1057
V O L U M E 2 8 , N O . 6, J U N E 1 9 5 6
scale.” I n t h e present study no morphological, x-ray, or optical evidence of tn-inning was noted.
Partial Powder X-Ray Diffraction Pattern hkl”
002 100
101
102 110 103 004 112 200 201 104
20%
203 114 105
d , x., Calcd. 3.672 3.589 3.226 2.567 2.072.5 2.0227 1,8362 1.8049 1.7948 1.7435 1,6348 1,6124 1.4475 1.3744 1.3590
d, A., Obsd. b 3.67 3.58 3.21 2.56 2.069 2.022 1.834 1.803 1.796 1.741 1.633 1.611 1.447 1.374 1.359
I/IiC 60 30 100 20 60 90 20 60
15
40 15 10 30 35 35
X-RAYDIFFRACTIOS DATA Diffraction Symbol. 6/i~zinmP-c-. Oftedal’s structure bel,ongs to space group PBs/mcni. Cell Dimensions. a0 = d ( 4 . 1 4 5 ) = 7.179 A,; c g = 7.345 A , ,
all +0.001 11.;c / a = 1.023. Cell volume 3(109.3) = 327.0 A 3 Transformation ILatrix for Hexamolecular Cell in T e r m r of
Dimolecular Cell. 110/120/001. Formula Weights per Cell. 3 ( 2 ) = 6. Formula Weight. 295.07. Density. 8.965 grams per cc. (calculated from authors’ cell dimensions; weight of unit atomic weight, 1.6602 X IO-*‘ gram).
OPTICALPROPERTIES
(29 additional indexable lines observed) Indices refer t o dimolecular pseudocell. b Philips 114.6-mm.-diameter powder camera, Straumanis mounting: X(CuKcr) = 1.5418A. c Relative ueak intensities above background from densitometer measurements
Uniaxial positive. Refractive Indices 15893 A , ) . no = 1.732 zk 0.002. R P = 1.738 zk 0.003; geometric nidan 11734. Molecular r e h t i o r i 13.2 cc. Color. 0 reddish violet, E brownish violet.
a
one based on t h e smaller cell indicated b y powder d a t a , spare group P6r/mmc. Keissenberg, precession, and powder photographs obtained in t h e present s t u d y , using customary exposure times, indicate t h e smaller, dimolecular cell. However, long-exposure oscillation photographs from a crystal rotated about a n a axis of t h e dimolecular cell (normal t o a n u axis of Oftedal’s hexamolecular cell) show tn-o faint layer lines intercalated between each pair of intense layer lines. T h e intense layer lines correspond t o a strong pseudo identity distance of 4.145 A,, t h e faint layer lines t o a t r u e i[lentity distance of 3(4.145 A , ) = 12.435 A,, t h u s confirming Oftedal’s cell. [According t o K a t z and Rabinowitch ( I ) , “Oftedal stated t h a t t h e true unit cell, as determined by Laue photographs, is orthorhombic. . .” T h e source of this idea is n o t clear. “ I n agreement with this view, British Forkers found b y goniometric measurements t h a t t h e crystals of UFa are probably orthorhombic.” An orthorhombic form of rare e a r t h trifluorides hits been described by Zalkin ( 6 ) . ] CRYSTAL blORPHOLOGY
Only anhedral crystals were obtained. Twinning. K a t z a n d Rabinowitch (1) s t a t e t h a t “all thcz crystals seem t o exist as triplrts, t,winne:d on a sntimirroscopic-
Absorption Spectrum (Band maxima in millimicrons and relative intensities a s viewed in a Zeiss prism iiiicrospectronietric eyepiece) Parallel t o 0 Parallel to E fi55 weak 652 strong 652 very strong 642 weak 030 medium weak 830 strong 018 weak 619 medium weak 612 medium weak, wide 590-609 medium s t r o n e 392 medium strong, wide 372 medium weak .5?2 medium strong 558 medium strong .lo8 medium weak 539 weak 528 medium weak, wide 528 medium weak 510 medium strong 510 medium strong, wide 493 strong, wide 493 medium strong, wide I
LITERATURE CITED
Katz, J. J., Rabinowitch, E., “Chemistry of Uranium. Part I. The Element, Its Binary and Related Compounds” ( S X E S VIII-5). n. 353. 3IrGran~-Hill.S e w York. 1951. Oftedal, I.,.Z.p h y s . Chem. B5, 272-91 (1929). I b i d . , B13, 190-200 (1931). Wyckoff, R . IT.G., “Crystal Structures,” vol. I, chap. V, p. 21 table pp. 17c, 23a, Interscience, New York, 1951. Zachariasen, W. H., Acta Crust. 2, 388-90 (1949). Zalkin, A., Tenrpleton, D. IT., J . Am. Chem. SOC.75, 2453-8 (1953). WORKdone under the auspices of t h e Atomic Energy Commission. Contribntions of crystallographic d a t a for this section should he sent to TTn1ti.i C . X r r r o n e , 3140 Suiitli Ilichignn Ave., Chicago 10, Ill.
MEETING REPORTS
Research Methods and Instrumentation
A
SYMPOSIUM on Recent Developments in Research Methods
and Instrumentation was held a t t h e Xational I n s t i t u t e s of Health, Bethesda, N d . , M a y 1 4 t o 16, in conjunction with t h e Sixth Annual Research E q u i p m e n t Exhibit. T h e following papers were presented.
