March, 1959 placed the degree of polymerization above 100. These solutions were initially 0.05 and 0.1 M in Sn(IV), and were prepared by the method involving precipitation of chloride with AgC104. Stable Sn(IV) solutions can be prepared in the presence of HC1 provided a sufficient excess of hydrochloric acid is added; presumably tin is then complexed to the species SnCl8-.' Solutions prepared with 1 M HC1 in excess of the component SnCI4 (0.05 Jd) remained apparently stable for over two years; with 0.5 M excess HCl, precipitation occurred over a period of a year, though during the time necessary for equilibrium ultracentrifugation, the solution was stable (see below); for 0.2 itd and less excess HC1, turbidity developed in less than a week. We have carried out centrifugations of solutions 0.05 M in Sn(IV) and 1.2, 0.7, 0.4, 0.3 and 0.2 M HCI in excess of the component Sn(0H)r. Enough NnCl was added to make the total supporting elect>rolyteconcentration equal to ca. 1 M . The results were computed* as apparent degrees of polymerization N e of sac14 on the assumption that the charge per monomer unit x' is zero, although the actual species in solution are not known. Other plausible choices of species and charge per monomeric unit do not affect the computed values of N e sufficiently to alter the principal conclusions. Volumes of SnC14 were computed from literature values of densities. 9 The results of the centrifugations are summarized in Fig. 1 as plots of N e vs. concentration of HC1 in excess of the component Sn(OH)r. Since the acidic solutions were all ca. 0.05 M in Sn(IV), the concentration of HCl in excess of the component SnCI4 niny be obtained by subtracting 0.2 from the values of M HCI on the abscissa. The apparent degree of polymerization appears to be unity at high HCI and rises abruptly for M HCl less than 0.7. In M HCI < 0.7, turbidity developed and precipitation occurred during the centrifugation, and the values plotted in Fig. l are rough estimates of N e for the material remaining in solution at the termination of centrifugation. There is no evidence for stable low molecular weight polymers intermediate between monomers and large aggregates. For the sake of completeness, the figure includes results on centrifugations in basic solutions presented in detail elsewhere.'O Here also, in the presence of a large excess of base, N e seems to be unity, with a slight increase in polymerization a t the composition Na2SiiO3. In the presence of less base than corresponds to this composition, polymerization (and rapid precipitation) occurs. Figure 1 also includes results of diffusion measurements by Jander and co-workers.'l These are plotted as k / ( D q ) 2 where D is the diffusion coefBcient and q is viscosity. The constant L = (7) See, e.#., L. A. Woodward and L. E. Anderson, J. Chem. Soc., 1284 (1957). (8) J. 8. Johnson, K. A. Kraue and G. Scatchard, T H IJOURNAL, ~ 68, 1034 (1954). (9) A. Heydweiller, 2. anorg. allgem. Chsm., 116, 42 (1921). (IO) J. S. Johnson and K. A. Kraus, J . A m . Chem. Soc., in press. (11) G. Jander. F. Busch and T.Aden, 2.anorg. allgem. Chm., 171, 345 (1929).
NOTES
f 3 0
il
441
4000[
100
I
,
4.0
,
,
,
I
I
0.5
EXCESS MOH-
.
,
,
,
I
0.0
I
I
,
I
I
I
I
I
I
I
I
I
I
1.0 EXCESS M HCI
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.
Fig. 1.-Polymerization of Sn(1V). Excess acid and base are computed for component Sn(OH)4: ultracentrifugation ( ~ 0 . 0 5M Sn(1V) unless specified); -&, diffusion coefficient measurements (0.05 Jf Si)(IV)) resented as function roughly proportional to degree of poyymerization and normalized to match centrifugation results in monomer region. (Jander, Busch and Aden, 2. anorg. allgem. Chem., 177, 345 (1929).)
-+-,
was introduced to match ultracentrifugation and diffusion measurements in the monomer region. Agreement between the two studies is good. Acknowledgment.-The authors are indebted to Miss Neva Harrison for technical assistance. REVERSIBLE SPECTRAL CHANGES I N RETINENE SOLUTIONS FOLLOWING FLASH ILLUMINATION'~2 BY E. W. ABRAHAMSON, R. G. ADAMSA N D V. J. WULFF Chemistry Department, State University College of Forestry at Syracuse University, and The Department of Zboloey, Syracuse University, Syracuse, N . Y . Received September 23,1968
In the course of our investigations of the spectroscopy and photochemistry of the visual pigments we have applied the technique of flash photolysisa to the study of retinene (vitamin A aldehyde) and its p-toluidine complex. Experimental Apparatus.-Two types of apparatus were used in these experiments, hereafter referred to as the flash spectrogra hic apparatus and the flash kinetic apparatus. I n the flas% spectrographic apparatus the flash source was a twoturn helical quartz tube filled with xenon gas (200 mm.) having duraluminum electrodes, and mounted inside a magnesium oxide-coated tubular reflector. The tube o erated at 4000 volts and approximately 400 joules. At center of the flash tube, mounted in the optical path, was a 50 mm. cylindrical cell containing a degassed solution of retinene. Along the optical path were mounted, in turn, a small spectral flash tube (General Electric FT-230) operating a t approximately 30 joules, a condensing lens, the cell containing retinene solution, a baffle system to minimize scattered light, a filter, and finally a cylindrical lens to focus the light beam onto the slit of a Bausch and Lomb
tfi
(1) Presented in part before the Division of Biological Chemistry at the 130th meeting of the American Chemical Society, Atlantic City, N. J.. September, 1966. (2) This reaearoh was supported in part by a Grant-in-Aid from The Research Corporation and by the O 5 c e of Naval Research, Department of the Navy,under contract No. NR 119-266. (3) G. Porter, Proc. Roy. Soc. (London), M O O . 284 (1950).
