Two distinct structures of the sandwich complex of scytonemin with iron and their relevance to astrobiology

Structural Chemistry - Scytonemin is a pigment synthesized by cyanobacteria and found in their sheath. The importance of this biomolecule is its photoprotective function, which is one of the major...     

Potential of High-Performance Liquid Chromatography for Distribution Coefficient Determination of 3-Hydroxyquinolin-4(1H)-one Derivatives

The potential of reversed-phase HPLC for the determination of distribution coefficient D _7.4 of selected 3-hydroxyquinolin-4(1H)-ones (3HQs) as compounds with significant biological activity was studied. Various stationary phases with C18 as well as hexyl-phenyl modification reflect current trends in RP-HPLC development such as higher sorbent silanophilicity, core–shell technology, hybrid and/or charged surface particles. Because of significant peak tailing of 3HQs at physiological pH on reversed-phase sorbents the separations at pH 3 were performed as well. Surprisingly, the pH change did not affect significantly the partition coefficients of 3HQs. Very affordable and common standards such as anisole, acetophenone, benzyl alcohol, brombenzene, ethylbenzoate and trichlorethylene were applied in the described methodology. The best linearity (R ² 0.9895) of the correlation between log P and log k _w for standards was obtained for hexyl-phenyl sorbent, but this stationary phase was shown to be unsuitable for HPLC separation of 3HQs. The highest linearity (R ² 0.9499) of the relationship between log D _7.4 determined by the classic shake-flask method and log D determined by means of HPLC for 3HQs was attained with Cortecs C18+ column at pH 7.4. The described methodology with Cortecs C18+ as stationary phase offers fast and accurate estimation of log D _7.4 of the tested 3HQs. In an effort to increase the throughput of the HPLC method for log D _7.4 determination, we evaluated almost aqueous mobile phase that contained only 3 % of acetonitrile. Although a worse correlation between log D _7.4 determined by shake-flask method and HPLC with almost aqueous mobile phase was observed, the described procedure offers a very simple and high-throughput alternative for the estimation of log D _7.4.

     

Membrane position of ibuprofen agrees with suggested access path entrance to cytochrome P450 2C9 active site

Cytochrome P450 2C9 (CYP2C9) is a membrane-anchored human microsomal protein involved in the drug metabolism in liver. CYP2C9 consists of an N-terminal transmembrane anchor and a catalytic cytoplasmic domain. While the structure of the catalytic domain is well-known from X-ray experiments, the complete structure and its incorporation into the membrane remains unsolved. We constructed an atomistic model of complete CYP2C9 in a dioleoylphosphatidylcholine membrane and evolved it by molecular dynamics simulations in explicit water on a 100+ ns time-scale. The model agrees well with known experimental data about membrane positioning of cytochromes P450. The entry to the substrate access channel is proposed to be facing the membrane interior while the exit of the product egress channel is situated above the interface pointing toward the water phase. The positions of openings of the substrate access and product egress channels correspond to free energy minima of CYP2C9 substrate ibuprofen and its metabolite in the membrane, respectively.     

Theoretical investigation of the equilibrium structure of the FSO<Subscript>3</Subscript> radical

Six different theoretical approaches (MP2, DFT-B3LYP/MPW3LYP, QCISD, UHF/ROHF-CCSD, UHF/ROHF-CCSD[T], and EOMIP-CCSD) were employed for a detailed theoretical investigation of a minimum on the potential surface of the fluorosulfate radical FSO₃ ground state. Optimized geometries, spin distributions, vibrational frequencies, and centrifugal distortion constants were calculated within C _3v and C ₁ initial symmetry constraints.     

