Supramolecular photosensitizers with enhanced antibacterial efficiency

Cationic Oligo(thiophene ethynylene) with Broad-Spectrum and High Antibacterial Efficiency under White Light and Specific Biocidal Activity against S. aureus in Dark

We designed and synthesized a novel oligo(thiophene ethynylene) (OTE) to investigate the antibacterial activities against Gram-positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram-negative (Ralstonia solanacearum and Escherichia coli) bacteria in vitro by photodynamic therapy (PDT). Notably, OTE presents broad-spectrum and greatly high antibacterial activities after white light irradiation at nanogram per milliliter concentrations. The half inhibitory concentrations (IC50) values obtained for S. aureus, S. epidermidis, E. coli, and R. solanacearum are 8, 13, 24, and 52 ng/mL after illumination for 30 min, respectively, which are lower than that of other PDT agents. Interestingly, OTE shows the specific and very strong dark killing capability against S. aureus at the concentration of 180 ng/mL for 30 min, which is the highest efficiency biocide against S. aureus without the need of irradiation to date. The antibacterial mechanism investigated demonstrated that reactive oxygen species or singlet-oxygen generated by OTE kills bacteria irreversibly upon white light irradiation, and OTE as a v-type oligomer exerts its toxicity directly on destroying bacterial cytoplasmic membrane in the dark. Importantly, the OTE shows no cell cytotoxicity and excellent biocompatibility. The results indicate that it is potential to provide versatile applications in the efficient control of pathogenic organisms and specific application for killing S. aureus.

Stimuli-responsive supramolecular materials: photo-tunable properties and molecular recognition behavior

A supramolecular system stabilized through complementary hydrogen bonding and displaying stimuli-responsive behavior has been fabricated into “recordable” and “rewritable” surface relief gratings operated under laser illumination.

Cooperative self-assembly of porphyrins with polymers possessing bioactive functions

This review covers recent research on design strategies for the cooperative self-assembly of porphyrins with polymers and its implementation as bioactive assembly.

Nanosupramolecular assembly of amphiphilic guest mediated by cucurbituril for doxorubicin delivery

A binary supramolecular nanoparticle was constructed through the complexation of cucurbit[6]uril with an amphiphilic polyamine by macrocycle-assisted aggregation strategy, which exhibited controlled drug loading and release behaviours.

Photolysis of a bola-type supra-amphiphile promoted by water-soluble pillar[5]arene-induced assembly

A novel monolayer supramolecular vesicle assembled from a pillararene-based bola-type supra-amphiphile was successfully constructed, which showed excellent photodegradable properties and might have potential applications in phototherapy.

Surface charge-conversion polymeric nanoparticles for photodynamic treatment of urinary tract bacterial infections

Urinary tract infections are typical bacterial infections which result in a number of economic burdens. With increasing antibiotic resistance, it is urgent that new approaches are explored that can eliminate pathogenic bacteria without inducing drug resistance. Antimicrobial photodynamic therapy (PDT) is a new promising tactic. It is a gentle in situ photochemical reaction in which a photosensitizer (PS) generates reactive oxygen species (ROS) under laser irradiation. In this work, we have demonstrated Chlorin e6 (Ce6) encapsulated charge-conversion polymeric nanoparticles (NPs) for efficiently targeting and killing pathogenic bacteria in a weakly acidic urinary tract infection environment. Owing to the surface charge conversion of NPs in an acidic environment, the NPs exhibited enhanced recognition for Gram-positive (ex. S. aureus) and Gram-negative (ex. E. coli) bacteria due to the charge interaction. Also, those NPs showed significant antibacterial efficacy in vitro with low cytotoxicity. The MIC value of NPs to E. coli is 17.91 μg ml(-1), compared with the free Ce6 value of 29.85 μg ml(-1). Finally, a mouse acute cystitis model was used to assess the photodynamic therapy effects in urinary tract infections. A significant decline (P < 0.05) in bacterial cells between NPs and free Ce6 occurred in urine after photodynamic therapy treatment. And the plated counting results revealed a remarkable bacterial cells drop (P < 0.05) in the sacrificed bladder tissue. Above all, this nanotechnology strategy opens a new door for the treatment of urinary tract infections with minimal side effects.

