Lower Rim Research Articles

Metal-Ion Specific Recognition with Amplified Transcription from Subnanometer to Submillimeter or Real-Time Domain by Self-Assembled Vanadyl Quartets.

Vanadyl(V) complexes 1 and 2 bearing a nematic liquid crystal (LC) like a p-heptoxyphenyl group or a fluorous-tag p-nonafluoroheptoxyphenyl (NFH) group at the C5 position of the N-salicylidene template were designed and synthesized. Each complex was subjected to MVO3-induced self-assembly to form metal-ion, encapsulated quartet clusters 3-M and 3'-M. The Na+ in cluster complex 3-Na or 3'-Na can be readily replaced by Rb+, Ag+, or Hg2+ in an aqueous layer to form cluster complexes by ion swapping at the H2O/CDCl3 bilayer interface. Selectivity profiles were examined with alkali-metal ions, Ag+, and Hg2+ through metal-ion competition experiments. The 3'-Na has an exclusive selectivity for Hg2+ in the presence of Zn2+ and Cd2+. Cluster complexes 3-M were utilized as chiral dopants to nematic LC materials. The effects of the encapsulated metal ions within the alkali family and Ag+ on Cano's line widths and helical pitch changes were viewed in wedge cells under a polarized microscope. Their correlations with the ionic radius were identified. The subnano information of the metal ions can thus be asymmetrically amplified to Cano's line spacings of the submilimeter domain. Conversely, the effects of the encapsulated alkali metal ions and Hg2+ in 3'-M on the interactions of their NFH tails toward fluorous silica gel (FSG) were performed via HPLC analyses. Their retention times became longer as the sizes of encapsulated, alkali metal ions increased. The increasing ion size from Na+ to Cs+ caused the four lower rim NFH tags of the cluster to be closer due to reduced cone angles. Their interactions among NFH tail groups on FSG became larger, thus leading to distinctive separations with tR from 7.36 to 10.27 min. The retention time difference between 3'-Na and 3'-Hg on HPLC was ∼3.6 min, resulting in discernible separation. The individual ion size differences on the subnano scale can thus be amplified and unambiguously established in the real time domain.

A Review of the Application of Resorcinarenes and SBA-15 in Drug Delivery

Due to the diseases that people face today, scientists dedicate a part of their research to the synthesis, characterization, and study of functional compounds for controlled drug delivery. On the one hand, resorcinarenes are macrocycles obtained by condensation reactions of resorcinol and aldehyde. They include an upper and a lower rim functioning with different groups that confer solubility to the macrocycle and favor interactions with other compounds, therefore the hydroxyl groups on the upper rim improve the formation of hydrogen bonds. Additionally, resorcinarenes feature a cavity studied for forming host-guest complexes. SBA-15, on the other hand, is a mesoporous silica characterized by ordered pores in its structure and a large surface area. As a result of its properties, it has been used for several purposes, including absorbents, drug delivery, catalysis, and environmental processes. This review shows the recent advances in synthesis methods, characterization, micelle formation, interaction with other compounds, and host-guest procedures, as well as techniques for evaluating toxicity, drug retention, and their preliminary uses in pharmacology for macrocycles, such as resorcin[4]arenes and SBA-15.

Direct C−H Functionalization of Calix[n](het)arenes (n=4,6): A Brief Update

AbstractCalix[4]arenes are, probably, the mostly explored macrocycles in the supramolecular chemistry. By means of the synthetic modification/functionalization of the upper or lower rims, as well as meso‐positions, the “host‐guest” properties of these macrocycles can be modulated in order to accommodate the guest molecules of various sizes and nature for supramolecular and coordination chemistry, and to perform various functions for materials science and for biomedical applications. In this review, we wish to highlight the most prospective synthetic approaches for the direct C−H functionalization of calixarene core with various functional moieties. Depending on the nature of the functional moiety these calix[4]arenes can serve as drug carriers and nano‐containers for the recognition, encapsulation or storage of bioactive molecules and for many other applications. Current review article deals with the recent examples of C(H)‐functionalization of calix[4]arenes, as well as selected patterns of direct C(H)‐modification of some calix[6]arenes and calix[4]pyrroles.

