Depletion flocculation of latex dispersion in ionic micellar systems

The flocculation behavior of anionic and cationic latex dispersions induced by addition of ionic surfactants with different polarities (SDS and cetyltrimethylammonium bromide (CTAB)) have been evaluated by rheological measurements. It was found that in identical polar surfactant systems with particle surfaces of SDS + anionic lattices and CTAB + cationic lattices, a weak and reversible flocculation has been observed in a limited concentration region of surfactant, which was analyzed as a repletion flocculation induced by the volume-restriction effect of the surfactant micelles. On the other hand, in oppositely charged surfactant systems (SDS + cationic lattices and CTAB + anionic lattices), the particles were flocculated strongly in a low surfactant concentration region, which will be based on the charge neutralization and hydrophobic effects from the adsorbed surfactant molecules. After the particles stabilized by the electrostatic repulsion of adsorbed surfactant layers, the system viscosity shows a weak maximum again in a limited concentration region. This weak maximum was influenced by the shear rate and has a complete reversible character, which means that this weak flocculation will be due to the depletion effect from the free micelles after saturated adsorption.     

Substrate dependence in aqueous Diels-Alder reactions of cyclohexadiene derivatives with 1,4-benzoquinone

A reactivity difference based on the position of substituents on cyclohexa-1,3- diene was observed for the title reaction. The effect of water as solvent was more distinct for 1-methyl-4-isopropylcyclohexa-1,3-diene than for 2-methyl-5-isopropylcyclohexa- 1,3-diene or non-substituted cyclohexa-1,3-diene. The effect of NaCl (salting-out) and guanidium chloride (salting-in) was also large for 1-methyl-4-isopropylcyclohexa-1,3- diene.     

Starburst dendrimer-supported pseudostationary phases for electrokinetic chromatography

Pseudo-stationary phases for electrokinetic chromatography were prepared by the alkylation of starburst dendrimers (SBDs). The SBD-supported pseudo-stationary phase with dodecyl groups showed higher efficiency than short-akyl derivatives, and maintained the hydrophobic property inthe presence of methanol. The dodecyl-modified SBD provided wide migration time windows ar high methanol content to effect the separation of sixteen aromatic hydrocarbons, the priority pollutants designated by EPA, in 65% methanol. The selectivity of polymer-supported pseudo-stationary phase can be varied simply by changing the length of the alkyl groups. The dodecyl SBD showed relatively similar selectivity as sodium dodecyl culfate micelle, whereas short alkyl derivatives showed preference towards rigid and planar compounds based on the rigid and planar compounds based on the rigid polymer backbones. The selectivity of SBD-supported pseudo-stationary phases was dominated by the chain length of the alkyl groups, with the minor effect of the structure of the core and the generation of SBD where alkyl groups were attached.     

Potentiometric flow-injection determination of boron by using a flow-through tetrafluoroborate ion-selective poly(vinyl chloride) membrane electrode

A highly sensitive tetrafluoroborate ion-selective poly(vinyl chloride) membrane electrode was constructed and applied to a detector in the flow-injection determination of boron. Boron at the 10 ng ml^?1 level can be determined by converting it to tetrafluoroborate ion in a flow of hydrofluoric acid. A sampling rate of 30 h^?1 was achieved with a relative standard deviation of less than 2%.     

Oxoaminium salts as initiators for cationic polymerization of vinyl monomers

Oxoaminium salt ( 1 ), derived from 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 2 ) by one-electron oxidation, could be an initiator for cationic polymerization of vinyl monomers such as isobutyl vinyl ether (IBVE), 2,3-dihydrofuran, p-methoxystyrene, N-vinyl pyrrolidone, etc., to give the corresponding polymers, when 1 had a low nucleophilic counter anion. Formation of the adducts of 1 and IBVE as well as ¹H-NMR and IR data suggested the formation of polymers containing N? O? C structure as the polymer head group. In the polymerization of IBVE, the effects of solvent and concentration of 1 were little observed, however the polymerization rate was dependent on temperature. Furthermore, the thermal reaction of the polymers obtained, which were regarded as prepolymers for block copolymerization and polymeric initiators for radical polymerization, was studied. For example, poly(2-benzylidene-1,3-dioxane) obtained by the polymerization of 2-benzylidene-1,3-dioxane with oxoaminium hexafluoroantimonate ( 1, X = SbF₆) was employed as an initiator for radical polymerization of MMA to give its block copolymer with PMMA. © 1993 John Wiley & Sons, Inc.     

