Phosphate buffer systems

Phosphate buffers are the principal intracellular buffering systems in living organisms, because the second pK of 6.7 is near neutrality. The protonated and unprotonated buffer species are H2P04 and HP042 , respectively. Their ratio depends on the pH of the cell. 

What quantity of 1M NaOH must be added to 100 ml of a solution of 0.1 M phosphoric acid to give a buffer solution at pH 7.5 What will be the total phosphate concentration  

Solution First, we must choose the correct pK. This is 6.7, because the desired buffer pH of 7.0 is nearest to that figure. At this pH, the acid is H2P04 and the conjugate base is HP042, as per Equation (3.16). Their total amount is 0.1 M x 100 mL = 10 mmol (i.e., [HP042 ] + [H2P04 ] = 10 mmol). Using the Henderson-Hasselbalch equation, we then have 7.0 = 

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To simulate blood conditions, a phosphate buffer system with a pH = 7.40 is desired. What mass of Na,HPQ4 must be added to 0.500 L of 0.10 M NaH2P04(aq) to prepare such a buffer ... 

An alternative approach to the microbial deracemization of secondary alcohols is to use two different microorganisms with complementary stereoselectivity. Fantin et al. studied the stereoinversion of several secondary alcohols using the culture supernatants of two microorganisms, namely Bacillus stearothermophilus and Yarrowia lipolytica (Figure 5.18) [31]. The authors tested three main systems for deracemization. First, they used the supernatant from cultures of B. stearothermophilus, to which they added Y. lipolytica cells and the racemic alcohols. Secondly, they used the culture supernatant of Y. lipolytica and added B. stearothermophilus cells and the racemic alcohols. Finally, they resuspended the cells of both organisms in phosphate buffer and added the racemic alcohols. The best results were obtained in the first system with 6-penten-2-ol (26) (100% ee and 100% yield). The phosphate buffer system gave... 

A phosphate buffer system (pH 6.5 - 7.0) Is useful for detecting small quantities of the hemoglobins H and Bart s these variants will both move toward the anode while Hb-A remains at the origin. Figure 3 gives some examples of separations that can be obtained. 

BSS with the addition of glutathione (oxidized) and dextrose as energy sources, bicarbonate as a physiological buffer, and a phosphate buffer system to maintain the products storage pH in the physiological range [296,297],... 

Moreover, several buffer systems exist in the body, such as proteins, phosphates, and bicarbonates. Proteins are the most important buffers in the body. Protein molecules contain multiple acidic and basic groups that make protein solution a buffer that covers a wide pH range. Phosphate buffers (HPO T /H2P07) are mainly intracellular. The pK of this system is 6.8 so that it is moderately efficient at a physiological pH of 7.4. The concentration of phosphate is low in the extracellular fluid but the phosphate buffer system is an important urinary buffer. Bicarbonate (H2C03/HC0 3) is also involved in pH control but it is not an important buffer system because normal blood pH 7.4 is too far from its pK 6.1 [144],... 

Two especially important biological buffers are the phosphate and bicarbonate systems. The phosphate buffer system, which acts in the cytoplasm of all cells, consists of H2POT as proton donor and HPOf as proton acceptor ... 

The phosphate buffer system is maximally effective at a pH close to its pKa of 6.86 (Figs 2-16, 2-18) and thus tends to resist pH changes in the range between about 5.9 and 7.9. It is therefore an effective buffer in biological fluids in mammals, for example, extracellular fluids and most cytoplasmic compartments have a pH in the range of 6.9 to 7.4. 

In the case of cesium no significant variations in [mJ0 were observed for (HA)W at least up to 1 g/L, neither in the acetate nor in the phosphate buffer system. Assuming the existence of 1 1 complexes only and taking the original sodium content in the sodium humate (27) as a measure for sites available for cesium complexa-tion, we find log 8 <1.2,... 

Benzene sulfonic acid Si-O-Si-C CHsCH -SOiH Ion exchange Separates cations, with divalent ions more strongly retained than monovalent ions phosphate buffer systems are often used, sometimes with low concentrations of polar nonaqueous modifiers added the presence of the benzene group on the benzenesulfonic acid moiety gives this phase a dual nature, and the ability to separate based upon nonpolar interactions... 

