J. Phys. Chem. 1988, 92, 7251-7255 Orlpinsl compoattbn T-/D
packing in the form of less staggering with enhanced alcohol/ surfactant ratio. The tie lines in the two-phase region in the surfactant-poor part of the diagram also deserve some comments. Figure 3A-C makes obvious the fact that the separation in the two-phase region is mostly between a toluene solution and the formamide solution. The higher the total surfactant concentration the more decanol and toluene are solubilized into the formamide solution and the less of them remain in the toluene solution. Figure 8 shows both the solution regions and the tie lines for the system with a toluene/decanol ratio equal to 1. The figure demonstrates the fact that the tie lines are outside the plane of the solubility regions. This trend has been observed earlier in formamidesodium dodecyl sulfate-hydrocarbon systems with hexano15' and is obviously valid also for systems, which contains lamellar liquid crystals.
ecanols 501 6 0
(Decanol 4 Toluene)/ Fomurridh50/60
Decanol
Forrnamide
7251
SDS
Figure 8. A comparison of tie lines and solubility regions for the phase diagram with toluene-decanol equivalent weight ratio, Figure 2.
along the molecular axis. For such a structure& changes in order parameters may take place without corresponding modifications of interlayer spacing. Hence, for the present system, in lieu of complementary information, the hypothesis remains of improved
Acknowledgment. This research was supported by a grant from N S F MSM-8716928. Registry No. Formamide, 75-12-7; sodium dodecyl sulfate, 151-21-3; decanol, 112-30-1;toluene, 108-88-3. (51) Friberg, S. E.; Rong, G. Lclngmuir 1988, 4, 796.
Albumin-Facilitated Fatty Acid Transport in a Liquid Membrane System Joe Otsuki,* Kazutoshi Iwamoto, and Manabu Sen0 Institute of Industrial Science, University of Tokyo, 7-22-1, Roppongi, Minato-ku, Tokyo 06, Japan (Received: March 30, 1988; In Final Form: June 22, 1988)
In an attempt to obtain informa.tion about the dynamic anect of albumin-facilitated transport, the rates of uptake, release, and transport of long-chain fatty acids (LFA) by bovine se im albumin (BSA) in a liquid membrane system were investigated. The system consisted of aqueous BSA solution and orgaiiic LFA solution. The shorter the hydrocarbon chain of LFA is, the larger is the transport rate. The uptake rate of LFA from the organic phase to the aqueous phase by BSA saturates at large LFA concentration in the organic phase. On the other hand, the rate of release of LFA from the BSA-LFA complex in the aqueous phase to the organic phase increases steeply as the total LFA concentration increases. The relationship of the rates with the association constants of LFA to BSA and the partition ratio of LFA between the aqueous and the organic phase was elucidated by developing a model of concentration profiles in the liquid membrane system which was applied to calculate the rates and correctly predicted the experimental results. The model suggests that the contribution of binding sites of different affinities to the transport changes as the LFA concentration in the receiving phase changes.
Introduction
Serum albumin transports many metabolites such as lipids, chromophores, drugs, and organic and inorganic ions by binding them in blood. A lot of researches have elucidated the interaction of albumin with these substrates under equilibrium conditions.' Physicochemical parameters such as association constants for various substances have been determined. One of the most investigated substrates of serum albumin is long-chain fatty acid (LFA). The association constants of LFA to human serum albumin (HSA) and bovine serum albumin (BSA) were determined based on the Scatchard analysis by Goodman2 and Spector et al.,3 respectively. Later, the stepwise analysis, which could be generally applied to multiple equilibrium reactions independently of mechanism,' was carried out for the interactions of LFA with BSA and HSA by Spector and coworker s ,495
(1) Spector, A. A. J. Lipid Res. 1975, 16, 165. (2) Goodman, D. S. J . Am. Chem. SOC.1958.80, 3892. (3) Spector, A. A,; John, K.;Fletcher, J. E. J. Lipid Res. 1969, 10, 56. (4) Spector, A. A.; Fletcher, J. E.; Ashbrook, J. D. Biochemistry 1971, 10, 3229.
