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Functionalized conducting polymers for development of new polymeric reagents
Reactive Polymers, 6 (1987) 221-227 Elsevier Science Publishers B.V., Amsterdam
221 Printed in The Netherlands
FUNCTIONALIZED CONDUCTING POLYMERS FOR DEVELOPMENT OF NEW POLYMERIC REAGENTS * TAKEO SHIMIDZU
Division of Molecular Engineering, Graduate School o[ Engineering, Kvoto Universi(v, Kvoto 606 (Japan) (Received September 3, 1986: accepted in revised form April 2, 1987)
Methods of preparation and applications of both functionalized conducting polymers and conducting polymers incorporating functional molecules are described. The development of such new polymeric reagents is illustrated by several examples.
INTRODUCTION There are many functional molecules. For their exploitation, conducting polymers are considered to be suitable matrices because their conductive properties may be used to probe the electronic structure and properties of functional molecules. We previously established a hybridization procedure for synthesis of conducting polymers with functional molecules by electrochemical polymerization [1,2] or chemical polymerization [2,3]. These functionalized conducting polymers show both the native function of the functional molecule and native conductivity. The present paper describes typical functions of conducting polymers incorporating functional molecules, methods of their preparation, and their utilization as polymeric reagents and in polymersupported reactions.
* Paper presented at the 3rd International Conference on Polymer-Supported Reactions in Organic Chemistry, Jerusalem, Israel, July 6-11, 1986 0167-6989/87/$03.50
1. PREPARATION OF CONDUCTING POLYMERS INCORPORATING FUNCTIONAL MOLECULES A functionalized conducting polymer may be prepared by electrolytic polymerization of pyrrole, thiophene, furan, aniline, etc., in presence of negatively charged functional molecules. The incorporation of the functional molecules is driven electrostatically by the positive charges of the partially oxidized conducting polymer matrices through a doping process, as shown in Scheme 1. Electrolytic polymerization may be easily achieved with a monomer solution in the presence of negatively charged functional molecules. A key concept of this preparative approach is that the resulting conducting polymer has a lower redox potential (doping-undoping) than its monomer; therefore anodic doping occurs simultaneously with electropolymerization. An electrolyte anion or functional anionic molecule is incorporated into the partially oxidized conducting polymer matrix so as to conserve its electroneutrality.
© 1987 Elsevier Science Publishers B.V.
222
F\ ®
@
m®
.=~
X=NH, S, 0
m F® F~ functional molecule Scheme 1
The resulting functionalized conducting polymers display their native functions; the functionalities and the conducting properties are not much reduced. Table 1 shows some examples. Chemical polymerization methods are also available for preparation of functionalized conducting polymers. Several techniques are shown in Table 2. In these cases, many kinds of functional molecules (negatively charged, neutral, positively charged) can be incorporated. Compared with the electrolytic polymerization method, the functions of several of the incorporated functional molecules and the conductivities of the resulting conducting polymers are reduced [2,3]. However, it is possible to texture a conducting layer anisotropically anywhere in the support.
2. PPy ELECTRODE INCORPORATING FeBPS AND ITS ELECTROCHROMISM Figure 1 shows the incorporation of tris(bathophenanthroline disulfonate) iron complex (FeBPS) into a poly(pyrrole) (PPy) matrix by galvanostatic electrolysis. The intensity of the absorption around 540 nm assigned to FeBPS increased over that assigned to PPy during electropolymerization of pyrrole. A sulfur content of 7.98% for the resulting FeBPS-PPy corresponded to a doping efficiency of 0.443 (ratio of sulfonate moieties to pyrrole units in PPy), which agreed with that reported previously for ordinary PPy [7]. FeBPS-PPy had as high a conductivity (7.0 S/cm) as ordinary PPy. FeBPS-PPy had a redox potential of 1.09 V on a Pt wire elec-
TABLE 1 Negatively charged functional molecules suitable for incorporation in conducting polymer matrices Group
Examples a
Function b
Organic molecule Metal complex
AQS, rose bengal, indigo carmine Lu(PTS) 2, Fe(BPS)n (BP)3_ ., Ru(BPS). (BP) 3_. MTPPS (M = H 2, Zn, Pd) FePTS [5], MTPS (M = Fe, Co, Mn) [6] RuO4- [4], PtCI] , AuCI~-, MnO4-, phosphotungstate PVSK. PSSNa, Nation® enzyme, nucleotide material
A,B A,B,C B E A,D,E F,G E,H
Inorganic metal ion Polyelectrolyte Biomaterial
a AQS = Anthraquinone-2-sulfonic acid. MTPPS = metal-tetra(4-sulfophenyl)porphyrin. MTPS = metaltetrasulfophthalocyanine. BPS = bathephenanthroline disulfonic acid. PVSK = potassium poly(vinylsulfate). PSSNa = sodium poly(styrene sulfonate) Nation® = Salt of sulfonated and highly fluorinated polymer (trademark of Du Pont) h A , electrochromism; B, photoelectric conversion; C, electrogenerated chemiluminescence; D, highly dispersed noble metal; E, catalyst; F, high mechanical strength conducting polymer; G, charge-controllable transport membrane; H, sensor.
