Acetonitrile Water Research Articles

Diester Chlorogenoborate Complex: A New Naturally Occurring Boron-Containing Compound

The natural compounds of boron have many applications, primarily as a dietary supplement. The research is based on the discovery that the diester chlorogenoborate complex can be detected and quantified from green coffee beans. The study reports that such a diester molecule can also be synthesized in a stable form via the direct reaction of boric acid and chlorogenic acid in a mixture of acetonitrile–water (1:1, v/v) and left to evaporate over a period of 48 h at room temperature, resulting in a spirocyclic form (diester complex). The diester complex, with its molecular structure and digestibility attributes, has potential application as a prebiotic in gut health and oral health, and as a micronutrient essential for microbiota in humans and animals.

Thermodynamic Analysis of the Solubility of Propylparaben in Acetonitrile–Water Cosolvent Mixtures

Parabens are substances used in the food, pharmaceutical and cosmetic industries. Recent studies have indicated that these substances have toxic potential, cause endocrine disruption and can easily bioaccumulate; therefore, their physicochemical properties are of industrial, biological and environmental interest. Due to their potential use in the development of more efficient and cleaner processes, the design of environmental recovery strategies and more reasonable designs for solubility in cosolvent mixtures, studies of thermodynamic analysis and mathematical modeling are of great interest. This research studies the solubility of propylparaben in acetonitrile + water cosolvent mixtures at nine temperatures by UV/Vis spectrophotometry, analyzing the solid phase by differential scanning calorimetry to evaluate possible polymorphic changes. The solubility of propylparaben is an endothermic process, where phase separation occurs at intermediate mixtures, reaching its minimum solubility in pure water at 278.15 K and the maximum solubility in pure acetonitrile at 315.15 K. The experimental data are well-correlated with the va not Hoff, Apelblat and Buchowski–Ksiazaczak models. The results revealed that possible microheterogeneity of the MeCN + W mixture can generate phase separation in intermediate mixtures, possibly due to the formation of solvates or hydrates.

Reversible thermochromic systems based on a new library of flavylium spirolactone leuco dyes

The aim of this work was the design, synthesis, and characterization of new chromogenic spirolactone dyes based on a 2-phenyl-1-benzopyrylium (flavylium) backbone for further development of thermochromic smart labels. The influence of electron-donating and electron-withdrawing groups on the five synthesized dyes was studied in terms of color modification, acid-base behavior and thermochromic properties. By using UV–Vis absorption and emission spectroscopies, molar absorptivity, oscillator strength, Stokes shift, and fluorescence quantum yield were determined for each dye to evaluate the impact on color and excited state properties of the designed structures. The acid-base behavior and the ability to evolve towards leuco species was assessed by titrations with triethylamine and N,N-diisopropylethylamine in non-polar and polar aprotic solvents such as acetonitrile and octan-1-ol. In addition, the reversibility of the color was also evaluated by titrations with polar protic solvents (water and ethanol) and Lewis acids (gallic acid and iron(III) chloride). The number of equivalents of base/acid required to reach the leuco product and then to reverse the color were determined by representing the absorption maximum as a function of added base/acid in acetonitrile (water content less than 0.01-v/v). Finally, the thermochromic properties were evaluated in the presence of long-chain organic amines and water-insoluble solvents with melting points close to room temperature. The synthesized compounds can switch between two species if the appropriate conditions are used. Moreover, the tests carried out to assess their thermochromic behavior concluded that all dyes display thermochromism to some extent. The dyes that have electron-withdrawing groups attached, such as cyano, display stronger chromogenic effects useful for future applications.

Molecular Composition and Biological Activity of a Novel Acetonitrile-Water Extract of Lens Culinaris Medik in Murine Native Cells and Cell Lines Exposed to Different Chemotherapeutics Using Mass Spectrometry.

