Mauricio Maldonado

In the present article, tetra(nonyl)calix[4]resorcinarene, tetra(p-methoxyphenyl)calix[4]resorcinarene, and tetra(p-bromophenyl)calix[4]resorcinarene were synthesized by the cyclocondensation method in acid medium. In the case of tetra(nonyl)calix[4]resorcinarene, only the crown conformer was obtained, while in the case of tetra(p-methoxyphenyl)calix[4]resorcinarene and tetra(p-bromophenyl)calix[4]resorcinarene, a conformational mixture (crown and chair) was formed, separated, and purified via the recrystallization technique. Subsequently, the per-O-acetylation reaction of the pure conformers was carried out. According to the RP-HPLC and ¹H-NMR results, the per-acetylation product of the crown conformer of tetra(nonyl)calix[4]resorcinarene retained its conformation, likewise the per-O-acetylation products of the chair conformer of tetra(p-methoxyphenyl)calix[4]resorcinarene and tetra(p-bromophenyl)calix[4]resorcinarene. On the other hand, the per-O-acetylation product of crown conformers of tetra(p-methoxyphenyl)calix[4]resorcinarene and tetra(p-bromophenyl)calix[4]resorcinarene gave rise to the formation of the boat conformer.

The aim of this work was to find an alternative method for the isolation and inactivation of 4-nitrophenol in aqueous solution by complexing it with cyclodextrins. For that, the inclusion complex between cyclodextrins and 4-nitrophenol (4-NP) was investigated using UV-Visible and 1H-NMR spectroscopies. These results allowed us to observe the existence of a strong interaction between (4-NP) and 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD). Moreover, other specific properties of this complex in solution were also analysed. Thus, apparent partial molar volumes, apparent partial molar adiabatic compressibilities, partial molar volumes of transfer and interaction and intrinsic volumes were determined, allowing to evaluate the characteristics of the complex formed.

Pyrogallol[4]arenes are polyhydroxylated compounds obtained by condensation between pyrogallol and different aldehydes. Depending on both the type of aldehyde (aromatic or aliphatic) and the reaction time, these compounds can be obtained in different conformations, the most common being the crown and chair conformations. Using the conventional synthesis method, it is possible to obtain, in addition to the chair or crown conformers, other molecular associations, such as dimer capsules. The research in this study focuses on the synthesis products obtained from the condensation between pyrogallol and propanal. These products were characterized using spectroscopic methods, revealing that it is possible to obtain, in addition to the crown conformation, the dimer capsule of the macrocycle. Finally, the volumetric properties of these conformers were evaluated in dimethyl sulfoxide (DMSO) solution at several temperatures.

Pyrogallol[4]arenes are polyhydroxylated compounds obtained by condensation between pyrogallol and different aldehydes. Depending on both the type of aldehyde (aromatic or aliphatic) and the reaction time, these compounds can be obtained in different conformations, the most common being the crown and chair conformations. Using the conventional synthesis method, it is possible to obtain, in addition to the chair or crown conformers, other molecular associations, such as dimer capsules. The research in this study focuses on the synthesis products obtained from the condensation between pyrogallol and propanal. These products obtained were characterized using spectroscopic methods, finding that it is possible to obtain, in addition to the crown conformation, the dimer capsule of the macrocycle. Finally, the volumetric properties of these conformers were evaluated in dimethylsulfoxide (DMSO) solution and at several temperatures.

The dichromate ion (Cr₂O₇²⁻), a highly toxic chromium VI species, is widely used in industrial processes, generating serious environmental problems when released into water bodies. This investigation proposes the use of a functionalized polymer as an adsorbent material for its removal in the aqueous phase. Poly(butyl methacrylate) (PBMA) was synthesized and modified by impregnation with resorcinarenes derived from long-chain aliphatic aldehydes. To improve the affinity for the dichromate, the resorcinarenes were functionalized with sulfomethyl groups by treatment with Na₂SO₃. The resulting matrices were characterized using IR-ATR, ¹H-NMR, and ¹³C-NMR, and their adsorbent performance was evaluated via UV-Vis spectroscopy in batch extraction assays. The results showed that the functionalized polymer exhibited a higher adsorption capacity than the base polymer, reaching up to 81.1% removal at pH 5.0 in one hour. These results highlight the potential of PBMA as an effective support and raise a promising research perspective for functionalized resorcinarenes in the development of new materials for the treatment of contaminated water.

