Reversibility of pH-induced dewetting of poly(vinyl pyridine) thin films on silicon oxide substrate

Thin PVP films deposited on a silicon oxide surface have been found to form a dewetting pattern when treated with basic solutions (pH > or = 10). We studied the dependence of pattern morphology on the polymer's molecular weight and thickness of the polymer layer, and observed the formation of three distinctive structures. The structure formed by large drops of polymer is characteristic of a polymer with low molecular weight and the thinnest polymer layer, whereas other samples form holes or a weblike pattern upon dewetting. These experiments have demonstrated for the first time the reversibility of the dewetting process in a liquid environment. The polymer layer has revealed reversible behavior toward flat film when exposed to a pH 4 buffer solution. More complex structures can be obtained by consecutive treatments with acidic (pH 4) and basic (pH 10) solutions. We used atomic force microscopy (AFM) to study both the morphology and elastic properties of polymers in media with different acidity, in order to determine the mechanism behind the dewetting process.     

Anisotropic pseudorotation of the photoexcited triplet state of fullerene C60 in molecular glasses studied by pulse EPR

Spin-polarized echo-detected electron paramagnetic resonance (EPR) spectra and the transversal relaxation rate T2(-1) of the photoexcited triplet state of fullerene C60 molecules were studied in o-terphenyl, 1-methylnaphthalene, and decalin glassy matrices. The model is composed of a fast (correlation time approximately 10(-12) s) pseudorotation of (3)C60 in a local anisotropic potential created by interaction of the fullerene molecule with the surrounding matrix molecules. In simulations, this potential is assumed to be axially symmetric around some axis of a preferable orientation in a matrix cage. The fitted value of the potential was found to depend on the type of glass and to decrease monotonically with a temperature increase. A sharp increase of the T2(-1) temperature dependence was found near 240 K in glassy o-terphenyl and near 100 K in glassy 1-methylnaphthalene and decalin. This increase probably is related to the influence on the pseudorotation of the onset of large-amplitude vibrational molecular motions (dynamical transition in glass) that are known for glasses from neutron scattering and molecular dynamics studies. The obtained results suggest that molecular and spin dynamics of the triplet fullerene are extremely sensitive to molecular motions in glassy materials.     

Hybrid group 15(E15)–group 14(E14) element cationic pyramidal structures E15[E144(SiR3)4]+: A DFT study

Hybrid cationic pyramidanes {E¹⁵[E¹⁴₄R₄]}⁺ (E¹⁵ = P–Bi; E¹⁴ = C–Ge, R = H, SiMe₃) have been studied by the DFT calculations, and their structures, electronic properties and bonding nature are discussed. Square-pyramidal geometry in the real neutral compounds {E¹⁵[E¹⁴₄(SiMe₃)₄]}⁺[AlCl₄]^? is preserved.     

Hypercoordinated carbon in C-doped boron fullerenes: a quantum chemical study

The structures and stability of C-doped boron fullerenes with the three-dimensional arrangement of non-classical pentacoordinated quasi-flat carbon centers were studied using the density functional theory (DFT) B3LYP/6-311+G(d,p) method. The doping with carbon atoms in apical positions above the five-membered rings stabilizes the spherical boron fullerene forms due to multicenter interactions of p_z-orbitals of the carbons and adjacent boron atoms. Increasing in the size of the fullerene cluster is accompanied by change in the bonding pattern and by flattening of the hypercoordinated carbon centers. Endohedral metal atoms significantly affect on the structure and stability of the fullerene systems with hypercoordinated carbon centers.     

Germanium,carbon‐germanium,and silicon‐germanium triangulenes

A series of germanium‐containing triangular molecules have been studied by density functional theory (DFT) calculations. The triangulene topology of the compounds provides for their high‐spin ground states and strong sign alternation of spin density and atomic charge distributions. High values of the exchange coupling constants witness ferromagnetic ordering of electronic structures of all studied triangulenes. The compounds bearing more electronegative atoms in a‐positions of the triangular networks possess higher aromatic character and stronger ferromagnetic ordering. © 2015 Wiley Periodicals, Inc.     

