J. Phys. Chem. 1984, 88, 2163-2167 fraction of counterions "bound" to the micelle shielding factor to give effective micellar charge activity coefficient product activity coefficient of species i mean stoichiometric activity coefficient osmotic coefficient on a stoichiometric basis apparent molar heat capacity relative apparent molar enthalpy
4"
2163
apparent molar volume
Registry No. Sodium dodecyl sulfate, 151-21-3; octylamine hydrobromide, 14846-47-0,
Supplementary Material Available: The coefficients k,, in eq 20-22 are given in the Appendix (4 pages). Ordering information is available on any current masthead page.
Viscosities and Excess Volumes of Binary Mixtures Formed by the Liquids Acetonitrile, Pentyl Acetate, 1-Chlorobutane, and Carbon Tetrachloride at 25 OC M. G. Prolongo, R. M. Masegosa, I. Herniindez-Fuentes, Departamento de Quimica Fhica, Facultad de Ciencias Quimicas, Universidad Complutense. Madrid-3, Spain
and A. Horta* Departamento de Quimica General y MacromolPculas, Facultad de Ciencias, Universidad a Distancia (U.N.E.D.),Madrid-3, Spain (Received: July 26, 1983; In Final Form: October 12, 1983)
Excess volumes (p) for the binary mixtures formed by acetonitrile or 1-chlorobutanewith pentyl acetate and dynamic viscosities (7)for the binary mixtures formed by acetonitrile with 1-chlorobutane, pentyl acetate, or carbon tetrachloride and for the mixture 1-chlorobutane+ pentyl acetate have been determined at 25 O C . These mixtures have interesting properties as mixed solvents of polymers. Their study should help in understanding the phenomenon of cosolvency in polymer systems. The results of P are discussed in terms of the influence of interactions between components, order and degree of packing in the mixtures, and of free volume differences. The viscosities are well correlated with the volume properties of the mixtures but not with their free energies of mixing. The method of Bloomfield and Dewan is used to predict 7 theoretically from known mixing functions.
Introduction The binary systems in this work have interesting characteristics with respect to the solubility of polymers. A t 25 O C the pure liquids acetonitrile (MeCN), 1-chlorobutane (ClBu), carbon tetrachloride (CC14), and pentyl acetate (PAC) are bad solvents of poly(methy1 methacrylate), while the mixtures of MeCN with any one of the other liquids act as very good solvents for such a polymer (they are powerful cosolvent mixtures).' The mixture ClBu PAC shows the opposite behavior, its solvent power being lower than that of the pure components.2 The solution properties of a polymer in a mixed liquid depend not only on the interactions between the polymer and each one of the liquids but also on the interactions between the liquids themselves. In fact, these interactions between liquids are decisive in determining the solubilization of the polymer and the expansion of the macromolecular coils in solution. In order to adequately interpret the thermodynamic behavior of polymers in mixed solvents, it is therefore necessary to know the properties of the binary liquid mixtures acting as solvents. In the present paper we report measurements of excess volume, p,a t 25 OC for the mixtures MeCN + PAC and ClBu + PAC and of the dynamic viscosity, 11, also at 25 O C for the following mixtures: MeCN + PAC, MeCN + ClBu, ClBu + PAC, and MeCN CC14. The dynamic viscosity is an integral property of the liquid mixture which has been related to the interactions between liquids3+ and also to the structure of the Our
Experimental Section Density. The densities, D, of the system MeCN + PAC have been measured in a digital densimeter (Anton Paar) provided with a measuring cell DMA 601 and an electronic unit DMA 60. The pure components have been used as calibrating substances. The temperature in the measuring cell was regulated to 25.00 f 0.005 "C. The estimated error in the density is f5 X g.~m-~. The densities of the system ClBu + PAC have been determined by pycnometry. The pycnometers, made with precision capillary tube, were calibrated with twice-distilled water. The height reached by the meniscus in the capillary was measured with a cathetometer of precision 0.01 mm. The temperature control was 25.00 f 0.005 OC and the precision in D f 2 X g~cm-~. Viscosity. The kinematic viscosities, Y, of the pure liquids and their mixtures have been determined with two modified Ubbelohde viscometers having a capillary radius of 0.45 mm. Both were calibrated at 25 'C by using benzene (C6H6),toluene (PhMe), cyclohexane (C6I-I12), n-hexane (n-C6Hi4), n-heptane (n-C7H16), chloroform (CHCl,), ClBu, PAC, MeCN, and CC14 as calibrating substances of known 7 and D. The values of 11 and D taken from the literature for these liquids are shown in Table I. The conversion of Y into 11 by use of D is well-known: 9 = v/D. The densities of the systems MeCN + ClBu and MeCN + CC14 have been taken from the l i t e r a t ~ r e . ~ J ~
(1) I. Fernlndez-PiBrola and A. Horta, Makromol. Chem., 182, 1705 (1981). (2) I. Fernlndez-PiBrola and A. Horta, Polym. Bull., 3, 273 (1980). (3) R. J. Fort and W. R. Moore, Trans. Faraday Soc., 62, 11 12 (1966). (4) P. Skubla, Colkcr. Czech. Chem. Commun., 46, 303 (1981). ( 5 ) V. A. Bloomfield and R. K. Dewan, J . Phys. Chem., 75, 31 13 (1971). ( 6 ) J. Nath and S. N. Dubey, J . Phys. Chem., 85, 886 (1981). (7) H. Vogel, and A. Weiss, Ber. Bunsenges.Phys. Chem., 86, 193 (1982).
