Solubility of Luteolin and Other Polyphenolic Compounds in Water, Nonpolar, Polar Aprotic and Protic Solvents by Applying FTIR/HPLC

In recent years, flavonoids have become a highly researched topic due to their health beneficial effects. Since flavonoids’ solubility plays a significant role in their use in pharmaceutical, food, biological, and chemical areas, the determination of suitable solvents is crucial. Fourier transform infrared (FTIR) analysis was used to characterize functional groups of several flavonoids and phenolic compounds, namely luteolin, hesperidin, quercetin, naringenin, gallic acid and tannic acid. Concentration dependence on transmittance was evaluated for these compounds in ethanol. Afterwards, luteolin was chosen as a model flavonoid, with its concentration correlated with transmittance using 15 solvents with different polarities. Luteolin solubility was further corroborated with high-performance liquid chromatography (HPLC). These results shed light on using FTIR as a semi-quantitative method for the initial screening of solvents and the solubility of different compounds while saving time and solvents. Hence, HPLC would only be needed as a final step for the most promising solvents.

The effect of protic solvents in the conversion of lignin from Earleaf Acacia tree

Lignin is one of main components of lignocellulosic along with cellulose and hemicellulose. It is a by-product of the paper and pulp industry, and has aromatic backbones making them an ideal renewable feedstock of aromatic compounds for a range of applications. Catalytic conversion of lignin from Earleaf Acacia tree was performed using high pressure/temperature reactor with Ru/C catalyst and protic solvents. The results showed that the conversion of lignin depends on the solvent polarity of protic solvents, and Ru/C catalyst enhanced the lignin conversion. Phenolic compounds are the main components of lignin conversion. Those compounds can be applied as a basement for bulk chemical and fuels.

18F-Fluorination Using Tri-Tert-Butanol Ammonium Iodide as Phase-Transfer Catalyst: An Alternative Minimalist Approach

The 18F syntheses of tracers for positron emission tomography (PET) typically require several steps, including extraction of [18F]fluoride from H2[18O]O, elution, and drying, prior to nucleophilic substitution reaction, being a laborious and time-consuming process. The elution of [18F]fluoride is commonly achieved by phase transfer catalysts (PTC) in aqueous solution, which makes azeotropic drying indispensable. The ideal PTC is characterized by a slightly basic nature, its capacity to elute [18F]fluoride with anhydrous solvents, and its efficient complex formation with [18F]fluoride during subsequent labeling. Herein, we developed tri-(tert-butanol)-methylammonium iodide (TBMA-I), a quaternary ammonium salt serving as the PTC for 18F-fluorination reactions. The favorable elution efficiency of [18F]fluoride using TBMA-I was demonstrated with aprotic and protic solvents, maintaining high 18F-recoveries of 96–99%. 18F-labeling reactions using TBMA-I as PTC were studied with aliphatic 1,3-ditosylpropane and aryl pinacol boronate esters as precursors, providing 18F-labeled products in moderate-to-high radiochemical yields. TBMA-I revealed adequate properties for application to 18F-fluorination reactions and could be used for elution of [18F]fluoride with MeOH, omitting an additional base and azeotropic drying prior to 18F-labeling. We speculate that the tert-alcohol functionality of TBMA-I promotes intermolecular hydrogen bonding, which enhances the elution efficiency and stability of [18F]fluoride during nucleophilic 18F-fluorination.

Synthesis and comparative solvatochromic studies of novel Mono azo ureido/thioureido benzimidazole dyes

Purpose This paper aims to synthesize new benzimidazole dyes aiming to study the solvent effects on their absorption in Ultraviolet-visible spectra. Design/methodology/approach Ureido/thioureido hydrazonamide benzimidazoles (U/THB) are prepared by condensation of N-aryl-1H-benzo[d]imidazole-2-carbohydrazonoyl bromides with ureido and/ or thioureido reagents. The target products are fully characterized for structural elucidation by means of their spectral and elemental methods. Solvatochromic behavior of U/THB dyes has been studied in different polar protic solvents at room temperature. Findings The absorption spectra distinguish two main bands at (350 nm–442 nm) and (308 nm–382 nm) referring to n-π* and π- π* transitions of the azo groups. Dimethyl formamide induces an extremely bathochromic transition comparing to the other protic solvents. The observed bathochromic shifts indicate strong interaction with solvents in the excited state. Most dyes show one absorbance in all solvents used, so they may exist in a single tautomeric form (hydrazo form). Research limitations/implications In the present paper, the synthesis of U/THB dyes was achieved by a simple and convenient pathway. In addition, the variations in substituents attached to the chromophoric moiety could also be studied. Practical implications The new U/THB dyes are accountable for providing good knowledge about their solvation and spectral properties of an order acceptable for industrial utilization. Social implications Synthesis of these new benzimidazole derivatives and study of their solvation and spectral properties provides good knowledge, which is very useful in many industrial applications (e.g. dye-sensitized solar cell, etc.). Originality/value The synthesized mono azo U/THB dyes are novel members in the benzimidazole family, where no details regarding the synthesis of such dyes are reported before in the literature. They are superior in terms of preparation, multiple applications and spectral properties.