Electrochemical detection of silver ions and the study of metal–polymer interactions on a polybenzidine film electrode

Silver ions (Ag(I)) were preconcentrated efficiently at open circuit from aqueous silver nitrate solution into polybenzidine (poly-Bz) film electrodes. The poly-Bz films were electrodeposited by means of cyclic voltammetry from benzidine (Bz) in acidic aqueous solutions. It was found that preconcentration of Ag(I) ions into the film is highly dependent on the pH, being more favored at neutral pH, that is, when the nitrogen in imine–amine groups in the polymer chain are not protonated. Under these conditions the Ag(I) ions do not compete with the H⁺ ions for the same site within the film. A simple diffusion model is assumed to explain the incorporation of Ag(I) ion into the poly-Bz electrodes. The distribution of the Ag(I) ion between the solution and film was established and a probable analytical application given.     

Use of a zeolite-modified electrode for the study of the methylviologen–sodium ion-exchange in zeolite Y

The electrochemical response of zeolite-modified carbon paste electrodes (ZMCPEs) has been exploited to plot the normalised ion-exchange isotherm of methylviologen and sodium in zeolite Y. Results observed from the proposed methodology agree well with those obtained using the conventional procedure. Selectivity was very high for the large organic divalent cation over sodium species, but the degree of exchange of methylviologen did not exceed 64%. Electrochemistry of ZMCPEs allows the in situ quantitative determination of methylviologen in the zeolite phase, without significant modification in the solution-phase concentrations, so that the ion-exchange isotherm can be plotted very rapidly and without any other chemical analysis.     

Simple hemoglobin–gold nanoparticles modified electrode for the amperometric detection of acrylamide

In this work we propose the design of an electrochemical setup (hemoglobin–gold-nanoparticles–ITO glass), used for the determination of a hemoglobin adduct (acrylamide). Acrylamide is neurotoxin and potential carcinogen, formed mainly in high temperatures processed food that contains large quantity of starch (French fries, baked bread). Acrylamide forms hemoglobin adducts, and our sensing device is based on this property, by passivating the hemoglobin-modified electrode by the addition of low concentrations of acrylamide. The sensitivity to acrylamide better as 0.1 μM makes this electrochemical cell configuration suitable for the detection of acrylamide in food products.     

Capacitive behavior of graphene–ZnO composite film for supercapacitors

Graphene–ZnO composite film was synthesized for its potential application in supercapacitors. Graphene was prepared by a modified Hummers method and hydrazine reduction process, and ZnO was deposited on graphene by ultrasonic spray pyrolysis. The electrochemical characteristics of the film were investigated through electrochemical impedance spectrometry, cyclic voltammetry and chronopotentiometry tests. The results showed that graphene–ZnO composite film exhibited an enhanced capacitive behavior with better reversible charging/discharging ability and higher capacitance values, by comparison to pure graphene or ZnO electrode.     

The effect of an alkylsilane monolayer on an indiumtin oxide surface on the electrochemistry of hexacyanoferrate

The presence of a disorganized octadecylsilane, C₁₈, monolayer on an indiumtin oxide (ITO) electrode has a profound effect on the electrochemistry of hexacyanoferrate, Fe(CN)₆^3?/4?. We found that the alkylsilane monolayer forms a hydrophobic matrix, which affects the heterogeneous rate of electron transfer of the metallic complex, depending on the nature of the counter cation presence in the solution. A model is suggested which accounts for these effects as well as for the changes in the formal redox potential that are observed.     

The change of the electron scattering at the gold film–poly-(o-aminophenol) film interface after partial degradation of the polymer film: its relation with the electron transport process within the polymer film

The objective of this work was to study the irreversible deterioration suffered by poly(o-aminophenol) (POAP) films when the upper positive potential limit (E_upl) is extended to values higher than a threshold value of 0.5 V vs. SCE. To this end three techniques were employed: cyclic voltammetry (CV), surface resistance measurements (SR) and rotating disc electrode voltammetry (RDEV). In a first series of experiments the working electrode was a POAP film deposited on a thin gold film whose thickness is of the order of the mean free path of conduction electrons of gold. A pronounced attenuation in both resistometric and voltammetric responses occurs after subjecting the electrode to potential cycling where E_upl>0.5 V, as compared with those corresponding to POAP films cycled only between $\text{?0.2}\text{V}\text{<E<0.5}\text{V}$. According to the interpretation of SR measurements, a more extended configuration of redox sites appears at the gold–POAP interface after polymer degradation, as compared with that corresponding to a film cycled only between $\text{?0.2}\text{V}\text{<E<0.5}\text{V}$.In a second series of experiments POAP films were deposited on a rotating disc electrode and after being subjected to the same degradation treatment as indicated above, RDEV experiments were performed. Decreasing D_e values were obtained as the polymer film became more degraded. On the basis of an electron-hopping model, this last tendency can also be ascribed to less compact distributions of redox sites after polymer degradation.     

