Discovery of A Synthetic Hub for Regio- and Stereoselective Construction of Triazolyl Vinyl Sulfonyl Fluorides

A new sulfonyl fluoride reagent 1-bromobut-3-ene-1,3-disulfonyl difluoride (BEDF) was developed. This unique reagent possesses two clickable functionalities to be used for both azide-alkyne cycloaddition click and SuFEx click reactions. This new reagent was applied for the regioselective construction of a class of novel triazolyl vinyl sulfonyl fluorides in which the C-4 position 1H-1,2,3-triazoles were functionalized with vinyl sulfonyl fluorides of exclusively E-configuration.

Direct Organocatalytic Chemoselective Synthesis of Pharmaceutically Active 1,2,3-Triazoles and 4,5'-Bitriazoles

Carbonyl-containing 1,4,5-trisubstituted- and 1,4-disubstituted-1,2,3-triazoles are well-known for their wide range of applications in pharmaceutical and medicinal chemistry, but their high-yielding metal-free synthesis has always remained challenging, as no comprehensive protocol has been outlined to date. Owing to their structural and medicinal importance, herein, we synthesized various carbonyl-containing 1,4,5-trisubstituted- and 1,4-disubstituted-1,2,3-triazoles and unsymmetrical 4,5'-bitriazoles with high yields and chemo-/regioselectivity from the library of 2,4-diketoesters and azides in a sequential one-pot manner through the combination of organocatalytic enolization, in situ [3 + 2]-cycloaddition, and hydrolysis reactions. The commercial availability of the starting materials/catalysts, diverse substrate scope, performance in a one-pot manner, chemo-/regioselectivity of organo-click reaction, quick synthesis of unsymmetrical 4,5'-bitriazoles, a large number of synthetic applications, and numerous medicinal applications of carbonyl-containing 1,2,3-triazoles are the key attractions of this metal-free organo-click work.

Probing rotaxane dynamics with 19F NMR/MRI: Unveiling the roles of mechanical bond and steric hindrance

BACKGROUND

Deciphering the molecular dynamics (MD) of rotaxanes is crucial for designing and refining their applications in molecular devices. This study employed fluorine-19 nuclear magnetic resonance (19F NMR) and magnetic resonance imaging (MRI) to unveil the interplay between mechanical bonds and steric hindrance in a series of fluorinated rotaxanes.

RESULTS

1H/19F NMR revealed stable "Z"-shaped wheel conformations minimizing steric clashes and favoring π-π interactions with the axle. Utilizing fluorines and axle protons as reporters, 1H/19F relaxation rates and solid-state 19F NMR studies demonstrated that mechanical bond primarily governs wheel motion, while steric hindrance dictates axle movement. Intriguingly, mechanical bond mainly affects local axle groups, leaving distant ones minimally impacted. MD simulations corroborated these findings. Temperature-dependent 19F NMR indicated that energy input enhances rotational motion and wheel conformational transitions. Furthermore, the drastic increase in 19F relaxation rates upon mechanical bond formation and steric hindrance enables sensitive and selective 19F MRI visualization of MD changes.

SIGNIFICANCE

This study, by elucidating the roles of internal and external factors on rotaxane molecular dynamics using 19F NMR/MRI, offers valuable insights that can advance the field of rotaxane-based molecular devices.

Advancements and strategic approaches in catenane synthesis

Catenanes, a distinctive category of mechanically interlocked molecules composed of intertwined macrocycles, have undergone significant advancements since their initial stages characterized by inefficient statistical synthesis methods. Through the aid of molecular recognition processes and principles of self-assembly, a diverse array of catenanes with intricate structures can now be readily accessed utilizing template-directed synthetic protocols. The rapid evolution and emergence of this field have catalyzed the design and construction of artificial molecular switches and machines, leading to the development of increasingly integrated functional systems and materials. This review endeavors to explore the pivotal advancements in catenane synthesis from its inception, offering a comprehensive discussion of the synthetic methodologies employed in recent years. By elucidating the progress made in synthetic approaches to catenanes, our aim is to provide a clearer understanding of the future challenges in further advancing catenane chemistry from a synthetic perspective.

