- Email: [email protected]
Effect of modifying polymethacrylic acid covalently bonded to porphyrin on its acid-base properties
1546
V. S. PSHEZHETSKII and A. V. UDALT$OV
14. Kh. SIMIONESCU, S. DUMITRESCU, I. NEGULESCU, V. PERCHEK, M. GRIGORASH, L DIAKONU, M. LYANKE and L. GORASH, Vysokomol. soyed. AI6: 790, 1974 (Translated in Polymer Sci. U.S.S.R. 16: 4, 911, 1974) 15. A. A. BERLIN and M. I. CHERKASHIN, VysokomoL soyed. A13: 2292, 1971 (Translated in Polymer Sci. U.S.S.R. 13: 10, 2581, 1971) 16. S. I. SIMIONESCU and V. PERCEC, Polymer Sci. Polymer Letters 17: 421, 1979 17. Primenenie spcktroskopii v khimii (Use of Spectroscopy in Chemistry). p. 298, Moscow, 1959 18. V. PERCEC, Polymer Bull. 10: 1, 1983
Polymer Science U.S.S.R. Vol. 30, No. 7, pp. 1546.-1S53, 1988 Printed in Poland
0032-3950]88 $10.00+ .00 O 1989 Pergamon Press plc
EFFECT OF MODIFYING POLYMETHACRYLIC ACID COVALENTLY BONDED TO PORPHYRIN ON ITS ACID-BASE PROPERTIES* V. S. PSHEZHETSKII and A. V. UDALT$OV M. V. Lomonosov State University,Moscow (Received 6 February 1987) Tctra(p-aminophcnyl) porphyrin was immobilized on PMAA and PMAA modified with cetylamine (PMAA-cetyl) and the effect of microcnvironment on the acid base proporties of the bound porphyrin was studied. The pK, of porphyrin immobilized on PMAA was increased to 7-9, while PMAA-cetyi was decreased to 0.8 compared with the pK---4 values for tetraphenyl porphyrin. The effects obtained are associated with the effect of the electrostatic field on the macro-ion and the hydrophobic microenvionment of porphyrin in the first and second systems respectively.
OF TH~ various models of t h e primary photosynthesis processes, important results on the stabilization of separated charges have been obtained recently with water soluble porphyrins containing ionogenic groups, and especiallypositivelycharged Zn porphyrins [1-3]. Data are available on the use of polyelectrolytesfor stabilizingseparated charges by interaction with the electrostaticfieldin macro-ions. However, these problems have been inadequately developed in polymer systems [4-6]. It must be expected that the immobilization of porphyrins on polymerization would lead to change in a number of properties of these macrocyclic molecules. In particular, in ionogenic water soluble polymers containing hydrophobic regions a change in the acid-base properties of the porphyrin is possible, as in the change in two-three orders of magnitude of the aliphatic amino groups in aqueous solution when these are immobilized in the hydrophobic regions of polymer molecules [7].
* Vysokomol. soyed. A30: No. 7, 1470-1475, 1988.
Effect of modifying polymethacrylic acid covalently bonded to porphyrin
1547
The o b j e c t o f this w o r k was to e x p l a i n to w h a t extent different p o l y m e r m a c r o e n v i r o n m e n t s affect the p r o t o n a t i o n o f H 2 - t e t r a ( p - a m i n o p h e n y l ) p o r p h y r i n ( H 2 T A P P ) , c o v a l e n t l y b o n d e d to w a t e r soluble polymers. This f o r m u l a t i o n o f the p r o b l e m is possible since p o r p h y r i n b o n d e d to a water soluble p o l y m e r acquires solubility in an a q u e o u s m e d i u m , which allows m o d i f i c a t i o n o f its molecules by ionogenic g r o u p s to be avoided. Chemically pure H2TAPP was used without additional purification. The H2TAPP chemically bonded to polymethacrylic acid ( H z T A P P - P M A A ) was obtained by interaction of porph~,rin with PMAA containing about 1% acid chloride groups [8]. The introduction of cetyl into the H z T A P P - P M A A was obtained by amidation of the carboxyl groups by cetylamine in the presence of dicyclohexylcarbodiimide [9]. To increase the hydrophobic character of the porphyrin, and also to prevent crosslinking of the polymer, the free amino groups of the H2TAPP, immobilized on PMAA were reacted with hexyl bromide, and the polymer was then purified by dialysis, and separated by subsequent lyophilic drying. The porphyrin content of both polymers was determined in 2 × 10 -2 molar triethylamine solution, pH about 1I, and spectrophotometrically from the integral intensity of the Cope band. In the H 2 T A P P - P M A A the molar (calculated on monomer units) H2PAPP : : PMAA ratio was 1 : 1800, as against 1 : 150 in the H2TAPP-PMAA-cetyl. The number of cetyl groups in the H2TAPP-PMAA-cetyl macromolecules was determined from the ratio of the vibration intensities of the amide and carboxyl groups in the IR spectra at 1570 and 1700 cm- t. The number of cetyl groups was 46 % of the monomer units in the P M A A . As judged by viscosity measurements the molecular mass of the HzTAPP-PMAA-cetyl, measured in 0.002 HCI was 9× 10~. The extinction coefficient of dimeric H2TAPP was obtained from analysis of the absorption spectra of a series of solutions with various dimer : monomer ratios in which the interconnection between the extinction coefficient and the Cope band half-width was studied. The value taken for the extinction coefficient of the dimeric porphyrin, as calculated on the monomer, was that value for which, with increase in the quantity of dimer in solution the relative broadening of the Cope band was not accompanied by a change in the extinction coefficient. The absorption spectra were obtained on a "Specord M-40" (East Germany) spectrophotometer. The pH chain was measured with a universal EV-74 pH meter. The p r o t o n a t i o n a n d d e p r o t o n a t i o n o f H 2 T A P P in s o l u t i o n were o b t a i n e d b y consecutive a d d i t i o n o r r e m o v a l o f p r o t o n s f r o m the central nitrogen a t o m s o f the p o r p h y r i n ring. T h e e q u i l i b r i u m o f these r e a c t i o n s was studied by s p e c t r o p h o t o m e t r i c titration o f two specimens CH3 CHa CH3 CH~ CH3
!
