Buffer medium

Enol ethers are readily attacked in buffered medium by electrophilic reagents such as halogens, A -haloamides, perchloryl fluoride and organic peracids to give a-substituted ketones. Similarly, electrophilic attack on... 

An acetoxy group at C-21 inhibits reaction of the 20-ketone with semi-carbazide hydrochloride,but in buffered medium 20-semicarbazones can be prepared in high yield even from 17-hydroxy-21-acetoxy compounds. ... 

B. Concentration of the metal ion to he titrated. Most titrations are successful with 0.25 millimole of the metal ion concerned in a volume of 50-150 mL of solution. If the metal ion concentration is too high, then the end point may be very difficult to discern, and if difficulty is experienced with an end point then it is advisable to start with a smaller portion of the test solution, and to dilute this to 100-150 mL before adding the buffering medium and the indicator, and then repeating the titration. 

In order to define the conditions of the growing cultures, buffered medium (VL) inoculated with E, coli ATCC 11775 and supplemented with nitrate, glucose and DMA was incubated at 37 C, and pH, nitrite concentration, nitrate concentration, cell growth and nitrosamine formation were followed (Fig. 1). Within 2 hrs, >90% of the nitrate is converted to nitrite (some of the nitrite is further reduced) and over 8 hrs the pH drops from 7.3 to 6.0. This would indicate that in experiments carried out for 20 hrs or more the control medium should be adjusted to pH 6.0 to 6.5 and nitrite should be added rather than nitrate. Such a control medium (VL) was supplemented with nitrite and DMA and NDMA formation was followed (Fig. 2). It can be seen that even without the addition of cells the rate of nitrosation is 4 fold greater than... 

Pectins were incubated in buffered medium in mild alkaline conditions (pH 8.5 to 11.2) at room temperature, leading to both demethylation and P-elimination. At higher pHs p-elimination had increased initial speed but soon plateaued. Demethylation was slower but proceeded until completion. It followed a (pseudo)-first order kinetics with respect to concentration of methylesterified carboxyl groups. A rate constant of 27.2 9.0 moT 1 min was calculated after correction for the pH variation during the course of the reaction. 

Beltran E, H Eenet, JE Cooper, CM Coste (2000) Kinetics of abiotic hydrolysis of isoxaflutole influence of pH and temperature in aqueous mineral buffered medium. J Agric Eood Chem 48 4399-4403. 

Pal, B., Sen, P.K. and Sen Gupta, K.K. (2001) Reactivity of alkanols and aryl alcohols towards tetrachloroaurate(lll) in sodium acetate-acetic acid buffer medium. Journal of Physical Organic Chemistry, 14, 284. 

S Chakrabarti, MZ Southard. Control of poorly soluble drug dissolution in conditions simulating the gastrointestinal tract flow. 1. Effect of tablet geometry in buffered medium. J Pharm Sci 85 313-319, 1996. 

DSG should be dissolved in an organic solvent prior to addition to an aqueous reaction medium. Suitable solvents include DMF and DMSO. To initiate a reaction, add an aliquot of the organic solution to the buffered medium containing the molecules to be crosslinked. Reaction buffers should not contain any competing amine compounds such as Tris or glycine,... 

Plants and single celled organisms have no means of autoregulating their operating temperature and thus their growth and replication are influenced by external conditions. Hence, we keep food at 4 °C in a refrigerator to prevent spoilage yet we incubate bacterial cultures at 37 °C and usually in a buffered medium when we wish to cultivate the cells for further study. 

Attention must be paid to the viability of the exeised tissue under in vitro conditions. Electrophysiologic characterization appears to be a valuable tool to indicate the viability of the tissue following excision. The viability of the tissue can be retained by continuous bubbling with O2/CO2 mixtures and addition of glucose to the buffer medium [11]. 

Recent research into the ter Meer reaction (Shugalei and Tselinskii 1994) has demonstrated that it actually chooses the chain ion-radical mechanism. Chain branching is attributed to air oxygen, after transformation into the superoxide ion (O2 see Section 1.7.1). The whole process of substitution in the aqueous-alkaline buffer medium is expressed by a 14-step sequence summed in Scheme 4.36. 

Typically, PB was added to the appropriate buffer medium and used Immediately to minimize any possible loss of peroxygen content. OP reagents were transferred via microliter syringe to a second buffer solution as for PB, solutions were used Immediately after preparation. The reactions were Initiated by transferring an appropriate volume of PB solution (via Plpetman automatic pipettor) to a cuvette and then similarly adding OP ester solution to bring the total reaction volume to 3.00 cm. ... 

Renewable energy sources such as wind and sunlight are intermittent, necessitating a buffer medium for the uninterrupted supply of energy to users. Both hydrogen and electricity need an... 

Broad profiling to annotate Solubility in buffer medium micro-Ames (genotoxicity)... 

Kinetic solubility This pragmatic approach starts with a concentrated compound solution in pure DM SO further diluted in a buffer medium. The amount of compound in solution is measured after a few minutes incubation either by recording its UV absorbance (with or without a chromatographic step) or precipitate formation using an optical method (turbidimetry, nephelometry or flow cytometry). This approach mimics the typical path of the compound in biochemical, cellular assays or in vivo animal models. Kinetic solubility usually serves as a quality filter prior to cell based assays (see paragraphs on solubility, permeability and cellular assays). 

Equilibrium solubility This approach is considered a first attempt to characterize the true thermodynamic solubility of the compound. It is used to rank-order compounds and to extract a structure-solubility relationship within the chemical series. In this assay, compounds are usually equilibrated for 24 h before analysis. One can start from powder, but this is a quite labor-intensive step. In most cases one starts from DMSO stock solutions (usually 10 mM) because it is much more efficient from a compound logistics viewpoint. The solvent is then usually removed and the compound is dried before addition of the buffer medium [15, 16]. 

Bartasiute A, Westerink BHC, Verpoorte E, Niederlander HAG. Improving the in vivo predictability of an on-line HPLC stable free radical decolorahon assay for antioxidant activity in methanol-buffer medium. Free Radical Biology Medicine. 2007 ... 

Due to the basicity of the (concave) pyridine, in a buffer most protons are located on the pyridine nitrogen. The concentration of free EtOH is small. Therefore in the standard pyridine buffer the C-protonation is faster than O-protonation. However, in a buffer containing a concave pyridine 3, the protonated nitrogen atoms of the concave pyridines 3 are shielded. This retards the C-protonation and a small concentration of protonated ethanol (EtOHj) is sufficient for O-protonation and the Nef-reaction. Thus, the Nef-reaction is possible in a buffered medium, under softer conditions than with mineral acids. The reaction was therefore called the Soft Nef-Reaction. 

Similar results were found by Griengl and co-workers [21] for HbHNL catalysis. Ethers, such as diisopropyl ether (DIPE) or tBME, were found to be the most suitable solvents. The transformation proceeds most efficiently at temperatures between 5 and 15 °C, and the formation of a stable emulsion seems to be of importance. A series of aldehydes were converted by this method (Figure 9.2). Compared to transformations in aqueous buffer medium [22], higher conversions and were achieved (Table 9.1) [21]. 

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