COMMUNICATIONS TO THE EDITOR
oi
Y
.. ..-
tt
7.825 t L
Z 7.815
4155
7.410
4
-
I
7.405
4
CHLOROPHYLL A
d
; i
7.400
ff---------7,100
I c z w a Q
2n
7.090
a 7,470
0
I
, , , , , , , , , , , , ,
3
6
CHLOROPHYLL B
9
I2
15
18
21
24
27
30 33
36
7.080
39 4 2
TI M E ( s e c )
Figure 1. Ejection of protons from chlorophyll-quinone systems in methanol. Right ordinate represents results obtained in air. The upward arrows represent light on; downward, light off. Top figure: chlorophyll a, 3.7 X M ; with quinone, 0.03 M . Bottom figure: chlorophyll b, 2.3 X l o + M ; with quinone, 0.03 M .
10-6 M . Proton ejection has also been observed in the present study with the quinone systems of pheophytin, bacteriochlorophyll, and hematoporphyrin. These studies will be reported later. A possible explanation of the observations is presented in the following simplified scheme CHLH h', CHLH*
(1)'
CHLH* --f CHLH'
(2)
The results presented in the present paper are not only important in gaining insight into the mechanism of the light-activated electron transfer of chlorophyll systems but also lend support to the current hypothesisll which relates the dissociation of some form of chlorophyll to the chemiosmotic12theory of photophosphorylation in photosynthesis. (6) R. Livingston, Quart. Rev. (London), 14, 174 (1960). (7) E. Fujimori and M. Tavla, Photochem. Photobwl., 5, 877 (1966). (8) R. Livingston and K. E. Owens, J . Am. Chem. soc., 7 8 , 3301 (1956). (9) G.0.Schenck, Nuturwissenschuften, 40, 205 (1953). (10) C. 0.Ritchie and G. H. Megerle, J. Am. Chem. soc., 89, 1447 (1967). (11) H.T. Witt, G. Doring, B. Rumberg, P. SchmidbMende, U. Siggel, and H. H. Stiehl in "Energy Conversion by the Photosynthetic Apparatus," Publication No. 19,Biology Department, Brookhaven National Laboratory, Upton, N. Y., 1967, p 161. (12) P. Mitchell, Nature, 191, 144 (1961).
PHOTOCHEMISTRY SECTION ENERGETICS BRANCH SPACEPHYSICS LABORATORY L. G. HANSCOM FIELD BEDFORD, MASSACHUSETTS 01730
K E N N E T P. H QUINLAN EIJI FUJIMORI
RECEIVED AUGUST14, 1967
The Intracrystalline Rearrangement of Constitutive Water in Hydrogen Zeolite Y
CHLH'(CHLH*)
+ Q +CHL. + Q . - + H +
(3)
where CHLH* and CHLH' are the excited singlet and triplet states of chlorophyll. The interaction of quinone with either of the excited states of chlorophyll as in eq 3 is well documented.6 Figure 1 also shows that the proton ejection activities are of the same order of magnitude whether air is present or not. This is surprising since both quinone and oxygen are known to compete for the excited states of chlorophyll.6 The role of the chlorophyll-oxygen in these light-activated reactions is uncertain. This aspect of the problem is currently under investigation. The ejected proton in the present system can originate from two possible sources: (A) reaction 3 and (B) the solvent, where CHLH. + is a cation of a weak base and Q . - is an anion of a strong acid. Studies performed in the aprotic solvent, dimethylformamide, show that a proton is ejected as in reaction 3. In this study a calomel electrode, containing a saturated solution of KC1 in dimethylformamide, was used. The theoretical behavior of this type of an electrode system has recently been shown by Ritchie and Megerle.1°
Sir: The loss of constitutive or chemical water from hydrogen zeolite Y occurs at temperatures above 500" at torr.'P2 We have found that this reaction occurs in several minutes, using an inert purge gas at 650 to 750" and approximately 760 torr. The product has poor thermal stability. Hydrogen zeolite Y heated 2-4 hr at 700-800" in an inert static atmosphere, where the chemical water remains in the environs of the hydrogen zeolite, yields a substance of unusually high thermal stability. This material remains crystalline on heating to 1000", whereas sodium and hydrogen zeolite Y both lose their zeolite crystal structure at temperatures below 950". McDaniel and Maher report the synthesis of a zeolite Y of similar high ~ t a b i l i t y . ~They do not define the critical requirements for its formation nor do they account for its composition. (1) H. A. Szymanski, D. N. Stamires, and G. R. Lynch, J. O p t . SOC. Am., 50, 1323 (1960).
(2) J. B. Uytterhoeven, L. G. Christner, and W. K . Hall, J . Phys. Chem., 69, 2117 (1965). (3) C. V. McDaniel and P. K. Maher, preprint of paper presented a t Molecular Sieve Conference, London, April 1967.
Volume 71, Number 12 November 1967
COMMUNICATIONS TO THE EDITOR
4156
Scheme I
V
Si
I I
V
0
Si
I
O
H
I &Si I
4Si-+A1
I
H f
+ 3H20
--.f
3 Si-0-H
H-0-Si
0
H
Si
0
f
+ Al(0H)a
I
I
m
I
Si
m
I
I1 V
V
Si
Si
I
O 3Si-O-Al
I
0
H
I I
&Si
l
f
iAI(OH):, + 3%-0-Al-0-Si II
0
I I
0
Si
m
Si
m
e f
+ HzO
I
In this stable zeolite, approximately 25% of the aluminum is present in cationic form. Clearly this cationic aluminum is derived from tetrahedrally coordinated aluminum that was initially in the anionic zeolite framework. About 80-9070 of this aluminum is exchanged by sodium ion on treatment with 0.10 N sodium hydroxide solution. The resulting sodium form of the aluminum-deficient zeolite is also markedly more thermally stable than the ordinary sodium zeolite Y. The cause of this increased stability is under study. This zeolite contains 175 (Si Al) tetrahedra per unit cell in the anionic framework compared with 192 universally recognized in faujasite. Obviously this stable material is chemically different from the usual fauj asites. We propose the mechanism shown in Scheme I to explain the role of chemical water and the formation of cationic aluminum. Reaction 1 is a hydrolysis involving chemically derived water. Any technique for keeping this water in the system during the heating process will result in a stable product. Reaction 2 is a neutralization involving the newly formed transient Al(0H)I and Brgnsted acid sites that still contain chemical water. The cationic aluminum species in
+
The Journal of Physical Chemistry
Al(OH)2@
I11 structure I11 may react with one or two additional protons t o yield Al(OH)2+and A13+. Studies to be reported later show that cationic aluminum has an average charge of 1.5, indicating the presence of both Al(OH)z+ and A1(OH)2+. Thermogravimetric studies of the stable material suggest that it contains no chemical water in its final form. Therefore, the four hydroxyl groups in structure I1 are probably lost as water, resulting in some type of Si-0-Si bonding. The nature of these sites is not presently known, but the pronounced contraction of the unit-cell dimensions of this material, relative to sodium and hydrogen zeolite Y, is probably related to the formation of the aluminum-deficient sites. Water derived from these sites and from the proposed hydroxylated aluminum cations is available for hydrolysis of additional Brpinsted acid sites. Details of our investigation will be reported later. MOBILRESEARCH AND GEORQE T. KERB DEVELOPMENT CORPORATION CENTRAL RESEARCH DIVISION LABORATORY PRINCETON, NEWJERSEY 08540 RECEIVED JUNE23, 1967
