Probing ion exchange in the triflic acid-guanidinium triflate system: a solid-state nuclear magnetic resonance study

Knowledge of ion exchange and transport behavior in electrolyte materials is crucial for designing and developing novel electrolytes for electrochemical device applications such as fuel cells or batteries. In the present study, we show that, upon the addition of triflic acid (HTf) to the guanidinium triflate (GTf) solid-state matrix, several orders of magnitude enhancement in the proton conductivity can be achieved. The static 1H and 19F solid-state NMR results show that the addition of HTf has no apparent effect on local molecular mobility of the GTf matrix at room temperature. At higher temperatures, however, the HTf exhibits fast ion exchange with the GTf matrix. The exchange rate, as quantified by our continuum T2 fitting analysis, increases with increasing temperature. The activation energy for the chemical exchange process was estimated to be 58.4 kJ/mol. It is anticipated that the solid-state NMR techniques used in this study may be also applied to other organic solid-state electrolyte systems to investigate their ion-exchange processes.

Automated detection of depression from brain structural magnetic resonance imaging (sMRI) scans

 Automated sMRI-based depression detection system is developed whose components include acquisition and preprocessing, feature extraction, feature selection, and classification. The core focus of the research is on the establishment of a new feature selection algorithm that quantifies the most relevant brain volumetric feature for depression detection at an individual level.

Estimation of changes in volume of individual lower-limb muscles using magnetic resonance imaging (during bed-rest)

Muscle size in the lower limb is commonly assessed in neuromuscular research as it correlates with muscle function and some approaches have been assessed for their ability to provide valid estimates of muscle volume. Work to date has not examined the ability of different measurement approaches (such as cross-sectional area (CSA) measures on magnetic resonance (MR) imaging) to accurately track changes in muscle volume as a result of an intervention, such as exercise, injury or disuse. Here we assess whether (a) the percentage change in muscle CSA in 17 lower-limb muscles during 56 days bed-rest, as assessed by five different algorithms, lies within 0.5% of the muscle volume change and (b) the variability of the outcome measure is comparable to that of muscle volume. We find that an approach selecting the MR image with the highest muscle CSA and then a series of CSA measures, the number of which depended upon the muscle considered, immediately distal and proximal, provided an acceptable estimate of the muscle volume change. In the vastii, peroneal, sartorius and anterior tibial muscle groups, accurate results can be attained by increasing the spacing between CSA measures, thus reducing the total number of MR images and hence the measurement time. In the two heads of biceps femoris, semimembranosus and gracilis, it is not possible to reduce the number of CSA measures and the entire muscle volume must be evaluated. Using these approaches one can reduce the number of CSA measures required to estimate changes in muscle volume by ~60%. These findings help to attain more efficient means to track muscle volume changes in interventional studies.

Real-time ultrasound measures of lumbar erector spinae and multifidus: reliability and comparison to magnetic resonance imaging

In this work we examine the reliability and validity (in comparison to magnetic resonance imaging; MRI) of real-time ultrasound measures of lumbar erector spinae thickness. We also consider the between-day reliability of the lumbar multifidus muscle area as measured via ultrasound. 23 male subjects aged 21-45 years were measured three times over the course of nine days by one operator. The first (L1) through to the fifth (L5) lumbar vertebral levels were measured on the left and right sides. MRI was performed on the same day as first ultrasound scanning. For between-day intra-rater reliability, intra-class correlation co-efficients (ICCs), standard error of the measurement, minimal detectable difference and co-efficients of variation (CVs) were calculated along with their 95% confidence intervals and Bland-Altman analysis was performed. On Bland-Altman analysis, erector spinae thickness and multifidus area ultrasound measures 'agreed' with equivalent MR measures, though the correlation between MR and ultrasound measures was typically poor to moderate. For both ultrasound measures, the ICCs ranged from 'moderate' to 'excellent' at individual vertebral levels, although multifidus area (CV ranged from 8 to 15%) was less reliable than erector spinae thickness (CV ranged from 6 to 10%). 'Agreement' on Bland-Altmann analysis was present between days for all ultrasound measures. Averaging between sides and between vertebral levels improved reliability. Average erector spinae thickness showed a CV of 5.5% (ICC 0.77) and average multifidus area 6.2% (ICC 0.80).

