Transparent Phase Research Articles

Enzymes and mediators hosted together in lipidic mesophases for the construction of biodevices

Self-assembled, highly viscous, and optically transparent lipidic cubic phases are employed as matrices for enzyme-glucose dehydrogenase and vitamin K derivatives differing in hydrophobicity: phylloquinone (VitK1), menaquinone (VitK2), and menadione (VitK3). The lipidic cubic mesophase has been employed to hold these electroactive biological molecules in close vicinity of the electrode surface in order to study their behavior in the lipid environment by electrochemical methods. Liquid–crystalline properties of the analyzed samples of non-doped and doped phase were identified using X-ray and polarized microscopy. Incorporation of the enzyme together with the mediator in the lipidic matrix results in the formation of a catalytically active and stable film on the electrode surface and makes the modified electrode useful for the development of biosensors. Single-walled carbon nanotubes were employed to nanostructure the electrode surface in order to increase the working area of the electrode.

Streptococcus pneumoniae in Biofilms Are Unable to Cause Invasive Disease Due to Altered Virulence Determinant Production

It is unclear whether Streptococcus pneumoniae in biofilms are virulent and contribute to development of invasive pneumococcal disease (IPD). Using electron microscopy we confirmed the development of mature pneumococcal biofilms in a continuous-flow-through line model and determined that biofilm formation occurred in discrete stages with mature biofilms composed primarily of dead pneumococci. Challenge of mice with equal colony forming units of biofilm and planktonic pneumococci determined that biofilm bacteria were highly attenuated for invasive disease but not nasopharyngeal colonization. Biofilm pneumococci of numerous serotypes were hyper-adhesive and bound to A549 type II pneumocytes and Detroit 562 pharyngeal epithelial cells at levels 2 to 11-fold greater than planktonic counterparts. Using genomic microarrays we examined the pneumococcal transcriptome and determined that during biofilm formation S. pneumoniae down-regulated genes involved in protein synthesis, energy production, metabolism, capsular polysaccharide (CPS) production, and virulence. We confirmed these changes by measuring CPS by ELISA and immunoblotting for the toxin pneumolysin and the bacterial adhesins phosphorylcholine (ChoP), choline-binding protein A (CbpA), and Pneumococcal serine-rich repeat protein (PsrP). We conclude that biofilm pneumococci were avirulent due to reduced CPS and pneumolysin production along with increased ChoP, which is known to bind C-reactive protein and is opsonizing. Likewise, biofilm pneumococci were hyper-adhesive due to selection for the transparent phase variant, reduced CPS, and enhanced production of PsrP, CbpA, and ChoP. These studies suggest that biofilms do not directly contribute to development of IPD and may instead confer a quiescent mode of growth during colonization.

Femtosecond digital in-line holography with the fractional Fourier transform: application to phase-contrast metrology

The possibility to analyze transparent phase objects using femtosecond digital in-line holography is demonstrated. We show that the diffraction patterns produced by the diffraction of 20-fs pulses by pure phase objects can be advantageously processed by using the fractional Fourier transform. The optimal fractional orders lead to the longitudinal location of the phase object while the analysis of the reconstructed patterns leads to its diameter and to the value of the phase shift. Simulations and experimental results are in good concordance. This work shows new important applications of these reconstruction techniques in the domain of digital phase-contrast metrology. We further show that the use of femtosecond pulses results in a significant reduction of coherent noise.

Transparent p/n diode device from a single zinc nitride sputtering target

Zinc oxide (ZnO) thin films showing bipolar conductivity were fabricated by sputtering of zinc nitride target in plasma containing mixture of Ar–O 2 gasses. Sputtering in pure Ar plasma produced conductive and opaque zinc nitride (ZnN) films while upon introduction of oxygen up to 30% into the plasma highly transparent single phase polycrystalline n-type ZnO films have been grown. ZnN sputtering in Ar plasma containing more than 30% oxygen produced p-type ZnO films. Hall-effect and photoluminescence measurements revealed the presence of zinc vacancies and nitrogen which are acting as acceptor dopants in p-type ZnO. A heterostructure was fabricated in a single deposition run consisting of n-ZnN and p-ZnO which exhibited rectifying behavior with 2–2.5 V turn-on voltage. Improvements on the formed p/n heterostructure as well as the potential of using single sputtering target in fabrication of Zn-based homo- and hetero-junctions are discussed.

