Cation complexation by chemically modified calixarenes. 11. Complexation and extraction of alkali cations by calix[5]- and -[6]arene ketones. Crystal and molecular structures of calix[5]arene ketones and Na+ and Rb+ complexes

A series of four calix[5]arenes and three calix[6]arenes (R-calixarene-OCH2COR1) (R = H or Bu-t) with alkyl ketone residues (R-1 = Me or Bu-t) on the lower rim have been synthesized, and their affinity for complexation of alkali cations has been assessed through phase-transfer experiments and stability constant measurements. The conformations of these ketones have been probed by H-1 NMR and X-ray diffraction analysis, and by molecular mechanics calculations. Pentamer 3 (R R-1 = Bu-t) possesses a symmetrical cone conformation in solution and a very distorted cone conformation in the solid state. Pentamer 5 (R = H, R-1 = Bu-t) exists in a distorted 1,2-alternate conformation in the solid state, but in solution two slowly interconverting conformations, one a cone and the other presumed to be 1,2-alternate, can be detected. X-ray structure analysis of the sodium and rubidium perchlorate complexes of 3 reveal the cations deeply encapsulated by the ethereal and carbonyl oxygen atoms in distorted cone conformations which can be accurately reproduced by molecular mechanics calculations. The phase-transfer and stability constant data reveal that the extent of complexation depends on calixarene size and the nature of the alkyl residues adjacent to the ketonic carbonyls with tert-butyl much more efficacious than methyl.

Studies on the biodegradation of fosfomycin: Synthesis of 13C-labeled intermediates, feeding experiments with rhizobium huakuii PMY1, and Isolation of Labeled Amino Acids from Cell Mass by HPLC

Racemic (1R*,2R*)-1,2-dihydroxy-[1- ^{13C ₁]propylphosphonic acid and 1-hydroxy-[1- 13C ₁]acetone were synthesized and fed to R. huakuii PMY1. Alanine and a mixture of valine and methionine were isolated as their N-acetyl derivatives from the cell hydrolysate by reversed-phase HPLC and analyzed by NMR spectroscopy. It was found that the carbon atoms of the respective carboxyl groups were highly 13C-labeled (up to 65 %). Hydroxyacetone is therefore considered an obligatory intermediate of the biodegradation of fosfomycin by R. huakuii PMY1.}

Mapping biological to clinical phenotypes during the development (21 days) and resolution (21 days) of experimental gingivitis

Aim: To characterize and map temporal changes in the biological and clinical phenotype during a 21-day experimental gingivitis study. Materials and Methods: Experimental gingivitis was induced over 21 days in healthy human volunteers (n = 56), after which normal brushing was resumed (resolution phase). Gingival and plaque indices were assessed. Gingival crevicular fluid was collected from four paired test and contra-lateral control sites in each volunteer during induction (Days 0, 7, 14 and 21) and resolution (Days 28 and 42) of experimental gingivitis. Fluid volumes were measured and a single analyte was quantified from each site-specific, 30s sample. Data were evaluated by analysis of repeated measurements and paired sample tests. Results: Clinical indices and gingival crevicular fluid volumes at test sites increased from Day 0, peaking at Day 21 (test/control differences all p

ON THE ORIGIN OF NH IN DIFFUSE INTERSTELLAR CLOUDS

The observation by Meyer & Roch of NH in the interstellar clouds towards zeta Per and HD 27778 cannot be explained with conventional gas-phase chemistry models. A simple non-equilibrium model for the zeta Per cloud, which incorporates the grain-surface production of NH and OH or, alternatively, NH3 and H2O, is able to reproduce the abundances of all observed species (except CH+) quite accurately. Moreover, chemical models which include grain-surface reactions can reproduce the observed abundance not only of NH but also of CN, which is efficiently formed at low temperatures, initiated by the reaction of NH with C+. Pure gas-phase models and cloud interface models, in which NH and CH+ are formed in a warm and tenuous environment, fail to explain the observed high abundance of CN. Hence the observation of NH in zeta Per and HD 27778 provides evidence for the presence of grain-surface reactions leading to molecules other than H-2. It is predicted that NH2 and NH3 should have abundances not much below that of NH if NH3 instead of NH is formed on grains. With or without surface reactions, the column densities of H2O and C2H are expected to be about 10(13) cm-2, and these molecules may be detectable in the zeta Per cloud.

