Application of host-guest chemistry in nanotube-based device fabrication: photochemically controlled immobilization of azobenzene nanotubes on patterned alpha-CD monolayer/Au substrates via molecular recognition

Photomanipulation of Minimal Synthetic Cells: Area Increase, Softening, and Interleaflet Coupling of Membrane Models Doped with Azobenzene-Lipid Photoswitches

Light can effectively interrogate biological systems in a reversible and physiologically compatible manner with high spatiotemporal precision. Understanding the biophysics of photo-induced processes in bio-systems is crucial for achieving relevant clinical applications. Employing membranes doped with the photolipid azobenzene-phosphatidylcholine (azo-PC), a holistic picture of light-triggered changes in membrane kinetics, morphology, and material properties obtained from correlative studies on cell-sized vesicles, Langmuir monolayers, supported lipid bilayers, and molecular dynamics simulations is provided. Light-induced membrane area increases as high as ≈25% and a ten-fold decrease in the membrane bending rigidity is observed upon trans-to-cis azo-PC isomerization associated with membrane leaflet coupling and molecular curvature changes. Vesicle electrodeformation measurements and atomic force microscopy reveal that trans azo-PC bilayers are thicker than palmitoyl-oleoyl phosphatidylcholine (POPC) bilayers but have higher specific membrane capacitance and dielectric constant suggesting an increased ability to store electric charges across the membrane. Lastly, incubating POPC vesicles with azo-PC solutions results in the insertion of azo-PC in the membrane enabling them to become photoresponsive. All these results demonstrate that light can be used to finely manipulate the shape, mechanical and electric properties of photolipid-doped minimal cell models, and liposomal drug carriers, thus, presenting a promising therapeutic alternative for the repair of cellular disorders.

Recent Advances in the Pharmaceutical and Biomedical Applications of Cyclodextrin-Capped Gold Nanoparticles

The real problem in pharmaceutical preparation is drugs' poor aqueous solubility, low permeability through biological membranes, and short biological t_1/2. Conventional drug delivery systems are not able to overcome these problems. However, cyclodextrins (CDs) and their derivatives can solve these challenges. This article aims to summarize and review the history, properties, and different applications of cyclodextrins, especially the ability of inclusion complex formation. It also refers to the effects of cyclodextrin on drug solubility, bioavailability, and stability. Moreover, it focuses on preparing and applying gold nanoparticles (AuNPs) as novel drug delivery systems. It also studies the uses and effects of cyclodextrins in this field as novel drug carriers and targeting devices. The system formulated from AuNPs linked with CD molecules combines the advantages of both CD and AuNPs. Cyclodextrins benefit in increasing aqueous drug solubility, loading capacity, stability, and size control of gold NPs. Also, AuNPs are applied as diagnostic and therapeutic agents because of their unique chemical properties. Plus, AuNPs possess several advantages such as ease of detection, targeted and selective drug delivery, greater surface area, high loading efficiency, and higher stability than microparticles. In the present article, we tried to present the potential pharmaceutical applications of CD-derived AuNPs in biomedical applications including antibacterial, anticancer, gene-drug delivery, and various targeted drug delivery applications. Also, the article highlighted the role of CDs in the preparation and improvement of catalytic enzymes, the formation of self-assembling molecular print boards, the fabrication of supramolecular functionalized electrodes, and biosensors formation.

Theoretical Study on Photothermal Properties of Azobenzene Sulfonate/Magnesium-Aluminum Hydroxide Composite Dye

The assembly of various azo dyes and pigments with inorganic layered materials could develop new types of intercalation materials. The electronic structures and photothermal properties of composite materials (AbS^--LDH) constituted by azobenzene sulfonate anions (AbS^-) and Mg-Al layered double hydroxide (LDH) lamella were theoretically studied at the M06-2X/def2-TZVP//M06-2X/6-31G(d,p) level using density functional theory and time-dependent density functional theory. Meanwhile, the influences of LDH lamella on the AbS^- in AbS^--LDH materials were investigated. The calculated results showed that the addition of LDH lamella could lower the isomerization energy barrier of CAbS^- anions (CAbS^- stands for cis AbS^-). The thermal isomerization mechanisms of AbS^--LDH and AbS were related to the conformational change of the azo group, out-of-plane rotation and in-plane inversion. The LDH lamella could reduce the energy gap of the n → π* and π → π* electronic transition and lead to a red-shift in the absorption spectra. When a polar solvent DMSO was applied, the excitation energy of the AbS^--LDHs was increased, making its photostability stronger than in nonpolar solvent and solvent-free.

