On the ternary B 2-phase in the Al-Co-Ga system

Summary Lattice parameter values were determined for the ternary B 2-phase in the Al-Co-Ga system, and it was found that a continuous solid solution exists between -AlCo and -CoGa. Phase boundaries of the ternary phase at 1 100 K were derived from the variation of the lattice parameter with composition.

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Über die ternäre B 2-Phase im System Al-Co-Ga

Zusammenfassung Im Bereich der ternären B 2-Phase im System Al-Co-Ga wurden die Werte des Gitterparameters bestimmt; es stellte sich heraus, daß eine durchgehende feste Lösung zwischen -AlCo und -CoGa besteht. Die Phasengrenzen der ternären Phase bei 1 100 K wurden aus der Änderung des Gitterparameters mit der Zusammensetzung abgeleitet.

     

Synthesis of functionalized rab GTPases by a combination of solution- or solid-phase lipopeptide synthesis with expressed protein ligation

Prenylated proteins with non-native functionalities are generally very difficult to obtain by recombinant or enzymatic means. The semisynthesis of preparative amounts of prenylated Rab guanosine triphosphatases (GTPases) from recombinant proteins and synthetic prenylated peptides depends largely on the availability of functionalised prenylated peptides corresponding to the proteins' native structure or modifications thereof. Here, we describe and compare solution-phase and solid-phase strategies for the generation of peptides corresponding to the prenylated C terminus of Rab7 GTPase. The solid-phase with utilisation of a hydrazide linker emerges as the more favourable approach. It allows a fast and practical synthesis of pure peptides and gives a high degree of flexibility in their modification. To facilitate the analysis of semisynthetic proteins, the synthesised peptides were equipped with a fluorescent group. Using the described approach, we introduced fluorophores at several different positions of the Rab7 C terminus. The position of the incorporated fluorescent groups in the peptides did not influence the protein-ligation reaction, as the generated peptides could be ligated onto thioester-tagged Rab7. However, it was found that the positioning of the fluorescent group had an influence on the functionality of the Rab7 proteins; analysis of the interaction of the semisynthetic Rab7 proteins with REP (Rab escort protein) and GDI (guanosine diphosphate dissociation inhibitor) molecules revealed that modification of the peptide side chains or of the C-terminal isoprenoid did not significantly interfere with complex formation. However, functionalisation of the C terminus was found to have an adverse effect on complex formation and stability, possibly reflecting low structural flexibility of the Rab GDI/REP molecules in the vicinity of the lipid-binding site.     

Protonization of purine, adenine, and guanine. NMR spectra and structure of mono, di, and tri cations

Proton NMR. spectra of purine, adenine, guanine and methylsubstituted guanines have been measured in CF₃COOH, FSO₃H and FSO₃H? SbF₅? SO₂ at 27° and low temperatures. These conditions permit to study multiple protonation of purines, using chemical shifts of CH, NH and OH protons. The spectra of mono-, di- and tri-cations are described and fully assigned.     

Separation of friend erythroleukaemic cell histones and high-mobility-group proteins by reversed-phase high-performance liquid chromatography

A procedure for the rapid separation of histones and high-mobility-group (HMG) proteins from Friend erythroleukaemic cells (line F4N) by reversed-phase high-performance liquid chromatography is reported. By using a Nucleosil 300-5 C₄, column and a multistep water—acetonitrile gradient containing 0.1% trifluoroacetic acid, the HMG-1 and HMG-2 proteins, several his subtractions including H1⁰, H4, H2B, two H2A variants and two H3 subtractions were separated. Under changed conditions, by applying a varied acetonitrile gradient system, even two H2B variants were fractionated. The methods described seem to be a real alternative to the time-consuming polyacrylamide gel electrophoresis.     

Synthesis of 2′-Deoxyribofuranosides of 8-Aza-7-deazaguanine and Related Pyrazolo[3,4-d]pyrimidines

