Electrochemical quartz crystal microbalance study of copper adatoms on Au(111) electrodes in solutions of perchloric and sulfuric acid

The adsorption of anions on highly ordered (111)-type gold electrodes with and without Cu adatoms in perchloric and sulfuric acid electrolyte solutions was investigated on an electrochemical quartz crystal microbalance. A distinct increase in mass due to the specific adsorption of hydrated bisulfate and perchlorate anions was observed in Cu²⁺-free solutions and their amounts were determined as a function of the potential. The composition of the Cu-adlayer (θ_Cu and θ_anion, coverages of Cu adatoms and co-adsorbed anions) during formation or removal in the potential sweep was also determined in both electrolyte solutions. A pair of reversible anodic and cathodic peaks in the voltammogram for the first Cu-upd region in H₂SO₄ was found to correspond well to the reversible changes in θ_Cu and θ_anion. In contrast, asymmetric features of the voltammograms for the second Cu-upd region in H₂SO₄ and for whole processes in HClO₄ corresponded to the large hysteresis in changes of θ_Cu and θ_anion, probably originating from a slow rearrangement of both species.     

Monitoring bacterial-demineralization of human dentine by electrochemical impedance spectroscopy

Objective

The purpose of this study was two-fold: (1) to monitor bacterial biofilm formation and bacteria-induced demineralization of dentine in situ by using electrochemical impedance spectrum (EIS); (2) to examine the relationship between EIS findings and changes in the chemical composition and ultrastructure of dentine during bacteria-induced demineralization.

Methods

In this study, dentine demineralization was induced by Streptococcusmutans (ATCC 25175) in the presence of sucrose in culture medium and was monitored using two EIS measurement systems (Type A with a working electrode and Type B without a working electrode). Scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) were employed to examine the morphology, element contents and crystallinity of hydroxyapatite (HAP) on the dentine surface. Transverse microradiography (TMR) was used to characterize the lesion depth and degree of mineral loss during demineralization.

Results

The resistance of the bulk dentine (R_d) and the apparent resistance of dentine (R_a) measured from the Type A and Type B EIS systems, respectively, decreased gradually with demineralization. The resistance of the biofilm formed on dentine surface was determined by fitting the EIS data with equivalent circuits. The presence of biofilm slightly increased R_a of dentine before demineralization. However, the electrochemical behavior of biofilm did not affect the decreasing impedance of dentine with demineralization. The SEM, EDX, XRD and TMR results demonstrated that the surface and bulk dentine gradually became more porous due to the loss of minerals during demineralization, which in turn resulted in the decrease in R_d and R_a values obtained from EIS systems.

Conclusions

This investigation highlighted EIS as a potential technique to monitor biofilm formation and bacterial-induced demineralization in situ.     

Evaluation of the relationship between salivation ability and blood flow velocity in the submandibular gland using pulsed Doppler ultrasonography

Objectives

To investigate the possibility of predicting salivation ability using pulsed Doppler ultrasonography.

Methods

Thirty healthy volunteers were enrolled in this study. The blood flow velocity in the submandibular gland before and during acid stimulation was recorded by pulsed Doppler ultrasonography. The changes in the maximum blood flow velocity (V _max) and minimum blood flow velocity (V _min) were analyzed and compared with the salivation abilities.

Results

Strong linear correlations between before and during acid stimulation were observed in the amount of salivation (R = 0.879, p < 0.05) and the V _max (R = 0.938, p < 0.05). The mean change rate in the stimulated V _max was 1.58 (range 1.10–4.58), and the mean (range) change rates in the V _max after 1, 3, and 5 min of acid stimulation were 0.96 (0.47–1.47), 0.97 (0.79–1.40), and 0.98 (0.70–1.23), respectively. No strong linear correlation was observed between the amount of salivation and the blood flow velocity.

Conclusions

Although it is known that an increase in the amount of salivation is closely related to an increase in the blood flow velocity in the salivary glands, our findings did not show a linear correlation between the amount of salivation and the blood flow velocity.     

Electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH) at a chlorogenic acid modified glassy carbon electrode

The redox response of chlorogenic acid solution at an inactivated glassy carbon electrode was investigated and an ECE mechanism was proposed for the electrode process. It has been shown that the oxidation of chlorogenic acid at an activated glassy carbon electrode leads to the formation of a deposited layer of about 4.5×10^?10 mol cm^?2 at the surface of the electrode. Cyclic voltammetry was used for the deposition process and the resulting modified electrode retains the activity of the quinone/hydroquinone group anticipated for a surface-immobilized redox couple. The properties of the electrodeposited films, during preparation under different conditions, and the stability of the deposited film were also examined. The pH dependence of the redox activity of these films was found to be 57 mV per pH unit, which is very close to the anticipated Nernstian dependence of 59 mV per pH unit. The modified electrode exhibits potent and persistent electrocatalysis for NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 430 mV and an increase in peak current. The electrocatalytic current increases linearly with NADH concentration from 0.1 to 1.0 mM. The apparent electron transfer rate constant, k_s, and the heterogeneous rate constant for electrooxidation of NADH, k_h, were also determined using cyclic voltammetry and rotating disk electrode voltammetry, respectively.     

Spectroelectrochemical study of the oxidation of aminophenols on platinum electrode in acid medium

The electrochemical oxidation of para-, meta- and ortho-aminophenols was carried out using a platinum electrode in aqueous acid medium. The spectroscopic results indicate that p-aminophenol suffers hydrolysis giving the formation of hydroquinone/p-benzoquinone. CO₂ has been detected by in situ FTIR spectroscopy as the main soluble oxidation product. The m-aminophenol oxidation produces a blocking polymeric film on the platinum surface. The main oxidation products detected by in situ infrared spectroscopy were CO₂ and quinone. Cyclic voltammetry and in situ FTIR spectroscopy were combined to study the redox processes of the conducting polymer obtained in the o-aminophenol oxidation. The spectroscopic results indicate that phenoxazine units are produced during the oxidation/reduction of poly(o-aminophenol).     

Role of the autonomic nervous system in regulating salivary mucin secretion by the canine submandibular gland in vivo

The secretion of mucin was assessed by measuring changes in protein and sialic acid concentrations in saliva. Electrical stimulation of the sympathetic nerve increased protein and sialic acid concentrations greatly but stimulation of the parasympathetic nerve by bethanechol (5–20 μg/kg, intravenously) caused a slight increase. Sympathomimetic drugs (1–10 μg/kg, intravenously) also increased protein and sialic acid concentrations (isoproterenol > adrenaline > noradrenaline). Mucin secretion was increased by $\text{H133}\text{22}$, a β₁ adrenoceptor agonist, or terbutaline. which is roughly equipotent. Adrenaline-induced mucin secretion was inhibited by propranolol, but not by tolazoline. These data suggest that mucin secretion is predominantly regulated by the sympathetic nervous system via β adrenoceptors. both β₁ and β₂.     

Adsorption,oxidation and reduction reactions of propargyl alcohol on palladium as studied by electrochemical mass spectrometry

The electrochemical behavior of propargyl alcohol (PA) on palladium electrodes in 0.1 M HClO₄ was studied by differential electrochemical mass spectrometry (DEMS). Experiments with the alcohol present in the bulk of the solution have shown that the sole oxidation product is CO₂. During potential cycling in the hydrogen adsorption/absorption region, C₃- (propylene and propane) and C₂- (ethane and traces of ethene/ethyne) hydrocarbons, as well as allyl alcohol, were produced. On the other hand, PA forms strongly bonded species on palladium which can be studied using a flow cell procedure. The maximum adsorption of PA was observed in the potential range 0.25–0.65 V. As for bulk studies, only CO₂ was detected during the oxidation of the residues. However, some differences should be mentioned in respect of the reduction reactions: only propane, propylene and allyl alcohol were observed from the adlayer. According to these results, and taking into account the values of the charges involved in the adsorption (Q_t) and oxidation (Q_ox) processes, different structures were proposed for the adsorbed species. From these structures, the formation of the reduction products was justified. Results were compared with previously reported data for platinum and gold in acid media.     

