Flash chromatography, peak

Carbonate ionophore I [ETH 6010] (heptyl 4-trifluoroacetylbenzoate) [129476-47-7] M 316.3, b 170°/0.02 Torr, d 0.909. Purified by flash chromatography (2g of reagent with 30g of Silica Gel 60) and eluted with EtOAc/hexane (1 19). The fractions that absorbed at 260nm were pooled, evapd and dried at room temp (10.3 Torr). The oily residue was distd in a bubbled-tube apparatus (170°/0.02 Torr). Its IR (CHCI3) had peaks at 1720, 1280, 940cm and its sol in tetrahydrofuran is 50mg/0.5mL. It is a lipophilic neutral ionophore selective for carbonate as well as being an optical humidity sensor. [Anal Chim Acta 233 41 1990.]... 

Isopiperitenone (0.5 g, 3.3 mmol), l,2-bis(trimeLhylsiloxy)cyclobutene (3.83 g, 16.7 mmol) and degassed pentane (50 111L) were placed in an Ace photochemical reactor and irradiated at rt with a 250-W Hg immersion lamp. Progress of the reaction was monitored by GC. When the peak corresponding to isopiperitenone had disappeared (3.5 h), the solvent was removed under reduced pressure and the residue distilled, bp 120 C/O.l Torr. The distillate was subjected to flash chromatography (petroleum ether hp 30-60 C/5% EtOAc), giving the desired product yield 0.31 g (24%). 

The stereochemistry of the Weinreb-based and phenyl ester based technique has been determined through studying the epimerization of the carbon located a to the aldehyde functional group.135 4 50 Crude products such as Boc-Phe-Val-Ala-H synthesized by both methods contain only one aldehydic peak meaning these techniques are devoid of racemi-zation. However, when the crude products were separated using flash chromatography with 0.1% pyridine as eluant, two aldehydic peaks appeared, which is indicative of some race-mization during separation. 55 4 511 ... 

The silylene precursor, 2,2-bis(2,6-diisopropylphenyl)hexamethyltrisilane (5), was pho-tolyzed with a low-pressure mercury lamp in a toluene solution of C7012. The adduct 12 obtained (equation 2) contains two isomers of (Dip)2SiC7o (12a and 12b) which were separated by flash chromatography on silica gel. FAB mass spectrometry of 12 displays a peak for adduct 12 at 1190-1194 as well as for C70 at 840-843 which arises from the loss of diarylsilylene. The UV-vis absorption spectra of 12 are virtually identical to those of C70 with bands at 333, 381 and 471 nm. AMI molecular orbital calculations... 

Fig. 4. Gas chromatographic separation of AF-FC 2 (active fraction of estrous urine extract after flash chromatography and TLC), upper chromatogram AF-HPLC (active fraction of estrous urine extract after FC, TLC, and HPLC), lower chromatogram, ly sample. DB-1-30N column (J W)(0.25 ym 0.32 mm) 30M helium carrier gas temperature-programmed 5%C/minute, 35°C to 330°C retention time depicted in minutes. Solvent peak eluted prior to 4 minutes.

Initially developed at Columbia University, flash chromatography is an air pressure driven hybrid of medium pressure and short column chromatography which has been optimized for particularly rapid separations. The resolution is measured in terms of the ratio of retention time (r) to peak width (w, w/2). It is measured by baseline resolution in the valley between the peaks and the distance from peak to peak. Sample size can be increased dramatically if less resolution is required. This innovative work by the Columbia University team demonstrated that column performance was quite sensitive to the rate of elution, and the best performance was accomplished with relatively high eluent flow rates. 

All reactions were carried out in 7.0 mL sample vials with a teflon sealed screwcap in a glovebox under an argon atmosphere. All purchased chemicals were used as received without further purification. Solvents were dried according to standard procedures, reactions were monitored by thin-layer chromatography (TLC) analysis and flash chromatography was carried out on sifica gel 60 (230-400 mesh). The chemical shifts are reported in ppm relative to solvent residual peak [6]. The NMR spectra were recorded at 400 MHz, NMR spectra were recorded at 100 MHz and NMR spectra were recorded at 376 MHz on a Varian... 

Purification of luciferin (Rudie etal., 1976). The luciferin fractions from the DEAE-cellulose chromatography of luciferase were combined and concentrated in a freeze-dryer. The concentrated solution was saturated with ammonium sulfate, and extracted with methyl acetate. The methyl acetate layer was dried with anhydrous sodium sulfate, concentrated to a small volume, then applied on a column of silica gel (2 x 18 cm). The luciferin adsorbed on the column was eluted with methyl acetate. Peak fractions of luciferin were combined, flash evaporated, and the residue was extracted with methanol. The methanol extract was concentrated (1 ml), then chromatographed on a column of SephadexLH-20 (2 x 80 cm) usingmethanol asthe solvent. The luciferin fractions eluted were combined and flash evaporated. The residue was... 

Fig. 11.4 shows the total ion current trace and some mass chromatograms obtained by flash evaporation pyrolysis gas chromatography-mass spectrometric analysis of the polluted sediment sample. All compounds present in this complex mixture were not listed. A selection was made to exemplify several aspects of the screening approach. The peak number correspond with the numbers in Table 11.1. Identifications were based on the same criteria as mentioned above. Although several components were shown to be real pyrolysis products, all the compounds are present as such in the sample and resulted from simple thermal extraction from the wire. This was shown in separate analyses using ferromagnetic wires with a Curie temperature of 358°C. 

---