Gauge Independent Atomic Orbital Research Articles

Spectroscopic, solvent interactions, topological analysis, docking evaluation with biological studies on 1,3,3-trimethyl-2-oxybicyclo[2.2.2] octane by anti-cancer proteins

In the current study the title molecules have been shown the anticancer properties of few cancers cell line and biological activity. Electron transition, solute solvent, experimental and computational exploring on the natural bio-molecular structure 1,3,3-tri methyl-2-oxybicyclo[2.2.2] octane stimulated by B3LYP/6–311++G (d,p) set. The 1TOBO molecular structure has identified from GC–MS study by extract of Zingiber Officianale Roscoe. The optimized parameters are correlated with XRD data and NBO expressed the delocalization of charge due to intermolecular interactions and their stronger stabilization E(2) = 4.01 Kcal/mol. The experimental spectral data recorded in the range 400–4000 cm−1 of 1TOBO and strong correlated with computational spectral have been estimated. The UV–vis spectra of corresponding gas phase and solvent-liquid estimated by TD-SCT process well agreement with reported spectra. 1H and 13C NMR spectrum have been capturing the chemical shifts of 1TOBO interpreted by Gauge Independent Atomic Orbital (GIAO) approach with carbinol solvent. The HOMO-LUMO values, Mulliken charges and MEP surface were used to predict the regioselectivity reaction in the region of electrophilic and nucleophilic attack. The topological analysis of LOL and ELF surfaces have been estimated and RDG-NCI map exhibits the van der Walls, steric effect and strong hydrogen bond interaction within the molecules. The Electron-hole distribution analysis revealed the electron transition of three excited states. Furthermore, the quantitative analysis of drug likeness and ADMET were studied. The molecular docking determines the lowest binding impact on the 1TOBO against cancer proteins 7QTZ, 1OXR have been estimated by Auto dock software.

Three new diterpenoids from the roots of Euphorbia fischeriana and their cytotoxicity

Euphorbiabietane F (1), a novel abietane diterpenoid with the unprecedented 6/6/5/6/5 carbon skeleton, one new strobane diterpenoid (2), together with one new pimarane diterpenoid (3) were isolated from the roots of Euphorbia fischeriana. The structures were elucidated by the extensive spectroscopic data, gauge-independent atomic orbital (GIAO) NMR calculations, the comparison of experimental and calculated ECD spectra, as well as single crystal X-ray diffraction. The cytotoxicity result suggested the moderate inhibition rate of 1 on the cell lines of HepG2 and A549.

Discovery of natural AMPK activator from the fruits of Xanthium sibiricum Patr.: Xanthiumine A, protoberberine alkaloid with unique C28 skeleton

Two protoberberine alkaloids with a unique C28 skeleton, named xanthiumines A (1) and B (2), respectively, were isolated from the fruits of Xanthium sibiricum Patr. Their structures including absolute configurations were unequivocally established by the comprehensive NMR and MS spectroscopic data analysis together with gauge-independent atomic orbital (GIAO) NMR calculations, and electronic circular dichroism (ECD) calculations. Compounds 1 and 2 are the first examples of natural protoberberine alkaloid with a phenolic acid group at C-13a. Their plausible biosynthetic pathway was proposed on the basis of the coexisting alkaloid monomer as the precursor. Furthermore, the effects and related molecular mechanism of compound 1 on hepatic lipid accumulation were also investigated in oleic acid (OA)-treated HepG2 cells.

Theoretical investigation of the conformational preference and spectroscopic analysis of cinnamoyl chloride and cinnamide

