Yoshimi Kurimura

Macromolecule metal complexes — Reactions and molecular recognition

In solution, macromolecule-metal complexes form microheterogenous regions occupied by the polymer-backbone where physicochemical properties differ from those of the bulk solution. Most of the significant reaction patterns of macromolecule-metal complexes are due to the characteristic nature of these microheterogenous regions. This article reviews recent studies of the reactions of macromolecule-metal complexes. For example, fundamental reactions such as complex formations, ligand substitution and electron transfer reactions, as well as interactions of metal complexes with biological substances, photochemical behavior, and molecular recognition are described.

KINETICS OF INTRA-POLYMER ELECTRON-TRANSFER REACTIONS IN MACROMOLECULE-METAL COMPLEXES

A macromolecule–metal complex with redox centres on the same polymer chain of partially quaternized poly(1-vinylimidazole)(QPVIm) has been designed. In this complex, Co(tfacacen)(tfacacen =N,N′-ethylenebis(1,1,1-trifluoro-4-iminopentan-2-one), a CoII–Schiff base complex, and quaternized imidazolium residues, an oxidizing agent, are both linked to a polymer backbone. The mechanism of the electron-transfer reaction between Co(tfacacen) and the quaternized imidazolium residue on this macromolecular complex have been investigated. The electron-transfer rate depends linearly on the concentration of CoII residues and the degree of quaternization but is independent of the concentration of quaternized imidazolium residue. These dependencies indicate that, under the experimental conditions, an intra-polymer electron-transfer reaction occurs in this system. The reaction product formed by reduction of the quaternized imidazolium residue was identified by means of 1H NMR and absorption spectroscopies. The results show that the predominant reduction product is 3-ethyl-4-imidazoline-containing polymer.

Conformational transition of poly(methacrylic acid-co-styrenesulfonic acid) in aqueous solution

The conformational transition of poly(methacrylic acid-co-styrenesulfonic acid) (PMAS) in aqueous solution was investigated by the luminescence probe method using Ru(bpy)32+ and viscometry. PMAS-8 (8 mol% styrenesulfonic acid (SS) residue) and PMAS-16 (16 mol% SS residue) revealed a unique conformational transition with changing negative charge on a polymer chain that had at least four conformations in aqueous solution. The luminescence behaviour of Ru(bpy)32+ and the viscosity characteristics of PMAS solution indicated that the conformational transition was brought about by changing the negative charge of the polymer chain.

Mechanism of the tris(bipyridine)ruthenium(II) photosensitized reversible redox reaction of a macrocyclic cobalt(III) complex in gelatin hydrogel and hydrosol

The Ru(bpy)2+3 photosensitized reduction of a macrocyclic CoIII complex, Co(N4)(OH2)3+2(N4= 5, 7, 7, 12, 14, 14-hexamethyl-1, 4, 8, 11-tetraazacyclotetradeca-4, 11-diene), has been investigated in the networks of gelatin hydrogel and hydrosol. In these systems, a net charge separation proceeds due to reduction of the CoIII complex by the excited state of Ru(bpy)2+3 and the scavenging of the oxidized species of Ru(bpy)2+3 by a gelatin molecule. The photochemically generated CoII complex species reacts slowly with the oxidized species of gelatin. Then a reversible photo-induced redox reaction of CoIII takes place repeatedly in these systems. The results indicate that the tyrosine residue in gelatin and the corresponding oxidized species in the oxidized form of gelatin act as a reducing agent for the oxidized form of the photosensitizer and an oxidizing agent for the reduced CoIII species, respectively.

Complexation of polymer-bound imino diacetate-type chelating agents with some transition-metal ions. Effect of charged polymer chains on chelate formation reactions

Acid dissociation constants (Ka) of the polymer-bound imino diacetate analogue, 4-vinylbenzylamine-N, N′-diacetate co-styrenesulphonte (P-SS) and 4-vinylbenzylamine-N, N′-diacetate co-N-vinylpyrrolidone (P-VPRo), and the formation constants of (P-SS)–M2+(M = Co, Ni, Cu) chelates have been determined by means of potentiometric titration and spectrophotometry, respectively. The values of Ka1 and Ka2 of P-SS and P-VPRo are smaller than those of the corresponding low molecular weight model compound, benzylamine-N, N′-diacetate (BDA), and the formation constants of the (P-SS)–M2+ chelates are larger than those of the corresponding BDA–M2+ chelates by a factor of 10–102, depending on the metal ions. The results obtained in the polymer system are largely explained in terms of a powerful microheterogeneous field effect of the anionic polyelectrolyte chain.

CHARACTERISTIC BEHAVIOUR OF THE COMPLEXATION OF COPPER(II) WITH POLYMER-BOUND VINYLIMIDAZOLE LIGANDS

Some polymer ligands of N-vinylimidazole-co-N-vinylpyrrolidone (Plm) having different mole fractions of N-vinylpyrrolidone have been prepared. Successive formation constants for the complexation of CuII with these Plms in aqueous solutions have been determined by means of spectrum deconvolution at pH 3.5. The present results demonstrate that the successive formation constants are given by K1=[CuL]/[Cu][L], K2=[CuL2]/[CuL], K3=[CuL3]/[CuL2] and K4=[CuL4]/[CuL3](charge omitted, L = imidazole residue on Plm). The results clearly indicate that the concentration ratio, [CuL] : [CuL2] : [CuL3] : [CuL4], is largely constant for a given Plm when the concentration of imidazole residues is varied. The values of K2, K3 and K4 decrease with increasing mole fraction of vinylpyrrolidone residues (VPRo) in the Plms. The successive formation constants increase in the order K2 K3 > K4) is found for Plm with a VPRo mole fraction of 0.8. Above this VPRo mole fraction, CuL4 species are rarely formed. These results also suggest that the distributions of CuLn species in CuII–Plm solutions can be controlled by adjusting the content of VPRo in the Plm.

