Homologous pairing in short double-stranded DNA-grafted colloidal microspheres.

Homologous pairing (HP), i.e., the pairing of similar or identical double-stranded DNA, is an insufficiently understood fundamental biological process. HP is now understood to also occur without protein mediation, but crucial mechanistic details remain poorly established. Unfortunately, systematic studies of sequence dependence are not practical due to the enormous number of nucleotide permutations and multiple possible conformations involved in existing biophysical strategies even when using as few as 150 basepairs. Here, we show that HP can occur in DNA as short as 18 basepairs in a colloidal microparticle-based system. Exemplary systematic studies include resolving opposing reports of the impact of % AT composition, validating the impact of nucleotide order and triplet framework and revealing isotropic bendability to be crucial for HP. These studies are enabled by statistical analysis of crystal size and fraction within coexisting fluid-crystal phases of double-stranded DNA-grafted colloidal microspheres, where crystallization is predicated by HP.

Utility of Chemical Upcycling in Transforming Postconsumer PET to PBT-Based Thermoplastic Copolyesters Containing a Renewable Fatty-Acid-Derived Soft Block.

Thermoplastic copolyesters (TPCs) are important structural components in countless high performance applications that require excellent thermal stability and outstanding mechanical integrity. Segmented multiblock architectures are often employed for the most demanding applications, in which semicrystalline segments of poly(butylene terephthalate) (PBT) are combined with various low T g soft blocks. These segmented copolymers are nearly always synthesized from pristine feedstocks that are derived from fossil-fuel sources. In this work, we show a straightforward, one-pot synthetic approach to prepare TPCs starting from high-molar mass poly(ethylene terephthalate) recyclate (rPET) combined with a hydrophobic fatty acid dimer diol flexible segment. Transesterification is exploited to create a multiblock architecture. The high molar mass and segment distribution are elucidated by detailed size-exclusion chromatography and proton and carbon nuclear magnetic resonance spectroscopy. It is also shown that rPET can be chemically converted to PBT through a molecular exchange, in which the ethylene glycol is substituted by introducing 1,4-butane diol. A series of copolymers with various compositions was prepared with either PET or PBT segments and the final thermal properties and mechanical performance is compared between the two different constructs. Ultimately, PBT-based TPCs crystallize faster and exhibit a higher modulus over the range of explored compositions, making them ideal for applications that require injection molding. This represents an ideal, sustainable approach to making conventional TPCs, utilizing recyclate and biobased components to produce high performance polymer constructs via an easily accessible upcycling route.

One-pot surfactant-free modulation of size and functional group distribution in thermoresponsive microgels.

Control over the size and functional group distribution of soft responsive hydrogel particles is essential for applications such as drug delivery, catalysis and chemical sensing. Traditionally, targeted functional group distributions are achieved with semi-batch techniques which require specialized equipment, while the preparation of size-tailored particles typically involves the use of surfactants. Herein, we present a simple and robust surfactant-free method for the modulation of size and carboxylic acid functional group distribution in poly(N-isopropylacrylamide) thermoresponsive microgels, employing reaction pH as the single experimental parameter. The varying distributions of carboxylic acid residues arise due to differences in kinetic reactivity, which are a function of the degree of dissociation of methacrylic acid, and thus of reaction pH. Incorporated charged residues induce a surfactant-like action during the particle nucleation stage, and impact the final particle size. Characterization with dynamic light scattering, and electron microscopy consistently supports the pH-tailored morphology of the microgels. A mathematical model which accounts for particle deformation on the imaging substrate also shows excellent agreement with the experimental results.

Cationic Molecular Umbrellas as Antibacterial Agents with Remarkable Cell-Type Selectivity.

