May, 1961
DIELECTRIC RELAXATION OF XQCEOLXGLYCINESOLCTIOXS
N&H4+ which is consistent with the results. Any other ion-molecule reaction considered must also be consistent with the experimental results outlined above. In view of the above considerations, it may be suggested tentatively that neutralization (step C) followed by decomposition of the electronically excited molecule and/or direct production of an excited azomethane molecule explains the majority of the results most satisfactorily. Essex12 favors direct molecular splitting on the collision of an electron with azomethane, without attachment of the electron or ionization. (12) H. Essex, J . Phys. Chem., 18, 42 (1954).
881
In this paper no unique explanation has been given for the formation of certain products such as Hz, CH, and CzHs formed in the presence of scavengers. It should be realized that, although the formation of these products cannot be accounted for on the basis of what is known about the photochemistry of this compound, it does not necessarily imply that they are formed by ionmolecule processes. Because little is known about the short wave length photolysis of organic compounds, it cannot be decided a t present whether certain unexplained products or effects have to be accounted for in terms of highly excited molecule or ion processes.
DIELECTRIC RELAXATION OF AQUEOUS GLYCINE SOLUTIOXS -4T 3.9 CENTIMETER WAVE LENGTH’ BY OSCARSANDUS AND BETTYB. LUBITZ Department of Electrical Engineering, T h e Radiation Laboratory, T h e University of Michigan, Ann Arbor, Mich. Received December 93. 1960
The dielectric constants and the dielectric loss factors of water and 0.25 to 1 M aqueous glycine solutions were measured at temperatures of 20 to 50’ a t 3.2 cm. wave length. At this frequency the appreciable dispersions allow more precise characterizations of the dispersion regions than those obtained with the use of lower frequency data alone. The critical wave lengths and the “high frequency” dielectric constants were calculated, assuming Debye behavior, from the data and the static dielectric constants found in the literature. It is shown that Debye behavior is consistent with the lower frequency data reported in the literature. It is also shown that the Oncley equation for the “high frequency” die1e;tric constants of proteins, assumed valid for glycine solutions, is not consistent with the results of this work or the lower lrequency data. The values for the critical wave lengths are in best agreement with that of Bateman and Potapenko obtained a t the highest frequency used heretofore ( A = 25.5 cm.). The high values for the “high frequency” dielectric constants indicate further dispersion regions. The thermodynamic functions of activation were calculated from the critical wave lengths.
Introduction Although several studies of the dielectric relaxation of aqueous glycine solutions have been done,2-6 none has been made in a region of relatively high dispersion; the highest has been a t 25.5 cm. (1180 R/Ic./sec.) by Bateman and Potapenko.* It appears that a study at a frequency closer to the critical frequency, where the differences of the dielectric parameters from the static values are relatively large, should lead to more accurate analyses of the dispersion regions of these solutions. With this in mind the dielectric parameters were rlet>ermineda t 3.2 cm. (9368 Mc./sec.) for water, 0.260, 0.500, 0.750 and 1.000 fll aqueous glycine solutions at, 30, 25, 30, 40 and 50’. Experimental C . P . glycine (Amend Dmg :tnd Chemical Company) \vas recrystallized froni boiling water, washed with 50%
cithanol, and dried in a vacuum desiccator over Drierite. This was repeated three times to ensure constant melting point (with decomposition) for two successive determinations. Distilled water, having a specific conductivity of 3 X 10” mhos/cm. a t 25’ was nsed to prepare a 500 m1:l M
(1) This research was sponsored by the Directorate of Intelliaence 2nd Eleotronio Warfare of Rome Air Development Center under Contract AF 30(602)1808. Presented in part before the Division of I’hyaical Chemistry a t the 138th A.C.S. Meeting, New York, N. Y., September, 1960. (2) H. Fricke and A . Parts, J. Phys. Chem.. 43, 1171 (1938). (3) J. B. Baternan and G. Potapenko, P h y s . Rev., 67, 1186 (1940). (4) W. P. Conner and C. P. Smyth. J . Am. Chem. Soc., 64, 1870 (1942). ( 5 ) W. L. G. Gent. Trans. Faraday SOC.,50, 1229 (1854).
