Functionalization of Polydimethylsiloxane with Diazirine-Based Linkers for Covalent Protein Immobilization.

Biomolecule attachment to solid supports is critical for biomedical devices, such as biosensors and implants. Polydimethylsiloxane (PDMS) is commonly used for these applications due to its advantageous properties. To enhance the biomolecule immobilization on PDMS, a novel technique is demonstrated using newly synthesized diazirine molecules for the surface modification of PDMS. This nondestructive process involves a reaction between diazirine molecules and PDMS through C-H insertion with thermal or ultraviolet activation. The success of the PDMS modification is confirmed by various surface characterization techniques. Bovine serum albumin (BSA) and immunoglobulin G (IgG) are strongly attached to the modified PDMS surfaces, and the amount of protein is quantified using iodine-125 radiolabeling. The results demonstrate that PDMS is rapidly functionalized, and the stability of the immobilized proteins is significantly improved with multiple types of diazirine molecules and activation methods. Confocal microscopy provides three-dimensional images of the distribution of immobilized IgG on the surfaces and the penetration of diazirine-based linkers through the PDMS substrate during the coating process. Overall, this study presents a promising new approach for functionalizing PDMS surfaces to enhance biomolecule immobilization, and its potential applications can extend to multimaterial modifications for various diagnostic and medical applications such as microfluidic devices and immunoassays with relevant bioactive proteins.

A Cleavable Crosslinking Strategy for Commodity Polymer Functionalization and Generation of Reprocessable Thermosets.

Covalently crosslinked polymeric materials, known as thermosets, possess enhanced mechanical strength and thermal stability relative to the corresponding uncrosslinked thermoplastics. However, the presence of covalent inter-chain crosslinks that makes thermosets so attractive is precisely what makes them so difficult to reprocess and recycle. Here, we demonstrate the introduction of chemically cleavable groups into a bis-diazirine crosslinker. Application of this cleavable crosslinker reagent to commercial low-functionality polyolefins (or to a small-molecule model) results in the rapid, efficient introduction of molecular crosslinks that can be uncoupled by specific chemical inputs. These proof-of-concept findings provide one potential strategy for circularization of the thermoplastic/thermoset plastics economy, and may allow crosslinked polyolefins to be manufactured, used, reprocessed, and re-used without losing value. As an added benefit, the method allows the ready introduction of functionality into non-functionalized commodity polymers.

Structure-function relationships in aryl diazirines reveal optimal design features to maximize C-H insertion.

Diazirine reagents allow for the ready generation of carbenes upon photochemical, thermal, or electrical stimulation. Because carbenes formed in this way can undergo rapid insertion into any nearby C-H, O-H or N-H bond, molecules that encode diazirine functions have emerged as privileged tools in applications ranging from biological target identification and proteomics through to polymer crosslinking and adhesion. Here we use a combination of experimental and computational methods to complete the first comprehensive survey of diazirine structure-function relationships, with a particular focus on thermal activation methods. We reveal a striking ability to vary the activation energy and activation temperature of aryl diazirines through the rational manipulation of electronic properties. Significantly, we show that electron-rich diazirines have greatly enhanced efficacy toward C-H insertion, under both thermal and photochemical activation conditions. We expect these results to lead to significant improvements in diazirine-based chemical probes and polymer crosslinkers.

Flexible polyfluorinated bis-diazirines as molecular adhesives.

Motivated by a desire to develop flexible covalent adhesives that afford some of the same malleability in the adhesive layer as traditional polymer-based adhesives, we designed and synthesized two flexible, highly fluorinated bis-diazirines. Both molecules are shown to function as effective crosslinkers for polymer materials, and to act as strong adhesives when painted between two polymer objects of low surface energy, prior to thermal activation. Data obtained from lap-shear experiments suggests that greater molecular flexibility is correlated with improved mechanical compliance in the adhesive layer.

A broadly applicable cross-linker for aliphatic polymers containing C-H bonds.

Addition of molecular cross-links to polymers increases mechanical strength and improves corrosion resistance. However, it remains challenging to install cross-links in low-functionality macromolecules in a well-controlled manner. Typically, high-energy processes are required to generate highly reactive radicals in situ, allowing only limited control over the degree and type of cross-link. We rationally designed a bis-diazirine molecule whose decomposition into carbenes under mild and controllable conditions enables the cross-linking of essentially any organic polymer through double C-H activation. The utility of this molecule as a cross-linker was demonstrated for several diverse polymer substrates (including polypropylene, a low-functionality polymer of long-standing challenge to the field) and in applications including adhesion of low-surface-energy materials and the strengthening of polyethylene fabric.

Amphiphilic nebramine-based hybrids Rescue legacy antibiotics from intrinsic resistance in multidrug-resistant Gram-negative bacilli.

The inability to discover novel class of antibacterial agents, especially against Gram-negative bacteria (GNB), compel us to consider a broader non-conventional approach to treat infections caused by multidrug-resistant (MDR) bacteria. One such approach is the use of adjuvants capable of revitalizing the activity of current existing antibiotics from resistant pathogens. Recently, our group reported a series of tobramycin (TOB)-based hybrid adjuvants that were able to potentiate multiple classes of legacy antibiotics against various MDR GNB. Herein, we report the modification of TOB-based hybrid adjuvants by replacing TOB domain by the pseudo-disaccharide nebramine (NEB) through selective cleavage of the α-d-glucopyranosyl linkage of TOB. Potent synergism was found for combinations of NEB-based hybrid adjuvants with multiple classes of legacy antibiotics including fluoroquinolones (moxifloxacin and ciprofloxacin), tetracyclines (minocycline), or rifamycin (rifampicin) against both wild-type and MDR P. aeruginosa clinical isolates. We also demonstrated that a combination of the optimized NEB-CIP hybrid 1b and rifampicin protects Galleria mellonella larvae from the lethal effects of extensively drug-resistant (XDR) P. aeruginosa. Mechanistic evaluation of NEB-based hybrid adjuvants revealed that the hybrids affect the outer- and inner membranes of wild-type P. aeruginosa PAO1. This study describes an approach to optimize aminoglycoside-based hybrids to yield lead adjuvant candidates that are able to resuscitate the activity of partner antibiotics against MDR GNB.