to 10 was determined to be 44.0 kcal mol?1 at the B3LYP/6–31+G(d,p) level. After formation of 10, the rearrangement to methylenesilacyclobutane 12 is highly exergonic by ?15.9 kcal mol?1, which makes this reaction promising. However, the conversion of 9 to 11 is calculated to be quite endergonic, by 26.5 kcal mol?1. 相似文献
The conformational propensities of the Aib residue on the example of two model peptides Ac-Aib-NHMe (1) and Ac-Aib-NMe2 (2), were studied by B3LYP and M06-2X functionals, in the gas phase and in the polar solvents. To verify the reliability of selected functionals, we also performed MP2 calculations for the tested molecules in vacuum. Polarizable continuum models (PCM and SMD) were used to estimate the solvent effect. Ramachandran maps were calculated to find all energy minima. Noncovalent intramolecular interactions due to hydrogen-bonds and dipole attractions between carbonyl groups are responsible for the relative stabilities of the conformers. In order to verify the theoretical results, the available conformations of similar X-ray structures from the Cambridge Crystallographic Data Center (CCDC) were analyzed. The results of the calculations show that both derivatives with the Aib residue in the gas phase prefer structures stabilized by intramolecular N–H?O hydrogen bonds, i.e., C5 and C7 conformations, while polar solvent promotes helical conformation with φ, ψ values equal to +/?60°, +/?40°. In addition, in the case of molecule 2, the helical conformation is the only one available in the polar environment. This result is fully consistent with the X-ray data.
Use and application of Schiff bases are extended to many different fields of technology. (ISE)M(CO)5 complex [M?=?Cr (1), Mo (2), W (3), and where ISE is 3[4-ethyl(phenly)imino][indoline-2-one]; and (ISB)M(CO)5 [M?=?Cr (4), Mo (5), W (6)], where ISB is 3[4-butly(phenly)imino][indoline-2-one] were investigated by computational methods. Computations were carried out using density functional theory (DFT) with B3LYP and CAM-B3LYP functionals, in conjunction with LanL2DZ basis set for metals and cc-PVTZ basis set for other atoms. Time-dependent density functional theory (TDDFT) was used at the same level to obtain the electronic transitions. Molecular orbital energies, UV-Vis spectra, and total electron densities of investigated molecules were shown in the gas phase and in THF. Metal complexes showed higher absorption coefficients compared to ISE and ISB in the visible region. Additionally, they displayed absorption peaks at longer wavelengths and full MLCT character in solution, and W complexes required less energy compared to the complexes of other investigated metal ions. Among the investigated systems, (ISE)W(CO)5 and (ISB)W(CO)5 complexes with lowest HOMO-LUMO gaps are found to be the best candidates for photosensitive material production.
In this study, the N,N,O metal chelator 2-pyridinecarboxaldehydeisonicotinoyl hydrazone (HPCIH, 1) and its derivatives 2-acetylpyridine-(HAPIH 2), 2-pyridineformamide-(HPAmIH, 3) and pyrazineformamide-(HPzAmIH, 4) were employed in the synthesis of four copper(II) complexes, [Cu(HPCIH)Cl2]·0.4H2O (5), [Cu(HAPIH)Cl2]·1.25H2O (6), [Cu(HPAmIH)Cl2]·H2O (7) and [Cu(HPzAmIH)Cl2]·1.25H2O (8). The compounds were assayed for their action toward Mycobacterium tuberculosis H37Rv ATCC 27294 strain and the human tumor cell lines OVCAR-8 (ovarian cancer), SF-295 (glioblastoma multiforme) and HCT-116 (colon adenocarcinoma). All copper(II) complexes were more effective in reducing growth of HCT-116 and SF-295 cells than the respective free hydrazones at 5 µg/mL, whereas only complex 7 was more cytotoxic toward OVCAR-8 lines than its ligand HPAmIH. 6 proved to be cytotoxic at submicromolar doses, whose IC50 values (0.39–0.86 µM) are similar to those ones found for doxorubicin (0.23–0.43 µM). Complexes 5 and 6 displayed high activity against M. tuberculosis (MIC = 0.85 and 1.58 µM, respectively), as compared with isoniazid (MIC = 2.27 µM), which suggests the compounds are attractive candidates as antitubercular drugs. 相似文献
A theoretical study was undertaken regarding the regioselective Lewis acid-promoted intramolecular cyclization of novel enaminones 1-3 leading to the corresponding benzofurans 4-5 and indoles 6. The density functional theory (DFT) and hard and soft acids and bases (HSAB) principle provided data to describe the electronic effects of the substituents in the reactivity of the benzene ring and the enaminone moiety. The condensed and local Fukui functions for nucleophilic and electrophilic attacks of the reactants accounted for the experimentally observed preference, in regard to precursors 1-3, of the cyclization between the C6′ carbon (rather than the C2′ carbon) of the benzene ring and the C3 center of the enaminone moiety.