stock solution of glycine. Aliquot portions were taken from the stock solution to makeoup the more dilute solutions. All concentrations refer to 25 The experimental setup is essentially that of Buchanang with a few modifications. Figure 1 gives a schematic diagram of the essential equipment. Tuners, not shown, are employed for impedance matching of the hybrid tee and cell. In addition to the hybrid tee and cell the main components consist of a Strand Labs stabilized signal generator Model 300, a Hetvlett-Packard precision waveguide attenuator Model X382A4,a Hewlett-Packard waveguide phase shifter Model X885A, a Hewlett-Packard frequency meter Model X532A, and a Vectron spectrum analyzer Model SA20 used as a receiver. The cell is fabricated from brass, and all the surfaces that come in contact with the sample are gold-plated. Pyres blocks are used to contain the liquid; the thickness is chosen to transform from the impedance of the air-filled waveguide to the impedance of the liquid-filled waveguide. The Pyrex blocks are cemented with Hysol (an epoxy resin manufactured by the Houghtoii Laboratories, Olean, Kew Tork). The temperature of each solution was held constant to 10.01’ with an arcuracy of 10.03’. The maximum errors in e’ and e’’ were & 2 and .t47”, respectively, but on the average the errors were approximately half the maxima. Fresh solution was used for each drtermination. The refractive indev of each of the solutions after a determination \vas rompared to the refractive indru of the initial solutions (results to he published) to determine the extent of evaporation and change of composition dining the dielectric detrrmination. I t was found that the change in composition was within the average error except with the 50” determinations where the errors approached the maximum for
.
E’’.
Corrections for e” for d.c. conductivity a t 3.2 cm. is insignificant due to the specific conductivities for these solutions of lo-‘ mhos/cm. (6) T. J. Buchanan, Pro?. 1 E . C , 99 Part III, G1 (1952).
BETTYB. LVBITZ
TABLE I DIELECTRIC PROPERTIES OF WATERAND AQUEOE GLYCINE SOLUTIO N? t, c, T x 10"
irculattnp Water Bath to Maintain
Constant Temperafur8
Frequency ,Meter
OC.
moles/l.
e'
20
0 0 250 500 .750 1 000
62 61 61 60 59
25
0 0.250 ,500 .750 1.000
64.5 63.8 63.3 62.2 61.8
0 0.250 ,500 ,750 1.000 0 0.250 ,500 ,750 1.000
Fig. l.--Schemat'ic diagram of equipment. ell's equations to the propagation of t mod(,) in a waveguide containing dielectric leads to the eqiiations e' = (A/X,,)2 - *"?/4xZ (A/2aj? (1) :tnd
+
E'' = A 3 ff/TAd (2) where 6 ' is the dicalectric constant and e" is the loss factor of the complex dielectric constant e * = e ' - ie", X is the freespace wave length = 3.2 em., Ad is the TT-ave length in the solution, CY is the att,enuation factor in nepers/cm., and n is the wide dimension of the waveguide so that 2a is the cutoff wave length = 4.572 cm. for the x-band waveguide used. -4measurenient is made in the following manner. The precision attenuator is adjusted t,o a convenient position and the inner waveguide is placed at, a convenient height, preferably close to the hottom but at a sufficient' height t o avoid unaccounted reflections. The phase shifter and noxiprecision attenuator are adjusted until there is no det,ect.able signal. Xow the inner waveguide, moved up to increase the sample length, and the precision attenuator are adjusted successively until again there is no detectable signal. The height moved by t,he inner waveguide bet,\?-ecnzero signals gives Ad, and the difference between the two settings ,of the precision attenuator gives Q! in db./Ad vhich must be converted t,o nepers /cm. before employment in equations 1 and 2. Checks on the values obtained may be mad(, by using different init,ial inner waveguide settings.
