Seiichiro Iijima

Amperometric determination of pyruvate, phosphate and urea using enzyme electrodes based on pyruvate oxidase-containing poly(vinyl alcohol)/polyion complex-bilayer membrane

Abstract An amperometric pyruvate-sensing electrode was prepared by immobilizing pyruvate oxidase (PyOx) on a polyion complex membrane. First, aqueous solutions of poly- l -lysine and poly(4-styrenesulfonate) were successively placed on a mercaptopropionic acid-modified gold surface and allowed to dry. A photo-crosslinked poly(vinyl alcohol) layer containing PyOx was then formed on the poly- l -lysine/poly(4-styrenesulfonate)-complex layer. The polyion complex layer was effective for eliminating electrochemical interferents such as l -ascorbic acid, uric acid, l -cysteine and acetaminophen, whereas the hydrogen peroxide produced through the PyOx-catalyzed reaction permeated easily through the layer. This resulted in a high sensitivity (detection limit, 50 nM) and a low interference level (e.g. the ratio of response for l -ascorbic acid to that for the same concentration of pyruvic acid, 0.18). The electrode could be used for determining phosphoric acid (detection limit, 0.2 μM), since PyOx consumes phospholic acid as the co-substrate during the course of pyruvate oxidation. Further, an amperometric urea-sensing electrode (detection limit, 0.5 μM) was prepared by coupling the phosphate-sensing system with urea amidolyase which catalyzes an ATP-consuming urea hydrolyzation.

RAPID MEASUREMENT OF TRANSAMINASE ACTIVITIES USING AN AMPEROMETRIC L-GLUTAMATE-SENSING ELECTRODE BASED ON A GLUTAMATE OXIDASE-POLYION COMPLEX-BILAYER MEMBRANE

Abstract An amperometric l -glutamate-sensing electrode was prepared by immobilizing glutamate oxidase (GlOx) on a polyion complex layer-modified electrode. First, a monolayer of 3-mercaptopropionic acid was made on the surface of a gold electrode by immersing it in an ethanol solution containing the modifier. Next, aqueous solutions of poly- l - lysine and poly(4-styrenesulfonate) were successively placed on the electrode surface and allowed to dry. Finally, a GlOx layer was formed on the poly- l- lysine/poly(4-styrenesulfonate)-complex layer by crosslinking the enzyme by the addition of a glutaraldehyde solution. The use of thin bilayer system with the inner, polyion complex membrane, which showed permselectivity based on the solute size with the molecular cut-off of ≈100, brought high performance characteristics to the l- glutamate-sensing electrode; it showed high sensitivity (detection limit, 20 nM), rapid response (100% response time, 3 s), low interferential level (the ratio of response for l -ascorbic acid to that for the same concentration of l -glutamic acid, 8×10−2), and high stability (usable for more than a month). The bilayer-based electrode was useful for the rapid measurement of glutamate–oxaloacetate transaminase (GOT) and glutamate–pyruvate transaminase (GPT) in serum sample: each transaminase (0.2–1000 U l−1) could be determined within 10 s.

Amperometric glucose-sensing electrode based on carbon paste containing poly (ethylene glycol)-modified glucose oxidase and cobalt octaethoxyphthalocyanine

Abstract An amperometric enzyme electrode for glucose was prepared by incorporating poly (ethylene glycol)-modified glucose oxidase and cobalt octaethoxyphthalocyanine [CoPc(OEt)8], a new mediator, into a carbon paste matrix. The polymer-modified enzyme exhibited a higher activity than the native enzyme in the hydrophobic carbon paste medium. CoPc(OEt)8 could oxidize the enzyme at more negative potentials than unsubstituted cobalt phthalocyanine (CoPc). Further, the CoPc(OEt)8-mediated enzyme electrode showed a high stability: the electrode response to glucose did not decrease for at least 4 weeks (or for 700 assays), whereas the glucose response from a CoPc-mediated enzyme electrode fell to half of the initial value within 2 weeks (or after 300 assays). CoPc(OEt)8, a paraffin-oil soluble derivative of CoPc, incorporated in the bulk of carbon paste, diffused towards the electrode surface so as to renew continuously the electrode surface, which resulted in the high stability of the new mediator-based enzyme electrode.

Structures and spin states of bis(tridentate)-type mononuclear and triple helicate dinuclear iron(II) complexes of imidazole-4-carbaldehyde azine.

