J. Phys. Chem. 1991,95,423-421 trostatic repulsion of negatively charged carboxylate ions. The reason for the remarkably effective catalysis of the heterogeneous copolymer-bound Co( 11)-tapc may be as follows: the copolymers have active and basic sites on the flexible backbone, and the polymer coil may hinder the undesirable dimerization reaction in Co(ll)-pc molecules by a shielding effect. The pyridine groups in the copolymer may also act as a function of the basic site and promote the formation of RS-.
Conclusion The central metal ions and the number of carboxylate ions on metallophthalocyanine affect the catalytic activities for the aerobic oxidation of 2-mercaptoethanol (RSH) catalyzed by (polycarboxyphtha1ocyaninato)metals in aqueous solution at pH 7.0 and at 25 "C. (Octacarboxyphthalocyaninato)iron(III)and -cobalt( 11) appears to be an effective homogeneous catalyst for the reaction. (Dicarboxyphtha1ocyaninato)metalsand Cu(I1)as well as Ni( 11)-phthalocyanine derivatives are less effective catalysts. The kinetics of aerobic oxidation catalyzed by (tetraand (octacarboxyphthalocyaninato)iron(IIl) and -cobalt(II) have been characterized in terms of a bisubstrate Michaelis-Menten
423
rate law. The rate law and spectral experiments indicate that the catalyzed reaction proceeds via the formation of a ternary activated complex where RS- and O2 reversibly coordinate with central metal on the phthalocyanine rings. The (tetracarboxyphthalocyaninato)cobalt(II) covalently bound to poly(2-vinylpyridine-co-styrene), in spite of being a heterogeneous system, is a remarkably effective catalyst. The K5value of the rate-controlling step for the polymeric heterogeneous system is about 3 times larger than that for the homogeneous Co(I1)-tapc system. The copolymer has active Co(I1) of the five-coordinate high spin and basic sites on the flexible backbone, and the polymer coil may hinder the considerable dimerization in Co(l1)-pc molecules with a shielding effect. The pyridine groups in the polymer may also act as a function of the basic sites and promote the formation of RS-. Acknowledgment. This work was supported by a Grant in Aid for Scientific Research on Priority Area of "Dynamic Interaction and Electronic Processes of Macromolecular Complexes" (No. 63,612,003) from the Ministry of Education Science and Culture, Japan.
Distance Distribution Function of Sodium Dodecyl Sulfate Micelles by X-ray Scattering
R. Itri
and L.
Q.Amaral*
Instituto de F h c a , Universidade de Siio Paulo. Caixa Postal 2051 6, Siio Paulo, CEP 01 498, Brazil (Received: January 2, 1990; In Final Form: July 6, 1990)
It is shown that for micellar solutions it is possible to analyze small-angleX-ray scattering curves through the distance distribution function p ( r ) , even for relatively high concentrations, in specific cases in which the intensity curve I ( q ) is dominated by a peak due to the inner structure of the micelle. This allows an independent determination of the micellar form factor P ( q ) . This procedure is compared with the conventional fitting of I ( q ) to the product of P ( q ) with the intermicellar interference function S(q), calculated from repulsive Coulomb interactions in the mean spherical approximation. p(r) functions are obtained for concentrations up to 15 wt % sodium dodecyl sulfate; micellar anisometries may be deduced from D,,, values.
Introduction Isotropic micellar solutions of sodium dodecyl (lauryl) sulfate in water (SLS/H,O), with and without additives, have been studied by several experimental techniques: light scattering,l%* fluore~cence,~ small-angle scattering of neutrons and X-rays (SAXS).8-10 The scattering curve I ( q ) as a function of (1) Missel, P. J.; Mazer, N. A,; Benedek, G. 8.; Young, C. Y.; Carey, M. C. J . Phys. Chem. 1980.84, 1044; 1983,87, 1264. Rohde, A.; Sackman, E. J. Colloid Interface Sci. 1979, 70, 494; J . Phys. Chem. 1980, 84, 1598. (2) Corti, M.;Degiorgio, V. Chem. Phys. Letr. 1978, 53, 237; Ann. Phys. 1978, 3, 303; Solution Chemistry of Surfactants; Mittal, K.L., Ed.; Plenum: New York, 1979; J . Phys. Chem. 1981, 85, 711. (3) Lianos, P.; Zana, R. J. Colloid Interface Sci. 1981, 84, 100. Lianos, P.; Lang, J.; Strazielle, C.; Zana, R. J . Phys. Chem. 1982, 86, 1019. (4) (a) Hayter, J. B.; Penfold, J. J . Chem. Soc., Faraday Trans. I 1981, 77, 1851. (b) Colloid Polym. Sci. 1983, 261, 1022. (5) Sheu, E. Y.; Wu,C. F.; Chen, S.H. Phys. Reu. A 1985, 32, 3807. Chen, S . H. Physica 1986, 1378, 183. Wu,C. F.; Sheu, E. Y.; Bendedouch, D.; Chen. S. H. Presented at the XVI Reunion de Fisica Estadistica, Oaxtepec, Mexico, Jan 12-15, 1987. (6) Chen, S.H.; Sheu, E. Y. Presented at the 10th Discussion Conference on Small Angle Scattering- and Related Methods. Prague. - Czechoslovakia. July 13-16, 1987. (7) Cabane, B.; Duplessix, R.; Zemb, T. J . Phys. (Les Ulis, Fr.) 1985, 46, 2161.