223 TABLE 2 Methods for preparation of conducting polymer composites by chemical polymerization
polymerization ~[~
Chemical
~'~-J-[~-~
SEPTAL
S
Monomer (M) Support (S) Oxidant (O) Solvent
0
or
M
o ><
~2['" d
6
or
0
0
or
M
doping resulting from steric hindrance encountered by FeBPS in the tangled PPy structure. As regards electrochemical preparation of functional conducting polymer-coated electrodes, the low undoping efficiency resulted in effective fixation of FeBPS in the polymer matrix.
3. P H O T O S E N S I T I Z E D PPy TRODE D O P E D WITH ZnTPPS
ELEC-
According to the same procedure, zinc tetra(4-sulfophenyl)porphyrin (ZnTPPS) was incorporated into PPy at a ratio of 0.341 and conductivity of 0.1 S / c m . The yield of incorporation was 7.9 × 10 -8 eq of sulfonate per coulomb. Figure 3 shows a typical photocurrent-potential curve of a Z n T P P S - P P y ITO
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0-
M
BLEND I NG
pyrrole, thiophene, furan, aniline, indole, their derivatives ion-exchange membrane, natural and synthetic membrane, porous glass, porous ceramics Lewis acid, halogen, peroxide, metal acid water, organic solvent, gas-phase reaction
trode, assigned to Fe2+/Fe 3+ in CH3CN, which agreed with the redox potential of FeBPS. Figure 2 shows the absorbance change around 540 nm of an FeBPS-PPy coated ITO electrode under various potentiostatic conditions. In Fig. 2(B) an inflection point appears at 1.1 V, the same potential as obtained by cyclic voltammetry. A distinct color change from bluish gray to dark red was observed on a transparent ITO electrode. The electrochromism was maintained over 1000 cycles of reversibility; its response time was < 100 ms. The incorporated FeBPS was hardly released from the PPy matrix even when FeBPS-PPy was sufficiently reduced. The incomplete un-
~3"
+Ms~y~
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Fig. 1. Time course of incorporation of FeBPS into PPy matrix under galvanostatic conditions: (e) absorbance at 540 nm; (©) absorbance at 380 nm; ( ~ ) absorbance at 620 nm.
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Fig. 2. (A) Visible absorption spectra of FeBPS-PPycoated ITO electrode at various potentials in CH3CN. (B) Absorbance change at 540 nm of FeBPS-PPy-coated ITO electrode at the same conditions at in (A).
224 {I00 hA) 6
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4¸ 2 -%.5
0 (V vs
SCE)
-4
Fig. 3. Photocurrent-potential curve of ZnTPPS-PPycoated ITO electrode in Fe(CN)63-/4- aqueous solution.
chemical properties of an anionic dye-PPy electrode, we demonstrated that PPy with incorporated metal-free HTPPS was able to cover particulate TiO 2 when pyrrole was photo-polymerized oxidatively in the presence of Ag ÷ (electron acceptor) and HTPPS under irradiation at a wavelength > 320 nm. This procedure is a potentially new method of photoelectrochemical surface modification of a semiconductor, resulting in a new polymeric reagent with a combined semiconductor function.
4. CHARGE-CONTROLLABLE P P y POLYELECTROLYTE C O M P O S I T E S electrode in water containing 2.0 mmol/1 of Fe(CN) 3-/4- under irradiation at a wavelength > 390 nm. At > 0.3 V an appreciable anodic photocurrent ( > 600 n A / c m 2) was observed by the photo-AC method using a lock-in amplifier and a light chopper (20 Hz). The agreement of the action spectrum of the photocurrent with the visible absorption spectrum indicates that the incorporated ZnTPPS plays a significant role as a sensitizer for the generation of the anodic photocurrent. The current quantum efficiency at 435 nm was ca. 0.1%. The photocurrent was proportional to the intensity of incident light. Other sensitizers, e.g., RuBPS, rose bengal, and indigo carmine, proved also to be of use as functional molecules, and the resulting PPy electrodes showed a considerable anodic photocurrent. These observations illustrate that this doping method endows PPy with photoresponsivity. Some particulate semiconductors catalyze photo-induced oxidative polymerization of pyrrole in the presence of an appropriate electron acceptor under their band-gap excitation. As a result, the surfaces of these semiconductors are covered with PPy [8], and the adhering PPy is effective as a hole carrier from the valence band in the semiconductor to any electrolytes [9]. Utilizing the electro-
Anionic polyelectrolytes, e.g., PVSK (potassium poly(vinylsulfate)), PSSNa (sodium poly(styrene-4-sulfonate)), and Nafion ® were also incorporated into PPy according to the same procedure as described above [10]. The resulting PPy had (1) high conductivity, (2) high tensile strength, (3) very low undoping efficiency, (4) homogeneous and dense PPy surface; it exhibited (5) "polyion complex" formation, and (6) pseudo-cathodic doping; and behaved as (7) a charge-controllable membrane. Property (5) indicates that the incorporated polyelectrolyte forms a polyion complex by electrostatic attraction between partially oxidized PPy and the negative charges of the polyelectrolyte. Properties (6) and (7) indicate that the very low undoping efficiency ( < 1%) of the incorporated polyelectrolyte resulted from strong polyion complex formation and that electrolyte cations were incorporated into the matrix in order to conserve electroneutrality when PPy was reduced. The composites thus prepared have cation-exchange properties [18]. Their fixedcharge polarity changed reversibly when the composite was reduced and oxidized [11]. The electrochemically regulated conducting ion exchange polymer was termed a "charge-controllable membrane". Figure 4 illustrates the
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Fig. 4. Polarity change of fixed charges in PPy/pentane sulfonate membrane (left) and PPy/PVS membrane (right) for oxidized and reduced states, as determined by membrane potential (Aq') measurements in a KCI concentration cell. (O) membrane as prepared, ( ~ ) reduced membrane at - 1.0 V vs. SCE. (O) oxidized membrane at + 2.0 V. A negative value of A~t, indicates the existence of a fixed positive charge in the membrane.