We evaluated the effects of a new extract (70% acetonitrile, 2E0217022196DIPFARMTDA) of Lens culinaris Medik (Terre di Altamura SRL, Altamura BA) to prevent cytotoxic damage from cisplatin, staurosporine, irinotecan, doxorubicin, and the glucocorticoid dexamethasone. The acetonitrile-water extract (range 0.1-5 mg/mL) was obtained by extracting 10 g of lentil flour with 50 milliliters of the acetonitrile-water extraction mixture in a 70:30 ratio, first for 3 h and then overnight in a shaker at room temperature. The next day, the extract was filtered and passed through a Rotavapor to obtain only the aqueous component and eliminate that with acetonitrile, and then freeze-dried to finally have the powdered extract. In vitro experiments showed that the extract prevented the cytotoxic damage induced by cisplatin, irinotecan, and doxorubicin on HEK293 and SHSY5Y cell lines after 24-96 h. In murine osteoblasts after 24-72 h of incubation time, the extract was cytoprotective against all chemicals. The extract was effective against dexamethasone, leading to synergic cell proliferation in all cell types. In bone marrow cells, the extract is cytoprotective after 72 h against doxorubicin, staurosporine, and dexamethasone. Instead, on muscle fibers, the extract has a synergic effect with chemotherapeutics, increasing cytotoxicity induced by doxorubicin and staurosporine. LC-MS attested to the existence of several phenolic structures in the extract. The most abundant families of compounds were flavonoids (25.7%) and mellitic acid (18%). Thus, the development of this extract could be implemented in the area of research related to the chemoprevention of damage to renal, neuronal, bone marrow cells, and osteoblasts by chemotherapeutics; moreover, it could be used as a reinforcer of cytotoxic action of chemotherapeutics on muscle fibers.

Ionization and lipophilicity in nonpolar media mimicking the cell membrane interior

Ionization and lipophilicity may vary with the environment. Therefore, in this study we provide some insight in the performances of different experimental techniques (potentiometry, UV–vis, shake-flask and chromatography) to determine ionization and lipophilicity in more nonpolar systems than those commonly used in drug discovery. To this purpose a pool of 11 compounds of pharmaceutical interest was firstly submitted to a few experimental techniques to measure pKa in water, water/acetonitrile mixtures and pure acetonitrile. Then we measured logP/logD with shake-flask and potentiometry in octanol/water and toluene/water and also determined a chromatographic lipophilicity index (log k’80 PLRP-S) in a nonpolar system.Results show that ionization decreases for both acids and bases in a coherent, significant but not dramatical extent when water is present in the system, but the picture is completely different in pure acetonitrile. Lipophilicity may vary or not with the environment according to the chemical structure of the investigated compounds as also revealed by electrostatic potential maps. Since the internal core of cell membranes is largely nonpolar, our results support the need of extending the pool of physicochemical descriptors to be determined in the various stages of drug discovery programs and indicate some experimental strategies for their determination.

Rapid LC-MS/MS Bosutinib Quantification with Applications in Metabolic Stability Estimation

Bosutinib (BOS) is FDA approved drug for the treatment of chronic phase (CP) Philadelphia chromosome-positive (Ph+) chronic myelogenous leukemia (CML). We report a fast, sensitive, and simple LC-MS/MS method, validated for the determination of BOS in human liver microsomes, utilizing tofacitinib (TOF) as the internal standard. The separation of BOS and TOF was done using a 1.8 μm C18 column (2.1 × 50 mm) at room temperature using the isocratic elution system of acetonitrile-water (30:70, v/v) containing 0.1 M formic acid at a flow rate of 0.15 mL/min, and a triple-quadrupole tandem mass spectrometer (TQD-MS) with an electrospray ionization (ESI) source that was operated in the positive ion mode. The method was validated according to the European Medicines Agency, and the rapid and specific quantification of BOS in human liver microsomes was achieved in the range of 5-200 ng/mL, with a determination coefficient of 0.999. Intra- and inter-day accuracy and precision values were <4% in all cases. The procedure is rapid, specific, reliable, and can be applied in metabolic stability evaluations since it is the first LC-MS/MS method specific to BOS quantification. The metabolic stability assessment of BOS showed high CLint (34.3 µL/min/mg) and short in vitro t1/2 values of 20.21 min, indicating that BOS may be rapidly eliminated from the blood by the liver.