Synthesis, structural, multitargeted molecular docking analysis of anti-cancer, anti-tubercular, DNA interactions of benzotriazole based macrocyclic ligand

Biologically important macromolecule 1, 1', 3, 3' Bis - [2,3,5,6-Tetramethyl-p-phenylenebis(methylene)] dibenzotriazlinium dibromide hydrate (BTD) was synthesized and characterized using FT-IR, NMR and single-crystal XRD (SCXRD). SCXRD revealed that the compound was crystallized as a monoclinic system and associated through weak intermolecular interactions like H-bonding and π- π stacking interactions. These weak intermolecular interactions in BTD were studied using Crystal Explorer and Gaussian. The calculated energies for the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) showed the stability and reactivity of the title compound. Molecular electrostatic potential (MEP) surface analysis was used to investigate the crystal's nucleophilic and electrophilic reactive sites. The molecular shape and intermolecular interactions in the crystal structure were determined using Hirshfeld surface analysis and fingerprint plots. Anticancer, anti-bacterial and DNA binding ability of BTD were investigated by experimental and theoretical techniques. The obtained results suggest that BTD possesses better anti-cancer, anti-bacterial and DNA binding abilities. The mode of action of antibiotic and anticancer approach was discussed. This provides promising therapeutic advantages for further development.

Template Assisted One-Pot Synthesis of [2], Linear [3], and Radial [4]Catenane via Click Reaction

Design and synthesis of higher order catenane are unexpectedly complex and involve precise cooperation among the precursors overcoming competing and opposing interactions. We achieved synthesis of [2], linear [3], radial [4] in a one-pot reaction by consecutive ring closing through click reactions. This synthesis gave three isolable products due to two, four, and six-click reactions between suitable coupling partners. Yields of the isolate templated-catenane decrease from lower to higher-ordered catenane (40 %, 12 %, and 4 %), probably due to the bite angle as well as the flexibility of the reacting partners. Removal of templating cobalt(III) ion leads to the formation of fully organic [2], linear [3], and radial [4]catenane. These synthesized catenanes were purified by column chromatography and characterized by 1H-NMR, 13C-NMR, and ESI-MS spectroscopy. The synthesized catenanes have free binding sites suitable for post-functionalization and may be used for the synthesis of higher-ordered catenane.

Capture of mechanically interlocked molecules by rhodium-mediated terminal alkyne dimerisation

The transition metal-mediated dimerisation of terminal alkynes is an attractive and atom-economic method for preparing conjugated 1,3-enynes. Using a phosphine-based macrocyclic pincer ligand, we demonstrate how this transformation can be extended to the synthesis of novel, hydrocarbon-based interlocked molecules: a rotaxane by 'active' metal template synthesis and a catenane by sequential 'active' and 'passive' metal template procedures.

A thermally driven rotaxane-catenane interconversion with a dynamic bis(hindered amino) disulfide

We have developed a versatile and simple synthetic method to produce a [3]catenane. Heating a rotaxane with bis(hindered amino) disulfide groups at both ends spontaneously and selectively produces the [3]catenane. The successful polymerization of the obtained [3]catenane provides a platform for the synthesis of various interlocking polymers.

From construction to application of a new generation of interlocked molecules composed of heteroditopic wheels

Over the last few decades, research on mechanically interlocked molecules has significantly evolved owing to their unique structural features and interesting properties. A substantial percentage of the reported works have focused on the synthetic strategies, leading to the preparation of functional MIMs for their applications in the chemical, materials, and biomedical sciences. Importantly, various macrocyclic wheels with specific heteroditopicity (including phenanthroline, amide, amine, oxy-ether, isophthalamide, calixarene and triazole) and threading axles (bipyridine, phenanthroline, pyridinium, triazolium, etc.) have been designed to synthesize targeted multifunctional mononuclear/multinuclear pseudorotaxanes, rotaxanes and catenanes. The structural uniqueness of these interlocked systems is advantageous owing to the presence of mechanical bonds with specific three-dimensional cavities. Furthermore, their multi-functionalities and preorganised structural entities exhibit a high potential for versatile applications, like switching, shuttling, dynamic properties, recognition and sensing. In this feature article, we describe some of the most recent advances in the construction and chemical behaviour of a new generation of interlocked molecules, primarily focusing on heteroditopic wheels and their applications in different directions of the modern research area. Furthermore, we outline the future prospects and significant perspectives of the new generation heteroditopic wheel based interlocked molecules in different emerging areas of science.

Active-metal template clipping synthesis of novel [2]rotaxanes

Mechanically interlocked molecules (MIMs) have been important synthetic targets in supramolecular chemistry due to their beautiful structures and intriguing properties. We present herein a new synthetic strategy to access [2]rotaxanes, namely active-metal template clipping. We discuss the design of the target [2]rotaxanes, synthesis and characterization of the axle, macrocycle precursors and macrocycles as well as preparation of the final [2]rotaxanes by active template copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) as key step of the synthesis. HRMS and NMR experiments have been performed to confirm the formation of the interlocked structures.

