Electrochemical characteristics of polyelectrolyte brushes with electroactive counterions

Cyclic voltammetry (CV) was employed to characterize the electrochemical behavior of polyelectrolyte brushes with immobilized electroactive counterions in response to external changes in concentration and composition of the supporting electrolyte and as a function of brush thickness. Poly(methacryloyloxy)ethyl-trimethyl-ammonium chloride (PMETAC) brushes were synthesized on Au substrates via atom transfer radical polymerization followed by ion-exchange with ferricyanide ions ([Fe(CN)6]3-) as redox probes. CV measurements of the modified PMETAC brushes showed the typical electrochemical response corresponding to a surface-confined electroactive species and the redox counterions, as [Fe(CN)6]3- species form stable ion pairs with the quaternary ammonium groups of the brush. The electron-transfer features of PMETAC brushes with different thicknesses, as characterized by CV and UV-vis spectroscopy, revealed that the charge density probed by CV was lower than the charge density measured by UV-vis spectroscopy. The electrode current decreased significantly with increasing concentration of supporting electrolyte due to the effect of the Donnan potential. Hydrophobic counterions, ClO4-, which induced brush collapse, lead to significantly reduced electrode currents.     

The encapsulation of ferrocyanide by copper(II) complexes of tripodal tetradentate ligands. Novel H-bonding networks incorporating heptanuclear and pentanuclear heterometallic assemblies

Substitution of the weakly binding aqua ligand in [Cu(tren)OH2](2+) and [Cu(tpa)OH2](2+) (tren = tris(2-aminoethyl)amine; tpa = tris(2-pyridylmethyl)amine) by a cyano ligand on ferricyanide results in the assembly of heteropolynuclear cations around the cyanometalate core. In water, the reduction of the Fe(III) core to Fe(II) generates complexes that feature heteropolycations in which ferrocyanide is encapsulated by the Cu(II) moieties: [(Cu(tpa)CN)6Fe][ClO4]8-3H2O 1, [(Cu(tren)CN)6Fe][ClO4]8-10H2O 2, [(Cu(tren)CN)6Fe][Fe(CN)6]2[ClO4]2-15.8H2O 3, and [(Cu(tren)CN)6Fe][(Cu(tren)CN)4Fe(CN)2][Fe(CN)6)]4-6DMSO-21H2O 4. The formation of discrete molecules, in preference to extended networks or polymeric structures, has been encouraged through the use of branched tetradentate ligands in conjunction with copper(II), a metal center with the propensity to form five-coordinate complexes. Complex 3 crystallizes in the monoclinic space group P2(1)/c (#14) with a = 14.8674(10), b = 25.9587(10), c = 27.5617(10) A, beta = 100.8300(10) degrees, and Z = 4, and it is comprised of almost spherical heptanuclear cations, [(Cu(tren)CN)6Fe](8+), whose charge is balanced by two ferricyanide and two perchlorate counteranions. Complex 4 crystallizes in the triclinic space group P1 (# 1) with a = 14.8094(8), b = 17.3901(7), c = 21.1565(11) A, alpha = 110.750(3), beta = 90.206(2), gamma = 112.754(3) degrees, and Z = 1, and it is comprised of the heptanuclear [(Cu(tren)CN)6Fe](8+) cation and pentanuclear [(Cu(tren)CN)4Fe(CN)2](4+) cation, whose terminal cyano ligands are oriented trans to each other. The charge is balanced exclusively by ferricyanide counteranions. In both complexes, H-bonding interactions between hydrogens on primary amines of the tren ligand, terminal cyano groups of the ferricyanide counterions, and the solvent of crystallization generate intricate 3D H-bonding networks.     

Voltammetric study of interfacial electron transfer between bis(cyclopentadienyl)iron in organic solvents and hexacyanoferrate in water.

The electron-transfer reaction between bis(cyclopentadienyl)iron(II) ([Fe(II)(C5H5)2]) in nitrobenzene and a hexacyanoferrate redox couple ([Fe(II/III)(CN)6](4-/3-)) in water at the nitrobenzene / water interface was studied using normal pulse voltammetry. The voltammetric results indicate that the electron-transfer reaction takes place by way of a so-called ion-transfer (IT) mechanism, of which the forward and backward rate constants of the homogeneous electron-transfer reaction between [Fe(II/III)(C5H5)2](0/+) and [Fe(II/III)(CN)6](4-/3-) in the water phase have been determined. The electron-transfer reaction between [Fe(II)(C5H5)2] in 1,2-dichloroethane and [Fe(II/III)(CN)6](4-/3-) in water at the 1,2-dichloroethane / water interface was shown to also take place by the IT-mechanism.     