Identification and molecular cloning of a novel amphibian Bowman Birk-type trypsin inhibitor from the skin of the Hejiang Odorous Frog; Odorrana hejiangensis.

In this study, an amphibian (Odorrana hejiangensis) skin extract was fractionated by reverse phase HPLC and fractions were screened for trypsin inhibitory activity. Using this initial approach, a novel trypsin inhibitory peptide was detected with an apparent protonated molecular mass of 1804.83Da, as determined by MALDI-TOF mass spectrometry. It was named Hejiang trypsin inhibitor (HJTI) in accordance. The primary structure of the biosynthetic precursor of HJTI was deduced from a cDNA sequence cloned from a skin-derived cDNA library. The primary structure of the encoded predicted mature active peptide was established as: GAPKGCWTKSYPPQPCS (non-protonated monoisotopic molecular mass - 1802.81Da). On the basis of this unequivocal amino acid sequence, a synthetic replicate was synthesized by solid phase Fmoc chemistry. This replicate displayed a moderately potent trypsin inhibition with a K(i) of 388nM. Bioinformatic analysis of the primary structure of this peptide indicated that it was a member of the Bowman-Birk family of protease inhibitors. The substitutions of Gln-14 and Ser-17 by Lys, resulted in an increase in cationicity and a small increase in potency to a K(i) value of 218nM. Neither HJTI nor its synthetic analog, possessed any significant antimicrobial activity.

Liquid-liquid slug flow: Hydrodynamics and pressure drop

In this paper, the hydrodynamics and the pressure drop of liquid-liquid slug flow in round microcapillaries are presented. Two liquid-liquid flow systems are considered, viz. water-toluene and ethylene glycol/water-toluene. The slug lengths of the alternating continuous and dispersed phases were measured as a function of the slug velocity (0.03-0.5 m/s), the organic-to-aqueous flow ratio (0.1-4.0), and the microcapillary internal diameter (248 and 498 mu m). The pressure drop is modeled as the sum of two contributions: the frictional and the interface pressure drop. Two models are presented, viz, the stagnant film model and the moving film model. Both models account for the presence of a thin liquid film between the dispersed phase slug and the capillary wall. It is found that the film velocity is of negligible influence on the pressure drop. Therefore, the stagnant film model is adequate to accurately predict the liquid-liquid slug flow pressure drop. The influence of inertia and the consequent change of the slug cap curvature are accounted for by modifying Bretherton's curvature parameter in the interface pressure drop equation. The stagnant film model is in good agreement with experimental data with a mean relative error of less than 7%.

Hydrodynamics and mixer-induced bubble formation in micro bubble columns with single and multiple-channels

A hydrodynamic characterization of an industrially used gas-liquid contacting microchannel. device is discussed, viz. the micro bubble column of IMM. Furthermore, similar characterization of a gas-liquid flow microchip of TU/e, with two tailored mixer designs, is used to solve fundamental issues on hydrodynamics, and therefore, to achieve further design and operating optimization of that chip and the IMM device. Flow pattern maps are presented in a dimensionless fashion for further predictions on new fluidic systems for optimum single-channel multiphase operation. Bubble formation was investigated in the two types of mixers and pinch-off and hydrodynamic decay mechanisms are observed. The impact of these mechanisms on bubble size, bubble size distributions, and on the corresponding flow patterns, i.e., the type of mixer design, can be decisive for the flow pattern map and thus, may be used to alter flow pattern maps. The bubble sizes and their distribution were improved for the tailored designs, i.e., smaller and more regular bubbles were generated. Finally, the impact of multi-channel distribution for gas and liquid flow is demonstrated. Intermediate flow patterns such as slug-annular flow, also found for single-phase operation, and the simultaneous coexistence of flow regimes are presented, with the latter providing evidence of flow maldistribution.

