Product angular distributions in the ultraviolet photodissociation of N2O

The angular distribution of products from the ultraviolet photodissociation of nitrous oxide yielding O((1)D) and N(2)(X Σ(g)(+)(1)) was investigated using classical trajectory calculations. The calculations modeled absorption only to the 2(1)A(') electronic state but used surface-hopping techniques to model nonadiabatic transitions to the ground electronic state late in the dissociation. Observed values of the anisotropy parameter β, which decrease as the product N(2) rotational quantum number j increases, could be well reproduced. The relatively low observed β values arise principally from nonaxial recoil due to the very strong bending forces present in the excited state. In the main part of the product rotational distribution near 203 nm, an unusual dynamical effect produces the decrease in β with increasing j; nonaxial recoil effects remain approximately constant while higher j product molecules arise from parent molecules that had their transition dipole moments aligned more closely along the molecular axis. In both low and high j tails of the rotational distribution, the variations in β with j are caused by changes in the extent of nonaxial recoil. In the high-j tail, additional torque present on the ground state potential energy surface following nonadiabatic transitions causes both the additional rotational excitation and the lower β values.     

Atropselective Dibrominations of a 1,1′‐Disubstituted 2,2′‐Biindolyl with Diverging Point‐to‐Axial Asymmetric Inductions. Deriving 2,2′‐Biindolyl‐3,3′‐diphosphane Ligands for Asymmetric Catalysis

On the ¹H NMR timescale, 2,2′‐biindolyls with (R)‐configured (1‐alkoxyprop)‐2‐yl, (1‐hydroxyprop)‐2‐yl, or (1‐siloxyprop)‐2‐yl substituents at C‐1 and C‐1′ are atropisomerically stable at <0 °C and interconvert at >30 °C. A 2,2′‐biindolyl (R,R)‐ 17 a of that kind and achiral (!) brominating reagents gave the atropisomerically stable 3,3′‐dibromobiindolyls (M)‐ and/or (P)‐ 18 a at best atropselectively—because of point‐to‐axial asymmetric inductions—and atropdivergently, exhibiting up to 95 % (M)‐ and as much (P)‐atropselectivity. This route to atropisomerically pure biaryls is novel and should extend to other substrates and/or different functionalizations. The dibromobiindolyls (M)‐ and (P)‐ 18 a furnished the biindolyldiphosphanes (M)‐ and (P)‐ 14 without atropisomerization. These syntheses did not require the resolution of a racemic mixture, which distinguishes them from virtually all biaryldiphosphane syntheses known to date. (M)‐ and (P)‐ 14 acted as ligands in catalytic asymmetric allylations and hydrogenations. Remarkably, the β‐ketoester rac‐ 25 c was hydrogenated trans‐selectively with 98 % ee; this included a dynamic kinetic resolution.     

Calculation of the frequencies and intensities in the infrared and raman spectra of cyclopropenone

By using the values of the vibrational frequencies of normal and deuterated cyclopropenone (II-d₀ , II-d₂ ) and ¹⁶ O-and ¹⁸ O-substituted dimethylcyclopropenone (III) as -well as the infrared and Raman intensities of II a consistent set of force constants has been derived for the cyclopropenone skeleton. The derived values show that the zwitterionic form makes a substantial contribution to the electronic ground state of the molecule. The combined frequency and intensity calculation - simulation of the infrared and the Raman spectrum - is shown to be a good method for making a proper assignment of calculated and observed vibrations and deriving realistic sets of force constants.     