Layer-by-layer thin film-coated electrodes for electrocatalytic determination of ascorbic acid

Multilayer thin films composed of poly(allylamine hydrochloride) (PAH) and carboxymethyl cellulose (CMC) have been prepared on the surface of a gold (Au) disk electrode by a layer-by-layer deposition of PAH and CMC and ferricyanide ions ([Fe(CN)₆]³⁻) were confined in the film. [Fe(CN)₆]³⁻ ions can be successfully confined in the films from weakly acidic or neutral [Fe(CN)₆]³⁻ solutions, while, in basic solution, [Fe(CN)₆]³⁻ ion was not confined. The [Fe(CN)₆]³⁻ ion-confined Au electrode showed clear redox peaks in the cyclic voltammogram around 0.35 V versus Ag/AgCl. The amounts of [Fe(CN)₆]³⁻ ions confined in the films depended on the thickness of the films or the number of layers in the LbL films. The [Fe(CN)₆]³⁻ ion-confined Au electrode was used for electrocatalytic determination of ascorbic acid in the concentration range of 1-50 mM.     

Cyclic voltammetry of the electron transfer reaction between bis(cyclopentadienyl)iron in 1,2-dichloroethane and hexacyanoferrate in water.

The electron transfer (ET) reaction between bis(cyclopentadienyl)iron(II) ([Fe(II)(C(5)H(5))2]) in 1,2-dichloroethane (1,2-DCE) and hexacyanoferrate redox couple ([Fe(II/III)(CN)6](4-/3-)) in water (W) at the interface has been studied by using cyclic voltammetry. The voltammetric results can be explained well by a theoretical equation for the so-called IT-mechanism, in which a homogeneous ET reaction between [Fe(C(5)H(5))2] (partially distributed from 1,2-DCE) and [Fe(CN)6](3-) takes place in the W phase and the resultant [Fe(C(5)H(5))2]+ ion is responsible for current passage across the interface. The forward rate constant of the homogeneous ET reaction, [Fe(C(5)H(5))2] + [Fe(CN)6](3-) = [Fe(C(5)H(5))2]+ + [Fe(CN)6](4-) in W phase, k(f)(IT), was determined to be (2.9 +/- 2.2)x 10(10) M(-1) s(-1), which was in good agreement with k(f)(IT) = (3.2 +/- 2.0)x 10(10) M(-1) s(-1), which had been determined by using normal-pulse voltammetry.     

Redox reactions of ferricyanide ions in layer-by-layer deposited polysaccharide films: a significant effect of the type of polycation in the films

Redox reactions of ferricyanide ions, [Fe(CN)6]3-, in polysaccharide thin films that were prepared by layer-by-layer (LbL) deposition on the surface of a gold electrode were studied electrochemically by cyclic voltammetry. LbL films composed of alginic acid (AGA) and carboxymethylcellulose (CMC) were successfully prepared using poly(ethyleneimine) (PEI) and poly(diallyldimethylammonium chloride) (PDDA) as the cationic counterparts in the electrostatic LbL deposition. The deposition behavior of the PEI-based films significantly depended on the pH of the solutions from which the LbL films were deposited, while the effects of pH were negligibly small for the PDDA-based films due to the pH-independent positive charges on the PDDA chains. The cyclic voltammograms (CVs) of [Fe(CN)6]3- ions on the LbL film-coated electrodes revealed that all the LbL films tested are permeable to [Fe(CN)6]3- ions and that the redox reactions of [Fe(CN)6]3- ions proceed smoothly in the LbL polysaccharide films. It was found that [Fe(CN)6]3- ions are concentrated in the films from the bulk solution, depending on the pH of the medium and on the type of polycations in the film. The PEI-based films concentrated [Fe(CN)6]3- ions more effectively in an acidic solution than in neutral and basic media, while the pH effect was not observed for the PDDA-based films. In addition, we found that the [Fe(CN)6]3- ions are confined in the LbL films due to a strong binding of the ions to the positively charged sites arising from the protonated amino groups in the films. The confined [Fe(CN)6]3- ions exhibited redox reactions in the films, with the redox potentials being shifted to the positive or negative direction in the PEI- or PDDA-based film, respectively, as compared to the redox potential of diffusing [Fe(CN)6]3- ions. Thus, significant effects of the type of polycation in the LbL films on the redox reactions of [Fe(CN)6]3- ions were observed.     

