Background removal procedure for rapid scan EPR

In rapid scan EPR the changing magnetic field creates a background signal with components at the scan frequency and its harmonics. The amplitude of the background signal increases with scan width and is more significant for weak EPR signals such as are obtained in the presence of magnetic field gradients. A procedure for distinguishing this background from the EPR signal is proposed, mathematically described, and tested for various experimental conditions.     

Gender effect on neurodegeneration and myelin markers in an animal model for multiple sclerosis

Background  

Multiple sclerosis (MS) varies considerably in its incidence and progression in females and males. In spite of clinical evidence, relatively few studies have explored molecular mechanisms possibly involved in gender-related differences. The present study describes possible cellular- and molecular-involved markers which are differentially regulated in male and female rats and result in gender-dependent EAE evolution and progression. Attention was focused on markers of myelination (MBP and PDGFαR) and neuronal distress and/or damage (GABA synthesis enzymes, GAD65 and GAD67, NGF, BDNF and related receptors), in two CNS areas, i.e. spinal cord and cerebellum, which are respectively severely and mildly affected by inflammation and demyelination. Tissues were sampled during acute, relapse/remission and chronic phases and results were analysed by two-way ANOVA.     

Heuristics and lower bounds for minimizing fuel consumption in hybrid-electrical vehicles

In hybrid electric vehicles, the electrical powertrain system has multiple energy sources that it can gather power from to satisfy the propulsion power requested by the vehicle at each instant. This paper focusses on the minimization of the fuel consumption of such a vehicle, taking advantage of the different energy sources. Based on global optimization approaches, the proposed heuristics find solutions that best split the power requested between the multi-electrical sources available. A lower bounding procedure is introduced to validate the quality of the solutions. Computational results show a significant improvement over previous results from the literature in both the computing time and the quality of the solutions.     

Highly Enantioselective Construction of Tricyclic Derivatives by the Desymmetrization of Cyclohexadienones

The asymmetric synthesis of tricyclic compounds by the desymmetrization of cyclohexadienones is presented. The reaction tolerated a large variety of substituents at different positions of the cyclohexadienone, and heterocyclic rings of different sizes were accessible. Density functional theory calculations showed that the reaction proceeds through an asynchronous [4+2] cycloaddition.     

Doping‐Induced Absorption Bands in P3HT: Polarons and Bipolarons

In this work, we focus on the formation of different kinds of charge carriers such as polarons and bipolarons upon p‐type doping (oxidation) of the organic semiconductor poly(3‐ hexylthiophene‐2,5‐diyl) (P3HT). We elucidate the cyclic voltammogram during oxidation of this polymer and present spectroscopic changes upon doping in the UV/Vis/near‐IR range as well as in the mid‐IR range. In the low‐oxidation regime, two absorption bands related to sub‐gap transitions appear, one in the UV/Vis range and another one in the mid‐IR range. The UV/Vis absorption gradually decreases upon further doping while the mid‐IR absorption shifts to lower energy. Additionally, electron paramagnetic resonance (EPR) measurements are performed, showing an increase of the EPR signal up to a certain doping level, which significantly decreases upon further doping. Furthermore, the absorption spectra in the UV/Vis range are analyzed in relation to the morphology (crystalline vs. amorphous) by using theoretical models. Finally, the calculated charge carriers from cyclic voltammogram are linked together with optical transitions as well as with the EPR signals upon p‐type doping. We stress that our results indicate the formation of polarons at low doping levels and the existence of bipolarons at high doping levels. The presented spectroscopic data are an experimental evidence of the formation of bipolarons in P3HT.     

Silver ion dynamics in the Ag5Te2Cl-polymorphs revealed by solid state NMR lineshape and two- and three-time correlation spectroscopies

The relation between structure and ion dynamics in the three polymorphs of Ag(5)Te(2)Cl has been investigated using (109)Ag, (125)Te, and (35)Cl NMR spectroscopies. Specifically, the influence of the structural phase transitions observed near 240 K (P2(1)/c<-->P2(1)/n) and near 332 K (P2(1)/n<-->I4/mcm) upon silver ion mobilities has been studied by temperature dependent (109)Ag NMR lineshapes and spin-lattice relaxation times. While the superionic high temperature phase alpha-Ag(5)Te(2)Cl is characterized by a molten cationic sublattice, fast ion dynamics in the medium-temperature phase beta-Ag(5)Te(2)Cl occurs in spatially restricted regions comprising all the crystallographically distinct silver sites. Temperature dependent magic-angle-spinning linewidths yield an activation energy of 0.38 eV, consistent with 0.44 eV measured from dc electric conductivities. For the low-temperature gamma-modification, results of two- and three-time (109)Ag correlation spectroscopies provide a detailed insight into the nature of the silver ionic hopping motion. Temperature dependent jump rates measured by two-time correlation functions yield an activation energy E(a)= 0.48 eV. (109)Ag NMR three-time correlation functions indicate that the non-exponential relaxation behavior of the silver ions can be attributed to a broad distribution of jump rates rather than correlated forward-backward jumps. Nevertheless, all the silver ions are mobile down to temperatures of about 185 K.     

