922
W. C. GOTTSCHALL, JR.,AND B. M. TOLBERT
The Solid-state Radiation Chemistry of Selected Transition Metal Chelates of Glycine and Alanine' by W. Carl Gottschall, Jr.,2 and Bert M. Tolbert University of Colorado, Department of Chemistry, Boulder, Colorado 80302
(Received August 23,1967)
The radiation chemistry of selected transition metal chelates of glycine and alanine has been investigated in the solid state. Ammonia was released in greatest yield upon dissolution of the cesium-137 r-irradiated samples and COZwas the chief gaseous product measured from the crystalline samples. Reliability of the COZ determinations after dissolution made this product the best basis of comparison between the chelates and their parent amino acid. G(C02) values were: glycine, 1.02; cadmium diglycinate monohydrate, 0.21; zinc diglycinate monohydrate, 0.28; cobalt triglycinate dihydrate, 0.32; nickel diglycinate dihydrate, 0.34; copper diglycinate monohydrate, 0.45; alanine, 0.89; nickel alaninate dihydrate, 0.21; zinc alaninate monohydrate, 0.53; and copper alaninate monohydrate, 0.99. G(NH8) values were: glycine, 4.3; alanine, 3.3; copper diglycinate monohydrate, 1.O; and cadmium diglycinate monohydrate, 0.8. Qualitative and quantitative similaritiesbetween the chelatesand their parent amino acid indicate similar decomposition mechanisms in agreement with the scheme proposed earlier by Tolbert.
Introduction The protection or enhanced sensitivity afforded an organic moiety by the presence of a transition metal ion is of obvious concern to radiation chemists. From mean lethal-dose data and tabulations of copper content in living organisms, Schubert3 has postulated a direct relationship-with increasing copper content, the organism exhibits greater stability toward radiation effects. On a less controversial scale, other authors have studied the effect of inorganic ions on the radiolysis of ~ r g a n i c ~and - ~ biochemical' compounds in aqueous solution. Anbar and Rona,8 in fact, reported that cupric and thallous ions enhanced decomposition of glycine, as evidenced by ammonia production, with nickel having no effect. Willix and G a r r i ~ o n on , ~ the other hand, report decreasing decomposition with increasing cupric concentration. I n an effort to resolve these apparent conflicts and to discern meaningful relations between radiation decomposition and the presence of various metallic ions, the study of simple amino acid chelates in the solid state was undertaken.
Experimental Section ( a ) Materials. The best grade commercial glycine and alanine from the California Corp. for Biochemical Research were recrystallized twice-first from glacial acetic acid and then from ethanol-water. An aliquot of labeled amino acid l-14C from Xuclear Chicago Corp. (calculated to yield amino acid of specific activity such that the chelate formed from it would have a specific activity of approximately 0.1 pcurie/mg) was pipetted into the solution immediately prior to the preparations. Procedures used for each of the specific chelatjes differed but slightly from the literature preparations.1°-16 Crystals obtained were recrystallized and dried in a vacuum desiccator over MgC104. SpeThe Journal of Physical Chemistry
cific activity of each chelate was checked by combustion in a modified Pregl furnace, followed by assay of the 14C02with a Cary vibrating reed electrometer. Sample analyses agreed with calculations as indicated below: Anal. Calcd for copper diglycinate monohydrate : C, 20.92; H, 4.39; N, 12.20; Cu, 27.66. Found: C, 21.38; H, 4.42; N, 12.23; Cu, 27.82. Calcd for cadmium diglycinate monohydrate: C, 17.25; H, 3.62; N, 10.06. Found C, 17.32; H, 3.66; N, 10.24. (b) Apparatus. The irradiations were performed in the University of Colorado cesium-137 y source. The source was calibrated at 2.78 0.02 X 1019eV/g hr by a Fricke dosimeter at 22O, using G(Fe3+) = 15.6. The mass spectra were run on a Consolidated Electrodynamics Corp. mass spectrometer Type 21-103 C.
