The furan microsolvation blind challenge for quantum chemical methods: First steps.

Herein we present the results of a blind challenge to quantum chemical methods in the calculation of dimerization preferences in the low temperature gas phase. The target of study was the first step of the microsolvation of furan, 2-methylfuran and 2,5-dimethylfuran with methanol. The dimers were investigated through IR spectroscopy of a supersonic jet expansion. From the measured bands, it was possible to identify a persistent hydrogen bonding OH-O motif in the predominant species. From the presence of another band, which can be attributed to an OH-π interaction, we were able to assert that the energy gap between the two types of dimers should be less than or close to 1 kJ/mol across the series. These values served as a first evaluation ruler for the 12 entries featured in the challenge. A tentative stricter evaluation of the challenge results is also carried out, combining theoretical and experimental results in order to define a smaller error bar. The process was carried out in a double-blind fashion, with both theory and experimental groups unaware of the results on the other side, with the exception of the 2,5-dimethylfuran system which was featured in an earlier publication.

Ab†Initio and DFT Studies on CO2 Interacting with Zn(q+)-Imidazole (q=0, 1, 2) Complexes: Prediction of Charge Transfer through σ- or π-Type Models.

Using first-principles methodologies, the equilibrium structures and the relative stability of CO2 @[Zn(q+) Im] (where q=0, 1, 2; Im=imidazole) complexes are studied to understand the nature of the interactions between the CO2 and Zn(q+) -imidazole entities. These complexes are considered as prototype models mimicking the interactions of CO2 with these subunits of zeolitic imidazolate frameworks or Zn enzymes. These computations are performed using both ab initio calculations and density functional theory. Dispersion effects accounting for long-range interactions are considered. Solvent (water) effects were also considered using a polarizable continuum model approach. Natural bond orbital, charge, frontier orbital and vibrational analyses clearly reveal the occurrence of charge transfer through covalent and noncovalent interactions. Moreover, it is found that CO2 can adsorb through more favorable π-type stacking as well as σ-type hydrogen-bonding interactions. The inter-monomer interaction potentials show a significant anisotropy that might induce CO2 orientation and site-selectivity effects in porous materials and in active sites of Zn enzymes. Hence, this study provides valuable information about how CO2 adsorption takes place at the microscopic level within zeolitic imidazolate frameworks and biomolecules. These findings might help in understanding the role of such complexes in chemistry, biology and material science for further development of new materials and industrial applications.

Spectral and quantum chemical studies on 1,3-bis(N(1)-4-amino-6-methoxypyrimidinebenzenesulfonamide-2,2,4,4-ethane-1,2-dithiol)-2,4-dichlorocyclodiphosph(V)azane and its erbium complex.

Novel 1,3-bis(N(1)-4-amino-6-methoxypyrimidine-benzenesulfonamide-2,2,4,4-ethane-1,2-dithiol)-2,4-dichlorocyclodiphosph(V)azane (L), was prepared and their coordinating behavior towards the lanthanide ion Er(III) was studied. The structures of the isolated products are proposed based on elemental analyses, IR, UV-VIS., (1)H NMR, (13)C NMR, (31)P NMR, SEM, XRD, mass spectra, effective magnetic susceptibility measurements and thermogravimetric analysis (TGA). Computational studies have been carried out at the DFT-B3LYP/6-31G(d) level of theory on the structural and spectroscopic properties of L and its binuclear Er(III) complex. Different tautomers of the ligand were optimized at the ab initio DFT level. Keto-form structure is about 17.7 kcal/mol more stable than the enol form (taking zpe correction into account). Simulated IR frequencies were scaled and compared with that experimentally measured. TD-DFT method was used to compute the UV-VIS spectra which compared by the measured electronic spectra.

Synthesis, spectroscopic, molecular orbital calculation, cytotoxic, molecular docking of DNA binding and DNA cleavage studies of transition metal complexes with N-benzylidene-N'-salicylidene-1,1-diaminopropane.

