Intercentre reproducibility of cardiac apparent diffusion coefficient and fractional anisotropy in healthy volunteers

Background

Diffusion tensor cardiac magnetic resonance (DT-CMR) enables probing of the microarchitecture of the myocardium, but the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) reported in healthy volunteers have been inconsistent. The aim of this study was to validate a stimulated-echo diffusion sequence using phantoms, and to assess the intercentre reproducibility of in-vivo diffusion measures using the sequence.

Methods and results

A stimulated-echo, cardiac-gated DT-CMR sequence with a reduced-field-of-view, single-shot EPI readout was used at two centres with 3 T MRI scanners. Four alkane phantoms with known diffusivities were scanned at a single centre using a stimulated echo sequence and a spin-echo Stejskal-Tanner diffusion sequence. The median (maximum, minimum) difference between the DT-CMR sequence and Stejskal-Tanner sequence was 0.01 (0.04, 0.0006) × 10^-3 mm²/s (2%), and between the DT-CMR sequence and literature diffusivities was 0.02 (0.05, 0.006) × 10^-3 mm²/s (4%).The same ten healthy volunteers were scanned using the DT-CMR sequence at the two centres less than seven days apart. Average ADC and FA were calculated in a single mid-ventricular, short axis slice. Intercentre differences were tested for statistical significance at the p < 0.05 level using paired t-tests. The mean ADC ± standard deviation for all subjects averaged over both centres was 1.10 ± 0.06 × 10^-3 mm²/s in systole and 1.20 ± 0.09 × 10^-3 mm²/s in diastole; FA was 0.41 ± 0.04 in systole and 0.54 ± 0.03 in diastole. With similarly-drawn regions-of-interest, systolic ADC (difference 0.05 × 10^-3 mm²/s), systolic FA (difference 0.003) and diastolic FA (difference 0.01) were not statistically significantly different between centres (p > 0.05), and only the diastolic ADC showed a statistically significant, but numerically small, difference of 0.07 × 10^-3 mm²/s (p = 0.047). The intercentre, intrasubject coefficients of variance were: systolic ADC 7%, FA 6%; diastolic ADC 7%, FA 3%.

Conclusions

This is the first study to demonstrate the accuracy of a stimulated-echo DT-CMR sequence in phantoms, and demonstrates the feasibility of obtaining reproducible ADC and FA in healthy volunteers at separate centres with well-matched sequences and processing.     

High resolution 3D diffusion cardiovascular magnetic resonance of carotid vessel wall to detect lipid core without contrast media

Background

Without the need of contrast media, diffusion-weighted imaging (DWI) has shown great promise for accurate detection of lipid-rich necrotic core (LRNC), a well-known feature of vulnerable plaques. However, limited resolution and poor image quality in vivo with conventional single-shot diffusion-weighted echo planar imaging (SS-DWEPI) has hindered its clinical application. The aim of this work is to develop a diffusion-prepared turbo-spin-echo (DP-TSE) technique for carotid plaque characterization with 3D high resolution and improved image quality.

Methods

Unlike SS-DWEPI where the diffusion encoding is integrated in the EPI framework, DP-TSE uses a diffusion encoding module separated from the TSE framework, allowing for segmented acquisition without the sensitivity to phase errors. The interleaved, motion-compensated sequence was designed to enable 3D black-blood DWI of carotid arteries with sub-millimeter resolution. The sequence was tested on 12 healthy subjects and compared with SS-DWEPI for image quality, vessel wall visibility, and vessel wall thickness measurements. A pilot study was performed on 6 patients with carotid plaques using this sequence and compared with conventional contrast-enhanced multi-contrast 2D TSE as the reference.

Results

DP-TSE demonstrated advantages over SS-DWEPI for resolution and image quality. In the healthy subjects, vessel wall visibility was significantly higher with diffusion-prepared TSE (p < 0.001). Vessel wall thicknesses measured from diffusion-prepared TSE were on average 35% thinner than those from the EPI images due to less distortion and partial volume effect (p < 0.001). ADC measurements of healthy carotid vessel wall are 1.53 ± 0.23 × 10⁻³ mm²/s. In patients the mean ADC measurements in the LRNC area were significantly lower (0.60 ± 0.16 × 10⁻³ mm²/s) than those of the fibrous plaque tissue (1.27 ± 0.29 × 10⁻³ mm²/s, p < 0.01).