Combining Excellent Selectivity with Broad Target Scope: Biosensing with Arrayed Deep Cavitand Hosts.

Simple macrocyclic water-soluble hosts such as cucurbiturils, cyclophanes, and calixarenes have long been used for biosensing via indicator displacement assays. Using multiple hosts and dyes in an arrayed format allows pattern recognition-based "chemical nose" sensing, which confers exquisite selectivity, even rivaling the abilities of biological recognition tools such as antibodies. However, a challenge in indicator displacement-based biosensing with macrocyclic hosts is that selectivity and scope are often inversely correlated: strong selectivity for a specific target can limit wide application, and broad scope sensing can suffer from a lack of selectivity between similar targets. This problem can be addressed by using water-soluble, self-folding deep cavitands as hosts. These flexible bowl-shaped receptors can be easily functionalized with different motifs at the upper and lower rim, and the large cavities can bind many different fluorescent dyes, causing either fluorescence enhancement or quenching upon binding.Cavity-based affinity is strongest for NMe3+ groups such as trimethyl-lysine, and we have exploited this for the site-selective recognition of post-translational lysine methylations in oligopeptides. The host recognizes the NMe3+ group, and by applying differently functionalized hosts in an arrayed format, discrimination between identical modifications at different positions on the oligopeptide is possible. Multiple recognition elements can be exploited for selectivity, including a defined, yet "breathable" cavity, and variable upper rim functions oriented toward the target.While the performance of the host/guest sensing system is impressive for lysine methylations, the most important advance is the use of multiple different sensing mechanisms that can target a broad range of different biorelevant species. The amphiphilic deep cavitands can both bind fluorescent dyes and interact with charged biomolecules. These non-cavity-based interactions, when paired with additives such as heavy metal ions, modulate fluorescence response in an indirect manner, and these different mechanisms allow selective recognition of serine phosphorylation, lysine acetylation, and arginine citrullination. Other targets include heavy metals, drugs of abuse, and protein isoforms. Furthermore, the hosts can be applied in supramolecular tandem assays of enzyme function: the broad scope allows analysis of such different enzymes as chromatin writers/erasers, kinases, and phosphatases, all from a single host scaffold. Finally, the indirect sensing concept allows application in sensing different oligonucleotide secondary structures, including G-quadruplexes, hairpins, triplexes, and i-motifs. Discrimination between DNA strands with highly similar structures such as G-quadruplex strands with bulges and vacancies can be achieved. Instead of relying on a single highly specific fluorescent probe, the synthetic hosts tune the fluorophore-DNA interaction, introducing multiple recognition equilibria that modulate the fluorescence signal. By applying machine learning algorithms, a classification model can be established that can accurately predict the folding state of unknown sequences. Overall, the unique recognition profile of self-folded deep cavitands provides a powerful, yet simple sensing platform, one that can be easily tuned for a wide scope of biorelevant targets, in complex biological media, without sacrificing selectivity in the recognition.

The incorporation of upper vs lower rim substituted thia- and calix[4]arene ligands into polydiacethylene polymeric bilayers for rational design of sensors to heavy metal ions