I
~ C H 2 - - C - - ( - - C H 2 - - ' C - - ) ~soo--
f
C~O
I
f
C~O
I
H~TAPP OH H2TAPP--PMAA
,I
I
I
- - C H ~ - - C ' - - - ( ~ C H 2 - - C ~ ) 1s o - - ( - - C H 2 - - C ~ ) 1ao ~
J
C~O
t
H2TAPP(C6HIa) H~TAPP--PMAA-cetyl
J
C---~O
8
OH
I
C---~O
I
H~N--CI6H33
O n t i t r a t i o n o f an a q u e o u s H 2 T A P P - P M A A solution in the acid r e g i o n with K O H solution, a decrease in intensity o f the a b s o r p t i o n b a n d with 2ma~=445 a n d 654 n m is observed. S i m u l t a n e o u s l y , the intensity o f the b a n d with 2ma~=420 n m (Fig. 1) increases. T h e spectral changes a r e a c c o m p a n i e d b y the a p p e a r a n c e o f f o u r isobestic p o i n t s at wavelengths o f 426, 464, 579, a n d 698 nm, i n d i c a t i n g t h a t with increase in p H a change in c o n c e n t r a t i o n o f t w o types o f a b s o r p t i o n centres takes place in the system, these centres being p r o t o n a t e d a n d d e p r o t o n a t e d forms o f H 2 T A P P . T h e s p e c t r u m o f
1548
V. S. PSHSZH~TSX.tt and A. V. UDALTSOV
deprotonated porphyrin corresponds to that of the monomer in characteristics. Using an effective extinction coefficient of the protonated form of porphyrin (eaf=0"44"x l0 s 1./mole.era) at 2=654 nm, which was determined at a pH of 3, where the porphyrin is completely protonated, since the pH increases do not result in a change in the spectrum, a relation was obtained for the concentration of the portonated form of porphyrin
t o.i 0.8-
-
,I 28
I 20
I
1. 12 ~. • l O-~ crn" t
FIo. 1. Spectral changes in HzTAPP, bonded to PMAA, for various aqueous solution pH values. The arrows denote the direction of change o f increase from 7.2 to 10.84.
as a function of pH (Fig. 2). The presence of two S-like transitions on the curve provides a basis for establishing the two equilibrium constants, which were determined at points where the degree of dissociation ~ of the titration system is equal to 0.5, using the Henderson-Hasselbach equation pK= pH + log
1--t2
(1)
The values found for the constants pKt and pK2 were 5"6 and 7"9 respectively. As can be seen from Fig. 2, at low pH values only 8 ~ of the porphyrin molecules are titrated. The deprotonation of these molecules takes place over the pH range 4.5-7.5, i.e. where 10--22 ~ of the PMAA is titrated (Fig. 2, curve 2). This is the pH region where a conformational transition is produced in the PMAA. The macromolecules of the secodnary conformation chains stabilized by hydrogen bonds and hydrophobic interactions change into the conformation of loose asymmetric negatively charged coils. The remaining part of the prophyrin titrated is already in the field of a negatively charged polyanion. As a result, the pK, for dissociation of the protonated porphyrin is increased by more than
Effect of modifying polymethacrylic acid covalently bonded to porphyrin
1549
C, mole ",~
I00
o¢
50
0.5
I-0 4
6
8
tO pH
FIG. 2. Number of ionized porphyrin moleeule~ e (I) and degree of ionization = of the PMAA (2) •as a function of solution pH. two pH units, to pH 7.9, so that to introduce a proton from the coil it is necessary to overcome the electrostatic field of the charged macromolecule. It is important to note that the pKa increase observed, which results from electrostatic interaction in the polyion is significantly larger than for the negatively charged porphyrin (Table). The lowest pK value corresponds to a tetrasulphur porphyrin derivative, and is close to the pK value of porphyrin in PMAA having, 10-22 ~ charged carboxyl groups. This result indicates that in the polymer the carboxylate anions are bonded more strongly to the porphyrin protons than the anions in the H2TPP(SO3)~molecule, in which the charges are located on the molecule periphery at distances of 7-9 A from its centre, where the positive charges are localized. The even higher pK value of H2TCPP- is evidently not associated with the effect of the carboxylate anion, but with the fact that the porphyrins are located in dodecyl sulphate micelles, the total negative charge of which is Considerable. However, in this case also the effect of the pK increase is not as marked as in the PMAA macromolecules, where there is a good possibility of local approach of the porphyrin molecules to the carboxyl anions. The absorption spectrum of porphyrin bonded to the polymer containing 40 ~ cetyl groups indicates the presence in the system of both monomer and dimer porphyrins. On acidifying an aqueous solution of H2TAPP-PMAA-cetyl with HC1 solution a decrease in intensity of the Cope band at 2==z= 427 nm is observed, and a simultaneous increase in intensity of the adsorption band of 2re=z=715 nm (Fig. 3). The presence of isobestic points at 2=442, 515, and 581 nm and the nature of the change in absorption indicate that as porphyrin is protonated a change occurs in the concentration of the two absorption centres, i.e. the ratio between the monomers and dimers on protonation of porphyrin is not disturbed. The effective extinction coefficient of protonated porphyrin (8af=0-45= l0 s 1./mole.cm) was determined by using data on absorption at 715 nm and the overall concentration of porphyrin particles (monomeric and dimeric). Figure 4a shows the relation between the concentration of protonated porphyrin and pH in the PMAA-cetyl macromolecule.