The rotational isomers of cinnamoyl chloride and cinnamide have been computed using the B3LYP method and the 6-311++G (d, p) basis set to calculate their molecular structure, conformational stability, and spectroscopic properties. Computations revealed that the s-cis rotamers of both compounds are the most stable rotamers in both the gas phase and in the solution. The s-trans rotational barrier is 8.76 kcal/mol and 5.63 kcal/mol for cinnamoyl chloride and cinnamide, respectively. Replacing the Cl group of the cinnamoyl chloride with the NH2 group in the cinnamide has reduced the highest occupied molecular orbital – lowest unoccupied molecular orbital (HOMO-LUMO) gap. The solvation effects on the conformational stability of rotamers have been studied in nine solvents (heptane, chloroform, tetrahydrofuran, dichloroethane, acetone, ethanol, methanol, dimethyl sulfoxide, and water) using the integral equation formalism of the polarizable continuum model. The chemical shifts of 13C and 1H NMR spectra have been simulated in the gas phase, dimethyl sulfoxide (DMSO), and chloroform using the gauge-independent atomic orbital (GIAO) method. The UV absorption spectral analysis has been computed in different solvents (chloroform, methanol, and water), and atomic charges calculated. The examination of vibrational wave numbers and their corresponding assignments revealed excellent agreement between simulated and experimental infrared spectra for the studied molecules.

Synthesis, spectroscopic analysis (FT-IR, FT-Raman, UV, NMR), non-covalent interactions (RDG, IGM) and dynamic simulation on Bis(8‑hydroxy quinoline) salicylate salicylic acid

Using spectrum techniques and density functional theory (DFT) reckonings, structural, vibrational and electrical characteristics of Bis(8‑hydroxy quinoline) salicylate salicylic acid (8HQSA) were determined. Characterizing the chemical under inquiry involved employing FT-IR, FT-Raman, UV–vis spectral studies and single crystal X-ray diffraction (SCXRD). For the characterization, the B3LYP approach inside the structure of DFT was employed, with a 6–311++G(d,p) basis set. The structural study shows that the stability of 8HQSA crystalline structure arising from N–H⋯O, C–O⋯H and O–H⋯O hydrogen bonding interactions. The 1H and 13C NMR chemical shifts were calculated using Gauge Independent Atomic Orbital (GIAO) technical. Vibrational frequencies and molecular geometry were computed and likened with experimental data. Here, non-covalent interactions were deeply analyzed in terms of topological parameters (AIM), electron localization function (ELF), localized orbital locator (LOL), Hirshfeld surface and reduced density gradient (RDG) method. Weak interactions such as H-bonds, van der Waals and steric effect in 8HQSA were visualized and quantified by the independent gradient density (IGM) based on the trimolecular density. The hyper-conjugative and the delocalization of charge in 8HQSA have been elucidated by natural bonding orbital (NBO) while its chemical reactivity was studied and discussed by using molecular electrostatic potential surface (MEP), frontier molecular orbital (FMOs), density of state (DOS) and partial density of state (PDOS). The positions of the molecule's nucleophilic and electrophilic groups were ascertained using Fukui analysis. To describe the size, structure, and reactive sites of the molecules, the molecular electrostatic potential and total electron density are calculated. With a band gap (2.58 eV), FMO study indicates that the material is both bioactive and stable. The ADMET factor and drug similarity are used to predict 8HQSA's pharmokinetic characteristics. Based on the findings, it can be concluded that the 8HQSA particle is optimally crystallised and recommended as a preventative measure against bacterial and fungal infections. The stability of the title compound has been investigated via molecular dynamics simulations. In-vitro antimicrobial activity results clearly reveal that in all the four strains, activity increases with increase in compound concentration and the inhibition of the strains also increases. From both molecular docking and In-vitro Antimicrobial Activity the title compound can be certified that it inhibits antimicrobial activity.

Pericyclic Cascade Reactions Affording Thienyl- and Benzo[b]thienyl-Fused Architectures: A Synthetic and Density Functional Theory Analysis of Asynchronous Diels-Alder Reactions of Thioarylmaleimides.

Herein, we report the synthesis and characterization of a series of thioarylmaleimides and their varied propensity toward highly selective domino Diels-Alder (D-A)/rearrangement, D-A/ene/elimination, and D-A/oxidation reactions to give three types of thienyl-fused architectures. Stereochemical assignment was achieved using a combination of nuclear magnetic resonance (NMR) studies, gauge independent atomic orbital (GIAO) NMR chemical shift calculations, and DP4+ analysis. Transition-state calculations support an asynchronous concerted mechanism and provide support for rationalizing the observed regio- and stereoselectivity.