Eight mononuclear chromium(III), manganese(II), iron(III), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes of Schiff's base ligand were synthesized and determined by different physical techniques. The complexes are insoluble in common organic solvents but soluble in DMF and DMSO. The measured molar conductance values in DMSO indicate that the complexes are non-electrolytic in nature. All the eight metal complexes have been fully characterized with the help of elemental analyses, molecular weights, molar conductance values, magnetic moments and spectroscopic data. The analytical data helped to elucidate the structure of the metal complexes. The Schiff base is found to act as tridentate ligand using N2O donor set of atoms leading to an octahedral geometry for the complexes around all the metal ions. Quantum chemical calculations were performed with semi-empirical method to find the optimum geometry of the ligand and its complexes. Additionally in silico, the docking studies and the calculated pharmacokinetic parameters show promising futures for application of the ligand and complexes as high potency agents for DNA binding activity. The interaction of the complexes with calf thymus DNA (CT-DNA) has been investigated by UV absorption method, and the mode of CT-DNA binding to the complexes has been explored. Furthermore, the DNA cleavage activity by the complexes was performed. The Schiff base and their complexes have been screened for their antibacterial activity against bacterial strains [Staphylococcus aureus (RCMB010027), Staphylococcus epidermidis (RCMB010024), Bacillis subtilis (RCMB010063), Proteous vulgaris (RCMB 010085), Klebsiella pneumonia (RCMB 010093) and Shigella flexneri (RCMB 0100542)] and fungi [(Aspergillus fumigates (RCMB 02564), Aspergillus clavatus (RCMB 02593) and Candida albicans (RCMB05035)] by disk diffusion method. All the metal complexes have potent biocidal activity than the free ligand.

Electronic structure and properties of neutral, anionic and cationic silicon-nitrogen nanoclusters.

We performed a G3 investigation of the possible stable structures of silicon-nitrogen SinNm clusters where m = 1-4, n = 1-4, m + n = 2-5. We considered the neutral, anionic and cationic molecular species in the singlet, doublet and triplet states, as appropriate. For neutral clusters, our data confirm previous DFT and post Hartree-Fock findings. For charged clusters, our results represent predictions. Several molecular properties related to the experimental data, such as the electronic energy, equilibrium geometry, binding energy (BE), HOMO-LUMO gap (HLG), and spin contamination mathematical left angle bracket S2 mathematical right angle bracket were computed. We also derived the vertical electron attachment (VEA), the adiabatic electron affinity (AEA), and the vertical ionization energy (VIE), of the neutral clusters. Similar to their carbon-nitrogen counterparts, the lowest energy structures for neutral and cationic silicon-nitrogen clusters are found to be linear or quasilinear. In contrast, anionic silicon-nitrogen clusters tend to form 3D structures as the size of the cluster increases.

A G3 study of the structure of carbon-nitrogen nanoclusters.

Possible structures of the carbon-nitrogen clusters of the form C(m)N(n) (m = 1-4, n = 1-4, m + n = 2-5) were predicted for the neutral, anion, and cation species in the singlet, doublet, and triplet states, whenever appropriate. The calculations were performed at the G3, MP2(fc)/6-311+G*, and B3LYP/6-311+G* levels of theory. Several molecular properties related to the experimental data--such as the electronic energy, equilibrium geometry, binding energy, HOMO-LUMO gap (HLG), and spin contamination --were calculated. In addition the vertical electron attachment, the adiabatic electron affinity, and vertical ionization energy, of the neutral clusters were calculated. Most of the predicted lowest energy structures were linear, whereas bent structures became more stable with the increase of the cluster size and increase of the number of the N atoms. In most of the predicted lowest energy structures, the N atom prefers the terminal position with acetylenic bond. The calculated BE of the predicted clusters increases with the increase of the cluster size for the neutral and cation clusters but decreases with the increase of the cluster size for the anion clusters. The predicted clusters are characterized by high HLG of about 11 eV on the average, with that of the anion clusters is smaller than that for the neutral and cation clusters. It is concluded then that the anion clusters are less stable than the corresponding neutral and cation clusters. Finally, the N(2) loss reaction is treated.