Use of the optical diffractometer [A. W. Hanson, H . Lipson. C. A. Taylor, Proc. Roy. SOC.AZ18, 371 (1953)] permits direct a n d detailed comparisons of the diffraction patterns of given models wit 11 the observed x-ray diffraction patterns. This study of optical transforms will be employed at several different levels of resolution. It can be employed to establish the molecular shape and orientation. t o recognize the presence and establish t h e orientation of regions of regular polypeptide chain configuration in the molecule, and t o study the detailed molecular stereochemistry. The correlation of these and other studies was described.
Protein Structure by Physical Methods Approach to the X-Ray Crystal Structure Study of Proteins. BARBARA W. Low, Harvard University, Cambridge, Mass.
Amino Acid Composition of Tropomyosins from Various Animal National Institutes of Health. Sources. K. LAKIAND D. R . KOMISZ, Bethesda, Md.
The complete structural formulas of the insulins of beef, sheep, and pig have been established by Sanger and his associates. The x-ray crystal structure study of this protein is based on the correlation of several interrelated procedures. These include a n extensive organic chemical study of a series of “heavy-atom” reagents in which the heavy atoms are attached at known specific sites in the molecule. Scale model studies of the insulin molecule have been carried out.
The amino acid composition of tropomyosins isolated from variouanimals was determined by using the Moore and Stein ion exchange chromatographic technique supplemented with other metho(l-. Tropomyosins from human uterus, calf heart, rabbit skeletal and uterus muscles, carp muscle, lobster, earthworm, and flatworni exhibited the characteristic uneven amino acid distribution first found in rabbit tropomyosin. Nevertheless, there is a noticeable
1058 tendency for greater randomness in amino acid distribution with the animals a t the lower phylogenetic level. This gradual change is even more pronounced in the over-all electrical charge of the tropomyosin niolecules. Instrumentation for Single Crystal X-Ray Diffraction Research on Proteins. DAVID H A R K K RPolytechnic , Institute of Brooklyn. Brooklyn, N. Y. I n order to describe the structure of a crystal, a minimum of three parameters must he determined for each atom in the asymmetric. unit. ,In a protein crystal t h e asymmetric unit is usually t h e molecule itself and contains some thousands of atoms: its description, therefore, requires about 10,000 parameters and a t least this number of d a t a must be measured. T h e data are t h e intensities of the x-ray beams diffracted by the crystal. Devices were described which allow the measurement of diffracted x-ray intensities of t h e rate of 50 a n hour by means of G.M. or proportional counters. The intensities of the 13,000 x-ray beams diffracted by a protein crystal can he measured in a couple of months with this set of instruments. A method for putting the intensities on an absoute basis was also described. Some preliminary results on protein structure was presented.
Advances in Methods of Emission SpectroscopyOptical, X-Ray, and Gamma-Ray Spectra The Flame a s a Source in Direct-Reading Spectroscopy. R.I..tRvrx MARGOSHES AXD BERTL. T'.ALLEE, Biophysics Research Laboratory. Department of Medicine, Harvard Medical School and Peter Bent Brigham Hospital, Boston, Mass. T h e choice of a source, monochromator, and receiver for spectrographic analysis depends upon the properties of each of these components and the nature of t h e sample. T h e conventional flame source is ideal for many types of analyses, particularly for the alkali metal.. and alkaline earths. The choice of other components is based on the nature of the light emitted in t h e source and the requirements of prrcision, sensitivity, and speed. T h e properties of the flame a s a spec'tmgraphic source and the nature of t h e excitation process in the flaine have been studied. T h e development of a high temperature flanie makes possible the precise determination of elements not excited by t h e cooler flames previously used. A direct-reading spectrometer, developed for use with a flame source, gives rapid, precise determinations of microgram amounts of several elements simultaneoudy. X-Ray Emission Spectroscopy. HERBERTh r m M . t x - , Naval Research Laboratory, Washington, D . C. The application of x-ray spectroscopy to elemental analysis has had spectacular success in recent years. Since t h e basic principles o f x-ray analysis have been well known for many decades, the new popularity can be attributed directly to the development of electronic^ means of intensity measurement. Geiger counters, proportional counters, and scintillation counters detect characteristic x-rays over t,he entire spectrum with high efficiencies. These detectors have been incorporated in various forms of spectrographs using crystal analyzer.-, and in simple x-ray photometers. Routine analysis may now he niade for all elements of higher atomic numbers t h a n magnesium. The applications cover t h e entire range of concentrations from major constituents to traces of the order of 1 p.p.ni. X-ray analysis is nondestructive and requires no direct contact with t h e sample. I t liandles many routine laboratory analyses with great speed compared to wet chemical methods and is readily applicable t o production problems such as the control of continuous flow processes. Gamma-Ray Spectroscopy. H. WiLLi.ihf KOCH,National Bureau of Standards, Washington, D. C. Gamma-rays emitted from radioactive nuclei can be used to identify and analyze t h e atoms of a sample under study. By detecting and sorting t h e energies of these gamma rays, t h e technique of gamma-ray spectroscopy using scintillation spectrometers enables fast quantitative determinations and exact identification of very small quantities of radioactive elements. Those specific isotopes t h a t have favorable radioactive decay characteristics can be detected in quantities of t h e order of one part of trace isotope to 1 trillion parts of host material. The basic tools needed to perform gamma-ray spectroscopy were discussed with particular emphasis on the characteristics of the essential component, t h e scintillation crystal.
ANALYTICAL CHEMISTRY Vapor-Phase Chromatography Gas-Liquid Partition Chromatography. C A R LH . DE.
