Interaction between myoglobin and hyaluronic acid in their layer-by-layer assembly: quartz crystal microbalance and cyclic voltammetry studies

Myoglobin (Mb), with different net surface charges at different pH in buffers and negatively charged hyaluronic acid (HA) at pH 5.0 in solutions were alternately adsorbed onto various solid surfaces and successfully assembled into {Mb/HA}(n) layer-by-layer films. The Mb in {Mb/HA}(n) films showed a quasi-reversible cyclic voltammetry (CV) response for its heme Fe(III)/Fe(II) redox couple. Quartz crystal microbalance (QCM) and CV were used to confirm the film growth and characterize the films. The interaction between Mb and HA and the influencing factors for Mb adsorption on HA surface, such as pH, Mb concentration, and ionic strength, were investigated in detail. The assembly driving force for {Mb/HA}(n) films, especially for the films assembled with like-charged Mb and HA, was found to be of electrostatic origin, while the secondary interaction such as hydrophobic interaction also plays an important role in some circumstances. Although the growth of {Mb(pH 7.0)/HA}(n) and {Mb(pH 9.0)/HA}(n) films was linear with the adsorption step, the exponential growth of {Mb(pH 5.0)/HA}(n) films was observed, especially when the films became thick. This exponential increase of mass and thickness with deposition step for {Mb(pH 5.0)/HA}(n) films was most probably attributed to the diffusion mechanism in which some HA molecules could diffuse in to and out of the whole films during the film assembly. Atomic force microscopy (AFM) results supported this speculation. UV-vis and IR spectroscopies of {Mb/HA}(n) films, combined with the comparative CV experiments of {Mb/HA}(n) and {catalase/HA}(n) films, suggest that Mb in the {Mb/HA}(n) multilayer films retains its near-native structure.     

Cyclic voltammetry and electrochemical quartz crystal microbalance studies of a rhodized platinum electrode in sulfuric acid solution

The adsorption properties of a rhodized platinum electrode in sulfuric acid were studied through simultaneous cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) measurements. The processes occurring at the Rh surface during the potential scan between 0.04 and 1.3 V were analyzed in terms of the changes in mass and charge. The apparent molar masses of the species adsorbed on Rh in different potential regions were determined from the mass–charge correlation. The results obtained suggest that the desorption of hydrogen UPD initially occurs in conjunction with the incorporation of mass due to the adsorption of bisulfate/sulfate ions between 0.04 V and 0.12 V; the apparent molar mass (M ₁) in this potential region is consistent with that of bisulfate ion, assuming that one sulfate species occupies the site originally occupied by five H atoms. Between 0.12 V and 0.20 V, the apparent molar mass, M ₂, is less than M ₁. This result may be associated with a structural rearrangement of the adsorbed sulfate species. The apparent molar mass, M ₃, was determined in the potential region of 0.20–0.56 V; the value obtained for M ₃ suggests that the adsorbed species are hydrated bisulfate ions (HSO₄⁻·4H₂O). Additionally, it was found that Rh oxides formed at the surface between 0.56 V and 1.3 V could not be directly identified from the correlation between charge and mass.     

Electrochemical quartz crystal microbalance study of ion transport accompanying charging-discharging of poly(pyrrole) films

Electrochemical quartz crystal microbalance studies on poly(pyrrole) electrodes revealed a complex nature of the potential-dependent sorption of ionic substances. It is found that the relative contribution of anions and cations to the overall charge transport process depends upon several factors, such as the oxidation state of the polymer, the composition of the supporting electrolyte as well as on the film thickness. The phenomena observed are discussed in terms of morphological transformations arising as a result of interactions between the polymer and the mobile substances. Received: 21 August 1998 / Accepted: 21 October 1998     

Electrochemical quartz crystal microbalance characterization of I(-) and its amperometric detection by microelectrode

The electrochemical redox mechanism of I(-) ion under different concentrations on gold electrodes was studied in detail using the EQCM technique (a combination of the QCM technique and cyclic voltammetry). The redox behavior of the I(-) ion on a gold microelectrode when no supporting electrolyte was added was compared with a conventional gold microelectrode. Due to the small current and the very low solution iR drop of the microelectrode, the actual oxidation potential of I(-) on the microelectrode was much more negative than that of the conventional electrode and its anodic peak was better defined. Therefore the gold microelectode was employed for the determination of I(-). A linear range of 1.0x10(-5)-0.1 mol l(-1) with a detection limit of 1.0x10(-6) mol l(-1) was obtained on the microelectrode in pure KI aqueous solution. Two samples were measured using this method and the results were in good agreement with those indicated or calculated..     