0022-3654/88/2092-7251$01 S O / O
These works concern the interaction under the equilibrium conditions. The transport process, however, consists of nonequilibrium steps such as uptake, migration, and release. Therefore, an approach is important from not only a static but also a dynamic point of view. In this paper, we report the behavior of albumin-facilitated LFA transport in liquid membrane system as a simple model of the biological transport system. The transport has been examined by both experimental and theoretical treatments and the significance of many binding sites of different affinities on a BSA molecule is discussed. Experimental Section
Materials. Defatted BSA (A6003) prepared from fraction V was purchased from Sigma Chemical Co. Special grade lauric and myristic acid were purchased from Tokyo Kasei Kogyo Co., and palmitic acid was from Wako Pure Chemicals Ltd. Reagent grade n-heptane was purchased from Wako and Takahashi Pure Chemical Co. All reagents were used without further purification. A 0.5 mM BSA solution containing 0.116 M NaC1, 0.0049 M ( 5 ) Ashbrook, J. D.; Spector, A. A.; Santos, E. C.; Fletcher, J. E. J. B i d . Chem. 1975, 250, 2333.
0 1988 American Chemical Society
7252 The Journal of Physical Chemistry, Vol. 92, No. 26, 1988
Otsuki et al.
p,;
My
+ *Myr.
apparatus for transport experiments. a, 5 mL of membrane phase containing 0.5 mM BSA; b, 100 mL of source phase containing 3 mM LFA c, 1 mL of receiving phase; d, a water bath controlled at 37.0 O C ; e, a pump which circulated the solution at the rate 3 mL/min; f, a magnetic stirrer. (b) An apparatus for uptake and release experiments. a, 1 mL of an organic phase, which was n-heptane containing LFA for uptake experiments and pure n-heptane for release experiments; b, 1 mL of 0.5 mM BSA solution;c, a water bath controlled at 37.0 O C ; d, a magnetic stirrer.
(a)
Figure 3. The uptake (a) and release (b) rates dependences on the initial
LFA concentrations in the heptane and aqueous phase, respectively. The points represent the experimental values. The solid lines represent the calculated results with parameters adjusted to fit the uptake experiments. i.
-
2 Source
3
5
4
Membrane
6
7
8 Receiving
Figure 4. Schematic representation of the liquid membrane system. Fundamental structures of the diffusion layers are identical with the
0
0"
0 1 2 3 4 Concentration(mmo1ii)
0 1 2 3 ' Concentration(mmoli1)
(bi
(a)
Figure 1. Schematic representation of experimental apparatuses. (a) An
0.0 0
5 10 Tirne(hr)
15
Figure 2. The time course of LFA concentrations in the receiving phase for the transport experiments. Plots represent experimental results and lines represent results of calculations with parameters determined by the comparison of experiments and calculations of uptake as mentioned in the text.
KCl, 0.0012 M MgS04, and 0.016 M sodium phosphate, pH 7.4, was used as an aqueous phase in all experiment^.^ This composition is similar to that of blood. Procedures of Transport Experiments. Transport experiments were performed with a U-shaped glass tube with an air channel for homogenizing the pressure in the tube (Figure la). The BSA solution (5 mL) was stirred at 400 rpm by means of a magnetic stirrer. The source phase (100 mL of a 3 mM LFA solution in n-heptane) was connected to a flask and circulated at 3 mL/min by a pump. The tube and the flask were placed in a water bath controlled at 37.0 OC. The changes in the concentration of LFA in the source and receiving phases were followed by analyzing 5 mL of the solutions with an HPLC-electrolytic conductometer. The column was ODS and the eluent was acetonitrile/water = 70/30 (v/v). Procedures of Uptake and Release Experiments. The transfer of LFA across aqueous/organic interface was examined by using a glass tube illustrated in Figure 1b. One milliliter of the albumin solution and 1 mL of n-heptane were placed in the glass tube. In the uptake experiments, the heptane phase contained various concentrations of LFA. In the release experiments, the aqueous phase contained various concentrations of BSA-LFA complex. The aqueous solution was stirred at 400 rpm by a magnetic stirrer. The aqueous and organic solutions were kept at 37.0 O C before the experiments, and the experiments were carried out in a water bath controlled at 37.0 O C . The LFA concentration changes in the organic phase were followed as described above. The aqueous solution containing BSA-LFA complex was prepared by extracting LFA from heptane to the BSA solution by a similar way in the uptake experiment. The total concentration of LFA in the aqueous phase was determined from the difference between the amounts of LFA in the organic phase before and after the extraction.
