Luís Proença

Electrocatalytic oxidation of d-sorbitol on platinum in acid medium: analysis of the reaction products

Abstract The electrocatalytic oxidation of d -sorbitol has been studied on polycrystalline platinum in 0.1 M HClO 4 . Prolonged electrolyses were carried out using a three potential plateau program with different values of the oxidation potentials. Chromatographic analyses showed that d -sorbitol was transformed into gluconic acid via the formation of glucose. Glucuronic acid and some degradation side products were also detected. When increasing the applied potential, the degradation of the initial molecule skeleton became more and more important. Moreover, a reaction mechanism for the electrooxidation of d -sorbitol was proposed and it was demonstrated that the consumption of d -sorbitol followed a first-order reaction law.

Effect of Cinnamon Tea on Postprandial Glucose Concentration.

Glycaemic control, in particular at postprandial period, has a key role in prevention of different diseases, including diabetes and cardiovascular events. Previous studies suggest that postprandial high blood glucose levels (BGL) can lead to an oxidative stress status, which is associated with metabolic alterations. Cinnamon powder has demonstrated a beneficial effect on postprandial glucose homeostasis in animals and human models. The purpose of this study is to investigate the effect of cinnamon tea (C. burmannii) on postprandial capillary blood glucose level on nondiabetic adults. Participants were given oral glucose tolerance test either with or without cinnamon tea in a randomized clinical trial. The data revealed that cinnamon tea administration slightly decreased postprandial BGL. Cinnamon tea ingestion also results in a significantly lower postprandial maximum glucose concentration and variation of maximum glucose concentration (p < 0.05). Chemical analysis showed that cinnamon tea has a high antioxidant capacity, which may be due to its polyphenol content. The present study provides evidence that cinnamon tea, obtained from C. burmannii, could be beneficial for controlling glucose metabolism in nondiabetic adults during postprandial period.

On the oxidation of d-sorbitol on platinum single crystal electrodes: a voltammetric and in situ FTIRS study

The electrooxidation of d-sorbitol on Pt(100), Pt(110), Pt(111) and stepped surfaces vicinal to the (111) pole was studied in perchloric acid medium. The reaction is markedly influenced by the crystalline surface structure. Long range order effects of (111) terraces were also observed. Adsorbed CO (linearly and bridge bonded to the surface, on a level which depends on the electrode surface orientation) was identified by in situ Fourier transform IR (FTIR) spectroscopy as the main poisoning species. Moreover, for Pt(111), glucono-δ-lactone and CO2 were identified as the main soluble reaction products.

Prevalence of Yeast Other than Candida albicans in Denture Wearers

PURPOSE The isolation of yeast species other than Candida albicans from the oral mucosa has been increasing in frequency, suggesting that those may constitute emerging potential oral colonizers. The purpose of this work was to determine whether yeast species other than C. albicans are associated with factors related to wearing of dental prostheses. MATERIALS AND METHODS tRNA-PCR fingerprinting and sequencing of the 26S rDNA D1/D2 domain were used to identify all yeasts isolated from CHROMagar™ Candida cultures of oral swabs collected from 178 patients. RESULTS Besides C. albicans, 13 other species were identified, corresponding to 34% of the yeast isolates. The majority of the non-C. albicans species were not detected as single colonizers but rather in co-colonization with one or two other yeasts, often with C. albicans. No significant associations were found with non-C. albicans species. On the contrary, the best-fitted logistic regression model predicts that either wearing a denture (adjusted odds = 4.6) or insufficient oral hygiene (adjusted odds = 2.3) are risks for colonization by yeast, in general. CONCLUSIONS The colonization with non-C. albicans species and co-colonization were not independently associated with any of the analyzed host-related factors. In particular, neither wearing a removable denture nor being elderly were significant predictors.

ELECTRO-OXIDATION OF D-SORBITOL ON PLATINUM IN PERCHLORIC MEDIUM: A VOLTAMMETRIC STUDY

The electrocatalytic oxidation of d-sorbitol on a polycrystalline platinum electrode, in perchloric aqueous medium, was studied by cyclic voltammetry under varying sweep rate, potential limits, stirring, temperature, pH and concentration of d-sorbitol. A value of about 50 kJ mol−1 was obtained for the apparent activation enthalpy of the oxidation reaction at 0.1 V vs. sme. The experimental rate equation is i = kCd-sorb0.4CH+−0.3.exp[0.4 FERT], valid for [d-sorbitol] < 0.1 mol dm−3 and pH < 1.

Electrosorption of d-sorbitol on Pt(110) and Pt(111) electrodes in acid medium: a study by programmed potential voltammetry

Abstract The adsorption and electro-oxidation of d -sorbitol on Pt(110) and Pt(111) single-crystal surfaces in acid medium was studied using programmed potential voltammetry (PPV). The coverage ( θ org ) of the surface and the number of electrons per site ( N eps ) involved in the electro-oxidation of the adsorbed species coming from the d -sorbitol electrosorption was estimated for both electrodes. Limiting values for θ org of 0.90 and 0.85, were obtained for Pt(111) and Pt(110), respectively, although the limit is reached at shorter adsorption times (100s) in the case of Pt(111). For Pt(111), N eps was found to increase the adsorption time reaching a value around 2 for long adsorption times, related to the formation of linearly-bonded CO, while for Pt(110) its value is near 1 in the range 0.5–300 s, corresponding to a mixture of different species, including multibonded and bridge-bonded CO, as confirmmed by EMIRS. A very fast oxidation process occurs at Pt(111), in contrast to Pt(110), where the strongly adsorbed species formed upon adsorption remain attached to the surface, blocking it almost completely. The reoxidation process taking place at Pt(111) prevails over the reduction of the oxygenated species formed on the platinum surface when a sufficiently high converage of the electrode surface ( θ org ≥ 0.8) is attained.

