Polyisoprenoid alcohols--recent results of structural studies

Polyisoprenoid alcohols (polyprenols and dolichols) are linear polymers of from several up to more than 100 isoprene units identified in almost all living organisms. Studies of their chemical structures have resulted in the discovery of new variants such as the recently described alloprenols with reversed configuration of the double bond in the alpha-isoprene unit. In parallel, structural elucidation of metabolically labeled plant dolichols has indicated that both the mevalonate and methylerythritol phosphate pathways are involved in the biosynthesis of dolichols in roots, leading to the construction of a spatial model of their biosynthesis. According to this model, in root cells, synthesis of the dolichol molecule is initiated in the plastids, and the resulting intermediates, oligoprenyl diphosphates, are exported to the cytoplasm and are elongated up to the desired chain length. The metabolic consequences of this putative model are discussed in the context of the enzymatic machinery involved.     

Crystal structure of the new FeSe(1-x) superconductor

The newly discovered superconductor FeSe(1-x) (x approximately 0.08, T(c)(onset) approximately 13.5 K at ambient pressure rising to 27 K at 1.48 GPa) exhibits a structural phase transition from tetragonal to orthorhombic below 70 K at ambient pressure-the crystal structure in the superconducting state shows remarkable similarities to that of the REFeAsO(1-x)F(x) (RE = rare earth) superconductors.     

Chemistry and biology of the aeruginosin family of serine protease inhibitors

The aeruginosins have been isolated from marine sponges and cyanobacterial waterblooms, sources that are phylogenetically distinct and the bodies of water are geographically well-separated. The aeruginosins comprise a central hydroxy- (or dihydroxy-) octahydroindole carboxamide core unit, onto which are appended unusual amino acids on the carboxy and amino termini as part of the linear peptide array. Potent inhibitory activity of serine proteases in vitro is exhibited by some of the aeruginosins as a result of the presence and proper deployment of three important pharmacophoric subunits: a P1 arginine mimetic, and two hydrophobic residues with interaction sites designated as P2 and P3. In this article, we provide the first comprehensive review on the chemistry and biology of the aeruginosins, with an emphasis on their sources, structural revisions, and total syntheses.     

Activity of lactoperoxidase when adsorbed on protein layers

Lactoperoxidase (LPO) is an enzyme, which is used as an antimicrobial agent in a number of applications, e.g., food technology. In the majority of applications LPO is added to a homogeneous product phase or immobilised on product surface. In the latter case, however, the measurements of LPO activity are seldom reported. In this paper we have assessed LPO enzymatic activity on bare and protein modified gold surfaces by means of electrochemistry. It was found that LPO rapidly adsorbs to bare gold surfaces resulting in an amount of LPO adsorbed of 2.9mg/m(2). A lower amount of adsorbed LPO is obtained if the gold surface is exposed to bovine serum albumin, bovine or human mucin prior to LPO adsorption. The enzymatic activity of the adsorbed enzyme is in general preserved at the experimental conditions and varies only moderately when comparing bare gold and gold surface pretreated with the selected proteins. The measurement of LPO specific activity, however, indicate that it is about 1.5 times higher if LPO is adsorbed on gold surfaces containing a small amount of preadsorbed mucin in comparison to the LPO directly adsorbed on bare gold.     

Highly Luminescent Cesium Lead Halide Perovskite Nanocrystals with Tunable Composition and Thickness by Ultrasonication

We describe the simple, scalable, single‐step, and polar‐solvent‐free synthesis of high‐quality colloidal CsPbX₃ (X=Cl, Br, and I) perovskite nanocrystals (NCs) with tunable halide ion composition and thickness by direct ultrasonication of the corresponding precursor solutions in the presence of organic capping molecules. High angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) revealed the cubic crystal structure and surface termination of the NCs with atomic resolution. The NCs exhibit high photoluminescence quantum yields, narrow emission line widths, and considerable air stability. Furthermore, we investigated the quantum size effects in CsPbBr₃ and CsPbI₃ nanoplatelets by tuning their thickness down to only three to six monolayers. The high quality of the prepared NCs (CsPbBr₃) was confirmed by amplified spontaneous emission with low thresholds. The versatility of this synthesis approach was demonstrated by synthesizing different perovskite NCs.     