behavior of this charge-controllable membrane. Using thus type of membrane, a deionization system [12] and a polymer battery [13] were constructed.
5. HIGHLY DISPERSED METAL ELECTRODES When a metalate ion such as PtC12- or AuC1 4 was used as electrolyte, we obtained PtCI24- -PPy and AuCI 4-p°lythi°phene composites. The incorporation of Pt 2+ and Au 3+ was confirmed by ESCA measurements. The phosphotungstate anion was also incorporated into PPy and the composite showed distinct electrochromism [14].
6. PPy COMPOSITES INCORPORATING OLIGONUCLEOTIDES FOR USE AS SENSORS When pyrrole was electropolymerized in the presence of adenosine triphosphate, poly(adenylic acid), uridine triphosphate, poly(uridylic acid), or a sequence-defined oligonucleotide as an electrolyte, all were efficiently incorporated into the PPy matrix [15-17]. The incorporation was confirmed by elemental analysis of phosphorus. The resulting PPy electrodes have in principle the capacity to recognize DNA and RNA analogs in an electrolytic solution through the change in rest potential resulting from base-base interactions by stacking and hydrogen bonding. The results in Table 3 show that PPy com-
226 TABLE 3 Surface potential changes of PPy electrodes incorporating nucleotidic materials in various nucleotide solutions Electrode
Substrate/10 -4 M
Potential change/10 -3 V
pA/PPy pA/PPy pU/PPy pU/PPy Poly A / P P y Poly A / P P y Poly U / P P y Poly U / P P y pApUpApUpApUpApU/PPy pApUpApUpApUpApU/PPy pApUpApUpApUpApU/PPy pApUpApUpApUpApU/PPy pApUpApUpApUpApU/PPy pApUpApUpApUpApU/PPy
pA pU pA pU Poly A Poly U Poly A Poly U pApUpApUpApUpApUpApUpApU pApUpApUpApUpApU pApUpApUpApU pApUpApU pCpGpCpGpCpGpCpG pCpGpCpGpCpG
-0.210 -0.113 -0.128 +0.210 -0.410 - 0.872 - 0.678 - 0.210 - 0.709 - 0.721 - 0.628 - 0.594 - 0.116 - 0.109
7. PPy COMPOSITES INCORPORATING NUCLEIC ACIDS AS POLYMERIC SUPPORTS
posite/Pt electrodes incorporating oligonucleotides can serve as sensors as a result of complementary base-base interactions, reflected by the changes in potential.
A conducting PPy polymer can easily incorporate a nucleic acid as dopant. AccordAPPLICATION
TO SYNTHESIS
( I )
HOMOOLIGONUCLEOTIDES
(PPY+--PU(PU)nU
> PPy (REDUCTION) PPy+--~pU(PU)nUP > PPY
PPY+---PU + U + PIM3
PPY+--~PA + 2 A + 2 PIM3
) PPY+~PAPAPA
~ PPY (REDUCTION)
+ pU(PU)nU 93% + pU(PU)nUP
7%
+ PAPAPA
CONY, 23% 2'5'-2'5' 441 2'5'-3'5' 20% 3'5'-2'5' 211 3'5'-3'5' 15%
APPLICATION TO SYNTHESIS ( I I ) >NPCL2
A
SEQUENCE-DEFINED OLIGONUCLEOTIDES PPY+---PUPA
• PPY + PUPA
) PUPA
PPY+--PU
~" ~ PPY+--PU>PN<~ ~.,T.ET~AZOLE) 80% (REDUCTION) (i 2 + H20) 96% 98~ U"I"-"'"~=PPY+--PUPU ) PPY + PUPD ) PUPU 89% 96% >NPCL2 A PPY+--PAPA ~ PPY + PAPA ) PAPA ppy+__pA~ppy+.__pA>PN<~AZOLE) 75% (REDUCTION) (I 2 + H20) 94% 88%
U
~PPY+----PAPU 80%
Scheme 2
~ PPY + PAPU
~ PAPD 94%
227
ingly, PPy can be used as a polymeric support. Both homo-oligoribonucleotides and sequence-defined oligoribonucleotides were synthesized using PPy as a polymeric support, as shown in Scheme 2. The results demonstrate that the conducting polymer can be used for both methods of synthesis of oligonucleotides. Advantage of this polymeric support are: (1) protection of the phosphoric acid moiety is unnecessary and (2) the resulting oligonucleotide is easily removed by electrolytic reduction of the conducting polymer support.
