Spectroscopic characterization of interstrand carbinolamine cross-links formed in the 5'-CpG-3' sequence by the acrolein-derived gamma-OH-1,N2-propano-2'-deoxyguanosine DNA adduct

The interstrand N2,N2-dG DNA cross-linking chemistry of the acrolein-derived gamma-OH-1,N2-propanodeoxyguanosine (gamma-OH-PdG) adduct in the 5'-CpG-3' sequence was monitored within a dodecamer duplex by NMR spectroscopy, in situ, using a series of site-specific 13C- and 15N-edited experiments. At equilibrium 40% of the DNA was cross-linked, with the carbinolamine form of the cross-link predominating. The cross-link existed in equilibrium with the non-crosslinked N2-(3-oxo-propyl)-dG aldehyde and its geminal diol hydrate. The ratio of aldehyde/diol increased at higher temperatures. The 1,N2-dG cyclic adduct was not detected. Molecular modeling suggested that the carbinolamine linkage should be capable of maintaining Watson-Crick hydrogen bonding at both of the tandem C x G base pairs. In contrast, dehydration of the carbinolamine cross-link to an imine (Schiff base) cross-link, or cyclization of the latter to form a pyrimidopurinone cross-link, was predicted to require disruption of Watson-Crick hydrogen bonding at one or both of the tandem cross-linked C x G base pairs. When the gamma-OH-PdG adduct contained within the 5'-CpG-3' sequence was instead annealed into duplex DNA opposite T, a mixture of the 1,N2-dG cyclic adduct, the aldehyde, and the diol, but no cross-link, was observed. With this mismatched duplex, reaction with the tetrapeptide KWKK formed DNA-peptide cross-links efficiently. When annealed opposite dA, gamma-OH-PdG remained as the 1,N2-dG cyclic adduct although transient epimerization was detected by trapping with the peptide KWKK. The results provide a rationale for the stability of interstrand cross-links formed by acrolein and perhaps other alpha,beta-unsaturated aldehydes. These sequence-specific carbinolamine cross-links are anticipated to interfere with DNA replication and contribute to acrolein-mediated genotoxicity.     

Molecular discrimination of N-protected amino acid esters by a self-assembled cylindrical capsule: spectroscopic and computational studies

A self-assembled, cylindrical capsule was used to bind N-alpha-protected amino acid esters. The reversible encapsulation was studied using NMR spectroscopy in deuterated mesitylene solution and by computer-aided molecular modeling. BOC-L-alanine alkyl esters and BOC-beta-alanine alkyl esters were tested as guests, and the relative binding affinities were established by direct competition experiments. A good correlation was found between the experimental and calculated relative binding affinities in these two series. Guests that were slightly longer than the internal dimensions of the cavity were accommodated by adopting compacted conformations.     

High-performance liquid chromatography analysis of four Leuzea carthamoides flavonoids

A simple and sensitive high-performance liquid chromatography method for the determination of four Leuzea carthamoides flavonoids, namely eriodictyol, patuletin, eriodictyol-7-beta-glucopyranoside, and 6-hydroxykaempferol-7-O-(6"-O-acetyl-beta-D-glucopyranoside), is presented. Using this method, quantitative composition of flavonoids ranged from 0.011% to 0.574% in dried plant material was determined. This method could be used in the future for the quantitative evaluation of major phenolic compounds in L. carthamoides.     

Turning Peptide Sequences into Ribbon Foldamers by a Straightforward Multicyclization Reaction

The conformational control of molecular scaffolds allows the display of functional groups in defined spatial arrangement. This is of considerable interest for developing fundamental and applied systems in both the fields of biology and material sciences. Peptides afford a large diversity of functional groups, and peptide synthetic routes are very attractive and accessible. However, most short peptides do not possess well‐defined secondary structures. Herein, we developed a simple strategy for converting peptide sequences into structured γ‐lactam‐containing oligomers while keeping the amino acids side chain diversity. We showed the propensity of these molecules to adopt ribbon‐like secondary structures. The periodic distribution of the functional groups on both sides of the ribbon plane is encoded by the initial peptide sequence.     

Accidental formation of Gd4(SiO4)2OTe: crystal structure and spectroscopic properties

Designing new functional materials with increasingly complex compositions is of current interest in science and technology. Complex rare‐earth‐based chalcogenides have specific thermal, electrical, magnetic and optical properties. Tetragadolinium bis[tetraoxidosilicate(IV)] oxide telluride, Gd₄(SiO₄)₂OTe, was obtained accidentally while studying the Gd₂Te₃–Cu₂Te system. The crystal structure was determined by means of single‐crystal X‐ray diffraction. The compound crystallizes in the space group Pnma. Three symmetry‐independent gadolinium sites were determined. The excitation and emission spectra were collected at room temperature and at 10 K. Gd₄(SiO₄)₂OTe appears to be a promising optical material when doped with rare‐earth ions.     

Physical properties and structure of thin conducting ion-beam modified polymer films

In this work, a complex investigation of the film surface composition, chemical bonding, conductivity, optical properties, density, hardness and Young's modulus of ion-beam-modified polyimide films was carried out. It was shown that the partial destruction of chemical bonding under ion bombardment leads to the formation of graphite-like, amorphous carbon islands, which increase the surface film conductivity by several orders of magnitude, from an insulating to a semiconducting region. Strong enhancements of both the conductivity and the optical absorption coefficient occur when the fraction of amorphous carbon clusters dispersed in a polyimide matrix reaches 40 %. The values of hardness, Young's modulus and density at high irradiation doses reach the values typical of a hydrogenated amorphous carbon.     

Electron spin resonance of copper pair centers in crystals with perovskite structure

Copper pair centers, which could be of interest for obtaining quantitative information about exchange interactions in superconductors based on cuprate perovskites, are observed in crystals with the perovskite structure by the ESR method. Such centers are investigated in KTaO₃:Cu and K_1−x Li_xTaO₃:Cu crystals. A model consisting of a chain of two equivalent Cu²⁺ ions and three oxygen vacancies, extending along the 〈 100〉 axis, is proposed for the centers. The exchange interaction in the pairs is ferromagnetic. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 12, 890–894 (25 June 1999)     

Synthesis and Characterization of Photocatalytic Porous Fe3+/TiO2 Layers on Glass

Wet chemical synthesis and preliminary photocatalytical characteristics of titania and Fe(III)-containing TiO₂ layers are presented. A highly stable coating colloids could be prepared under base- as well as acid-catalyzed condensation conditions. Structural properties of the as-prepared wet gels and sintered films were investigated using SEM, TEM, XRD as well as optical absorption spectroscopy, DTA-TG analysis and photomineralisation studies. X-ray amorphous wet titania gel layers start to crystallize at 500°C forming the characteristic anatase phase. In the presence of iron ions (Fe/Ti = 1), nanocrystalline FeTiO₃ ilmenite phase forms. Both TiO₂ and Fe-containing TiO₂ films demonstrate a photocatalytic activity in the process of the photomineralization of dichloroacetic acid.     

Temperature Shift of the Zero-Phonon f–f Lines of Er3+ Luminescence in Quantum Paraelectric KTaO3

Physics of the Solid State - In KTaO3:Er crystals, we observed a temperature shift, unusual for rare earth impurities, for narrow zero-phonon luminescence lines, due to the 4S3/2 → 4I13/2,...