High-Internal-Phase Emulsion Tailoring Polymer Amphiphilicity towards an Efficient NIR-Sensitive Bacteria Filter

Emulsions having a high internal-phase volume fraction—termed as HIPEs for high internal phase emulsions—are in high demand as templates for functional macroporous materials. Designing molecular surfactants with appropriate amphiphilicity plays a critical role in the HIPE preparation. In this study, successful tailoring of the amphiphilicity of the originally hydrophobic block co-polymer of polystyrene-b-polyvinylpyridine (PS-b-P4VP) is reported. In combination with trifluoroacetic acid, less than 5 wt% of the polymer-CF3COOH system is feasible as a surfactant for HIPE preparation; this is lower than the amounts typically needed for commonly used commercial surfactants. Using the HIPEs as templates, well-defined closed- and open-cell macroporous triacrylate-based monoliths are fabricated simply through the adjustment of the ratio of the water phase to oil phase. After coating the resulting macroporous material with polypyrrole nanoparticles, the system can be exploited as an NIR-sensitive filter for bacteria; it not only excludes oversized bacteria, but it also kills the bacteria with the help of NIR-induced heat.

A supramolecular nanovehicle toward systematic, targeted cancer and tumor therapy

A supramolecular nanovehicle (denoted as SNV) was fabricated by encapsulating zinc phthalocyanine (ZnPc) and doxorubicin (DOX) into a copolymer (PVP-b-PAA-g-FA), so as to achieve systematic and synergistic chemotherapy-photodynamic therapy (PDT), targeted tumor imaging and therapy. The sophisticated copolymer designed in this work can load the PDT photosensitizer (ZnPc) and chemotherapy drug (DOX) simultaneously, which exhibits an excellent performance in chemotherapy-PDT targeted cancer and tumor therapy for both in vitro studies performed with HepG2 cells and in vivo tests with mice. This work provides a new drug formulation with a chemotherapy-PDT synergistic effect by virtue of the supramolecular material design, which possesses the advantages of an ultra-low drug dosage and highly-efficient in vivo targeted tumor imaging/therapy.

A Supramolecular Antibiotic Switch for Antibacterial Regulation

A supramolecular antibiotic switch is described that can reversibly "turn-on" and "turn-off" its antibacterial activity on demand, providing a proof-of-concept for a way to regulate antibacterial activity of biotics. The switch relies on supramolecular assembly and disassembly of cationic poly(phenylene vinylene) derivative (PPV) with cucurbit[7]uril (CB[7]) to regulate their different interactions with bacteria. This simple but efficient strategy does not require any chemical modification on the active sites of the antibacterial agent, and could also regulate the antibacterial activity of classical antibiotics or photosensitizers in photodynamic therapy. This supramolecular antibiotic switch may be a successful strategy to fight bacterial infections and decrease the emergence of bacterial resistance to antibiotics from a long-term point of view.

Supramolecular free radicals: near-infrared organic materials with enhanced photothermal conversion

A novel kind of supramolecular free radical with significantly improved free radical yield and enhanced near-infrared (NIR) photothermal conversion has been fabricated. Perylene diimide (PDI) can undergo chemical reduction to generate PDI radical anions. Cucurbit[7]uril (CB[7]), a bulky hydrophilic head, was utilized to encapsulate the two end groups of the PDI derivative via host-guest interactions, thus hindering its aggregation and suppressing the dimerization and quenching of PDI radical anions in aqueous solution. Due to the increased concentration of radical anions and their absorption above 800 nm, the efficiency of NIR photothermal conversion was significantly improved. Compared with free radicals fabricated by covalent chemistry, the supramolecular free radicals established here could provide a facile approach for the promoted formation of aromatic free radicals, thus opening up a new strategy for the design of NIR photothermal materials with enhanced photothermal conversion.

