The electrochemistry and thin-layer luminescence spectroelectrochemistry of rhodamine 6G at a 4,4′-bipyridine-modified gold electrode

We report on the first direct electrochemistry and fluorescence spectroelectrochemistry of rhodamine 6G at a 4,4′-bipyridine-modified gold electrode. The value of n determined in spectropotentiostatic experiments at 1.87×10^?6 mol l^?1 of rhodamine 6G in 0.20 mol l^?1 KCl solution is 1.15, and the experimental value obtained for E⁰′ is ?0.787 V versus Ag ∣ AgCl ∣ KCl_sat, which agrees very well with the value (E⁰′=?0.791 V) obtained using cyclic voltammetry at a modified gold electrode. The values of the diffusion coefficients D_O and D_R for the oxidized and reduced forms of rhodamine 6G calculated from results of potential step and in situ fluorescence measurement experiments are 4.0×10^?6 cm² s^?1 and 4.2×10^?6 cm² s^?1, respectively. Cyclic voltammograms of rhodamine 6G show that the peak current I_p is proportional to the square root of the potential scan rate v^1/2, the ratio of the reduction to the oxidation peak height is about unity, and the separation of both reduction and reoxidation peak potentials ΔE_P is essentially constant at 135 mV at low scan rates. These results indicate that electrochemistry of rhodamine 6G at a 4,4′-bipyridine-modified gold electrode is a quasi-reversible one-electron electrode process.     

Pseudopolarography of trace metals. Part II. The comparison of the reversible,quasireversible and irreversible electrode reactions

The theoretical and experimental pseudopolarographic curves of reversible, quasireversible and irreversible electrochemical reactions were compared and evaluated. The measurements were performed on a stationary mercury drop electrode (SMDE, PAR 303A), using differential pulse anodic stripping voltammetry (DPASV). A good agreement between the theoretical and the experimental shift of the half-wave potential with an increasing accumulation time was obtained for the reversible pseudopolarograms of 10^?7 mol dm^?3 Cd(II) (in 0.1 mol dm^?3 NaClO₄, pH ～2). As compared with the curve of the logarithmic analysis of the polarogram, the corresponding curve of the pseudopolarogram is steeper in the region of the half-wave potential. It has been shown that even though the pseudopolarograms are quasireversible or irreversible, there is a range at the foot of the curves with a reversible slope (usually below 10% of the total/limiting current). It has been verified that the range of this reversible slope can be extended by increasing the accumulation time, lowering the mercury drop size and diminishing the thickness of the diffusion layer. The estimated value for its approximative evaluation is about 1% of the total/limiting current. This is essential for the determination of the corresponding electrochemical parameters, such as: the formal potential (E°^′), transfer coefficient (α) and rate constant (k_s). From the experimentally obtained reversible slope of the (pseudo)polarographic curves of Zn(II) (in 1 mol dm^?3 NaClO₄, pH 4.7 ± 0.1), the parameters for the quasireversible electrochemical reactions were estimated as follows: E°^′=?0.964 ± 0.002 V, α=0.24 ± 0.02 and k_s～2–3×10^?3 cm s^?1. It is shown that an accurate transfer coefficient can be calculated from the curves of the logarithmic analysis of the quasireversible pseudopolarograms, which is not the case for the polarographic curves. The irreversible system, tested on the electrochemical reaction of the CdNTA complex (in 0.1 mol dm^?3 NaClO₄, pH 7.9 ± 0.1), shows relatively good agreement between the experimental and the theoretical dependences. The (pseudo)polarographic measurements enabled approximate estimation of the electrochemical parameters (E°^′=?0.835 ± 0.010 V, α=0.55 ± 0.02 and k_s=1.0 ± 0.4 × 10^?4 cm s^?1) which are in fairly good agreement with the literature data.     

