Struktur und Mechanismus bei Fragmentierungsreaktionen 1. Teil. Die stereoisomeren 10-Chlor-decahydro-isochinoline. Fragmentierungsreaktionen, 23. Mitteilung

cis-10-Chloro-N-methyl-decahydro-isoquinoline ( 5 ) and its trans-isomer 6 undergo heterolytic fragmentation in 80% ethanol by different mechanisms. As predictable on stereo-chemical grounds the cis-isomer 5 reacts by the accelerated synchronous mechanism, the trans-isomer 6 , however, by the two-step carbonium ion mechanism. Synchronous fragmentation therefore dominates over the two-step process even when the latter would lead to a relatively stable tertiary carbonium ion. In both cases the more highly substituted and thermochemically more stable olefinic fragment 8 is formed.     

Synthesis of pyrene and benzo[a]pyrene adducts at the exocyclic amino groups of 2'-deoxyadenosine and 2'-deoxyguanosine by a palladium-mediated C-N bond-formation strategy

Single-electron oxidation of the carcinogenic hydrocarbon benzo[a]pyrene (BaP) is thought to result in a radical cation intermediate and this species has been proposed to cause alkylation at the nitrogens of the purine nucleobases. Although several different nucleoside adducts have been isolated as arising from this mode of metabolic activation, there are no selective, total syntheses of the stable exocyclic amino group adducts formed by the single-electron oxidation of any hydrocarbon with the purine 2'-deoxynucleosides to date. In this paper we disclose the synthesis of the model adducts N(6)-(1-pyrenyl)-2'-deoxyadenosine and N(2)-(1-pyrenyl)-2'-deoxyguanosine as well as the first synthesis of the carcinogen-linked nucleoside derivatives N(6)-(6-benzo[a]pyrenyl)-2'-deoxyadenosine and N(2)-(6-benzo[a]pyrenyl)-2'-deoxyguanosine via a palladium-mediated C-N bond formation. Two different coupling strategies were attempted: coupling of an aryl bromide with a suitably protected nucleoside and the coupling of an arylamine with a suitable halonucleoside. The former had somewhat limited applicability in that only N(6)-(1-pyrenyl)-2'-deoxyadenosine was prepared by this method; on the other hand, the latter was more general. However, there are noteworthy differences in the amination reactions at the C-6 and C-2 positions. Reactions at the C-6 resulted in the competing formation of a 1:2 amine-nucleoside adduct in addition to the desired monoaryl nucleoside. Such a dimer formation was not observed at the C-2. The C-2 adducts, however, displayed an interesting conformational behavior.     

Field gradient electrophoresis

The class of equilibrium gradient methods utilizes the opposition of two forces, at least one of which changes in magnitude with position, to separate and concentrate analytes. The drawback of many methods of this type is that the production of two opposing forces requires in comparison to standard methods, such as capillary electrophoresis, a relatively complex apparatus. In addition, for techniques such as electric field gradient focusing, hydrodynamic flow leads to Taylor dispersion, which limits the attainable concentration factor. We propose a new method, gradient field electrophoresis, which achieves analyte separation and focusing with only one spatially varying force, an electric field gradient. A model for the method is developed and used to analyze peak capacity. Experimental results for a protein (R-phycoerythrin) are given and compared to the model.     

Identifizierung von sechs Komponenten des Spurpheromons der Ameisenart Lasius fuliginosus. Vorläufige Mitteilung

Hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, and dodecanoic acid are components of the trail pheromone of the ant species Lasius fuliginosus. The acids were extracted from the contents of the rectal ampullae and identified by the mass spectra and gas chromatographic retention times of the corresponding methyl esters.     

Sample evaporation in conventional GC split/splitless injectors. Part 1: Some quantitative estimates concerning heat consumption during evaporation

During sample evaporation in conventional vaporizing injection, the supply of heat to the evaporating liquid is a problem, first because the amounts of heat consumed are relatively large and, secondly, because the heat must be transferred to the sample within a very short time. Times available for evaporation, required amounts of heat, possible sources of heat, and the time required to transfer the heat to the sample liquid are discussed. It is shown that mixing with carrier gas contributes little heat to the evaporation process, but also that packings with glass wool have too low a heat capacity to deliver the required amount of heat to the evaporating sample. Transfer of heat from the insert wall to the sample easily requires several seconds, even if cooling of the vaporizing zone by 20° is accepted. Thus “flash evaporation” is usually impossible and most liquids must be held in the vaporizing chamber to allow full evaporation.     