An Inorganic Click Reaction for the Synthesis of Interlocked Molecules

We describe the use of the cyaphide-azide 1,3-dipolar cycloaddition reaction for the synthesis of a new class of inorganic rotaxanes containing gold(I) triazaphosphole stoppers. Electron-deficient bis-azides, which thread perethylated pillar[5]arene in aromatic solvents, readily react with two equivalents of Au(IDipp)(CP) (IDipp=1,3-bis-(2,6-diisopropylphenyl)-imidazol-2-ylidene) to afford interlocked molecules via an inorganic click reaction. These transformations proceed in good yields (ca. 65 %) and in the absence of a catalyst. The resulting organometallic rotaxanes are air- and moisture-stable and can be purified by column chromatography under aerobic conditions. The targeted rotaxanes were characterized by multi-element nuclear magnetic resonance (NMR) spectroscopy, mass-spectrometry, and single-crystal X-ray diffraction.

One-pot nucleophilic substitution-double click reactions of biazides leading to functionalized bis(1,2,3-triazole) derivatives

The nucleophilic substitution of benzylic bromides with sodium azide was combined with a subsequent copper-catalyzed (3 + 2) cycloaddition with terminal alkynes. This one-pot process was developed with a simple model alkyne, but then applied to more complex alkynes bearing enantiopure 1,2-oxazinyl substituents. Hence, the precursor compounds 1,2-, 1,3- or 1,4-bis(bromomethyl)benzene furnished geometrically differing bis(1,2,3-triazole) derivatives. The use of tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) as ligand for the click step turned out to be very advantageous. The compounds with 1,2-oxazinyl end groups can potentially serve as precursors of divalent carbohydrate mimetics, but the reductive cleavage of the 1,2-oxazine rings to aminopyran moieties did not proceed cleanly with these compounds.

Catenane and Rotaxane Synthesis from Cucurbit[6]uril-Mediated Azide-Alkyne Cycloaddition

The chemistry of mechanically interlocked molecules (MIMs) such as catenane and rotaxane is full of new opportunities for the presence of a mechanical bond, and the efficient synthesis of these molecules is therefore of fundamental importance in realizing their unique properties and functions. While many different types of preorganizing interactions and covalent bond formation strategies have been exploited in MIMs synthesis, the use of cucurbit[6]uril (CB[6]) in simultaneously templating macrocycle interlocking and catalyzing the covalent formation of the interlocked components is particularly advantageous in accessing high-order catenanes and rotaxanes. In this review, catenane and rotaxane obtained from CB[6]-catalyzed azide-alkyne cycloaddition will be discussed, with special emphasis on the synthetic strategies employed for obtaining complex [n]rotaxanes and [n]catenanes, as well as their properties and functions.

Stimuli-responsive rotaxane-branched dendronized polymers with tunable thermal and rheological properties

Aiming at the creation of polymers with attractive dynamic properties, herein, rotaxane-branched dendronized polymers (DPs) with rotaxane-branched dendrons attached onto the polymer chains are proposed. Starting from macromonomers with both rotaxane-branched dendrons and polymerization site, targeted rotaxane-branched DPs are successfully synthesized through ring-opening metathesis polymerization (ROMP). Interestingly, due to the existence of multiple switchable [2]rotaxane branches within the attached dendrons, anion-induced reversible thickness modulation of the resultant rotaxane-branched DPs is achieved, which further lead to tunable thermal and rheological properties, making them attractive platform for the construction of smart polymeric materials.

Balancing ring and stopper group size to control the stability of doubly threaded [3]rotaxanes

Synthesizing doubly threaded [3]rotaxanes requires the use of larger rings than more traditional singly threaded [2]rotaxanes. A key challenge in accessing stable doubly threaded [3]rotaxanes with large rings is finding the right combination of ring to stopper size. In this study, a series of doubly threaded [3]rotaxanes derived from five different sized macrocycles in the size range of 40-48 atoms and two different stopper groups, which contain 1 or 2 tris(p-t-butylbiphenyl)methyl moieties, were prepared and their kinetic stability examined. These interlocked compounds were synthesized using a metal-templated approach and fully characterized utilizing a combination of mass spectrometry, NMR spectroscopy, and size-exclusion chromatography techniques. The effect of ring size on the stability of the doubly threaded [3]rotaxane was investigated via kinetic stability tests monitored using 1H-NMR spectroscopy. By tightening the macrocycle systematically every 2 atoms from 48 to 40 atoms, a wide range of doubly threaded interlocked molecules could be accessed in which the rate of room temperature slippage of the macrocycle from the dumbbells could be tuned. Using the larger stopper group with a 48-atom ring results in no observable rotaxane, 46-44 atom macrocycles result in metastable rotaxane species with a slippage half-life of ∼5 weeks and ∼9 weeks, respectively, while macrocycles of 42 atoms or smaller yield a stable rotaxane. The smaller sized stopper is not able to fully stabilize any of the [3]rotaxane structures but metastable [3]rotaxanes are obtained with slippage half-lives of 25 ± 2 hours and 13 ± 1 days using macrocycles with 42 or 40 atoms, respectively. These results highlight the dramatic effect that relatively small ring size changes can have on the structure of doubly threaded [3]rotaxanes and lay the synthetic groundwork for a range of higher order doubly threaded interlocked architectures.