8
9
10
11
In conclusion, it may be stated that conducting polymer matrices provide an interesting and useful focus for expansion of the fields of polymeric reagent research and molecular engineering.
12
REFERENCES
14
1 T. Shimidzu, T. lyoda and K. Fukui, Functionalizations of conducting polymer modified electrodes, Ann. Rep. Jpn. Chem. Fiber Res., 42 (1985) 71. 2 T. Shimidzu and T. lyoda, Functionalized conducting polymer membranes--In pursuit of novel function of membrane, Membrane, 11 (1986) 71. 3 T. Shimidzu, T. Iyoda and K. Fukui, Conducting polymer composite membrane, Ann. Rep. Jpn. Chem. Fiber Res., 43 (1986) 51. 4 R. Naufi, The incorporation of ruthenium oxide in polypyrrole films and the subsequent photooxidation of water at n-gap photoelectrode, J. Electrochem. Soc., 130 (1983) 2126. 5 R.A. Bull, F.-R. Fan and A.J. Bard, Polymer films on electrodes. 13. Incorporation of catalysts into electronically conductive polymers. Iron phthalocyanine in polypyrrole, J. Electrochem. Soc., 131 (1984) 687. 6 K. Okabayashi, O. Ikeda and H. Tamura, Electrochemical doping with meso-tetrakis(4-sulfonatophenyl)-porphyrin cobalt of a pyrrole film electrode, Chem. Comm., (1983) 1821. 7 M. Salmon, A.F. Diaz, A.J. Logan, M. Knounbi and J. Bargon, Chemical modification of conducting
13
15
16
17
18
polypyrrole films, Mol. Cryst. Liq. Cryst., 83 (1982) 265. Y. Taniguchi, H. Yoneyama and H. Tamura, Hydrogen evolution on surface-modified powder photocatalysts in aqueous ethanol solutions, Chem. Lett., (1983) 269. A.J. Frank and Honda, Oxygen and hydrogen generation from water on polymer-coated CDS photoanodes, J. Phys. Chem., 86 (1982) 1933. T. lyoda, A. Ohtank T. Shimidzu and K. Honda, Charge-controllable membrane. Polypyrrole polyelectrolyte composite membrane through anodic doping process, Chem. Lett., (1986) 687. T. Shimidzu, A. Ohtani, T. lyoda and K. Honda, A functionalized polypyrrole film prepared by chemical polymerization at a vapor-liquid interface, J. Chem. Soc. (London), Chem. Commun., (1986) 1414. T. Shimidzu, A. Ohtani, T. Iyoda and K. Honda, Effective adsorption desorption of cations on a polypyrrole-polyanion composite anode, J. Chem. Soc. (London), Chem. Commun., (1986) 1415. T. Shimidzu, A. Ohtani, T. lyoda and K. Honda, A novel type of polymer battery using a pyrrole-polyanion composite electrode, J. Chem. Soc. (London), Chem. Commun., (1987) 327. T. Shimidzu, A. Ohtani, A. Aiba, T. lyoda and K. Honda, Preparation and electrochromism of phosphotungstate incorporating polypyrrole, J. Chem. Soc., in preparation. T. Shimidzu, K. Yamana, K. Nakamichi, and A. Murakami, Uridine oligonucleotide synthesis by the reaction of uridine with tri(imidazole-l-yl) phosphine, J. Chem. Soc., Perkin Trans. I, (1981) 2294. T. Shimidzu, K. Yamana, N. Kanda and S. Maikuma, A simple and convenient synthesis of 3 ' - 5 ' - or 2 ' - 5 ' - l i n k e d oligoribonucleotide by polymerization of unprotected ribonucleoside using phosphorus tris-azole, Nucleic Acids Res., 12 (1984) 3257. T. Shimidzu, K. Yamana and S. Maikuma, Aminophosphordichloridite. A new phosphorylating reagent for one-pot synthesis of 3' 5'- or 2 ' - 5 ' - l i n ked diribonucleotide having definite sequence, Tetrahedron Lett., 25 (1984) 4237. T. Shimidzu, A. Ohtani, T. lyoda and K. Honda, Charge-controllable polypyrrole/polyelectrolyte composite membranes. Part II. Effect of incorporated anion size on the e l e c t r o c h e m i c a l oxidation-reduction process, J. Electroanal. Chem., 224 (1987) 123.
