Sodium and Calcium Laurylamidomethylsulfate: Aqueous Micellar Phases, Their Properties, and a Precipitate of Vesicles

A new anionic surfactant (M-LAMS) that is capable of forming intermolecular hydrogen bonds was investigated. Inverse solubilities of Na and Ca salts were found. Critical micelle concentration and aggregation behavior were determined by surface tension, light scattering, electric birefringence, and SANS measurements. It is found that the Na salt forms globular micelles while the Ca salt forms rodlike micelles. The phase behavior of the micellar solutions with increasing cosurfactant concentration was also studied. It is observed that 100 mM Na-LAMS solutions in the presence of 100 mM CaCl(2) undergo several phase transformations with increasing n-hexanol concentration. We found not only the expected micellar L(1) phase and a lamellar phase at concentrations quite low for this kind of system, but also a novel phase: At a cosurfactant/surfactant ratio x(C) of 1.2 a white precipitate is formed at the bottom of the sample. With increasing ratio x(C) the precipitate dissolves into a liquid crystalline L(alpha) phase that at x(C)=3.2 is transformed into an L(3) or sponge phase. Investigation by FF-TEM, light microscopy, and SANS shows that the precipitate consists of agglomerated polydisperse multilamellar vesicles. The vesicles consist of densely packed bilayers that contain little water. The bilayer thickness is about 20 ? and independent of its composition whereas the interlamellar distance is strikingly linked to concentrations of cosurfactant (surfactant/cosurfactant ratio) and electrolyte. With increasing cosurfactant content, the bilayers become less rigid and resulting thermal undulations force the membranes apart and weaken their interactions until a common L(alpha) phase is formed. This transition is an example of a bonding-nonbonding transition of membranes. Copyright 2001 Academic Press.     

NO-Mediated aromatic nitration during decomposition of phenolic S-nitrosothiols in non-aqueous aerobic medium

Five novel S-nitrosothiol compounds (6-10) derived from L-cysteine were generated in solution and their decomposition rate was followed by UV spectroscopy. In acetonitrile, compounds 9 and 10 were the most stable of this series with a half-life of 24 h. The final organic decomposition products of the five S-nitrosothiols were also analysed. Derivatives 8, 9, and 10, possessing a phenolic hydroxyl group, afforded an unexpected decomposition pathway, with nitration of aromatic ring occurring in non-aqueous media. A mechanism involving a phenoxy radical seems to be implicated.     

Zur Reaktion des Germaniums mit Germaniumtetrachlorid und zur Existenz der Oxidchloride GeOCl2 und GeOCl6 im Gleichgewicht

On the Reaction of Germanium with Germanium Tetrachloride and on the Existence of the Oxidechlorides GeOCl₂ and GeOCl₆ at the Equilibrium The above equilibrium was measured in a Gauge-manometer and the enthalpy of formation and the entropy for GeCl₂,g were derived from these results. From total pressure measurements and transport experiments of GeO₂ with GeCl₄ follows, that the oxidechlorides Ge₂OCl₆ and GeOCl₂ are not present in measurable concentrations, that means the enthalpy of formation of GeOCl₂ must be higher than ?327 kJ · mol^?1.     

Synthetische und NMR-spektroskopische Untersuchungen der Benzylaminaddition an N-Maleyl-aminosäurederivate

Summary During the addition of amines to maleylamino acids in general -amino derivatives are formed. In order to change the reactivity within the vinylogous maleyl system we introduced the -benzylester group into the starting compound N-(cis--carboxyacryloyl)-phenylalanine methylester1. The obtained benzylester2 is adding benzylamine in -position yielding N-benzyl--aspartyl(-benzyl)-phenylalanine methylester4. The addition reaction was investigated by¹H-NMR-spectroscopy. The structures of the compounds have been confirmed by elemental analysis, IR,¹H-NMR and¹³C-NMR spectroscopy.

     

High regio-, chemo-, and stereoselectivity via low-temperature 4 + 3 cycloadditions. Convergent synthesis of multifunctionalized vinylmetals (M = Si, Sn) and S-vinyl benzenecarbothioates

A series of enantiomerically pure 8-oxabicyclo[3.2.1]oct-6-en-3-ones functionalized in the unsaturated two-carbon bridge has been prepared by the title reaction. Carbocation reactivity has been fined-tuned at -95 degrees C and adjusted to diene nucleophilicity. Conventional electrophilic substitution of 3-silylated and 3-stannylated furan is suppressed in favor of the rapid 4 + 3 cycloaddition mode. In the case of cycloadduct 13A, stereoselectivity (17:1) is perfectly matched to regioselectivity (17:1). High stereoselection as well as unprecedented regioselection and chemoselection is attributed to the low-temperature cycloaddition protocol and the design of chiral auxiliary and tether.     

