Reinterpretation of Dynamic Vibrational Spectroscopy to Determine the Molecular Structure and Dynamics of Ferrocene.

Molecular distortion of dynamic molecules gives a clear signature in the vibrational spectra, which can be modeled to give estimates of the energy barrier and the sensitivity of the frequencies of the vibrational modes to the reaction coordinate. The reaction coordinate method (RCM) utilizes ab initio-calculated spectra of the molecule in its ground and transition states together with their relative energies to predict the temperature dependence of the vibrational spectra. DFT-calculated spectra of the eclipsed (D5h ) and staggered (D5d ) forms of ferrocene (Fc), and its deuterated analogue, within RCM explain the IR spectra of Fc in gas (350 K), solution (300 K), solid solution (7-300 K), and solid (7-300 K) states. In each case the D5h rotamer is lowest in energy but with the barrier to interconversion between rotamers higher for solution-phase samples (ca. 6 kJ mol-1 ) than for the gas-phase species (1-3 kJ mol-1 ). The generality of the approach is demonstrated with application to tricarbonyl(η4 -norbornadiene)iron(0), Fe(NBD)(CO)3 . The temperature-dependent coalescence of the ν(CO) bands of Fe(NBD)(CO)3 is well explained by the RCM without recourse to NMR-like rapid exchange. The RCM establishes a clear link between the calculated ground and transition states of dynamic molecules and the temperature-dependence of their vibrational spectra.

Structural investigation of mM Ni(II) complex isomers using transmission XAFS: the significance of model development.

High-accuracy transmission XAFS determined using the hybrid technique has been used to refine the geometries of bis(N-n-propyl-salicylaldiminato) nickel(II) (n-pr Ni) and bis(N-i-propyl-salicylaldiminato) nickel(II) (i-pr Ni) complexes which have approximately square planar and tetrahedral metal coordination. Multiple-scattering formalisms embedded in FEFF were used for XAFS modelling of the complexes. Here it is shown that an IFEFFIT-like package using weighting from experimental uncertainty converges to a well defined XAFS model. Structural refinement of (i-pr Ni) was found to yield a distorted tetrahedral geometry providing an excellent fit, χr(2) = 2.94. The structure of (n-pr Ni) is best modelled with a distorted square planar geometry, χr(2) = 3.27. This study demonstrates the insight that can be obtained from the propagation of uncertainty in XAFS analysis and the consequent confidence which can be obtained in hypothesis testing and in analysis of alternate structures ab initio. It also demonstrates the limitations of this (or any other) data set by defining the point at which signal becomes embedded in noise or amplified uncertainty, and hence can justify the use of a particular k-range for one data set or a different range for another. It is demonstrated that, with careful attention to data collection, including the correction of systematic errors with statistical analysis of uncertainty (the hybrid method), it is possible to obtain reliable structural information from dilute solutions using transmission XAFS data.

High-accuracy X-ray absorption spectra from mM solutions of nickel (II) complexes with multiple solutions using transmission XAS.

A new approach is introduced for determining X-ray absorption spectroscopy (XAS) spectra on absolute and relative scales using multiple solutions with different concentrations by the characterization and correction of experimental systematics. This hybrid technique is a development of standard X-ray absorption fine structure (XAFS) along the lines of the high-accuracy X-ray extended range technique (XERT) but with applicability to solutions, dilute systems and cold cell environments. This methodology has been applied to determining absolute XAS of bis(N-n-propyl-salicylaldiminato) nickel(II) and bis(N-i-propyl-salicylaldiminato) nickel(II) complexes with square planar and tetrahedral structures in 15 mM and 1.5 mM dilute solutions. It is demonstrated that transmission XAS from dilute systems can provide excellent X-ray absorption near-edge structure (XANES) and XAFS spectra, and that transmission measurements can provide accurate measurement of subtle differences including coordination geometries. For the first time, (transmission) XAS of the isomers have been determined from low-concentration solutions on an absolute scale with a 1-5% accuracy, and with relative precision of 0.1% to 0.2% in the active XANES and XAFS regions after inclusion of systematic corrections.

Measurement of the X-ray mass attenuation coefficients of silver in the 5-20†keV range.

The X-ray mass attenuation coefficients of silver were measured in the energy range 5-20 keV with an accuracy of 0.01-0.2% on a relative scale down to 5.3 keV, and of 0.09-1.22% on an absolute scale to 5.0 keV. This analysis confirms that with careful choice of foil thickness and careful correction for systematics, especially including harmonic contents at lower energies, the X-ray attenuation of high-Z elements can be measured with high accuracy even at low X-ray energies (<6 keV). This is the first high-accuracy measurement of X-ray mass attenuation coefficients of silver in the low energy range, indicating the possibility of obtaining high-accuracy X-ray absorption fine structure down to the L1 edge (3.8 keV) of silver. Comparison of results reported here with an earlier data set optimized for higher energies confirms accuracy to within one standard error of each data set collected and analysed using the principles of the X-ray extended-range technique (XERT). Comparison with theory shows a slow divergence towards lower energies in this region away from absorption edges. The methodology developed can be used for the XAFS analysis of compounds and solutions to investigate structural features, bonding and coordination chemistry.

Stereochemical analysis of ferrocene and the uncertainty of fluorescence XAFS data.