Determination of sugars and sugar alcohols in infant formula by high performance liquid chromatography with evaporative light-scattering detector

A method was established for the simultaneous determination of five sugars (fructose, glucose, sucrose, lactose, maltose) and five sugar alcohols (erythritol, xylitol, sorbitol, mannitol, maltitol) in infant formula by high performance liquid chromatography-evaporative light scattering detector. After the samples were extracted with acetonitrile–water solution, precipitated by acetic acid, and purified with solid phase extraction cartridge, ALLChrom Rocksil Carbohydrate ES column was adopted for separation, and isocratic elution was conducted at the flow rate of 1.0 mL/min with acetonitrile-0.04 % ammonia solution as the mobile phase. The analytes were detected by an evaporative light-scattering detector, and quantified by external standard method. The linear ranges of the 10 components were 0.04–4.0 g/L with the correlation coefficients greater than 0.999, and the limits of quantification (S/N = 10) of the method were 0.08–0.4 g/100 g. The relative standard deviation of the lactose parallel samples reached 1.29 %, and the recoveries of the other 9 components ranged from 80.4 % to 99.4 % with the relative standard deviation of 2.8 %-7.1 %. The method performs well in sensitivity and separation, which is suitable for the simultaneous quantitative determination of sugars and sugar alcohols in infant formula.

Hydrolytic Stability of Unsubstituted Hydrazones of Aromatic Carbonyl Compounds in Reversed-Phase HPLC

Unsubstituted hydrazones RR′C=NNH2 are unstable during gas chromatographic separation. Testing of their resistance to hydrolysis under reversed-phase HPLC showed that aromatic ketone hydrazones are stable. In contrast, aldehyde hydrazones are only stable in neutral methanol–water systems (in the absence of acidic modifiers). In acetonitrile–water systems containing 0.1% of formic acid, only aromatic ketone hydrazones are stable, while aldehyde derivatives are completely hydrolyzed. This difference in stability must be taken into account in determining other compounds of these classes. To detect the hydrolysis of analytes, we compared the retention indices of the initial carbonyl compounds and hydrazones at different volume ratios of organic modifiers and aqueous phases and different pH values of the eluent, the relative absorbance values of the characterized components A(254/220) = A(254)/A(220), and the chromatography–mass spectrometric data.

Relationships of Enantioselective Retention of Chiral Oxazolopyrroloquinolones on a Stationary Phase with Grafted Ristocetin А Antibiotic from Aqueous Methanol Solutions

The mechanisms of retention and separation of the enantiomers of chiral oxazolopyrroloquinolones on a stationary phase with graftеd macrocyclic antibiotic ristocetin A under conditions of high-performance liquid chromatography with aqueous methanol mobile phases have been studied. The retention factor was found to decrease monotonically when the CH3OH concentration in the mobile phase increased to 90 vol %; then it slightly increased as the composition of the mobile phase approached pure methanol. The thermodynamics of adsorption of oxazolopyrroloquinolones in different regions of this dependence was studied. A mathematical model has been proposed; it describes well the experimental data and allows for analyte solvation in the mobile phase and competitive adsorption (with mobile phase components) on a chiral selector. The results were compared with previously obtained data for water–acetonitrile mobile phases. The reasons for the observed differences were discussed.

Establishment of LC-MS/MS Method for Determination of GMDTC in Rat Plasma and Its Application in Preclinical Pharmacokinetics.

