Molecular origin of structural defects in the zinc phthalocyanine film.

Controlling the growth of thin phthalocyanine films is a long-term challenge for the science of applied nanomaterials. So, this contribution deals with films of unsubstituted zinc phthalocyanine (ZnPc) and seeks to acquire structural information that is unavailable via physical experiments, thus, finding out how the film morphology can be seriously improved. A model of the vapor-deposited film has been created using the molecular dynamics method. Specifically, the ZnPc molecules are dosed into the simulation box under normal conditions, reproducing key features of the real film, such as the trimolecular wetting layer and the island-like three-dimensional (3D) phase that is structured like the α-polymorph; then all film fragments are characterized via their radial distribution functions and mean-squared displacements. The simulation model indicates that the 3D phase starts to develop smoothly through multimolecular cofacial stacking but finally becomes fragmental because the wetting layer is too meager to be a good platform for regular film growth. Accordingly, the film morphology may be improved if the wetting layer is thickened via restraining the vertical development of the 3D phase. Following this idea, uniform ZnPc films impaired by neither grain boundaries nor coarser defects were deposited from solutions and visualized at the nanometer scale.

Liquid crystalline poly(propylene imine) dendrimer-based iron oxide nanoparticles.

Poly(propylene imine) dendromesogens (generations from 1 to 4) have been utilized for the synthesis and stabilization of ferrimagnetic Fe2O3 nanoparticles. Reduction of Fe(iii) with further oxidation of Fe(ii) results in the formation of highly soluble nanocomposites of iron oxides in a dendrimer, which are stable under a wide range of temperatures. The magnetic iron oxide nanoparticles were investigated by MALDI-ToF MS spectrometry and elemental analysis. To establish the type of mesophase, X-ray measurements were performed at different temperatures. The calculations of X-ray results demonstrate a hexagonal columnar packing of the molecules in the mesophase. Observation of the samples by TEM gives information about the size of the compounds as well as direct evidence of the implementation of Fe2O3 nanoparticles into dendrimers. Physical parameters of the magnetic nanoparticles (magnetic moment, effective magnetic anisotropy) have been determined from analyses of the EPR data.

Amine-assisted solubilization of unsubstituted zinc phthalocyanine for film deposition purposes.

Typical zinc phthalocyanines (ZnPc) exhibit poor solubility in common solvents and, hence, are processed into thin films mostly from the vapor phase. The present work discloses how these limitations can be effectively overcome. Specifically, highly concentrated molecular solutions of unsubstituted ZnPc are prepared by combining a weakly structured ZnPc polymorph with binary liquid systems composed of a π-accepting solvent and a simple nitrogenous base, such as ammonia or tertiary aliphatic amine. The amine-assisted solubilization of ZnPc is rationalized by quantitative analysis of optical spectra and electrostatic potential maps of the dye molecule. A volatile aminoalcohol is proposed in order to rationally modify the habit of ZnPc crystallites and concurrently to produce uniform deposition of the crystallites by drop-casting the dye solutions onto a glass substrate. Finally, a versatile algorithm for wet-processed ZnPc films is declared.

[Effect of buried bound water in protein-ligand association processes].

The role of water molecules on the protein-ligand interface during macromolecular association has been determined. The free energy of association of insulin has been calculated by the molecular mechanics method using the continuum Poisson-Boltzman models. The previously developed scheme of the decomposition of association free energy onto contributions from individual interactions has been used to calculate intermolecular interactions, the solvation free energy, and the entropies of the process of macromolecular association. An analysis of the calculated oscillation spectra indicated that the presence of water molecules on the protein-protein interface promotes an increase in the contribution of vibration entropy to the free energy of association due to the enhancement of the flexibility of the complex. It was shown that water molecules involved in the formation of protein-water-ligand hydrogen bond change the balance of forces in the system.

Hydrogen Abstraction Acetylene Addition and Diels-Alder Mechanisms of PAH Formation: A Detailed Study Using First Principles Calculations.

Extensive ab initio Gaussian-3-type calculations of potential energy surfaces (PES), which are expected to be accurate within 1-2 kcal/mol, combined with statistical theory calculations of reaction rate constants have been applied to study various possible pathways in the hydrogen abstraction acetylene addition (HACA) mechanism of naphthalene and acenaphthalene formation as well as Diels-Alder pathways to acenaphthalene, phenanthrene, and pyrene. The barrier heights; reaction energies; and molecular parameters of the reactants, products, intermediates, and transition states have been generated for all types of reactions involved in the HACA and Diels-Alder mechanisms, including H abstraction from various aromatic intermediates, acetylene addition to radical sites, ring closures leading to the formation of additional aromatic rings, elimination of hydrogen atoms, H disproportionation, C2H2 cycloaddition, and H2 loss. The reactions participating in various HACA sequences (e.g., Frenklach's, alternative Frenklach's, and Bittner and Howard's routes) are demonstrated to have relatively low barriers and high rate constants under combustion conditions. A comparison of the significance of different HACA mechanisms in PAH growth can be made in the future using PES and molecular parameters obtained in the present work. The results show that the Diels-Alder mechanism cannot compete with the HACA pathways even at high combustion temperatures, because of high barriers and consequently low reaction rate constants. The calculated energetic parameters and rate constants have been compared with experimental and theoretical data available in the literature.