Schlüsselreaktionen einer synthese des sibirosamins

[2,3]-Sigmatropic rearrangement and vic. $\text{cis}$-oxyamination of 3-$\text{C}$-methyl-ald-m-enopyranosides are the key steps for the synthesis of a sibirosamine precursor.     

Excitation dynamics of Rydberg states in C<Subscript>60</Subscript>

The electron and nuclear dynamics of C₆₀ fullerenes irradiated with femtosecond laser pulses are investigated with photoelectron and photoion spectroscopy. The focus of this work is the detailed exploration of the population mechanism of Rydberg levels within the excitation process of neutral C₆₀. The effect of excitation wavelength, intensity, chirp, and polarization on the kinetic energy distribution of photoelectrons in single-pulse experiments gives first insight into the underlying processes. In combination with time-resolved two-color pump-probe spectroscopy depending on either pump, or probe pulse intensity, a more complete picture of the interaction can be drawn. The results point towards a very interesting but nevertheless complex behavior including four steps: (i) non-adiabatic multielectron excitation of the HOMO (h_u) → LUMO+1 (t_1g) transition; (ii) thermalization within the hot electron cloud on a time scale below 100 fs, followed by a coupling of energy to vibrational modes of the molecule via doorway state(s); (iii) population of electronically excited Rydberg states by multiphoton absorption, and (iv) single photon ionization from the excited Rydberg states. This excitation process results in a characteristic sequence of photoelectron lines in the photoemission spectra. The comparison of the experimental results with recent theoretical work gives convincing evidence that non-adiabatic multielectron dynamics (NMED) plays a key role for the understanding of the response of C₆₀ to short-pulse laser radiation.     

Exponential decay lifetimes of excitons in individual single-walled carbon nanotubes

The dynamics of excitons in individual semiconducting single-walled carbon nanotubes was studied using time-resolved photoluminescence (PL) spectroscopy. The PL decay from tubes of the same (n,m) type was found to be monoexponential, however, with lifetimes varying between less than 20 and 200 ps from tube to tube. Competition of nonradiative decay of excitons is facilitated by a thermally activated process, most likely a transition to a low-lying optically inactive trap state that is promoted by a low-frequency phonon mode.     

Photopolymerization of C<Subscript>60</Subscript> and Li@C<Subscript>60</Subscript> studied by second-harmonic generation and infrared spectroscopy

The photopolymerization of C₆₀ and Li@C₆₀ films was investigated by means of optical second-harmonic generation. The films were deposited under ultra-high-vacuum conditions and irradiated in situ with an Ar⁺ laser at 514 nm. The second harmonic generated by a Nd:YAG laser working at 1064 nm was monitored after different steps of irradiation. Photopolymerization was observed after very low irradiation doses, of the order of 10²⁰ photons/cm², and confirmed with infrared absorption spectroscopy. Similar kinetics for C₆₀ and Li@C₆₀ were observed. The measurements give evidence for photopolymerization of the endohedral fullerene Li@C₆₀. PACS 78.30.Na; 82.50.Hp; 81.05.Tp     

Inhibitors of the K+(Na+)/H+ exchanger of human red blood cells

The effect of substances as possible inhibitors of the K+(Na+)/H+ exchanger in the human red cell membrane has been tested on the (ouabain+bumetanide+EGTA)-resistant K+ influx in both physiological (HIS) and low ionic strength (LIS) solution with tracer kinetic methods. It is demonstrated that high concentrations of quinacrine (1 mM) and chloroquine (2 mM) inhibit the residual K+ influx in LIS solution to 60% and 85%, respectively, but activate it in HIS solution. Thus, chloroquine suppressed the 10-fold LIS-induced activation of the flux nearly completely. Amiloride derivatives were able to inhibit the K+ influx in both HIS and LIS solution. EIPA (75 microM) reduced the flux by about 20% and 55% in HIS and LIS solution, respectively. Newly developed drugs (HOE 642, 1 mM; HOE 694, 0.5 mM) designed to inhibit Na+/H+ exchanger isoforms showed an inhibition of the residual K+ influx of 40% and 33% in HIS and 65% and 44% in LIS solution, respectively, without haemolysis. The inhibitory effect of HOE 642 persisted in HIS (24%) and LIS (48%) solutions when Cl- was replaced by CH3SO4-. The K(+)-Cl- cotransport inhibitor DIOA (100 microM) stimulated the residual K+ influx in both solutions. It is, therefore, concluded that the K(+)-Cl- cotransporter does not contribute to the residual K+ influx both in HIS and LIS media. Okadaic acid decreased the residual K+ influx by 40% and 25% in HIS and LIS solution, respectively, showing that the residual K+ influx is affected by phosphatases like other ion transport pathways. The results show that the residual K+ influx can be decreased further by inhibiting the K+(Na+)/H+ exchanger. It remains still unclear to what extent the K+(Na+)/H+ exchanger is inhibited by the different substances used. However, the ground state membrane permeability for K+ is much smaller than assumed so far.     

