Quenching quench solution preparation

E. Quench and purification. While the butyllithium addition is taking place, an acidic ethanol quench solution is prepared in a 3-L, two-necked, round-bottomed flask, equipped with a mechanical stirrer and a 250-mL, pressure-equalizing dropping funnel. The flask is charged with 1 L of absolute ethanol and the funnel with 250 mL of acetyl chloride. The ethanol is stirred rapidly and the flask is cooled with an ice bath as the acetyl chloride is added over a 30-40-min period and then the cooling bath is removed and stirring is continued for 20-30 min. After the main reaction mixture has been stirred for 30 min at room temperature, it is cooled with a dry ice-acetone bath. The acidic ethanol solution is cooled with an ice bath and the cold, main reaction mixture is quenched by addition (via a double-ended needle) into the rapidly stirred, cold, acidic ethanol solution over a 3 to 3.5 hr period (Note 16). 

A fully automated system for performing detailed studies has been developed to improve the reproducibility and throughput (Fig. 12.2) [8]. It consists of two functional components a sample-deuteration device and a protein processing unit. The preparation operations (shown at the top of Fig. 12.2) are performed by two robotic arms equipped with low volume syringes and two temperature-controlled chambers, one held at 25 °C and the other held at 1 °C. To initiate the exchange experiment, a small amount of protein solution is mixed with a deuter-ated buffer and the mixture is then incubated for a programmed period of time in the temperature-controlled chamber. This on-exchanged sample is immediately transferred to the cold chamber where a quench solution is added to the mixture. 

Quenching with the aminated resin appeared absolutely necessary to avoid cleavage of the aminopropylpolysiloxane. After filtration, the aminopropyl-polysiloxane can be stored at -18°C in the CH Cl /MeOH solution without decomposition. Analysis by SEC can be made from THE solutions prepared after incomplete evaporation of the CH Clj/methanol mixture. Actually, they cannot be easily stored for long times and the polymers cannot be dried without degradation. Their sensitivity to TMSI appeared much higher compared with NBoc-functionalized hyperbranched poly(siloxysilanes) or NBoc-functionalized highly crosslinked siloxanes networks formed by sol-gel chemistry [27]. 

Pyrene Solution Preparation. Pyrene was purchased fi om Aldrich Chemical Company and used directly. A phosphate buffer, pH 6 upon dilution was used (6). For the fluorescence quenching experiments an aqueous pyrene stock solution was prepared fi-om a 2.05 x 10" solution of pyrene in methanol 1.5 ml of the methanolic pyrene solution was mixed with 498.5 ml of pH 6 buffer water to give a concentration of 6.15 X 10" M aqueous pyrene. The pyrene fluorescence intensity tended to be more stable if the solution were allowed to mix 1 hour before use. 

Solution Preparation Note clean glassware and cuvettes thoroughly before using. Interference from impurities can lead to a tremendous waste of time and money. Wash cuvettes with soap, de-ionized water and wash acetone, and rinse with spectroscopic-grade MeOH. Keep your work area clean Impurities that fluoresce or that quench fluorescence are the bane of fluorescence spectroscopy. 

Fe S 0.1 M Na2S solution was mixed with S (3 1 molar ratio) at 180°C. After complete dissolution of S, the solution was mixed at 140°C with 0.4 M Fe(NH4)2(SO4)2 (both solutions prepared with fresh boiled water to minimize concentration of oxygen) in a specially designed reactor and aged for 30 min. The mixture was then quenched, hltered, and dried under a nitrogen atmosphere. 

Aim effect of initial pH quenching effect of additional carbonate Solution preparation ... 

Table III shows the results obtained with two crystalline preparations of the polysaccharide. Single crystals and a "quench precipitate" (prepared by quickly chilling a polymer solution in ice to precipitate the polysaccharide with minimal crystallinity) were compared. The extent of degradation of lamellar crystals is highly temperature dependent, with the total fraction of polymer digested at any temperature being finite and quite reproducible from one batch of crystals to another. Incubation up to 20 hours causes no additional decrease in turbidity nor do the crystals inactivate the enzyme. The plateau in absorbance is evidence of a "two region" model of crystal morphology, i.e., one with both accessible and inaccessible zones. The extent of digestion at 20°C of the lamellar crystalline material is to be compared with that of the "quench precipitate" form at the same temperature.

Prepare NADPH stock solution (20 mM) in water, test compound stock solution (20 mM) in appropriate solvent, / -(+ )-pulegone (Fig. 14.1) stock solution (20 mM) in water acetonitrile (1 1), dGSH stock solution (20 mM, Note 4), potassium phosphate buffer (0.1 M, pH 7.4), and chilled quenching solution (5 mM dithiothreitol in methanol). Human liver microsomes (20 mg/mL) are thawed on ice. 

The first semiautomated HX-MS system was described by Virgil Woods in 2001 and was based around the decoupled experimental paradigm [44], Woods outlined an end-to-end HX workflow, titled DXMS, that began with (manual) sample preparation and freezing of samples in quench solution. When ready, samples were placed in a modified HPLC autosampler able to perform the thawing, digestion, and LC-MS analysis. Although this automation was never commercialized, it was in use for over a decade and was demonstrated to be extremely productive. 

Remove the quenching solution and wash the membrane pieces four times with 500 1 water. Perform a final wash with 500 1 of digestion buffer. Remove this buffer and replace with fresh digestion buffer. Use the minimal volume needed to submerge the membrane piece(s) (generally between 20 and 100 1). Add 1 1 of the freshly prepared enzyme solution. The digestion proceeds for 4 to... 

Carbethoxy)-3-rnethyl-3,4,5,6-tetrahydrO 2H-pentalen-l-one (2). A solution of ethyl 2-ethytidene-3-(1-cyclopenten-1-yl)-3-oxo-propanoate 1 (210 mg. 1 mmol) in CH2CI2 (10 mL) was stirred with SnCU (780 mg, 3 mmol) lor 24 h at 20°C After quenching with water (50 mL), the organic layer was washed (N3HCO3), dned (UgS04) and punlied by preparative TLC to afford 62 5 mg of 2 (30%)... 

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