221 Printed in The Netherlands
FUNCTIONALIZED CONDUCTING POLYMERS FOR DEVELOPMENT OF NEW POLYMERIC REAGENTS * TAKEO SHIMIDZU
Division of Molecular Engineering, Graduate School o[ Engineering, Kvoto Universi(v, Kvoto 606 (Japan) (Received September 3, 1986: accepted in revised form April 2, 1987)
Methods of preparation and applications of both functionalized conducting polymers and conducting polymers incorporating functional molecules are described. The development of such new polymeric reagents is illustrated by several examples.
INTRODUCTION There are many functional molecules. For their exploitation, conducting polymers are considered to be suitable matrices because their conductive properties may be used to probe the electronic structure and properties of functional molecules. We previously established a hybridization procedure for synthesis of conducting polymers with functional molecules by electrochemical polymerization [1,2] or chemical polymerization [2,3]. These functionalized conducting polymers show both the native function of the functional molecule and native conductivity. The present paper describes typical functions of conducting polymers incorporating functional molecules, methods of their preparation, and their utilization as polymeric reagents and in polymersupported reactions.
* Paper presented at the 3rd International Conference on Polymer-Supported Reactions in Organic Chemistry, Jerusalem, Israel, July 6-11, 1986 0167-6989/87/$03.50
1. PREPARATION OF CONDUCTING POLYMERS INCORPORATING FUNCTIONAL MOLECULES A functionalized conducting polymer may be prepared by electrolytic polymerization of pyrrole, thiophene, furan, aniline, etc., in presence of negatively charged functional molecules. The incorporation of the functional molecules is driven electrostatically by the positive charges of the partially oxidized conducting polymer matrices through a doping process, as shown in Scheme 1. Electrolytic polymerization may be easily achieved with a monomer solution in the presence of negatively charged functional molecules. A key concept of this preparative approach is that the resulting conducting polymer has a lower redox potential (doping-undoping) than its monomer; therefore anodic doping occurs simultaneously with electropolymerization. An electrolyte anion or functional anionic molecule is incorporated into the partially oxidized conducting polymer matrix so as to conserve its electroneutrality.
© 1987 Elsevier Science Publishers B.V.
222
F\ ®
@
m®
.=~
X=NH, S, 0
m F® F~ functional molecule Scheme 1
The resulting functionalized conducting polymers display their native functions; the functionalities and the conducting properties are not much reduced. Table 1 shows some examples. Chemical polymerization methods are also available for preparation of functionalized conducting polymers. Several techniques are shown in Table 2. In these cases, many kinds of functional molecules (negatively charged, neutral, positively charged) can be incorporated. Compared with the electrolytic polymerization method, the functions of several of the incorporated functional molecules and the conductivities of the resulting conducting polymers are reduced [2,3]. However, it is possible to texture a conducting layer anisotropically anywhere in the support.
2. PPy ELECTRODE INCORPORATING FeBPS AND ITS ELECTROCHROMISM Figure 1 shows the incorporation of tris(bathophenanthroline disulfonate) iron complex (FeBPS) into a poly(pyrrole) (PPy) matrix by galvanostatic electrolysis. The intensity of the absorption around 540 nm assigned to FeBPS increased over that assigned to PPy during electropolymerization of pyrrole. A sulfur content of 7.98% for the resulting FeBPS-PPy corresponded to a doping efficiency of 0.443 (ratio of sulfonate moieties to pyrrole units in PPy), which agreed with that reported previously for ordinary PPy [7]. FeBPS-PPy had as high a conductivity (7.0 S/cm) as ordinary PPy. FeBPS-PPy had a redox potential of 1.09 V on a Pt wire elec-
TABLE 1 Negatively charged functional molecules suitable for incorporation in conducting polymer matrices Group
Examples a
Function b
Organic molecule Metal complex
AQS, rose bengal, indigo carmine Lu(PTS) 2, Fe(BPS)n (BP)3_ ., Ru(BPS). (BP) 3_. MTPPS (M = H 2, Zn, Pd) FePTS [5], MTPS (M = Fe, Co, Mn) [6] RuO4- [4], PtCI] , AuCI~-, MnO4-, phosphotungstate PVSK. PSSNa, Nation® enzyme, nucleotide material
A,B A,B,C B E A,D,E F,G E,H
Inorganic metal ion Polyelectrolyte Biomaterial
a AQS = Anthraquinone-2-sulfonic acid. MTPPS = metal-tetra(4-sulfophenyl)porphyrin. MTPS = metaltetrasulfophthalocyanine. BPS = bathephenanthroline disulfonic acid. PVSK = potassium poly(vinylsulfate). PSSNa = sodium poly(styrene sulfonate) Nation® = Salt of sulfonated and highly fluorinated polymer (trademark of Du Pont) h A , electrochromism; B, photoelectric conversion; C, electrogenerated chemiluminescence; D, highly dispersed noble metal; E, catalyst; F, high mechanical strength conducting polymer; G, charge-controllable transport membrane; H, sensor.
