Evidence of the withdrawing effect of a pyridinium N-cation on the electrochemical reduction of gold (III) tetraphenylporphyrin

1-(Au^III-meso-tetraphenylporphyrin)-4-pyridinium dication Au^IIITPP⁺-β-Py⁺, formed by a pyridinium cation bearing a charged gold porphyrin at the N-position, has been synthetised and studied by stationary voltammetry, cyclic voltammetry, UV–Vis spectroelectrochemistry and exhaustive coulometry. The pyridinium cation and the porphyrin ring are both electroactive species on the investigated range of potentials. The obtained results allowed to discriminate the sites of the different charge transfers and to propose a mechanism for the three first electrochemical reduction processes involved. The gold porphyrin reduces before the reduction of the pyridinium cation whose signal is intercalated between two reduction steps of the porphyrin. A transient dimeric gold porphyrin is detected. The withdrawing effect of the pyridinium cation on the reduction potentials of the porphyrin is discussed and quantified.     

Factors influencing the ion-exchange preconcentration and voltammetric behaviour of redox cations at polyestersulfonated ionomer coated electrodes in acetonitrile solutions

Glassy carbon electrodes coated with the poly(estersulfonate) Kodak AQ55 were used in acetonitrile solutions of various supporting electrolytes to study the ion-exchange voltammetric behaviour of some electroactive cations, namely the monocharged cation (ferrocenylmethyl)trimethylammonium (FA⁺) and the dications Ru(bpy)₃²⁺ (bpy=2,2′-bipyridine), methylviologen, butylviologen and heptylviologen. For all the electroactive cations, it was found that the success in their ion-exchange is determined by the size of the supporting electrolyte cation. In particular, lowering the steric hindrance of the supporting electrolyte cation results in a more significant ion-exchange competition with the electroactive cation. As far as different redox analytes are concerned, it was observed that the preconcentration efficiency increases with increasing charge and for electroactive species with the same ionic charge, parallels the order of decreasing steric hindrance. In the case of the viologens, this last factor seems to overcome the hydrophobic one, where the small (but less hydrophobic) methylviologen is preconcentrated more efficiently than the large (but more hydrophobic) heptylviologen.     

Preparation of sulfonated overoxidized polypyrrole film applicable as an SPME tool for cationic analytes

The use of a solid-phase microextraction (SPME) method with a new design of functionalized stable overoxidized sulfonated polypyrrole (OSPPy) film electrode to extract metal ions (Ni(II) and Cd(II)) without derivatization from water of high saline content is described. Different cation uptake behavior is obtained for OSPPy and overoxidized polypyrrole. The cation uptake and release properties of the OSPPy film electrode were examined under both open circuit and controlled potential conditions for prospective applications in electrochemically controlled solid-phase microextraction (EC-SPME). The cation uptake is enhanced if a positive potential is applied to the electrode. Accumulated cations are released rapidly from the film if the applied potential is switched to a negative value. The cation uptake and release mechanism is affected both by the cation exchange at the negative sulfonate and carboxylate groups on the film and by the altered solution pH occurring at the counter electrode caused by the applied potential. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) measurements on the two films have confirmed the presence of a sulfur content in the films and shown that covalently bound sulfonate preferentially dopes the polymer even in the presence of a large excess of BF₄^? anions. Our preliminary fundamental results show that this new polymer offers a wide potential range for electroanalytical exploration from selective electrodes to separation and/or preconcentration sampling devices.     

Electrochemical reduction of l-(meso-tetraphenylporphyrin)-pyridinium cations

1-(M-meso-tetraphenylporphyrin)-4-R-pyridinium cations MTPP-β-(4-R-Py⁺) (M = H₂, Zn^II, Ni^II, Cu^II or Pd^II, R = H, phenyl or pyridine), formed by a pyridinium cation bearing a porphyrin, metalated or not, at the N-position, were synthesised electrochemically and studied by polarography, stationary and cyclic voltammetry, UV–Vis spectroelectrochemistry and exhaustive coulometry. The pyridinium and the porphyrin rings are both electroactive species in the range of potentials investigated. The results allowed us to discriminate the distinct sites of the different charge transfers and to propose a mechanism for the primary electrochemical reduction step which corresponds to a one-electron transfer to the pyridinium cation. The redox behaviour of the pyridinium in these systems depends on the nature of the core of the porphyrin (free-base or metalated). The differences observed between the free-base and the metalated porphyrin systems were explained by differences in the distribution of the electronic density on the porphyrin ligand in the two types of molecules. In the metalated porphyrin–pyridinium systems, the measured reduction potentials of the pyridinium cation were correlated with the electronegativity ${\chi }_{\mathrm{M}}^{\mathrm{P}}$ of the metal in the porphyrin core. The obtained correlation revealed the occurrence of strong coulombic interactions between the metal in the porphyrin and the pyridinium. The chemical reactivity of the electrochemically generated pyridinium radical depends on the substitution at the 4-position of the ring. The generation of a dimeric species following the first electron transfer to the pyridinium cation was detected by cyclic voltammetry.     

