Comprehensive portrait of cholesterol containing oxidized membrane.

Biological membranes are under significant oxidative stress caused by reactive oxygen species mostly originating during cellular respiration. Double bonds of the unsaturated lipids are most prone to oxidation, which might lead to shortening of the oxidized chain and inserting of terminal either aldehyde or carboxylic group. Structural rearrangement of oxidized lipids, addressed already, is mainly associated with looping back of the hydrophilic terminal group. This contribution utilizing dual-focus fluorescence correlation spectroscopy and electron paramagnetic resonance as well as atomistic molecular dynamics simulations focuses on the overall changes of the membrane structural and dynamical properties once it becomes oxidized. Particularly, attention is paid to cholesterol rearrangement in the oxidized membrane revealing its preferable interaction with carbonyls of the oxidized chains. In this view cholesterol seems to have a tendency to repair, rather than condense, the bilayer.

Characterization of the interaction between the tumour suppressor p53 and heme and its role in the protein conformational dynamics studied by various spectroscopic techniques and hydrogen/deuterium exchange coupled with mass spectrometry.

The tumour suppressor p53 regulates the expression of a myriad of proteins that are important for numerous cellular processes, including apoptosis, cell cycle arrest, DNA repair, metabolism, and even autophagy and ferroptosis. Aside from DNA, p53 can interact with many types of partners including proteins and small organic molecules. The ability of p53 to interact with heme has been reported so far. In this study, we used various spectroscopic studies to conduct a thorough biophysical characterization of the interaction between p53 and heme concerning the oxidation, spin, coordination, and ligand state of heme iron. We found that the p53 oligomeric state and zinc biding ability are preserved upon the interaction with heme. Moreover, we described the effect of heme binding on the conformational dynamics of p53 by hydrogen/deuterium exchange coupled with mass spectrometry. Specifically, the conformational flexibility of p53 is significantly increased upon interaction with heme, while its affinity to a specific DNA sequence is reduced by heme. The inhibitory effect of DNA binding by heme is partially reversible. We discuss the potential heme binding sites in p53 with respect to the observed conformational dynamics changes and perturbed DNA-binding ability of p53 upon interaction with heme.

Role of the paramagnetic donor-like defects in the high n-type conductivity of the hydrogenated ZnO microparticles.

The magnetic and electronic properties of the hydrogenated highly conductive zinc oxide (ZnO) microparticles were investigated by electron paramagnetic resonance (EPR) and contactless microwave (MW) conductivity techniques in the wide temperature range. The EPR spectra simulation allowed us to resolve four overlapping EPR signals in ZnO microparticles. The Lorentzian EPR line with isotropic g-factor 1.9623(5) was related to the singly ionized oxygen vacancy. Another Lorentzian line with g|| = 1.9581(5), g⊥ = 1.9562(5) was attributed to the zinc interstitial shallow donor center, while EPR signal with g|| = 1.9567(5), g⊥ = 1.9556(5) and Gaussian lineshape was assigned to the hydrogen interstitial shallow effective-mass-like donor. The EPR signal with g|| = 1.9538(5), g⊥ = 1.9556(5) and Lorentzian lineshape was tentatively attributed to the shallow donor center. The charge transport properties in ZnO microparticles have been investigated by the contactless MW conductivity technique at T = 5-296 K. Two conduction mechanisms, including ionization of electrons from the shallow donors to the conduction band and hopping conduction process, have been distinguished. The hopping conduction process follows Mott's variable-range hopping T-1/4 law at T = 10-100 K. The evaluated values of the average hopping distance (15.86 Å), and hopping energy (1.822 meV at 40 K) enable us to estimate the donor concentration in the investigated ZnO microparticles as ~ 1018 cm-3.

Infrared, Raman and Magnetic Resonance Spectroscopic Study of SiO2:C Nanopowders.

Optical and magnetic properties of SiO2:C nanopowders obtained by chemical and thermal modification of fumed silica were studied by Fourier transform infrared spectroscopy, Raman, continuous wave (CW) electron paramagnetic resonance (EPR), echo-detected EPR and pulsed electron nuclear double resonance (ENDOR) spectroscopy. Two overlapping signals of Lorentzian lineshape were detected in CW EPR spectra of the initial SiO2:C. The EPR signal at g = 2.0055(3) is due to the silicon dangling bonds, which vanishes after thermal annealing, and the second EPR signal at g = 2.0033(3) was attributed to the carbon-related defect (CRD). The annealing of the SiO2:C samples gives rise to the increase of the CRD spin density and shift to the higher g-values due to the appearance of the oxygen in the vicinity of the CRD. Based on the temperature-dependent behavior of the CRD EPR signal intensity, linewidth and resonance field position we have attributed it to the spin system with non-localized electrons hopping between neighboring carbon dangling bonds, which undergo a strong exchange interaction with a localized spin system of carbon nanodots. The observed motional narrowing of the CRD EPR signal in the temperature interval from 4 to 20 K indicates that electrons are mobile at 4 K which can be explained by a quantum character of the conductivity in the vicinity of the carbon layer. The electrons trapped in quantum wells move from one carbon nanodot to another by hopping process through the energy barrier. The fact that echo-detected EPR signal at g = 2.0035(3) was observed in SiO2:C sample annealed at T ann ≥ 700 °C serves as evidence that non-localized electrons coexist with localized electrons that have the superhyperfine interaction with surrounding 13C and 29Si nuclei located at the SiO2:C interface. The presence of the superhyperfine interaction of CRD with 1H nuclei indicates the existence of hydrogenated regions in SiO2:C sample.