Flat manifolds isospectral on p-forms

We study isospectrality on p-forms of compact flat manifolds by using the equivariant spectrum of the Hodge-Laplacian on the torus. We give an explicit formula for the multiplicity of eigenvalues and a criterion for isospectrality. We construct a variety of new isospectral pairs, some of which are the first such examples in the context of compact Riemannian manifolds. For instance, we give pairs of flat manifolds of dimension n=2p, p≥2, not homeomorphic to each other, which are isospectral on p-forms but not on q-forms for q∈p, 0≤q≤n. Also, we give manifolds isospectral on p-forms if and only if p is odd, one of them orientable and the other not, and a pair of 0-isospectral flat manifolds, one of them Kähler, and the other not admitting any Kähler structure. We also construct pairs, M, M′ of dimension n≥6, which are isospectral on functions and such that β_p(M)<β_p(M’), for 04 and ? ₂ ² , respectively.     

A new cobalt carbonyl-carbon disulphide cluster containing a Co3C and a Co3S pyramid symmetrically linked by a CS2-bridge: sym-SCo6(CO)16C(CS2)

sym-(CO)₉Co₃C(CS₂)Co₃(CO)₇S has been isolated from the mixture formed in the reaction of Co₂(CO)₈ with CS₂. This is the fifth member of the C_mS_nCo_p(CO)_q family identified by X-ray diffraction studies. The molecular structure of the title compound is discussed and briefly compared with that of the asymmetric isomer and related compounds.     

Investigation of the heterogeneity of hemoglobin by cation-exchange chromatography on Bio-REX 70

The use of Bio-Rex 70 cation-exchange resin for chromatography of normal and diabetic hemoglobin provides a reproducible pattern of the "fast components". Particular attention to the choice of sample preparation, pH of elution, and the increase of ionic strength by sodium chloride linear gradients results in the separation of Hb-A1b into two components and in the isolation of a new component eluting between Hb-A1c and Hb-A0. Experiments with [3H]glucose and the colorimetric test (thiobarbituric acid) normally used to determine the extent of non-enzymatic glycosylation, as well as an increase of this component in diabetic samples compared with normoglycemic ones and a significant linear correlation with Hb-A1c, indicate that this component should be a part of the hemoglobins glucosylated on the epsilon-NH2 group of the lysines of both chains and/or the hemoglobin glucosylated on the alpha-NH2 of the valine of the alpha-chain. We propose to call this component Hb-A1x, pending confirmation of its identity. Normally Hb-A1x accounts for about 3% of Hb-A, but up to 5-7% of glucosylated hemoglobins should be confined to the early part of Hb-A0. In diabetics, the percentage of Hb-A1x rises to 4-5% and that of the other glucosylated hemoglobins increases to 12-16%.     

Hydrogel supported chiral imidazolidinone for organocatalytic enantioselective reduction of olefins in water

Chiral products play an important role particularly in the field of medicinal chemistry, where it is known that enantiomers often have very different biological properties and effects. One of the most powerful tool to obtain a product as a single enantiomer is asymmetric catalysis. Recently, organocatalysis, i.e. the use of small organic molecules to catalyze enantioselective transformations, has emerged as a prominent field in asymmetric synthesis. In this work, the use of hydrogels as a support for a chiral imidazolidinone organocatalyst (MacMillan catalyst) and its application in the reduction of activated olefins mediated by the Hantzsch ester is reported for the first time. Results showed a good activity of hydrogels in respect to both yield and enantioselection.     

Modeling the Evolution and Rupture of Pendular Liquid Bridges in the Presence of Large Wetting Hysteresis

A model has been developed to predict the shape evolution, rupture distance and postrupture liquid distribution of a pendular liquid bridge between two unequally sized spherical particles in the presence of wetting hysteresis. Two different simplifications of the bridge geometry were considered: a toroidal and a parabolic approximation. The liquid bridge was assumed to rupture through its thinnest neck leaving liquid distributed on each sphere. Experimental measurements showed that the rupture distance was well predicted by both profile approximations by assuming that rupture occurred when the liquid-vapor interfacial area of the bridge and the postrupture droplets was equal. Both bridge profile approximations only correctly predicted the evolution of the apparent contact angle and the extent of postrupture liquid distribution when the solid-liquid interfacial area measured throughout the separation was included in the calculations. This is because during the pendular liquid bridge elongation, the three-phase contact line usually begins to slip on at least one of the spheres. The parabolic profile approximation was slightly more accurate than the toroidal one. The toroidal approximation is more difficult to use because one of the parameters passes through infinity as the bridge changes from convex to concave in shape. In some cases the toroidal approximation was also unable to generate a solution. Copyright 2000 Academic Press.     

Further EPR-spin trapping studies of the photoinitiating activity of Irgacure 369

The radicals formed upon visible light irradiation of the photoinitiator 2-benzyl-2-dimethylamino-4′-morpholinobutyrophenone (Irgacure 369), 1, were investigated by means of EPR spectroscopy coupled with the spin trapping technique both in the absence and in the presence of a monomer. The results suggest a dual behavior of 1 that may act both as a Type I and a Type II photoinitiator. From experiments carried out in the presence of 2-ethoxythioxanthone (Pila 124), 2, an additive commonly used in combination with 1 as sensitizer, it is inferred that 2 mainly acts via hydrogen abstraction from 1.     

Orientation-selective incorporation of transmembrane F0F1 ATP synthase complex from micrococcus luteus in polymer-supported membranes

We report the vectorial incorporation of a highly asymmetric F0F1 ATP synthase complex from Micrococcus luteus into polymer-supported membranes. Dynamic light scattering and cryo electron microscopy confirm that the use of weak surfactants (bile acid) allows for the non-disruptive protein incorporation into lipid vesicles. Spreading of vesicles with ATP synthase onto a cellulose support results in a homogeneous distribution of proteins, in contrast to a patchy image observed on bare glass slides. The orientation of ATP synthase can be identified using an antibody to the ATP binding site as well as from topographic profiles of the surface. The method to "align" transmembrane proteins in supported membranes would open a possibility to quantify protein functions in biomimetic model systems.     

Optimization of a rapid capillary electrophoresis ESI-IT tandem mass spectrometry method for the analysis of short-chain carnitines in human plasma

A capillary electrophoresis (CE) method coupled to electrospray ionization ion trap tandem mass spectrometry (ESI-IT-MS/MS) is described for the rapid analysis of carnitine, acetylcarnitine, and propionylcarnitine in human plasma. Optimization of the procedure was achieved by a reduced sample pretreatment and after examining several physicochemical parameters that influence both the CE separation and the MS analytes detection. The analysis of total carnitine in human plasma after hydrolysis of short-chain metabolites is also shown. The analysis of carnitine and metabolites was obtained in less than 10 min using a 200 mM ammonium formate buffer, pH 2.5, with high sensitivity and specificity using the MS detection in product ion scan mode. The method was tested for quantitative recovery using dialyzed human plasma as matrix and showed linearity in the concentrations ranges 20–160, 1–32, and 0.25–8 μM for carnitine, acetylcarnitine, and propionylcarnitine with (squared) correlation coefficients of 0.9984, 0.9995, and 0.9991, respectively. The intraday and intermediate analysis repeatability and accuracy are within 15% of relative standard deviation (RSD) at low, medium, and high concentration and within/or slight exceeding 20% at the lower limit of quantitation (LLOQ). The method is sensitive for determining carnitine and its metabolites in human plasma with high specificity.