Thermodynamic and kinetic basicities of the carbon and oxygen ends of enolates. Their role in the reductive cleavage electrochemistry of α-substituted acetophenones

The electrochemical reductive cleavage of α-substituted acetophenones may follow a mechanism in which electron transfer and bond breaking are concerted, as with α-chloro-acetophenone, or a mechanism where the two steps are successive, as with, e.g. α-benzoyloxy–acetophenone. In both cases, the resulting phenacyl radical is immediately reduced, giving rise to the phenacyl enolate, the protonation of which is expected eventually to yield acetophenone. However, in cyclic voltammetry, the acetophenone wave, present at low scan rates, vanishes upon raising the scan rate. The disappearance of the wave is observed at lower scan rates when an acid, such as phenol, is added to the solution. This surprising behavior is the result of the oxygen end of the enolate being a thermodynamically weaker but kinetically faster base than its carbon end.     

Organic-phase enzyme electrode for phenolic determination based on a functionalized sol–gel composite

An amperometric biosensor for monitoring phenols in the organic phase was constructed by the silica sol–gel immobilization of tyrosinase on a glassy carbon electrode. The organic–inorganic hybrid materials with different sol–gel precursors and polymers were optimized, and the experimental conditions, such as the effect of the solvent, operational potential and enzyme loading were explored for the optimum analytical performance of the enzyme electrode. The biosensor can reach 95% of steady-state current in about 18 s, and the trend in the sensitivity of different phenols is as follows: catechol>phenol>p-cresol. In addition, the apparent Michaelis–Menten constants (K_m^app) and the stability of the enzyme electrode were discussed.     

Kinetics of the ferric/ferrous electrode reaction on Nafion®-coated electrodes

Cyclic and convolution voltammetry is used to study the kinetics of the ferric/ferrous electrode reaction on Nafion® coated Au and Pt electrodes in a perchloric acid solution. The reaction is characterized by the standard rate constant k_s⁰≈10^?6 cm s^?1 of the electron transfer across the metal ∣ Nafion® interface and by the diffusion coefficient of the ferric ion in the Nafion film D^(m)=(6.7±1.4)×10^?8 cm² s^?1. The Nafion® film apparently prevents the trace anions present in the perchloric acid solution (e.g. chlorides and sulfates) reaching the electrode surface and, thereby, influencing the ferric/ferrous electron transfer reaction via the inner-sphere catalysis. In addition, the polymer phase introduces a steric factor which causes the rate of the electron transfer reaction to decrease compared to the uncoated electrode, and proportionally the ion diffusion flux toward the metal surface, so that the values of the ratio k_s⁰/D^1/2 for the coated and uncoated electrodes are comparable. It is proposed that the considerably higher rate of the electron transfer on the Nafion® coated electrode in the sulfuric acid solution is due to the catalytic effect of sulfate or hydrogensulfate anions, which are transported through the Nafion® film as the sulfate complexes of the ferric cation, i.e. FeSO₄⁺ and FeHSO₄²⁺. The catalytic effect of oxides on the Nafion® coated electrodes is demonstrated.     

Comparative study on the influence of temperature,electrode potential and alloy bulk composition on hydrogen electrosorption into Pd–Pt and Pd–Au alloys

Hydrogen electrosorption into Pd-rich (>70% at. Pd in the bulk) Pd–Pt and Pd–Au alloys has been studied in acidic solutions (0.5 M H₂SO₄) using cyclic voltammetry and chronoamperometry. The influence of temperature (in the range between 283 and 328 K), electrode potential and alloy bulk composition on hydrogen electrosorption properties is presented. It has been found that with increasing temperature the maximum amount of absorbed hydrogen decreases and the potential of absorbed hydrogen oxidation peak and the potential of the α–β phase transition are shifted negatively. Pd alloying with Pt or Au results in lower potential of absorbed hydrogen oxidation peak and lower maximum amount of absorbed hydrogen. The region of the α–β phase transition for Pd–Pt alloys is placed at lower potentials as compared to pure Pd indicating lower thermodynamic stability of the β-phase. In the case of Pd–Au alloys the phase transition region is placed at higher potentials indicating higher thermodynamic stability of the β-phase. The values of time needed for electrode saturation with hydrogen and its removal decrease with increasing temperature and increasing bulk content of the alloying metals. The results have confirmed earlier suggestions that in the presence of both α- and β-phases of absorbed hydrogen the slow process of the phase transition controls the rate of the overall electrosorption process in thin Pd-based electrodes. The amounts of electrosorbed hydrogen for α- and β-phase boundaries, i.e. α_max and β_min, have been determined from the integration of the initial parts of current–time responses in hydrogen absorption and desorption processes.     