Spectroscopic (FT-IR, FT-Raman, NMR and UV–vis), quantum calculation, molecular structure, solvent interaction, ADME and molecular docking investigation on 4-oxo-4h-1-benzopyran-2-carboxylic acid

The present work, spectroscopic and quantum computational study has been carried out for the molecule 4-oxo-4H-1-benzopyran-2-carboxylic acid. The stable conformer of the title molecule was identified using Potential Energy Surface (PES) scan. The structural and geometrical parameters of the stable conformer of the molecule were determined by Density Functional Theory (DFT) using B3LYP method along with the basis set 6-311++G(d,p) through Gaussian 09 W software. The theoretical and experimental investigations such as Vibrational (FT-IR and FT-Raman), UV–visible and NMR analysis were done. The FT-IR were recorded in the region of (4000–400 cm−1) and FT-Raman in the region of (4000–100 cm−1), and the vibrational bands were compared with the theoretical values. Carbon NMR and Proton NMR spectra have been analyzed in DMSO solution. The theoretical chemical shift values were determined using Gauge Independent Atomic Orbital (GIAO) method. The intermolecular and intra-molecular bonding of orbitals and transfer of charge were studied using the Natural Bond Orbital (NBO) analysis. The respective transitional study was done through UV–vis's spectra and theoretical values predicted using TD-DFT (Time Dependent – DFT) method for both gas and solvent (ethanol) state. HOMO (Highest Occupied Molecular Orbital) – LUMO (Lowest Unoccupied Molecular Orbital) energy gap results prove the exchange of charges inside the molecule. Molecular Electrostatic Potential (MEP) is used to identify the nucleophilic and electrophilic sites of the molecule. To check the bioactive nature of the title molecule the drug-likeness was determined. Molecular docking is used to analyze the biological activity of the title molecule. The distribution of torsional angles in a protein structure is viewed by the Ramachandran plots of the molecules.

Unexpected structural preference with metallophilic Ag-Au contacts in silver(I)-N-heterocyclic carbene cluster; experimental and theoretical approach.

A novel synthetic donor-atom-selective approach has been adopted for the synthesis of a heterobimetallic cluster of a new NCN-pincer, 1,3-bis-(1-methyl-1H-benzo[d]imidazol-2-yl-methyl)-1H-imidazol-3-ium hexafluorophosphate (1·HPF6). The complex [Ag3(1)3][PF6]3 (2) has been prepared via the Ag2O route; which undergoes transmetallation to yield a cluster that seems to be the first example of the heterobimetallic trinuclear system [Au-Ag2(1)2Cl][PF6]2, 3. Finally, the trinuclear cluster geometries of 2 and 3 were confirmed via SCXRD studies. Interestingly, Au(I) binds preferentially with soft donor Ccarbene, which transmetallated from the cluster of 2. In both the cyclic trinuclear clusters, the M-M interactions were further inspected using gauge independent atomic orbital (GIAO) computations. Both 2 and 3 are luminescent and possess σ-aromaticity; the NICS values indicate that 3 is more aromatic than 2.

Synthesis, X-ray diffraction, DFT, and molecular docking studies of isonicotinohydrazide derivative

Abstract The synthesized compound N′-benzylidene-isonicotinohydrazide (N-BINH), was experimentally characterized using XRD and distinguished by using experimental spectroscopic methods. DFT, B3LYP method along with 6-311++G(d,p) basis set were applied to determine the optimal molecular geometry and vibrational wave numbers. Gauge Independent Atomic Orbital (GIAO) method and DFT were used to calculate the chemical shifts for 13C and 1H NMR in chloroform solvent. MEP analysis reveals that the site with an oxygen atom is the most reactive part of the N-BINH molecule. Computed UV–visible spectrum in MeOH and gas phase was generated by using the TD-DFT technique. The investigation also looked at electron localization function properties. Hirshfeld analysis demonstrates the 3D intermolecular interactions of the crystal surface, while fingerprint plots were used to elucidate the 2D interactions. By calculating the electrophilicity index, it was theoretically shown that the titled molecule could be bioactive. Further, molecular docking analysis was used to investigate the biological activity of the N-BINH with four distinct receptors to assess the finest ligand–protein interactions and similarity to the dynamic constituent.