Transport of ionic charge and solvent in poly(3-octylthiophene) films: An electrochemical quartz crystal microbalance study

The results of a study of poly(3-octylthiophene) films with the aid of an electrochemical quartz microbalance are presented. The effect of the nature of the electrolyte anion on the determined weights of mobile species that are transported through the film/electrolyte interface is discussed. The obtained results point to a substantial role played by the solvent transport in the course of the electrode reaction. The results concerning the influence exerted by the electrode material on the observed regularities are presented.     

电化学石英晶体微天平的近期应用进展

本文对近几年来电化学石英晶体微天平（EQCM）在吸附，膜的形成，腐蚀和电沉积等方面的应用进行了概述，并对其应用现状和前景进行了分析。     

Stereoregularity of poly(2-vinylpyridine) and poly-(4-vinylpyridine)

In order to determine the stereoregularity of poly(4-vinylpyridine), 4-vinylpyridine-β,β-d₂ was synthesized from 4-acetylpyridine. The ¹H-NMR spectra of the deuterated and nondeuterated polymers were measured and analyzed. From the ¹H-NMR spectra of poly(4-vinylpyridine-β,β-d₂), triad tacticity can be obtained, while the ¹H-NMR spectra of nondeuterated poly(4-vinylpyridine) give the fraction of isotactic triad. The ¹³C-NMR spectra of poly(4-vinylpyridine) were also observed, and the spectra of C₄ carbon of polymers were assigned by the pentad tacticities. The fraction of isotactic triad of poly(2-vinylpyridine) and poly(4-vinylpyridine) obtained under various polymerization conditions were determined. The radical polymerization and anionic polymerizations with phenylmagnesium bromide and n-butyllithium as catalysts of 4-vinylpyridine gave atactic polymers.     

Kinetics of adsorption of poly(vinylimidazole) (PVI) onto copper surfaces investigated by quartz crystal microbalance studies

Organic corrosion inhibitors offer a huge potential of lowering product cost and manufacturing complexity in printed circuit board industry. Up to now, there is no reliable and fast method available to classify materials according to their ability to prevent copper from corrosion based on kinetic data of adsorption. We investigated the potential of the recently presented fast impedance-scanning quartz microbalance (FIS-QCM) to perform such studies. We selected poly(vinylimidazole) (PVI) that is known for its excellent ability to prevent copper from corrosion. However, kinetics and free energy of adsorption of PVI were never investigated. This paper presents the results of these studies. Reliable kinetic data were obtained, and the measurements show also the excellent frequency stability of this device that enables the detection of very small changes in resonance behaviour of the sensor quartz crystal, even below 1?Hz.     

Electrochemical quartz crystal microbalance study of R-SNO with immobilization on self-assembled monolayer of [Co(tpy-SH)Cl2]

Au/[Co(tpy-SH)Cl₂] electrode was prepared by self-assembled monolayer (SAM) of Au and then synthesized [Co(tpy-SH)Cl₂] and showed good reproducibility in electrochemical properties. The observed formal potential for Co^2+/3+using this electrode was 0.05 V in phosphate buffer at pH 5.6. A strong desorption peak at 0.5 V was observed for deposited R-SNO. The resistance of solutions with Au/[Co(tpy-SH)Cl₂] and Au/[Co(tpy-SH) (R-SNO)_x] electrodes was similar; however, the larger resistance of electron transfer was observed for Au/[Co(tpy-SH) (R-SNO)_x] electrode that incorporated one R-SNO in an electroactive site. A relative standard deviation for calibration curve (r=0.98) was 8% and a liner response was observed for the concentration from 5.8×10⁻¹ M to 5.8×10⁻⁶ M. Interference from amino acids that do not contain a thiol group was 5% or less.     