Novel voltammetric responses of a 1,1′-ferrocene bis(methylene aza-18-crown-6) receptor to group 1 and 2 metal cations in acetonitrile

A 1,1′-ferrocene bis(methylene aza-18-crown-6) ligand (L) and its inclusion complexes with Na⁺, K⁺, Ba²⁺ and Mg²⁺ are studied in acetonitrile by cyclic and square wave voltammetry. The ligand-metal complex stoichiometry is found to vary from 1:1 to 1:2 with increasing concentration of the metal cation. There is also a binding selectivity for dications over monocations. Simultaneous addition of Mg²⁺ and Ba²⁺ gives rise to a novel voltammetric feature which is rationalised by the formation of three different species; the symmetrical homobimetallic complexes, L—2Ba²⁺ and L—2Mg²⁺, and the asymmetrical heterobimetallic complex, L—Ba²⁺—Mg²⁺. L is therefore a redox active receptor capable of the simultaneous electrochemical recognition of different metal cations. An electrostatic model is proposed to account for the observed changes in the mean potential of L upon cation complexation.     

In situ resonance Raman spectroelectrochemistry of polypyrrole doped with dodecylbenzenesulfonate

In situ Raman spectroelectrochemistry was performed on cycled polypyrrole films incorporating dodecylbenzenesulfonate (DBS). It was found that under 457.9 nm excitation, the neutral form was resonant and the bands due to the neutral form of the polymer dominated the spectra. Spectra obtained using 514.5 nm excitation displayed a strong neutral contribution but bands due to the radical cation and dication were also visible. At 632.8 nm excitation, the bands assigned to the radical dication were dominant, with a noticeable contribution from the dication in the oxidised state. The strength of the radical cation contribution is unusual as it made only a weak contribution in the UV–vis adsorption spectra. The CC backbone stretching band between 1560 and 1590 cm^?1 was found to be made up of a contribution of bands due to the radical cation and neutral forms with a separate band at 1620 cm^?1 for the dication form. The results show that by carefully selecting the excitation wavelength, resonance Raman is a powerful tool for analysing the changes in oxidation states of a conducting polymer under potential cycling.     

Voltammetric investigation of the anodic dimerization of p-halogenoanilines in DMF: Reactivity of their electrogenerated cation radicals

The electrodimerization mechanisms of p-chloro- and p-bromoaniline were studied in unbuffered DMF medium. By combined application of conventional and fast voltammetry (100 kV s^?1 range), the primary radical cation intermediates, formed by the one electron oxidation of each p-halogenoaniline were characterized. The overall reaction path involves a dimerization via a N–C bond formation and de-halogenation at the para position. A detailed mechanistic investigation demonstrates that this proceeds through a fast reversible deprotonation of the primary radical cation followed by the subsequent N–C bond formation between the resulting radical and its parent radical cation which is the rate-determining step of the sequence (e-p-RRC-p kinetic sequence). The effect of a relatively strong, but weakly nucleophilic base, 2,6-lutidine, has been also investigated and confirmed the involvement of the fast deprotonation pre-equilibria. The fast voltammetric experiments were simulated and the apparent rate constants for the overall deprotonation/dimerization sequence obtained on the basis of peak potential shift analysis were thus confirmed.     

Electrochemical oxidation in different media of bis(p-phenylene crown ether) as a symmetrical molecule bearing two identical redox centers

The oxidation of the long chain polyether p-disubstituted benzene derivative (BO5O5) and the related macrocyclic paracyclophane (BBO5O5) have been investigated by cyclic voltammetry at different concentrations (10⁻³–3×10⁻² M) and potential scan rates (0.05–250 V s⁻¹). At about 10⁻³ M in CH₃CN or CH₂Cl₂ containing a perchlorate salt as the supporting electrolyte, BO5O5 was oxidized reversibly into moderately stable radical cations. The formal potential E°′ corresponding to this first oxidation step was found to be shifted towards more positive values when the cation was changed from Bu₄N⁺ to Na⁺, and this variation may be ascribed to the coordination of the alkali cation by the polyether chains. At higher concentrations of the reactant and in a thoroughly dried medium, no deposit of a polymeric material onto the electrode surface was electrogenerated. At low scan rates and under the same conditions, the oxidation of BBO5O5 gave rise to two closely spaced, irreversible processes. The radical cations involved in each step were thought to be highly reactive towards nucleophilic species present in solution. At high scan rates, a single reversible one-electron transfer was observed, the formal potential of which varied with the nature of the electrolyte cation in the same way as for BO5O5. The heterogeneous charge-transfer rate constants estimated for BO5O5 and BBO5O5 were compared with the values predicted by the Marcus theory. As for BO5O5, attempts to electropolymerize BBO5O5 were unsuccessful.     

