Disproof of the Overall Enzymatic Biosynthesis of Vindoline from Tryptamine and Secologanin by Cell-Free Extracts from the Leaves of Catharanthus roseus (L.) G. DON

A cell-free extract, which was isolated from the leaves of mature Catharanthus roseus plants by a previously published procedure, does not convert a mixture of secologanin and radiolabelled tryptamine to vindoline, as was recently claimed. The radioactivity in the purified alkaloid extract determined by earlier workers is certainly due to ‘impurities’ in the presumed ‘vindoline’. This was shown by extensive purification of the alkaloid extract (which contained added unlabelled vindoline as a carrier) followed by chemical conversion of vindoline to two derivatives and subsequent purification, ultimately giving unlabelled deacetylvindoline.     

(Cyclophan-Metall)-Komplexe: Synthese und Kristallstruktur von ([3.3]Paracyclophan)gallium(I)-tetrabromgallat(III)

Cyclophane-Metal Complexes: Synthesis and Crystal Structure of ([3.3]Paracyclophane)gallium(I) Tetrabromogallate(III) [3.3]Paracyclophane forms 1:1 complexes 2a and 2b with both Ga[GaCl₄] and Ga[GaBr₄]. The crystalline products obtained from toluene solution at room temperature are much less sensitive to air and moisture than most other arene complexes of Ga(I). Solubilities in standard organic solvents are very low, suggesting coordination polymers. The X-ray diffraction analysis of 2b confirms the presence of a two-dimensional network. Both aromatic rings of each cyclophane molecule are η⁶-coordinated from the outer side to Ga(I)-atoms. The position of these metal cations is 2.75 Å above the ring centres. The arene rings are parallel within each cyclophane, but tilted by 48.5° with respect to those of the neighbouring cyclophane. The coordination sphere of the Ga(I) centres is completed by two Br-atoms of two GaBr anions, which link the Ga(I) cations to give … Ga[GaBr₄] Ga[GaBr₄]Ga … strands. The double interconnection of the Ga(I)-atoms gives rise to a two-dimensional sheet structure, which is thus different from the structure of the previously described Ga[GaBr₄] complex of [2.2]paracyclophane, where a three-dimensional network was observed.     

Methodology for the preparation of 2-argininylbenzothiazole

An efficient process to produce kilogram quantities of a key argininylbenzo[d]thiazole intermediate was developed for the preparation of the tryptase inhibitor RWJ-56423. A variety of activated arginine esters and benzo[d]thiazole nucleophiles were evaluated as coupling partners. Our work led to the selection and optimization of an argininyl imidazolide ester and benzothiazol-2-yl MgCl nucleophile. This paper focuses on the preparation, use, and stability of the benzothiazol-2-yl Grignard reagents.     

Identification and relative quantification of adenosine to inosine editing in serotonin 2c receptor mRNA by CE

A new method has been developed allowing the identification and relative quantification of different forms of mRNA after RNA editing. This method was applied to the serotonin 2c receptor mRNA that potentially exhibits 32 different forms after adenosine to inosine editing at five different sites located in a row of 13 nucleotides. CE was used to characterize fluorescently labeled ssDNA molecules on the basis of their conformational polymorphism. The relative amount of these 32 mRNA forms has been estimated by measuring the fluorescence intensity of each individual DNA strand. Accuracy of quantification was established by diluting one form into another or into a mixture of cDNA, showing linear and precise proportion of each form (0.06 相似文献   

Conformations and dynamics of the phosphodiester backbone of a DNA fragment that bears a strong topoisomerase II cleavage site

The dynamics of the DNA phosphodiester backbone conformations have been studied for a strong topoisomerase II cleavage site (site 22) using molecular dynamics simulations in explicit water and in the presence of sodium ions. We investigated the backbone motions and more particularly the BI/BII transitions involving the epsilon and zeta angles. The consensus cleavage site is adjacent to the phosphate which shows the most important phosphodiester backbone flexibility in the sequence. We infer that these latter properties could be responsible for the preferential cleavage at this site possibly through the perturbation of the cleavage/ligation activities of the topoisomerase II. More generally, the steps pur-pur and pyr-pur are those presenting the highest BII contents. Relations are observed between the backbone phosphodiester BI/BII transitions and the flexibility of the deoxyribose sugar and the helical parameters such as roll. The roll is sequence dependent when the related phosphate is in the BI form, whereas this appears not to be true when it is in the BII form. The BI/BII transitions are associated with water migration, and new relations are observed with counterions. Indeed, it is observed that a strong coupling exists between the BII form and the presence of sodium ions near the adjacent sugar deoxyribose. The presence of sodium ions in the O4' surroundings or their binding could assist the BI to BII transition by furnishing energy. The implications of these new findings and, namely, their importance in the context of the sequence-dependent behavior of BI/BII transitions will be investigated in future studies.     

