Enantiomeric purity deviations of radiolabelled amino acids obtained from chiral columns

Enantiomeric purity (EP) is an important value which denotes the relative percentage of the L-isomer with respect to the D-isomer. For 11C and 18F-labelled amino acid (AA) radiopharmaceutical (RP) production, EP represents a quality control parameter specified in European and national monographs for particular RPs. In most instances, EP value of greater then 90 or 95% (depending on AA type) is required as part of the quality control (QC) value of a RP following radiosynthesis. In common practice, two chromatographic columns are used for the EP determination of RPs: Crownpak CR(+) (Daicel), which contains a crown ether stationary phase or Chirobiotic T (Astec), which contains silica-bound glycoproteins as the stationary phase. The application of column Crownpak CR(+) requires that only perchloric acid solution (with pH 1–2) may be used, as the retention capability of the stationary phase is greatly reduced using organic solvents. This work intends to identify which chromatographic system is more accurate and reliable for EP determination as part of QC. We performed a series of parallel injections of the same batch of the widely used AA RPs [11C]MET and [18F]FET on the two aforementioned columns. The EP determination using column Crownpak CR(+) consistently provided a lower EP value compared to the Chirobiotic T column; the EP deviation between the respective columns was found to range from 2.4–4.0% for the same RP sample. Furthermore, the EP value was influenced by a sample’s dilution factor, e.g. the EP was observed to increase up to 1.5% when the radioactive sample had a fivefold dilution factor. This phenomenon was consistent for both Crownpak CR(+) and Chirobiotic T columns. Finally, a series of standard solutions of non-radioactive methionine with various ratios of L-and D-isomers was analyzed. The data obtained for non-radioactive methionine confirmed that column Crownpak CR(+) incorrectly provided a higher D-enantiomer concentration, whereas Chirobiotic T was found to provide a lower D-enantiomer concentration of the same sample. The deviation from the theoretical EP value was between 0.67 and 1.92%.

Polyvinylpyrrolidone as a Corrosion Inhibitor for Carbon Steel in a Perchloric Acid Solution: Effect of Structural Size

Polymers are materials composed of macromolecules characterized by duplicates of smaller molecules that are covalently bonded together to provide a set of properties. Corrosion inhibition by such compounds is usually attributed to their adsorption on the metal-solution interface. The inhibition effect of different sizes of polyvinylpyrrolidone (PVP) on the corrosion of carbon steel (C-steel) in solutions of perchloric acid was investigated. The inhibition efficiency increases as the size of the inhibitor and its concentration increases, but decreases as the temperature increases and can reach a value of 81.53% and 5.0x10^-3 mol L^-1(PVP: 58,000 g mol^-1) at 30°C. The most remarkable inhibition efficiency was confirmed by the presence of the film formed on the metal surface by scanning electron microscopy. The kinetic and thermodynamic parameters for the corrosion of C-steel and adsorption of the inhibitor were determined and discussed. The combination of PVP with potassium iodide produced a strong synergistic effect on the inhibition of C-steel corrosion leading to a significant improvement in the inhibition efficiency. Quantum chemical parameters were studied using density functional theory to determine the possible relationship between the inhibitor and its electronic properties.

Experimental and Theoretical Studies of Eosin Y Dye as Corrosion Inhibitors for Carbon Steel in Perchloric Acid Solution

The adsorption behavior and the inhibition performance of Eosin Y Dye for carbon steel corrosion in 1 M perchloric acid solution have been carried using weight loss and scanning electron micrograph (SEM) techniques as well theoretical calculations based on density functional theory (DFT). The studied inhibitor concentrations were between 5´10-5 M and 5´10-3 M. Results obtained revealed that Eosin Y is an effective inhibitor and its inhibition efficiency increases with increasing concentration to attain 96.91% at 5´10-3 M at 30 °C. Thermodynamic parameters such as adsorption heat, adsorption entropy and adsorption free energy were obtained from experimental data of the temperature studies of the inhibition process at five temperatures ranging from 20 to 60 °C. It was found that the adsorption of Eosin Y could prevent steel from weight loss and the adsorption accorded with the Langmuir adsorption isotherm. The free energy of adsorption showed that the corrosion inhibition takes place by spontaneous physicochemical adsorption of inhibitor molecules on the carbon steel surface. SEM and DFT studies confirm the adsorption of Eosin Y on carbon steel surface. Copyright © 2020 BCREC Group. All rights reserved

Reverse Phase Chiral HPLC Method for Enantiomeric Excess Determination of 2-Aminobutanamide

A reverse phase chiral HPLC method was developed for the determination of (R)-2-aminobutanamide isomer content in (S)-2-amino-butanamide key starting material for levetiracetam drug substance by using a CROWNPAK CR (+) column. Perchloric acid solution (0.05 %) was used as mobile phase and the flow rate was finalized as 0.3 mL/min. UV detection wavelength was 200 nm and column temperature was set as 15 ºC. The limit of detection and limit of quantification were 0.0002 mg/mL and 0.0005 mg/mL, respectively. The linearity calibration curve of (R)-2-aminobutanamide was shown good from the range of 0.0005 mg/mL to 0.004 mg/mL. The recovery of (R)-2-aminobutanamide isomer was between the range of 93 to 106 % in presence of (S)-2-aminobutanamide. The method was validated and found to be precise, accurate and robust. The method can be used for determination of (R)-2-aminobutanamide in presence of (S)-2-aminobutanamide, which is the key intermediate for preparation of levetiracetam. This method was validated in as per ICH Q2 (R1) and USP validation of compendial methods (1225).

Electrocatalytic hydrogenation of guaiacol in diverse electrolytes using a slurry reactor

Electrocatalytic hydrogenation-hydrogenolysis (ECH) of guaiacol was performed in an H-cell type of slurry reactor configuration with Pt/C catalyst. Different pairs of electrolytes, in catholyte-anolyte combinations, were investigated by constant potential chronocoulometry, showing that the acidic anolyte is preferable for an effective ECH. The advantages of this slurry reactor are mainly attributed to the enhanced Faradaic efficiency and recoverability of the catalyst. High guaiacol conversion (>90%) can be achieved at mild conditions (307 K, 1 atm) in perchloric acid solution (0.5 M), resulting in 54% cyclohexanol selectivity at moderate Faradaic efficiency (53%) and low catalyst loading. This work opens up the possibility of renewable synthesis of valuable chemicals from biomass-derived substrates via electrocatalytic reduction process at mild conditions.