1,3-Diketone calix [4]arene (CA) and thiacalix [4]arene (TCA), with the hydrophobic substituents introduced onto lower or upper rims respectively, form mixed aggregates with 10,12-pentacosadiynoic acid (PCDA) through the thin film hydration technique. Computer simulations, showing the arrangement of TCA and CA molecules in supramolecular clusters with PCDA molecules, suggest that PCDA assemblies with both cyclophanes are a convinient basis for the coordination of metal ions. However, photopolymerization of mixed aggregates reveals more disruption of the vesicular nanostructure of polydiacetylene (PDA) when CA molecules are included compared to TCA. The incorporation of the TCA and CA ligands influences the ability of the mixed PDA-bilayers to conformational and spectral changes and provides tight coordination of Tb3+ ions and efficient sensitizing of the Tb3+-centered luminescence. The PDA-bilayers incorporated by terbium TCA complex provide more sensitive response on the series of heavy metal ions vs their CA-based analogues. The surface exposed TCA rims and carboxylate moieties of PDA provide two different binding sites for Tb3+ and heavy metal ions. Both distribution of Tb3+ and heavy metal ions between these sites and heterometallic complex formation are revealed as the factors affecting the luminescence response of PDA-TCA terbium complex in the solutions of heavy metal ions. The interplay between these factors is the reason for the different luminescence response of PDA-TCA terbium complex on Cd2+, Hg2+ and Pb2+ ions. The PDA-vesicles incorporated by terbium TCA complex exhibit easier phase separation vs the PDA vesicles themselves, which favors the extraction of Pb2+ ions.

EFFICIENT AND SELECTIVE ANTITUMOR AGENTS BASED ON CATIONIC CALIXARENES: SYNTHESIS, CHARACTERIZATION, AND ANTIPROLIFERATIVE PROPERTIES

Research work on the preparation of anti-tumor agents with active properties is still a major field for the pharmaceutical industry to promote more potent anticancer drugs to the market. However, one of the main disadvantages of current and future anticancer drugs is selectivity. Therefore, in recent decades, a new perspective has to be developed for chemotherapy, such as "targeted" drugs and minimal side effects. Calixarenes, composed of phenolic units linked by methylene bridges are versatile kinds of macrocyclic compounds in supramolecular chemistry that can be modified to hydrophilic and hydrophobic cavities. The biocompatibility of calixarene derivatives allows them to be used in the development of in vivo and in vitro applications. For this reason, the calixarenes with different active groups, have been synthesized by many researchers as a target structure, and their biological activities and in particular their anti-cancer properties, have been studied. The purpose of the current study is to synthesize calix[4]arene derivatives bearing the cationic group at the lower rim and investigation their cytotoxic effect for several cancerous cells. Results demonstrated that calix[4]arene derivative having 5-bromopenty trimethylammonium bromide moieties (CN) and calix[4]arene derivative having 3-bromopropyl-triphenylphosphonium bromide moieties (CP) compounds selectively inhibits proliferation of A549 (13.42 µM) and HeLa (17.05 µM) and Hep-2 cells (>200 µM and 162.71 µM), respectively.

Thiacalixarenes with Sulfur Functionalities at Lower Rim: Heavy Metal Ion Binding in Solution and 2D-Confined Space.

Sulfur-containing groups preorganized on macrocyclic scaffolds are well suited for liquid-phase complexation of soft metal ions; however, their binding potential was not extensively studied at the air–water interface, and the effect of thioether topology on metal ion binding mechanisms under various conditions was not considered. Herein, we report the interface receptor characteristics of topologically varied thiacalixarene thioethers (linear bis-(methylthio)ethoxy derivative L2, O2S2-thiacrown-ether L3, and O2S2-bridged thiacalixtube L4). The study was conducted in bulk liquid phase and Langmuir monolayers. For all compounds, the highest liquid-phase extraction selectivity was revealed for Ag+ and Hg2+ ions vs. other soft metal ions. In thioether L2 and thiacalixtube L4, metal ion binding was evidenced by a blue shift of the band at 303 nm (for Ag+ species) and the appearance of ligand-to-metal charge transfer bands at 330–340 nm (for Hg2+ species). Theoretical calculations for thioether L2 and its Ag and Hg complexes are consistent with experimental data of UV/Vis, nuclear magnetic resonance (NMR) spectroscopy, and single-crystal X-ray diffractometry of Ag–thioether L2 complexes and Hg–thiacalixtube L4 complex for the case of coordination around the metal center involving two alkyl sulfide groups (Hg2+) or sulfur atoms on the lower rim and bridging unit (Ag+). In thiacrown L3, Ag and Hg binding by alkyl sulfide groups was suggested from changes in NMR spectra upon the addition of corresponding salts. In spite of the low ability of the thioethers to form stable Langmuir monolayers on deionized water, one might argue that the monolayers significantly expand in the presence of Hg salts in the water subphase. Hg2+ ion uptake by the Langmuir–Blodgett (LB) films of ligand L3 was proved by X-ray photoelectron spectroscopy (XPS). Together, these results demonstrate the potential of sulfide groups on the calixarene platform as receptor unit towards Hg2+ ions, which could be useful in the development of Hg2+-selective water purification systems or thin-film sensor devices.