A supramolecular strategy for tuning the energy level of naphthalenediimide: Promoted formation of radical anions with extraordinary stability

We report a supramolecular strategy to promote and stabilize the formation of naphthalenediimide (NDI) radical anions. The LUMO and HOMO energy of NDI are lowered significantly by introducing cucurbit[7]uril (CB[7]) to each side of a designed NDI molecule through supramolecular complexation. This promotes efficiently the photo-induced electron transfer process between NDI and bromide anions in aqueous solution. The resulting NDI supramolecular radical anions are of outstanding stability. They are even stable in aqueous solution at higher temperatures of 40 °C and 60 °C. It is anticipated that this supramolecular strategy may provide a facile method for stabilizing radicals towards the development of novel materials with spin-based properties and optical properties in the visible and near-infrared regions.

Photophysical Properties of a Post-Self-Assembly Host/Guest Coordination Cage: Visible Light Driven Core-to-Cage Charge Transfer

Supramolecular systems are capable of unique photophysical properties due to possible interactions between subcomponents, such as between an encapsulated molecule and its cage in a host/guest environment. Here, we report that the encapsulation of a chromophore by a metallacage dramatically enhances its photophysical properties. In the visible region, the encapsulated photosensitizer achieves a 6.5-fold enhancement to its absorptivity. The triplet lifetime of the encapsulated photosensitizer is three times longer than that of its free analogue. These enhancements are attributed to two key factors: (i) encapsulation-induced core-to-cage charge transfer (CCCT) generates new visible-light absorbing states, accounting for the enhanced absorption, and (ii) the microenvironment inside the metallacage inhibits nonradiative decay processes, resulting in prolonged triplet lifetime. The CCCT arises from the electrostatic interaction between the delocalized electrons of the guest coronene and the positive charge associated with the metallacage host. The work herein provides insight into the CCCT phenomenon.

Luminescent platinum(ii) complexes with self-assembly and anti-cancer properties: hydrogel, pH dependent emission color and sustained-release properties under physiological conditions

Luminescent platinum(ii) complexes show anti-cancer and pH-dependent self-assembly and sustained-release properties under physiological conditions.

Supramolecular interactions are of paramount importance in biology and chemistry, and can be used to develop new vehicles for drug delivery. Recently, there is a surge of interest on self-assembled functional supramolecular structures driven by intermolecular metal–metal interactions in cellular conditions. Herein we report a series of luminescent Pt(ii) complexes [Pt(C^N^N^pyr)(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> NR)]⁺ [HC^N^N^pyr = 2-phenyl-6-(1H-pyrazol-3-yl)-pyridine)] containing pincer type ligands having pyrazole moieties. These Pt(ii) complexes exert potent cytotoxicity to a panel of cancer cell lines including primary bladder cancer cells and display strong phosphorescence that is highly sensitive to the local environment. The self-assembly of these complexes is significantly affected by pH of the solution medium. Based on TEM, SEM, ESI-MS, absorption and emission spectroscopy, and fluorescence microscopy together with cell based assays, [Pt(C^N^N^pyr)(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> NR)]⁺ complexes were observed to self-assemble into orange phosphorescent polymeric aggregates driven by intermolecular Pt(ii)–Pt(ii) and ligand–ligand interactions in a low-pH physiological medium. Importantly, the intracellular assembly and dis-assembly of [Pt(C^N^N^pyr)(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> NR)]⁺ are accompanied by change of emission color from orange to green. These [Pt(C^N^N^pyr)(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> NR)]⁺ complexes accumulated in the lysosomes of cancer cells, increased the lysosomal membrane permeability and induced cell death. One of these platinum(ii) complexes formed hydrogels which displayed pH-responsive and sustained release properties, leading to low-pH-stimulated and time-dependent cytotoxicity towards cancer cells. These hydrogels can function as vehicles to deliver anti-cancer agent cargo, such as the bioactive natural products studied in this work.

Gram-positive antimicrobial activity of amino acid-based hydrogels

Antimicrobial hydrogels are prepared based on the co-assembly of commercial Fmoc-phenylalanine and Fmoc-leucine, which act as the hydrogelator and antimicrobial building block, respectively. This co-assembled antimicrobial hydrogel is demonstrated to exhibit selective bactericidal activity for gram-positive bacteria while being biocompatible with normal mammalian cells, showing great potential as an antimicrobial coating for clinical anti-infective applications.