Electrocatalytic oxidation of nitrite on a carbon paste electrode modified with Co(II) porphyrin adsorbed on SiO2/SnO2/Phosphate prepared by the sol–gel method

This paper describes the immobilization of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphyrin ion on SiO₂/SnO₂/Phosphate obtained by the sol–gel processing method. The porphyrin was adsorbed on the surface of the modified material and furthermore metallized in situ with Co(II) ion. The porphyrin metallation process was followed using UV–Vis spectroscopy by inspecting the Q bands of the free and metallated porphyrin. A carbon paste electrode modified with material containing metallated porphyrin was used to study the electro-catalytic oxidation of nitrite ions by means of cyclic voltammetry, chronoamperometry and RDE voltammetry. The modified electrode was very stable and exhibited the electro-catalytic oxidation of nitrite ions at 0.72 V vs. SCE by a two electron mechanism producing nitrate ions at pH 5.4. The kinetic parameters of the electrode reaction process were calculated; (1 ? α)n_a was 0.479, D was (5.3 ± 0.11) × 10^?5 cm s^?1, and k⁰ could be determined as (5.4 ± 0.14) × 10^?3 cm s^?1.     

Trace determination of rare earths by adsorption voltammetry at a carbon paste electrode

A novel adsorption voltammetry has been described for the determination of trace rare earths in the presence of alizarin complexon (ALC) at a carbon paste electrode (CPE). A sensitive adsorptive oxidation peak was found for the complexes of middle and heavy rare earths(III) with ALC in a supporting electrolyte of 0.12 M HAc + NaAc and 0.03 M potassium biphthalate (pH 5.0) for linear-scanning from −0.2 to 0.8 V at 100 mV s⁻¹. The sensitivity of the heavy rare earths (Dy, Ho, Er, Tm, Yb, and Lu) is higher than that of other rare earths. Under the optimized procedure, a detection limit of 5.0 × 10⁻¹⁰ M holmium(III) (S/N=3) was realized for a 120 s preconcentration and the linear current–concentration relationship was observed up to 2.0 × 10⁻⁷ M. The relative standard deviation is 3.8% for 20 successive determinations of 4.0 × 10⁻⁸ M Ho(III) on the same electrode surface. The electrode processes of the adsorbed complex were investigated. The method developed was applied for determination of the sum of rare earths (except La, Ce, Pr, Nd, and Sc) in rare earth nodular cast iron samples with satisfactory results.     

Voltammetric characterisation of the radical anions of 4-nitrophenol, 2-cyanophenol and 4-cyanophenol in N,N-dimethylformamide electrogenerated at gold electrodes

The electrochemical reductions of 4-nitrophenol, 2-cyanophenol and 4-cyanophenol were studied in N,N-dimethylformamide (DMF) at gold macro- and microdisk electrodes. It was inferred at the gold macroelectrode that the reduction of the parent molecule to the corresponding radical anion is chemically irreversible due to a rapid protonation process in which the basic radical anion reacts with the acidic parent compound. The use of microdisk electrodes and fast scan cyclic voltammetry (144 kV s⁻¹) for the reduction of each of the three compounds of interest failed to outrun the kinetics of the protonation reaction, suggesting a fast process with a second-order rate constant in excess of 1 × 10⁷ M⁻¹ s⁻¹.     

Ruthenium purple-containing zeolite modified electrodes and their application for the detection of glucose

Zeolite-entrapped ruthenium purple particles (denoted NaY ∣ RP) were prepared by exchanging Fe³⁺ into zeolite Y (NaY) and reacting further with ruthenium hexacyanide (Ru(CN)₆^4?). Although XRD and diffuse-reflectance UV-vis absorption analyses suggested that the RP_(NaY) particles were basically amorphous, the resulting electrode prepared from these particles and glucose oxidase (GOx) displayed a remarkable sensitivity to glucose. The limiting current showed a linear relationship with the bulk activity of glucose up to 4 mM (pH 5.1, phosphate), covering a range from 10^?6 to 10^?3 M. Flow-injection analysis, in addition, showed the detection limit reaching a level as low as 0.1 μM. Data simulation showed that the electrode sensitivity followed an electrocatalytic (EC′) mechanism based on the reduction of H₂O₂ by the reduced ruthenium purple. Accordingly, the reaction rate constant (pseudo-first-order) and the effective activity of RP were determined to be 110 M^?1 s^?1 (pH 5) and 1.5×10^?9 mol cm^?2, respectively. Electrochemical impedance spectroscopic (EIS) analysis showed that the charge-transfer resistance of the zeolite-electrode decreased systematically with the stepwise addition of glucose into the system. The exchange rate constant (k_o) and the diffusion coefficient of electrons (D_e) in the zeolite film were estimated to be 5×10^?6 cm s^?1 and 6×10^?10 cm² s^?1, respectively. These experimental results suggested that the RP sites in the NaY ∣ RP particles were separated widely with the average distance between the adjacent RP sites estimated to be about 1×10^?4 cm or equivalent to 500 supercages, which agreed well with the results obtained from data simulation.     