Non-radial pulsation, rotation and outburst in the Be star omega Orionis from the MuSiCoS 1998 campaign

omega Ori (HD37490, HR1934) is a Be star known to have presented variations. In order to investigate the nature and origin of its short-term and mid-term variability, a study is performed of several spectral lines (Halpha, Hdelta, HeI 4471, 4713, 4921, 5876, 6678, CII 4267, 6578, 6583, Mg II 4481, Si III 4553 and Si II 6347), based on 249 high signal-to-noise high-resolution spectra taken with 8 telescopes over 22 consecutive nights during the MuSiCoS (Multi SIte COntinuous Spectroscopy) campaign in November-December 1998. The stellar parameters are revisited and the projected rotational velocity (v sin i = 179 km s(-1)) is redetermined using several methods. With the MuSiCoS 98 dataset, a time series analysis of line-profile variations (LPVs) is performed using the Restricted Local Cleanest (RLC) algorithm and a least squares method. The behaviour of the velocity of the centroid of the lines, the equivalent widths and the apparent vsini for several lines, as well as Violet and Red components of photospheric lines affected by emission (red He i lines, Si II 6347, CII 6578, 6583) are analyzed. The non-radial pulsation (NRP) model is examined using phase diagrams and the Fourier-Doppler Imaging (FDI) method. The LPVs are consistent with a NRP mode with l = 2 or 3, \m\ = 2 with frequency 1.03 cd(-1). It is shown that an emission line outburst occurred in the middle of the campaign. Two scenarios are proposed to explain the behaviour of a dense cloud, temporarily orbiting around the star with a frequency 0.46 c d(-1), in relation to the outburst.

APEASPFIRFamide, a novel FMRFamide-related decapeptide from Caenorhabditis elegans: Structure and myoactivity

To date, 9 FMRF amide-related peptides (FaRPs) have been identified in Caenorhabditis elegans. Eight of these peptides are encoded on the flp-1 gene. However, AF2 (KHEYLRF amide) which was not co-encoded was the most abundant FaRP identified in ethanolic extracts. Further radioimmunometrical screening of acidified ethanol extracts of C. elegans has revealed the presence of other novel FaRPs, which are not encoded on the flp-l gene. One of these peptides has been isolated by sequential rpHPLC and subjected to Edman degradation analysis and gas-phase sequencing and the unequivocal primary structure of the decapeptide Ala-Pro-Glu-Ala-Ser-Pro-Phe-Ile-Arg-Phe-NH2 was determined following a single gas-phase sequencing run. The molecular mass of the peptide was found to be 1133.7 Ha, determined using a time-of-flight mass spectrometer. Synthetic replicates of this peptide were found to induce a profound relaxation of both dorsal and ventral somatic muscle-strip preparations of Ascaris suum with a threshold for activity of 10 nM. The inhibitory response was not dependent on the presence of nerve cords, indicating a post-synaptic site-of-action. The relaxation was Ca++- and Cl--independent but was abolished in high-KI medium and could be distinguished from those of other inhibitory nematode FaRPs, including PF1 (SDPNFLRFamide)and PF1 (KPNFIRF amide). (C) 1997 Academic Press.

Cavity cooling of atoms: Within and without a cavity

We compare the efficiencies of two optical cooling schemes, where a single particle is either inside or outside an optical cavity, under experimentally-realisable conditions. We evaluate the cooling forces using the general solution of a transfer matrix method for a moving scatterer inside a general one-dimensional system composed of immobile optical elements. Assuming the same atomic saturation parameter, we find that the two cooling schemes provide cooling forces and equilibrium temperatures of comparable magnitude.

Design and experimental validation of liquid crystal-based reconfigurable reflectarray elements with improved bandwith in F-band

A reconfigurable reflectarray which exploits the dielectric anisotropy of liquid crystals (LC) has been designed to operate in the frequency range from 96 to 104 GHz. The unit cells are composed of three unequal length parallel dipoles placed above an LC substrate. The reflectarray has been designed using an accurate model which includes the effects of anisotropy and inhomogeneity. An effective permittivity that accounts for the real effects of the LC has also been used to simplify the analysis and design of the unit cells. The geometrical parameters of the cells have been adjusted to simultaneously improve the bandwidth, maximize the tunable phase-range and reduce the sensitivity to the angle of incidence. The performance of the LC based unit cells has been experimentally evaluated by measuring the reflection amplitude and phase of a reflectarray consisting of 52x54 identical cells. The good agreement between measurements and simulations validate the analysis and design techniques and demonstrate the capabilities of the proposed reflectarray to provide beam scanning in F band.