model presented by Lamb et a1.6 The double lines indicate the aqueous/organic interfaces. The vertical axis corresponds to the concentrations of respective chemical species.
Results and Discussion Transport. Figure 2 depicts the time course of the LFA concentrations in the receiving phase in the transport experiments. The concentrations in the source phase are almost unchanged since its volume is large. In the initial stage of the transport, the concentration in the receiving phase hardly increases. After several hours, the concentrations in the receiving phase begins to increase and then the system reaches steady state. The shorter the hydrocarbon chain of LFA is, the greater is the rate of transport. At first glance, the order of transport rates appears to be in accord not with the binding constants of BSA but with the hydrophilicity of LFA. Quantitative treatment described later in the subsection Mechanism of Transport, however, indicates that both of these factors are related to the transport rate. Uptake and Release. In the uptake and the release experiments, the LFA concentration in the heptane phase changes linearly with time at an early stage and the rates of uptake and release are calculated from the slope of the graphs of concentration vs time. Figure 3 shows the rate dependence on the initial concentration of LFA. The rate of uptake reaches a saturated value at high LFA concentration, which is a common characteristic of reactions in which the combination of ligand with substrate is involved such as an enzymatic reaction and a carrier transport. The rates are in the same order as that of transport. On the other hand, the rate of release increases steeply as the initial LFA concentration increases. Mechanism of Transport. Liquid Membrane Model. In order to analyze quantitatively the experimental results, a model presented by Lamb et a1.6 was extended to apply to a system in whcih a carrier (BSA) has many binding sites with different association constants to its substrates (LFA) and to include the flux of unbound substrate. A representation of the extended theoretical model is given in Figure 4. The fundamental structure and the way of numbering the diffusion layers are the same as in the treatment by Lamb et aL6 Positions are indicated by (6) Lamb, J. D.; Christensen, J. J.; Oscarson, J. L.; Nielsen, B. L.; Asey, B. W.; Izatt, R M . J . Am. Chem. SOC.1980, 102, 6820.
The Journal of Physical Chemistry, Vol. 92, No. 26, 1988 7253
Albumin-Facilitated Fatty Acid Transport TABLE I: The Association Constants of LFA to BSA in Phosphate-Buffered Saline (pH 7.4) at 37 OC Based on the Scatchard Model3 binding class fatty acid K , X lod M-’ K2 X M-I K, X M-I
lauric myristic palmitic
0.139
1.39
1.8
2.2 6.8
4.5 5.0
5.4
10
subscripts attached to variables. LFA (F) diffuses through the organic diffusion layer (1-2) and partitions into the aqueous membrane phase at the interface (2) with the partition ratio (PR,). The partition ratio is defined as PR2 = F , h / F 2 w
(1)
where FZh and F,, are the concentrations of LFA at the interface (2) in the heptane side and the aqueous side, respectively. It is assumed that the rate at which LFA partitions into the aqueous membrane phase is adequately high compared to the rate of diffusion. While LFA diffuses through the aqueous diffusion layer (2-4), the LFA binds to the binding site (A,) of the ith class of BSA (A) and the complex (AiF) is formed. The mean distance through which the unbound LFA diffuses in the aqueous diffusion layer before reaching equilibrium with BSA is 1,. BSA is considered as having three classes of binding sites3 The number of sites (ni) belonging to each class (i) is n, = 3, n2 = 3, and n3 = 63. Then, the concentrations of respective chemical species at the position 3 are given by niATKiF3 AiF3 = 1 KiF3 ~
+
i = 1,2,3
where AT is the total concentration of BSA. The association of the sites in ith class to each LFA are given in constants (K,) Table I.’ The concentrations in the bulk membrane are safely assumed to be homogeneous by stirring. The processes at the releasing side are of symmetric nature as those at the uptake side described above and the next relations hold (3)
g1 AZF
0 0 0 2 0 4 0 6 0 8 10 x
0 0 02 0 4 0 6 08 1 0 x
00 0 2 0 4 0 6 0 8 1 0
la)
(bl
IC)
x
Figure 5. Concentration profiles in the aqueous diffusion layers obtained by the steady-state assumption for myristic acid transport. The source phase concentration of myristic acid is 3 mmol/L. The concentrations in the receiving phase are (a) 0, (b) 0.3, and (c) 1 mmol/L.