t350
V. S. PSI~ZHE'rsKII and A. V. UDALTSOV
D
O
1"2
0"2
0"8
0.1
0.#
I
20
76
I
l
I
I
28
2#
20
76
I
12 A ~ lO'~acrn"f
I
12 A, !0 -3,crn"
Fie. 3. Spectra changes in H2TAPP bonded to macromolecular PMAA-cetyl at different solution pH value. The arrows show the direction of pH drop from 11"7to 0.06.
Determination of the number of protons taking place in the acid-base equilibrium provided a means of establishing the nature of the protonated porphyrin, using an expression for the overall dissociation constant of the charged porphyrin, i.e.
[H+]" [HzTAPP] K,- [H.+zTAPI~+] On taking logarithms the expression obtained is log [H2TAPP] : [H. + 2TAPP" +J = log K . - n log [H +]
(2)
If the region of the titration curve corresponding to the transition from unprotonated porphyrin to protonated porphyrin is constructed in the coordinates of (2), assuming a linear relation it is possible to determine the total number of protons n taking part in the equilibrium. The value of n determined from the linear relations (Fig. 4b) is equal to 2. Consequently, the protonation of porphyrin on PMAA-cetyl takes place at two nitrogen atoms. In alkaline media ( p H ~ 11), when the PMAA-cetyl macromolecules are charged, their dimensions, as judged from quasi-elas• light scattering are 700 A at zero ionic strength and 600 A in 0,05 M KCI solution. Since in aqueous medium the cetyl groups, about 250 of which on average are present in the macromolecule, form
Effect of modifying polymethacrylic acid covalently bonded to porphyrin
1551
t~ 7P 0"3
C, mole
t7
I00
2
03
50
I
2
j
I_
,
O'B
I
#
I
8
o.6
l
I
~.o pH
FIO. 4. Number of ionized porphyrin molecules c as a function of solution pH (a) and log/~ as a function of the pH of the aqueous H2TAPP-PMAA-cctyl solution (b): / - a q u e o u s H 2 T A P P PMAA solution; 2 - a q u e o u s dimethylforraamid¢ ( 1 : 1 ) solution of H2TAPP-PMAA-cctyl; b - fl-[H2TAPP] : [H, + 2TAPP n+ ].
h y d r o p h o b i c r e g i o n s consisting o f s o m e tens o f cetyl groups, o n average the m a c r o m o l e c u l e c o n t a i n s t w o - f o u r h y d r o p h o b i c regions. I t c a n b e a s s u m e d t h a t m o n o m e r i c a n d d i m e r i c H 2 T A P P molecules are localized in these regions b e c a u s e o f the high degree o f h y d r o p h o b i c c h a r a c t e r o f the p o r p h y r i n itself, a n d even m o r e so o f p o r p h y r i n a l k y l a t e d at the free a m i n o g r o u p s b y hexyl b r o m i d e .
E F F E C T OF C H A N G E O N THE
Porphyrin H2TPP H2TCPPH2TPP(SOs),~H 2 T A P P - PMAA°'2H2TAPP - - PMAA °"s H2TMaAPp* + H2TMPP(3) 4 + H2TAPP - PMAA-cetyl
pK
OF SUBSTITUTED P O R P H Y R I N S
PK3 4* 6-1t 4"9
i ] l I
pKa., -_
5-6
--
i
3"6 2.0 --
i I
7"9
0.83
Literature [10] [11] [11] Given work ditto [12] [lll Given work
* The basicity parameters pKa for the m o n o - c a t i o n / f r ~ base equilibrium in benzene; t and in aqueous 2.5 ~ N a docecylsulphate solution. Note. The parameter p/t'3,4, characterizes t h e d i c a t i o n / f r ~ base equilibrium; H 2 T P P denotes tetraphenylporphyrin, H 2 T C F P tetracarboxypheaylporphyrin, H 2 T P P ( S O 3 ) I - - - tetra(4-sulphonatopheuyl)porphyrin, H 2 T M a A P I ~ + ~ tetra(N,N,N-trimcthylamino-4-ph(myl)porph~in, H2TMPP(3) 4 + - terraiN-methyl3 -pyridine)porphyria.
T h e a c i d - b a s e e q u i l i b r i u m c o n s t a n t for H 2 T A P P l o c a t e d in t h e h y d r o p h o b i c r e g i o n m u s t d e p e n d o n t w o factors, i.e. the degree o f h y d r o p h o b i c c h a r a c t e r o f the m i c r o e n v i r o n m e n t a n d t h e p r e s e n c e o f a c h a r g e on the p o r p h y r i n itself o r in its closest e n v i r o n m e n t .
