ChemPhysChem

The cover picture shows a spatial pattern of morphology-dependent elastic response of supported membranes to gravitationally settled microscopic glass beads. Beads differentiate lipid monolayers (red regions) from fluid bilayers (yellow regions) by inducing a qualitatively different elastic response, characterized by nondeformed binding for lipid monolayers (uncoated beads) and a wetting or membrane wrapping for bilayers (membrane wrap enveloping the beads). These results presented by Parikh et al. on page 1678 indicate the importance of interleaflet coupling and bilayer fluidity in determining elastic response of supported membranes. They also suggest a new, simple technique to probe mechanical properties of substrate-supported fluid membranes. The art work was designed by James Evans.

The Nobel Prize in Physics 2005 falls in the realm of light (see picture; a) classical and b) quantum physics observation of light), and it is awarded to three scientists: Roy Glauber, John Hall and Theodor Hänsch. Roy Glauber succeeded in describing a general method for observing photons. He formulated a theory that gives optics a quantum-mechanical basis.

Smart structures: DNA tile based self-assembly provides an attractive route to create nanoarchitectures of programmable patterns (see figure). It also offers excellent scaffolds for directed self-assembly of nanometer-scale materials ranging from nanoparticles to proteins, with potential applications in constructing nanoelectronic/nanophotonic devices and protein/ligand nanoarrays.

Designer materials: The authors propose a design strategy for a quasicrystalline material composed of discrete molecular entities. The molecular quasicrystal (see figure), which is based on a standard Penrose tiling, is energetically stable and gives rise to a 10-fold symmetric diffraction pattern. The strategy may be further exploited to design molecular quasicrystals based on a range of different types of quasiperiodic arrays.

Dispersion of the Verdet constant is determined experimentally and theoretically for benzene, toluene, and p-xylene as pure liquids. Both theory and experiment show that the amplitude of the Verdet constant decreases when methyl groups are added to the benzene ring, due to the decreasing number density with the increasing size of the molecule. The picture shows the Verdet constants of benzene, toluene, and p-xylene as a function of wavelength and compares theory with experiment.

Size governs conformation: Adsorption of light alkanes to Mg and Ca cations exchanged in faujasite is studied by ab initio calculations and topologic analysis of electron density distribution functions. The conformation of the adsorbed alkanes depends on the cation, due to differences in bonding within the adsorption complexes controlled by the size of the exchanged cation.

Spherical hydrocarbons: Perhydrogenation of icosahedral fullerenes, C₈₀ and C₁₈₀, produces remarkably stable C₈₀H₈₀ and C₁₈₀H₁₈₀ fulleranes (see picture). The authors show that the controlled synthesis of the fulleranes opens up a new branch of chemistry through their functionalization.

Update required! The differences between dependable computed and experimental enthalpies of formation of larger hydrocarbons, growing systematically with size, are traced to an about 0.5 kJ mol⁻¹ error in the canonical best estimate of the enthalpy of formation of atomic carbon (see figure). The results obtained in this study call for an update of Δ_f(C_gas).

Sliding and rotation of cyclodextrins (CDs) along the polymer main chain of polyrotaxanes significantly increases the binding ability for and molecular recognition of guest molecules by multifaceted inclusion complexation (see schematic diagram). The cyclodextrin-conjugated polyrotaxanes were obtained by attaching β-CDs to an α-CD/poly(ethylene glycol) polyrotaxane backbone via peptide bonds.

On the move! A block-selective mobile polyrotaxane, synthesized in a one-pot sequence using anthracene (AN) capping agents, examines the movement of α-cyclodextrins (α-CDs) along the chains of a PEI-b-PEG-b-PEI copolymer (see figure). By labeling the α-CDs with fluorescein (FL) and monitoring the fluorescence resonance energy transfer, the intramolecular block-selective movement of α-CDs is characterized in response to pH variation.