Characterization of vestibular schwannoma tissues using liquid chromatography-tandem mass spectrometry analysis of specific peptide fragments separated by in-sample tryptic protein digestion followed by mathematical analysis

Vestibular schwannoma is the most common benign neoplasm of the cerebellopontine angle. Its first symptoms include hearing loss, tinnitus, and vestibular symptoms, followed by cerebellar and brainstem symptoms, along with palsy of the adjacent cranial nerves. However, the clinical picture has unpredictable dynamics and currently, there are no reliable predictors of tumor behavior. Hence, it is desirable to have a fast routine method for analysis of vestibular schwannoma tissues at the molecular level. The major objective of this study was to verify whether a technique using in-sample specific protein digestion with trypsin would have the potential to provide a proteomic characterization of these pathological tissues. The achieved results showed that the use of this approach with subsequent liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of released peptides allowed a fast identification of a considerable number of proteins in two differential parts of vestibular schwannoma tissue as well as in tissues of control healthy samples. Furthermore, mathematical analysis of MS data was able to discriminate between pathological vestibular schwannoma tissues and healthy tissues. Thus, in-sample protein digestion combined with LC-MS/MS separation and identification of released specific peptides followed by mathematical analysis appears to have the potential for routine characterization of vestibular schwannomas at the molecular level. Data are available via ProteomeXchange with identifier PXD045261.     

Solid-state C NMR and molecular modeling studies of acetyl aleuritolic acid obtained from Croton cajucara Benth

Solid-state ¹³C nuclear magnetic resonance (¹³C NMR) with magic-angle spinning (MAS) and with cross-polarization and magic-angle spinning (CP/MAS) spectra, and differential scanning calorimetry (DSC) techniques were used to obtain structural data from a sample of acetyl aleuritolic acid (AAA) extracted from the stem bark of Croton cajucara Benth. (Euphorbiaceae) and recrystallized from acetone. Since solid-state ¹³C NMR results suggested the presence of more than one molecule in the unitary cell for the AAA, DSC analysis and molecular modeling calculations were used to access this possibility. The absence of phase transition peaks in the DSC spectra and the dimeric models of AAA simulated using the semi-empirical PM3 method are in agreement with that proposal.     

First Total Syntheses of Novel Non-Enzymatic Polyunsaturated Fatty Acid Metabolites and Their Identification in Edible Oils

Oxidative stress (OS) is an in vivo process leading to free radical overproduction, which triggers polyunsaturated fatty acid (PUFA) peroxidation resulting in the formation of racemic non-enzymatic oxygenated metabolites. As potential biomarkers of OS, their in vivo quantification is of great interest. However, since a large number of isomeric metabolites is formed in parallel, their quantification remains difficult without primary standards. Three new PUFA-metabolites, namely 18-F_3t-isoprostane (IsoP) from eicosapentaenoic acid (EPA), 20-F_4t-neuroprostane (NeuroP) from docosahexaenoic acid (DHA) and 20-F_3t-NeuroP from docosapentaenoic acid (DPA_n-3) were synthesized by two complementary synthetic strategies. The first one relied on a racemic approach to 18(RS)-18-F_3t-IsoP using an oxidative radical anion cyclization as a key step, whereas the second used an enzymatic deracemization of a bicyclo[3.3.0]octene intermediate obtained from cyclooctadiene to pursue an asymmetric synthesis. The synthesized metabolites were applied in targeted lipidomics to prove lipid peroxidation in edible oils of commercial nutraceuticals.     

Comparison of double-pulse and single-pulse laser-induced breakdown spectroscopy techniques in the analysis of powdered samples of silicate raw materials for the brick-and-tile industry

Single- and double-pulse laser-induced breakdown spectroscopy techniques applied to the analysis of pressed pellets of silicate raw materials were compared in terms of precision, sensitivity and limits of detection. Two Nd:YAG lasers (1064 and 532 mm) in an orthogonal configuration with a reheating arrangement have been employed. The main factors influencing system performance were optimized, i.e. laser pulse energies and interpulse separation. The behaviour of plasma temperature was studied over a period of time and calibration curves for Mg were constructed for both the single and double-pulse setup. When comparing the single- and double-pulse techniques, limits of detection of Si and Mg for the double-pulse technique were found to be 10 times lower.