Self-Healing of a Copper(I) [2]Rotaxane Shuttle Monitored by Fluorescence

We demonstrate self-healing of the shuttling dynamics of a molecular machine operating by negative feedback. When zinc(II) was added to the copper(I)-loaded [2]rotaxane shuttle [Cu(R)]⁺, copper(I) was replaced, thereby generating the static zinc(II)-loaded [2]rotaxane [Zn(R)]²⁺. Loss of the dynamics was accompanied by a fluorescence enhancement at λ = 364 nm. Notably, the released copper(I) ions catalyzed the formation of a bis-triazole ligand, which selectively captured zinc(II). As a result, the copper(I) was restored in the rotaxane, and the dynamic shuttling motion of [Cu(R)]⁺ was regained. The healing was conveniently followed by diagnostic fluorescence changes.

Effect of non-covalent self-dimerization on the spectroscopic and electrochemical properties of mixed Cu(i) complexes

A series of six new Cu(i) complexes with ([Cu(N-{4-R}pyridine-2-yl-methanimine)(PPh₃)Br]) formulation, where R corresponds to a donor or acceptor p-substituent, have been synthesized and were used to study self-association effects on their structural and electrochemical properties. X-ray diffraction results showed that in all complexes the packing is organized from a dimer generated by supramolecular π stacking and hydrogen bonding. ¹H-NMR experiments at several concentrations showed that all complexes undergo a fast-self-association monomer-dimer equilibrium in solution, while changes in resonance frequency towards the high or low field in specific protons of the imine ligand allow establishing that dimers have similar structures to those found in the crystal. The thermodynamic parameters for this self-association process were calculated from dimerization constants determined by VT-¹H-NMR experiments for several concentrations at different temperatures. The values for K _D (4.0 to 70.0 M^-1 range), ΔH (-1.4 to -2.6 kcal mol^-1 range), ΔS (-0.2 to 2.1 cal mol^-1 K^-1 range), and ΔG ₂₉₈ (-0.8 to -2.0 kcal mol^-1 range) are of the same order and indicate that the self-dimerization process is enthalpically driven for all complexes. The electrochemical profile of the complexes shows two redox Cu(ii)/Cu(i) processes whose relative intensities are sensitive to concentration changes, indicating that both species are in chemical equilibrium, with the monomer and the dimer having different electrochemical characteristics. We associate this behaviour with the structural lability of the Cu(i) centre that allows the monomeric molecules to reorder conformationally to achieve a more adequate assembly in the non-covalent dimer. As expected, structural properties in the solid and in solution, as well as their electrochemical properties, are not correlated with the electronic parameters usually used to evaluate R substituent effects. This confirms that the properties of the Cu(i) complexes are usually more influenced by steric effects than by the inductive effects of substituents of the ligands. In fact, the results obtained showed the importance of non-covalent intermolecular interactions in the structuring of the coordination geometry around the Cu centre and in the coordinative stability to avoid dissociative equilibria.

The Story of the Little Blue Box: A Tribute to Siegfried Hünig

The tetracationic cyclophane, cyclobis(paraquat-p-phenylene), also known as the little blue box, constitutes a modular receptor that has facilitated the discovery of many host-guest complexes and mechanically interlocked molecules during the past 35 years. Its versatility in binding small π-donors in its tetracationic state, as well as forming trisradical tricationic complexes with viologen radical cations in its doubly reduced bisradical dicationic state, renders it valuable for the construction of various stimuli-responsive materials. Since the first reports in 1988, the little blue box has been featured in over 500 publications in the literature. All this research activity would not have been possible without the seminal contributions carried out by Siegfried Hünig, who not only pioneered the syntheses of viologen-containing cyclophanes, but also revealed their rich redox chemistry in addition to their ability to undergo intramolecular π-dimerization. This Review describes how his pioneering research led to the design and synthesis of the little blue box, and how this redox-active host evolved into the key component of molecular shuttles, switches, and machines.

Metal catalyzed C-H functionalization on triazole rings

The present review covers advancement in the area of C-H functionalization on triazole rings, by utilizing various substrates with palladium or copper as catalysts, and resulting in the development of various substituted 1,2,3- and 1,2,4-triazoles. Synthesis of these substituted compounds is necessary from the perspective of pharmaceutical, medicinal, and materials chemistry.

