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The synthesis of styrene chiral copolymers with aminoacid maleimides and the effect of the aminoacid radicals on macromolecular structure
0032-3950/79/0301-0636507.50/0
~ P o l y m e r Science U.S.S.R. Vol. 21, pp. 636-644. ¢~) P e r g a m o n Press Ltd. 1979. Printed in P o l a n d
TH~ SYNTHESIS OF S T Y R E N E CHIRAL COPOLYMERS W I T H AlVIINOACID M A L E I M I D E S A N D T H E E F F E C T OF T H E AMINOACID R A D I C A L S ON MACROMOLECULAR S T R U C T U R E * A. T.
BARYSItNIKOV, V. K . LATOV, V. M. BELIKOV, A. I. VINOGRADOVA and
M. I. FASTOVSKAYA Organometallic Compounds Institute, U.S.S.R. A c a d e m y of Sciences
(Received 24 February 1978) Copolymers of styrene with chiral aminoacid mateimides have been synthesized and their properties have been investigated. The aminoacid type has been found to affect the ionization process and the chiroptical properties of the aqueous eopolymer solutions. This has been associated with the influence of the various aminoacid radicals on the conformations of the polymer chain and of individual chain units. These macromolecules have been found not to be accepted as aqueous solutions in spiral conformations.
THE eopolymers of styrene with the maleimides of L- and D-alanine [1], and of L-phenylalanine [2] had been synthesized earlier; they were used to synthesize asymmetrical hydrogenation catalysts for olefines [3]. The purpose of the work reported here was to broaden the range of styrene copolymers with the maleimides of various aminoacids so as to gain knowledge about the dependence of the copolymer properties on the type of the used aminoacid. EXPERIMENTAL The copolymers were preduced from the chiral aminoacids marketed by the firm "Reah a l " . The mol.wt, of the copolymers were determined in an E P - 6 8 I precision ebulliograph. Determination of the optical rotation dispersion and the circular dichrolsm. The approp r i a t e solutions were prepared by mixing 2-5~/o copolymer selutions in methyl cellulose with phosphate buffer. These contained 2-5~o of the methyl cellulose (MC) and 0.1-0.5 g/100 ml eopolymer in 0.05 ~ phosphate buffer for the measurements of the optical rotation dispersion, but 5~o MC and 0.05-0.2 g/100 ml copolymer in 0.25 ~ buffer of p H = 7 . 3 for determining the circular dichroism. The determination temperature was 25°C. A " P o l a m a t A " polarimeter was used with a 2 d m cell to record the optical rotation dispersion curves in the visible range. The circular dichroism spectra were recorded by means of a "Dichographe 1%. J. Makr I I I " in a 1 em long cell; the instrument was manufactured by the firm '~Jobin Y v o n " . Potentiometric titration. 18 ml of water was mixed with 1 ml of a 2 × 10 -2 n acetone solution of the copolymer and 1.0 z¢ aqueous ]qaC1. The t i t r an t was a 0.01 1~ aqueous solution -of N a O H and the instrument a pH-340. Nitrogen was used for the inert gas flow. * Vysokomol. soyed. A21: No. 3, 581-588, 1979. 636
Synthesis of styrene chiral eopolymers
637
RESULTS
An atactic copolymer of styrene and maleic acid anhydride was synthesized. The aminoacid derivatives (CMA) were produced b y reacting this copolymer with a-aminoacids in DMF [1]. The properties of the synthesized copolymers are listed in the Table. Yields in excess of 70~o were obtained with all the aminoacids used. The imide structure of the eopolymers was confirmed b y the nitrogen and COOH group contents, b u t also b y I R spectroscopy of identical copolymers based on L-alanine [1]. The mol.wt, and the arrange number of chain units ( ~ = 14.5-43.5) calculated from the former indicated the progress of main chain decomposition in the copolymer during the synthesis with the aminoacid derivatives ( ~ = 120). The optical rotation produced b y the chiral copolymer solutions is known to depend on the ehirality of the macromolecular chain as well as that of the main chain unit. This point was clarified b y examining the optical rotation dispersion of solutions in an acid medium ( p H ~ 5 ) as well as a neutral (pH=7.3). These conditions were selected because the studied copolymers are non-ionic (ionization a < 0 . 1 ) at p H 5 and their chain conformations will therefore be mainly determined b y the H bonds in the COOH groups, and b y the hydrophobic reactions of the aminoacid radical R with the styrene ring. The copolymers are ionized (a~ 0.7-0.8) at p H = 7 . 3 which will obviously produce conformation changes. The hydrophobic reactions and the H bonds could have produced spiral conformations in the ehiral copolymers in the former case. K 7 ~ i 0 -s
-5o
2,
1o-e
o9
FIG. 1. The K values for copolymer solutions in acid and neutral media (Dr ude equation). The numbers against the points are those for the copolyrners given in the Table; also used i n Figs. 2-5.