Reentrant behavior of grafted poly(sodium styrenesulfonate) chains investigated with a quartz crystal microbalance

Poly(sodium styrenesulfonate) (PSSNa) chains have been grafted onto a SiO(2)-coated resonator surface. The conformational changes of grafted chains have been investigated using a quartz crystal microbalance with dissipation (QCM-D) in the presence of monovalent or multivalent salts as a function of ionic strength. In the case of monovalent counterions, the changes in frequency (Δf) and dissipation (ΔD) indicate that the highly extended PSSNa chains first shrink into a loose and inhomogeneous layer as the ionic strength increases. As the ionic strength increases further, the chains will collapse and form a denser and more homogeneous layer. In the case of divalent or trivalent counterions, the grafted PSSNa chains also collapse into a dense layer as the ionic strength increases. However, when the ionic strength is above a critical value, the chains would re-expand so that the layer becomes partially extended due to the charge inversion. Additionally, the effect of ion-specificity on the conformational changes of the chains has also been examined.     

Collapse and swelling of thermally sensitive poly(N-isopropylacrylamide) brushes monitored with a quartz crystal microbalance

Thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) brushes grafted on SiO2-coated quartz crystal surface were prepared with a surface-immobilized initiator. Using quartz crystal microbalance (QCM), we investigated the collapse and swelling of the brushes in water in real time. Both frequency and dissipation of PNIPAM brushes were found to gradually change throughout a temperature range 20-38 degrees C, indicating that PNIPAM brushes undergo a continuous collapse transition in contrast with PNIPAM chains free in dilute solution exhibiting a sharp coil-to-globule transition. This result is in accordance with the previous theoretical prediction. The nonuniformity and stretching of PNIPAM brushes as well as the cooperativity between collapse and dehydration transitions are thought to be responsible for the continuity. On the other hand, a hysteresis was also observed in the cooling process. This is not only due to the intrachain and interchain interactions formed in the collapsed state but also to the nonuniform structure and stretching of the high-density brushes.     

Fast and reversible CO2 quartz crystal microbalance response of vinylimidazolium‐based poly(ionic liquid)s

A series of poly(ionic liquid)s (pILs) based on the 1‐vinyl‐3‐hexylimidazolium polymerizable cation and on the bis(trifluoromethylsulfonyl)imide, nonafluoro‐1‐butanesulfonate, dodecylbenzenesulfonate, heptadecafluorooctanesulfonate, and 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11‐heptadecafluoroundecanoate anions have been synthesized and characterized. Their sorption/desorption response towards CO₂ has been tested through quartz crystal microbalance investigations. The obtained results show that all of the pILs here reported are featured by peculiar CO₂ sorption properties as they display fast and linear response, reversibility without any memory effect, and reproducibility, suggesting that anion plays a key role in determining sensitivity. Copyright © 2011 John Wiley & Sons, Ltd.     

Supramolecular interactions between beta-cyclodextrin and hydrophobically end-capped poly(ethylene glycol)s: a quartz crystal microbalance study

In this study, the supramolecular interactions occurring between beta-cyclodextrin-based surfaces and macromolecular chains modified at one end with naphthyl, adamantyl, or phenyladamantyl hydrophobic groups were investigated by means of a quartz crystal microbalance. beta-Cyclodextrin-functionalized gold electrodes were obtained through the amide-coupling reaction between mono-6-deoxy-6-amino-beta-cyclodextrin and 11-mercaptoundecanoic acid self-assembled monolayer allowing the reproducible preparation of densely grafted surfaces with host properties. The interaction data obtained for the three different modified poly(ethylene glycol)s are in good agreement with our previous studies performed by high performance liquid chromatography and surface plasmon resonance. This evidences that the driving force for the supramolecular interaction is based on the inclusion of the hydrophobic terminal group of the chains within the cyclodextrin cavities. The reversibility of the inclusion process was proven through the regeneration of the original host properties of the sensing surfaces using sodium dodecylsulfate as a competitor for the desorption of the poly(ethylene glycol) chains.     

trans-[RuCl2(phosphane)2(1,2-diamine)] and Chiral trans-[RuCl2(diphosphane)(1,2-diamine)]: Shelf-Stable Precatalysts for the Rapid,Productive, and Stereoselective Hydrogenation of Ketones

A turnover number (TON) of 2 400 000 and a turnover frequency (TOF) of 63 s⁻¹ are achieved with the chiral Ru^II complex 1 (R=p-CH₃C₆H₄) in the asymmetric hydrogenation of acetophenone. Carbonyl-selective asymmetric hydrogenation of α,β-unsaturated ketones proceeds in the presence of these Ru^II catalysts, and 4-substituted cyclohexanones are selectively converted into cis alcohols.     

