Synthesis,NMR‐Spectroscopy,and Molecular Structure of a Phosphonyl Ene Diamine

First examples of ene diamines with a phosphonate function at the C=C double bond were obtained by the reaction of dialkyl H‐phosphonates with bis(N‐tert‐butyl)‐diimine derived from glyoxal, [1,4‐bis(tert‐butyl)‐1,4‐diaza‐1,3‐butadiene], and isolated as hydrochlorides. Preferentially the cis‐diamine is formed. The new phosphonates are characterized by multinuclear NMR spectroscopy(¹H, ¹³C, ³¹P). In addition the methyl ester 8a was characterized by ^14,15N NMR spectroscopy as well as by several 2D NMR techniques and single‐crystal X‐ray diffraction, unequivocally establishing the ene diamine structure. In the crystal dimers of the cations are formed by P–O ··· H–N hydrogen bonding.     

Accurate distance determination of nucleic acids via Förster resonance energy transfer: implications of dye linker length and rigidity

In Fo?rster resonance energy transfer (FRET) experiments, the donor (D) and acceptor (A) fluorophores are usually attached to the macromolecule of interest via long flexible linkers of up to 15 ? in length. This causes significant uncertainties in quantitative distance measurements and prevents experiments with short distances between the attachment points of the dyes due to possible dye-dye interactions. We present two approaches to overcome the above problems as demonstrated by FRET measurements for a series of dsDNA and dsRNA internally labeled with Alexa488 and Cy5 as D and A dye, respectively. First, we characterize the influence of linker length and flexibility on FRET for different dye linker types (long, intermediate, short) by analyzing fluorescence lifetime and anisotropy decays. For long linkers, we describe a straightforward procedure that allows for very high accuracy of FRET-based structure determination through proper consideration of the position distribution of the dye and of linker dynamics. The position distribution can be quickly calculated with geometric accessible volume (AV) simulations, provided that the local structure of RNA or DNA in the proximity of the dye is known and that the dye diffuses freely in the sterically allowed space. The AV approach provides results similar to molecular dynamics simulations (MD) and is fully consistent with experimental FRET data. In a benchmark study for ds A-RNA, an rmsd value of 1.3 ? is achieved. Considering the case of undefined dye environments or very short DA distances, we introduce short linkers with a propargyl or alkenyl unit for internal labeling of nucleic acids to minimize position uncertainties. Studies by ensemble time correlated single photon counting and single-molecule detection show that the nature of the linker strongly affects the radius of the dye's accessible volume (6-16 ?). For short propargyl linkers, heterogeneous dye environments are observed on the millisecond time scale. A detailed analysis of possible orientation effects (κ(2) problem) indicates that, for short linkers and unknown local environments, additional κ(2)-related uncertainties are clearly outweighed by better defined dye positions.     

Application of ICP-MS for Multielement Analysis in Small Sample Amoun ts of Pathological Thyroid Tissue

 As a result of the Chernobyl nuclear power plant accident in 1986, thyroid pathologies occurred among children in some regions of Belarus. Besides the irradiation of children’s thyroids by radioactive iodine and caesium nuclides, toxic elements from fallout are a direct risk to health. Inductively coupled plasma quadrupole-based mass spectrometry was used for multielement determination in small amounts (1–10 mg) of thyroid tissue samples obtained during thyroid operations in Minsk hospitals. The accuracy of the applied analytical technique for small biological sample amounts was checked using NIST Standard Reference Material oyster tissue (SRM 1566b) and by comparison with independent analytical methods, such as neutron activation analysis. Almost all essential elements as well as a number of toxic elements such as Cd, Pb, Hg, U etc. were determined in a multitude of human and animal thyroid tissues (up to 1 mg sample material) by quadrupole-based ICP-MS using micronebulization. In general, the thyroid tissue affected by pathology is characterized by higher calcium content. Some other elements, among them Fe, Mn, V, As, Cr, Ni, Pb, U, Ba, Sb, were also accumulated in such tissue. The results obtained will be used as initial material for further specific studies of the role of particular elements in thyroid pathology development. Received November 15, 1999. Revision March 15, 2000.     

Synthesis and characterization of high surface area TiO2/SiO2 mesostructured nanocomposite

Recently titania synthesis was reported using various structuration procedures, leading to the production of solid presenting high surface area but exhibiting moderate thermal stability. The study presents the synthesis of TiO₂/SiO₂ nanocomposites, a solid that can advantageously replace bulk titania samples as catalyst support. The silica host support used for the synthesis of the nanocomposite is a SBA-15 type silica, having a well-defined 2D hexagonal pore structure and a large pore size. The control of the impregnation media is important to obtain dispersed titania crystals into the porosity, the best results have been obtained using an impregnation in an excess of solvent. After calcination at low temperature (400 °C), nanocomposites having titania nanodomains (～2–3 nm) located inside the pores and no external aggregates visible are obtained. This nanocomposite exhibits high specific surface area (close to that of the silica host support, even with a titania loading of 55 wt.%) and a narrow pore size distribution. Surprisingly, the increase in calcination temperature up to 800 °C does not allow to detect the anatase to rutile transition. Even at 800 °C, the hexagonal mesoporous structure of the silica support is maintained, and the anatase crystal domain size is evaluated at ～10 nm, a size close to that of the silica host support porosity (8.4 nm). Comparison of their physical properties with the results presented in literature for bulk samples evidenced that these TiO₂/SiO₂ solids are promising in term of thermal stability.     

Distinction between surface hydroxyl and ether groups on boron-doped diamond electrodes using a chemical approach

While it is clearly established that oxidation of as-grown boron-doped diamond (BDD) interfaces results in the introduction of different surface oxygen functions such as ether, carbonyl and hydroxyl groups, there is no reported approach which can clearly distinguish between the different surface functions. For further surface functionalization, it is important to quantify the presence of each group on the diamond surface. In this paper, the presence and amount of surface hydroxyl groups is identified using esterification of the COH groups with trifluoroacetic acid. The presence of CF₃ group in the acid allowed the identification and estimation of the amount of surface hydroxyl groups using X-ray photoelectron spectroscopy (XPS).