No abstract

iln il~terpretatio~~ of A H ancl A S for the nu tarot at ion of D-glucose, D-uylose, maltose, ldctosc, and ccllobiosc is given in terms of changes in the hydmtion of the reducing 11)1clro\yl group I n this part of the paper we shall attempt to give an iilterpretation of the experirneiltal results shown in Table I and Fig. 4 of Part I." We shall first consider the conformations of the sugars used in I'art I and note that in all of them the neighboring groups of the reducing carbon are identical.There is a large body of evidence for strong hydrogen bonding betweell the sugar hydroxyl groups and adjacent water nlolecules in aqueous solution. On the basis of the known coilformatioils of the sugars and of the structure of water it is possible to come to tentative conclusions about the packing of the water molecules about the sugar molecule, and to predict that an equatorial hydroxyl group will be more stroilgly hydrated than an axial group. We also fiild that the reducing hydroxyl of the sugars of Part I is bonded to the adjacent water molecule in the same manner, with only slight variations in bond length.The large value of A S for mutarotatioll of the various sugars call be associated with changes in the frequency of torsional oscillatioil of this reducing hydroxyl group about the C(I,-O axis. On the basis of a simple model of the hydrogen bond between the group and the water molecule, the order of magnitude of this frequency can be calculated and shown to be low enough to give a large contributiotl to the entropy.Using the hydrogen bond model, the order of magnitude of the variation of A S ancl A I I amongst the sugars is calculated, and the slope of A I I vs. A S in Fig. 4 of Part I can be estimated theoretically.Finally A F for the nlutarotatioil of the sugars call be viewed in the light of the free energies of interactioil between adjacent hydroxyl groups in the cyclitols which have beell the subject of thermodynamic study by Angyal and McHugh (1). Because the pyranose ring contains an oxygen atom, whereas the cyclitol ring does not, a difference exists between group interactions in the two cases. CONFORi\lI:lTIONS OF T H E SUGARSReeves (2) has shown that of the two chair and six boat coilformations possible lor the hexopyranoses the chair conformatiotls are ilormally preferred. More recent work in Reeves' laboratory (3, 4) has indicated the possibility of a boat conformation in some of the pyranoses, the tenclency of hydroxyl groups to take up equatorial positioils apparently overcoming the normal stereochemical preference for the chair conformation. 'JIanuscript received Novernber 12, 1957.

No 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.

This study investigated the adsorption capacity and adsorption mechanism of phosphate by calcined aluminum oxide (GB) at temperatures of 200 to 1150• C. The results showed that GB and GB calcined at a temperature of 200• C exhibited almost no adsorption capacity, and GB calcined at temperatures of 300 or 400• C exhibited the highest adsorption capacity. After that, adsorption capacity tended to decrease with increasing calcination temperature. The specific surface area and the concentration of surface hydroxyl groups exhibited the highest values in GB calcined at temperatures of 300 and 400• C. From the above facts, it is conjectured that the specific surface area and concentration of surface hydroxyl groups contribute to the adsorption of phosphate in calcined GB.The results of X-ray diffraction showed that the structure of GB changed drastically at temperatures of 200 to 300• C and 900 to 1000 • C. Also, it was evident that phosphate was adsorbed selectively even in complex solution systems containing chloride, nitrate, sulfate, hydrogen carbonate and phosphate ions, and that calcined GB is suitable for adsorption of phosphate. For the adsorption of phosphate, it was found that the optimum pH is around 4. When calcined GB is suspended in purified water, it is thought that hydroxyl groups form through dissociative adsorption with water molecules, and that these hydroxyl groups conduct ion exchange with phosphate.