Mutarotation measurement

Table VI (see p. 53) gives a summary of mutarotation measurements made by the authors for a group of sugars under comparable conditions. The mutarotation constants are expressed to the base 10. If it is desired to use the natural logarithmic base, equation 7 is changed only by replacement of the base 10 by the base e, by multiplying exponents mi and m2 by 2.3026.

Hydrogen-ion concentration effect on enzyme kinetics, 292, 327 on phosphorylase action, 355 mutarotation measurement by, 52... 

Reduction of sugar sulfonates by lithium aluminum hydride, 269 Refractive index, mutarotation measurement by, 50 R-Enzyme, 363 Rhamnose... 

Mutarotation Measure- ment Temp- erature, degrees AH (cal.deg.-1 mol- ) AG (cal.mol-1) AS (e. u.) Refer- ences... 

Isbell HS, Pigman WW (1937) Bromine oxidation and mutarotation measurements of a- and p-aldoses. J Res Natl Bur Stand 18 141-194... 

A continuously recording polariscope has been developed (46b) which should aid mutarotation measurements. 

The optical rotations just cited for each isomer are those measured immediately after each one is dissolved m water On standing the rotation of the solution containing the a isomer decreases from +112 2° to +52 5° the rotation of the solution of the p isomer increases from +18 7° to the same value of +52 5° This phenomenon is called mutarotation What is happening is that each solution initially containing only one anomeric form undergoes equilibration to the same mixture of a and p pyranose forms The open chain form is an intermediate m the process... 

When measured at 40° with Lintner s soluble potato starch, the ratio of the dextrinogenic to the saccharogenic activities is approximately 6 to 1 for the amylase of Aspergillus oryzae. This value is given by both crude and purified preparations of the amylase if the measurements are carried out under comparable conditions. This constancy in the ratio of these two activities has led to the conclusion that, like pancreatic amylase, the amylase of Aspergillus oryzae is not accompanied in nature by beta amylase. Reacting mixtures of the amylase of Aspergillus oryzae and starch exhibit alpha mutarotation.72... 

In our first measurements with solutions of 0.5 M a-D-galactose in 0.5 M boric acid, the constants of the mutarotation and of the change in the conductivity agreed very well. 

With a-lactose the negative influence was less than with the jS-lactose and during the mutarotation reaction the conductivity increased in the case of the former, while it became less in the case of /3-lactose. The two isomers were very carefully purifled. Table VIII gives a review of the measurements. ... 

Measurement. Rotations were measured with a Rudolph Model 200 photoelectric polarimeter operating from a sodium vapor lamp. Water was circulated through 20-cm. tubes with glass end plates, from a bath maintained at 25.0° 0.1°. The runs on the mutarotation of D-glucose showed excellent first-order dependence over two half lives. In studies on the mutarotation of glucosamine hydrochloride in the presence of varying concentrations of sodium hydroxide and metal salt, it was necessary to add the alkali first, then the metal salt, to avoid precipitation. 

The rates of mutarotation of glucose, in the presence of 0 to 0.238M imidazole and of 0 to 0.230M benzimidazole at 25°, have been measured the rate constant data are given in Table I. Linear plots of the observed rate constants for glucose vs. the molarity of imidazole or benzimidazole (Im or BIm) are obtained. The straight lines follow the equations... 

Bruice and Schmir (3) have shown that for a series of imidazole derivatives, klm depends on the base strength of the catalyst and since pKA is an approximate measure of base strength, the value of klm should increase with increase in pKA. Table I shows that this is indeed the case. Imidazole, pKA = 7.08, has a catalytic constant eight times larger than that of benzimidazole, pKA = 5.53. Bronsted and Guggenheim (2) have obtained a linear relationship between log k/ and pKA for a series of carboxylic acids in the pKA range of 2 to 5, where kB is the carboxvlate anion basic catalytic constant for the mutarotation of glucose and Ka is the acid dissociation constant of the acid. Our results for imidazole and benzimidazole fit fairly well into the Bronsted plot. 

When either isomer is dissolved in water, there is a gradual change from one form to the other until equilibrium is established, i.e. mutarotation. These changes may be followed by measuring the change in optical rotation with time until, at equilibrium, the specific rotation is +55.4°. 

Mutarotation has been shown to be a first-order reaction, the velocity constant being independent of reaction time and concentration of reactants. The rate of mutarotation increases 2.8 times with a 10°C rise in temperature. By applying the law of mass action, equations have been developed to measure the rate of the reversible reaction between the a and (3 forms of lactose. If a dilute lactose solution at constant temperature contain a moles of a and b moles of /3, then the amount of (3 formed (x) per unit of time is... 

Equations similar to those for mutarotation have been derived, expressing the relationship between the solubility behavior of the two forms of lactose and the equilibrium or rate constants (Hudson 1904). The constants derived by both mutarotation and solubility methods are in agreement. The solubility equations have been used to develop procedures for measuring a- and /3-lactose in dry milk (Roetman 1981). 

The original experimental evidence for concerted acid-base catalysis of the mutarotation in benzene is now considered unsound133 134 and concerted acid-base catalysis has been difficult to prove for nonenzy-matic reactions in aqueous solution. However, measurements of kinetic isotope effects seem to support Swain and Brown s interpretation.135 Concerted acid-base catalysis by acetic acid and acetate ions may have been observed for the enolization of acetone136 and it may be employed by enzymes.1363... 

Fig. 2.54. Two-dimensional carbon-proton shift correlation of mutarotated D-lactose (1 mol/L in deuterium oxide , 3C 100.6 MHz H 400.1 MHz measuring time 90min transform lime 2.5 min) (a) stacked plot [64] (b) contour plot. 

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