Usage de l'algégbre de lie su(n) dans l'étude des systémes quantiques á n états. IV. Geometrie du domaine des vecteurs de cohérence

The density operator of an n level quantum system is known to be a positive semidefinite, hermitian operator of trace one. In a previous article we have established, through su(n) algebras, a formalism where density operators are built from coherence vectors in a n² ? 1 dimension, real, Euclidean space. The last two conditions are then automatically satisfied. Being positive semidefinite means a restriction to the domain of coherence vectors. In this article we clarify this domain and obtain several equivalent tests to know if a given vector is part of it.     

Generalized existence conditions for surface states of a semi-infinite Kronig–Penney crystal

A derivation of most general existence conditions for surface states of a semi-infinite Kronig–Penney crystal is reported. They reduce to Steslicka's conditions under a subsidiary restriction and also indicate that the surface-state energies may lie in the allowed bulk bands. Numerical computations supporting the qualitative conclusions are provided.     

Synthese und pericyclische Reaktionen von 4, 4a-Dehydro-α-bicyclofarnesensäureester

The title compound 3 was isolated after pyrolysis of cis/trans- 1 at 240°, respectively of cis/trans- 8 at 156°. Thermolysis of cis/trans- 8 at 111° resulted in the deconjugated product 9 , which subsequently could be rearranged via a [1,7] H-shift preferentially into the trans-isomer of 8 . Upon heating at 250°, 3 underwent a series of pericyclic reactions to furnish 11 , whereas epi- 3 did not react under these conditions.     

Hydrogen storage in borohydrides Comparison of hydrolysis conditions of LiBH<Subscript>4</Subscript>, NaBH<Subscript>4</Subscript> and KBH<Subscript>4</Subscript>

The hydrogen storage capabilities of alkaline borohydrides through a hydrolyzing process were determined by taking into consideration the hydration of the end products. Comparison of LiBH₄, NaBH₄ and KBH₄ showed their storage capacities to be dependent on the composition of the metaborate formed. This composition is ruled by the hydrolysis conditions, especially the temperature reached during the reaction and the stability of the hydrates. The borohydride with the highest hydrogen content in the solid state, LiBH₄, could be less efficient than KBH₄ if the hydrolysis is performed at 120°C.     

Photoreactivating Enzyme for (6–4) Photoproducts in Cultured Goldfish Cells

We previously reported that when cultured goldfish cells are illuminated with fluorescent light, photorepair ability for both cyclobutane pyrimidine dimers and (6–4) photoproducts increased. In the present study, it was found that the duration of the induced photorepair ability for cyclobutane pyrimidine dimers was longer than that for (6–4) photoproducts, suggesting the presence of different photolyases for repair of these two major forms of DNA damage. A gel shift assay was then performed to show the presence of protein(s) binding to (6–4) photoproducts and its dissociation from (6–4) photoproducts under fluorescent light illumination. In addition, at 8 h after fluorescent light illumination of the cell, the binding of pro-tein(s) to (6–4) photoproducts increased. The restriction enzymes that have recognition sites containing TT or TC sequences failed to digest the UV-irradiated DNA pho-toreactivated by using Escherichia coli photolyase for cyclobutane pyrimidine dimers, indicating that restriction enzymes could not function because (6–4) photoproducts remained in recognition sites. But, when UV-irradiated DNA depleted of cyclobutane pyrimidine dimers was incubated with extract of cultured goldfish cells under fluorescent light illumination, it was digested with those restriction enzymes. These results suggested the presence of (6–4) photolyase in cultured goldfish cells as in Dro-sophila, Xenopus and Crotalus.     

Über die acetolysenprodukte der cyanhydrine von 4-pyridazoin und 4-pyridoin: Struktur und ungewöhnliche reaktivität 9. Mitteilung über pyridazine

4-Pyridazoinecyanohydrin was found to be converted into the 1,4-dihydropyridazine derivative 2a on treatment with acetic anhydride. Structures of 2a and the corresponding 4-pyridine derivative 2b were assigned on the basis of spectroscopic data. Chromatography of 2a on silica gel using methanol as eluent yielded methyl 4-pyridazinecarboxylate. The pyridine derivative 2b under similar conditions was converted into a mixture of methyl isonicotinate and 4-pyridinylmethyl acetate. Mechanisms of these unexpected reactions are discussed.     

Efficient Discrimination of Single Nucleotide Polymorphisms (SNPs) Using Oligonucleotides Modified with C5‐Pyrene‐Functionalized DNA and Flanking Locked Nucleic Acid (LNA) Monomers

Oligodeoxyribonucleotides modified with 5‐[3‐(1‐pyrenecarboxamido)propynyl]‐2′‐deoxyuridine monomer X and proximal LNA monomers display higher affinity for complementary DNA, more pronounced increases in fluorescence emission upon DNA binding, and improved discrimination of SNPs at non‐stringent conditions, relative to the corresponding LNA‐free probes across a range of sequence contexts. The results reported herein suggest that the introduction of LNA monomers influences the position of nearby fluorophores via indirect conformational restriction, a characteristic that can be utilized to develop optimized fluorophore‐labeled probes for SNP‐discrimination studies.     

