Electrical conductance of conjugated oligomers at the single molecule level

We determine and compare, at the single molecule level and under identical environmental conditions, the electrical conductance of four conjugated phenylene oligomers comprising terminal sulfur anchor groups with simple structural and conjugation variations. The comparison shows that the conductance of oligo(phenylene vinylene) (OPV) is slightly higher than that of oligo(phenylene ethynylene) (OPE). We find that solubilizing side groups do neither prevent the molecules from being anchored within a break junction nor noticeably influence the conductance value.     

Kinetically Tunable Photostability of Fluorogen‐Activating Peptide–Fluorogen Complexes

Ease of genetic encoding, labeling specificity, and high photostability are the most sought after qualities in a fluorophore for biological detection. Furthermore, many applications can gain from the fluorogenic nature of fluoromodules and the ability to turn on the same fluoromodules multiple times. Fluorogen‐activating peptides (FAPs) bind noncovalently to their cognate fluorogens and exhibit enhanced photostability. Herein, the photostabilities of malachite green (MG)‐binding and thiazole‐orange‐binding FAPs are compared under limiting‐ and excess‐fluorogen conditions to establish distinct mechanisms for photostability that correspond to the dissociation rate of the FAP–fluorogen complex. FAPs with slow dissociation show evidence of dye encapsulation and protection from photo or environmental degradation and single‐step bleaching at the single molecule level, whereas those with rapid dissociation show repeated cycles of binding and enhanced photostability by exchange of bleached fluorogen with a new dye. A combination of generalizable selection pressure based on bleaching, flow cytometry, and site‐specific amino acid mutagenesis is used to obtain a modified FAP with enhanced photostability, due to rapid dissociation of the MG fluorogen. These studies shed light on the basic mechanisms by which noncovalent association can effect photostable labeling, and demonstrate novel reagents for photostable and intermittent labeling of biological targets.     

Directed evolution of epoxide hydrolase from A. radiobacter toward higher enantioselectivity by error-prone PCR and DNA shuffling

The enantioselectivity of epoxide hydrolase from Agrobacterium radiobacter (EchA) was improved using error-prone PCR and DNA shuffling. An agar plate assay was used to screen the mutant libraries for activity. Screening for improved enantioselectivity was subsequently done by spectrophotometric progress curve analysis of the conversion of para-nitrophenyl glycidyl ether (pNPGE). Kinetic resolutions showed that eight mutants were obtained with up to 13-fold improved enantioselectivity toward pNPGE and at least three other epoxides. The large enhancements in enantioselectivity toward epichlorohydrin and 1,2-epoxyhexane indicated that pNPGE acts as an epoxyalkane mimic. Active site mutations were found in all shuffled mutants, which can be explained by an interaction of the affected amino acid with the epoxide oxygen or the hydrophobic moiety of the substrate. Several mutations in the shuffled mutants had additive effects.     

Design and synthesis of a bimodal target-specific contrast agent for angiogenesis

[structure: see text] A bimodal target-specific contrast agent based on a cyclic peptide containing the target-specific NGR sequence, gadolinium(III) diethylenetriaminepentaacetic acid (Gd(III)DTPA), and Oregon Green 488 (OG488) suitable for both MR imaging and optical imaging of angiogenesis is developed. The synthetic strategy for this target-specific contrast agent exploits the use of highly efficient, chemoselective reactions, such as native chemical ligation, and gives a straightforward approach for double labeling of peptides in general.     

Synthesis of a soluble poly(fluorenone)

The synthesis and characterisation of a soluble poly(fluorenone) is presented, a polymer with high electron affinity with potential for use in plastic electronic devices as an n-type material.     

Functionalized 2,2'-bipyridines and 2,2':6',2' '-terpyridines via stille-type cross-coupling procedures

Stille-type cross-coupling procedures are utilized in order to prepare a variety of functionalized 2,2'-bipyridines and 2,2':6',2' '-terpyridines. Such N-heterocyclic compounds are of great interest as chelating ligands for transition-metal ions in the field of supramolecular chemistry. Various mono- and disubstitued 2,2'-bipyridines were synthesized in high yields and multigram scales using a modular design principle. The terpyridines may be functionalized in one step with different substituents at the outer pyridine rings and at the 4'-position of the centered ring, leading to multifunctionalized compounds. The initially obtained methyl ester and ethyl ester groups can be simply converted into bromomethyl and hydroxymethyl groups which allow further functionalization reactions.     

Nickel-oxido structure of a water-oxidizing catalyst film

The atomic structure of an electrodeposited Ni catalyst film is dominated by extensive di-μ-oxido bridging between Ni(III/IV) ions, as revealed by X-ray absorption spectroscopy. The structure is surprisingly similar to that of an analogous Co-based film and colloidal Mn-based catalysts. Structural requirements for water oxidation are discussed.     

Chiral Chalcogenyl-Substituted Naphthyl- and Acenaphthyl-Silanes and Their Cations

Cyclic silylated chalconium borates 13 [B(C₆F₅)₄] and 14 [B(C₆F₅)₄] with peri-acenaphthyl and peri-naphthyl skeletons were synthesized from unsymmetrically substituted silanes 3 , 4 , 6 , 7 , 9 and 10 using the standard Corey protocol (Chalcogen Ch=O, S, Se, Te). The configuration at the chalcogen atom is trigonal pyramidal for Ch=S, Se, Te, leading to the formation of cis- and trans-isomers in the case of phenylmethylsilyl cations. With the bulkier tert-butyl group at silicon, the configuration at the chalcogen atoms is predetermined to give almost exclusively the trans-configurated cyclic silylchalconium ions. The barriers for the inversion of the configuration at the sulfur atoms of sulfonium ions 13 c and 14 a are substantial (72–74 kJ mol⁻¹) as shown by variable temperature NMR spectroscopy. The neighboring group effect of the thiophenyl substituent is sufficiently strong to preserve chiral information at the silicon atom at low temperatures.     

Rank annihilation correction for the amendment of instrumental inconsistencies

The globalisation of the analysis of a series of individual measurements often results in more robust and reliable outcomes. However, instrumental drifts that can occur between individual measurements destroy the ideal data structure and thus the advantages. A method based on rank annihilation factor analysis (RAFA) is introduced for the correction of several types of instrumental inconsistencies. It can be applied to many series of bilinear datasets. Experimental examples discussed in this paper comprise the successful correction of non-uniform retention time drifts in chromatography due to temperature or pressure changes, wavelength shifts in IR spectroscopy in an industrial control situation, and background absorption shifts in UV-VIS spectroscopy applied to equilibrium investigations.