Effect of analyte properties on the kinetic performance of liquid chromatographic separations

Advances in modern high-performance liquid chromatography (HPLC) have led to increased interest in the comparison of the ultimate performance limits of methodologies aimed at increasing the resolving power per unit time. Kinetic plot-based methods have proven invaluable in facilitating such evaluations. However, in bridging the gap between fundamental comparisons and the eventual practical applicability of kinetic performance data, the effect of analyte properties have thus far largely been neglected. Using pharmaceutical compounds as representative real-life analytes, it is demonstrated that noteworthy differences in the optimal kinetic performance of a chromatographic system are observed compared to data for common test compounds. For a given stationary phase particle size, higher optimal- and maximum plate numbers, corresponding to increased analysis times, are measured for pharmaceutical compounds. Moreover, it is found that the optimal particle size/maximum pressure combination depends on the analyte under investigation, with the beneficial range of efficiencies for small particles shifted towards higher plate numbers for drug molecules. It is further demonstrated that the pH of the mobile phase plays a crucial role in determining the kinetic performance of pharmaceutical compounds. These data clearly indicate that data for test compounds do not reflect the performance attainable for pharmaceutical compounds and highlights the importance of using real-life samples to perform kinetic evaluations.     

A Spirocyclohexyl Nitroxide Amino Acid Spin Label for Pulsed EPR Spectroscopy Distance Measurements

Site‐directed spin labeling and EPR spectroscopy offer accurate, sensitive tools for the characterization of structure and function of macromolecules and their assemblies. A new rigid spin label, spirocyclohexyl nitroxide α‐amino acid and its N‐(9‐fluorenylmethoxycarbonyl) derivative, have been synthesized, which exhibit slow enough spin‐echo dephasing to permit accurate distance measurements by pulsed EPR spectroscopy at temperatures up to 125 K in 1:1 water/glycerol and at higher temperatures in matrices with higher glass transition temperatures. Distance measurements in the liquid nitrogen temperature range are less expensive than those that require liquid helium, which will greatly facilitate applications of pulsed EPR spectroscopy to the study of structure and conformation of peptides and proteins.     

Bacteria, colonic fermentation, and gastrointestinal health

The colonic microbiota plays an important role in human digestive physiology and makes a significant contribution to homeostasis in the large bowel. The microbiome probably comprises thousands of different bacterial species. The principal metabolic activities of colonic microorganisms are associated with carbohydrate and protein digestion. Nutrients of dietary and host origin support the growth of intestinal organisms. Short-chain fatty acids (SCFAs), predominantly acetate, propionate, and butyrate, are the principal metabolites generated during the catabolism of carbohydrates and proteins. In contrast, protein digestion yields a greater diversity of end products, including SCFAs, amines, phenols, indoles, thiols, CO2, H2, and H2S, many of which have toxic properties. The majority of SCFAs are absorbed from the gut and metabolized in various body tissues, making a relatively small but significant contribution to the body's daily energy requirements. Carbohydrate fermentation is, for the most part, a beneficial process in the large gut, because the growth of saccharolytic bacteria stimulates their requirements for toxic products associated with putrefaction, for incorporation into cellular proteins, thereby protecting the host. However, as digestive materials move along the gut, carbohydrates become depleted, which may be linked to the increased prevalence of colonic disease in the distal bowel.     

Cyclic alumosiloxanes and alumosilicates: exemplifying the Loewenstein rule at the molecular level

The cyclic alumosiloxane [{LAl(μ-O)(Ph(2)Si)(μ-O)}(2)] (3) and alumosilicate [{LAl(μ-O){((t)BuO)(2)Si}(μ-O)}(2)] (4) were obtained by reaction of the appropriate R(2)Si(OH)(2) precursor (R = Ph, O(t)Bu) with [{LAl(H)}(2)(μ-O)] (1), providing a nice illustration of the Loewenstein rule at work at the molecular level.