Functional supramolecular polymers for biomedical applications

As a novel class of dynamic and non-covalent polymers, supramolecular polymers not only display specific structural and physicochemical properties, but also have the ability to undergo reversible changes of structure, shape, and function in response to diverse external stimuli, making them promising candidates for widespread applications ranging from academic research to industrial fields. By an elegant combination of dynamic/reversible structures with exceptional functions, functional supramolecular polymers are attracting increasing attention in various fields. In particular, functional supramolecular polymers offer several unique advantages, including inherent degradable polymer backbones, smart responsiveness to various biological stimuli, and the ease for the incorporation of multiple biofunctionalities (e.g., targeting and bioactivity), thereby showing great potential for a wide range of applications in the biomedical field. In this Review, the trends and representative achievements in the design and synthesis of supramolecular polymers with specific functions are summarized, as well as their wide-ranging biomedical applications such as drug delivery, gene transfection, protein delivery, bio-imaging and diagnosis, tissue engineering, and biomimetic chemistry. These achievements further inspire persistent efforts in an emerging interdisciplin-ary research area of supramolecular chemistry, polymer science, material science, biomedical engineering, and nanotechnology.

Tuning the surface activity of gemini amphiphile by the host-guest interaction of cucurbit[7]uril

This research is aimed to develop an effective supramolecular route for tuning the surface activity of the surfactant. To this end, cationic gemini amphiphiles and cucurbit[7]uril (CB[7]) were complexed in water, and each hydrophobic chain of the gemini amphiphiles was bound with a CB[7]. The steric hindrance of CB[7] prevented the two hydrophobic chains from getting closed to each other, leading a significant change of surface activity. Before supramolecular complexation, the surface activity of the gemini amphiphile is relatively high, which can generate the foams easily. However, the foam generated by gemini amphiphile can be destructed by adding CB[7], suggesting that the suface activity is lowed after the supramolecular complexation. The surface activity can recover after adding 1-adamantanamine hydrochloride, which has a stronger ability to bind CB[7]. Therefore, a controllable foaming and defoaming process can be realized. It is highly anticipated that supramolecular chemistry for tuning amphiphilicity of surfactants may find application in the fields that fast foaming and defoaming are needed.

Synthesis and characterization of water-soluble polythiophene derivatives for cell imaging

In this work, four water-soluble polythiophene derivatives (PT, PT-DDA, PT-ADA, and PT-ADA-PPR) with different pendant moieties were synthesized via oxidative copolymerization by FeCl₃. By increasing the hydrophobic ability of side chain moieties, there is a gradually blue shift for the maximum absorption wavelength and red shift for the maximum emission wavelength, a reducing trend for fluorescence quantum yields, a growing trend for Stokes shift, and an increasing trend for the mean sizes in the order of PT, PT-ADA, and PT-DDA. All the synthesized polymers show low toxicity and good photostability and accumulate in the lysosomes of A549 cells. Furthermore, the introduction of porphyrin group to PT-ADA side chain (PT-ADA-PPR) broadens the absorption and emission ranges of PT-ADA. PT-ADA-PPR could be excited at two different excitation wavelengths (488 nm and 559 nm) and exhibits two emission pathways, and dual-color fluorescence images (orange and red) of PT-ADA-PPR accumulated in A549 cells are observed. Thus, PT-ADA-PPR could be used as an excellent dual-color fluorescent and lysosome-specific imaging material.

A bivalent cationic dye enabling selective photo-inactivation against Gram-negative bacteria

Selective photoinactivation against Gram-negative bacteria over Gram-positive bacteria was successfully realized by a bivalent triarylmethane dye.

Photocontrollable release and enhancement of photodynamic therapy based on host–guest supramolecular amphiphiles

A light-controlled porphyrinic photosensitizer release system was developed based on host–guest TPP–Azo/PEG–β-CD supramolecular amphiphiles, which could significantly enhance the efficiency of photodynamic therapy.

Supramolecular self-assembled nanoparticles for chemo-photodynamic dual therapy against cisplatin resistant cancer cells

Supramolecular self-assembled nanoparticles were constructed to overcome cisplatin resistance using a platinum(iv) prodrug and porphyrin as the host and guest molecules, respectively.

