Vibrational dynamics of fullerene molecules adsorbed on metal surfaces studied with synchrotron infrared radiation

Infrared (IR) spectroscopy of chemisorbed C₆₀ on Ag (111), Au (110) and Cu (100) reveals that a non-IR-active mode becomes active upon adsorption, and that its frequency shifts proportionally with the charge transferred from the metal to the molecule by about 5 cm^-1 per electron. The temperature dependence of the frequency and the width of this IR feature have also been followed for C₆₀/Cu (100) and were found to agree well with a weak anharmonic coupling (dephasing) to a low-frequency mode, which we suggest to be the frustrated translational mode of the adsorbed molecules. Additionally, the adsorption is accompanied by a broadband reflectance change, which is interpreted as due to the scattering of conduction electrons of the metal surface by the adsorbate. The reflectance change allows determination of the friction coefficient of the C₆₀ molecules, which results in rather small values (∼2×10⁹ s^-1 for Ag and Au, and ∼1.6×10⁹ s^-1for Cu), consistent with a marked metallic character of the adsorbed molecules. Pre-dosing of alkali atoms onto the metal substrates drastically changes the IR spectra recorded during subsequent C₆₀ deposition: anti-absorption bands, as well as an increase of the broadband reflectance, occur and are interpreted as due to strong electron–phonon coupling with induced surface states. Received: 6 June 2001 / Accepted: 23 October 2001 / Published online: 3 April 2002     

Local and global chirality at surfaces: succinic acid versus tartaric acid on Cu110

A detailed comparison of tartaric acid (HOOC-CHOH-CHOH-COOH) and succinic acid (HOOC-CH(2)-CH(2)-COOH) molecules on a Cu(110) surface is presented with a view to elucidate how the two-dimensional chirality exhibited by such robust, chemisorbed systems is affected when both OH groups of the former molecule are replaced with H groups, a stereochemical change that leaves the metal-bonding functionalities of the molecule untouched but destroys both chiral centers. It is found that this change does not significantly affect the thermodynamically preferred chemical forms that are adopted, namely the doubly deprotonated bicarboxylate at low coverages (theta 相似文献   

Strukturuntersuchungen an Siliziden

Zusammenfassung Die Struktur der isotypen Phasen V₃Si₂, Nb₃Si₂, Ta₃Si₂ und Cr₃Si₂ wurden nach dem Vorschlag vonAronsson (RaumgruppeD _2d ¹¹) gerechnet. Die röntgenographische Analyse dieser Phasen spricht mehr für eine Zusammensetzung von M₅Si₃.Im System Nb–Si und Ta–Si wurde eine isotype Phase gefunden, die als Hoch- bzw. Tieftemperaturmodifikation der M₃Si₂-Phasen angesprochen werden kann. Sie läßt sich tetragonal indizieren.Die durch Kohlenstoff stabilisierten M₅Si₃-Phasen mitD 8₈-Typ bilden bei V₅Si₃–Nb₅Si₃ eine lückenlose Mischreihe, während bei dem Paar V₅Si₃–Zr₅Si₃ möglicherweise eine geringe Mischungslücke besteht.VSi₂ und NbSi₂ sind ebenfalls im festen Zustande lückenlos mischbar; das System VSi₂–MoSi₂ zeigt eine sehr starke Löslichkeit auf der VSi₂-Seite. MoSi₂ nimmt dagegen nur wenig VSi₂ auf.Mit 2 Abbildungen.Herrn Professor Dr.Emil Abel aus Anlaß seines 80. Geburtstages in aufrichtiger Verehrung gewidmet.     

Quality by Design Approach for Development of W/O Type Microemulsion-Based Transdermal Systems for Atenolol

The objective of the present investigation was to develop microemulsion-based transdermal systems of highly water soluble drug, Atenolol, by quality by design technique. Atenolol-loaded W/O microemulsions were optimized using D-optimal design with concentrations of oil, surfactants mixture, and water as independent variables, which was converted into microemulsion-based gel (MBG). The results of in vitro permeation of the optimized batch of Atenolol-loaded MBG revealed significant increase in permeability parameters as compared to its convention gel. All results suggested suitability of W/O type MEs as carriers for transdermal delivery of highly water soluble drug, Atenolol.     

