Preliminary Investigation of Organocatalyst Activity Based on C ‐Arylcalix [4]‐2‐Methylresorcinarene Sulfonic Acid Materials for Biodiesel Production

Inclusion Complexation of Remdesivir with Cyclodextrins: A Comprehensive Review on Combating Coronavirus Resistance-Current State and Future Perspectives

Cyclodextrin (CD) derivatives have gained significant attention in biomedical applications due to their remarkable biocompatibility, unique inclusion capabilities, and potential for functionalization. This review focuses on recent advancements in CD-based assemblies, specifically their role in improving drug delivery, emphasizing remdesivir (RMD). The review introduces CD materials and their versatile applications in self-assembly and supramolecular assembly. CD materials offer immense potential for designing drug delivery systems with enhanced activity. Their inherent inclusion capabilities enable the encapsulation of diverse therapeutic agents, including RMD, resulting in improved solubility, stability, and bioavailability. The recent advances in CD-based assemblies, focusing on their integration with RMD have been concentrated here. Various strategies for constructing these assemblies are discussed, including physical encapsulation, covalent conjugation, and surface functionalization techniques. Furthermore, exploring future directions in these fields has also been provided. Ongoing research efforts are directed toward developing novel CD derivatives with enhanced properties, such as increased encapsulation efficiency and improved release kinetics. Moreover, the integration of CD-based assemblies with advanced technologies such as nanomedicine and gene therapy holds tremendous promise for personalized medicine and precision therapeutics.

Homo- and Heteromultinuclear Pseudocapsules Assembled from Calix[6]-mono-crown-5 and Alkali Metal Ions

The formation of pseudocapsule type homo- and heteromultinuclear complexes of calix[6]-mono-crown-5 (H₄L) encapsulating from 4 to 6 alkali metal ions is reported. H₄L reacts with KOH to yield a hexanuclear potassium(I) complex [K₆(HL)₂(CH₃OH)₂]·CHCl₃ (1) in which two bowl-shaped tripotassium(I) complex units are linked in a rim-to-rim fashion via the interligand C-H···π interactions. In the same reaction condition, RbOH afforded a tetranuclear rubidium(I) complex [Rb₄(H₂L)₂(CH₃OH)₂(μ-H₂O)₂]·6CHCl₃ (2). In 2, again two bowl-shaped dirubidium(I) complex units are held together by two bridging water molecules and C-H···π interactions that act as a glue to generate such an elegant pseudocapsule. Interestingly, a mixture of KOH and RbOH yielded a heterotetranuclear complex [K₂Rb₂(H₂L)₂(CH₃OH)₂(μ-H₂O)₂]·6CHCl₃ (3). Similarly, two heterodinuclear bowl units [KRb(H₂L)] in 3 are held together by two bridging water molecules and C-H···π interactions to form a heteromultinuclear pseudocapsule. In each heterodinuclear K⁺/Rb⁺ bowl unit of 3, Rb⁺ occupies the center of the crown loop while K⁺ locates inside the calix rim. Consequently, the proposed host discriminates not only on the types and numbers of the metal ions but also on their positional preferences in forming pseudocapsules. Solution studies by nuclear magnetic resonance and electrospray ionization-mass support the heterometallic (K⁺/Rb⁺) complexation by showing the superior binding affinity of Rb⁺ over K⁺ toward the crown loop. These results demonstrate how the metal-driven pseudocapsules are formed and present a new perspective on the metallosupramolecules of the calixcrown scaffold.

Utilization of vanillin to prepare sulfated Calix[4]resorcinarene as efficient organocatalyst for biodiesel production based on methylation of palmitic acid and oleic acid

Recently, biodiesel production from palm oils has been thoroughly investigated to substitute crude oil due to its scarcity. However, the biodiesel production process is time-consuming due to its slow kinetics; thus, concentrated sulfuric acid has been used to fasten the reaction process in some industries. Unfortunately, sulfuric acid is a toxic, corrosive, and non-environmentally friendly catalyst. In this study, we prepared sulfated Calix[4]resorcinarene derived from vanillin as an efficient organocatalyst to replace sulfuric acid. The catalytic activity of sulfated Calix[4]resorcinarenes was evaluated through the methylation of palmitic acid and oleic acid as model compounds due to their abundant amounts in palm oil. The Calix[4]resorcinarene and sulfated Calix[4]resorcinarenes have been obtained through a one-pot reaction in 71.8-98.3% yield. Their chemical structures were confirmed by using FTIR, NMR and HRMS spectrometry analyses. The results showed that the sulfated Calix[4]resorcinarene exhibited high catalytic activity for methyl palmitate and methyl oleate productions in 94.8 ± 1.8 and 97.3 ± 2.1% yield, respectively, which was comparable to sulfuric acid (96.3 ± 1.8 and 95.9 ± 2.5%). The optimum condition was achieved by using 0.020 wt equivalent of organocatalyst for 6 h reaction process at 338 K. The methylation of palmitic acid and oleic acid fits well with the first-order kinetic model (R² = 0.9940-0.9999) with a reaction rate constant of 0.6055 and 1.1403 h^-1, respectively. Further investigation reveals that the hydroxyl group of vanillin plays a pivotal role in the organocatalytic activity of sulfated Calix[4]resorcinarene.