Voltammetric determination of aminobiphenyls at a boron-doped nanocrystalline diamond film electrode

Voltammetric behavior of 2-aminobiphenyl, 3-aminobiphenyl, and 4-aminobiphenyl at a boron-doped nanocrystalline diamond film electrode was investigated using cyclic voltammetry and differential pulse voltammetry. Optimum conditions have been found for the determination of those genotoxic substances by differential pulse voltammetry at the above given electrode in the concentration range of 2 × 10⁻⁷ to 1 × 10⁻⁵ mol/L.     

Effect of alkyl substituents on excited state intramolecular proton transfer dynamics of jet-cooled bis(benzoxazolyl)phenoles

Structural factors affecting the dynamics of the excited state intramolecular proton transfer (ESIPT) are studied for alkyl derivatives of 2,5-bis(2-benzoxazolyl)phenol. Two fluorescence bands with equal decay times are observed in solution, while only one--emitted by the phototautomer--in supersonic jet. All evidence indicates the existence of a potential barrier in the S(1) state. Upon deuteration of the OH group the laser induced fluorescence (LIF) excitation spectra become much sharper as a result of slowing down the proton transfer reaction. Two conformers (rotamers) of each compound in the ground state were detected using hole burning technique. With a help of theoretical calculations three vibrations were identified as the most active ones in reducing the distance between two heavy atoms, N and O, involved in H-bond formation. The widths of (0,0) transitions in LIF excitation spectra decrease with increasing size or number of alkyl substituents at terminal aromatic rings. The corresponding calculated rate constants of ESIPT reaction ( approximately 10(12) s(-1)) decrease approximately three times upon the substituent effect. In contrast, model compound 2,5-bis(2-benzoxazolyl)-4-methoxyphenol (BBMP) with OCH(3) parasubstituent in central ring slows down the ESIPT reaction to such an extent that double, primary and phototautomeric, fluorescences coexist.     

Peptide Charge Derivatization as a Tool for Early Detection of Preeclampsia by Mass Spectrometry—A Comparison with the ELISA Test

Early detection of any preeclampsia biomarkers may lower the risk of mortality, both for a mother and a child. Our study focuses on techniques for preeclampsia biomarker identification by comparing the results of a method using liquid chromatography mass spectrometry in multiple reaction monitoring mode (LC-MS/MS) with those by the enzyme-linked immunosorbent assay (ELISA) test, as well as by comparing the obtained results with clinical data. In the proposed LC-MS/MS method a tryptic digest peptide charge derivatization strategy was used as a tool for sensitive detection of podocin, i.e., a previously discovered preeclampsia biomarker present in urine samples from pregnant women. Urine samples from pregnant women with diagnosed preeclampsia were collected at different stages of pregnancy and from healthy subjects, and then were analyzed by ELISA test and the proposed method with LC-MS/MS. Charge derivatization of the ε amino group of C-terminal lysine residues in tryptic digests by 2,4,6-triphenylpyrylium salt was performed to increase the ionization efficiency in the LC-MS/MS mode. Podocin was identified at the early stage of pregnancy, while its detection using an ELISA test was not possible. The protocol for urine sample preparation was optimized. Our results show that the proposed method by LC-MS/MS in combination with peptide charge derivatization, provides an ultrasensitive tool for diagnosis of preeclampsia, and provides earlier detection than a clinical diagnosis or ELISA test. The proposed solution may revolutionize medical diagnostics.     

Optical Spectra of Oligofurans: A Theoretical Approach to the Transition Energies,Reorganization Energies,and the Vibronic Activity

There is experimental evidence of high vibronic activity that accompanies the allowed transition between the ground state and the lowest electronic singlet excited state of oligofurans that contain two, three, and four furan rings. The absorption and emission spectra of the three lowest oligofurans measured at liquid nitrogen temperature show distinct fine structures that are reproduced using the projection-based model of vibronic coupling (with Dushinsky rotation included) parameterized utilizing either Density Functional Theory (DFT, with several different exchange-correlation functionals) or ab initio (CC2) quantum chemistry calculations. Using as a reference the experimental data concerning the electronic absorption and fluorescence for the eight lowest oligofurans, we first analyzed the performance of the exchange-correlation functionals for the electronic transition energies and the reorganization energies. Subsequently, we used the best functionals alongside with the CC2 method to explore how the reorganization energies are distributed among the totally symmetric vibrations, identify the normal modes that dominate in the fine structures present in the absorption and emission bands, and trace their evolution with the increasing number of rings in the oligofuran series. Confrontation of the simulated spectra with the experiment allows for the verification of the performance of the selected DFT functionals and the CC2 method.