6'38
A.T.
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e~
al.
lIIiI ' IIJ~
~,o
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,,~
o
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9o.
¢,
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1 ¢'~2 ~~ 2¢ q 2 ¢~1~
o 0
I=1
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Synthesis of styrene chiral copolymers
639
Smooth optical rotation dispersion curves were got in the 578-366 nm range with all the investigaSed copolymers in both the media; t h e y were positive in the case of D - a n d negative for the L-aminoacid derivatives. The exceptions were the D- and L-alanines in neutral medium where the reverse was true. All the curves are subject to the single term Drude equation; this indicates t h a t the solutions are free from any substantial amount of macromolecules w i t h a spiral conformation. One can therefore assume t h a t the contribution by t h e macromolecular chirality to the optical rotation is very slight and, depends on t h a t of the elementary chain units of the copolymers. The latter is confirmed b y the similar molar rotation values [¢]C~A (per chain unit) in both the media (see Table) and t h a t constants Ks, determined from the Drude equation at p H ~ 5, are in a direct relation with constants K 7 found at phi--7.3 (Fig. 1). These characteristics point to the chirality of the macromolecules and their type of reaction with the medium remaining very much the same when the degree of ionization changes, which is accompanied by a change in the shape of the macromolecules from a chaotically coiled state to a more stretched one [3, 4].
pKef
~pKe~9
9
/0 /1 8
..4¢/..*fCr'Z~2
8
2
10o °11
1
4 ° --~9 I
I
I
I
~
I
0.3
I
0.8 Fro. 2
]
o~
O.9
1
r
lOOO 20oo aooo ~FAA , c~I/mo/e Fro. 3
FIG. 2. The potentiometrie titration curves produced from the aqueous copolymer solutions. FIG. 3. The pK°'~ 9 dependence on the hydrophobieity of the original aminoacids.
The existence of the above changing in shape when becoming more neutraI" was confirmed by the results of the potentiometric titration of their aqueous solutions. As these polymers are polycarboxylic acids, their pKe~ depends on the neutralization ~ (Fig. 2). An increase of ~, according to the theory about carboxylic poly-electrolytes [4], means t h a t the macromolecule which is chaotically coiled at a : 0 will gradually uncoil and take on a stretched chain conformation. This process is known to b e due to an electrostatic repellance of the negatively charged groups which aceu-
640
A.T.
BARYSHNIKOV et aZ.
mulate a n d increase the energy necessary for the" further ionization of the C 0 0 H groups while reducing their acidity at the same time. The uncoiling of the macro:molecule partly compensates for the energy increase due to the proton dissociation which takes place when the free energy of the polymer matrix changes; the electrostatic potential remains almost the same as a result when the coil changes t o the stretched chain and this will be evident as only a slight pKe~ change in this region when ~ becomes larger. The uncoiling will be complete when an abrupt pKe~ increase occurs, i.e. at ~>0.6. Similar phenomena were noticed b y many investigators, amongst them also were L a t o v and co-workers [3] and Libinson
[4]. The free electrostatic energy AGe (~) of carboxylic polyelectrolytes, essential for the removal of an equivalent number of protons at ionisation ~, and also the p K ° got b y extrapolation to ~ = 0 of the initial p a r t of the pKef-a response line (~=0.1-0.25) is known to be described b y the folio wing equation: 0.43
pKe~--PK°---- RT AGe(~)----ApKe~ In a simpler form AGe(a) [5] can be regarded as being the sum of the free e n e r g y changes due to the change in macromolecular conformation (chiefly depending on hydrophobicity) and as the consequence of repelling forces being created between the ionized secondary carboxyl groups. I f the second term is constant for the investigated copolymers, AGe(a) and ApKe~ ought to be in a direct correlation with the hydrophobicity of the aminoacids. As Fig. 3 shows, T;-0.9 Tr0.9 Tr0 there i s a linear correlation between the zJp~ef =p/t-el--p/~ , found from the potentiometric curves, and the hydrophobicity of the aminoacids AFAA [6], which indicates the existence of a substantial effect of the hydrophobicity of the aminoacid radicals on the t y p e of m acromolecular conformation in