The Development and Validation of a Stability-Indicating UHPLC-DAD Method for Determination of Perindopril l-Arginine in Bulk Substance and Pharmaceutical Dosage Form

A stability-indicating ultra-high-performance liquid chromatography (UHPLC) method with a diode array detector was developed and validated for the determination of cis/trans isomers of perindopril l-arginine in bulk substance and pharmaceutical dosage form. The separation was achieved on a Poroshell 120 Hilic (4.6 × 150 mm, 2.7 µm) column using a mobile phase composed of acetonitrile–0.1 % formic acid (20:80 v/v) at a flow rate of 1 mL min^?1. The injection volume was 5.0 µL and the wavelength of detection was controlled at 230 nm. The selectivity of the UHPLC-DAD method was confirmed by determining perindopril l-arginine in the presence of degradation products formed during acid–base hydrolysis and oxidation as well as degradation in the solid state, at an increased relative air humidity and in dry air. The method’s linearity was investigated in the ranges 0.40–1.40 µg mL^?1 for isomer I and 0.40–2.40 µg mL^?1 for isomer II of perindopril l-arginine. The UHPLC-DAD method met the precision and accuracy criteria for the determination of the isomers of perindopril l-arginine. The limits of detection and quantitation were 0.1503 and 0.4555 µg mL^?1 for isomer I and 0.0356 and 0.1078 µg mL^?1 for isomer II, respectively.     

An Approach to Transfer Methods from HPLC to UHPLC Techniques in Some Carbapenems

Stability-indicating LC methods were developed and validated for the quantitative determination of doripenem, meropenem and tebipenem in the presence of their degradation products formed during forced degradation studies. Isocratic HPLC and UHPLC separations were performed with a core–shell Kinetex 1.7, 2.6 and 5 µm, all C18, 100A, 100 × 2.1 mm columns and the mobile phase composed of acetonitrile and 12 mmol L⁻¹ ammonium acetate in different ratios. The flow rates of the mobile phase were: 0.5 mL min⁻¹ for 1.7 µm column, and 1.0 mL min⁻¹ for 2.6 and 5 µm ones. Detection wavelength was 298 nm and temperature was set at 30 °C. All analysed drugs were exposed to stress conditions which caused their hydrolysis and thermal degradation. The methods were validated by evaluation of linearity, accuracy, precision, selectivity and robustness. Proposed methods were successfully applied for the determination of investigated antibiotics during kinetic studies in aqueous solutions and in the solid state. The advantages of chromatographic procedures which are based on the use of C18 stationary phases with different particle sizes in the analysis of selected carbapenems were discussed.

     

Photosensitized Damage Inflicted on Plasma Membranes of Live Cells by An Extracellular Generator of Singlet Oxygen—A Linear Dependence of A Lethal Dose on Light Intensity

We describe a study of the influence of a dose rate, i.e. light intensity or photon flux, on the efficiency of induction of a loss of integrity of plasma membranes of live cells in culture. The influence of a photon flux on the size of the light dose, which was capable of causing lethal effects, was measured in an experimental system where singlet oxygen was generated exclusively outside of live cells by ruthenium(II) phenantroline complex. Instantaneous, sensitive detection of a loss of integrity of a plasma membrane was achieved by fluorescence confocal imaging of the entry of this complex into a cell interior. We demonstrate that the size of the lethal dose of light is directly proportional to the intensity of the exciting light. Thus, the probability of a photon of the exciting light inflicting photosensitized damage on plasma membranes diminishes with increasing density of the incident photons.     

Simple and Efficient Method for the Protection of Hydroxyl Groups as 4-Methoxybenzyl Ethers

PMB ethers of alcohols are obtained in good yields and under mild conditions using the 4-methoxybenzyl N-allyl thiocarbamate and N-bromosuccinimide (NBS)/TfOH as the catalyst. The present method is very fast, simple, and efficient.     

Enantioselective addition of phenylacetylene to aldehydes catalyzed by a d-glucosamine-derived sulfonamide-titanium complex

We present the synthesis of β-hydroxy sulfonamides derived from d-glucosamine and their application as ligands in titanium tetraisopropoxide promoted enantioselective addition of phenylacetylene to benzaldehyde and selected aromatic and aliphatic aldehydes. The N-3,5-bis(trifluoromethyl)benzenesulfonamido-d-glucosamine derivative was chosen as the most efficient ligand for this addition. The reaction is highly enantioselective for several aromatic aldehydes and enantiomeric excesses up to 92% were obtained.     

Thiol-functionalized anthraquinones: mass spectrometry and electrochemical studies

Abstract  

In this work, the synthesis of various thiol-functionalized anthraquinone compounds is presented. The studied compounds were characterized by mass spectrometry and the main fragmentation pathways are discussed. The compounds studied formed stable self-assembled monolayers (SAMs) in the gold surface. The parameters for the reduction processes in the gold surface of the studied new anthraquinones were determined by cyclic voltamperometry tests.     

Stability and structure of mixed-ligand metal ion complexes that contain Ni2+, Cu2+, or Zn2+, and Histamine, as well as adenosine 5'-triphosphate (ATP4-) or uridine 5'-triphosphate (UTP(4-): an intricate network of equilibria

With a view on protein–nucleic acid interactions in the presence of metal ions we studied the “simple” mixed‐ligand model systems containing histamine (Ha), the metal ions Ni²⁺, Cu²⁺, or Zn²⁺ (M²⁺), and the nucleotides adenosine 5′‐triphosphate (ATP^4?) or uridine 5′‐triphosphate (UTP^4?), which will both be referred to as nucleoside 5′‐triphosphate (NTP^4?) . The stability constants of the ternary M(NTP)(Ha)^2? complexes were determined in aqueous solution by potentiometric pH titrations. We show for both ternary‐complex types, M(ATP)(Ha)^2? and M(UTP)(Ha)^2?, that intramolecular stacking between the nucleobase and the imidazole residue occurs and that the stacking intensity is approximately the same for a given M²⁺ in both types of complexes: The formation degree of the intramolecular stacks is estimated to be 20 to 50 %. Consequently, in protein–nucleic acid interactions imidazole–nucleobase stacks may well be of relevance. Furthermore, the well‐known formation of macrochelates in binary M²⁺ complexes of purine nucleotides, that is, the phosphate‐coordinated M²⁺ interacts with N7, is confirmed for the M(ATP)^2? complexes. It is concluded that upon formation of the mixed‐ligand complexes the M²⁺? N7 bond is broken and the energy needed for this process corresponds to the stability differences determined for the M(UTP)(Ha)^2? and M(ATP)(Ha)^2? complexes. It is, therefore, possible to calculate from these stability differences of the ternary complexes the formation degrees of the binary macrochelates: The closed forms amount to (65±10) %, (75±8) %, and (31±14) % for Ni(ATP)^2?, Cu(ATP)^2?, and Zn(ATP)^2?, respectively, and these percentages agree excellently with previous results obtained by different methods, confirming thus the internal validity of the data and the arguments used in the evaluation processes. Based on the overall results it is suggested that M(ATP)^2? species, when bound to an enzyme, may exist in a closed macrochelated form only, if no enzyme groups coordinate directly to the metal ion.