Determination of 8-hydroxy-2'-deoxyguanosine in untreated urine by capillary electrophoresis with UV detection

A capillary electrophoresis method with UV detection was developed for the determination of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in untreated urine samples. The calibration graph for 8-OHdG in urine is linear in the concentration range 10-500 mg/l. and the detection limit is 5 mg/l (17 microM). 8-OHdG was determined in urine from oncological patients treated by radiation therapy. Its concentrations relative to creatinine were found to be in the range 10-47 microg 8-OHdG/l mg creatinine (4-19 micromol 8-OHdG/mmol creatinine). The overall time of the analysis of a urine sample was less than 15 min.     

Mimicking the Ice Recrystallization Activity of Biological Antifreezes. When is a New Polymer “Active”?

Antifreeze proteins and ice‐binding proteins have been discovered in a diverse range of extremophiles and have the ability to modulate the growth and formation of ice crystals. Considering the importance of cryoscience across transport, biomedicine, and climate science, there is significant interest in developing synthetic macromolecular mimics of antifreeze proteins, in particular to reproduce their property of ice recrystallization inhibition (IRI). This activity is a continuum rather than an “on/off” property and there may be multiple molecular mechanisms which give rise to differences in this observable property; the limiting concentrations for ice growth vary by more than a thousand between an antifreeze glycoprotein and poly(vinyl alcohol), for example. The aim of this article is to provide a concise comparison of a range of natural and synthetic materials that are known to have IRI, thus providing a guide to see if a new synthetic mimic is active or not, including emerging materials which are comparatively weak compared to antifreeze proteins, but may have technological importance. The link between activity and the mechanisms involving either ice binding or amphiphilicity is discussed and known materials assigned into classes based on this.     

Paramagnetic Lanthanide NMR Probes Signalling Changes in Zinc Concentration by Emission and Chemical Shift: A Proof of Concept Study

A zinc-selective probe based on a set of rare earth complexes of a modified DO3A macrocyclic ligand incorporating a tris-pyridylamine (TPA) moiety has been structurally characterised in solution and in the solid-state. One pyridine group possesses a tert-butyl substituent to serve as an NMR reporter group. The mono-capped square-antiprismatic Dy complex has a long bond (2.83 Å) to an apical N atom (pK_a 5.70 Eu) and binds to one water molecule on zinc binding. Zinc binding is reversible and involves all of the exocyclic ligand N donors; it is signalled by large (ratiometric) changes in Eu emission intensity, and by dramatic changes in the size (>50 ppm) and sign of the chemical shift of the paramagnetically shifted tBu resonances in Tb, Dy and Tm complexes. Slow trans-metallation was observed, leading to formation of an unusual di-zinc species in which one zinc ion is seven-coordinate and the other is six-coordinate.     

Diels-Alder cycloaddition for fluorophore targeting to specific proteins inside living cells

The inverse-electron-demand Diels-Alder cycloaddition between trans-cyclooctenes and tetrazines is biocompatible and exceptionally fast. We utilized this chemistry for site-specific fluorescence labeling of proteins on the cell surface and inside living mammalian cells by a two-step protocol. Escherichia coli lipoic acid ligase site-specifically ligates a trans-cyclooctene derivative onto a protein of interest in the first step, followed by chemoselective derivatization with a tetrazine-fluorophore conjugate in the second step. On the cell surface, this labeling was fluorogenic and highly sensitive. Inside the cell, we achieved specific labeling of cytoskeletal proteins with green and red fluorophores. By incorporating the Diels-Alder cycloaddition, we have broadened the panel of fluorophores that can be targeted by lipoic acid ligase.     

The h-SbxWO3+2x Oxygen Excess Antimony Tungsten Bronze

We describe the previously unreported oxygen excess hexagonal antimony tungsten bronze with composition Sb_0.5W₃O₁₀, in the following denoted as h-Sb_xWO_3+2x with x=0.167, to demonstrate its analogy to classical A_xWO₃ tungsten bronzes. This compound forms in a relatively narrow temperature range between 580 °C<T<620 °C. It was obtained as a dark-blue polycrystalline powder, and as thin, needle-shaped, blue single crystals. h-Sb_xWO_3+2x crystallizes in the hexagonal space group P6/mmm with the cell parameters a=7.4369(4) Å and c=3.7800(2) Å. The antimony and excess oxygen occupy the hexagonal channels within the network of corner-sharing WO₆ octahedra. h-Sb_xWO_3+2x has a resistivity of ρ_{300 K}≈1.28 mΩ cm at room temperature, with little if any temperature-dependence on cooling. DFT calculations on a simplified model for this compound find a metallic-like electronic structure with the Fermi level falling within rather flat bands, especially around the Γ point.     