Nature calls: The lotus leaf is held as a symbol of purity due to its ability to remain clean after emerging from murky ponds. Its superhydrophobic surface, which removes undesired particles in water droplets, is mimicked by a simple and inexpensive method involving self-generation of superhydrophobic films on copper substrates. The resulting films (water contact angle of 170±1.6°, see picture) show good self-cleaning properties.

Probing membranes: Nonspecific interactions between glass beads and supported lipid membranes act as a simple tool to characterize their local structure and mechanical properties. The beads differentiate monolayers (see figure B) from fluid bilayers (A) by inducing a qualitatively different elastic response, characterized by undeformed binding for monolayers and membrane wrapping for bilayers.

Energy breakdown: Photodissociation of mercaptan in the second absorption band has been studied by velocity map imaging. CH₃ fragment images (see figure) show a structure directly related to the vibrational population of the SH counterfragment. An inverted SH vibrational population has been measured suggesting a non-adiabatic fast photodissociation.

Bimetallic nanoparticles are successfully formed on the surface of TiO₂ (see figure) with Ag shell layer (n_L) control. Pt@Ag/TiO₂ exhibits unique photocatalytic performances for reduction of nitorobenzene at n_L≤1, however when n_L exceeds ≈1 they are similar to those of Ag/TiO₂. Furthermore at the critical value of n_L≈1, the surface properties of Pt@Ag nanoparticles change from Pt to Ag.

Simulations reveal order: Cell dynamic simulations probe the evolution of asymmetric and symmetric diblock copolymers under electric fields. The results suggest that the sphere phase is stable under weak electric fields, but a threshold electric intensity exists for the sphere-to-cylinder phase transition (see figure).

Nanoprobes: Single molecules, used as nanoprobes to detect elementary charge trajectories, provide a three dimensional single-electron displacement within a few seconds with an accuracy better than 0.006 nm (figure shows simplified 1-D triangulation of an electron). This significantly exceeds the accuracy with which the probe molecule itself can be localized in the same measuring time by single-molecule microscopy.

A selective interface: The specific modification of Cys102 with dT₁₈ provides a tether to the single-walled carbon nanotube (SWNT) sidewall, resulting in an orientation of yeast cytochrome c (YCC) that facilitates docking of redox enzymes and subsequent electron transfer (see figure). Oligonuclotide-modified YCC on a SWNT thus provides a selective interface between nanoscopic electronic devices and complex enzymes.

Single-molecule mechanics: The dynamic response of single polymer chains to an oscillatory applied force is reported. Viscoelastic properties can be extracted from both thermally and magnetically forced motion. The figure shows a schematic representation of the conformational changes of the poly(ethylene glycol) molecule and how these relate to the dependence of the internal friction on the applied force.

The importance of being negative: The primary photochemistry of the photoactive yellow protein (PYP), a photoreceptor for bacterial photomotility, relies on the trans–cis photoisomerization of its anionic p-coumaric acid chromophore. The authors investigate the influence of the protonation state of ester and ketone derivatives (see figure) of the PYP chromophore on the photoisomerization pathway in solution.

Model refinement: The excited-state chemistry of protochlorophyllide a, the precursor of chlorophyll a by means of picosecond time-resolved fluorescence (see figure) is discussed. A detailed spectral characterization of the emission significantly refines the kinetic model deduced from ultrafast absorption measurements in terms of a branching of the initial excited-state population into a reactive and a nonreactive path.

Covalent fixation in cluster fullerenes: FTIR, Raman and DFT analysis show that a strong covalent Sc₃N–C₇₈ cage interaction determines the vibrational structure of the Sc₃N@C₇₈ cluster fullerene. The authors show that an ionic interaction between separated Sc₃N⁶⁺ and C₇₈⁶⁻ ions does not account for the geometric and vibrational properties (see picture for geometric structure).

