Increasing antibiotic activity by rapid bioorthogonal conjugation of drug to resistant bacteria using an upconverted light-activated photocatalyst.

Antibiotic vancomycin (Van) is often used as the drug of last resort to treat methicillin resistant Staphylococcus aureus. Due to the emergence of Van-resistant microbes, it is necessary to continuously design strategies to increase the efficacy of Van against resistant cells. In this study, an efficient method of bio-conjugating Van to bacteria is proposed using near-infrared (NIR)-light activation. A Nd3+-sensitized upconversion nanocrystal (UCNC) decorated with toluidine blue O (TB) on its surface undergoes upconverted energy transfer from the UCNC to TB when excited by 808 nm light. The photoexcited TB then catalyses the conversion of the dihydrotetrazine (dHTz) moiety in a Van-dHTz conjugate system to tetrazine which undergoes an efficient inverse electron demand Diels-Alder reaction with prior attached norbornene molecules on bacterial cell walls. The enhanced affinity of Van to bacteria by covalent bonding improves the activity of the drug against drug-resistant Enterococci, and the MIC is reduced by 6- to 7-fold as compared to neat Van. We demonstrate that the mode of action is due to increased inhibition of peptidoglycan cell wall biosynthesis. The findings in this study demonstrate that on-demand NIR-light activated bioorthogonal conjugation of Van to microbes is a viable alternative treatment in combating drug-resistant bacteria.

Lipopolysaccharide-affinity copolymer senses the rapid motility of swarmer bacteria to trigger antimicrobial drug release.

An intelligent drug release system that is triggered into action upon sensing the motion of swarmer P. mirabilis is introduced. The rational design of the drug release system focuses on a pNIPAAm-co-pAEMA copolymer that prevents drug leakage in a tobramycin-loaded mesoporous silica particle by covering its surface via electrostatic attraction. The copolymer chains are also conjugated to peptide ligands YVLWKRKRKFCFI-NH2 that display affinity to Gram-negative bacteria. When swarmer P. mirabilis cells approach and come in contact with the particle, the copolymer-YVLWKRKRKFCFI-NH2 binds to the lipopolysaccharides on the outer membrane of motile P. mirabilis and are stripped off the particle surface when the cells move away; hence releasing tobramycin into the swarmer colony and inhibiting its expansion. The release mechanism is termed Motion-Induced Mechanical Stripping (MIMS). For swarmer B. subtilis, the removal of copolymers from particle surfaces via MIMS is not apparent due to poor adherence between bacteria and copolymer-YVLWKRKRKFCFI-NH2 system.

Edge-on gating effect in molecular wires.

This work demonstrates edge-on chemical gating effect in molecular wires utilizing the pyridinoparacyclophane (PC) moiety as the gate. Different substituents with varied electronic demands are attached to the gate to simulate the effect of varying gating voltages similar to that in field-effect transistor (FET). It was observed that the orbital energy level and charge carrier's tunneling barriers can be tuned by changing the gating group from strong electron acceptors to strong electron donors. The single molecule conductance and current-voltage characteristics of this molecular system are truly similar to those expected for an actual single molecular transistor.

Loss of collective motion in swarming bacteria undergoing stress.

The collective motion of Bacillus subtilis in the presence of a photosensitizer is disrupted by reactive oxygen species when exposed to light of sufficient dosages and is partially recovered when light irradiation is suspended. The transition from a highly collective to a more random motion is modeled using an improved self-propelled model with alignment rule. The increment in noise level describes the enhanced uncertainty in the motion of swarming bacteria under stress as observed experimentally.

Unconventional multiple ring structure formation from evaporation-induced self-assembly of polymers.

The formation of multiring deposits of poly(2-vinylpyridine) (P2VP) from the evaporation of a P2VP-(2,6-lutidine + water) drop on a glass substrate does not conform to the conventional pinning-depinning mechanism. Instead, ringlike deposits are formed when the droplet undergoes several cycles of spreading and receding where, for each spreading event, a P2VP ridge is formed at the contact line when the polymer flows toward the outward advancing edge. The complex interplay between an outward solutal-Marangoni flow due to a higher concentration of the polymer at the contact line and an inward solvent-Marangoni flow arising from the differences in volatilities and surface tensions of the pure solvent components plays an important role in enhancing the droplet spreading rate. The newly discovered surface patterning mechanism has important implications in the development of novel techniques for inducing self-assembly of functional materials from evaporating drops.

Domain coalescence-induced nucleation and anomalous growth of holes in thin polymer blend film.

The phase evolution of a thin polymer blend film of polystyrene (PS) and poly(2-vinyl pyridine) (P2VP) triggered by solvent annealing is examined at both the bulk and single-(macro)molecule levels using wide-field microscopy (WFM). The transitions between different evolutionary stages in the nucleation and growth process are clearly visualized in real time and without intermittent breaks. The nucleation of PS holes arises from the coalescence and growth of P2VP domains and the holes expand in a complex manner involving the dewetting of PS and the absorption of P2VP domains into the holes.

Multifunctional divalent vancomycin: the fluorescent imaging and photodynamic antimicrobial properties for drug resistant bacteria.

A simple and specific divalent vancomycin-porphyrin has been developed. This divalent vancomycin-porphyrin conjugate indicates promising properties in fluorescent imaging and photodynamic inactivation of vancomycin-sensitive and vancomycin-resistant enterococci (VRE) bacterial strains.

Visualizing polymer crystallization in ultrathin layers using a single-macromolecule tracking method.

Single-(macro) molecule tracking is used for the first time here to study the crystallization process in ultrathin layers of single poly(ethylene oxide) (PEO) chains. Diffusion trajectories of macromolecules diffusing toward the crystal followed by deposition onto the crystal-growth front display different types of motion, such as Brownian and directed motions, prior to crystallization. We show that PEO chains in the amorphous layer and in the less concentrated or depleted zone exhibit Brownian motion of different diffusion rates as a result of heterogeneities in the environment.

The combined catalytic action of solid acids with nickel for the transformation of polypropylene into carbon nanotubes by pyrolysis.

The effects of both organically modified montmorillonite (OMMT) and Ni(2)O(3) on the carbonization of polypropylene (PP) during pyrolysis were investigated. The results from TEM and Raman spectroscopy showed that the carbonized products of PP were mainly multiwalled carbon nanotubes (MWNTs). Surprisingly, a combination of OMMT and Ni(2)O(3) led to high-yield formation of MWNTs. X-ray powder diffraction (XRD) and GC-MS were used to investigate the mechanism of this combination for the high-yield formation of MWNTs from PP. Brønsted acid sites were created in degraded OMMT layers by thermal decomposition of the modifiers. The resultant carbenium ions play an important role in the carbonization of PP and the formation of MWNTs. The degradation of PP was induced by the presence of carbenium ions to form predominantly products with lower carbon numbers that could be easily catalyzed by the nickel catalyst for the growth of MWNTs. Furthermore, carbenium ions are active intermediates that promote the growth of MWNTs from the degradation products with higher carbon numbers through hydride-transfer reactions. The XRD measurements showed that Ni(2)O(3) was reduced into metallic nickel (Ni) in situ to afford the active sites for the growth of MWNTs.