Microviscosity-Assisted Disaggregation of a Model Ophthalmic Drug and FRET-Controlled Singlet Oxygen Generation in Lyotropic Liquid Crystals

Different phases of lyotropic liquid crystals (LLCs), made up of mesogen-like sodium dodecyl sulfate (SDS), mainly bestow different bulk viscosities. Along with this, the role of microviscosities of the individual LLC phases is of immense interest because a minute change in it due to guest incorporation can cause significant alteration in their property as a potential energy transfer scaffold. Recently, LLCs have been identified as plausible drug delivery agents for ocular treatments. In this direction, the present work illustrates photophysical modulations of an important laser dye as well as an ophthalmic medicine, coumarin 6 (C6), inside different LLC phases in an aqueous medium. C6 molecules spontaneously accumulate in water, leading to aggregation-caused quenching (ACQ) of fluorescence. However, the different phases of the LLCs prepared from SDS and water helped in disintegrating the C6 colonies to various extents depending upon the microviscosity. The heterogeneity in the LLC phases, in turn, could modulate the Förster resonance energy transfer (FRET) between C6 and the LLC incorporated with N-doped carbon nanoparticles (N-CNPs). The N-CNPs act as potential photosensitizers and generate singlet oxygen (1O2), a reactive oxygen species (ROS), to different extents. Microviscosities of the prepared LLCs were calculated by using fluorescence correlation spectroscopy (FCS). The different phases of the LLCs, viz., lamellar and hexagonal, with different microviscosities controlled the extent of C6 disaggregation and hence the FRET and the ROS generation. The results are encouraging since ROS generation has a significant role in the vision mechanism and PDT-based applications. LLC-based drug administration with potential FRET to control ROS generation may become handy in ophthalmology. The LLC phases used in this experiment not only served the purpose of drug delivery but also the photophysical events therein are compatible with the ocular environment.

ESIPT-based fluorescent enhanced probes prompted by methylated β-cyclodextrin for the detection of thiophenols

Thiophenol and its derivatives are compounds with high toxicity to organisms and environmental pollution, so it is necessary to detect the level of thiophenols in the environment and biological samples. The probes 1a-b were obtained by introducing the 2,4-dinitrophenyl ether group into diethylcoumarin-salicylaldehyde based compounds. And they can form host-guest compounds with methylated β-cyclodextrin (M-β-CD), the association constants of inclusion complexes are 49.2 M-1, 125 M-1 respectively. The fluorescence intensities of probes 1a-b at 600 nm (1a) and 670 nm (1b) increased significantly in thiophenols detection. Meanwhile, with the addition of M-β-CD, the hydrophobic cavity of M-β-CD significantly increased the fluorescence intensity of probes 1a-b, thus the detection limits of probes 1a-b to thiophenols were reduced from 410 nM, 365 nM to 62 nM, 33 nM respectively. Whereas, the good selectivity and short response time of probes 1a-b towards thiophenols was not affected in the presence of M-β-CD. Moreover, probes 1a-b were used for further water sample detection and HeLa cell imaging experiments due to their good response to thiophenols and the results suggested that probes 1a-b had the potential to detect the content of thiophenols in water samples and living cells.

Thiolated α-cyclodextrin: The likely smallest drug carrier providing enhanced cellular uptake and endosomal escape

This study aimed to evaluate the effect of thiolated α-cyclodextrin (α-CD-SH) on the cellular uptake of its payload. For this purpose, α-CD was thiolated using phosphorous pentasulfide. Thiolated α-CD was characterized by FT-IR and ¹H NMR spectroscopy, differential scanning calorimetry (DSC), and powder X-ray diffractometry (PXRD). Cytotoxicity of α-CD-SH was evaluated on Caco-2, HEK 293, and MC3T3 cells. Dilauryl fluorescein (DLF) and coumarin-6 (Cou) serving as surrogates for a pharmaceutical payload were incorporated in α-CD-SH, and cellular uptake was analyzed by flow cytometry and confocal microscopy. Endosomal escape was investigated by confocal microscopy and hemolysis assay. Results showed no cytotoxic effect within 3 h, while dose-dependent cytotoxicity was observed within 24 h. The cellular uptake of DLF and Cou was up to 20- and 11-fold enhanced by α-CD-SH compared to native α-CD, respectively. Furthermore, α-CD-SH provided an endosomal escape. According to these results, α-CD-SH is a promising carrier to shuttle drugs into the cytoplasm of target cells.

Sonochemical preparation of folate-decorated reductive-responsive carboxymethylcellulose-based nanocapsules for targeted drug delivery

In this study, a biocompatible folate-decorated reductive-responsive carboxymethylcellulose-based nanocapsules (FA-RCNCs) were designed and prepared via sonochemical method for targeted delivery and controlled release of hydrophobic drugs. The shell of FA-RCNCs was cross-linked by disulfide bonds formed from hydrosulfuryl groups on the thiolated carboxymethylcellulose (TCMC) and encapsulated hydrophobic drug dispersed in the oil phase into nanocapsules. Moreover, the size and morphology of drug loaded FA-RCNCs were characterized by DLS, SEM and CLSM which indicated that the synthesized nanocapsules have suitable size range and excellent stability for circulating in the bloodstream. The drug release rate of FA-RCNCs could be controlled by adjusting their sizes and shell thickness, which could be dominated by the concentration of TCMC and sonochemical conditions. Furthermore, the obtained FA-RCNCs could be ingested into Hela cells via folate-receptor (FR)-mediated endocytosis and quickly release drugs under reductive environment, which demonstrated that FA-RCNCs could become potential hydrophobic drugs carries for cancer therapy.

