Dessicant additives

Transfer the filtrate to a ceramic evaporating dish and heat on a water bath until a crystalline scum forms on the top. Cool the dish quickly then filter the mess on the vacuum Buchner to yield 96g of Methylamine Hydrochloride. Concentrate the filtrate once again to obtain a second crop of crystals, -IQg. Concentrate the filtrate a third time as far as possible using the water bath, then store the dish in a vacuum dessicator loaded with Sodium Hydroxide in the bottom for 24 hours. Add Chloroform to the residue left in the crucible to dissolve out Dimethylamine Hydrochloride (distill off the Chloroform to recover - good stuff) then filter on the venerable old vacuum Buchner funnel to yield an additional 20g of Methylamine Hydrochloride, washing the crystals in the funnel with a small poiiion of Chloroform ( 10mL). 

Preparative Photolysis. The preparative photolysis of an aqueous solution (pH=8.5) of AETSAPPE (2.5 M) was conducted in a 1-inch diameter quartz test tube in a Rayonet Reactor (Southern New England Radiation Co.) fitted with 254 nm lamps. Within two hours the solution gelled and the reaction was terminated. Upon acidification the solution cleared, and the product could be re-precipitated by addition of base. This indicates loss of the thiosulfate functionality. The product was dissolved in dilute HC1, precipitated with acetone, and filtered. This process was repeated three times, and the final precipitate was washed with water. The product (20 to 30 mg) was dried in vacuo for 24 hours and stored in a dessicator until use. Comparison of the13 C NMR spectrum of the product with the starting AETSAPPE 13C NMR spectrum clearly shows that the thiosulfate methylene peak shifted upfield, from 39 ppm to 35 ppm. The complete 13 C NMR and IR analysis of the product were consistent with the disulfide product. Further, elemental analysis of the product confirmed that the product was the desired disulfide product 2-amino (2-hydroxy 3-(phenyl ether) propyl) ethyl disulfide (AHPEPED) Expected C 58.39, H 7.08, N 6.20, S 14.18 actual C 58.26, H 7.22, N 6.06, S 14.28. 

Sample powders were dried in a vacuum oven at 60 C for 7 hours and cooled to minimize the hysteresis effect prior to storage in the dessicators of various water activities. In addition to Drierite, five saturated salt solutions were used in dessicators. These salt solutions were lithium chloride, magnesium chloride, potassium carbonate, sodium nitrite and potassium chloride. Their water activities were 0.110, 0.330, 0.440, 0.650 and 0.850, respectively, at 20 C. Each sample contained 1.2 to 1.5 g powder and four-week equilibration time was employed. The percentage of... 

D-Glucurono-3,6-lactone (3.0 g, 17.0 mmol) is suspended in concentrated hydrochloric add (3 mL) and shaken with ethanethiol (3 mL) for 30 min at 0°C. The reaction mixture is poured into ice water (6 mL), and the solution is then extracted with ethyl acetate (2 x 30 mL). Evaporation of the extracts yields a thick syrup, which is dissolved in methanol, and again evaporated to a syrup, winch is then dried in a vacuum dessicator. The syrup is again dissolved in methanol (20 mL), and the solution is neutralizai by the slow addition of a concentrated solution of sodium hydroxide in methanol. Scratching the sides of the flask promotes crystallization and the product is collected by filtration and washed with methanol... 

Quinoxaline (25,9 g, 19.9 mol) and TsOMe (37.1 g, 19.9 mol) in anhyd cyclohexane (60 mL) were refluxed for 8 h. After addition of EtjO the precipitated solid was filtered, rinsed with F.qO and dried over NaOH in a dessicator. 

When coated with 90 nm of gold, the substrates produced were found to provide consistent enhancement for up to 2 weeks after evaporation, when stored in a dessicator. Silver-coated substrates generally provided enhancement factors that were only consistent when used within 48 h after evaporation, due to oxide layer formation. In addition, gold is known to be markedly more biologically inert than... 

A trifluoroacetylation procedure (Levy and Paselk 1973), performed entirely under non-aqueous conditions, appears to eliminate the side-reactions involving disulfide bonds. In this procedure, insulin hydrochloride (24 mg, 4 pmoles) was dissolved in dimethylformamide (5.0 ml) (pre-purified by distillation at 0.2 mm Hg, after refluxing for 2 hr over calcium hydride), and triethylamine (10 pi, 72 pmole), and stirred at 24°C for 5 min. Ethylthioltrifluoroacetate (18.4 mg, 120 pmoles) dissolved in dimethylformamide (1.15 ml) was added to the insulin solution. The reaction was allowed to proceed for 60 min. The product was precipitated by the addition of anhydrous ether (40 ml). The precipitate was isolated by centrifugation, washed with acetone, and ether, and then dried in a dessicator over P2O5 under high vacuum. 

Deposition of a self-assembled monolayer within MCM-41 requires the addition of water to achieve complete monolayer coverage. This is due to the fact that the final step in the synthesis of MCM-41 is a calcination step (typically at S40°C), and as a result the surface is completely dessicated and severely silanol depleted [5]. The silanol population seems to vary somewhat fiom lab to lab, but is clearly related to the calcination time and tenq>erature. Failure to include this water limits the surface chemistry to simple silanol capping reactions, and as a result the degree of surface coverage is limited to the number of surface silanols. 

The addition of Na2C03 serves the dual purpose of stopping the reaction and maximizing the fluorescence of the product, MU, as described above. The initial levels of fluorescence in the extract (at time=0) are often largely contributed by the traces of pre-hydrolyzed substrate (i.e., methyl umbelliferone) in commercial substrate preparations, or coumarins in the extract. It should be pointed out, in fact, that the GUS produced by one transformed plant cell can easily be measured using unpurified commercial MUG and a relatively low-tech fluorimeter (Jefferson et al., unpublished data). To minimize the levels of zero-time fluorescence (the MU in the MUG) the solid stocks of MUG should be kept frozen and dessicated, and the bottle not opened when it is still cold (condensation of water from the air will stimulate hydrolysis in the bottle). The MUG in extraction buffer is fine in the refrigerator for a couple of weeks, but will eventually begin to show increased fluorescence. 

A disadvantage of evaporative techniques is that volatiles of interest may be lost by codistillation. Unfortunately, the loss of different components will not be uniform or predictable. Therefore, quantitative results may be in error even when multiple internal standards are employed. Since the aroma isolate typically contains a small amount of water (from the food product or distillate), care must be taken to remove water prior to concentration. While this is typically done via the addition of dessicants (e.g., anhydrous magnesium sulfate or sodium sulfate), an alternative would be to freeze out the water [48]. Failure to remove the water will result in steam distillation of the volatile components, and thus cause substantial losses during the concentration step. 

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