Tetra-Substituted p-Tert-Butylcalix[4]Arene with Phosphoryl and Salicylamide Functional Groups: Synthesis, Complexation and Selective Extraction of f-Element Cations.

A new series of lanthanide (1–5) and uranyl (6) complexes with a tetra‐substituted bifunctional calixarene ligand H2L is described. The coordination environment for the Ln3+ and UO2 2+ ions is provided by phosphoryl and salicylamide functional groups appended to the lower rim of the p‐tert‐butylcalix[4]arene scaffold. Ligand interactions with lanthanide cations (light: La3+, Pr3+; intermediate: Eu3+ and Gd3+; and heavy: Yb3+), as well as the uranyl cation (UO2 2+) is examined in the solution and solid state, respectively with spectrophotometric titration and single crystal X‐ray diffractometry. The ligand is fully deprotonated in the complexation of trivalent lanthanide ions forming di‐cationic complexes 2 : 2 M : L, [Ln2(L)2(H2O)]2+ (1–5), in solution, whereas uranyl formed a 1 : 1 M : L complex [UO2(L)(MeOH)]∞ (6) that demonstrated very limited solubility in 12 organic solvents. Solvent extraction behaviour is examined for cation selectivity and extraction efficiency. H2L was found to be an effective extracting agent for UO2 2+ over La3+ and Yb3+ cations. The separation factors at pH 6.0 are: βUO 22+ /La 3+ =121.0 and βUO 22+ /Yb 3+ =70.0.

Development of tBu-phenyl Acetamide Appended Thiacalix[4]arene as "Turn-ON" Fluorescent Probe for Selective Recognition of Hg(II) Ions.

Herein, a novel N-(4-(tert-butyl)-phenyl)-2-chloroacetamide functionalized thiacalix[4]arene architecture, viz TCAN2PA has been synthesized and the sensing behaviour towards metal ions were explored. The probe, TCAN2PA displayed "turn-on" fluorescence response towards Hg(II) ions in acetonitrile over a series of competing common metal ions. A bathochromic shift in absorption band along with a significant "Turn-On" fluorescence behaviour of TCAN2PA was observed upon interaction with Hg(II) ions. The lower rim modification of thiacalixarene with N-(4-(tert-butyl)-phenyl)-2-chloroacetamide actively contributes toward the fluorescence property due to the presence of strong electron-donating aryl amido substituent. Fluorescence titration experiments were conducted to find out the limit of detection and to understand binding stoichiometry as well. The electron transfer interactions between the electron rich TCAN2PA host with Hg(II) ions have been postulated which is also supported by computational modelling insights.

New 2-D silver(I) coordination network constructed from thiomethyl group-substituted p-tert-butylthiacalix[]arene.

New ligand based on p-tertbutyltetrathiacalix[4]arene blocked in 1,3-alternate conformation, was achieved via a multistep synthesis with the introduction of thiomethylpropoxy groups on the lower rim which leads to a neutral tecton. The combination of this p-tertbutyltetrathiacalix[4]arene (p-TCA-2), in 1, 3-alternate imposed conformation, with tetrahedral Ag(I)SbF6 salt, leads to the formation of neutral, new 2-D coordination network, which was structurally investigated in the solid state by X-ray diffraction methods on a single crystal.

