4422
J. Phys. Chem. 1982, 86, 4422-4426
likely to undergo further reactions. The large value of the second-order decay constant (1.4 f 0.3) x lo9 M-ls-l r eported above requires that reaction 12 occur on essentially every collision. The fact that RSS. does not undergo reaction 14 implies that in water it forms an S-H bond weaker than RS-H, which has a dissociation energy of -90 kcal mol-’.32 Perthiyl is, however, able to abstract H atoms from dihydroflavin (FH,) and the flavin radical (FH.) in reactions 15 and 16. Since D F H - H is -59 kcal m ~ l - lDS-H , ~ ~of RSS. must be larger, and lie in the range 60-90 kcal mol-’. The total sulfhydryl yields and the observation of perthiyl radical are clearly consistent with the stoichiometry
Acknowledgment. We acknowledge financial support from the University of Calgary and the Natural Sciences and Engineering Research Council of Canada.
(32) J. G. Calvert and J. N. Pitts, Jr., ‘Photochemistry”, Wiley, New York, 1966, p 826. (33) D. A. Armstrong, to be submitted for publication.
(34) Yu M. Torchinskii, “Sulfhydryl and Disulfide Groups of Proteins“, translated by H. B. F. Dixon, Consultants Bureau, New York, 1974.
of reaction 9. However, the yields of tetrasulfide from reaction 12 and of RSH are obscured by the secondary thermal reactions 18-20. These are similar to reactions postulated earlier to explain exchanges in polysulfide^.^-^^ As in those cases RS- rather than RSH may be the active species,34but this point was not pursued here. The net effect of the thermal reactions is to convert the trisulfide to lower and higher polysulfides, and eventually to produce elemental sulfur.
Photoexcited Inclusion Complexes of ,&Naphthol with a-, p-, and y-Cyclodextrins in Aqueous Solutions Takehlko Yorozu,
Mlklo Hoshlno, Masashl Imamura,
The Institute of Physical and Chemical Research, Wako-shi, Saitama 35 1, Japan
and Haruo Shiruka Department of Chemistry, Faculty of Engineering, Gunma University, Kiryu-shi, Gunma 376, Japan (Received: February 25, 1982; In Final Form: July 2, 1982)
Structural differences among inclusion complexes of CY-,@-,and y-cyclodextrins (CDx’s)with @-naphthol(Naph) were studied by means of optical absorption, fluorescence, and circular dichroism (CD) spectrometry. The fluorescence study revealed that @-naphtholis very loosely packed in a y-CDx cavity, whereas it is tightly packed in a @-CDxcavity. The rate of proton dissociation is markedly depressed by inclusion, particularly in the case of CY-CDx inclusion. These facts, along with Corney-Pauling-Koltun (CPK) molecular model and CD studies, suggest that the hydroxyl group of @-naphtholis hidden in the a-CDx cavity, while the naphthyl group is largely exposed to a water phase. It is also found that the rate of fluorescence quenching of the inclusion complexes by iodide ion is dependent on the CDx cavity size. It is shown that not only the naphthyl group but also the hydroxyl group of @-naphtholplays an important role in the electron-transfer quenching.
Introduction Cyclodextrin (CDx) consists of six or more linked glucopyranose rings and forms a doughnut-shaped compound.’ The number of glucose units of CDx is designated a for six,@ for seven, y for eight, and so forth. The interior of the toruses of CDx’s is relatively apolar compared to water and therefore is capable of including aromatic compounds, alkyl halides, gases, etc., as guest molecules in the cavity.2 In a previous study we found the marked effects of @-CDxinclusion on the absorption and fluorescence spectra of benzene derivative^.^ The fluorescence enhancement observed in that system was interpreted in terms of the increase in the rate of the radiative process, the decrease in rotational freedom, and elimination of water molecules (1) Bender, M. L.; Komiyama, M. ”Cyclodextrin Chemistry”; Springer-Verlag: West Berlin, 1978; Chapter 2. (2) Cramer, F.; Saenger, W.; Spatz, H.-Ch. J. Am. Chem. SOC. 1967, 89, 14-20. (3) Hoshino, M.; Imamura, M.; Ikehara, K.; Hama, Y. J . Phys. Chem. 1981,85, 1820-3.