Temperature changes in a cemented mandibular endoprosthesis: in vitro and in vivo studies

Using polymethylmethacrylate (PMMA) cement in cemented endoprostheses may cause heat necrosis and prosthesis failure due to the highly exothermic reaction. This study determined the magnitude and duration of temperature change during the cementation of a mandibular endoprosthesis in an in vitro and in vivo Macaca fasicularis model. In the in vivo study the median maximum temperature (T_max) around the mandible-prosthesis unit (MPU) was 31.0 °C with the peak T_max at hole 1 (1 mm from stem). The in vitro study recorded a lower T_max and indicated a trend that increased spacing (groove) around the prosthesis results in a higher T_max. All the T_max MPU measurements were lower than normal body temperature (38 °C). In the in vivo study the median maximum temperature change (T_maxΔ) was 1.8 °C; in the vitro study, the T_maxΔ of the 4 mm groove width was significantly higher than all others. Temperature increases were transient, with the temperature returning to baseline a median of 6.0 min after T_max. Histological analysis showed surrounding tissue at the cement-bone interface with mild inflammation. Within the parameters tested, there was minimal risk of thermal damage. The temperature changes were influenced by the quantity of cement used and the distance from the prosthesis stem.     

Voltammetric and EQCM investigation of conductive films formed by electroreduction of Ru(L)(CO)2Cl2 compounds

Electroreduction of trans(Cl) and cis(Cl)Ru(L)(CO)₂Cl₂ (L=bpy=2,2′-bipyridine, dmbpy=4,4′-dimethyl-2,2′-bipyridine) in CH₃CN and DMSO resulted in electrode-adhering films and the reactions were studied by voltammetry and the electrochemical quartz crystal microbalance. These methods were complemented by hydrodynamic rotating ring-disc and quartz crystal impedance methods. The deposition was strongly influenced by the type of solvent, polarisation mode and electrolyte stirring, but for all compounds, rapid charge transfer was found. For monomers with trans(Cl)Ru(bpy)(CO)₂Cl₂, the two-electron reduction and Ru⁰Ru⁰ polymerisation process suggested in the literature was confirmed. Some adsorption of CH₃CN was also indicated and for potentiostatic deposition in static solution the impedance measurements indicated increased film viscoelasticity. Depositions with cis(Cl)Ru(bpy)(CO)₂Cl₂ were more complex and the rate declined gradually in static solution. In stirred solution a straightforward polymer formation took place. For trans(Cl)Ru(dmbpy)(CO)₂Cl₂ the literature mechanism could not be confirmed and large deviations were observed during the early stages of deposition. The trans(Cl) dimer, [Ru(bpy)(CO)₂Cl]₂ displayed a lower current efficiency during film formation than the monomer and no simple deposition mechanism could be suggested. For the trans(Cl)[Ru(dmbpy)(CO)₂Cl]₂ dimer a straightforward deposition was found. The films could be removed by electrooxidation and mass/charge data show that the films break up in large fragments. The reduction and deposition process for trans(Cl) monomers (L=bpy, dmbpy) was light sensitive and the mass of films deposited during cyclic voltammetry (CV) was doubled when the electrode was irradiated.     

A review on the characterization of a novel oral Veillonella species,V. tobetsuensis,and its role in oral biofilm formation

The genus Veillonella consists of small, strictly anaerobic, gram-negative cocci that lack flagella, spores, and a capsule. Although 11 species have been established in the genus Veillonella, five species, namely V. atypica, V. denticariosi, V. dispar, V. parvula, and V. rogosae, are recognized as oral Veillonella. The main habitats of oral Veillonella are the tongue, dental biofilm, and the buccal mucosa, and correspondingly it has been suggested that oral Veillonella contributes to oral biofilm formation and may lead to the formation of dental disease such as periodontitis.Recently, unknown strains displaying all phenotypic characteristics of the genus Veillonella were isolated from human tongue biofilm. The production of a major cellular fatty acid (C_13:0 and C_17:1ω8) was consistent with that of other members of the genus Veillonella. Based on the comparative analysis of 16S rDNA, dnaK, and rpoB gene sequences, the unknown strains represent a novel species, and were named Veillonella tobetsuensis.V. tobetsuensis was detected by PCR using specific primers based on the dnaK gene sequence in 5 out of 27 subjects with other oral Veillonella species. The prevalence of V. tobetsuensis ranged from 7.6 to 20.0% in these subjects.Using the wire method, all six oral Veillonella species stimulated the formation of biofilm by Streptococcus gordonii. The greatest amount of biofilm was formed by S. gordonii in the presence of V. tobetsuensis. These results suggest that among the oral Veillonella species, V. tobetsuensis plays an important role in biofilm formation by S. gordonii.     