PANI-Fe3O4@ZnO nanocomposite as magnetically recoverable organometallic nanocatalyst promoted synthesis of new Azo chromene dyes and evaluation of their antioxidant and antimicrobial activities

A new series of azo chromene dyes were synthesized via a facile cyclocondensation reaction of (E)-1,2-diphenyl-1-diazene and 4-aminocoumarin with 1:2 molar ratio catalyzed by the polyaniline-Fe₃O₄@ZnO nanocomposite (PANI-Fe₃O₄@ZnO). The salient features of this protocol lie in simple experimental procedure, moderate reaction conditions, and uses PANI-Fe₃O₄@ZnO nanocomposite as a magnetically separable heterogeneous catalyst. Two well-known methods were employed for assessing the antioxidant abilities of the target compounds, including free radical trapping of 2,2-diphenyl-1-picrylhydrazyl (DPPH), as well as ferric reducing antioxidant power assay. Also, several synthesized compounds were screened for their in vitro antimicrobial activities by employing the disk diffusion test on Gram-negative as well as Gram-positive bacteria.

Self-Assembling Peptidic Bolaamphiphiles for Biomimetic Applications

Bolaamphiphile, which is a class of amphiphilic molecules, has a unique structure of two hydrophilic head groups at the ends of the hydrophobic center. Peptidic bolaamphiphiles that employ peptides or amino acids as their hydrophilic groups exhibit unique biochemical activities when they self-organize into supramolecular structures, which are not observed in a single molecule. The self-assembled peptidic bolaamphiphiles hold considerable promise for imitating proteins with biochemical activities, such as specific affinity toward heterogeneous substances, a catalytic activity similar to a metalloenzyme, physicochemical activity from harmonized amino acid segments, and the capability to encapsulate genes like a viral vector. These diverse activities give rise to large research interest in biomaterials engineering, along with the synthesis and characterization of the assembled structures. This review aims to address the recent progress in the applications of peptidic bolaamphiphile assemblies whose densely packed peptide motifs on their surface and their stacked hydrophobic centers exhibit unique protein-like activity and designer functionality, respectively.

Substituent and Solvent Polarity on the Spectroscopic Properties in Azo Derivatives of 2-Hydroxynaphthalene and Their Difluoroboranes Complexes

Novel fluorescent dyes such as difluoroborane complexes of 1-phenylazonaphthalen-2-ol derivatives were successfully synthesized and characterized with a focus on the influence of a substituent and a solvent on the basic photophysical properties. ¹H, ¹¹B, ¹³C, ¹⁵N, and ¹⁹F nuclear magnetic resonance (NMR) spectra of substituted 1-phenylazonaphthalen-2-ol difluoroboranes and their parent azo dyes were recorded and discussed. The absorption and emission properties of synthesized compounds were investigated in solvents of varying polarity. They were found to be fluorescent despite the presence of the azo group. The azo group rotation was blocked by complexing with -BF₂ to get a red shift in absorption. Solvent-dependent spectral properties of compounds were investigated using Lipper-Mataga and Bakhshiev plot. The calculated DFT energies and Frontier Molecular Orbitals calculations of the studied compounds were proved to be consistent with the experimental observations.

TEMPO catalyzed oxidative dehydrogenation of hydrazobenzenes to azobenzenes

A metal-free direct oxidative dehydrogenation approach for the synthesis of azobenzenes from hydrazobenzenes has been developed by using TEMPO as an organocatalyst for the first time. The reaction proceeded in open air under mild reaction conditions. A wide range of hydrazobenzenes readily undergo dehydrogenation to give the corresponding azobenzenes in excellent yields.

Metal-free cascade reactions of aziridines with arylalkynes and aryldiazoniums: facile access to arylazopyrrolines

A novel and facile approach to synthesize arylazopyrroline scaffolds via metal-free cascade reactions of aziridines with arylalkynes and aryldiazoniums has been developed, providing access to a variety of 4-arylazo-2-pyrrolines in a highly concise fashion. This efficient process, which can be performed at the gram scale, enjoys operational simplicity and mild and metal-free conditions.

Interactions of the cis and trans states of an azobenzene photoswitch with lysozyme induced by red and blue light

Exploring the interaction between an azobenzene-based photoswitch and natural protein can help elucidate how the photo-control of an optical molecule participates in the transmission and delivery of proteins, as well as the effects of azo-switch trans and cis states on protein configurations. In this study, fluorescence analysis, circular dichroism spectroscopy, molecular docking, and molecular dynamics simulations were used to study the interaction among different configurations of tetra-ortho-methoxy substituted azobenzene di-maleimide (toM-ABDM), a red light-induced optical azo-switch, and lysozyme (LYZ). Results showed that toM-ABDM caused the static quenching of LYZ. The cis toM-ABDM had stronger binding affinity than trans toM-ABDM. The noncovalent interaction, hydrogen bonds and van der Waals forces, could not regulate the conformation of LYZ in photo-control. A binding model of toM-ABDM and LYZ in different forms induced by red and blue light was further established by computer simulation.

