EPR and ENDOR analysis of Fe3+ impurity centers in fluoroelpasolite lattices

Fe(3+) ions in hexagonal and cubic fluoroelpasolite crystals (A(1)(2)B(I)M(III)F(6)) have been investigated in a combined Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR) study. A detailed analysis of the ENDOR spectra for the nearest (19)F and (23)Na shells in X (9.5 GHz) and Q band (34 GHz) allowed the complex EPR spectra to be disentangled and to determine the spin Hamiltonian parameters for the various S = 5/2 Fe(3+) centres. W-band (95 GHz) EPR measurements as a function of temperature were performed to provide unambiguous evidence about the absolute signs of the Zero Field Splitting (ZFS) and SuperHyperFine (SHF) parameters for Fe(3+) in Cs(2)NaAlF(6) as already determined from the ENDOR work. It could be concluded that all principal (19)F hyperfine values were positive, in agreement with earlier assignments in the literature for related systems. A comparative analysis of the (19)F SHF data for Fe(3+) at a perfectly octahedral site in the cubic crystal, and at two slightly trigonally distorted environments in the hexagonal crystals, indicates that the metal-to-ligand distance changes upon doping. The obtained set of parameters concerning one defect in various analogous environments can furthermore be used to test different methods of theoretical calculations for ZFS and SHF values.     

Experimental and theoretical study of the metallotropic migrations in cyclooctatetraeneosmiumtricarbonyl

Experimental verification of the mechanism of metallotropic migrations in cyclooctatetraeneosmiumtricarbonyl (3) by means of 2D EXSY NMR spectroscopy confirmed the mechanism of [1,2]-Os shifts with low activation barrier (E(A) = 5.9 +/- 0.2 kcal mol(-1), ln A = 32 +/- 1). Transition-state structure for this rearrangement obtained at the B3LYP/SDD level of theory testifies for the activation energy of 6.5 kcal mol(-1) and supports well the selective [1,2]-Os shifts observed for 3.     

Electron paramagnetic resonance and electron nuclear double resonance of NaCl:Rh2+: A comparison between similarly doped Bridgman- and solution-grown single crystals

In a recent electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) study several new rhodium related centres in a Bridgman-grown crystal were reported. For two centres a detailed microscopic model was established. The primary Rh²⁺ centre was identified as a [RhCl₆]^4? complex with a single charge compensating Na⁺ vacancy in a next nearest neighbour position. A second centre was identified as a rhodium dimer. Two other Rh²⁺ centres, with apparent axial symmetry, remained unidentified. In the present study a detailed comparison between Rh²⁺ defects in Bridgman- and solution-grown NaCl crystals is presented. One of the previously unidentified Rh²⁺ centres is shown not to be axial but to have orthorhombic-I symmetry and is identified as a cis-[RhCl₆]^4? complex with two next nearest neighbour Na⁺ vacancies. For the primary centre additional ENDOR interactions confirm the model mentioned above. Finally a comparison is made between the temperature stability of the primary and orthorhombic-I centre in Bridgman-grown and similarly doped solution-grown NaCl crystals.     

Conformation resolved induced infrared activity: trans- and cis-formic acid isolated in solid molecular hydrogen

We report combined experimental and theoretical studies of infrared absorptions induced in solid molecular hydrogen by different conformers of formic acid (HCOOH, FA). FTIR spectra recorded in the H(2) fundamental region (4120-4160 cm(-1)) reveal a number of relatively strong trans-FA induced Q-branch absorptions that are assigned by studying both FA-doped parahydrogen (pH(2)) and normal hydrogen (nH(2)) samples. The induced H(2) absorptions are also studied for HCOOD doped nH(2) crystals for both the trans and cis conformers that show resolvable differences. Samples containing >90% of the higher energy cis-HCOOD conformer are produced by in situ IR pumping of the OD stretching overtone of trans-HCOOD using narrow-band IR light. Minimum energy structures for 1:1 complexes of H(2) and FA are determined using ab initio methods. The measured differences in the cis- versus trans-HCOOD induced spectra are in qualitative agreement with the frequencies and intensities calculated for the identified cluster structures as discussed in terms of the model of specific interactions.     

Identification of primary free radicals in trehalose dihydrate single crystals X-irradiated at 10 K

Primary free radical formation in trehalose dihydrate single crystals X-irradiated at 10 K was investigated at the same temperature using X-band Electron Paramagnetic Resonance (EPR), Electron Nuclear Double Resonance (ENDOR) and ENDOR-induced EPR (EIE) techniques. The ENDOR results allowed the unambiguous determination of six proton hyperfine coupling (HFC) tensors. Using the EIE technique, these HF interactions were assigned to three different radicals, labeled R1, R2 and R3. The anisotropy of the EPR and EIE spectra indicated that R1 and R2 are alkyl radicals (i.e. carbon-centered) and R3 is an alkoxy radical (i.e. oxygen-centered). The EPR data also revealed the presence of an additional alkoxy radical species, labeled R4. Molecular modeling using periodic Density Functional Theory (DFT) calculations for simulating experimental data suggests that R1 and R2 are the hydrogen-abstracted alkyl species centered at C5' and C5, respectively, while the alkoxy radicals R3 and R4 have the unpaired electron localized mainly at O2 and O4'. Interestingly, the DFT study on R4 demonstrates that the trapping of a transferred proton can significantly influence the conformation of a deprotonated cation. Comparison of these results with those obtained from sucrose single crystals X-irradiated at 10 K indicates that the carbon situated next to the ring oxygen and connected to the CH(2)OH hydroxymethyl group is a better radical trapping site than other positions.     