Synthesis and Biological Activity of Oxidation Products of the Antiprogestine Mifepristone

Summary.  Selenium dioxide oxidation allows the selective introduction of a hydroxyl group at position 6 of the steroid skeleton of the antihormone (11β, 17β)-11-(4-dimethylamino-phenyl)-17-hydroxyl-17-(1-propynyl)-estra-4,9-dien-3-one (mifepristone, RU 486) and leads in a one-step procedure to two diastereomeric oxidation products. Their structure (6α- and 6β-hydroxy-mifepristone) was determined by NMR spectroscopy. The antiprogestinic activity of the oxidation products is comparable to that of mifepristone. Received August 25, 2000. Accepted (revised) October 24, 2000     

MaxSynBio: Avenues Towards Creating Cells from the Bottom Up

A large German research consortium mainly within the Max Planck Society (“MaxSynBio”) was formed to investigate living systems from a fundamental perspective. The research program of MaxSynBio relies solely on the bottom‐up approach to synthetic biology. MaxSynBio focuses on the detailed analysis and understanding of essential processes of life through modular reconstitution in minimal synthetic systems. The ultimate goal is to construct a basic living unit entirely from non‐living components. The fundamental insights gained from the activities in MaxSynBio could eventually be utilized for establishing a new generation of biotechnological processes, which would be based on synthetic cell constructs that replace the natural cells currently used in conventional biotechnology.     

How Nature Adapts Chemical Structures to Curved Surfaces

Guided by the symmetry in a natural way, periodic potential surfaces partition the space in solid crystalline compounds. The arrangement of atoms, clusters and molecules obviously follows the (in general) curved shape of these ‘space partitioners’. In structures, the atoms therefore choose only a very limited subset of the infinite set of possible positions. In collective structures the periodic surfaces separate areas of different interactions between atoms, clusters, and molecules. In a certain sense, they can be considered as inner surfaces, a knowledge of which reveals insights into the organization of crystalline matter. There are many good indications that the weakly bonded electrons in the highest occupied orbitals are preferably localized in the region of the space partitioners. Dynamic processes as well can be correlated to the shape of the periodic surfaces. Moreover, the surfaces are didactically very helpful in making accessible the complicated three-dimensional relations in collective structures because the main features are projected onto (although curved) two-dimensional creations. The application of periodic potential surfaces to such a variety of compounds as quartz, brass and alpha-amylose underscores their general significance. Simple qualitative considerations already reveal the manifold relations to animate and inanimate nature through to mathematics, art and architecture. It appears that, in a very universal sense, the adaption of structures to a collective order finds a natural solution through curvature.     

Quantitative determination of phosgene doses by reflectometric badge readout

Commercial phosgene dosimeter badges are lacking precise and sensitive analysis when used only by visual comparison to a color reference. To meet the discussed occupational standard set to 54 ppm min, objective quantification by reflectance measurement is proposed. At 573 nm, the pink dye (“Koenig´s salt”) formed at the membrane surface by reaction of phosgene, and aromatic amine shows a strict linear relationship in reflectance between doses of 10 and 300 ppm min. The detection limit is calculated to 29 ppm min.     

Product distribution of peroxynitrite decay as a function of pH, temperature, and concentration.

The decay of peroxynitrite [O=NOO(-), oxoperoxonitrate(1-)] was examined as a function of concentration (0.050-2.5 mM), temperature (5-45 degrees C), and pH (2.2-10.0). Below 5 degrees C and pH 7, little amounts of the decomposition products nitrite and dioxygen are formed, even when the peroxynitrite concentration is high (2.5 mM). Instead, approximately > or =90% isomerizes to nitrate. At higher pH, decomposition increases at the expense of isomerization, up to nearly 80% at pH 10.0 at 5 degrees C and 90% at 45 degrees C. Much less nitrite and dioxygen per peroxynitrite are formed when the peroxynitrite concentration is lower; at 50 microM and pH 10.2, < or =40% decomposes. In contrast to two other reports (Pfeiffer, S.; Gorren, A. C. F.; Schmidt, K.; Werner, E. R.; Hansert, B.; Bohle, D. S.; Mayer, B. J. Biol. Chem. 1997, 272, 3465-3470, and Coddington, J. W.; Hurst, J. K.; Lymar, S. V. J. Am. Chem. Soc. 1999, 121, 2438-2443), we find that the extent of decomposition is dependent on the peroxynitrite concentration.