223 TABLE 2 Methods for preparation of conducting polymer composites by chemical polymerization
polymerization ~[~
Chemical
~'~-J-[~-~
SEPTAL
S
Monomer (M) Support (S) Oxidant (O) Solvent
0
or
M
o ><
~2['" d
6
or
0
0
or
M
doping resulting from steric hindrance encountered by FeBPS in the tangled PPy structure. As regards electrochemical preparation of functional conducting polymer-coated electrodes, the low undoping efficiency resulted in effective fixation of FeBPS in the polymer matrix.
3. P H O T O S E N S I T I Z E D PPy TRODE D O P E D WITH ZnTPPS
ELEC-
According to the same procedure, zinc tetra(4-sulfophenyl)porphyrin (ZnTPPS) was incorporated into PPy at a ratio of 0.341 and conductivity of 0.1 S / c m . The yield of incorporation was 7.9 × 10 -8 eq of sulfonate per coulomb. Figure 3 shows a typical photocurrent-potential curve of a Z n T P P S - P P y ITO
28e.-
5
o
.(3 %-
3
..£21
<
0-
M
BLEND I NG
pyrrole, thiophene, furan, aniline, indole, their derivatives ion-exchange membrane, natural and synthetic membrane, porous glass, porous ceramics Lewis acid, halogen, peroxide, metal acid water, organic solvent, gas-phase reaction
trode, assigned to Fe2+/Fe 3+ in CH3CN, which agreed with the redox potential of FeBPS. Figure 2 shows the absorbance change around 540 nm of an FeBPS-PPy coated ITO electrode under various potentiostatic conditions. In Fig. 2(B) an inflection point appears at 1.1 V, the same potential as obtained by cyclic voltammetry. A distinct color change from bluish gray to dark red was observed on a transparent ITO electrode. The electrochromism was maintained over 1000 cycles of reversibility; its response time was < 100 ms. The incorporated FeBPS was hardly released from the PPy matrix even when FeBPS-PPy was sufficiently reduced. The incomplete un-
~3"
+Ms~y~
DI PP [ NG
0.4 I
Fig. 1. Time course of incorporation of FeBPS into PPy matrix under galvanostatic conditions: (e) absorbance at 540 nm; (©) absorbance at 380 nm; ( ~ ) absorbance at 620 nm.
1.ov
~
0.3 0.2
~o.1
01 2 3456 ElectroiysisTime
(rain)
~
o 400 600 800 0 (B) WGvelength(rim) ,
(A)
1.~0 V vs, SCE
2.0
Fig. 2. (A) Visible absorption spectra of FeBPS-PPycoated ITO electrode at various potentials in CH3CN. (B) Absorbance change at 540 nm of FeBPS-PPy-coated ITO electrode at the same conditions at in (A).
224 {I00 hA) 6
¸
4¸ 2 -%.5
0 (V vs
SCE)
-4
Fig. 3. Photocurrent-potential curve of ZnTPPS-PPycoated ITO electrode in Fe(CN)63-/4- aqueous solution.
chemical properties of an anionic dye-PPy electrode, we demonstrated that PPy with incorporated metal-free HTPPS was able to cover particulate TiO 2 when pyrrole was photo-polymerized oxidatively in the presence of Ag ÷ (electron acceptor) and HTPPS under irradiation at a wavelength > 320 nm. This procedure is a potentially new method of photoelectrochemical surface modification of a semiconductor, resulting in a new polymeric reagent with a combined semiconductor function.
4. CHARGE-CONTROLLABLE P P y POLYELECTROLYTE C O M P O S I T E S electrode in water containing 2.0 mmol/1 of Fe(CN) 3-/4- under irradiation at a wavelength > 390 nm. At > 0.3 V an appreciable anodic photocurrent ( > 600 n A / c m 2) was observed by the photo-AC method using a lock-in amplifier and a light chopper (20 Hz). The agreement of the action spectrum of the photocurrent with the visible absorption spectrum indicates that the incorporated ZnTPPS plays a significant role as a sensitizer for the generation of the anodic photocurrent. The current quantum efficiency at 435 nm was ca. 0.1%. The photocurrent was proportional to the intensity of incident light. Other sensitizers, e.g., RuBPS, rose bengal, and indigo carmine, proved also to be of use as functional molecules, and the resulting PPy electrodes showed a considerable anodic photocurrent. These observations illustrate that this doping method endows PPy with photoresponsivity. Some particulate semiconductors catalyze photo-induced oxidative polymerization of pyrrole in the presence of an appropriate electron acceptor under their band-gap excitation. As a result, the surfaces of these semiconductors are covered with PPy [8], and the adhering PPy is effective as a hole carrier from the valence band in the semiconductor to any electrolytes [9]. Utilizing the electro-
Anionic polyelectrolytes, e.g., PVSK (potassium poly(vinylsulfate)), PSSNa (sodium poly(styrene-4-sulfonate)), and Nafion ® were also incorporated into PPy according to the same procedure as described above [10]. The resulting PPy had (1) high conductivity, (2) high tensile strength, (3) very low undoping efficiency, (4) homogeneous and dense PPy surface; it exhibited (5) "polyion complex" formation, and (6) pseudo-cathodic doping; and behaved as (7) a charge-controllable membrane. Property (5) indicates that the incorporated polyelectrolyte forms a polyion complex by electrostatic attraction between partially oxidized PPy and the negative charges of the polyelectrolyte. Properties (6) and (7) indicate that the very low undoping efficiency ( < 1%) of the incorporated polyelectrolyte resulted from strong polyion complex formation and that electrolyte cations were incorporated into the matrix in order to conserve electroneutrality when PPy was reduced. The composites thus prepared have cation-exchange properties [18]. Their fixedcharge polarity changed reversibly when the composite was reduced and oxidized [11]. The electrochemically regulated conducting ion exchange polymer was termed a "charge-controllable membrane". Figure 4 illustrates the
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1 0 -1
I I IIII
[
|
1 0 ° 10 -2
C1/tool dm -3
I
I IIIIll
i
1 0 -1
I
I II
10 °
C1/rno[ dm -3
Fig. 4. Polarity change of fixed charges in PPy/pentane sulfonate membrane (left) and PPy/PVS membrane (right) for oxidized and reduced states, as determined by membrane potential (Aq') measurements in a KCI concentration cell. (O) membrane as prepared, ( ~ ) reduced membrane at - 1.0 V vs. SCE. (O) oxidized membrane at + 2.0 V. A negative value of A~t, indicates the existence of a fixed positive charge in the membrane.
