Reversible mechanical protection: building a 3D "suit" around a T-shaped benzimidazole axle

The T-shaped benzimidazolium/crown ether recognition motif was used to prepare suit[1]anes. These novel mechanically interlocked molecules (MIMs) were fully characterized by 1H and 13C NMR spectroscopy, single-crystal X-ray diffraction, UV-vis absorption and fluorescence spectroscopy. By conversion to a suit[1]ane, a simple benzimidazole was shown to be protected from deprotonation by strong base. Moreover, it was demonstrated that this unique three-dimensional encapsulation can be made reversible, thus introducing the concept of "reversible mechanical protection"; a protecting methodology that may have potential applications in synthetic organic chemistry and the design of molecular machinery.

Highly specific noninvasive photoacoustic and positron emission tomography of brain plaque with functionalized croconium dye labeled by a radiotracer

Highly-efficient targeting probes are desirable for disease diagnosis and functional imaging. However, most of the current near-infrared (NIR) probes suffer from low signal conversion, insufficient photostability, poor probe specificity, and limited functions. Herein, an NIR ultrahigh absorbing croconium dye for amyloid (CDA) was designed and synthesized to specifically bind to cerebrovascular amyloid without antibody linkage. This unique CDA is able to strongly bind the hydrophobic channels of amyloid beta (Aβ) fiber with a very strong binding energy of -9.3 kcal mol-1. Our experimental results demonstrate that the amphipathic dye with an intense absorption peak at 800 nm generated a significant local temperature surge under low-power laser irradiation. Compared with representative prominent indocyanine green, Prussian blue, and gold nanorods, this probe can produce the strongest photoacoustic signal based on the same mass concentration. Labeled with radioactive 18F, this multifunctional probe allowed for the ultrasensitive photoacoustic tomography (PAT)/positron emission tomography (PET)/fluorescence imaging of Aβ plaques in the brain cortex. Featured with high spatial resolution and optical specificity, PAT was intrinsically suitable for imaging pathological sites on cortical vessels, whereas PET revealed whole-body anatomy with quantitative biodistribution information. Our study shows that a CDA-based functionalized dye aided with PAT and PET is capable of plaque diagnosis and localization.

Selective photothermal inactivation of cells labeled with near-infrared croconaine dye

Laser irradiation of a mixed population of two cell lines produced cell death only in the cells that were labeled with croconaine dye.

Enhancing the photothermal stability and photothermal efficacy of AuNRs and AuNTs by grafting with Ru(ii) complexes

In this paper, we found that the ruthenium complex-functionalized AuNRs (AuNRs@Ru) and AuNTs (AuNTs@Ru) exhibited better photothermal stability and higher photothermal efficiency than AuNRs and AuNTs.In vivotumor model studies showed that AuNRs@Ru and AuNRs@Ru were effective for the photothermal destruction of tumors.

Croconaine rotaxane for acid activated photothermal heating and ratiometric photoacoustic imaging of acidic pH

Absorption of 808 nm laser light by liposomes containing a pH sensitive, near-infrared croconaine rotaxane dye increases dramatically in weak acid. A stealth liposome composition permits acid activated, photothermal heating and also acts as an effective nanoparticle probe for ratiometric photoacoustic imaging of acidic pH in deep sample locations, including a living mouse.

A calamitic mesogenic near-infrared absorbing croconaine dye/liquid crystalline elastomer composite

In this work, we report the first example of a calamitic mesogenic near-infrared (NIR) absorbing organic dye, made by functionalizing a thiophene-croconaine chromophore rigid core with two symmetric long flexible alkyl chains. The liquid crystal (LC) NIR dye YHD796 exhibits a sharp and intense NIR absorption band with a maximum absorption peak at 796 nm. Taking advantage of the improved solubility of YHD796 dispersed in mesogenic molecules, a homogeneously-aligned mono-domain liquid crystalline elastomer (LCE)/YHD796 composite film is successfully prepared by applying the classical LC-cell-alignment method and in situ photo-polymerization of photocurable LC monomer mixtures. This LCE/YHD796 composite film performs a fully reversible contraction/expansion response towards NIR light stimulus due to the photo-thermal heating effect induced by the YHD796 dye well-dispersed in the LCE matrix.