the solution. Some derivatives of the aromatic aminoacids, especially the copolymers based on L-tyrosine and L-tryptophan, are not covered b y this dependence. The majority of the produced chiral copolymers are subject in each conformation to the optical shift rule of Cluff-Lutz,Irginson, i.e. identical changes of o n e of the substituents on the asymmetrical C atom (amino-group to imide ring) will result in a monotypical optical rotation change in the copolymer when com:pared with the original aminoacids. The fulfilment of this rule points to an adeq u a t e reaction of the aminoacid radicals with the environment in the main chain units. There is also a linear dependence between [¢]CMA and [ ~ ] ~ in the original aminoacids (Fig. 4) [7]. The deviation from this dependence is taken to be evidence of the specifics of these reactions which are due to compositional differences of the aminoaeid radicals R. A direct proportionality between [¢]CMA and [~]AA exists for both the conform a t i o n s of the majority of eopolymers, as Fig. 4 shows. A t p H ~ 5 and the statist i c a l coil conformation, where the H bonds and the hydrophobic reactions are
Synthesis of styrene ehiral copolymers
641
superior to the electrostatic however, the aromatic aminoacid derivatives will be outside the general series, and probably form their own. I n a neutral medium and where the chain is in the stretched conformation, the electrostatic reactions between the carboxyl groups in the branches will be dominant and the aromatic aminoacid derivatives will all be on ~ straight line, except where the copolymers are based on L-valine, L-isoleucine or L-glutamie acids; deviation from lifiearity will occur in these cases. [¢. rCMA
•
I00
•8
/o~ 8
so
re:A,,
"5
\ 10 °
\\ o9
/oll
l~JtJ
•
A
o 8
\
g.\ -3OO \
\
o/l
FIG. 4. The molar rotations of the copolymers at 578 nm as a function of the molar rotations of the original aminoacids. A: pH=5-5, B: pH= 7.3. The copolymers based on aromatic aminoacids thus differ from those based on the respective aliphatic ones in the type of the [~]CMA--[~b]AA and ApKe~-AF~ functions. The reaction between aromatic hydrocarbons is known to be energetically more favourable t h a n their reactions with aliphatic hydrocarbons. One can assume in analogy t h a t the reactions of the styrene rings with the aromatic substituents of aminoacids will be more intense t h a n with aliphatic in the case of copolymers. This alsc seems to be the reason for the deviation of their properties from the correlations detected for aliphatie aminoaeids. A more detailed study of the reasons for the deviation from the linear dependence in the case ofL-valine, L-isoleucine and L-glntamic acid in a neutral medium (Fig. 4) was made by recording the cir_ular dichroism spectra of the aromatic and imide chromophores of the copolymers in the 210-300 nm range at p H = 7 . ~ (Fig. 5).
• 42
A.T. B~¥SmCIKOV et
al.
The absorption peaks produced by the aromatic chromophores were in the 260-270 n m range and were of low intensity (A~ ~ 0.05); the exception were the Z-tryptophan copolymers where the indole rings produced intense peaks of
0-5~
8
JO0
f
.,,l.nrn
-s.or-( .FIG, 5, The circular dichroism spectra of the aqueous copolymer solutions (pH=7.3),
The absorption lines of average intensity (A~ ~ 0.3) at about 247 and 230 n m be'~ong to the imide chromophores; this agrees well with the literature data [1, 10]. The larger intensity 210 n m absorption peaks also seem to belong to the carbonyl groups of the imide or the carboxyl groups. The total effect of these lines obyiously determines the size and the sign in front of the rotation in the visible range. T h e less intense and negative rotations produced in the visible range by the L-tyrosine copolymers, when compared with those given by other polymeric aromatic aminoacid derivatives (see Table), can therefore be explained by the existence of the positive circular dichroism lines in the 230-270 n m absorption range. The absorption peak by the carbonyl chromophores was verified by synthe,sizing an ethylene copolymer with the L-isoleucine maleimide which does not contain aromatic chromophores. The circular dichroism spectra of this copolymer a s well as those of the stymne-maleimide cop01ymer (Fig. 5), contained two poorly
Synthesis of styrene ehiral eopolymers
643
