Alternate HPLC method for the analysis of tetrabutylammonium hydroxide in [18F]fluorodeoxythymidine (FLT)

Tetrabutylammonium hydroxide is a common reagent used in the synthesis of [¹⁸F]Fluorodeoxythymidine (FLT) for positron emission tomography imaging. The British Pharmacopeia monograph for the analysis of [¹⁸F]FLT was released in 2015 incorporating a HPLC method for the analysis of tetrabutylammonium hydroxide. We describe alternate HPLC conditions that mitigate the challenges in fulfilling the system suitability requirements such as signal to noise and symmetry factor that are specified in the monograph. Our method was validated by analyzing tetrabutylammonium hydroxide at a range of concentrations to determine the linearity (R²?=?0.994), accuracy (≤9.2%) and precision (≤3.2%). Our method does not affect the analysis of [¹⁸F]FLT and it complies with all requirements in the BP monograph.     

A tandem cross-coupling/S(N)Ar approach to functionalized carbazoles

A novel route to functionalized carbazoles utilizing a tandem Suzuki cross-coupling/SNAr protocol is described. This process was found to be compatible with a variety of electron-withdrawing groups including aldehydes, esters, and sulfones. Using this method, a concise total synthesis (four steps, 50% overall yield) of the carbazole alkaloid glycosinine was achieved.     

Spinodal decomposition in a model colloid-polymer mixture in microgravity

We study phase separation in a deeply quenched colloid-polymer mixture in microgravity on the International Space Station using small-angle light scattering and direct imaging. We observe a clear crossover from early-stage spinodal decomposition to late-stage, interfacial-tension-driven coarsening. Data acquired over 5 orders of magnitude in time show more than 3 orders of magnitude increase in domain size, following nearly the same evolution as that in binary liquid mixtures. The late-stage growth approaches the expected linear growth rate quite slowly.     

Fish and Chips: a microfluidic perfusion platform for monitoring zebrafish development

We have developed a multi-channel microfluidic perfusion platform for culturing zebrafish embryos and capturing live images of various tissues and organs inside the embryo. The Fish and Chips was micro-fabricated in silicon and glass for reproducibility and accuracy of the microfluidic structure. The microfluidic platform consists of three parts: a microfluidic gradient generator, a row of eight fish tanks, in which the fish embryos are individually placed, and eight output channels. The fluidic gradient generator supports dose-dependent drug and chemical studies. A unique perfusion system ensures a uniform and constant flow of media to the fish tank while the wastes are efficiently removed. The fish tanks restrict the embryo movements, except rotationally, for live imaging of internal tissues and organs. The embryos showed developmental abnormalities under the influence of the drug valproic acid (VPA).     

Mechanical Properties of Thermo-Reversible Colloid Liquid Crystal Composites

Abstract

The mechanical properties of concentrated dispersions of sterically-stabilised colloidal particles in nematic hosts are explored using a combination of optical microscopy and viscoelastic shear measurements. Starting from an initially homogeneous dispersion in an isotropic host, it is found that the kinetics of the isotropic-nematic transition lead to the formation of a percolated particle network that imparts surprising mechanical rigidity to the resulting colloid/liquid crystal composite. Specifically, the viscoelastic storage modulus G′ is observed to rise by approximately 5 orders of magnitude within a few degrees of the bulk isotropic-nematic transition temperature. Using 4-4′pentyl cyano-biphenyl as the solvent, the composite at room temperature is a self-supporting soft solid over a wide range of particle concentrations. The particle microstructure depends sensitively on thermal treatment and particle concentration and it is found that faster cooling enhances the visoelastic moduli of the composite. Also, several classes of network topology have been identified. In all cases studied to date, the particles can be redispsersed upon heating the solvent through the nematic-isotropic transition. The formation of the composite is therefore thermally reversible. A rigorous theory to account for the observed mechanical properties is not currently available.     

Assessment of pulmonary artery pulse wave velocity in children: An MRI pilot study

Purpose

To assess the feasibility of measuring pulmonary artery (PA) pulse wave velocity (PWV) in children breathing ambient air and 12% oxygen.

Methods

Velocity-encoded phase-contrast MR images of the PA were acquired in 15 children, aged 9–12 years, without evidence of cardiac or pulmonary diseases. PWV was derived as the ratio of flow to area changes during early systole. Each child was scanned twice, in air and after at least 20 minutes into inspiratory hypoxic challenge. Intra-observer and inter-observer variability and repeatability were also compared.

Results

PA PWV, which was successfully measured in all subjects, increased from 1.31 ± 0.32 m/s in air to 1.61 ± 0.58 m/s under hypoxic challenge (p = 0.03). Intra- and inter-observer coefficients of variations were 9.0% and 15.6% respectively. Good correlation within and between observers of r = 0.92 and r = 0.72 respectively was noted for PA PWV measurements. Mean (95% limit of agreement) intra- and inter-observer agreement on Bland–Altman analysis were − 0.02 m/s (− 0.41–0.38 m/s) and -0.28 m/s (− 1.06–0.49 m/s).

Conclusion

PA PWV measurement in children using velocity-encoded MRI is feasible, reproducible and sufficiently sensitive to detect differences in PA compliance between normoxia and hypoxia. This technique can be used to detect early changes of PA compliance and monitor PAH in children.     

Structure determination of Pt‐coated Au dumbbells via fluctuation X‐ray scattering

A fluctuation X‐ray scattering experiment has been carried out on platinum‐coated gold nanoparticles randomly oriented on a substrate. A complete algorithm for determining the electron density of an individual particle from diffraction patterns of many particles randomly oriented about a single axis is demonstrated. This algorithm operates on angular correlations among the measured intensity distributions and recovers the angular correlation functions of a single particle from measured diffraction patterns. Taking advantage of the cylindrical symmetry of the nanoparticles, a cylindrical slice model is proposed to reconstruct the structure of the nanoparticles by fitting the experimental ring angular auto‐correlation and small‐angle scattering data obtained from many scattering patterns. The physical meaning of the refined structure is discussed in terms of their statistical distributions of the shape and electron density profile.     

Shear banding and flow-concentration coupling in colloidal glasses

We report experiments on hard-sphere colloidal glasses that show a type of shear banding hitherto unobserved in soft glasses. We present a scenario that relates this to an instability due to shear-concentration coupling, a mechanism previously thought unimportant in these materials. Below a characteristic shear rate γ(c) we observe increasingly nonlinear and localized velocity profiles. We attribute this to very slight concentration gradients in the unstable flow regime. A simple model accounts for both the observed increase of γ(c) with concentration, and the fluctuations in the flow.