Graphical Abstract A theoretical study (DFT/HSAB) describes the electronic effects of the substituents in the reactivity of the benzene ring and the enaminone moiety of enaminones I to explain their Lewis acid-promoted regioselective intramolecular cyclization, which exclusively leads to the corresponding benzofurans and indoles II
To understand the chemical behavior of uranyl complexes in water, a bis-uranyl [(phen)(UO2)(μ2–F)(F)]2 (A; phen?=?phenanthroline, μ2?=?doubly bridged) and its hydrated form A?·?(H2O)n (n?=?2, 4 and 6) were examined using scalar relativistic density functional theory. The addition of water caused the phen ligands to deviate slightly from the U2(μ2–F)2 plane, and red-shifts the U–F-terminal and U?=?O stretching vibrations. Four types of hydrogen bonds are present in the optimized hydrated A?·?(H2O)n complexes; their energies were calculated to fall within the range 4.37–6.77 kcal mol-1, comparable to the typical values of 5.0 kcal mol-1 reported for hydrogen bonds. An aqueous environment simulated by explicit and/or implicit models lowers and re-arranges the orbitals of the bis-uranyl complex.
Figure
A bis(uranyl) complex [(phen)(UO2)(μ2–F)(F)]2 (A) and its solvated form A?·?(H2O)n were examined using scalar relativistic density functional theory. Hydrogen bonds cause the phen ligand to slightly deviate from the equatorial plane of the uranyl ion, resulting in a pronounced red-shift of the U–F-terminal and U?=?O asymmetric stretching vibrations. The calculated energies fall within 4.4?–6.8 kcal/mol. Explicit and/or implicit aqueous solvation re-arranges the molecular orbitals of the complex 相似文献
The compounds terrein (1), butyrolactone I (2), and butyrolactone V (3) were isolated from the ethyl acetate extract (EtOAc) of the endophytic fungus Aspergillus terreus—F7 obtained from Hyptis suaveolens (L.) Poit. The extract and the compounds presented schistosomicidal activity against Schistosoma mansoni; at 100 µg/mL for EtOAc extract, 1297.3 µM for compound 1, 235.6 µM for compound 2, and 454.1 µM for compound 3, they killed 100% of the parasites after 72 h of treatment. Compounds 1, 2, and 3 exerted moderate leishmanicidal activity against Leishmania amazonensis (IC50 ranged from 23.7 to 78.6 µM). At 235.6 and 227.0 µM, compounds 2 and 3, respectively, scavenged 95.92 and 95.12% of the DPPH radical (2,2-diphenyl-1-picryl-hydrazyl), respectively. Regarding the cytotoxicity against the breast tumor cell lines MDA-MB-231 and MCF-7, compound 2 gave IC50 of 34.4 and 17.4 µM, respectively, while compound 3 afforded IC50 of 22.2 and 31.9 µM, respectively. At 117.6 µM, compound 2 inhibited the growth of and killed the pathogen Escherichia coli (ATCC 25922). Compounds 1, 2, and 3 displayed low toxicity against the normal line of human lung fibroblasts (GM07492A cells), with IC50 of 15.3?×?103, 3.4?×?103, and 5.8?×?103 µM, respectively. This is the first report on (i) the in vitro schistosomicidal and leishmanicidal activities of the EtOAc extract of A. terreus—F7 and compounds 1, 2, and 3; and (ii) the antitumor activity of compounds 2 and 3 against MDA-MB-231 and MCF-7 cells. 相似文献