层层自组装法制备普鲁士蓝修饰电极及对过氧化氢的测定

Fe3+可与电沉积在玻碳电极表面的对氨基苯磺酸发生静电吸附作用并与[Fe(CN)6]4-形成普鲁士蓝(PB),进一步交替重复吸附Fe3+和[Fe(CN)6]4-反应,形成PB晶体.该晶体对还原过氧化氢(H2O2)具有很高的电化学活性.通过循环伏安法、交流阻抗法和计时电流法对传感器进行了电化学表征.研究了该传感器对H2O2的电催化作用,探讨了工作电位,PH值及干扰物质对响应电流的影响.结果表明,在磷酸盐缓冲溶液中(pH =5.4,0.1 mol/L),响应电流与H2O2的浓度在0.97 ～ 32.33 mmol/L范围内具有良好的线性关系,相关系数为0.9993,传感器的响应时间小于5 s,检测限为0.48 mmol/L( S/N为3).     

The detection of DNA deamination by electrocatalysis at DNA-modified electrodes

The method of electrocatalysis based on using a methylene blue (MB) as an electrochemical indicator and ferricyanide ions [Fe(CN)6]3- as an electron acceptor was applied in screening DNA for lesions caused by deamination of nucleobases. The damaged DNA was modeled by short 18-mer oligonucleotides containing the different number of mismatched target bases (uracil instead of cytosine residues). The hybridization capacity of these oligomers with complementary probes (immobilized on gold electrodes or free) was investigated by both electrochemical methods and UV spectroscopy. We have shown that the amplitude of the reduction signal corresponding to ferricyanide ions considerably increases in the presence of MB. This electrocatalytic effect allowed us to detect the changes in electrochemical properties of DNA caused by dU.dG mismatches. Using differential pulse voltammetry and cyclic voltammetry, we showed that the electron transport from the electrode through the double-stranded DNA to MB and then to ferricyanide ions is suppressed by the mismatches in duplex structure. According to UV-monitored melting data, single or multiple wobble dU.dG base pairs destabilize 18-mer DNA duplex by 9-27 degrees C.     

Electron transport through a self-assembled monolayer of thiol-end-functionalized tetraphenylporphines and metal tetraphenylporphines

The monolayers of several thiol-end-functionalized tetraphenylphophines (SH-TPP) and metal tetraphenylporphines (SH-MTPP) were self-assembled on gold surfaces and identified by cyclic voltammetry (CV), electrochemical impedance spectroscopy, scanning electrochemical microscopy, and the contact angle. The CV peaks of the [Fe(CN)6]3-/ [Fe(CN)6]4- couple were used to identify the efficiency of electrons transferring through the self-assembled monolayer (SAM). The results suggested that SH-TPP and SH-MTPP could form high-quality SAMs on gold surfaces. The SAMs blocked electron transport from the gold electrode to solution. When the length of the thiol-end-link spacer (alkyl group) increased, the electron transport ability of the SAM decreased because of the increased insulator properties of the alkyl chain. With the insertion of metallic ions, the electron transport ability of the SAM of SH-MTPP increased compared to that of the SAM of SH-TPP, which was probably due to the fact that (i) the insertion of metallic ions changed the molecular structure and the molecular structure of SH-MTPP played an important role in electron transport through the SAM and (ii) the insertion of metallic ions increased the electron tunneling probability through the monolayer.     