where a is the association factor for heptane (1.0) and water (2.6), M is the molecular weight of heptane (100) and water (1 8), T is the temperature (310 K), 4 is the viscosity of heptane (0.42 cP) and water (1.01 cP), and Vis the molar volume of LFA (300 cm3/mol used as a representative value). By substitution of eq 2, 3, 6, and 7 into eq 5, J is obtained as the solution of a equation of the fourth order which can be solved numerically. Concentration Profiles in the Diffusion Luyers. The model used so far tacitly assumed that the concentrations in the diffusion layers changed linearly with the distance from the interface. The profiles of the concentrations without the assumption could be obtained by using the steady-state conditions as follows. For simplicity, I,, 12, Is, and l6 are assumed to be zero and only the aqueous diffusion layers (3-4, 5-6) are considered, Dimensionless distance x is defined as x = d/(13
+ 14)
(9)
where d is the distance from the source/membrane interface (bulk membrane phase is omitted). Consequently, x is zero at the source/membrane interface and unity at the membrane/receiving interface. Since the condition of steady state is that the total flux of LFA is equal throughout the diffusion layers
where CI is a constant. Integrating eq 10 with respect to x gives 3
PR7
= F1h/F7w
(4)
DF,F
+ DACAiF = Clx + C , i= 1
Since the total flux J of LFA is the sum of the flux Joof the unbound LFA and the flux Ji of each complex
where the integration constants C1and C2 are determined by the boundary conditions as
3
J = CJi
(11)
3
CI = C2 - [ D F ~ + F DACAiFIx=1
i-0
i= 1
(12)
3
C2 = [ D F ~ F +DACAiFIx=o i= 1
where DFwand DA (6.9 X cm2/s)’ are diffusion coefficients of LFA and BSA, respectively, in aqueous solution. Assuming that the system is at the steady state, the unbound LFA concentrations at position 3 and 6 are given by the following equations6 F3
= (Fl - J11/DFb)/PR2 - J12/DF,
Fs = (Fa
+ Jls/D~,)/pR7 + J I ~ / D F ~
(6) (7)
where DFh is the diffusion coefficient of LFA in heptane. The values of DF, (5.0 X 10” cm2/s) and DF (1.8 X 10” cmz/s) were estimated by using Wilke’s equation6,$ D = 7.4 X 1 0 - 8 ( a M ) 1 / 2 T / q ~ ~ 6
(8)
(7) Peters, Jr. T.In The Plasma Proteins; Putnam, F. W., Ed.;Academic: New York, 1975; Vol. 1, p 133. (8) Wilke, C. R.; Chang, P.AIChE. J . 1955, 1, 264.
(13)
Equation 11 shows that not the concentrations but the sum of the products of the diffusion coefficients and the concentrations of the respective chemical species change linearly with the distance from the interface. The calculated concentration profiles with eq 11 for the transport of myristic acid are given in Figure 5. It indicates that, when the LFA concentration in the receiving phase is not zero, the concentration profiles are almost linear. When the LFA concentration in the receiving phase is zero, the concentration gradients are different from place to place. Consequently, the linear approximation of concentration gradients is reasonable except when the LFA concentration in the receiving phase is very near to zero. The molar ratio (MR,) of LFA bound to the binding sites in the ith class to BSA in the bulk membrane phase is defined as MRO =
Fx=0.5/AT
(14)
1254
The Journal of Physical Chemistry, Vol. 92, No. 26, 1988
Otsuki et al.