Sodium (S)-2-(dithiocarboxylato((2S,3R,4R,5R)-2,3,4,5,6-pentahydroxyhexyl)amino)-4(methylthio)butanoate (GMDTC) is the first compound to use cadmium repellent as an indication. In this paper, we established and validated a bioanalytical method for the determination of GMDTC in rat plasma, and used it to determine the drug concentrations in the plasma of rats after intravenous dosing in different genders and dosages. After pretreating the plasma samples with an acetonitrile-water-ammonia solution (70:30:1.25, v/v/v), liquid chromatographic separations were efficiently achieved with a XBridge C18 column using a 5 min gradient system of aqueous ammonium bicarbonate and 95% acetonitrile-water solution (95:5, v/v) as the eluent. The GMDTC and metolazone (internal standard, IS) detection were carried out using high-performance liquid chromatography coupled with triple quadrupole mass spectrometry (LC-MS/MS), monitored at m/z 390.06-324.1 (for the GMDTC, tR: 2.03 min) and m/z 366.0-259.2 (for IS, tR: 3.88 min). The GMDTC was stable under various testing conditions, and this analytical method conforms to the verification standard of biological analysis methods. The half-life (t1/2) was determined to be 0.54-0.65 h for the intravenous, mean distribution volume and clearances were 1.08-2.08 L/kg and 1-3 L/h/kg, respectively. The AUC0-t and AUC0-∞ found after increasing the dosage exhibited a linear relationship with the administered dose. There were no statistically significant differences in the values obtained for the different genders at dosages of 50, 100 and 250 mg/kg, respectively (p > 0.05). This is the first report of a bioanalytical method to quantify GMDTC in rat plasma using LC-MS/MS, which provides useful information for the study of its pharmacological effects and clinical applications.

Liquid–liquid phase separation and crystallization of aspirin polymorphs from a water–acetonitrile mixed solvent medium through a swift cooling process

Screening of form-I and form-II polymorphs of the pharmaceutical solid aspirin in the vicinity of liquid–liquid phase separation in water–acetonitrile solvent mixtures through a novel swift cooling crystallization process is successfully attained.

Nanoscale carbon dot-embedded metal-organic framework for turn-on fluorescence detection of water in organic solvents.

An easy-to-use, highly selective, and real-time organic solvent quality assessment is desirable to detect water contamination in organic solvents. Herein, a one-step procedure using ultrasound irradiation was used for encapsulating nanoscale carbon dots (CDs) into metal-organic framework-199 (HKUST-1) to form CDs@HKUST-1 composite. The CDs@HKUST-1 exhibited very weak fluorescence due to photo-induced electron transfer (PET) from the CDs to the Cu2+ centers, acting as a fluorescent sensor in its off-state. The designed material can detect and discriminate water from other organic solvents, driven by turn-on fluorescence. This highly sensitive sensing platform could be applied for the detection of water in ethanol, acetonitrile, and acetone with wide linear detection ranges of 0-70% v/v, 2-12% v/v, and 10-50% v/v and limits of detection of 0.70% v/v, 0.59% v/v, and 1.08% v/v, respectively. The detection mechanism is attributed to the interruption of the PET process due to the release of fluorescent CDs after treatment with water. A smartphone-based quantitative test was successfully developed to monitor the water content in organic solvents utilizing CDs@HKUST-1 and a phone color processing application, thus making it possible to develop an on-site, real time and easy-to-use sensor for water detection.