Electropolymerization of ferrocene bis-amide derivatives: a possible route to an electrochemical sensory device

The electrochemical behaviour of ferrocene bis-amide derivatives in the presence and in the absence of an alkali metal cation is described. Voltammetric studies confirm the selective complexation ability of these compounds towards Li⁺ among the alkali metal cations. Platinum and glassy carbon electrodes have been modified by electropolymerization of pyrrole-substituted ferrocene bis-amide derivatives. The influence of the alkali metal cation on both the electropolymerization step and on the redox behaviour of the resulting films has been studied. The formation of a complex between polymerizable ferrocene bis-amide derivatives and Li⁺ leads to an increase in the deposition efficiency. In aqueous media, the redox potential of the electroactive film depends on the nature and the concentration of the counter-anion of the electrolyte.     

Development of tissue conditioner capable of binding with anti-microbial protein lactoferrin

PurposeThis study focused on the anti-microbial protein human lactoferrin (hLF) commonly found in saliva, and tried to develop biocompatible dental materials that have higher anti-microbial effects.MethodsA lyophilized cation exchange resin was added to tissue conditioner at 4 wt% and 8 wt%. The amount of hLF binding to the tissue conditioner and their anti-microbial effect against Candida albicans was investigated. Then their mechanical properties and cytotoxicity were examined.ResultsTissue conditioner containing cation exchange resin was bound with hLF and had an anti-microbial effect against C. albicans. In addition, their physical properties were sufficient and they were harmless to human fibroblasts.ConclusionThe clinical application of cation exchange resin for tissue conditioner can be effective for the prevention and treatment of denture stomatitis and systemic opportunistic infections since it is thought that these materials will increase the local concentration of anti-microbial protein in saliva at the lesion site.     

Kinetics of ferrocenium cation transfer across ionic liquid/water interface using recessed microelectrode

The transfer of an electrochemically-produced ferrocenium cation across a hydrophobic ionic liquid (IL) microdroplet/water interface was kinetically studied by a recessed microelectrode. Cyclic voltammograms of ferrocene in an IL microdroplet injected into a cylindrical recess on a microelectode in water were measured as a function of the phase-boundary potential between the IL and water phases. The transfer rate constant of the ferrocenium cation at the IL/water interface could be determined by the digital simulations as well as a simple estimation based on the efficient diffusion in the micrometer-sized droplet system. The ion transfer rates were analyzed by the Butler–Volmer equation and were significantly influenced by the type of the IL. The IL dependence on the ion transfer rate is discussed in terms of the physical properties of the ILs.     

Electrocatalytic deposition of poly(3-bromothiophene)

The influence of a catalytic amount (e.g. 0.1%) of 2,2′-bithiophene on the electrochemical polymerization of 3-bromothiophene has been investigated. The presence of bithiophene in the polymerization medium decreases the minimum potential required for poly(3-bromothiophene) deposition, and increases the polymerization rate at a given potential. However, the electrochemical generation of 3-bromothiophene cation radicals is required for poly(3-bromothiophene) formation, indicating that radical-monomer coupling is not a significant polymerization pathway. The main role of bithiophene in promoting poly(3-bromothiophene) deposition appears to be as a nucleation initiator. A negligible quantity of bithiophene is incorporated into the polymer.     

La Tomografia Computerizzata 3D nella diagnosi cefalometrica delle disgnazie dento-maxillo-facciali

Objectives

The aim of this work was to compare traditional radiographic cephalometry with that based on three-dimensional computed tomography (3D CT) and to evaluate the pros and cons of two different 3D CT methods.

Materials and methods

Two adult patients were examined with traditional radiographic methods and with two different tomographic techniques: fan beam CT and cone beam CT. The cephalograms obtained with these methods were analyzed with a traditional digital cephalometric approach and with 3D cephalometric software.