Electron-deficient bonding in rhomboid rings

The bonding environment of boron is usually thought about in terms of localized 2c-2e/3c-2e bonding (as in diborane) or completely delocalized polyhedral bonding (as in B(12)H(12)(2)(-)). Recently, a number of boron compounds having a rhomboidal B(4) framework have been synthesized; these show an amazing variation in their skeletal electron count, one that cannot be interpreted in familiar ways. In this report, we systematically explore the origin of the range of electron counts in these compounds. We find that four skeletal MOs are primarily responsible for keeping the B(4) skeleton together. As a subunit in a macropolyhedral environment, termed rhombo-B(4), such an arrangement of B atoms deviates from Wade's rule by three electron pairs (if treated as a distorted arachno system derived from B(6)H(6)(2)(-)). Aided by this analysis, we examine the nature of bonding in Na(3)B(20), where the rhombo-B(4) unit forms linear chains fusing closo-B(7) units. Theory suggests that this structure requires one more electron per formula unit for optimal bonding. Finally, we study the nature of bonding in beta-SiB(3), where silicon atoms also adopt the rhomboid framework.     

Enantioselektive Synthese von Allyl-, Propargyl- und 4-En-2-inyl-aminen durch 1,2-Addition von Organocer-Reagenzien an chirale Aldimine

Enantioselective Synthesis of Allyl-, Propargyl-, and 4-En-2-ynyl-amines via 1,2-Addition of Organocerium Reagents to Chiral Aldehyde Imines (E)- and (Z)-Allyl-, propargyl-, and 4-en-2-ynyl-amines 5 and 14 , useful bifunctional building blocks and of pharmaceutical interest, are synthesized in high enantiomeric purity (e.e. ≥ 97%). Key step is the diastereoselective 1,2-addition (d.e. 86 to ≥ 98%) of organocerium reagents to chiral α,β-unsaturated aldehyde imines 3 or 8 to produce adduct amines 4 and 9 (Schemes 1 and 4, resp.). The propargylamine 9 is a substrate for Pd-catalyzed coupling with alkenyl halides to produce the enynylamine 11a and the thienyl-substituted alkynylamine 11b . The chiral auxiliary (S,S)- 2 is removed from 4 and 11 in 3 steps affording the title compounds 5 and 14 . Diastereoisomer enrichment of the hydrochloride of 6 by crystallization is possible.     

Designed Beta‐Turn Mimic Based on the Allylic‐Strain Concept: Evaluation of Structural and Biological Features by Incorporation into a Cyclic RGD Peptide (Cyclo(‐L‐arginylglycyl‐L‐α‐aspartyl‐))

The (3R,5S,6E,8S,10R)‐11‐amino‐3,5,8,10‐tetramethylundec‐6‐enoic acid (ATUA; 1 ), which was designed as a βII′‐turn mimic according to the concepts of allylic strain and 2,4‐dimethylpentane units, was incorporated into a cyclic RGD peptide. The three‐dimensional structure of cyclo(‐RGD‐ATUA‐) (=cyclo(‐Arg‐Gly‐Asp‐ATUA‐)) 4 in H₂O was determined by NMR techniques, distance geometry calculations and molecular‐dynamics simulations. The RGD sequence of 4 shows high conformational flexibility but some preference for an extended conformation. The structural features of the RGD sequence of 4 were compared with the RGD moiety of cyclo(‐RGDfV‐) (=cyclo(‐Arg‐Gly‐Asp‐D ‐Phe‐Val‐)). In contrast to cyclo(‐RGDfV‐), which is a highly active αvβ3 antagonist and selective against αIIbβ3, cyclo(‐RGD‐ATUA‐) shows a lower activity and selectivity. The structure of the ATUA residue in the cyclic peptide resembles a βII′‐turn‐like conformation. Its middle part, adjacent to the C?C bond, strongly prefers the designed and desired structure.     

Biosynthesis of 4-methylproline in cyanobacteria: cloning of nosE and nosF genes and biochemical characterization of the encoded dehydrogenase and reductase activities

The biosynthesis of the unusual amino acid 4-methylproline in the Nostoc genus of cyanobacteria was investigated on the genetic and enzymatic level. Two genes involved in the biosynthesis were cloned and the corresponding enzymes, a zinc-dependent long-chain dehydrogenase and a Delta(1)-pyrroline-5-carboxylic acid (P5C) reductase homologue, were overexpressed in Escherichia coli and biochemically characterized. Putative substrates were synthesized to test enzyme substrate specificities, and deuterium labeling studies were carried out to reveal the stereospecificities of the enzymatic reactions with respect to the substrates as well as to the coenzymes.