Cd(II) and Pd(II) Mixed Ligand Complexes of Dithiocarbamate and Tertiary Phosphine Ligands-Spectroscopic, Anti-Microbial, and Computational Studies.

Mixed ligand complexes of Pd(II) and Cd(II) with N-picolyl-amine dithiocarbamate (PAC-dtc) as primary ligand and tertiary phosphine ligand as secondary ligands have been synthesized and characterized via elemental analysis, molar conductance, NMR (1H and 31P), and IR techniques. The PAC-dtc ligand displayed in a monodentate fashion via sulfur atom whereas diphosphine ligands coordinated as a bidentate mode to afford a square planner around the Pd(II) ion or tetrahedral around the Cd(II) ion. Except for complexes [Cd(PAC-dtc)2(dppe)] and [Cd(PAC-dtc)2(PPh3)2], the prepared complexes showed significant antimicrobial activity when evaluated against Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans and Aspergillus niger. Moreover, DFT calculations were performed to investigate three complexes {[Pd(PAC-dtc)2(dppe)](1), [Cd(PAC-dtc)2(dppe)](2), [Cd(PAC-dtc)2(PPh3)2](7)}, and their quantum parameters were evaluated using the Gaussian 09 program at the B3LYP/Lanl2dz theoretical level. The optimized structures of the three complexes were square planar and tetrahedral geometry. The calculated bond lengths and bond angles showed a slightly distorted tetrahedral geometry for [Cd(PAC-dtc)2(dppe)](2) compared to [Cd(PAC-dtc)2(PPh3)2](7) due to the ring constrain in the dppe ligand. Moreover, the [Pd(PAC-dtc)2(dppe)](1) complex showed higher stability compared to Cd(2) and Cd(7) complexes which can be attributed to the higher back-donation of Pd(1) complex.

Enhancing the Catalytic Activity of Mo(110) Surface via Its Alloying with Submonolayer to Multilayer Boron Films and Oxidation of the Alloy: A Case of (CO + O2) to CO2 Conversion.

In-situ formation of boron thin films on the Mo(110) surface, as well as the formation of the molybdenum boride and its oxide and the trends of carbon monoxide catalytic oxidation on the substrates formed, have been studied in an ultra-high vacuum (UHV) by a set of surface-sensitive characterization techniques: Auger and X-ray photoelectron spectroscopy (AES, XPS), low-energy ion scattering (LEIS), reflection-absorption infrared spectroscopy (RAIRS), temperature-programmed desorption (TPD), electron energy loss spectroscopy (EELS) and work function measurements using the Anderson method. The boron deposited at Mo(110) via electron-beam deposition at a substrate temperature of 300 K grows as a 2D layer, at least in submonolayer coverage. Such a film is bound to the Mo(110) via polarized chemisorption bonds, dramatically changing the charge density at the substrate surface manifested by the Mo(110) surface plasmon damping. Upon annealing of the B-Mo(110) system, the boron diffuses into the Mo(110) bulk following a two-mode regime: (1) quite easy dissolution, starting at a temperature of about 450 K with an activation energy of 0.4 eV; and (2) formation of molybdenum boride at a temperature higher than 700 K with M-B interatomic bonding energy of 3.8 eV. The feature of the formed molybdenum boride is that there is quite notable carbon monoxide oxidation activity on its surface. A further dramatic increase of such an activity is achieved when the molybdenum boride is oxidized. The latter is attributed to more activated states of molecular orbitals of coadsorbed carbon monoxide and oxygen due to their enhanced interaction with both boron and oxygen species for MoxByOz ternary compound, compared to only boron for the Mox'By' double alloy.

Insights into the mechanism of inhibition of phospholipase A2 by resveratrol: An extensive molecular dynamics simulation and binding free energy calculation.