Sample evaporation in conventional split/splitless GC injectors. Part 3: Retaining the liquid in the vaporizing chamber

As most sample liquids tend to pass through an empty injector insert at a speed which is too high to enable complete evaporation, movement of the liquid must be arrested before it reaches the column entrance. Stopping the liquid means deposition on to a surface; this, however, is possible only after the temperature of the surface has been cooled to (or below) the boiling point of the liquid (solvent). The performance of different means of stopping the liquid has been tested visually (by the method described in Part 2). Baffles on the wall of the injector insert had hardly any effect on evaporation: the band of liquid leaving the syringe needle performed a perfect slalorn around them. The inverted cup proved more efficient, but the best performance was obtained from a light plug of glass wool: owing to its low thermal mass, the first fibers to be met by the liquid are immediately cooled to the solvent boiling point, allowing the liquid to wet it. The sample liquid is sucked up by the glass wool, from where the sample evaporates relatively slowly, often over a period of several seconds.     

Assembly of Photosystem I and II during the Early Phases of Light-Induced Development of Chloroplasts from Proplastids in Spirodela oligorrhiza

The aquatic higher plant Spirodela oligorrhiza , which contains proplastids when grown in the dark, was used to study light-dependent chloroplast development. Low-temperature (77 K) and room temperature fluorescence were utilized in situ on whole plants to examine plastid development. The dark-grown plants contain two 77 K fluorescence peaks, at 633 nm (F633) and at 657 nm (F657), with F633 dominating. The F657 species represents protochlorophyllide that is bound to protochloro-phyllide oxidoreductase. It was rapidly phototrans-formed to chlorophyllide (within 5 s) via a monomolec-ular reaction. Free protochlorophyllide (F633) was converted to chlorophyllide during a 3 h exposure to light. Photosystem (PS) assembly in Spirodela could be detected 2 h after the plants were first exposed to light, with the PSII reaction center (77 K fluorescence at 684 nm) appearing slightly before the PSI reaction center (77 K fluorescence at 725 nm). After the first reaction centers were formed the antenna complexes were added; the light-harvesting complex (LHC) I of PSI appeared after 8 h, and 47 kDa chlorophyll protein of PSII appeared between 12 h and 24 h. After 30 h of exposure to light, the plants acquired the ability to perform a light state transition, marking the appearance of functional LHCII complexes in the developing chloroplast. Finally, it was found that photosynthetic activity, as measured by room temperature chlorophyll fluorescence, accelerated con-comitantly with detection of the antenna complexes. Therefore, although reaction centers are detected very early during the proplastid to chloroplast conversion, they may have little activity or be unstable until the antennae are present.     

Platinum and palladium imido and oxo complexes with small natural bite angle diphosphine ligands

Treatment of L(2)MCl(2) (M = Pt, Pd; L(2) = Ph(2)PCMe(2)PPh(2) (dppip), Ph(2)PNMePPh(2) (dppma)) with AgX (X = OTf, BF(4), NO(3)) in wet CH(2)Cl(2) yields the dinuclear dihydroxo complexes [L(2)M(mu-OH)](2)(X)(2), the mononuclear aqua complexes [L(2)M(OH(2))(2)](X)(2), the mononuclear anion complexes L(2)MX(2), or mixtures of complexes. Addition of aromatic amines to these complexes or mixtures gives the dinuclear diamido complexes [L(2)Pt(mu-NHAr)](2)(BF(4))(2), the mononuclear amine complexes [L(2)M(NH(2)Ar)(2)](X)(2), or the dinuclear amido-hydroxo complex [Pt(2)(mu-OH)(mu-NHAr)(dppip)(2)](BF(4))(2). Deprotonation of the Pd and Pt amine or diamido complexes with M'N(SiMe(3))(2) (M' = Li, Na, K) gives the diimido complexes [L(2)M(mu-NAr)](2) associated with M' salts. Structural studies of the Li derivatives indicate association through coordination of the imido nitrogen atoms to Li(+). Deprotonation of the amido-hydroxo complex gives the imido-oxo complex [Pt(2)(mu-O)(mu-NAr)(dppip)(2)].LiBF(4).LiN(SiMe(3))(2), and deprotonation of the dppip Pt hydroxo complex gives the dioxo complex [Pt(mu-O)(dppip)](2).LiN(SiMe(3))(2).2LiBF(4).     

