Impacts of gold nanoparticle charge and ligand type on surface binding and toxicity to Gram-negative and Gram-positive bacteria

Although nanomaterials facilitate significant technological advancement in our society, their potential impacts on the environment are yet to be fully understood. In this study, two environmentally relevant bacteria, Shewanella oneidensis and Bacillus subtilis, have been used as model organisms to elucidate the molecular interactions between these bacterial classes and Au nanoparticles (AuNPs) with well-controlled and well-characterized surface chemistries: anionic 3-mercaptopropionic acid (MPA), cationic 3-mercaptopropylamine (MPNH₂), and the cationic polyelectrolyte poly(allylamine hydrochloride) (PAH). The data demonstrate that cationic, especially polyelectrolyte-wrapped AuNPs, were more toxic to both the Gram-negative and Gram-positive bacteria. The levels of toxicity observed were closely related to the percentage of cells with AuNPs associated with the cell surface as measured in situ using flow cytometry. The NP concentration-dependent binding profiles were drastically different for the two bacteria strains, suggesting the critical role of bacterial cell surface chemistry in determining nanoparticle association, and thereby, biological impact.     

Electronic structure of a vapor-deposited metal-free phthalocyanine thin film

The electronic structure of a vapor-sublimated thin film of metal-free phthalocyanine (H2Pc) is studied experimentally and theoretically. An atom-specific picture of the occupied and unoccupied electronic states is obtained using x-ray-absorption spectroscopy (XAS), core- and valence-level x-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT) calculations. The DFT calculations allow for an identification of the contributions from individual nitrogen atoms to the experimental N1s XAS and valence XPS spectra. This comprehensive study of metal-free phthalocyanine is relevant for the application of such molecules in molecular electronics and provides a solid foundation for identifying modifications in the electronic structure induced by various substituent groups.     

Synthesis of 2,3,10,11 -tetraalkoxy-substituted tetrahydrobenzo [a] naphtho [1,2-g] quinolizines

2 Four3,10,11-tetraalkoxy-substituted 5,6,15,15a-tetrahydro-8H-benzo[a]naphtho[1,2-g]-quinolizines were prepared by the Pictet-Spengler cyclization of the respective 1-(6,7-dialkoxy-2-naphthylmethyl)-6,7-dialkoxy-1,2,3,4-tetrahydroisoquinolines. The latter compounds were obtained by a chemical reduction of the corresponding dihydro compounds, which, in turn, were formed by a Bischler-Napieralski cyclization of the appropriate amides.     

Highly efficient proteinase assay with chromogenic substrates and its application in a study of enzyme inhibitors

A simple and rapid method for the determination of enzyme activities with chromogenic substrates is described. Trypsin and papain were used as model proteinases and N-benzoyl-dl-arginine p-nitroanilide (BAPNA) was applied as substrate. The enzyme assay was performed on a multi-scale using 96-well microtitration plates and product release was detected with the aid of an automatic plate reader, widely used in ELISA tests. The procedure was used for electrophoretic studies of trypsin and a crude papain preparation. It was also applied for the investigation of N-peptidyl-O-acylhydroxylamine proteinase inhibitors. In comparison with commonly used procedures with chromogenic substrates, the proposed approach consumes markedly reduced amounts of all reagents. It allows an almost unlimited number of samples to be assayed in a short time and should be applicable to the detection and determination of any enzyme activitiy where chromogenic substrates are applicable.     

High spin level structure of 63 143 Eu80

The level scheme of ¹⁴³ Eu has been extended to I=75/2 in an experiment with the NORDBALL Compton-suppressed Ge detector array and the ¹¹⁰ Pd(³⁷ Cl, 4n) reaction. Most of the scheme shows irregular structure of multiparticle excitations. A strongly populated straight cascade of more than 10 stretched E2 transitions suggests the onset of collectivity.     

Spectroscopy of neutron deficient 108Te

The neutron deficient nucleus ¹⁰⁸Te was studied in the ⁵⁴Fe(⁵⁸Ni,2p2n) reaction. A detector system consisting of 4 Euroball cluster detectors, a charged-particle detector ball and a 16 element neutron multiplicity filter was used to detect the emitted particles and γ rays. A new, significantly extended level scheme was constructed on the basis of γγ-coincidence relations. Spin values for the states were determined from angular distribution ratios. The experimental results are discussed in terms of the shell model. Received: 7 September 1998     

First identification of excited states in the T_z\! = \!1/2 nucleus 93 Pd

The first experimental information about excited states in the N = Z + 1 nucleus ⁹³Pd is presented. The experiment was performed using a 205 MeV ⁵⁸Ni beam from the Vivitron accelerator at IReS, Strasbourg, impinging on a bismuth-backed ⁴⁰Ca target. Gamma-rays, neutrons and charged particles emitted in the reactions were detected using the Ge detector array Euroball, the Neutron Wall liquid-scintillator array and the Euclides Si charged-particle detector system. The experimental level scheme is compared with the results of new shell model calculations which predict a coupling scheme with aligned neutron-proton pairs to greatly influence the level structure of nuclei at low excitation energies.Received: 28 October 2003, Revised: 4 December 2003, Published online: 26 January 2004PACS: 21.10.Hw Spin, parity, and isobaric spin - 23.20.Lv transitions and level energies - 27.60. + j - 21.60.Cs Shell model     

Bonding of saturated hydrocarbons to metal surfaces

The adsorption of octane on Cu(110) was studied by x-ray absorption and x-ray emission spectroscopy, in combination with spectrum calculations in the framework of density functional theory, as a model system for alkane adsorption on transition metals. Significant electron sharing between the adsorbate and metal surface and involvement of both bonding and antibonding C-H molecular orbitals in the molecule-metal bond was found. The calculations were extended to the case of octane adsorbed on Ni(110), and the position of the metal d band was found to be important for the bonding. The results were generalized to show that this is important for the efficiency as an alkane dehydrogenation catalyst.     

Soft X-ray appearance potential spectroscopy of O chemisorbed on Ti,Cr, Fe and Ni

We wish to report the observation of O 1s level soft X-ray appearance potential spectra for O adsorbed on clean polycrystalline surfaces of Ti, Cr, Fe and Ni. The spectra are detectable in the chemisorption regime and are then characterized by one single peak at the threshold. The peak is thought to be related to an enhanced local density of unfilled valence states on the oxygen atoms. These simple spectra are in sharp contrast to the multipeaked O 1s level spectra observed from the surface oxides grown after prolonged oxygen exposures.