behavior of this charge-controllable membrane. Using thus type of membrane, a deionization system [12] and a polymer battery [13] were constructed.
5. HIGHLY DISPERSED METAL ELECTRODES When a metalate ion such as PtC12- or AuC1 4 was used as electrolyte, we obtained PtCI24- -PPy and AuCI 4-p°lythi°phene composites. The incorporation of Pt 2+ and Au 3+ was confirmed by ESCA measurements. The phosphotungstate anion was also incorporated into PPy and the composite showed distinct electrochromism [14].
6. PPy COMPOSITES INCORPORATING OLIGONUCLEOTIDES FOR USE AS SENSORS When pyrrole was electropolymerized in the presence of adenosine triphosphate, poly(adenylic acid), uridine triphosphate, poly(uridylic acid), or a sequence-defined oligonucleotide as an electrolyte, all were efficiently incorporated into the PPy matrix [15-17]. The incorporation was confirmed by elemental analysis of phosphorus. The resulting PPy electrodes have in principle the capacity to recognize DNA and RNA analogs in an electrolytic solution through the change in rest potential resulting from base-base interactions by stacking and hydrogen bonding. The results in Table 3 show that PPy com-
226 TABLE 3 Surface potential changes of PPy electrodes incorporating nucleotidic materials in various nucleotide solutions Electrode
Substrate/10 -4 M
Potential change/10 -3 V
pA/PPy pA/PPy pU/PPy pU/PPy Poly A / P P y Poly A / P P y Poly U / P P y Poly U / P P y pApUpApUpApUpApU/PPy pApUpApUpApUpApU/PPy pApUpApUpApUpApU/PPy pApUpApUpApUpApU/PPy pApUpApUpApUpApU/PPy pApUpApUpApUpApU/PPy
pA pU pA pU Poly A Poly U Poly A Poly U pApUpApUpApUpApUpApUpApU pApUpApUpApUpApU pApUpApUpApU pApUpApU pCpGpCpGpCpGpCpG pCpGpCpGpCpG
-0.210 -0.113 -0.128 +0.210 -0.410 - 0.872 - 0.678 - 0.210 - 0.709 - 0.721 - 0.628 - 0.594 - 0.116 - 0.109
7. PPy COMPOSITES INCORPORATING NUCLEIC ACIDS AS POLYMERIC SUPPORTS
posite/Pt electrodes incorporating oligonucleotides can serve as sensors as a result of complementary base-base interactions, reflected by the changes in potential.
A conducting PPy polymer can easily incorporate a nucleic acid as dopant. AccordAPPLICATION
TO SYNTHESIS
( I )
HOMOOLIGONUCLEOTIDES
(PPY+--PU(PU)nU
> PPy (REDUCTION) PPy+--~pU(PU)nUP > PPY
PPY+---PU + U + PIM3
PPY+--~PA + 2 A + 2 PIM3
) PPY+~PAPAPA
~ PPY (REDUCTION)
+ pU(PU)nU 93% + pU(PU)nUP
7%
+ PAPAPA
CONY, 23% 2'5'-2'5' 441 2'5'-3'5' 20% 3'5'-2'5' 211 3'5'-3'5' 15%
APPLICATION TO SYNTHESIS ( I I ) >NPCL2
A
SEQUENCE-DEFINED OLIGONUCLEOTIDES PPY+---PUPA
• PPY + PUPA
) PUPA
PPY+--PU
~" ~ PPY+--PU>PN<~ ~.,T.ET~AZOLE) 80% (REDUCTION) (i 2 + H20) 96% 98~ U"I"-"'"~=PPY+--PUPU ) PPY + PUPD ) PUPU 89% 96% >NPCL2 A PPY+--PAPA ~ PPY + PAPA ) PAPA ppy+__pA~ppy+.__pA>PN<~AZOLE) 75% (REDUCTION) (I 2 + H20) 94% 88%
U
~PPY+----PAPU 80%
Scheme 2
~ PPY + PAPU
~ PAPD 94%
227
ingly, PPy can be used as a polymeric support. Both homo-oligoribonucleotides and sequence-defined oligoribonucleotides were synthesized using PPy as a polymeric support, as shown in Scheme 2. The results demonstrate that the conducting polymer can be used for both methods of synthesis of oligonucleotides. Advantage of this polymeric support are: (1) protection of the phosphoric acid moiety is unnecessary and (2) the resulting oligonucleotide is easily removed by electrolytic reduction of the conducting polymer support.
