The Thermodynamics of Mutarotation of Some Sugars: I. Measurement of the Heat of Mutarotation by Microcalorimetry

Abstract

The heats of mutarotation of D-glucose, D -X Y~O S~, lactose, maltose, and cellobiose have been determined sing a microcalori~r~eter of the Tian-Calvet type. Part I of this paper describes the experimental work and the results obtained. Discussion of these results is reserved for Part 11.Since the discovery of the phenomenon of mutarotation, much work has been done t o elucidate the kinetics and mechanism of the reaction as well as t o study the stability of the various forms postulated. Some attempt has also been made t o determine the heats of mutarotation of the sugars from the temperature dependence of the equilibrium constants for the mutarotations (I). The only direct measurement of a heat of mutarotation has been performed by S t~~r t e v a n t (2, 3) for D-glucose using an adiabatic calorimeter. I t seemed desirable, however, to have values for other sugars, particularly for those undergoing an opposing first-order mutarotation, in order to make a comparison of the appropriate thermodynamic quantities. MATERIALSThe sugars studied were all of reagent grade purity, and were obtained as almost pure a or p anomers by slow recrystallization from slightly supersaturated aqueous or alcoholic solutions according t o the method of Hudson and Dale (4).T h e "purity", i.e. the percentage of a or P anomer in the "a" or "P" sugar, may be determined polarinletrically using known optical rotations. These experiments were performed a t O°C. Isbell and Pigman ( 5 ) have determined the optical rotations a t 0" C. for both anomers of D-glucose and lactose and for a-D-xyl0se and p-maltose. They have also obtained a value a t this temperature for P-cellobiose (6). T h e optical rotations a t 20" C. for the other anomers required have been obtained by Hudson and Yanovsky ( 7 ) using an indirect method requiring the separation of only one of the anomers of the sugar. Their values have been used t o find the "purity" of the sugars a t O0 C. Since the "purities" of the sugars, save for cellobiose, were nearly loo%, this introduces a negligible uncertainty. In the case of cellobiose, the "purity" was sufficiently far from 100% t o warrant a polarimetric run a t a higher temperature.T h e water used in all experiments was ordinary distilled water, saturated with COz, and of p H approximately 5.5. Since the rate of mutarotation of D-glucose is constant (8) between p H 2 and 7 , buffering of the solution (8, 9) was deemed unnecessary for a determination of the heats of mutarotation. EXPERIMENTALT h e Tian-Calvet nlicrocalorimeter has been described in various p~iblications (10,11,12), but an outline of its more relevant characteristics will be given here. Although arranged differentially, it consists essentially of a cell in which the reaction takes place 'il/lanuscript received Nonenzber 12, 1957.

Anomeric discrimination and rapid analysis of underivatized lactose, maltose, and sucrose in vegetable matrices by U‐HPLC–ESI‐MS/MS using porous graphitic carbon

“…5C). Our measured equilibrium compositions at 20 °C for lactose and maltose were, respectively, ca 61 and 62% of the β anomer, in good agreement with literature values of 57.3–62.3% for lactose and 61.9–63.9% for maltose 19, 23, 24…”

An amperometric enzyme biosensor for real‐time measurements of cellobiohydrolase activity on insoluble cellulose

“…Pc CDH is essentially inactive against the α‐anomer (Higham et al, 1994) and the CDH‐biosensor therefore specifically detects the β‐anomer of cellobiose (and the β‐form of higher cello‐oligosaccharides). The retaining mechanism of Tr Cel7A implies that its products are solely β‐anomers (Claeyssens et al, 1990), and as mutarotation is slow with a half‐time of about 2 h at the temperature and pH used here (Kabayama and Patterson, 1958), the electrode signal can be used directly as a measure of the initial hydrolytic activity. Conversely, the mutarotation equilibrium of cellobiose has to be taken into account in the calibrations.…”

“…Conversely, the mutarotation equilibrium of cellobiose has to be taken into account in the calibrations. This was done by using equilibrated standard solutions and correcting the nominal concentration of cellobiose by the equilibrium composition (64.4% b-D-cellobiose at pH 5.5 and 24.88C) (Kabayama and Patterson, 1958). Enzyme activity measurements with the CDH-biosensor were benchmarked against high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) as described below.…”

Recent progress in electrochemical oxidation of saccharides at gold and copper electrodes in alkaline solutions

“…However there is also a compounding problem associated with the behaviour of saccharides in solution because of their readiness to undergo complex mutarotations. Studies aimed at elucidating these phenomena have been based on the rational involving acidity of OH groups [9], hydration numbers [10,11], the ratio of equatorial vs axial OH groups [12,13], anomeric effect [14], the hydrophobic or hydrophilic index [15], partial molar heat capacities, isothermal compressibilities and expansibilities [16] as well as various enthalpy measurements [17] that have been reported. A comprehensive and amicably agreed theory has yet to emerge.…”