A High-Affinity "Synthavidin" Receptor for Squaraine Dyes

Strong-binding host-guest pairings in aqueous media have potential as "supramolecular glues" in biomedical techniques, complementing the widely-used (strept)avidin-biotin combination. We have previously found that squaraine dyes are bound very strongly by tetralactam macrocycles possessing anthracenyl units as cavity walls. Here we show that replacing the anthracenes with pentacyclic 5,7,12,14-tetrahydro-5,7,12,14-tetraoxapentacene (TOP) units generates receptors which bind squaraines with increased affinities (around Ka =1010  m-1 ) and improved selectivities. Binding can be followed through changes to squaraine fluorescence and absorbance. The TOP units are easy to prepare and potentially variable, while the TOP-based receptor shows improved photostability, both in itself and in complex with squaraines. The results suggest that this system could prove valuable in the further development of practical "synthavidin" chemistry.

Evaluation of the antibacterial properties and in-vitro cell compatibilities of doped copper oxide/hydroxyapatite composites

Mg, Zn and Ce-doped CuO/HA composites were prepared by a two-step sol-gel and hydrothermal process. SEM images showed a spherical appearance of HA and a needle-like morphology for doped CuO. XRD patterns revealed that all doped CuO/HA composites exhibited a hexagonal crystal structure of HA and a monoclinic crystal structure of CuO with no impurities. ICP analysis indicated that with the increase of loading amount of doped CuO, the concentrations of Cu²⁺ ions and doping ions released from composites increased. Moreover, CuO/HA composites exhibit improved antibacterial properties against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as compared with HA. When the loading amount of doped CuO in composites increased to 15 wt%, the composites exhibited the best antibacterial activity and complete bacterial growth inhibition effect. Furthermore, the CCK-8 assay revealed that the doped CuO/HA composites are noncytotoxic and can promote the proliferation of osteosarcoma cells. This work highlights the potential of the doped CuO/HA composites with significant antibacterial activity, bioactivity and cell compatibility for potential biomedical applications in dental implants and bone regeneration.

Self-Assembly of Stimuli-Responsive [2]Rotaxanes by Amidinium Exchange

Advances in supramolecular chemistry are often underpinned by the development of fundamental building blocks and methods enabling their interconversion. In this work, we report the use of an underexplored dynamic covalent reaction for the synthesis of stimuli-responsive [2]rotaxanes. The formamidinium moiety lies at the heart of these mechanically interlocked architectures, because it enables both dynamic covalent exchange and the binding of simple crown ethers. We demonstrated that the rotaxane self-assembly follows a unique reaction pathway and that the complex interplay between crown ether and thread can be controlled in a transient fashion by addition of base and fuel acid. Dynamic combinatorial libraries, when exposed to diverse nucleophiles, revealed a profound stabilizing effect of the mechanical bond as well as intriguing reactivity differences between seemingly similar [2]rotaxanes.

Synthesis and evaluation of the structural and antibacterial properties of doped copper oxide

Mg, Zn, and Ce-doped CuO NPs exhibit significantly enhanced antibacterial activity due to the synergetic effect of Cu²⁺ and ROS generation.

Remote-Controlled Release of Singlet Oxygen by the Plasmonic Heating of Endoperoxide-Modified Gold Nanorods: Towards a Paradigm Change in Photodynamic Therapy

The photodynamic therapy of cancer is contingent upon the sustained generation of singlet oxygen in the tumor region. However, tumors of the most metastatic cancer types develop a region of severe hypoxia, which puts them beyond the reach of most therapeutic protocols. More troublesome, photodynamic action generates acute hypoxia as the process itself diminishes cellular oxygen reserves, which makes it a self-limiting method. Herein, we describe a new concept that could eventually lead to a change in the 100 year old paradigm of photodynamic therapy and potentially offer solutions to some of the lingering problems. When gold nanorods with tethered endoperoxides are irradiated at 808 nm, the endoperoxides undergo thermal cycloreversion, resulting in the generation of singlet oxygen. We demonstrate that the amount of singlet oxygen produced in this way is sufficient for triggering apoptosis in cell cultures.

Internal and external stereoisomers of squaraine rotaxane endoperoxide: synthesis, chemical differences, and structural revision

Photooxygenation of permanently interlocked squaraine rotaxanes with anthracene-containing macrocycles produces the corresponding squaraine rotaxane endoperoxides (SREPs) quantitatively. SREPs are stored at low temperature, and upon warming, they undergo clean cycloreversion, releasing singlet oxygen and emitting light. The structural elucidation in 2010 assigned the structure as the SREP-int stereoisomer, with the endoperoxide unit directed inside the macrocycle cavity. New experimental and computational evidence reported here proves that the initial, kinetic photooxygenation product is the less stable SREP-ext stereoisomer with the endoperoxide unit directed outside the macrocycle. The photophysical properties and subsequent reactivity of mechanically strained SREP-ext depend on the size of the end groups of the encapsulated squaraine dye. If the end groups are sufficiently large to prevent dissociation of the interlocked components, the strained SREP-ext stereoisomer undergoes clean thermal cycloreversion. However, smaller squaraine end groups allow transient dissociation, resulting in a pseudorotaxane dissociation/association process that produces SREP-int as the thermodynamic stereoisomer that does not cyclorevert. The large difference in endoperoxide reactivity for the two SREP stereoisomers illustrates the power of the mechanical bond to induce cross-component steric strain and selective enhancement of a specific reaction pathway. The new insight enabled synthetic development of triptycene-containing squaraine rotaxanes with high fluorescence quantum yields and large Stokes shifts.

In vivo imaging using polymeric nanoparticles stained with near-infrared chemiluminescent and fluorescent squaraine catenane endoperoxide

Polystyrene nanoparticles stained with squaraine catenane endoperoxide exhibit remarkably high chemiluminescence and enable optical imaging of biodistribution in living mice. Whole-body chemiluminescence imaging was much more effective than fluorescence at identifying lung accumulation of the nanoparticles.

Understanding the antibacterial mechanism of CuO nanoparticles: revealing the route of induced oxidative stress

To date, there is still a lack of definite knowledge regarding the interaction of CuO nanoparticles with bacteria and the possible permeation of the nanoparticles into bacterial cells. This study was aimed at shedding light on the size-dependent (from the microscale down to the small nanoscale) antibacterial activity of CuO. The potent antibacterial activity of CuO nanoparticles was found to be due to ROS-generation by the nanoparticles attached to the bacterial cells, which in turn provoked an enhancement of the intracellular oxidative stress. This paradigm was confirmed by several assays such as lipid peroxidation and reporter strains of oxidative stress. Furthermore, electron microscopy indicated that the small nanoparticles of CuO penetrated the cells. Collectively, the results reported herein may reconcile conflicting concepts in the literature concerning the antibacterial mechanism of CuO nanoparticles, as well as highlight the potential for developing sustainable CuO nanoparticles-based devices for inhibiting bacterial infections.