0022-365418212086-4422$0 1.2510
surrounding fluorescent molecules in the cavity. Obviously, these spectroscopic studies of CDx inclusion complexes provide information not only on interaction of CDx’s with guest molecules but also on the changes of chemical properties of guest molecules by inclusion in the ground and photoexcited states. The present study aims to reveal the difference in environmental changes around the guest molecule, @-naphthol, and its chemical property changes in the ground and photoexcited states by the inclusion of CY-, p-, and y-CDx’s, such as molecular structure of the complex, rate of proton dissociation, and fluorescence quenching efficiency by I- ion. Experimental Section @-Naphthol(Naph) was purified by sublimation under reduced pressure. Purified p-cyclodextrin (0-CDx) was obtained by recrystallizing it twice from aqueous solutions. a-and y-CDx’s were kindly provided by Dr. H. Horikoshi of The Institute of Physical and Chemical Research and used as received. Sodium iodide was used as supplied. 0 1982 American Chemical
Society
The Journal of Physical Chemistty, Vol. 86, No. 22, 1982 4423
Complexes of @-Naphthol with Cyclodextrlns
2 1 I I 0.27-
0.31
A
0
5.0
10.0
15.0
Flgure 2. Plots of D Aagainst ( D x- Dxo)/C,obtained with aqueous &CDx solutions of Naph. X = 330 nm; 295 K.
O
3b0
I
320
3LO
I
360
I
nm Flgure 1. Absorption spectra of Naph (1.1 X l.0-4M) in aqueous @-CDxsolutions: (a) without P-CDx; (b) 1.9 X lo3 M &COX; (c) 4.5 X M p-CDx; (d) 8.9 X M @-CDx; (e) 1.8 X IO-* M 0-CDx. WAVELENGTH
Absorption and fluorescence spectra were recorded on a Hitachi 200-20 spectrophotometer and MPF-4 spectrofluorimeter, respectively. Circular dichroism (CD) spectra were recorded on an automatic recording spectropolarimeter, Jasco 5-20. Fluorescence quantum yield measurements of neutral and anionic species of Naph* were done by comparison with the fluorescence spectrum of quinine bisulfate 0.1 M H2S04solution (a = 0.54). Fluorescence lifetimes were measured at 295 f 1 K by using a Hitachi nanosecond time-resolved fluorimeter (a pulse width of 11 ns) and the convolution method was applied when they were shorter than 20 ns. Samples were not degassed because the decrease in fluorescence intensity by aeration was less than 2 70.
WAVELENGTH
/
nm
Flgure 3. Fluorescence spectra of Naph (1.1X M) in aqueous M &COX; (c) 1.9 @-COXsolutions: (a) wfthout @-Cox; (b) 9.3 X X M @-CDx; (d) 4.5 X M @-CDx; (e) 8.9X M P-CDx; (f) 1.8 X lo-* M @-CDx.
Results Spectroscopic Studies. Figure 1shows the absorption spectra of Naph in aqueous solutions at pH 6.2 containing @-CDxa t various concentrations. An isosbestic point is observed a t 310 nm, which reflects an equilibrium: Naph$-CDx Naph + 0-CDx
nm. Fluorescence quantum yield of anionic species at pH 12, where Naph and NaphCDx are completely dissociated to their anionic species, Naph- and Naph-CDx, in the ground state, were found to be identical. Photophysical processes of Naph* and its inclusion complex are summarized as follows:
The dissociation constant, K (=[Naph][@-CDx]/[Naph-pCDx]), is calculated by
(i)
(Dx - DXO)/C, = (Dxm- D x ) / K
(ii) (ii’)
Naph*
(iii)
Naph*-
where C, denotes the concentration of @-CDx. 0x0,Dx,and DAm stand for the optical densities a t a wavelength of X a t @-CDx concentrations of nil, C,, and a, respectively. Figure 2 shows a plot of ( D A- Dxo)/C,against D x a t X = 330 nm a t 295 K; K determined from the slope is (1.9 f 0.2) x 10-3 M. The fluorescence intensity of Naph in aqueous solution at pH 6.2 is enhanced by the addition of P-CDx as shown in Figure 3. The spectra were obtained by irradiation of light a t the isosbestic point (310 nm). On the basis of the acid-base dissociation equilibrium of the excited state of @-naphthol,Naph*, the observed two emission bands are attributed to the neutral (353 nm) and anionic (420 nm) species of Naph*. As the concentration of @-CDxis increased, the fluorescence quantum yield of the neutral species increases while that of the anionic species decreases with an isoemissive point at 392
Naph*
(iii’) (iv) (v) (V’)
Naph*-
- -+ - + Naph-
Naph*.P-CDx Naph*.P-CDx
+ H+
Naph hu Naph* Naph
Naph*-
hu’
(1)
@(3)
Naph*-$-CDx
-
(3)
+ H+
Naphe@-CDx+ hu
9(5)
(4) (5)
Naph@CDx
Naph-Sp-CDx
Naph*-.P-CDx
(2)
@(2)
Naph-
Naph*-@-CDx
(vi) Naph*-+-CDx (vi’)
-
+ hu’
(P(6) (6)
Naph-SP-CDx
where 9(i)stands for the fluorescence quantum yield for process i. Fluorescence evolution from excited neutral
4424
The Journal of Physical Chemistry, Vol. 86, No. 22, 1982
Yorozu et al.