A simple and rapid method for identifying and semi-quantifying peptide hormones in isolated pancreatic islets by direct-tissue matrix-assisted laser desorption ionization time-of-flight mass spectrometry

We describe a new, simple, robust and efficient method based on direct‐tissue matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) mass spectrometry that enables consistent semi‐quantitation of peptide hormones in isolated pancreatic islets from normal and diabetic rodents. Prominent signals were measured that corresponded to all the main peptide hormones present in islet‐endocrine cells: (α‐cells) glucagon, glicentin‐related polypeptide/GRPP; (β‐cells) insulin I, insulin II, C‐peptide I, C‐peptide II, amylin; (δ‐cells) somatostatin‐14; and (PP‐cells), and pancreatic polypeptide. The signal ratios coincided with known relative hormone abundances. The method demonstrated that severe insulin deficiency is accompanied by elevated levels of all non‐β‐cell‐hormones in diabetic rat islets, consistent with alleviation of paracrine suppression of hormone production by non‐β‐cells. It was also effective in characterizing hormonal phenotype in hemizygous human‐amylin transgenic mice that express human and mouse amylin in approx. equimolar quantities. Finally, the method demonstrated utility in basic peptide‐hormone discovery by identifying a prominent new Gcg‐gene‐derived peptide (theoretical monoisotopic molecular weight 3263.5 Da), closely related to but distinct from GRPP, in diabetic islets. This peptide, whose sequence is HAPQDTEENARSFPASQTEPLEDPNQINE in Rattus norvegicus, could be a peptide hormone whose roles in physiology and metabolic disease warrant further investigation. This method provides a powerful new approach that could provide important new insights into the physiology and regulation of peptide hormones in islets and other endocrine tissues. It has potentially wide‐ranging applications that encompass endocrinology, pharmacology, phenotypic analysis in genetic models of metabolic disease, and hormone discovery, and could also effectively limit the numbers of animals required for such studies. Copyright © 2011 John Wiley & Sons, Ltd.     

Electron paramagnetic resonance study of S− and S− 3

Abstract

Two new sulphur are reported in monocristalline rubidiumchloride doped with rubidium and sulphur, and irradiated with X-rays at room temperature. By an extensive comparison with other experimental data on chalcogen centres in alkali halides an interstitial RbCl:S^? and a substitutional RbCl:S^? ₃ model is proposed for these paramagnetic defects. Theoretical calculations confirm the S^? ion model for the former.     

Some Exact Solutions of Two Fifth Order KdV-type Nonlinear Partial Differential Equations

We consider the generalized integrable fifth order nonlinear Korteweg-de Vries (fKdV) equation. The extended Tanh method has been used rigorously, by computational program MAPLE, for solving this fifth order nonlinear partial differential equation. The general solutions of the fKdV equation are formed considering an ansatz of the solution in terms of tanh. Then, in particular, some exact solutions are found for the two fifth order KdV-type equations given by the Caudrey-Dodd-Gibbon equation and the another fifth order equation. The obtained solutions include solitary wave solution for both the two equations.     

Torsional vibrations of wet clutches: influence of mechanical parameters

Using a small scale test-rig a number of experiments were performed in which the imposed disk velocity v _disk, the different mechanical parameters of the test-rig (damping c and tangential stiffness k), and normal load were varied independently.     

The Catline for Deep Regression

Motivated by the notion of regression depth (Rousseeuw and Hubert, 1996) we introduce thecatline, a new method for simple linear regression. At any bivariate data setZ_n={(x_i, y_i);i=1, …, n} its regression depth is at leastn/3. This lower bound is attained for data lying on a convex or concave curve, whereas for perfectly linear data the catline attains a depth ofn. We construct anO(n log n) algorithm for the catline, so it can be computed fast in practice. The catline is Fisher-consistent at any linear modely=βx+α+ein which the error distribution satisfies med(e | x)=0, which encompasses skewed and/or heteroscedastic errors. The breakdown value of the catline is 1/3, and its influence function is bounded. At the bivariate gaussian distribution its asymptotic relative efficiency compared to theL¹line is 79.3% for the slope, and 88.9% for the intercept. The finite-sample relative efficiencies are in close agreement with these values. This combination of properties makes the catline an attractive fitting method.