ChemPhysChem

The cover shows a composite image depicting the vapor deposition and self-assembly of an organic ligand and Cu metal atoms into a two-dimensional supramolecular architecture on a single crystal metal surface. The lower part of the image is a scanning tunneling microscopy topograph showing the highly ordered nanostructure with single molecule resolution. S. L. Tait, M. Ruben, et al. demonstrate on page 2495 that the ligand, 5,5'-bis(4-pyridyl)(2,2'-bipyrimidine), assembles with Cu adatoms to form the same robust, two-dimensional network on three surfaces, which differ significantly in lattice constant and symmetry.

Towards the goal of the alchemist: Tailoring of material properties—including the reversible transition from shiny metallic to transparent—can be achieved today by means of controlled hydrogen loading (see picture). Thin-film metal hydrides are used as indicators to visualize solid-state diffusion or as model systems in the search for novel light-weight hydrogen-storage materials.

Electric field and viscosity: In expectation of a large electrorheological (ER) effect, the authors study a side-on liquid crystalline polysiloxane compound and demonstrate that a larger ER effect occurs in the low-viscosity nematic phase of “side-on” liquid crystalline polymers (LCPs) as compared to “side-end” LCPs (see figure).

Pick and choose: Achieving acceptable selectivities from alcohols to desirable aldehydes or ketones remains a challenge. Bulk Au(111) pre-covered with atomic oxygen is highly selective for the partial oxidation of 1- and 2-propanol. Insights into intrinsic mechanistic details for high-surface-area gold-based catalysts (see scheme) are also presented.

Theoretical spectroscopy: The first wave-function based super-molecular computation of an exciton-coupled electronic CD spectrum for a merocyanine dimer is presented. Results are based on a fully DFT-D optimized structure and excitation energies are obtained with the perturbative SCS-CIS(D) approach. The theoretical data are in very good agreement with those from experiment.

The vibrational spectra of the yttrium-doped gold clusters Au₄Y, Au₅Y, and Au₆Y are recorded by using photodissociation techniques and assigned with the aid of DFT calculations. While neutral Au₆Y possesses a highly fluxional nonplanar C_2v structure, the anion Au₆Y⁻ is characterized by a planar cyclic D_6h form and can be regarded as a σ-aromatic six-membered cycle (see picture).

Multifunctional catalysts: Nickel–gold alloy nanoparticles (NPs) are synthesized in solution, by means of a fast butyllithium reduction method, and then used to prepare NiO-stabilized Au NP catalysts through a phase-transformation process (see scheme). The silica-supported catalysts exhibit a remarkable resistance to sintering and are highly active for CO oxidation.

Pucker up! A novel approach enabling direct measurements of biomolecular transfer across lipid bilayer membranes, using surface plasmon resonance, is demonstrated. The figure shows the transfer of sucrose (S) through melittin pores formed in surface-attached liposomes. By measuring the shift in refractive index in the volume enclosed by the liposomes, the sucrose transfer can be time-resolved and quantified.

The road not taken: Many paths diverge on the road to photodamage prevention in cytosine. Previous work has focused on determining a dominant relaxation mechanism. Ab initio excited-state molecular dynamics studies show that there is not a single dominant path, but rather many distinct paths involving different quenching mechanisms (see figure).

Reliable SERS: The fabrication of SERS-active metal structures with predictable and reliable signals is notoriously difficult. This problem is overcome by producing self-assembled nanoparticle–molecular monolayer plane junctions that generate remarkably reproducible SERS signals at the single-junction level (see figure).

Isostructural coordination architectures in two dimensions on different substrates require sufficient metal-organic bonding strength to overcome templating effects from the surface. The network structure in this STM image was grown on Cu(100) and was also produced on Ag(111) and Ag(100) surfaces, due to robust three-fold NCu coordination interactions stabilizing the network.

Taking charge: DFT and semiempirical calculations on the neutral and charged states of four dendrimeric tris(5-diarylamino-5-thienyl)-terminated starburst compounds (see picture) indicate that charging leads to quinoid-type structural changes, preferably on the dendrimers terminated by phenothiazinyl fragments. Charging also results in planarization of the molecular side arms.

More or less attracted: Bond dissociation energies of neutral and cationic HgX molecules range from less than 1 kcal mol⁻¹ to as much as 60 kcal mol⁻¹. Combining relativistic theory with coupled cluster methodology, bonding in 28 HgX molecules and their cations is investigated. The majority of HgX molecules are weakly covalently bonded.