Efficacy of a mouthrinse based on hydroxyapatite to reduce initial bacterial colonisation in situ

ObjectiveThe present in situ - investigation aimed to specify the impact of pure hydroxyapatite microclusters on initial bioadhesion and bacterial colonization at the tooth surface.DesignPellicle formation was carried out in situ on bovine enamel slabs (9 subjects). After 1 min of pellicle formation rinses with 8 ml of hydroxyapatite (HA) microclusters (5%) in bidestilled water or chlorhexidine 0.2% were performed. As negative control no rinse was adopted. In situ biofilm formation was promoted by the intraoral slab exposure for 8 h overnight. Afterwards initial bacterial adhesion was quantified by DAPI staining and bacterial viability was determined in vivo/in vitro by live/dead-staining (BacLight). SEM analysis evaluated the efficacy of the mouthrinse to accumulate hydroxyapatite microclusters at the specimens’ surface and spit-out samples of the testsolution were investigated by TEM.ResultsCompared to the control (2.36 × 10⁶ ± 2.01 × 10⁶ bacteria/cm²), significantly reduced amounts of adherent bacteria were detected on specimens rinsed with chlorhexidine 0.2% (8.73 × 10⁴ ± 1.37 × 10⁵ bacteria/cm²) and likewise after rinses with the hydroxyapatite testsolution (2.08 × 10⁵ ± 2.85 × 10⁵ bacteria/cm², p < 0.001). No demonstrable effect of HA-particles on Streptococcus mutans viability could be shown. SEM analysis confirmed the temporary adsorption of hydroxyapatite microclusters at the tooth surface. Adhesive interactions of HA-particles with oral bacteria were shown by TEM.ConclusionHydroxyapatite microclusters reduced initial bacterial adhesion to enamel in situ considerably and could therefore sensibly supplement current approaches in dental prophylaxis.     

Electrochemical behavior of iodide at a nickel pentacyanonitrosylferrate film modified aluminum electrode prepared by an electroless procedure

The surface of an aluminum disk electrode was modified by a thin film of nickel pentacyanonitrosylferrate and used for electrocatalytic oxidation of iodide. The cyclic voltammogram of the modified Al electrode showed surface redox behavior due to the [Ni^IIFe^III/II(CN)₅NO]^0/1? redox couple. The modifying layer shows excellent catalytic activity toward the oxidation of iodide. Different supporting electrolytes containing different alkali metal cations affected the apparent formal potential of the redox films and thus, changed the thermodynamic tendency and kinetics of the modifying film toward the catalytic oxidation of iodide. This was explained by including the concept of a surface coverage normalized-catalytic current. The kinetics of the catalytic reaction were investigated by cyclic voltammetry and rotating disk electrode voltammetry in a suitable supporting electrolyte. The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. The heterogeneous rate constant for the catalytic reaction, k, diffusion coefficient of iodide in solution, D, and transfer coefficient, α, were found to be 5.8 × 10² M^?1 s^?1, 1.3 × 10^?5 cm² s^?1 and 0.66, respectively. In addition the effect of electrode surface coverage on the dynamic range of a calibration curve was investigated. Under optimum conditions a linear calibration graph was obtained over an iodide concentration range of 2–100 mM.     

Contributions of stress corrosion and cyclic fatigue to subcritical crack growth in a dental glass-ceramic

