Stabilizers citrate

Some pertinent degradants from glass are silica lamination, especially in phosphate buffer after 6 or more months of stability. Citrate and EDTA can induce complexing agents as well as high levels of sodium, aluminum, barium, and iron. 

Some salts are able to form complexes with drug molecules in the formulation, and thus influence photochemical stability. Citrates are common buffers that can have a dual role as chelating agents. Recent studies show an interaction between primaquine and citrate in aqueous solutions. The photochemical stabilization of primaquine occurring in the presence of citrate is probably caused by the observed interaction between the drug and the buffer. The mechanisms involved are under investigation (Kristensen et al to be published). 

Two nucleation processes important to many people (including some surface scientists ) occur in the formation of gallstones in human bile and kidney stones in urine. Cholesterol crystallization in bile causes the formation of gallstones. Cryotransmission microscopy (Chapter VIII) studies of human bile reveal vesicles, micelles, and potential early crystallites indicating that the cholesterol crystallization in bile is not cooperative and the true nucleation time may be much shorter than that found by standard clinical analysis by light microscopy [75]. Kidney stones often form from crystals of calcium oxalates in urine. Inhibitors can prevent nucleation and influence the solid phase and intercrystallite interactions [76, 77]. Citrate, for example, is an important physiological inhibitor to the formation of calcium renal stones. Electrokinetic studies (see Section V-6) have shown the effect of various inhibitors on the surface potential and colloidal stability of micrometer-sized dispersions of calcium oxalate crystals formed in synthetic urine [78, 79]. 

The reason why lanthanides of high atomic number emerge first is that the stability of a lanthanide ion-citrate ion complex increases with the atomic number. Since these complexes are formed by ions, this must mean that the ion-ligand attraction also increases with atomic number, i.e. that the ionic radius decreases (inverse square law). It is a characteristic of the lanthanides that the ionic radius... 

Complexing agents, which act as buffers to help control the pH and maintain control over the free metal—salt ions available to the solution and hence the ion concentration, include citric acid, sodium citrate, and sodium acetate potassium tartrate ammonium chloride. Stabilizers, which act as catalytic inhibitors that retard the spontaneous decomposition of the bath, include fluoride compounds thiourea, sodium cyanide, and urea. Stabilizers are typically not present in amounts exceeding 10 ppm. The pH of the bath is adjusted. 

Pasteurized Process Cheese. Sodium citrate is used in pasteurized process and sHced cheese as an emulsifying salt to stabilize the water and oil emulsion and improve process cheese body and texture (64). 

Dairy Products. Sodium citrate is an important stabilizer used in whipping cream and vegetable-based dairy substitutes. Addition of sodium citrates to ice cream, ice milk, and frozen desserts before pasteurization and homogenization reduces the viscosity of the mix, making it easier to whip. 

Electroplating. Aluminum can be electroplated by the electrolytic reduction of cryoHte, which is trisodium aluminum hexafluoride [13775-53-6] Na AlE, containing alumina. Brass (see COPPERALLOYS) can be electroplated from aqueous cyanide solutions which contain cyano complexes of zinc(II) and copper(I). The soft CN stabilizes the copper as copper(I) and the two cyano complexes have comparable potentials. Without CN the potentials of aqueous zinc(II) and copper(I), as weU as those of zinc(II) and copper(II), are over one volt apart thus only the copper plates out. Careful control of concentration and pH also enables brass to be deposited from solutions of citrate and tartrate. The noble metals are often plated from solutions in which coordination compounds help provide fine, even deposits (see Electroplating). 

Citrate synthase catalyzes the metabolically important formation of citrate from ace-tyl-CoA and oxaloacetate [68]. Asp-375 (numbering for pig CS) has been shown to be the base for the rate-limiting deprotonation of acetyl-CoA (Fig. 5) [69]. An intennediate (which subsequently attacks the second substrate, oxaloacetate) is believed to be formed in this step the intermediate is thought to be stabilized by a hydrogen bond with His-274. It is uncertain from the experimental data whether this intermediate is the enolate or enol of acetyl-CoA related questions arise in several similar enzymatic reactions such as that catalyzed by triosephosphate isomerase. From the relative pK values of Asp-375... 

Figure 2 Stability of /3-poly(L-malate) measured by its activity to inhibit purified DNA polymerase a of P. polyceph-alum. The relative degree of inhibition is shown (100 rel. units refer to complete inhibition). The DNA polymerase assay was carried out in the presence of 5 /tg/ml /S-poly(L-malate) as described [4]. The polymer was preincubated for 7 days at 4°C in the following buffer solutions (50 mM) KCl/HCl (—A—). Citrate (—V—). 2-(A/-Morpholino)-ethanesulfonic acid, sodium salt (—O—). Sodium phosphate (— —). N-(2-Hydroxyethyl)piperazine-N -(2-ethanesul-fonic acid), sodium salt (— — ). N,N-b s (2-Hydroxyethyl)-glycine, sodium salt (—T—). Tris/HCl (— —). 3-(Cyclo-hexylamino)-l-propanesulfonic acid, sodium salt (— —).

Sample Collection and Enzyme Stability. Serum samples are collected with chemically clean, sterile glassware. Blood is allowed to clot at room temperature, the clot is gently separated from the test tube with an applicator stick, and the blood is centrifuged for 10 minutes at 1,000 g. If the red cells are known to contain the enzymes whose activity is being measured, as in the case of LD, even slightly hemolyzed serums must be discarded. When acid phosphatase is to be measured, the serum should be placed immediately in ice and processed as soon as possible, or it should be acidified by the addition of a small amount of sodium citrate. Anticoagulants such as EDTA, fluoride and oxalate inhibit some serum enzymes. However, heparin activates serum lipoprotein lipase. 

N. A. and Liz-Marzan, L. M. (2004) Mechanism of strong luminescence photoactivation of citrate-stabilized water-soluble nanoparticles with CdSe cores./. Phys. Chem. B, 108,15461-15469. 

Buffer salts also can exert a secondary salt effect on drug stability. From Table 5 and Fig. 5 it is clear that the rate constant for an ionizable drug is dependent on its pKa. Increasing salt concentrations, particularly from polyelectrolytes such as citrate and phosphate, can substantially affect the magnitude of the pKa, causing a change in the rate constant. (For a review of salt effects, containing many examples from the pharmaceutical literature see Ref. 116.)... 

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