Conclusions

Diffusion-prepared CMR allows, for the first time, 3D DWI of the carotid arterial wall in vivo with high spatial resolution and improved image quality over SS-DWEPI. It can potentially detect LRNC without the use of contrast agents, allowing plaque characterization in patients with renal insufficiency.

Electronic supplementary material

The online version of this article (doi:10.1186/s12968-014-0067-z) contains supplementary material, which is available to authorized users.     

In vivo contrast free chronic myocardial infarction characterization using diffusion-weighted cardiovascular magnetic resonance

Background

Despite the established role of late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) in characterizing chronic myocardial infarction (MI), a significant portion of chronic MI patients are contraindicative for the use of contrast agents. One promising alternative contrast free technique is diffusion weighted CMR (dwCMR), which has been shown ex vivo to be sensitive to myocardial fibrosis. We used a recently developed in vivo dwCMR in chronic MI pigs to compare apparent diffusion coefficient (ADC) maps with LGE imaging for infarct characterization.

Methods

In eleven mini pigs, chronic MI was induced by complete occlusion of the left anterior descending artery for 150 minutes. LGE, cine, and dwCMR imaging was performed 8 weeks post MI. ADC maps were derived from three orthogonal diffusion directions (b = 400 s/mm²) and one non-diffusion weighted image. Two semi-automatic infarct classification methods, threshold and full width half max (FWHM), were performed in both LGE and ADC maps. Regional wall motion (RWM) analysis was performed and compared to ADC maps to determine if any observed ADC change was significantly influenced by bulk motion.

Results

ADC of chronic MI territories was significantly increased (threshold: 2.4 ± 0.3 μm²/ms, FWHM: 2.4 ± 0.2 μm²/ms) compared to remote myocardium (1.4 ± 0.3 μm²/ms). RWM was significantly reduced (threshold: 1.0 ± 0.4 mm, FWHM: 0.9 ± 0.4 mm) in infarcted regions delineated by ADC compared to remote myocardium (8.3 ± 0.1 mm). ADC-derived infarct volume and location had excellent agreement with LGE. Both LGE and ADC were in complete agreement when identifying transmural infarcts. Additionally, ADC was able to detect LGE-delineated infarcted segments with high sensitivity, specificity, PPV, and NPV. (threshold: 0.88, 0.93, 0.87, and 0.94, FWHM: 0.98, 0.97, 0.93, and 0.99, respectively).

Conclusions

In vivo diffusion weighted CMR has potential as a contrast free alternative for LGE in characterizing chronic MI.     

Allogeneic Mesenchymal Precursor Cells in Type 2 Diabetes: A Randomized,Placebo-Controlled,Dose-Escalation Safety and Tolerability Pilot Study

OBJECTIVE

To assess the safety, tolerability, and feasibility of adult allogeneic bone marrow–derived mesenchymal precursor cells (MPCs) in type 2 diabetes inadequately controlled with metformin either alone or with one additional oral antidiabetic agent.

RESEARCH DESIGN AND METHODS

The study was a dose-escalating randomized placebo-controlled trial assessing one intravenous (IV) infusion of MPCs (rexlemestrocel-L; Mesoblast Inc.) 0.3 × 10⁶/kg (n = 15), 1.0 × 10⁶/kg (n = 15), or 2.0 × 10⁶/kg (n = 15) or placebo (n = 16). Study duration was 12 weeks.