Kinetic and equilibrium studies of the complexations of polymer-bound imidazole ligands with a macrocylic cobalt(III) complex

The rate and equilibrium constants of the first- and second-step complexations of the axial sites of a macrocyclic CoIII complex, Co(N4)(OH2)3+2(N4= Me6[14]4,11-dieneN4), with polymer-bound imidazole ligands such as N-vinylimidazole-co-N-vinylpyrrolidone (Plm) and partially quarternized poly(N-vinylimidazole)(QPlm) in aqueous solutions have been determined by means of spectrophotometry at pH 6.5. A unique aspect of the behaviour of the complex formation of the polymer ligands is that the formation of Co(N4)(Plm)3+2 from Co(N4)(B)(Plm)m+(m= 3 for B = H2O or m= 2 for B = OH–) proceeds via an intramolecular process, whereas that of the corresponding ligation for the non-polymer system follows second-order kinetics. For the polymer system the concentration ratio, [Co(N4)(Plm)3+2]/[Co(N4)(B)(Plm)m+], at the equilibrium state is independent of the concentration of the polymer ligand. The effect of polymer ligand on the rate and equilibrium of the complex formations are discussed in the light of the results obtained.

Intra-polymer electron-transfer reaction between partially quaternized poly(1-vinylimidazole) and a cobalt(II) Schiff-base complex: effect of alkyl chain length

A macromolecule–metal complex having redox centres on the polymer backbone of partially quaternized poly(1-vinylimidazole)(QPVIm) has been designed. This complex consisted of a divalent Co(tfacacen) complex [tfacacen =N,N′-ethylenebis (1,1,1-trifluoro-4-iminopentan-2-one)] coordinated to imidazolyl residues on QPVIm and also of quaternized imidazolium residues linked covalently to the same polymer backbone. The Co(tfacacen) and the quaternized imidazolium residues act as reducing and oxidizing agents, respectively. The intra-polymer electron-transfer reaction between Co(tfacacen) and the quaternized imidazolium residue has been investigated in connection with alkyl chain length in the quaternized imidazolium residue. The order of increasing reaction rate was ethyl < n-butyl < n-hexyl regarding alkyl chains in the quaternized imidazolium residues. Further, the reaction rate dramatically increased by addition of water. The facts suggest that Co(tfacacen) solvophobically interacts with the alkyl chains in the quaternized imidazolium residues. Viscosity measurements showed that the volume of the polymer domain of QPVIm, which was the reaction site, increased with increasing alkyl chain length, degree of quaternization, and amount of water added to DMF. This was attributed to a decrease in electrostatic attraction between the imidazolyl and quaternized imidazolium residues. Therefore, these results suggested that an increase of alkyl chain length and addition of water results in the enhancement of reaction rate.

Tris(bipyridine)ruthenium(II)-photosensitized reduction of a CoIII–Schiff base complex in a network of gelatin hydrogel and in an aqueous gelatin solution

The Ru(bpy)2+3 photosensitized reduction of a CoIII–Schiff base complex proceeds effectively in a network of gelatin hydrogel and in an aqueous gelatin solution under anaerobic conditions. In both systems, a reduced intermediate species of the CoIII complex coordinated to a gelatin molecule, which has an absorption maximum at 450 nm (R450), was initially generated. After irradiation had been stopped, R450 turned slowly to the diaqua CoII–Schiff base complex in the hydrogel system whereas it was oxidized gradually to the initial CoIII–Schiff base complex in an aqueous gelatin solution. It is suggested from the results obtained that the gelatin acts as the ligand for the CoIII complex, and both the electron donor and, probably, electron acceptor for the photosensitized reactions in both the systems.

Effect of the Conformation of Polymer Chain on the Reduction Rate of Polyacrylatopentaamminecobalt(III) by Polymer-Bound Ferrous Chelates and the Excited State of Tris(Bipyridine)Ruthenium(Ii)

Abstract Electron transfer reactions of Co(NH3)5PAA (PAA = polyacrylic acid) with either the polyanionic polymer-bound ferrous chelate, Fe11P-SS (P-SS = vinylbenzylaminediacetate-co-styrenesulfonate) or the uncharged polymer-bound ferrous chelate, Fe11P-VPRo (P-VPRo = vinylbenzylaminediacetate-co-vinylpyrrolidone), and the Ru(bpy)2+ 3 photosensitized reduction of Co(NH3)5PAA have been investigated in aqueous solutions at pH 5.4, I = 0.06 (I is ionic strength), and 25°C. For the ferrous chelate reductions, the second-order rate constants for Fe11-PSS and Fe11P-VPRo were almost equal to that for the corresponding nonpolymer-bound ferrous chelate, Fe11BDA (BDA = benzylaminediacetate). The results indicate that there is no appreciable steric hindrance due to the polymer chains of the polymer-bound ferrous chelates and that the effect of columbic repulsion force between the polyanion chains can be ignored for the reaction of Co(NH3)5PAA with Fe11P-SS. The results also suggest that there are two kinds of the pe...