An [FeIII34] Molecular Metal Oxide

The dissolution of anhydrous iron bromide in a mixture of pyridine and acetonitrile, in the presence of an organic amine, results in the formation of an [Fe₃₄] metal oxide molecule, structurally characterised by alternate layers of tetrahedral and octahedral Fe^III ions connected by oxide and hydroxide ions. The outer shell of the complex is capped by a combination of pyridine molecules and bromide ions. Magnetic data, measured at temperatures as low as 0.4 K and fields up to 35 T, reveal competing antiferromagnetic exchange interactions; DFT calculations showing that the magnitudes of the coupling constants are highly dependent on both the Fe‐O‐Fe angles and Fe?O distances. The simplicity of the synthetic methodology, and the structural similarity between [Fe₃₄], bulk iron oxides, previous Fe^III–oxo cages, and polyoxometalates (POMs), hints that much larger molecular Fe^III oxides can be made.     

An unexpected formation of pyrazolopyrimidines during the attempted to obtain 5-substituted tetrazoles from carbonitriles

In this Letter, we described the synthesis of new 5-(5-amino-1-aryl-1H-pyrazole-4-yl)-1H-tetrazoles 2a–c from 5-amino-1-aryl-1H-pyrazole-4-carbonitriles 1a–c as well as the unexpected 1H-pyrazolo[3,4-d]pyrimidine derivatives 6a–c from 5-amino-1-aryl-3-methyl-1H-pyrazole-4-carbonitriles 4a–c, instead of 5-(5-amino-1-aryl-3-methyl-1H-pyrazole-4-yl)-1H-tetrazoles 5a–c as desired. In an attempt to obtain these tetrazole derivatives containing the methyl group at C3-position in the pyrazole ring, the amino group in 5-amino-1-(4-methoxyphenyl)-3-methyl-1H-pyrazole-4-carbonitrile 4c was protected by the reaction with sodium hydride and di-tert-butyl-dicarbonate (Boc). The tetrazole derivative 5c was synthesized from the protected compound 7c using analogue methodology to obtain 2a–c and 6a–c.     

Systematic Study of the Interaction Between VIV Centres and LnIII Ions in Well Defined {V 2 IV LnIII}{AsIIIW9O33}2 Sandwich-Type Clusters: Part 2

The gadolinium (Gd) member of a new type of heteropolytungstates that contain one lanthanide and two transition metal ions in a triangular arrangement is reported. The compound NaK₆Gd_0.33 [((VO)₂Gd(H₂O)₄K₂(H₂O)₂(Na)(H₂O)₂)(α-B-AsW₉O₃₃)₂]·24H₂O (1) was prepared from acidified aqueous solutions of Na₂WO₄·2H₂O, As₂O₃ and VOSO₄·5H₂O to which Gd³⁺ ions were added. The single crystal X-ray structure analysis (monoclinic, space group P2₁/m) shows that the anion consists of two [α-B-As^IIIW₉O₃₃]^9? trilacunary Keggin-type units linked by two VO²⁺, one Gd³⁺ as well as weakly by two K⁺ and one Na⁺ ions, resulting in a sandwich-type structure with idealized C _2v symmetry. The problem of positioning crystal lattice and special polyoxometalate sites with different cations is discussed also in connection with supramolecular chemistry aspects and as an option for further research. A fit of the magnetic susceptibility yielded exchange coupling constants of J _VV = ?2.55 cm^?1 (anti-ferromagnetic) between the vanadium ions and J _GdV = 0.6 cm^?1 (ferromagnetic) between the Gd and each of the two vanadium ions. The complete magnetochemical analysis also revealed a partial occupancy of the Na⁺ sites in the counter-cation–water system by Gd³⁺ ions (0.33 Gd³⁺ ions in total).     

Changes of organic acids and phenolic compounds contents in grapevine berries during their ripening

Changes of total content of phenolic substances, alteration in total titratable acidity and differences in tartaric acid content in grapes of four white (Müller-Thurgau — MT, Pinot Blanc — Rulandské bílé in Czech, RB, Sauvignon (Sg), and Muscat Ottonel — Mu?kát Ottonel in Czech, MO) and two blue (Dornfelder — Df and Blue Frankish — Frankovka in Czech, Fr) grapevine varieties throughout their growth, ripening and maturing (July–November). Potentiometric titration was applied for the determination of total titratable acids in grapes (expressed as tartaric acid equivalents in g L^?1). A spectrophotometric method according Rebelein based on the formation of a colored complex of ammonium metavanadate and tartaric acid was used for determination of tartaric acid in green juice made by pressing unripe grapes. A spectrophotometric method based on reduction of phosphomolybdato-tungsten complex in alkaline solution using Folin-Ciocalteau reagent was applied for determination of total content of phenolic substances (TCP).

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