(8) C. Jambon and G. Delmas, Can. J . Chem., 55, 1360 (1977). (9) I. Fernlndez-PiBrola and A. Horta, J . Chim. Phys. Phys.-Chim. Biol., 77, 27 (1980). (10) J. A. Riddik and W. B. Bunger, "Techniques of Chemistry", Vol. 11, Wiley-Interscience, New York, 1970. (1 1) J. Timmermans, "Physico-Chemical Constants of Pure Organic Compounds", Elsevier, Amsterdam, 1950 and 1965. (12) I. Brown and F. Smith, Aust. J . Chem., 7, 269 (1954).
+
+
0022-3654/84/2088-2163$01.50/0
results will be analyzed in terms of both kinds of contributions.
0 1984 American Chemical Society
2164
The Journal of Physical Chemistry, Vol. 88, No. 10, 1984
Prolong0 et al.
TABLE I: Densities and Viscosities of Various Liquids Used in Calibration (Values at 25 "C) 6'
10'71, P
0.6028b
'This work.
PhMe
C,H,,
n-C6H,,
n-C,Hl,
CHC1,
ClBu
0.8623Ib 0.5516b
0.77389b 0.898b
0.65482' 0.294c
0.67951' 0.386c
1.47988b 0.542c
0.88093' 0.427c
H6
D,g . ~ r n ' ~ 0.87368'
Reference 10.
PAC 0.87208' 0.862b
cc1, 1.58439b 0.909b
Reference 11.
TABLE 11: Coefficients ( A j )of Eq 2 Fitted to the Experimental V" at 25 "C (in cm3mol-') and Standard Deviation of the Fit (u) mixture A0 ClBU + PAC 0.168 MeCN + PAC -0.362
MeCN 0.77667' 0.342b
A1 -0.037 -0.031
A2 -0.021 -0.083
I a
A3 A4 0 0.107 0 0.03 0.051 0.103 0.0006
- 0 ,1
The precision in efflux times was 0.1 s. The control of temperature was 25.0 f 0.05 O C . The precision in the determination of q is f0.3% (equivalent to fO.OO1 X P in absolute values). All liquids and their mixtures were filtered through sintered glass disks inside closed funnels to prevent evaporation. Materials. Liquids have been Carlo Erba R.P.E. freshly distilled before use. Their purity, determined by GL chromatography, was never less than 99.7%. The mixtures were prepared by weight with precision f5 X g, or 5 X g in the case of density determinations.