Polyelectrolyte-modified inverse microemulsions and their use as templates for the formation of magnetite nanoparticles

This paper is focused on the characterization of polyelectrolyte-modified inverse microemulsions and their use as templates for the synthesis of magnetite nanoparticles. It is shown that the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) of low molar mass can be incorporated into the individual inverse microemulsion droplets (L2 phase) consisting of heptanol, water, and an amphoteric surfactant with a sulfobetaine head group. Up to a polymer concentration of 20% by weight in the aqueous phase and for different molecular weights of the polymer, an isotropic phase still exists. At a PDADMAC concentration of 10% the area of the isotropic L2 phase is shifted in direction to the water corner. In the percolated area of the L2 phase, i.e., at higher water content, a temperature-dependent change in the conductivity can by observed, and bulk water can be detected by means of differential scanning calorimetry measurements. The unusual temperature-dependent behavior of the polymer-modified system, i.e., the conductivity decrease with increasing temperature, can be explained by temperature-sensitive polyelectrolyte-surfactant interactions, influencing the droplet-droplet interactions. These PDADMAC-modified microemulsions can be successfully used as a template for the formation of ultrafine magnetite particles, in contrast to the nonmodified microemulsion, where the process is misdirected due to the "disturbing" effect of the surfactants. However, in the presence of PDADMAC the surfactant head groups were masked, and therefore magnetite can be synthesized. During the process of magnetite formation the PDADMAC controls the particle growing and stabilizes spherical magnetite particles with a diameter of 17 nm, which can be redispersed without a change in size.     

Polyoxometalate-based metal organic frameworks (POMOFs): structural trends, energetics, and high electrocatalytic efficiency for hydrogen evolution reaction

The grafting of the triangular 1,3,5-benzene tricarboxylate linkers (denoted trim) on tetrahedral ε-Keggin polyoxometalates (POMs) capped by Zn(II) ions, formed in situ under hydrothermal conditions, has generated three novel POM-based metal organic frameworks (POMOFs). (TBA)(3)[PMo(V)(8)Mo(VI)(4)O(36)(OH)(4)Zn(4)][C(6)H(3)(COO)(3)](4/3)·6H(2)O (ε(trim)(4/3)) is a 3D open-framework built of molecular Keggin units connected by trim linkers, with channels occupied by tetrabutylammonium (TBA) counterions. ε(trim)(4/3) is a novel (3,4)-connected net, named ofp for open-framework polyoxometalate, and computer simulations have been used to evaluate its relative stability in comparison with ctn- and bor-like polymorphs, showing the stability of this novel phase directly related to its greatest density. A computational study was also undertaken with the aim of locating TBA molecules, the positions of which could not be deduced from single crystal X-ray diffraction, and further rationalizes their structure directing role. In (TBA)(3)[PMo(V)(8)Mo(VI)(4)O(37)(OH)(3)Zn(4)][C(6)H(3)(COO)(3)] (ε(2)(trim)(2)), the building unit is not the molecular Keggin but a dimerized form of this POM. Their connection via trim linkers generates a 3D framework with channels filled by TBA cations. In (TBA)(3)[PMo(V)(8)Mo(VI)(4)O(37)(OH)(3)Zn(4)][C(6)H(3)(COO)(3)]·8H(2)O ([ε(trim)](∞)), zigzag chains are connected via the organic linkers, forming 2D grids. Modified electrodes were fabricated by direct adsorption of the POMOFs on glassy carbon or entrapment in carbon paste (CPE). A remarkable electrocatalytic hydrogen evolution reaction (HER) was detected with a yield greater than 95%, and a turnover number as high as 1.2 × 10(5) was obtained after 5 h. The reported POMOF-based electrodes are more active than platinum, with a roughly 260 mV anodic shift. Finally, the electrocatalytic activities of ε(trim)(4/3)/CPE electrodes in various XCl (X = Li, Na, K, Cs) media have been studied. This allowed us to detect a cation effect and propose an electrocatalytic mechanistic pathway for the HER.