TABLE I: Dissociation Constants ( K )and Various Quantum Yield Ratios for CDx Complexes Calculated from Fluorescence Spectra Naph, CDx
1O2K/M
@(5)1 @ ( 3 ) / @ ( 2 ) @ ( 6 ) / @ ( 5 ) O(2)
Naph. 0.79 I 0.03 0.57 a-CDx 0.16 t 0.03 0.57 Naph. P-CDX Naph. 1.9 t 0.2 0.57 Y-CDX
0.02 0.075 t 1.5 t 0 . 2 0.006 I 0 . 0 2 0.14 t 0.04 1 . 4 0.1 I
+
0.02 0.53
i
f
0.1
1 . 0 T 0.2
TABLE 11: Lifetimes (7)and Quenching Rate Constants (k,) by 1- of the Singlet Excited State of @-Naphtholin the Absence and the Presence of CDx’s
Ii
’
y’
5L - _ - L
Naph.CDx
4.6
free
(gp59’)
Tins
t
0.5
4.4 i 0.7
a-CDx 5.0 i 0.5 1.1 I 0.2 ---A 0 3
0 2
O-CDX Y-CDX
O L
R
Figure 4. Plot of (R, - R)/C, against R according to eq 11 for aqueous P-CDx solutions of Naph.
species in the absence and the presence of @-CDxare expressed by (ii) and (v) and that from anionic species by (iii) and (vi). The rates of recombination between the guest molecules and CDx’s and dissociation of the inclusion complex are at most on the order of 107-108 M-’ s-l and IO6s-l, respectively.2 Regarding the lifetimes of Naph* and Naph*- which are on the order of and low8s, respectively, it is reasonably assumed that no dissociation reaction of the inclusion complex and no association reaction between Naph and CDx occur in the photoexcited state, since C, is on the order of 10-2-10-3 M. The fluorescence quantum yields, F , of the neutral and anionic species are then expressed by F(neutra1) = [@(2)Caca+ @(5)EbCb]/(caCa+ CbCb) (7) F(anionic) = [@(3)taC,+ @(6)~bCb]/(t,C,+ CbCb)
(8)
where C and t are the concentration and the molar absorption coefficient a t the excitation wavelength, respectively, for free Naph (suffix a) and @-CDxinclusion complex (b). The ratio of F(anionic) to F(neutral), denoted as R, is written as (9) R = [@(3)f 7@(6)Cb/C,I/[@(2) + y@(5)Cb/Cal where y = tb/Ca. Substituting K = CaCB/Cb into eq 9, one obtains R = [@(3)+ y@(6)C,/K1/[@(2) + Y @ ( ~ ) C ~ / K ] (10) which is transformed into (Ro - R)/C, = r[R@(5)/@(2)- @(6)/@(2)1/K
(11)
where Ro = @(3)/@(2). The value of 0.57 f 0.02 is estimated for Ro from the fluorescence spectrum of Naph in the absence of @-CDx. Figure 4 shows a plot of (R, - R)/C, against R according to eq 11. Since ta = q,, y = 1. From the slope and the intercept, @(6)/@(5)is calculated to be 0.14 f 0.04. Measurements of the sum of fluorescence quantum yields of neutral and anionic species of Naph* were done by using quinine bisulfate as a reference, and the sum was found to be invariant at various concentrations of 0-CDx, i.e. (P(2) + (P(3) = (P(5) + @(6) (12) Then, eq 1 2 can be transformed into @(2)[1+ Ro] = @(5)[1+ @(6)/@(5)] (13)
6.5 4.6
t i
0.7 0.5
1.6 f 0 . 2 4 . 2 t 0.7
I
3.0
I1
0
I
A‘
50
[I-]
/
I
10.0 10-*M
Figure 5. Stern-Volmer plots for fluorescence quenching of Naph by NaI (a) without CDx and in the presence of (b) y-CDx (2.5X lo-* M), (c) &CDx (1.3 X lo-’ M),(d) a-CDx (1.3 X lo-* M). and denote the fluorescence quantum yield of Naph neutral species in the absence and the presence of NaI, respectively.