resolved peaks at about 230 and 245 nm, b u t none in the 260-270 nm range typical for the aromatic chromophores. The amides, b u t also the mono- and di-N-alkylamides are capable of forming conjugated systems in the absence of steric hindrance [11]. This capacity is most distinct in the case of amides with H bonds on the N atom, i.e. those free of steric obstacles. Depending on the properties of the solvent, one will find one ,of the following mesomeric forms to be dominant in this case: +
R*--NH--C--II ~ R*--NH~-C--B, II
]
0 I
OII
which affects the progress of the optical rotation dispersion curves of these compounds [12]. In this connection one can assume the existence of similar structures I I I and IV for the imide derivatives of aminoacids:
IIl
IV
Two peaks cou'.d form in the absorption range of the imide form: the longer wave (about 147 nm), belonging to the conjugated structure IV, and the short wave (about 230 rim) belonging to III. As the intensity ratio of these peaks will obviously characterize also the relative quantities of these structures, one can reckon structure IV to be dominant in the majority of the copolymers, while I I I will be dominant only in those based on L-valine or L-isoleucine (Fig. 5). A similar difference can be explained b y the presence of bulky and fl-branched substituents in the last two polymers in addition to the main-chain styrene rings. These substituents will cause sterie obstacles which upset the coplanarity of the imide ring and consequently lead to the formation of structure II][. These facts also appear to be the cause of the circular dichroie-spectral differences typical for the L-valine and L-isoleucine copolymers (Fig. 5), and are the explanation for the deviation of their molar rotation from the linear deper~dence (Fig. 4). The deviation in the case of the glutamie acid derivative seems to be caused b y the presence of additional ionic groups~nd deviation of the chain unit conformations associated with it. The 2o values (see Table) change b u t little during eonformatiou changes in the majority of cases. They are normally in the absorption range of the imide a n d aromatic chromophores and characterize their total contribution to t h e optical rotation b y the copolymers.
644
V.A.
K~ANov
et al.
The produced styrene copolymers w i t h the maleimides of chiral aminoaeids thus made it possible to examine the dependence of their properties on those of the original aminoacids. We found the type of the latter to strongly affect the ionization and the chiroptical properties of the aqueous copolymer solutions, and also those of the m a c r o m o l e c u l e s in t h e m ; the latter a p p e a r n o t to f o r m a n y spiral conformations. Translated by K. A. ALLEIq REFERENCES l. V. K. LATOV and K. K. BABIEVSKII, Izv. Akad. Nauk SSSR, Seriya khim., 2036, 1972 2. V. K. LATOV, V . M . BELIKOV, M. A. BELYAYEVA, A. I. VINOGRADOVA a n d S. D. SOINOV, Izv. Akad. N a u k SSSR, Seriya khim., 2481, 1977 3. V. K. LATOV, V. M. BELIKOV, K. K. BABIEVSI(II and A. I. VINOGRADOVA, Izv. Akad. N a u k SSSR, Seriya khim., 2764, 1973 4. G. S. LIBINSON, Fiziko-khimicheskie svoistva karbeksilnykh kationitov (The Physicochemical Properties of Carboxyl Cation-exchangers). p. 36, "Nauka", 1969 5. I. MICHAELI a n d A. KATCHALSKY, J. Polymer Sci. 23: 683, 1957 6. G. TANFORD, J. Am. Chem. Soc. 84: 4240, 1962 7. M. C. OTEY, J. P. GREENSTEIN, M. WINITZ and S. M. BIRNBAUM, J. Am. Chem. Soc. 77: 3112, 1955 8. W. KAUZMANN, Advances Protein Chem. 14: 1, 1959 9. A. E. P. WATSON, I. A. MeCLURE, J. E. BENNETT and G. C. BENSON, J. Phys. Chem. 69: 2753, 1965 10. H. R. DAVE a n d M. K. HARGREAVES, Chem. Commun., 743, 1967 11. J. T. EDWARD and S. C. R. MEACOCK, Chem. Ind., 536, 1955 12. V. M. POTAPOV, V. M. DEM'YANOVICH and A. P. TERENT'EV, Zh. obshch, khim. 35: 1340, 1965
Polymer ScienceU.S.S.R.Vol. 21, pp. 644-652. (~) PergamonPress Ltd. 1979.Printedin Poland
0032-3950/79/0301-0644507.50/0
COMPLEX FORMING POLYMERIC SORBENTS TUNED TO THE SORBED ION* V. A. KABANOV, _h. A. EFENDIEV a n d D. D. ORUDZHEV M. V. Lomonosov State University, Moscow I n s t i t u t e for Theoretic Problem in Chemical Technology, Azerb.S.S.R. Academy of Sciences
(Received 24 _February 1978) Crosslinked, complex forming, polymeric sorbents based on a diethylvinyl phosphonate-acrylic acid copolymer aimed at the sorption of copper ions by the position of its macromolecules has been produced. The general principle is to react a linear * Vysokomol. soyed. A21: No. 3, 589-595, 1979.
