Iminopropadienones R–NCCCO and carbon suboxide, C3O2. Theoretical and experimental C NMR spectra

The ¹³C NMR data of five iminopropadienones R–NCCCO as well as carbon suboxide, C₃O₂, have been examined theoretically and experimentally. The best theoretical results were obtained using the GIAO/B3LYP/6-31+G**//MP2/6-31G* level of theory, which reproduces the chemical shifts of the iminopropadienone substituents extremely well while underestimating those of the cumulenic carbons by 5–10 ppm. The computationally faster GIAO/HF/6-31+G**//B3LYP/6-31G* level is also adequate.     

Structure-fate relationships of organic chemicals derived from the software packages E4CHEM and WHASSE

A risk assessment of chemicals is to be performed on the basis of the model EUSES, developed by the Commission of the European Union. The model package E4CHEM (Exposure Estimation for Potentially Ecotoxic Environmental Chemicals), developed in 1984-1992, is presented and applied in this paper as a model which allows a model-supported evaluation of chemicals. E4CHEM consequently does not have the wide applicability and technical comfort of the more recently developed model EUSES. The simulation models of E4CHEM characterize the chemical behavior in the environment by many aspects. Hence, there is a need to condense all of these aspects to get a clear impression of what will be the fate of the chemicals. Starting with the already published concept of exposure maps, we will discuss how partial orders may be helpful in establishing generalized structure-fate relationships. The software WHASSE is applied.     

Numerically exact, time-dependent treatment of vibrationally coupled electron transport in single-molecule junctions

The multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) theory within second quantization representation of the Fock space, a novel numerically exact methodology to treat many-body quantum dynamics for systems containing identical particles, is applied to study the effect of vibrational motion on electron transport in a generic model for single-molecule junctions. The results demonstrate the importance of electronic-vibrational coupling for the transport characteristics. For situations where the energy of the bridge state is located close to the Fermi energy, the simulations show the time-dependent formation of a polaron state that results in a pronounced suppression of the current corresponding to the phenomenon of phonon blockade. We show that this phenomenon cannot be explained solely by the polaron shift of the energy but requires methods that incorporate the dynamical effect of the vibrations on the transport. The accurate results obtained with the ML-MCTDH in this parameter regime are compared to results of nonequilibrium Green's function theory.     

Untersuchungen zur Anwendung des Eichzusatzverfahrens

Zusammenfassung Die Anwendung des Eichzusatzverfahrens zur Eliminierung von Analysenfehlern durch Eichkurvenschwankungen wird mit Hilfe der statistischen Fehlerrechnung untersucht. Gleichungen und Diagramme zum Vergleich der Reproduzierbarkeit von Analysenergebnissen bei Anwendung des Zusatz verfahrens und bei Auswertung der Messungen nach einer festgelegten Eichkurve sowie zur Beurteilung des Einflusses der relativen Größe des Zusatzes auf die Reproduzierbarkeit der Ergebnisse werden angegeben. Zur Prüfung auf systematische Fehler und für eine rasche qualitative Gesamtbeurteilung der Brauchbarkeit des Zusatz-Verfahrens im speziellen Fall wird die Anwendung des aus der Spektralanalyse bekannten Streudiagramms empfohlen.

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Summary The application of the standard addition method for elimination of analytical errors caused by fluctuating calibration curves is investigated using mathematical statistics. Formulas and diagrams are given to compare the reproducibility of analytical results obtained by the standard addition method and by using a fixed calibration curve, and to estimate the influence of the relative quantity of addition on the reproducibility of the analytical results. It is recommended to use the scatter diagram known from emission spectroscopy to discover systematic errors and as a rapid qualitative test of the usefulness of the standard addition method.

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Die Verff. sind Herrn Dr. rer. nat. J. Barthel vom Institut für angewandte Physik der Reinststoffe Dresden der Deutschen Akademie der Wissenschaften zu Berlin für seine Unterstützung bei der Klärung der mathematischen Fragen zu besonderem Dank verpflichtet.     

Upper critical magnetic fields of the heavy fermion superconductors CeCu2Si2, UPt3, and UBe13: Comparison between experiment and theory

We report measurements of the upper critical magnetic field,B _c2 (T), on single crystal and polycrystalline samples of the heavy-fermion superconductors CeCu₂Si₂, UPt₃ and UBe₁₃. Comparison is made with experimental results for a conventional superconductor (CeRu₃Si₂) and with results of the weak-coupling theory applied to both ans-wave superconductor in the dirty-limit and ap-wave superconductor. New anomalies are discovered to add to the unusualB _c2 (T) behavior.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Computation of cavity shapes,sizes, and plasticities

A new molecular mechanics approach has been developed and used to scan the optimum geometry (size and shape) of a host molecule and the energy cost for the deformation of the bonding cavity, based on a general, unspecific guest with given docking sites and a variable size. Lagrange multipliers are used to constrain the sum of internal coordinates (host–guest docking-site distances), and no assumptions with respect to the type and strength of the host–guest bonding have to be made. This new approach has been fully implemented in a molecular mechanics program, and it is used to compute the size, shape, and plasticity of a rigid, asymmetrical, tetradentate (N_amine)₂(N_pyridine)₂ ligand. It is shown that all other methods for the computation of ligand hole sizes that have been reported so far are not able to compute the ligand cavities independently of the metal ion, and they lead to strikingly different shapes, sizes, and plasticities. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 781–785, 1999     

A chiral poly(para-phenyleneethynylene) (PPE) derivative

We have investigated the chiroptical properties of novel PPEs containing chiral side chains. The synthesis of poly(2,5-bis[2-(S)-methylbutoxy]-1,4-phenyleneethynylene) (BMB-PPE) was achieved in a Heck-type aryl-aryl cross coupling (M _n = 10 000, D_p = 40). The very good solubility of BMB-PPE allows for a detailed study of its chiroptical properties. Our studies demonstrate that the bisignated CD spectra of BMB-PPE are associated with an intermolecular aggregation phenomena.