电位调控制备还原氧化石墨烯的电催化性能研究

本文通过控制电位还原氧化石墨烯,可控制备不同含氧官能团的石墨烯纳米材料。以多巴胺、[Fe(CN)_6]~(3-)、NADH为电活性探针,研究了石墨烯表面含氧官能团、缺陷、表面荷电性质以及导电性等对石墨烯电催化性能的影响。研究发现,低还原程度的氧化石墨烯表面含有大量缺陷和丰富的官能团,能够促进多巴胺自催化反应,也有利于K_3[Fe(CN)_6]在电极表面的电子转移;随着氧化石墨烯还原程度提高,其导电性逐渐得到改善,且其表面官能团和缺陷位点数量逐渐减少,对NAD~+的吸附变弱,因而能促进NADH发生电催化氧化。     

Localized surface plasmon resonance (LSPR) sensitivity of Au nanodot patterns to probe solvation effects in polyelectrolyte brushes

We report localized surface plasmon resonance (LSPR) of hexagonal Au nanodot arrays to detect changes in the thickness and conformation of poly[2-(methacryloyloxy)ethyltrimethyl ammonium chloride] (PMETAC) brushes.     

聚电解质中阳离子对铁氰化钾还原过程影响的原位显微红外光谱电化学

采用原位显微红外光谱电化学方法研究了聚电解质中不同阳离子（Ｌｉ＋,Ｎａ＋,Ｋ＋和ＴＢＡ＋）存在下铁氰化钾的电化学还原过程．观察到支持电解质阳离子对Ｆｅ（ＣＮ）３－／４－６振动频率的影响,探讨了还原反应机理     

一种铂网栅薄层光谱电化学池的制作及表征

以铂网栅电极作工作电极,设计制作了一种应用于紫外-可见光谱电化学研究的新型光透薄层电化学池（OTTLE）,并以铁氰化钾-亚铁氰化钾体系对此光谱化学池进行了表征。铁氰化钾-亚铁氰化钾体系在该池中有良好的循环伏安特性,并可获得良好的紫外-可见光谱。测得的克式量电位E^0,电子转移数n与文献结果一致。     

Explanation for the apparent absence of collapse of polyelectrolyte brushes in the presence of bulky ions

The conformational behavior of poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC) brushes with different chain density in the presence of large benzyltributylammonium chloride (BTBAC) ions has been studied by a Quartz Crystal Microbalance with Dissipation (QCM-D) and Scanning Force Microscopy. Dense brushes do not collapse in the presence of BTBAC solutions of increasing ionic strength, contrary to what is observed in the presence of NaCl. Brush collapse can be observed for low-ionic-strength solutions of BTBAC when the brush density has been reduced. These phenomena can be explained by considering the Hofmeister series as well as ion size and free space in the brush.     

Incorporation of substitutionally labile [V(III)(CN)6]3- into prussian blue type magnetic materials

A Prussian blue (PB) type material containing hexacyanovanadate(III), Mn(II)1.5[V(III)(CN)6].(0.30)MeCN (1), was formed from the reaction of [V(III)(CN)6](3-) with [Mn(NCMe)6](2+) in MeCN. This new material exhibits ferrimagnetic spin- or cluster-glass behavior below a Tc of 12K with observed magnetic hysteresis at 2 K (Hcr = 65 Oe and Mrem = 730 emu.Oe/mol). Reactions of [V(III)(CN)6](3-) with [M(II)(NCMe)6](2+) (M = Fe, Co, Ni) in MeCN lead to either partial (M = Co) or complete (M = Fe, Ni) linkage isomerization, resulting in compounds of Fe(II)(0.5)V(III)[Fe(II)(CN)6].(0.85)MeCN (2), (NEt4)(0.10)Co(II)(1.5- a)V(II)a[Co(III)(CN)6]a [V(III)(CN)6](1-a)(BF4)(0.10).(0.35)MeCN (3), and (NEt4)(0.20)V(III)[Ni(II)(CN)4](1.6).(0.10)MeCN (4) compositions. Compounds 2-4 do not magnetically order as a consequence of diamagnetic cyanometalate anions being present, i.e., [Fe(II)(CN)6](4-), [Co(III)(CN)6](3-), and [Ni(II)(CN)4](2-). Incorporation of [V(III)(CN)6](3-) into PB-type materials is synthetically challenging because of the lability of the cyanovanadate(III) anion.     

