Chemistry - A European Journal

The cross-testing of the CytC intrinsic ET mechanisms at the Au/SAM junctions (hydroxy-terminated n-alkanethiol self-assembled monolayers) in the freely diffusing regime revealed a gradual turnover from the adiabatic to nonadiabatic mechanism through the intermediate regime. In their Full Paper on page 7041 ff., R. van Eldik, D. E. Khoshtariya et al. describe their investigations involving variation of the SAM thickness (n=2, 3, 4, 6, 11, with n=4 found to be a turnover point), the relative solution viscosity, and the hydrostatic pressure (up to 150 MPa).

A single electron changes everything! Many fundamental concepts of organic chemistry, such as symmetry, aromaticity, or bonding, exhibit interesting variations in radical cations formed by one-electron oxidation of hydrocarbons. This paper reviews the role of state symmetry correlations, Jahn–Teller distortions, delocalization, and fractional bonding for the reaction pathways of these interesting reactive intermediates.

A new one-dimensional ferrimagnetic arrangement of Mn^III ions and the tetracyano-p-quinodimethane (TCNQ) radical has been obtained in [Mn(5-TMAMsaltmen)(TCNQ)](ClO₄)₂ (see picture) (5-TMAMsaltmen=N,N′-(1,1,2,2-tetramethylethylene) bis(5-trimethylammoniomethylsalicylideneiminato)), which exhibits single-chain magnet behavior as shown by the detailed analysis of its thermodynamic and dynamic properties.

Compare and understand: Combined kinetic and thermodynamic studies of intact (unbound) cytochrome c freely diffusing to gold electrodes modified by hydroxyl-terminated alkanethiol self-assembled monolayers (SAMs; see figure) revealed novel intrinsic links between local/global structural and functional characteristics and between dynamic effects of high pressure and solution viscosity, and demonstrated changeover of the charge-transfer mechanism with the variation of charge-transfer distance (SAM thickness).

Anchored at the entrance of the active site, l- and d-histidine residues activate carbonic anhydrases (isoforms hCA I, II, IV, VA, VII, and XIV) to different extents. X-ray crystallography showed that these activators participated in extended networks of hydrogen bonds with amino acid residues/water molecules present in the cavity, which explains their different efficacy and interaction patterns with various isozymes (see picture).

Powerful quantum chemical calculations were combined with reaction rate measurements to elucidate the catalytic activity of Ti-, Zr- and Sn-beta zeolites for Lewis acid catalysed redox reactions. The difference in reactivity of the three materials is explained in terms of the molecular orbital distribution of the active sites and the adsorbed reactants.

Anions for tennis! Inorganic tennis balls (ITB) have been studied both in solution and the solid state. The cavity in an ITB is flexible and encapsulates various anions selectively. An example is shown here.

Staying power: The persilylated phosphoranyl radicals 1–6 represent the first persistent noncyclic phosphoranyl radicals. EPR detection and kinetic studies of these new, very persistent (t_1/2 = 45 min at room temperature) phosphoranyl radicals are presented. (EPR=electron paramagnetic resonance.)

One-pot cubes: The assembly of targeted cubane-like metal complexes (for example, see figure) from simple building blocks can be achieved in one-pot reaction systems.

Global communication between the decks in the [2.2]paracyclophane unit is elucidated by comparison of the electronic absorption spectra of a series of compounds (see scheme) described herein.

Structure–activity relationships in rhamnolipids: The first synthesis of a glycolipid library by hydrophobically assisted switching phase (HASP) synthesis is presented. The obtained rhamnolipids (RL) are potent stimulators of the innate immune system, acting through secretion of tumor necrosis factor α (TNFα), with high specificity regarding structural variations in the lipid part.

Battery powered: Measurement of the potential difference between two microreference electrodes placed in real Li-ion batteries allowed determination of the concentration gradient in the electrolyte. The diffusion coefficient of Li⁺ ions in the electrolyte and the diffusion overpotential from the electrolyte were also obtained (see scheme).

