Silica buffered

Streptonegrin (negrin, 5-amino-6-[7-amino-5,8-dihydro-6-methoxy-5,8-dioxo-2-quinolinyl]-4-[2-hydroxy-3,4-dimethoxyphenyl]-3-methyl-2-pyridinecarboxylic acid) [3930-19-6] M 506.5, m 262-263°, 275°(dec). Purified by TLC on pH 7-buffered silica gel (made from a slurry of Silica Gel 60 and 4(X)ml of 0.05M phosphate buffer pH 7.0) and eluted with 5% MeOH/CHClj. The extracted band can then be recrystd from Me2CO or dioxane as almost black plates or needles. It is soluble in pyridine, Me2NCHO, aqueous NaHCOy (some dec), and slightly soluble in MeOH, EtOH, EtOAc and H2O. It has a pKa value in the range 6.2-6.4 (dioxane/H2O 1 1) and UV 248, 375-380nm (e 38400 and 17400). [Weinreb et al. JACS 104 536 1982 Rao et al. JACS 85 2532 1963]. It is an antineoplastic and causes severe bone marrow depression [Wilson et al. Antibiot Chemother 11 147 7967]. 

R Schwarzenbach. HPLC of hop acids on buffered silica gel systems. J Am Soc Brew Chem 37 ISO-184, 1979. 

It was only in 1956, a hundred years after the isolation of taxine, that Graf in WUrzburg showed by electrophoresis that taxine is actually a mixture of several compounds [20], By column chromatography on buffered silica gel he obtained three constituents in a pure state taxine A (1%), taxine B (30%) and taxine C (traces), the alphabetical designation presumably referring to their order of isolation [20]. 

Paper Chromatography.—Solvent systems have been developed for the separation of trichloromethyl- phenyl-, and pentafiuorophenyl-phosphonic and -phosphinic acids. Phosphoramidates and their hydrolysis products have been chromatographed, using triethylamine as a buffer. Silica gel on glass-fibre sheets may be used to separate inositol from its phosphate and to analyse phosphatide glyceryl ethers. ... 

The separation of acidic or basic products may cause difficulties in adsorption chromatography. Reversed-phase or ion-exchange chromatography would be more suitable but solubility problems may arise. One answer is to use buffered silica, as shown in Figure 9.9. The silica is treated either as bulk material or in the column with a buffer solution of a suitable pH (acidic buffer for acidic samples, basic buffer for... 

Size exclusion (SEC) DNA fragments in a buffer Silica or polymer particles containing a suitable size distribution of pores Separation according to DNA fragment effective size... 

Teichert et al. [45] were the first to carry out TLC of amines. The hydrochlorides were dissolved in 70% alcohol and applied in 1 to 10 [xg amounts. The hi /-values and experimental conditions for the separation are summarised in Table 94. As can be seen from the table, only a partial improvement in separation is achieved by buffering silica gel G layers with a mixture of 0.2M primary potassium phosphate and 0.2 M secondary sodium phosphate (1 -h 1) or with 0.15M sodium acetate solution. 

Amine Silica gel G-Iaycr Buffered silica gel G layer Cellulose powder layer VE... 

This double spot formation is not observed on silica gel or alumina layers. The sensitivity to oxidation of the adrenaline derivatives is, however, increased by the metal or heavy metal impurities present in such layers. Adrenaline and noradrenaline have therefore been chromatographed on buffered silica gel layers (Sorensen buffer, pH 6.8), prepared with addition of sodium bisulphite and using 10% ethanol as solvent [163]. The sympathomimetics and the secondary products formed by oxidation tend moreover to form complex salts this manifests itself in elongated spots. Silica gel layers which had been prepared with O.IM EDTA have been used with the solvent acetone-formic acid-water (70 + 10 + 20) for the separation of adrenaline, noradrenaline and various substances of similar structure [110] silica gel HR (Krm 88) ought to be especially advisable for this purpose. On the other hand, Halmekoski [74] has made use of this very ability of the adrenaline-type of sympathomimetic to form complexes, in order to accomplish fractionation on buffered layers containing molybdate, tungstate or borax components... 

Fig. 227. Separation of sugars (0.5 (xg of each) on a buffered silica gel G layer. Visualization with anisaldehyde-sulphuric acid [1]...

The resolution of simple sugars on silica gel G is enhanced by impregnating the plates with 0.02 M sodium acetate [7], 0.02 M [7] and 0.1 N [8, 24] boric acid, 0.02 M sodium borate [6] or pH 8 phosphate buffer [25]. The preparation of these plates is described in section II. Table 198 summarizes the hEf data obtained with a variety of solvents on buffered silica gel G layers. 

Chromatography on acetate and borate-buffered silica gel G layers [26] has been used for the identiflcation of sugars in blood and urine. 

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