(8) Zcmb, T.; Charpin, P. J. Phys. (Les Ulis, Fr.) 1985, 46, 249. (9) (a) Reiss-Husson, F.; Luzzati, V. J . Phys. Chem. 1964.68, 3504. (b) J . Colloid Interface Sci. 1966. 21, 534. (IO) Itri, R. Master Dissertation, lnstituto de Fisica, Universidade de SHo Paulo, 1986.
the scattering vector 4' presents a peak, resulting from the product of the micellar form factor P ( q ) and the micellar interference function S(q). Calculations of S(q) assuming Coulomb repulsive interaction have been performed through the mean spherical approximation (MSA) developed by Hayter and Penfoldl' and the rescaled mean spherical approximation (RMSA) by Hansen and Hayter.', SANS resultsH have been analyzed through fitting of the I ( q ) curve with parameters of both micellar form P(q) and micellar interactions S(q). This approach does not give therefore independent information on the two functions, what may lead to unphysical results, particularly for concentrated solutions. SAXS results have been analyzed up to now through the same procedure only for a 2 wt % SLS solution, allowing a unified and consistent interpretations of SAXS and SANS results, since the form factor P ( q ) is different for the two scattered waves. We address in this paper SAXS results in more concentrated solutions, aiming to obtain independent information on the micellar form factor. In the pioneering work of Reiss-Husson and L u ~ z a t iSAXS ,~ curves in the SLS/H20 system have been studied through the isotropic I-hexagonal Ha liquid crystalline phase transition. A fitting has been made only for the more diluted solutions (up to 15 wt % SLS) in terms of a spherical micellar model, neglecting interaction effects; the observed peak is attributed to the inner micellar structure. In a recent study of this systemI3 we have (11) Hayter, J. B.; Penfold, J. Mol. Phys. 1981, 42, 109. (12) Hansen, J. P.; Hayter, J. B. Mol. Phys. 1982, 6, 651.
0022-365419 1/2095-0423%02.50/0 0 1991 American Chemical Society
424
focused the interference peaks along the I-Ha transition through a detailed discussion of the distribution of amphiphilic and water moieties. It was concluded that a small micellar growth occurs until 0.5 M SLS ( I 5 wt %), with axial ratio u increasing up to 1.5 value. Saturation occurs for more concentrated solutions in the I phase. Further micellar growth into spherocylinders occurs at the I-Hcv transition. Since the calculations of S ( q ) are made within a spherical approximation, it is important to have an alternative and independent procedure to obtain information on the micellar form from the SAXS curves. The distance distribution function p ( r ) of a particle is widely u ~ e d ' ~in Jthe ~ analysis of scattering curves in systems of particles in solution, when the dilution is so high that interference may be neglected. In usual cases the particle has no inner structure and p ( r ) is directly related to the particle form and dimension. Cases of particles with inner structure have been less studied. I b ~ 1 6 ~ 1 We shall show that for micellar solutions it is possible to analyze the scattered curve through the p ( r ) function, even for relatively high concentrations, in specific cases in which I(q) is dominated by a peak due to the inner structure of the micelle. Experimental Section Commercial Merck SLS (99% purity) and deionized and bidistilled water were used. Solutions were homogenized through agitation and centrifugation. Samples conditioned in sealed glass capillaries of I -mm i.d. were investigated by small-angle X-ray scattering at room temperature, 22 f 1 O C . Scattering curves were obtained with a small-angle Rigaku-Denki goniometer, using a line beam transmission geometry. Cu Ka radiation was used with a graphite monochromator between the sample and the scintillation detector. The scattered intensity Jobs was corrected by subtracting a background (parasitic scattering plus electronic noise). In general, the solvent scattering is also subtracted. In our case, it is not known a priori the amount of water bounded to the micelle and the possible variation of this amount with concentration. We have not subtracted