FT-IR Analysis of P. aeruginosa Bacteria Inactivation by Femtosecond IR Laser Radiation

We report the successful inactivation of P. aeruginosa strain by femtosecond infrared (IR) laser radiation at the resonant wavelengths of 3.15 μm and 6.04 μm, chosen due to the presence of characteristic molecular vibrations in the main structural elements of the bacterial cells in these spectral ranges: vibrations of amide groups in proteins (1500–1700 cm−1), and C-H vibrations in membrane proteins and lipids (2800–3000 cm−1). The underlying bactericidal structural molecular changes were revealed by the stationary Fourier-transform IR spectroscopy, with the spectral peaks parameters being obtained by Lorentzian fitting with the hidden peaks revealed by the second derivative calculations, while no visible damage to the cell membranes was identified by scanning and transmission electron microscopy. © 2023 by the authors.Ministry of Education and Science of the Russian Federation, MinobrnaukaThis research was funded by the Ministry of Science and Higher Education of the Russian Federation (Ural Federal University Program of Development within the Priority-2030 Program)

Pyrolysis of Polyacrylonitrile/Technical Hydrolytic Lignin Composites

One important problem is utilization of technical hydrolytic lignin (the waste formed in paper-and-pulp and hydrolysis industry). For a practical implementation, the essential task of transforming insoluble hydrolytic lignin into low molecular weight products with high degree of functionalization should be performed. In prospect, these products can serve as raw materials for synthesis of various organic compounds demanded in chemical industry. Among other things, activation and fragmentation of hydrolytic lignin yields low molecular weight compounds which may be used for modifying synthetic polymers (polymer-analogous transformations). In the present work, the search for the optimal solvents (activators) for technical hydrolytic lignin (THL) has been conducted; the dimethyl sulfoxide/water binary mixture proved to be the best solvent. Methods of thermal analysis (thermogravimetric analysis, TGA; differential thermal analysis, DTA; differential scanning calorimetry, DSC; thermal volumetric analysis, TVA) combined with pyrolysis-gas chromatography/mass spectrometry (GC-MS) were used to determine the grades of technical hydrolytic lignin most suitable for activation and fragmentation. The necessary conditions for thermal treatment of lignin samples and concentrations of initial compounds (lignin and polyacrylonitrile, PAN) in the binary solvent mixture (dimethyl sulfoxide/water) facilitating maximum THL fragmentation and its successful interaction with PAN were found. When using the dimethylsulfoxide-water binary mixture (70:30 mass ratio) as a solvent, homogeneous forming solution of initial components (THL-PAN) was prepared. With the use of syringe method, form-stable fibers with a maximum lignin content of 80% and strength of about 50 MPa were obtained. Analytical pyrolysis of composites (products of THL-PAN interaction in the binary solvent) allowed us to suggest a mechanism for THL fragmentation involving the binary solvent

SIZE-DEPENDENT PHONON-ASSISTED ANTI-STOKES PHOTOLUMINESCENCE IN NANOCRYSTALS OF ORGANOMETAL PEROVSKITES

Anti-Stokes photoluminescence (ASPL), which is an up-conversion phonon-assisted process of the radiative recombination of photoexcited charge carriers, was investigated in methylammonium lead bromide (MALB) perovskite nanocrystals (NCs) with mean sizes that varied from about 6 to 120 nm. The structure properties of the MALB NCs were investigated by means of the scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. ASPL spectra of MALB NCs were measured under near-resonant laser excitation with a photon energy of 2.33 eV and they were compared with the results of the photoluminescence (PL) measurements under nonresonant excitation at 3.06 eV to reveal a contribution of phonon-assisted processes in ASPL. MALB NCs with a mean size of about 6 nm were found to demonstrate the most efficient ASPL, which is explained by an enhanced contribution of the phonon absorption process during the photoexcitation of small NCs. The obtained results can be useful for the application of nanocrystalline organometal perovskites in optoelectronic and all-optical solid-state cooling devices

Anti-Stokes Photoluminescence in Halide Perovskite Nanocrystals: From Understanding the Mechanism towards Application in Fully Solid-State Optical Cooling

Anti-Stokes photoluminescence (ASPL) is an up-conversion phonon-assisted process of radiative recombination of photoexcited charge carriers when the ASPL photon energy is above the excitation one. This process can be very efficient in nanocrystals (NCs) of metalorganic and inorganic semiconductors with perovskite (Pe) crystal structure. In this review, we present an analysis of the basic mechanisms of ASPL and discuss its efficiency depending on the size distribution and surface passivation of Pe-NCs as well as the optical excitation energy and temperature. When the ASPL process is sufficiently efficient, it can result in an escape of most of the optical excitation together with the phonon energy from the Pe-NCs. It can be used in optical fully solid-state cooling or optical refrigeration

Features of the Chemical Composition and Structure of Birch Phloem Dioxane Lignin: A Comprehensive Study

Understanding the chemical structure of lignin in the plant phloem contributes to the systematics of lignins of various biological origins, as well as the development of plant biomass valorization. In this study, the structure of the lignin from birch phloem has been characterized using the combination of three analytical techniques, including 2D NMR, Py-GC/MS, and APPI-Orbitrap-HRMS. Due to the specifics of the phloem chemical composition, two lignin preparations were analyzed: a sample obtained as dioxane lignin (DL) by the Pepper’s method and DL obtained after preliminary alkaline hydrolysis of the phloem. The obtained results demonstrated that birch phloem lignin possesses a guaiacyl–syringyl (G-S) nature with a unit ratio of (S/G) 0.7–0.9 and a higher degree of condensation compared to xylem lignin. It was indicated that its macromolecules are constructed from β-aryl ethers followed by phenylcoumaran and resinol structures as well as terminal groups in the form of cinnamic aldehyde and dihydroconiferyl alcohol. The presence of fatty acids and flavonoids removed during alkaline treatment was established. Tandem mass spectrometry made it possible to demonstrate that the polyphenolic components are impurities and are not incorporated into the structure of lignin macromolecules. An important component of phloem lignin is lignin–carbohydrate complexes incorporating xylopyranose moieties

Effect of Silicate Additive on Structural and Electrical Properties of Germanium Nanowires Formed by Electrochemical Reduction from Aqueous Solutions

Layers of germanium (Ge) nanowires (NWs) on titanium foils were grown by metal-assisted electrochemical reduction of germanium oxide in aqueous electrolytes based on germanium oxide without and with addition of sodium silicate. Structural properties and composition of Ge NWs were studied by means of the scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. When sodium silicate was added to the electrolyte, Ge NWs consisted of 1–2 at.% of silicon (Si) and exhibited smaller mean diameter and improved crystallinity. Additionally, samples of Ge NW films were prepared by ultrasonic removal of Ge NWs from titanium foils followed with redeposition on corundum substrates with platinum electrodes. The electrical conductivity of Ge NW films was studied at different temperatures from 25 to 300 °C and an effect of the silicon impurity on the thermally activated electrical conductivity was revealed. Furthermore, the electrical conductivity of Ge NW films on corundum substrates exhibited a strong sensor response on the presence of saturated vapors of different liquids (water, acetone, ethanol, and isopropanol) in air and the response was dependent on the presence of Si impurities in the nanowires. The results obtained indicate the possibility of controlling the structure and electrical properties of Ge NWs by introducing silicate additives during their formation, which is of interest for applications in printed electronics and molecular sensorics