TABLE Ii: The Constants for the Partition Ratios of LFA between the Phosphate-Buffered Saline (pH 7.4) and n-Heptane at 37 "C? fatty acid PRx PRY, M-' lauric 4.7 1.86 x 105
myristic palmitic
86.3 489
I
x 107 1.48 X IO9
4.65
A Method of Calculation. For the calculation of the uptake rate J,, only the left half of Figure 4 was considered. Then, instead of eq 5 the following equation was used.
0 1 2 3 Conc. of rec. phase(rnrnol/l)
3
J" =
CJui
0.0
n -
+ (PRx2 + ~ P R Y F , ~ ) I / ~ ) / ~(17)
'
JO 1
.i
'
, 2
3
Conc. of rec. phase(mrno1A)
(a)
i-0
First of all, J , was calculated by eq 16 using the initial values (F4 = AiF4 = 0). This value of J , could not be used to predict the experimental results since the J , changes remarkably when the LFA concentration at the position 4 changes slightly from zero. Then, J , was multiplied by the interface area (AR = 1.5 cm2) and a period (dt), and divided by the volumes of the aqueous phase (V, = 1.O cm3) and the heptane phase ( v h = 1.O cm3) to calculate the concentration changes of the total LFA in the aqueous phase (4)and the LFA (F,) in the heptane phase, respectively, after the time dt. The partition ratios (PR) are functions of the LFA concentrations at the interface9 and are represented by PR2 = (PRx
I
(b)
Figure 6. (a) The dependences of transport rate by each binding class on the concentration in the receiving phase calculated for myristic acid. Jo is the rate of transport by unbound LFA and Ji (i = I , 2, 3) are by the ith class of binding sites of BSA. (b) The proportion of the contribution of LFA unbound and bound to each binding class to the transport rate.
0
u
0 1 2 3 Conc of rec. phase(mrnoli1)
0.0
u
0 1 2 3 Conc of rec. phase(mrnol/y)
where PRx and PRY are characteristic constants to each LFA and the values are given in Table 11. Each time new values of FI and J , were determined, the new value of PR2 was calculated by using the relation6
Figure 7. (a) Dependences of the ratios (molar ratio: MRi) of the mole of LFA unbound (MR,) and bound to each binding class to BSA on the
(18)
concentration in the receiving phase calculated for myristic acid transport. (b) The proportion of the molar ratios.
F2h
= F, - J u l l / D f i
and eq 17. The value of time dt was set so as to change the concentrations less than 5% and was the order of seconds. The concentrations of respective species (F4 and A,F,) were determined from the total concentration by numerical computation. The procedures were repeated until the time reached approximately 10 min. The decrease of LFA concentration (F,) was divided by the time to produce the initial rate of uptake. The method of calculating the release rate was the same as just above except for the initial conditions (F8 = 0) and the direction of the fluxes. The concentration changes in the case of the transport were calculated not by using eq 5 directly but by using the calculated results of uptake and release as mentioned above repeatedly and alternatively to predict the transport behavior correctly from the initial stage of the reaction which had not reached the steady state yet. Results of Calculations. The thickness of diffusion layers, 1, = I,, l2 = Is, and l3 = l6 were adjusted to give the best fits to the experimental results of uptake rate dependence on the initial LFA concentration (Figure 3a). The thicknesses of the diffusion layers, I , and l2 + lj, which are common under the same stirring conditions irrespective of the kind of LFA, were estimated as 200 and 15 pm, respectively. Although the value of l2 is considered to be different according to the kinds of LFA and binding site, only the same value was used for each LFA. The values were estimated to be 0.1 and 0.3 pm for myristic and palmitic acid, respectively. The value of l2 for lauric acid could not be determined since the rate showed little dependence on l2 and the calculations were carried out by using zero for 12. The results of calculations with these values are shown by solid lines in Figure 3a. A simpler treatmentlo," which assumes that the equilibrium is reached (9) Simpson, R. B.; Ashbrook, J. D.; Santos, E. C.; Spector, A. A. J . Lipid Res. 1974, 15, 415. (10) Schultz, S.G. Basic Principles of Membrane Transport; Cambridge University Press: London, 1980.