*
(1) Supported in part by Contract AT(l1-1)-690 from the United States Atomic Energy Commission. (2) Department of Chemistry, University of Denver, Denver, Colo. 80210. (3) J. Schubert, Nature, 200, (4904); 376 (1963). (4) J. baxendale and D. Smithies, J . Chem. Phya., 23, 604 (1955). (6) J. Baxendale and D. Smithies, J . Chem. SOC.,779 (1959). (6) A. Sugimori and G. Tsuchihashi, BuZ1. Chem. SOC.J a p a n , 33, 713 (1960). (7) J. Butler and A. Robins, Radiation Res., 19, 582 (1983). (8) M. Anbar and P. Rona, Proc. Chem. Soc.. 244 (1963). (9) R. L. Willix and W. M. Garrison, J . Phys. Chem., 69, 1579 (1965). (10) W. C. Gottschall, Jr., Ph.D. Thesis, University of Colorado, Boulder, Colo., 1964. (11) E. Abderhalden and E. Schnitzler, Z . Physik. Chem., 163, 94 (1927). (12) I. Fedorov and T. Balakaeva, Russ. J . Inorg. Chem., 5, 737 (1960). (13) A . Stosick, J . Am. Chem. Soc., 67, 365 (1945). (14) J. Dubsky and A. Rabas, Spisy Vydavane Priodovedeckou Fak. Masary. Univ., 123, 3 (1930); Chem. Abstr., 25, 2655 (1931). (15) H. Ley and H. Winkler, Ber., 42, 3894 (1909).
923
RADIATION CHEMISTRY OF SELECTED TRANSITION METALCHELATES
T
Sample tubes were broken directly in the gas sampling system. The gas chromatograph used was a Perkin-Elmer vapor fractometer Model 154. A simple device was constructed of Tygon tubing and brass connectors to permit breakage of the irradiated sample tubes directly in the carrier stream. (c) Procedure. The procedures used have been detailed elsewhere16 and essentially consisted of l4COZ assay with a vibrating reed electrometer and ionization chambers. The NH3 was determined by the Conway microdiff usion nethod17 with the Russell colorimetric procedurels results read on a Beckman spectrophotometer at 628 mb. Dry analyses for Hz and other products were determined via gas chromatography and mass spectrometry. Specific gravities were determined by the flotation method of Bernal and C r o w f o ~ t . ’ ~
-
1
X * COPPER GLYCINATE MONOHYDRATE 0 3 CADMIUM GLYCINATE MONOHYDRATE
1
ENERGY INPUT, rv/qm. x 1 6 ~ ~
Results Figures 1-4 show the mole per cents of COzproduced from the irradiated chelates as a function of dose. The curves are linear to good approximations with small deviations at the highest doses on some probably indicating a decrease in the original material present. Difficulties due to contamination by radiation products are unavoidable but minimized by utilizing the line slope at the lowest doses to determine the G values. Table I lists the G(NH3) values for several of the chelates and parent amino acid.
Figure 1.
X = COBALT TRIGLYCINATE DIHYDRATE 0 ElNC GLYCINATE MONOHYDRATE 1.2-
Table I : Initial G( NHa) Values on Dissolving Irradiated Solid Compounds Compound
Q(NHs)
Glycine Alanine Cu(Glyh*HzO Cd( Gly), * HzO
4.3 3.3 1.0 0.8
Other products were not quantitatively determined, but qualitatively resembled those of the parent amino acid. l6 Quantitative similarities were observed whereever checked. All yields and G values in this paper were determined via wet techniques, i.e., analysis after dissolution. This should be stressed, since dry results from gas chromatography or mass spectrometry of the irradiated samples consistently gave much lower quantitative yields.”J Extensive trapping or adsorption of gaseous radiation products has been demonstratedz0 and this study confirms these results, as well as indicating that much of the NH3 yield may result from hydrolysis of truly primary products, perhaps imines.
