Stability of the reagent

The stability of the reagent is much improved by replacing MeOH with Me0CH2CH20H, and this forms the basis of the present-day Karl Fischer reagent. 

The stability of the reagent in acid solution, together with its ability to complex a wide range of metals, make it a very useful general extracting reagent, especially for heavy metals. The chief applications of APDC in quantitative analysis are as follows ... 

The authors also demonstrated a low-technology method for recording the chemiluminescent signal of the bDNA assay. The light emission was recorded on black-and-white film Polaroid film using a handheld camera. The bDNA assay could be applicable to field situations because of the stability of the reagents and the ability to record the data without the use of sophisticated equipment. 

Stability of the Reagent The stability of the original Karl Fischer reagent initially prepared with an excess of methanol was found to be fairly poor and hence, evidently needed frequent standardization. However, it was estabtished subsequently that the stability could be improved significantly by replacing the methanol by 2-methoxyethanol. 

The scope of this reaction type, discovered in our laboratory 8 years ago, is strikingly restricted by the fact that aromatic residues are necessary for activating the substrates, for stabilization of the reagents, and in some cases of the products as well. 

A study of the scope of the reaction has shown that mono- and disubstituted alkenes and, particularly, aryl-substituted alkenes are the best substrates. Various limitations have been noted, some not unexpected (sensitivity to steric effects), others quite surprising (complex reactivity of cyclohexenes). Nevertheless, the exceptionally high stability of the reagent should make it available from the shelf, and in appropriate cases its use is to be considered as an alternative to the Simmons-Smith reaction. 

Diazo compounds with electron withdrawing substituents were introduced both to improve the stability of the reagent in the dark (Table 3.1) and to... 

The stability of the reagent to the assay conditions should also be ascertained. The instability of azides and diazo compounds towards thiols was mentioned earlier, and it would be prudent to ensure that all new reagents whether they contain familiar photoactivatable groups or not are stable to the prevailing chemical and enzymatic conditions. In an attempt to label the cAMP receptor of D. discoideum, Wallace and Frazier (1979b) found that 8-N rcAMP was converted to NrAMP by the phosphodiesterase of a crude membrane preparation. The NrAMP specifically labeled actin and not the cAMP receptor. 

Except for the abnormally low yield with lactim ethers derived from 3-carbethoxylactams with amidines depends on the stability of the reagents.120 Lactim ethers, just as aliphatic imino ethers, are labile to acidic and alkaline media, hence the yields depend on the rate of cyclization. With basic or enolizable amidines, the... 

The great advantages of this method compared to other more conventional methods, such as coupling with DCC, are the easy separation of the products from reagent-derived coproducts, the absence of racemization, low cost, and the stability of the reagent. 

The fundamental principles of assay design are discussed in the comprehensive review by Ekins. Suitable protocols can be found in the references already cited for other radioimmunoassays. Assay conditions should favor binding of the antigen to the antibody and assure stability of the reagents during incubation. The assays are usually carried out in protein-fortified isotonic buffers at a pH close to neutrality. While it is usual... 

Presumably, the difficulties associated with Zn(CF3)2L2 trifluorometh-ylations could be considerably reduced by utilizing a more weakly coordinating base. This alteration of the ligand, however, would almost surely reduce the thermal stability of the reagent. For example, in the weakly coordinating solvent CH2C12, the decomposition temperature of unligated Zn(CF3)2 has been determined to be — 40°C (26). 

The loading of the resin 135 was calculated to be of the order of 3.4 mmol [69]. However, the stability of the reagent proved to be limited, and it had to be prepared immediately before use. Using 2 equiv. of the phosphonate resin, alkenes 136 were prepared from the corresponding carbonyl compounds 137 in good yields within 1 h at room temperature simply by stirring the mixture in THE. 

The reactions of ailylboranes, -silanes and -stannanes with carbonyl compounds and imines always take place with double-bond migration, and the structural stability of the reagent is a common problem that is encountered ( 2.7). The reactions of ailylboranes and -boronates occur without catalysis, while those of allylsilanes and -stannanes usually require the presence of a Lewis add [253], The mechanism of the reactions of allylboron derivatives is concerted, and the addition occurs via a six-membered cyclic transition state. A slightly distorted chair transition state model in which the oxygen of the carbonyl group is coordinated to the boron atom is usually invoked (Figure 6.42). Various steric and polar interactions dictate whether the Si or Re face of the prochiral aldehyde is attacked (models C j... 

However, 1,3 elimination can occur at elevated T, although the stability of the reagents is higher in solution than in the solid ... 

The stability of the reagent has been questioned by some users, and a test was made to examine this problem. A set of solutions A and B was stored for one month. Another set of solutions was mixed to (A + B) and similarly stored. After the storage period a fresh set of reagents was prepared, and all three sets of reagents were tested. They gave identical readings, but the premixed and stored reagent was unstable in the spectrophotometer. 

Unlike the light-producing reactions described above, peroxyoxalate chemiluminescence is not well suited to aqueous conditions, due to the limited solubility and stability of the reagents in that solvent. This system has been used to detect compounds that can act as efficient fluorophores (e.g., amino-substituted polyaromatic hydrocarbons), or after derivatization of the target analytes with... 

This technique does have several drawbacks involving, for example, the specificity of the derivatizing reagent, the determination of the extent of the reaction, the determination of the number of functional groups that have reacted, and the stability of the reagent to X-rays. The question of whether reactions that occur in solution can be extended to a two-dimensional surface remains unanswered. 

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