(a)
(b)
immediately at the interface, that is l2 and I, are zero, gives less fit to the experimental results. The calculated release rate dependences on the initial concentration with parameters estimated above are shown in Figure 3b. They are in good agreement in the tendency that the rate of release accelerates as the initial LFA concentration increases. This acceleration is owing to a steep increase in the concentration of unbound LFA at high total LFA concentration in the aqueous phase. Results of calculations for the transports are given in Figure 2. The parameters used are the same as those adjusted for uptake experiments described above. The results of experiments and calculations are in very good agreement, although the absolute value of time is not adjusted since the stirring conditions and then the width of diffusion layers were different from those in the uptake experiments. The Contribution of Various Binding Sites to the Transport. To elucidate the significance of many binding sites with different affinities, the binding to and the flux by each class of binding sites were estimated for the transport of myristic acid by using eq 5 , 14, and 15. For simplicity, I , , 12, 15, and l6 were put to zero. The dependences of Ji and MRi on the LFA concentration in the receiving phase are given in Figures 6 and 7, respectively. Ji represents the contribution of class i to the transport and MR, represents the number of LFA molecules bound to the class i. As the concentration in the receiving phase increases from zero to 3 mmol/L, which is the same as in the source phase, the total flux decreases at first abruptly and then slowly, and the proportion of J 1 decreases and Jz is almost constant, while the proportions of J3 and Jo increase. On the other hand, Figure 7 indicates that the molar ratios in the bulk membrane are constant at all the concentrations in the receiving phase except at the region very (1 1) Behr, J. P.; Kirch, M.; Lehn, J. M. J. Am. Chem. Soc. 1985,107,241.
J. Phys. Chem. 1988, 92, 7255-7257 near to zero. Three binding sites of the class 1 are almost saturated. LFA binds on two sites of class 2. A little LFA binds on the sites of class 3 since its association constants are very small though the number of sites are quite large. Besides, little unbound LFA exists. These results show that, as the LFA concentration in the receiving phase increases, the relative contribution of weaker binding sites and unbound LFA to the transport increases, though the total transport decreases, while the molar ratios of each binding class in the bulk membrane do not change. When the concentration in the receiving phase is very small, BSA transports LFA more effectively compared with the case where BSA would have only binding sites of just a medium affinity, since the stronger binding sites release more LFA. On the other hand, a change in the source phase gives little effect on the contribution of the different binding sites.
7255
Conclusions
BSA transports lauric, myristic, and palmitic acid at a decreasing rate through the aqueous liquid membrane. While the rate of uptake reaches saturation at high LFA concentration in the organic phase, that of release accelerates at high total LFA concentration in the aqueous phase because of the steep increase of unbound LFA. The model developed here correctly predicts the rate of LFA transport facilitated by BSA which has many binding sites with various association constants to LFA. The model reveals that the contribution of each binding site with different association constant to the transport changes, as the LFA concentration in the receiving phase changes.
Acknowledgment. This work was partly supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture.
Molecular Aggregation and Fluorescence Quenching of a Cetylstilbazolium Betaine El-Zeiny M. Ebeid,* Shaker T. Abdel-Halim, and Mahmoud H. Abdel-Kader Department of Chemistry, Faculty of Science, University of Tanta. Tanta, Egypt (Received: October 5, 1987; In Final Form: March 10, 1988)
Molecular aggregation of 4-hydroxy-1-cetylstilbazoliumbetaine (Cl6MH+)has been studied by lifetime, spectroscopic,and conductometric techniques. Its fluorescence undergoes a substantial quenching on using both methyl and cetyl iodide as quenchers. The mechanism of fluorescence quenching is also discussed.
