New tetralactam hosts for squaraine dyes

Controlling the Supramolecular Polymerization of Squaraine Dyes by a Molecular Chaperone Analogue

Molecular chaperones are proteins that assist in the (un)folding and (dis)assembly of other macromolecular structures toward their biologically functional state in a non-covalent manner. Transferring this concept from nature to artificial self-assembly processes, here, we show a new strategy to control supramolecular polymerization via a chaperone-like two-component system. A new kinetic trapping method was developed that enables efficient retardation of the spontaneous self-assembly of a squaraine dye monomer. The suppression of supramolecular polymerization could be regulated with a cofactor, which precisely initiates self-assembly. The presented system was investigated and characterized by ultraviolet-visible, Fourier transform infrared, and nuclear magnetic resonance spectroscopy, atomic force microscopy, isothermal titration calorimetry, and single-crystal X-ray diffraction. With these results, living supramolecular polymerization and block copolymer fabrication could be realized, demonstrating a new possibility for effective control over supramolecular polymerization processes.

Boto R, Ferreira D, R. Fernandes J, Almeida P, F. V. Ferreira L, Souto EB, Silva AM, V. Reis L. Quinoline‑ and Benzoselenazole-Derived Unsymmetrical Squaraine Cyanine Dyes: Design, Synthesis, Photophysicochemical Features and Light-Triggerable Antiproliferative Effects against Breast Cancer Cell Lines

Photodynamic therapy is an innovative treatment approach broadly directed towards oncological diseases. Its applicability and efficiency are closely related to the interaction of three main components, namely a photosensitizer, light and molecular triplet oxygen, which should drive cell death. Recently, several studies have demonstrated that squaraine cyanine dyes have a set of photophysical and photochemical properties that have made of these compounds’ potential photosensitizers for this therapeutic modality. In the present research work, we describe the synthesis and characterization of four quinoline- and benzoselenazole-derived unsymmetrical squaraine cyanine dyes. Except for the precursor of aminosquaraine dyes, i.e., O-methylated derivative, all dyes were evaluated for their behavior and absorption capacity in different organic and aqueous solvents, their ability to form singlet oxygen, their light-stability, and in vitro phototherapeutic effects against two human breast cancer cell cultures (BT-474 and MCF-7). Regardless of the nature of the used solvents, the synthesized dyes showed intense absorption in the red and near-infrared spectral regions, despite the formation of aggregates in aqueous media. Dyes showed high light-stability against light exposure. Despite the low ability to produce singlet oxygen, aminosquaraine dyes demonstrated worthy in vitro phototherapeutic activity.

Paired Agent Fluorescence Imaging of Cancer in a Living Mouse Using Preassembled Squaraine Molecular Probes with Emission Wavelengths of 690 and 830 nm

New methods are described for the construction of targeted fluorescence probes for imaging cancer and the assessment of tumor targeting performance in a living mouse model. A novel noncovalent assembly process was used to fabricate a set of structurally related targeted fluorescent probes with modular differences in three critical assembly components: the emission wavelength of the squaraine fluorochrome, the number of cRGDfK peptide units that target the cancer cells, and the length of the polyethylene glycol chains as pharmacokinetic controllers. Selective targeting of cancer cells was proven by a series of cell microscopy experiments followed by in vivo imaging of subcutaneous tumors in living mice. The mouse imaging studies included a mock surgery that completely removed a fluorescently labeled tumor. Enhanced tumor accumulation due to probe targeting was first evaluated by conducting Single Agent Imaging (SAI) experiments that compared tumor imaging performance of a targeted probe and untargeted probe in separate mouse cohorts. Although there was imaging evidence for enhanced tumor accumulation of the targeted probe, there was moderate scatter in the data due to tumor-to-tumor variability of the vasculature structure and interstitial pressure. A subsequent Paired Agent Imaging (PAI) study coinjected a binary mixture of targeted probe (with emission at 690 nm) and untargeted probe (with emission at 830 nm) into the same tumor-burdened animal. The conclusion of the PAI experiment also indicated enhanced tumor accumulation of the targeted probe, but the statistical significance was much higher, even though the experiment required a much smaller cohort of mice. The imaging data from the PAI experiment was analyzed to determine the targeted probe's Binding Potential (BP) for available integrin receptors within the tumor tissue. In addition, pixelated maps of BP within each tumor indicated a heterogeneous spatial distribution of BP values. The results of this study show that the combination of fluorescent probe preassembly and PAI is a promising new way to rapidly develop targeted fluorescent probes for tumors with high BP and eventual use in clinical applications such as targeted therapy, image guided surgery, and personalized medicine.