therefore the water scattering from Jobs;the subtracted parasitic scattering consisted of the measured intensity without sample multiplied by the sample attenuation. The experimental points for q < 0.06 A-' ( q = scattering vector = 4*/X sin 8) have been abandoned because of the strong influence of parasitic scattering. Analysis Method General Theory. For a system of N independent particles, such that the position of the center of mass is not correlated with the particle size and orientation, the scattered intensity is given by4s7J4 I(q) = N{(lF(4')I2)+ ( F ( 4 ' ) ) 2 [ S ( q-) 111 where F(4) is the scattering amplitude or form factor of one particle, the average is taken over the possible particle orientations, and S ( q ) is the interparticle structure factor
where the ?i are the particle position vectors. Defining A ( q ) = (IF(4)I2)- ( F ( q ' ) ) 2results in l ( q ) = N S ( q ) ( F ( q ) ) 2 + A(q)1 The dcviation A(q) is zero for a monodisperse system of spheres and is very small for spheroidal particles with anisometry u < 1 .5.4.'8 Aq is however significant even for spherical particles if ~~
Itri and Amaral
The Journal of Physical Chemistry, Vol. 95, No. I , 1991
~
~~
there is polydispersity; for systems with small polydispersity ( 0.3 M (Table 11) may be related to the interdependence of P ( q ) and S(q) in the adjustment to I ( q ) . A p ( r ) function for a 2 wt % solution has been obtained from SANS,7 giving D,,, = 43 A. The apparent discrepancy in our
w.
I
01
'
r (AI
(A)
Figure 3. P ( r ) intraparticle distance distribution function. (a) Influence of the background for small r values and influence of micellar interference for large r values. (b) Best function with proper choice of background and cutoff (q < 0.05
0 0
I
00
600
40 0
r
1
t
-
-
427
J. Phys. Chem. 1991,95, 427-431 results is due to the fact that SANS is more sensible to the paraffinic core; this result is compatible with an ellipsoid with a smaller dimension a = R and v I 1.32. We stress that the p(r) !!kction in SAXS studies seems to have been obtained previously only in micellar solutions with addition of salt,2s which is responsible for micellar growth. Micellar growth (eventually preceded by aggregation2) in the system SLS/ (25) Muller, K. Presented at the 10th Discussion Conference on Small angle scattering and related methods, Prague, Czechoslovakia,July 1987;also private communication of unpublished results.
water/salt has also been observed by light scattering.'+2 In binary systems, on the contrary, micelles seem to grow only near the I-Ha transition.13 Acknowledgment. Thanks are due to Dr. Otto Clatter for his computer program, to him and Dr. K. Muller for helpful discussions, and to Dr. J. Mestnik Filho for collaboration in elaboration of software for P(q) calculations. R. Itri has a postgraduate FAPESP fellowship. Registry No. SLS, 151-21-3.
Spectroscopic Characterization of meso-Tetrakis(l-methylpyridinium-4-yl)porphyrins, [(TMpyP)H2I4+ and [(TMPYP)M]~+,in Aqueous Micellar Media, Where M = V02+, Cu(II), and Zn(I1) K. M. Kadish,* B. G. Maiya? and C. Araullo-McAdams Department of Chemistry, University of Houston, Houston, Texas 77204-5641 (Received: January I I , 1990; In Final Form: June 27, 1990)
Spectroscopic characterization of [(TMpyP)H2I4+and [(TMpyP)MI4+,where M = Cu(II), Zn(lI), or V 0 2 + and TMpyP = meso-tetrakis(1-methylpyridinium-4-yl)porphyrin, was carried out in water and in aqueous solutions containing the anionic surfactant sodium dodecyl sulfate (SDS), the cationic surfactant cetyltrimethylammonium bromide (CTAB), or the neutral surfactant Triton X-100 (TX-100). UV-visible, 'H NMR, and ESR spectral data indicate that these tetracationic porphyrins interact with and exist as monomeric entities in the anionic SDS micelle. In contrast, neither the cationic nor the neutral micelle shows an interaction with the investigated porphyrins. Comparisons are made between the data for tetracationic and tetraanionic porphyrins in different micellar media and it is suggested that intercalation of the positively charged porphyrins in SDS is due to Coulombic rather than hydrophobic interactions.
