Photoinduced force microscopy as a novel method for the study of microbial nanostructures.

A detailed comparison of the capabilities of electron microscopy and nano-infrared (IR) microscopy for imaging microbial nanostructures has been carried out for the first time. The surface sensitivity, chemical specificity, and non-destructive nature of spectroscopic mapping is shown to offer significant advantages over transmission electron microscopy (TEM) for the study of biological samples. As well as yielding important topographical information, the distribution of amides, lipids, and carbohydrates across cross-sections of bacterial (Escherichia coli, Staphylococcus aureus) and fungal (Candida albicans) cells was demonstrated using PiFM. The unique information derived from this new mode of spectroscopic mapping of the surface chemistry and biology of microbial cell walls and membranes, may provide new insights into fungal/bacterial cell function as well as having potential use in determining mechanisms of antimicrobial resistance, especially those targeting the cell wall.

Photophysical Exploration of Two Isomers of Octaethyltrioxopyrrocorphin.

The introduction of three ß-oxosubstituents to octaethylporphyrin by means of an oxidation/rearrangement reaction generates the trioxopyrrocorphin chromophore. Pyrrocorphins (hexahydroporphyrins) are generally nonaromatic, but we recently demonstrated trioxopyrrocorphins to possess considerable aromatic character. This contribution explores the photophysical characteristics of these unusual chromophores. In agreement with density functional theory modeling, the UV-vis and magnetic circular dichroism spectra of the two─out of the four possible─triketone regioisomers investigated conform to the Gouterman model of porphyrinoid optical spectra, in alignment with their aromaticity. Their excited-state dynamics shed further light on the degree to which ß-oxo substitutions tune the photophysical properties of porphyrinoids. Introduction of ß-oxo functionalities increases the rate and yield of intersystem crossing and shortens the triplet state lifetime. Unexpectedly, the singlet oxygen generation yield of both pyrrocorphins remains relatively high, with modes of distortion from planarity likely enhancing triplet energy transfer. This work thus expands our understanding of a rare class of porphyrinoids and further characterizes them as sustaining aromatic porphyrinic π-systems. Our findings suggest triple ß-oxo substitution as a viable route toward the development of novel, high-singlet oxygen yield porphyrinic photosensitizers.

Clearing an ESKAPE Pathogen in a Model Organism; A Polypyridyl Ruthenium(II) Complex Theranostic that Treats a Resistant Acinetobacter baumannii Infection in Galleria mellonella.

In previous studies we have described the therapeutic action of luminescent dinuclear ruthenium(II) complexes based on the tetrapyridylphenazine, tpphz, bridging ligand on pathogenic strains of Escherichia coli and Enterococcus faecalis. Herein, the antimicrobial activity of the complex against pernicious Gram-negative ESKAPE pathogenic strains of Acinetobacter baumannii (AB12, AB16, AB184 and AB210) and Pseudomonas aeruginosa (PA2017, PA_ 007_ IMP and PA_ 004_ CRCN) are reported. Estimated minimum inhibitory concentrations and minimum bactericidal concentrations for the complexes revealed the complex shows potent activity against all A. baumannii strains, in both glucose defined minimal media and standard nutrient rich Mueller-Hinton-II. Although the activity was lower in P. aureginosa, a moderately high potency was observed and retained in carbapenem-resistant strains. Optical microscopy showed that the compound is rapidly internalized by A. baumannii. As previous reports had revealed the complex exhibited no toxicity in Galleria Mellonella up to concentrations of 80 mg/kg, the ability to clear pathogenic infection within this model was explored. The pathogenic concentrations to the larvae for each bacterium were determined to be≥105 for AB184 and≥103 CFU/mL for PA2017. It was found a single dose of the compound totally cleared a pathogenic A. baumannii infection from all treated G. mellonella within 96 h. Uniquely, in these conditions thanks to the imaging properties of the complex the clearance of the bacteria within the hemolymph of G. mellonella could be directly visualized through both optical and transmission electron microscopy.

Tailoring the Intersystem Crossing and Triplet Dynamics of Free-Base Octaalkyl-ß-oxo-Substituted Porphyrins: Competing Effects of Spin-Vibronic and NH Tautomerism Relaxation Channels.

