Unusual C-I···O Halogen Bonding in Triazole Derivatives: Gelation Solvents at Two Extremes of Polarity and Formation of Superorganogels

Emerging Aspects of Triazole in Organic Synthesis: Exploring its Potential as a Gelator

Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) - commonly known as the "click reaction" - serves as the most effective and highly reliable tool for facile construction of simple to complex designs at the molecular level. It relates to the formation of carbon heteroatomic systems by joining or clicking small molecular pieces together with the help of various organic reactions such as cycloaddition, conjugate addition, ring-opening, etc. Such dynamic strategy results in the generation of triazole and its derivatives from azides and alkynes with three nitrogen atoms in the five-membered aromatic azole ring that often forms gel-assembled structures having gelating properties. These scaffolds have led to prominent applications in designing advanced soft materials, 3D printing, ion sensing, drug delivery, photonics, separation, and purification. In this review, we mainly emphasize the different mechanistic aspects of triazole formation, which includes the synthesis of sugar-based and non-sugar-based triazoles, and their gel applications reported in the literature for the past ten years, as well as the upcoming scope in different branches of applied sciences.

Optical Chemical Sensing of Iodide Ions: A Comprehensive Review for the Synthetic Strategies of Iodide Sensing Probes, Challenges, and Future Aspects

Among several anions, iodide (I^- ) ions play a crucial role in human biological activities. In it's molecular form (I₂ ), iodine is utilized for several industrial applications such as syntheses of medicines, fabric dyes, food additives, solar cell electrolytes, catalysts, and agrochemicals. The excess or deficiency of I^- ions in the human body and environmental samples have certain consequences. Therefore, the selective and sensitive detection of I^- ions in the human body and environment is vital for monitoring their overall profile. Amongst various analytical techniques for the estimation of I^- ions, optical-chemical sensing possesses the merits of high sensitivity, selectivity, and utilizing the least amount of sensing materials. The distinctive aims of this manuscript are (i) To comprehensively review the development of optical chemical sensors (fluorescent & colorimetric) reported between 2001-2021 using organic fluorescent molecules, supramolecular materials, conjugated polymers, and metal-organic frameworks (MOFs). (ii) To illustrate the design and synthetic strategies to create specific binding and high affinity of I^- ions which could help minimize negative consequences associated with its large size and high polarizability. (iii) The challenges associated with sensitivity and selectivity of I^- ions in aqueous and real samples. The probable future aspects concerning the optical chemical detection of I^- ions have also been discussed in detail.

Fine-Tuning of Molecular Structures to Generate Carbohydrate Based Super Gelators and Their Applications for Drug Delivery and Dye Absorption

Carbohydrate-based low molecular weight gelators (LMWGs) exhibit many desirable properties making them useful in various fields including applications as drug delivery carriers. In order to further understand the structural connection to gelation properties, especially the influence of halide substitutions, we have designed and synthesized a series of para-chlorobenzylidene acetal protected D-glucosamine amide derivatives. Fifteen different amides were synthesized, and their self-assembling properties were assessed in multiple organic solvents, as well as mixtures of organic solvents with water. All derivatives were found to be gelators for at least one solvent and majority formed gels in multiple solvents at concentrations lower than 2 wt%. A few derivatives rendered remarkably stable gels in aqueous solutions at concentrations below 0.1 wt%. The benzamide 13 formed gels in water and in EtOH/H2O (v/v 1:2) at 0.36 mg/mL. The gels were characterized using optical microscopy and atomic force microscopy, and the self-assembly mechanism was probed using variable temperature 1H-NMR spectroscopy. Gel extrusion studies using H2O/DMSO gels successfully printed lines of gels on glass slides, which retained viscoelasticity based on rheology. Gels formed by the benzamide 13 were used for encapsulation and the controlled release of chloramphenicol and naproxen, as well as for dye removal for toluidine blue aqueous solutions.

The effect of vicinal di-halo substituents on the organogelling properties of aromatic supramolecular gelators and their application as soft templates

Vicinal di-halo substituents have a determinant effect on the supramolecular self-assembly and properties of aromatic physical gelators with application as soft templates.

Novel liquid crystalline organogelators based on terephthalic acid and terephthalaldehyde derivatives: properties and promotion through the formation of halogen bonding

Terephthalic acid-based aromatic amides A1 and A2 and a terephthalaldehyde Schiff-base SB are synthesized, allowing stable gelation with numerous types of organic solvents.

Theoretical and experimental studies of an oseltamivir-triazole-based thermoresponsive organogel

Low-molecular weight organic gelators have been of significant interest in recent years because of their interesting properties and potential applications in sensing technology, biomedicine and drug delivery. Herein, the synthesis, characterization and gelation properties of new oseltamivir conjugates are reported. The oseltamivir-triazole conjugate 1 was synthesized via a click-reaction in a 75% yield. The key features of this conjugate include the presence of amide, flexible ester linkages and a triazole scaffold linking a hydrophobic alkyl chain. The conjugate 1, possessing a long alkyl chain, showed gelation properties in various apolar organic solvents. This gelation behavior was not observed in the case of the deesterified conjugate 2; this indicated the necessity of the alkyl chain for gelation. The gelator 1 showed thermoreversible gelation properties in a range of linear alkane solvents (from n-pentane to n-dodecane). A scanning electron microscopic study suggests that the gelator 1 exists as cross-linked structures, which are self-aggregated in the range of submicrometers, as supported by extensive 1H-NMR studies. The rheological parameters supported the occurrence of a soft gelation process, and the gel formed in n-decane was found to be stiffer than that formed in n-hexane. Computational studies suggested that the gelation behavior was indeed due to micelle formation and dependent on the lipophilicity of solvents.

Expanding the limits of amide-triazole isosteric substitution in bisamide-based physical gels

Gelation of organic solvents using N,N'-((1S,2S)-cyclohexane-1,2-diyl)didodecanamide (C12-Cyc) is driven by its self-assembly via antiparallel hydrogen bonds and van der Waals intermolecular interactions. In this work we carried out a dual isosteric substitution of the two amide groups with 1,2,3-triazole rings affording the corresponding isosteric gelator (click-C12-Cyc). A detailed comparative study in terms of the gelation ability and gel properties demonstrated that the 1,2,3-triazoles can take over all of the functions derived from the amide groups offering a versatile strategy for tuning the properties of the corresponding gels. This is not an obvious outcome because the directional amide groups in C12-Cyc constitute the source of the hydrogen bonds to build the 3D self-assembled network. Furthermore, theoretical calculations revealed that click-C12-Cyc can adopt a wide variety of interacting patterns, whose relative stability depends on the polarity of the environment, this is in good agreement with the experimental data obtained regarding its gelation ability. Other important features of click-C12-Cyc for potential practical applications are its non-cytotoxic character and its phase-selective gelation of water-oil mixtures.

A healing ionomer crosslinked by a bis-bidentate halogen bond linker: a route to hard and healable coatings

A bis-bidentate halogen bond linker was introduced into a fully organic, phosphate based ionomer, yielding a crosslinked network with healing abilities and improved mechanical properties.