1552
V. S. PSHi3ZHBTSKIIand A. V. UDALT$OV
As shown in the Table the porphyrins carrying four positive charges have pKa values in aqueous solution lower than those of uncharged H2TAPP in benzene, which indicates the significant electrostatic effect of the positive charge on the pKa value of porphyrin. The effect of charge on the pKa of porphyrin is even greater with pyridine containing molecules, where the positive charge is delocalizcd with respect to the macrocyclic molecule conjugation system. The protonation of H2TAPP in the polymer starts in the pH region 2.5 and finishes at pH 0.2 (Fig. 4a). The value of the equilibrium constant corresponding to this pH region [according to (1)] is equal to 0.83. This must be associated both with the hydrophobic character of the porphyrin microenvironment in the polymer and the presence in its molecule of identical charges, i.e. with both factors which lower the porphyrin basicity. The hydrophobic character is determined by the cetyl groups on the polymer, and the charges on the porphyrin arise on protonation of its three alkylated amino groups. Hydrophobic interactions in H2TAPP-PMAA-cetyl can be weakened by addition to the system of an organic solvent mixed with water, which should result in an increase in hydration of the porphyrin and a corresponding increase in the pKa. Figure 4a shows a curve for the titration of porphyrin bonded to PMAA-cetyl in an H20 : DMFA-1 : 1 mixture. Under these conditions the pK, of H2TAPP is increased to 4-65, i.e. it has an intermediate value between the cases under consideration. Accordingly, it must be concluded that in polymer systems a porphyrin molecule microenvironment can be realized which changes the pK~ values of the molecules by seven units. By varying the microenvironment it is possible to change the porphyrin basicity over wide limits. A change in the acid-base properties of porphyrin the polymer microenvironment is manifested to a much greater extent than with low molecular weight systems. The authors wish to thank V. A. Kabanov for useful notes made during discussion of this work. Translated by N. STANDI~N JREFERENCES
1. M. S. RICHOUX and A. HARRIMAN,J. Chem. Soc. Faraday Trans. I 78: 1873, 1982 2. A. HARRIMAN, G. PORTER and M. S. RICHOUX, J. Chem. Soc. Faraday Trans. II 77: 833, 1981 3. G. BLONDEEL, A. HARRIMAN,G. PORTER and A. WILOWSKA,J. Chem. Soc. Faraday Trans. II 80: 867, 1984 4. J. W. OTVOS, T. Ye. CASTI and M. CALVIN, Sci. Papers Inst. Phys. and Chem. Research 78: 129, 1984 5. D. MEYERSTEIN, J. RADANI, M. S. MATHESON and D. MEISEL, J. Phys. Chem. 28: 1979, 1978 6. M. NANGO, T. DANNHAUSER, D. HUANG, K. SPEARS, L. MORRISON and P. A. LEACH, Macromolecules17: 1898, 1984 7. V. S. PSHEZHETSKH and A. P. LUKYANOVA,Bioorg. khim. 2:110, 1976 8. I. G. RISE[, G. V. PONOMAREV, L M. B ~ V S K I I , K. A. ASKAROV and V. S. PSHEZHETSKII, IV Vsesoyuz. konf. po khimii i primeneniyu porfirinov (Fourth All-Union Conference on the Chemistryand Applications of Porphyrins), Erevan, 1984
Products of hydrolytic cocondensation of (organochlorosilyl)ODMS
1553
9. L. FIZER and M. FIZER, Reagenty dlya organicheskogo sinteza (Reagents for Organic Synthesis) vol. 1, Moscow, 1970 10. A. HARRIMAN and M. S. RICHOUX, J. Photochem. 27: 205, 1984 11. C. N. WILLIAMS and P. HAMBRIGHT, Inorgan. Chem. 17: 2687, 1978 12. A. SHAMIN and P. HAMBRIGHT, Inorgan. Chem. 19: 564, 1980
0032-3950/88$10.00+.00
PolymerScienceU.S.S.R. Vol.30, No. 7, pp. 1553-1559,1988 Printed in Poland
1989 Pergamon Press plc
A STUDY OF THE PRODUCTS OF HYDROLYTIC COCONDENSATION OF (ORGANOCHLOROSILYL)OLIGODIMETHYL SILOXANE AND PHENYLTRICHLOROSILANE* T. A. LARINA, I. I. TVERDOKHLEBOVA, S.-S. A. PAVLOVA, A. Yu. RABKINA, T. V. STRELKOVA, B. G. ZAVIN, A. A. ZHDANOV, V. A. TSYRYAPKIN and S. O. PUPYNINA A. N. Nesmeyanov Institute of Element-Organic Compounds, U.S.S.R. Academy of Sciences
(Received 16 February 1987) The products of the hydrolytic cocondensation of a tetrafunctional oligodimethyl siloxane and phenyltrichlorosilane are studied. Depending on the synthesis conditions, the block polymers obtained have multimodal, bimodal, or monomodal distributions. The block copolymer fractions are heterogeneous in composition. The constants of the Mark-KuhnHouwink equation are determined for benzene solution at 20°C.
THE object of this work was to study block copolymers obtained by hydrolytic cocondensation of linear tetrafunctional (organochlorosilane) oligodimethylsiloxane with phenyltrichlorosilane. The macromolecules of such polymers are formed by alternating
linear oligodimethylsiloxane (ODMS)- l - S i - O - | C6Hs
~
~
I
and oligophenylsilsesquioxane
/
l ~ ~, CH3 /" 1 (OPSSO)- - Si - Ox.5 - / m blocks. This combination of different blocks having equ'librium flexibility [1] and a high degree of rigidity [2], should result in the formation of * Vysokomol. soyed. A30: No. 7, 1476-1480, 1988.