RESULTS

Subjects (21 women, 40 men) with a mean ± SD baseline HbA_1c 8.3 ± 1.0% (67 ± 10.9 mmol/mol), BMI 33.5 ± 5.5 kg/m², and diabetes duration 10.1 ± 6.0 years were enrolled at 18 U.S. sites. No acute adverse events (AEs) were associated with infusion. No serious AEs, serious hypoglycemia AEs, or discontinuations due to AEs over 12 weeks were found. No subjects developed donor-specific anti-HLA antibodies or became sensitized. The safety profile was comparable among treatment groups. Compared with placebo, a single IV infusion of rexlemestrocel-L reduced HbA_1c at all time points after week 1. The adjusted least squares mean ± SE dose-related differences in HbA_1c from placebo in the rexlemestrocel-L groups ranged from −0.1 ± 0.2% (−1.1 ± 2.2 mmol/mol) to −0.4 ± 0.2% (4.4 ± 2.2 mmol/mol) at 8 weeks and from 0.0 ± 0.25% to −0.3 ± 0.25% (−3.3 ± −2.7 mmol/mol) at 12 weeks (P < 0.05 for 2.0 × 10⁶/kg dose at 8 weeks). The clinical target HbA_1c <7% (53 mmol/mol) was achieved by 33% (5 of 15) of the subjects who received the 2.0 × 10⁶/kg dose vs. 0% of those who received placebo (P < 0.05).

CONCLUSIONS

This short-term study demonstrates the safety and feasibility of up to 246 million MPCs in subjects with type 2 diabetes.     

Preparation methods and release kinetics of Litsea cubeba essential oil microcapsules

In this paper, using β-cyclodextrin (β-CD) as the shell material, LCEO (Litsea cubeba essential oil) microcapsules were prepared by various preparation methods, such as grinding, saturated solution, freeze-drying and spray-drying. The encapsulation yield, encapsulation efficiency, retention rate of the microcapsules and the citral content of the microcapsules were investigated. The surface morphologies of the microcapsules were observed using SEM (Scanning Electronic Microscopy); the entrapment efficiencies of the microcapsules were detected using IR (Infrared Spectrum) analysis; the citral contents of microcapsules were detected by GC (Gas Chromatography) analysis. The highest encapsulation efficiency for the microcapsules was obtained using spray-drying, followed by freeze-drying, saturated aqueous solution and grinding, while the encapsulation yield followed the opposite sequence to the encapsulation efficiency. At a specific storage temperature (15 °C) and humidity (60%), spray-drying had the most satisfactory protective effect on citral in LCEO, followed by freeze-drying and saturated aqueous solution, while the grinding method appeared to provide the worst protective effect. Avrami''s model was used to simulate the release rates of the four kinds of microcapsules. The release mechanism parameters of microcapsules prepared by grinding, saturated aqueous solution, freeze-drying and spray-drying were 0.961, 1.096, 1.156 and 0.945, respectively. The release rate constants of microcapsules prepared by grinding, saturated aqueous solution, freeze-drying and spray-drying were 2.53 × 10⁻², 2.22 × 10⁻², 1.84 × 10⁻², and 7.27 × 10⁻³ d⁻¹, respectively. It was concluded that the release reactions of the microcapsules prepared by grinding or spray-drying lay between the diffusion limiting kinetics and the first-order release kinetics, and the release reactions of the microcapsules prepared by saturated aqueous solution or freeze-drying were larger than the first-order release kinetics.

LCEO microcapsules were prepared by various preparation methods such as grinding, saturated solution, freeze-drying, spray-drying with β-CD used as the wall material. Avrami''s model was used to simulate the release rates of microcapsules.     

Contributors to Mortality in High-Risk Diabetic Patients in the Diabetes Heart Study

OBJECTIVE

Not all individuals with type 2 diabetes and high coronary artery calcified plaque (CAC) experience the same risk for adverse outcomes. This study examined a subset of high-risk individuals based on CAC >1,000 mg (using a total mass score) and evaluated whether differences in a range of modifiable cardiovascular disease (CVD) risk factors provided further insights into risk for mortality.

RESEARCH DESIGN AND METHODS

We assessed contributors to all-cause mortality among 371 European American individuals with type 2 diabetes and CAC >1,000 from the Diabetes Heart Study (DHS) after 8.2 ± 3.0 years (mean ± SD) of follow-up. Differences in known CVD risk factors, including modifiable CVD risk factors, were compared between living (n = 218) and deceased (n = 153) participants. Cox proportional hazards regression models were used to quantify risk for all-cause mortality.