Partition coefficients in the octanol-pH 7.4-phosphate-buffer system. c Nitrothiazole oxidation-reduction potentials (volts) as calculated from their half-wave potentials, as determined using a Polarecord E 261 polarograph (Metrohm AG, Herisau, Switzerland) and a saturated Ag/AgCl reference electrode. Measurements were performed at 20°C and a drop time of 1 drop/2.8 sec. The compounds were dissolved in 1 ml dimethyl formamide and added to 24 ml of a borax-potassium biphosphate buffer of pH 7.3 [prepared according to J. M. Kolthoff, J. Biol. Chem. (1925) 68, 135]. A pH of 7.4 resulted. Standard error of determination 3 mv. 

Table 1 Shifts in pH during non-equilibrium freezing with phosphate buffer systems...

As discussed in Chapter 1, at a blood pH of 7.4, the ratio of [HCO3 ] to [H2CO3] is 20 1 and the system s buffering capacity can neutralize a large amount of acid. The system is independently regulated by the kidneys, which control the plasma HCOj level, and by the respiratory rate, which regulates the Pco2- Protein and phosphate buffer systems also operate in plasma and erythrocytes. Proteins are especially important buffers in the intracellular fluid. The hydroxyapatite of bone also acts as a buffer. 

Since biological systems are dynamic, with many different processes taking place and many different substances present, buffers are necessary to prevent the kind of wide variation of pH that can inhibit proper enzyme catalysis. Thus, a proper pH aids in regulating the reaction rates associated with certain enzymes and maintaining them at levels appropriate for their particular functions. Two important biological buffers are the phosphate buffer system that regulates pH for the fluid inside cells and the carbonic acid buffer system that regulates pH for blood plasma. The chemical equations for these buffers are shown below for an aqueous solution. 

Phosphate buffer system) (Carbonic acid buffer system)... 

The phosphate buffer system consists of serum inorganic phosphate (3.5 to 5 mg/dL), intracellular organic phosphate, and calcium phosphate in bone. Extracellular phosphate is present only in low concentrations, so its usefulness as a buffer is limited however, as an intracellular buffer, phosphate is more useful. Calcium phosphate in bone is relatively inaccessible as a buffer, but prolonged metabolic acidosis will result in the release of phosphate from bone. 

On slow warming the sample from — 20°, the indicator remained neutral until the temperature reached about —5°, at which point it shifted to a pH of about 4.0, then gradually returned to neutral on thawing. This unexpected result indicated that acidification was also important in the neutral phosphate buffer system. 

This is one step in the Stamicarbon caprolactam process whereby the reaction is performed in a phosphate buffer system using a catalyst activator. Overhydrogenation will form ammonium salts and underhydrogenation nitrogen and nitrous oxide. Although not a Fine Chemical example it clearly demonstrates the synergistic effect of platinum on palladium. 

An average rate of metabolic activity produces roughly 22,000 mEq acid per day. If all of this acid were dissolved at one time in unbuffered body fluids, their pH would be less than 1. However, the pH of the blood is normally maintained between 7.36 and 7.44, and intracellular pH at approximately 7.1 (between 6.9 and 7.4). The widest range of extracellular pH over which the metabolic functions of the liver, the beating of the heart, and conduction of neural impulses can be maintained is 6.8 to 7.8. Thus, until the acid produced from metabolism can be excreted as CO2 in expired air and as ions in the urine, it needs to be buffered in the body fluids. The major buffer systems in the body are the bicarbonate-carbonic acid buffer system, which operates principally in extracellular fluid the hemoglobin buffer system in red blood cells the phosphate buffer system in all types of cells and the protein buffer system of cells and plasma. 

The reaction of HIL and methylglyoxal at pH 5 performed in water yielded 2 8 mol% sotolone compared to 7.4 mol% when using the phosphate buffered system This suggests a catalytic effect of phosphate on the formation of sotoione from HIL. 

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