Stereospecific Synthesis of 2-Oxazinyl-4-oxoazetidinecarbamates Starting from a 1,2-Diazepine. A new type of intramolecular transbenzoylation

Azeitidinodiazepines 4b and 4c react with acylnitroso dienophiles 5a–c , specifically from their convexe α-side, but in a non-regiospecific way, leading thereby stereospecifically to the expected adducts 6a–d and 7a–d . The three-dimensional structures of 6a and 7a were determined by X-ray analyses which corroborated their NMR data. OsO₄ cis-glycolization occurred in good yield with the inverse adducts 7a and 7e and led to the rearranged products 10 . These latter ones result from an intramolecular N- to O-transbenzoylation of the short-lived intermediates 9 followed by fragmentation of the animal function. X-Ray analysis of 7a showed the N(10) atom to be pyramidal, a result which demonstrates that it does not have any pronounced benzamide character; otherwise no such N- to O-transbenzoylation would have taken place. Structure and relative configuration of 10a were ascertained by X-ray analysis which confirmed its NMR data as well as the stereochemical outcome of its formation.     

Revisiting the crystal structure and thermal properties of NaMgAl(oxalate)3 x 9 H2O/Cr(III): an extraordinary spectral hole-burning material

We have reinvestigated the crystal structure and thermal properties of NaMgAl(oxalate)(3).9H(2)O. In the thermal gravimetric analysis the steps of dehydration and decomposition/oxidation yield a mass change that is commensurate with 9 water molecules of hydration. Dehydration steps occur at 127, 171, and 201 degrees C whereas the oxalate ligand decomposes in steps at 403 and 424 degrees C with a final oxidation step at 692 degrees C. A refinement of the single crystal X-ray diffraction data taken at 200 K affirms the P3c1 space group with nine water molecules of hydration and unit cell parameters a = b = 16.7349(2) A and c = 12.6338(1) A with Z = 6. The structures can be described in terms of modulations of an idealised Z = 1 structure in P3[combining macron]lm. T-Cycle experiments of spectral holes in the R(1)-line yield a single Gaussian barrier with T(0) +/- sigma(T) of 46 +/- 21 K and three barriers with 40 +/- 12, 70 +/- 10, 107 +/- 5 K for perprotonated and partially deuterated (46%) NaMgAl(oxalate)(3).9H(2)O/Cr(iii) 0.5%, respectively.     

Metal Complexes with Macrocyclic Ligands Part XXX. Synthesis and structure of halocuprates of tetraprotonated 1,4,8,11-tetraazacyclotetradecane and its Cu2+ complex

By mixing acidic solutions of 1,4,8,11-tetraazacyclotetradecane (Cy) with CuX₂ (X = Cl^?, Br^?), either the hexahalocuprates of the tetraprotonated form of the macrocycle ([CyH₄] [CuX₆]) or the tetrahalocuprates of its Cu²⁺ complex ([CuCy] [CuX₄]) are obtained. The structures of the chloro derivatives are established by X-ray diffraction analysis. In [CyH₄] [CuCl₆], the Cu²⁺ is in a tetragonally distorted octahedral geometry with four short and two long Cu? Cl bonds. The tetraprotonated macrocycle is centrosymmetric, and its conformation is exodentate, so that the four ammonium groups are as far as possible from each other to minimize the electrostatic repulsion. In [CuCy] [CuCl₄], the Cu²⁺ ion complexed by the macrocycle is surrounded by four N-atoms in a square-planar arrangement. In addition, the axial positions are occupied by two Cl^? ions of two CuCl units, which act as bridges. The macrocycle is in the trans-III-configuration. The other Cu²⁺ ion is coordinated by four Cl^? ions in a distorted tetrahedral geometry. IR and VIS spectra of the chloro and bromo derivatives are used to discuss the structure of the bromo species.     

Metal complexes with macrocyclic ligands. Part XXXIV. Geometrical and conformational changes during the on/off reaction of the side chain in the CuII complex of 11-(3-aminopropyl)-1,4,7,11-tetraazacyclotetradecane

Solution studies of the Cu²⁺ complex with 11-(3-aminopropyl)-1,4,7,11-tetraazacyclotetradecane(L) indicate that, depending on the pH and on the age of the solution, different species are present. Dissolving the solid [CuL](ClO₄)₂ in slightly acidic solution gives the protonated complex AH , characterized by an absorption maximum at 574 nm, by a relatively fast proton-induced dissociation kinetics and by the typical colour change in basic solution to give the deprolonated form A with coordinated side chain. AH slowly interconverts in acidic solution to a new species BH , which has an absorption maximum at 547 nm, and which is kineticaily more stable against acid dissociation and shows no coordination of the amino group of the side chain. In alkaline solution, however, the deprotonated form B deliver A in a base induced reaction. The X-ray diffraction studies of A and BH allow to determine the geometry of the metal ion and the configuration of the macrocycle. In A , the Cu²⁺ is pentacoordinated by the five N-atoms of the ligand and the macrocycle is in the RRSR configuration, whereas in BH the Cu²⁺ is octahedrally coordinated by the four N-atoms of the macrocycle and two axial perchlorate O-atoms with the macrocycle in the RRRS configuration. The amino group of the side chain is protonated and not coordinated. Thus, the on/off equilibrium of the side chain not only changes the geometry of the metal ion, as is generally found, but also alters the macrocyclic moiety.     

DSC by the TGA/SDTA851e Considering Mass Changes

DSC measurements in open pans are often disturbed by mass losses such as sublimation during melting or release of water during chemical reactions. By simultaneous DSC and TG measurements the DSC signal can be corrected. For this purpose, a temperature dependent calibration function has to be determined by which the SDTA signal from the TGA/SDTA851^e measuring cell can be converted into a heat flow curve (DSC). By this procedure, accurate heat of melting can be determined despite ongoing sublimation in open pans. This method is illustrated with reference of the melting of anthracene. Additionally, condensation reactions were investigated and analyzed by DSC/TG even under ambient pressure, knowing the heat of evaporation. Using phenol formaldehyde resins the influence of the presence or the release of volatile reaction products on the reaction rate and kinetic parameters were studied. In general, the method can be used to correct DSC curves for thermal effects related to mass change. This revised version was published online in July 2006 with corrections to the Cover Date.     

Charge collection in amorphous silicon solar cells: Cell analysis and simulation of high-efficiency pin devices

The drift length L_drift = μτE within the i layer of a-Si:H solar cells is a crucial parameter for charge collection and efficiency. It is strongly reduced not only by light-induced reduction of μτ, but also by electric field deformation ΔE by charges near the p–i and i–n interfaces. Here, a simple model is presented to estimate contributions of free carriers, charges trapped in band tails and charged dangling bonds to ΔE. It is shown that the model reproduces correctly trends observed experimentally and by ASA simulations: charged dangling bonds contribute most to ΔE of meta-stable cells. Electrons trapped in the conduction band tail near the i–n interface lead to the strongest field deformation in the initial state, while positively charged dangling bonds near the p–i interface get more important with degradation under AM1.5g spectrum. The measurable parameter V_coll is proposed as an indirect parameter to estimate the electric field, and an experimental technique is presented that could enable the distinction of defects near the p–i and the i–n interfaces.     

Sambucinic Acid,a New Metabolite of Fusarium sambacinum. 45th communication on verrucarins and roridins

Sambucinic acid (5), a C₁₅-trichothecene with a modified strure, has been isolated from cultures of Fusarium sambucinum. The structure is established by spectroscopic data and X-ray diffraction analysis. A hypothetical biogenetic pathway is proposed.