Search results for "Ridge"
showing 10 items of 531 documents
Intra-Helical Salt Bridge Contribution to Membrane Protein Insertion.
2021
ABSTRACTSalt bridges between negatively (D, E) and positively charged (K, R, H) amino acids play an important role in protein stabilization. This has a more prevalent effect in membrane proteins where polar amino acids are exposed to a very hydrophobic environment. In transmembrane (TM) helices the presence of charged residues can hinder the insertion of the helices into the membrane. This can sometimes be avoided by TM region rearrangements after insertion, but it is also possible that the formation of salt bridges could decrease the cost of membrane integration. However, the presence of intra-helical salt bridges in TM domains and their effect on insertion has not been properly studied ye…
Use of reversed-phase C18 Sep-Pak cartridges for the purification and concentration of sepiapterin and other pteridines
1985
Abstract Several pteridines have been tested for their ability to bind to C 18 Sep-Pak. Riboflavin, sepiapterin, deoxysepiapterin, 6-acetyl-7,8-dihydropterin, 6-acetyldihydrohomopterin and 3′-hydroxysepiapterin were strongly retained and all but 6-acetyldihydrohomopterin quantitatively recovered upon elution with 2 ml of methanol. The effect of the concentration and volume of the sample, pH and salt concentration on the retention of sepiapterin have been studied. The procedure was very useful for the purification, desalting, solvent exchange and concentration of pteridines having high affinity for the cartridge. C 18 Sep-Pak has been applied succesfully to sample clean-up prior to high-perf…
Oxidation of alcohols to carbonyl compounds with CrO3.SiO2 in supercritical carbon dioxide.
2006
Supercritical carbon dioxide (scCO2) is an effective reaction medium to perform the oxidation of primary and secondary aliphatic alcohols to the corresponding carbonyl compounds with chromium trioxide supported on silica. These reactions were performed by flowing a solution of the alcohol in scCO2 through a column containing the supported reagent and recovering the product by depressurization. This method avoids the use of organic solvents and the contamination of the products with chromium species.
Bridge-Clamp Bis(tetrazine)s with [N] 8 π-Stacking Interactions and Azido- s -Aryl Tetrazines: Two Classes of Doubly Clickable Tetrazines
2020
Click chemistry at a tetrazine core is useful for bioorthogonal labeling and crosslinking. Introduced here are two new classes of doubly clickable s-aryl tetrazines synthesized by Cu-catalyzed cross-coupling. Homocoupling of o-brominated s-aryl tetrazines leads to bis(tetrazine)s structurally characterized by tetrazine cores arranged face-to-face. [N]8 π-stacking interactions are essential to the conformation. Upon inverse electron demand Diels-Alder (iEDDA) cycloaddition, the bis(tetrazine)s produce a unique staple structure. The o-azidation of s-aryl tetrazines introduces a second proximal intermolecular clickable function that leads to double click chemistry opportunities. The stepwise i…
ChemInform Abstract: (S)-Proline Benzyl Ester as Chiral Auxiliary in Lewis Acid-Catalyzed Asymmetric Diels-Alder Reactions.
1989
Asymmetric Diels-Alder reaction of cyclopentadiene (I) with (S)-proline benzyl ester (II) yields a mixture of the diastereomeric cycloadducts (R)-(III) and (S)-(IV).
ChemInform Abstract: Studies on Bicyclo[3.3.1]nonanes for Synthesis of Cyclooctenes.
2010
This paper describes a full conformational and stereochemical study of bicylo[3.3.1]nonanes, obtained from the reaction between cinnamaldehyde and 1-morpholine 1-cyclohexene. NMR data and stereochemistry were unequivocally established and assigned by two-dimensional experiments and single-crystal X-ray analysis. The crystal structure of a minor compound, 4, is reported. Cyclooctenes, which are present in natural products with biological activities, were synthesized from the bicyclononanes via the Wharton fragmentation.
Spin transition in heptanuclear star-shaped iron(III)–antimony(V) NCS- and CN-bridged compounds
2009
Abstract The precursor [FeIII(L)Cl] (LH2 = N,N′-bis(2′-hydroxy-benzyliden)-1,6-diamino-3-azahexane) has been prepared and Mossbauer spectroscopy assigned a high-spin (S = 5/2) state at room temperature. The precursor is combined with the bridging units [SbV(X)6]− (X = CN−, NCS−) to yield star-shaped heptanuclear clusters [(LFeIII–X)6SbV]Cl5. The star-shaped compounds are in general high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers switch to the low-spin state as indicated by Mossbauer spectroscopy, i.e. multiple electronic transitions. While the cyano-bridged complex performs a multiple spin transition the thiocyanate-compound shows no significant popul…
Kinetische untersuchungen zur reaktionsfähighkeit von chlormethylgruppen in methylendiphenolen
1984
The chloromethyl derivatives of 16 differently substituted methylenediphenols were synthesized for the first time. To compare their reactivity, the solvolysis in methanol and the animolysis with an excess of p-nitroaniline in dimethyl sulfoxide were studied kinetically at 25°C. The rate constants for the methanolysis do not differ very much, beside of the fact that para-chloromethyl derivatives react about 100 times faster than ortho-chloromethyl derivatives. However, for the aminolysis a large acceleration up to 103 was found for compounds having both hydroxyl groups in ortho-position to the methylene bridge. Obviously, the cleavage of the OH bond, which occurs in the rate determining step…
Post-Processing via Cation Exchange Cartridges: Versatile Options
2012
New 68Ge/68Ga radionuclide generators provide the positron emitter 68Ga (T½ = 67.7 min) as an easily available and relatively inexpensive source of a PET nuclide for labeling of interesting targeting vectors. However, currently available “ionic” 68Ge/68Ga radionuclide generators are not necessarily optimized for the routine synthesis of 68Ga-labeled radiopharmaceuticals in a clinical environment. Post-processing of 68Ge/68Ga generators using cation exchange resins provides chemically and radiochemically pure 68Ga with 97±2% within less than 4 min, with 68Ge almost completely removed, and ready for online labeling. This simple, fast, and efficient technology can be extended for new applicati…
Kinetik der bromierung von phenolen und phenolischen mehrkernverbindungen, 2. Die reaktionsfähigkeit isomerer zweikernverbindungen
1976
Die Geschwindigkeit der Bromierung von 6 isomeren Zweikernverbindungen mit jeweils einer reaktionsfahigen Stelle (Hydroxydimethylbenzyl-methylphenole 1, 2 und 3) wurde in Eisessig bei 22°C UV-spektroskopisch bestimmt. Fur die Reaktion in ortho-Stellung zur phenolischen Hydroxy-Gruppe ergibt sich eine Verminderung der Geschwindigkeit um den Faktor 3–3,5 wenn zwischen den Hydroxy-Gruppen der beiden Phenolbausteine eine intramolekulare Wasserstoffbrucke sterisch moglich ist (1a). In den anderen Fallen (1b, 2a, 2b) verlauft die Bromierung ungefahr ebenso schnell wie bei 2,4-Dimethylphenol. Die schneller verlaufende Reaktion in para-Stellung (3a, 3b) wird durch eine Wasserstoffbrucke um den Fakt…