Three modes of interactions between anions and phenolic macrocycles: a comparative study.

Macrocyclic polyphenolic compounds such as resorcin[4]arenes can be considered as multidentate anion receptors. In the current work, we combine new experimental data and reports from the previous literature (solution data and deposited crystal structures from the CCDC) to systematically analyze binding motifs between resorcin[4]arene derivatives and anions, determine the role of supporting interactions from CH donors, ion pairing and estimate their relative strength. We have found that in medium polarity solvents (THF) anion binding is a main driving force for the formation of complexes between resorcinarenes and Alk4NX salts. Three binding modes have been detected using 1H NMR and DOSY, depending on the type of additional interactions. Mode I was observed for upper-rim unsubstituted resorcinarenes, which use OH groups and aromatic CH from the upper rim as hydrogen bond donors to form multidentate and multivalent binding sites at the upper rim. Mode II was observed for upper-rim halogenated resorcinarenes (tetrabromo- and tetraiodo-derivatives), which use OH groups and aliphatic CH atoms from the bridges to support the chelation of anions between aromatic units. This binding mode is also multidentate and multivalent, but weaker and more anion-selective than mode I (works effectively for chlorides but not for bromides). For O-substituted derivatives, mode III is observed, with anions bound in a nest formed by aromatic CH atoms in the lower rim (multidentate but monovalent binding). The relative strength of these three binding modes, their solvent-dependence, and emergence in the crystal structures (CCDC) have been evaluated.

Tetraamidoindolyl calix[4]arene as a selective ion pair receptor for LiCl

A calix[4]arene (1) functionalized with amidoindole groups on the upper rim and with propyl groups on the lower rim extracts LiCl and LiBr selectively.

Sharing the salt bowl: counterion identity drives N-alkyl resorcinarene affinity for pyrophosphate in water

The binding affinity for pyrophosphate (PPi) in aqueous media by N-alkyl ammonium resorcinarene salts can be enhanced via using weakly coordinating counter anions and modifying the upper rims of the receptors and the lower rim hydroxyl groups.

Историко-археологические исследования Тарской крепости

In Russian archaeology, there has been a steady increase in the attention of scientists to the study of materials of Russian pioneers who founded the first Siberian towns, one of which is Tara.The first two centuries of its existence, the town was the southernmost outpost of the Russians in the Irtysh region, a military, trade and diplomatic center. During excavations in 2007-2020, an expedition of the Omsk archaeologists studied the sections of the Tara fortress proper, its guard part and the posad. In the cultural layer up to 4.5 meters thick, from 3 to 7 building horizons were cleared with the remains of up to 11 lower rims of residential (the estate of a rich tarchanin with all the buildings was excavated almost completely), economic structures (cellars, baths, wells), the remains of wooden pavements, gutters, boxes for garbage collection, the remains of fences and stockades that separate one dwelling from another. Studied two fortress towers - Knyazhya and Tobolskaya - and storage for gunpowder. There were also found places where the workshops of a tanner, a potter, a place for the production of mica windows were located. The good preservation of wooden structures and products made from organic materials (leather, wood, birch bark, silk and cotton fabrics) was facilitated by the special conditions for the formation of a wet cultural layer saturated with manure and wood chips.Foundations of churches destroyed during the years of Soviet power were found (Tikhvin, Assumption, Pyatnitskaya). The foundation of the Nikolsky Cathedral was excavated, around which there was a church cemetery. The objects found in the cultural layer allow us to speak about the directions of the Tara trade: China, the Bukhara Khanate, the European part of the Muscovite state and, through it, the western countries: definitely Poland and Venice. The same finds indicate that not only ethnic Russians from the northern parts of the state and indigenous Siberian Tatars lived in Tara, but also immigrants from the Polish-Lithuanian state (“Lithuania”, “Poles”, “Germans”), Sarts (Bukharlyk, Kirghiz) from Small and Big Bukharia.The obtained materials correlate well with the data of written sources, information on the geography and statistics of the peoples of the Irtysh region, and significantly supplement and expand the ideas of scientists about one of the first Siberian cities.

