Melatonin is an indoleamine with functions as neurohormone, that is well known as pharmaceutical or healthcare product. Like many pharmaceutical compounds, melatonin is recognized to be an unstable molecule, principally sensitive to light and high temperatures. Storage conditions, including temperature and light, over different storage periods have been considered as important factors in melatonin degradation. This research describes for the first time, the utilization of natural deep eutectic solvents (NADES) as green alternatives to organic solvents for improving the stability of the hormone under various storage conditions. The results showed that temperature and light effect on melatonin content during the storage presented a diverse behavior according to the solvent. At low temperatures, the hydrophilic eutectic systems based on choline chloride-glycerol and lactic acid-glucose, along with water, were the most effective in extending the shelf life of the hormone compared to conventional solvents. However, at high temperature, this behavior was reversed. Regarding the effect of light, it significantly affects the stability of melatonin, primarily UV exposure. The eutectic systems appear to be the best medium for melatonin stability under this condition. These findings highlight the potential of NADES for their protective role in the stability of the compound that could be explained in terms of their viscosity and the hydrogen bond interactions within the solute and the eutectic systems.
Acidic ionic liquids are a subset of ionic liquids where the cation or anion possess acidic properties with huge applications in various fields. Here we describe environmentally safe and highly efficient conjugate addition of aromatic and aliphatic amines to α, β-unsaturated compounds in the presence of novel acidic ionic liquids. The acidic ionic liquid catalyst was prepared by combining benzyl chloride with 2-(dimethylamino) ethanol and SnCl2 in a simpler manner. The resulting acidic ionic liquid was characterized using SEM, EDS and FTIR spectroscopy. In the presence of ionic liquids, a wide variety of amines undergo facile conjugate addition to α, β-unsaturated compounds affording the corresponding β-amino compounds in good to excellent yields (72–97 %), shorter reaction times (1–4 h) and mild reaction conditions (60 °C). Furthermore, the study demonstrated the sustainability of the process by showcasing that the acidic ionic liquids could be reclaimed and reused for up to five cycles without compromising their catalytic effectiveness.
The study is dedicated to the investigation of the catalytic activity of zinc carboxylates in the condensation reaction of camphor with aliphatic diamines. The reaction of camphor with 1,6-hexanediamine was selected as the model system. The research demonstrated that the reaction does not proceed without a catalyst, while the use of zinc carboxylates as catalysts leads to a higher conversion and selectivity compared to the classical catalyst for this reaction, Et2O∙BF3. The best results were achieved using zinc 2-ethylhexanoate, which provided an 88.4 % conversion of camphor and a 76.9 % selectivity for the formation of diimine. It was established that the catalytic activity of zinc carboxylates in the condensation reaction of camphor with diamines is related to the structure of the acid residue of the salt. Based on the obtained data, a reaction mechanism was proposed, associated with the formation of a complex between the zinc carboxylate and the initial amine, which is confirmed by FTIR and UV–vis spectroscopic data.
This study presents a facile method for assessing the effect of anion functional group substitution on the water affinity of phosphonium-acetate ionic liquids. By combining the same cation with three different α-substituted carboxylate anions, the effect of anion functional group substitution on the IL miscibility with water and hygroscopicity was experimentally evaluated and rationalized using COSMO-RS sigma profile analysis. Lower critical solution temperature (LCST) phase separation experiments and water vapor partial pressure measurements revealed that there is a stark α-substitution dependency on the affinity of water for acetate [AcO], pivalate [PivO], and trifluoroacetate [TFA] derived tributyl(octyl)phosphonium [P4448] ILs. It was found that the IL water affinities varied as: [P4448][AcO] > [P4448][PivO] > [P4448][TFA]. With the lowest water partial pressure and no LCST driven phase separation, [P4448][AcO] exhibited a high affinity for water. On the other hand, [P4448][PivO] and [P4448][TFA] exhibited LCST-driven phase separation and room temperature immiscibility, respectively, with higher water partial pressures, as a result of relatively weak water affinities. COSMO-RS sigma profile analysis revealed that the aliphatic carboxylate anions should incorporate apolar interactions commensurate with or greater than the polar hydrogen bond acceptor interactions for phase immiscibility of the corresponding IL with water. It was found that the relative magnitudes of apolar and polar interactions, assessed using the anion sigma profile peak intensity ratio (Ir), are directly correlated with the IL water affinity, and inversely correlated with the solution water activity coefficient. Therefore, it was concluded that Ir forms a quantitative link between the structural changes at the molecular level and the bulk water affinity exhibited by the ionic liquid as a whole.
The indiscriminate application of diverse broad-spectrum antimicrobials has escalated nosocomial infections into a critical global public health quandary. Currently, traditional antibiotics' efficacy against these infections becomes limited, necessitating a concerted pursuit of more efficacious antimicrobial agents. It is noteworthy that taurine (tau) and cepharanthine (cep) are both biologically active compounds, with taurine constituting a vital nutrient to human health and cepharanthine exhibiting certain antibacterial attributes. However, while cepharanthine displays intrinsic antibacterial features, its monomeric utility is constrained. This study thus investigated the formulation process of merging taurine with cepharanthine, and rigorously assessed the antimicrobial potential of the taurine-cepharanthine complex (denoted as [cep][tau]). The outcomes indicated that this complex, [cep][tau], exhibited antibacterial activity against Staphylococcus aureus and Klebsiella pneumoniae, which was on par with the efficacy of cepharanthine on its own. This observation implies that taurine did not antagonize the antibacterial potency of cepharanthine, offering novel avenues for the development of innovative pharmaceuticals targeting hospital-acquired infections.