SIMULTANEOUS DETERMINATION OF CHLOROGENIC ACIDS AND CAFFEINE BY REVERSED-PHASE HPLC

A variant of simultaneous determination of chlorogenic (monocaffeoylquinic and dicaffeoylquinic) acids and caffeine in coffee (drink) using reversed-phase chromatography with spectrophotometric detection has been developed. For separation, a gradient mode is proposed exploring of two components of the mobile phase containing 3 vol.% of formic acid and 6 and 20 vol.% acetonitrile in distilled water and chromatographic column 150×4.6 mm Symmetry C18, 3.5 μm. Column thermostat temperature is 30 °C. The choice of the type and concentration of the acidifier of the mobile phase is justified in the work. It has been established that the acidity of the mobile phases should not be lower than pH 2 in order to transfer most of the chlorogenic acids to the non-ionized state. The dependences of the retention of monocaffeoylquinic acids and caffeine on the concentration of acetonitrile and formic acid, which is more effective in the selectivity of separation compared to orthophosphoric acid in the mobile phase, are determined. The selectivity of the separation of these compounds depends more on the concentration of formic acid than on the concentration of acetonitrile. Concentrations of chlorogenic acids and caffeine were determined in drinks from two varieties of coffee, coffee husk (dried pericarp of coffee fruits) (produced in Vietnam) and for comparison of two more variants – Arabica coffee from roasted grains and from green decaffeinated grains from other manufacturers. It is shown that coffee husk is a valuable raw material for the preparation of an alternative drink. Thus, when using 1 g of coffee husk when brewing 100 ml of boiling water, a drink containing about 10 mg (per 100 ml) of monocaffeoylquinic acids, about 6 mg of dicaffeoylquinic acids and about 3 mg of caffeine was obtained. For citation: Blinova I.P., Oleinits E.Yu., Salasina Ya.Yu., Deineka V.I., Vu Thi Ngoc Anh, Nguyen Van Anh Simultaneous determination of chlorogenic acids and caffeine by reversed-phase HPLC. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 2. P. 45-52. DOI: 10.6060/ivkkt.20236602.6711.

Phosphorylated amelogenin N-terminal peptides regulate calcite crystal cluster formation in a water–acetonitrile system

The function of phosphorylated organic additives can be enhanced by changing the secondary structure of the organic matrix which may provide a new strategy for novel crystal synthesis.

Voltammetric and Fluorimetric Studies of Dibenzoylmethane on Glassy Carbon Electrodes and Its Interaction with Tetrakis (3,5-Dicarboxyphenoxy) Cavitand Derivative

Due to the medical importance of dibenzoylmethane, one of the aims of the study was to find an appropriate packing material and a biologically friendly co-solvent to help its introduction into living systems. Accordingly, redox properties of dibenzoylmethane were investigated on glassy carbon electrodes in acetonitrile and in 1-propanol with cyclic voltammetry, and showed a diffusion-controlled process. In the anodic window, an oxidation peak appeared at around 1.9 V in both solvents. Cycling repeatedly between 0 and 2 V, the reproducibility of this peak was acceptable, but when extending the window to higher potentials, the electrode deactivated, obviously due to electrode material. The addition of the investigated tetrakis(3,5-dicarboxyphenoxy) cavitand did not significantly change the voltammograms. Further electrochemical experiments showed that the coexistence of water in acetonitrile and 1-propanol drastically reduces the solubility of dibenzoylmethane. Moreover, very rapid electrode deactivation occurred and this fact made the use of electrochemical methods complicated. Considering that both the cavitand and dibenzoylmethane are soluble in dimethyl sulfoxide, the interaction of these species was investigated and formation of stable complexes was detected. This observation was verified with fluorescence quenching studies. The mixture of water and dimethyl sulphoxide also dramatically improved the solubility of the cavitand-dibenzoylmethane complex at high excess of water. The addition of cavitand improved the solubility of dibenzoylmethane, a property which supports the application of dibenzoylmethane in therapy.

Comparative Study of the Lipophilicity of Selected Anti-Androgenic and Blood Uric Acid Lowering Compounds.

