The increasing prevalence of multidrug-resistant (MDR) pathogens has promoted the development of innovative approaches, such as drug repurposing, synergy, and efficient delivery, in complement to traditional antibiotics. In this study, we present an approach based on biocompatible nanocarriers containing antimicrobial cations and known antibiotics. The matrices were prepared by coordinating Ga-III or In-III to formulations of chitosan/tripolyphosphate or catechol-functionalized chitosan with or without encapsulated antibiotics, yielding particles of 100-200 nm in hydrodynamic diameter. MDR clinical isolates of Pseudomonas aeruginosa were found to be effectively inhibited by the nanocarriers under nutrient-limiting conditions. Fractional inhibitory concentration (FIC) indices revealed that cation- and antibiotic-encapsulated nanomatrices were effective against both Gram-negative and Gram-positive pathogens. Metallophores, such as deferoxamine (DFO), were probed to facilitate the sequestration and transport of the antimicrobial cations Ga-III or In-III. Although the antimicrobial activities were less significant with DFO, the eradication of biofilm-associated bacteria showed promising trends against P. aeruginosa and Staphylococcus epidermidis. Interestingly, indium-containing compounds showed enhanced activity on biofilm formation and eradication, neutralizing P. aeruginosa under Fe-limiting conditions. In particular, In-III-cross-linked catechol-modified chitosan matrices were able to inhibit pathogenic growth together with DFO. The nanocarriers showed low cytotoxicity toward A549 cells and improvable CC50 values with NIH/3T3 cells.

The opportunistic pathogen Pseudomonas aeruginosa develops increasing resistance toward even the most potent antibiotics. Like other bacteria, the pathogen produces a number of virulence factors including metallophores, which constitute an important group. Pseudomonads produce the iron-chelating metallophore (siderophore) pyochelin, which, in addition to its iron-scavenging ability, is an effector for the transcriptional regulator PchR in its FeIII-bound form (ferripyochelin). In the present study, docking studies predicted a major ferripyochelin binding site in PchR, which prompted the exploration of nor-pyochelin analogues to produce tight binding to PchR, and thereby upregulation of the pyochelin metabolism. In addition, we investigated the effects of using the analogues to bind the antimicrobial cations GaIII and InIII. Selected analogues of nor-pyochelin were synthesized, and their GaIII- and InIII-based complexes were assessed for antimicrobial activity. The results indicate that the GaIII complexes inhibit the pathogens under iron-limited conditions, while the InIII-based systems are more effective in iron-rich media. Several of the GaIII complexes were shown to be highly effective against a multidrug-resistant P. aeruginosa clinical isolate, with minimum inhibitory concentrations (MICs) of <= 1 mu g/mL. Similarly, two of the InIII-based systems were particularly effective against the isolate, with an MIC of 8 mu g/mL. These results show high promise in comparison with other, traditionally potent antibiotics, as the compounds generally indicated low cytotoxicity toward mammalian cells. Preliminary mechanistic investigations using pseudomonal transposon mutants suggested that the inhibitory effects of the InIII-based systems could be due to acute iron deficiency as a result of InIII-bound bacterioferritin.

Real-time tracking of intracellular carbohydrates remains challenging. While click chemistry allows bio-orthogonal tagging with fluorescent probes, the reaction permanently alters the target molecule and only allows a single snapshot. Here, we demonstrate click-free mid-infrared photothermal (MIP) imaging of azide-tagged carbohydrates in live cells. Leveraging the micromolar detection sensitivity for 6-azido-trehalose (TreAz) and the 300-nm spatial resolution of MIP imaging, the trehalose recycling pathway in single mycobacteria, from cytoplasmic uptake to membrane localization, is directly visualized. A peak shift of azide in MIP spectrum further uncovers interactions between TreAz and intracellular protein. MIP mapping of unreacted azide after click reaction reveals click chemistry heterogeneity within a bacterium. Broader applications of azido photothermal probes to visualize the initial steps of the Leloir pathway in yeasts and the newly synthesized glycans in mammalian cells are demonstrated.

Complex dynamic systems displaying interdependency between nitroaldol and boronic ester reactions have been demonstrated. Nitroalkane-1,3-diols, generated by the nitroaldol reaction, were susceptible to ester formation with different boronic acids in aprotic solvents, whereas hydrolysis of the esters occurred in the presence of water. The boronic ester formation led to significant stabilization of the nitroaldol adducts under basic conditions. The use of bifunctional building blocks was furthermore established, allowing for main chain nitroaldol-boronate dynamers as well as complex network dynamers with distinct topologies. The shape and rigidity of the resulting dynamers showed an apparent dependency on the configuration of the boronic acids.

A family of responsive enaminitrile molecular switches showing tunable turn-on fluorescence upon switching and aggregation is reported. When activated by the addition of acid/base, isomerization around the C & boxH;C bond could be effectuated, resulting in complete and reversible switching to the E- or Z-isomers. Typical aggregation-induced emission (AIE) could be recorded for one specific state of the different switches. By subtle tailoring of the parent structure, a series of compounds with emissions covering almost the full visible color range were obtained. The switchable AIE features of the enaminitrile structures enabled their demonstration as solid-state chemosensors to detect acidic and basic vapors, where the emission displayed an "off-on-off" effect. Furthermore, switching to the Z-configuration could be driven out-of-equilibrium through transient changes in acidity while giving rise to fluorescence. Single-crystal X-ray diffraction measurements suggested a luminescence mechanism based on restriction of intramolecular rotation and an intramolecular charge transfer effect in the AIE luminogens. Responsive enaminitrile molecular switches showing tunable turn-on fluorescence upon switching and aggregation are presented. The switches were emissive over the visible color range and responsive aggregation-induced emission could be recorded. When applied as solid-state chemosensors, the switches could be used to detect acidic and basic vapors while displaying "off-on-off". image