~ P o l y m e r Science U.S.S.R. Vol. 21, pp. 636-644. ¢~) P e r g a m o n Press Ltd. 1979. Printed in P o l a n d
TH~ SYNTHESIS OF S T Y R E N E CHIRAL COPOLYMERS W I T H AlVIINOACID M A L E I M I D E S A N D T H E E F F E C T OF T H E AMINOACID R A D I C A L S ON MACROMOLECULAR S T R U C T U R E * A. T.
BARYSItNIKOV, V. K . LATOV, V. M. BELIKOV, A. I. VINOGRADOVA and
M. I. FASTOVSKAYA Organometallic Compounds Institute, U.S.S.R. A c a d e m y of Sciences
(Received 24 February 1978) Copolymers of styrene with chiral aminoacid mateimides have been synthesized and their properties have been investigated. The aminoacid type has been found to affect the ionization process and the chiroptical properties of the aqueous eopolymer solutions. This has been associated with the influence of the various aminoacid radicals on the conformations of the polymer chain and of individual chain units. These macromolecules have been found not to be accepted as aqueous solutions in spiral conformations.
THE eopolymers of styrene with the maleimides of L- and D-alanine [1], and of L-phenylalanine [2] had been synthesized earlier; they were used to synthesize asymmetrical hydrogenation catalysts for olefines [3]. The purpose of the work reported here was to broaden the range of styrene copolymers with the maleimides of various aminoacids so as to gain knowledge about the dependence of the copolymer properties on the type of the used aminoacid. EXPERIMENTAL The copolymers were preduced from the chiral aminoacids marketed by the firm "Reah a l " . The mol.wt, of the copolymers were determined in an E P - 6 8 I precision ebulliograph. Determination of the optical rotation dispersion and the circular dichrolsm. The approp r i a t e solutions were prepared by mixing 2-5~/o copolymer selutions in methyl cellulose with phosphate buffer. These contained 2-5~o of the methyl cellulose (MC) and 0.1-0.5 g/100 ml eopolymer in 0.05 ~ phosphate buffer for the measurements of the optical rotation dispersion, but 5~o MC and 0.05-0.2 g/100 ml copolymer in 0.25 ~ buffer of p H = 7 . 3 for determining the circular dichroism. The determination temperature was 25°C. A " P o l a m a t A " polarimeter was used with a 2 d m cell to record the optical rotation dispersion curves in the visible range. The circular dichroism spectra were recorded by means of a "Dichographe 1%. J. Makr I I I " in a 1 em long cell; the instrument was manufactured by the firm '~Jobin Y v o n " . Potentiometric titration. 18 ml of water was mixed with 1 ml of a 2 × 10 -2 n acetone solution of the copolymer and 1.0 z¢ aqueous ]qaC1. The t i t r an t was a 0.01 1~ aqueous solution -of N a O H and the instrument a pH-340. Nitrogen was used for the inert gas flow. * Vysokomol. soyed. A21: No. 3, 581-588, 1979. 636
Synthesis of styrene chiral eopolymers
637
RESULTS
An atactic copolymer of styrene and maleic acid anhydride was synthesized. The aminoacid derivatives (CMA) were produced b y reacting this copolymer with a-aminoacids in DMF [1]. The properties of the synthesized copolymers are listed in the Table. Yields in excess of 70~o were obtained with all the aminoacids used. The imide structure of the eopolymers was confirmed b y the nitrogen and COOH group contents, b u t also b y I R spectroscopy of identical copolymers based on L-alanine [1]. The mol.wt, and the arrange number of chain units ( ~ = 14.5-43.5) calculated from the former indicated the progress of main chain decomposition in the copolymer during the synthesis with the aminoacid derivatives ( ~ = 120). The optical rotation produced b y the chiral copolymer solutions is known to depend on the ehirality of the macromolecular chain as well as that of the main chain unit. This point was clarified b y examining the optical rotation dispersion of solutions in an acid medium ( p H ~ 5 ) as well as a neutral (pH=7.3). These conditions were selected because the studied copolymers are non-ionic (ionization a < 0 . 1 ) at p H 5 and their chain conformations will therefore be mainly determined b y the H bonds in the COOH groups, and b y the hydrophobic reactions of the aminoacid radical R with the styrene ring. The copolymers are ionized (a~ 0.7-0.8) at p H = 7 . 3 which will obviously produce conformation changes. The hydrophobic reactions and the H bonds could have produced spiral conformations in the ehiral copolymers in the former case. K 7 ~ i 0 -s
-5o
2,
1o-e
o9
FIG. 1. The K values for copolymer solutions in acid and neutral media (Dr ude equation). The numbers against the points are those for the copolyrners given in the Table; also used i n Figs. 2-5.