Interaction of C60 with carbon nanotubes and graphite

The interaction of C60 with single-wall carbon nanotubes (SWNTs) and graphite is studied experimentally by thermal desorption spectroscopy and theoretically by molecular-mechanics and molecular-dynamics calculations. The van der Waals parameters and force field for C60-graphene and C60-SWNT interactions are derived from the low-coverage C60 binding energy to the graphite surface. We use these to compare the efficiency of different mechanisms by which C60 can be encapsulated into SWNTs.     

Happy New Year

This is the first issue of EPJ D in 2001, the new century in the new millennium! This is therefore appropriate timing for introducing some modifications in the journal. However, there is no need for a revolution. EPJ D is a healthy journal, which receives an increasing flow of excellent papers, but it is our continuing concern to adapt the journal to the evolution of science and to publish a better journal. So what's new in 2001? By examining the list of topics covered by EPJ D, you will find changes. To emphasize a few active fields, new sections have been added so that physicists working on these subjects can find immediately the papers belonging to their domain. For example, there is presently a large community working on quantum gases and Bose-Einstein condensation. For this community and those working on laser cooling of atoms, molecules, ions, we have created a section Laser Cooling and Quantum Gas. In the same manner, to satisfy those interested in quantum information, entanglement, quantum cryptography, we have extended the Quantum Optics section to Quantum Optics and Quantum Information. A new section has also been created for Ultrafast Phenomena and for the processes occurring in High Intensity Fields. The introduction of this section is triggered by the rapid development of femtosecond lasers and their numerous applications ranging from time-resolved spectroscopy of biological molecules to X-ray generation. Another new and exciting field, bringing even more interdisciplinary into our journal is molecules of biological interest in the gas phase. Finally, the section Nonlinear Dynamics has been polished. It is now the natural place to publish results dealing the fundamental aspects of chaotic systems and the manifestation of these phenomena in Atoms, Molecules and Optics. However, these new sections do not mean that EPJ D is now only devoted to a few fashionable subjects. Papers dealing with more traditional topics are obviously highly welcomed and they should find their place in one of the other sections. We have also decided to have regular publication of topical issues. We plan to publish two topical issues each year. In 2001, the topics of these issues will be Clusters and Femtosecond Spectroscopy. Another evolution concerns the Rapid Notes. Although they have existed since the start of the journal and they correspond to a regular demand of our community (fast publication of short papers, less than 4 pages, describing important advances), the EPJ D Rapid Notes were not very popular. We wish to make them more attractive. First, by increasing the rapidity of publication: our aim is to publish a Rapid Note 3 months at most after its reception by the editorial office. For this purpose the Editors, the Editorial Office and the Publisher will give the highest priority to these Rapid Notes. Second, by using a different lay-out to separate and distinguish them from the other papers of the same issue. Furthermore, if you wish to communicate with an editor it will be no longer necessary to look for his email address. To achieve better connections between authors and editors, every editor can now be reached through the electronic address first name.last name@epjd.org. The mail will be directly forwarded towards his personal address. Finally, we expect that 2001 will be the real beginning of a new type of publication that combines the possibilities of the printed journal and of the on-line edition. First as soon as a paper is accepted and proofread, it will appear on the on-line version by using the Digital Object Identifier (DOI) system, and can therefore be quoted. There are however additional advantages. For example, it is now possible to have a short paper published in the printed journal and an extended version on-line, with supplementary material (tables, figures, complements) and possibly various multimedia documents. Obviously, if there are additional materials in the on-line version, this will be mentioned on the printed version. Technical information is available hereafter. We hope that all these small advances will make the journal more attractive. However, what makes a journal alive are really the authors. Therefore, we wish you many results, many discoveries and we hope that you will provide us with lots of excellent papers. Happy New Year! The publisher informs the authors of the possibility to published “electronic-only" materials. Electronic-only material is designed to provide supplementary information which is either too voluminous to be printed or is designed specifically for the Web, such as illustration in colour. Electronic-only material may include but is not restricted to: •(Large) tables • Appendices • Programmes • Images, videos For more information on the submission of this material, (file requirements, etc.), please contact the production office at: articles@edpsciences.org     

Electron-phonon interaction in single-wall carbon nanotubes: A time-domain study

We investigate the electron-phonon (e-ph) interaction in single-wall carbon nanotube samples at room temperature using femtosecond time-resolved photoemission. By probing electrons from the vicinity of the Fermi level we are able to study the e-ph interaction in the metallic nanotube species only. The observed electron dynamics can be used to calculate e-ph scattering matrix elements for two likely scattering scenarios: forward scattering from twistons and backscattering by longitudinal acoustic phonons. The corresponding matrix elements reveal an intrinsically weak e-ph interaction approximately 50% smaller than predicted by tight-binding calculations.