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PubMed2006

Comparison of decanethiolate gold nanoparticles synthesized by one-phase and two-phase methods.

We investigated the differences between the decanethiolate gold nanoparticles synthesized by two different routes: one-phase and two-phase methods. Their properties were compared in bulk and at the air-water interface by transmission electron microscopy (TEM), X-ray reflectivity (XR), extended X-ray absorption fine structure (EXAFS) spectroscopy, X-ray powder diffraction (XRD), thermal gravimetric analysis (TGA), time-of-flight secondary-ion mass spectrometry (TOF-SIMS), electron paramagnetic resonance (EPR), and Langmuir-Blodgett technique. The mean nanoparticles sizes obtained by EXAFS and XRD were found to be smaller than those by the TEM measurements. We explained these differences by the structural disorder and multiple twinning in the nanoparticles. The one-phase particles were found by EXAFS to be smaller and had a higher grafting density of thiol chains than the two-phase particles. We attributed these differences to the enhanced disorder of the one-phase particles. At the air-water interface, the one-phase particles did not spread, while the two-phase particles spread and formed Langmuir films. TEM and XR results revealed that the close-packed monolayer of the two-phase particles collapsed and folded into multilayer films upon further compression.

Journal Article↗
PubMed2003

Comprehensive coupled reversed-phase reversed-phase separations of a complex isomeric mixture.

Using predictions based on results obtained from Information Theory and Factor Analysis for the two-dimensional separation of a complex isomeric mixture, a practical experimental comprehensive coupled reversed phase-reversed phase chromatographic system was developed. In total four reversed phase-reversed phase systems were studied, each of which theory predicted would be able to resolve essentially equal numbers of components. However, in practice only one of these coupled systems realised the theoretical potential. This system employed as the first dimension, a C18 stationary phase with methanol as the mobile phase and as the second dimension, carbon clad zirconia as the stationary phase and acetonitrile as the mobile phase. In this system, 27 of the 32 isomers of a mixture of oligostyrenes were resolved. Failure of the remaining coupled systems to achieve the theoretical potential was attributed to high solute crowding, low efficiency of separation space utilisation and long analysis times in the second dimension.

Journal Article↗
PubMed1999

Head-up tilt testing potentiated with oral nitroglycerin: a randomized trial of the contribution of a drug-free phase and a nitroglycerin phase in the diagnosis of neurally mediated syncope.

BACKGROUND: Since the pharmacological challenge with nitroglycerin (NTG) follows the initial drug-free phase in current tilt testing protocols, the effects of nitroglycerin alone and the appropriate duration of the basal phase are unknown. METHODS: To optimize the test, a randomized intra-patient comparison of two protocols was undertaken: a conventional nitroglycerin test (cHUT) consisting of passive upright posture at 60 degrees for 45 min followed, if negative, by sublingual NTG 0.4 mg spray, with the test continued for 20 min; and, accelerated nitroglycerin test (aHUT) consisting of passive upright posture at 60 degrees for 5 min--to rule out orthostatic hypotension--followed by sublingual NTG 0.4 mg spray, with the test continued for 20 min. Eighty-four consecutive patients (33 males; mean age 55+/-22) with unexplained syncope underwent both cHUT and aHUT in a randomized sequence with a 24-72 h interval between them. Additionally, 25 age-matched control subjects underwent aHUT. RESULTS: In the drug-free phase, cHUT was positive in 15/84 patients (18%) and aHUT in 1/84 patients (1%). After NTG, cHUT and aHUT showed the same positivity rate of 33% (28/84 patients). The overall positivity rate was therefore higher with cHUT than with aHUT (51% vs 35%, P=0.04). Times to syncope were 29+/-12 min, (range 2-44) for cHUT drug-free phase, 5+/-2 min (range 2-9) for cHUT NTG phase, and 5+/-2 min (range 2-9) for aHUT. Only one (4%) of the control subjects had a positive response to aHUT. CONCLUSIONS: The contribution of NTG to the diagnosis is independent of the presence of an unmedicated phase. The appropriate duration of the NTG phase is 10 min. aHUT has good specificity, but a positivity rate lower than cHUT; thus a drug-free phase is necessary to increase the sensitivity of the test.