High Affinity Macrocycle Threading by a Near-Infrared Croconaine Dye with Flanking Polymer Chains

Croconaine dyes have narrow and intense absorption bands at ∼800 nm, very weak fluorescence, and high photostabilities, which combine to make them very attractive chromophores for absorption-based imaging or laser heating technologies. The physical supramolecular properties of croconaine dyes have rarely been investigated, especially in water. This study focuses on a molecular threading process that encapsulates a croconaine dye inside a tetralactam macrocycle in organic or aqueous solvent. Macrocycle association and rate constant data are reported for a series of croconaine structures with different substituents attached to the ends of the dye. The association constants were highest in water (Ka ∼ 10(9) M(-1)), and the threading rate constants (kon) increased in the solvent order H2O > MeOH > CHCl3. Systematic variation of croconaine substituents located just outside the croconaine/macrocycle complexation interface hardly changed Ka but had a strong influence on kon. A croconaine dye with N-propyl groups at each end of the structure exhibited a desirable mixture of macrocycle threading properties; that is, there was rapid and quantitative croconaine/macrocycle complexation at relatively high concentrations in water, and no dissociation of the preassembled complex when it was diluted into a solution of fetal bovine serum, even after laser-induced photothermal heating of the solution. The combination of favorable near-infrared absorption properties and tunable mechanical stability makes threaded croconaine/macrocycle complexes very attractive as molecular probes or as supramolecular composites for various applications in absorption-based imaging or photothermal therapy.

Tuning the Energy Gap by Supramolecular Approaches: Towards Near-Infrared Organic Assemblies and Materials

Near-infrared (NIR) organic materials are of great importance for both fundamental research and practical applications. While much effort has been taken to covalently design and synthesize NIR organic materials with a low energy gap, there are supramolecular approaches for tuning the energy gap to noncovalently fabricate NIR organic assemblies and materials. In this concept article, we summarize and discuss several supramolecular approaches, including the fabrication of charge transfer supramolecular complexes, the fabrication of supramolecular J-aggregates, and the fabrication of supramolecularly stabilized organic radicals. The nature of noncovalent interactions in supramolecular approaches can provide NIR organic assemblies and materials with unique properties such as reversibility, stimuli-responsiveness, recyclability, and adaptive abilities.

NIR-driven Smart Theranostic Nanomedicine for On-demand Drug Release and Synergistic Antitumour Therapy

Smart nanoparticles (NPs) that respond to external and internal stimulations have been developing to achieve optimal drug release in tumour. However, applying these smart NPs to attain high antitumour performance is hampered by limited drug carriers and inefficient spatiotemporal control. Here we report a noninvasive NIR-driven, temperature-sensitive DI-TSL (DOX/ICG-loaded temperature sensitive liposomes) co-encapsulating doxorubicin (DOX) and indocyanine green (ICG). This theranostic system applies thermo-responsive lipid to controllably release drug, utilizes the fluorescence (FL) of DOX/ICG to real-time trace the distribution of NPs, and employs DOX/ICG to treat cancer by chemo/photothermal therapy. DI-TSL exhibits uniform size distribution, excellent FL/size stability, enhanced response to NIR-laser, and 3 times increased drug release through laser irradiation. After endocytosis by MCF-7 breast adenocarcinoma cells, DI-TSL in cellular endosomes can cause hyperthermia through laser irradiation, then endosomes are disrupted and DI-TSL ‘opens’ to release DOX simultaneously for increased cytotoxicity. Furthermore, DI-TSL shows laser-controlled release of DOX in tumour, enhanced ICG and DOX retention by 7 times and 4 times compared with free drugs. Thermo-sensitive DI-TSL manifests high efficiency to promote cell apoptosis, and completely eradicate tumour without side-effect. DI-TSL may provide a smart strategy to release drugs on demand for combinatorial cancer therapy.

Clean Photothermal Heating and Controlled Release from Near-Infrared Dye Doped Nanoparticles without Oxygen Photosensitization

The photothermal heating and release properties of biocompatible organic nanoparticles, doped with a near-infrared croconaine (Croc) dye, were compared with analogous nanoparticles doped with the common near-infrared dyes ICG and IR780. Separate formulations of lipid-polymer hybrid nanoparticles and liposomes, each containing Croc dye, absorbed strongly at 808 nm and generated clean laser-induced heating (no production of (1)O2 and no photobleaching of the dye). In contrast, laser-induced heating of nanoparticles containing ICG or IR780 produced reactive (1)O2, leading to bleaching of the dye and also decomposition of coencapsulated payload such as the drug doxorubicin. Croc dye was especially useful as a photothermal agent for laser-controlled release of chemically sensitive payload from nanoparticles. Solution state experiments demonstrated repetitive fractional release of water-soluble fluorescent dye from the interior of thermosensitive liposomes. Additional experiments used a focused laser beam to control leakage from immobilized liposomes with very high spatial and temporal precision. The results indicate that fractional photothermal leakage from nanoparticles doped with Croc dye is a promising method for a range of controlled release applications.