Four new platinum(II) complexes: PtIIL1·H2O (C1, H2L1 = C20H16N2O2), PtIIL2Cl2 (C2, L2 = C22H16N2O2), PtIIL3Cl2·H2O (C3, L3 = C20H16N2), PtIIL4Cl2·0.4H2O (C4, L4 = C18H14N4) have been synthesized and characterized by using various physico-chemical techniques. The binding interaction of the four platinum(II) complexes C1–C4 with calf thymus (CT)-DNA has been investigated by UV–Vis and fluorescence emission spectrometry. The apparent binding constant (Kapp) values follow the order: C3 > C1 > C2 > C4. In addition, fluorescence spectrometry of bovine serum albumin (BSA) with the four platinum(II) complexes C1–C4 showed that the quenching mechanism might be a static quenching procedure. For C1–C4, the number of binding sites was about one for BSA and the binding constants follow the order: C3 (7.08 × 105M?1) > C1 (2.82 × 105M?1) > C2 (0.85 × 105M?1) > C4 (0.15 × 105M?1). With the single condition change such as absence of an external agent, the DNA cleavage abilities of C3 exhibit remarkable changes. In addition, the cytotoxicity of C3 in vitro on tumor cells lines (MCF-7, HepG2 and HT29) were examined by MTT and showed better antitumor effects on the tested cells. 相似文献
The linear nickel-nitrosyl complex [Ni(NO)(L3)] supported by a highly hindered tridentate nitrogen-based ligand, hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate (denoted as L3), was prepared by the reaction of the potassium salt of the ligand with the nickel-nitrosyl precursor [Ni(NO)(Br)(PPh3)2]. The obtained nitrosyl complexes as well as the corresponding chlorido complexes [Ni(NO)(Cl)(PPh3)2] and [Ni(Cl)(L3)] were characterized by X-ray crystallography and different spectroscopic methods including IR/far-IR, UV–Vis, NMR, and multi-edge X-ray absorption spectroscopy at the Ni K-, Ni L-, Cl K-, and P K-edges. For comparative electronic structure analysis we also performed DFT calculations to further elucidate the electronic structure of [Ni(NO)(L3)]. These results provide the nickel oxidation state and the character of the Ni-NO bond. The complex [Ni(NO)(L3)] is best described as [NiII(NO–)(L3)], and the spectroscopic results indicate that the phosphane complexes have a similar [NiII(NO–)(X)(PPh3)2] ground state. 相似文献
Four new imidazole-based ligands, 4-((1H-imidazol-4-yl)methyl)-2-phenyl-4,5-dihydrooxyzole (LOL1), 4-((1H-imidazol-4-yl)methyl)-2-(tert-butyl)-4,5-dihydrooxyzole (LOL2), 4-((1H-imidazol-4-yl)methyl)-2-methyl-4,5-dihydrooxyzole (LOL3), and N-(2,2-dimethylpropylidene)-2-(1-trityl-1H-imidazol-4-yl-)ethyl amine (Limz1), have been synthesized. The corresponding copper(I) complexes [Cu(I)(LOL1)(CH3CN)]PF6 (CuLOL1), [Cu(I)(LOL2)(CH3CN)]PF6 (CuLOL2), [Cu(I)(LOL3)(CH3CN)]PF6 (CuLOL3), [Cu(I)(Limz1)(CH3CN)2]PF6 (CuLimz1) as well as the Cu(I) complex derived from the known ligand bis(1-methylimidazol-2-yl)methane (BIMZ), [Cu(I)(BIMZ)(CH3CN)]PF6 (CuBIMZ), are screened as catalysts for the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC-H2) to 3,5-di-tert-butylquinone (3,5-DTBQ). The primary reaction product of these oxidations is 3,5-di-tert-butylsemiquinone (3,5-DTBSQ) which slowly converts to 3,5-DTBQ. Saturation kinetic studies reveal a trend of catalytic activity in the order CuLOL3 ≈ CuLOL1 > CuBIMZ > CuLOL2 > CuLimz1. Additionally, the catalytic activity of the copper(I) complexes towards the oxygenation of monophenols is investigated. As substrates 2,4-di-tert-butylphenol (2,4-DTBP-H), 3-tert-butylphenol (3-TBP-H), 4-methoxyphenol (4-MeOP-H), N-acetyl-l-tyrosine ethyl ester monohydrate (NATEE) and 8-hydroxyquinoline are employed. The oxygenation products are identified and characterized with the help of UV/Vis and NMR spectroscopy, mass spectrometry, and fluorescence measurements. Whereas the copper complexes with ligands containing combinations of imidazole and imine functions or two imidazole units (CuLimz1 and CuBIMZ) are found to exhibit catalytic tyrosinase activity, the systems with ligands containing oxazoline just mediate a stoichiometric conversion. Correlations between the structures of the complexes and their reactivities are discussed. 相似文献