Theoretical determination of electronic, geometric and spectroscopic properties of some 1,2,4-triazol derivatives

In this study, molecular geometric optimization of five 4,5-dihydro-1H-1,2,4-triazol-5-one derivative compounds was obtained using Density Functional Theory, (DFT, B3LYP)/ Hartree Fock, (HF, B3LYP) methods on the basis set of 6-311G (d,p) in order to find the most stable geometric shape of the studied compounds. FT-IR and UV-vis spectral values were performed by using gauge independent atomic orbital (GIAO) methods with Gaussian G09W package program. IR frequency datas of investigated five compounds were calculated in gas phases and are multiplied with appropriate scala factors. The identification of the calculated IR data was performed in the veda4f program. Additionally, bond angles, bond lengths, dipole moments, highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy and total energy, mulliken charges and molecular electrostatic potential (MEP) of five compounds were calculated using same methods and set.

Study of different interactions in piperazine benzoate and its effect on biological properties: Experimental and theoretical approach

Piperazine benzoate (PPB), an antibacterial molecule, was synthesized and characterized using FT-IR, FT-Raman, UV, and NMR spectra as well as biological research. The optimized geometry of the molecule was performed using Gaussian'09w programme at B3LYP with 6–311G++(d,p) basis set. Hyper conjugative interaction σ(CH) → σ*(OH) enhances NH…O interaction and C-H…O interaction arises mainly from charge transfer between the molecules. The electronic transitions in the molecule were exhibited by comparing the UV–vis spectrum with the observed spectrum using the TD-DFT method in gaseous phase. FMO analysis, natural charge analysis, and global chemical reactivity descriptors methods were investigated. PPB is a soft molecule with significant polarizability and chemical reactivity because of its low molecular orbital energy gap. Normal coordinate analysis (NCA) was used to determine the detailed interpretation of the fundamental modes. The chemical shifts of the molecule were determined from the recorded 13C and 1H NMR spectra using the gauge independent atomic orbital (GIAO) method. Using NBO analysis, concerns related to molecular stability and bond strength have been presented. The topological properties were studied using MEP, ELF, and LOL maps. From AIM findings, the PPB is defined by two BCPs, one each for an ON…H and CO…H type hydrogen bond. Through RDG investigation, the interactions inside the PPB molecule were examined. The interaction areas in the molecular structure of PPB are confirmed by the RDG graph data. PPB's absorption rate was 78.18 percent. This figure led to the conclusion that PPB had the highest percentage of absorption. Bacterial proteins were used for molecular docking, and docking parameters were derived. Based on Lipinski's rule of five, drug similarity was determined, and the ADMET variables were also predicted.

Spectroscopic properties (FT-IR, NMR and UV) and DFT studies of amodiaquine

Amodiaquine (AQ) was synthesized by a condensation reaction and characterized by experimental FT-IR, 1H and 13C nuclear magnetic resonance (NMR) and UV spectroscopies. In the present work, Density Functional Theory (DFT) calculations using B3LYP method with 6–311++G(d,p) and 6–311++G(2d, p) basis sets were performed, first, to confirm its structure, then to explain its reactive nature through its molecular properties such as natural charges, local and global reactivity descriptors or natural bond orbital (NBO). The 1H and 13C NMR chemical shifts were calculated by using the gauge-independent atomic orbital (GIAO) method, while the electronic UV–Vis spectrum is predicted using the time-dependent density functional theory (TD-DFT). Globally, the computerized results showed close similarity with the experimental values.The calculated energy band gap (ELUMO-EHOMO) value of AQ was found to be 4.09 eV suggesting that it could be considered as a hard molecule with high stability, supported by global reactivity descriptors. Molecular electrostatic potential (MEP) analysis revealed heteroatoms (oxygen and nitrogen) as the most putative nucleophilic sites when hydrogen atoms to which they are linked appear as electrophilic sites. The potential use of amodiaquine as non-linear optical (NLO) material and its thermodynamic indicators have also been assessed.

