Instability and entanglement of the ground state of the Dicke model

Using tools of quantum information theory we show that the ground state of the Dicke model exhibits an infinite sequence of instabilities (quantum-phase-like transitions). These transitions are characterized by abrupt changes of the bi-partite entanglement between atoms at critical values kappa(j) of the atom-field coupling parameter kappa and are accompanied by discontinuities of the first derivative of the energy of the ground state. We show that in a weak-coupling limit (kappa1 < or = kappa < or = kappa2) the Coffman-Kundu-Wootters inequalities are saturated, which proves that for these values of the coupling no intrinsic multipartite entanglement (neither among the atoms nor between the atoms and the field) is generated by the atom-field interaction. We show that in the strong-coupling limit the entangling interaction with atoms leads to a highly sub-Poissonian photon statistics of the field mode.     

A photoelectron spectroscopy study of ultra-thin epitaxial alumina layers grown on Cu(111) surface

Thin epitaxial alumina layers were grown on the Cu(111) surface using simultaneous aluminum deposition and oxygen exposure. Different substrate temperatures during the deposition resulted in layers with different thicknesses, growth rates, crystallinity and epitaxy. Low energy electron diffraction measurements confirmed the epitaxial growth for substrate temperatures above 870 K. The Al 2p doublet was studied by means of photoelectron spectroscopy in order to determine the alumina termination at the metal-oxide interface. A strong dependence on the preparation temperature was found and both aluminum and oxygen terminated interfaces were created.     

Flavin–cyclodextrin conjugates: effect of the structure on the catalytic activity in enantioselective sulfoxidations

A series of flavin–cyclodextrin conjugates has been prepared and tested in the enantioselective oxidations of prochiral aromatic and aliphatic sulfides with hydrogen peroxide. The newly prepared conjugates contain isoalloxazinium or alloxazinium moieties attached to the primary rim of α- and β-cyclodextrins at the C-6 positions. In addition, flavinium units were attached to the secondary rim of the β-cyclodextrin macrocycle. The relationship between the structural features and the catalytic performance of the conjugates, including those recently reported by us, was analyzed. The rate and enantioselectivity of the sulfoxidations catalyzed by flavin–cyclodextrin conjugates are influenced mainly by the size of the cyclodextrin cavity, the type of flavin unit (alloxazine or isoalloxazine), and by the relative orientation of the flavin and cyclodextrin moieties.     

Determination of Low Contents of Fenpiverine Bromide by Extraction Spectrophotometry

An ion-pair extraction spectrophotometry method was developed for the determination of fenpiverine bromide in tablets. To determine this substance it was necessary to find experimental conditions that would allow eliminating the influence of other components of the tablets. Attention was paid to the fact that a suitable pH of water phase was necessary to achieve high selectivity.Received December 11, 2002; accepted April 24, 2003 Published online July 28, 2003     

Immobilization in biotechnology and biorecognition: from macro- to nanoscale systems

Biological molecules such as enzymes, cells, antibodies, lectins, peptide aptamers, and cellular components in an immobilized form are extensively used in biotechnology, in biorecognition and in many medicinal applications. This review provides a comprehensive summary of the developments in new immobilization materials, techniques, and their practical applications previously developed by the authors. A detailed overview of several immobilization materials and technologies is given here, including bead cellulose, encapsulation in ionotropic gels and polyelectrolyte complexes, and various immobilization protocols applied onto surfaces. In addition, the review summarises the screening and design of an immobilization protocol, practical applications of immobilized biocatalysts in the industrial production of metabolites, monitoring, and control of fermentation processes, preparation of electrochemical/optical biosensors and biofuel cells.     