Zinc doped ferrite magnetic resonance imaging contrast agent for atherosclerosis

 This project focuses on the development of zinc doped ferrite nanoparticle based MRI contrast agents with enhanced contrast and site-specific targeting for atherosclerosis diagnosis. The engineered nanocomplexes developed were validated through MRI scans using rat models with potential for multimodal imaging and effective therapy.

Locally sparsified compressive sensing in magnetic resonance imaging

Magnetic Resonance Imaging (MRI) is a widely used technique for acquiring images of human organs/tissues. Due to its complex imaging process, it consumes a lot of time to produce a high quality image. Compressive Sensing (CS) has been used by researchers for rapid MRI. It uses a global sparsity constraint with variable density random sampling and L1 minimisation. This work intends to speed up the imaging process by exploiting the non-uniform sparsity in the MR images. Locally Sparsified CS suggests that the image can be even better sparsified by applying local sparsity constraints. The image produced by local CS can further reduce the sample set. This paper establishes the basis for a methodology to exploit non-uniform nature of sparsity and to make the MRI process time efficient by using local sparsity constraints.

Cerebral responses to innocuous somatic pressure stimulation following aerobic exercise rehabilitation in chronic pain patients: a functional magnetic resonance imaging study

Objective: The purpose of this research was to assess the functional brain activity and perceptual rating of innocuous somatic pressure stimulation before and after exercise rehabilitation in patients with chronic pain.

Materials and methods: Eleven chronic pain patients and eight healthy pain-free controls completed 12 weeks of supervised aerobic exercise intervention. Perceptual rating of standardized somatic pressure stimulation (2 kg) on the right anterior mid-thigh and brain responses during functional magnetic resonance imaging (fMRI) were assessed at pre- and postexercise rehabilitation.

Results: There was a significant difference in the perceptual rating of innocuous somatic pressure stimulation between the chronic pain and control groups (P=0.02) but no difference following exercise rehabilitation. Whole brain voxel-wise analysis with correction for multiple comparisons revealed trends for differences in fMRI responses between the chronic pain and control groups in the superior temporal gyrus (chronic pain > control, corrected P=0.30), thalamus, and caudate (control > chronic, corrected P=0.23). Repeated measures of the regions of interest (5 mm radius) for blood oxygen level-dependent signal response revealed trend differences for superior temporal gyrus (P=0.06), thalamus (P=0.04), and caudate (P=0.21). Group-by-time interactions revealed trend differences in the caudate (P=0.10) and superior temporal gyrus (P=0.29).

Conclusion: Augmented perceptual and brain responses to innocuous somatic pressure stimulation were shown in the chronic pain group compared to the control group; however, 12-weeks of exercise rehabilitation did not significantly attenuate these responses.

7Li NMR measurements of polymer gel electrolytes

Ion conducting polymer gels prepared from (ethylene oxide)_n grafted methacrylates, ethylene carbonate (EC), gamma butyrolactone (gBL), and lithium hexafluorophosphate are studied by means of nuclear magnetic resonance spectroscopy. This study shows that there are at least two possible lithium sites with different mobility. The lithium-ions with lower mobility dominate at room temperature, but this is changed as the temperature is increased. The NMR results also show that the ⁷Li spin–spin relaxation time decreases with increasing length of the grafted ethylene oxide side chains, indicating a stronger interaction between the polymer and the Li-ions, and hence, a lower mobility of the Li-ions.