One ligand, two imaging probes: The inclusion of two picolinate groups on a triazacyclononane framework affords a new ligand leading to a mono-aquo gadolinium complex with favourable electronic relaxation properties for magnetic resonance imaging applications and to a terbium complex with high luminescence quantum yield (see scheme).

Optimizing photorefractive performance is expected to be facilitated by molecular design and host-matrix engineering. This study has established for the first time the strategic role of the polarity of the surrounding medium ε_r in determining photorefractive molecular performance (see picture). Complementary experimental and computational tools have been used to gain new insights into the photorefractive molecular properties of push–pull dipolar chromophores in terms of structural and media-polarity effects.

Accelerated electron transfer: The heterogeneous electron-transfer rate constant k_s of Hb/C₆₀-MWCNT (MWCNT=multiple-walled carbon nanotube) was determined to be 0.39 s⁻¹ (a), which is more than one order of magnitude greater than that of Hb/MWCNT (0.03 s⁻¹) (c).

Activation with zeolites: Zeolite Y was used to bring a copper–histidine complex into an activated, entactic form (see figure). A combination of different spectroscopic characterization techniques (XAS, UV/Vis/NIR, ESR, Raman, and IR spectroscopy) was used to identify the different copper–histidine species.

Take four! A broad range of differently substituted dihydropyrimidines and thiazines can be efficiently prepared using a four-component reaction between phosphonates, nitriles, aldehydes, and iso(thio)cyanates (see scheme). The scope and limitations of this multicomponent reaction are fully described.

Pd catalysis: In the presence of a catalytic amount of [Pd(MeCN)₄](BF₄)₂, syn- and anti-β-hydroxyenones undergo nonoxidative 6-endo-trig ring closure to form highly substituted tetrahydropyranones (see scheme). This palladium-mediated reaction is under kinetic control and operates with a high level of diastereocontrol.

Cells adhere to boronate-containing copolymer brushes: Copolymers end-grafted onto solids enable sugar-specific adhesion and facile detachment of carbohydrate particles and cells (see picture). The grafted materials can be used for reversible immobilization and separation of cells.

Electron delocalization indexes derived from electron-pair densities have been demonstrated to be useful indicators of electron resonance in amides. A linear relation was found between the rotational barrier (ΔG_rot) for the amides and the delocalization index (δ_ON) between the nitrogen and oxygen atoms (see figure).

Organometallic cyclizations: A novel one-pot synthetic sequence that transforms three/four simple starting materials into highly substituted and diastereomerically pure cyclopentanols or 1,4-cyclohexanediols has been developed (see scheme). These multicomponent cyclization reactions represent an efficient synthetic tool to introduce molecular complexity.

Synthetic quinoproteins: Ubiquinone-0 and menaquinone-0 were bound through a thioether linkage to N-acetyl cysteine methyl ester and a de novo-designed synthetic four-helix bundle protein, and were characterized in detail (see picture). The redox potentials of the quinones in aqueous solution indicate a minor effect by the sulfur linkage but a substantial shift of 200–300 mV by the protein. Redox-induced Fourier transform infrared (FTIR) difference spectroscopy shows special features of the sulfur-substituted quinones.

Stereoselective preparation of cyclopentafullerene derivatives: Novel fullerene products fused with full-carbon five-membered rings were obtained from reactions between C₆₀ and tertiary amines in either the absence or the presence of an aldehyde (see scheme). Reaction mechanisms involving unusual carbonnitrogen bond breaking in tertiary amines were proposed. ODCB=o-dichlorobenzene.

Nitrogen makes all the difference! Novel NIR fluorescent, conformationally restricted aza-BODIPY dyes, such as that depicted here, were prepared by an efficient process. These dyes possess intense absorption, strong fluorescence, and high chemical and photostability.