Contribution of different carbons of glucose to volatile acids during glucose catabolism in a human salivary sediment system.

Experiments were carried out to determine the contribution of different labelled carbons of the glucose molecule to the formation of acetic and propionic acid in a suspended salivary sediment (SSS) system using radioactive glucose, labelled at its different carbon atoms viz., [U-¹⁴C]-glucose, [¹⁴C₁]-glucose, [¹⁴C₂]-glucose and [¹⁴C_3,4]-glucose. The volatile acids formed were determined by a multi-auto-radiographic chromatographic technique, and measured by liquid scintillation. The results suggested that most of the added glucose was catabolized via the Embden-Meyerhof glycolysis (EM) pathway as shown by the fact that substantial amounts of radioactive acetate and propionate were produced from [¹⁴C₁]-glucose and [¹⁴C₂]-glucose. Some labelled acetate was formed with [¹⁴C_3,4]-glucose and cannot be explained on the basis of the EM pathway. An alternative pathway that occurs in Leuconostoc mesenteroides was proposed.     

Response of human enamel to topical application of ammonium fluoride

In-vitro uptake of F by intact enamel from 0.62 M solutions of NH₄F was greater than that from NaF at low pH, but similar at nearly neutral or alkaline pH. Fluoride contents in enamel biopsies taken 2 weeks after a 3 min topical treatment with the acid solutions also were higher for the NH₄F treatment. The in-vitro and in-vivo uptake from both solutions was enhanced by pretreating the enamel for one minute with 0.05 M phosphoric acid. Examination by the electron microscope of the F-exposed enamel before and after washing revealed the deposit formed from NH₄F was retained more tenaciously than that formed from NaF. X-ray diffraction patterns showed formation of CaF₂ when ground enamel was treated with either of the two acid fluoride solutions.     

Monitoring acid-demineralization of human dentine by electrochemical impedance spectroscopy (EIS)

Objective

The purpose of this study was to monitor in situ acid-induced demineralization of dentine by using electrochemical impedance spectroscopy (EIS) and correlate the EIS findings with changes in the chemical composition and ultrastructure of dentine.

Method

EIS was used to monitor the process of demineralization of dentine induced by an acid model. Scanning electron microscopy (SEM) was used to examine the ultrastructure, while energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis were employed to investigate the changes in the chemical composition of surface dentine with demineralization.

Results

Two kinds of equivalent circuits that matched the histological structure of dentine were used to fit the EIS data. The parameters R_d, which is the resistance of the bulk of dentine layer and R_ct, which is the charge transfer associated with the penetration of electrolyte into the dentinal tubules, decreased with increasing duration of demineralization. SEM images showed that the smear layer on the dentine and peritubular dentine disappeared with demineralization. The EDX results showed that the content of calcium and phosphorus decreased consistently with the decreasing content of HAP as shown by the XRD results. The findings from this study suggested that the changes in R_d and R_ct determined by the EIS corresponded well with the variation in structure and composition of dentine.

Conclusions

EIS could be employed to monitor structural and chemical compositional changes induced by acid-demineralization on dentine surface.     

Quantitative studies of acid beta-glycerophosphatase activity in developing rat teeth and bones.