a0
Substitution of Ro = 0.57 f 0.02 and @(6)/@(5)= 0.14 f 0.04 into eq 13 gives @(5)/@(2)= 1.4 f 0.1. From this value and the slope in Figure 4 (@(5)/K@(2)), K is evaluated to be (1.6 f 0.3) X M, which is in good agreement with that obtained from absorption spectral data (Figure 2). In Table I, the dissociation constants, K, and various quantum yield ratios, @(3)/@(2),@(6)/@(5),and @(5)/@(2), obtained from the fluorescence spectral data are summarized for a-, @-,and y-CDx inclusion complexes. Fluorescence Quenching Studies. Figure 5 shows the Stern-Volmer plots for the fluorescence quenching of Naph and inclusion complexes by sodium iodide (NaI). Concentrations of CDx’s were adjusted (ca. lo-* M) so that all the Naph molecules would be included in the CDx cavity. Results clearly indicate that quenching efficiency is fairly depressed when Naph is included in a- and @CDx’s. The Stern-Volmer constant for Naph is 20.0 f 0.5, and those in the presence of a-, 6-, and y-CDx’s are 5.8 f 0.8, 10.0 f 0.6, and 19.0 f 0.5 M-l, respectively. Similar Stern-Volmer constants were obtained from the lifetime measurements. The lifetimes and the quenching rate constants in the absence and the presence of CDx’s are shown in Table 11. No effect was observed on the lifetime of Naph* and the quenching rate constant for y-CDx inclusion.
The Journal of Physical Chemistry, Vol. 86, No. 22, 1982 4425
Complexes of &Naphthol with Cyclodextrlns
represents the fluorescence quantum yield of naphtholate anion, Naph*-. Since fluorescence quantum yields of Naph- and Naph-CDx measured at pH 12 were identical, @iE/@kte= 1.0 for the a-, 0-, and y-CDx inclusion complexes. Thus, eq 14 can be transformed into
50
4 -5 I 200
I
1
250
300
WAVELENGTH
I
350
/ nm
Flgure 6. Circular dichroism spectra of Naph-CDx inclusion complexes: p-COX complex (-): y-CDx complex (---). a-CDx complex [Naph] = 1.1 X lO-‘M, [CDx] = 1.3 X lo-* M. (..e);
Circular Dichroism Studies. Useful information on the structural difference among three kinds of inclusion complexes is expected to be obtained from circular dichroism (CD) spectra. Figure 6 shows CD spectra induced in the absorption region of Naph when included in CDx cavities. The inclusion complexes with P- and y-CDx’s show negative CD bands at wavelengths longer than 260 and 280 nm, respectively; these bands are ascribed to L,’ and LJ states of Naph. A large positive CD is observed for the 0-CDx inclusion complex between 210 and 250 nm; the CD once becomes negative around 200 nm and then turns to positive below 190 nm. In the case of the y-CDx inclusion complex, whose CD bands slightly shift to red compared with the P-CDx inclusion complex, the intensity of the negative CD band around 200 nm is approximately equal to that of the positive CD band around 230 nm. The signs of the CD bands of the a-CDx inclusion complex a t wavelengths longer than 210 nm are all opposite to those of the P- and y-CDx inclusion complexes. These results suggest that, although slight differences exist between the CD of the P- and y-CDx inclusion complexes, these structures are thought to be similar. The weak CD observed for the y-CDx complex is probably due to its large dissociation constant. On the other hand, the structure of the a-CDx complex appears to be distinctly different from those of the 0-and y-CDx complexes. Discussion Fluorescence Spectra and Lifetimes of Inclusion Complexes. Table I shows that the dissociation constants ( K ) of the inclusion complexes depend markedly on the cavity size of CDx’s. The smallest K value for the P-CDx inclusion complex implies that the cavity size of P-CDx is effective for the inclusion of one Naph molecule. On the other hand, the cavity size of a-CDx seems smaller and that of y-CDx too spacious. This spatial consideration is consistent qualitatively with the results that the K values for the CY- and r-CDx inclusion complexes are substantially larger than that of the P-CDx inclusion complex. The rate constants for the proton dissociation process of the inclusion complexes, k?:, are evaluated from the lifetimes as follows. @of Naph* and Naph*CDx, Tfree and qnC, (6)/@(3)is expressed as @(6)/@(3)=