Methods for the quantification of statistically valid measures of the uncertainties associated with X-ray absorption fine structure (XAFS) data obtained from dilute solutions using fluorescence measurements are developed. Experimental data obtained from 10 mM solutions of the organometallic compound ferrocene, Fe(C(5)H(5))(2), are analysed within this framework and, following correction for various electronic and geometrical factors, give robust estimates of the standard errors of the individual measurements. The reliability of the refinement statistics of standard current XAFS structure approaches that do not include propagation of experimental uncertainties to assess subtle structural distortions is assessed in terms of refinements obtained for the staggered and eclipsed conformations of the C(5)H(5) rings of ferrocene. Standard approaches (XFIT, IFEFFIT) give refinement statistics that appear to show strong, but opposite, preferences for the different conformations. Incorporation of experimental uncertainties into an IFEFFIT-like analysis yield refinement statistics for the staggered and eclipsed forms of ferrocene which show a far more realistic preference for the eclipsed form which accurately reflects the reliability of the analysis. Moreover, the more strongly founded estimates of the refined parameter uncertainties allow more direct comparison with those obtained by other techniques. These XAFS-based estimates of the bond distances have accuracies comparable with those obtained using single-crystal diffraction techniques and are superior in terms of their use in comparisons of experimental and computed structures.

Synthesis of PEDOT:PSS Solution-Processed Electronic Textiles for Enhanced Joule Heating.

Textile-based flexible and wearable electronic devices provide an excellent solution to thermal management systems, thermal therapy, and deicing applications through the Joule heating approach. However, challenges persist in designing such cost-effective electronic devices for efficient heating performance. Herein, this study adopted a facile solution-processed strategy, "dip-coating", to develop a high-performance Joule heating device by unformly coating the intrinsically conducting polymer (CP) poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) onto the surface of cotton textiles. The structural and morphological attributes of the cotton/CP mixture were evaluated using various characterization techniques. The electrothermal characteristics of the cotton/CP sample included rapid thermal response, uniform surface temperature distribution up to 94 °C, excellent stability, and endurance in heating performance under various mechanical deformations. The real-time illustration of the fabric heater affixed on a human finger has demonstrated its outstanding potential for thermal therapy applications. The fabricated heater may further expand it purposes toward deicing, defogging, and defrosting applications.

Prediabetes, diagnosed and undiagnosed diabetes, their risk factors and association with knowledge of diabetes in rural Bangladesh: The Bangladesh Population-based Diabetes and Eye Study.

BACKGROUND: The aim of the present study was to determine the prevalence and risk factors of prediabetes and diagnosed and undiagnosed diabetes mellitus (DM) in rural Bangladesh. METHODS: Using a population-based cluster random sampling strategy, 3104 adults aged ≥30 years were recruited. Fasting capillary blood glucose, blood pressure, height, weight, waist circumference, and knowledge, attitudes, and practice related to diabetes were recorded. Diabetes was defined as fasting glucose (FG) ≥7.0 mmol/L or a self-reported diagnosis of diabetes; impaired FG (IFG) was defined as FG ≥ 6.1 and <7.0 mmol/L. RESULTS: The overall crude prevalence of DM was 7.2% (95% confidence interval [CI] 6.3%-8.1%; n = 222), of which 55% (n = 123) was previously undiagnosed (UDM). The prevalence of IFG was 5.3% (95% CI 4.5%-6.1%; n = 163). The age-standardized prevalence of DM and IFG was 6.6% and 5.0%, respectively. The prevalence of UDM was higher in people of lower socioeconomic status (59% vs. 31%; P < 0.001). Of those with known DM, 56% had poor glycemic control (FG ≥ 7.0 mmol/L) and 37% were not on medication. Overall knowledge of DM was poor; only 16.3%, 17.8%, and 13.4% of those with UDM, IFG, and normal FG knew that diabetes causes eye disease, compared with 55.6% of those with known DM (Ptrend < 0.001). CONCLUSIONS: In this rural Bangladeshi community, UDM was high. Lower socioeconomic status was associated with a higher risk of UDM. Overall knowledge of DM was poor. Public health programmes should target those of low socioeconomic status and aim to increase knowledge of DM in rural Bangladesh.

Knowledge, attitudes and practice of diabetes in rural Bangladesh: the Bangladesh Population based Diabetes and Eye Study (BPDES).

BACKGROUND: To assess the Knowledge, Attitudes and Practice (KAP) amongst the general community regarding type 2 diabetes mellitus (DM) in rural Bangladesh. METHODS: Data was collected using cluster random sampling from 3104 adults residing in a rural district in Bangladesh. Participants underwent a KAP questionnaire survey regarding assessing diabetes, socio-demographic and medical history. Descriptive, Chi-square and regression analyses were performed. RESULTS: Participants were aged between 30 and 89 years (M = 51, SD= 11.8) and 65.5% were female. The prevalence of diabetes was found to be 8.3%. The majority (93%) reported to have heard of diabetes, yet only 4% knew what a glucose tolerance test was. Only 50% reported that they knew physical inactivity was a risk factor. Age, gender, level of education and socio-economic status (SES) were significantly associated with KAP. A lower proportion (41%) of older participants (aged ≥65 years) reported that they knew that dietary modifications assist in diabetes control compared to those aged less than 35 years (69%), p<0.001. Males (ß = 0.393, 95% CI = 0.142-0.643), and any level of education compared to no schooling (ß = 0.726, 95% CI = 0.596, 0.857) reported significantly more knowledge, after multivariate adjustments for covariates. Participants aged under 35 years, (odds ratio (OR)= 1.73, 95% CI = 1.22-2.43) had significantly higher positive attitudes towards treatments of diabetes compared to those aged ≥65 years. Of the 99 people with known diabetes, more than 50% (n = 52) never had their blood sugar levels checked since diagnosis. CONCLUSIONS: Knowledge of diabetes and its risk factors is very limited in rural Bangladesh, even in persons diagnosed with type 2 DM. The development of public health programmes to increase knowledge of diabetes and its complications is required to assist people living in rural Bangladesh to control and management of diabetes.