Classifications, properties, recent synthesis and applications of azo dyes

In this work, we have presented a very detailed review of the different classification of azo dyes as a function of the number of azo groups and the appropriate functional groups. Then we pointed out some chemical properties of these dyes such as reactivity, isomerization and tautomerism and listed. In the following, we have summarized some recent syntheses of azo dyes and the mechanism of azo dye/polymer conjugation. Finally, we indicate the principle of Gewald's reaction and its application to the synthesis of new azo dyes.

Molecularly engineered hole-transport material for low-cost perovskite solar cells

Triphenylamine-N-phenyl-4-(phenyldiazenyl)aniline (TPA-AZO) is synthesized via a facile CuI-catalyzed reaction and used as a hole transport material (HTM) in perovskite solar cells (PSCs), as an alternative to the expensive spiro-type molecular materials, including commercial 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD). Experimental and computational investigations reveal that the highest occupied molecular orbital (HOMO) level of TPA-AZO is deeper than that of spiro-OMeTAD, and optimally matches with the conduction band of the perovskite light absorber. The use of TPA-AZO as a HTM results in PSC prototypes with a power conversion efficiency (PCE) approaching that of the spiro-OMeTAD-based reference device (17.86% vs. 19.07%). Moreover, the use of inexpensive starting reagents for the synthesis of TPA-AZO makes the latter a new affordable HTM for PSCs. In particular, the cost of 1 g of TPA-AZO ($22.76) is significantly lower compared to that of spiro-OMeTAD ($170-475). Overall, TPA-AZO-based HTMs are promising candidates for the implementation of viable PSCs in large-scale production.

Light triggered encapsulation and release of C60 with a photoswitchable TPE-based supramolecular tweezers

Stimuli responsive hosts for C₆₀ can control its binding and release on demand. A photoswitchable TPE based supramolecular host can encapsulate C₆₀ in the Z-form with a markedly different visual change in the colour. In addition, the Z-1 bound C₆₀ has been characterized by various spectroscopic methods and mass spectrometry. Upon exposure to visible light (>490 nm), the host switches to the E-form where the structural complementarity with the guest is destroyed as a result of which the C₆₀ is disassembled from the host. The results described herein reveals an actionable roadmap to pursue further advances in component self-assembly particularly light-induced association and dissociation of a guest molecule.

Threading-gated photochromism in [2]pseudorotaxanes

Rigid, Y-shaped imidazole compounds containing the bis(thienyl)ethene moiety were designed and synthesized. The 4,5-bis(benzothienyl)-2-phenylimidazolium cations were then used as axles for [2]pseudorotaxane formation with 24-membered crown ether wheels. It was demonstrated using 1H NMR spectroscopy, UV-Vis absorption and emission spectroscopies that this host-guest interaction results in significant changes in the photochromic properties of the imidazolium axles. This is a rare example of gated photochromism, which exploits the recognition event of an interpenetrated molecular system to tune the photochromic properties in one of the components.

Immobilized antimony species on magnetite: a novel and highly efficient magnetically reusable nanocatalyst for direct and gram-scale reductive-coupling of nitroarenes to azoarenes

In this study, magnetic nanoparticles of Fe3O4@SbF x from the immobilization of SbF3 on magnetite were synthesized. The prepared nanocomposite system was then characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, vibrating sample magnetometry and inductively coupled plasma optical emission spectroscopy. Next, the catalytic activity of Fe3O4@SbF x MNPs was highlighted by one-pot reductive-coupling of aromatic nitro compounds to the corresponding azoarene materials with NaBH4. The reactions were carried out in refluxing EtOH within 6-25 min to afford the products in high yields. The reusability of the Sb-magnetite system was also studied for 6 consecutive cycles without significant loss of catalytic activity. This synthetic protocol provided several advantages in terms of introducing a novel catalytic system based on antimony species for direct and gram-scale preparation of azoarenes from nitroarenes, low loading of the nanocatalyst, mild reaction conditions, using ethanol as a green and economic solvent and high yield of the products.