Reentrant behavior of poly(N-isopropylacrylamide) brushes in water-methanol mixtures investigated with a quartz crystal microbalance

The solvent composition induced reentrant behavior of poly(N-isopropylacrylamide) (PNIPAM) chains grafted on a SiO2 surface in water-methanol mixtures was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D) at 20 degrees C. The frequency and energy dissipation responses showed that the grafted PNIPAM chains sharply collapse when the methanol content (x(m)) reaches approximately 17 mol %. In the range 17-50 mol %, the grafted chains remain in a collapsed state. Further increase of the methanol content leads to an abrupt reswelling of the collapsed chains at x(m) > approximately 50 mol %. The sharp reentrant swelling-to-collapse-to-swelling transition was attributed to the water-methanol complexation instead of the preferential adsorption effect. Our results also suggest that the water-methanol complexation is not induced by hydrophobic interaction but by hydrogen bonding.     

Electrochemical and quartz crystal microbalance studies of lead(II) deposition and stripping in the presence of copper on a gold electrode modified with 2,2′-bipyridyl in polyaniline

Electrochemical and quartz crystal microbalance (QCM) measurements were used to determine the mechanisms of anodic stripping voltammetry (ASV) processes during lead determination in samples containing copper on a solid electrode modified by 2,2′-bipyridyl (Bpy) in polyaniline (PANI). Deposition of lead and copper results in the formation of solid solutions, which may change the results. An improvement of lead determination was achieved by the formation of stable copper complexes with Bpy. The molecules of Bpy were immobilized on a solid electrode in a PANI film. Deposition and stripping of lead and lead with copper were compared on three different electrodes: gold, gold coated with PANI and gold coated with PANI modified by Bpy. The results were used to propose mechanisms of deposition and stripping processes as well as a practical procedure of using this kind of electrode.     

Early Relaxation Dynamics in the Photoswitchable Complex trans-[RuCl(NO)(py)4]2+

The design of photoswitchable transition metal complexes with tailored properties is one of the most important challenges in chemistry. Studies explaining the underlying mechanisms are, however, scarce. Herein, the early relaxation dynamics towards NO photoisomerization in trans-[RuCl(NO)(py)₄]²⁺ is elucidated by means of non-adiabatic dynamics, which provided time-resolved information and branching ratios. Three deactivation mechanisms (I, II, III) in the ratio 3:2:4 were identified. Pathways I and III involve ultrafast intersystem crossing and internal conversion, whereas pathway II involves only internal conversion.     

Monitoring the mechanical properties of the solid electrolyte interphase(SEI) using electrochemical quartz crystal microbalance with dissipation

Stable solid electrolyte interphase(SEI) has been well established to be critical for the reversible operation of Li(ion) batteries,yet our understanding of its mechanical properties currently remains incomplete.Here,we used an electrochemical quartz crystal microbalance combined with dissipation monitoring(EQCM-D) to investigate SEI formation.By quantitatively estimating in-situ,the change in mass,shear modulus,and viscosity of the SEI,we show that the SEI formation in propylene carbonate(PC)-and ethylene carbonate/diethyl carbonate(EC/DEC)-based electrolytes involves the growth of a rigid laye r followed by a viscoelastic layer,whereas a distinct "one-layer" rigid model is applicable to the SEI formulated in tetraethylene glycol dimethyl ether(TEGDME)-based electrolyte.With the continuous formation of the SEI,its shear modulus decreases accompanied by an increase in viscosity.In TEGDME,the lightest/thinnest SEI(mass lower than in PC by a factor of nine) yet having the greatest stiffness(more than five times that in PC) is obtained.We attribute this behavior to differences in the chemical composition of the SEIs,which have been revealed by tracking the mass-change-per-mole-of-electrontransferred using EQCM-D and further confirmed by X-ray photoelectron spectroscopy.