Mononuclear [Fe(H(2)L(R))(2)](2+) and dinuclear [Fe(2)(H(2)L(R))(3)](4+) (R = H, 2-Me, 5-Me) complexes containing the new imidazole-4-carbaldehyde azine ligand (H(2)L(H)) and its derivatives (H(2)L(2-Me) and H(2)L(5-Me)) prepared from the condensation reaction of 4-formylimidazole or 2-methyl- or 5-methyl-4-formylimidazole with hydrazine (2:1) were prepared, and their magnetostructural relationships were studied. In the mononuclear complexes, H(2)L(R) acts as an unsymmetrical tridentate ligand with two imidazole nitrogen atoms and one azine nitrogen atom, while in the dinuclear complexes, H(2)L(R) acts as a dinucleating ligand employing four nitrogen atoms to form a triple helicate. At room temperature, [Fe(2)(H(2)L(H))(3)](ClO(4))(4) and [Fe(2)(H(2)L(2-Me))(3)](ClO(4))(4) were in the high-spin (HS) and low-spin (LS) states, respectively. The results are in accordance with the ligand field strength of H(2)L(2-Me) with electron-donating methyl groups being stronger than H(2)L(H), with the order of the ligand field strengths being H(2)L(2-Me) > H(2)L(H). However, in the mononuclear [Fe(H(2)L(H))(2)](ClO(4))(2) and [Fe(H(2)L(2-Me))(2)](ClO(4))(2) complexes, a different order of ligand field strengths, H(2)L(H) > H(2)L(2-Me), was observed because [Fe(H(2)L(H))(2)](ClO(4))(2) was in the LS state while [Fe(H(2)L(2-Me))(2)](ClO(4))(2) was in the HS state at room temperature. X-ray structural studies revealed that the interligand steric repulsion between a methyl group of an H(2)L(2-Me) ligand and the other ligand in [Fe(H(2)L(2-Me))(2)](ClO(4))(2) is responsible for the observed change in the spin state. Two kinds of crystals, needles and blocks, were isolated for [Fe(2)(H(2)L(H))(3)](BF(4))(4), and both exhibited a sharp spin transition, [LS-HS] <--> [HS-HS]. The spin transition of the block crystals is more abrupt with a hysteresis, T(c) upward arrow = 190 K and T(c) downward arrow = 183 K with DeltaT = 7 K.

Enzyme electrodes based on self-assembled monolayers of thiol compounds on gold

Thiol monolayers prepared on gold electrodes have been proved to be useful as the anchor layers to immobilize enzymes molecules. An ion complex layer containing enzyme molecules can be prepared by the co-adsorption of the enzyme and poly-l-lysine onto a mercaptopropionic acid-modified gold surface. Enzymes, such as glutamate oxidase, glucose oxidase and lactate oxidase, were immobilized with high surface densities, and the enzyme-immobilized electrodes could be used for detecting the corresponding enzyme substrate. The UV irradiation onto the surface of gold electrode modified with an N3-functionalized thiol in an enzyme solution produced an enzyme layer, which was formed through the photoreaction between the N3-group and enzyme molecule. The activity of the immobilized enzyme (glucose oxidase) was rather low. However, the photochemical method is still interesting because it can provide the photolithographic patterning of enzyme layers.

One-dimensional Spin-crossover iron(II) complexes bridged by intermolecular imidazole-pyridine NH· · · N hydrogen bonds, [Fe(HLMe)3]X2 (HLMe = (2-Methylimidazol-4-yl-methylideneamino-2-ethylpyridine; X = PF6, ClO4, BF4)