NOTES
442
Vol. 63
Fig. 1.
1.0
0.8
4
\
60.6 M
d
0.4 0.2
0.0 5
10 15 20 25 30 35 Time, microseconds. Fig. 2.-Decay kinetics of the triplet state of transretinene in tetrahydrofuran; X 4500 A. 0, 4.0 X lo-' M ; 4.0 x M ; k = 7.2 X set.-'.
+,
6.0
5.0
-.
*
4.0
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o, 3.0 X
2.0
'7. 1.0
>,.
0.0 2 10
3000 3500 4000 4500 5000 5500 600 Wave length, A. Fig. 3.-Absorption spectra: , rhodopsin in aqueous digitonin solution; ----- , p-toluidine complex of transretinene in tetrahydrofuran (0.25 M HCI); -I-, neoretinene b in ethanol.
-
Medium Quartz Spectrograph .4 By using a pulse generator (Grass Instrument Mode1 5-4) and appro riate triggering circuits it was possible to trigger first t$e photolytic flash and after a measurable delay, the spectral flash. To correct for scattered light entering the optical path the ground state spectrum was taken by firing the spectral flash before the photolytic flash. The flash kinetic apparatus used in these experiments was the same as used and described by Linschitz and Sarkanena6 It differed from the flash spectrographic apparatus in that it employed a steady, intense zirconium arc point source in place of the spectral flash, and a large aperture Bausch and Lomb Grating Monochromator replaced the spectrograph. Spectral changes a t various wave lengths were detected by a multiplier-phototube whose response was displayed as a single sweep oscillogram on an oscilloscope (Tektronix, Model 535). Materials.-trans-Retinene, kindly donated to us by C. D. Robeson of Distillation Products Industries, waa used without further purification. Methylcyclohexane and tetrahydrofuran were purified by fractional distillation over sodium. p-Toluidine was twice recrystallized from water. Procedure.-A reservoir attached to the hotolysis cell was filled with solution to a predetermined vofume. Excess solvent was added and the system closed by a ground joint and stopcock. The solution was degassed and the excess solvent removed by distillation on a high vacuum system. Absorption spectra of the solutions before and after flashing were measured on a Cary Recording Spectrophotometer, Model 11, using a special adapter to position the photolysis cell, Calculations.-Rate data from oscillograms (Fig. 2 ) were enlarged and the percentage transmission (ordinate) was converted to absorbance. I n Fig. 3, Dois the difference in absorbance between an arbitrary zero time on the decay curve (Fig. 2 ) , taken after the completion of the flash, and the final absorbance at the completion of the decay. D is the corresponding difference in absorbance between any time t after zero time and the final absorbance. Rate Data.-Decay kinetics of the species produced by flash illumination were obtained by calibrating each oscillogram as follows: A cell containing solvent only was flashed with the shutter to the steady scanning arc closed. This furnished a zero transmission base line together with a (4) Loaned to us b y Professor Nathan Ginsberg, Department of Physics, Syracuse University. ( 5 ) H. Linsohitz and K. Sarkanen, J . Am. Chem. Soc., BO, 4826 (1958).