ObjectiveThe objective of this study was to test the following hypotheses: (1) both cyclic degradation and stress-corrosion mechanisms result in subcritical crack growth (SCG) in a fluorapatite glass-ceramic (IPS e.max ZirPress, Ivoclar-Vivadent) and (2) there is an interactive effect of stress corrosion and cyclic fatigue to accelerate subcritical crack growth.MethodsRectangular beam specimens were fabricated using the lost-wax process. Two groups of specimens (N = 30/group) with polished (15 μm) or air-abraded surface were tested under rapid monotonic loading. Additional polished specimens were subjected to cyclic loading at two frequencies, 2 Hz (N = 44) and 10 Hz (N = 36), and at various stress amplitudes. All tests were performed using a fully articulated four-point flexure fixture in deionized water at 37 °C. The SCG parameters were determined using the ratio of inert strength Weibull modulus to lifetime Weibull modulus. A general log-linear model was fit to the fatigue lifetime data including time to failure, frequency, peak stress, and the product of frequency and logarithm of stress in ALTA PRO software.ResultsSCG parameters determined were n = 21.7 and A = 4.99 × 10⁻⁵ for 2 Hz, and n = 19.1 and A = 7.39 × 10⁻⁶ for 10 Hz. After fitting the general log-linear model to cyclic fatigue data, the coefficients of the frequency term (α₁), the stress term (α₂), and the interaction term (α₃) had estimates and 95% confidence intervals of α₁ = −3.16 (−15.1, 6.30), α₂ = −21.2 (−34.9, −9.73), and α₃ = 0.820 (−1.59, 4.02). Only α₂ was significantly different from zero.Significance(1) Cyclic fatigue does not have a significant effect on SCG in the fluorapatite glass-ceramic evaluated and (2) there was no interactive effect between cyclic degradation and stress corrosion for this material.     

Pre-heating effects on extrusion force,stickiness and packability of resin-based composite

ObjectivesTo measure temperature effects on stickiness and packability of representative resin-based composites and the effect of pre-heating time on pre-cure properties of Viscalor, including extrusion force.MethodsFive resin-based composites (RBC) and an additional RBC, Viscalor, used with a Caps Warmer (VOCO, Germany) were studied. The extrusion force (N) and extruded mass (g) were measured from Viscalor compules heated in T3 mode for 30 s (T3-30 s) and 3 min (T3-3 min). For stickiness and packability measurements, RBCs were packed into a brass cylindrical cavity controlled at 22 and 37 °C. A flat-ended probe was lowered into the RBC pastes at constant speed. Stickiness: F_max (N) and W_s (N mm), and packability: F_p (N), were measured. Viscalor was LED photo-cured at 1200 mW/cm² for 40 s. The degrees of conversion at 5 min and 24 h post cure (DC_5min and DC_24h) of Viscalor (no heat, T3-30 s and T3-3 min) were measured by ATR-FTIR. Data were analysed by one-way ANOVA, independent t-test and Tukey post-hoc tests (p < 0.05).ResultsThe maximum temperature of the Caps Warmer, in T3 mode, reached 68 °C in 20 min. Viscalor temperatures of 34.5 °C and 60.6 °C were recorded after 30 s and 3 min pre-heating, respectively. Pre-heating significantly reduced extrusion force and increased extruded mass, especially after 3 min. RBCs varied in F_max, W_s and F_p (p < 0.05). Temperature also affected F_max (p = 0.000), W_s (p = 0.002) and F_p (p = 0.000). Pre-heating Viscalor for either 30 s or 3 min did not increase the post-cure DC at either 5 min or 24 h, relative to no pre-heating (p > 0.05).SignificanceThe composites varied to an extent in stickiness and packability but the overall magnitudes remained within a clinically acceptable range. Pre-heating was beneficial in placement of Viscalor and caused no adverse effects through premature polymerization.     

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.     

Novel studies on the electrochemical oxidation of 2-[4-(N,N-dimethylamino)phenyl]-6-methyl benzothiazole (DPMB) in acetonitrile at platinum electrodes

The electrochemical oxidation mechanism of 2-[4-(N,N-dimethylamino)phenyl]-6-methyl benzothiazole (DPMB) is studied in a 0.1 M N(C₄H₉)₄ClO₄ + acetonitrile (ACN) reaction medium by cyclic (CV) and square wave voltammetries (SWV) as well as by controlled potential bulk electrolysis at platinum electrodes. The primary radical cation formed by the one electron oxidation of DPMB undergoes a deprotonation process, which is the rate-determining step, followed by a radical–radical coupling. On the other hand, an initial quasi-reversible monoelectronic charge transfer mechanism is inferred from cyclic and square wave voltammograms recorded at scan rates and frequencies higher than 0.4 V s^?1 and 40 Hz, respectively. Diffusion coefficients of DPMB at different temperatures were calculated from the quasi-reversible convoluted cyclic voltammograms. DigiSim® and COOL software were used to fit the quasi-reversible cyclic and square wave voltammetric responses, respectively. Formal potentials, formal rate constants and positive transfer coefficients at different temperatures were evaluated from the fitting of cyclic voltammograms. The experimental activation parameters were also determined. The effects of the analytical concentration of the reagent and the temperature, as well as the addition of trifluoracetic acid and a strong base such as lutidine on the electrochemical responses are discussed. A general reaction mechanism as well as probable structures for dimeric products are proposed.Besides, the presence of an acid–base equilibrium in DPMB solutions is also studied by employing UV–Vis spectroscopic measurements at different trifluoracetic acid concentrations. An apparent value of (1.5 ± 0.2) × 10³ M^?1 was estimated for the DPMB basic constant at 20.0 °C     

