Application of PEDOT‐CNT Microelectrodes for Neurotransmitter Sensing

In this work, composite microelectrodes from poly(3,4‐ethylenedioxythiophene) (PEDOT) and carbon nanotubes (CNT) are characterized as electrochemical sensing material for neurotransmitters. Dopamine can be detected using square wave voltammetry at these microelectrodes. The CNTs improve the sensitivity by a factor of two. In addition, the selectivity towards dopamine in the presence of ascorbic acid and uric acid was examined. While both electrodes, PEDOT and PEDOT‐CNT are able to detect all measured concentrations of dopamine in the presence of uric acid, small concentrations of dopamine and ascorbic acid are only distinguishable at PEDOT‐CNT electrodes. Changing the pH has a strong influence on the selectivity. Moreover, it is possible to detect concentrations as low as 1 µM dopamine in complex cell culture medium. Finally, other catecholamines like serotonin, epinephrine, norepinephrine and L ‐dopa are also electrochemically detectable at PEDOT‐CNT microelectrodes.     

Enantioselective Recognition of Dopa Enantiomers in the Presence of Ascorbic Acid or Tyrosine

A simple sensor was obtained through N‐isobutyryl‐L ‐(D )‐cysteine enantiomers self‐assembled monolayer. It was demonstrated that the N‐isobutyryl‐cysteine modified gold electrodes can enantioselectively recognize 3,4‐dihydroxyphenylalanine (dopa) enantiomers. The electrocatalytic behaviors of enantiomers were analyzed with cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Selectivity of the chiral surface was estimated by investigating two mixture enantiomers (dopa‐ascorbic acid and dopa‐tyrosine), it certified that the sensor was only satisfactorily used to specific recognize dopa enantiomers. The possible mechanism for the enantioselective recognition was discussed.     

Chemie freier cyclischer vicinaler Tricarbonyl‐Verbindungen (‘1,2,3‐Trione') Teil 2. Redox‐Reaktionen von 1,2,3‐Trionen mit En‐1,2‐diolen (‘Reduktonen'), 2‐Alkoxy‐en‐1‐olen,En‐1,2‐diaminen und verwandten Spezies

Chemistry of Free Cyclic Vicinal Tricarbonyl Compounds (‘1,2,3‐Triones'). Part 2. Redox Reactions of 1,2,3‐Triones with Ene‐1,2‐diols (‘Reductones'), 2‐Alkoxy‐en‐1‐ols, Ene‐1,2‐diamines, and Related Species . Midstanding carbonyl groups of cyclic 1,2,3‐triones 4 possess outstanding electrophilic (electron‐pair accepting) as well as oxidizing (one‐electron accepting) properties. Their reactions with selected electron‐rich CC bonds as efficient nucleophiles (A_N reactions) and as efficient reducing agents (SET (single electron transfer) reactions) are studied. In a few cases, short‐lived charge‐transfer colors could be observed. Particularly, free didehydro‐5,6‐O‐isopropyliden‐L ‐ascorbic acid ( 4g ), its O,C‐adduct 8g to 5,6‐O‐isopropylidene‐L ‐ascorbic acid ( 1g ), and – via an independent pathway – the ostensible C,C‐dimer 10a of mono‐dehydrodimedone reductone were prepared. Intermediate radical anions 4 ^.− can be considered to be ideal representatives of dicapto‐dative radicals. Novel large‐scale syntheses of 3,4‐dihydroxyfuran‐2(5H)‐one ( 1e ) and of its vicinal trione 4e are presented.     

Miniemulsion polymerization initiated by L‐ascorbic acid and sulfonate/sulfate surfactants

Styrene miniemulsions that were stabilized by common anionic surfactants (sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, and disulfonated alkyl diphenyl oxide sodium salt) polymerized at 25 °C in the presence of L ‐ascorbic acid without the addition of a free‐radical initiator. The polymerizations exhibited high rates and molecular weights, with conversions greater than 70% achieved in less than 1 h and weight‐average molecular weights greater than 1 × 10⁶ g/mol. Polymers did not form in the absence of L ‐ascorbic acid. Although the final conversion was only slightly independent on the L ‐ascorbic acid concentration, it was dependent on the surfactant concentration. The rate and final conversion were also strongly dependent on the surfactant type. Moreover, it was possible to initiate polymerizations with a monomer‐soluble derivative of L ‐ascorbic acid (L ‐ascorbic acid 6‐palmitate), although the rates were dramatically reduced compared with those when water‐soluble L ‐ascorbic acid was used. High yields and high‐molecular‐weight polymers were also produced with butyl acrylate and methyl methacrylate with L ‐ascorbic acid in the presence of sodium dodecyl benzene sulfonate. The initiation was attributed to an interaction between the surfactant and L ‐ascorbic acid, which formed a redox initiation system that generated radicals capable of adding monomer. These results are of particular significance for redox‐initiated emulsion/miniemulsion polymerizations with L ‐ascorbic acid as the reducing agent and with sulfate or sulfonate surfactants. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 69–80, 2007     

