Buffer pair

This method was employed for transesterification reactions with both a-chymotrypsin and subtilisin Carlsberg with a variety of H+/Na+ buffers [53]. With both enzymes (which differ widely in secondary and tertiary structures) and two polar solvents, acetonitrile and THF, the activating effect of the solid-state buffer was clearly evident (Table 3.3). The observation that a variety of buffer pairs show success in activating two dissimilar enzymes in synthetically useful solvents makes this method for activation promising and novel. 

Logarithms to the base 10 are used in both equations. These equations are useful in preparing buffers and in thinking about what fraction of a substance exists in a given ionic form at a particular value of pH. From Eq. 3-7 it is easy to show that when the pH is near the pKa relatively large amounts of acid or base must be added to change the pH if the concentrations of the buffer pair A and HA are high. 

The salts of the buffer pairs responsible for control of the pH of plasma and extracellular fluid involve sodium as the principal cation, while the cellular buffers involve potassium salts. See also Acid-Base Regulation (Blood) and Diuretic Agents. 

All three methods for generating pH gradients depend on electrolytic, or protolytic, mechanisms to form pH gradients. The pH gradients obtained with carrier ampholytes and the buffer pairs are linear, but IPGs can be constructed that are nonlinear.2... 

To hold the material in the separation chamber at the operating pH in the presence of the applied electrical field, the buffers must not migrate out of the chamber as a result of the field. The buffers must, thus, have low electrophoretic mobilities. This requirement is met by the choice of suitable compounds that remain largely undissociated. Appropriate buffer pairs are available under the trade name of RotoLytes (Table 2). 

IEF buffer pairs are intended for use as a final purification step when it is desirable to obtain protein preparations that are demonstrably free of carrier ampholytes, such as for use as pharmaceuticals or in sensitive bioassays. With the buffer pairs, it is not necessary to carry out lengthy dialysis or other procedures for ampholyte removal. The correct choice of buffer pair is that combination for which the pi of the protein of interest falls in the middle of the pH gradient (which, of course, means that the pi must be determined beforehand). The desired proportion of the buffers (Table 2), at 100 mM final total concentration, is mixed with the sample solution prior to being placed the separation chamber and the IEF run is conducted according to the instructions of the manufacturer of the chamber. 

TABLE 2 pH Gradients Obtainable with pH Gradient-Forming Buffer Pairs"... 

Buffer pair components0 Overall pH range Approximate pH gradients" ... 

In each buffer pair, component A is the more acidic member of the pair and component B is the more basic of the two constituents of the pair. 

When the acidic (A) and basic (B) components of a particular buffer pair are mixed in the proportions shown (80%A 20%B 50%A 50%B or 20%A 80%B) and used for pH control in the Rotofor cell, the tabulated approximate pH gradients will be generated. Other ratios of the A and B components can also be used. See Refs. 24 and 25. 

When RotoLyte buffer pairs are used to establish the pH, the operation of the Rotofor cell is the same as with carrier ampholytes. The choice of the proper buffer pair requires that the pi of the protein of interest be known. The sample is diluted with water to half the chamber volume and then mixed with an equal volume of the appropriate blend of buffers (Table 2). Refractionation is usually not required with buffer pairs. A single run often gives the protein of interest in the desired degree of purity. 

Because the dissociation of acid-base pairs is an equilibrium reaction, the relationship between hydrogen ion concentration or pH and the relative concentrations of the acid and base can be described mathematically in terms of the dissociation constant for the acid-base buffer pair. When expressed as a logarithmic relationship, where pK is the negative logarithm of the dissociation constant this is known as the Henderson-Hasselbalch equation ... 

Carbonic acid represents the respiratory component of the buffer pair because its concentration is directly proportional to the PCO2, which is determined by ventilation. Bicarbonate represents the metabolic component because the kidney may alter its concentration by reabsorption, generating new bicarbonate, or altering elimination. The bicarbonate buffer system easily adapts to changes in acid-base status by alterations in ventilatory elimination of acid (PCO2) and/or renal elimination of base (HCO3). 

By means of this preliminary analysis, we have studied the buffer pair (amongst those listed heretofore) which gave the best effect and the least complexing (binding) effect on the sodium, potassium and calcium ions. 

Table 7 shows the effect of the concentration of the buffer pair HEPES/NaHEPES (pH 7.4 at 37 C) on the determination of sodium and potassium. 

Garbonic acid, which forms when carhon dioxide dissolves in water, and bicarbonate ion form one of several buffer pairs that keep the pH of blood within the necessary safe range. 

Before delving into titration curves for diprotic systems, you should realize that there are two buffer pairs derived from the acid H2A. H2A and HA constitute one buffer pair and HA and A constitute a second pair. For the acid H2A, there are two Henderson-Hasselbalch equations, both of which are always true. If you happen... 

By studying the ring opening of (rac)-2-phenyl-4-benzyl-5(4H)-oxazolone with butanol catalysed by CALB in organic media, it has been possible to correlate the protonation state of the enzyme with the enantioselectivity of the reaction [36]. The protonation state was controlled by the use of either organo-soluble bases or solid-state buffers of known pfC. Both triethylamine and the buffer pair CAPSO/CAPSO.Na [CAPSO = 3-(cyclohexylamino)-2-hydroxy-l-propanesulfonic acid] were found to increase the enantioselectivity of reactions catalysed by CALB and also the lipase from Mucor miehei. The effect of solvent, water activity and temperature on the enantioselectivity of reactions catalysed by lipases and hydroxynitrile lyases (enzymes that catalyse the addition of cyanide to aldehydes) has been reported [37]. 

Every buffer consists of a buffer pair. In most cases the components are a weak acid and its salt. To make a buffer solution, a weak acid in solution is mixed with a salt of its conjugate base (e.g. acetic acid and sodium acetate). The resultant chemical reactions in solution are shown in Table 1.2. Since the acid is weak, it only partially dissociates, as shown in reaction 1 of Table 1.2. The... 

A buffer consists of a buffer pair it is a mixture of a weak acid and its salt. 

Buffer pair consists of buffer add HA and buffer base A ... 

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