Dec.. 1960
COMMUNICATIONS TO THE EDITOR
Racemization Procedure .-Solutions having initial rotations of 2-6' were heated in a constant temperature bath until the rotation had decreased by one-half. The rotations were measured with a Kern polarimeter, and the re-
1959
producibility was f0.03'. The high pressure apparatus and sample holder already have been described.* (8) K.
R. Brower, J . Am. Cham. Soc., 80, 2105 (1958).
COMMUNICATIONS TO THE EDITOR TRIMERIC BISMUTH(1) : AN X-RAY DIFFRACTION STUDY OF SOLID AND MOLTEN BISMUTH(1) CHLOROALUMINATE
tained' a t this laboratory from measurements of optical absorp6ion.
t
sir:
50 This report summarizes an X-ray diffraction study of molten, polycrystalline, and monocrystalline BiA1C14 which indicates the occurrence of a trimer of bismuth atoms separated by 3.04 A. in the configuration of an equilateral triangle. The compound was prepared as previously described. l X-Ray diffraction patterns of the powder and melt were measured with monochromatized M o K a radiation in the range of (4?r/X) sin 0 less than 16. The powder pattern included diffuse as well as Bragg scattering. The patterns were interpreted, by procedures described elsewhere12m3 to yield the radial pair distribution functions shown in Fig. 1. The principal feature of both functions, a prominent sharp peak a t about 30.0 A. partially resolved from another a t about 3.4 A., requires the existence of a bismuth polymer. Further analysis, to be described in detail elsewhere, led to the probable configuration (Bi3)3+. The figure demonstrates by means of synthetic peaks that the proposed model is consistent with the observed distributions. Single crystals of BiA1C14have been shown4 to be rhombohedral with space group R3c, a = 12.12 A., 0 .I 2 3 4 5 6 CY = 58' 23', 2 = 6. This cell accounts for the powder pattern of BiAlCL, thereby demonstrating f , A. the identity of the two materials. Equivalent bis- Fig. 1.-Radial pair distribution functions for BiAlCL, solid muth atoms a t a separation of 3 A. can be accomand melt, from X-ray diffraction data. modated in this cell only if related by the triad axis; DIVISION thus the symmetry of the crystal also indicates the CHEMISTRY OAKRIDGENATIONAL LABORATORY H. A. LEVY existence of a trimer. OAK RIDGE,TENNESSEE M. A. BREDIG FOR THE U.S.A.E.C. M. D. DANFORD The finding of the trimer (Bi3)3+casts consider- OPERATED BY UNIONCARBIDE CORPORATION P. A. AGRON able doubt on an earlier tentative p r o p o ~ a lbased ,~ RECEIVED OCTOBER12, 1960 on cryoscopic and vapor pressure data, of a species (BQ2+in the system Bi-BiC1,. Recent measure(7) C. R. Boston and G. P. Smith, Jr., personal communication, to ments6 of e.m.f. in molten Bi-BiCL solutions also be published. suggest the species (Bi3)3+ in this system. Additional evidence of polymer formation has been obSORPTION O F GASEOUS HYDROGEN (1) -1. D. Corbett and R. K. hIcMullm, J. A m . Chem. Soc.. 7 8 , 2906 CHLORIDE BY NYLON AND PROTEINS
50r
(1956). (2) H.-4. Levy, P. A. Agron and M. D. Danford, J. Chem. Phys., 30, 1486 (1959); 31, 1458 (1959). (3) H. A. Levy, P. 4. Agron. hl. -4.Bredig and M. D. Danford, Annals of the h'ew Y o r k Academy of Scaences, 79, 762 (1960). (4) H..4. Levy, P. A. Agron and R. D. Ellison, t o be reported. ( 5 ) M. A. Bredig, THIS JOURNAL, 63, 978 (1959). (6) L. E. Topol, S. J. Yosim and R. A. Osteryoung. Xeeting American Chemical Society, New York, N. Yo, 1960,division of Physical Chemistry. Abstracts p. 6-6.
Sir: I n the course of work published in 1956' it was noticed that when Nylon with sorbed hydrogen chloride was exposed to water vapor or liquid water, it lost its tensile strength, felt sticky to the (1) L. 13. Reyerson and L. E. Peterson, THISJOURNAL,60, 1172 (1956).
