Search results for "ALK"

Coupling of the guanosine glycosidic bond conformation and the ribonucleotide cleavage reaction: implications for barnase catalysis.

2007

To examine the possible relationship of guanine-dependent GpA conformations with ribonucleotide cleavage, two potential of mean force (PMF) calculations were performed in aqueous solution. In the first calculation, the guanosine glycosidic (Gχ) angle was used as the reaction coordinate, and computations were performed on two GpA ionic species: protonated (neutral) or deprotonated (negatively charged) guanosine ribose O2 ′. Similar energetic profiles featuring two minima corresponding to the anti and syn Gχ regions were obtained for both ionic forms. For both forms the anti conformation was more stable than the syn, and barriers of ∼4 kcal/mol were obtained for the anti → syn transition. Str…

2,5-Dialkoxysubstituierte Oligo- und Poly(1,4-phenylenethenylen)e

1994

2,5-Dialkoxy Substituted Oligo- and Poly(1,4-phenyleneethenylene)s O-Alkylation and regioselective Rieche formylation of 2-methylhydroquinone (1) yields the 2,5-dialkoxy-4-methylbenzaldehydes 4a–j. The corresponding azomethines 5a–j enter in a strongly alkaline medium a selfcondensation reaction leading to the title compounds 6/7a–j. These conjugated oligomers and polymers possess highly regular structures with exclusively (E)-configurated double bonds. GPC, IR, 1H-, 13C-NMR and MS-FD measurements were used for their characterization. Somewhat different results were obtained for the similarly prepared Schiff base 5l which contains chlorine substituents in the side chains. Cleavage of hydrog…

Stereoselective Synthesis of γ-Fluorinated α-Amino Acids Using 2-Hydroxy-3-pinanone as an Auxiliary

2000

(+)-(S)-2-Amino-4-fluorobutanoic acid (5a) (> 96% ee), its α-methylated derivative (+)-(S)-5b (85% ee), and (−)-(S)-2-amino-4-fluoro-4-pentenoic acid (10) (81% ee) were synthesized by diastereoselective alkylation in the presence of LDA at low temperatures. Alkylation of (+)-(R,R,R)-2-hydroxy-3-pinanone based imines of glycine tert-butyl ester 1a or alanine isopropyl ester 1b with 1-bromo-2-fluoroethane (2) or 3-bromo-2-fluoropropene (7), respectively, followed by stepwise deprotection was used. The selectivity of the alkylation increased by lithium/magnesium exchange or for 1b also by addition of DMPU. Differences in the reactivity of enolate alkylations of enantiomerically pure or racemic…

Relaxation of electron-hole pairs and scintillation mechanism in alkali halide crystals

1997

Abstract The mechanism of the ionizing radiation energy transfer from host lattice to luminescence centers is discussed taking into account the results of the recent experimental investigations of electron-hole pair relaxation in alkali iodide crystals. The high scintillation yield in CsI-Tl, CsI-Na and partially in Nal-Tl crystals is explained by the process of the motion and capture of a one-center self-trapped exciton by impurity ions.

On the Correlations Between Constitution and Scintillation Properties in the p-Oligophenylene Series

1968

Abstract The paper deals with the problem: What properties are requested from an organic scintillator solute and what structural principles are given to realize, or at least to influence them especially by looking at the p-oligophenylene series? According to their importance and also in respect to more or less special purposes one can distinguish the following sequence: 1) An organic scintillator solute must have a sufficient solubility in all types of solvents used for this counting method. As a result of extensive systematic studies substitution of larger alkyl groups has been recognized as a very effective principle of solubilization. By use of branched, particularly long-chain branched …

Iron‐Catalyzed C( sp 2 )−C( sp 3 ) Cross‐Coupling of Chlorobenzamides with Alkyl Grignard Reagents: Development of Catalyst System, Synthetic Scope, …

2018

ISOLATION OF RAT LIVER EPOXIDE HYDRATASE: PROPERTIES AND SUBSTRATE SPECIFICITY OF THE PURE ENZYME

1977

ABSTRACT The microsomal enzyme epoxide hydratase has been purified to homogeneity as judged by electrophoretical, ultracentrifugal and immunological criteria and by C- and N-terminal analysis. The preparation procedure consisted of solubilisation using the non-ionic detergent cutscum, (NH4)2SO4 precipitation, ion-exchange chromatography on DEAE-cellulose and cellulose phosphate and hydrophobic chromatography on butyl-sepharose. The product was detergent-free, had a relatively high content of hydrophobic amino acids and tended to aggregate in aqueous solutions. The protein had a minimum molecular weight of 49,000 ± 500 with a sedimentation coefficient of S20w≃ 3. Antibodies raised against th…

Semicarbazides as gel forming agents for common solvents and liquid crystals

2006

This paper describes the synthesis of 14 new gelling agents with semicarbazide groups as H-bonding motifs and alkyl- and/or azobenzene side groups. They gel solvents like decaline, 1,2-dichlorobenzene and toluene and liquid crystalline mixtures. X-Ray structure analysis shows that the semicarbazides are connected by H-bonds, each molecule to four neighbours. As a result a ribbon is formed with a core of H-bonded semicarbazide groups and alkyl chains sticking to the side. IR measurements show an unchanged H-bonding motif in large crystals and in the gel fibres, even in LC-mixture. During heating the gel melts (rheology), while the H-bonding motif of the crystal disappears (IR and DSC measure…

O-Alkylation of a lignite humic acid by phase-transfer catalysis

2006

A mild phase-transfer catalytic reaction has been conducted to O-alkylate the acidic functions of a lignite humic acid (HA), using tetrabutylammonium hydroxide as the phase-transfer catalyst. The HA acidic functional groups were made to react, in tetrahydrofuran, by nucleophilic substitution with several alkyl halides-methyl iodide, and ethyl, propyl, and butyl, and benzyl bromide. The occurrence of the O-alkylation reaction was assessed by elemental analysis and 1H NMR, CPMAS 13C NMR, and FTIR spectroscopy. Bonding of alkyl groups increased the carbon and hydrogen content and the H/C ratios of all the humic reaction products. Increased nitrogen in the reaction products suggested incomplete…

Chemical Synthesis of 2′-O-Alkylated siRNAs

2010

Chemical synthesis has been a major endeavor to create active siRNAs. The downregulation of mRNA by 21-mer double-stranded siRNAs can be improved by using modified nucleotides, especially 2'-O-alkylated ones. Besides the commercially available 2 cent-O-methyl ribosides, 2'-alkyl groups bearing positive charges are especially promising candidates. We have shown that in a proper formulation they are superior to unmodified siRNAs. This may be due to enhanced stability and most probably to a better uptake into the cells.