A density functional theory (DFT) study of cct-As, ccc, and cct-CO isomers of the ruthenium dihydride complex RuH2(CO)2(AsMe2Ph)2 is reported (see Scheme for the labeling isomer 34 structures of RuH2(CO)2(AsMe2Ph)2). Complex geometries and relative energies of different isomers have been calculated with both B3LYP and M06-2X functionals. The results show that the B3LYP calculated Boltzmann populations of cct-As, ccc, and cct-CO isomers are 65.5, 34.2, and 0.3%, respectively. These are in better agreement with the experimental data than those calculated at the M06-2X level. However, the calculations of 1H NMR chemical shifts were found to be better described with M06-2X than with B3LYP or with HF level of theories. In addition, a transition state between the two most stable isomers was determined through DFT/(B3LYP or M06-2X) calculations.
Increase of the atmospheric concentration of halogenated organic compounds is partially responsible for a change of the global climate. In this work we have investigated the interaction between halogenated ether and water, which is one of the most important constituent of the atmosphere. The structures of the complexes formed by the two most stable conformers of enflurane (a volatile anaesthetic) with one and two water molecules were calculated by means of the counterpoise CP-corrected gradient optimization at the MP2/6–311++G(d,p) level. In these complexes the CH…Ow hydrogen bonds are formed, with the H…Ow distances varying between 2.23 and 2.32 Å. A small contraction of the CH bonds and the blue shifts of the ν(CH) stretching vibrations are predicted. There is also a weak interaction between one of the F atoms and the H atom of water, with the Hw…F distances between 2.41 and 2.87 Å. The CCSD(T)/CBS calculated stabilization energies in these complexes are between ?5.89 and ?4.66 kcal?mol?1, while the enthalpies of formation are between ?4.35 and ?3.22 kcal?mol?1. The Cl halogen bonding between enflurane and water has been found in two complexes. The intermolecular (Cl···O) distance is smaller than the sum of the corresponding van der Waals radii. The CCSD(T)/CBS stabilization energies for these complexes are about ?2 kcal?mol?1.
Figure
Complex between enflurane and water molecules 相似文献
In an effort to replace the widely used ruthenium metal complexes with low-cost, earth abundant iron complexes as photosensitizers for dye-sensitized solar cell (DSSC) applications, herein we report the computational design of heteroleptic iron complexes (FC1–3) coordinated with benzimidazole-phenylcarbene (C^N) ligands. DFT and TDDFT calculations predicted the stronger σ-donating and π-accepting nature of phenyl carbene ligands substituted with electron-withdrawing CF3, donating –N(CH3)2, and benzothiazine annulation than the imidazole carbene ligands (FC4); consequently, the metal-ligand bond distances and interactions that influence the ordering of charge transfer states with respect to metal centered states are altered in FC1–3 complexes. Detailed analysis based on energy decomposition analysis, spin density distribution analysis, and ab initio ligand field theory parameters were enabled to understand the nature of heteroleptic ligand interactions with the rest of the metal complex. The results from the study shed light on the judicious choice of ligands, as the same non-innocent ligand that is experimentally proven as favorable for Ru-dyes (TC1) is found to be detrimental for Fe-dyes (FC1). Among the complexes studied, the FC3 complex is a promising sensitizer for DSSC with 1,3MLCT energy level well separated from 3,5MC, thereby preventing the deactivation of MLCT. The outcome of the study is therefore an important step toward the development of photosensitizers based on iron metal.
