Size-dependent reactivity of VnO+ (n = 1-9) clusters with ethane.

Cost-effective and readily accessible 3d transition metals (TMs) have been considered as promising candidates for alkane activation while 3d TMs especially the early TMs are usually not very reactive with light alkanes. In this study, the reactivity of Vn+ and VnO+ (n = 1-9) cluster cations towards ethane under thermal collision conditions has been investigated using mass spectrometry and density functional theory calculations. Among Vn+ (n = 1-9) clusters, only V3-5+ can react with C2H6 to generate dehydrogenation products and the reaction rate constants are below 10-13 cm3 molecule-1 s-1. In contrast, the reaction rate constants for all VnO+ (n = 1-9) with C2H6 significantly increase by about 2-4 orders of magnitude. Theoretical analysis evidences that the addition of ligand O affects the charge distribution of the metal centers, resulting in a significant increase in the cluster reactivity. The analysis of frontier orbitals indicates that the agostic interaction determines the size-dependent reactivity of VnO+ cluster cations. This study provides a novel approach for improving the reactivity of early 3d TMs.

Comparative study of the interactions between ovalbumin and three alkaloids by spectrofluorimetry.

The interaction between ovalbumin (OVA) and three purine alkaloids (caffeine, theophylline and diprophylline) was investigated by the aid of intrinsic and synchronous fluorescence, ultraviolet-vis absorbance, resonance light-scattering spectra and three-dimensional fluorescence spectra techniques. Results showed that the formation of complexes gave rise to the fluorescence quenching of OVA by caffeine, theophylline, and diprophylline. Static quenching was confirmed to results in the fluorescence quenching. The binding site number n, apparent binding constant KA and corresponding thermodynamic parameters were measured at different temperatures. The binding process was spontaneous molecular interaction procedures in which both enthalpy and Gibbs free energy decreased. Van der Waals forces and hydrogen bond played a major role in stabilizing the complex. The comparison between caffeine, theophylline, and diprophylline was made, and thermodynamic results showed that diprophylline was the strongest quencher and bound to OVA with the highest affinity among three compounds. The influence of molecular structure on the binding aspects was reported.

Cytokine expression in gingival crevicular fluid around teeth opposing dental implants and 3-unit fixed partial dentures in a cross-sectional study.

OBJECTIVE: This study aimed to study the cytokines in gingival crevicular fluid (GCF) of the teeth opposing to dental implants and 3-unit fixed partial dentures (FPDs). MATERIALS AND METHODS: A total of 74 participants were recruited for this cross-sectional study. Based on the status of lower first molars, the participants were divided into dental implants group and 3-unit FPDs group. Social index and oral hygiene were recorded. Occlusal loading was evaluated with a T-scan. GCF was sampled from the upper first molar and assessed with a commercial cytokine assay kit. RESULTS: Forty three dental implants patients and 31 3-unit FPDs patients received all of the clinical and laboratory evaluation. The dental implants group had a higher occlusion force distribution on first molars region. IL-10, IL-17, RANK had a higher mean in dental implants group and was associated with occlusion force of first molar. There was a weakly association between IL-10 and dental implants in the binary logistic regression analyses. CONCLUSIONS: In this study, the teeth opposing implants have a higher level of cytokines in the GCF than teeth opposing to 3-unit FPDs in periodontal healthy participants because of the poor osseoperception of dental implants. IL-10 might reflect a higher occlusion force in dental implants region. CLINICAL RELEVANCE: This study provided that different tooth restoration methods could influence the periodontal status of the contact teeth.

Stopped-flow kinetic fluorimetric studies of the interaction of Ru(II) complex with DNA and its analytical application.

A simple, rapid, and sensitive stopped-flow kinetic fluorometric approach was established for the assay of DNA in synthetic samples and real samples by using the measures of initial reaction rate. The increased initial reaction rate is in proportion to the concentration of DNA in the range of 2.0x10(-8)M to 2.1x10(-6)M. The optimum conditions for various parameters on which the binding of Ru(phen)(2)(dppz)(2+) to DNA depends, were investigated. The influence of various surfactants on the interaction was discussed. Furthermore, stopped-flow techniques were employed to determine kinetic parameters of Ru(phen)(2)(dppz)(2+) binding to DNA under pseudo-first-order conditions. It was found that the interaction of Ru(phen)(2)(dppz)(2+) with DNA was very fast. A two-step reaction mechanism, a fast phase followed by a slow phase, was proposed.

[Investigation of temporomandibular joint space of healthy adults by using cone beam computed tomography].

OBJECTIVE: To investigate the condyle position in the fossa and obtain the reference ranges of Temporomandibular joint (TMJ) space of 50 healthy adults (100 joints) by using cone beam computed tomography (CBCT). METHODS: Fifty healthy adults (100 joints) were selected and undergone CBCT examination in the intercuspal position. Five different methods of joint space measurement were used based on the joint sagittal middle layer of CBCT images and the results were analysed statistically. RESULTS: The reference ranges of TMJ space of CBCT images by using five measurement methods were obtained. The results of the linear measurement methods demonstrated that there were no significant differences between anterior and posterior spaces (Z0.05),no significant differences between the two side joint spaces including anterior, posterior and superior spaces (t0.05 ),and also no significant differences in ln (P/A) values between two side joints (t0.05). CONCLUSION: All the results of the five measurement methods showed that the condyle was located in the center of the fossa with a variation in the healthy adults in intercuspal position.The CBCT image of the sagittal middle layer of the joint could show the joint space accurately and has an important value in the research related to the changes of TMJ space.