We synthesized a combinatorial library of dendrons that display a cluster of cationic charges juxtaposed with a hydrophobic alkyl chain, using the so-called "molecular umbrella" design approach. Systematically tuning the generation number and alkyl chain length enabled a detailed study of the structure-activity relationships in terms of both hydrophobic content and number of cationic charges. These discrete, unimolecular compounds display rapid and broad-spectrum bactericidal activity comparable to the activity of antibacterial peptides. Micellization was examined by pyrene emission and dynamic light scattering, which revealed that monomeric, individually solvated dendrons are present in aqueous media. The antibacterial mechanism of action is putatively driven by the membrane-disrupting nature of these cationic surfactants, which we confirmed by enzymatic assays on E. coli cells. The hemolytic activity of these dendritic macromolecules is sensitively dependent on the dendron generation and the alkyl chain length. Via structural optimization of these two key design features, we identified a leading candidate with potent broad-spectrum antibacterial activity (4-8 µg/mL) combined with outstanding hemocompatibility (up to 5000 µg/mL). This selected compound is >1000-fold more active against bacteria as compared to red blood cells, which represents one of the highest selectivity index values ever reported for a membrane-disrupting antibacterial agent. Thus, the leading candidate from this initial library screen holds great potential for future applications as a nontoxic, degradable disinfectant.

Quantification of functional crosslinker reaction kinetics via super-resolution microscopy of swollen microgels.

Super resolution microscopy (SRM) brings the advantages of optical microscopy to the imaging of nanostructured soft matter, and in colloidal microgels, promises to quantify variations of crosslink densities at unprecedented length scales. However, the distribution of all crosslinks does not coincide with that of dye-tagged crosslinks, and density quantification in SRM is not guaranteed due to over/under-counting dye molecules. Here we demonstrate that SRM images of microgels encode reaction rate constants of functional cross linkers, which hold the key to correlating these distributions. Combined with evolution of microgel particle radii, the functional cross linker distributions predict consumption versus time with high fidelity. Using a Bayesian regression approach, we extract reaction rate constants for homo and cross propagation of the functional crosslinker, which should be widely useful for predicting spatial variations in crosslink density of gels.

Inclusion of Quercetin in Gold Nanoparticles Decorated with Supramolecular Hosts Amplifies Its Tumor Targeting Properties.

Despite the anticancer potential of natural products (NPs), their limited bioavailability necessitates laborious derivatization or covalent conjugation to delivery vehicles. To unleash their potential, we developed a nanohybrid delivery platform with a noncovalently tunable surface. Initially, the active compound was encapsulated in a macrocycle, p-sulfonatocalix[4]arene, enabling a 62 000-fold aqueous solubility amplification as also a 2.9-fold enhancement in its cytotoxicity with respect to the parent compound in SW-620 colon cancer cells. A pH stimuli responsive behavior was recorded for this formulate, where a programmable release of quercetin from the macrocycle was monitored in an acidic environment. Then, a nanoparticle gold core was decorated with calixarene hosts to accommodate noncovalently NPs. The loaded nanocarrier with the NP quercetin dramatically enhanced the cytotoxicity (>50-fold) of the parent NP in colon cancer and altered its cell membrane transport mode. In vivo experiments in a mouse 4T1 tumor model showed a reduction of tumor volume in mice treated with quercetin-loaded nanoparticles without apparent toxic effects. Further analysis of the tumor-derived RNA highlighted that treatment with quercetin-loaded nanoparticles altered the expression of 27 genes related to apoptosis.

3D mapping of nanoscale crosslink heterogeneities in microgels.

The majority of swollen polymer networks exhibit spatial variations in crosslink density. These spatial heterogeneities are particularly important in colloidal gel particles, or microgels, where they manifest themselves on the nanoscale and impact mechanical and transport properties. Despite their importance, the real space nanostructure of these heterogeneities at the individual particle level has remained elusive. Using state of the art super-resolution microscopy known as Whole cell 4Pi Single Molecule Switching Nanoscopy (W-4PiSMSN) we demonstrate 3D nanoscale mapping of spatial crosslink heterogeneities in a model system of poly(N-isopropylacrylamide) colloidal gel particles containing a novel fluorophore tagged crosslinker. We reveal the presence of higher crosslink density clusters embedded in a lower crosslink density matrix within the core of individual microgel particles, a phenomenon that has been predicted, but never been observed before in real space. The morphology of the clusters provides insight into the kinetics of microgel formation. This study also provides proof-of-concept 3D super-resolution imaging of spatial heterogeneities in bulk hydrogels.