Enzyme-responsive pillar[5]arene-based polymer-substituted amphiphiles: synthesis, self-assembly in water, and application in controlled drug release

Pillar[5]arene-based PEG-substituted amphiphiles form enzyme-responsive micelles in water useful for drug-delivery.

BODIPY-based macromolecular photosensitizer with cation-enhanced antibacterial activity

The macromolecular photosensitizer could bind and eliminate bacteria efficiently.

A cross-linked supramolecular polymer constructed from pillar[5]arene and porphyrine via host–guest interactions

A novel supramolecular polymer, DMeP5@TImPor, was successfully constructed via host–guest interactions between the host molecule, bis-(methoxy-pillar[5]arene) (DMeP5), and the guest molecule, 5,10,15,20-tetrakis{butoxy-4-(1H-imidazol-1-yl)}porphyrine (TImPor).

Interfacial fabrication of functional supramolecular polymeric networks for photocatalysis

Supramolecular polymeric networks based on host-enhanced π-π interaction have been obtained at a liquid-solid interface through the layer-by-layer (LbL) assembly of porphyrin bearing four naphthalene groups and cucurbit[8]uril. The fabricating progress of supramolecular networks at interface can be efficiently controlled, simply by adjusting the layer-pair number of LbL films. Moreover, upon irradiation of visible light, these supramolecular networks exhibit good catalytic features for the oxidation of various phenols. It is anticipated that this strategy of fabricating supramolecular polymeric networks at the interface has potential applications in the fields of sewage disposal and biocatalysis, just to name a few.

Selective photodynamic inactivation of bacterial cells over mammalian cells by new triarylmethanes

Three new triarylmethane dyes (TAMs), MPCV, DPCV, and AEV, were synthesized and their photodynamic inactivation abilities against E. coli and human pulmonary carcinoma A549 cells were compared to two commercial TAMs, CV and EV. The enhanced hydrophilicity of MPCV and AEV decreases their cellular uptake to A549 cells dramatically. However, their binding affinity toward E. coli cells are comparable to that of CV and EV by virtue of the improved electrostatic attraction with highly negatively charged E. coli outer membranes. MPCV and AEV were also found to generate hydroxyl radicals more efficiently upon irradiation than CV and EV. Consequently, MPCV and AEV exhibited markedly improved photodynamic inactivation of E. coli cells but remarkably diminished photodynamic inactivation of A549 cells than CV and EV. The photodynamic inactivation ability of DPCV was much lower than that of CV due to its high propensity for bleaching in neutral aqueous solution. Our work demonstrates that the introduction of protonatable groups in a proper manner into the structures of TAMs may lead to selective binding and photodynamic inactivation toward bacterial cells over mammalian cells. This strategy may be extended to other types of photodynamic antimicrobial chemotherapy (PACT) agents to improve their clinical potential.

Photodynamic inactivation of bacteria and viruses using two monosubstituted zinc(II) phthalocyanines

A zinc(II) phthalocyanine substituted with a triamino moiety and its tri-N-methylated analogue have been prepared and characterized with various spectroscopic methods. Both compounds remain non-aggregated in N,N-dimethylformamide and in water containing 0.05% Cremophor EL (v/v), and can generate singlet oxygen effectively. The photodynamic activities of these compounds have been examined against a range of bacterial strains, including the Gram-positive methicillin-sensitive Staphylococcus aureus ATCC 25923 and methicillin-resistant Staphylococcus aureus ATCC BAA-43, and the Gram-negative Escherichia coli ATCC 35218 and Pseudomonas aeruginosa ATCC 27853. Both photosensitizers are highly cytotoxic, particularly for the two Gram-positive strains, for which as low as 5 nM of dye is required to induce a 4-log reduction of their viability. The tri-N-methylated derivative has also been shown to be able to effectively inhibit the growth of a series of clinical strains of Staphylococcus aureus and Escherichia coli, and biofilms of methicillin-resistant Staphylococcus aureus ATCC 67928 and ATCC 68507, and Staphylococcus epidermidis ATCC 35984. In addition, the photodynamic inactivation of a range of viruses using these two compounds has also been investigated. Both compounds are highly photocytotoxic against the enveloped viruses influenza A virus (H1N1) and herpes simplex virus type 1 (HSV1), but exhibit no significant cytotoxicity toward the non-enveloped viruses adenovirus type 3 (Ad3) and coxsackievirus (Cox B1).