Electrochemical behavior of quercetin: Experimental and theoretical studies

Electrochemical oxidation of quercetin, as important biological molecule, has been studied in 0.1 M phosphate buffer solution, using cyclic voltammetry, chronoamperometry, rotating disk electrode voltammetry as well as quantum mechanical calculations. The heterogeneous charge transfer rate constant, k′, transfer coefficient, α, and exchange current density, j₀, for oxidation of quercetin at the glassy carbon electrode are determined as 4.84 × 10^?2 cm s^?1, 0.65 ± 0.01 and (1.17 ± 0.39) × 10^?7 A cm^?2, respectively. The formal potential, E^0′, of quercetin is pH dependent with a slope of ?60.1 mV per unit of pH which is close to the anticipated Nernstian value of ?59 mV for a two electrons and two protons process. The standard formal potential, E⁰, of quercetin was found to be equal with 558 mV versus saturated calomel electrode (SCE). The mechanism of oxidation was deduced from voltammetric data in various pHs and also in different concentrations of quercetin. The diffusion coefficient of quercetin was calculated as 3.18 × 10^?6 cm² s^?1 for the experimental condition, using chronoamperometric results. The results of density functional theory (DFT) calculations for the oxidation of quercetin in aqueous solution, are also presented. The theoretical standard electrode potential of quercetin is obtained to be 568 mV versus SCE, which is in good agreement with the experimental value. The discrepancy between theoretical and experimental values is only 10 mV. The agreement verifies the accuracy of experimental method and the validity of mathematical model.     

The electrochemical behavior of p-sulfonated calix[4]arene

The electrochemical behavior of p-sulfonated calix[4]arene was studied. In aqueous solution, p-sulfonated calix[4]arene can be oxidized when the potential is more than 0.7 V versus SCE. It is confirmed that the reaction is an irreversible two-electron transfer electrochemical reaction. The anodic peak potential, E_p, is affected by the acidity of the solution. E_p shifts in the negative direction when the pH increases. The electron transfer coefficient, α, is 0.65. At 25 °C, the diffusion coefficient of p-sulfonated calix[4]arene is 3.1 × 10^?5 cm² s^?1. The activation energy, E_a, for the electrochemical reaction is (18.8 ± 0.2) kJ mol^?1.     

Effect of propionaldehyde or 2,3-butanedione additives on the mechanical properties of Bis-GMA analog-based composites

ObjectivesThe purpose of this study was to evaluate the effect of two additives, propionaldehyde/aldehyde or 2,3-butanedione/diketone, on mechanical properties of Bis-GMA-based composites containing TEGDMA, propoxylated Bis-GMA (CH₃Bis-GMA) or propoxylated fluorinated Bis-GMA (CF₃Bis-GMA).MethodsThree control composites, Bis-GMA/diluent monomer (25/75 mol%), and six test composites, Bis-GMA/diluent monomer/aldehyde or diketone (17/51/32 mol%) were prepared. All composites contained hybrid treated filler (barium aluminosilicate glass/pyrogenic silica; 60 wt%), and 0.2 wt% each of camphorquinone and N,N-dimethyl-p-toluidine. Degree of conversion (DC%), flexural strength (FS), modulus of elasticity (E), modulus of resilience (R) and diametral tensile strength (DTS) were determined. DC% (n = 3) was investigated by FT-IR. For FS and E, beam-shaped specimens (25 mm × 2 mm × 2 mm) were prepared (n = 6), stored for 7 days in 37 °C deionized water and tested on an Instron utilizing a three-point loading jig (0.5 mm/min). The R-values were obtained from the following equation: R = (FS)²/2E. For DTS, cylindrical specimens (4 mm × 8 mm) were prepared (n = 6), stored for 7 days in 37 °C deionized water and diametrically loaded on an Instron (0.5 mm/min). Data were analyzed by one-way ANOVA and Tukey's test (α = 0.05).ResultsIncorporation of additives led to an increase in DC%, FS and E for Bis-GMA/TEGDMA and Bis-GMA/CH₃Bis-GMA systems. R-values for all systems were unaffected by addition of additives. They had no significant effect on DC% or mechanical properties of Bis-GMA/CF₃Bis-GMA.SignificanceThe findings correlate with the ability of additives to improve degree of conversion of some composite systems thereby enhancing mechanical properties.     