6'38
A.T.
BARvs~r~xov
e~
al.
lIIiI ' IIJ~
~,o
]
,,~
o
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tO
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Synthesis of styrene chiral copolymers
639
Smooth optical rotation dispersion curves were got in the 578-366 nm range with all the investigaSed copolymers in both the media; t h e y were positive in the case of D - a n d negative for the L-aminoacid derivatives. The exceptions were the D- and L-alanines in neutral medium where the reverse was true. All the curves are subject to the single term Drude equation; this indicates t h a t the solutions are free from any substantial amount of macromolecules w i t h a spiral conformation. One can therefore assume t h a t the contribution by t h e macromolecular chirality to the optical rotation is very slight and, depends on t h a t of the elementary chain units of the copolymers. The latter is confirmed b y the similar molar rotation values [¢]C~A (per chain unit) in both the media (see Table) and t h a t constants Ks, determined from the Drude equation at p H ~ 5, are in a direct relation with constants K 7 found at phi--7.3 (Fig. 1). These characteristics point to the chirality of the macromolecules and their type of reaction with the medium remaining very much the same when the degree of ionization changes, which is accompanied by a change in the shape of the macromolecules from a chaotically coiled state to a more stretched one [3, 4].
pKef
~pKe~9
9
/0 /1 8
..4¢/..*fCr'Z~2
8
2
10o °11
1
4 ° --~9 I
I
I
I
~
I
0.3
I
0.8 Fro. 2
]
o~
O.9
1
r
lOOO 20oo aooo ~FAA , c~I/mo/e Fro. 3
FIG. 2. The potentiometrie titration curves produced from the aqueous copolymer solutions. FIG. 3. The pK°'~ 9 dependence on the hydrophobieity of the original aminoacids.
The existence of the above changing in shape when becoming more neutraI" was confirmed by the results of the potentiometric titration of their aqueous solutions. As these polymers are polycarboxylic acids, their pKe~ depends on the neutralization ~ (Fig. 2). An increase of ~, according to the theory about carboxylic poly-electrolytes [4], means t h a t the macromolecule which is chaotically coiled at a : 0 will gradually uncoil and take on a stretched chain conformation. This process is known to b e due to an electrostatic repellance of the negatively charged groups which aceu-
640
A.T.
BARYSHNIKOV et aZ.
mulate a n d increase the energy necessary for the" further ionization of the C 0 0 H groups while reducing their acidity at the same time. The uncoiling of the macro:molecule partly compensates for the energy increase due to the proton dissociation which takes place when the free energy of the polymer matrix changes; the electrostatic potential remains almost the same as a result when the coil changes t o the stretched chain and this will be evident as only a slight pKe~ change in this region when ~ becomes larger. The uncoiling will be complete when an abrupt pKe~ increase occurs, i.e. at ~>0.6. Similar phenomena were noticed b y many investigators, amongst them also were L a t o v and co-workers [3] and Libinson
[4]. The free electrostatic energy AGe (~) of carboxylic polyelectrolytes, essential for the removal of an equivalent number of protons at ionisation ~, and also the p K ° got b y extrapolation to ~ = 0 of the initial p a r t of the pKef-a response line (~=0.1-0.25) is known to be described b y the folio wing equation: 0.43
pKe~--PK°---- RT AGe(~)----ApKe~ In a simpler form AGe(a) [5] can be regarded as being the sum of the free e n e r g y changes due to the change in macromolecular conformation (chiefly depending on hydrophobicity) and as the consequence of repelling forces being created between the ionized secondary carboxyl groups. I f the second term is constant for the investigated copolymers, AGe(a) and ApKe~ ought to be in a direct correlation with the hydrophobicity of the aminoacids. As Fig. 3 shows, T;-0.9 Tr0.9 Tr0 there i s a linear correlation between the zJp~ef =p/t-el--p/~ , found from the potentiometric curves, and the hydrophobicity of the aminoacids AFAA [6], which indicates the existence of a substantial effect of the hydrophobicity of the aminoacid radicals on the t y p e of m acromolecular conformation in the solution. Some derivatives of the aromatic aminoacids, especially the copolymers based on L-tyrosine and L-tryptophan, are