Administration, Oral↗
PubMed2002

n:m phase synchronization with mutual coupling phase signals.

We generalize the n:m phase synchronization between two chaotic oscillators by mutual coupling phase signals. To characterize this phenomenon, we use two coupled oscillators to demonstrate their phase synchronization with amplitudes practically noncorrelated. We take the 1:1 phase synchronization as an example to show the properties of mean frequencies, mean phase difference, and Lyapunov exponents at various values of coupling strength. The phase difference increases with 2pi phase slips below the transition. The scaling rules of the slip near and away from the transition are studied. Furthermore, we demonstrate the transition to a variety of n:m phase synchronizations and analyze the corresponding coupling dynamics. (c) 2002 American Institute of Physics.

Journal Article↗
PubMed2004

The role of pore size and stationary phase composition in preventing aqueous-induced retention time loss in reversed-phase HPLC.

The phenomenon of aqueous mobile phase induced retention time loss, which has also been referred to as phase-collapse behavior, is investigated using a variety of stationary phases with an aqueous mobile phase. The loss of retention of several water-soluble B vitamins is measured as a function of silica pore size, bonded-phase chemistry, and bonded stationary phase density. It is found that these variables influence the magnitude of the retention time loss behavior and that controlling/optimizing these variables can result in a stationary phase with sufficient retention of the analyte without the column exhibiting the so-called phase-collapse behavior.

Journal Article↗
PubMed1991

The study of lipid-protein interactions: effect of melittin on phase transition of phosphatidylethanolamine and sensitivity of phospholipases to phase state.

The effects of melittin on the bilayer-to-inverted hexagonal (HII) phase transition of egg phosphatidylethanolamine (EPE) and the influence of the phase state of membrane matrix on hydrolysis of EPE by phospholipases have been studied. The phase transitions were measured using the fluorescent probe N-(7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylethanolamine (N-NBD-PE) and differential scanning calorimetry. In the presence of melittin at a lipid-to-melittin molar ratio (R1) of 200, 100, and 20, the phase transition of EPE disappeared, indicating that melittin stabilizes the bilayer structure. In the presence of 10 mol% of cholesterol, the phase transition temperature (TH) decreased and TH was observed even in the presence of melittin at R1 of 200 and 100. The fluorescence intensity of the tryptophan residue of melittin is sensitive to the phase transition and the wavelength of emission maxima shift from 352 to 337 nm upon addition of EPE and EPE-cholesterol (10 mol%) at R1 of 200. Kinetic parameters for phospholipase-catalyzed hydrolysis of EPE in bilayer and HII phases showed that HII phase of EPE is a poorer substrate for phospholipases and that cholesterol decreases the susceptibility of EPE to phospholipases.

Enzyme Stability↗
PubMed2005

Phase-dependent treatment of delayed sleep phase syndrome with melatonin.

STUDY OBJECTIVE: Delayed sleep phase syndrome (DSPS) is a circadian-rhythm sleep disorder characterized by abnormally late sleep and wake times. Melatonin, taken in the evening, advances sleep and circadian phase in patients with DSPS. However, little is known about the most effective dose or time of administration. In the present study, we tested the effectiveness of melatonin to advance the timing of sleep and circadian phase in individuals with DSPS. DESIGN: Following baseline assessment of sleep and circadian phase, subjects were randomly assigned to 1 of 3 treatment groups. The administration of melatonin (0.3 or 3.0 mg) or placebo was double-blinded. SETTING: All procedures were conducted on an outpatient basis. PARTICIPANTS: Thirteen subjects with DSPS, recruited via flyers, advertisements, and referrals from the Sleep Clinic, completed this study. INTERVENTIONS: Melatonin (0.3 or 3.0 mg) or placebo was administered between 1.5 and 6.5 hours prior to dim light melatonin onset for a 4-week period. MEASUREMENTS AND RESULTS: Both doses of melatonin advanced the circadian phase of endogenous melatonin. The magnitude of phase advance in dim-light melatonin onset correlated strongly with the time of melatonin administration, with earlier times being more effective (r2 = 0.94, P < .0001). Similar, though weaker, relationships were obtained between the timing of melatonin administration and changes in sleep time. CONCLUSIONS: These results indicate that melatonin advances the circadian clock and sleep in patients with DSPS in a phase-dependent manner. This is the first study that reports a relationship between timing of melatonin administration and phase changes in patients with DSPS.