Diffusion-weighted imaging with histogram analysis of the apparent diffusion coefficient maps in the diagnosis of parotid tumours

The aim of this study was to investigate the role of diffusion-weighted imaging (DWI) with histogram analysis of apparent diffusion coefficient (ADC) maps in the characterization of parotid tumours. This prospective study included 39 patients with parotid tumours. All patients underwent magnetic resonance imaging with DWI, and ADC maps were generated. The whole lesion was selected to obtain histogram-related parameters, including the mean (ADC_mean), minimum (ADC_min), maximum (ADC_max), skewness, and kurtosis of the ADC. The final diagnosis included pleomorphic adenoma (PA; n = 18), Warthin tumour (WT; n = 12), and salivary gland malignancy (SGM; n = 9). ADC_mean (×10^?3 mm²/s) was 1.93 ± 0.34 for PA, 1.01 ± 0.11 for WT, and 1.26 ± 0.54 for SGM. There was a significant difference in whole lesion ADC_mean among the three study groups. Skewness had the best diagnostic performance in differentiating PA from WT (P = 0.001; best detected cut-off 0.41, area under the curve (AUC) 0.990) and in discriminating WT from SGM (P = 0.03; best detected cut-off 0.74, AUC 0.806). The whole lesion ADC_mean value had best diagnostic performance in differentiating PA from SGM (P = 0.007; best detected cut-off 1.16 × 10^?3 mm²/s, AUC 0.948). In conclusion, histogram analysis of ADC maps may offer added value in the differentiation of parotid tumours.     

Antibacterial and antibiofilm efficacy of k21-E in root canal disinfection

ObjectivesThe aim of the current project was to study the antimicrobial efficacy of a newly developed irrigant, k21/E against E. faecalis biofilm.MethodsRoot canals were instrumented and randomly divided into the following groups: irrigation with saline, 6% NaOCl (sodium hypochlorite), 6% NaOCl + 2% CHX (Chlorhexidine), 2% CHX, 0.5% k21/E (k21 - quaternary ammonium silane) and 1% k21/E. E. faecalis were grown (3-days) (1 × 10⁷ CFU mL⁻¹), treated, and further cultured for 11-days. Specimens were subjected to SEM, confocal and Raman analysis and macrophage vesicles characterized along with effect of lipopolysaccharide treatment. 3T3 mouse-fibroblasts were cultured for alizarin-red with Sortase-A active sites and Schrödinger docking was performed. TEM analysis of root dentin substrate with matrix metalloproteinases profilometry was also included. A cytotoxic test analysis for cell viability was measured by absorbance of human dental pulp cells after exposure to different irrigant solutions for 24 h. The test percentages have been highlighted in Table 1.ResultsAmong experimental groups, irrigation with 0.5% k21/E showed phase separation revealing significant bacterial reduction and lower phenylalanine 1003 cm⁻¹ and Amide III 1245 cm⁻¹ intensities. Damage was observed on bacterial cell membrane after use of k21/E. No difference in exosomes distribution between control and 0.5%k21/E was observed with less TNFα (*p < 0.05) and preferential binding of SrtA. TEM images demonstrated integrated collagen fibers in control and 0.5%k21/E specimens and inner bacterial membrane damage after k21/E treatment. The k21 groups appeared to be biocompatible to the dental pulpal cells grown for 24 h.SignificanceCurrent investigations highlight potential advantages of 0.5% k21/E as irrigation solution for root canal disinfection.     