RESULTS

Deceased participants had a longer duration of type 2 diabetes (P = 0.02) and reduced use of cholesterol-lowering medications (P = 0.004). Adjusted analyses revealed that vascular calcified plaque scores were associated with increased risk for mortality (hazard ratio 1.31–1.63; 3.89 × 10⁻⁵ < P < 0.03). Higher HbA_1c, lipids, and C-reactive protein and reduced kidney function also were associated with a 1.1- to 1.5-fold increased risk for mortality (3.45 × 10⁻⁶ < P < 0.03) after adjusting for confounding factors.

CONCLUSIONS

Even in this high-risk group, vascular calcification and known CVD risk factors provide useful information for ongoing assessment. The use of cholesterol-lowering medication seemed to be protective for mortality.     

Disposable gold nanoparticle functionalized and bare screen-printed electrodes for potentiometric determination of trazodone hydrochloride in pure form and pharmaceutical preparations

In the present study, screen-printed electrodes unmodified and chemically modified with gold nanoparticles were used as sensitive electrochemical sensors for the determination of trazodone hydrochloride. The sensors were based on the use of a tetraphenylborate ion association complex as an electroactive material in screen-printed electrodes with dioctyl phthalate (DOP) as a solvent mediator modified with gold nanoparticles which improve the electrode conductivity and enhance the surface area. The sensors displayed a stable response for 5, 6 and 7 months with a reproducible potential and linear response over the concentration range 1 × 10⁻⁵–1 × 10⁻² mol L⁻¹ at 25 ± 1 °C with Nernstian slopes of 57.50 ± 0.66, 58.30 ± 0.45 and 59.05 ± 0.58 mV per decade and detection limits of 7.9 × 10⁻⁶, 7.6 × 10⁻⁶ and 6.8 × 10⁻⁶ mol L⁻¹ for sensor 1, 2 and 3 respectively. The analytical performance of the screen printed electrodes in terms of selectivity coefficients for trazodone hydrochloride relative to the number of potentially interfering substances was investigated. The proposed method has been applied successfully for the analysis of the drug in its pure and dosage forms and there is no interference from any common pharmaceutical additives.

In the present study, screen-printed electrodes unmodified and chemically modified with gold nanoparticles were used as sensitive electrochemical sensors for the determination of trazodone hydrochloride.     

Depth profiling X-ray photoelectron spectroscopy and atomic force microscopy of Cd(ii)- and Pb(ii)-selective electrodes based on nano metal sulfides

This research involved constructing and studying plastic membrane Cd(ii)- and Pb(ii)-ion selective electrodes of the coated wire type based on nanoparticles of CdS and PbS as ionophores, respectively. The electrodes exhibited average linear concentration ranges of 1.0 × 10⁻⁶ to 1.0 × 10⁻² and 9.6 × 10⁻⁷ to 1.0 × 10⁻² M, average detection limits of 8.6 × 10⁻⁷ and 5.8 × 10⁻⁷ M, pH ranges of 2.2–5.8 and 2.9–5.9, and average calibration graph slopes of 28.56 and 28.81 mV per concentration decade, respectively. Both electrodes showed high selectivity towards many inorganic cations. Depth profiling X-ray photoelectron spectroscopy of fresh and expired membranes proved that: (a) the nanoparticles were homogeneously dissolved in the polymeric network and (b) the limitation of the life span of the plastic membrane was due to leaching of the active ingredient from the membrane surface to the bathing solution. The topography of fresh, active, and expired membranes as imaged by atomic force microscopy revealed the formation of a gel layer at the surface of the active electrode and drastic deformation of the expired membrane''s surface.

Nanoparticles of CdS and PbS as ionophres for plastic membrane metal cations electrodes.     