A kinetic spectrophotometric method for the determination of nitrite by stopped-flow technique.

A novel and highly sensitive stopped-flow kinetic spectrophotometric method for the determination of nitrite, based on monitoring the variation in the absorbance of the intermediate within a very short period, has been developed. The optimum conditions for various parameters on which the reaction of nitrite with perphenazine depends, were investigated. It was found that the initial reaction rate increased linearly with increasing nitrite concentration in the range from 1.0 x 10(-8) to 6.0 x 10(-6) M. The detection limit was calculated to be 4.8 x 10(-9) M. This method was used for the determination of nitrite in natural and drinking-water with satisfactory results. The influence of cationic, non-ionic and anion surfactants was also studied in this work.

Kinetic spectrophotometric method for determination of perphenazine based on monitoring the oxidation intermediate by applying a stopped-flow technique.

A novel and high-sensitive stopped-flow kinetic spectrophotometic method for the determination of perphenazine based on monitoring the variation of absorbance of the intermediate within a few seconds has been developed. The optimum conditions for various parameters on which the forming of the intermediate depends, were investigated. It was found that the initial reaction rate increased linearly with an increase in the perphenazine concentration in the range from 1.0 x 10(-5) to 1.6 x 10(-4)M. The detection limit was calculated to be 5.3 x 10(-6)M. The kinetics of the reaction was established by the aid of single-mixing or double-mixing stopped-flow techniques, a successive reaction model was proposed to analyze and simulate the reaction. The influence of both ascorbic acid and NADH on the time courses was also investigated.

[Radiographic study on joint space changes of patients with anterior disc displacement of temporomandibular disorders].

OBJECTIVE: To compare the temporomandibular joint space and condylar position on transcranial projections between the patients with anterior disc displacement (ADD) and the healthy controls. To investigate the diagnostic value of the condylar position for the ADD patients. METHODS: 120 joints of 120 ADD patients and 30 joints of healthy adults, who were taken transcranial projections, were included in this study. The transcranial projections were scanned with precise scanning apparatus and saved as joint photographic group image. The joint spaces were measured with the software of Auto CAD. Two different quantitative methods of joint space measurement, ZHANG Zhen-kang's method and Kamelchuk's method, were used based on the transcranial projections. The ln(P/A) values were calculated (P:width of the posterior joint space; A: width of the anterior joint space). Concentric position of the condyle was defined if ln(P/A) value was between -0.25 and +0.25. If ln(P/A) was larger than +0.25, the condylar position was defined as anteriorly eccentric. Posteriorly eccentric position was indicated when ln(P/A) value was lower than -0.25. The results were compared and software SPSS 12.0 was used for statistical analysis. RESULTS: The results of the two linear measurement methods demonstrated that the superior and posterior joint spaces of the ADD patients were narrower than those of the healthy controls significantly (P < 0.05), while the anterior joint spaces of the ADD patients had no significant differences with those of the controls (P > 0.05). In addition, there were significant differences in ln(P/A) values of joint spaces between the patients with ADD patients and the controls (P < 0.05). CONCLUSION: Posterior position of the condyle could be a sign of existence of ADD, but ADD could not be diagnosed only by the posterior condyle position showed on the transcranial projections because of the variation of the condylar position.

Spectral and kinetic studies on the interaction between oxyhaemoglobin and peroxynitrite: a comparison with hydrogen peroxide.

Interaction between oxyhaemoglobin and peroxynitrite was studied using stopped-flow rapid-scan spectrophotometry. The influence of pH, peroxynitrite concentration and temperature on the pseudo-first-order rate constants was studied and the activation energy calculated. The kinetic curve for the oxyhaemoglobin-peroxynitrite reaction showed that a fast reaction occurred in the initial seconds, followed by a slow process of decrease in absorbance. The biphasic reaction kinetics of oxyhaemoglobin with peroxynitrite or hydrogen peroxide demonstrated the existence of an intermediary species. For the first time a rapid-scan stopped-flow spectrophotometry study is presented, yielding spectral and kinetic data of the reaction.

AtGLB1 enhances the tolerance of Arabidopsis to hydrogen peroxide stress.

Hydrogen peroxide (H2O2) as a widespread molecule plays an important role in plant stress responses. Here, we showed that an Arabidopsis line overexpressing hemoglobin 1 (AtGLB1) can enhance its tolerance to severe hypoxic stress. In our research, Arabidopsis lines with different hemoglobin levels were employed to study the relationship between H2O2 level and the tolerance to hypoxic stress. The relatively low endogenous H2O2 level of AtGLB1-overexpressing plants could be one of the main factors for the increased tolerance of plants to hypoxic stress. Further investigation indicated that the activity of the antioxidant system involved in scavenging H2O2 increased in all three lines examined during hypoxic treatment, while only the line overexpressing AtGLB1 could retain these relatively high levels up to 48 h of the treatment, suggesting that the antioxidant system might play a role in the low H2O2 level of Arabidopsis overexpressing AtGLB1.