Ultrasonic Studies of Solid Azobenzene-Decorated Polymer Thin Films

This work investigates the effect of ultrasound on switching of cis azobenzene isomers to their trans counterparts in solid films of methyl methacrylate and methacryloyloxyazobenzene copolymers [P(MMA/MOAB)]. Ultraviolet-visible and 1H nuclear magnetic resonance spectroscopies demonstrate that 46% of the cis isomer converts to the trans form purely by ultrasonic agitation and 46% converts to the trans isomer by localized ultrasound-induced heating effects. Comparative studies of isomerization by ultrasound wave, heat, and visible irradiation show that ultrasound exposure requires a longer time to switch the cis-to-trans conformation. The estimated activation energy for the cis-to-trans conversion in solid polymer films is shown to be comparable to previous values of azobenzene isomerization, indicating that incorporation of the chromophore in a polymeric system affects the kinetics of transition but not the barriers to conformational change.

Photoswitching of Azobenzene-Based Reverse Micelles above and at Subzero Temperatures As Studied by NMR and Molecular Dynamics Simulations

We designed and studied the structure, dynamics, and photochemistry of photoswitchable reverse micelles (RMs) composed of azobenzene-containing ammonium amphiphile 1 and water in chloroform at room and subzero temperatures by NMR spectroscopy and molecular dynamics simulations. The NMR and diffusion coefficient analyses showed that micelles containing either the E or Z configuration of 1 are stable at room temperature. Depending on the water-to-surfactant molar ratio, the size of the RMs remains unchanged or is slightly reduced because of the partial loss of water from the micellar cores upon extensive E → Z or Z → E photoisomerization of the azobenzene group in 1. Upon freezing at 253 or 233 K, E-1 RMs partially precipitate from the solution but are redissolved upon warming whereas Z-1 RMs remain fully dissolved at all temperatures. Light-induced isomerization of 1 at low temperatures does not lead to the disintegration of RMs remaining in the solution; however, its scope is influenced by a precipitation process. To obtain a deeper molecular view of RMs, their structure was characterized by MD simulations. It is shown that RMs allow for amphiphile isomerization without causing any immediate significant structural changes in the micelles.

Supramolecular Self-Assembly into Biofunctional Soft Nanotubes: From Bilayers to Monolayers

The inner and outer surfaces of bilayer-based lipid nanotubes can be hardly modified selectively by a favorite functional group. Monolayer-based nanotubes display a definitive difference in their inner and outer functionalities if bipolar wedge-shaped amphiphiles, so-called bolaamphiphiles, as a constituent of the monolayer membrane pack in a parallel fashion with a head-to-tail interface. To exclusively form unsymmetrical monolayer lipid membranes, we focus herein on the rational molecular design of bolaamphiphiles and a variety of self-assembly processes into tubular architectures. We first describe the importance of polymorph and polytype control and then discuss diverse methodologies utilizing a polymer template, multiple hydrogen bonds, binary and ternary coassembly, and two-step self-assembly. Novel biologically important functions of the obtained soft nanotubes, brought about only by completely unsymmetrical inner and outer surfaces, are discussed in terms of protein refolding, drug nanocarriers, lectin detection, a chiral inducer for achiral polymers, the tailored fabrication of polydopamine, and spontaneous nematic alignment.

Ionic Liquid Promoted Diazenylation of N-Heterocyclic Compounds with Aryltriazenes under Mild Conditions

An efficient, mild, and metal-free approach to direct diazenylation of N-heterocyclic compounds with aryltriazenes using Brønsted ionic liquid as a promoter has been developed for the first time. Many N-heterocyclic azo compounds were synthesized in good to excellent yields at room temperature under an open atmosphere. Notably, the promoter 1,3-bis(4-sulfobutyl)-1H-imidazol-3-ium hydrogen sulfate could be conveniently recycled and reused with the same efficacies for at least four cycles.

Light-Triggered Switching of Reversible and Alterable Biofunctionality via β-Cyclodextrin/Azobenzene-Based Host-Guest Interaction

Most of the recent reports focused on using cyclodextrin/azobenzene/polymer for reversible immobilization of biomolecules, the reversible photoswitching of biofunctions via universal and low-cost strategy, were barely investigated. Herein, we report light-triggered switching of reversible and alterable biofunctionality on silicon interface via β-cyclodextrin/azobenzene based host-guest interaction. Biofunctional azobenzene-grafted polymers were synthesized and assembled onto β-cyclodextrin anchored interfaces to form "smart" monolayers of light-triggered switchable brushes. The photoresponsive interfaces exhibit reversible and alterable biofunctionality switching from antibacterial/hemostatic to bioadhesion/anticoagulant upon ultraviolet and visible (UV-vis) light cycles.