Adult↗
PubMed2001

Damage-spreading phase and damage-frozen phase in a solid-on-solid model.

Based on the recently suggested scaling ansatz [Phys. Rev. E 62, 3376 (2000)] for damage spreading in the surface roughening phenomenon, the characteristics of the damage-spreading phase and damage-frozen phase in a two-dimensional solid-on-solid model that has a roughening transition at T=T(R) are studied. In the damage-spreading phase, which exists for T>T(R), the average vertical damage-spreading distance d(perpendicular)(d(//)=0,L,T) and the average lateral damage-spreading distance D(//)(L,T) are shown to satisfy d(perpendicular)(d(//)=0,L,T) approximately ln L and D(//)(L,T) approximately L, respectively. In the damage-frozen phase, which exists for T infinity,T) approximately finite and D(//)(L-->infinity,T) approximately finite. From these results it is concluded that the damage-spreading phase describes the surface roughening phase well and the damage-frozen phase describe the smooth phase well.

Journal Article↗
PubMed2001

Phase synchronization of chaotic systems with small phase diffusion.

The geometric theory of phase locking between periodic oscillators is extended to phase coherent chaotic systems. This approach explains the qualitative features of phase locked chaotic systems and provides an analytical tool for a quantitative description of the phase locked states. Moreover, this geometric viewpoint allows us to identify obstructions to phase locking even in systems with negligible phase diffusion, and to provide sufficient conditions for phase locking to occur. We apply these techniques to the Rössler system and a phase coherent electronic circuit and find that numerical results and experiments agree well with theoretical predictions.

Journal Article↗
PubMed2002

Metastable liquid-liquid phase transition in a single-component system with only one crystal phase and no density anomaly.

We investigate the phase behavior of a single-component system in three dimensions with spherically-symmetric, pairwise-additive, soft-core interactions with an attractive well at a long distance, a repulsive soft-core shoulder at an intermediate distance, and a hard-core repulsion at a short distance, similar to potentials used to describe liquid systems such as colloids, protein solutions, or liquid metals. We showed [Nature (London) 409, 692 (2001)] that, even with no evidence of the density anomaly, the phase diagram has two first-order fluid-fluid phase transitions, one ending in a gas-low-density-liquid (LDL) critical point, and the other in a gas-high-density-liquid (HDL) critical point, with a LDL-HDL phase transition at low temperatures. Here we use integral equation calculations to explore the three-parameter space of the soft-core potential and perform molecular dynamics simulations in the interesting region of parameters. For the equilibrium phase diagram, we analyze the structure of the crystal phase and find that, within the considered range of densities, the structure is independent of the density. Then, we analyze in detail the fluid metastable phases and, by explicit thermodynamic calculation in the supercooled phase, we show the absence of the density anomaly. We suggest that this absence is related to the presence of only one stable crystal structure.

Journal Article↗
PubMed2005

Dielectric spectroscopy of a binary mixture of liquid crystals showing wide temperature range twisted grain boundary phase with re-entrant cholesteric phase.

