Stability in acidic

Superdex is stable to the same conditions as cross-linked Sepharose media (see earlier). The chemical stability in acidic and basic solutions, as well as ionic and hydrophobic interactions of various molecules, has been studied... 

The 14e compound MTO readily forms coordination complexes of the type MTO-L and MTO-L2 with anionic and uncharged Lewis bases [96], These yellow adducts are typically five- or six-coordinate complexes, and the Re-L system is highly labile. Apart from their fast hydrolysis in wet solvents, MTO-L adducts are much less thermally stable then MTO itself. The pyridine adduct of MTO, for instance, decomposes even at room temperature. In solution, methyltrioxorhenium displays high stability in acidic aqueous media, although its decomposition is strongly accelerated at increased hydroxide concentrations [97, 98], Thus, under basic aqueous conditions MTO decomposes as shown in Equation (4). 

The stability of the enzyme-polymer complex and its dissociation upon the variation of pH depends on the structural and other physico-chemical properties of CP and enzyme molecule. Thus, a Biocarb-T heteroreticular biosorbent (Fig. 26) is characterized by a stability of its complex with ot-amylase (under the condition of its stabilization) in acid solutions and a complete dissociation of the complex during isolation of the active enzyme at pH 7-8. 

Compared to the corresponding polycrystalline metal chalcogenides, chalcogenide glasses exhibit better chemical stability in acidic and redox media and often... 

Low (1-1.5) A,X Relatively low stability of framework. Low stability in acids. High stability in bases. High concentration of acid groups with moderate acid strength. Hydrophilic. 

Despite its limited stability in acid (1), guar gum has been used to thicken 3-15% hydrochloric acid (121). An allyl ether -guar gum adduct has been proposed for use as an acid viscosifier (122). Zr(IV) crosslinked CMHEC has been used to thicken hydrochloric acid (81). 

Smith, A.E. and Fitzpatrick, A. The loss of five thiolcarbamate herbicides in nonsterile soils and their stability in acidic and... 

Erythromycins are macrolide antibiotics produced by bacterial fermentation. Fluoiination of erythromycin has been studied as a strategy to insure better stability in acidic medium and/or to achieve better bioavailability. An erythromycin, fluorinated at C-8, flurithromycin, was launched several years ago. Its preparation involves an electrophilic fluorination, with CF3OF [119] or with an N-F reagent A/-fluorobenzenesulfonimide (NFSI) [120], of the 8,9-anhydroerythromy-cin-6,9-hemiacetal or of the erythronolide A (Fig. 44). 

Erythromycins are macrolide antibiotics produced by bacterial fermentation. Fluori-nation of erythromycin has been studied to ensure abetter stability in acidic medium and/or a better bioavailability. 

Other Fluorinated Antibiotic Drugs Flurithromydn is an erythromycin fluorinated atC-9. It was launched some years ago (Figure 8.21). Its preparation involves electrophilic fluorination of 8,9-anhydroerythromycin-6,9-hemiacetal or of erythronolide A with CFsOF, or with a N— F reagent (NFSI) (cf. Chapter 4). The advantage of the fluorine substitution is a better stability in acidic medium and an increased bioavailability. Two erythromycins fluorinated at C-14 are in clinical development HMR-3562 and HMR-3787). 

Pb02 Lead dioxide is an electrode material of relatively high electronic conductivity and high stability in acidic media, useful at high positive potentials. 

Only the + 2 state of cobalt has thermodynamic stability in acid solution. The instability of Co3+ is referred to in Section 5.3. Only the + 3 states of Rh and Ir are stable in acid solution their +3/0 standard reduction potentials are quite positive, consistent with their nobility . In alkaline solutions the + 2 and + 3 states of the elements exist as insoluble hydroxides. 

Structure Stability in acid and base. Product with KOterrBu-DMSO Product with (PhjP)jRhCl... 

Nowadays polyorganosilazanes are used more and more often. Until recently, due to the small hydrolytic stability (in acid and neutral media) of compounds with a Si—N bond, the possibility of their practical application seemed doubtful. However, the increased ability to hydrolyse and the chemical activity of the Si—N bond in polyorganosilazanes predetermined their industrial applications. It was found that polyorganosilazanes are hydrolysed when kept in air even at room temperature, with 80-85% of si-lazane bonds replaced by siloxane bonds. Probably, due to the high gas permeability of siloxane film the ammonia released during the hydrolysis is withdrawn out of the system without disrupting the film, even in case of considerable thickness (1-2 mm). 

The stabilities of silyl ethers are closely related to the electronic and steric effect of the substituents on the silicon atom and are generally proportional to the steric hindrance provided by the substituents. Moreover, electron-withdrawing substituents on the silicon atom increase the stability of the silyl groups toward acid but decrease their stability toward base. Consequently, their stability in acid follows the order TMSSelective deprotection among these groups can thus be achieved... 

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