High affinity threading of a new tetralactam macrocycle in water by fluorescent deep-red and near-infrared squaraine dyes

A new tetralactam macrocycle was prepared and found to encapsulate deep-red and near-infrared squaraine and croconaine dyes in water with tunable threading kinetics. The new supramolecular paradigm of guest back-folding was used to increase macrocycle/squaraine affinity by 370-fold and achieve an association constant of 2.8 × 109 M-1.

Bright G-Quadruplex Nanostructures Functionalized with Porphyrin Lanterns

The intricate arrangement of numerous and closely placed chromophores on nanoscale scaffolds can lead to key photonic applications ranging from optical waveguides and antennas to signal-enhanced fluorescent sensors. In this regard, the self-assembly of dye-appended DNA sequences into programmed photonic architectures is promising. However, the dense packing of dyes can result in not only compromised DNA assembly (leading to ill-defined structures and precipitates) but also to essentially nonfluorescent systems (due to π-π aggregation). Here, we introduce a two-step "tether and mask" strategy wherein large porphyrin dyes are first attached to short G-quadruplex-forming sequences and then reacted with per-O-methylated β-cyclodextrin (PMβCD) caps, to form supramolecular synthons featuring the porphyrin fluor fixed into a masked porphyrin lantern (PL) state, due to intramolecular host-guest interactions in water. The PL-DNA sequences can then be self-assembled into cyclic architectures or unprecedented G-wires tethered with hundreds of porphyrin dyes. Importantly, despite the closely arrayed PL units (∼2 nm), the dyes behave as bright chromophores (up to 180-fold brighter than the analogues lacking the PMβCD masks). Since other self-assembling scaffolds, dyes, and host molecules can be used in this modular approach, this work lays out a general strategy for the bottom-up aqueous self-assembly of bright nanomaterials containing densely packed dyes.

Molecular recognition using tetralactam macrocycles with parallel aromatic sidewalls

This review summarizes the supramolecular properties of tetralactam macrocycles that have parallel aromatic sidewalls and four NH residues directed into the macrocyclic cavity. These macrocycles are versatile hosts for a large number of different guest structures in water and organic solvents, and they are well-suited for a range of supramolecular applications. The macrocyclic cavity contains a mixture of polar functional groups and non-polar surfaces which is reminiscent of the amphiphilic binding pockets within many proteins. In water, the aromatic surfaces in the tetralactam cavity drive high affinity due the hydrophobic effect and the NH groups provide secondary interactions that induce binding selectivity. In organic solvents, the supramolecular factors are reversed; the polar NH groups drive high affinity and the aromatic surfaces provide the secondary interactions. In addition to an amphiphilic cavity, macrocyclic tetralactams exhibit conformational flexibility, and the combination of properties enables them to be effective hosts for a wide range of guest molecules including organic biscarbonyl derivatives, near-infrared dyes, acenes, precious metal halide complexes, trimethylammonium ion-pairs, and saccharides.

Homo and heteroassembly of amide-based [2]rotaxanes using α,α′-dimethyl-p-xylylenediamines

The selective formation of [2]rotaxanes affords two out of seven possible interlocked isomers thanks to a marked conformational preference.