Phospholipase A2 (PLA2) is one of the enzymes involved in the development of cardiovascular diseases, vascular inflammation, risk of heart attacks, and strokes. This enzyme is responsible for catalyzing the hydrolytic cleavage of ester bonds of phospholipids in the biological pathway of inflammation. To prevent the undesired hydrolysis of phospholipids, the catalytic activity of PLA2 needs to be blocked. Resveratrol is a plant-derived polyphenol inhibitor, proven to have anti-inflammatory properties. However, there is still substantial ambiguity about its inhibitory function. The present study uncovers a detailed molecular mechanism behind the resveratrol action in inhibition of PLA2, by applying and comparing two 200-ns molecular dynamics simulations. The results of structural analyses revealed that the binding of resveratrol to PLA2 reduces the content of ß-sheets and increases a 5-helix to PLA2 structure, producing more folding and stability in protein. In the active site, the resveratrol is placed between the N-terminal α-helix and the newly formed 5-helix through the hydrophobic interactions with ILE19 and LEU3 residues, as well as the hydrogen bond interactions. These interactions play the role of a network at the entrance of the enzyme active site and prevent the penetration of water molecules into the PLA2 cavity. A high occupancy hydrogen bonding has been identified between SER23 of the protein and hydroxyl group of resveratrol. Furthermore, the estimation of binding free energy verified the binding affinity of resveratrol is thermodynamically sufficient to be stably bounded to PLA2. It also proved that the van der Waals interactions, particularly hydrophobic interactions, have the most significant role in PLA2-resveratrol binding and stability. Overall, our results provide useful information on the stepwise mechanism of the inhibition of PLA2 enzyme by resveratrol, as a target for improving the pharmacological applications.

The topology impact on hydrogen storage capacity of Sc-decorated ever-increasing porous graphene.

Hydrogen storage capacity of different scandium (Sc)-decorated topological porous graphene (PG) was examined through density functional theory calculations. PGs were selected considering odd and even topological symmetries. Our calculations demonstrate that the most preferable sites for adsorption of Sc are located on the center of carbon rings on the perimeter of pores of all sizes. This results in stronger polarization and hybridization perpendicular to the surface leading to enhanced binding. Thus, all PGs are suitable for hydrogen storage under surrounded settings. Furthermore, results showed that the adsorption energies of H2 molecules increased gradually with the size of pores. Analysis of charge density difference showed that the presence of Sc could play an efficient role for stronger adsorption of hydrogen molecules rather than increasing pore sizes. Furthermore, projected densities of states indicate that favorable systems for hydrogen storage are those that have higher overlap of individual states at Fermi level. Compared with H2 adsorption on pure graphene, injecting topological defect such as hexagon porous and decoration with a transition metal atom such as Sc can effectively create much more conductive states at Fermi energy. Eventually, Sc decoration leads to n-type doping of PGs that help in much easier transportation of charge carriers and desirable storage of H2 molecules.

Conformational switching of CO on graphene: the role of electric fields.

Molecular switches on solid surfaces raise an important issue in digital electronic devices. It has been frequently tried to design devices to perform basic functions at the molecular scale. In this paper, the Perdew-Burke-Ernzerhof (PBE) and PBE+van der Waals (vdW) were utilized in the framework of density functional theory (DFT) to model CO optimization on a graphene surface. Among the different external stimuli, electric fields serving as a useful probe were used to activate CO switching properties. The molecular conformation of CO, total dipole orientation, and charge transfer orientation were manipulated by turning an external electric field ON and OFF. The molecular conformation switched from a parallel orientation in a negative electric field towards a perpendicular orientation in a positive electric field. The total dipole moment switched from - 8.56 Debye (D) in an electric field of - 1.0 V/Å to 3.64 D in an electric field of + 1.0 V/Å. Charge transfer was seen to switch with the electric field switching. In the negative electric field, the charges were transferred from graphene to CO, while a reverse transfer occurred in the positive electric field. In addition, it was shown that CO desorption occurred in an electric field of greater than ± 1.0 V/Å. Eventually, the ON-to-OFF state transition was accompanied by switching between the positive and negative dipole moments, adsorption and desorption states, and positive and negative charge transfers when the external field direction and intensity were switched.

Hydrogen bonds in galactopyranoside and glucopyranoside: a density functional theory study.