Thermogravimetric analysis of soot combustion in the presence of ash and soluble organic fraction

Soot (Printex U, PU) combustion in the presence of ash and soluble organic fraction (SOF) was studied by thermogravimetric analysis (TGA). The comprehensive combustion index, combustion stability index and peak temperature were collected to evaluate the combustion performance of soot/ash/SOF mixtures. Compared with SiO₂, Fe₂O₃ and CaSO₄ nanoparticles, ZnO nanoparticles efficiently accelerate soot combustion with excellent oxygen carrying abilities. When the weight ratio of the PU/ZnO mixture is 1 : 1, this acceleration effect is maximized in the soot combustion process. The comprehensive combustion and combustion stability indices increase from 0.667 × 10⁻⁷%² min⁻² °C⁻³ and 23.53 × 10⁵ to 1.296 × 10⁻⁷%² min⁻² °C⁻³ and 39.53 × 10⁵, compared to pure PU, respectively. Compared with the PU/ZnO mixture, the soot combustion had inferior results after adding two oils as the simulative SOF. The 15W lubricant had the minimum negative impact compared to 0# diesel fuel. The comprehensive combustion and combustion stability indices reach the maximum values of 1.074 × 10⁻⁷%² min⁻² °C⁻³ and 33.29 × 10⁵ at the 1 : 1 : 0.1 weight ratio of PU/ZnO/15W, which grew by 62% and 42% compared to pure PU, respectively. This work contributes to an understanding of the combined effect of ash and SOF on soot combustion.

Soot (Printex U, PU) combustion in the presence of ash and soluble organic fraction (SOF) was studied by thermogravimetric analysis (TGA).     

Novel potentiometric sensors for determination of ondansetron hydrochloride in pure and dosage form

A new and sensitive potentiometric method has been developed and characterized for four novel sensors responsive to ondansetron hydrochloride. The potentiometric sensor method includes advancement of ondansetron hydrochloride sensors using a membrane comprised of molybdophosphoric acid (MPA) and ondansetron as an electro-active material in a polyvinylchloride (PVC) matrix membrane plasticized with di-butyl phthalate (DBPH), ortho-nitrophenyloctyl ether (O-NPOE), di-octyl phthalate (DOPH), or di-butyl phosphate (DBP). The validity of sensors in the present work has been examined, and steady and reproducible responses were obtained over the concentration ranges of 7.3 × 10⁻⁵ to 1.0 × 10⁻², 6.6 × 10⁻⁶ to 1.0 × 10⁻², 1.0 × 10⁻⁵ to 1.0 × 10⁻², and 2.0 × 10⁻⁵ to 1.0 × 10⁻² M for DBPH-, O-NPOE-, DOPH-, and DBP-ondansetron, respectively. The sensors revealed Nernstian gradients of 59.61 ± 0.50, 57.71 ± 0.23, 53.01 ± 0.14, and 53.20 ± 0.35 mV per decade individually with pH ranges of 2.5–5.5 in DBPH and 3.5–5.0 in O-NPOE electrodes, and 4.0–5.5 for both individual DOPH and DBP plasticized film-based sensors. The time responses for the sensors were 30, 32, 31, and 29 s for DBPH-, O-NPOE-, DOPH-, and DBP-ondansetron, respectively. The developed sensors also exhibited high selectivity towards ondansetron hydrochloride against different interfering species of inorganic particles with long-term stability of approximately 41, 36, 18, and multiple days for the DBPH, O-NPOE, DOPH, and DBP electrodes.

A new and sensitive potentiometric method has been developed and characterized for four novel sensors responsive to ondansetron hydrochloride.     

Enhanced physical properties of γ-Al2O3–rGO hybrids prepared by solvothermal and hot-press processing