Selective Detection of Ascorbic Acid Using Octacyanomolybdate‐Doped‐Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Film Modified Glassy Carbon Electrode

The present work describes oxidation of ascorbic acid (AA) at octacyanomolybdate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐Mo(CN) film modified glassy carbon electrode in 0.1 M H₂SO₄. The modified electrode has been successfully prepared by means of electrostatically trapping Mo(CN) mediator in the cationic film of glutaraldehyde‐cross‐linked poly‐L ‐lysine. The dependence of peak current of modified electrode in pure supporting indicates that the charge transfer in the film was a mixed process at low scan rates (5 to 200 mV s^?1), and kinetically restrained at higher scan rates (200 to 1000 mV s^?1). Cyclic voltammetry and rotating disk electrode (RDE) techniques are used to investigate the electrocatalytic oxidation of ascorbic acid and compared with its oxidation at bare and undoped PLL‐GA film coated electrodes. The rate constant of catalytic reaction k obtained from RDE analysis was found to be 9.5×10⁵ cm³ mol^?1 s^?1. The analytical determination of ascorbic acid has been carried out using RDE technique over the physiological interest of ascorbic acid concentrations with a sensitivity of 75 μA mM^?1. Amperometric estimation of AA in stirred solution shows a sensitivity of 15 μA mM^?1 over the linear concentration range between 50 and 1200 μM. Interestingly, PLL‐GA‐Mo(CN) modified electrode facilitated the oxidation of ascorbic acid but not responded to other electroactive biomolecules such as dopamine, uric acid, NADH, glucose. This unique feature of PLL‐GA‐Mo(CN) modified electrode allowed for the development of a highly selective method for the determination of ascorbic acid in the presence of interferents.     

Interference‐Free Electrochemical Detection of Nanomolar Dopamine Using Doped Polypyrrole and Silver Nanoparticles

This paper presents a new approach to detect dopamine in nanomolar range using an electrochemical sensor utilizing a composite made of chitosan‐stabilized silver nanoparticles and p‐toluene sulfonic acid‐doped ultrathin polypyrrole film. Studies included cyclic voltammogram, amperometry, differential pulse voltammetry and also investigation by electrochemical impedance spectroscopy. A detection limit of 0.58 nM was achieved in the linear range 1×10^?9 M to 1.2×10^?7 M. High sensitivity towards DA, good reproducibility and long‐term stability have been demonstrated without interference from ascorbic acid, uric acid, epinephrine, L ‐dopa, glucose. The sensing system was successfully applied for quantitative determination of dopamine in commercially available human blood serum.     

A Novel L‐Cysteine Electrochemical Sensor Using Sulfonated Graphene‐poly(3,4‐Ethylenedioxythiophene) Composite Film Decorated with Gold Nanoparticles

By exploiting the electrostatic interaction between positively charged 3,4‐ethylenedioxythiophene cation radicals and negatively charged sulfonated graphene (SG) sheets, we prepared a poly(3,4‐ethylenedioxythiophene)‐sulfonated graphene (SG‐PEDOT) composite film by a one‐step electrochemical process. The composite was further decorated with gold nanoparticles (AuNPs) and employed as an electrode material for the detection of L ‐cysteine (Cys). The SG‐PEDOT composite film is shown to provide a rough surface for the electrodeposition of AuNPs and to improve substrate accessibility and interaction with Cys. Moreover, the AuNPs‐decorated composite exhibits better electrocatalytic performance than that of a SG‐PEDOT composite only. Under optimum experimental conditions, the amperometric current of the sensor is linearly related to the concentration of Cys in the 0.1 to 382 µM range, and the detection limit is 0.02 µM (at S/N=3). The modified electrode displays favorable selectivity, good stability and high reproducibility. The method was successfully applied to the detection of Cys in spiked human urine.     