not covered b y this dependence. The majority of the produced chiral copolymers are subject in each conformation to the optical shift rule of Cluff-Lutz,Irginson, i.e. identical changes of o n e of the substituents on the asymmetrical C atom (amino-group to imide ring) will result in a monotypical optical rotation change in the copolymer when com:pared with the original aminoacids. The fulfilment of this rule points to an adeq u a t e reaction of the aminoacid radicals with the environment in the main chain units. There is also a linear dependence between [¢]CMA and [ ~ ] ~ in the original aminoacids (Fig. 4) [7]. The deviation from this dependence is taken to be evidence of the specifics of these reactions which are due to compositional differences of the aminoaeid radicals R. A direct proportionality between [¢]CMA and [~]AA exists for both the conform a t i o n s of the majority of eopolymers, as Fig. 4 shows. A t p H ~ 5 and the statist i c a l coil conformation, where the H bonds and the hydrophobic reactions are
Synthesis of styrene ehiral copolymers
641
superior to the electrostatic however, the aromatic aminoacid derivatives will be outside the general series, and probably form their own. I n a neutral medium and where the chain is in the stretched conformation, the electrostatic reactions between the carboxyl groups in the branches will be dominant and the aromatic aminoacid derivatives will all be on ~ straight line, except where the copolymers are based on L-valine, L-isoleucine or L-glutamie acids; deviation from lifiearity will occur in these cases. [¢. rCMA
•
I00
•8
/o~ 8
so
re:A,,
"5
\ 10 °
\\ o9
/oll
l~JtJ
•
A
o 8
\
g.\ -3OO \
\
o/l
FIG. 4. The molar rotations of the copolymers at 578 nm as a function of the molar rotations of the original aminoacids. A: pH=5-5, B: pH= 7.3. The copolymers based on aromatic aminoacids thus differ from those based on the respective aliphatic ones in the type of the [~]CMA--[~b]AA and ApKe~-AF~ functions. The reaction between aromatic hydrocarbons is known to be energetically more favourable t h a n their reactions with aliphatic hydrocarbons. One can assume in analogy t h a t the reactions of the styrene rings with the aromatic substituents of aminoacids will be more intense t h a n with aliphatic in the case of copolymers. This alsc seems to be the reason for the deviation of their properties from the correlations detected for aliphatie aminoaeids. A more detailed study of the reasons for the deviation from the linear dependence in the case ofL-valine, L-isoleucine and L-glntamic acid in a neutral medium (Fig. 4) was made by recording the cir_ular dichroism spectra of the aromatic and imide chromophores of the copolymers in the 210-300 nm range at p H = 7 . ~ (Fig. 5).
• 42
A.T. B~¥SmCIKOV et
al.
The absorption peaks produced by the aromatic chromophores were in the 260-270 n m range and were of low intensity (A~ ~ 0.05); the exception were the Z-tryptophan copolymers where the indole rings produced intense peaks of
0-5~
8
JO0
f
.,,l.nrn
-s.or-( .FIG, 5, The circular dichroism spectra of the aqueous copolymer solutions (pH=7.3),
The absorption lines of average intensity (A~ ~ 0.3) at about 247 and 230 n m be'~ong to the imide chromophores; this agrees well with the literature data [1, 10]. The larger intensity 210 n m absorption peaks also seem to belong to the carbonyl groups of the imide or the carboxyl groups. The total effect of these lines obyiously determines the size and the sign in front of the rotation in the visible range. T h e less intense and negative rotations produced in the visible range by the L-tyrosine copolymers, when compared with those given by other polymeric aromatic aminoacid derivatives (see Table), can therefore be explained by the existence of the positive circular dichroism lines in the 230-270 n m absorption range. The absorption peak by the carbonyl chromophores was verified by synthe,sizing an ethylene copolymer with the L-isoleucine maleimide which does not contain aromatic chromophores. The circular dichroism spectra of this copolymer a s well as those of the stymne-maleimide cop01ymer (Fig. 5), contained two poorly
Synthesis of styrene ehiral eopolymers
643
