Single molecule nanoparticles of the conjugated polymer MEH-PPV, preparation and characterization by near-field scanning optical microscopy

We have developed a straightforward method for producing a stable, aqueous suspension of hydrophobic, fluorescent pi-conjugated polymer nanoparticles consisting primarily of individual conjugated polymer molecules. Features of the method are the facile preparation, purity, unique optical properties, and small size (approximately 5-10 nm) of the resulting nanoparticles. The results of TEM, scanning force microscopy, and near-field scanning optical microscopy of particles cast from the suspension indicate that the particles are single conjugated polymer molecules. The NSOM results yield estimates of the optical cross-sections of individual conjugated polymer molecules. The UV-vis absorption spectra of the nanoparticle suspensions indicate a reduction in conjugation length attributed to deformations of the polymer backbone. Fluorescence spectra of the aqueous nanoparticle suspensions indicate interactions between segments of the polymer chain and intramolecular energy transfer.     

Degradation studies of some polyesters and polycarbonates: 3—Polyglycollide

The thermal degradation of polyglycollide has been studied by similar techniques to those used in investigations of polyactide (Parts 1 and 2). From the results obtained, it is concluded that the decomposition is complex. At temperatures a little over 200°C, polyglycollide breaks down primarily by ester interchange processes, giving glycollide and larger cyclic oligomers of the repeat structure. The simultaneous formation of carbon dioxide, however, indicates a further mode of breakdown at low temperatures: decarboxylation of chain ends is suggested and this also allows the appearance of methyl glycollate as a product to be explained. At higher temperatures, the proportion of carbon dioxide in the products increases and formaldehyde, ketene and carbon monoxide are formed: these features are accounted for by chain scission processes. The energy of activation found for polyglycollide decomposition (average result 21 kcal mol^?1) is lower than that for polylactide (28 kcal mol^?1), probably for steric reasons, since the degradation processes for the two polymers show many similarities.     

Chemical synthesis and immunological evaluation of entirely carbohydrate conjugate Globo H-PS A1

An anticancer, entirely carbohydrate conjugate, Globo H-polysaccharide A1 (Globo H-PS A1), was chemically prepared and immunologically evaluated in C57BL/6 mice. Tumor associated carbohydrate antigen Globo H hexasaccharide was synthesized in an overall 7.8% yield employing a convergent [3 + 3] strategy that revealed an anomeric aminooxy group used for conjugation to oxidized PS A1 via an oxime linkage. Globo H-PS A1, formulated with adjuvants monophosphoryl lipid A and TiterMax® Gold. After immunization an antigen specific immune response was observed in ELISA with anti-Globo H IgG/IgM antibodies. Specificity of the corresponding antibodies was determined by FACS showing cell surface binding to Globo H-positive cancer cell lines MCF-7 and OVCAR-5. The anti-Globo H antibodies also exhibited complement-dependent cellular cytotoxicity against MCF-7 and OVCAR-5 cells.

An anticancer, entirely carbohydrate conjugate, Globo H-polysaccharide A1 (Globo H-PS A1), was chemically prepared and immunologically evaluated in C57BL/6 mice.     

Quantification of singlet oxygen production in the reaction of superoxide with hydrogen peroxide using a selective chemiluminescent probe

A sensitive chemiluminescent probe that selectively reacts with singlet oxygen in the presence of superoxide and hydrogen peroxide has been used to quantify the production of singlet oxygen in the reaction of superoxide with hydrogen peroxide. The yield of singlet oxygen from this reaction was found to be low (0.2% relative to the initial superoxide concentration). No evidence for the formation of hydroxyl radical was observed in this reaction, ruling out the Haber-Weiss mechanism as a major singlet oxygen formation pathway. No singlet oxygen production was observed in the reaction of superoxide with 2-nitrobenzoic acid, which has a pKa similar to that of hydrogen peroxide, rendering the protonation of superoxide, followed by its disproportionation, an unlikely explanation for the formation of singlet oxygen in this system. The low yields of singlet oxygen and hydroxyl radical suggest that their formation in this reaction should be relatively unimportant in biological systems.     