Analysis by partial reflection spectrometry of protonated tetraphenylporphyrin adsorbed at a liquid-liquid interface

Visible reflection spectra of diprotonated meso-tetraphenylporphyrin adsorbates spontaneously formed at a dodecane-aqueous sulfuric acid interface have been measured using a home-made device comprising a prism-cell and variable-angle optics. The tilt angle of the pyrrole ring plane was estimated to be 47 degrees from the interface normal by use of an experimentally evaluated molecular density (1.20x10(-10) mol cm(-2)) of the diprotonated molecule in a monolayer form at the liquid-liquid interface. Positive and negative bands have been observed in the p-polarized partial internal reflection (p-PIR) spectra, whose band locations correspond to those in p-polarized external reflection (p-ER) spectra. Nevertheless, the bands in the p-PIR exhibited reversed sign to those of p-ER spectra. These suggest that the surface selection rule of the p-PIR spectrometry has a reversal rule of p-ER and p-PIR can also be used for the analysis of molecular orientation.     

N-Arylation of 4-fluoro-5-trimethylsilyl-1H-pyrazole

The 1,3-dipolar cycloaddition reaction of fluoro(trimethylsilyl)acetylene prepared in situ with an excess of diazomethane smoothly proceeded to give the corresponding 4-fluoro-5-trimethylsilyl-1H-pyrazole in 84% yield. The copper iodide-catalyzed N-arylation of the fluorinated pyrazole with a variety of aryl iodides afforded N-aryl-4-fluoropyrazoles as desilylation products in good to excellent yields.     

Three New Lanostane Triterpenoids from Inonotus obliquus

Three new lanostane‐type triterpenoids, inonotsulides A, B, and C ( 1 – 3 , resp.) were isolated from the sclerotia of Inonotus obliquus (Pers .: Fr.) (Japanese name: Kabanoanatake; Russian name: Chaga). Their structures were determined to be (20R,24S)‐3β,25‐dihydroxylanost‐8‐en‐20,24‐olide ( 1 ), (20R,24R)‐3β,25‐dihydroxylanost‐8‐en‐20,24‐olide ( 2 ), and (20R,24S)‐3β,25‐dihydroxylanosta‐7,9(11)‐dien‐20,24‐olide ( 3 ) on the basis of chemical transformation, NMR spectroscopy including 1D and 2D (¹H,¹H‐COSY, NOESY, HMQC, HMBC), EI‐MS, and single‐crystal X‐ray analysis.     

Studies on imidazole derivatives and related compounds. 3. Regioselective glycosylation of 4-carbamoylimidazolium-5-olate

In the synthesis of glycosyl derivatives of 4-carbamoylimidazolium-5-olate ( 2 ) by the silyl-Hilbert-Johnson method using trimethylsilyl trifluoromethanesulfonate as catalyst, we obtained N-3 nucleosides 5 as major products and N-1,N-bis-nucleosides 6 as minor ones. The desired N-1 nucleosides 4 were isolated in only low yields. However, the yields of 4 were improved by adding ca. One equivalent of stannic chloride to the silylated 4-carbamoylimidazolium-5-olate ( 3 ). On the basis of nuclear magnetic resonance (¹³C and ²⁹Si) and ultraviolet spectroscopic studies, we verify the formation of σ-complexes between the silylated base 3 and the Lewis acid (stannic chloride or trimethylsilyl trifluoromethanesulfonate), and the propose the structures of these complexes and the reaction mechanism.