A fluorescence turn-on probe, an azide-masked and trehalosederivatized carbazole (Tre-Cz), was developed to image mycobacteria. The fluorescence turn-on is achieved by photoactivation of the azide, which generates a fluorescent product through an efficient intramolecular C-H insertion reaction. The probe is highly specific for mycobacteria and could image mycobacteria in the presence of other Gram-positive and Gram-negative bacteria. Both the photoactivation and detection can be accomplished using a handheld UV lamp, giving a limit of detection of 10(3) CFU/mL, which can be visualized by the naked eye. The probe was also able to image mycobacteria spiked in sputum samples, although the detection sensitivity was lower. Studies using heat-killed, stationary-phase, and isoniazid-treated mycobacteria showed that metabolically active bacteria are required for the uptake of Tre-Cz. The uptake decreased in the presence of trehalose in a concentration-dependent manner, indicating that Tre-Cz hijacked the trehalose uptake pathway. Mechanistic studies demonstrated that the trehalose transporter LpqY-SugABC was the primary pathway for the uptake of Tre-Cz. The uptake decreased in the LpqY-SugABC deletion mutants Delta lpqY, Delta sugA, Delta sugB, and Delta sugC and fully recovered in the complemented strain of Delta sugC. For the mycolyl transferase antigen 85 complex (Ag85), however, only a slight reduction of uptake was observed in the Ag85 deletion mutant Delta Ag85C, and no incorporation of Tre-Cz into the outer membrane was observed. The unique intracellular incorporation mechanism of Tre-Cz through the LpqY-SugABC transporter, which differs from other trehalose-based fluorescence probes, unlocks potential opportunities to bring molecular cargoes to mycobacteria for both fundamental studies and theranostic applications.

Dynamic covalent gels are synthesized from an aromatic trialdehyde and a,?-dinitroalkanes via the nitroaldol reaction in organic solvents. The gelation process can be fine-tuned by changing the starting nitroalkanes, solvents, feed concentration, catalyst loading, or reaction temperature. The resulting organogels demonstrate good structural integrity and excellent self-healing ability. Intact xerogels are produced upon drying, without damaging the network, and the solvent-free network can recover its gel form in the presence of an organic solvent. Furthermore, the crosslinked dynameric gel depolymerize to small molecules in response to excess nitromethane.

Through a dynamic polymerization and self-sorting process, a range of lowellane macrocycles have been efficiently generated in nitroaldol systems composed of aromatic dialdehydes and aliphatic or aromatic dinitroalkanes. All identified macrocycles show a composition of two repeating units, resulting in tetra-beta-nitroalcohols of different structures. The effects of the building block structure on the macrocyclization process have been demonstrated, and the influence from the solvent has been explored. In general, the formation of the lowellanes was amplified in response to phase-change effects, although solution-phase structures were, in some cases, favored.

In this work, we show that the addition of thiourea (TU) initiated broad-spectrum antimicrobial activity of otherwise inactive D-maltose-capped gold nanoclusters (AuNC-Mal). For example, AuNC-Mal/TU was effective against multidrug-resistant Pseudomonas aeruginosa with a minimum inhibitory concentration (MIC) of 1 mu g mL(-1) (2.5 mu M [Au]) while having 30-60 times lower in vitro cytotoxicity against mammalian cells. The reaction of AuNC-Mal and TU generated the antimicrobial species of [Au(TU)(2)](+) and smaller AuNCs. TU increased the accumulation of Au in bacteria and helped maintain the oxidation state as Au-I (vs. Au-III). The modes of action included the inhibition of thioredoxin reductase, interference with the Cu-I regulation and depletion of ATP. Moreover, the antimicrobial activity did not change in the presence of colistin or carbonyl cyanide 3-chlorophenylhydrazone, suggesting that AuNC-Mal/TU was indifferent to the outer membrane barrier and to bacterial efflux pumps.

Auranofin, a gold(I)-complex with tetraacetylated thioglucose (Ac(4)GlcSH) and triethylphosphine ligands, is an FDA-approved drug used as an anti-inflammatory aid in the treatment of rheumatoid arthritis. In repurposing auranofin for other diseases, it was found that the drug showed significant activity against Gram-positive but was inactive against Gram-negative bacteria. Herein, the design and synthesis of gold nanoclusters (AuNCs) based on the structural motif of auranofin are reported. Phosphine-capped AuNCs are synthesized and glycosylated, yielding auranofin analogues with mixed triphenylphosphine monosulfonate (TPPMS)/Ac(4)GlcSH ligand shells. These AuNCs are active against both Gram-negative and Gram-positive bacteria, including multidrug-resistant pathogens. Notably, an auranofin analogue, a mixed-ligand 1.6 nm AuNC 4b, is more active than auranofin against Pseudomonas aeruginosa, while exhibiting lower toxicity against human A549 cells. The enhanced antibacterial activity of these AuNCs is characterized by a greater uptake of Au by the bacteria compared to Au-I complexes. Additional factors include increased oxidative stress, moderate inhibition of thioredoxin reductase (TrxR), and DNA damage. Most intriguingly, the uptake of AuNCs are not affected by the bacterial outer membrane (OM) barrier or by binding with the extracellular proteins. This contrasts with Au-I complexes like auranofin that are susceptible to protein binding and hindered by the OM barrier.