In this study, a solvothermal method was employed for the first time to fabricate hybrids composed of cross-linked γ-Al₂O₃ nanorods and reduced graphite oxide (rGO) platelets. After calcination and hot-press processing, monoliths of Al₂O₃–rGO hybrids were obtained with improved physical properties. It was found that the oxygen-containing groups on graphene oxide were beneficial for the adsorption of aluminum isopropoxide, leading to a uniform dispersion of rGO with Al₂O₃, which was obtained by hydrolysis of aluminum isopropoxide during the solvothermal reaction. The hybrid, which was subsequently calcinated for 3 h showed electrical conductivity of 6.7 × 10¹ S m⁻¹ together with 90% higher mechanical tensile strength and 80% higher thermal conductivity as compared to the bare Al₂O₃. In addition, the dielectric constant of the hybrid was 12 times higher than that of the bare Al₂O₃. In this study, the highest values of electrical conductivity (8.2 × 10¹ S m⁻¹), thermal conductivity (2.53 W m⁻¹ K⁻¹), dielectric constant (10⁴) and Young''s modulus (3.7 GPa) were obtained for the alumina–rGO hybrid calcinated for 1 h. XRD characterization showed that an increase in calcination temperature and further hot-press processing at 900 °C led to enhanced crystallinity in the γ-Al₂O₃ nanorods in the hybrid, resulting in enhanced physical properties in the hybrids.

After calcination and hot-press processing, monoliths of γ-Al₂O₃–rGO hybrids are obtained with improved physical properties.     

Laser-treated glass platform for rapid wicking-driven transport and particle separation in bio microfluidics

In this work, we present a laser-based fabrication technique for direct patterning of micro-channels consisting of interconnected micro-cracks on soda-lime glass. Using a CO₂ laser to deposit energy at a linear rate of 18.75 to 93.75 mJ mm⁻¹, we were able to manipulate the micro-crack formation, while enabling rapid manufacturing and scalable production of cracked-glass microfluidic patterns on glass. At the higher end of the energy deposition rate (93.75 mJ mm⁻¹), the laser fabricated microfluidic channels (1 mm wide and 20 mm long) had extremely fast wicking speeds (24.2 mm s⁻¹, ×10 faster than filter paper) as a result of significant capillary action and laser-induced surface hydrophilization. At the lower end (18.75 mJ mm⁻¹), 3–4 μm wide micro-cracked crevices resulted in an increased mesh/sieve density, hence, more efficiently filtering particle-laden liquid samples. The reproducibility tests revealed an averaged wicking speed of 10.6 ± 1.5 mm s⁻¹ measured over 21 samples fabricated under similar conditions, similar to that of filter paper (∼85%). The micro-cracked channels exhibited a stable shelf life of at least 82 days with a wicking speed within 10–13 mm s⁻¹.

In this work, we present a laser-based fabrication technique for direct patterning of micro-channels consisting of interconnected micro-cracks on soda-lime glass.     

A technology for strongly improving methane production from rice straw: freeze–thaw pretreatment

Overcoming the complex three dimensional structure of biomass is a major challenge in enhancing anaerobic digestion (AD) efficacy. Freeze–thaw pretreatment was proposed herein in order to improve methane production from rice straw. The effect was notable: average methane content for group-A (−4 °C) and -B (−20 °C) were A1 (−4 °C, 12 h): 40.0%, A2 (−4 °C, 24 h): 40.5%, A3 (−4 °C, 48 h): 42.2%; B1 (−20 °C, 12 h): 44.2%, B2 (−20 °C, 24 h): 45.7%, B3 (−20 °C, 48 h): 46.0%, the increases were 88.8–99.1% and 108.8–117.2%, respectively, compared with control (CK) (21.2%). Total methane production for group-A and -B were A1: 22.8 mL g⁻¹ TS, A2: 24.7 mL g⁻¹ TS, A3: 27.8 mL g⁻¹ TS; B1: 29.9 mL g⁻¹ TS, B2: 31.3 mL g⁻¹ TS, B3: 32.0 mL g⁻¹ TS, compared with CK (7.6 mL g⁻¹ TS), the increases were 200.0–265.8%, 293.4–321.1%, respectively. The technical digestion time (T₈₀) was shortened by 8 days. Therefore, the maximum methane production was obtained under conditions of −20 °C and 48 h. This study proposed an efficient pretreatment method that broadens the horizon of improving biomass conversion into bioenergy.

Overcoming the complex three dimensional structure of biomass is a major challenge in enhancing anaerobic digestion (AD) efficacy.     

