Absorption Lineshapes in Two-Dimensional Electron Spin Resonance and the Effects of Slow Motions in Complex Fluids

A methodology for obtaining pure absorption two-dimensional electron spin resonance spectra is presented for the case of large inhomogeneous broadening and/or slow motions. For slow motions, the spectra consist of “complex Lorentzians” superimposed with complex weighting factors, presenting a challenge to obtaining absorption spectra. It is shown how absorption-type spectra can be recovered for the two-pulse COSY and SECSY experiments in such cases. For three-pulse 2D ELDOR experiments, absorption lineshapes can be obtained for the autopeaks, whereas the cross peaks would be of mixed-mode character, in general. However, for practical cases the dispersive components in the cross peaks will be relatively small. Theoretical and experimental absorption spectra are provided to illustrate the method and to show the improved resolution obtained from absorption lineshapes. In particular, the variation in linewidths across a SECSY spectrum, which is a key component in elucidating motional dynamics, is clearly rendered in the pure absorption mode. A convenient method for introducing the necessary phase corrections for the slow-motional spectra is also provided.     

A note on Reed-Muller codes

In this paper we study linear codes that are obtained by annexing some vectors to the basis vectors of a Reed-Muller code of order r.     

Development and validation of a sensitive LC/MS/MS method for the determination of γ‐tocotrienol in rat plasma: application to pharmacokinetic studies

γ‐Tocotrienol has attracted much attention owing to its multiple health benefits. This study developed and validated a simple, specific, sensitive and reliable LC/MS/MS method to analyze γ‐tocotrienol in rat plasma. Plasma samples (50 μL) were extracted with internal standard solution (25 ng/mL of itraconazole) in acetonitrile (200 μL) with an average recovery of 44.7% and an average matrix effect of ?2.9%. The separation of γ‐tocotrienol and internal standard from the plasma components was achieved with a Waters XTerra® MS C₁₈ column with acetonitrile–water as mobile phase. Analysis was performed under positive ionization electrospray mass spectrometer via the multiple reaction monitoring. The standard curve was linear over a concentration range of 10–1000 ng/mL with correlation coefficient values >0.997. The method was validated with intra‐ and inter‐day accuracy (relative error) ranging from 1.79 to 9.17% and from 2.16 to 9.66%, respectively, and precision (coefficient of variation) ranged from 1.94 to 9.25% and from 2.37 to 10.08%, respectively. Short‐term stability, freeze–thaw stability and the processed sample stability tests were performed. This method was further applied to analyze γ‐tocotrienol plasma concentrations in rats at various time points after administration of a 2 mg/kg single intravenous dose, and a pharmacokinetic profile was successfully obtained. Copyright © 2012 John Wiley & Sons, Ltd.     

Dual row modules and polyhedra of blocking group problems

Corresponding to every group problem is a row module. Duality for group problems is developed using the duality or orthogonality of the corresponding row modules. The row module corresponding to a group problem is shown to include Gomory's fractional cuts for the group polyhedron and all the vertices of the polyhedron of the blocking group problem. The polyhedra corresponding to a pair of blocking group problems are shown to have a blocking nature i.e. the vertices of one include some of the facets of the other and mutatis mutandis. The entire development is constructive. The notions of contraction, deletion, expansion and extension are defined constructively and related to homomorphic liftings and suproblems in a dual setting. Roughly speaking a homomorphic lifting is dual to forming a subproblem. A proof of the Gastou-Johnson generalization of Gomory's homomorphic lifting theorem is given, and dual constructions are discussed. A generalization of Gomory's subadditive characterization to subproblems is given. In the binary case, it is closely related to the work of Seymour on cones arising from binary matroids.     

Stereoselective ketal-tethered intramolecular diels-alder cycloadditions. An approach to the 2-oxadecalin spiroketal core of antifungal agent fusidilactone C

[reaction: see text] An approach toward the 2-oxadecalin spiroketal core of fusidilactone C via a rare ketal-tethered intramolecular Diels-Alder cycloaddition is described here. This intramolecular Diels-Alder cycloaddition is highly endo-selective and overall depended upon the nature of solvents and Lewis acids. We also observed some remarkable rate acceleration in MeOH.     

Anti-endotoxin agents. 1. Development of a fluorescent probe displacement method optimized for the rapid identification of lipopolysaccharide-binding agents

Lipopolysaccharides (LPS), otherwise termed 'endotoxins', are outer-membrane constituents of Gram-negative bacteria. Lipopolysaccharides play a key role in the pathogenesis of 'Septic Shock', a major cause of mortality in the critically ill patient. Therapeutic options aimed at limiting downstream systemic inflammatory processes by targeting lipopolysaccharide do not exist at the present time. We have defined the pharmacophore necessary for small molecules to specifically bind and neutralize LPS, and have shown using animal models of sepsis that the sequestration of circulatory LPS by small molecules is a therapeutically viable strategy. Assays reported previously in the literature do not lend themselves well to the rapid screening of large numbers of structurally diverse compounds. In this report, we describe a highly sensitive and robust fluorescent displacement assay using BODIPY TR cadaverine (BC), which binds specifically to the toxic center of LPS, lipid A, and is competitively displaced by compounds displaying an affinity for lipid A. The assay clearly discriminates subtle differences in the binding of polymyxin B, and its nonapeptide derivative, with LPS. The spectral properties of the BODIPY fluorophore are ideally suited for screening diverse structural classes of compounds, including those with conjugated aromatic groups, or with chromophores in the 260-500 nm range. The fluorescent probe: LPS complex is stable under physiologically relevant salt concentrations, resulting in the rapid rejection of spurious binders interacting via non-specific electrostatic interactions, and, therefore, in greatly improved dispersion of ED(50)values.     

Structures of cleomiscosins,coumarinolignoids of cleome viscosa seeds1

Structures of cleomiscosins A, B and C, three new coumarino-lignoids isolated from the seeds of Cleome viscosa Linné, have been established as 1a, 2a and 1f irrespectively, on the basis of spectral and chemical evidence. The compounds exhibited liver-protective properties.     

A crosslinked preparation ofE. coli β-D-galactosidase

β-D-Galactosidase fromE. Coli was crosslinked using glutaraldehyde and two bisimidoesters. With glutaraldehyde and dimethyl adipimidate (DMA), it is possible to obtain preparations having higher activity than the native enzyme. Glutaraldehyde and DMA gave preparations showing enhanced thermal stability. The preparation crosslinked with DMA, when used for continuous hydrolysis of lactose in milk, was found to be significantly better than the native enzyme.     

Determination of total chromium in terrestrial and marine samples by electrothermal atomic absorption spectrometry after pressure digestion

A comparison between two commonly used sample digestion procedures was performed for the determination of total chromium in biological matrices. Ten reference materials (terrestrial and marine matrices) have been digested in HNO₃, HNO₃ + HClO₄ and HNO₃ + HF, respectively, under pressure in quartz vessels of a high pressure asher (HPA) or in PTFE bombs with external heating. Much lower chromium values than expected were obtained in most of the reference materials by using quartz vessels with nitric acid because of adsorption of chromium at quartz surfaces. Determinations after sample digestion in PTFE vessels with external heating showed expected results, except in some reference materials which precipitated more silica. An improvement of the results was observed by using a mixture of nitric acid and perchloric acid, but only the combination of nitric acid and a small amount of HF provided the desired results in all the reference materials studied. Received: 29 January 1997 / Revised: 20 May 1997 / Accepted: 22 May 1997