Fluorimetric determination of the levels of urinary neopterin and serum thiobarbituric acid reactive substances in the nonagenarians

Twelve self-sustaining nonagenarians, 10 women and two men, aged 94+/-3 years, and eight institutionalised nonagenarians, eight women, aged 91+/-1 year as well as 11 control subjects, seven women and four men, aged 84+/-5 years entered the study. Urinary neopterin, an indicator of systemic immune activation, and serum thiobarbituric acid reactive substances (TBARS), a marker of lipoperoxidation, were determined initially, and collection of the blood and urine samples was repeated at 3-month interval. Neopterin was measured in the urine specimens by reversed-phase high performance liquid chromatography. A C(18) reversed-phase column 3.3x150 mm, 5 mum-diameter packing Separon SGX was used. Potassium phosphate buffer (15 mmol l(-1), pH 6.4) at flow rate of 0.8 ml min(-1) was used as mobile phase. After centrifugation (5 min, 1300xg) and diluting 100 mul of urine specimens with 1.0 ml of mobile phase containing 2 g of disodium-EDTA per litre, a 20 mul sample was injected on a column. Neopterin was identified by its native fluorescence (353 nm excitation, 438 nm emission). Creatinine was determined by Jaffé kinetic reaction after dilution of sample 1:50 (v/v). The concentration of neopterin in urine was expressed as neopterin/creatinine ratio (mumol mol(-1) creatinine). TBARS were determined spectrofluorometrically using LS-5 spectrofluorimeter (excitation wavelength 528 nm, emission wavelength 558 nm) after extraction with n-butanol treatment with thiobarbituric acid. The significance of differences between nonagenarians and control group was examined by ANOVA-Kruskal-Wallis tests, using statistical software NCSS 6.0.21 (Kaysville, UT, 1996). The decision on significance was based on P=0.05. Urinary neopterin was significantly higher in institutionalised compared to self-sustaining subjects and controls (625+/-565 vs. 203+/-63 mumol mol(-1) creatinine, and 198+/-128 mumol mol(-1) creatinine, respectively, P=0.006). The serum TBARS were higher in both groups of nonagenarians (3.23+/-1.16 mumol l(-1) and 2.69+/-0.39 vs. 2.12+/-0.83 mumol l(-1) for the self-sustaining, institutionalised and controls, respectively, P=0.023). We conclude that the fluorimetric determinations of urinary neopterin and serum TBARS can be useful for the monitoring health status in the elderly patients.     

Missing-link macrocycles: hybrid heterocalixarene analogues formed from several different building blocks

The synthesis and structural characterization of hybrid heterocalix[4]arene analogues containing pyrrole, benzene, methoxy-substituted benzene, and pyridine subunits is described. Macrocycles 1 and 2, examples of calix[2]benzene[2]pyrrole and calix[1]benzene[3]pyrrole systems, respectively, are synthesized by the condensation of pyrrole and an appropriate phenylbis(carbinol). Macrocycles 3 and 7, examples of calix[2]benzene[1]pyridine[1]pyrrole and calix[1]pyridine[3]pyrrole, respectively, are synthesized by the use of a carbene-based pyrrole-to-pyridine ring-expansion procedure. Single-crystal X-ray analysis reveals that compounds 1a, 1b, and 2b adopt 1,3-alternate conformations in the solid state, whereas compounds 3 and 7 display structures that are best described as "flattened partial cones" in terms of their conformation. (Series a refers to pure benzene-derived systems, whereas series b indicates macrocycles containing 5-methoxyphenyl subunits). In the solid state, the methoxy-functionalized macrocycles 1b and 2b, and the chloropyridine-containing macrocycle 7 exist as dimers. In the case of 1a and 7, these compounds interact with neutral solvent in the solid state. The conformations of the macrocycles in solution were explored by temperature-dependent proton NMR and NOESY spectral analysis. At 188 K, macrocycles 1a and 2a adopt flattened 1,3-alternate conformations, whereas macrocycles 3 and 7 exist in the form of flattened partial-cone conformations. Standard proton NMR titration analyses were carried out in the case of macrocycles 1a and 2a, and reveal that at least the second of these systems is capable of binding fluoride and chloride anions in CD(2)Cl(2) solution at room temperature (K(a)=571 and 17M(-1) in the case of 2a and F(-) and Cl(-), respectively).     