Results The results are given in Table I. The static dielect'ric constants of mat'er mere determined from the equation given by lllaryott mid Smith' log
eo,+,' =
log
e,,,t
- 0.00200 (t' - t )
( 31
n-here is the static dielect'ric constant a t t'O C., and that for tu C. The static dielectric constant's of t,he glycine solutions u-ere obtained from the st'at'ic dielectric constants of water using the Maryott and Smith equation and t,he dielectric increments of Wynian and ?tIcMeekin.S The dielectric increment' is defined as en = EO,II.,O
+ SC
(5)
with u st:tntiard deviation of & 0.01. It was assumed, in order to det,eriniae 7 : ~ i i t l e m from c'. f f ' . and t,hat thr data can be rcpir'( 7 ) A . A . blaryott and E. R . Smith, "Tahlrs of Diplpctrir ('onstants of Pure Liquids," National FIiirnsir of Standards Cirriilitr ;,I i. 1 0 Allgust 1951, I. ( 8 ) .T. \f-yman, J r . . :iu,I T, I,. I I c J l w k i n , .1. A m . Ciiem. S O C . , 66,
,'.
908 (1933).
30
40
(see.)
eo
e''
XC ( e m . )
4 1 8 5 2
0 949 1 21 1 50 1 77 2 00
1 79 2 31 2 83 3 33 3 77
6.4 16.4 21.9 25.4 27.5
28.4 30.7 32.6 34.1 36.0
78.5 84.1 89.8 95.4 101.1
0.837 1.12 1.38 1.65
1.58 2.11 2.60 3.11 5.48
6.9 17.4 23.2 27.2 28.8
65.7 65.3 64.7 64.2 63.4
25.7 28 3 30.5 32.6 31.2
76.8 82 4 88.0 93.6 99.2
0.7:34 1.03
1.38 1.94 2.45 2.88 :3 35
6.2 18.3 24.8 28 1 30. T
G6.2 66.0 65 7 65.8 65.8
20.0 23.8 26.3 28.8 31.2
73.3 78.8 84.3 89.8 95.3
0.577 0.914 1.20 1.42 1 FI
16 20 23 25 28
70 75 80 86 91
8 9 1 0 2
31 33 34 36 37
0 65 G 0 250 65 9 500 66 3 ,750 66 2 1 000 66 8
50
5 2 7 0 4
80 86 91 97 103
!)
2 2 7 5
1.85
1.30 1 58 1 78
1 .09 1.72
5.26 2.67 3.03
0 ( 0 442'1 (0 833) 1 50 4 0 7!10 2 00 8 1 06 3 40 2 1 32 2 79 7 1 48
1.7 '11 . i 28 3 31 2 32.8 (0.7) 22.9 29.2 33.2 34.2
sented by the Debye equation.. in the fornl T
=
(€0
-
i6)
€')/we"
and -
em
-
,1 (C"
(7 )
E')
where T is the relaxation time, w is the radian frequency, and ern is the high frequency dielectric constant. The critical frequency A, is calculated from the relation i8)
A, = 2xcr
where c i,i the velocity of light 111free-space. Flgure 2 gives representative plots of E" zvrsus e' a t 25' corresponding to the Cole nnd Cole equation of Debye behaviorg
( 4)
where eo is the st,at8icdielectric constant of the solution, t O , ~ ?iso the static dielectric constant of water, 6 is the dielectric increment, and C is the concentration in molesjliter. Since the dielectric increments were given from 0 t,o 2 j 0 , it was necessary to extrapolate to find the required values at' 30, 40 and 50". The values of 6 from 10 t o 25" were found to be a linear function of the temperaturr. The least square equation is 6 = 23.50 - 0.03681
T-01. G5
[e'
-
(Ell
+ ern)/21? +
€"l
=
[(EO
-
Ecc)/2I* (9)
The values of E' and 'E were least-squared as functions of conre-itration to the equc1' t 1011' ' E'
= S'C
+
and e'!
=
6°C
(10)
E"?O
+ e""?o
(11)
The values of the constants and their itandard deviations are given in Table IT. The qimntities 6' : ~ n d6" are the tlielc>c.tric:ind abwrption coefficient in(*renientb, reipectively. l'h(. iwiistaiit+ were then leabt-qiiarwl it> functioiis of tcinperatiiw. T h e result>:irv 6 ' = 0 I,iX8/ E'Ifri)
=
11
x5 i.t.t11tl
-0.00X78t2
(It?
