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A study computed the adsorption and dissociation of thiophene on the MoP(001), [gamma]-Mo2N(100), and Ni2P(001) surfaces by using the density functional theory method. Results reveal that thiophene adsorbs dissociatively on MoP(001), while nondissociatively on [gamma]-Mo2N(100) and Ni2(001).

The complexation mechanism of several flavonoids with iron is examined by using the first-principles electronic structure calculations based on density functional theory (DFT). Optical absorption spectra have served as signatures for identifying various complexes and for the iron-quercetin complexes, the redshift of the first absorbance peak is described by narrowing the optical gap of quercetin because of Fe(d)-O(p) orbital hybridization.

Conclusive evidence is provided for the existence of an intact bilayer on Cu(110) consisting of mainly of H-down bilayer at a temperature less than 160 K. This result show that considering density functional theory energy alone is dangerous in determining water structures in experiment and much attention has to be paid to the comparisons of different factors, such as work function change, kinetic barriers and spectroscopic characters.

We present density functional theory (DFT) results on the structural, electronic, and optical properties of Cu−flavonoid complexes for molar ratios 1:1, 1:2, and 1:3. We find that the preferred chelating site is close to the 4-oxo group and in particular the 3−4 site followed by the 3′−4′ dihydroxy group in ring B. For the Cu−quercetin complexes, the large bathochromic shift of the first absorbance band upon complexation, which is in good agreement with experimental UV−vis spectra, results from the reduction of the electronic energy gap. The HOMO states for these complexes are characterized by π-bonding between the Cu d orbitals and the C, O p orbitals except for the case of 1:1 complex (spin minority), which corresponds to σ-type bonds. The LUMO states are attributed to the contribution of Cu pzorbitals. Consequently, the main features of the first optical absorption maxima are essentially due to π → π* transitions, while the 1:1 complex exhibits also σ → π* transitions. Our optical absorption calculations based on time-dependent DFT demonstrate that the 1:1 complex is responsible for the spectroscopic features at pH 5.5, whereas the 1:2 complex is mainly the one responsible for the characteristic spectra at pH 7.4. These theoretical predictions explain in detail the behavior of the optical absorption for the Cu−flavonoid complexes observed in experiments and are thus useful in elucidating the complexation mechanism and antioxidant activity of flavonoids. [ABSTRACT FROM AUTHOR]

We investigate the electronic coupling between a TiO 2nanowire and a natural dye sensitizer, using state-of-the-art time-dependent first-principles calculations. The model dye molecule, cyanidin, is deprotonated into the quinonoidal form upon adsorption on the wire surface. This results in its highest occupied molecular orbital (HOMO) being located in the middle of the TiO 2bandgap and its lowest unoccupied molecular orbital (LUMO) being close to the TiO 2conduction band minimum (CBM), leading to greatly enhanced visible light absorption with two prominent peaks at 480 and 650 nm. We find that excited electrons are injected into the TiO 2conduction band within a time scale of 50 fs with negligible electron−hole recombination and energy dissipation, even though the dye LUMO is located 0.1−0.3 eV lower than the CBM of the TiO 2nanowire. [ABSTRACT FROM AUTHOR]

Manipulation of shape anisotropy of building blocks is creating diverse and complex assemblies, in particular in the field of colloid science. Self-assembly of block copolymers has created a great number of nano-objects and/or nanostructures. Herein we report the design and synthesis of a series of block copolymers with varying shape anisotropy using polyhedral oligomeric silsesquioxane (POSS) cluster and linear poly(ethylene oxide)s (PEO) with different molecular weights. The POSS-b-PEO block copolymers were prepared by means of first gathering one to four POSS clusters using short linear or dendritic linkers and then covalently linking them with linear PEO blocks. In this way, the shape anisotropy of the POSS-b-PEO block copolymers is varied widely. We found that the PEO block crystallization in a selected solvent drives the block copolymers to self-assemble into large nanothick sheets. We characterized the sheets using TEM and XRD and found a structure of one PEO crystalline layer sandwiched by two POSS layers. Then, we measured the melting, recrystallization, and remelting processes of the sheets using DSC and observed an effect of varying shape anisotropy on the melting and recrystallization temperatures of the PEO and POSS layer and the crystallinity of the crystalline PEO layer. We proposed ideal molecular structures to depict PEO crystalline structure and POSS packing in the sheets and then semiquantitatively discussed the effect of the varying shape anisotropy on the sheet formation from solution and on PEO melting and crystallization in the nanoconfined space. [ABSTRACT FROM AUTHOR]