A combined SAXS/WAXS investigation of the phase behaviour of di-polyenoic membrane lipids

AbstractReal-time measurements of the SAXS/WAXS diffraction patterns of aqueous dispersions (1:1 wt/wt) of the di-polyenoic lipids di-18:2 PC, di-18:3 PC, di-18:2 PE and di-18:3 PE were made over the temperature range 10° to about −80°C. The results of these measurements were compared to similar measurements performed on the corresponding di-18:0 and di-18:1 derivatives. SAXS measurements of the temperature dependence of lamellar repeat distances show that the di-polyenoic lipids undergo broad second-order transitions between their gel and liquid-crystal lamellar phases spanning 30–40°C. The di-18:1 and di-18:0 derivatives, in contrast, undergo abrupt first-order transitions. The gel phases of the di-18:0 derivatives are characterised by two-component WAXS patterns with a sharp component close to 0.42 nm and a broader component at narrower spacings. On cooling, these lipids appear to undergo an initial transition to an Lβ, phase followed by a conversion to an Lc phase. The gel phases of the di-18:1 derivatives also show two-component patterns but with the sharp component centred closer to 0.44 nm. The di-polyenoic lipids, in contrast, are characterised by a single broad peak centred at a spacing of about 0.42 nm, close to that of conventional Lβ, phases. The changes in lamellar repeat distance accompanying the transitions in the di-monoenoic and di-polyenoic lipids, all of which occur in the frozen state, are very similar, indicating that the acyl chains of the polyenoic lipids are close to their maximum extension in the gel state. The WAXS patterns of the polyenoic lipids suggest that the saturated upper parts of the acyl chains are packed on a regular hexagonal lattice while their polyunsaturated termini remain relatively disordered

The development and validation of a scoring tool to predict the operative duration of elective laparoscopic cholecystectomy

Background: The ability to accurately predict operative duration has the potential to optimise theatre efficiency and utilisation, thus reducing costs and increasing staff and patient satisfaction. With laparoscopic cholecystectomy being one of the most commonly performed procedures worldwide, a tool to predict operative duration could be extremely beneficial to healthcare organisations. Methods: Data collected from the CholeS study on patients undergoing cholecystectomy in UK and Irish hospitals between 04/2014 and 05/2014 were used to study operative duration. A multivariable binary logistic regression model was produced in order to identify significant independent predictors of long (> 90 min) operations. The resulting model was converted to a risk score, which was subsequently validated on second cohort of patients using ROC curves. Results: After exclusions, data were available for 7227 patients in the derivation (CholeS) cohort. The median operative duration was 60 min (interquartile range 45–85), with 17.7% of operations lasting longer than 90 min. Ten factors were found to be significant independent predictors of operative durations > 90 min, including ASA, age, previous surgical admissions, BMI, gallbladder wall thickness and CBD diameter. A risk score was then produced from these factors, and applied to a cohort of 2405 patients from a tertiary centre for external validation. This returned an area under the ROC curve of 0.708 (SE = 0.013, p  90 min increasing more than eightfold from 5.1 to 41.8% in the extremes of the score. Conclusion: The scoring tool produced in this study was found to be significantly predictive of long operative durations on validation in an external cohort. As such, the tool may have the potential to enable organisations to better organise theatre lists and deliver greater efficiencies in care

A double area detector system for simultaneous small and wide-angle X-ray scattering

A novel area detector has been designed for material science SR studies, capable of simultaneously collecting the diffraction data in two angular regimes. The detector for collecting wide-angle X-ray scattering (WAXS) data consists of four taper-coupled CCDs arranged as a 2 x 2 mosaic with a central aperture about 40 mm in diameter, so permitting the inclusion of a distant on-axis CCD detector for small-angle X-ray scattering (SAXS). The distance of the SAXS detector from the sample can be varied over the range of 0.27m to about 2m. The overall aperture of WAXS detector is approximately 200 x 200mm2 allowing the measurement of the diffraction patterns from 5o to 45o with an average angular resolution of 0.05o. The parallax error for large angles is substantially reduced as the individual WAXS CCDs are tilted towards the specimen location. both WAXS and SAXS diffraction data are simultaneously collected at 30 MB/s data rate, which is equivalent to 6 complete frames per second. Each pixel value is digitised using low- and high gain Analogue-to-Digital Converters (ADCs) which effectively increase the detector's overall dynamic range. The detector will be used in the study of a whole range of time-dependent phenomena, most importantly reaction kinetics, materials processing and real-time deformation studies. This paper discusses the unusual geometry fo the system, how it relates to design optimisation and the techniques for recovering combined SAXS/WAXS patters

Development of large area CCD-based X-ray detector for macromolecular crystallography

Discussed is the design and development of an area CCD-based X-ray detector system that uses the first CCD imagers specially designed for macromolecular crystallography. The system is intended to produce the highest quality data for physically small crystals at synchrotron sources through the use of CCDs. The readout noise is 5 electrons rms at a 1 MHz pixel rate at the high responsivity setting

Development of large area CCD-based X-ray detector for macromolecular crystallography

Discussed is the design and development of an area CCD-based X-ray detector system that uses the first CCD imagers specially designed for macromolecular crystallography. The system is intended to produce the highest quality data for physically small crystals at synchrotron sources through the use of CCDs. The readout noise is 5 electrons rms at a 1 MHz pixel rate at the high responsivity setting.</p