c
L
;
"Eu
--0.05 w
>
Results Excess Volume. P has been determined from density measurements according to 1
0
where M, is the molar mass of component j and x, its mole fraction in the mixture. D refers to values in the mixtures, and 0,to pure for the MeCN( 1) + PAc(2) and component j . The results of ClBu (1) + PAC (2) systems are given in Figure 1. As we can see, P is negative in MeCN PAC and positive (and very small) in ClBu PAC. The results have been fitted to a Redlich-Kister equation:
.i
+
+
W
n
P = xlxzCA,(x, - x2)' 1x0
+
Aq = 11
0
t"
03
0
In each case the optimum number of coefficients, A,, was ascertained from an examination of the variation of the standard deviation, 6,with n. The values for the coefficients A, and the standard deviation of the fit for each system are given in Table 11. Viscosity. The dynamic viscosities for the systems MeCN (1) + PAC (2), MeCN (1) ClBu (2), MeCN (1) CC14 (2), and ClBu (1) PAC (2) are listed in Table 111. The increment Aq is defined as
+
>
(2)
+
- (xlm + x2112)
(3)
120
XI
Figure 1. Excess volume (p) of the systems (a) MeCN (1) and (b) ClBu (1) PAC (2).
+
q being the value for pure component j . In Figure 2 we show the different behaviors with respect to Av exhibited by the systems studied here. In MeCN ClBu Aq practically vanishes; in MeCN + C C 4 and in ClBu PAC Aq is negative, and in MeCN PAC Aq is positive. For ideal mixtures the simple equation given by ArrheniusI3
+
+
+
that is, as deviation of q in the mixture from simple additivity, TABLE 111: Viscosity (71) of the Binary Liquid Mixtures at 25 "C as a Function of Mole Fraction Composition ( x ) MeCN (1) t ClBu (2) X1
10271, P
0.0706 0.1269 0.2010 0.2831 0.3636 0.4597 0.5008 0.5501 0.5976 0.6929 0.7999 0.8624 0.9229 0.9562 1
0.426 0.418 0.413 0.407 0.401 0.394 0.386 0.383 0.378 0.374 0.366 0.355 0.349 0.344 0.340 0.340
0
MeCN (1)
+ PAC (2)
MeCN (1)
+ CCl,
ClBu (1) + PAC(2)
(2)
Xl
10271, P
XI
10271, P
0.1280 0.2389 0.4153 0.5471 0.6539 0.7377 0.8087 0.8683 0.9183 0.9618 1
0.861 0.808 0.762 0.684 0.616 0.556 0.506 0.46 1 0.423 0.392 0.364 0.340
0 0.0979 0.1861 0.3442 0.4830 0.5 149 0.6508 0.7749 0.8742 0.9447 1
0.909 0.822 0.762 0.665 0.583 0.565 0.490 0.429 0.386 0.360 0.340
0
+ PAC(2)
XI
,
0 0.1364 0.2626 0.3783 0.4869 0.5870 0.6804 0.7689 0.8504 0.9266 1
lO*ri, P 0.861 0.796 0.737 0.683 0.636 0.592 0.553 0.517 0.484 0.455 0.426
The Journal of Physical Chemistry, Vol. 88, No. 10, 1984 2165
Viscosities and Excess Volumes of Binary Mixtures
c
VI
TABLE IV: Values of d (Eq 5) Obtained from the Experimental Viscosities of Table 111 and Excess Volume VE (x,= 0.5) at 25 “C ~
mixture MeCN + ClBu ClBu t PAC MeCK + PAC MeCN + CC1, a
a!
d
This work.
vE,~ m ~ m 0 1 - l
0‘ 0.16‘ 0.44 + 0 . 4 7 ~ ~ ‘ 0.11‘
Reference 9.
0.145b 0.042a -0.091’ -0.122c
Reference 12.
VI
‘X
0
N
s F
a
- 0 .02
where d is taken to reflect the nonideality of the system. Parameter d has been usually regarded as an approximate measure of the strength of the interactions between component^.^^'^ However, more recently it has been shown that in certain cases d can also be correlated with the difference in molecular volume of the components and with the entropy of mixing.’ Therefore, d should be accepted as representing different sources of nonideality in the mixture. For the systems studied here, d remains approximately constant except in the case of MeCN PAC where d depends on composition. Similar deviations from eq 5 have been reported before for other systems als0.~3’~ The values of d obtained from the results of Table I11 are given in Table IV. We can see that the largest d is for MeCN + PAC.
+
-0.06; 0
I
4
0.5
1
X1
+
Figure 2. A7 of the systems ( 0 )MeCN (1) PAC(2), ( 0 )MeCN (1) ClBu (2), (0) ClBu (1) PAC (2), and (0)MeCN (1) CC14 (2) as a function of mole fraction composition xl.
