Wide compositional and structural diversity in the system Tl/Bi/P/Q (Q=S, Se) and observation of vicinal P-Tl J coupling in the solid state

The compounds alpha-TlBiP2Se6 (I), beta-TlBiP2Se6 (II), TlBiP2S6 (III), Tl3Bi3(PS4)4 (IV), TlBiP2S7 (V), and Tl3Bi(PS4)2 (VI) were synthesized, and the structures of I-V were determined by single-crystal X-ray diffraction analysis. The structure of I features infinite chains. Those of compounds II, III, and V are layered. The structure of IV features a three-dimensional framework. Tl4Bi2(PS4)2(P2S6) (VII) was also prepared for comparison to the title compounds. The band gaps of each compound are 1.23, 1.27, 1.81, 1.88, 2.06, 1.98, and 1.97 eV for I-VII, respectively. Compounds I, III, IV, and VI melt congruently at 544, 595, 495, and 563 degrees C, respectively, and compounds II, V, and VII melt incongruently at 544, 509, and 600 degrees C, respectively. Solid-state 31P NMR spectroscopy of the reported compounds demonstrates chemical shifts and chemical shift anisotropies in line with related chalcophosphate materials. Evidence for two-bond P-Tl J coupling was observed in 31P NMR spectra (J=481-1781 Hz), and to the best of our knowledge, this is the first example of two-bond P-Tl J coupling and the first example of P-Tl coupling in the solid state. It was possible to assign chemical shifts of inequivalent 31P atoms from the same [PxQy]z- anion type based on different modes of metal ion coordination to the chalcogen. These assignments provide information about the vicinal metal ion contribution to the 31P chemical shift.     

31P solid state NMR studies of metal selenophosphates containing [P2Se6]4-, [P4Se10]4-, [PSe4]3-, [P2Se7]4-, and [P2Se9]4- ligands

31P solid-state nuclear magnetic resonance (NMR) spectra of 12 metal-containing selenophosphates have been examined to distinguish between the [P(2)Se(6)](4-), [PSe(4)](3-), [P(4)Se(10)](4-), [P(2)Se(7)](4-), and [P(2)Se(9)](4-) anions. There is a general correlation between the chemical shifts (CSs) of anions and the presence of a P[bond]P. The [P(2)Se(6)](4-) and [P(4)Se(10)](4-) anions both contain a P[bond]P and resonate between 25 and 95 ppm whereas the [PSe(4)](3-), [P(2)Se(7)](4-), and [P(2)Se(9)](4-) anions do not contain a P[bond]P and resonate between -115 and -30 ppm. The chemical shift anisotropies (CSAs) of compounds containing [PSe(4)](3-) anions are less than 80 ppm, which is significantly smaller than the CSAs of any of the other anions (range: 135-275 ppm). The smaller CSAs of the [PSe(4)](3-) anion are likely due to the unique local tetrahedral symmetry of this anion. Spin-lattice relaxation times (T(1)) have been determined for the solid compounds and vary between 20 and 3000 s. Unlike the CS, T(1) does not appear to correlate with P-P bonding. (31)P NMR is also shown to be a good method for impurity detection and identification in the solid compounds. The results of this study suggest that (31)P NMR will be a useful tool for anion identification and quantitation in high-temperature melts.     

On the singularity of Green's tensor for a perfectly conducting semi-infinite cone

This paper is intended to clarify a misunderstanding concerningthe source singularity of the electric Green's tensor for aperfectly conducting semi-infinite cone of circular cross-section.Tai's series expansion of the Green's tensor is known to lacka singular term at the source region. Jones has reconstructedthe solution to this problem and has pointed out the differencebetween his result and that of Tai. The aim of our paper isto demonstrate that, although Jones's closed-form solution iscorrect, there is a mistake in his comparison with Tai's seriessolution. We conclude that one of the two additional singularterms that Jones claims as missing from Tai's formula must beomitted. Besides, we compare Jones's closed-form solution withSmyshlyaev's solution to the very same problem. We concludethat the magnetic field expressions given by Jones and Smyshlyaevcoincide, but a singular term is missing from Smyshlyaev's expressionfor the electric field.     

Working group report: Collider Physics

This is summary of the activities of the working group on collider physics in the IXth Workshop on High Energy Physics Phenomenology (WHEPP-9) held at the Institute of Physics, Bhubaneswar, India in January 2006. Some of the work subsequently done on these problems by the subgroups formed during the workshop is included in this report.     