Early detection of bacteria using SPR imaging and event counting: experiments with Listeria monocytogenes and Listeria innocua

Foodborne pathogens are of significant concern in the agrifood industry and the development of associated rapid detection and identification methods are of major importance. This paper describes the novel use of resolution-optimized prism-based surface plasmon resonance imaging (RO-SPRI) and data processing for the detection of the foodborne pathogens Listeria monocytogenes and Listeria innocua. With an imaging spatial resolution on the order of individual bacteria (2.7 ± 0.5 μm × 7.9 ± 0.6 μm) over a field of view 1.5 mm², the RO-SPRI system enabled accurate counting of individual bacteria on the sensor surface. Using this system, we demonstrate the detection of two species of Listeria at an initial concentration of 2 × 10² CFU mL⁻¹ in less than 7 hours. The surface density of bacteria at the point of positive detection was 15 ± 4 bacteria per mm². Our approach offers great potential for the development of fast specific detection systems based on affinity monitoring.

A dedicated SPR apparatus optimized for individual bacteria observation and a new strategy for early detection of microorganisms in growth.     

Fabrication of low-density carbon-bonded carbon fiber composites with an Hf-based coating for high temperature applications

A novel Hf-based anti-oxidation coating has been prepared on the surface of low-density carbon-bonded carbon fiber composites (CBCFs). The coating exhibits a gradient transition structure, with mainly HfB₂, Hf₂Si and SiC ceramics. Oxyacetylene torch testing has been utilized to evaluate the ablation resistance under the condition ranging from 1.6 MW m⁻² to 2.2 MW m⁻² for 300 s. The experimental results show that the as-prepared Hf-based coating can effectively protect CBCFs under high-temperature oxidation conditions. The surface maximum temperature can reach 1616–2037 °C, and the mass ablation rates vary from −3.5 × 10⁻⁵ g s⁻¹ cm⁻² to 1.5 × 10⁻⁵ g s⁻¹ cm⁻². The formation of a dense SiO₂ glass layer embedded with HfO₂ grains or particle accumulation in the HfO₂ layer is responsible for the good ablation resistance.

A novel low-density CBCF composite with an Hf-based coating was designed and prepared, which exhibited a good ablation resistance at the maximum temperature range of 1616–2037 °C for 300 s.     

A novel catalytic kinetic method for the determination of mercury(ii) in water samples

Mercury(ii) ions act as catalyst in the substitution of cyanide ion in hexacyanoruthenate(ii) by pyrazine (Pz) in an acidic medium. This property of Hg(ii) has been utilized for its determination in aqueous solutions. The progress of reaction was followed spectrophotometrically by measuring the increase in absorbance of the yellow colour product, [Ru(CN)₅Pz]³⁻ at 370 nm (λ_max, ε = 4.2 × 10³ M⁻¹ s⁻¹) under the optimized reaction conditions; 5.0 × 10⁻⁵ M [Ru(CN)₆⁴⁻], 7.5 × 10⁻⁴ M [Pz], pH 4.00 ± 0.02, ionic strength (I) = 0.05 M (KCl) and temp. 45.0 ± 0.1 °C. The proposed method is based on the fixed time procedure under optimum reaction conditions. The linear regression (calibration) equations between the absorbance at fixed times (t = 15, 20 and 25 min) and [Hg(ii)] were established in the range of 1.0 to 30.0 × 10⁻⁶ M. The detection limit was found to be 1.5 × 10⁻⁷ M of Hg(ii). The effect of various foreign ions on the proposed method was also studied and discussed. The method was applied for the determination of Hg(ii) in different wastewater samples. The present method is simple, rapid and sensitive for the determination of Hg(ii) in trace amount in the environmental samples.

Mercury(ii) ions act as catalyst in the substitution of cyanide ion in hexacyanoruthenate(ii) by pyrazine (Pz) in an acidic medium.     

