July, 1957
COMMUNICATIONS TO THE EDITOR
1023
COMMUNICATION TO THE EDITOR AN ELECTRON DIFFRACTION STUDY OF NICKEL-COPPER CATALYST Sir:
sult obtained from measurement of the lattice constants of the catalyst.
I n the present study, the wave length of the appolied electron wave was altered from 0.02 to 0.05 A. The electrons of the rather long wave length grazed the surfaces of the catalyst particles. On the other hand, the electrons of the rather short wave length could penetrate the particles.‘ A procedure of the electron diffraction using alternate wave lengths was of use for investigation of the surface and the inner structures of the catalyst particles. A powder of nickel-copper catalyst was employed here as a sample. An aqueous solution containing nickel and copper nitrates (Ni:Cu = 60:40 by atom per cent.) was dried and then calcined. A mixture of the oxides thus prepared was reduced with hydrogen a t 200” for two weeks. Diffraction patterns obtained from the sample were always characteristic of a single face centered cubic lattice. This characteristic was independent of the ch%nge of the wave length from 0.0250 to 0.0441 A. This informs us of the fact that there is found a solid solution consisting of nickel and copper. A diffraction pattern was taken from pure nickel and copper by means of double exposure, under the same conditions regarding wave length and camera length. I n this pattern, the rings characteristic of nickel were distinctly separated from those of copper. This pattern corresponded to a mechanical mixture of nickel and copper, distinguishable from the pattern of the solid solution. We could estimate the lattice constants of the Ni-Cu solid solutions from the diffraction patterns obtained, independent of the wave lengths of the applied electrons. According to the lattice constants here measured, there arg found pure nickel (3.52 A,), pure copper (3.62 A.) and the Ni-Cu solid solution with concentration gradient on as well as in the catalyst particles. I n the electron diffraction patterns obtained from a mechanical mixture of nickel and copper, it was remarked that the diffraction rings characteristic of nickel were perturbed by Lorentz effect. As a matter of fact, the rings from ferromagnetic nickel and those from non-magnetic copper did not appear as eo-centric circles. A diffraction pattern was taken from the present catalyst and from a gold foil by means of double exposure. Here a magnetic effect was observable a t the rings from the catalyst. This implies that the powder of the catalyst contains the particles in a ferromagnetic state, i.e., it, contains the nickel-rich phases of the Ni-Cu system.2 This fact is in line with the re(1) S. Yamaguchi, J. A p p l . Phzls., 25, 811 (1954); s. G. Ellis,
TOKYO. JAPAN
ibid.. $3, 1034 (1952); G.I\lbllenstedt. Nachr. Wiasen. Gbttingen, No. 1 , 83 (1016); S. Yamaguchi and T. T a k e ~ c h i J. , CoZZ. Sci., in prcss. (2) N. F. Mott and H . Joues, “The Theory of the Properties of Metals aud Alloys,” Oxford a t the Clarendon Press, 1936, p. !97; H.Morris and P. W. Selwood, J. A m . Ckem. Soc.. 65, 2345 (1943).
SCIENTIFIC RES.INSTITUTE, LTD.
SHIGETO YAMAGUCHI T. TAKEUCHI RECEIVED MAYG, 1957
31 KAMIFUJI (HONGO)
THE INTERPRETATION OF HYDRODYNAMIC PROPERTIES OF PROTEINS’ Sir: It has been asserted in a recent paper2 that it is “impossible” to relate the effective hydrodynamic volume (V,) of a dissolved protein molecule to its partial specific volume (%), and that the relation between the two3
v, = (fir/moz+ m
o)
(1)
(where 61 is specific solvation and vIo the specific volume of free solvent) is “erroneous.” This communication will show that this assertion is unfounded, being based on misconceptions inherent in the Scheraga-Mandelkern treatment4 of the hydrodynamic properties of proteins. Scheraga and Mandelkern4 criticized equation 1 on two counts: (1) because it identifies the volume of a domain about the molecule with the volume of the hydrodynamic particle; (2) because the volume of this domain is computed as the sum of (M/N)fizand 6 1 ( 1 M / N ) vas ~ ~if solvent entered the domain with no change in volume. The first of these criticisms, however, does not apply to equation l a t all, as Wang5 already has pointed out. Assumption (1) is an integral part of all hydrodynamic treatments which are based on the Stokes-Perrin or Einstein-Simha equations, including the Scheraga-Mandelkerii treatment. The assumption is not circumvented by calling the hydrodynamic particle an “effective” particle and its volume an “effective” volume. A21 physicochemical models are “e$ectiue” in this sensen6 Scheraga and Mandelkern’s second objection is also invalid. Once a domain about the molecule has been defined as a rigid particle, then the mass of this particle may be written as ( d f / N )(1 8,) , where 61, defined by this relation, is the mass of solvent effectively associated with each gram of protein substance. Equation 1 then follows a t once from the definition of %i without any assumption regarding the volume occupied by solvent within the particle.’
+
(1) This work was supported by researoll grant RG-2350 from the National Institutes of Health, Public Health Service, and by a grant from the National Science Foundation. (2) G. I. Loeb and H. A. Scheraga, THISJOURNAL, 60, 1633 (1956). (3) C. Tanford and J. G. Buzsell, ibid., 60, 225 (1956). I n this reference v b wa8 used in place of V. of the present paper. (4) H. A. Scheraga and L. Mandelkern, J. Am. Chem. Soc., 75, 179 (1953). (5) J. H.Wang, J . rim. Chem. Soc.. 76, 4755 (1954). (6) T o avoid this assumption requires use of a theory not based on rigid particle hydrodynamics. such as the general theory of irrevereible proceses of J. G. Kirbwood, J. PoZurner Sci., la, 1 (1954).
1024
COMMUNICATIONS TO THE EDITOR
Vol. 61
Scheraga and c o - ~ o r k e r s ~have . ~ correctly emphasized that two unknown quantities, shape and volume, appear in the hydrodynamic equations. Thus two separate hydrodynamic properties must be measured, and two equations solved simultaneously, if a description of the hydrodynamic particle is to be obtained. This operation may be performed graphically, by the procedure of Oncley,* or algebraically, as is done by Scheraga and M a n d e l k e r ~ ~Either .~ way, however, the combination of viscosity data with diffusion or sedimentation, as in the evaluation of Scheraga and Mandelkern’s 6 function, represents a poor choice of measurements, for the relation between this pair of properties is most insensitive to shape. Numerous superior combinations of data have been suggested
by Oncley.* Most recently Wanga has recommended combination of any of the traditional hydrodynamic measurements with a determination of the coefficient of self-diffusion of water. The statements by Loeb and Scheraga2 that “hydrodynamic properties are not very sensitive to changes in shape” and that (‘this insensitivity is a characteristic feature of hydrodynamic methods” are patently false. These statements apply only to the particular combination of hydrodynamic properties used to obtain the p function.
(7) The use of equation 1 is in any event irrelevant t o the determination of shape. Mathematically i t just involves the replacement of one unknown parameter (Ve) by another (81). This has no effect whatever on the mathematical operations used t o determine shape from experimental data.
(8) J. L. Oncley in E. J. Cohn and J. T. Edsall, “Proteins, Amino Acids and Peptides,” Reinhold Publishing Corp., New York, N. Y., 1943, p. 582. (9) Department of Chemistry, State University ofIowa, Iowa City, Iowa. John Simon Guggenheim Memorial Fellow, 1956-57.
STERLING CHEMISTRY LABORATORY YALEUNIVERSITY CHARLES TAN FORD^ NEWHAVEN,CONN. RECEIVED FEBRUARY 11,1957
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