Electrochemical Behaviour and Rapid Determination of L‐Dopa at Electrochemically Pretreated Screen Printed Carbon Electrode

A simple and rapid voltammetric method based on a disposable electrochemically pretreated screen‐printed carbon electrode is proposed for the determination of L ‐dopa. Under optimum differential pulse voltammetry conditions a limit of detection of 3.6×10^?7 M for L ‐dopa was obtained. The method was successfully applied to the determination of L ‐dopa in a commercial pharmaceutical formulation.     

Synthesis of star‐shaped poly(D,L‐lactic acid‐alt‐glycolic acid)‐b‐poly(L‐lactic acid) with the poly(D,L‐lactic acid‐alt‐glycolic acid) macroinitiator and stannous octoate catalyst

Two types of three‐arm and four‐arm, star‐shaped poly(D,L ‐lactic acid‐alt‐glycolic acid)‐b‐poly(L ‐lactic acid) (D,L ‐PLGA50‐b‐PLLA) were successfully synthesized via the sequential ring‐opening polymerization of D,L ‐3‐methylglycolide (MG) and L ‐lactide (L ‐LA) with a multifunctional initiator, such as trimethylolpropane and pentaerythritol, and stannous octoate (SnOct₂) as a catalyst. Star‐shaped, hydroxy‐terminated poly(D,L ‐lactic acid‐alt‐glycolic acid) (D,L ‐PLGA50) obtained from the polymerization of MG was used as a macroinitiator to initiate the block polymerization of L ‐LA with the SnOct₂ catalyst in bulk at 130 °C. For the polymerization of L ‐LA with the three‐arm, star‐shaped D,L ‐PLGA50 macroinitiator (number‐average molecular weight = 6800) and the SnOct₂ catalyst, the molecular weight of the resulting D,L ‐PLGA50‐b‐PLLA polymer linearly increased from 12,600 to 27,400 with the increasing molar ratio (1:1 to 3:1) of L ‐LA to MG, and the molecular weight distribution was rather narrow (weight‐average molecular weight/number‐average molecular weight = 1.09–1.15). The ¹H NMR spectrum of the D,L ‐PLGA50‐b‐PLLA block copolymer showed that the molecular weight and unit composition of the block copolymer were controlled by the molar ratio of L ‐LA to the macroinitiator. The ¹³C NMR spectrum of the block copolymer clearly showed its diblock structures, that is, D,L ‐PLGA50 as the first block and poly(L ‐lactic acid) as the second block. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 409–415, 2002     

Dopamine and Glucose Sensors Based on Glassy Carbon Electrodes Modified with Melanic Polymers

This work deals with the study of polymers electrogenerated from different catechols at glassy carbon electrodes and the analytical applications of the resulting modified electrodes for dopamine quantification and glucose biosensing. The electropolymerization was performed from a 3.0×10^?3 M catechol solution (catechol, dopamine, norepinephrine, epinephrine or L ‐dopa in a 0.050 M phosphate buffer pH 7.40) by applying 1.00 V for 60 min. The properties of the polymers are very dependent on the nature of the catechol, L ‐dopa being the best. Glassy carbon electrodes modified with melanic polymers electrogenerated from L ‐dopa and norepinephrine were found to be suitable for dopamine determinations in flow systems, although the behavior was highly dependent on the nature of the monomer. Detection limits of 5.0 nM dopamine and interferences of 9.0 and 2.6% for 5.0×10^?4 M ascorbic acid and 5.0×10^?5 M dopac, respectively, were obtained at the glassy carbon electrode modified with a melanin‐type polymer generated from L ‐dopa (using 1.0×10^?3 M AA in the measurement solution). The advantages of using a melanin‐type polymer generated from dopamine to improve the selectivity of glucose biosensors based on carbon paste electrodes containing Pt and glucose oxidase (GOx) are also discussed. The resulting bioelectrodes combines the high sensitivity of metallized electrodes with the selectivity given by the polymeric layer. They exhibit excellent performance for glucose with a rapid response (around 10 seconds per sample), a wide linear range (up to 2.5×10^?2 M glucose), low detection limits (143 μM) and a highly reproducible response (R.S.D of 4.9%). The bioelectrodes are highly stable and almost free from the interference of large excess of easily oxidizable compounds found in biological fluids, such as ascorbic acid (AA), uric acid (UA) and acetaminophen.     

