ChemPhysChem

The cover picture shows biomimetic, zwitterionic polymer brushes grown in situ using atom-transfer radical polymerization from a macroinitiator attached to planar mica surfaces. The brushes are characterized by several different methods, including X-ray reflectometry and optical interferometry (lower right). Using a surface-force balance (SFB), the brushes were shown to be very robustly attached to the mica. This opens the way to versatile modification of mica surfaces, for application in many areas of research where the molecular smoothness of planar mica sheets is crucial, including studies of surface forces and lubrication using the SFB. Find out more in the Communication by Chen et al. on page 1303.

Instrumental advances: The current status and the possibility of new applications of Fourier transform infrared spectroscopy are presented. Systematic analyses of highly resolved infrared spectra of molecules (structures shown in figure) are discussed in relation to biophysical-chemical, astrophysical and atmospheric applications as well as to the necessary first steps towards detecting parity violation in chiral molecules by spectroscopy.

Enzyme mechanisms: Using ab initio methods and natural bond orbital analysis, negative hyperconjugation is shown to govern L-lactate oxidation chemistry and may help to determine its enzymatic dehydrogenation mechanism. The picture shows the negative hyperconjugation interaction between the lone pair on the oxygen atom and the σ*(CαHα) orbital.

Photochromic process: Organoboron-functionalized 1,2-dithienylcyclopentene shows photochromism. Its absorption spectra can be modulated by fluoride and mercuric ions. The maximum of the photostationary state shifts from 560 to 490 nm upon the addition of fluoride anions and to 450 nm upon the addition of mercuric cations. The modulation mechanism is investigated.

Binary ionic liquids are used to prepare two thermostable and highly conductive gel electrolytes (A and B). Quasi-solid-state dye-sensitized solar cells using these electrolytes show high power conversion efficiencies of up to 5.8 % at 20 °C and work well over a wide temperature range (20–80 °C), as shown by plots of photocurrent density versus voltage (see picture), and remain in the gel state even at 80 °C (inset).

Back and forth: Poly(4-vinylpyridine)-based inverse opal structures are fabricated. These systems are suitable for developing durable photonic paper systems and can serve as a platform to create printed “photonic circuits” (see picture, left), molecular gating systems, and chemosensors. The novel inverse opals (see scanning electron microscopy image, top right) can be reversibly collapsed (see SEM image, bottom right) and regenerated by modifying the pyridine moieties of the polymer.

Robust polymer brushes are grown from a planar mica surface (see figure) using atom-transfer radical polymerization. The brushes are characterized by X-ray photoelectron spectroscopy, X-ray reflectometry, atomic force microscopy, optical interferometry, and surface forces.

Microreactor: Linear dichroism and UV-thermal measurements of duplex DNAs in a continuous-flow microchannel system are presented and the results compared to those from batchwise labscale systems. The observed shift in thermal stability is induced by the conformational change under shear stress (see figure).

A rotor-spinning technique is developed for carrying out in situ studies of adsorption processes by solid-state NMR spectroscopy. The method is suitable for the study of adsorption at the liquid/solid interface, does not require any modification of the NMR instrumentation, and allows spectra to be recorded immediately from the start of the adsorption process (see picture).

Exchange mechanisms: Experiments and density functional calculations confirm that Li⁺ has a coordination number of four in DMSO and in water/DMSO mixtures, and both solvents coordinate equally strongly to the Li⁺ ion. Ligand exchange on [Li(DMSO)₄]⁺ proceeds via a limiting associative mechanism (see picture, ΔH and ΔE in kcal mol⁻¹; Li light yellow, O red, S yellow, C black, H white).

Up to speed: Electron transfer in self-assembled monolayers of complex redox-active oligophenylenevinylene molecular wires is examined by ultrafast cyclic voltammetry. If the redox center is buried within long hydrophobic diluents, counterion movement towards the redox entity becomes rate-limiting. This effect is examined for superexchange and electron-hopping mechanisms (see picture).

Dicationic complexes: Unimolecular reactivity of [Ca(thiourea)]²⁺ dications shows the formation of new doubly charged species, namely [Ca,H,N,C,S]²⁺ and [Ca(NH₃)]²⁺ (blue arrows in figure). This proves the existence of a Ca²⁺ dication solvated by only one molecule of NH₃ (or HNCS) in the gas phase. Monocations are also produced via several coulomb explosion processes (red arrows).

Side by side: Characterization of the charge-transfer complex hexakis(n-hexyloxy)triphenylene-2,4,7-trinitro-9-fluorenone (HAT6-TNF) by a variety of methods predicts a novel structure with TNF molecules between rather than within the discotic columns (see picture; HAT6: circles; TNF: schematic chemical formula).

Fine-tuning: The origin of the metal and ligand contributions to the emission of a Pr(III) complex (see figure) is investigated. Analysis of spectroscopic data reveals the excitation energy pathway, and the authors show that the emission is modified by molecular distortion, particularly by rotation of the phenyl groups in the ligand.

One red shift, the other blue: Halothane- and fluoroform-acetone complexes (see figure) both contain a CH⋅⋅⋅O bond; however, the halothane complex exhibits a small red shift of the CH stretching frequency upon complexation, and fluoroform shows a pronounced blue shift. This intriguing problem is investigated in detail theoretically.

From white to blue: A Prussian blue (Fe^II–Fe^III) film is layered on a WO₃/[Ru(bpy)₃]²⁺ hybrid film. Prussian white (Fe^II–Fe^II) is oxidized to Fe^II–Fe^III by electrochemically generated Ru^III in the bilayer film (see picture, left), as well as by photochemically generated Ru^III in a [Ru(bpy)₃]²⁺-sensitized oxidation reaction (right).

Magic angle: The transfer of coherence from neighboring nuclei, such as ¹³C or ¹H, to single- or double-quantum transitions of ¹⁴N nuclei enable ¹⁴N NMR spectra to be obtained. The experimental ¹⁴N double-quantum powder pattern (— in picture) of L-alanine is compared to the simulation (- - - -) to determine the quadrupolar coupling constant (C_Q) and the asymmetry parameter (η_Q) of ¹⁴N.

When little is good: Density functional theory and molecular dynamics (MD) studies show that dynamical variations in local geometry affect the chemical shielding anisotropy (CSA) relaxation of the carbonyl nucleus in proteins by less than 10 %. The picture shows autocorrelation functions for the NMR shielding parameters σ_zz of residues 8 and 9 in the 10 ns MD simulation of the protein calmodulin.

Higher excited states: A singlet–singlet annihilation mechanism was found to promote one chromophore into a higher excited state, thus allowing observation of an ultrashort-living intermediate charge-transfer (CT) state in the S_n–S₁ deactivation pathway (see picture).

Analysing phenol: The structural changes of phenol upon electronic excitation are quantified experimentally and theoretically. A Franck–Condon analysis of the fluorescence emission spectra confirms the local nature of the excitation.

Looking at the ground state: The cis and trans isomers of 4-styrylpyridine cannot interconvert in the S₀ ground state because of the high energy barrier associated with the thermally activated isomerization pathway (see picture; θ_C is the torsion angle around the central CC bond). The relative stabilities of the two isomers and the transition state were determined using ab initio methods. Car–Parrinello molecular dynamics simulations evidenced the highly flexible nature of the molecule.