Theoretical study of the structure and bonding in ThC2 and UC2

The electronic structure and various molecular properties of the actinide (An) dicarbides ThC(2) and UC(2) were investigated by relativistic quantum chemical calculations. We probe five possible geometrical arrangements: two triangular structures including an acetylide (C(2)) moiety, as well as the linear AnCC, CAnC, and bent CAnC geometries. Our calculations at various levels of theory indicate that the triangular species are energetically more favorable, while the latter three arrangements proved to be higher-energy structures. Our SO-CASPT2 calculations give the ground-state molecular geometry for both ThC(2) and UC(2) as the symmetric (C(2v)) triangular structure. The similar and, also very close in energy, asymmetric (C(s)) triangular geometry belongs to a different electronic state. DFT and single-determinant ab initio methods failed to distinguish between these two similar electronic states demonstrating the power of multiconfiguration ab initio methods to deal with such subtle and delicate problems. We report detailed data on the electronic structure and bonding properties of the most relevant structures.     

Cyclodextrins as growth controlling agents for enhancing the catalytic activity of PVP-stabilized Ru(0) nanoparticles

Cyclodextrins act as growth controllers in the synthesis of PVP-stabilized Ru(0) nanoparticles, leading to enhancement of the catalytic activity in the hydrogenation of furfural.     

Alkynoate Synthesis through the Vinylogous Reactivity of Rhodium(II) Carbenoids

Siloxy group migration: A rhodium(II) carbenoid approach has been developed for the synthesis of alkynoates. This transformation combines the addition of enol ethers at the vinylogous position of β-siloxy-substituted vinyldiazo derivatives with a siloxy group migration to give the products as single diastereomers.     

Differentiation of monoiodothyronines using electrospray ionization tandem mass spectrometry

In this work two monoiodothyronines, 3-T1 and 3'-T1, have been analyzed using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Fragmentation patterns were proposed based on our data obtained by ESI-MS/MS. MS2 spectra in either negative or positive ion mode can be used to differentiate 3-T1 and 3'-T1. Based on the relative abundance of fragment ions in MS2 spectra in the negative ion mode, quantification of the 3-T1 and 3'-T1 isomers in mixtures is achieved without prior separation. Solid-phase extraction in combination with ESI-MS/MS provides a practicable procedure that can be used to determine the molar ratio of 3-T1 and 3'-T1 in human serum with an error less than 3%. The detection limits for 3-T1 and 3'-T1 were 0.5 and 0.7 pg/microL, respectively.     

Differentiation of diiodothyronines using electrospray ionization tandem mass spectrometry

Diiodothyronines 3,5-diiodothyronine (3,5-T2), 3',5'-diiodothyronine (3',5'-T2), and 3,3'-diiodothyronine (3,3'-T2) are important metabolites of 3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine (rT3; reverse T3). In this paper, a novel and rapid method for identifying and quantifying 3,5-T2, 3',5'-T2 and 3,3'-T2 has been introduced using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Fragmentation patterns were proposed on the basis of our data obtained by ESI-MS/MS. MS2 spectra in either negative ionization mode or positive ionization mode can be used to differentiate 3,5-T2, 3',5'-T2 and 3,3'-T2. On the basis of the relative abundance of fragment ions in MS2 spectra under the positive ionization mode, quantification of the 3,5-T2, 3',5'-T2 and 3,3'-T2 isomers in mixtures is also achieved without prior separation.     

meso-1,2-Bis­(methyl­azo)-1,2-di­phenyl­ethane

The title compound, meso-1,2-bis­(methyl­diazenyl)-1,2-di­phenyl­ethane, C₁₆H₁₈N₄, is arranged in a disordered manner around an inversion point. The N—N atom distances in the azo group of 1.192 (8) and 1.195 (8) Å, and the C—C atom distances in the ethyl­ene moiety at 1.512 (8) and 1.503 (8) Å in the two models [refined to 51.7 (6) and 48.3 (6)% occupancies] were not significantly different.     

Preparation and crystal structure of a quadruply bonded dimolybdenum complex with trans-crotonate ligands

A quadruply bonded dimolybdenum complex with trans-crotonate ligands, Mo₂(O₂CC₃H₅)₄, was synthesized and characterized by UV–VIS, IR, and NMR spectra. The crystal structure was determined by an X-ray single crystal diffraction analysis. The title complex (C₁₆H₂₀O₈Mo₂, M _w = 532.2) crystallized in the triclinic space group P-1 with the following crystallographic parameters: a = 10.236(2) ?, b = 10.393(2) ?, c = 10.524(2) ?, α = 89.59(1)°, β = 73.34(1)°, γ = 70.78(2)°, V = 1008.1(3) ?³, Z = 2, D _c = 1.753 Mg m⁻³, μ(Mo Kα = 0.71073 ?, F(000) = 528, and final R ₁ = 0.041, wR ₂ = 0.114 for observed reflections 2889 (I > 2σ(I)). The Mo₂ ⁴⁺ unit was surrounded by four trans-crotonate ligands resulting in a paddle wheel structure with one disordered trans-crotonate ligand. Molecules are bonded together by means of interactions consisting of the donation of lone pairs of electron on carboxylate O atoms on one molecule to the Mo atom on an adjacent complex. A new pattern of intermolecular bonding is observed.     

Sequence Elucidation of an Unknown Cyclic Peptide of High Doping Potential by ETD and CID Tandem Mass Spectrometry

Identification of an unknown substance without any information remains a daunting challenge despite advances in chemistry and mass spectrometry. However, an unknown cyclic peptide in a sample with very limited volume seized at a Pennsylvania racetrack has been successfully identified. The unknown sample was determined by accurate mass measurements to contain a small unknown peptide as the major component. Collision-induced dissociation (CID) of the unknown peptide revealed the presence of Lys (not Gln, by accurate mass), Phe, and Arg residues, and absence of any y-type product ion. The latter, together with the tryptic digestion results of the unusual deamidation and absence of any tryptic cleavage, suggests a cyclic structure for the peptide. Electron-transfer dissociation (ETD) of the unknown peptide indicated the presence of Gln (not Lys, by the unusual deamidation), Phe, and Arg residues and their connectivity. After all the results were pieced together, a cyclic tetrapeptide, cyclo[Arg-Lys-N(C₆H₉)Gln-Phe], is proposed for the unknown peptide. Observations of different amino acid residues from CID and ETD experiments for the peptide were interpreted by a fragmentation pathway proposed, as was preferential CID loss of a Lys residue from the peptide. ETD was used for the first time in sequencing of a cyclic peptide; product ions resulting from ETD of the peptide identified were categorized into two types and named pseudo-b and pseudo-z ions that are important for sequencing of cyclic peptides. The ETD product ions were interpreted by fragmentation pathways proposed. Additionally, multi-stage CID mass spectrometry cannot provide complete sequence information for cyclic peptides containing adjacent Arg and Lys residues. The identified cyclic peptide has not been documented in the literature, its pharmacological effects are unknown, but it might be a “designer” drug with athletic performance-enhancing effects.