There are only few materials, which have shown long temperature range twisted grain boundary (TGB) phases. One such material is the chiral binary mixture of 7OCB and 5* CBB (mole ratio 0.8 and 0.2) which shows unique phase sequence of cholesteric ( N*) , a wide temperature range TGBA (approximately 31 degrees C) and reentrant cholesteric (N*re) phases. In the present work we are reporting the dielectric spectroscopy of the above mixture with a chiral analog of earlier reported nematic (N) , smectic- A (SmA) , and reentrant nematic (Nre) phase sequences [Phys. Rev. A 46, 7733 (1992)] for different conditions of molecular orientations. Two modes of dielectric relaxations have been detected in a homeotropically aligned sample with unusually low relaxation frequencies for one of them. Planar oriented molecules in the TGBA phase show a soft mode of relaxation and support the recently proposed theory for the soft mode relaxation of the TGBA phase [Phys. Rev. E 65, 11701 (2001)]. By applying the dc electric field on planar oriented molecules in the TGBA phase, it has been possible to obtain a helix free homeotropically aligned TGBA phase.

Journal Article↗
PubMed1991

A multisolution method of phase determination by combined maximization of entropy and likelihood. V. The use of likelihood as a discriminator of phase sets produced by the SAYTAN program for a small protein.

The use of a likelihood criterion associated with maximum-entropy (ME) extrapolation for selecting phase sets as part of a new multisolution phasing strategy, already applied to solving small crystal structures from single-crystal data [Gilmore, Bricogne & Bannister (1990). Acta Cryst. A46, 297-308] and X-ray powder diffraction data [Gilmore, Henderson & Bricogne (1991). Acta Cryst. A47, 830-841], has been tested on the small protein avian pancreatic polypeptide (APP) with 301 non-H atoms in the asymmetric unit in space group C2. A collection of 50 phase sets for APP were provided by Woolfson & Yao. They had been generated from random starting phases by the SAYTAN procedure [Woolfson & Yao (1990). Acta Cryst. A46, 409-413] using data to a resolution of 0.98 A. Six of these had an unweighted mean absolute phase error, mean value of magnitude of delta phi, of less than 50 degrees, the remainder having phase errors of 60 degrees or more. However, none of the conventional figures of merit were able to identify these preferred sets. Each phase set was subjected to our standard procedure of entropy maximization and of evaluation of the log-likelihood gain resulting from the associated ME extrapolation. With only a small subset of data (to 2 A resolution), the likelihood criterion identified unambiguously the phase sets with mean value of magnitude of delta phi less than 50 degrees. In contrast, conventional figures of merit showed no such ability.(ABSTRACT TRUNCATED AT 250 WORDS)

Pancreatic Polypeptide↗
PubMed1999

PBR: a heavy-atom refinement and phasing procedure to reduce phase bias when heavy-atom derivatives contain common sites.

A procedure, called PBR (phase-bias reduction), has been developed to properly refine heavy-atom derivatives and to generate less biased heavy-atom phases when these derivatives contain common heavy-atom sites. Two independent events are obtained by splitting the refinement and phasing calculations into two stages, the first in which one of the derivatives having common sites is used together with the native amplitudes and the second in which both derivatives with common sites are used simultaneously, with one of them being used as the native data set. Improved centroid phases and the corresponding figures of merit are obtained by phase combination. This procedure has been used in the structure determination of the iron-cluster-containing protein -pyruvate-ferredoxin oxidoreductase. When the common heavy-atom sites are properly treated by the PBR procedure, the resulting calculated centroid phases are improved with respect to classical heavy-atom refinement centroid phases where all derivatives are refined together. This leads to improved electron-density distributions, since anomalous difference Fourier maps calculated with the PBR-refined centroid phases and corresponding figures of merit show more clearly the positions of the iron sites.

Methods↗
PubMed1997

Masking period patterns of Schroeder-phase complexes: effects of level, number of components, and phase of flanking components.