Monohalogenated methyl- and methoxy-benzoic acids: A combined experimental and quantum chemical theoretical study on their structure, vibrational analysis and molecular parameters

In this paper, the molecules 3-fluoro-2-methylbenzoic acid; 3-chloro-2-methoxybenzoic acid; and 3-bromo-2-methylbenzoic were investigated using experimental and quantum chemical theoretical approach for vibrational and electronic properties from the optimized structure. Becke three parameter Lee–Yang–Parr density functionals along with 6-311++G(d,p) basis set were employed to compute their geometric optimization, fundamental frequencies and molecular parameters. The detected FT-IR and FT-Raman spectra were compared with their simulated spectra and the rms error between the detected and simulated vibrational frequencies was found at 6.17, 7.22 and 6.76 cm−1 for FMA, CMA and BMA, respectively. All the vibrational fundamentals were assigned unequivocally using potential energy distribution (PED) obtained in the computations. 1H and 13C NMR chemical shifts were evaluated by integrating the gauge-independent atomic orbital (GIAO) method with DFT and compared with corresponding experimental values. TD-DFT approach was followed to compare the simulated absorption maxima (λmax) in DMSO-d6 solvent with observed values and interpreted in terms of HOMO and LUMO. The global reactive descriptors were estimated from the associated energies of HOMO and LUMO which describe the reactivity and stability of the molecules. Molecular electrostatic potential (MEP) surface has been determined using the charge density distributions to demonstrate electrophilic and nucleophilic nature of the molecules. DFT computations also ascertained the applicability of the titled molecules as NLO materials from the computed values of dipole moment and hyperpolarizability. Thermodynamic parameters and rotational constants were also evaluated employing rigid rotor harmonic oscillator approximation. Natural bond orbital (NBO) analysis confirmed the charge delocalization due to intra-molecular interactions.

Ring opening ring closure reactions with 5,9-diethyl-7-(chromon-3-yl)-7-hydroquinolino[3′,4′:5,6]pyrano[3,2-c]quinoline-6,8(5H,9H)-dione with some 1,2-binucleophiles: Synthesis, characterization, DFT study and biological activity

The chemical behaviour of electron deficient substrate 1 was investigated with some 1,2-bi-nucleophilic reagents. Reaction of substrate 1 with hydrazine derivatives namely hydrazine hydrate, phenylhydrazine, 7‑chloro-4-hydrazinoquinoline and 3-hydrazino-5,6-diphenyl-1,2,4-triazine led to 7-pyrazolylquinolinopyranoquinolines 2, 3, 6 and 7, respectively. These reactions proceed through γ-pyrone ring opening followed by pyrazole ring closure. Moreover, treating compound 1 with hydroxylamine hydrochloride provided 7-isoxazolylquinolino[3′,4′:5,6]pyrano[3,2-c]quinoline 8. The molecular structures were optimized utilizing DFT/B3LYP functional with 6–311G+(d,p) basis sets for all compounds. Moreover, global reactivity descriptors like chemical potential (μ), electronegativity (χ), hardness (η), softness (S) and electrophilicity index (ω) were computed to predict the chemical reactivity and kinetic stability of the synthesized compounds. The locations susceptible to attack by electrophiles and nucleophiles were examined at the same theoretical level by using molecular electrostatic potential (MEP) and condensed Fukui functions. The NMR chemical shifts were computed by the Gauge Independent Atomic Orbital (GIAO) method and compared to the experimental results. The first hyperpolarizability of the prepared compounds is higher than urea, so serves as good candidate for nonlinear optical (NLO) materials. The synthesized substances were tested for their efficacy as antimicrobial agents against a variety of bacterial and fungal species. Additionally, the present compounds revealed some antitumor activity (compounds 3 and 7 showed activity comparable to cis-platin, used as a reference drug in the assay). Furthermore, the synthesized compounds were moderately compliant with Lipinski's rule of five, suggesting that related compounds might be suitable for oral administration as medications.