We demonstrate that ß-oxo-substitution provides effective fine-tuning of both steady-state and transient electronic properties of octaalkyl-ß-mono-oxochlorin and all isomers of the ß,ß'-dioxo-substituted chromophores. The addition of a carbonyl group increases the Qy oscillator strength and red-shifts the absorption spectra. Each oxo-substitution results in a 2-fold increase in the singlet to triplet state intersystem crossing (ISC) rates, resulting in a 4-fold ISC rate increase for the dioxo-substituted chromophores. The effects of oxo-substitution on the ISC rate are thus additive. The progressive increase in the ISC rates correlates directly with the spin-vibronic channels provided by the C═O out-of-plane distortion modes, as evidenced by density functional theory (DFT) modeling. The triplet states, however, were not evenly affected by ß-oxo-substitution, and reduction in the triplet lifetime seems to be influenced instead by the presence of NH tautomers in the dioxoisobacteriochlorins.

Structural and Photophysical Characterization of All Five Constitutional Isomers of the Octaethyl-ß,ß'-dioxo-bacterio- and -isobacteriochlorin Series.

It is well-known that treatment of ß-octaethylporphyrin with H2 O2 /conc. H2 SO4 converts it to a ß-oxochlorin as well as all five constitutional isomers of the corresponding ß,ß'-dioxo-derivatives: two bacteriochlorin-type isomers (ß-oxo groups at opposite pyrrolic building blocks) and three isobacteriochlorin-type isomers (ß-oxo-groups at adjacent pyrrolic building blocks). By virtue of the presence of the strongly electronically coupled ß-oxo auxochromes, none of the chromophores are archetypical chlorins, bacteriochlorins, or isobacteriochlorins. Here the authors present, inter alia, the single crystal X-ray structures of all free-base diketone isomers and a comparative description of their UV-vis absorption spectra in neutral and acidic solutions, and fluorescence emission and singlet oxygen photosensitization properties, Magnetic Circular Dichroism (MCD) spectra, and singlet excited state lifetimes. DFT computations uncover underlying tautomeric equilibria and electronic interactions controlling their electronic properties, adding to the understanding of porphyrinoids carrying ß-oxo functionalities. This comparative study lays the basis for their further study and utilization.

Deciphering the Mechanisms of Bacterial Inactivation on HiPIMS Sputtered CuxO-FeOx-PET Surfaces: From Light Absorption to Catalytic Bacterial Death.

The production of nontoxic, affordable, and efficient antibacterial surfaces is key to the well-being of our societies. In this aim, antibacterial thin films have been prepared using earth-abundant metals deposited using high-power impulse magnetron sputtering (HiPIMS). The sputtered FeOx, CuxO, and mixed CuxO-FeOx films exhibited fast bacterial inactivation properties under exposure to indoor light (340-720 nm) showing total bacterial inactivation within 180, 120, and 60 min, respectively. The photocatalytic mechanisms of these films were investigated, from the absorption of photons up to the bacteria's fate, by means of ultrafast transient spectroscopy, flow cytometry, and malondialdehyde (MDA) quantification justifying the cell wall disruption. The primary driving force leading to bacterial inactivation was found to be the oxidative stress at the interface between the sputtered thin films and the microorganism. This was justified by using engineered porinless bacteria disabling the possible ion diffusion leading to internal bacterial inactivation. Such stress is a direct consequence of the photogenerated electron-hole pairs at the interface of the sputtered layers. By diffuse reflectance spectroscopy, we found that both FeOx and CuxO present a band gap of ∼2.9 eV (>425 nm), while the mixed CuxO-FeOx thin film has a band gap below 2.3 eV (>540 nm). The structure and atomic composition of the films were characterized by energy-dispersive X-ray, X-ray photoelectron, and optical spectroscopy. While the composition and metal oxidation states are distinct in all three films, the difference in photocatalytic efficiency can, at first sight, be explained as the direct consequence of their absorbance and the unique interaction between Fe and Cu oxides in the composite film.

Current-Induced Magnetic Polarons in a Colloidal Quantum-Dot Device.

Electrical spin manipulation remains a central challenge for the realization of diverse spin-based information processing technologies. Motivated by the demonstration of confinement-enhanced sp-d exchange interactions in colloidal diluted magnetic semiconductor (DMS) quantum dots (QDs), such materials are considered promising candidates for future spintronic or spin-photonic applications. Despite intense research into DMS QDs, electrical control of their magnetic and magneto-optical properties remains a daunting goal. Here, we report the first demonstration of electrically induced magnetic polaron formation in any DMS, achieved by embedding Mn2+-doped CdSe/CdS core/shell QDs as the active layer in an electrical light-emitting device. Tracing the electroluminescence from cryogenic to room temperatures reveals an anomalous energy shift that reflects current-induced magnetization of the Mn2+ spin sublattice, that is, excitonic magnetic polaron formation. These electrically induced magnetic polarons exhibit an energy gain comparable to their optically excited counterparts, demonstrating that magnetic polaron formation is achievable by current injection in a solid-state device.