Current Physical Chemistry - Current Issue

A comprehensive analysis of the conformational space of the three most abundant naturally occurring methoxylated anthocyanidins -peonidin, petunidin, and malvidin-, as well as their frontier molecular orbitals (HOMO-LUMO) was performed for the first time to explain bioactivities of interest, such as antioxidant and antimutagenic activities.

Planar (P) and non-planar (Z) conformers were analyzed in vacuum and in various solvents (using polarizable continuum model; PCM), including acetic acid, methanol, and water, at the B3LYP/6-311++G** level of theory. Boltzmann averages were also calculated, thereby achieving the quantitative contribution of each conformation to the total population. Physical properties such as dipole moment and polarizability were also evaluated for each conformer and the entire conformational space.

Thirty-five new conformers were reported for peonidin, thirty-four for petunidin, and nineteen for malvidin. Correct characterization of the whole conformational space for these compounds demonstrated the coexistence of positively charged quinoidal structures, together with other resonance structures. Solvent polarity, incorporation of donor groups into ring B, together with the percentage contribution of P and Z conformers within the conformational space modified the antioxidant activity of these compounds. The percentage atom contributions to HOMO were appropriate to demonstrate antimutagenic activity as enzyme inhibitors, as well as the steric and electrostatic requirements to form the pharmacophore.

Peonidin was the strongest antioxidant anthocyanidin and malvidin was the anthocyanidin with the best antimutagenic activity. The methodology proved to be a useful tool to explain specific bioactivities in anthocyanins and related flavonoid compounds.

Electron Paramagnetic Resonance (EPR), also known as Electron Spin Resonance (ESR) is a powerful, nondestructive, and nonintrusive characterization technique to evaluate unpaired electrons in paramagnetic substances. Unpaired electrons are found in free radicals and transition metals and are the main source of physical-chemistry changes in inorganic and organic substances. Thus, EPR characterization has a wide range of applicability in catalysis, photonics, electrochemistry, biology, medicine, semiconductors, biofuels, and radiation dosimetry.

However, to extract useful data from EPR analysis, a set of measurement parameters have to be adjusted. The present study aims to report how an EPR parametrization such as the number of scans, modulation amplitude and sweep time are effective in the characterization of europium-thulium co-doped yttria (YET) nanoparticles.

Based on results, EPR spectra of YET particles with suitable signal/noise ratio and resolution could be achieved using 10 scans, modulation amplitude of 4G, and sweep time of 10.2s.

These findings are promising data to advance toward formation of new materials based on rare-earth oxides for radiation dosimetry.

Among the various types of quantum dots, Carbon Quantum Dots (CQDs) have emerged as a particularly promising class of nanomaterials. CQDs are characterized by their tunable photoluminescence, high chemical stability, low toxicity, and excellent biocompatibility, making them suitable for a wide range of applications, including bioimaging, sensing, drug delivery, and energy-related devices. Recent research has focused on enhancing the optical properties of CQDs through doping with rare earth elements, which introduces unique photoluminescence properties due to their distinct electronic configurations and energy transitions. Photon upconversion, a process where lower-energy photons are absorbed and re-emitted as higher-energy photons, is a key area of interest in CQD research. This phenomenon is particularly useful in applications that require high-energy ultraviolet light, such as bioimaging and photocatalysis. The ability of CQDs to exhibit photon upconversion, alongside their traditional downconversion photoluminescence, adds to their versatility and potential for innovative applications. The objective of this study is to synthesize and characterize pure and rare earth-doped Carbon Quantum Dots (CQDs) using a hydrothermal method with gelatin as the precursor. The research aims to investigate the photoluminescent properties of these CQDs, with a particular focus on their photon upconversion capabilities and emission stability. By exploring the effects of doping and synthesis conditions on the optical characteristics of CQDs, the study seeks to enhance their potential for applications in fields such as bioimaging, fluorescent marking, solar cell efficiency enhancement, and other technologies requiring stable and reliable luminescence. The ultimate goal is to demonstrate the suitability of these synthesized CQDs for various scientific and practical applications, contributing to advancements in nanomaterial research and technology.

The hydrothermal bottom-up method for synthesizing Carbon Quantum Dots (CQDs) involves dissolving 0.5 grams of gelatin in 25 mL of doubly deionized water with continuous stirring to create a uniform solution. This solution is then transferred into a 50 mL Teflon-lined autoclave, which is placed in a muffle furnace set to 160°C. The mixture undergoes a hydrothermal reaction under controlled heat and pressure for 4 hours, converting the gelatin into CQDs. After heating, the autoclave is allowed to cool gradually, stabilizing the synthesized CQDs with distinctive optoelectronic properties.

Gelatin-based pure and doped Carbon Quantum Dots (CQDs) were synthesized using the hydrothermal method, and their photoluminescent and up-conversion properties were studied. Photoluminescence was observed at different excitation frequencies. At an excitation wavelength of 314 nm, the emission wavelengths for P-CQD, C-CQD, and L-CQD were 395 nm, 402 nm, and 398 nm, respectively. For an excitation wavelength of 341 nm, the emissions were 402 nm, 422 nm, and 417 nm. Photon up-conversion was examined using a 420 nm excitation, showing emission frequency variations with doping.

The synthesized gelatin-based pure and doped CQDs exhibited distinct photoluminescent and up-conversion properties, with emission wavelengths varying according to the excitation frequencies and types of doping. The observed shifts in emission wavelengths, especially under up-conversion at 420 nm excitation, demonstrate that doping influences the optical behavior of CQDs. This tunability of emission frequencies is particularly promising for frequency conversion applications, such as enhancing the spectral absorbance range of solar cells, potentially improving their efficiency by enabling better utilization of the solar spectrum.

Green synthesized nanoparticles have gained wide interest in today’s world due to their inherent features like rapidity, eco-friendliness, and cost-effectiveness. In this study, zinc oxide (ZnO) nanoparticles were synthesized using an aqueous extract of Ixora coccinea leaves. X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) studies were used to analyze the structural and morphological properties of prepared Zinc Oxide nanoparticles.

The sol-gel method of synthesis via the green route was introduced to synthesize pure Zinc oxide nanoparticles. Silver-doped zinc oxide nanoparticles were also prepared using the same method.

The XRD studies showed the crystalline nature and revealed the purity of Zinc Oxide nanoparticles. The specific functional groups responsible for reduction, stabilization, and capping agents present in the nanoparticles were examined using Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy. The bacterial destruction was better for ZnO nanoparticles than reported for plant extracts and standard drugs.

This study proves that zinc oxide nanoparticles contain natural anti-microbial agents through green synthesis, which may serve to produce drugs for antimicrobial therapeutics.