纤维素凝胶电解质及其在超级电容器中的应用

以纸浆为原料制备得到一种粘胶液,经静置水化交联,得到一种纤维素凝胶电解质(XWD-NaOH);添加亚铁氰化钾,使获得的新型纤维素凝胶电解质(XWD-NaOH-K 4[Fe(CN)6])呈现良好的氧化还原活性,电导率达15.3 mS/cm;与XWD-NaOH相比,XWD-NaOH-K 4[Fe(CN)6]电解质超级电容器,在0.5 A/g电流密度下,比电容、功率密度和能量密度分别提高了57%、111%和214%,并且体系具有更低的内阻、电荷转移电阻及高的循环稳定性。     

功能化碳纳米管的电化学性质及在6-巯基嘌呤分析检测中的应用

采用修饰单壁碳纳米管(SWNT、SWNT-COOH或SWNT-OH)及多壁碳纳米管(MWNT、MWNT-COOH或MWNT-OH)的石墨电极研究配位阴离子[Fe(CN)6]3-和配位阳离子[Co(phen)3]3+的电化学行为与吸附性能,借助[Co(phen)3]3+在碳纳米管(CNT)的强吸附特性制备[Co(phen)3]3+/CNT/C修饰电极,以其应用于6-MP的分析检测.结果表明:1)在CNT修饰电极上[Fe(CN)6]3-/4-呈现很好的氧化还原可逆性,而[Co(phen)3]3+则显示明显的吸附控制特征.2)[Co(phen)3]3+在多壁碳纳米管修饰电极上的吸附量较单壁碳纳米管大,但经羧基化或羟基化后,吸附量减小,而且在羧基化表面的吸附量较羟基化的大.3)[Co(phen)3]3+与6-MP间存在明显的相互作用,其配位产物的还原峰电流与6-MP浓度呈线性关系.     

Electrochemical behavior of the system ferricyanide-ferrocyanide at a graphite-epoxy composite electrode

Cyclic and direct voltammetry with linear potential sweep has been used for the investigation of the dependence of the reversibility and reduction current in the system Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ on the concentrations of LiCl, NaCl, KCl, and CsCl solutions. The electrode was made of a graphite-epoxy composite and activated by mechanically cutting a surface layer directly in the solution and deactivated by the long-term storage in the air. The selected type of the graphite electrode and the method used to activate its surface provides the reversibility and diffusion control of the electrode process in the system Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ regardless of the composition of the supporting solution. In the case of the deactivated electrode, the degree of irreversibility of this process depends on the form and concentration of metal chloride in the supporting electrolyte and the diffusion transfer is complicated by the adsorption of compounds formed between the ferricyanide and the cation of the supporting solution.     

Electrochemical impedance spectroscopy of poly (1-ethyl 3-(2-methacryloyloxy ethyl) imidazolium chloride) brushes with locally generated Pd

The electrochemical impedance spectroscopy of polyelectrolyte brushes (poly (1-ethyl 3-(2-methacryloyloxy ethyl) imidazolium chloride) (PEMEIm-Cl) incorporated with locally generated palladium nanoparticles was first studied, which exhibits evidently different electrochemical behavior with the PEMEIm-Cl brushes in electrolyte solution. The PEMEIm-Cl brush containing Pd nanoparticles exhibits high electrocatalytic activity for the reduction of oxygen. Furthermore, the electrocatalytic activity of PEMEIm-Cl/Pd brush for oxygen reduction was highly tunable by changing the thickness of the composite film.     

Enzyme-free impedimetric glucose sensor based on gold nanoparticles/polyaniline composite film

A non-enzymatic impedimetric glucose sensor was fabricated based on the adsorption of gold nanoparticles (GNPs) onto conductive polyaniline (PANI)-modified glassy carbon electrode (GCE). The modified electrode (GCE/PANI/GNPs) was characterized by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The determination of glucose concentration was based on the measurement of EIS with the mediation of electron transfer by ferricyanide ([Fe(CN)₆]^3?). The [Fe(CN)₆]^3? is reduced to ferrocyanide ([Fe(CN)₆]^4?), which in turn is oxidized at GCE/PANI/GNPs. An increase in the glucose concentration results in an increase in the diffusion current density of the [Fe(CN)₆]^4? oxidation, which corresponds to a decrease in the faradaic charge transfer resistance (R _ct). A wide linear concentration range from 0.3 to 10 mM with a lower detection limit of 0.1 mM for glucose was obtained. The proposed sensor shows high sensitivity, good reproducibility, and stability. In addition, the sensor exhibits no interference from common interfering substances such as ascorbic acid, acetaminophen, and uric acid.