V. S. PSHEZHETSKII and A. V. UDALT$OV
14. Kh. SIMIONESCU, S. DUMITRESCU, I. NEGULESCU, V. PERCHEK, M. GRIGORASH, L DIAKONU, M. LYANKE and L. GORASH, Vysokomol. soyed. AI6: 790, 1974 (Translated in Polymer Sci. U.S.S.R. 16: 4, 911, 1974) 15. A. A. BERLIN and M. I. CHERKASHIN, VysokomoL soyed. A13: 2292, 1971 (Translated in Polymer Sci. U.S.S.R. 13: 10, 2581, 1971) 16. S. I. SIMIONESCU and V. PERCEC, Polymer Sci. Polymer Letters 17: 421, 1979 17. Primenenie spcktroskopii v khimii (Use of Spectroscopy in Chemistry). p. 298, Moscow, 1959 18. V. PERCEC, Polymer Bull. 10: 1, 1983
Polymer Science U.S.S.R. Vol. 30, No. 7, pp. 1546.-1S53, 1988 Printed in Poland
0032-3950]88 $10.00+ .00 O 1989 Pergamon Press plc
EFFECT OF MODIFYING POLYMETHACRYLIC ACID COVALENTLY BONDED TO PORPHYRIN ON ITS ACID-BASE PROPERTIES* V. S. PSHEZHETSKII and A. V. UDALT$OV M. V. Lomonosov State University,Moscow (Received 6 February 1987) Tctra(p-aminophcnyl) porphyrin was immobilized on PMAA and PMAA modified with cetylamine (PMAA-cetyl) and the effect of microcnvironment on the acid base proporties of the bound porphyrin was studied. The pK, of porphyrin immobilized on PMAA was increased to 7-9, while PMAA-cetyi was decreased to 0.8 compared with the pK---4 values for tetraphenyl porphyrin. The effects obtained are associated with the effect of the electrostatic field on the macro-ion and the hydrophobic microenvionment of porphyrin in the first and second systems respectively.
OF TH~ various models of t h e primary photosynthesis processes, important results on the stabilization of separated charges have been obtained recently with water soluble porphyrins containing ionogenic groups, and especiallypositivelycharged Zn porphyrins [1-3]. Data are available on the use of polyelectrolytesfor stabilizingseparated charges by interaction with the electrostaticfieldin macro-ions. However, these problems have been inadequately developed in polymer systems [4-6]. It must be expected that the immobilization of porphyrins on polymerization would lead to change in a number of properties of these macrocyclic molecules. In particular, in ionogenic water soluble polymers containing hydrophobic regions a change in the acid-base properties of the porphyrin is possible, as in the change in two-three orders of magnitude of the aliphatic amino groups in aqueous solution when these are immobilized in the hydrophobic regions of polymer molecules [7].
* Vysokomol. soyed. A30: No. 7, 1470-1475, 1988.
Effect of modifying polymethacrylic acid covalently bonded to porphyrin
1547
The o b j e c t o f this w o r k was to e x p l a i n to w h a t extent different p o l y m e r m a c r o e n v i r o n m e n t s affect the p r o t o n a t i o n o f H 2 - t e t r a ( p - a m i n o p h e n y l ) p o r p h y r i n ( H 2 T A P P ) , c o v a l e n t l y b o n d e d to w a t e r soluble polymers. This f o r m u l a t i o n o f the p r o b l e m is possible since p o r p h y r i n b o n d e d to a water soluble p o l y m e r acquires solubility in an a q u e o u s m e d i u m , which allows m o d i f i c a t i o n o f its molecules by ionogenic g r o u p s to be avoided. Chemically pure H2TAPP was used without additional purification. The H2TAPP chemically bonded to polymethacrylic acid ( H z T A P P - P M A A ) was obtained by interaction of porph~,rin with PMAA containing about 1% acid chloride groups [8]. The introduction of cetyl into the H z T A P P - P M A A was obtained by amidation of the carboxyl groups by cetylamine in the presence of dicyclohexylcarbodiimide [9]. To increase the hydrophobic character of the porphyrin, and also to prevent crosslinking of the polymer, the free amino groups of the H2TAPP, immobilized on PMAA were reacted with hexyl bromide, and the polymer was then purified by dialysis, and separated by subsequent lyophilic drying. The porphyrin content of both polymers was determined in 2 × 10 -2 molar triethylamine solution, pH about 1I, and spectrophotometrically from the integral intensity of the Cope band. In the H 2 T A P P - P M A A the molar (calculated on monomer units) H2PAPP : : PMAA ratio was 1 : 1800, as against 1 : 150 in the H2TAPP-PMAA-cetyl. The number of cetyl groups in the H2TAPP-PMAA-cetyl macromolecules was determined from the ratio of the vibration intensities of the amide and carboxyl groups in the IR spectra at 1570 and 1700 cm- t. The number of cetyl groups was 46 % of the monomer units in the P M A A . As judged by viscosity measurements the molecular mass of the HzTAPP-PMAA-cetyl, measured in 0.002 HCI was 9× 10~. The extinction coefficient of dimeric H2TAPP was obtained from analysis of the absorption spectra of a series of solutions with various dimer : monomer ratios in which the interconnection between the extinction coefficient and the Cope band half-width was studied. The value taken for the extinction coefficient of the dimeric porphyrin, as calculated on the monomer, was that value for which, with increase in the quantity of dimer in solution the relative broadening of the Cope band was not accompanied by a change in the extinction coefficient. The absorption spectra were obtained on a "Specord M-40" (East Germany) spectrophotometer. The pH chain was measured with a universal EV-74 pH meter. The p r o t o n a t i o n a n d d e p r o t o n a t i o n o f H 2 T A P P in s o l u t i o n were o b t a i n e d b y consecutive a d d i t i o n o r r e m o v a l o f p r o t o n s f r o m the central nitrogen a t o m s o f the p o r p h y r i n ring. T h e e q u i l i b r i u m o f these r e a c t i o n s was studied by s p e c t r o p h o t o m e t r i c titration o f two specimens CH3 CHa CH3 CH~ CH3
!