Masking period patterns (MPPs) were obtained for maskers consisting of harmonics 2-20 of a 100-Hz fundamental. The signal was always a 5-ms 1100-Hz sinusoid presented 152, 154, 156, 158, or 160 ms after the start of a 400-ms masker. Experiment 1 replicated the finding that, for a masker level of 69 dB component, the shape of the MPP depended strongly on the phases of the components: Summing them in positive Schroeder phase led to a threshold variation of about 18 dB across the MPP, but summing them in negative Schroeder phase produced a flat MPP [A. Kohlrausch and A. Sander, J. Acoust. Soc. Am. 97, 1817-1829 (1995)]. Reducing the level of the positive-phase masker resulted in a systematic flattening of the MPP, whereas the negative-phase MPPs were flat both at high and at low levels. Experiment 2 showed that removing all components of a positive-phase masker except those close to the signal raised thresholds at the minimum of the MPP. In contrast, a similar manipulation applied to the negative-phase masker produced a uniform elevation of the MPP. Experiment 3 showed that an analogous effect could be obtained by manipulating the phases of masker components remote from the signal. It is shown that several features of the data can be simulated using a nonlinear model of the auditory periphery [C. Giguère and P.C. Woodland, J. Acoust. Soc. Am. 95, 331-342 (1994)].

Auditory Threshold↗
PubMed1981

Shigella sonnei phase I and phase II: susceptibility to direct serum lysis and opsonic requirements necessary for stimulation of leukocyte redox metabolism and killing.

The synthesis of the lipopolysaccharide O-specific repeat polymer by Shigella sonnei phase I is a clearly defined bacterial virulence factor necessary for penetrating epithelial cells; S. sonnei phase II does not synthesize this antigen and is uniformly avirulent. The serum opsonic requirements, relative to differences in gross lipopolysaccharide structure, were investigated by quantification and comparison of polymorphonuclear leukocyte (PMNL) metabolism and PMNL-mediated microbicidal action to phase I and phase II organisms, using normal and immune serum. The stimulation of PMNL O2-redox metabolism, as required for oxidative killing, was quantified by a chemiluminescent technique, using luminol as a chemilumigenic substrate. Susceptibility to direct serum or serum PMNL-mediated killing was evaluated by serum and serum-phagocytic killing assays. Stimulation of PMNL metabolism and phagocytic killing of S. sonnei phase I required opsonification by specific phase I antibody plus the classical pathway of complement. S. sonnei phase II was susceptible to direct complement-mediated serum killing. Likewise, opsonification of the phase II microbe, as measured by PMNL-associated chemiluminescence, was effected by complement in the absence of immune antibody. These data demonstrate the importance of the O-specific repeat polymer in protecting the microbe from the microbicidal action of PMNL and the bacteriolytic action of serum.

Animals↗
PubMed1984

Chemical and immunological characterization of lipopolysaccharides from phase I and phase II Coxiella burnetii.

Lipopolysaccharides (LPSs) isolated from phase I and phase II Coxiella burnetii (LPS I and LPS II, respectively) were analyzed for chemical compositions, molecular heterogeneity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and immunological properties. The yields of crude phenol-water extracts from phase I cells were roughly three to six times higher than those from phase II cells. Purification of LPSs by ultracentrifugation gave similar yields for both LPS I and LPS II. Purified LPS I and LPS II contained roughly 0.8 and 0.6% protein, respectively. The fatty acid constituents of the LPSs were different in composition and content, with branched-chain fatty acids representing about 15% of the total. beta-Hydroxymyristic acid was not detected in either LPS I or LPS II. A thiobarbituric acid-periodate-positive compound was evident in the LPSs; however, this component was not identified as 3-deoxy-D-mannooctulosonic acid by gas and paper chromatographies. LPS II contained D-mannose, D-glucose, D-glyceromannoheptose, glucosamine, ethanolamine, 3-deoxy-D-mannooctulosonic acid-like material, phosphate, and fatty acids. LPS I contained the unique disaccharide galactosaminuronyl glucosamine and nine unidentified components in addition to the components of LPS II. The hydrophobic, putative lipid A fraction of LPS I and LPS II contained the above constituents, but the hydrophilic fraction was devoid of ethanolamine. The LPS I disaccharide galactosaminuronyl glucosamine was found in both fractions of the acetic acid hydrolysates. Analysis of LPSs by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by silver staining indicated that LPS II was composed of only one band, whereas LPS I consisted of six or more bands with irregular spacing. Ouchterlony immunodiffusion tests demonstrated that LPS I reacted with phase I but not with phase II whole-cell hyperimmune antibody, and LPS II reacted neither with phase I nor phase II hyperimmune antibody. From these results, it was concluded that the chemical structures of LPSs from C. burnetii were different from those of the LPSs of gram-negative bacteria; however, the LPS structural variation in C. burnetii may be similar to the smooth-to-rough mutational variation of saccharide chain length in gram-negative bacteria.

