Corrections have been examined for infrared measurements of the enthalpy change, AH, and the partial molar volume change, AV, for the rupture of an intramolecular hydrogen bond of some hydroxyketones and ohalophenols in dilute solutions. Expressions of AH and AV were given by allowing for the temperature and pressure dependences of these quantities, and the molar integrated intensities. The temperature and pressure coefficients of the molar integrated intensities were assumed to be given by experimental values of model compounds which are similar to the molecules concerned, but which do not exhibit conformational equilibrium. It has been found that the corrections are not small enough to be negligible, compared with the values obtained by the usual procedures.Solvation is an important factor in determining the conformation of a wide variety of molecules in solution, from simple to complex biological m~lecules.'-~ Molecules with weak to moderate intramolecular hydrogen bonds are particularly interesting. Usually, the functional groups (OH, NH, , C=O etc.) which take part in hydrogen bonding interact with the solvent fairly strongly and, therefore, conformations involving intramolecular hydrogen bonds will be easily influenced by solvation. The effects of solvation on these intramolecular hydrogen bonds are characterized by changes in the enthalpy and in the partial molar volume, A H and AV, respectively, for their rupture. These properties can be conveniently obtained from analysis of the effects of temperature and pressure on the IR spectra. The observed values are usually given by4-6where R is the gas constant, and I , and are the integrated intensities of the bands due to the hydrogen-bond-free (HBfree) and the intramolecularly hydrogen-bonded (HB) conformers, respectively. Usually, observed values of ln(I,/I,) are approximately linear with both 1/T and p, and the slopes of these plots provide reasonable values of AHob, and A%,,, which are useful for examining the effect of s~lvation.'-~ However, it should be remembered that the above relationships are derived on the basis of the following assumptions:(1) the ratio of the molar integrated intensities, af/c(b, is independent of both temperature and pressure; (2) A H is independent of temperature; (3) A V is independent of pressure. These assumptions are not always valid and this may affect the values of A H and A V to some extent. The molar integrated intensities will, more or less, vary with temperature and pressure. This is partly due to changes in the effect of the internal dielectric field,8 which depends on the solvent density. Both A H and AV, which are good measures of the state of solvation, should also be dependent on both temperature and -f Part 3: Ref. 7.
The flocculation method using polymer materials and water solvent was applied to the separation of Nd and Dy. Dy was precipitated preferentially from Dy and Nd mixture solution by poly(allylamine) and adipic acid as flocculation agents. The recovery ratio of Dy was 80%, and the purity of Dy was 76% by optimization of the molar ratio of the amino group of poly(allylamine) to rare-earth metal ions.
The volume–temperature behavior of various molded specimens of polytetrafluoroethylene was measured under various external pressures in the range of 0 to 50°C. The lower of the two closely spaced room‐temperature transition points, designated θ (°C.), which was obtained from the volume–temperature curves under various pressures, increased linearly with the external pressure P (kg./cm.2). The values of dP/dθ for the various molded samples studied ranged from 49.1 to 67.2 kg./cm.2 °C., and were characteristic of the samples. The heats of transition due to the lower transition and to the two transitions combined, ΔH20 and ΔHtotal, respectively, under atmospheric pressure, were calculated from the Clapeyron equation by use of the observed values of dP/dθ and the volume changes at the transitions ΔV20 and ΔVtotal (cc./g.). The calculated transition heats ΔH20 varied from 1.03 to 1.68 cal./g., and ΔHtotal varied from 1.17 to 2.02 cal./g.; hence the ratio (ΔH20/ΔHtotal)calc ranged from 0.84 to 0.88. In addition, the heats of transition of the same samples were measured by means of an adiabatic calorimeter under atmospheric pressure. The transition heats observed for ΔH20 ranged from 0.96 to 1.85 cal./g., and those for ΔHtotal ranged from 1.18 to 2.25 cal./g., and hence (ΔH20/ΔHtotal)obs was between 0.77 and 0.89. The values of heats of room‐temperature transition obtained by these two different methods were in fairly good agreement, which shows that the Clapeyron equation is applicable to the room‐temperature transition of polytetrafluoroethylene, as it is to melting points of other polymers.
FT-IR spectra of collagen films set in a vacuum chamber have been measured as a function of time for evacuation at 35 and 75 °C. From the difference in the spectra before and after evacuation, three distinct peaks were found at 3080, 3240, and 3480 cm−1. The latter two peaks have been assigned to two types of water molecules bound in the collagen films from comparison with frequencies of solid and liquid water. The intensity change of these peaks with the evacuation time, therefore, indicates progress of the desorption of water from the collagen film. The first peak, its frequency being too low to be assigned to water, may be assigned to some functional groups of collagen which bind tightly to the water molecules. This suggestion is supported by the fact that the rate of intensity change during evacuation is approximately the same for the 3080- and 3240-cm−1 peaks. On the other hand, the intensity of the 3480-cm−1 peak changes faster, which means that the water molecules assigned to this peak are more loosely bound in the collagen film than are those assigned to the 3240-cm−1 peak. It has been found that the rate coefficients of water desorption decrease with the evacuation time. This result is probably due to the effect of the diffusion of water through the collagen film.
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