Parallel Allosteric Inhibition of Shuttling Motion and Catalysis in a Silver(I)-loaded [2]Rotaxane

A dynamic silver(I)-loaded [2]rotaxane shuttle (k₂₉₈ = 135 kHz) was converted allosterically into a conformationally restricted [2]rotaxane due to the creation of a bulky imine in the center of the axle component. Only the dynamic silver(I)-loaded [2]rotaxane was able to catalyze a 6-endo-cyclization reaction, whereas the static one was catalytically quiet. The mechanism of catalyst deactivation was elucidated.

NDI-integrated rotaxane/catenane and their interactions with anions

Complexation of alkali and alkaline earth metal ions with the heteroditopic Phen-ester oxy-ether macrocyclic wheel (PhenMC) is established for the synthesis of interlocked molecular systems. The single crystal X-ray structure of Na-bound PhenMC confirms the hexacoordinated geometry around the Na ion in the macrocycle. Further, Ca-ion-bound PhenMC (Ca-PhenMC) is explored with a fluorophoric azide-terminated NDI (naphthalene diimide) axle (NDIAz) for the synthesis of fluorophoric [2]rotaxane (NDIROT) and [2]catenane (NDICAT) via Cu(I)-catalyzed cycloaddition reaction. Characterizations of these two new interlocked molecular systems are performed by ESI-MS, NMR, UV-vis and PL spectroscopic studies wherever applicable. Moreover, the new molecular systems are explored towards anion sensing applications via colorimetric, UV-vis-NIR, PL and other spectroscopic studies.

The construction of phosphonate triazolyl by copper(II)-catalyzed furan dearomatized [3 + 2] cycloaddition

Triazole phosphonates are valuable structural motifs in chemical biology and the subject of growing recent interest. A novel methodology to synthesize triazolyl phosphonates starting from furfuryl phosphonate alcohols and organo-azides was developed. This method involved an intermolecular copper-catalyzed dearomatized [3 + 2] cycloaddition/furan ring-opening cascade reaction. A strategy involving a three-component reaction was realized for quick access to triazole phosphonates.

Aza-Oxa-Triazole Based Macrocycles with Tunable Properties: Design, Synthesis, and Bioactivity

A modular platform for the synthesis of tunable aza-oxa-based macrocycles was established. Modulations in the backbone and the side-chain functional groups have been rendered to achieve the tunable property. These aza-oxa-based macrocycles can also differ in the number of heteroatoms in the backbone and the ring size of the macrocycles. For the proof of concept, a library of macrocycles was synthesized with various hanging functional groups, different combinations of heteroatoms, and ring sizes in the range of 17-27 atoms and was characterized by NMR and mass spectrometry. In light of the importance of the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction and the significance of triazole groups for various applications, we employed the click-reaction-based macrocyclization. The competence of the synthesized macrocycles in various biomedical applications was proven by studying the interactions with the serum albumin proteins; bovine serum albumin and human serum albumin. It was observed that some candidates, based on their hanging functional groups and specific backbone atoms, could interact well with the protein, thus improving the bioactive properties. On the whole, this work is a proof-of-concept to explore the backbone- and side-chain-tunable macrocycle for different properties and applications.

Emerging impact of triazoles as anti-tubercular agent

Tuberculosis, a disease of poverty is a communicable infection with a reasonably high mortality rate worldwide. 10 Million new cases of TB were reported with approx 1.4 million deaths in the year 2019. Due to the growing number of drug-sensitive and drug-resistant tuberculosis cases, there is a vital need to develop new and effective candidates useful to combat this deadly disease. Despite tremendous efforts to identify a mechanism-based novel antitubercular agent, only a few have entered into clinical trials in the last six decades. In recent years, triazoles have been well explored as the most valuable scaffolds in drug discovery and development. Triazole framework possesses favorable properties like hydrogen bonding, moderate dipole moment, enhanced water solubility, and also the ability to bind effectively with biomolecular targets of M. tuberculosis and therefore this scaffold displayed excellent potency against TB. This review is an endeavor to summarize an up-to-date innovation of triazole-appended hybrids during the last 10 years having potential in vitro and in vivo antitubercular activity with structure activity relationship analysis. This review may help medicinal chemists to explore the triazole scaffolds for the rational design of potent drug candidates having better efficacy, improved selectivity and minimal toxicity so that these hybrid NCEs can effectively be explored as potential lead to fight against M. tuberculosis.