I
~ C H 2 - - C - - ( - - C H 2 - - ' C - - ) ~soo--
f
C~O
I
f
C~O
I
H~TAPP OH H2TAPP--PMAA
,I
I
I
- - C H ~ - - C ' - - - ( ~ C H 2 - - C ~ ) 1s o - - ( - - C H 2 - - C ~ ) 1ao ~
J
C~O
t
H2TAPP(C6HIa) H~TAPP--PMAA-cetyl
J
C---~O
8
OH
I
C---~O
I
H~N--CI6H33
O n t i t r a t i o n o f an a q u e o u s H 2 T A P P - P M A A solution in the acid r e g i o n with K O H solution, a decrease in intensity o f the a b s o r p t i o n b a n d with 2ma~=445 a n d 654 n m is observed. S i m u l t a n e o u s l y , the intensity o f the b a n d with 2ma~=420 n m (Fig. 1) increases. T h e spectral changes a r e a c c o m p a n i e d b y the a p p e a r a n c e o f f o u r isobestic p o i n t s at wavelengths o f 426, 464, 579, a n d 698 nm, i n d i c a t i n g t h a t with increase in p H a change in c o n c e n t r a t i o n o f t w o types o f a b s o r p t i o n centres takes place in the system, these centres being p r o t o n a t e d a n d d e p r o t o n a t e d forms o f H 2 T A P P . T h e s p e c t r u m o f
1548
V. S. PSHSZH~TSX.tt and A. V. UDALTSOV
deprotonated porphyrin corresponds to that of the monomer in characteristics. Using an effective extinction coefficient of the protonated form of porphyrin (eaf=0"44"x l0 s 1./mole.era) at 2=654 nm, which was determined at a pH of 3, where the porphyrin is completely protonated, since the pH increases do not result in a change in the spectrum, a relation was obtained for the concentration of the portonated form of porphyrin
t o.i 0.8-
-
,I 28
I 20
I
1. 12 ~. • l O-~ crn" t
FIo. 1. Spectral changes in HzTAPP, bonded to PMAA, for various aqueous solution pH values. The arrows denote the direction of change o f increase from 7.2 to 10.84.
as a function of pH (Fig. 2). The presence of two S-like transitions on the curve provides a basis for establishing the two equilibrium constants, which were determined at points where the degree of dissociation ~ of the titration system is equal to 0.5, using the Henderson-Hasselbach equation pK= pH + log
1--t2
(1)
The values found for the constants pKt and pK2 were 5"6 and 7"9 respectively. As can be seen from Fig. 2, at low pH values only 8 ~ of the porphyrin molecules are titrated. The deprotonation of these molecules takes place over the pH range 4.5-7.5, i.e. where 10--22 ~ of the PMAA is titrated (Fig. 2, curve 2). This is the pH region where a conformational transition is produced in the PMAA. The macromolecules of the secodnary conformation chains stabilized by hydrogen bonds and hydrophobic interactions change into the conformation of loose asymmetric negatively charged coils. The remaining part of the prophyrin titrated is already in the field of a negatively charged polyanion. As a result, the pK, for dissociation of the protonated porphyrin is increased by more than
Effect of modifying polymethacrylic acid covalently bonded to porphyrin
1549
C, mole ",~
I00
o¢
50
0.5
I-0 4
6
8
tO pH
FIG. 2. Number of ionized porphyrin moleeule~ e (I) and degree of ionization = of the PMAA (2) •as a function of solution pH. two pH units, to pH 7.9, so that to introduce a proton from the coil it is necessary to overcome the electrostatic field of the charged macromolecule. It is important to note that the pKa increase observed, which results from electrostatic interaction in the polyion is significantly larger than for the negatively charged porphyrin (Table). The lowest pK value corresponds to a tetrasulphur porphyrin derivative, and is close to the pK value of porphyrin in PMAA having, 10-22 ~ charged carboxyl groups. This result indicates that in the polymer the carboxylate anions are bonded more strongly to the porphyrin protons than the anions in the H2TPP(SO3)~molecule, in which the charges are located on the molecule periphery at distances of 7-9 A from its centre, where the positive charges are localized. The even higher pK value of H2TCPP- is evidently not associated with the effect of the carboxylate anion, but with the fact that the porphyrins are located in dodecyl sulphate micelles, the total negative charge of which is Considerable. However, in this case also the effect of the pK increase is not as marked as in the PMAA macromolecules, where there is a good possibility of local approach of the porphyrin molecules to the carboxyl anions. The absorption spectrum of porphyrin bonded to the polymer containing 40 ~ cetyl groups indicates the presence in the system of both monomer and dimer porphyrins. On acidifying an aqueous solution of H2TAPP-PMAA-cetyl with HC1 solution a decrease in intensity of the Cope band at 2==z= 427 nm is observed, and a simultaneous increase in intensity of the adsorption band of 2re=z=715 nm (Fig. 3). The presence of isobestic points at 2=442, 515, and 581 nm and the nature of the change in absorption indicate that as porphyrin is protonated a change occurs in the concentration of the two absorption centres, i.e. the ratio between the monomers and dimers on protonation of porphyrin is not disturbed. The effective extinction coefficient of protonated porphyrin (8af=0-45= l0 s 1./mole.cm) was determined by using data on absorption at 715 nm and the overall concentration of porphyrin particles (monomeric and dimeric). Figure 4a shows the relation between the concentration of protonated porphyrin and pH in the PMAA-cetyl macromolecule.