Supra-amphiphiles: a new bridge between colloidal science and supramolecular chemistry

In addition to conventional amphiphiles, an emerging research area is supra-amphiphiles, which are constructed on the basis of noncovalent interactions and dynamic covalent bonds. In this feature article, we have provided a general introduction to the concept, design principles, and topologies of supra-amphiphiles, starting from some rationally tailored building blocks. In addition, we highlight some progress in the functional assembly of supra-amphiphiles, such as responsive nanoscale carriers, antibacterial and antitumor agents, fluorescent-based chemical sensors, and enzyme mimics. The supra-amphiphile is a new bridge between colloidal science and supramolecular chemistry, and it is a field where we can make full use of our imaginative power.

Self-assembly and optical properties of a porphyrin-based amphiphile

A porphyrin-based amphiphile that exhibits various self-assembled nanostructures in different solvents has been successfully prepared. The effect of aggregated structure on optical properties of this amphiphile has been well investigated. Furthermore, this porphyrin-based amphiphile and its assemblies show dynamic/reversible variations in morphology and optical properties in response to light.

Oligolysine-conjugated zinc(II) phthalocyanines as efficient photosensitizers for antimicrobial photodynamic therapy

A series of zinc(II) phthalocyanines conjugated with an oligolysine chain (n=2, 4, and 8) were synthesized and characterized by using various spectroscopic methods. As shown by using UV/Vis and fluorescence spectroscopic methods, these compounds were nonaggregated in N,N-dimethylformamide, and gave a weak fluorescence emission and high singlet oxygen quantum yield (Φ(Δ) =0.86-0.89) as a result of their di-α-substitution. They became slightly aggregated in water with 0.05 % Cremophor EL, but they could still generate singlet oxygen effectively. The antimicrobial photodynamic activities of these compounds were then examined against various bacterial strains, including the Gram-positive methicillin-sensitive Staphylococcus aureus ATCC 25923 and methicillin-resistant Staphylococcus aureus ATCC BAA-43, and the Gram-negative Escherichia coli ATCC 35218 and Pseudomonas aeruginosa ATCC 27853. Generally, the dyes were much more potent toward the Gram-positive bacteria. Only 15 to 90 nM of these photosensitizers was required to induce a 4 log reduction in the cell viability of the strains. For Escherichia coli, the photocytotoxicity increased with the length of the oligolysine chain. The octalysine derivative showed the highest potency with a 4 log reduction concentration of 0.8 μM. Pseudomonas aeruginosa was most resistant to the photodynamic treatment. The potency of the tetralysine derivative toward a series of clinical strains of Staphylococcus aureus was also examined and found to be comparable with that toward the nonclinical counterparts. Moreover, the efficacy of these compounds in photodynamic inactivation of viruses was also examined. They were highly photocytotoxic against the enveloped viruses influenza A virus (H1N1) and herpes simplex virus type 1 (HSV1), but exhibited no significant cytotoxicity against the nonenveloped viruses adenovirus type 3 (Ad3) or coxsackievirus (Cox B1). The octalysine derivative also showed the highest potency with an IC(50) value of 0.05 nM for the two enveloped viruses.

Asymmetric and symmetric bolaform supra-amphiphiles: formation of imine bond influenced by aggregation

A series of bolaform supra-amphilphiles with different symmetries were fabricated through dynamic benzoic imine bond formation. The pH dependence of imine formations of these supra-amphiphiles were characterazied. We found that the extent of the imine formation of these supra-amphiphies were different. The supra-amphiphiles with a poorer symmetry always exhibited a lower imine formation at a given pH. Therefore, the varied extent of imine bond formation indicate the different aggregations of these supra-amphilphiles, which are controlled by the molecular symmetry of the supra-amphiphiles.

Porphyrin-containing hyperbranched supramolecular polymers: enhancing 1O2-generation efficiency by supramolecular polymerization

Porphyrin-containing hyperbranched supramolecular polymers were obtained in aqueous solution, which can function as photosensitizers.