Resorcinarenes are polyhydroxylated platforms consisting of 4, 5, 8, or more units of resorcinol. The numbers refer to the number of resorcinol units, with 4-unit platforms being the most stable. Investigation into their use in pharmaceutical applications has increased due to high versatility and functionalization. They exhibit significant flexibility due to their methylene bridges and to the interactions of hydrogen bridges and van der Waals forces. These platforms can be used in an increasing number of applications, which include the functionalization of nanoparticles and relevant materials, the synthesis of catalysts, the removal of contaminants, and analytical separations in analytes such as benzodiazepines and norepinephrine. For this last application, resorcinarenes are functionalized with specific important functional groups. Polymers were developed in the 20th century for the development of materials with significant improvements in thermal and mechanical properties. They are cross-linked polymeric structures, mainly made up of monomers such as styrene, divinylbenzene acrylate, vinylpyridine, and vinyl acetate, among others. They often have a homogeneous, porous structure, but this structure can vary significantly depending on the type of solvent used. Therefore, they have been applied in the functionalization of the polyhydroxylated platforms. In this review, the structure, properties, and synthesis of resorcinarenes, as well as the use of polymeric matrices, are analyzed, emphasizing the functionalization of organic polymers using resorcinarenes. Furthermore, the respective applications in controlled drug delivery, pharmaceutical transport, and therapeutics, which are diverse and show promising growth, will be explored.

Calix[4]resorcinarenes are polyhydroxylated macrocyclic compounds with four units of resorcinol. These compounds can be derivatized through modifications at the upper rim, allowing reactivity with secondary amines to produce Mannich base derivatives via Mannich-type aminomethylation reactions. In this paper, we report the reaction of C-tetra(propyl)calix[4]resorcinarene with piperidine in acetonitrile. The aminomethylated compound C-2,8,14,20-tetra(propyl)-5,11,17,23-tetrakis(N–(piperidine)methyl)calix[4]resorcinarene was obtained with a 52% yield, with an exact mass of 1044.6994 u and a mass error of 7.6 ppm. The reaction progress and product formation were monitored by RP-HPLC, and the compound was characterized using LC ESI-TOF/MS, one- and two-dimensional ¹H and ¹³C NMR, and FTIR spectroscopy. Chromatographic and spectroscopy data are presented and discussed.

The molecular interactions of water-soluble crown resorcinarenes with choline were analyzed. To this end, four sulfonated resorcinarenes were synthesized and characterized by ATR-IR, ¹H-NMR, and ¹³C-NMR spectroscopy. The molecular interaction studies with choline were carried out through FT-IR spectroscopy, ¹H-NMR titrations, and conductimetric titrations, with which it was possible to determine that the complexes formed 1:1 stoichiometries with the host, in addition to showing good interaction in the electronic cavity of the macrocycle, demonstrating great potential for host–guest systems for choline detection in aqueous media. Finally, the incidence of the structural aspects of sulfonated resorcinarenes were analyzed.

The separation and purification of molecular compounds and their functionalized derivatives is a common challenge in organic synthesis. In particular, calix[4]resorcinarenes present a high potential for chemical derivatization at their upper edge by aminomethylation reactions, and these compounds and their derivatives require appropriate analytical methodologies for their analysis, separation, and purification. In this study, C-tetra(propyl)calix[4]resorcinarene was synthesized and functionalized with maleimide groups by optimized aminomethylation reactions, obtaining a mixture of mono-, di-, tri-, and tetrasubstituted compounds. Initial separation by RP-HPLC with a core-shell column showed poorly resolved peaks, indicating a loss of separation efficiency. Therefore, a monolithic C18 column was used, which significantly improved the separation, thanks to its larger pore volume and continuous structure facilitating the diffusion of these bulky molecules, notably improving efficiency. Finally, the six compounds functionalized with maleimide groups were efficiently separated and enriched by RP-SPE by analytical method transfer, and the two peptides of six and the thirteen residues derived from LfcinB (20–25): RRWQWR were synthesized by SPPS-Fmoc/tBu and purified. These were modularly linked by the Michael thiol-maleimide addition reaction obtaining six (peptide)_n-resorcinarene conjugates. The analytical method by RP-HPLC with a monolithic C18 column, the separation and purification by RP-SPE were used transversally in all the steps to obtain compounds with adequate purities and quantities. Finally, the antibacterial activities of the six conjugates were evaluated against E. coli and E. faecalis strains, and it was determined that three aminomethylated compounds and one monosubstituted conjugate showed activity against E. faecalis. Our work established a new modular conjugation strategy between calix[4]resorcinarenes and peptides by thiol-maleimide click chemistry, and a methodology of separation, purification, and enrichment for these products by RP-HPLC and RP-SPE, which permitted us to obtain quantities with purities appropriate for their characterization by NMR, LC-MS and antibacterial activity assays.