Supramolecular interactions of nonsteroidal anti-inflammatory drug in nanochannels of molecular containers: a spectroscopic, thermogravimetric and microscopic investigation

Supramolecular host-guest complexation between the nonsteroidal anti-inflammatory drug indomethacin (IMC) and molecular containers were investigated. The weakly fluorescent drug molecule becomes highly fluorescent on complexation with different molecular containers, and time-resolved fluorescence emission spectroscopy reveals that the lifetime components of IMC significantly increase in the presence of molecular containers, compared with the lifetimes in neat water. The respective solid host-guest complexes were synthesised and characterised by Fourier transform infrared and (1) H nuclear magnetic resonance spectroscopic analysis. Microscopy techniques were used to analyse modifications of the surface morphology, owing to the formation of supramolecular complexes. The effect of the molecular container on the optical properties of IMC has also been investigated to determine the effect of nanochannels of different size and structure.

Interaction of bolaform surfactants with p-sulfonatocalix[4]arene: the role of two positive charges in the binding

The inclusion binding manners of bolaform surfactants of type C(n)R6(2+) 2Br(-) with different spacer lengths (n = 6, 12) and terminal headgroup volumes (R = methyl, ethyl) by p-sulfonatocalix[4]arene were studied. The combination of ITC parameters (binding constants and complexation enthalpy and entropy) and NMR chemical shifts and NOE cross-peaks obtained upon complexation allows us to propose different binding modes. The results point out that the spacer length has an influence on the binding stoichiometry. The bolaforms with larger spacer lengths between polar head groups enable the formation of 2:1 complexes in addition to 1:1, while with the shorter spacer they form only 1:1 complexes. On the other hand, the formation of 1:1 complexes is not affected by the headgroup volume or the spacer length of the bolaform. Unexpectedly, a complex binding mode was observed where both positive charged terminal groups of the bolaform are accommodated in the cavity of the calixarene. The inclusion of both terminal groups of the guests can be related to its own structure but also evidence the high flexibility of the calixarene.

Supramolecular polymerization of supramonomers: a way for fabricating supramolecular polymers

This communication describes a new method of fabricating supramolecular polymers through supramolecular polymerization of supramonomers.

Designing a photoresponsive molecularly imprinted system on a silicon wafer substrate surface

A photoresponsive molecularly imprinted system was prepared on a silicon wafer substrate surface via the host-guest complex of grafted 4-(3-triethoxysilylpropyiureido)azobenzene (TSUA) and mono-6-deoxy-6-((p-chlorosulfonyl)-benzoic acid)-β-cyclodextrin (CBA-β-CD), and the acid-base pair interactions/hydrogen bonds between CBA-β-CD and the template molecules, including theophylline (TPE) and 4-hydroxybenzoic acid (4-HA). A molecular imprinting cycle "imprinting → extracting → uptaking → shuffling" was also defined in the study, the processes of uptaking and shuffling were investigated in detail by equilibrium binding experiments, and the Langmuir adsorption isotherm and Scatchard equation were used to evaluate the binding affinity and the theoretical binding sites of the molecularly imprinted (MIS), nonimprinted (NIS), and pure (PS) silicon wafer substrates. Compared with the NISs and PSs, the MISs showed a significantly higher adsorption capacity for the template molecules. More importantly, the MISs showed a reimprinted ability; after the process of shuffling, the molecularly imprinted systems on the substrate surface were destroyed, and new imprinted systems could be fabricated for the recognition of other template molecules after washing the substrates under irradiation at 450 nm. Moreover, the selective adsorption for the MISs was investigated, which indicated that the MISs showed specific affinity to the template molecules (TPE or 4-HA).

Metal chelates anchored to poly-L-peptides and linear D,L-α-peptides with promising nanotechnological applications

Regular configurationally alternating amino acid sequences generate cyclic and linear helical peptides with a local β-conformation able to self-assemble in nanowires and nanoscaffolds directed and stabilized by hydrogen bonds. The possibility of modulating the chemical profile of the various amino acid residues containing reactive side chains means that peptides could be flexible templates for creating various building blocks. A method for the design of molecules with potential spintronic properties is described. Peptides containing lysine residues, the side chains of which are bridged through the formation of metal chelates via Schiff bases, could provide stable molecular channels. When metal chelates with high electron spin states are used, their coupling could generate materials that are interesting due to their magnetic properties as well as for the patterning of nanometric lattices driven by their orientation under a magnetic field. With this aim, three alternating D- and L-lysine-containing octapeptides are synthesized and the formation of their bis(pyridoxalaldimine) copper(II) chelate derivatives is shown by absorption and circular dichroism spectroscopies.