Cyclodextrin Encapsulated pH Sensitive Dyes as Fluorescent Cellular Probes: Self-Aggregation and In Vitro Assessments

We have designed and synthesized a series of novel, supramolecular, long-lived fluorescent probes based on the host-guest inclusion complexes formation between fluorescent indolizinyl-pyridinium salts and β-cyclodextrin. Fluorescence and electrospray ionisation mass spectrometry experiments, supported by theoretical molecular docking studies, were utilized in the monitoring of the inclusion complexes formation, evidencing the appearance of corresponding 1:1 and 1:2 species. Additionally, the influence of the guest molecule over the aggregation processes of the cyclodextrin inclusion complexes was investigated by transmission electron microscopy. The absence of cytotoxicity, cellular permeability, long-lived intracellular fluorescence, and in time specific accumulation within acidic organelles identified the investigated supramolecular entities as remarkable candidates for intracellular fluorescence probes. Co-staining experiments using specific organelle markers revealed the fact that, after a 24-h incubation period, the inclusion complexes accumulate predominantly in lysosomes rather than in mitochondria. This study opens new possibilities for a broad range of fluorescent dyes with solubility and high toxicity issues, able to form inclusion complexes with β-cyclodextrin, to be tested as intracellular fluorescence probes.

Direct Correlation of Single-Particle Motion to Amorphous Microstructural Components of Semicrystalline Poly(ethylene oxide) Electrolytic Films

Semicrystalline polymers constitute some of the most widely used materials in the world, and their functional properties are intimately connected to their structure on a range of length scales. Many of these properties depend on the micro- and nanoscale heterogeneous distribution of crystalline and amorphous phases, but this renders the interpretation of ensemble averaged measurements challenging. We use superlocalized widefield single-particle tracking in conjunction with AFM phase imaging to correlate the crystalline morphology of lithium-triflate-doped poly(ethylene oxide) thin films to the motion of individual fluorescent probes at the nanoscale. The results demonstrate that probe motion is intrinsically isotropic in amorphous regions and that, without altering this intrinsic diffusivity, closely spaced, often parallel, crystallite fibers anisotropically constrain probe motion along intercalating amorphous channels. This constraint is emphasized by the agreement between crystallite and anisotropic probe trajectory orientations. This constraint is also emphasized by the extent of the trajectory confinement correlated to the width of the measured gaps between adjacent crystallites. This study illustrates with direct nanoscale correlations how controlled and periodic arrangement of crystalline domains is a promising design principle for mass transport in semicrystalline polymer materials without compromising their mechanical stability.

β-Cyclodextrin Encapsulated Coumarin 6 on Graphene Oxide Nanosheets: Impact on Ground-State Electron Transfer and Excited-State Energy Transfer

We report a unique phenomenon of physical adsorption of coumarin 6-β-cyclodextrin (C6-β-CD) inclusion nanostructures on graphene oxide (GO) nanosheets, thus inducing ground-state electron transfer from the C6-β-CD composite to GO. On excitation, the C6-β-CD composite initially transfers energy to the attached GO surface and subsequently collides with similar C6-β-CD@GO adducts leading to dynamic quenching of energy. The ground-state two-electron transfer process has been confirmed by cyclic voltammetry in aqueous medium, whereas the excited-state processes were inferred from steady-state and time-resolved fluorescence spectroscopy. The concept is developed toward conceiving control over the ground-state electron transfer and excited state energy transfer from the C6-β-CD composite by the adsorbed electron accepting medium (GO in this case). The C6-β-CD composite has been prepared to isolate single C6 molecules that readily undergo microcrystal formation in aqueous medium. The results show its potential toward fabrication of energy-harvesting antenna for further applications.

Aggregation of Nile Red in Water: Prevention through Encapsulation in β-Cyclodextrin

The present work, based on various spectroscopic investigations, vividly demonstrates the self-association of Nile red (NR) in aqueous medium. The rapid decrease in the absorbance as well as emission of NR in water bears the signature of the aggregation process. Appearance of a new blue-shifted absorption band in addition to the original one and a drastic decrease in the emission intensity imply that the aggregation is of H-type. Poor solubility of NR in water, hydrophobic interaction, and the planar structure of the dye are ascribed to favor the formation of the aggregate in the aqueous medium. Absorption-based kinetic studies reveal the aggregation process to be second order, thereby establishing the aggregate to be a dimer. Similar kinetic profiles of the absorbance of NR in the presence and absence of light confirm that the aggregation process is not photoassisted. The presence of an isosbestic point in the absorbance spectra and an isoemissive point in the time-resolved area normalized emission spectra bears the evidence of equilibrium between the dimeric and the monomeric species of NR in the ground state as well as in the photoexcited state. Encapsulation of the monomer of NR within the hydrophobic cavity of β-cyclodextrin is demonstrated to prevent the aggregation process.

Revival of the nearly extinct fluorescence of coumarin 6 in water and complete transfer of energy to rhodamine 123

The nearly extinct fluorescence of coumarin 6 in water due to microcrystal formation is revived by micelles. Practically complete transfer of energy from coumarin 6 to rhodamine 123 through resonance energy transfer could be achieved.

Revival, enhancement and tuning of fluorescence from Coumarin 6: combination of host–guest chemistry, viscosity and collisional quenching

The self-quenched fluorescence of Coumarin 6 can be revived by host–guest chemistry and further increased by about 40% on increasing the solvent viscosity and hence restricting the motion of the molecules.