Alkyl and aryl dicationic derivatives of cyclic triphosphenium ions

Direct alkylation of cyclic triphosphenium ions by triflates to give di-ium dications is only possible for small organic substituents on the attacking reagent. The dicationic products are not intrinsically unstable, however, and in many instances they may be synthesised by an alternative route, pioneered by Schmidpeter and co-workers. These species may be readily identified in solution by (31)P NMR spectroscopy. The crystal and molecular structures of five such derivatives have been ascertained for the first time by single crystal X-ray diffraction at 120 K. The results confirm that normal single P-P bond lengths are present in the dications, in contrast with the monocationic parent cyclic triphosphenium ions, where structural determinations have shown that the P-P bond lengths are intermediate between single and double bonds.     

Formation of nanooctahedra in molybdenum disulfide and molybdenum diselenide using pulsed laser vaporization

Pulsed laser vaporization has been used to produce nanooctahedra of MoS2 and MoSe2. The nanooctahedra primarily form in two- or three-layer nested octahedra, although nesting up to five layers has been observed. Tilting the TEM sample stage and mapping how the images of single particles transformed provided the evidence to verify their octahedral geometry. Analysis of 30 two- and three-layered octahedra showed that their outer edge lengths clustered at approximately 3.8 nm and approximately 5.1 nm, respectively. This discreet sizing and the high symmetry of these closed nanooctahedra represent the closest inorganic analogy yet to the carbon fullerenes. The geometrical implications for forming octahedra from these layered compounds are investigated by considering different atomic arrangements assuming either trigonal prismatic or octahedral coordination around the Mo atom and yields two possible configurations for the actual structure of the nanooctahedra. A preliminary survey of pulsed laser vaporization of other layered metal chalcogenides shows that these dichalcogenides differ in their tendency to form small closed layered fullerene-like structures. These materials can be ranked from highest tendency to lowest as follows: NbSe2, WS2, WSe2, SnS2, TaS2, GaS, ReS2, and MoTe2.     

Synthesis and characterization of a chromium(V) cis-dioxo bis(1,10-phenanthroline) complex and crystal and molecular structures of its chromium(III) precursor

The first structurally characterized Cr(V) dioxo complex, cis-[CrV(O)2(phen)2](BF4) (2, phen=1,10-phenanthroline) has been synthesized by the oxidation of a related Cr(III) complex, cis-[Cr(III)(phen)2(OH2)2](NO3)3.2.5H2O (1, characterized by X-ray crystallography), with NaOCl in aqueous solutions in the presence of excess NaBF4, and its purity has been confirmed by electrospray mass spectrometry (ESMS), EPR spectroscopy, and analytical techniques. Previously reported methods for the generation of Cr(V)-phen complexes, such as the oxidation of 1 with PbO2 or PhIO, have been shown by ESMS to lead to mixtures of Cr(III), Cr(V), Cr(VI), and in some cases Cr(IV) species, 3. Species 3 was assigned as [CrIV(O)(OH)(phen)2]+, based on ESMS and X-ray absorption spectroscopy measurements. A distorted octahedral structure for 2 (CrO, 1.63 A; Cr-N, 2.04 and 2.16 A) was established by multiple-scattering (MS) modeling of XAFS spectra (solid, 10 K). The validity of the model was verified by a good agreement between the results of MS XAFS fitting and X-ray crystallography for 1 (distorted octahedron; Cr-O, 1.95 A; Cr-N, 2.06 A). Unlike for the well-studied Cr(V) 2-hydroxycarboxylato complexes, 2 was equally or more stable in aqueous media (hours at pH=1-13 and 25 degrees C) compared with polar aprotic solvents. A stable Cr(III)-Cr(VI) dimer, [Cr(III)(Cr(VI)O4)(phen)2]+ (detected by ESMS), is formed during the decomposition of 2 in nonaqueous media. Comparative studies of the oxidation of 1 by NaOCl or PbO2 have shown that [Cr(V)(O)2(phen)2]+ was the active species responsible for the previously reported oxidative DNA damage, bacterial mutagenicity, and increased incidence of micronuclei in mammalian cells, caused by the oxidation products of 1 with PbO2. Efficient oxidation of 1 to a genotoxic species, [Cr(V)(O)2(phen)2]+, in neutral aqueous media by a biological oxidant, hypochlorite, supports the hypothesis on a significant role of reoxidation of Cr(III) complexes, formed during the intracellular reduction of Cr(VI), in Cr(VI)-induced carcinogenicity. Similar oxidation reactions may contribute to the reported adverse effects of a popular nutritional supplement, Cr(III) picolinate.     

Reaction of Aziridinones with Thiourea: A Novel Synthesis of Specifically Substituted Glycocyamidines and Hydantoins

The reaction of aziridinones with thiourea produces glycocyamidines bearing substituents at positions 1 and 5, which have been converted into hydantoins.     

Seams near seams: the Jahn-Teller effect in the 1E" state of N3+

The (1)E(") electronic state of cyclic N(3) (+) arising from the singly excited electron configuration e('3)e(") is studied using multireference configuration interaction wave functions and a quadratic Jahn-Teller Hamiltonian determined from those calculations. It is shown that these two states have both a symmetry-required seam of conical intersections at D(3h) geometries and three proximal symmetry equivalent C(2v) seams, located on a circle with radius rho(0) from the D(3h) intersection. rho(0), a function of Q(s), the breathing mode, is quite small but only attains a value of zero at Q(s) (crit)=1.252 A, resulting in a confluence or intersection node of the three C(2v) seams with the D(3h) seam. At this point only, g= parallelg(Q(s)) parallel, the norm of half the energy difference gradient, the linear Jahn-Teller term, vanishes and the intersection is of the Renner-Teller type. The close proximity of the previously unreported C(2v) seams to the D(3h) seam over the range of Q(s) considered is a consequence of the small values of g, compared to the quadratic Jahn-Teller term. The present analysis has important implications in the study of Jahn-Teller effects in ring systems and provides insight into a recent report that characterized this D(3h) seam as a Renner-Teller or glancing intersection.     

QCD parametrization of the ργ, ωγ and Φγ couplings: whyf ργ:f ωγ=3:1 in spite of flavor breaking

Zeitschrift für Physik C Particles and Fields - A quasi no flavor breaking theorem, derived from QCD for a class of hadronic states, is used to show that the ratio of ?γ to...     

MOLECULAR CHANGES DURING THE PHOTOOXIDATION OF α-CRYSTALLIN IN THE PRESENCE OF UROPORPHYRIN

Singlet oxygen reacts preferentially with three amino acids in proteins, His, Trp and Met. In order to study the specific molecular events that result from such oxidations, calf a-crystallin was photooxidized in the presence of uroporphyrin and the reactions were investigated by high performance liquid chromatography peptide mapping using a photodiode array detector followed by fast atom bombardment mass spectrometry (FAB-MS). From these studies, the following conclusions can be inferred: (1) Upon photooxidation residue Met-68 of the B chain is oxidized to Met sulfoxide, whereas residue Trp-60 remains intact. (2) Two of the 16 His residues in a-crystallin are photooxidized with an apparent pK_a of ca 7.0. (3) FAB-MS analysis suggests that residue Lys-166 close to the C-terminal end of the A chain forms a cross-link with the His-7 residue close to the N-terminal end of the A chain. This may be either an inter- or intramolecular cross-link.