Disruption of Hierarchical Clustering in the Vela OB2 Complex and the Cluster Pair Collinder 135 and UBC 7 with Gaia EDR3: Evidence of Supernova Quenching

Abstract We identify hierarchical structures in the Vela OB2 complex and the cluster pair Collinder 135 and UBC 7 with Gaia EDR3 using the neural network machine-learning algorithm StarGO. Five second-level substructures are disentangled in Vela OB2, which are referred to as Huluwa 1 (Gamma Velorum), Huluwa 2, Huluwa 3, Huluwa 4, and Huluwa 5. For the first time, Collinder 135 and UBC 7 are simultaneously identified as constituent clusters of the pair with minimal manual intervention. We propose an alternative scenario in which Huluwa 1–5 have originated from sequential star formation. The older clusters Huluwa 1–3, with an age of 10–22 Myr, generated stellar feedback to cause turbulence that fostered the formation of the younger-generation Huluwa 4–5 (7–20 Myr). A supernova explosion located inside the Vela IRAS shell quenched star formation in Huluwa 4–5 and rapidly expelled the remaining gas from the clusters. This resulted in global mass stratification across the shell, which is confirmed by the regression discontinuity method. The stellar mass in the lower rim of the shell is 0.32 ± 0.14 M ⊙ higher than in the upper rim. Local, cluster-scale mass segregation is observed in the lowest-mass cluster Huluwa 5. Huluwa 1–5 (in Vela OB2) are experiencing significant expansion, while the cluster pair suffers from moderate expansion. The velocity dispersions suggest that all five groups (including Huluwa 1A and Huluwa 1B) in Vela OB2 and the cluster pair are supervirial and are undergoing disruption, and also that Huluwa 1A and Huluwa 1B may be a coeval young cluster pair. N-body simulations predict that Huluwa 1–5 in Vela OB2 and the cluster pair will continue to expand in the future 100 Myr and eventually dissolve.

STRUCTURE AND SPECTRAL-LUMUINESCENT PROPERTIES OF LANTHANIDE-CONTAINING COMPLEXES WITH AZACROWN CALIXARENES

Lanthanide complexes with calix[4]arenes lower rim substituted with two azacrown ether fragments are reported. The size of the substituent cavity varied from 4 to 6 heteroatoms. The complexes were analyzed by means of IR, NMR, ESI mass spectroscopy. It is assumed that the coordination of Ln(III) ions occurs through the donor atoms of the lower rim; the counter anion and solvent molecule are also coordinated. Lanthanide-centered characteristic luminescence was observed in Eu(III), Tb(III) and Yb(III) complexes. The most efficient 4f-luminescence is observed for terbium-containing complexes with benzo-crown-derived ligands. The pathways of the sensitization of 4f-luminescence are discussed.

Effect of preorganization and amphiphilicity of calix[4]arene platform on functional properties of viologen derivatives

A series of novel amphiphilic cavitands of calix[4]resorcinols with viologen fragments on the upper rim synthesized through a combination of viologen moieties and amphiphilic macrocyclic skeleton is reported. The influence of their structure on self-assembly, solubilization and biological properties was found. The driving force of the self-assembly of the synthesized macrocycles is the hydrophobic interactions of their hydrocarbon chains through additional π-stacking interaction between the aromatic rings of neighboring macrocycle molecules, which is enhanced with an increase in the length of the alkyl chains on the lower rim. The lower hemotoxicity of long-chain viologen macrocycles, relative to viologen surfactant, the ability to bind therapeutic molecules and the selective cytotoxic activity to tumor cells are explicit references to viologen derivatives of calix[4]resorcinols as promising drug nanocontainers.