Discussion The preceding results indicate that the presence of some transition metal ions in a biochemical complex do
Figure 2.
indeed cause increased radiation stability. I n no cme was the protection an order of magnitude and the similarity, both quantitatively and qualitatively, to the decomposition pattern of the parent amino acids indicates a close parallel in their decomposition mechanisms. The mechanistic spheme proposed earlier16 hence seems applicable. (16) W. C. Gottschall and B. M. Tolbert, submitted for publication in J. Phys. Chem. (17) E . Conway, “Microdiffusion Analysis and Volumetric Error,” Crosby Lockwood and Son Ltd., London, 1957. (18) J. Russell, J. Biol. Chem., 156,457 (1945). (19) J. Bernal and D. Crowfoot, Nature, 134, 809 (1934). (20) J. Cunningham and H. Heal, Trans. Fa~aduySoc., 54, 1366 (1958).
Volume 72, Number 3 March 1968
924
W. C . GOTTSCHALL, JR., AND B. M. TOLBERT
Table I1 : Decarboxylation G( COZ)Values for Glycine and Alanine Chelates with Comparative Values for Physical Properties Metal21 ion‘s 1st ion pair, eV
Metal21 ion‘s 2nd ion pair,
Metal21 ion’s oovalent
Compound
Initial Q correoted for edensity
Metal21 ion’s ionic radjus,
eV
A
A
Cd( Gly)z. HzO Zn( Gly), .HzO CO(Gly), * 2H20 Ni(Gly), .2Hz0 CU(Gly)z * HzO Ni( Ala)2.2Hz0 Zn( Ala),. HaO Cu(Ala)z HzO
0.21 0.28 0.32 0.34 0.45 0.21 0.53 0.99
8.96 9.36 7.81 7.61 7.68 7.61 9.36 7.68
16.84 17.89 17.3 18.2 20.34 18.2 17.89 20.34
1.413 1,249 1.157 1.149 1.173 1,149 1.249 1.173
0.97 0.74 0.4 0.69 0.70 0.69 0.74 0.70
,a*,
Density, g/cml
Relative free space22
2.32 1.84 1.82 1.84 1.83
169 175 161 167 174
1.74
207
:
1.2
x
NICKEL GLYCINATE DIHYDRATE
0
NICKEL ALANINATE DIHYDRATE
1121 is a compilation of these parameters. Most are self-explanatory. The “free space”22 values are the crystal volume per ion pair less the calculated cation and anion volumes, this quantity to the exponential based on Cunningham’s diff usion-theory model. This model successfully predicted decomposition values of selected nitrates. Later work on other nitrates and on the rates of Nos- decomposition and NOz- formation failed to confirm this theory.23 Our results have shown no correlation with free space. The one successful correlation found for the glycine chelates in this study, log stability constants vs. G values, is illustrated in Figure 5. If one postulates an imDortant primary radiation effect to be ejection of an oxygen electron, this series logically follows. A recent GLYCINE CHELATES
Figure 3.
0 2.4 -
14
1
I
X
* s
ZINC ALANINATE MONOHYDRATE
2 POINTS
COPPER ALANINATE MONOHYDRATE
t
*.O
i
/
1
/
i I
I 0.1
I
0.2
/// cd
I
0.3
I
0.4
G(C02) VALUE
Figure 5. Figure 4.
Correlation of these results with various physical parameters proved fruitless with one exception. Table The Journal of Physical Chemistry
(21) “Handbook of Chemistry and Physics,” 36th ed, Chemical Rubber Publishing Co., Cleveland, Ohio, 1954-1955. (22) J. Cunningham, J. Phys. Chem., 6 5 , 628 (1961). (23) C. Hochanadel, Rad. Res., 15, 546 (1961).