t350
V. S. PSI~ZHE'rsKII and A. V. UDALTSOV
D
O
1"2
0"2
0"8
0.1
0.#
I
20
76
I
l
I
I
28
2#
20
76
I
12 A ~ lO'~acrn"f
I
12 A, !0 -3,crn"
Fie. 3. Spectra changes in H2TAPP bonded to macromolecular PMAA-cetyl at different solution pH value. The arrows show the direction of pH drop from 11"7to 0.06.
Determination of the number of protons taking place in the acid-base equilibrium provided a means of establishing the nature of the protonated porphyrin, using an expression for the overall dissociation constant of the charged porphyrin, i.e.
[H+]" [HzTAPP] K,- [H.+zTAPI~+] On taking logarithms the expression obtained is log [H2TAPP] : [H. + 2TAPP" +J = log K . - n log [H +]
(2)
If the region of the titration curve corresponding to the transition from unprotonated porphyrin to protonated porphyrin is constructed in the coordinates of (2), assuming a linear relation it is possible to determine the total number of protons n taking part in the equilibrium. The value of n determined from the linear relations (Fig. 4b) is equal to 2. Consequently, the protonation of porphyrin on PMAA-cetyl takes place at two nitrogen atoms. In alkaline media ( p H ~ 11), when the PMAA-cetyl macromolecules are charged, their dimensions, as judged from quasi-elas• light scattering are 700 A at zero ionic strength and 600 A in 0,05 M KCI solution. Since in aqueous medium the cetyl groups, about 250 of which on average are present in the macromolecule, form
Effect of modifying polymethacrylic acid covalently bonded to porphyrin
1551
t~ 7P 0"3
C, mole
t7
I00
2
03
50
I
2
j
I_
,
O'B
I
#
I
8
o.6
l
I
~.o pH
FIO. 4. Number of ionized porphyrin molecules c as a function of solution pH (a) and log/~ as a function of the pH of the aqueous H2TAPP-PMAA-cctyl solution (b): / - a q u e o u s H 2 T A P P PMAA solution; 2 - a q u e o u s dimethylforraamid¢ ( 1 : 1 ) solution of H2TAPP-PMAA-cctyl; b - fl-[H2TAPP] : [H, + 2TAPP n+ ].
h y d r o p h o b i c r e g i o n s consisting o f s o m e tens o f cetyl groups, o n average the m a c r o m o l e c u l e c o n t a i n s t w o - f o u r h y d r o p h o b i c regions. I t c a n b e a s s u m e d t h a t m o n o m e r i c a n d d i m e r i c H 2 T A P P molecules are localized in these regions b e c a u s e o f the high degree o f h y d r o p h o b i c c h a r a c t e r o f the p o r p h y r i n itself, a n d even m o r e so o f p o r p h y r i n a l k y l a t e d at the free a m i n o g r o u p s b y hexyl b r o m i d e .
E F F E C T OF C H A N G E O N THE
Porphyrin H2TPP H2TCPPH2TPP(SOs),~H 2 T A P P - PMAA°'2H2TAPP - - PMAA °"s H2TMaAPp* + H2TMPP(3) 4 + H2TAPP - PMAA-cetyl
pK
OF SUBSTITUTED P O R P H Y R I N S
PK3 4* 6-1t 4"9
i ] l I
pKa., -_
5-6
--
i
3"6 2.0 --
i I
7"9
0.83
Literature [10] [11] [11] Given work ditto [12] [lll Given work
* The basicity parameters pKa for the m o n o - c a t i o n / f r ~ base equilibrium in benzene; t and in aqueous 2.5 ~ N a docecylsulphate solution. Note. The parameter p/t'3,4, characterizes t h e d i c a t i o n / f r ~ base equilibrium; H 2 T P P denotes tetraphenylporphyrin, H 2 T C F P tetracarboxypheaylporphyrin, H 2 T P P ( S O 3 ) I - - - tetra(4-sulphonatopheuyl)porphyrin, H 2 T M a A P I ~ + ~ tetra(N,N,N-trimcthylamino-4-ph(myl)porph~in, H2TMPP(3) 4 + - terraiN-methyl3 -pyridine)porphyria.
T h e a c i d - b a s e e q u i l i b r i u m c o n s t a n t for H 2 T A P P l o c a t e d in t h e h y d r o p h o b i c r e g i o n m u s t d e p e n d o n t w o factors, i.e. the degree o f h y d r o p h o b i c c h a r a c t e r o f the m i c r o e n v i r o n m e n t a n d t h e p r e s e n c e o f a c h a r g e on the p o r p h y r i n itself o r in its closest e n v i r o n m e n t .