Epitaxial Magnetic Oxide Nanocrystals Via Phase Decomposition of Bismuth Perovskite Precursors

The phase instability of bismuth perovskite (BiMO₃), where M is a ferromagnetic cation, is exploited to create self-assembled magnetic oxide nanocrystal arrays on oxide supports. Conditions during pulsed laser deposition are tuned so as to induce complete breakdown of the perovskite precursor into bismuth oxide (Bi₂ O₃ ) and metal oxide (M-O_x ) pockets. Subsequent cooling in vacuum volatizes the Bi₂ O₃ leaving behind an array of monodisperse nanocrystals. In situ reflective high energy electron diffraction beam is exploited to monitor the synthesis in real-time. Analysis of the patterns confi rms the phase separation and volatization process. Successful synthesis of M-O_x, where M = Mn, Fe, Co, and Cr, is shown using this template-free facile approach. Detailed magnetic characterization of nanocrystals is carried out to reveal the functionalities such as magnetic anisotropy as well as larger than bulk moments, as expected in these oxide nanostructures.

Yersinia pseudotuberculosis and Yersinia pestis show increased outer membrane permeability to hydrophobic agents which correlates with lipopolysaccharide acyl-chain fluidity

The hydrophobic probe N-phenyl-1-naphthylamine accumulated less in non-pathogenic Yersinia spp. and non-pathogenic and pathogenic Yersinia enterocolitica than in Yersinia pseudotuberculosis or Yersinia pestis. This was largely due to differences in the activity of efflux systems, but also to differences in outer membrane permeability because uptake of the probe in KCN/arsenate-poisoned cells was slower in the former group than in Y. pseudotuberculosis and Y. pestis. The probe accumulation rate was higher in Y. pseudotuberculosis and Y. pestis grown at 37 degrees C than at 26 degrees C and was always highest in Y. pestis. These yersiniae had LPSs with shorter polysaccharides than Y. enterocolitica, particularly when grown at 37 degrees C. Gelliquid-crystalline phase transitions (Tc 28-31 degrees C) were observed in LPS aggregates of Y. enterocolitica grown at 26 and 37 degrees C, with no differences between non-pathogenic and pathogenic strains. Y. pseudotuberculosis and Y. pestis LPSs showed no phase transitions and, although the fluidity of LPSs of Y. pseudotuberculosis and Y. enterocolitica grown at 26 degrees C were close below the Tc of the latter, they were always in a more fluid state than Y. enterocolitica LPS. Comparison with previous studies of Salmonella choleraesuis subsp. choleraesuis serotype minnesota rough LPS showed that the increased fluidity and absence of transition of Y. pseudotuberculosis and Y. pestis LPSs cannot be explained by their shorter polysaccharides and suggested differences at the lipid A/core level. It is proposed that differences in LPS-LPS interactions and efflux activity explain the above observations and reflect the adaptation of Yersinia spp. to different habitats.

Using sketch-map coordinates to analyze and bias molecular dynamics simulations

When examining complex problems, such as the folding of proteins, coarse grained descriptions of the system drive our investigation and help us to rationalize the results. Oftentimes collective variables (CVs), derived through some chemical intuition about the process of interest, serve this purpose. Because finding these CVs is the most difficult part of any investigation, we recently developed a dimensionality reduction algorithm, sketch-map, that can be used to build a low-dimensional map of a phase space of high-dimensionality. In this paper we discuss how these machine-generated CVs can be used to accelerate the exploration of phase space and to reconstruct free-energy landscapes. To do so, we develop a formalism in which high-dimensional configurations are no longer represented by low-dimensional position vectors. Instead, for each configuration we calculate a probability distribution, which has a domain that encompasses the entirety of the low-dimensional space. To construct a biasing potential, we exploit an analogy with metadynamics and use the trajectory to adaptively construct a repulsive, history-dependent bias from the distributions that correspond to the previously visited configurations. This potential forces the system to explore more of phase space by making it desirable to adopt configurations whose distributions do not overlap with the bias. We apply this algorithm to a small model protein and succeed in reproducing the free-energy surface that we obtain from a parallel tempering calculation.

Scaling of the entanglement spectrum near quantum phase transitions

The entanglement spectrum describing quantum correlations in many-body systems has been recently recognized as a key tool to characterize different quantum phases, including topological ones. Here we derive its analytically scaling properties in the vicinity of some integrable quantum phase transitions and extend our studies also to nonintegrable quantum phase transitions in one-dimensional spin models numerically. Our analysis shows that, in all studied cases, the scaling of the difference between the two largest nondegenerate Schmidt eigenvalues yields with good accuracy critical points and mass scaling exponents.