Herstellung von ‘Semialdehyd’-Derivaten von Asparaginsäure- und Glutaminsäure durch Rosenmund-Reduktion

Preparation of ‘Semialdehyde’ Derivatives of Aspartic and Glutamic Acid via the Rosenmund Reduction Suitably protected aspartic-acid ‘β-semialdehyde’ and glutamic-acid ‘γ-aldehyde’ derivatives can be obtained, in good yield by Rosenmund reduction of the corresponding acid chlorides. Benzyloxycarbonyl (Z) and (tert-butoxy)carbonyl (Boc) protecting groups are not affected under these reaction conditions. The sensitive aldehydes, which are obtained in higher purity than by hydride reductions, can directly be used for further transformations like aldol-type reactions.     

Phosphono- und Phosphinoameisensäurederivate via Alkoxycarbonylphosphon- und -phosphinsäuretrimethylsilylester

Phosphono-Phosphinoformic Acid Derivatives via Alkoxycarbonylphosphono and Phosphino Acid Trimethylsilylesters The sodium salts, the chlorides and amides of the phosphono- and phosphinoformic acid esters are easily prepared under various conditions from the corresponding alkoxycarbonyl-P-trimethylsilylesters. The alkoxycarbonyl group of the synthesized compounds it not Stable in acidic solution because of an autocatalytic decarboxylation. Under these conditions the chlorides and amides are hydrolyzed too. The Structure of the compounds prepared are discussed by means of their n.m.r. data.     

Theoretical Calculations and Hydrothermal Processing of BaWO<Subscript>4</Subscript> Materials Under Environmentally Friendly Conditions

The hydrothermal processing conditions of BaWO₄ was studied by using a thermodynamic model of electrolytic solutions in order to avoid the empirical trial-and-error mode for optimizing synthesis of this material. The approach used makes it possible to predict the optimum conditions through stability and yield diagrams, which relate the equilibrium concentration of all species present as a function of temperature, solution pH, and input reagent concentrations. The theoretical predictions were verified by experiments at the predicted optimum conditions. The results showed that the thermodynamic model is adequate to predict the hydrothermal synthesis conditions under which BaWO₄ is stable and can be obtained as a phase-pure form.     

Die Reaktion von Eisen(III) mit Brenzkatechin-3,5-disulfonsäure (Tiron) und Äthylendiamintetraessigsäure

The Reaction of Iron(III) with Catechol-3,5-Disulphonic Acid (Tiron) and Ethylene Diamine-Tetracetic Acid In the system iron(III)-Tiron-EDTA a ternary chelate could be detected besides the well known complexes in a weak acid solution. By means of spectro-photometric measurements under various conditions (concentration of ligands) we found [FeHYL]^4? with λ_max = 555 nm und ε₅₅₅ = 2500 l · mol^?1 · cm^?1. The formation of the ternary chelate is an inner-complex reaction of displacing, in which donor atoms of the EDTA in FeY^? are replaced by Tiron. By graphic methods the equilibrium constants could be calculated from the measurements.     

Enäther als Reaktionspartner von Organometallen II Hydroxyäthyl-allene und andere Folgeprodukte aus Dihydrofuran-Derivaten

Upon treatment with organolithium compounds, 2-alkyl-4,5-dihydrofurans undergo ring opening through β-elimination leading to the corresponding 3,4-dien-1-ol. If 3-chloro-2-methyl-4,5-dihydrofuran serves as a substrate, however, no 3-chloro-3,4-dien-1-ol can be isolated though it acts as a reaction intermediate. Its formation is slow compared to subsequent replacement of halogen by the organic moiety of the alkyllithium reagent. Thus penta-3,4-dien-1-ols are formed, which may isomerize, however, under certain reaction conditions affording terminal acetylenes. These as well as their allene precursors can be converted with sodium in ammonia into pent-4-en-1-ol or, respectively, pent-3-en-1-ol derivates.     

Halogenierte Pentan-4-olid-carbonsäuren

Halogenated pentane-4-olide carboxylic acids. A new synthesis of halogenated pentane-4-olide-4-carboxylic acids starting from α-methylideneglutaronitrile is reported. Different reaction conditions yielded 1,2-dichloro-2,4-butane dicarboxylic acid instead, the decarboxylation of which gave access to 3-chloro-but-3-ene-1-carboxylic acid.     

Cortisol-eine ausgezeichnete Testsubstanz für die Qualitätsprüfung von Einführsystemen

Cortisol is thermally unstable. It is easily decomposed by loss of ketence and water. The spectrum of the resulting 11β-hydroxy-Δ⁴-androsten-3,17-dion can be superimposed upon the spectrum of the undecomposed cortisol, which only can be obtained free of the decomposition product under carefully controlled conditions. The thermal degradation product can be eaisly detected by its molecular peak at mass 302 and a key fragment at mass 163, which are nearly absent in the spectrum of cortisol. Cortisol is therefore an excellent testing material for the quality of inlet systems.     