Enantioselective Guest Effect on the Spin State of a Chiral Coordination Framework

The diversity of spin crossover (SCO) complexes that, on the one hand, display variable temperature, abruptness and hysteresis of the spin transition, and on the other hand, are spin‐sensitive to the various guest molecules, makes these materials unique for the detection of different organic and inorganic compounds. We have developed a homochiral SCO coordination polymer with a spin transition sensitive to the inclusion of the guest 2‐butanol, and these solvates with (R)‐ and (S)‐alcohols demonstrate different SCO behaviours depending on the chirality of the organic analyte. A stereoselective response to the guest inclusion is detected as a shift in the temperature of the transition both from dia‐ to para‐ and from para‐ to diamagnetic states in heating and cooling modes respectively. Furthermore, the Mössbauer spectroscopy directly visualizes how the metallic centres in a chiral coordination framework differently sense the interaction with guests of different chiralities.     

Assessing the Viability of Extended Nonmetal Atom Chains in MnF4n+2 (M=S and Se)

Theoretical investigations to evaluate the viability of extended nonmetal atom chains on the basis of molecular models with the general formula M_nF_4n+2 (M=S and Se) and corresponding solid‐state systems exhibiting direct S? S or Se? Se bonding were performed. The proposed high‐symmetry molecules were found to be minima on the potential energy surface for all S_nF_4n+2 systems studied (n=2–9) and for selenium analogues up to n=6. Phonon calculations of periodic structures confirmed the dynamic stability of the ‐(SF₄–SF₄)_∞‐ chain, whereas the analogous ‐(SeF₄–SeF₄)_∞‐ chain was found to have a number of imaginary phonon frequencies. Chemical bonding analysis of the dynamically stable ‐(SF₄–SF₄)_∞‐ structure revealed a multicenter character of the S? S and S? F bonds. A novel definition and abbreviation (ENAC) are proposed by analogy with extended metal atom chain (EMAC) complexes.     

On Generators of the Tame Automorphism Group of Free Metabelian Lie Algebras

We prove that the tame automorphism group TAut(M _n ) of a free metabelian Lie algebra M _n in n variables over a field k is generated by a single nonlinear automorphism modulo all linear automorphisms if n ≥ 4 except the case when n = 4 and char(k) ≠ 3. If char(k) = 3, then TAut(M ₄) is generated by two automorphisms modulo all linear automorphisms. We also prove that the tame automorphism group TAut(M ₃) cannot be generated by any finite number of automorphisms modulo all linear automorphisms.     

Commensurate registry and chemisorption at a hetero-organic interface

We present evidence for a partly chemisorptive bonding between single monolayers of copper-II-phthalocyanine (CuPc) and 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) that are stacked on Ag(111). A commensurate registry between the two molecular layers and the substrate, i.e., a common crystallographic lattice for CuPc and PTCDA films as well as for the Ag(111) surface, indicates that the growth of the upper layer is dominated by the structure of the lower. Photoemission spectroscopy clearly reveals a gradual filling of the lowest unoccupied molecular orbital of PTCDA due to CuPc adsorption, which proves the chemisorptive character.     

Mini‐beam collimator enables microcrystallography experiments on standard beamlines

The high‐brilliance X‐ray beams from undulator sources at third‐generation synchrotron facilities are excellent tools for solving crystal structures of important and challenging biological macromolecules and complexes. However, many of the most important structural targets yield crystals that are too small or too inhomogeneous for a `standard' beam from an undulator source, ～25–50 µm (FWHM) in the vertical and 50–100 µm in the horizontal direction. Although many synchrotron facilities have microfocus beamlines for other applications, this capability for macromolecular crystallography was pioneered at ID‐13 of the ESRF. The National Institute of General Medical Sciences and National Cancer Institute Collaborative Access Team (GM/CA‐CAT) dual canted undulator beamlines at the APS deliver high‐intensity focused beams with a minimum focal size of 20 µm × 65 µm at the sample position. To meet growing user demand for beams to study samples of 10 µm or less, a `mini‐beam' apparatus was developed that conditions the focused beam to either 5 µm or 10 µm (FWHM) diameter with high intensity. The mini‐beam has a symmetric Gaussian shape in both the horizontal and vertical directions, and reduces the vertical divergence of the focused beam by 25%. Significant reduction in background was achieved by implementation of both forward‐ and back‐scatter guards. A unique triple‐collimator apparatus, which has been in routine use on both undulator beamlines since February 2008, allows users to rapidly interchange the focused beam and conditioned mini‐beams of two sizes with a single mouse click. The device and the beam are stable over many hours of routine operation. The rapid‐exchange capability has greatly facilitated sample screening and resulted in several structures that could not have been obtained with the larger focused beam.