Biochemical characterization of the acid phosphatase activity in hard tissues was carried out using hydrolysis of β-glycerophosphate (β-GP), pyrophosphate (P-P_i) and p-nitrophenylphosphate (p-NPP) by homogenates and extracts of molar tooth buds and tibiae. The activity in tooth buds with β-GP (β-GPase activity) was increased by Triton X-100, was relatively stable at 50 °C, was inhibited by tartrate and MES buffer, and was as high as the p-NPPase activity. In contrast, p-NPPase activity was not affected by Triton X-100 or MES, was only partially inhibited by tartrate, and was very labile at 50 °C. The activity with P-P_i was much lower than that with β-GP and p-NPP and showed more similarity with p-NPPase activity than with β-GPase activity.It is suggested that acid phosphatase activity in odontogenic tissue is provided by at least two enzymes: (1) a tartrate-sensitive enzyme that provides most of the activity seen with β-GP and some of the activity with p-NPP; (2) a tartrate-resistant enzyme that accounts for some of the activity with p-NPP and all of the activity with P-P_i. As activity with both p-NPP and β-GP was higher in 2nd molars than in 1st molars, from which the pulps had been removed, it is suggested that both enzymes are primarily concerned with matrix formation rather than with matrix resorption or mineralization of the enamel. For bone extracts, the observations indicated striking similarities between p-NPPase activity and P-P_iase activity and marked differences when activities with β-GP and p-NPP were compared, which support the conclusion by others that the enzyme hydrolyzing β-GP in bone is different from that hydrolyzing p-NPP and P-P_i.     

Early bone response to sandblasted,dual acid-etched and H2O2/HCl treated titanium implants: an experimental study in the rabbit

The aim of this study was to evaluate the influence of a roughened H₂O₂/HCl heat-treated titanium surface on peri-implant bone formation at an early stage in vivo. 24 Ti₆Al₄V alloy implants were used; half were treated by sandblasted and dual acid-etched treatments (control group), while the others were treated by sandblasted, dual acid-etched and H₂O₂/HCl heat treatments (test group). The morphology and roughness were analyzed by field emission SEM and atomic force microscopy. The implants were inserted into the femora of 12 adult white rabbits. After 2 and 4 weeks, femora block specimens were prepared for histological and histomorphometric analysis. SEM micrographs showed that multilevel and different sized pits were formed on both surfaces. New bone formation was observed on both implant surfaces. Test implants demonstrated a greater mean percentage of bone-implant contact as compared with controls at 2 (46.84 vs. 41.81, p=0.000) and 4 weeks (49.43 vs. 44.87, p=0.006) of healing. It is concluded that the H₂O₂/HCl heat-treated rough titanium surface promoted enhanced bone apposition during the early stages of new bone formation around the implant.     

Amperometric biosensing of cinnamic acid using a spinach-based biocatalytic electrode

A new amperometric bioelectrode for cinnamic acid, based on the cinnamic acid hydroxylase activity of spinach leaves, is described. Such a bioelectrode addresses the commercial unavailability and instability of the pure enzyme. The incorporation of spinach leaves within a carbon paste matrix thus results in a fast response (t_95% = 12 s) to dynamic changes in the substrate concentration. The effect of vatious experimental parameters, such as pH, applied potential, flow rate or paste composition, is explored. Flow injection measurements yield a detection limit of 2×10^?4 M, with linearity up to 4×10^?3 M, and a relative standard deviation of 22.0% (n = 25). Analogous measurements of dopamine, based on the polyphenol oxidase activity of spinach leaves are also reported.     

The effect of frequency of calcium hydroxide dressing change and various pre- and inter-operative factors on the endodontic treatment of traumatized immature permanent incisors

Abstract – Aim: The objectives of this clinical study were as follows: (i) to determine the effect of frequency of calcium hydroxide [Ca(OH)₂] dressing change on the apical barrier formation in immature permanent incisors with necrotic pulps and (ii) to investigate the effect of various clinical factors before and during treatment that may be associated with the frequency of Ca(OH)₂ dressing changes. Methods: The study involved 21 healthy subjects, 8–12 years old. Twenty‐three immature traumatized permanent maxillary central incisors were treated using Ca(OH)₂ powder mixed with barium sulfate and distilled water. The progress of barrier formation was reviewed after 6 months of first placement of Ca(OH)₂ and then every 3 months until the detection of an apical barrier. Clinical and radiographic evaluations were performed before and after treatment. Data were evaluated using a chi‐square test. Results: Apical barrier formation was successful for all 23 teeth. Seventeen teeth (74%) needed only a single application of Ca(OH)₂, while six teeth (26%) required more than one application. The average time of apical barrier formation was 30 weeks, and the mean number of Ca(OH)₂ dressing changes was 1.3. A significant positive association was found between teeth that presented with displacement and the number of Ca(OH)₂ dressing changes (P = 0.004). Conclusion: An initial 6‐month application of Ca(OH)₂ dressing followed by 3‐month replacements (usually in teeth presenting with displacement and/or sinus tracts) may be successfully used in apexification treatment. This would assist in reducing the number of Ca(OH)₂ dressing changes, number of appointments, cost of treatment and radiation exposure.     