PROPERTIES 01' ORGANIC-WATER MIXTURES epr study by Sinclair and HannaZ4confirms this concept. They find the initial fragment in irradiated L-alanine at 80" I< has an unpaired electron localized mainly on the carboxy group. All evidence points to similar octahedral coordination for the transition metal ions in the solid-state c h e l a t e ~ , thus ~ ~ - eliminating ~~ any special geometric energy considerations or widely differing entropy effects. The generally observed increase in N :+metal bond strengths, Cu > I% > Zn > Cd, parallels this stability constant order moreover, and hence one would assume variations in electron density on the oxygen atom still to exist but be less pronounced than, say, the variations among the alkali metal salts. I n fact, the observed G(CO2)variation is lower than that observed for these saltsI6 and, hence, this theory seems capable of explaining both series. Application to the alanine chelates indicates a discrepancy, however, with zinc apparently out of line. A possible explanation is a different crystal structure for the zinc complex, since zinc normally exhibits tetrahedral coordination, whereas nickel and copper usually are found in octahedral or
925 square-planar coordination. The crystal structure would obviously be expected to exert great influence on radiation chemistry of crystalline compounds and, of course, y radiation can deposit sufficient energy to disrupt any electron and break any bond. Other ligand series are currently being investigated to further check the validity of the proposed mechanism.
Acknowledgments. W. C. G. wish to acknowledge support from a University of Colorado Fellowship, a Du Pont Teaching Fellowship, and an NIH Predoctoral Fellowship in successive years during which the research was performed. (24) J. W. Sinclair and M. W. Hanna, J . Phys. Chem., 71, 84 (1967).
Wl. Calvin and A. Martell, "Chemistry of the Metal Chelate Compounds," Prentice-Hall, New York, N. Y . ,1952. (26) D. Sen, S. Mizushima, C. Curran, and J. Quagliano, J . Am. Chem. Soc., 77, 211 (1955). (27) A. Saraceno, I. Nakagawa, S. Mizushima, C. Curran, and J. Quagliano, ibid., 80, 5018 (1958). (28) D. Sweeny, C. Curran, and J. Quagliano, ibid., 77, 5508 (1955). (29) K. Tomita and I. Nitta, Bull. Chem. SOC. Japan, 34, 286 (1961). (25)
Properties of Organic-Water Mixtures. VI.
Activity Coefficients of
Sodium Chloride in Saturated Water-Pyridine Mixtures at 5 and 25"l by Richard J. Raridon, Willis H. Baldwin, and Kurt A. Kraus Oak Ridge National Laboratorg, Oak Ridge, Tennessee 57851
(Received August 23, 1367)
The solubility of NaCl in mixtures of pyridine and water was determined a t 5 and 25" by packed-column techniques. Miscibility limits of pyridine and water in saturated NaCl solutions were established as a function of temperature. The pyridine-water system, saturated with NaC1, was found to have a lower consolute temperature of 11" with a broad minimum from 20 to 40 wt % pyridine. From the solubility data, activity coefficient ratios, r*,of NaC1 were computed. The values of r* at S o , where the system is completely miscible, and at 25", wherc a miscibility gap from 6 to 63 wt % pyridine is present, did not differ appreciably. Comparison is made of activity coefficient ratios with salt rejection by hyperfiltration membranes containing poly(4-vinylpyridine).
As part of the study of water desalination by hyperfiltration (separation of salts from mater by filtration through suitable membranes under pressure) thermodynamic and transport data for a variety of organicwater mixtures have been measured. Previous papers298 dealt with the comparison of activity coefficients of several salts, including NaC1, in water-organic mixtures a t saturation. Several of these solvent systems showed miscibility gaps with salts present. When using model
solution systems for predicting properties of membranes, one wonders about the direct applicability of (1) (a) Research sponsored by The Office of Saline Water, U. S. Department of the Interior under a Union Carbide Corp. contract with the U. S. Atomic Energy Commission; (b) previous paper in series: A. E. Marcinkowsky, H. 0. Phillips, and K. A. Kraus, J . Phys. Chem., 69, 3968 (1965). (2) K. A. Kraus, R. J. Raridon, and W. H. Baldwin, J . Am. Chem. SOC.,86, 2571 (1964). (3) C. F. Coleman, J . Phys. Chem., 69, 1377 (1965).
Volume '72, Number 3 March 1968