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.

Unexpected high photothemal conversion efficiency of gold nanospheres upon grafting with two-photon luminescent ruthenium(II) complexes: A way towards cancer therapy?

The design and development of functional hybrid nanomaterials is currently a topic of great interest in biomedicine. Herein we investigated the grafting of Ru(II) polypyridyl complexes onto gold nanospheres (Ru@AuNPs) to improve the particles' near infrared (NIR) absorption, and ultimately allow for application in photothermal cancer therapy. As demonstrated in this article, these ruthenium(II) complexes could indeed significantly enhance gold nanospheres' two-photon luminescence (PTL) intensity and photothermal therapy (PTT) efficiency. The best dual functional nanoparticles of this study were successfully used for real-time luminescent imaging-guided PTT in live cancer cells. Furthermore, in vivo tumor ablation was achieved with excellent treatment efficacy under a diode laser (808 nm) irradiation at the power density of 0.8 W/cm(2) for 5 min. This study demonstrates that the coupling of inert Ru(II) polypyridyl complexes to gold nanospheres allows for the enhancement of two-photon luminescence and for efficient photothermal effect.

Spatial modulation spectroscopy for imaging and quantitative analysis of single dye-doped organic nanoparticles inside cells

Imaging of non-fluorescent nanoparticles in complex biological environments, such as the cell cytosol, is a challenging problem. For metal nanoparticles, Rayleigh scattering methods can be used, but for organic nanoparticles, such as dye-doped polymer beads or lipid nanoparticles, light scattering does not provide good contrast. In this paper, spatial modulation spectroscopy (SMS) is used to image single organic nanoparticles doped with non-fluorescent, near-IR croconaine dye. SMS is a quantitative imaging technique that yields the absolute extinction cross-section of the nanoparticles, which can be used to determine the number of dye molecules per particle. SMS images were recorded for particles within EMT-6 breast cancer cells. The measurements allowed mapping of the nanoparticle location and the amount of dye in a single cell. The results demonstrate how SMS can facilitate efforts to optimize dye-doped nanoparticles for effective photothermal therapy of cancer.

Amino-ether macrocycle that forms CuII templated threaded heteroleptic complexes: a detailed selectivity, structural and theoretical investigations

Self-sorting behavior of a newly synthesized macrocycle with divalent metal ions and aromatic ligands via pseudorotaxane formation has been described.

Facile fabrication of a near-infrared responsive nanocarrier for spatiotemporally controlled chemo-photothermal synergistic cancer therapy

Remote-controlled nanocarriers for drug delivery are of great promise to provide timely, sensitive and spatiotemporally selective treatments for cancer therapy. Due to convenient and precise manipulation, deep penetration through tissues and excellent biocompatibility, near-infrared (NIR) irradiation is a preferred external stimulus for triggering the release of loaded drugs. In this work, for spatiotemporally controlled chemo-photothermal synergistic cancer therapy, a NIR responsive nanocarrier was fabricated using reduced graphene oxide nanosheets (rNGO) decorated with mesoporous silica shell and the subsequent functionalization of the thermoresponsive polymer brushes (pNIPAM-co-pAAm) at the outlet of the silica pore channels. rNGO, which combined with the mesoporous silica shell provide a high loading capacity for anticancer drugs (doxorubicin, DOX), was assigned to sense NIR irradiation for the manipulation of pNIPAM-co-pAAm valve to control the diffusion of loaded DOX. Under NIR irradiation, rNGO would generate heat, which could not only elevate the surrounding temperature over the low critical solution temperature (LCST) of pNIPAM-co-pAAm to open the thermoresponsive polymer valve and promote the diffusion of DOX, but also kill the cancer cells through the hypothermia effect. By manipulating NIR irradiation, the nanocarrier exhibited efficiently controlled release of loaded DOX both in the buffer and in living HeLa cells (the model cancer cells), providing powerful and site-targeted treatments, which can be attributed to synergistic effects of chemo-photothermal therapy. To sum up, this novel nanocarrier is an excellent drug delivery platform in remote-controlled chemo-photothermal synergistic cancer therapy via NIR irradiation.