Hydrogen abstraction: The mechanisms of the reactions: CH₃C(O)CH₂F+OH/Cl→products (R1/R2) and CH₃C(O)CF₃+OH/Cl→products (R3/R4) (see figure) were studied over a wide temperature range (200–2000 K) using the dual-level direct dynamics method. The results indicate that the hydrogen abstraction predominantly takes place at the fluoromethyl position.

Electrolysis on an insulator (see figure, a) is conducted in molten CaCl₂ (1173 K) to produce a conductor (see figure, b). The process takes place following the predictions of a novel model, which is based on electrochemical reactions at the dynamic insulator|conductor|electrolyte three-phase interlines.

High complexant symmetry is an important factor that should be taken into account when enhancing the first hyperpolarizability β₀ of alkalides by chemical doping. Thus, β₀ values of Li⁺(NH₃)₄M⁻ (M=Li, Na, K) with the T_d-symmetric (NH₃)₄ complexant are more than four times larger than those of Li⁺(calix[4]pyrrole)M⁻ with the C_4v-symmetric complexant. The picture shows the 0.035 isosurfaces of the HOMO in Li⁺(NH₃)₄M⁻.

Revelations into the interstellar world: The Ar–HCO⁺ complex is under investigation to test and validate current computational methods for obtaining reliable pressure broadenings and shifts. Measurements are carried out at 77 K and are compared to close-coupling calculations performed on a potential energy surface (see figure) accounting for interactions extending from small to very large separations between the ion and the perturber.

Growing pains: Hydrogen abstraction reactions by methyl radicals on the zigzag and armchair edges of perylene (see picture) are studied by density functional theory to explore the various growth pathways. The results obtained with six different functionals are compared with those from ab initio methods. A cascade of reactions is possible that leads to the growth of a graphene sheet on a graphite surface.

Unexpected fragments: Solvolysis products of the anticancer drug cisplatin [Pt^II(NH₃)₂Cl₂] are investigated by mass spectrometry and density functional calculations. The picture shows collision-activated fragmentation of [Pt^II(NH₃)₂(CH₃OH)Cl]⁺ with loss of water. The corresponding reaction profile showing transition states (TS) and intermediates is depicted inside the mass spectrum.

Two typical cuts in the singlet and triplet potential energy surfaces of F+N₃ reactions around the region of the minimum energy crossing point (MECP) at the intersection seam and the singlet transition state are shown in the figure, which is used to clarify the reaction mechanism. The authors demonstrate that the adiabatic reaction leading to NF(a¹Δ) is the major channel, whereas the nonadiabatic reaction through the MECP—which leads to NF(X³Σ⁻)—is a minor channel.

Catalytic cycle: A large quantum mechanical (QM) cluster is used to investigate the role of Fe-BEA zeolites (see figure) in the reduction of nitrogen oxides. The use of a large cluster accounts for several diffusion pathways in the zeolites which lead to different activation barriers. The theoretical results for the full catalytic cycle (oxidation and reduction) compare favorably to experimental values.

Modeling methanol steam reforming: The chemical composition of PdZn(111) and Cu(111) in contact with water and hydrogen under pertinent reaction conditions (see figure; p_H2=partial pressure of hydrogen, γ=surface energy) are studied as models for catalysts of methanol steam reforming surface. Using thermodynamic analysis based on density functional calculations, the most favorable surface compositions for a given p_H2 are determined.

Lanthanide cations react with D₂O at room temperature in a helium bath at 0.35 Torr by O-atom transfer, OD transfer and D₂O addition. D₂O is not highly reactive towards lanthanide cations and is less reactive than aliphatic alcohols and phenol. The reactivities of all these molecules exhibit a periodic variation across the lanthanide series (see picture; k=rate coefficient, k_c=capture or collision rate coefficient).

Influential short range: In a Mott insulator of the organic radical 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA), the two-electron probability distribution (see figure) obtained by first-principles (multiple scattering) T matrix calculations, indicates clearly the formation of a “Coulomb hole”. This short-range electron correlation reduces significantly the on-site Coulomb energy.