Kristallchemische Untersuchungen an Monogalliden von Seltenen Erdmetallen

Zusammenfassung HoGa kristallisiert im CrB-Strukturtyp. EuGa und YbGa bilden sich nicht. Die Existenz des CrB-Strukturtyps mit NdGa, SmGa, ErGa, TmGa und LuGa wird bestätigt. Das Auftreten von CrB- und FeB-Strukturen wird untersucht.

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HoGa crystallizes in the CrB structure type. EuGa and YbGa do not form. The occurrence of the CrB structure type with NdGa, SmGa, ErGa, TmGa, and LuGa is corroborated. A discussion of the CrB and FeB structure types is given.

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Supramolecular assembly of strongly chemisorbed size- and shape-defined chiral clusters: S- and R-alanine on Cu(110)

The bonding and self-assembly of a chirally organized monolayer of alanine on the Cu(110) surface has been investigated using reflection-absorption infrared spectroscopy, low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). This multitechnique approach has enabled an in-depth understanding of the hierarchy of chirality transfer: from a single adsorbed molecule, to size-defined chiral clusters, and then to an overall chiral assembly. The data have indicated that the alanine is in its anionic form, bound to the copper surface through the oxygens of the ionized carboxylate group and the nitrogen of the neutral amino group. Importantly, the methyl group is held away from the surface, resulting in direct chirality transfer into the footprint of the adsorbed alanine molecules, with the local adsorption motif for S-alanine being the mirror image of that created for R-alanine. STM has shown that S-alanine molecules self-organize to form size-defined chiral clusters of six or eight molecules at the surface, interspersed with chiral channels of bare metal. Together, these clusters and channels further self-assemble into a chiral array with one unique chiral domain sustained across the entire surface. A similar chiral assembly, but with the mirror organization, has been observed for R-alanine. Structural models for the individual clusters are proposed, and in conjunction with LEED data, overall models for these chiral phases of both S- and R-alanine have been constructed. Overall, this adsorption system has been found to be both strongly chemisorbed and capable of extensive intermolecular H-bonding, causing stresses that lead not only to the chiral self-organization of molecules but also to a specific self-organization of the empty chiral channels and spaces that intersperse the structure which, in turn, chirally assemble across macroscopic length scales to give a surface with global organizational chirality.     

Magnetic resonance imaging of bone after radiation

Magnetic resonance imaging (MRI) was performed in 22 patients at various times (0-3) years) following radiation therapy to the spine. T1 and T2 weighted images were obtained at 0.5 Tesla. Increased signal was seen after 800-6000 rads (8-60 Gy). Marrow effects corresponded to radiation ports. Recurrent tumor was clearly separated from fatty replacement. This was much better seen on T1 weighted images. Five patients that had MRI during their course of radiotherapy (XRT) did not have increased signal on T1 images of the bone marrow. The earliest fatty marrow change was seen nine days following completion of 3000 rads (30 Gy) XRT over one month's duration. One patient who received 800 rads (8 Gy) to the upper thoracic spine for eosinophilic granuloma had no radiation effects on MRI when imaged 16 days following completion of XRT given over five days. Fatty marrow change was seen in this patient on MRI six months later. MRI was particularly useful in defining the extent of prior radiation effects when repeat therapy was needed.     

Ternäre Erdalkali-und Seltene Erd-Silicide und-Germanide mit AlB2-Struktur

Zusammenfassung Der AlB₂-Strukturtyp (C 32) wurde für SrGeZn, elf Verbindungen mit der ZusammensetzungRGe_1,33Cu_0,67 und vierzehn Silicide der FormelRSi_1,33Cu_0,67 aufgefunden, wobeiR ein Atom der Erdalkaligruppe oder der Seltenen Erdelemente symbolisiert. Das Auftreten von binären und ternären Vertretern dieses Strukturtyps wird in Beziehung gesetzt zu einem bestimmten Bereich der Valenzelektronenkonzentration.

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Ternary alkaline earth- and rare earth-silicides and-germanides with AlB₂-structure

The AlB₂ type structure was found with SrGeZn, eleven phases of compositionRGe_1,33Cu_0,67 and fourteen silicides of compositionRSi_1,33Cu_0,67 whereR indicates an alkaline earth or a rare earth element. The occurence of binary and ternary representatives of this structure type can be correlated with a certain range of valence electron concentration.