This study aimed to evaluate the lipophilicity of a series substances lowering the concentration of uric acid in blood and anti-androgen drugs by thin-layer chromatography in reversed-phase systems (RP-TLC, RP-HPTLC) and computational methods. The chromatographic parameter of lipophilicity (RMW) of tested compounds was determined on three stationary phases, i.e., RP18F254, RP18WF254 and RP2F254, using ethanol-water, propan-2-ol-water and acetonitrile-water in various volume compositions as mobile phases. The chromatographic analysis led to determining the experimental value of the lipophilicity parameter for each of the tested compounds, including those for which the experimental value of the partition coefficient (logPexp) as a measure of lipophilicity is not well described in available databases, such as febuxostat, oxypurinol, ailanthone, abiraterone and teriflunomide. The chromatographic parameters of lipophilicity were compared with the logP values obtained with various software packages, such as AClogP, AlogPs, AlogP, MlogP, XlogP2, XlogP3, ACD/logP and logPKOWWIN. The obtained results indicate that, among selected chromatographic parameters of lipophilicity, both experimental and calculated logP values gave similar results, and these RP-TLC or RP-HPTLC systems can be successfully applied to estimate the lipophilicity of studied heterocyclic compounds belonging to two different pharmacological groups. This work also illustrates the similarity and difference existing between the tested compounds under study using the chemometric methods, such as principal component analysis (PCA) and cluster analysis (CA). In addition, a relatively new approach based on the sum of ranking differences (SRD) was used to compare the chromatographically obtained and theoretical lipophilicity descriptors of studied compounds.

An Efficient HPLC–PDA Coupled With Supel™ Tox DON SPE Approach for the Analysis of Deoxynivalenol Contamination in Cereal Grains and Feedstuffs in Jiangxi Province

Deoxynivalenol (DON) was commonly found in grains and feedstuffs, which can cause human chronic diseases. In this study, a quick and reliable method was developed for the determination of DON in grains and feedstuffs in Jiangxi Province market. The sample was extracted with acetonitrile–water (84:16, v/v), then purified by Supel™ Tox DON SPE column, and detected by high-performance liquid chromatography (HPLC). The results showed that the calibration curve of DON showed good linearity in the range of 0.01–10.0 μg/mL, and the correlation coefficient R2 = 0.9999. The recovery of DON in the spiked maize sample was 94.8–98.5% by spiking with DON at 0.2 µg/g, 1.0 µg/g, and 2.0 µg/g. The RSD was between 2.5 and 3.3%. This method was used to analyze 120 samples, including 90 grains and 30 feedstuffs, collected from the Jiangxi Province market. The results showed that 81 samples of grains were positive with 90.0% positive rates, and 30 samples of feedstuff were positive with 100% positive rates. Maximum concentration of DON was 0.7 μg/g in oat and 6.9 μg/g in wheat feedstuffs, respectively. Fortunately, the positive samples of grains were safe levels in comparison with National standards for food safety limits of mycotoxins in food (1.0 μg/g), while, the feedstuff of oats was over the Maximum Guideline Level of 16.7% (the Maximum Residue Limit, MRL is 5.0 μg/g). The results of this study about current DON pollution in the grains and feedstuffs on the Jiangxi Province market have not been previously reported.

Novel Validated LC-MS/MS Method For Simultaneous Estimation of Celecoxib and Amlodipine in Rat Plasma and Its Application to A Pharmacokinetic Study

The combination of celecoxib (CLX) and Amlodipine (AMD) was approved for hypertensive patients with osteoarthritis by US-FDA. Hence, a potential analytical method that can simultaneously quantify these two drugs is required. In view of this, a novel and fully validated liquid chromatography-electrospray ionization-tandem mass spectrometric (LC-ESI-MS/MS) method has been established for the quantification of CLX and AMD in rat plasma simultaneously. protein precipitation extraction technique was employed for the extraction of analytes and their deuterated analogues from rat plasma quantitatively. The analytes were separated using the mobile phase comprising of acetonitrile–water with 0.1% formic acid buffer (70:30 v/v) and a flow-rate of 1.0 mL/min and 10 min run time on Agilent SB-C18 analytical column. The multiple reaction monitoring transitions, m/z 504.7→98.1 for CLX, 492.8→129.3 for AMD; 385.6→102.8 for CLX-D4 and 496.8.5→412.3 for AMD-D4 were utilized for the analysis in order to attain high selectivity. The method showed good sensitivity and linearity in the range of the concentration 20–800 ng/mL for CLX and 0.25–10 ng/mL for AMD respectively. Moreover, the method also displayed decent accuracy (87.9-100.27% and 99.28-103.26%) for CLX and AMD and precision according to US-FDA guidelines. The precision values for inter- and intra-day were between 1.92.02-7.085% and 0.083-3.43% and for CLX and AMD respectively. Further, the results of the pharmacokinetic parameters including Cmax, tmax, AUC0-t, AUC0-∞ and t1/2 values of drugs indicated that the developed method is valuable for the successful quantification of the analytes in rat plasma. The developed method is significant and is useful for simultaneous quantification of CLX and AMD.