+
+
+
0.10
1
VI
8 8
0.08
I-
N
s
0.06
.-0
7
0.OL
F
+
0.02
0
-0.0; 0
0.5 X1
1
+
Figure 3. q - qid of the systems ( 0 ) MeCN (1) PAC (2), (0) ClBu (1) PAC(2), (0)MeCN(1) + CC14 (2), and ( 8 )MeCN (1) ClBu
+
Discussion and Calculations In Table IV we compare the magnitude of p in the four binary mixtures MeCN + ClBu, MeCN + PAC, MeCN + CC14, and ClBu + PAC. Several effects may contribute to the value of p. In the systems studied here, we can recognize four different effects as being important: (1) the breaking of liquid order on mixing; (2) unfavorable interactions between groups; (3) differences in molecular volume; and (4) differences in free volume between liquid components. Let us consider each one of these effects. Acetonitrile is a somewhat ordered liquid in which the molecules are orientationally correlated in parallel and perpendicular dispositions.I6 In the mixtures containing MeCN, one of the effects which may contribute to is the disruption of such orientational correlations of the MeCN molecules on mixing. The contribution of this effect to p is expected to be positive. A second effect whose contribution to p is also expected to be positive is the existence of unfavorable interactions between groups. One such interaction seems to act between the -CN group of MeCN and the -CHzgroups of alkyl chains (e.g. in ClBu or PAC), as has been discussed elsewhere.” This interaction obviously is nonexistent in MeCN CC14 and ClBu + PAC mixtures. An effect which is expected to act on p in the opposite sense to the two effects just discussed, and which should give thus a negative contribution to p,is the difference in molecular size between the two mixture components. Different molecular sizes lead to interstitial accommodation in the mixture and hence to a negative contribution to p.The molecules of MeCN are the smallest of all considered here. Therefore, this effect should be important in the mixtures in which MeCN is one of the components. PAC has the largest molar volume, and hence the negative contribution to due to interstitial accommodation should be larger in the MeCN + PAC mixture. Another effect, also of structural nature, and which again should give a negative contribution to p is the difference in free volume between components. MeCN has the largest free volume of all four liquids considered here, and the free volume difference between MeCN and the second component in the mixture is in the order CC14 > PAC > ClBu, exactly the same order as the -p values in these systems. Summarizing, we can say that in MeCN + ClBu and in MeCN + PAC all four effects may contribute to p,but the structural ones, (3) and (4), are larger with PAC than with ClBu, and this
(2) as a function of mole fraction composition xl.
+
is used to describe the isothermal dynamic viscosity. Deviations from this ideal behavior of the experimental results for the mixtures studied here are shown in Figure 3, where we plot 7 - Tld for each system as a function of the mixture composition. We can see that MeCN ClBu shows ideal behavior, whereas the other three systems have positive deviations, these being largest in MeCN PAC. Grunberg and Nissan14 have proposed an empirical equation to describe 7 of real mixtures: In 9 = x1 In q1 + x2 In qz + x,x2d (5)
+
+
(13) S. Arrhenius, Z Phys. Chem., Stoechiom. Verwandtschaftsl., 1,256 (1887). (14) L. Grunberg and A. H. Nissan, Nature (London), 164, 799 (1949).
(15) J. H. Dymond and K. J. Yound, Znt. J . Thermophys., 2,237 (1981). (16) H. Michel and E. Lippert, “Organic Liquids Structure Dynamics and
Chemical Properties”, A. D. Buckingham, E. Lippert, and S. Bratos, Eds., Wiley, New York, 1978. (17) I. A. Mclure and A. Trejo Rodriguez, J . Chem. Thermodyn., 12,745 ( 1980).
2166
The Journal of Physical Chemistry, Vol. 88, No. 10, 1984
Prolongo et al.