2-Methylimidazol-4-yl-methylideneamino-2-ethylpyridine (abbreviated as HL(Me)) is the 1:1 condensation product of 2-methyl-4-formylimidazole and 2-aminoethylpyridine and functions as a bidentate ligand to the iron(II) ion to produce the 3:1 complexes together with anions, [Fe(HL(Me))(3)]X(2) (X = PF(6) (1), ClO(4) (2), BF(4) (3)). The magnetic susceptibilities, differential scanning calorimetric measurements, and Mossbauer spectral measurements demonstrated that complexes 1, 2, and 3 showed a steep one-step spin crossover (SCO) between the high-spin (HS, S = 2) and low-spin (LS, S = 0) states with small thermal hysteresis. Three complexes have an isomorphous structure and are crystallized in the same monoclinic space group, C2/c, both in the HS and LS states. The iron(II) ion has the octahedral coordination geometry of a facial isomer with N(6) donor atoms of three bidentate ligands, in which an imidazole and an imine nitrogen atom per ligand participate in the formation of the coordination bond, but the pyridine nitrogen is free from coordination. The complex cation fac-[Fe(HL(Me))(3)](2+) is a chiral species with a Delta or Lambda isomer, and the adjacent Delta and Lambda isomers are linked alternately by an intermolecular imidazole-pyridine NH...N hydrogen bond to produce an achiral 1D chain. The two remaining imidazole moieties per complex are hydrogen-bonded to the anions that occupy the space among the chains. The SCO profile becomes steeper with the decrease of the anion size (73.0 A(3) for PF(6)(-), 54.4 A(3) for ClO(4)(-), and 53.4 A(3) for BF(4)(-)). The SCO transition temperature T(1/2) of the PF(6) (1), ClO(4) (2), and BF(4) (3) salts estimated from the magnetic susceptibility measurements are (T( downward arrow) = 151.8 K, T( upward arrow) = 155.3 K), (T( downward arrow) = 184.5 K, T( upward arrow) = 186.0 K), and (T( downward arrow) = 146.4 K, T( upward arrow) = 148.2 K), respectively, indicating that the T(1/2) value is not in accord with the anion size.

Moessbauer Spectroscopic Study of Magnetic Ordering in Oxalate-Bridged Cr(III)-Fe(II) and Fe(III)-Fe(II) Systems

Abstract Magnetic ordering phenomena in mixed-metal assemblies {NBu4[Fe(II)M(III)(ox)3]}3∞ (M=Cr (1), Fe (2)) were studied by using 57Fe Moessbauer spectroscopy, where NBu4 +=tetra(n-butyl)ammonium ion, ox2-=oxalate ion. Nuclear Zeeman splittings were observed in the Moessbauer spectra of both 1 and 2 at low temperatures (below 10 K for 1 and 41 K for 2), which indicated the occurrence of three-dimensional magnetic ordering in these complexes under zero applied field.

Use of Polydimethylsiloxane for Constructing Amperometric Glucose‐Sensing Enzyme Electrode with Low Interference Level

Glucose-sensing electrodes based on the cathodic detection of oxygen consumption through the glucose oxidase (GOx) reaction were constructed by using polydimethylsiloxane (PDMS). One electrode, a PDMS/GOx-bilayer electrode was fabricated by placing an enzyme layer on a PDMS-coated electrode, which was prepared by dip-coating from an aqueous dispersion of the siloxane polymer. Another enzyme electrode, an electrode with a PDMS layer containing lipid-modified GOx, was prepared by placing aqueous dispersions of the polymer and the modified enzyme on the base electrode surface and drying. The electrode using modified GOx could easily be prepared and suitable for measuring glucose in high concentrations (around 5 mM), compared to the bilayer-based system. On the other hand, both the electrodes could be used for the selective determination of glucose: the permselectivity of PDMS made it possible to monitor the oxygen consumption rate without serious electrochemical interferences.

Magnetic susceptibility of some mixed-metal compounds NBu4Fe(II)[Fe(III)xCr(III)1 − x(ox)3]

Abstract The magnetic susceptibility behavior of the mixed-metal molecular-based compounds NBu 4 Fe(II)[Fe(III) x Cr(III) 1 − x (ox) 3 ] has been investigated in the temperature range 5–290 K. The compounds exhibit a crossover from ferromagnetic ordering for NBu 4 Fe(II)[Cr(III)(ox) 3 ] to ferrimagnetic ordering for NBu 4 Fe(II)[Fe(III)(ox) 3 ] as a function of concentration. The increasing substitution of Cr(III) ions by Fe(III) ions showed gradual increases in T N and in the value of the Curie-Weiss constant. The compounds with x > 0.4 have been found to exhibit a spin-glass-like behavior in the temperature region below the magnetic transition temperature. The coexistence of a disordered structure and competition between the ferromagnetic and ferrimagnetic interactions could lead to the observed spin-glass-like behavior in these compounds.

Ferrocene-attached l-lysine polymers as mediators for glucose-sensing electrodes

Abstract Two kinds of water-soluble polymers having ferrocenyl groups were prepared by the reactions of ferrocenoyl chloride with a homopolymer and a copolymer of l -lysine. The polymers acted as electron mediators between electrodes and the reduced form of glucose oxidase. Amperometric glucose-sensing electrodes were constructed by the simultaneous immobilization of each polymeric mediator and glucose oxidase near the surface of a glassy carbon electrode with a semipermeable membrane. The sensing-electrode using the ferrocene-attached l -lysine homopolymer was usable for the determination of glucose concentrations up to 6 mM.