Syntheses of gramicidin s analogs containing D-Serine or a dehydroalanine residue,and asymmetric hydrogenation of the dehydroalanine

Gramicidin S (GS) analogs, (D-Ser(Bzl)^4,4′]-GS ($\text{17}$), [D-Ser^4,4′]-GS ($\text{18}$), and [L-Orn(Boc)^2,2′,D-Ser^4,4′]-GS ($\text{19}$) were synthesized and $\text{17}$ showed high antibacterial activity. One residue of D-Ser in $\text{19}$ was converted asymmetrically to D-Ala via α,β-dehydroalanine.     

Lithium intercalation in layer structured compound β-ZrNCl

A layer structured crystal -ZrNCl forms a lithium intercalation compound Li_xZrNCl. The upper limit for x determined on the compound prepared by the n-butyl lithium technique is 0.29. In the electrochemical process, a pressed -ZrNCl cathode is further reduced up to x=11.25 at potentials as low as 0.80.6 V relative to Li/Li⁺. The lithium intercalate swells in various polar solvents, increasing the basal spacing. However, in contrast to the salt-like intercalates of transition metal chalcogenides and FeOCl, the lithium intercalated -ZrNCl does not form hydration phases, but reacts with water, evolving hydrogen. These results can be interpreted in terms of the formation of an alloy-like intercalate like the alkali intercalates of graphite. On intercalation, -ZrNCl is changed from pale yellow-green to black in color, and the electrical conductivity increases by a factor of 10⁶.     

The ion-pair formation between dodecylsulfate and ammine-complexes of copper(II), nickel(II), zinc(II), palladium(II) and platinum(II), and the extraction behavior of the ammine-complexes by using sodium dodecylsulfate

A micellar solution of sodium dodecylsulfate (SDS) exhibits the property of being separated into two phases due to a temperature change or the addition of salts. The ammine-complexes of copper(II), nickel(II) and palladium(II) reacted with the dodecylsulfate anion to form the corresponding ion-pair, and were extracted into the SDS gel phase. The SDS plays the roles of a pairing-ion for the ammine-complexes and of an extraction medium. The ion-pair extraction mechanism was investigated; the extractability of metals was given by the function of the solubility products of the ion-pairs. This method was applied to the mutual separation of Ni(II)/Cu(II) and Pd(II)/Pt(II). The driving force for the extraction was an electrostatic interaction between the cationic complex and the surfactant anion. The use of the SDS gel as ion-exchanger is also expected.     

Synthesis of a soluble ureido-naphthyridine oligomer that self-associates via eight contiguous hydrogen bonds

[structure; see text] An iterative synthetic route to organic-soluble ureido-naphthyridine oligomers has been developed. Use of this protocol allowed synthesis of a short ureido-naphthyridine oligomer, which presents a self-complementary DDAADDAA hydrogen bonding array (D = hydrogen bond donor, A = hydrogen bond acceptor). Strong self-association via eight hydrogen bonds was observed in organic solution.     

Palladium-catalyzed coupling of alkenyl iodides with ethynyl oxiranes: Synthesis of epoxy enediyne core intermediates related to neocarzinostatin chromophore

Coupling of functionalized cyclopentenyl iodides with ethynyl oxiranes has been achieved by using catalytic amount of Pd(CH₃CN)₂Cl₂ and CuI in the presence of i-Pr₂NEt in moderate to good yields.     

Polymerization of coordinated monomers. I. Stereoregulation in the free-radical polymerization of methyl methacrylate-zinc chloride or methyl methacrylate–stannic chloride complexes

Stereoregulation in free-radical polymerization was studied for the polymerization of the 2:1 or 1:1 complex of methyl methacrylate with ZnCl₂ or SnCl₄. The complexes were polymerized with the use of a free-radical initiator or γ-ray irradiation either in the liquid or solid state at various temperatures ranging from ?196 to 110°C, and the tacticities of the resulting polymers were determined by NMR spectroscopy. The polymers had different and characteristic values of tacticities depending upon the complex species, i.e., the kind of metal chloride and the stoichiometry. The tacticities were found to be independent of the polymerization temperature in both the liquid and solid states, in contrast with the fact that tacticities of the polymer from pure monomer changed markedly with the temperature. A temperature dependence appeared in the polymerization system, which contained more monomer than that corresponding to the 2:1 complex. The effect of the viscosity or the solid phase on the stereoregulation was examined in comparison with the polymerization of a mixture of methyl methacrylate and liquid paraffin. Two possible explanations regarding the stereoregulation mechanism are offered in relation to the structures of the complexes.     