The N(1)- and N(2)-(2′-deoxyribofuranosides) 1 and 2 , respectively, of 8-aza-7-deazaguanine were prepared via phase-transfer glycosylation in the presence or absence of Bu₄NHSO₄ as catalyst of 6-amino-4-methoxy-lH-pyrazolo[3,4-d]pyrimidine ( 7c ) with 2-deoxy-3,5-di-O-(p-toluoyl)-α-D -erythro-pentofuranosyl chloride ( 10 ). On a similar route, but without catalyst and employing THF as organic phase, the 6-amino-4-chloronucleosides 11b and 12b were synthesized from 7a and converted into the N(1)-and N(2)-substituted 4-thioxo analogues 17a and 18a , respectively. The ratio of N(1)- to N(2)-glycosylation was 2:1 for 7c and 1:1 for 7a , viz. depending on the nucleobase structure. The rate of the H⁺-catalyzed N-glycosyl hydrolysis was strongly decreased for the N(2)-(β-D -2′-deoxyribofuranosides) as compared to the N(1)-compounds. However, the N(1)-nucleoside 1 , which is an isostere of 2′-deoxyguanosine, is sufficiently stable to be employed later in solid-phase oligonucleotide synthesis.     

Investigation on anodized aluminium

Results of examinations with TEM, SEM, EDX, ISS, SIMS and AES on sulphuric acid anodized films on aluminium are reported. Important technical information about the 20-μm thick coatings were obtained by monolayer and depth analysis. The fine structure of the oxide film and its modifications during a sealing process are discussed. Possibilities to prevent sealing smut on the surface are shown. The metal distribution inside the films which are coloured electrolytically with metal salts, is investigated.     

Two types of intramolecular addition of an Al-N multiple-bonded monomer LAlNAr' arising from the reaction of LAl with N3Ar' (L = HC[(CMe)(NAr)]2, Ar' = 2,6-Ar2C6H3, Ar = 2,6-iPr2C6H3)

The reaction of beta-diketiminated aluminum(I) monomer LAl with a large bulky azide N3Ar' (L = HC(CMeNAr)2, Ar' = 2,6-Ar2C6H3, Ar = 2,6-iPr2C6H3) in the temperature range from -78 degrees C to room temperature affords two different isomers 2 and 3, which have been characterized by spectroscopic and X-ray structural analyses, as well as elemental analysis. The variable-temperature 1H NMR kinetic studies of this reaction indicate the existence of the monomer LAlNAr' (1) at low temperature and the thermal stability of the compounds increases in the order of 1 < 2 < 3.     

Fibre optic fluorometric enzyme sensors for hydrogen peroxide and lactate,based on horseradish peroxidase and lactate oxidase

An optical biosensor for the determination of hydrogen peroxide based on immobilized horseradish peroxidase is described. The fluorescence of the dimeric product of the enzyme catalysed oxidation of homovanillic acid is utilized to determine the concentration of H₂O₂. The membrane-bound enzyme is attached to a bifurcated fibre bundle permitting excitation and detection of the fluorescence by a fluorometer. The response of the sensor is linear from 1 to 130 M hydrogen peroxide; the coefficient of variation is 3%. The sensor is stable for more than 10 weeks. The operating pH for maximal sensor response is 8.15. This allows the sensor to be used in combination with oxidase reactions producing hydrogen peroxide, as is demonstrated with a co-immobilized lactate oxidase-horseradish peroxidase optode for the determination of L-lactate. The fluorescence intensity of this sensor depends linearly on the concentration of lactate between 3 and 200 M and a throughput of 10 samples per hour is possible. The precision is in the same range as that of the monoenzyme optode. The lifetime of the bienzyme sensor for lactate is considerably shorter than that of the peroxidase sensor; it is limited by the stability of the immobilized lactate oxidase enzyme. The sensor has been applied to the determination of lactate in control serum.     

Zum Mechanismus der nucleophilen Addition an 2,3-Dihydrodipyrrin-1(10H)-one

¹H NMR-spectroscopic investigations of the acid catalyzed addition of methanol to dihydrodipyrrinones (Z)-2, (E)-2, and4 show the C-protonation of their enamide parts to be the first and rate determining step forming the key intermediate, the N-acyl-immonium ion N⁺. Its ability to add nucleophiles diastereoselectively can be used to prepare the adductsl-3 andl-5. Exclusive formation of thelike-isomer can be explained by a stereoelectronically favoured approach of the nucleophile and by the thermodynamically favoured arrangement of the bulky ring substituents. Both explanations are based on low temperature X-ray crystal structure determinations: in the first place, the orientation of the added nucleophile could be found to be nearly parallel to the -plane of the lactam unit and quasi-axial with respect to theenvelope-like conformation of the five-ring lactam; in the second place, the relative orientation of the methoxycarbonyl-metyl-group at C-3 and the pyrrolylmethyl-substituent at C-4 could be found to be atrans-quasi-diequatorial one.