+ +
could explain why p is negative in MeCN PAC and positive in MeCN + ClBu. In the case of MeCN CC14, one of the positive contributions, (2), is missing; hence, the negative effects could dominate, rendering VE C 0. The dynamic viscosities of liquid mixtures have been related to their thermodynamic proper tie^.^-^ Thus, in mixtures having strong interactions between components (negative deviations from Raoult's law), it has been found that d of eq 5 is po~itive,~f+'* while in mixtures deviating positively from the ideal law, in which no specific interactions are present, it has been found that d is negative. It has been shown that q - qld can be correlated not only with HE but with other mixing functions such as SEand p as well. Thus, in the case of athermal (HE= 0) mixtures of spherical molecules with p = 0, it has been found that d is correlated with the mixture entropy due to the different sizes of the molecule^.^ Also, the sign of Aq has been found to correlate with the sign of p in a number of systems, Aq being positive when p is n e g a t i ~ e . ~To, ~interpret the dynamic viscosity of liquid mixtures, it is therefore necessary to consider the different thermodynamic properties of the mixture and the factors both energetic and structural which can give rise to such properties. Of the four systems considered here, the three containing MeCN have unfavorable interactions between components, yielding high HE > 0 and GE > 0 values, as reported el~ewhere.~-'~ > 0 it has been previously found d < 0.3 In the systems with However, of the three MeCN-containing mixtures studied here, d > 0 in two of them and d N 0 in the third one. It seems then that the influence of interactions or energetic factors (contained in HE and GE) on q is superseded in these systems by the influence of other effects, tentatively, the structural or volume-dependent factors. Thus, in the two MeCN-containing mixtures with d > 0 (MeCN PAC and MeCN + CC14) p is negative, and in the mixture with d N 0 (MeCN ClBu) p is positive. In the fourth system studied here, ClBu PAC, HEor GE is not known. They should be very small according to regular mixture theory predictions, because both liquids have practically the same cohesive energy density. In this system d > 0, again probably due to structural effects. The largest positive d is for the MeCN PAC pair. In this system a positive Aq is also observed (Aq is negative for the rest of the systems). In MeCN PAC happens as if some kind of attractive interaction existed between the MeCN and PAC molecules which decreased the fluidity of their mixtures, this in spite of the positive GE found e~perimentally.'~ We have discussed elsewhere19that in this system there may be a favorable interaction between the nitrile and ester groups of the MeCN and PAC molecules and that this interaction may be overrid by the unfavorable ones between the nitrile and methylene groups, thus yielding an overall positive GE.But it is possible that such an attractive nitrile-ester interaction, acting locally, be responsible for the enhanced viscosity observed in this system. The correlation of q with the thermodynamic properties of the mixture can be made quantitative by use of the theoretical scheme developed by Bloomfield and D e ~ a n In . ~ this scheme, q is calculated by using two semiempirical theories: the absolute reaction rate theory and the free volume theory. The experimental q is factored into contributions:
+
+
+
+
+
+
In q = In qid a! In qfv + P In tar (6) with qfv and tarrepresenting the deviations from ideal behavior calculated by the free volume theory (q&)and the absolute reaction rate theory (qar), respectively. a! and /3 are coefficients usually made equal to 1 . In this scheme lnqfv=-----1
P-1
X1
XZ
P1-1
P2-1
~
(7)
I
a
h
1
Cb
i
0.3 ----I
0
0.5
1
0.5
0
X1
*I
Figure 4. Calculated viscosities Vid (-), qidqfv qidqar(GE)(---), q i d l f a r ( p ) (----), and ? i d q f & r ( p ) (---) for the systems (a) MeCN (1) + CCI4 (2), (b) MeCN (1) PAC(2), (c) MeCN (1) + ClBu (2), and (d) ClBu (1) PAC (2) as a function of mole fraction composition x , . (-*-e-),
+
+
where GR is the residual free energy of mixing and P i s the reduced volume. Pcan be calculated from the excess volume and GR from the excess free energy as
P= P/(X,P1 GR RT
+ Xzv*,) +
+ $2&
(9)
GE RT
where qj is the segment fraction of component i: +i= xiPi/(xlPl + x Z P 2 ) . The core volumes, P,for the components are P (cm3.mol-l) = 40.03 (MeCN),9 81.1 1 (ClBu)? 115.55 ( P A c ) , ~ ~ and 75.43 (CC14).21 For the mixtures studied here we have available experimental data on p and on GE (except for ClBu PAC), so that we can calculate qfv and qar directly from experiment. The results thus obtained for Vidr)f, and VidTar are shown in Figure 4. The values of qarcalculated from experimental GE's are the ones denoted as qar(GE). We see that the estimates of q derived from free volume theory, namely are reasonably close to the experimental data. However, the results of q,dqar(GE)are totally inadequate. In the systems for which qidqar(GE) has been calculated, deviations from ideality in GE are positive and large. q does not follow the behavior predicted from such large positive GE values. In previous applications of the Bloomfield and Dewan scheme, qarhas been calculated from the interaction parameter of the Flory theory of solutions, Xlz. The value of this parameter is obtained by fitting theory to experimental results for some excess property such as HE, p,or GE. If we follow this same procedure and obtain such X12from the fit of the Flory theory to the experimental p (at x1 = 0.5) for our systems and then calculate qarby using such X12parameter values, the results thus obtained for qidqar are as shown in Figure 4. The qar results calculated from the X l z pa-
+
~
(18) A. Kumar, 0. Prakash, and S. Prakash, J . Chem. Eng. Data, 26,64
(1981). (19) R. M. Masegosa, M. G. Prolongo, I. Hernbndez-Fuentes, and A. Horta, Ber. Bunsenges. Phys. Chem., 88, 103 (1984).