Introduction
Tetraanionic porphyrins of the type [(TPPS)H2]" and [(TPPS)MI4-, where M is V 0 2 + , Cu(II), or Zn(I1) and TPPS is meso-tetrakis( 4-sulfonatophenyl)porphyrin, are micellized and exist as monomers in both cationic (cetyltrimethylammonium bromide, CTAB) and neutral micelles (Triton X-100, TX-1 00) but are present as aggregates in the anionic micelle sodium dodecyl sulfate (SDS).' Tetracationic porphyrins such as [(TMpyP)H2I4+ (where TMpyP = meso-tetrakis( I-methylpyridinium-4-y1)porphyrin) can also exist as monomers or aggregates in both aqueous and micellar ~ n e d i a . ~ -Fluorescence, ~ 'H NMR, and UV-visible spectral data indicate the presence of monomers in SDS solutions, but the results are not self-consistent in aqueous media and have been interpreted in terms of both an aggregated3v4 and nonaggregated2*5free-base complex. Several derivatives of [(TMpyP)H2I4+and [(TMpyP)MI4+ have also been tested as sensitizers for photodynamic therapy in various biological media.68 A comprchensive study of [(TMpyP)H2I4+in different micellar media has never been published nor has there been any published study dealing with the micellar interactions of tetraacationic free-base and metalated water-soluble porphyrins under the same solution conditions. This is done in the present paper, which reports the interactions between SDS, CTAB, or TX-100 and [(TMpyP)H2I4+or [(TMpyP)MI4+,where M = V 0 2 + , Cu(II), or Zn(1l). Structures of the investigated porphyrins are shown in Figure 1. Experimental Section
The instrumentation and spectral methods employed in this study have been described in a previous publication.' 'HN M R 'Present address: School of Chemistry, University of Hyderabad, Hyderabad 5001 34, India.
0022-3654191/2095-0427$02.50/0
TABLE I: UV-Visible Spectral Data for tbe Tetracationic Porphyrins in Aqueous and Micellar Media" A, nm (iO-)c) comdex H,O 0.1 M SDS 0.1 M CTAB 5% TX-100 [(TMpyP)H2I4+ 421 (109) 426 (189) 422 (220) 422 (190)
518 (13.2) 557 (5.2) 586 (5.9) [(TMpyP)ZnI4+ 436 (129) 564 (10.9) 606 (3.6) [(TMpyP)V0l4+ 439 (192) 564 (15.1) 604 (3.4) [(TMpyP)Cu14+ 424 (214) 548 (18.0) 602 (2.0)
519 (13.7) 560 (4.8) 590 (5.2) 444 (137) 568 (12.5) 610 (4.2) 440 (175) 562 (13.5) 607 (3.1) 429 (203) 550 (18.8) 605 (2.0)
518 (14.5) 554 (4.8) 586 (6.3) 436 (138) 563 (11.2) 606 (3.3) 439 (201) 562 (16.1) 602 (3.7) 424 (218) 549 (19.0) 602 (2.0)
"Porphyrin concentrations ranged between 5.0 X
519 (14.0) 556 (4.7) 588 (5.0) 436 (133) 563 (10.6) 606 (2.9) 439 (188) 564 (14.6) 604 (3.8) 424 (196) 548 (17.0) 602 (1.9)
lo-' and 9.0X lo-' M.
chemical shifts are reported with respect to tetramethylsilane (TMS), which was used as an external reference. DPPH ( g = ( I ) Kadish, K. M.; Maiya, G. B.; Araullo, C.; Guilard, R. Inorg. Chem.
__
19119. 28. 2125 . . .-., -, -
(2) Williams, G.N.;Williams, R. F. X.;Lewis, A.; Hambright, P. J. Inorg. Nucl. Chem. 1979, 41, 41. (3) Kano, K.; Miyake, T.; Uomoto, K.; Sato, T.; Ogawa, T.; Hashimoto, S. Chem. Leu. 1983, 1867. (4) Kano, K.; Nakajima, T.; Takei, M.; Hashimoto, S . Bull. Chem. SOC. Jpn. 1987, 60, 1281. (5) Pasternack, R. F.; Huber, P. R.; Boyd, P.; Engasser, G.; Francesconi, L.;Gibbs, E.; Fasella, P.; Venturo, G. C.. Hinds, L. de C. J. Am. Chem. Soc. 1972, 94, 45 1 1. (6) Moan, J.; Peng, Q.; Evensen, J. F.; Berg, K.; Vestern, A,; Rimington, C. Photochem. Phorobiol. 1987, 46, 713.
0 1991 American Chemical Society