Molecular structural analysis, conformers and spectral (FT-IR, FT-Raman, NMR and UV-Visible), Importance of solvent role in molecular, ADME and molecular docking investigation on alpha-cyano-4-hydroxycinnamic acid

The primary objective of research to reveals the effective drug treatment for corona virus disease (COVID-19). The current study on alpha-cyano-4-hydroxycinnamic acid (ACHC), the theoretical predictions were done by using Gaussian 09 W software on the basis of DFT/ TDFT/B3LYP methods with basis set of 6–311++G (d, p). The vibrational wavenumbers were obtained from the observed FT-IR and FT-Raman spectra and these vibrations were assigned on the basis of their potential energy distribution (PED) contribution. 1H and 13C NMR chemical shift of the molecule were computed by using Gauge independent atomic orbital (GIAO) method. In UV-Visible analysis the electronic transition was predicted by Time-dependent self-consistent field (TD-SCF)/DFT method. NBO analysis was done to understand the possible the intermolecular interaction, electron transition within the donor and acceptor orbitals of the molecule. The HOMO and LUMO indicates the prominent charge transfer possibilities and its energy gap shows stability of the molecule. A molecular electrostatic potential (MEP) image shows the electrophilic and nucleophilic sites of the molecule. Molecular docking analysis was carried out against Agaricus bisporus tyrosinase (2Y9X) and severe acute respiratory syndrome corona virus 2 (6LZG).

A new steroid with potent antimicrobial activities and two new polyketides from Penicillium variabile EN-394, a fungus obtained from the marine red alga Rhodomela confervoides.

Three new compounds, including one steroid named penivariod A (1) and two polyketides penivarides A and B (2 and 3), as well as six known derivatives (4-9) were isolated from Penicillium variabile EN-394, a fungus afforded from the marine red alga Rhodomela confervoides. Their structures were elucidated by analysis of the HRESIMS, 1D and 2D NMR. The absolute stereochemistry was determined by X-ray crystallographic data, gauge-independent atomic orbital (GIAO) NMR shift calculation followed by DP4+ analysis combined with calculated electronic circular dichroism (ECD). Antimicrobial activities for the new compounds (1-3) were evaluated against human- and aquatic-pathogenic bacteria as well as plant pathogenic fungi. Compound 1 exhibited potent antimicrobial activity against most of the pathogenic strains, especially for Escherichia coli and Pseudomonas aeruginosa, with MIC values of 1.0 and 2.0 μg ml-1, respectively.

Theoretical investigation of anion perfluorocubane.

In this work, we did a theoretical exploration of C8F8 (Ib) and its anion radical analogue (IIb) in this work. By investigating the thermochemistry of electron capture, we find that the free energy associated with the conversion of C8H8 (Ia) into its anion radical analogue IIa is of the order of + 92.83 kcal.mol-1, while the conversion of Ib into IIb is - 6.42 kcal.mol-1. Therefore, species IIb is thermodynamically more stable than its neutral analogue. Natural bond orbitals (NBO) analyses revealed that compound Ib exhibits a relative electronic stability as a function of intramolecular delocalisations of the type [Formula: see text] of the order of 2.70 kcal.mol-1. Similar delocalizations for Ia are energetically lower (1.45 kcal.mol-1). Topological analyses of compounds Ib and IIb indicate that the addition of an electron to Ib enhances the covalency of the C-C bond, as can be seen by the reduction in the ellipticity of the C-C bond. The opposite is observed for Ia, whose addition of the electron (leading to IIa) reduces the covalency of the C-C bond. By comparing the free and packaged forms of the species, it is found that, in the crystalline form, the system will present greater relative stability due to the dispersive interactions involved, as evidenced by non-covalent interactions (NCI) analysis. Finally, it was possible to verify that the manifestation of the current density with a lower paratropic and less antiaromatic character in Ib and IIb point to C8F8 as a strong candidate for electron capture. Geometry optimization calculations were carried out, for all monomer structures using the hybrid functional B3LYP-D3 and the 6-31+G(d,p) basis set. To determine the formation thermochemistry of the ions, electronic energy corrections was performed using the DLPNO-CCSD(T)/aug-cc-pVTZ/C method. Starting from the optimised forms, shielding, nuclear magnetic resonance (NMR) spectra employing gauge-independent atomic orbital (GIAO), and NBO calculations were performed for these monomers, using the PBE0 functional and the pCSseg-2 atomic basis set. The magnetochemical analysis of ring currents was performed using the GIMIC formalism. For the topological analysis, it was applied the combination DLPNO-CCSD(T)/aug-cc-pVTZ/C, previously used for correcting the electronic energy.