(20) R. M. Masegosa, M. G. Prolongo, I. Hernandez-Fuentes, and A. Horta, Macromolecules, in press. (21) J. Vbzquez, L. Blas, R. M. Masegosa, M. G. Prolongo, I. Hernbndez-Fuentes, and A. Horta, Makromol. Chem., in press.
J. Phys. Chem. 1984, 88, 2167-2173 rameter fitted to p data are the ones denoted in the figure by var(p).As we can see, if we use the small experimental p to calculate var,the estimates of derived from the absolute reaction rate theory (namely vidvar(p))are reasonably good. The combination of the two theories in the form
2167
Free volume and degree of packing seem to be more important than interaction energies in determining 7. The systems studied here have large deviations from ideality in the energy functions (@,GE), but such deviations are not reflected in 7. The theoretical prediction of 7 is possible if the deviations from ideality are taken into account in the flow activation free energy through the small instead of through the large GE. In systems with smaller deviations from ideality, the correlation between 7 and thermodynamic properties is probably less dependent on the mixing property chosen, and agreement can be more easily achieved.
7 = vidqfvvar(p)
which is derived by making a = /3 = 1 in eq 6, is also shown in Figure 4. vidvfv and vidvar(p)are also particular cases of eq 6 with a = 0, = 1 and a = 1, /3 = 0, respectively. We see that the experimental results can be reproduced in all the cases by properly choosing the coefficients a and p at some intermediate values. In conclusion, the viscosity of the mixtures studied here is well correlated with the volume properties but not with the free energy.
Acknowledgment. Thanks are due to J. Vgzquez for his collaboration in part of the experimental work. Registry No. MeCN, 75-05-8; PAC,628-63-7;ClBu, 109-69-3;CC14, 56-23-5.
Photophysical Investigations of Chiral Amine Guest-Cyclodextrin Host Interactions and Diastereomerlc Recognition Chieu D. Tran’ and Janos H. Fendler* Department of Chemistry, Clarkson College of Technology, Potsdam, New York I3676 (Received: July 27, 1983; In Final Form: October 31, 1983)
Inclusion of (-)-a-(1-naphthyl)ethylamine,(-)-NEA, and (+)-a-(1-naphthyl)ethylamine,(+)-NEA, in a-,@-, and y-cyclodextrins has been investigated by steady-state and subnanosecond time-resolved fluorescence techniques. Addition of 5.0 X M a-cyclodextrin did not affect the fluorescence lifetime (7) of (-)-NEA in water (7 = 5.28 f 0.20 ns). In the presence of 5.0 X M 0-and y-cyclodextrin 7 became 16.6 0.20 and 5.95 k 0.06 ns, respectively. The rotational correlation time, rR,of (-)-NEA in P-cyclodextrin was found to be 697 f 57 ps. 7R values of (-)-NEA in water, and a- and y-cyclodextrins, in both the absence and the presence of cyclic alcohol spacers, were too small to be measured by our system. These data were rationalized in terms of the inclusion of (-)-NEA along its long axis into the cavity of @-cyclodextrin. Molecular dimensions render (-)-NEA too tight to fit into the cavity of a-cyclodextrin along either of its axes. (-)-NEA cannot fit into the cavity of y-cyclodextrin along its short axis, but the fit along its long axis is too loose. Quenching constants determined by steady-state and time-resolved fluorescence, and Ksv‘, for the quenching of (3-cyclodextrin entrapped (-)-NEA fluorescence were found to be identical (25.9 M-l). Conversely, in water Ksv‘ = 13.9 M-l and Ksvm= 67.6 M-I. Entrapment in @-cyclodextrin protects (-)-NEA from static quenching. No differences were found between (-)-NEA and (+)-NEA in their fluorescence lifetimes in 0-cyclodextrin or in the quenching of their fluorescence by chiral (-)-a-phenethylamine in water. Diastereomeric discrimination in the excitation and emission spectra as well as in 7 values was however observed between (+)-NEA and (-)-NEA in the 60:40 Me2SO:H20,particularly in the presence of 5.0 X M P-cyclodextrin. Fluorescence intensities in these systems decayed biexponentially in the 325-350-nm detection range, and monoexponentially at 375 and 395 nm.