=
(it:ciitl
(
(lex
(I:lay, 1961
T.4BLE
LEASTSQUARES CONSTAXTS OF 6'
-3.64 -2.80 -2.28 -0.40 1.08
20 25 30 40 50
-0.003683t'
6"
log
E
E;O
THE E' A N D e"
Stand. dev.
62.8 64.5 65.8 66.1 G5.G
10.02 i .2 + .1 f .1 =k . 2
6"
5.84 7.44 8.52 10.24 11.48
EQUATIONS
f"H2o
Stand. dev.
31.6 28.6 26.0 21.1 li.2
f .2 f .3 f ,1 =k . 2
+
A, = Xmn
+ 6x0 C
(16)
The constants are given in Table 111.
30 40 50
This Work
0
0 Maryott and Smith' 0
30, 20
Maryott and Smith' and Wyman and McMeekinO
/h
-0
1 82 1.62 1.13 1.19 1.11
1.98 1.92 1.95 1.93 1.74
AF'
=
Rl'
111
[A0kT/'2ack]
AS* =
AH* - AF*
1, 'C.
kcal./mole
kcal./mole
20 25 30 40 50 20 25 30 40 50 20 25 30 40
2.3; 2.34 2.31
3.94
50 20 25 30
2.74
0.500
(17)
0 .i 5 0 (19)
u-here AF* is the free energy of activation, AH* is the enthalpy of activation, AS* is the entropy of activation, k is the Boltzmann constant, T is the absolute temperature, h is the Planck constant, and R is the gas constant. AH*, assumed independent of temperature, was determined from the slopes of the least-squared linear equations of log A, T us. 1 ' T . The results of the thermodynamic functions of activation are given in Table
IT'. Discussion The values of e' and e", 7 and A, (except a t 50') for water are in good agreement with the results of Buchanan6 and Hasted and El Sabeh.ll The determination of water served not only as a base for the glycine solutions, but also as a check on the operation of the equipment. The values of 7 and A, for mater a t 50' are not in particularly good agreement with the literature values due to the small difference of EO - e' in equation 6 a t this temperature. The values of ern for water are even in poorer agreement since not only does an error occur because of the et - e' difference, but also the error in E" is enhanced by squaring and the difference between the two terms of equation 7 (10) S. Glasstone, K. Laidler and I3 Eyring, "The Theory of Rate Processes," iMcGraw-Hill Book Co , New York, N Y , 1941 (11) J. B. Hasted and S. H. RI. E l Sabeh, Tians. Fayaday Soc.. 49, 1003 (1953).
c;LYCINI? $OL7:TI(JKS AF*, 4H*.
moles/l.
0.250
and
Iv
F V s C%IOXR O F .kCTIVATIO X 0E' .\U Il',O I' i
O( HP( ))
=to.03
The thermodynamic functions of activat'ion are given by
30 40 50 60 70 00 90 100 110 relaxation of aqueous plj.cine solutions at 2,i" 'r.4.BI.E
1NERMODY A' AMIC
dev., orn.
i .05 i .04 i .O!) f .06
20
r -
Stand.
SAC
XII?O
IO
Fig. %.--I)ielectric
C,
TABLE I11 LEASTSQUARES CONSTANTS OF THE A, EQUATIOX 20 25
885
+ 0.4415t
- 1.43 ,(stand. dcv. = i0.10) (14) = -0.00882t 1.677 (stand. dev. of ~''H~O= k0.1) (15)
oc.
GLYCINESOLVTIOSS
f0.1
The values for A, were least-squared as a function of concentration t'o the equation
t,
1
11
~'HZO
t
oc.
OF AQUEOUS
40
1,000
50 20 25 30 40 50
..