Oberflächenzusammensetzung und katalytische Aktivität von Nickel–Kupfer-Legierungen

The decomposition of formic- acid vapour has been studied on annealed nickel-copper alloy films. The activity pattern of short-time annealed alloys reveals two maxima and in the range of 50% Ni a minimum. The maxima disappear, when the films are annealed for a longer time. One gets nearly the same variations of the curves of short-and long-time annealed films, when plotting the initial change of electric resistance of the films during reaction against the composition. It is concluded that depending on annealing conditions the surface of the alloys is more or less covered by a copper-rich alloy phase. This is supported by X-ray analysis, confirming the formation of two alloy phases.     

Endocyclische SN-Reaktionen am gesättigten Kohlenstoff? Vorläufige Mitteilung

Fig. 1 illustrates a definition of the terms endocyclic and exocyclic SN-reactions, referring to intramolecular nucleophilic substitution processes that occur by an SN₂-analogous mechanism. Crossing experiments show that the methyl transfer I → II (see scheme 1) does not follow the formally appealing mechanism of the endocyclic SN-process III; the reaction proceeds intermolecularly under all conditions investigated. Kinetic measurements indicate that the methyl transfer XI → XII (see scheme 3) occurs in a similar fashion. This behaviour is believed to follow from the preference of tetrahedral carbon for backside attack by the nucleophile in SN₂-reactions. The general experience, according to which intramolecular reaction paths over cyclic transition states with ring sizes of 5 or 6 are preferred to their intermolecular counterparts, is not to be extrapolated to SN₂-reactions at tetrahedral carbon.     

Reactivity of 2‐Methyl‐4H‐3,1‐benzoxazin‐4‐ones and 2‐Methyl‐4H‐pyrido[2,3‐d][1,3]oxazin‐4‐one under Microwave Irradiation Conditions

The reactivity of variably substituted 2‐methyl‐4H‐3,1‐benzoxazin‐4‐ones and 2‐methyl‐4H‐pyrido[2,3‐d][1,3]oxazin‐4‐one towards carbon and oxygen nucleophiles under microwave irradiation conditions was investigated. Optimization of the reaction conditions of oxazinones with carbon nucleophiles led to the synthesis of a series of 4‐hydroxy‐quinolin‐2‐ones and 4‐hydroxy‐1,8‐naphthyridin‐2‐ones in high yields, whereas reaction with a variety of alcohols proceeded smoothly to the formation of the corresponding N‐acetyl‐anthranilates and nicotinates.     

CpPEt2As4—An Organic‐Substituted As4 Butterfly Compound

Cp^PEt₂As₄ (Cp^PEt=C₅(4‐EtC₆H₄)₅) ( 1 ) is synthesized by the reaction of Cp^PEt. radicals with yellow arsenic (As₄). In solution an equilibrium of the starting materials and the product is found. However, 1 can be isolated and stored in the solid state without decomposition. As₄ can be easily released from 1 under thermal or photochemical conditions. From powder samples of Cp^PEt₂As₄, yellow arsenic can be sublimed under rather mild conditions (T=125 °C). A similar behavior for the P₄‐releasing agent was determined for the related phosphorus compound Cp^BIG₂P₄ ( 2 ; Cp^BIG=C₅(4‐nBuC₆H₄)₅). DFT calculations show the importance of dispersion forces for the stability of the products.     

Simplifying the setup for vacuum‐outlet GC: Using a restriction inside the injection port

The application of vacuum GC has several advantages over pressurized GC. One of the key characteristics is that the optimal gas velocity is very high. Combined with short capillary columns of wide internal diameter, this results in short analysis times using standard GC‐MS equipment. To make vacuum GC possible using a GC‐MS system, a restriction must be positioned at the injection side of the column. This restriction is usually made of deactivated 0.1 mm i.d. fused‐silica tubing which is coupled to the analytical column. Such restrictions will work, but practical challenges are found in coupling, reducing dead volume and robustness. A new way of making restrictions is by incorporating the restriction into the injection port. Using well‐defined short pieces of fused silica with internal diameter of 0.025 mm, one can make a restriction using a Press‐Tight® type connector, and position this inside the injection port. By doing this, the restriction is very short and at high temperature all the time. Activity plays a minimal role, and also leaks will not be an issue as the coupling is in 100% inert gas. Data obtained using this concept is promising as vacuum GC becomes easier and more robust.     

Gerüstumlagerung eines α,β -ungesättigten γ,δ-Epoxiketons bei der Birch-Reduktion: Strukturaufklärung mittels 13C-INADEQUATE-NMR-Spektroskopie

Skeleton Rearrangement of an α-β-Unsaturated γ,δ-Epoxyketone during Birch Reduction: Structure Elucidation by Means of ¹³C-INADEQUATE-NMR Spectroscopy When the γ-epoxide 2 of β-ionone is treated under standard Birch-reduction conditions, unexpectedly a 70% combined yield of regioisomeric octalones 4 and 5 is isolated. These products unquestionably result form cleavage of the central epoxide C?C bond. The structure of compounds 4 and 5 could be determined by means of ¹³C-INADEQUATE-NMR spectroscopy.