Metastable doubly threaded [3]rotaxanes with a large macrocycle

Ring size is a critically important parameter in many interlocked molecules as it directly impacts many of the unique molecular motions that they exhibit. Reported herein are studies using one of the largest macrocycles reported to date to synthesize doubly threaded [3]rotaxanes. A large ditopic 46 atom macrocycle containing two 2,6-bis(N-alkyl-benzimidazolyl)pyridine ligands has been used to synthesize several metastable doubly threaded [3]rotaxanes in high yield (65-75% isolated) via metal templating. Macrocycle and linear thread components were synthesized and self-assembled upon addition of iron(ii) ions to form the doubly threaded pseudo[3]rotaxanes that could be subsequently stoppered using azide-alkyne cycloaddition chemistry. Following demetallation with base, these doubly threaded [3]rotaxanes were fully characterized utilizing a variety of NMR spectroscopy, mass spectrometry, size-exclusion chromatography, and all-atom simulation techniques. Critical to the success of accessing a metastable [3]rotaxane with such a large macrocycle was the nature of the stopper group employed. By varying the size of the stopper group it was possible to access metastable [3]rotaxanes with stabilities in deuterated chloroform ranging from a half-life of <1 minute to ca. 6 months at room temperature potentially opening the door to interlocked materials with controllable degradation rates.

BINOL as a chiral element in mechanically interlocked molecules

In this minireview we present the use of the axially chiral 1,1'-binaphthyl-2,2'-diol (BINOL) unit as a stereogenic element in mechanically interlocked molecules (MIMs). We describe the synthesis and properties of such BINOL-based chiral MIMs, together with their use in further diastereoselective modifications, their application in asymmetric catalysis, and their use in stereoselective chemosensing. Given the growing importance of mechanically interlocked molecules and the key advantages of the privileged chiral BINOL backbone, we believe that this research area will continue to grow and deliver many useful applications in the future.

Noncovalently bound and mechanically interlocked systems using pillar[n]arenes

Pillar[n]arenes are pillar-shaped macrocyclic compounds owing to the methylene bridges linking the para-positions of the units. Owing to their unique pillar-shaped structures, these compounds exhibit various excellent properties compared with other cyclic host molecules, such as versatile functionality using various organic synthesis techniques, substituent-dependent solubility, cavity-size-dependent host-guest properties in organic media, and unit rotation along with planar chiral inversion. These advantages have enabled the high-yield synthesis and rational design of pillar[n]arene-based mechanically interlocked molecules (MIMs). In particular, new types of pillar[n]arene-based MIMs that can dynamically convert between interlocked and unlocked states through unit rotation have been produced. The highly symmetrical pillar-shaped structures of pillar[n]arenes result in simple NMR spectra, which are useful for studying the motion of pillar[n]arene wheels in MIMs and creating sophisticated MIMs with higher-order structures. The creation and application of polymeric MIMs based on pillar[n]arenes is also discussed.

Phenanthroline based rotaxanes: recent developments in syntheses and applications

The advancements in the field of mechanically interlocked molecular systems (MIMs) has concurrently restructured the material chemistry frontiers and provided ample scope to explore new dimensions for applications and diversity creation. Among all these molecular entities, rotaxanes have a special locale and many research groups over the globe have contributed to their current niche in supramolecular chemistry. From refinements for better yielding synthetic strategies to their application oriented designs, this field has come a long way and is well inclined for further developments. In this review, we aim to document the contemporary developments in the synthesis of phenanthroline (phen) based rotaxanes. In addition to providing a comprehensive account of various subtypes of these rotaxanes and their stitching strategies, their applications, wherever discernible, will be duely highlighted.

Distinctive features and challenges in catenane chemistry

From being an aesthetic molecular object to a building block for the construction of molecular machines, catenanes and related mechanically interlocked molecules (MIMs) continue to attract immense interest in many research areas. Catenane chemistry is closely tied to that of rotaxanes and knots, and involves concepts like mechanical bonds, chemical topology and co-conformation that are unique to these molecules. Yet, because of their different topological structures and mechanical bond properties, there are some fundamental differences between the chemistry of catenanes and that of rotaxanes and knots although the boundary is sometimes blurred. Clearly distinguishing these differences, in aspects of bonding, structure, synthesis and properties, between catenanes and other MIMs is therefore of fundamental importance to understand their chemistry and explore the new opportunities from mechanical bonds.

New Acetamidine Cu(II) Schiff base complex supported on magnetic nanoparticles pectin for the synthesis of triazoles using click chemistry

In this project, the new catalyst copper defines as Fe3O4@Pectin@(CH2)3-Acetamide-Cu(II) was successfully manufactured and fully characterized by different techniques, including FT-IR, XRD, TEM, FESEM, EDX, VSM, TGA, and ICP analysis. All results showed that copper was successfully supported on the polymer-coated magnetic nanoparticles. One of the most important properties of a catalyst is the ability to be prepared from simple materials such as pectin that's a biopolymer that is widely found in nature. The catalytic activity of Fe3O4@Pectin@(CH2)3-Acetamide-Cu(II) was examined in a classical, one pot, and the three-component reaction of terminal alkynes, alkyl halides, and sodium azide in water and observed, proceeding smoothly and completed in good yields and high regioselectivity. The critical potential interests of the present method include high yields, recyclability of catalyst, easy workup, using an eco-friendly solvent, and the ability to sustain a variety of functional groups, which give economical as well as ecological rewards. The capability of the nanocomposite was compared with previous works, and the nanocomposite was found more efficient, economical, and reproducible. Also, the catalyst can be easily removed from the reaction solution using an external magnet and reused for five runs without reduction in catalyst activity.

