The intrinsic mixed acidity constant (pK,) of glutamic acid polymers has been determined from potentiometric titrations of poly-DL-glutamic acid in aqueous solutions of various NaCl concentrations and at two temperatures (25 and 48 "), thus making the difficult extrapolations of poly-L-glutamic acid titration curves more certain. These experiments indicate that p& is nearly independent of temperature but varies from 4.58 in 0.01 M NaCl to 4.32 in 0.40 M NaC1. Similar studies of the titration of poly-L-glutamic acid as a function of temperature and NaCl concentration give the standard Gibbs free-energy change per amino acid residue for the transition from un-ionized CY helix to un-ionized random coil (AGOIN) for each of the various conditions; AGOjN depends on temperature, but only slightly, if at all, on salt concentration. From the temperature dependence of the free energy, we find that AH"/N is 975 & 50 cal/(residue mole), and that AS"/N is 2.67 =t 0.1 cal/(residue mole deg). We find that there is no measurable effect of polymer concentration on these thermodynamic parameters and conclude that nonequilibrium aggregation is not present. It is demonstrated that, for poly-L-glutamic acid, three independent measures of helix content agree, namely ultraviolet absorption, titration, and optical rotatory dispersion. The helix content of un-ionized poly-DL-glutamic acid is estimated, from its extinction coefficient at 200 mp, to be 62%. The implications of these experiments for molecular theories of the conformation of polyamino acids in aqueous solutions are examined. It is found that assignment of the contribution of individual molecular forces (e.g., hydrogen bonding, hydrophobic bonding) to the over-all free energy of transition, whether that assignment is semiemprical or a priori, will have to be made with considerably more precision than has thus far been possible, if such theories are to be meaningful. n view of the pervasiveness of the a-helical conforma-

A method of preparation of solid amorphous water is reported, along with a demonstration of the absence of crystalline ice. The samples described are the first to be completely free of contamination with crystalline ice.Despite the attention it has received, the theoretical interpretation of the properties of water is not satisfactory. Many models of water have been proposed; almost all are based on assumptions partly or wholly in contradiction with available experimental data. Indeed, the single universally accepted structural feature is the existence of local tetrahedral coordination of water molecules, suggested by Bernal and Fowler (1) Burton and Oliver in 1935 (2). Since then investigations of some of its properties have been published, but the available literature is remarkably small. Our interest in this material arises from the speculation that its structure is closely related to that of ordinary water. The promise that the random network model of water structure can be developed quantitatively, and the supporting results of the computer experiments of Rahman and Stillinger (3), further enhance our interest.Several earlier studies of "vitreous ice" (2-8) have included accounts of the preparative techniques. Only Ghormley has used temperatures of deposition below 770K. His method and data, when compared with our method and the data obtained in these studies, convince us that previous preparations of "vitreous ice" were not pure amorphous solid water. That "vitreous ice" was impure was suggested long ago by Pryde and Jones (5) on the basis of the large spread in the reported thermal properties. We shall refer to the material prepared by these earlier investigations as precrystalline ice. As of the date of preparation of this report, no attempt has been made to find a glass transition temperature in the material we have prepared, hence the description of amorphous solid water as glassy will be avoided (9). This paper reports the method of preparation of pure amorphous solid water. As will be seen, the x-ray characterization of this substance is essentially a null experiment. Preliminary confirmation of the similarity of liquid water and amorphous solid water has been obtained from infrared and spectroscopic studies, which will be reported elsewhere. METHODS AND MATERIALSA schematic diagram of our apparatus is displayed in Fig. 1

No abstract