8
9
10
11
In conclusion, it may be stated that conducting polymer matrices provide an interesting and useful focus for expansion of the fields of polymeric reagent research and molecular engineering.
12
REFERENCES
14
1 T. Shimidzu, T. lyoda and K. Fukui, Functionalizations of conducting polymer modified electrodes, Ann. Rep. Jpn. Chem. Fiber Res., 42 (1985) 71. 2 T. Shimidzu and T. lyoda, Functionalized conducting polymer membranes--In pursuit of novel function of membrane, Membrane, 11 (1986) 71. 3 T. Shimidzu, T. Iyoda and K. Fukui, Conducting polymer composite membrane, Ann. Rep. Jpn. Chem. Fiber Res., 43 (1986) 51. 4 R. Naufi, The incorporation of ruthenium oxide in polypyrrole films and the subsequent photooxidation of water at n-gap photoelectrode, J. Electrochem. Soc., 130 (1983) 2126. 5 R.A. Bull, F.-R. Fan and A.J. Bard, Polymer films on electrodes. 13. Incorporation of catalysts into electronically conductive polymers. Iron phthalocyanine in polypyrrole, J. Electrochem. Soc., 131 (1984) 687. 6 K. Okabayashi, O. Ikeda and H. Tamura, Electrochemical doping with meso-tetrakis(4-sulfonatophenyl)-porphyrin cobalt of a pyrrole film electrode, Chem. Comm., (1983) 1821. 7 M. Salmon, A.F. Diaz, A.J. Logan, M. Knounbi and J. Bargon, Chemical modification of conducting
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polypyrrole films, Mol. Cryst. Liq. Cryst., 83 (1982) 265. Y. Taniguchi, H. Yoneyama and H. Tamura, Hydrogen evolution on surface-modified powder photocatalysts in aqueous ethanol solutions, Chem. Lett., (1983) 269. A.J. Frank and Honda, Oxygen and hydrogen generation from water on polymer-coated CDS photoanodes, J. Phys. Chem., 86 (1982) 1933. T. lyoda, A. Ohtank T. Shimidzu and K. Honda, Charge-controllable membrane. Polypyrrole polyelectrolyte composite membrane through anodic doping process, Chem. Lett., (1986) 687. T. Shimidzu, A. Ohtani, T. lyoda and K. Honda, A functionalized polypyrrole film prepared by chemical polymerization at a vapor-liquid interface, J. Chem. Soc. (London), Chem. Commun., (1986) 1414. T. Shimidzu, A. Ohtani, T. Iyoda and K. Honda, Effective adsorption desorption of cations on a polypyrrole-polyanion composite anode, J. Chem. Soc. (London), Chem. Commun., (1986) 1415. T. Shimidzu, A. Ohtani, T. lyoda and K. Honda, A novel type of polymer battery using a pyrrole-polyanion composite electrode, J. Chem. Soc. (London), Chem. Commun., (1987) 327. T. Shimidzu, A. Ohtani, A. Aiba, T. lyoda and K. Honda, Preparation and electrochromism of phosphotungstate incorporating polypyrrole, J. Chem. Soc., in preparation. T. Shimidzu, K. Yamana, K. Nakamichi, and A. Murakami, Uridine oligonucleotide synthesis by the reaction of uridine with tri(imidazole-l-yl) phosphine, J. Chem. Soc., Perkin Trans. I, (1981) 2294. T. Shimidzu, K. Yamana, N. Kanda and S. Maikuma, A simple and convenient synthesis of 3 ' - 5 ' - or 2 ' - 5 ' - l i n k e d oligoribonucleotide by polymerization of unprotected ribonucleoside using phosphorus tris-azole, Nucleic Acids Res., 12 (1984) 3257. T. Shimidzu, K. Yamana and S. Maikuma, Aminophosphordichloridite. A new phosphorylating reagent for one-pot synthesis of 3' 5'- or 2 ' - 5 ' - l i n ked diribonucleotide having definite sequence, Tetrahedron Lett., 25 (1984) 4237. T. Shimidzu, A. Ohtani, T. lyoda and K. Honda, Charge-controllable polypyrrole/polyelectrolyte composite membranes. Part II. Effect of incorporated anion size on the e l e c t r o c h e m i c a l oxidation-reduction process, J. Electroanal. Chem., 224 (1987) 123.