March, 1959
NOTES
443
tem crossing, That this appears to be the mechanism for triplet population in the case of retinene is substantiated by the fact that in the flash illumination of the corresponding alcohol, vitamin A, where no n-n states are possible, no long-lived states are evident. Results and Discussion Retinene readily forms protonated Schiff base A series of flash spectrograms of solutions of complexes with aminesg showing a marked red shift trans-retinene in methylcyclohexane was taken a t in the absorption spectrum due to the introduction various time intervals following flash illumination. of charge resonance into the conjugated system. A spectrogram taken ten microseconds after flash- The visual pigment, rhodopsin, is believed to be ing showed pronounced bleaching of the ground just such a complex between neo-retinene b and the state absorption peak at 3700 A. accompanied by protein, opsin. a marked increase in absorption in the region of The p-toluidine complex of trans-retinene has an 4400 A. At 100 microseconds after flashing t,he absorption spectrum very similar to rhodopsin spectrum was identical to that of the ground state. (Fig. 3). When oxygen free solutions of this comApparently flash illumination of trans;retinene plex in tetrahydrofuran (0.25 M in HC1) were flash produces a new species absorbing a t 4400 A. which illuminated, neither transient nor irreversible specrapidly reverts to the ground state in times of the tral changes could be detected. This was not an order of ten microseconds. In air saturated solu- unexpected result since no n-n transition is postions these effects are barely detectable indicating sible in the protonated complex and hence no longthat oxygen markedly quenches the new species. lived triplet state is likely to be populated. The decay kinetics of this new species were folTo the extent that the protonated p-toluidine lowed on the flash kinetic apparatus and a typical complex is representative of rhodopsin the above oscillogram is shown in Fig. 1. Rate data obtained results are consistent with two of the mechanisms from the oscillograms are shown in Fig. 2. The proposed for the primary photochemical process in linearity of the log Do/Dvs. time plot shows that the the bleaching of rhodopsin : namely, photoisomeridecay is first order up to ground state retinene con- zation” and photoionization. l 2 centrations as high as 4.0 X M. Acknowledgments.-We wish to thank ProReasonable consideration of the structure of reti- fessor Henry Linschitz for the use of his flash nene, the decay kinetics and the excitation energies photolysis apparatus’* and his helpful suggestions involved essentially rule out ionized or free radical and interest in this work. We also acknowledge the fragments as the new species. The fact that it has a assistance of Drs. K. V. Sarkanen, Moshe Levy and rather long lifetime (hip = 9.9 X second) and Sonja Gross in various phases of the investigation. is markedly quenched by oxygen suggest that the S. Ball, F. P. Collins. P. D. Dalvi and R. A. Morton, Biochem. new species is the lowest triplet state of retinene J . ,(9) 46, 304 (1949). showing a triplet-triplet absorption peak a t 4400 A. (10) R. A. Morton and G. A. J. Pitt, ibid.. 59, 128 (1955). (11) R. Hubbard and C. C. St. George, .I. Gen. Phvsiol., 41, 524 This behavior is in essential agreement with the results obtained in the flash illumination of anthra- (1958). (12) C. Reid, ”Excited States in Chemistry and Biology,” Academic cene6 and chlorophyll5 although the first-order rate Press, New York, N. Y., 1957, p. 161. constants for the t8riplet decay in these cases are (13) Developed and constructed with the help of AEC support (Syracuse University Contract No. AT(30-1)-820). considerably smaller. If the new species is indeed a triplet it is not likely that it is populated by direct internal conversion (intersystem crossing) from the n-n excited DIFFUSION EFFECTS I N T H E TRANSPIRATION METHOD OF VAPOR PRESSURE singlet state as is the case with anthracene,b since reasonable estimates of the total yield of actinic MEASUREMENT’ light from the flash and the extent of population of BY ULRICK MERTEN the long-lived state are inconsistent with the relaJay Hopkina Laboratory for Pure and Applied Science, CeneraE tively short maximum (radiative) lifetime (-2 x John Atomic Division of Ueneral Dynamics Corporation, San Diego, California second) of the n-a excited singlet state and Received September 8 4 , 1968 the lower limit of lo-’ second imposed on the raAn important technique for the determination diationless transition between states of different of vapor pressures is the one variously known as the multiplicity in hydrocarbons.7 I n retinene where the conj’ugation includes an transpiration or transportation method. In esoxygen atom there is the possibility that an n-a sence, the measurement consists of passing R stream singlet state lies at somewhat lower energies than of an inert gas over the ssmple of interest a t a the n-n singlet.8 Under these conditions internal known rate which is slow enough to achieve satconversion can occur rapidly (-10-l2 second) from uration of this “carrier” gas with the vapor. The the n-n t o the n-n singlet. The radiative life- vapor from the sample is then condensed a t some time of a n n-n singlet is sufficiently long (10-5 to point downstream and the vapor pressure is callo-’ second) to permit appreciable population of a culated from the amount of the sample material lower lying n-n triplet state through intersys- collected in a known time period. The application of the method to studies of vapor pressures of (6) G. Porter and M. Windsor, Disc. Faradav SOC.,ll, 183 (1954). inorganic compounds a t elevated temperature has (7) One of us (EWA) is indebted to Professor Michael Kasha for an scattered time profile of the flash (Fig. 1, uppermost trace). The shutter then was opened and a single sweep taken without flashing t o obtain the 100% transmission line (lowest trace). The solvent cell then was replaced by an identical cell containing solution and the solution flashed with the shutter to the scanning arc open.
~~
enlightening discussion on radiationless transitions. (8) J. R. Platt, J . Opt. SOC.Amer., 48, 262 (1953).
(1) This work was supported in pert by the Cornmiasion under Contract AT(04-3) 164.
U. 8. Atomio Energy