13C-13C and (15)N-(13)C correlation spectroscopy of membrane-associated and uniformly labeled human immunodeficiency virus and influenza fusion peptides: amino acid-type assignments and evidence for multiple conformations

Many viruses which cause disease including human immunodeficiency virus (HIV) and influenza are "enveloped" by a membrane and infection of a host cell begins with joining or "fusion" of the viral and target cell membranes. Fusion is catalyzed by viral proteins in the viral membrane. For HIV and for the influenza virus, these fusion proteins contain an approximately 20-residue apolar "fusion peptide" that binds to target cell membranes and plays a critical role in fusion. For this study, the HIV fusion peptide (HFP) and influenza virus fusion peptide (IFP) were chemically synthesized with uniform (13)C, (15)N labeling over large contiguous regions of amino acids. Two-dimensional (13)C-(13)C and (15)N-(13)C spectra were obtained for the membrane-bound fusion peptides and an amino acid-type (13)C assignment was obtained for the labeled residues in HFP and IFP. The membrane used for the HFP sample had a lipid headgroup and cholesterol composition comparable to that of host cells of the virus, and the (13)C chemical shifts were more consistent with beta strand conformation than with helical conformation. The membrane used for the IFP sample did not contain cholesterol, and the chemical shifts of the dominant peaks were more consistent with helical conformation than with beta strand conformation. There were additional peaks in the IFP spectrum whose shifts were not consistent with helical conformation. An unambiguous (13)C and (15)N assignment was obtained in an HFP sample with more selective labeling, and two shifts were identified for the Leu-9 CO, Gly-10 N, and Gly-10 Calpha nuclei. These sets of two shifts may indicate two beta strand registries such as parallel and antiparallel. Although most spectra were obtained on a 9.4 T instrument, one (13)C-(13)C correlation spectrum was obtained on a 16.4 T instrument and was better resolved than the comparable 9.4 T spectrum. More selective labeling and higher field may, therefore, be approaches to obtaining unambiguous assignments for membrane-associated fusion peptides.     

Native conformation at specific residues in recombinant inclusion body protein in whole cells determined with solid-state NMR spectroscopy

Inclusion bodies are insoluble aggregates that are formed by bacteria to store excess recombinant protein produced during expression. The structure of the protein in inclusion bodies is poorly understood but it has been hypothesized that the protein may form misfolded beta sheet aggregates. This paper presents an isotopic labeling and solid-state nuclear magnetic resonance approach to determine the secondary structure of individual residues within a recombinant influenza virus "FHA2" protein in inclusion bodies. The inclusion bodies were studied either in the context of the unlysed hydrated E. coli cells or in the hydrated pellet formed from centrifugation of the material insoluble in the cell lysate. The native structure of FHA2 is predominantly helical and native helical structure was also observed for several specific residues in the inclusion body FHA2. This approach will be applicable to structural analysis of many inclusion body proteins and should provide useful information for optimizing solubilization and purification protocols of these proteins.     

P6Se12]4-: a phosphorus-rich selenophosphate with low-valent P centers

The new selenophosphate Rb4P6Se12 features the trans-decalin-like, [P6Se12]4- anion, a phosphorus-rich species that possesses three parallel P-P bonds and formally P2+ and P4+ centers. The synthesis of Rb4P6Se12 was accomplished with the reductive addition of P to RbPSe6 and represents an interesting example of how alkali chalcophosphates can serve as starting materials to produce new compounds under mild reaction conditions.     

Improved resolution and detection of 31P-Tl J-couplings at 21 T in 31P magic angle spinning NMR spectra of inorganic compounds containing Tl/Bi/P/S

For crystalline compounds containing Tl, Bi, P, and S, greatly improved chemical shift resolution was observed in 31P magic angle spinning spectra obtained at 21 T relative to spectra obtained at 9.4 T. In Hz units, the spectral linewidths were not strongly dependent on the applied field, which may be a result of a significant contribution to the linewidths from transverse relaxation. Comparison of the spectra at the two different fields confirmed that spectral splittings were due to two-bond phosphorus-thallium J-coupling. These results suggest that ultra-high field may be a useful tool to improve spectral resolution of spin 12 nuclei in crystalline inorganic compounds.