Gas-phase degradation of 2-butanethiol initiated by OH radicals and Cl atoms: kinetics,product yields and mechanism at 298 K and atmospheric pressure

Relative rate coefficients and product distribution of the reaction of 2-butanethiol (2butSH) with OH radicals and Cl atoms were obtained at atmospheric pressure and 298 K. The experiments were performed in a 480 L borosilicate glass photoreactor in synthetic air coupled to a long path “in situ” FTIR spectrometer. The rate coefficients obtained by averaging the values from different experiments were: k_OH = (2.58 ± 0.21) × 10⁻¹¹ cm³ per molecule per s and k_Cl = (2.49 ± 0.19) × 10⁻¹⁰ cm³ per molecule per s. The kinetic values were compared with related alkyl thiols and homologous alkyl alcohols, where it was found that thiols react faster with both oxidants, OH radicals and Cl atoms. SO₂ and 2-butanone were the major products identified for the reactions of 2-butanethiol with OH radicals and Cl atoms. The product yield of the reaction of 2-butanethiol and OH radicals were (81 ± 2)%, and (42 ± 1)% for SO₂ and 2-butanone, respectively. For the reactions of 2-butanethiol with Cl atom, yields of SO₂ and 2-butanone were (59 ± 2)% and (39 ± 2)%, respectively. A degradation mechanism was proposed for the pathways that leads to formation of identified products. The product distribution observed indicated that the H-atom of the S–H group abstraction channel is the main pathway for the reaction of OH radicals and Cl atoms with 2-butanethiol.

Relative rate coefficients and product distribution of the reaction of 2-butanethiol (2butSH) with OH radicals and Cl atoms were obtained at atmospheric pressure and 298 K.     

One-pot synthesis of poly(ionic liquid)s with 1,2,3-triazolium-based backbones via clickable ionic liquid monomers

Clickable α-azide-ω-alkyne ionic liquid monomers were developed and subsequently applied to the one-pot synthesis of ionically conducting poly(ionic liquid)s with 1,2,3-triazolium-based backbones through a click chemistry strategy. This approach does not require the use of solvents, polymerisation mediators, or catalysts. The obtained poly(ionic liquid)s were characterized by NMR, differential scanning calorimetry, thermogravimetric analysis, and impedance spectroscopy analysis. Moreover, these poly(ionic liquid)s were cross-linked via N-alkylation with a dianion quarternizing agent to achieve enhanced ionic conductivity and mechanical strength. The resulting free-standing films showed a Young''s modulus up to 4.8 MPa and ionic conductivities up to 4.60 × 10⁻⁸ S cm⁻¹ at 30 °C. This facile synthetic strategy has the potential to expand the availability of poly(ionic liquid)s and promote the development of functional materials.

Clickable ionic liquid monomers realize the one-pot synthesis of ionically conducting poly(ionic liquid)s with 1,2,3-triazolium-based backbones via click chemistry.     

A thio-β-cyclodextrin functionalized graphene/gold nanoparticle electrochemical sensor: a study of the size effect of the gold nanoparticles and the determination of tetrabromobisphenol A

In this study, a novel tetrabromobisphenol A (TBBPA) sensor was fabricated based on a CTAB-capped gold nanoparticle (AuNPs)-thio-β-cyclodextrin (SH-β-CD)/graphene oxide modified glassy carbon electrode (GCE). The peak current of TBBPA was dramatically enhanced by the AuNPs with a diameter of 6.2 nm on the modified electrodes compared with the other sized particles (10.1 or 16.1 nm). To further improve the electrochemical performance of the modified electrode, the influence of pH of the buffer solution and the accumulation time on the determination were investigated. The optimum pH and accumulation time were 7.0 and 180 s, respectively. The developed sensor exhibited good reproducibility, and excellent sensitivity and selectivity, showing a low detection limit (1.2 × 10⁻⁹ mol L⁻¹) and a linear range from 1.5 × 10⁻⁸ to 7 × 10⁻⁶ mol L⁻¹. In addition, a possible oxidization mechanism of TBBPA was also discussed. Finally, this sensor was successfully applied to detect TBBPA in water samples, and the results were consistent with those acquired by high-performance liquid chromatography.

In this study, a novel tetrabromobisphenol A (TBBPA) sensor was fabricated based on a CTAB-capped gold nanoparticle (AuNP)-thio-β-cyclodextrin (SH-β-CD)/graphene oxide modified glassy carbon electrode (GCE).