Computer-aided design of molecular machines: techniques, paradigms and difficulties

With their development in the past decade, molecular machines, which achieve specific tasks by responding to external stimuli, have gradually come to be regarded as powerful tools for a wide range of applications, rather than interesting molecular toys. This conceptual change in turn motivates scientists to design molecular machines with complex architectures. Due to the lack of general principles bridging the functions and the chemical structures of molecular machines, experience-based design becomes difficult with the increase of size and complexity of the architectures. Computer-aided molecular-machine design, therefore, has attracted widespread attention on account of its ability to model and investigate complex molecular architectures without too much time and expense required for synthetic experiments. Using leading-edge numerical-simulation techniques, the mechanisms underlying achieving tasks through response to external stimuli of a large number of existing molecular machines have been successfully explored. Based on the experience of studying existing molecular machines, generalized methodologies of predicting the properties and working principles of molecular candidates have been established, paving the way for de novo computer-aided design of molecular machines. In this perspective, we introduce cutting-edge techniques that have been applied for investigating and designing molecular machines. We show paradigms of computer-aided design of molecular machines, which can serve as guidelines for the investigation of new supramolecular architectures. Moreover, we discuss the limitations and possible future developments of current techniques and methodologies in the field of computer-aided design of molecular machines.

Macrocyclic vs. [2]catenane btp structures: influence of (aryl) substitution on the self templation of btp ligands in macrocyclic synthesis

The synthesis of four 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) olefin based ligands 3, 4, 11 and 12 is described and their attempted use to form mechanically interlocked molecules using ring closing metatheses (RCM) reactions. The btp ligands were modified in two ways, in 3 and 4 the aryl substitution pattern was changed from 4^th position to 3^rd position and in the case of 11 and 12, the arms were replaced with aliphatic chains. Our study demonstrates that for all four ligands, the RCM reactions only result in the formation of macrocyclic structures, which in three of the cases, were structurally characterised in both solution (using NMR and HRMS) and in the solid-state using X-ray crystallography. NMR studies were also carried out to investigate if these ligands could preorganise in solution via hydrogen bonding interactions. This study provides a handle of how such precursor substitution can be used to direct the formation of macrocycles or mechanically interlocked structures.

Single nanoparticle identification coupled with auto-identify algorithm for rapid and accurate detection of L-histidine

In this work, an auto-identify sensor was constructed for rapid and high-precision detection of L-histidine. The proposed strategy is based on the auto-identify algorithm and the aggregation of alkynyl and azide functionalized gold nanoparticles induced by the Cu⁺ catalyzed azides and alkynes cycloaddition (CuAAC) reaction. Specially, the color of scattering light spots for the aggregated gold nanoparticle (AuNPs) caused by CuAAC reaction was quite different from that of the monomers. However, L-histidine can bind to Cu²⁺ and inhibits the production of Cu⁺, hence preventing the aggregation of AuNPs. Therefore, there is a distinct change of color as the addition of L-histidine under dark-field microscopy. Then, L-histidine can be quantitatively detected by combining the color change with the Meanshift algorithm accurately and automatically. Such proposed method has been successfully applied for the detection of L-histidine in serum sample with satisfying result.

Pyrazine Based Type-I Sensitizing Assemblies for Photoreduction of Cu(II) in 'One-Pot Three-Component' CuAAC Reaction Under Aerial Conditions

Photosensitizing assemblies of pyrazine derivative PDA have been developed which exhibit a high photostability, 'lighted' excited state, balanced redox potential, high transportation potential and activate oxygen via type-I pathway only. These PDA assemblies in combination with Cu(II) ions catalyze the CuAAC reaction via in situ reduction of Cu(II) ions without any reducing or stabilizing agent. The present protocol has wide substrate scope with recyclability of the catalytic system up to six catalytic cycles and is applicable to gram-scale synthesis.

