Subject silica layer

A promising modification of the silver island approach involves protection of the island film with a very thin layer of silica (46). The silica layer is thin enough so that molecules on its surface are still subject to field enhancement, although the chemical enhancement between silver and adsorbate is lost. The silver islands are protected from adsorption of atmospheric impurities and the field enhancement is quite stable with time. Silica-protected Ag island films do not exhibit the large enhancements encountered with bare Ag islands or electrochemical roughening, but the decreased enhancement may be more than compensated by improved reproducibility for many analytical applications. 

The oxidation of silicon has been studied extensively due to the need for formation of dielectric silica layers on silicon by thermal oxidation for semiconductor devices. Deal and Grove (1965) have written a classic paper on this subject in which gas phase diffusion rates, linear reaction rates of oxygen with silicon, as well as oxygen transport rates through the growing silica scale are all considered. It was found that silicon oxidation can be described by a linear parabolic rate law ... 

Detection and result The chromatogram was dried in a stream of warm air for 10 min, immersed in the reagent solution for 3 s and then subjected to intense UV radiation (high pressure lamp, A = 365 nm) for up to 10 min. Terephthalic (hRf 0 - 5), pimelic (hRf 55), suberic (hRf 60), sebacic (hRf 65 — 70) and benzoic acids (hRf 70 — 75) together with sorbic, malic, adipic, citric, tartaric, lactic and fumaric acids only exhibited a reaction on silica gel layers at higher concentrations. 4-Hydroxybenzoic, salicylic and acetylsalicylic acids fluoresced light blue after irradiation. The detection limit per chromatogram zone was 0.5 pg for salicylic acid and more than 5 pg for benzoic acid. 

C. Isolation and purification of XK-62-2 100 g of the white powder obtained in the above step B are placed to form a thin, uniform layer on the upper part of a 5 cm0X 150 cm column packed with about 3 kg of silica gel advancely suspended in a solvent of chloroform, isopropanol and 17% aqueous ammonia (2 1 1 by volume). Thereafter, elution is carried out with the same solvent at a flow rate of about 250 ml/hour. The eluate is separated in 100 ml portions. The active fraction is subjected to paper chromatography to examine the components eluted. XK-62-2 is eluted in fraction Nos. 53-75 and gentamicin Cja is eluted in fraction Nos. 85-120. The fraction Nos. 53-75 are combined and concentrated under reduced pressure to sufficiently remove the solvent. The concentrate Is then dissolved in a small amount of water. After freeze-drying the solution, about 38 g of a purified preparate of XK-62-2 (free base) is obtained. The preparate has an activity of 950 units/mg. Likewise, fraction Nos. 85-120 are combined and concentrated under reduced pressure to sufficiently remove the solvent. The concentrate is then dissolved in a small amount of water. After freeze-drying the solution, about 50 g of a purified preparate of gentamicin Cja (free base) is obtained. 

A mixture of 4.98 g of acetoacetic acid N-benzyl-N-methylaminoethyl ester, 2.3 g of aminocrotonic acid methyl ester, and 3 g of m-nitrobenzaldehyde was stirred for 6 hours at 100°C in an oil bath. The reaction mixture was subjected to a silica gel column chromatography (diameter 4 cm and height 25 cm) and then eluted with a 20 1 mixture of chloroform and acetone. The effluent containing the subject product was concentrated and checked by thin layer chromatography. The powdery product thus obtained was dissolved in acetone and after adjusting the solution with an ethanol solution saturated with hydrogen chloride to pH 1 -2, the solution was concentrated to provide 2 g of 2,6-dimethyl-4-(3 -nitrophenyl)-1,4-dihydropyridlne-3,5-dicarboxylic acid 3-methylester-5- -(N-benzyl-N-methylamino)ethyl ester hydrochloride. The product thus obtained was then crystallized from an acetone mixture, melting point 136°Cto 140°C (decomposed). 

Synthetic Method 1 6-(dimethylamino)-3-(N-acetyl-N-methylamino)-10-acetylphenothiazine 8a (procedure from US. Patent 4,652,643).5 A mixture of 9.0g of 6-(dimethylamino)-3-(methylamino)phenothiazin-5-ium chloride (Azure B), 150.0ml of acetic anhydride, and lO.Og of zinc dust was maintained at reflux temperature for approximately 4 hs. After the reaction mixture was cooled to ambient temperature, it was poured into ice water with stirring and 300ml of toluene was added. After stirring for approximately 30 min the toluene layer was separated and washed twice, once with tap water and once with saturated aqueous sodium chloride solution. The toluene was then distilled off at reduced pressure. The residue which remained was dissolved in ethyl acetate and separated into various components by subjecting the solution to column chromatography using silica gel as substrate. Elution with ethyl acetate yielded a white-colored solid. 

Lipids can be identified and quantified using thin-layer chromatography (TEC) and gas chromatography (GC) (Galliard, 1968). Extraction of lipids is achieved by homogenizing potato tubers with isopropanol in a blender, followed by a series of filtrations and extractions with chloroform-methanol (2 1). Chloroform is removed by rotary evaporation and the residue is redissolved in benzene-ethanol (4 1). This extract is passed through a DEAE-cellulose column, and the fractions collected are subjected to TEC on 250 p,m layers of silica gel G, using three solvent systems. Fatty acid methyl esters for GC analysis are prepared by transmethylation of the parent lipids, or by diazomethane treatment of the free fatty acids released by acid... 

A solution of 4o<-homo-5of-cholest-3-en-l-one (104 mg, 0.26 mmol) in hBuOH (30 mL) in a Pyrex tube was irradiated with a 450-W high-pressure Hg arc under N2 for 17 h. The solvent was removed under reduced pressure to give an oily product (109 mg) which was subjected to preparative layer chromatography (silica gel, hexane) to afford three fractions. The most mobile fraction, lx-vinyl-3,4-bisnor-5 x,l03c-cholestane, was obtained as an oil yield 24mg (23%). 

A solution of mixed A. jV-diethyl-l,l,2,3,3,3-hexafluoropropanamine (10) and 11 (2.2 g, 10 mmol) in CH,C12 (15 mL) was added dropwise to a solution of ethyl 2-hydroxy-2-(4-tolyl)acetate (14 0.78 g, 4 mmol) in CH2C12 (20 mL) at rt. After stirring for 24 h, the mixture was poured into H20 and was extracted with i-Pr20. The combined organic layers were washed with H20, dried (Na,CO,) and concentrated. The residue was subjected to column chromatography (silica gel, hexane/EtOAc 9 1). The first elution gave ethyl 2-fluoro-2-(4-tolyl)acetate (15) yield 0.47 g (60%). 

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