Single‐Walled Carbon Nanotubes on Tungsten Wires: A New Class of Microelectrochemical Sensors

This paper reports the fabrication and the outstanding performance characteristics of novel microelectrodes consisting of tungsten (W) wires coated with homogeneous layers of single‐walled C nanotubes (SWNT). A series of studies using cyclic voltammetry indicate that the SWNT‐modified W electrodes possess interesting electrochemical features. In fact, they are able to catalyse electron transfer reactions involving a series of inorganic and biological molecules. These electrodes are characterized by a fast electron transfer, a wide working potential window, and a low background current. Moreover they demonstrate excellent reproducibility, good stability in various chemical media, and very high sensitivity towards a series of inorganic and organic compounds. The SWNT modified microelectrodes have been tested for the capacity to electrochemically detect ferrocene monocarboxylic acid and potassium hexacyanoferrate as well of a series of interesting biological molecules which include catechol, caffeic acid, DOPAC, ascorbic acid, L ‐tyrosine, acetaminophen, guanine, uric acid, and the neurotransmitters dopamine, epinephrine, and serotonin (5‐HT) hydrochloride. The advantages of the SWNT‐modified W electrodes are illustrated by comparing their analytical performance with that of conventional electrodes.     

Living polymerization of D,L‐3‐methylglycolide initiated with bimetallic (Al/Zn) μ‐oxo alkoxide and copolymers thereof

D,L ‐3‐Methylglycolide (MG) was successfully polymerized with bimetallic (Al/Zn) μ‐oxo alkoxide as an initiator in toluene at 90 °C. The effect of the initiator concentration and monomer conversion on the molecular weight was studied. It is shown that the polymerization of MG follows a living process. A kinetic study indicated that the polymerization approximates the first order in the monomer, and no induction period was observed. ¹H NMR spectroscopy showed that the ring‐opening polymerization proceeds through a coordination–insertion mechanism with selective cleavage of the acyl–oxygen bond of the monomer. On the basis of ¹H NMR and ¹³C NMR analyses, the selective cleavage of the acyl–oxygen bond of the monomer mainly occurs at the least hindered carbonyl groups (P₁ = 0.84, P₂ = 0.16). Therefore, the main chain of poly(D,L ‐lactic acid‐co‐glycolic acid) (50/50 molar ratio) obtained from the homopolymerization of MG was primarily composed of alternating lactyl and glycolyl units. The diblock copolymers poly(ϵ‐caprolactone)‐b‐poly(D,L ‐lactic acid‐alt‐glycolic acid) and poly(L ‐lactide)‐b‐poly(D,L ‐lactic acid‐alt‐glycolic acid) were successfully synthesized by the sequential living polymerization of related lactones (ϵ‐caprolactone or L ‐lactide). ¹³C NMR spectra of diblock copolymers clearly show their pure diblock structures. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 357–367, 2001     

Immobilization of Tyrosinase on Chitosan — An Optimal Approach to Enhance the Productivity of L‐DOPA from L‐Tyrosine

Tyrosinase was immobilized on Chitosan (CTS) beads to produce 3,4‐dihydroxy‐L‐phenylalanine (L ‐DOPA) from L ‐tyrosine. Epichlorohydrin (ECH), ethylene glycol diglycidyl ether (EGDE), and glutaraldehyde (GLU) were used as coupling agents, respectively. Ultraviolet/visible measurements on CTS films showed that the reaction intermediate (L ‐dopaquinone) attacked the amino groups on CTS, so the amine residues on chitosan were capped by acetic acid anhydride (Ac) or formaldehyde (Fm) to avoid the deactivation of the immobilized tyrosinase. The pH and temperature of the maximal rate to produce L‐DOPA were investigated. GLU (coupling agent) and Ac (capping agent) were selected for practical utility. A 7.5% (w/v) concentration of GLU was found to attain maximal activity of the immobilized enzyme. The thermal stability of tyrosinase immobilized on CTS‐GLU‐Ac, and after treatment with sodium borohydride, was enhanced to a great extent. The L ‐DOPA converting efficiency in the environmental conditions of this study decreased from 45.1% to 39.9% (between 1^st and 30^th batch). This immobilized tyrosinase can be used practically in the production of L‐DOPA from L‐tyrosine.     