Synthesis, structure, spectroscopic properties, and electrochemistry of (1,8,15,22-tetrasubstituted phthalocyaninato)lead complexes

Three (1,8,15,22-tetrasubstituted phthalocyaninato)lead complexes Pb[Pc(alpha-OR)(4)] [H(2)Pc(alpha-OC(5)H(11))(4) = 1,8,15,22-tetrakis(3-pentyloxy)phthalocyanine; H(2)Pc(alpha-OC(7)H(15))(4) = 1,8,15,22-tetrakis(2,4-dimethyl-3-pentyloxy)phthalocyanine; H(2)Pc(alpha-OC(10)H(7))(4) = 1,8,15,22-tetrakis(2-naphthyloxy)phthalocyanine] (1-3) have been prepared as racemic mixtures by treating the corresponding metal-free phthalocyanines H(2)Pc(alpha-OR)(4) (4-6) with Pb(OAc)(2).3H(2)O in refluxing n-pentanol. The molecular structure of Pb[Pc(alpha-OC(5)H(11))(4)] (1) in the solid state has been determined by single-crystal X-ray diffraction analysis. This compound, having a nonplanar structure, crystallizes in the monoclinic system with a P2(1)/c space group. Each unit cell contains two pairs of enantiomeric molecules, which are linked by weak coordination of the Pb atom of one molecule with an aza nitrogen atom and its neighboring oxygen atom from the alkoxy substituent of another molecule, forming a pseudo-double-decker supramolecular structure in the crystals with a short ring-to-ring separation, 2.726 A, and thus a strong ring-ring pi-pi interaction. The decreased molecular symmetry for these complexes has also been revealed by the NMR spectra of 1 and 2. The methyl protons of the 3-pentyloxy and 2,4-dimethyl-3-pentyloxy side chains of 1 and 2, respectively, are chemically inequivalent. In addition to the elemental analysis and various spectroscopic characterizations, these compounds have also been electrochemically studied. Two one-electron oxidations and up to five one-electron reductions have been revealed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods.     

Steric and Electronic Effects, Enantiospecificity, and Reactive Orientation in DNA Binding/Cleaving by Substituted Derivatives of [SalenMn(III)](+)

Twenty-six derivatives of [SalenMn(III)](+) (1) bearing halogen, nitro, amino, ether, alkyl, or aryl substituents on the aromatic rings and/or at the imine positions or containing 1,3-propylene-, 1,2-phenylene-, 1,2-cyclohexane-, or 1,2-diphenylethylenediamine in place of ethylenediamine as the bridging moiety have been synthesized. The DNA binding/cleaving properties of these complexes in the presence of terminal oxidants have been examined using DNA affinity cleaving techniques. Active derivatives produced DNA cleavage from the minor groove at sites containing multiple contiguous A:T base pairs. For aryl-substituted derivatives, DNA cleavage efficiency was found to vary with both the identity and position of attachment of substituents. The precise patterns of cleavage at A:T target sites varied with the position of attachment of substituents, but not with the identity of the substituents. The results suggest that substituents alter specificity through both steric and electronic effects. The 3,3'-difluoro and -dichloro derivatives produced cleavage patterns that match those of the parent complex, suggesting that the activated form of 1 produces cleavage from an orientation in which the concave edge of the complex faces away from the floor of the DNA minor groove. Bridge modifications yield complexes with reduced DNA cleaving activity relative to 1. DNA cleaving efficiency was found to vary with both the structure and stereochemistry of the bridge. Cleavage efficiency for the complex derived from (R,R)-cyclohexanediamine was 5 times greater than that for the (S,S) enantiomer. Cleavage patterns produced by the enantiomeric complexes at A:T rich target sites were different, demonstrating enantiospecific recognition and cleavage of right-handed double-helical DNA.