Results and Conclusions

Computed Tomography provides more accurate information than traditional radiography since it eliminates the problems of deformation, magnifi cation, superimposition, and artifacts. It is especially useful in the presence of oral-maxillofacial dysgnathia since it allows study of the skull in each of the three dimensions. Cone beam technology uses a low dose of radiation and is less costly for patients and medical structures. With 3D cephalometric software, one can fully exploit the 3D data obtained with CT. It is especially valuable in the study of patients with maxillofacial asymmetry since the two sides of the face can be examined separately and then compared.     

Observations on calcium-induced stability of salivary proteins in a lipid-extraction system.

The system described for investigating the effects of small ions on macromolecules of saliva may be applied to other solutions and is amenable to manipulation in order to obtain more specific information. Studies using aqueous solutions of saliva fractions previously separated by gel filtration are being conducted with C/M solutions containing various bivalent cation chloride salts. Preliminary results from these current studies have demonstrated that when the proteins are stabilized they vary as a function of the cation used.     

Direct electrochemistry and enzymatic activity of bacterial polyhemic cytochrome c3 incorporated in clay films

Quartz crystal microbalance and voltammetric measurements are used to study the electroenzymatic activity of incorporated bacterial polyhemic cytochrome c₃ in clay minerals. Two different natural clays have been chosen, i.e., kaolinite and montmorillonite, which differ in structure, swelling property and cation exchange capacity. Comparative voltammetric studies of various electroactive species at clay-modified pyrolytic graphite electrodes are first undertaken, which allow the complete characterization of the clay deposit. Then, the incorporation process of bacterial polyhemic cytochrome c₃ in the two clays is studied coupling quartz crystal microbalance and voltammetric measurements. Based on their respective characteristics, each clay yields a different behavior of the incorporated cytochrome c₃, with significantly different electroactive fractions of the immobilized protein. The consequences of the interactions between the protein and the clays on the enzymatic activity of cytochrome c₃ is then further examined. Firstly, the influence of the incorporation of cytochromes in clays on the metal reductase activity developed by bacterial polyheme c-type cytochromes is discussed. Secondly, hydrogenase enzymatic reactions are studied inside the clay films. An electrode is constructed by immobilizing hydrogenase in the clay and progressively incorporating either artificial (methyl viologen) or physiological (cytochrome c₃) hydrogenase partner. It is shown that this modified electrode yields an efficient and stable response for either H₂ consumption or evolution over a large range of pH.     

Resonance frequency measurements in vivo and related surface properties of magnesium-incorporated, micropatterned and magnesium-incorporated TiUnite®, Osseotite®, SLA® and TiOblast® implants

Objective: To investigate implant stability using resonance frequency measurements of topographically changed and/or surface chemistry‐modified implants in rabbit bone. Material and methods: Six groups of microstructured, screw‐shaped titanium implants: two oxidized, cation‐incorporated experimental implants [Mg implants and MgMp implants with micropatterned thread flanges (80–150 μm wide and 60–70 μm deep)] and four commercially available clinical implants (TiUnite^®, Osseotite^®, SLA^®, and TiOblast^®) were installed in 10 rabbit tibia for 6 weeks. The surface properties of the implants were characterized in detail using several analytical techniques. Implant stability was measured using a resonance frequency analyzer (Osstell^?). Results: Surface characterization of the implants revealed microstructured, moderately rough implant surfaces varying 0.7–1.4 μm in S_a (mean height deviation), but with clear differences in surface chemistry. After 6 weeks, all implants showed statistically significantly higher increases in implant stability. When compared with one another, MgMp implants showed the most significant mean implant stability quotient (ISQ) value relative to the others (P≤0.016). In terms of increment (ΔISQ) in implant stability, MgMp implants showed a significantly greater value as compared with Osseotite^® (P≤0.005), TiOblast^® (P≤0.005), TiUnite^® (P≤0.005), SLA^® (P≤0.007), and Mg implants (P≤0.012). In addition, transducer direction dependence of resonance frequency analysis (RFA) measurements was observed such that the differences in the mean ISQ values between longitudinal and perpendicular measurements were significant at implant placement (P≤0.004) and after 6 weeks (P≤0). Conclusion: The present study found that implant surface properties influence RFA measurements of implant stability. Surface chemistry‐modified titanium implants showed higher mean ISQ values than did topographically changed implants. In particular, cation (magnesium)‐incorporated micropatterns in MgMp implants may play a primary role in ΔISQ.     