An in situ IR reflectance spectroscopic study of the electro-oxidation of d-sorbitol on platinum

Abstract An in situ infrared (IR) reflectance spectroscopic study of the electrooxidation of d -sorbitol on polycrystalline platinum in perchloric acid medium was carried out by Fourier transform IR spectroscopy (FTIRS), under the SNIFTIRS and SPAIRS variants. Additional information was obtained by electrochemically modulated IR reflectance spectroscopy (EMIRS). In situ IR spectra show that the electrooxidation of d -sorbitol on platinum proceeds via a dual-path mechanism involving both reactive and poisoning intermediates. Linearly and bridge-bonded CO, resulting from the dissociative adsorption of d -sorbitol, which were identified as the main poisoning species present at the surface, are fully oxidised to CO 2 at higher potentials. The superficial coverage in adsorbed CO was found to be function of the electrode potential. Moreover, the electrooxidation process can occur without breaking the initial molecule skeleton, indicating that molecular adsorption of d -sorbitol is also possible. d -glucono-(δ and γ)-lactones, D -glucose and CO 2 were identified as the main reaction products.

Electro-oxidation of d-mannitol on platinum single crystal surfaces

Abstract The adsorption and oxidation reactions of d -mannitol at platinum single crystal electrodes with basal orientations have been studied by combining cyclic voltammetry and in situ FTIR spectroscopy. Cyclic voltammetric results have shown that, as far as current densities are concerned, the Pt(110) surface is the least active and more poisonable surface among the three platinum basal planes. The deactivation of Pt(100) and Pt(111) surfaces was found to be similar, although, higher current densities are obtained for Pt(100). FTIR spectroscopic experiments have indicated that CO is formed upon d -mannitol dissociative adsorption on the three basal platinum surfaces. This adsorbed intermediate, which was identified as the main poisoning species, is bonded to the platinum surface both in a linearly and bridge bonding mode and on a ratio which depends on the electrode surface orientation. The electro-oxidation process was found to be strongly dependent on the platinum crystalline surface structure. Moreover, additional voltammetric experiments performed on the three sets of platinum stepped surfaces have shown that the adsorption and oxidation reactions of d -mannitol are sensitive to the symmetry of the bidimensional domains as well as to the distribution of orientated defects (monoatomic steps) on the platinum surfaces.

Prevalence and extent of chronic periodontitis and its risk factors in a Portuguese subpopulation: a retrospective cross-sectional study and analysis of Clinical Attachment Loss

Objectives To assess the prevalence and extent of chronic periodontitis, and its risk factors in a Portuguese subpopulation referred to periodontal examination. Methods This retrospective cross-sectional study used a subset of data from patients who sought dental treatment in a university dental clinic in the Lisbon metropolitan area. The sample consisted of 405 individuals (225 females/180 males), aged 20–90 years. All patients underwent a full-mouth periodontal examination and chronic periodontitis was defined as Clinical Attachment Loss (CAL) ≥ 3 mm affecting two or more teeth. Aggressive periodontitis cases were excluded from the analysis. Results Prevalence of chronic periodontitis was 83.5% (95% CI [80.4–86.6%]). For these subjects, CAL ≥ 3 mm affected 86.0% (95% CI [84.7–87.2]) of sites and 83.7% (95% CI [81.7–85.6]) of teeth, respectively. Mean CAL ranged from 3.6 to 4.3 mm, according to age. In the multivariate logistic regression model, smoking (OR = 3.55, 95% CI [1.80–7.02]) and older age (OR = 8.70, 95% CI [3.66–20.69] and OR = 4.85, 95% CI [2.57–9.16]), for 65+ and 45–64 years old, respectively, were identified as risk indicators for CAL ≥ 3 mm. Conclusions This particular Portuguese adult subpopulation had a high prevalence of chronic periodontitis, with severe and generalized clinical attachment loss, and its presence was significantly associated with age and smoking. This data should serve to prepare future detailed epidemiological studies and appropriate public health programs.

IL-6 and TNF-α salivary levels according to the periodontal status in Portuguese pregnant women

Background Periodontitis is associated with increased concentration of inflammatory markers and saliva has been proposed as a non-invasive diagnostic fluid in oral and systemic diseases. The levels of salivary biomarkers, such as cytokines, could potentially be used to distinguish periodontal healthy individuals from subjects with periodontal disease. The purpose of this study was to characterize the salivary levels of two inflammatory biomarkers associated with periodontitis, interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α), in order to assess whether these cytokines salivary levels could potentially be used to complement periodontitis pregnant women diagnose. Methods Forty-four pregnant women were distributed into three groups, according to their periodontal status: healthy, mild/moderate periodontitis and severe periodontitis. Unstimulated saliva was collected and analysis of TNF-α and IL-6 salivary levels were performed with Immulite®. Results Women with periodontitis exhibited significantly higher levels (p = 0.001) of salivary IL-6 and TNF-α compared with the healthy group: 25.1 (±11.2) pg/mL vs. 16.3 (±5.0) pg/mL and 29.7 (±17.2) pg/mL vs. 16.2 (±7.6) pg/mL, approximately 1.5 and 1.8 times more, respectively. Additionally, cytokines were significantly increased (p < 0.05) in severe periodontitis compared to periodontal healthy pregnant women. Conclusions These results revealed that IL-6 and TNF-α salivary biomarkers provide high discriminatory capacity for distinguishing periodontal disease from periodontal health in pregnant women.