(14) where the suffixes, inc and free, denote the inclusion complex and the free molecule, respectively, and aion (ri,ck~@PjX’E)/(rfreek~:e@~ne)
Shizuka et al. have estimated the value of kf:le to be (5.8 f 0.3) X lo7 s-1.4 Substituting k$:e = (5.8 f 0.3) X lo7 s-l and the values of @(6)/@(5),@(5)/@(2),and @(3)/@(2) listed in Table I and T values in Table 11, one obtains rate constants for the proton dissociation of the inclusion complexes as (0.8 f 0.2) X lo7, (1.7 f 0.4) X lo’, and (6.0 f 1.0) X lo7 s-l for a-, 0-and y-CDx’s, respectively. The marked depression of the proton dissociation rate observed for Naph-a-CDx, seemingly unexpected from the viewpoint of its cavity size, suggests that only the hydroxyl group of Naph can be included in its cavity but the naphthyl group is too large to be included and would be exposed to an aqueous layer. The hydrophobic environment inside the cavity depresses the proton dissociation process of the hydroxyl group. A major factor governing the slight increase in lifetime, compared with the lifetime of free Naph, by inclusion with a-CDx, i.e., the depression of the nonradiative deactivation process of the a-CDx inclusion complex, is regarded as being due to the decrease in the proton dissociation rate. @Naphthol must be packed tightly in a @-CDxcavity; this gives rise to the depression of both proton dissociation and deactivation by vibrational relaxation processes in the singlet excited state. The longer lifetime of the Naph.8CDx inclusion complex than that of the Naph-a-CDx is due to both of these effects. Less depression of the proton dissociation rate suggests that the hydroxyl group of Naph in the cavity is located near an aqueous layer and has weaker interaction with 0-CDx. The results in Tables I and I1 suggest that y-CDx scarcely interacts with Naph; this is reasonably conceivable in terms of their molecular sizes. Structures of the Inclusion Complexes and Fluorescence Quenching. The induced CD studies of CDx inclusion complexes show that the signs of the induced CD are determined solely by the relative orientation of the dipole moment of guest molecules in the CDx ~ a v i t y . A ~ dipole moment polarized parallel to the cavity of CDx gives positive CD and that polarized perpendicular gives negative CD. Since the mixing of L,’ and Lbl states of Naph appears to be enhanced by hydroxyl-group substitution at the 0 position, both L,1 and Lbl bands are considered to be polarized largely along the short axis of the molecule.6 On the basis of these results mentioned above, the present induced CD results indicate that the naphthyl group is included axially in the 6- and y-CDx cavities, whereas, in the a-CDx cavity, it must be included so as to take a configuration equatorial to the cavity; this configuration is not realized in a smaller cavity of a-CDx. Hence, only the hydroxyl group of Naph may be included in the a-CDx cavity while the naphthyl group, which is equatorial to the cavity, is exposed largely to an aqueous layer. Schematic configurations of NaphCDx inclusion complexes are illustrated in Figure 7. This conception of molecular structures of inclusion complexes is quite consistent with (4) Tsutsumi, K.; Shizuka, H. 2.Phys. Chem. (Frankfurt am Main) 1980,122, 129-42. (5) (a) Harata, K.; Uedaira, H. Bull. Chem. SOC.Jpn. 1975,48,375-8. (b) Harata, K. Ibid. 1979,52, 1807-12. (6) Lyle, S. M.; Lim, E. C. Chem. Phys. Lett. 1972, 17, 367-9.