Introduction
There is a growing interest in the preparation and characterization of surfactant molecules containing photochemically reactive functional groups. Monolayer assemblies of such surfactants have wide applications in photoresists as well as photomemory.' Merocyanine dye (Ia) is a prototype compound containing a moiety that exhibits some unique characteristics in the areas of solvatochromismZ4 and thermochrorni~rn~ as well as photovoltaic devices based on organic solar cells6
Ia
Ib (1) Yabe, A,; Kawabata, Y.; Ouchi, A.; Nakamura, T.; Tanaka, M. Proceedings of the 12th International Conference on Photochemistry, Tokyo, 1985. Nakanishi, E.; Okada, S.; Ichimura, K. Proceedings of the 12th International Conference on Photochemistry, Tokyo, 1985. Barni, E.; Savarino, P.; Laronere, R.;Viscardi, G.; Pelizzetti, E. J . Heterocycl. Chem. 1986, 23, 209. Nakanishi, F. J . Chem. Soc., Chem. Commun. 1984, 1543. (2) Botrel, A.; Le Beuze, A.; Jacques, P.; Strub, H. J. Chem. Soc.,Faraday Trans. 2 1984,80, 1235-1252. (3) Jacques, P. J . Phys. Chem. 1986, 90, 5535-5539. (4) (a) Abdel-Halim, S. T. Ph.D. Thesis, Tanta University, 1986. (b) Abdel-Halim, S. T.; Abdel-Kader, M. H.; Steiner, U. J . Phys. Chem., submitted for publication. (5) Lohr, J. E.; Kortiim, G. Ber. Bunsen-Ges. Phys. Chem. 1966, 70,817. (6) Chamberlain, G. A.; Cooney, P. J.; Dennison, S. Nature 1981,45,289. Moriizumi, T.; Kudo, K. Appl. Phys. Lett. 1981, 38, 85.
0022-365418812092-7255$01 SO10
In the present article, we present further characterization of the title compound using thermoanalytical techniques. We also report the molecular aggregation in C16MH+dye in relation to steady-state and time-resolved emission spectroscopy. The fluorescence quenching caused by short- and long-chain quenchers is also examined. Experimental Section
The cetylstilbazolium betaine (I) was synthesized according to literature procedures.' The last crystallization was carried out from ethanol containing traces of ammonia to give predominantly the basic form (Ib). The product thus isolated contains water of crystallization that constitutes ca. 8.78% of its weight according to moisturemetry measurements. The percentage of water in the prepared samples have been estimated with a Mitsubishi Moisturemeter, Model CA-02 (Japan). Thermal analysis of the product has been carried out with a Du Pont 990 thermal analyzer (for differential scanning calorimetry; DSC) and a Heraeus TA unit Model TA 500 S (for thermogravimetric analysis; TGA). Cetyl iodide (Merck-Schuchardt 98%) and methyl iodide (Prolabo) used in fluorescence quenching were used as supplied. Steady-state fluorescence spectra together with fluorescence yields (&) and photochemical quantum yields (&) were measured with a Shimadzu RF 510 spectrofluorometer. Lifetime measurements were carried out by Prof. A. J. Lees of Binghamton University using a system that has been described earlier? Fluorescence quantum yields have been measured relative to N,N'-bis(2,5-di-tert-butylphenyl)-3,4,9,1O-perylenebis(dicarboximide) for which & = 0.99 in methanol (Aex = 365 nm).' (7) Donchi, K. F.; Robert, G. P.; Ternai, B.; Derrick, P. J. Aust. J . Chem. 1980, 33, 2199. (8) Ebeid, E. M.; Lees, A. J. J . Phys. Chem. 1987, 91, 5792. (9) Langhals, H. Chem. Ber. 1985, 118, 4641.
0 1988 American Chemical Society