Comprehensive study on degradation profile of firocoxib and structural elucidation of its key degradation products

Firocoxib is widely used in veterinary medicine as a non-steroidal analgesic and anti-inflammatory drug substance. Herein, a comprehensive study on the degradation profile of firocoxib was performed through force degradation studies to understand its degradation profile and characterize its major degradation products (DPs). Firocoxib drug substance was subjected to acidic, alkaline, oxidation (H2O2, KMnO4, and K2Cr2O7), thermal (solid and solution state), and photolytic (solid and solution state) stress degradation, as recommended in the ICH guidelines. Firocoxib and its major DPs were adequately separated by investigational HPLC method, which utilized a HALO C18 (100 × 2.1 mm, 2.0 µm) column. Mobile phase-A for the HPLC method is composed of 0.1% formic acid in water and mobile phase-B acetonitrile. A total of six major DPs were observed for firocoxib drug substance under these stress degradation conditions. Structural elucidation of the DPs performed using liquid chromatography-high resolution mass spectrometry and comparison of their fragmentation profile with that of the parent compound. For further structural confirmation of two major DPs, DP-2 and DP-6 were isolated and purified from the stressed samples using a preparative HPLC and analyzed by comprehensive nuclear magnetic resonance (NMR) spectroscopy studies. Most probable mechanistic pathways for the formation of DPs of firocoxib under various stress degradation conditions were postulated to understand its degradation profile. Based on the results from forced degradation, firocoxib was found to be quite stable under basic and thermal conditions, and somewhat unstable under acidic, oxidative, and photolytic conditions. The results of this study should facilitate quality monitoring and establish a stability profile of firocoxib drug substance and drug products. These results may also assist in the design and development of new formulations made with firocoxib drug substance with desired shelf life.

Selective Photocatalytic Transformation of Lignin to Aromatic Chemicals by Crystalline Carbon Nitride in Water–Acetonitrile Solutions

The photocatalytic conversion of lignin to aromatic compounds in aqueous solutions is a promising approach. We herein report a crystalline carbon nitride prepared by high-temperature thermal polymerization and alkali-metal molten salt treatment, which was then applied in the selective conversion of lignin to aromatic compounds. The results showed that the tri-s-tri-C3N4 presented a relatively high activity and selectivity for the conversion of lignin in aqueous solutions. In a 95% water-acetonitrile solution, it achieved a relatively high conversation rate of lignin, reaching 62.00%, and the selectivity of the C-C bond cleavage was high, at 86.8%. The characterization results obtained by TEM, UV-vis/DRS, PL, and transient photocurrent response showed that the ultra-high activity of tri-s-tri-C3N4 was mainly due to the improvements in crystallinity and light absorption. Mechanism studies showed that the dispersion of the catalyst and the combination of lignin and catalyst in aqueous solvents with different acetonitrile ratios were the main factors affecting lignin conversion. As the water content in the solutions increased, the primary active sites were converted from h+ to ·O2-. This study revealed the interactions between lignin, photocatalysts, and reaction solutions, providing a theoretical basis for the photocatalytic conversion of lignin in aqueous solutions.