Vibrational predissociation of H5 +

The full nine-dimensional vibrational Hamiltonian for H5 + described in the literature [Kraemer et al., J. Mol. Spectrosc. 164, 500 (1994)] is adopted here for an approximate evaluation of the spectral linewidths of the observed H-H stretching modes of the H5 + ion and the corresponding modes of its D5 + isotopomer. In this approximation the high dimensionality of the original Hamiltonian is reduced to a three-dimensional model Hamiltonian which takes only the H-H stretching modes and the molecular dissociation mode into consideration assuming that they are adiabatically separable from the remaining modes. To make the calculations numerically feasible, the molecular degenerate ("skeletal") vibrations are assumed to take place in harmonic potentials, and the effect of the internal propeller rotation is completely disregarded. The linewidths calculated in this approximation are too small to explain the broad shapes of the observed spectral transitions. It can thus be argued that the failure to resolve rotational structure in the observed bands is mainly due to spectral congestion and only partly due to predissociation of the H5 + cluster.     

31P chemical shift tensors for canonical and non-canonical conformations of nucleic acids: a DFT study and NMR implications

31P chemical shift anisotropy (CSA) tensors have been calculated for a set of selected DNA and RNA backbone conformations using density functional theory. The set includes canonical A-RNA, A-DNA, BI-DNA, BII-DNA, ZI-DNA, and ZII-DNA as well as four A-RNA-type, seven non-A-RNA-type, and three non-canonical DNA conformations. Hexahydrated dimethyl phosphate has been employed as a model. The 31P chemical shift tensors obtained are discussed in terms of similarities in the behavior observed for gauche-gauche (gg) and gauche-trans (gt) conformations around the P-O bonds. We show that torsion angles alpha and zeta are major determinants of the isotropic chemical shift deltaiso and of the deltaCSA11 component of the traceless chemical shift tensor, which is revealed in separate ranges of both deltaiso and deltaCSA11 for gg- and gt-conformers, respectively. A clear distinction between the two conformation types has not been found for the deltaCSA22 and deltaCSA33 components, which is attributed to their different directional properties. The 31P CSA tensors exhibit considerable variations resulting in large spans of approximately 16 ppm for deltaCSA11 and approximately 22 ppm for deltaCSA22 and deltaCSA33. We examine the consequences of the CSA variations for predicting the chemical shift changes upon partial alignment deltacsa and for the values of CSA order parameters extracted from the analysis of 31P NMR relaxation data. The theoretical 31P CSA tensors as well as the experimental 31P CSA tensor of barium diethyl phosphate (BDEP) are used to calculate deltacsa for two eclipsed orientations of the CSA and molecular alignment tensors. Percentage differences between the CSA order parameters obtained using the theoretical 31P CSA tensors and the experimental 31P CSA tensor of BDEP, respectively, are also determined.     

Negative electrospray, ion trap multistage mass spectrometry of synthetic fragments of the O-PS of Vibrio cholerae O:1

Saccharides (mono through hexasaccharides) that mimic the terminal epitopes of O-antigens of Vibrio cholerae O:1, serotypes Ogawa and Inaba, were studied by electrospray ion trap (ESI IT) mass spectrometry (MS) in the negative mode. Anionized adducts are the characteristic ions formed by the capture of H(3)O(2)(-) under the condition of ESI MS analysis. The reactive species are produced by reaction of hydroxyl anions with the molecule of water. Thus the [M + H(3)O(2)](-) have the highest m/z value in the ESI IT negative mass spectra. After dissociation of adducts by loss of 2H(2)O the [M-H](-) ions are produced. The fragmentation pathways were confirmed by multistage measurements (MS(n)). The predominant pathway of fragmentation of the mono- and oligomers is the elimination of a molecule of alpha- hydroxy--gammabutyrolactone from the 4-(3-deoxy-L-glycero-tetronamido) group. The other characteristic pathway occurs by shortening the length of oligosaccharides. In this way, conversion of the Ogawa to Inaba fragments takes place under the conditions of measurement. Negative ESI MS/MS provided sufficient information about molecular mass, the number of saccharide residues, basic structure of saccharides, about the tetronamide part of the compounds investigated and allowed Ogawa and Inaba serotypes to be distinguished.