Strong oscillations in molecular valence photoemission intensities

Photoemission from the two outermost ionizations [highest occupied molecular orbitals (HOMO and HOMO-1)] of Mg(eta(5)-C(5)H(5))(2) has been studied with synchrotron radiation in the gas phase. Strong oscillations in the HOMO-1/HOMO ratio, qualitatively similar to those well-known for fullerenes, are found. Excellent agreement with the experimental ratio is provided by accurate cross section calculations both at the density-functional theory and time-dependent density-functional theory level, indicating that a many electron response has a minor role for this effect. A comparison with the calculated values for other metal sandwich compounds indicate that the presence of oscillations is a widespread phenomenon, and a potential source of interesting information on the structural and electronic properties of the target molecule.     

Effect of size and protein environment on electrochemical properties of gold nanoparticles on carbon electrodes

We studied the electrochemical properties of gold nanoparticles (GNPs) and their complexes with proteins using square-wave voltammetry. Effect of the nanoparticle size and detection procedure was explored upon the oxidation of GNPs on a glassy carbon electrode (GCE). For pre-characterized GNPs of 13, 35 and 78 nm diameter, the oxidation peak potential was + 0.98, + 1.03 and + 1.06 V vs. Ag/AgCl, respectively. The conjugation of GNPs with four different proteins was verified by UV–Vis spectroscopy and atomic force microscopy indicated the formation of protein shells around GNPs. This process hampered the oxidation of GNPs on bare GCE causing pronounced decrease in the current response by an average factor of 72. GCE modification with carbon nanotubes weakly influenced the sensitivity of GNP detection but resulted in a 14.5-fold signal increase averaged for all GNP–protein complexes. The acidic dissolution and electrodeposition of GNPs or their complexes adsorbed on GCE allowed superior signal amplification directly proportional to nanoparticle size. The results are useful for the optimization of voltammetric analysis of GNP–protein complexes and can be extended to the characterization of other metal nanostructures and their complexes with biological components.     

Metallic nanostructures in a polymer matrix and substrate fabrication and structural characterization

Metal nanostructures are of considerable interest in the field of plasmonics and metamaterials and could have a wider impact if they are successfully embedded in a stable, inert and flexible polymer matrix. Fabrication of such structures is challenging for a variety of reasons including thermal stability, material compatibility with processing steps and general handling of material. In this work we have demonstrated the fabrication of metal nanostructures and embedded them in a polymer. Furthermore, these structures were fabricated on a flexible polymer membrane and detached from a carrier substrate. Characterization of these structures was performed with SEM, TEM and EDS.     

An efficient synthesis of nitrogen-containing heterocycles via a tandem carbenoid N-H insertion/ring-closing metathesis sequence

A series of five- to eight-membered nitrogen-containing heterocycles were prepared via a general and efficient one-pot, two-component sequence featuring rhodium-catalyzed insertion of a vinyl-substituted α-diazocarbonyls into the N-H bond of a series of tert-butoxycarbonyl-(Boc)-protected amines, followed by ring-closing metathesis catalyzed by ruthenium benzylidene complexes. This methodology allows easy and convenient access to highly functionalized azacycloalkenes in moderate yields and excellent chemoselectivity in a single transformation.     

Critical role of water and the structure of inverse micelles in the Brust-Schiffrin synthesis of metal nanoparticles

Although Brust-Schiffrin two-phase synthesis is a popular method for synthesizing ligand-protected metal nanoparticles with an average size of less than 5 nm, the details on how the reactions can be controlled from a mechanistic point of view are still unclear, therefore hindering efforts to synthesize monodisperse metal nanoparticles. It was recently discovered that this method is basically an inverse-micelle-based synthesis (Li, Y.; Zaluzhna, O.; Xu, B.; Gao, Y.; Modest, J. M.; Tong, Y. Y. J. J. Am. Chem. Soc.2011, 133, 2092). In this letter, the critical role of water and the structure of inverse micelles in typical synthesis of gold nanoparticles were further investigated. We found that (1) water encapsulated in the inverse micelles of [TOA](+) that also hosted metal ions formed a hydrophilic microenvironment that acted as a reaction-enabling proton-accepting medium for the thiol protons (RS-H) and (2) not only the presence but also the amount of water in the reaction medium has a profound effect on the Au(I) precursor species (a pure [TOA][AuX(2)] complex or a mixture of a [TOA][AuX(2)] complex and polymeric [Au(I)SR](n) species), the reduction of Au(III) by thiols, and the formation of uniform small metal nanoparticles. A quantitative analysis of the (1)H NMR of the encapsulated water enabled an estimation of the size and composition of the involved inverse micelles.     

Self-organizing surface-initiated polymerization: facile access to complex functional systems

Facile access to complex systems is crucial to generate the functional materials of the future. Herein, we report self-organizing surface-initiated polymerization (SOSIP) as a user-friendly method to create ordered as well as oriented functional systems on transparent oxide surfaces. In SOSIP, self-organization of monomers and ring-opening disulfide exchange polymerization are combined to ensure the controlled growth of the polymer from the surface. This approach provides rapid access to thick films with smooth, reactivatable surfaces and long-range order with few defects and high precision, including panchromatic photosystems with oriented four-component redox gradients. The activity of SOSIP architectures is clearly better than that of disordered controls.     

Comprehensive core-level study of the effects of isomerism, halogenation, and methylation on the tautomeric equilibrium of cytosine

Core-level X-ray photoemission and near-edge X-ray absorption fine structure spectra of 5-methylcytosine, 5-fluorocytosine, and isocytosine are presented and discussed with the aid of high-level ab initio calculations. The effects of the methylation, halogenation, and isomerization on the relative stabilities of cytosine tautomers are clearly identified spectroscopically. The hydroxy-oxo tautomeric forms of these molecules have been identified, and their quantitative populations at the experimental temperature are calculated and compared with the experimental results and with previous calculations. The calculated values of Gibbs free energy and Boltzmann population ratios are in good agreement with the experimental results characterizing tautomer equilibrium.