COMMUNICATIOSS TO THE EDITOR
1960
touch, turned white, and became opaque. This was ascribed to hydrolysis of pept,ide bonds in the Nylon.2 I n contrast, no peptide bonds were hydrolyzed in the protein ,&lactoglobulin when it was subjected to a similar treatment.2 After this work had been completed, certain observations led to a reinvestigation of the phenomenon exhibited by Nylon. Dry polycaprolactam with sorbed hydrogen chloride (about one molecule of HC1 per peptide bond) was exposed to water vapor in an evacuated tube a t room temperature. The Kylon slowly deliquesced; after twenty-three hours it formed a clear, ext,remely viscous solution. When water was added, the usual white, opaque material was formed. This was extracted thoroughly with water. I n the extracts, chloride was determined by a mercurimetric met,hod and free acid by t8itration in a ~ e t o n o . The ~ difference was within experimental error showing that no appreciable quantity of degradation products had been extracted. I n the solid residue, basic groups were determined by a modification of the methyl orange binding method of Myagkov and P a k ~ h v e r . ~The content of basic groups proved not to be appreciably different from that of the untreated polycaprolactam, suggesting a molecular weight of the order of 50,000. These results indicated that no appreciable hydrolysis of peptide bonds in the Kylon had taken place. The breakdown of the structure of the Nylon may be attributed to the extreme solubilit,y of Nylon in concentrated hydrochloric acid. A detailed report of this work will appear in the Compt. rend. trav. Lab. Carlsberg. (2) W. S. Hnojeuyj and L. H. Reyerson, ibid., 64, 1199 (1960). (3) K. Linderstrijm-Lang, Compt. rend. trau. Lab. Carlsberg, 17, No. 4 (1927). (4) V. A. Myagkov and A. B. Pakshver, Zhur. Prikl. Khim., 29, 1703 (1956)
Vol. 64
I n the work reported on the sorption of dry gaseous hydrogen chloride on p-lactoglobulin,2 the simple assumption was made that the HC1 was strongly bonded to all nitrogen amine groups present in the side chains of the prot,ein. Because of the varying character of these amine groups the bondings cannot be of equal strengths. I n titration studies in aqueous and similar media, only N o = 42 out of the 57 amine groups in the side chains and N-terminal groups of this protein bind acid; for insulin (dimer of molecular weight close to 12,000) the number of such basic groups is N o = 12. If these lower values of N O are used, then the ratios of %/No(n = the number of strongly held HC1 molecules) are given in Table I. TABLE I Temp., OC.
-78.9 0 20 27 30 (room temp.) 40 GO
--,3-Laotoglobulin-
--InsulinMg./g.
215 72 51
.. .
40 33.2 ,
..
Blmoles/
n
n/No
35.4 5 . 9 11.8 2 . 0 8.4 1.4
n
n/No
... ...
... ...
...
...
...
...
g.
...
. . . 1,5404 5 7 . 4 1.367 6 . 6 1.1 ... ... ...
.. ,
5 . 5 0 . 9 1,4630 54.6 1.300 . . , 1.1763 4 3 . 9 1.045
..,
For either Protein the lowest value of n/No observed is close to unity as expected if the Strongly bound hydrogen chloride is in chemical combination with the basic groups of the Prot,ein. CARLSBERG LABORATORY COPENHAGEN, VALBY,DENMARK, AND GORDON JOHANSEN SCHOOL OF CHEMISTRY LLOYDH. REYERSON UNIVERSITY OF MINNESOTA 14, MI”. MINNEAPOLIS RECEIVED DECEMBER 1, 1960
ADDITIONS AND CORRECTIONS 1957, Vol. 61 L. A. Girifalco and R. J. Good. A Theory for Estimation of Surface and Interfacial Energies. 1. Derivation and Application to Interfacial Tension. Page 905. Equation 23, first line, should read @ = @mb
x
ammnb.
Page 977. Column 1, line 12, for “2700” read “2820.” 1960, Vol. 64 Hamy p. Leftin and w.Keith Hall. The Nature of the Species Responsible for the Long Wave Length Absorption Band in Acidic Solutions of Olefins. Page 383. I n Col. 1, lines 6-8 of (2), should read: ‘I. . (C&)&=CHC6HsJ (CGH&C=C(CIHS)~,(C~HS)ZC= CH-CH=C(CaH& and, as has . . .” R. J. Good and L. A. Girifalco. A Theory for Estimation of Surface and Interfacial Energies. 111. Estimation of Surface Energies of Solids from Contact Angle Data. Page 561. In Col. 2, Equation 4 should rend
h i g o Addamiano. The Melting Point of Cadmium . . Sulfide. Page 1253-1254. The author comments: (‘In this note, the minimum pressure under which cadmium sulfide was observed to melt was referred to as “critical” pressure. As the adjective “critical” usually denotes physical parameters a t the critical point, I should have used the more correct terminology of triple point pressure. I wish to thank Dr. J. 0. Betterton, Jr., (Oak Ridge National Laboratory, Oak Ridge, Tennessee) for calling my attention to this lapsus linguae. My determination has been substantiated by W. Page 562. I n Col. 2, Equation 12a should read E. Medcalf and R. H. Fahrig, J . Electrochem. Soc., 105,719 (1958), who report for CdS a m.p. of approximately 1500” under a pressure of 200 atm. Also, recent vapor pressure Page 563. I n col. 1, line 9: for reference 13, read 14; data (H. Spandau and F. Klanberg, Z. anorg. u. atlgem. and in the first line of footnote 12, for ref. 14 read 13.-R. J. Chem., 295, 309 (1958)) for CdS, in the interval 950-1175’, lead to an extrapolated value of 2.3 atm. a t 1475O, again GOOD. in agreement with my determination.-ARRIGO ADDAMIANO. 0. K. Rice. The Thermodynamics of Non-uniform Systems, and the Interfacial Tension near a Critical Point. 1959, Vol. 63 P. Balestic and M. Magat. A Note on the Radiation InPage 979. In col. 2, line 12, for ( ~ A ~ / ~ cread ) K c(bAf/ duced Synthesis of Lauth’s Violet. dc)6c.--O. K. RICE.
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