*
Introduction Cyclodextrins are naturally occurring doughnut-shaped chiral macrocyclic oligomer^.^-^ Internal diameters and depths of cyclohexaamylose or a-cyclodextrin (4.5-6.0 and 4.5 A), cycloheptaamylose or P-cyclodextrin (6.0-8.0 and 7.0 A), and cyclooctaamylose or y-cyclodextrin (8.0-10.0 and 7.0 A) provide cavities for appropriately sized guest molecule^.^ The recognized potential of cyclodextrin-guest interactions as models for enzyme active sites has prompted the numerous investigations of these ~ y s t e m s .Substantial ~ ~ ~ ~ ~ rate enhancements and chiral recognitions have, however, only been realized in flexibly capped cyclodextrins which efficiently stabilized the transition states of reactive sub(1) Present address: Environmental Chemistry Division, Department of Applied Science, Brookhaven National Laboratory, Upton, NY, 11973. (2) Bender, M. L.; Komiyama, M. “Cyclodextrin Chemistry”; SpringerVerlag: New York, 1978. (3) Saenger, W. Angew Chem., In!. Ed. Eng. 1980, 19, 344-62. (4) Tabushi, I. Acc. Chem. Res. 1982, 15, 66-72. ( 5 ) Hinze, W. L. In “Separation and Purification Methods”; Van Oss, C. J., Ed.; Marcel Dekker: New York, 1981; Vol. 10, pp 159-237. (6) Fendler, J. H.; Fendler, E. J. ‘Catalysis in Micellar and Macromolecular Chemistry”; Academic Press: New York, 1975. (7) Fendler, J. H. “Membrane Mimetic Chemistry”; Wiley-Interscience: New York, 1982. 0022-3654/84/2088-2167$01.50/0
st rate^.^^^ Precise and favorable geometric arrangements between the host and the guest molecules as the reactants proceed through the transition state to products determine the catalytic efficiency of cyclode~trins.~A knowledge of guest-host geometries and the parameters which influence these are, therefore, of some importance. Interactions of enantiomeric (-)-a-(1-naphthyl)ethylamine, (-)-NEA, and (+)-a-(1-naphthyl)ethylamine, (+)-NEA, with a-, p-, and y-cyclodextrins in the absence and presence of spacers have been investigated in the present work by subnanosecond time-resolved fluorescence lifetime and anisotropy measurements. This work represents our continued search for factors which may bring about enhanced chiral discriminations. Photophysical methods have been demonstrated to be highly sensitive for examining chiral interaction^'^'^ and have been fruitfully utilized (8) Breslow, R. Isr. J . Chem. 1979, 18, 187-91. (9) Breslow, R.; Czarniecki, M. F.; Emert, J.; Hamaguchi, H. J . Am. Chem. SOC.1980, 102, 762-70. (10) Yoruzo, T.; Hayashi, K.; Irie, M. J . A m . Chem. SOC.1981, 103, 5480-4. (11) Tran, C. D.; Fendler, J. H. J . A m . Chem. SOC.1980, 102, 2923-8. (1 2) Tran, C. D.; Beddard, G. S.; McConnell, R.; Hoyng, C.; Fendler, J. H. J. Am. Chem. SOC.1982,104,3002-7. Tran, C. D.; Beddard, G . S. Ibid.
1982, 104, 6741-7.
0 1984 American Chemical Society