Electrochemical layer-by-layer modified imprinted sensor based on multi-walled carbon nanotubes and sol–gel materials for sensitive determination of thymidine

A novel electrochemical sol–gel imprinted sensor for sensitive and convenient determination of thymidine was developed. Thin film of molecularly imprinted sol–gel polymers with specific binding sites for thymidine was cast on carbon electrode by electrochemical deposition. Multi-walled carbon nanotubes (MWCNTs) were introduced for the enhancement of electronic transmission and sensitivity. The morphology and performance of the imprinted film was characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV) and amperometric measurements (i–t) in detail. The results showed that the imprinted film exhibited high selectivity toward thymidine. The linear range is over the range from 2 to 22 μmol L⁻¹, and the linear regression equation for thymidine is I = 0.867C + 0.232 with the detection limit of 1.6 × 10⁻⁹ mol L⁻¹(S/N = 3). The imprinted sensor was successfully employed to detect thymidine in some zidovudine-tablet samples.     

Effects of chlorhexidine-containing adhesives on the durability of resin–dentine interfaces

Objectives

This study evaluated the effect of addition of diacetate CHX in different concentrations into two simplified etch-and-rinse (ER) adhesive systems (XP Bond [XP] and Ambar {AM}) on the ultimate tensile strength (UTS), degree of conversion (DC), 60-day cumulative water sorption (WS), solubility (SO) and CHX release (CR) as well as the immediate (IM) and 1-year (1Y) resin–dentine bond strength (μTBS) and nanoleakage (NL).

Methods

Ten experimental adhesive systems were formulated according to the addition of CHX diacetate (0 [control], 0.01, 0.05, 0.1 and 0.2%) in the two ER. For UTS and DC, specimens were constructed and tested after 24 h. For WS, SO and CR, after specimens build-up, they were stored in water and the properties measured after 60 days. The occlusal enamel of fifty molars was removed and the adhesives were applied in dentine surface after 37% phosphoric acid etching. After composite resin build-ups, specimens were longitudinally sectioned to obtain resin–dentine bonded sticks (0.8 mm²). Specimens were tested in tension at 0.5 mm/min in the IM or 1Y. For NL, 2 bonded sticks from each tooth were prepared and analyzed under SEM. The data were submitted to appropriate statistical analysis (α = 0.05).

Results

The addition of CHX did not influence UTS, DC, WS and SO (p < 0.05). Higher CR was observed in adhesives with higher concentration of CHX (p < 0.05). After 1Y, significant reductions of μTBS and increases of NL were observed in the control groups (p < 0.05). Reductions of μTBS and increase of NL over time were not observed (AM) for CHX-containing adhesives or it was less pronounced than the control (XP) regardless of the CHX concentration.

Conclusions

The addition of CHX diacetate in concentrations until 0.2% in the simplified ER adhesive systems may be an alternative to increase the long-term stability of resin–dentine interfaces, without jeopardizing the adhesives’ mechanical properties evaluated.     

Effect of the Progression of Fusobacterium nucleatum–induced Apical Periodontitis on the Gut Microbiota

IntroductionFusobacterium nucleatum, which is involved in the development of periodontal disease and apical lesions, can be transmitted to the colon and metastasize to colorectal cancer, suggesting a link between oral and systemic diseases. We analyzed the effects of F. nucleatum on bacterial flora in the gut and surrounding organs in a rat model of apical periodontitis and analyzed the infection route to the gut and distant organs.MethodsWe induced apical periodontitis in rat molars by infecting the dental pulp with F. nucleatum and then took X-ray images and performed histopathologic analyses. Next, we removed the maxilla, gut, heart, liver, and kidney from the rats at 0, 2, 4, and 8 weeks postsurgery and then extracted DNA samples and performed polymerase chain reaction and microbiome analyses using the Illumina MiSeq (Illumina Co, Tokyo, Japan).ResultsThe presence of inflammatory cell infiltration confirmed apical periodontitis from 2–8 weeks. Polymerase chain reaction and microbiome analyses revealed F. nucleatum in the rat gut from 2 weeks and in the kidney from 8 weeks. The rat gut, heart, liver, and kidney exhibited altered bacterial flora, including a marked decrease in Verrucomicrobia and an increase in Proteobacteria after 2 weeks and increases in Bacteroidetes and Firmicutes after 4 weeks.ConclusionsThe onset of F. nucleatum–induced apical periodontitis changed the bacterial flora in the rat gut, heart, liver, and kidney, with a confirmed progressing infection in the large intestines.     