2 . xi 2.63 2 (il 2.G
1, 9 2
1 .46
2.71
2.73 2.74 2.75 2.82 2.88 2.80 2.81 2.84
2.80 2.95
5 3:) 5 3; 5.38
5 3ti
2.2tj
2.52 2.51 2.51 2,54
ea1
0.83
1.23
.. -2.05 -1.98 -1 .n5 - 1 !)8 - 1 98 -:;. 90 -3.9(i - 3 . 9:3 - :3 . 99 -3.9ii -&48 -6.41 - c, . :3:3 -6.:35 - G . :34
- 5 . :3{i - R . a0 -5.31 - 5 30 - 3 . 32
is small. These circumstances are so aggrayated a t 50" that e m is quit'e inaccurat'e. For the foregoing reasons the values of 7, A,, and ern for water a t 50" are not used in calculations. The situation is quite different for the glycine solutions where large differences between the dielectric parameters occur. This should lead to fairly accurate results. When a protein is dissolved in water, the general relationship between e' and e'' with frequency is shown in Fig. 3.12 The low-frequency dispersion region is due pr'marily to the protein, while the high-frequency dispersion region is due primarily to the water since the relaxation time for t'he protein is several orders of magnit'ude larger than that for water. With the assumptions that the "highfrequency" dielectric const,ant'of the 1ow-frequenc)dispersion region, e m in Fig. 3, is due largely to the contribution of the solvent molecules and that the (12) 3 . L. Oncley. in E. J . Cohn and J. T . Edsall, "Proteins. Amino Acids and Peptides," Reinhold l'ubl. Corp., New Y o r k . X. Y..ISJ1S, Chapter 22.
OSCARSAXDUS AND BETTYB. LUBITZ
88-1
Vol. 65
dispersion behavior compared to those of protein solutions. Nevertheless, equation 20, or the same c0 f o r H 0 ------underlying assumptions, has been used to cal€' - ----;e culate e m in order to determine the relasatim times of aqueous glycine solutions, for example. by Oncley,12 Conner and Smyth4 and Gent.a Equation 20 shows that ern for aqueous glycine solutions should be slightly less than the static dielectric constant of water; e , = 75.0 for n 1il.l glycine solution compared t o an ec for water of 78.5 a t 23". The results of this work together with others a t lower frequencies are in disagreement with the dispersion of aqueous glycine solutions characterized by equatioii 20. This is shown in Fig. 4n where e" is plotted against E' for a 1 M glycine solution at 21.5". The static dielectric constant and the point from this work are calculated from the least-squared equations. The intermediate point is taken from Geiit.5 Gent's point is in good agreement ITith the results of Debye behavior determined from the other two points. The three points cannot be fitted to a semicircle whose center is appreciably below the €'-axis, indicating little if any distribution of relaxation times. Figure 4b shows that the results of Bateman and Potapenko3 Io+ are also in essential agreement with Debye behavior determined from the other two points. Since the data of Bateman and Potapenko are fragmentary, it is assumed that the temperature of their work is a t 20" since the value of the static dielectric increment they use is the value a t this temperature. In addition, it is assumed that their values of the dielectric and absorption coefficient increments a t 25.5 cm. are based on the static 2 0 1 (b' values for mater rather than the values of e' and e" of water a t the frequency and temperature of I f measurement. The latter give r c 4 t s that arc o-LJ+ ! : I ! ! I too high, and are not coiisistent with the values of 20 30 40 50 60 70 80 90 100 I10 Fig. 4.-Dielectric relaxation of 1 i U aqueous glycine; a. Wyman and hlchleekin. The critical wave lengths of 8.6 em. a t 21" 21.5'; b, 20'. determined by Fricke and Parts,2 9.4 cm. at 25" volume occupied hy t'he protein has an e m equal b y Conner and Smythj4and 15.8 cm. a t 21.3" hy t o unity, Oncley12 obtains an equation for e , Gent5 are much higher than those reported in this in Fig. 3 as work. The value of 4.9 em. a t 20" determined by Bateman and Potapenko3 is in best agreement. t m = EO.IIzC - (€O,HzO - 1) T7c (20) Extrapolation of the data in thiq work indicates where V is t,he volume in cc. displaced by one mole that a value of 4.9 em. a t 20" is reached a t about of anhydrous protein, usually approximated by the 1.6 J f glycine. Since the rriticxl