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.     

英国索尔特高级化学课程(A2)教材配套复习材料Revise中有机化学知识的呈现特点与思考

针对与英国索尔特高级化学课程(A2)相匹配的复习材料Revise中有机化学内容的基本呈现方式、知识点的考查及习题设置特点进行相关分析,并对我国中学化学教材编写及其化学教学提出几点思考和启示。     

Development and validation of an HPLC method for tetracycline‐related USP monographs

A novel reversed‐phase HPLC method was developed and validated for the assay of tetracycline hydrochloride and the limit of 4‐epianhydrotetracycline hydrochloride impurity in tetracycline hydrochloride commercial bulk and pharmaceutical products. The method employed L1 (3 µm, 150 × 4.6 mm) columns, a mobile phase of 0.1% phosphoric acid and acetonitrile at a flow rate of 1.0 mL/min, and detection at 280 nm. The separation was performed in HPLC gradient mode. Forced degradation studies showed that tetracycline eluted as a spectrally pure peak and was well resolved from its degradation products. The fast degradation of tetracycline hydrochloride and 4‐epianhydrotetracycline hydrochloride in solution was retarded by controlling the autosampler temperature at 4 °C and using 0.1% H₃PO₄ as diluent. The robustness of the method was tested starting with the maximum variations allowed in the US Pharmacopeia (USP) general chapter Chromatography <621>. The method was linear over the range 80–120% of the assay concentration (0.1 mg/mL) for tetracycline hydrochloride and 50–150% of the acceptance criteria specified in the individual USP monographs for 4‐epianhydrotetracycline hydrochloride. The limit of quantification for 4‐epianhydrotetracycline hydrochloride was 0.1 µg/mL, 20 times lower than the acceptance criteria. The method was specific, precise, accurate and robust. Copyright © 2014 John Wiley & Sons, Ltd.     

Engineering the future of rheology within the UK

This short communication reviews the past, current and future state of rheology within the UK. It is a personal view that predicts in the future there will be significant changes in UK rheology, mainly because of the way universities, industry and most of all funding agencies have changed their priorities in the area of science and engineering.     

Electron energy loss spectra of the silicon 2p, 2s, carbon 1s and valence shells of tetramethylsilane

Inner shell excitation spectra of tetramethylsilane, (CH₃)₄Si, have been measured in the silicon 2s, 2p (L_I,II,III-shell) and carbon is (K-shell) regions using electron energy-loss spectroscopy at an impact energy of 2.5 keV and a scattering angle of ~1°. The high-resolution valence shell spectrum has also been observed at an impact energy of 3 keV and a zero degree scattering angle. The silicon 2p spectra are compared and contrasted with published photoabsorption spectra of SiF₄, SiH₄, and other related Si-containing molecules with varying ligands.     

The British Put Option

Abstract

We present a new put option where the holder enjoys the early exercise feature of American options whereupon his payoff (deliverable immediately) is the ‘best prediction’ of the European payoff under the hypothesis that the true drift of the stock price equals a contract drift. Inherent in this is a protection feature which is key to the British put option. Should the option holder believe the true drift of the stock price to be unfavourable (based upon the observed price movements) he can substitute the true drift with the contract drift and minimize his losses. The practical implications of this protection feature are most remarkable as not only can the option holder exercise at or above the strike price to a substantial reimbursement of the original option price (covering the ability to sell in a liquid option market completely endogenously) but also when the stock price movements are favourable he will generally receive higher returns at a lesser price. We derive a closed form expression for the arbitrage-free price in terms of the rational exercise boundary and show that the rational exercise boundary itself can be characterized as the unique solution to a nonlinear integral equation. Using these results we perform a financial analysis of the British put option that leads to the conclusions above and shows that with the contract drift properly selected the British put option becomes a very attractive alternative to the classic American put.     

An approach to the ionic cholinergic interaction. Theoretical treatment of the interaction between tetramethylammonium and acetate ions

The interaction between the anionic site of cholinesterase and the cationic end of acetylcholine is estimated by considering a simplified model. The effect of the aqueous environment on the stability of the aggregate is considered.     

A lanthanide induced shift (LIS) investigation of the conformation of cyclohexanones in solution

The solution conformations of cyclohexanone1 and 4-t-butyl cyclohexanone2 have been obtained by the use of the LIS given by Yb(fod)₃. A starting geometry for the substrates was obtained by molecular mechanics calculations. The use of a two-site model for lanthanide-substrate complexing, together with iteration on the¹H and¹³C induced shifts allowed the angle of pucker of the cyclohexanone rings to be determined. In contrast, a one-site model gave no acceptable solutions. The cyclohexanone ring is somewhat flatter at the carbonyl end than cyclohexane, the angle of pucker (α) being reduced from 51° to 49° i.e. the dihedral angle (ω₁₂) is reduced trom 56 to 51°. In 4-t-butyl-cyclohexanone the angle of pucker at the carbonyl end is further reduced. The solution conformation of1 agrees closely with that deduced by MM calculations; interestingly, the conformation of2 is essentially identical with the geometry found in the crystal.     

An equivalent cores calculation of solid-state and adsorbate shifts in X-ray photoelectron spectroscopy

An equivalent cores model is used to calculate the observed binding energy shifts in the X-ray photoelectron spectra of atoms when bonding to form a solid phase. Good agreement is found with experimental data both for the formation of elemental metals and for the adsorption of gases on metal surfaces.