Determination of Letrozole in Tablet Formulations by Reversed Phase High Performance Liquid Chromatography

Purpose: To develop a simple, rapid, accurate and cost-effective reversed phase high performance liquid chromatography (RP-HPLC) method for letrozole in bulk and in tablets. Methods: Development of a method for the determination of letrozole, an anti-cancer drug, by RPHPLC was undertaken using a new mobile phase of acetonitrile:water (50:50, v/v). The eluent was monitored at 265 nm. Results: The optimized conditions developed showed a linear response from 160 to 240 μg/mL, with a correlation coefficient (R2) of 0.999. The limit of detection (LOD) and limit of quantification ( LOQ) were 136 and 160 μg/mL, respectively. The assay values for the two branded letrozole tablets tested were 99.2 and 100.2 %, respectively with % relative standard deviation (RSD) of 0.781 and 0.568, respectively. The bench top stability data of the drug in the mobile phase indicate that the drug was stable in the mobile phase for 24 h. Recovery data were good. Placebo study for specificity and interference of common excipients showed that the method was specific and free from interfering substances. Conclusion: Therefore, the fully validated method developed was sensitive enough to carry out routine analysis of letrozole in tablet formulations with regard to its run time, simplicity of sample preparation and accuracy

Flower-like Layered NiCu-LDH/MXene Nanocomposites as an Anodic Material for Electrocatalytic Oxidation of Methanol

Direct methanol fuel cell (DMFC) technology has grabbed much attention from researchers worldwide in the realm of green and renewable energy-generating technologies. Practical applications of DMFCs are marked by the development of highly active, efficient, economical, and long-lasting anode catalysts. Layered double hydroxide (LDH) nanohybrids are found to be efficient electrode materials for methanol oxidation. In this study, we synthesized NiCu-LDH/MXene nanocomposites (NCMs) and investigated their electrochemical performance for methanol oxidation. The formation of NCM was verified through field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller (BET), and X-ray photoemission spectroscopy (XPS) analyses. The cyclic voltammetry, chronoamperometry, and electron impedance spectroscopy techniques were carried out to assess the electrocatalytic ability of the methanol oxidation reaction. The incorporation of MXene enhanced the methanol oxidation 2-fold times higher than NiCu-LDH. NCM-45 exhibited high peak current density (86.9 mA cm–2), enhanced electrochemical active surface area (7.625 cm2), and long-term stability (77.8% retention after 500 cycles). The superior performance of NCM can be attributed to the synergistic effect between Ni and Cu and, further, the electronic coupling between LDH and MXene. Based on the results, NCM nanocomposite is an efficient anodic material for the electrocatalytic oxidation of methanol. This study will open the door for the development of various LDH/MXene nanocomposite electrode materials for the application of direct methanol fuel cells

Harvesting CaCO₃ Polymorphs from In Situ CO₂ Capture Process

The in situ sequestration of CO₂ using alkanolamine and organometallic calcium (OMC) offers an ecofriendly method for synthesizing a diverse range of calcite, vaterite, and aragonite polymorphs of CaCO₃. Aqueous <i>N</i>-methyldiethanolamine (MDEA) has high CO₂ loading capacity with low regeneration energy, but rate of CO₂ absorption was found to be slow. The driving force for the binding between CO₂ and MDEA could be enhanced by the presence of bovine carbonic anhydrase (bCA). The absorbed CO₂ was converted to stable carbonates through the addition of an OMC. The bCA enzyme both accelerated the CO₂ absorption and mineralization in the amine–CO₂–OMC system and improved the catalytic efficiency to 1.07 × 10⁴ M^–1 s^–1. The enthalpy of in situ mineralization, the mechanism underlying the CO₂ absorption process, and the formation of an aggregated composition of CaCO₃ were examined using calorimetric, NMR, and X-ray diffraction techniques, respectively. The crystal formation depended crucially on the mineralization process involving the anions of the OMC precursors. The CaO-based sorbents derived from the CaCO₃ polymorphs shows good CO₂ capture capacity on combustion process, and the consecutive re-formation–regeneration cycles of the CaO sorbents followed the trend aragonite > vaterite > calcite. Hence, the MDEA–OMC–bCA system offers a promising method for transitioning between CaCO₃ polymorphs

Carbonic Anhydrase Promotes the Absorption Rate of CO₂ in Post-Combustion Processes

The rate of carbon dioxide (CO₂) absorption by monoethanol amine (MEA), diethanol amine (DEA), <i>N</i>-methyl-2,2′-iminodiethanol (MDEA), and 2-amino-2-methyl 1-propanol (AMP) solutions was found to be enhanced by the addition of bovine carbonic anhydrase (CA), has been investigated using a vapor–liquid equilibrium (VLE) device. The enthalpy (−Δ<i>H</i>_abs) of CO₂ absorption and the absorption capacities of aqueous amines were measured in the presence and/or absence of CA enzyme via differential reaction calorimeter (DRC). The reaction temperature (Δ<i>T</i>) under adiabatic conditions was determined based on the DRC analysis. Bicarbonate and carbamate species formation mechanisms were elucidated by ¹H and ¹³C NMR spectral analysis. The overall CO₂ absorption rate (flux) and rate constant (<i>k</i>_app) followed the order MEA > DEA > AMP > MDEA in the absence or presence of CA. Hydration of CO₂ by MDEA in the presence of CA directly produced bicarbonate, whereas AMP produced unstable carbamate intermediate, then underwent hydrolytic reaction and converted to bicarbonate. The MDEA > AMP > DEA > MEA reverse ordering of the enhanced CO₂ flux and <i>k</i>_app in the presence of CA was due to bicarbonate formation by the tertiary and sterically hindered amines. Thus, CA increased the rate of CO₂ absorption by MDEA by a factor of 3 relative to the rate of absorption by MDEA alone. The thermal effects suggested that CA yielded a higher activity at 40 °C

CO₂ Absorption and Sequestration as Various Polymorphs of CaCO₃ Using Sterically Hindered Amine

One aspect of the attempt to restrain global warming is the reduction of the levels of atmospheric CO₂ produced by fossil fuel power systems. This study attempted to develop a method that reduces CO₂ emissions by investigating the absorption of CO₂ into sterically hindered amine 2-amino-2-methyl-1-propanol (AMP), the acceleration of the absorption rate by using the enzyme carbonic anhydrase (CA), and the conversion of the absorption product to stable carbonates. CO₂ absorbed by AMP is converted via a zwitterion mechanism to bicarbonate species; the presence of these anions was confirmed with ¹H and ¹³C NMR spectral analysis. The catalytic efficiency (<i>k</i>_cat/<i>K</i>_m), CO₂ absorption capacities, and enthalpy changes (Δ<i>H</i>_abs) of aqueous AMP in the presence or absence of CA were found to be 2.61 × 10⁶ or 1.35 × 10² M^–1 s^–1, 0.97 or 0.96 mol/mol, and −69 or −67 kJ/mol, respectively. The carbonation of AMP-absorbed CO₂ was performed by using various Ca²⁺ sources, viz., CaCl₂ (CAC), Ca­(OOCCH₃)₂ (CAA), and Ca­(OOCCH₂CH₃)₂ (CAP), to obtain various polymorphs of CaCO₃. The yields of CaCO₃ from the Ca²⁺ sources were found in the order CAP > CAA > CAC as a result of the effects of the corresponding anions. CAC produces pure rhombohedral calcite, and CAA and CAP produce the unusual phase transformation of calcite to spherical vaterite crystals. Thus, AMP in combination with CAA and CAP can be used as a CO₂ absorbent and buffering agent for the sequestration of CO₂ in porous CaCO₃