J. Phys. Chem. 1902, 86,4426-4429
4426
Naph.d-C3x
Napbp-CDx
Naph 7-CDx
Flgure 7. Schematic configurations of (a) Naph-a-CDx, (b) Naph.0CDx, and (c) Naph-y-CDx inclusion complexes.
the results summarized in Tables I and 11. The results on the fluorescence quenching by iodide ions for the inclusion complexes, in particular for the a-CDx inclusion complex, suggest that the hydroxyl group of Naph plays a key role in the quenching by electron transfer between I- ion and Naph. The observed quenching rate constants, which are approximately diffusion controlled for the CDx inclusion complexes, indicate that the
quenching occurs by collision. The Naph-a-CDx inclusion complex, in which collision of the hydroxyl group of Naph and I- is hindered by inclusion, has the lowest quenching rate constant. The Naph.p-CDx inclusion complex, where the naphthyl group can also be included in the cavity, has a low quenching efficiency, but not so conspicuous as that for the a-CDx inclusion complex. These results suggest that, in the electron-transfer quenching of Naph with I-, collision of the hydroxyl group rather than the naphthyl group of Naph with I- is essential. This conclusion can be supported by the pronounced charge-transfer character of the hydroxyl group to the naphthyl group observed for Naph in the singlet excited state, i.e.7
(7) Godfrey, T. S.; Porter, G.; Suppan, P. Discuss. Faraday SOC.1965, 39, 194-9.
Fluorescence Studies of Pyrene Inclusion Complexes with cy-, p-, and y-Cyclodextrins in Aqueous Solutions. Evidence for Formation of Pyrene Dimer in y-Cyclodextrin Cavity Takehlko Yorozu, Mlklo Hoshlno, and Masashl Imamura The Institute of Physical and Chemical Research, Wako-shi, Saitama 351, Japan (Receive& February 25, 1982, I n Final Form: July 2, 1982)
The absorption and fluorescence spectra and fluorescence lifetimes of pyrene (Py) in aqueous cy-, 0-and y-cyclodextrin (CDx) solutions were studied. Strong excimer fluorescence of Py was observed only for aqueous y-CDx solutions. The excitation spectrum of the excimer fluorescence is markedly broader than that of monomer fluorescence. The measurement of fluorescence lifetimes reveals that the formation of the excimer is completed within the duration of an excitation pulse (0.8 ns). These results indicate that the excimer is not produced by Py* + Py Pyz*. Probably, the Py molecules are included as a dimer in the y-CDx cavity. The spectroscopic differences of P y among a-, p-, and y-CDx solutions indicate that the important factor in Py-CDx binding is the correct size of the cavity for inclusion.
-
Introduction a-, p-, and y-cyclodextrins (CDx’s) consisting of six, seven, and eight glucose residues, respectively, have lipophilic cavities with different inner diameters. They form host-guest inclusion complexes with molecules, ions, etc.’ Evidence for the formation of inclusion complexes has been provided from kinetic data: NMR? and circular dichroism ~ p e c t r a . Although ~ stoichiometry of the complex formation is usually 1:l in aqueous solutions, one host-two guests inclusion complexes may be feasible to form for y-CDx which has the largest cavity among the three CDx’s. This paper reports an example of the one host-two guests complexation between pyrene dimer (Py,) and y-CDx studied by fluorescence and absorption spectroscopy.
Pyrene (Py) is known as a typical aromatic compound exhibiting excimer fluorescnece resulting from collisional interaction between excited and ground-state monomers. Nevertheless, no evidence has been reported for the formation of the excimer or ground-state dimer of Py inside the y-CDx cavity.
Experimental Section Pyrene (Py) was purified by recrystallizing it 3 times from ethanol. P-Cyclodextrin (p-CDx) was purified by recrystallizing it twice from aqueous solution. Highly purified a- and y-CDx’s were provided by Dr. H. Horikoshi of The Institute of Physical and Chemical Research and were used as received. The samples were prepared by the following procedures. Py (0.1 mg) was dissolved in 1 L of distilled water by stirring it for about 1 h ([Py] = 4.9 X (1) Bender, M. L.; Komiyama, M. “Cyclodextrin Chemistry”; Spring M). Cyclodextrin was then added to a 100-mL er-Verlag: West Berlin, 1978; Chapter 2. (2) Cramer, F.; Saenger, W.; Spatz, H.-Ch. J. Am. Chem. SOC.1967, aqueous Py solution. The concentration of CDx’s was 1.0 89, 14-20. X M throughout the experiments. Absorption spectra (3) Demarco, P. V.; Thakker, A. L. J. Chem. SOC.,Chem. C O ~ ~ U R . were recorded on a Hitachi 200-20 spectrophotometer and 1970, 2-4. (4) Harata, K.; Uedaira, H. Bull. Chem. SOC.J p n . 1975, 48, 375-87. fluorescence spectra on an MPF-4 fluorescence spectro-
0 1982 American Chemical Society 0022-3654/82/2086-4426$01.25/0