resolved peaks at about 230 and 245 nm, b u t none in the 260-270 nm range typical for the aromatic chromophores. The amides, b u t also the mono- and di-N-alkylamides are capable of forming conjugated systems in the absence of steric hindrance [11]. This capacity is most distinct in the case of amides with H bonds on the N atom, i.e. those free of steric obstacles. Depending on the properties of the solvent, one will find one ,of the following mesomeric forms to be dominant in this case: +
R*--NH--C--II ~ R*--NH~-C--B, II
]
0 I
OII
which affects the progress of the optical rotation dispersion curves of these compounds [12]. In this connection one can assume the existence of similar structures I I I and IV for the imide derivatives of aminoacids:
IIl
IV
Two peaks cou'.d form in the absorption range of the imide form: the longer wave (about 147 nm), belonging to the conjugated structure IV, and the short wave (about 230 rim) belonging to III. As the intensity ratio of these peaks will obviously characterize also the relative quantities of these structures, one can reckon structure IV to be dominant in the majority of the copolymers, while I I I will be dominant only in those based on L-valine or L-isoleucine (Fig. 5). A similar difference can be explained b y the presence of bulky and fl-branched substituents in the last two polymers in addition to the main-chain styrene rings. These substituents will cause sterie obstacles which upset the coplanarity of the imide ring and consequently lead to the formation of structure II][. These facts also appear to be the cause of the circular dichroie-spectral differences typical for the L-valine and L-isoleucine copolymers (Fig. 5), and are the explanation for the deviation of their molar rotation from the linear deper~dence (Fig. 4). The deviation in the case of the glutamie acid derivative seems to be caused b y the presence of additional ionic groups~nd deviation of the chain unit conformations associated with it. The 2o values (see Table) change b u t little during eonformatiou changes in the majority of cases. They are normally in the absorption range of the imide a n d aromatic chromophores and characterize their total contribution to t h e optical rotation b y the copolymers.
644
V.A.
K~ANov
et al.
The produced styrene copolymers w i t h the maleimides of chiral aminoaeids thus made it possible to examine the dependence of their properties on those of the original aminoacids. We found the type of the latter to strongly affect the ionization and the chiroptical properties of the aqueous copolymer solutions, and also those of the m a c r o m o l e c u l e s in t h e m ; the latter a p p e a r n o t to f o r m a n y spiral conformations. Translated by K. A. ALLEIq REFERENCES l. V. K. LATOV and K. K. BABIEVSKII, Izv. Akad. Nauk SSSR, Seriya khim., 2036, 1972 2. V. K. LATOV, V . M . BELIKOV, M. A. BELYAYEVA, A. I. VINOGRADOVA a n d S. D. SOINOV, Izv. Akad. N a u k SSSR, Seriya khim., 2481, 1977 3. V. K. LATOV, V. M. BELIKOV, K. K. BABIEVSI(II and A. I. VINOGRADOVA, Izv. Akad. N a u k SSSR, Seriya khim., 2764, 1973 4. G. S. LIBINSON, Fiziko-khimicheskie svoistva karbeksilnykh kationitov (The Physicochemical Properties of Carboxyl Cation-exchangers). p. 36, "Nauka", 1969 5. I. MICHAELI a n d A. KATCHALSKY, J. Polymer Sci. 23: 683, 1957 6. G. TANFORD, J. Am. Chem. Soc. 84: 4240, 1962 7. M. C. OTEY, J. P. GREENSTEIN, M. WINITZ and S. M. BIRNBAUM, J. Am. Chem. Soc. 77: 3112, 1955 8. W. KAUZMANN, Advances Protein Chem. 14: 1, 1959 9. A. E. P. WATSON, I. A. MeCLURE, J. E. BENNETT and G. C. BENSON, J. Phys. Chem. 69: 2753, 1965 10. H. R. DAVE a n d M. K. HARGREAVES, Chem. Commun., 743, 1967 11. J. T. EDWARD and S. C. R. MEACOCK, Chem. Ind., 536, 1955 12. V. M. POTAPOV, V. M. DEM'YANOVICH and A. P. TERENT'EV, Zh. obshch, khim. 35: 1340, 1965
Polymer ScienceU.S.S.R.Vol. 21, pp. 644-652. (~) PergamonPress Ltd. 1979.Printedin Poland
0032-3950/79/0301-0644507.50/0
COMPLEX FORMING POLYMERIC SORBENTS TUNED TO THE SORBED ION* V. A. KABANOV, _h. A. EFENDIEV a n d D. D. ORUDZHEV M. V. Lomonosov State University, Moscow I n s t i t u t e for Theoretic Problem in Chemical Technology, Azerb.S.S.R. Academy of Sciences
(Received 24 _February 1978) Crosslinked, complex forming, polymeric sorbents based on a diethylvinyl phosphonate-acrylic acid copolymer aimed at the sorption of copper ions by the position of its macromolecules has been produced. The general principle is to react a linear * Vysokomol. soyed. A21: No. 3, 589-595, 1979.