The effect of nano-particle TiO2 fillers on structure and transport in polymer electrolytes

Nano-particle oxide fillers including TiO₂, SiO₂ and Al₂O₃ have previously been shown to have a significant affect on the properties of polymer electrolytes, especially those based on polyether–lithium salt systems. In some cases, conductivity increases of more than one order of magnitude have been reported in crystalline PEO-based complexes. In this work, we report on the effects of TiO₂ on a completely amorphous polyether-based system to remove the complication of multiple phases presented by the semi-crystalline nature of PEO. Multinuclear magnetic resonance spectroscopy has shown that the lithium ion environment is changed by the addition of filler. Vibrational spectroscopy shows that the filler influences the disordered-longitudinal acoustic modes (DLAM) in the case of an amorphous polyether and suggests an interaction between the filler surface and the polymer. Positron annihilation lifetime spectroscopy indicates an increase in free volume upon addition of filler to an amorphous polyether–salt complex, coinciding with an apparent increase in polymer mobility as determined from ¹H T₂ NMR measurements. Impedance spectroscopy has shown clear evidence of an inter-phase region that may be more or less conductive than the bulk polymer electrolyte itself. The data support a model which includes conduction through an interfacial region in addition to the bulk polymer

An nmr investigation of ionic structure and mobility in plasticized solid polymer electrolytes

²³Na and ¹⁹F nuclear magnetic resonance spectroscopy is used to investigate the effect of plasticizer addition on ionic structure and mobility in a urethane crosslinked polyether solid polymer electrolyte. The incorporation of dimethyl formamide and propylene carbonate plasticizers in a sodium triflate/polyether system results in an upfield chemical shift for the ²³Na resonance consistent with decreased anion-cation association and increased cation-plasticizer interactions. The ¹⁹F resonances appears less susceptible to changes in chemical environment with only minor chemical shift changes recorded. Spin lattice relaxation measurements for the ¹⁹F nucleus are also reported. Two minima are observed in the relaxation measurements consistent with both an inter and intramolecular relaxation mechanism.

Composition effects in polyetherurethane-based solid polymer electrolytes

Nuclear magnetic resonance spectroscopy (n.m.r.), dynamic mechanical thermal analysis (d.m.t.a.) and AC impedance techniques have been used in combination to probe the effect of electrolyte composition in an archetypal solid polymer electrolyte (SPE). A series of solid polymer electrolytes (SPEs) based on a urethane-crosslinked trifunctional poly(ethylene glycol) polymer host containing dissolved ionic species (LiClO₄ and LiCF₃SO₃) have been studied. D.m.t.a. has established that increasing LiClO₄ concentration causes a decrease in the polymer segmental mobility, owing to the formation of transient crosslinks via cation-polymer interaction. Investigation of the distribution of mechanical/structural relaxation times for the LiClO₄/polymer complex with d.m.t.a. reveals that increasing LiClO₄ concentration causes a slight broadening of the distribution, indicating a more heterogeneous environment. Results of n.m.r. ⁷Li T₁ and T₂ relaxation experiments support the idea that higher salt concentrations encourage ionic aggregation. This is of critical importance in determining the conductivity of the material since it affects the number of charge carriers available. Introduction of the plasticiser tetraglyme into the LiClO₄-based SPEs suppresses the glass transition temperature of the SPE, and causes a significant broadening of the relaxation time distribution (as measured by d.m.t.a.).

Solid state NMR analysis of polypyrrole grown in a phosphonium ionic liquid

³¹P, ¹⁹F and ¹³C solid state NMR analysis has been used to investigate the intercalation/de-intercalation of both anions and cations in electrochemically synthesized polypyrrole films. Use of a phosphonium-based ionic liquid, tri(hexyl)(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)amide, allows the separate detection of the cation and anion by analysis of the phosphorous and fluorine resonances, respectively. Initial results indicate the incorporation of both cations and anions during film growth in the ionic liquid. There is a notable change in the ³¹P chemical shift of the cation on incorporation into the film, consistent with a significant change in environment compared to the pure ionic liquid. Despite its large size, the phosphonium cation can be completely expelled from the film by oxidation.