Sensitivity enhancement of solid-state NMR spectra of half-integer spin quadrupolar nuclei: Double- or single-frequency sweeps? Insights from the hyperbolic secant experiment

Improved sensitivity enhancements of the central NMR transition of non-integer spin quadrupolar nuclei in MAS powder samples are realized when only a single satellite transition spinning side band is irradiated using a conventional double-frequency sweep experiment compared to irradiation of the entire spinning side band manifold. For example, for ⁸⁷Rb in RbClO₄, enhancement factors of 2.2 versus 1.9 are observed when only one satellite transition spinning side band is targeted versus the entire spinning side band manifold. Similarly, for ²⁷Al in Al(acac)₃, the corresponding enhancement was 3.4 compared to 2.6.     

An Integrated Approach toward NanoBRET Tracers for Analysis of GPCR Ligand Engagement

Gaining insight into the pharmacology of ligand engagement with G-protein coupled receptors (GPCRs) under biologically relevant conditions is vital to both drug discovery and basic research. NanoLuc-based bioluminescence resonance energy transfer (NanoBRET) monitoring competitive binding between fluorescent tracers and unmodified test compounds has emerged as a robust and sensitive method to quantify ligand engagement with specific GPCRs genetically fused to NanoLuc luciferase or the luminogenic HiBiT peptide. However, development of fluorescent tracers is often challenging and remains the principal bottleneck for this approach. One way to alleviate the burden of developing a specific tracer for each receptor is using promiscuous tracers, which is made possible by the intrinsic specificity of BRET. Here, we devised an integrated tracer discovery workflow that couples machine learning-guided in silico screening for scaffolds displaying promiscuous binding to GPCRs with a blend of synthetic strategies to rapidly generate multiple tracer candidates. Subsequently, these candidates were evaluated for binding in a NanoBRET ligand-engagement screen across a library of HiBiT-tagged GPCRs. Employing this workflow, we generated several promiscuous fluorescent tracers that can effectively engage multiple GPCRs, demonstrating the efficiency of this approach. We believe that this workflow has the potential to accelerate discovery of NanoBRET fluorescent tracers for GPCRs and other target classes.     

Dechlorination of chloroethylenes by cob(I)alamin and cobalamin model complexes

Cobalt-mediated dehalogenation reactions, specifically those that employ cobalamin, have attracted particular attention because these complexes rapidly degrade tetrachloroethylene (PCE) and trichloroethylene (TCE), which are common groundwater contaminants. Although questions remain about the relative importance of several pathways, both radicals and organometallic intermediates, specifically chlorovinyl complexes, play an important role in these processes. This Perspective highlights recent studies focused on elucidating the mechanism of chloroethylene degradation, including experimental studies on PCE and TCE dechlorination, computational studies, preparation of model complexes, and the study of model catalytic systems.     

An Experimental Method to Measure Gaseous Diffusivity in Tight and Partially Saturated Porous Media via Continuously Monitored Mass Spectrometry

Transport in Porous Media -     

Dual-Mode Superresolution Imaging Using Charge Transfer Dynamics in Semiconducting Polymer Dots

In a conjugated polymer-based single-particle heterojunction, stochastic fluctuations of the photogenerated hole population lead to spontaneous fluorescence switching. We found that 405 nm irradiation can induce charge recombination and activate the single-particle emission. Based on these phenomena, we developed a novel class of semiconducting polymer dots that can operate in two superresolution imaging modes. The spontaneous switching mode offers efficient imaging of large areas, with <10 nm localization precision, while the photoactivation/deactivation mode offers slower imaging, with further improved localization precision (ca. 1 nm), showing advantages in resolving small structures that require high spatial resolution. Superresolution imaging of microtubules and clathrin-coated pits was demonstrated, under both modes. The excellent localization precision and versatile imaging options provided by these nanoparticles offer clear advantages for imaging of various biological systems.