The effects of ULF–TENS stimulation on gnathology: the state of the art

Aims: The aim of this study was to evaluate the state of the art in the current literature regarding the effect of ultra low frequency–transcutaneous electrical nerve stimulation (ULF–TENS) on patients with temporomandibular disorders (TMD).

Methodology: The authors reviewed the literature through a thorough manual and electronic research on PubMed database (using the Medical Subject Headings thesaurus) and subsequent analysis of all the found papers regarding the effect of TENS on TMD patients. No randomized controlled trials on the investigated topic were found. Only eight papers regarding controlled clinical trials (CCT) were selected according to the search strategy selection criteria.

Results: According to the available literature and the authors’ experience, ULF–TENS seems to be a valid support in the management of TMD patients, but also a ‘provocative’ tool, so its application should always be monitored by electromyographic and electrognathographic analysis (before and after TENS). Conclusions: Further clinical studies (mainly randomized controlled trials) on ULF–TENS application in neuromuscular gnathology are needed.     

Effect of pretreatments on the metal–ceramic bonding strength of a Pd–Ag alloy

Objectives

The purpose of this study was to evaluate the efficacy of surface treatments on the bonding properties between a metal and ceramic.

Methods

Sixty metal specimens were divided equally into four groups of 15 samples each. These groups received different treatments (Gr1: 250 μm Al₂O₃ + preoxidation; Gr2: 250 μm Al₂O₃ + degassing; Gr3: 120 μm Al₂O₃ + preoxidation; Gr4: 120 μm Al₂O₃ + degassing). Bond strengths were evaluated using a three-point bending test. The results were analyzed using 2-way ANOVA and Tukey's test. Scanning electron microscopy and energy dispersive spectroscopy were used to observe the microscopic features, elemental compositions and distributions, and diffusion in the specimens. Mechanical profiler was used to measure the roughness of metal surface.

Results

The bond strengths of the four groups ranged from 45.00 ± 3.63 MPa to 51.61 ± 5.91 MPa, with significant differences (P < .05). The specimen that received the pretreatment of 250 μm Al₂O₃ air-particle abrasion + degassing had the highest bond strength. Heating under different oxygen partial pressures caused the final Pd–Ag alloys to have varying degrees of internal oxidation and different quantities of metallic nodules. None of the elements in either the ceramic or the Pd–Ag alloy layer diffused into the other layer.

Conclusions

The metal–ceramic specimen subjected to air-particle abrasion with 250 μm Al₂O₃ and degassed before porcelain firing had significantly higher bond strength than specimens treated differently.     

Consideration of effect of the amount of mandibular setback on the submental region in the planning of orthodontic–orthognathic treatment

Aesthetic outcome has gained in importance in the treatment of patients with orthognathic problems. Historically, Class III malocclusions have historically been treated by isolated mandibular setback and maxillary advancement, whereas bimaxillary procedures have recently become the more common option. Functional outcome and stability have been discussed previously. The aim of this observational study was to evaluate the effect of mandibular setback (BSSO) on the cervical region. We studied 38 Class III patients (20 women and 18 men, mean (SD) age 25 (0.8) years) who we identified from our clinical records and who were treated between 1 January 2002 and 30 December2012 with mandibular setback procedures and followed up for 6 months. To study the effect of the amount of mandibular setback on the aesthetic outcome we have distinguished between patients with less than 5 mm setback and those with 5 mm or more. In patients whose mandibular setback was less than 5 mm there was no significant change in cervical length. However, it decreased significantly in patients in whom the movement was 5 mm or more. Postoperatively the lip–chin–throat angle (p = 0.02), the length of the lower lip (p = 0.002), and the length of the upper lip (p = 0.003) from the aesthetic line also differed significantly between the 2 groups. Our observations strongly suggest that all these relations should be considered when treatment is being planned to avoid an unpleasant aesthetic impact on the chin region.     

Application of BMP-2/FGF-2 gene–activated scaffolds for dental pulp capping

Clinical Oral Investigations - To evaluate the effect of non-viral gene therapy on human dental pulp stem cells (DPSCs) in an in vitro and an ex vivo model. Nanoplexes comprising polyethyleneimine...