Graphical abstract Potential photosensitzers based on earth-abundant, low cost iron metal have been designed for dye sensitized solar cell applications.
In this work we studied the structural and electronic properties of the metal–Schiff base complexes Ni\( {\mathrm{L}}_2^2 \) (1), Pd\( {\mathrm{L}}_2^1 \) (2), Zn\( {\mathrm{L}}_2^2 \) (3), and Ni\( {\mathrm{L}}_2^1 \)(4), where L1 and L2 are Schiff bases synthesized from salicylaldehyde and 2-hydroxy-5-methylbenzaldehyde, respectively. Natural bond analysis showed that in complexes 1 and 2, the metal ion coordinates to the ligands through electron donation from lone pairs on ligand nitrogen and oxygen atoms to s and d orbitals on the metal ion. In complex 3, metal–N and metal–O bonds are formed through charge transfer from the lone pairs on nitrogen and oxygen atoms to an s orbital of Zn. Dimethylation of the phenolate rings in the ligands decreases the energy gap and redshifts the spectrum of the nickel complex. The main absorptions observed were assigned on the basis of singlet-state transitions. The simulated spectra of the two complexes 1 and 2 are characterized by excited states with ligand-to-ligand charge-transfer (LLCT), metal-to-ligand charge-transfer (MLCT), ligand-to-metal charge-transfer (LMCT), and metal-centered (MC) character.
Detailed ab initio molecular orbital calculations on the interactions of molecular hydrogen, H2, with various poly-aromatic hydrocarbons (PAHs) as a model system for graphene were carried out to accurately describe the physisorption phenomenon. The binding energies corrected for the basis set superposition error, ΔEbind(BSSE), were obtained using the optimized geometries at the MP2 level with a large basis set and were compared with the single point binding energies, denoted as ΔEbind(BSSE-s), using large basis sets on the geometries optimized at the small basis sets, such as SVP and TZVP. The calculations showed that the ΔEbind(BSSE-s) values were similar to those at the MP2 level with the large basis sets. The binding strength increased gradually with increasing size of the PAHs. The ΔEbind(BSSE-s) for an infinite graphene sheet was estimated to be ?1.70 kcal mol?1 using the non-linear curve fitting method. The present work could be expected to provide more useful and reliable information on H2 physisorption.
Graphical abstract Detailed ab initio molecular orbital calculations on the interactions of molecular hydrogen with various poly-aromatic hydrocarbons as a model system for graphene indicate that the perpendicular type A is the most favorable and the binding energy on an infinite graphene sheet is estimated to be ?1.70 kcal mol?1.
Calculation predicted the interacting forms of halopentafluorobenzene C6F5X (X=F, Cl, Br, I) with triethylphosphine oxide which is biologically interested and easily detected by 31P NMR. The interaction energy and geometric parameters of resultant halogen or π-hole bonding complexes were estimated and compared. Moreover, the bonding constants were determined by 31P NMR. Both theory and experiments indicated the C6F6 and C6F5Cl interact with triethylphosphine oxide by π-hole bonding pattern, while C6F5I by halogen/σ-hole bonding form. For C6F5Br, two interactions are comparative and should coexist competitively. The calculated interaction energies of σ-hole bonding complexes, ?5.07 kcal mol?1 for C6F5Br?O=P and ?8.25 kcal mol?1 for C6F5I?O=P, and π-hole bonding complexes, ?7.29 kcal mol?1 for C6F6?O=P and ?7.24 kcal mol?1 for C6F5Cl?O=P, are consistent with the changing tendency of bonding constants measured by 31P NMR, 4.37, 19.7, 2.42 and 2.23 M?1, respectively.
Figure
The competitive σ-hole···O=P and π-hole···O=P bonds between C6F5X (X=F, Cl, Br, I) and O=PEt3相似文献