Reaction of α,β-unsaturated carbodiimides with enamines leading to fused pyridine derivatives

The treatment of (5,5-dimethyl-3-oxo-1-cyclohexenyl)iminotriphenylphosphorane ( 2 ) with phenyl isocyanate ( 3a ) gave N-(5,5-dimethyl-3-oxo-1-cyclohexenyl)-N'-phenylcarbodiimide ( 4a ) in situ. The reaction of 4a with enamines proceeded smoothly to afford the pyridine ring formation with the elimination of amine. This means that 4a is regarded as a new class of 2-aza-1,3-butadiene. The scopes and limitation of this reaction are also discussed.     

Adsorption and Recovery of Ionic Surfactants by β-Cyclodextrin Polymer

The adsorption and recovery of ionic surfactants, such as dodecylbenzenesulfonic acid (DBS) and benzalkonium chloride (BKC), from an aqueous solution were studied using the β-cyclodextrin polymer (β-CDP). BKC always demonstrated a higher adsorption efficiency than DBS in batch tests, isotherms, and column tests. The adsorption characteristics of the surfactants seemed to be caused by inclusion into β-CD, and they were easily determined using the Langmuir adsorption isotherm. Furthermore, the surfactants adsorbed by β-CDP were easily released by shaking it with a mixture of water and methanol. Recovery efficiency was dependent on the mixture ratio of the solvent, and regenerated β-CDP was reusable as an adsorbent.     

Membrane formation mechanism and permeation properties of a novel porous polyimide membrane

The transport properties of a novel porous fluorinated polyimide membrane fabricated by a wet phase inversion process were studied with a stirred dead‐end filtration cell. The porous membrane‐forming solvents were tetrahydrofuran (THF), acetone, N,N‐dimethylacetamide (DMAc), N‐methylpyrrolidone (NMP), N,N‐dimethylformamide (DMF), and dimethylsulfoxide (DMSO). The phase separation phenomena in a ternary system of polyimide/solvent/water were investigated from cloud point curves by a titration method and binary interaction parameters. Solvent–water demixing in the system has been found to play very important roles in determining the structure and surface morphology of the polyimide membrane. The porous fluorinated polyimide membranes showed pore sizes from 4 to 500 nm and permeation properties from ultrafiltration to a microfiltration range. In this study, we particularly focused on fouling of the polyimide membranes, because fouling decreases the flux and increases the resistance. Interestingly, the porous polyimide membrane showed excellent water flux recovery after water cleaning compared with that of the polyethersulfone (PSf) membrane, which suggest that for a 6FDA‐6FAP membrane, the protein–membrane and protein–protein interaction was not so strong compared with those in a PSf membrane. Copyright © 2002 John Wiley & Sons, Ltd.     

Flow-injection determination of sodium and potassium by separationon a silica column and extraction-spectrophotometry with benzo-18-crown-6 and tetrabromophenolphthalein ethyl ester

Sodium and potassium ions in waters are determined by flow-injection extraction-spectrophotometry. The ion-association complexes formed between the metal/crown ether cations and the tetrabromophenolphthalein ethyl ester anion (TBPE^-) are extracted into chlorobenzene/benzene (1:3) and the absorbance of the organic phase is measured after phase separation with a porous membrane. Sodium and potassium are separated on-line with a column (1 mm i.d.×30 cm) packed with silica gel (100-200 mesh). The manifold comprises four streams, each at 0.8 ml min^?1. The sample is injected into a water stream and mixed with a reagent stream containing lithium acetate and benzo-18-crown-6 before entering the silica gel column; after the separation, the stream is mixed with EDTA (trilithium salt) and lithium hydroxide, and then with the extraction solution containing TBPE.H. Extraction proceeds in a 2-m coil; the absorbance of the organic phase is measured at 620 nm. CAlibration graphs are linear inthe ranges 0–×10^?3 M sodium and 0–2×10^?4 M potassium. The sample throughput is 15 h^?1. The procedure is applicable to river and tap waters.