Surface matters: The formation of hydrogen-bonded chains of diphenyl oxalic amide in the bulk is compared to surface-confined cases on Au(111) and Ag(111). By restriction to 2D, the originally infinitely long chains, connected via a double hydrogen bond motif (picture, left), turn into chiral chains of racemic mixtures of conformationally adapted molecules (picture, right).

The absorption spectrum of A–T DNA is computed for the first time in aqueous solution using realistic models. The agreement between experimental and calculated spectra is good (see figure), and the analysis allows the identification of all the electronic transitions hidden in the broad band. The lowest-energy dark excited state is assigned to a charge-transfer state between two stacked adenine bases.

A model Langmuir monolayer of anionic lipid dimyristoylphosphatidate interacting with Na⁺ (see picture) and Ca²⁺ ions is studied by molecular dynamics simulations. The effect of the cations on the monolayer properties is negligible in the solid phase but enhanced in the gas phase, where the higher degree of dehydration of sodium versus calcium ions is partly compensated by the formation of lipid–ion–lipid bridges.

Which one is it? 1-1′-bicyclohexylidene is an olefin with a disputed UV spectrum, which shows two strong absorption bands instead of one. Accurate CASPT2//CASSCF calculations put an end to this puzzle: both bands are due to the vibronic structure of a single very broad valence ππ* transition topped with a 3s-Rydberg state (see picture).

Molecular allsorts: The structural trends of three families (see picture) of polyhedral black phosphorus nanostructures are predicted by systematic quantum chemical studies. The tetrahedral cages are thermodynamically favored over the octahedral and icosahedral structures, although large octahedral structures become nearly as stable as the tetrahedral ones.

The presence of Zn influences the activation of small C₁–n-C₄ alkanes by the Brønsted acid site of zeolite by preliminary dissociative adsorption of the alkane on ZnO species, located in vicinity of acidic SiOHAl groups (see Scheme). This is manifested by the regioselectivity of H/D exchange for C₃ and n-C₄ and by changes in the kinetic parameters of the exchange for all C₁–n-C₄ alkanes.

Vibrational signatures: The structural characterization of protonated, phosphorylated (p) dipeptide [GpY+H]⁺ reveals vibrational bands that are characteristic of the phosphorylated residue and bands that are sensitive to the environment of the phosphate group, when compared with monopeptides [GpY+H]⁺ and [pS+H]⁺. The picture shows a comparison of the spectra of the peptides in the 900–1730 cm⁻¹ fingerprint region (G=glycine, S=serine, Y=tyrosine).

Quantum dots quantified: Cyclic voltammetric measurements are used for the first time to obtain the band edge positions and quasi-particle gaps of diffusing CdSe quantum dots as a function of their size. The results fit well to semi-empirical calculations. Thus cyclic voltammetry is a powerful tool to study the band structure parameters of quantum dots.

Microwave heating increases both the activation energy and the pre-exponential factor of the SAPO-11 synthesis compared to conventional heating. The increase in the pre-exponential factor dominates the activation energy, hence microwaves enhance this synthesis. The graph shows the Arrhenius plot for the crystallization rate of SAPO-11 synthesis under microwave and conventional heating.

Matters of state: 2,5-Dihydroxybenzoic acid (see picture) is used as a model in the study of hydrogen or proton dislocations in intramolecular hydrogen-bonded systems in the ground, electronically excited and ionic states. By applying various partially new techniques of combined IR/UV spectroscopy in molecular-beam experiments, the best quantification is obtained from the CO stretching mode in all electronic states.

Let there be more light! TPA-substituted anthracene derivatives result in stable organic light-emitting diodes. The more balanceable hole and electron transport in TPA-substituted anthracene, together with the easier hole-injection and hole-trapping mechanism, leads to high electroluminescence efficiency (see picture; ETL: electron transport layer; HTL: hole transport layer).

A crucial role is played by the electrolyte in the electrochemical response of nanostructured electrodes in lithium batteries, according to new X-ray photoelectron spectroscopy results (see spectra). The presence of vinylene carbonate as additive inhibits electrolyte decomposition at the surface of Sb nanoparticle electrodes, thus leading to an enhanced reversibility of the electrochemical reaction and an improved capacity retention on cycling.

Three in a row: The ionization of small cationic helium clusters is analyzed by investigating the equilibrated cluster structural energy obtained after their optimization in the presence of two competing cores (see picture). The results show that upon equilibration of the ionized clusters, the trimeric ionic core should be the more abundant residual species.