Selective and Sensitive Electrochemical Sensor for L‐Methionine at Physiological pH Using Functionalized Triazole Polymer Film Modified Electrode

This communication describes the determination of an essential amino acid, L ‐methionine (L ‐Met) in the presence of important interferents, ascorbic acid (AA) and uric acid (UA) at physiological pH using a glassy carbon electrode modified with an electropolymerized film of 3‐amino‐5‐mercapto‐1,2,4‐triazole (p‐AMTa). The bare glassy carbon electrode fails to show a voltammetric signal for L ‐Met in the presence of AA and UA at pH 7.2. However, the p‐AMTa electrode separates the voltammetric signals of AA, UA and L ‐Met with pronounced oxidation currents. The amperometric current of L ‐Met was increased linearly from 1.0×10^?7 to 1×10^?4 M and the detection limit was found to be 4.12×10^?10 M (S/N=3).     

Chiral discrimination of β‐3‐homo‐amino acids using the kinetic method

Chiral discrimination of seven enantiomeric pairs of β‐3‐homo‐amino acids was studied by using the kinetic method and trimeric metal‐bound complexes, with natural and unnatural α‐amino acids as chiral reference compounds and divalent metal ions (Cu²⁺ and Ni²⁺) as the center ions. The β‐3‐homo‐amino acids were selected for this study because, first of all, chiral discrimination of β‐amino acids has not been extensively studied by mass spectrometry. Moreover, these β‐3‐homo‐amino acids studied have different aromatic side chains. Thus, the emphasis was to study the effect of the side chain (electron density of the phenyl ring, as well as the difference between phenyl and benzyl side chains) for the chiral discrimination. The results showed that by the proper choice of a metal ion and a chiral reference compound, all seven enantiomeric pairs of β‐3‐homo‐amino acids could be differentiated. Moreover, it was noted that the β‐3‐homo‐amino acids with benzyl side chains provided higher enantioselectivity than the corresponding phenyl ones. However, increasing or decreasing the electron density of the aromatic ring by different substituents in both the phenyl and benzyl side chains had practically no role for chiral discrimination of β‐3‐homo‐amino acids studied. When copper was used as the central metal, the phenyl side chain containing reference molecules (S)‐2‐amino‐2‐phenylacetic acid (L ‐Phg) and (S)‐2‐amino‐2‐(4‐hydroxyphenyl)‐acetic acid (L ‐4′‐OHPhg) gave rise to an additional copper‐reduced dimeric fragment ion, [Cu^I(ref)(A)]⁺. The inclusion of this ion improved noticeably the enantioselectivity values obtained. Copyright © 2010 John Wiley & Sons, Ltd.     

3,4‐Dihydroxy‐L‐phenylalanine for Preparation of Gold Nanoparticles and as Electron Transfer Promoter in H2O2 Biosensor

3,4‐Dihydroxy‐L ‐phenylalanine (dopa) and 2‐(3,4‐dihydroxyphenyl)ethylamine (dopamine) were investigated as reducing agent and stabilizer for synthesis of gold nanoparticles (AuNPs) by one‐pot heating of a solution of HAuCl₄/dopa or dopamine. AuNPs with different sizes were obtained by controlling the mass ratios of HAuCl₄/dopa or dopamine. The formation mechanism for AuNPs was also proposed. Immobilization of horseradish peroxidase (HRP) and promotion of its electron transfer by polydopa film were investigated for preparation of H₂O₂ biosensor. Alkaline dopa solution was dropped onto a gold electrode for the formation of polydopa film. HRP was immobilized on the polydopa film through interactions between heme centre of HRP and the amine and carboxyl groups in polydopa. The AuNPs embedded in the polydopa film improved the electron transfer efficiency. These two factors allowed successful development of a H₂O₂ sensor with HRP@polydopa‐AuNPs electrode. Due to its biocompatibility, the polydopa‐AuNPs film provided good retention of enzyme activity and long‐term stability of the sensor. A rapid catalytic response (3 s) and a linear range from 0.006 to 5.0 mmol L^?1 were obtained for H₂O₂. This facile preparation strategy can be extended to other enzyme‐based biosensors.     

Investigation of a Biosensor Based on Phenylalanine Dehydrogenase Immobilized on a Polymer‐Blend Film for Phenylketonuria Diagnosis

We investigated a L ‐phenylalanine (L ‐phe) biosensor, functionalized through enzyme immobilization on a polymer‐blend film. The electron mediator 3,4‐dihydroxybenzaldehyde (3,4‐DHB) was employed at the electrode surface to improve direct oxidation of NADH to NAD⁺ and no additional reagents is required to be added to the sample solution. The bioactivated electrode was coated with a semi‐permeable cellulose acetate membrane in order to prevent dissolution of biofunctionalized polymer‐blend film. This constructed enzyme electrode is the first selective biosensor for phenylketonuria (PKU) detection. The sensitivity of the enzyme electrode was determined as 12.014 mA/M cm². The Michaelis–Menten and current responses as well as sensitivity of the electrode showed improved values than those of previous works. This selective biosensor presented an excellent electroanalytical response for L ‐phe, with a high steady‐state current being obtained after 20 s. The sensitivity of our biodevice is quite sufficient for the purpose of PKU detection because the reference range of clinical concern for L ‐phenylalanine concentration is C_{L ‐phe}>0.5 mM. This surface‐bioactivated enzyme electrode retained more than 80 % of its electrocatalytic activity after 16 days.     

