X‐ray absorption spectroscopy at the Ni?K edge in Stackhousia tryonii Bailey hyperaccumulator

Young plants of Stackhousia tryonii Bailey were exposed to 34 mM Ni kg^?1 in the form of NiSO₄· 6H₂O solution and grown under controlled glasshouse conditions for a period of 20 days. Fresh leaf, stem and root samples were analysed in vivo by micro x‐ray absorption spectroscopy (XAS) at the Ni? K edge. Both x‐ray absorption near edge structure and extended x‐ray absorption fine structure spectra were analysed, and the resulting spectra were compared with spectra obtained from nine biologically important Ni‐containing model compounds. The results revealed that the majority of leaf, stem and root Ni in the hyperaccumulator was chelated by citrate. Our results also suggest that in leaves Ni is complexed by phosphate and histidine, and in stems and roots, phytate and histidine. The XAS results provide an important physiological insight into transport, detoxification and storage of Ni in S. tryonii plants. Copyright © 2008 John Wiley & Sons, Ltd.     

Self‐trapped N?H vibrational states in the polymorphs of glycine,L‐ and DL‐alanine

The polarized Raman spectra of the oriented single crystals of L ‐ and DL ‐alanine, α‐, β‐ and γ‐polymorphs of glycine have been studied at 3–300 K. Regularly spaced band packets have been observed in the spectral range of 2500–3000 cm⁻¹, with intensity decreasing noticeably on heating. These band packets were interpreted as the manifestations of the existence of N H self‐trapped states in these systems at low temperatures. The analysis of the polarized spectra has shown that the self‐trapping is observed exclusively for the NH stretching vibration of the amino groups, which is related to the NH···O hydrogen bonds along the head‐to‐tail chains of zwitterions in the crystal structures. The wavenumber of this NH stretching vibration, however, was proposed to depend not solely on the length of this NH···O hydrogen bond, but also on the lengths of all the other NH···O hydrogen bonds formed by the NH₃⁺ and the COO⁻ groups in the structure linking the head‐to‐tail chains with each other. The arguments in favor of the hypothesis that the self‐trapping in these systems can be mediated by zero‐point quantum motions, and not by lattice phonons, are considered. The unusually low wavenumber (2500 cm⁻¹) observed for the NH stretching vibration and indicating at the formation of a very strong NH···O bond is interpreted based on considering the effect of the crystalline environment on the formation and properties of the NH···O bonds in the head‐to‐tail chains of amino acid zwitterions. The results are interesting for understanding the factors determining the dynamics and structural instability of crystalline amino acids and also for biophysical chemistry, as the hydrogen bonded chains formed by amino acid zwitterions in the crystals can mimic the peptide chains. Copyright © 2009 John Wiley & Sons, Ltd.     

Involvement of weak C?H···X hydrogen bonds in metal‐to‐semiconductor regime change in one‐dimensional organic conductors (o‐DMTTF)2X (X = Cl,Br, and I): combined IR and Raman studies

We report on the infrared (IR) and Raman studies of the three isostructural quasi‐one‐dimensional cation radical salts of 3,4‐dimethyl‐tetrathiafulvalene (o‐DMTTF)₂X (X = Cl, Br, and I), which all exhibit metallic properties at room temperature and undergo transitions to a semiconducting state in two steps: a soft metal‐to‐semiconductor regime change in the temperature region T_ρ = 5–200 K and then a sharp phase transition at about T_MI = 50 K. Polarized IR reflectance spectra (700–16 000 cm⁻¹) and Raman spectra (50–3500 cm⁻¹, excitation λ = 632.8 nm) of single crystals were measured as a function of temperature (T = 5–300 K) to assess the eventual formation of a charge‐ordered state below 50 K. Additionally, the temperature dependence of the IR absorption spectra of powdered crystals in KBr discs was also studied. The Raman spectra and especially the bands related to the CC stretching vibration of o‐DMTTF provide unambiguous evidence of uniform charge distribution on o‐DMTTF down to the lowest temperatures, without any modification below 50 K. However, the temperature dependence of Raman spectra indicates a regime change below about 200 K. Temperature dependence of both electronic dispersion and vibrational features observed in the IR spectra also clearly confirms the regime change below about 200 K and shows the involvement of C H···X hydrogen bonds in the electronic localization; some spectral changes can be also related with the phase transition at 50 K. Additionally, using density functional theory methods, the normal vibrational modes of the neutral o‐DMTTF⁰ and cationic o‐DMTTF⁺ species, as well as their theoretical IR and Raman spectra, were calculated. The theoretical data were compared with the experimental IR and Raman spectra of neutral o‐DMTTF molecule. Copyright © 2011 John Wiley & Sons, Ltd.     

Low toxic and highly luminescent CdSe/Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>S quantum dots with thin organic SiO<Subscript>2</Subscript> coating for application in cell imaging

A silanization process was employed to transfer hydrophobic quantum dots (QDs) prepared via an organic route at high temperature into water phase. The QDs were further coated with a thin organic SiO₂ shell to form QDs@SiO₂ composite nanoparticles by ligand exchange or remaining initial organic ligands on the surface. In this study, QDs with different ligands, either trioctylphosphine oxide (TOPO) or oleic acid (OA), were employed to investigate the effects of ligands on the reverse micelles in preparing QDs@SiO₂ nanoparticles. In the preparing process, hydrophobic QDs were silanized by partially hydrolyzed tetraethyl orthosilicate (TEOS). For TOPO-capped CdSe QDs, surface TOPO ligands were completely replaced by partially hydrolyzed TEOS. As for OA-capped CdSe/Cd _x Zn_1?x S QDs, surface OA ligands were partially replaced. It was found that the ligand exchange drastically reduced the photoluminescence (PL) efficiency of CdSe QDs. Furthermore, the cytotoxicity studies of QDs@SiO₂ have been carried out in detail. The results indicate that CdSe/Cd _x Zn_1?x S QDs@SiO₂ composite nanoparticles exhibit lower cytotoxicity compared with CdSe QDs@SiO₂, because the SiO₂ shell and remained OA ligand layer can effectively prevent the leakage of toxic Cd²⁺ ions. Meanwhile, it was found that these CdSe/Cd _x Zn_1?x S QDs@SiO₂ nanocomposites could keep excellent PL properties even for 24 h incubating with Siha cells, which indicating that our prepared composite nanoparticles are potentially applicable for cell imaging in biological systems.