V O L U M E 2 3 , NO. 7, J U L Y 1 9 5 1
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Amino Acid Composition of Proteins and Foods. Analytical Methods and Results. Richard J . Block and D k m a Boiling,
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601 pages. 2nd ed., revised and enlarged. xx Thomas, Springfield, Ill., 1951. Price, 810.50.
Charles C
T h e authors state in the preface t h a t their object is to present
t o the average reader the widely scattered literature on the methods and results of protein analysis in t h e most easily usable form. T h e y have succeeded in including most of t h e important contribution* up to about 1948. A list of 86 papers, appended to the bibliography of 1160 titles as too late t o be included in t h e text, contains 74 1949 publications. This lag is unfortunate in a field which has been rapidly developing. T h e novice could not depend solely upon the many detailed directions of methods outlined without further reading. From this point of view perhaps so much detail on many outmoded methods is superfluous. In general, the treatment of methods is uneven. Afore space is given to H detailed description of the Craig countercurrent apparatus than to microbiological methods. T h e basal media shown for the latter were those proposed in 1946. Paper chiomatographic methods ale described in qome dptail.
T h e 230 tables of amino acid analyses will probably be of greatest usefulness, although here also the reader will have t o use critical judgment in many cases to distinguish the more likely values. T h e final chapter contains ten tables showing t h e amounts of amino acids supplied by the components of t h e diets of several different income groups in the United States. This book will be a necessary addition to the libraries of those interested in food and protein composition. Paper and printing are ercellent, HAROLD S. OLCOTT
Proceedings of First International Polarographic Congress T h e first two volumes of the Proceedings of the First International Polarographic Congress, held in Prague in February 1951, are now ready for distribution. Volume I contains (in English, German, French, or Italian) 44 communications in some 550 pages, sent as contributions to be published in honor of Heyr0vskj.k 60th birthday. I t also contains 200 pages of abbreviated papers in Russian, German, English, or French. Volume I1 presents in 250 pages a full bibliography of polarographic literature from 1922 to 19.50, revised by Heyrovskj. and collaborators. Both volumes may be obtained through OrhiP-E\port-Inij,ol.t, Kfirodni 37, Prague I, Czechoslovakin.
Molecular Structure and Spectroscopy ~ S Y N P O S on I ~ Molecular X Structure and Spect,roscopy was
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held at Ohio State Universit! , Columbus, Ohio, June 11 to 15, 1951, under the joint sponsorship of Ohio State University a n d the -4merican Physical Society. Abstracts of t h e papers of greatest interest to analytical chemists are presented here. Determination of Low-Temperature Ultraviolet Absorption Spectra with the Cary Spectrophotometer. R. N. J O X EA~X D D. S. KEIR,Division of Chemistry. Kational Research Council, Ottawa, Ont., Canada
-1low-temperature quartz cell has been developed which fits convenientll- into the upper cell compartment of the Cary spectrophotometer. The cell has a path length of 4 cm.; a vacuum jacket provides thermal insulation and temperature can be regulated within a range of *tia ( ' . by a controlled gravity flow of liquid nitrogen. The cell is being applied t o the determination of the ultraviolet absorption spectra of polynuclear aromatic hydrocarbons in solution in binary mixtures of isopentane and methyl cyclohexane at temperatures down t o - 170' C . Emission Spectra of Some Free Polyatomic Radicals. P. .J. DYSE, Division of Physics, National Research Council, Ottawa. Ont.. Canada Two inerhoda of exciting the spectra of free radicals were descrihed. The first is, essentially, a photochemical method. -4vapor is irradiated with short-ware length (Schumann region) radiation. I n this frequency range one quantum is sufficiently energetic to dissociate the molecule into two radicals or atoms. one of which is electronically excited. The spectrum of the radical or atom is then observed as a fluorescence. The second method consists of a high-frequency (electiodeles.9: discharge in which the conditions of power input, pressure, and rate of flow have been adjusted t o give mild excitation duch that the spectra of secondary (diatomic) decomposition products are not predominant. The ethylene flame hands, attributed hy their discoverer to the radical HCO, have been observed in fluorescence in formaldehyde. and a fen- of the stronger members of the system have been excited in a discharge in formaldehyde. These observations support the original assignment which has recently been criticized. .I hand system lying in the blue and near-ultraviolet can be observed in fluorescence in formic acid. This was originally attributed t o the HCO radical, b u t the present work has shown that it is more probably due to the HCOn radical. The hand system can also be excited in the discharge in formic acid with much higher intensity. -4 new haiid .;>-stein excited in the discharge in fast flowing acetJ-lene
was briefly described. The emitter is not known; but it is. fairly certainly, polyatomic. Theory of Spectra of Molecular Complexes. R . S. MULLIKES, Physics Department, University of Chicago, Chicago, 111. Generalization of previous ideas [especially of Weiss and Brackmann; also Pauling, Dewar, and Woodward. See Mulliken, J . Am. Chem. SOC.,72, 600 (1950); J . Chem. Phys., 19, 514 (1951)l gives a simple quantum-mechanical theory of molecular complexes. Let -4 be an electron acceptor (Lewis acid) and B a base (electron donor). Typically, A may be a neutral molecule or a positive atom-ion, B a neutral molecule or negative atom-ion. For example, A may he I? or dg'; B may be benzene or I-. Most often, A and B have even-electron diamagnetic structures. Then d and B , and therefore the complex A . B in its ground state, have totally synimetrical singlet (1-41) n-ave functions. These can be written as $.v = a$o hlC.1 .. (1) [Equation 1 can be improved by additional terms. If B and B (or 9and B+) are identical, or are nearly alike in acid and base properties, these terms are indispensable.] Here $0 is usually a no-bond function $ ( A B ) , and $1 a dative func- B+) with covalent bond between A - and B - (weak in tion $(k loose complexes, strong in molecules such as RaN.BX3). Complementary t o ii. of Equation 1, the complex (in addition to states with A or B alone excited) has a characteristic excited electronic state
+
$ E = a'& - b'$o
+
+-
...
(2)
l n intense absorption band $.v + + E is predicted, even for a loose complex. Essentially, this probably often accounts for the colora observed when molecular complexes are formed. These X + E spectra may be called (in general, intermolecular) charge-transfer spectra. They constitute a generalization of the familiar intense interatomic charge-transfer (S+ V ) spectra of molecules. The S + E oscillator strength, f, is easily computed. For the Bz.1 complex (Bz = henzene), assuming the In axis to lie parallel to the Bs plane with its center on the z-axis (Bz symmetry axis), in Debye units) f = (4.704 X 1 0 - ' ) r p ~ . v *( y in cm.-'. = a ' b e ( z g , - 2 1 ~ ) (aa' - b h ' ) & ( Z B , - 2) with
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where S is an overlap integral of estimated value 0.1. Hildebrand and Benesi's strong A3000 transition may he identified as X + E of Bz.13. Using Fairbrother's dielectric constant measurements on IZ in Bz solution. 0 . 7 0 is then obtained for the permanent dipole moment of Bz.12. This yields 0.17 for b in Equation 1 (b* = 0.028). From b and S, a. a ' , and b'. and then estimating a L- z i 7 as 3.4 d.,PE.V