1552
V. S. PSHi3ZHBTSKIIand A. V. UDALT$OV
As shown in the Table the porphyrins carrying four positive charges have pKa values in aqueous solution lower than those of uncharged H2TAPP in benzene, which indicates the significant electrostatic effect of the positive charge on the pKa value of porphyrin. The effect of charge on the pKa of porphyrin is even greater with pyridine containing molecules, where the positive charge is delocalizcd with respect to the macrocyclic molecule conjugation system. The protonation of H2TAPP in the polymer starts in the pH region 2.5 and finishes at pH 0.2 (Fig. 4a). The value of the equilibrium constant corresponding to this pH region [according to (1)] is equal to 0.83. This must be associated both with the hydrophobic character of the porphyrin microenvironment in the polymer and the presence in its molecule of identical charges, i.e. with both factors which lower the porphyrin basicity. The hydrophobic character is determined by the cetyl groups on the polymer, and the charges on the porphyrin arise on protonation of its three alkylated amino groups. Hydrophobic interactions in H2TAPP-PMAA-cetyl can be weakened by addition to the system of an organic solvent mixed with water, which should result in an increase in hydration of the porphyrin and a corresponding increase in the pKa. Figure 4a shows a curve for the titration of porphyrin bonded to PMAA-cetyl in an H20 : DMFA-1 : 1 mixture. Under these conditions the pK, of H2TAPP is increased to 4-65, i.e. it has an intermediate value between the cases under consideration. Accordingly, it must be concluded that in polymer systems a porphyrin molecule microenvironment can be realized which changes the pK~ values of the molecules by seven units. By varying the microenvironment it is possible to change the porphyrin basicity over wide limits. A change in the acid-base properties of porphyrin the polymer microenvironment is manifested to a much greater extent than with low molecular weight systems. The authors wish to thank V. A. Kabanov for useful notes made during discussion of this work. Translated by N. STANDI~N JREFERENCES
1. M. S. RICHOUX and A. HARRIMAN,J. Chem. Soc. Faraday Trans. I 78: 1873, 1982 2. A. HARRIMAN, G. PORTER and M. S. RICHOUX, J. Chem. Soc. Faraday Trans. II 77: 833, 1981 3. G. BLONDEEL, A. HARRIMAN,G. PORTER and A. WILOWSKA,J. Chem. Soc. Faraday Trans. II 80: 867, 1984 4. J. W. OTVOS, T. Ye. CASTI and M. CALVIN, Sci. Papers Inst. Phys. and Chem. Research 78: 129, 1984 5. D. MEYERSTEIN, J. RADANI, M. S. MATHESON and D. MEISEL, J. Phys. Chem. 28: 1979, 1978 6. M. NANGO, T. DANNHAUSER, D. HUANG, K. SPEARS, L. MORRISON and P. A. LEACH, Macromolecules17: 1898, 1984 7. V. S. PSHEZHETSKH and A. P. LUKYANOVA,Bioorg. khim. 2:110, 1976 8. I. G. RISE[, G. V. PONOMAREV, L M. B ~ V S K I I , K. A. ASKAROV and V. S. PSHEZHETSKII, IV Vsesoyuz. konf. po khimii i primeneniyu porfirinov (Fourth All-Union Conference on the Chemistryand Applications of Porphyrins), Erevan, 1984
Products of hydrolytic cocondensation of (organochlorosilyl)ODMS
1553
9. L. FIZER and M. FIZER, Reagenty dlya organicheskogo sinteza (Reagents for Organic Synthesis) vol. 1, Moscow, 1970 10. A. HARRIMAN and M. S. RICHOUX, J. Photochem. 27: 205, 1984 11. C. N. WILLIAMS and P. HAMBRIGHT, Inorgan. Chem. 17: 2687, 1978 12. A. SHAMIN and P. HAMBRIGHT, Inorgan. Chem. 19: 564, 1980
0032-3950/88$10.00+.00
PolymerScienceU.S.S.R. Vol.30, No. 7, pp. 1553-1559,1988 Printed in Poland
1989 Pergamon Press plc
A STUDY OF THE PRODUCTS OF HYDROLYTIC COCONDENSATION OF (ORGANOCHLOROSILYL)OLIGODIMETHYL SILOXANE AND PHENYLTRICHLOROSILANE* T. A. LARINA, I. I. TVERDOKHLEBOVA, S.-S. A. PAVLOVA, A. Yu. RABKINA, T. V. STRELKOVA, B. G. ZAVIN, A. A. ZHDANOV, V. A. TSYRYAPKIN and S. O. PUPYNINA A. N. Nesmeyanov Institute of Element-Organic Compounds, U.S.S.R. Academy of Sciences
(Received 16 February 1987) The products of the hydrolytic cocondensation of a tetrafunctional oligodimethyl siloxane and phenyltrichlorosilane are studied. Depending on the synthesis conditions, the block polymers obtained have multimodal, bimodal, or monomodal distributions. The block copolymer fractions are heterogeneous in composition. The constants of the Mark-KuhnHouwink equation are determined for benzene solution at 20°C.
THE object of this work was to study block copolymers obtained by hydrolytic cocondensation of linear tetrafunctional (organochlorosilane) oligodimethylsiloxane with phenyltrichlorosilane. The macromolecules of such polymers are formed by alternating
linear oligodimethylsiloxane (ODMS)- l - S i - O - | C6Hs
~
~
I
and oligophenylsilsesquioxane
/
l ~ ~, CH3 /" 1 (OPSSO)- - Si - Ox.5 - / m blocks. This combination of different blocks having equ'librium flexibility [1] and a high degree of rigidity [2], should result in the formation of * Vysokomol. soyed. A30: No. 7, 1476-1480, 1988.