Lasso Proteins-Unifying Cysteine Knots and Miniproteins

Complex lasso proteins are a recently identified class of biological compounds that are present in considerable fraction of proteins with disulfide bridges. In this work, we look at complex lasso proteins as a generalization of well-known cysteine knots and miniproteins (lasso peptides). In particular, we show that complex lasso proteins with the same crucial topological features-cysteine knots and lasso peptides-are antimicrobial proteins, which suggests that they act as a molecular plug. Based on an analysis of the stability of the lasso piercing residue, we also introduce a method to determine which lasso motif is potentially functional. Using this method, we show that the lasso motif in antimicrobial proteins, as well in that in cytokines, is functionally relevant. We also study the evolution of lasso motifs, their conservation, and the usefulness of the lasso fingerprint, which extracts all topologically non-triviality concerning covalent loops. The work is completed by the presentation of extensive statistics on complex lasso proteins to analyze, in particular, the strange propensity for "negative" piercings. We also identify 21 previously unknown complex lasso proteins with an ester and a thioester bridge.

Halogen-Bonding Strapped Porphyrin BODIPY Rotaxanes for Dual Optical and Electrochemical Anion Sensing

Anion receptors employing two distinct sensory mechanisms are rare. Herein, we report the first examples of halogen-bonding porphyrin BODIPY [2]rotaxanes capable of both fluorescent and redox electrochemical sensing of anions. 1 H NMR, UV/visible and electrochemical studies revealed rotaxane axle triazole group coordination to the zinc(II) metalloporphyrin-containing macrocycle component, serves to preorganise the rotaxane binding cavity and dramatically enhances anion binding affinities. Mechanically bonded, integrated-axle BODIPY and macrocycle strapped metalloporphyrin motifs enable the anion recognition event to be sensed by the significant quenching of the BODIPY fluorophore and cathodic perturbations of the metalloporphyrin P/P+. redox couple.

Triazole-based, optically-pure metallosupramolecules; highly potent and selective anticancer compounds

Functionalised triazole aldehydes are used in the highly selective self-assembly of water-compatible, optically pure, low symmetry Fe(ii)- and Zn(ii)-based metallohelices. Sub-micromolar antiproliferative activity is observed against various cancerous cell lines, accompanied by excellent selectivity versus non-cancerous cells and potential for synergistic combinatorial therapy with cisplatin.

Prolinamide plays a key role in promoting copper-catalyzed cycloaddition of azides and alkynes in aqueous media via unprecedented metallacycle intermediates

Room temperature copper-catalyzed cycloaddition of azides and alkynes (CuAAC) proceeds in the presence of a prolinamide ligand in aqueous media via unique metallacycles.

Synthetic platform for mono-functionalised tridentate macrocycles as key precursors of mechanically-linked macromolecular systems

Macrocycles bearing a variety of functional groups give access to a wide range of synthetic methods for further derivatisation or preparation of more complex structures such as mechanically interlocked molecules or polymeric materials.

Optical sensing of anions by macrocyclic and interlocked hosts

This review summarises recent developments in the use of macrocyclic and mechanically-interlocked host molecules as optical sensors for anions.

Molecular Sensing with Host Systems for Hyperpolarized 129Xe

Hyperpolarized noble gases have been used early on in applications for sensitivity enhanced NMR. 129Xe has been explored for various applications because it can be used beyond the gas-driven examination of void spaces. Its solubility in aqueous solutions and its affinity for hydrophobic binding pockets allows "functionalization" through combination with host structures that bind one or multiple gas atoms. Moreover, the transient nature of gas binding in such hosts allows the combination with another signal enhancement technique, namely chemical exchange saturation transfer (CEST). Different systems have been investigated for implementing various types of so-called Xe biosensors where the gas binds to a targeted host to address molecular markers or to sense biophysical parameters. This review summarizes developments in biosensor design and synthesis for achieving molecular sensing with NMR at unprecedented sensitivity. Aspects regarding Xe exchange kinetics and chemical engineering of various classes of hosts for an efficient build-up of the CEST effect will also be discussed as well as the cavity design of host molecules to identify a pool of bound Xe. The concept is presented in the broader context of reporter design with insights from other modalities that are helpful for advancing the field of Xe biosensors.

A comparison of the catalytic efficiency of copper-based bimetallic nanoparticles in the click reactions

Compared to monometallic nanoparticles, bimetallic nanoparticles have attracted wide attention due to their physical properties, excellent catalytic activity, high regioselectivity, selectivity, and stability. Here, we have first synthesized 10 different kinds of graphene quantum dot–stabilized Cu-based bimetallic nanoparticles (including CoCu, NiCu, RuCu, RhCu, PdCu, AgCu, IrCu, AuCu, FeCu, and PtCu) and compared their catalytic activities in a CuAAC click reaction. Among them, RhCu provides the highest yield of the desired product in the click reaction (77%). The catalytic activity of these MCu in the click reaction is in the order: RhCu > PdCu > AuCu > CoCu > PtCu > AgCu > NiCu > CuNP > RuCu > FeCu > IrCu.