The first and second nearest neighbour Cr3+ pairs in ruby

The optical spectrum of the exchange coupled first nearest neighbour Cr³⁺ pairs in ruby was studied by absorption, fluorescence and excitation spectroscopy. It was analysed by means of the group theoretical considerations given in part I [1]. The analysis could be verified by measuring the Zeeman effect in fields up to 150 KG. The Zeeman splitting deviates considerably from that of pure spin states even for the orbital singulet of the pair ground state. The exchange integrals of the ground state are found to beJ=–115 cm^–1 andj=–0.7 cm^–1.This work was supported by the Deutsche Forschungsgemeinschaft, SFB 65     

Validating additive correction schemes against gradient-based extrapolations

The use of additive correction schemes to obtain structures and vibrational frequencies of increasingly larger molecules is becoming more common. Such approaches, based on the cubic extrapolation formula applied directly to the quantity of interest, have been successfully validated only at the highest levels of computational accuracy: for coupled cluster methods with comparably large basis sets. Here, a systematic validation of geometries and vibrational frequencies is carried out, including more affordable and relevant levels of theory, such as the Møller-Plesset perturbation theory applied with smaller basis sets. Comparisons of such additive schemes against the more rigorous gradient-based extrapolation are presented. The cbs () routine of the open-source quantum-chemistry package Psi4 has been extended for this purpose. The results confirm that geometries and frequencies of covalently bound species obtained with additive correction schemes are in an excellent agreement with the results of gradient-based extrapolations. However, when applied to systems involving noncovalent interactions, the errors due to such schemes are significantly larger. In general, we propose the application of gradient-based extrapolations, as they incur no extra cost compared to additive schemes.     

Triggering the Directional Selectivity of a Ring‐Closure Reaction Leads to Pyridoazacarbazoles with Anticancer Properties

We herein describe a facile and versatile synthetic route to the tetracyclic system of 6‐substituted 5,6‐dihydro‐11H‐pyrido[3,2‐i]‐1‐azacarbazoles with promising anticancer properties. These derivatives are built up by an elegant one‐step base‐catalyzed synthetic procedure from commercially available building blocks. One additional step provides the corresponding skeleton hitherto unknown in the literature. The possibility to synthesize a large library of compounds with various substitution patterns utilizing this method underlines the importance of this synthetic procedure.     

CPMD Simulation of a Bimolecular Chemical Reaction: Nucleophilic Attack of a Disulfide Bond under Mechanical Stress

Previous single‐molecule atomic force microscopy (AFM) experiments showed a change in the reactivity of a bimolecular substitution reaction with a definite force acting on a protein containing disulfide bonds. Using Car–Parrinello molecular dynamics (CPMD) simulations, we analyse the relevant reaction pathways for the breaking of a disulfide bond in the presence of nucleophiles.     

Donorstabilized Monometaphosphates and Phosphonates- Structure,Bonding, and Reactivity

Abstract

Previoudy we reported on the preparative use of donorstabilized monometaphosphates, Py.PO₂Cl and Py.PS₂Cl[¹]. ³P MAS investigations as well as X-ray single crystal analysis have been carried out. The isotropic chemical shift of the sulfur compound shows the typical downfield shift (106 ppm) with respect to the oxygen compound The chemical shift anisotropy gives additional information. The relative large spans ω (Py.PO₂Cl: 401 ppm, Py.PS₂Cl: 461 ppm) [²] reveal strong deviations from tetrahedral symmetry (ω = 0 ppm) in agreement with the structural data. The values of the skew parametem K (0.64 and 0.71 resp.) reflect the trend to axial symmetry (k = ± l). X-ray diffraction and NMR data suggest a structural model corresponding to a concentration of double bond character on the two P-X bonds. This model is consistent with the extremely short P-X bond length (1.449 Å and 1.921 Å rasp.) as well as the large P-X-P bond angles (126.4°and 123.7° resp.).     

Review of the analytical techniques for sesquiterpenes and sesquiterpene lactones

In this paper the analytical techniques of about the last 2 decades for sesquiterpenes including their lactones are reviewed. For sesquiterpenes, methods like GC, GC-EI-MS, GC-CI-MS, GC-MS-MS, GC-FT-IR, GC-UV, GC-AES, 13C-NMR, PY-GC-MS, HPLC, HPLC-TSP, SFE, SFC, SFC-UV are available, GC combined with MS is the most widespread. Sesquiterpene lactones can be analysed by HPLC, HPLC-TSP, HPLC-APCI, HPLC-ESI, HPLC-PB, HPLC-NMR, SFC, MEKC, GC, GC-MS, TLC and OPLC. Here HPLC is the method of choice. The usefulness of the individual methods are briefly discussed.     

Zur Bestimmung des Albumingehaltes in Serum, Urin u. a.

Ohne Zusammenfassung     

Ges?ttigte L?sungen zur Herstellung von Standardl?sungen

Ohne Zusammenfassung