Speciation of a water-soluble chromium porphyrin by spectral and electrochemical methods

A water-soluble chromium porphyrin, [Cr^IIITF₄TMAP]⁵⁺ (chromium(III) meso-tetrakis(2,3,5,6-tetrafluoro-N,N,N-trimethyl-4-anilinium)yl) porphyrin) was synthesized and the spectral and electrochemical properties were examined. In aqueous solution, [Cr^IIITF₄TMAP]⁵⁺ exhibits two pK_as at 7.04 and 10.07. The cyclic voltammogram showed that a reversible reduction wave appeared at ?0.84 V in pH 5.0 buffer solution, which is assigned as the Cr^III/II redox couple. The oxidation formal potentials were obtained by spectroelectrochemistry. With suitable control of the oxidation potentials and solution conditions, the high valent oxo-Cr^IV and oxo-Cr^V porphyrins were obtained. The ligand trans to the oxygen atom is either H₂O or OH^?, depending on the pH of the solution. In this paper, oxo-Cr^VTF ₄TMAP is thus the first reported water-soluble Cr^V porphyrin that can be generated electrochemically and chemically. Electrogenerated oxo-Cr^V porphyrin species catalyzed the oxidation of cyclopent-2-ene-1-acetic acid to cyclopent-2-ene-4-one-1-acetic acid in the presence of dioxygen and returned to oxo-Cr^IV porphyrin, which is not reactive toward the substrate.     

Hydrolysis of phytate and its inositol phosphate intermediates by an acid and an alkaline phosphatase.

The hydrolysis of phytate (IP₆) and its inositol phosphate intermediates (IP₁, IP₂, IP₃, IP₄ and IP₅) by an acid and an alkaline phosphatase was examined. In all cases, the pH of optimum hydrolysis with acid phosphatase was 5.0; with alkaline phosphatase, the optimal pH increased with increase in the substrate concentration. K_m, V_max and P_i inhibition experiments collectively indicated that IP₂, IP₃ and IP₄ are hydrolyzed the most rapidly and IP₁ the least. Since IP₁ is the last inositol phosphate formed during sequential hydrolysis of phytate, it is suggested that the slow rate of IP₁ hydrolysis and its sensitivity to P₁ inhibition would have a major regulatory role in the overall hydrolysis of phytate.     

Effect of pH on Galla chinensis extract's stability and anti-caries properties in vitro

ObjectivesConsidering that Galla chinensis extract (GCE) solution has a low pH, which might dissolve dental enamel, we investigated the effects of elevation of pH on GCE stability, and on its anti-caries properties.DesignsStability of GCE solutions, either in H₂O (pH less than 4.0) or when buffered at pH 5.5, 7.0 and 10.0, was assessed from UV–VIS spectra. Inhibition of enamel demineralization was determined in a pH-cycling set up, comprising treatments with either GCE solutions or negative control buffers and acid and neutral buffer immersions. Demineralization was assessed by calcium in the acetate buffers. To determine antimicrobial properties, polymicrobial biofilms were formed after saliva inoculation on glass surfaces which were treated after 48 h. Treatment output parameters were lactic acid formation and viability, the latter by colony forming unit (CFU) counts.ResultsAt pH 7.0 and higher GCE solutions changed colour and absorption spectra in UV–VIS, indicative of chemical changes. Regarding enamel demineralization, significant inhibitions (P < 0.05) were found for all GCE treatments when compared with corresponding controls. In polymicrobial biofilms, GCE reduced the acid production, compared with the negative controls (P < 0.05). However, this difference was only significant at the lower pH values.ConclusionsGCE solutions were unstable under neutral and alkaline conditions. pH did not significantly influence the inhibiting effect of GCE on enamel demineralization. However, GCE was not effective on polymicrobial biofilms at alkaline pH (8.5). To avoid enamel damage due to acidic treatment, GCE solutions should be used at about pH 5.5.