An inclusion complex of β-Cyclodextrin-L-Phenylalanine : 1H NMR and molecular docking studies

An inclusion host-guest complex between β-cyclodextrin (β-CD) and L-phenylalanine (LPhe) was investigated using ¹H nuclear magnetic resonance spectroscopy and molecular docking techniques. ¹H chemical shift changes of β-CD were used to calculate the stability constant (K_stb) of the complex. On the basis of the Hildebrand-Benesi method, the K_stb of the 1:1 complex in D₂O solution at 300 K, pD 7.6 was of 25.5 M^-1, implying a fast intermolecular exchange rate process. Interestingly, docking simulation indicates the toroidal space can be occupied by L-Phe with two favorable arrangements. For the predicted model with the higher probability score, the L-Phe aromatic ring is facing to the secondary hydroxyl groups of β-CD. Results from NMR and docking simulation are in good agreement with the x-ray structures of β-CD/L-phenylalanine derivatives.

Associations between smoking status, lifestyle and lipoprotein subclasses

Background: Although the relationship between cigarette smoking and cardiovascular disease (CVD) is well-established, the underlying mechanisms remain unclear. Smokers have a more atherogenic lipid profile but this may be mediated by lifestyle-related factors. Because detailed analysis of lipoprotein subclasses using nuclear magnetic resonance spectroscopy (NMR) may improve characterisation of lipid abnormalities, we applied the technique to investigate the relationships between smoking status, other lifestyle-related risk factors and lipoproteins in a contemporary cohort.

Methods: A total of 612 participants (360 women) aged 40-69 years at baseline (1990-1994) enrolled in the community-based Melbourne Collaborative Cohort Study had plasma lipoproteins measured using NMR. Data were analysed separately for men and women.

Results: After adjusting for other lifestyle-related risk factors, mean total low-density lipoprotein (LDL) particle concentration was higher for female smokers than non-smokers. Both medium and small LDL particle concentrations contributed to this difference. Both total high-density lipoprotein (HDL) and large HDL particle concentrations were lower for female smokers than non-smokers. The proportion at increased risk (according to NMR-determined particle size and number) was higher for female smokers than non-smokers. For men, there were few differences in lipoprotein measures related to smoking.

Conclusions: Female smokers have a more atherogenic lipoprotein profile than non-smokers, and this difference is independent of lifestyle-related risk factors. Lipoprotein profiles did not differ greatly between male smokers and non-smokers. These data reinforce the importance for women of not smoking.

1H-NMR and mass spectrometric characterization of the metabolic response of juvenile Atlantic salmon (Salmo salar) to long-term handling stress

Stressors of various kinds constantly affect fish both in the wild and in culture, examples being acute water temperature and quality changes, predation, handling, and confinement. Known physiological responses of fish to stress such as increases in plasma cortisol and glucose levels, are considered to be adaptive, allowing the animal to cope in the short term. Prolonged exposure to stressors however, has the potential to affect growth, immune function, and survival. Nonetheless, little is known about the mechanisms underlying the long-term stress response. We have investigated the metabolic response of juvenile Atlantic salmon (Salmo salar) to long-term handling stress by analyzing fish plasma via ¹H nuclear magnetic resonance spectroscopy and ultra high performance liquid chromatography–mass spectrometry (UPLC–MS), and comparing results with controls. Analysis of NMR data indicated a difference in the metabolic profiles of control and stressed fish after 1 week of stress with a maximum difference observed after 2 weeks. These differences were associated with stress-induced increases in phosphatidyl choline, lactate, carbohydrates, alanine, valine and trimethylamine-N-oxide, and decreases in low density lipoprotein, very low density lipoprotein, and lipid. UPLC-MS data showed differences at week 2, associated with another set of compounds, tentatively identified on the basis of their mass/charge. Overall the results provided a multi-faceted view of the response of fish to long-term handling stress, indicating that the metabolic disparity between the control and stress groups increased to week 2, but declined by weeks 3 and 4, and revealed several new molecular indicators of long-term stress.