Antibacterial polyketides and ascochlorins from deep-sea cold-seep-derived fungus Furcasterigmium furcatum (syn. Acremonium furcatum)

Three new secondary metabolites, including a new polyketide, acrefurcatone A (1), a new ascochlorin analogue, acremochlorin N (2), and 3-phenylcyclopentane-1,2-diol (±-3), a pair of new naturally occurring enantiomers, along with nine known ascochlorins (4–12), were identified from Furcasterigmium furcatum CS-280 (syn. Acremonium furcatum CS-280), a fungus isolated from the deep-sea cold-seep sediment samples collected in the South China Sea. Their structures were determined by detailed interpretation of NMR spectroscopic and mass spectrometric data. The relative configurations of compounds 1–3 were assigned by NOESY correlations combined with gauge-independent atomic orbital (GIAO) NMR shift calculations and DP4+ probability analysis, while their absolute configurations were assigned by time-dependent density functional (TDDFT) ECD calculations and specific rotation calculations. Compound 1 exhibited potent activity against the human pathogenic bacterium Pseudomonas aeruginosa, with a minimum inhibitory concentration (MIC) value of 8 μg/mL. The isolated ascochlorins also showed potent activities against aquatic bacteria, especially for Vibrio harveyi and V. alginolyticus, with MIC values comparable to chloramphenicol. Analysis of the structure-activity relationship indicated that the cinnamate derivative, such as compound 1, or the presence of chlorine atom in ascochlorin derivatives, such as compounds 4, 6, and 7, significantly enhanced the antibacterial activities. This is the first report of anti-Vibrio activities for ascochlorin derivatives.

Synthesis, characterization, DFT, non-covalent interactions and antioxidant activity of N2O2-type template complexes of Zn(II)-derived from 5-ethoxy-2-hydroxy-acetophenone-S-methylthiosemicarbazone

The N2O2-tetradentate Schiff-base complex of zinc(II) was synthesized by the template reaction of 5-ethoxy-2-hydroxy-acetophenone-S-methylthiosemicarbazone and 2-hydroxy-benzaldehyde (1)/2-hydroxy-4-methoxy-benzaldehyde (2). The compounds were characterized by elemental analysis, UV–visible, FT-IR, 1H NMR spectra, and thermogravimetric analyses. Antioxidant activities of the compounds were determined with Cupric Reducing Antioxidant Capacity and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays. The molecular geometries and vibrational frequencies were calculated using density functional theory (DFT/B3LYP) with the 6-311++G(d,p) basis set. The 1H NMR chemical shift values of the ligand and complexes in the ground state were calculated with the gauge-independent atomic orbital (GIAO) approach applying the same method and the basis set and compared with the experimental data. Using the TD-DFT method, electronic absorption spectra of the complexes were predicted at the same level. Also, the non-covalent interaction (NCI) plot index analysis reveals the presence of different kinds of non-covalent interactions in all complexes.

Combined NMR Spectroscopy and Quantum-Chemical Calculations in Fluorescent 1,2,3-Triazole-4-carboxylic Acids Fine Structures Analysis.

The peculiarities of the optical properties of 2-aryl-1,2,3-triazole acids and their sodium salts were investigated in different solvents (1,4-dioxane, dimethyl sulfoxide DMSO, methanol MeOH) and in mixtures with water. The results were discussed in terms of the molecular structure formed by inter- and intramolecular noncovalent interactions (NCIs) and their ability to ionize in anions. Theoretical calculations using the Time-Dependent Density Functional Theory (TDDFT) were carried out in different solvents to support the results. In polar and nonpolar solvents (DMSO, 1,4-dioxane), fluorescence was provided by strong neutral associates. Protic MeOH can weaken the acid molecules' association, forming other fluorescent species. The fluorescent species in water exhibited similar optical characteristics to those of triazole salts; therefore, their anionic character can be assumed. Experimental 1H and 13C-NMR spectra were compared to their corresponding calculated spectra using the Gauge-Independent Atomic Orbital (GIAO) method and several relationships were established. All these findings showed that the obtained photophysical properties of the 2-aryl-1,2,3-triazole acids noticeably depend on the environment and, therefore, are good candidates as sensors for the identification of analytes with labile protons.