W:ITT lengths arc 111u~ur tr1ilcapartial molal volume of the prot'ein. Sham, Janscii and L i n e ~ e a v e r 1have ~ shown that equation 20 tions of the concentration for rach tempersd t urc, holds for &lactoglobulin in aqueous glycine solu- :in increment in A, per mole over that of watcr may t>ionu. However, the assumpt'ion that e, is con- hc defined by equation 16 and drsignatrd Axp. ut,ant with frequency until onset of the high-fre- Yahies of 6 i c for different temperatures are listed quency dispersion region has been shown to be in Table 111. It IS noticed that these vahirs of iiicorrect for hemoglobin by S c h r ~ a n . ' ~Grant15 6xr are essentially constant with tenipcratiirc, c'trrpt furt,her discusses the lack of agreement between :it 50". If the 1-aluc a1 50", which IS riot :is :ICt,hr low-frequency region and high-frequency regioii curate as the others, is omittcd, nil :iveragc valut. of a h o of 1.93 cm. is ohtained. This value corext,rapolationsto em. The relaxation tinics of aqueous glycino solu- responds to an increment in 7 per mnle, designated tions are iiot much great>er than that, of water. l)y 6r and defined by an equatioii similar to oq11:~This could cause some significant differences in tion 16, of 1.04 X lo-" sec. The high values for E , obtained in this work (13) T.M.Shaw, E. F. Jansen and H. Lineweaver, J . Ckem. Phjis., indicate further dispersion regions at high fre12, 439 (1944). (14) H.P. Schwan, in C. A. Tobiea and J. H. Lawrence, "Advanrea quencies. These may be due, essentially, to LLfree" i n Biological and Medical Physics," Academia Press, New York, N. Y . , water. 1Y.57,Vol. 5. The positivc value for the entropy of activatioll (1.5) E. k1. Grant, Ph.48. M e d i c i n e and Biology, 2, 17 (1957). €0
a
I
\
B! A
3I‘ay, 1961
S P E C I F I C RTOLECULAR I N T E R . 4 C T I O S S I N
RIGIDh I E D I i
88,j
of water listed in Table IT’ is consistent with the solutions where the entropy increases. This can view that the orienting species is the molecule be explained by the partial disruption of the rotatitself formed by the breaking of hydrogen bonds and ing domains by the additional glycine molecules. not a “po1ymer.’’11,16The negative values of A#* However, the errors involved in calculating the for the glycine solutions indicate the rotation of entropies of activation are such that the increase domains formed by cooperating molecules. The observed may be fictitious. entropy of activation decreases with increasing Acknowledgment.-The authors wish to thank concentration except between the 0.75 and 1 M Mr. Ralph E. Hiatt for his valuable discussions and suggestions. (16) E. H. Grant, J. Chem. Phys., 2 6 , 1575 (1937).
INFRARED ET’IDENCE OF SPECIFIC MOLECULAR INTERACTIONS I N RIGID MEDIA AT LOW TEMPERATURES BY G. ALLEN,A. D. KENNEDY AND H. 0. PRITCHARD Department of Chemistry, University of Manchester, Manchester I S , England Received December BS, 1960
In a n experiment designed to trap and study the absorption spectrum of the methyl radical in the 3000 cm.-l region, a spectral feature was observed having many of the expected properties, but which was eventually found to be due to a specific interaction between ethane and di-t-butyl peroxide. Subsequently, a variety of similar interactions were found between other pairs of stable molecules.
Di-t-butyl peroxide has a number of attractive features as a source of methyl radicals. The thermal decomposition into two acetone molecules and two methyl radicals is clean and takes place at quite low temperatures. Furthermore, in the 3000 cm.-l region the absorption intensities of the undecomposed peroxide and of the product acetone are an order of magnitude less than the absorption intensity of ethane, and of that to be expected for the methyl radical. Under suitable conditions, therefore, it would only be necessary to look for the methyl spectrum superimposed on the ethane absorption which must always be present. CFzClzmas chosen as the matrix because it is inert, it has no absorption in the 3000 cm.-l region, and it forms a clear glass which is rigid a t 77OK., but which becomes less rigid before the melting point (l15°1