Dynamic self-assembly of mannosylated-calix[4]arene into micelles for the delivery of hydrophobic drugs

Carbohydrate–lectin interactions and glycol-molecule-driven self-assembly are powerful yet challenging strategies to create supramolecular nanostructures for biomedical applications. Herein, we develop a modular approach of micellization with a small molecular mannosylated-calix[4]arene synthetic core, CA4-Man3, to generate nano-micelles, CA4-Man3-NPs, which can target cancer cell surface receptors and facilitate the delivery of hydrophobic cargo. The oligomeric nature of the calix[4]arene enables the dynamic self-assembly of calix[4]arene (CA4), where an amphiphile, functionalized with mannose units (CA-glycoconjugates) in the upper rim and alkylated lower rim, afforded the CA4-Man3-NPs in a controllable manner. The presence of thiourea units between calixarene and tri-mannose moiety facilitated the formation of a stable core with bidentate hydrogen bonds, which in turn promoted mannose receptor targeted uptake and helped in the intracellular pH-responsive release of antineoplastic doxorubicin (Dox). Physiochemical features including the stability of the nanomicelle could circumvent the undesirable leakage of the cargoes, ensuring maximum therapeutic output with minimum off-targeted toxicity. Most importantly, surface-enhanced Raman scattering (SERS) was utilized for the first time to evaluate the critical micelle concentration during the formation, cellular uptake and intracellular drug release. The present study not only provides an architectural design of a new class of organic small molecular nanomicelles but also unveils a robust self-assembly approach that paves the way for the delivery of a wide range of hydrophobic chemotherapeutic drugs.

Investigation of H-bonding of p-(3-carboxymethyl-1-adamantyl)calix[6]arene by IR spectroscopy

The IR spectra of calix[6]arenes with adamantylacetic acid (1) and adamantyl (2) substituents along the upper rim of the molecule were studied. It was shown that the formation of an intramolecular H-bond between carboxyl groups on the upper rim of the calix[6]arene molecules with adamantylacetic acid fragments does not weaken the cyclic cooperative H-bond at the lower rim of the macrocycle, which is confirmed by DFT calculations. The calculation has shown that molecules 1 and 2 take on the conformation of a compressed cone.The reactivity of adamantylcalix[6]arenes changes due to the association of carboxyl groups. The formation of dimeric complexes due to H-bonds of carboxyl groups along the upper rim of molecule 1 does not lead to a noticeable redistribution of the charges of hydroxyl groups on the lower rim.Heating a sample of 1 to a temperature of 180 °C destroys a small part of the H-bonds between neighboring carboxyl groups, as evidenced by the appearance of a weak band at 3535 cm–1. However, after cooling to room temperature, the H-bonds between the carboxyl groups are restored.Heating up to 355° С-leads to irreversible changes in the H-bonding system, but even at this temperature, structure destruction has not been observed.

Azocalix[4]arene-Rhodamine Supramolecular Hypoxia-Sensitive Systems: A Search for the Best Calixarene Hosts and Rhodamine Guests.

A potential hypoxia-sensitive system host-guest complex of three calixarenes (including two with four anionic carboxyl and sulphonate azo fragments on the upper rim and a newly synthesized bis-azo adduct of calixarene in the cone configuration with azo fragments on the lower rim with the most widespread cationic and zwitterionic rhodamine dyes (123, 6G and B)) was studied using UV-VIS spectrometry and fluorescence as well as 1D and 2D NMR techniques. It was found that all three calixarenes form a complex with rhodamine dyes with a 1:1 composition. The association constants of calixarene-dye complexes with sulfonate calixarenes, especially in the case of tetra-anionic calixarene, turned out to be higher compared with carboxyl calixarene due to the more intense electrostatic interactions. For the first time using an HRESI MS technique, it was shown that the treatment of rhodamine 6G and 123 with sodium dithionite (SDT) produces a non-fluorescent leuco form of the dye, and only rhodamine B can be used with SDT without the occurrence of a side reduction. Moreover, it was identified that in addition to the reduction in the azo groups, SDT causes partial cleavage of the aryl ether bonds. The found features of SDT should be taken into account when SDT is used as an azoreductase mimic.