Application of multi-walled carbon nanotubes functionalized with hemin for oxygen detection in neutral solution

Functionalization of multi-walled carbon nanotubes (MWNTs) is of paramount importance for developing new sensors. In this study, a hemin-modified MWNT electrode was successfully constructed. Upon saturation, the amount of adsorbed hemin is estimated as 2.7 × 10^?9 mol cm^?2, which is 39 times larger than the value of the hemin monolayer. The electrochemical behavior of the hemin-modified MWNT electrode has been characterized by cyclic voltammetry (CV). The electron-transfer coefficient (α) is found to be 0.38 with a heterogeneous electron transfer rate (k) of 2.9 s^?1 for the adsorbed hemin. Both MWNT and hemin-modified MWNT electrodes show ideal reversibility in 5 mM K₃[Fe(CN)₆] in the range of 0.02–1.00 V s^?1, indicating fast electron-transfer kinetics. CV of the hemin-modified MWNT electrode in pH 7.4 phosphate buffer solution (PBS) clearly shows the dioxygen reduction peaks close to 0 V (vs. Ag|AgCl). These results are useful in the development of a novel oxygen sensor for working at a relatively low potential.     

Fracture toughness of cross-linked and non-cross-linked temporary crown and fixed partial denture materials

ObjectivesTemporary crowns and fixed partial dentures are exposed to considerable functional loading, which places severe demands on the biomaterials used for their fabrication (= temporary crown & bridge materials, t-c&b). As the longevity of biopolymers is influenced by the ability to withstand a crack propagation, the aim of this study was to investigate the fracture toughness of cross-linked and non-cross-linked t-c&bs.MethodsFour different t-c&bs (Luxatemp AM Plus, Protemp 3 Garant, Structur Premium, Trim) were used to fabricate bar shaped specimens (2 mm × 5 mm × 25 mm, ISO 13586). A notch (depth 2.47 mm) was placed in the center of the specimen using a diamond cutting disc and a sharp pre-crack was added using a razor blade. 60 specimens per material were subjected to different storage conditions (dry and water 37 °C: 30 min, 60 min, 4 h, 24 h, 168 h; thermocycling 5–55 °C: 168 h) prior to fracture (3-point bending setup). The fracture sites were inspected using SEM analysis. Data was subjected to parametric statistics (p = 0.05).ResultsThe K_IC values varied between 0.4 and 1.3 MPa m^0.5 depending on the material and storage time. Highest K_IC were observed for Protemp 3 Garant. Fracture toughness was significantly affected by thermocycling for all dimethacrylates (p < 0.05) except for Structur Premium. All dimethacrylates showed a linear-elastic fracture mechanism, whereas the monomethacrylate showed an elasto-plastic fracture mechanism.SignificanceDimethacrylates exhibit a low resistance against crack propagation immediately after curing. In contrast, monomethacrylates may compensate for crack propagation due to plastic deformation. However, K_IC is compromised with increasing storage time.     

Effect of silane and MDP-based primers on physico-chemical properties of zirconia and its bond strength to resin cement

ObjectiveTo evaluate the effect of surface treatments on yttria-tetragonal zirconia polycrystal (Y-TZP) characteristics and on resin-mediated zirconia bond.MethodsY-TZP slabs were grit blasted with 45 μm alumina or with 30 μm silica-coated alumina particles. The chemical treatments were: no-chemical treatment (NC), silane-containing primer (SP), MDP (10-Methacryloyloxydecyl dihydrogen phosphate) and silane-containing primer (MPS), MDP-containing primer (MP) and MDP and silane-containing adhesive (MPA). Contact angle as a function of surface roughness (θ_m) and surface roughness parameter (Sdr) were measured using Fringe Projection Phase Shifting (FPPS). Surface free energy (γ_s^TOT) was calculated with a goniometer. Chemical interaction between primers/adhesive and zirconia was analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Resin cement microshear bond strength (μSBS) was analyzed at either 24-h or 8-months water storage (37 °C). θ_m values, Sdr values, γ_s^TOT and μSBS values were analyzed using Analysis of variance (ANOVA) and post hoc Tukey test (α = 0.05).ResultsChemical treatment had an effect (p < 0.001) on all surface parameters analyzed: θ_m, γ_s^TOT and Sdr. MP-treated group showed higher incidence of P–O–Zr bonds than the other groups, indicating more chemical linkages. Grit blasting (p < 0.001) and the interaction chemical treatment*storage (p < 0.001) did not affect μSBS; all silane-containing primers showed significant drop in μSBS after aging.SignificanceMDP and/or silane-based solutions affect the physicochemical properties of blasted-zirconia. An MDP-based primer is fundamental to achieve a stable resin-zirconia bonding, but the chemical reactivity of MDP is impaired when this molecule is present in a multicomponent system.