Density functional theory calculations on two glycosides, namely, n-octyl-ß-D-glucopyranoside (C(8)O-ß-Glc) and n-octyl-ß-D-galactopyranoside (C(8)O-ß-Gal) were performed for geometry optimization at the B3LYP/6-31G level. Both molecules are stereoisomers (epimers) differing only in the orientation of the hydroxyl group at the C4 position. Thus it is interesting to investigate electronically the effect of the direction (axial/equatorial) of the hydroxyl group at the C4 position. The structure parameters of X-H∙∙∙Y intramolecular hydrogen bonds were analyzed, while the nature of these bonds and the intramolecular interactions were considered using the atoms in molecules (AIM) approach. Natural bond orbital analysis (NBO) was used to determine bond orders, charge and lone pair electrons on each atom and effective non-bonding interactions. We have also reported electronic energy and dipole moment in gas and solution phases. Further, the electronic properties such as the highest occupied molecular orbital, lowest unoccupied molecular orbital, ionization energy, electron affinity, electronic chemical potential, chemical hardness, softness and electrophilicity index, are also presented here for both C(8)O-ß-Glc and C(8)O-ß-Gal. These results show that, while C(8)O-ß-Glc possess- only one hydrogen bond, C(8)O-ß-Gal has two intramolecular hydrogen bonds, which further confirms the anomalous stability of the latter in self-assembly phenomena.

Study of Winsor I to Winsor II transitions in a lattice model.

Experiments show that with increasing temperature, microemulsion systems undergo Winsor transitions. The transitions occur from Winsor I (oil droplets in water media) to Winsor II (water droplets in oil media) via Winsor III (bicontinuous phase) with an increase in the temperature. In this paper, it has been shown, for the first time, how one can study the qualitative effects of temperature, head, tail, and oil chain lengths, on these transitions. Simple cubic lattice with excluded volume and periodic boundary conditions is used to mimic the box of the simulation as a bulk of solution. The simulations have been done using the standard traditional Metropolis algorithm in the canonical ensemble (N, V, T). Configurational bias Monte Carlo and reptation moves are used with an equal probability to relax the systems. A very simple interaction model, i.e., the repulsions of water (or heads of surfactants) with oil (or tails of surfactants), is used due to the main characteristic of oil-water mixtures or amphiphilic molecule that is the hydrophobicity. The interfacial tension between oil and water (gammaow) is related to the averaged total energy of the lattice. The model shows that the Winsor III has a minimum interfacial tension (gammaow) similar to experimental results. Changing the phase structure from Winsor III to Winsor I (or Winsor II), increases the interfacial tension which is in agreement with experiments. To relate interfacial tension with the interaction parameter, the simple theory of Bragg-Williams has been used. All of the results such as the effects of oil chain length, head and tail beads number are all similar to the experimental results. Using the Davies method for calculating hydrophilic-lypophilic Balance (HLB), similar to the experimental results, Winsor III phase is formed at HLB value nearly to 10.

Complexation between a macromolecule and an amphiphile by Monte Carlo technique.

Using a simple modified version of Larson's model, we studied the complexation between a macromolecule and an amphiphile in a dilute range of concentrations. The main characteristic of amphiphile molecules, that is, the hydrophobicity of the tails and hydrophilicity of the heads, is used to model the self-assembling process. Contrary to the molecular thermodynamics approaches, no prior shape was considered for the aggregates and the system was allowed to choose the most stable structure. For true ensemble averaging, without any synthetic results, configurational bias Monte Carlo and reptation moves are used to produce a Markov chain of configurations. From the results, it is found that the macromolecule causes the clusters of surfactants to be formed at a concentration much lower than the critical micelle concentration. Furthermore, the shape of the clusters tends to be more spherical, which is in line with theory and experiments. From the results, it is learned how a polymer can change the behavior of an amphiphilic molecule. All of the results are in good qualitative agreement with experimental and molecular thermodynamics results. Furthermore, the model predicts network formation between bound clusters at high concentrations of the surfactant.

Polymer-centered theory in comparison with surfactant-centered theory: a lattice Monte Carlo study.

Lattice Monte Carlo simulation is used to study micellization of both pure and surfactant-polymer mixture, with an emphasis on cluster size distribution. The amphiphile molecule is of the type H(4)T(4) where the H (head) monomers like the solvent molecules and the T (tail) monomers are solvophobic. To compare polymer- and surfactant-centered theories, copolymers with the structure of (H(4)T(4))(5) are used instead of homopolymers. Since above copolymer molecules have the structural unit like the structure of surfactant molecules, it is possible to study the competition between the binding of surfactant molecules to the copolymer and the micellization in a copolymer-free solution. Results show that, first, surfactant molecules bind to the copolymer molecules, and not until copolymers are saturated do micelles form. Furthermore, it is shown that for the model used in this paper, the polymer-centered theory is more appropriate than the surfactant-centered theory, and finally the cooperative nature of cluster formation on copolymers is also discussed.