Acetylation↗
PubMed1995

Growth phase-dependent induction of stationary-phase promoters of Escherichia coli in different gram-negative bacteria.

RSF1010-derived plasmids carrying a fusion of a promoterless lacZ gene with the sigma s-dependent growth phase-regulated promoters of Escherichia coli, bolAp1 and fic, were constructed. The plasmids were mobilized into the gram-negative bacterial species Acetobacter methanolicus, Xanthomonas campestris, Pseudomonas putida, and Rhizobium meliloti. The beta-galactosidase activities of bacterial cultures were determined during exponential and stationary growth phases. Transcriptional activation of the fic promoter in the different bacteria was growth phase dependent as in E. coli and was initiated generally during the transition to stationary phase. The induction of the bolA promoter was also growth phase dependent in the bacteria tested. While the expression in E. coli and R. meliloti was initiated during the transition from exponential to stationary phase, the induction in A. methanolicus, P. putida, and X. campestris started some hours after stationary growth phase was reached. In all the species tested, DNA fragments hybridizing with the rpoS gene of E. coli were detected. The results show that in different gram-negative bacteria, stationary-phase-specific sigma factors which are structurally and functionally homologous to sigma s and are able to recognize the promoter sequences of both bolA and fic exist.

Bacterial Proteins↗
PubMed2002

Blockade of fatty acid oxidation mimics phase II-phase III transition in a fasting bird, the king penguin.

This study tests the hypothesis that the metabolic and endocrine shift characterizing the phase II-phase III transition during prolonged fasting is related to a decrease in fatty acid (FA) oxidation. Changes in plasma concentrations of various metabolites and hormones and in lipolytic fluxes, as determined by continuous infusion of [2-(3)H]glycerol and [1-(14)C]palmitate, were examined in vivo in spontaneously fasting king penguins in the phase II status (large fat stores, protein sparing) before, during, and after treatment with mercaptoacetate (MA), an inhibitor of FA oxidation. MA induced a 7-fold decrease in plasma beta-hydroxybutyrate and a 2- to 2.5-fold increase in plasma nonesterified fatty acids (NEFA), glycerol, and triacylglycerols. MA also stimulated lipolytic fluxes, increasing the rate of appearance of NEFA and glycerol by 60-90%. This stimulation might be partly mediated by a doubling of circulating glucagon, with plasma insulin remaining unchanged. Plasma glucose level was unaffected by MA treatment. Plasma uric acid increased 4-fold, indicating a marked acceleration of body protein breakdown, possibly mediated by a 2.5-fold increase in circulating corticosterone. Strong similarities between these changes and those observed at the phase II-phase III transition in fasting penguins support the view that entrance into phase III, and especially the end of protein sparing, is related to decreased FA oxidation, rather than reduced NEFA availability. MA could be therefore a useful tool for understanding mechanisms underlying the phase II-phase III transition in spontaneously fasting birds and the associated stimulation of feeding behavior.

3-Hydroxybutyric Acid↗