Synthesis,Spectroscopy, and Structures of Mono‐ and Dinuclear Copper(I) Halide Complexes with 1,3‐Imidazolidine‐2‐thiones

Copper(I) halides with triphenyl phosphine and imidaozlidine‐2‐thiones (L ‐NMe, L ‐NEt, and L ‐NPh) in acetonitrile/methanol (or dichloromethane) yielded copper(I) mixed‐ligand complexes: mononuclear, namely, [CuCl(κ¹‐S‐L ‐NMe)(PPh₃)₂] ( 1 ), [CuBr(κ¹‐S‐L ‐NMe)(PPh₃)₂] ( 2 ), [CuBr(κ¹‐S‐L ‐NEt)(PPh₃)₂] ( 5 ), [CuI(κ¹‐S‐L ‐NEt)(PPh₃)₂] ( 6 ), [CuCl(κ¹‐S‐L ‐NPh)(PPh₃)₂] ( 7 ), and [CuBr(κ¹‐S‐L ‐NPh)(PPh₃)₂] ( 8 ), and dinuclear, [Cu₂(κ¹‐I)₂(μ‐S‐L ‐NMe)₂(PPh₃)₂] ( 3 ) and [Cu₂(μ‐Cl)₂(κ¹‐S‐L ‐NEt)₂(PPh₃)₂] ( 4 ). All complexes were characterized with analytical data, IR and NMR spectroscopy, and X‐ray crystallography. Complexes 2 – 4 , 7 , and 8 each formed crystals in the triclinic system with P$\bar{1}$ space group, whereas complexes 1 , 5 , and 6 crystallized in the monoclinic crystal system with space groups P2₁/c, C2/c, and P2₁/n, respectively. Complex 2 has shown two independent molecules, [(CuBr(κ¹‐S‐L ‐NMe)(PPh₃)₂] and [CuBr(PPh₃)₂] in the unit cell. For X = Cl, the thio‐ligand bonded to metal as terminal in complex 4 , whereas for X = I it is sulfur‐bridged in complex 3 .     

Chemical synthesis of poly‐γ‐glutamic acid by polycondensation of γ‐glutamic acid dimer: Synthesis and reaction of poly‐γ‐glutamic acid methyl ester

α‐Methyl glutamic acid (L ‐L )‐, (L ‐D )‐, (D ‐L )‐, and (D ‐D )‐γ‐dimers were synthesized from L ‐ and D ‐glutamic acids, and the obtained dimers were subjected to polycondensation with 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride and 1‐hydroxybenzotriazole hydrate as condensation reagents. Poly‐γ‐glutamic acid (γ‐PGA) methyl ester with the number‐average molecular weights of 5000∼20,000 were obtained by polycondensation in N,N‐dimethylformamide in 44∼91% yields. The polycondensation of (L ‐L )‐ and (D ‐D )‐dimers afforded the polymers with much larger |[α]_D | compared with the corresponding dimers. The polymer could be transformed into γ‐PGA by alkaline hydrolysis or transesterification into α‐benzyl ester followed by hydrogenation. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 732–741, 2001     

An L‐Lactate Amperometric Enzyme Electrode Based on L‐Lactate Oxidase Immobilized in a Laponite Gel on a Glassy Carbon Electrode. Application to Dairy Products and Red Wine

A biosensor based on the immobilization of Lactate oxidase in laponite–organosilasesquioxane films on glassy carbon electrode for the quantification of L ‐lactate in wine and dairy products is presented. The bioelectrode showed a very high sensitivity (0.33±0.01) A cm^?2 M^?1 and a short time response (10 s) for less than 1 U of enzyme. No significant interferences, including ascorbic acid, were detected. For red wine, matrix effects assigned to polyphenols and anthocyanins were observed, which ware easily overcome by sample dilution. Our L ‐lactate determinations were in good agreement with those of two standard methods.