Spectroscopic characterization and crystal structure of cis-Bis(N-(2-benzoyl)-N′,N′-diphenylthioureato-k 2O,S)nickel(II)

The title compound [Ni(C₂₀H₁₅N₂OS)₂] is prepared by the reaction of metal acetate with the corresponding acylthiourea derivative. The complex is characterized by elemental analysis, IR, ¹H and ¹³C NMR, and its structure is determined by single crystal X-ray diffraction. The Ni(II) ion is coordinated by the S and O atoms of two N-benzoyl-N??,N??-diphenylthiourea ligands in a slightly distorted square-planar coordination geometry. The two O and two S atoms are mutually cis to each other. The substance crystallizes triclinic (P-1 space group) with cell dimensions a = 10.7262(9) ?, b = 12.938(3) ?, c = 14.2085(12) ?, ?? = 74.650(4)°, ?? = 78.398(4)°, ?? = 68.200(5)°, and two formula units in the unit cell. The structure is very close to the related N-(2-furoyl) Ni complex reported previously.     

On Stability Analyses of Three Classical Buckling Problems for the Elastic Strut

It is common practice in analyses of the configurations of an elastica to use Jacobi??s necessary condition to establish conditions for stability. Analyses of this type date to Born??s seminal work on the elastica in 1906 and continue to the present day. Legendre developed a treatment of the second variation which predates Jacobi??s. The purpose of this paper is to explore Legendre??s treatment with the aid of three classical buckling problems for elastic struts. Central to this treatment is the issue of existence of solutions to a Riccati differential equation. We present two different variational formulations for the buckling problems, both of which lead to the same Riccati equation, and we demonstrate that the conclusions from Legendre and Jacobi??s treatments are equivalent for some sets of boundary conditions. In addition, the failure of both treatments to classify stable configurations of a free-free strut are contrasted.     

On almost clopen continuity

Recently the class of clopen continuous functions between topological spaces has been generalized by the definition of the class of almost clopen continuous functions. The aim of this paper is to reconsider this second class of functions from the perspective of change of topology. Indeed, we show that the concept of almost clopen continuity coincides with the classical notion of continuity provided that suitable changes are made to the topologies of the domain and codomain of the function. We investigate some of the consequences of this situation.     

Controlling the expansion into vacuum—the enabling technology for trapping atmosphere-sampled particulate ions

A new inlet has been designed to control the kinetic energy distributions of ions into a large-radius, frequency-adjusted, linear quadrupole ion trap. The work presented here demonstrates trapping singly-charged, intact proteins in the 10 to 200 kDa range injected from the atmosphere. The trapped ions were held while collisions with a buffer gas removed the remaining amounts of expansion-induced kinetic energy. The ions were then ejected from the trap on-demand into an awaiting detector. There is no low mass limit for ion injection and trapping. The upper limit presented in this study was defined by the limit of the conversion dynode-based detector at ∼1.5 MDa. Trapping larger masses should be achievable. The transmission and capture efficiency across the entire mass range should be very high because the entire flow from the inlet empties directly into the trap. The kinetic energy distribution of massive ions is the primary reason for the working range limitation of mass spectrometers. Trapping ions with collisional cooling before mass analysis permits the motion of the ions to be completely defined by the applied fields. For this reason, this new inlet and trapping system represents a large step toward sensitive, high-resolution mass spectrometry into the megadalton range and beyond.     

From amines to diketopiperazines: a one-pot approach

An efficient one-pot synthesis is described for the preparation of 1,4-disubstituted piperazine-2,5-diones starting from a suitable amine and chloroacetyl chloride in the presence of an aqueous base. The resulting chloroacetamide is cyclised in situ by employing the phase-transfer (PT) catalyst, benzyltriethylammonium chloride (TEBA). The products are isolated in excellent yields of up to 90%.     

Mannose7 Glycan Isomer Characterization by IMS-MS/MS Analysis

The isomers of the Man₇GlcNAc₂ glycan obtained from bovine ribonuclease B have been characterized by ion mobility spectrometry-tandem mass spectrometry (IMS-MS/MS). In these experiments, [Man7 + 2Na]²⁺ precursors having different mobilities are selected by ion mobility spectrometry and analyzed by MS/MS techniques in an ion trap. The fragmentation spectra obtained for various precursor ions are specific, suggesting the isolation or enrichment of different glycan isomers. One fragment ion with a mass-to-charge ratio (m/z) of 903.8 is found to correspond to the loss of an internal mannose residue of a specific isomer. Extracted fragment ion drift time distributions (XFIDTDs) yield distinctive precursor ion drift time profiles indicating the existence of four separate isomers as proposed previously.     

Molecular Modeling of Two Disaccharides Containing Fructopyranose Linked to Glucopyranose

Abstract

Ramachandran energy surfaces for the disaccharides leucrose and turanose were computed using MM3. For each molecule, thirty-two combinations of hydroxyl and primary alcohol group orientations were considered. The calculations used a dielectric constant of 4.0 and the maps were generated on a 20° grid-spacing. The models compared well with the corresponding crystal structures except for significant deviations in some of the anomeric C-O bond lengths.     

Impact of normal-phase gradient elution in chiral chromatography: a novel,robust, efficient and rapid chiral screening procedure

Novel normal-phase gradient systems have been employed for fast high-throughput chiral analyses of Discovery compounds in our research laboratories in Eli Lilly and Company. In this report, we describe an automated screening approach based on gradient elution, in order to achieve accurate enantiomeric excess determinations, and chiral separations when needed, in the shortest possible timeframe. Baseline resolution of enantiomers has been obtained for over 85% of the samples so tested. For the remaining cases, complete enantioseparation by isocratic optimisation is generally achieved in a single shot. This technique has been proven to be robust and is now standard operating procedure at our analytical research laboratories.