Substituent effects on the electrochemical and spectral characteristics of N,N,N′,N′-tetraaryl-p-phenylenediamine derivatives

Mixed-valence compounds of N,N,N′,N′-tetraaryl-p-phenylenediamine derivatives (PDs) with various electron-donating and -withdrawing substituents have been synthesized and their electrochemical and spectral characteristics have been investigated. According to the molecular symmetry, PDs are grouped as two series. The two series of PDs follow Hammett relationships both in the first and the second half-wave oxidation potentials. The isomeric cation radical/dication redox couples occur at the same potentials and the cation radicals exhibit similar absorption maxima and band shapes in the NIR regions, implying the highly delocalized electronic structures in the singly oxidized states. The stability of the oxidation products was monitored with UV/vis/NIR spectroelectrochemical investigations. PDs with electron-withdrawing substituents are stable after one electron oxidation, while PDs with electron-donating substituents are stable after one and two electron oxidation.     

龈沟液中基质金属蛋白酶-9含量与正畸牙根吸收相关性的实验研究

目的 探讨龈沟液中基质金属蛋白酶-9(MMP-9)含量与正畸牙根吸收的相关性,为临床诊断牙根吸收寻找简单、灵敏的检测指标.方法 选择5只6月龄的小型猪作为研究对象,以其下颌第一乳侧切牙作为实验牙,通过施加300 g过大拉力建立动物模型.每周提取实验牙的龈沟液,并应用SDS-PAGE,Western Blot和Gel Doc凝胶成像系统定量检测龈沟液中MMP-9含量的改变.同时在第1、2、4、7周将动物处死,制作实验牙的病理切片,观察发生牙根吸收的情况.根据牙根吸收出现的时间将所有实验动物分为未吸收组和吸收组,对其龈沟液中MMP-9含量进行统计学分析.结果 牙齿受力后,龈沟液中的MMP-9含量先升高,在发生牙根吸收的第2周则减少,然后逐渐升高,在第3、4周达高峰后又逐渐减少.牙根吸收组和未吸收组龈沟液中MMP-9含量的差异有显著的统计学意义.结论 龈沟液中的MMP-9参与了正畸源性牙根吸收过程.     

An electrochemical impedance study of Alloy-22 in NaCl brine at elevated temperature: II. Reaction mechanism analysis

The development of deterministic models for predicting the accumulation of corrosion damage to high level nuclear waste (HLNW) canisters requires the acquisition of values for various model parameters. In the present work, we describe the extraction of values for various parameters in the point defect model (PDM) for the growth of passive films on Alloy-22, from electrochemical impedance data for this alloy measured in saturated NaCl brine (6.2 m, m = mol kg^?1) at 80 °C, as described in Part I. The barrier layer of the passive film on Alloy-22 in the passive region (V < 0.6 V_SHE) is postulated to be defective chromic oxide (Cr_2 + xO_3 ? y) with n-type electronic character. The data suggest that the barrier layer is cation rich (x > y) with cation interstitials being the principal defect, but it is not possible to exclude oxygen vacancies, unequivocally, as being the principal defect. If the barrier layer is cation rich, the phase is estimated to have the composition Cr_2.028O₃ close to the metal|film interface, whereas if it is oxygen deficient, the stoichiometry is estimated to be Cr₂O_2.981 at the same location. The thickness of the barrier layer in the passive region is found to increase linearly with voltage while the passive current density is constant. In the transpassive range (V > 0.6 V_SHE), the passive film is found to be a p-type semi conductor, and the thickness of the barrier layer decreases, while the log of the passive current increases, with increasing applied potential. These observations are consistent with the predictions of the PDM for passive films on metals and alloys, including the transition from the passive to the transpassive states, which is predicted to coincide with a change in oxidation state of the chromium species being ejected from the barrier layer from Cr(III) to Cr(VI) and with the oxidative dissolution of the film. The principal defect in the barrier layer in the transpassive state appears to be the Cr(III) cation vacancy, which is generated by the oxidative ejection of cations from the barrier layer. Optimization of the PDM on the impedance data has yielded a set of parameter values for the passive state that can be used in deterministic models for predicting the accumulation of general corrosion damage to Alloy-22 in HLNW repositories.     

Purification of rabbit bone morphogenetic protein derived from bone, dentin, and wound tissue after tooth extraction

Bone morphogenetic protein (BMP) was extracted from bone matrix, dentin matrix, and wound tissue after tooth extraction in rabbits, and purified. These purified fractions were shown to be homogeneous by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis (SDS-PAGE), and induced new bone in situ in 3 weeks when implanted into the calf muscles of Wistar rats. The dentin matrix-derived BMP was different from the other two types in molecular weight and the properties revealed in the process of purification. However, each tissue-derived BMP was shown to induce new bone growth in a bioassay of xenogenic implantation. For this reason, BMP is thought to have subunits with certain commonalities in different tissue.