Chemically pumped N2O laser

Optical gain and laser oscillation has been achieved in N₂O through selective excitation of the (001) state by vibrational energy transfer from CO². The CO² is produced by the flash photolysis initiated chemical reaction: O + CS → CO² + S.     

Facile ketene-ketene and ketene-ketenimine rearrangements: a study of the 1,3-migration of alpha-substituents interconverting alpha-imidoylketenes and alpha-oxoketenimines, a pseudopericyclic reaction

Theoretical calculations (B3LYP/6-311+G(3df,2p)//B3LYP/6-31G) of the 1,3 migration of NR(2) transforming alpha-oxoketenimines 1 to alpha-imidoylketenes 3 and vice versa indicate that this process is a pseudo-pericyclic reaction with a low activation energy (NH(2) 97 kJ mol(-1), N(CH3)(2) 62 kJ mol(-1)). The oxoketenimines were found to be more stable (by 18-35 kJ mol(-1)) which is in line with experimental observations. The hindered amine rotation in the amide and amidine moieties adjacent to the cumulenes are important in the migration of the NR(2) group, as one of the rotation transition states is close to the 1,3 migration pathway. This gives an interesting potential energy surface with a valley-ridge inflection (VRI) between the orthogonal hindered amine rotation and 1,3 migration transition states. The imidoylketene may also undergo ring closure to an azetinone 5; however, this is metastable, and under the conditions that allow the 1,3-migration, the oxoketenimine 1 will be favored. The imine NH E/Z-interconversion of the ketenimine group takes place by inversion and has a low activation barrier ( approximately 40 kJ mol(-1)). In all the amidines examined the E/Z-interconversion of the imine function was predicted to be by rotation with a high barrier (>80 kJ mol(-1)), in contrast to all other reported imine E/Z-interconversions which are by inversion.     

Eine Note zum System PC

Corresponding to a graduation of the comprehension predicateC there arise two systems PC₁ and PC₂. PC₁ represents constructive mathematics whereas PC₂ as a restricted enlargement of PC₁ enables one to deal with full set theory. Unnatural definitions likeKuratowski's ordered pair and identification of 0 and are avoided. In PC₁ the postulate introduced for ordered pairs holds not only for sets but for classes generally. The comprehension condition in PC₁ implicitly contains a set axiom for at most denumerable calsses and for ordered pairs. By introduction of the concept ordered self-pair the real numbers are interpreted as self-pairs of (non denumerable) equivalence classes of concentrated ratioal sequences and they can be shown to be sets in PC₁.

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Motto: Funktoren- und Axio-meneinsparung ist mitunter am falschen Platz.

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Diese Arbeit schließt an die in Mh. Math.82, 81–116 (1976) erschienene Arbeit Peano-Systeme desselben Autors an.     

Platinum drug adduct formation in the nucleosome core alters nucleosome mobility but not positioning

Nucleosome positioning and reorganization regulate DNA site exposure in chromatin. Platinum anticancer agents form DNA adducts that disrupt nuclear activities, triggering apoptosis. Mechanistic insight would aid in the development of improved therapies to circumvent drug toxicity and resistance. We show that platinum adducts formed by reaction of cisplatin or oxaliplatin with the nucleosome core inhibit histone octamer-DNA sliding but do not cause significant alteration of positioning. Thus, adduct formation reinforces positional preferences intrinsic to the DNA sequence, which indicates that modulation of platinum drug site selectivity by histone octamer association may relate to nucleosome-specific properties of DNA. This sheds light on platinum drug-mediated inhibition of chromatin remodeling in vivo and suggests that adducts can shield their own repair and interfere with genomic activities by directly altering nucleosome dynamics.     

A second gradient theoretical framework for hierarchical multiscale modeling of materials

A theoretical framework for the hierarchical multiscale modeling of inelastic response of heterogeneous materials is presented. Within this multiscale framework, the second gradient is used as a nonlocal kinematic link between the response of a material point at the coarse scale and the response of a neighborhood of material points at the fine scale. Kinematic consistency between these scales results in specific requirements for constraints on the fluctuation field. The wryness tensor serves as a second-order measure of strain. The nature of the second-order strain induces anti-symmetry in the first-order stress at the coarse scale. The multiscale internal state variable (ISV) constitutive theory is couched in the coarse scale intermediate configuration, from which an important new concept in scale transitions emerges, namely scale invariance of dissipation. Finally, a strategy for developing meaningful kinematic ISVs and the proper free energy functions and evolution kinetics is presented.     

Fulminating Gold and Silver

This Essay deals with the fascinating and highly explosive compounds fulminating gold and fulminating silver, which are easily made by treatment of gold dissolved in aqua regia with ammonia, and by reaction of silver oxide or silver salts with ammonia, respectively. Fulminating gold in particular captivated the alchemists in the 16th to 18th centuries. Numerous preparations were described, as well as numerous attempts to make volatile, sublimable or distillable gold, and to use the products so obtained (which were most likely gold chlorides) to make the sought‐after tincture, which would “heal” the “impure” metals and transform them into gold, and equally be a panacea to cure all human illnesses.     

Falling‐Solid Flash Vacuum Pyrolysis: An Efficient Preparation of Arylacetylenes

Automated falling‐solid flash vacuum pyrolysis allows the rapid and efficient synthesis of a variety of arylacetylenes from 4‐arylmethylidene‐5(4H)‐isoxazolone derivatives, which were prepared from aldehyde precursors. The acetylenes are readily obtained in multigram quantities.     

Identification of deoxynucleoside—polyaromatic hydrocarbon adducts by capillary zone electrophoresis—Continuous Flow-fast atom bombardment mass spectrometry

Capillary zone electrophoresis coupled to continuous flow-fast atom bombardment mass spectrometry is shown to have utility for the detection and characterization of adducts formed by the covalent attachment of four polyaromatic hydrocarbon (PAH) and amino-PAH compounds to deoxyguanosine. Normal scanning provided structural information for a 1.3 ng injection of a model adduct, while 1.3 ng of each of a mixture of adducts was sufficient to determine their molecular weights by monitoring the constant neutral loss of deoxyribose. Exploitation of this loss in the multiple reaction monitoring mode resulted in the detection of low picogram amounts of target adducts in mixtures.     

Nucleophilic and Electrophilic Properties of Carbenes,II. 4-Biphenylyl-4-pyridylcarbene

Flash pyrolysis of 4-biphenylyl-4-pyridyldiazomethane ( 4 gave 7-phenyl-2-azafluorene) 5 , which was also synthesized from 3-mesitoylpyridine in four steps. 4-Biphenylyl-4-pyridyl-[¹³C]-diazomethane ( 9 ) was prepared from isonicotinic [¹³C]-acid chloride in three steps. Flash pyrolysis of 9 established that 4a- and 4b-[¹³C]-7-phenyl-2-azafluorenes are formed in a carbene-carbene rearrangement in which ring expansion of the biphenyl part dominates over that of the pyridine ring. These results support the postulate that carbene-carbene rearrangements are favoured by a nucleophilic interaction between the filled singlet carbene sp² (σ) orbital and the lowest unoccupied molecular orbital (LUMO) of the aromatic ring.