Large-Scale and Highly Oriented Liquid Crystal Phase in Suspensions of Polystyrene-block-poly(l-lactide) Single Crystals

A large number of lozenge-shaped and sandwiched polystyrene-block-poly(L-lactide) (PS-b-PLLA) single crystals were prepared by the self-seeding technique. The single crystals were nearly monodispersed in both thickness and diameter. They are well-dispersed because of the steric stabilization offered by tethered PS in p-xylene, which is a good solvent for PS. The suspensions were observed to separate into a transparent upper phase and a turbid lower phase. The lower phase showed uniform iridescent stripes extending over the whole tube between crossed polarizers. The birefringence demonstrates the liquid crystal order, and the uniform stripes reveal that the phase is a well-oriented single domain. The phase-transition concentration is rather low. Polarizing light microscopy (PLM) images show Schlieren texture and thread-like texture. Small-angle X-ray scattering (SAXS) results showed that the single crystals in the liquid crystal phase oriented horizontally with a vertical repeat distance of about 70 nm. Additionally, the possible structure of the liquid crystal phase is being discussed. The novel disclike colloidal particle might be useful for anisotropic photonic materials.

How Evolutionary Crystal Structure Prediction Works—and Why

Once the crystal structure of a chemical substance is known, many properties can be predicted reliably and routinely. Therefore if researchers could predict the crystal structure of a material before it is synthesized, they could significantly accelerate the discovery of new materials. In addition, the ability to predict crystal structures at arbitrary conditions of pressure and temperature is invaluable for the study of matter at extreme conditions, where experiments are difficult. Crystal structure prediction (CSP), the problem of finding the most stable arrangement of atoms given only the chemical composition, has long remained a major unsolved scientific problem. Two problems are entangled here: search, the efficient exploration of the multidimensional energy landscape, and ranking, the correct calculation of relative energies. For organic crystals, which contain a few molecules in the unit cell, search can be quite simple as long as a researcher does not need to include many possible isomers or conformations of the molecules; therefore ranking becomes the main challenge. For inorganic crystals, quantum mechanical methods often provide correct relative energies, making search the most critical problem. Recent developments provide useful practical methods for solving the search problem to a considerable extent. One can use simulated annealing, metadynamics, random sampling, basin hopping, minima hopping, and data mining. Genetic algorithms have been applied to crystals since 1995, but with limited success, which necessitated the development of a very different evolutionary algorithm. This Account reviews CSP using one of the major techniques, the hybrid evolutionary algorithm USPEX (Universal Structure Predictor: Evolutionary Xtallography). Using recent developments in the theory of energy landscapes, we unravel the reasons evolutionary techniques work for CSP and point out their limitations. We demonstrate that the energy landscapes of chemical systems have an overall shape and explore their intrinsic dimensionalities. Because of the inverse relationships between order and energy and between the dimensionality and diversity of an ensemble of crystal structures, the chances that a random search will find the ground state decrease exponentially with increasing system size. A well-designed evolutionary algorithm allows for much greater computational efficiency. We illustrate the power of evolutionary CSP through applications that examine matter at high pressure, where new, unexpected phenomena take place. Evolutionary CSP has allowed researchers to make unexpected discoveries such as a transparent phase of sodium, a partially ionic form of boron, complex superconducting forms of calcium, a novel superhard allotrope of carbon, polymeric modifications of nitrogen, and a new class of compounds, perhydrides. These methods have also led to the discovery of novel hydride superconductors including the "impossible" LiH(n) (n=2, 6, 8) compounds, and CaLi(2). We discuss extensions of the method to molecular crystals, systems of variable composition, and the targeted optimization of specific physical properties.

Does transparent nematic phase exist in 5CB/DDAB/water microemulsions? From the viewpoint of temperature dependent dielectric spectroscopy

Liquid crystal colloids have received tremendous attention because of its great potential both in the understanding of the liquid crystalline phase and in searching for new application of liquid crystals. Inverse microemulsion composed of 4-cyano-4-n-pentylbiphenyl (5CB), didodecyl dimethyl ammonium bromide, and water was investigated by means of broadband dielectric spectroscopy in this study. Based on the understanding of previous investigations on the same system, the isotropic phase was taken into account to quantitatively characterize the bulklike relaxations after the isotropic-to-nematic phase transition. Analogous results concerning the phase transition and phase composition to other investigations were obtained. In addition to bulklike relaxations, a new relaxation was observed at the frequency range about two orders lower than bulklike relaxations. This new relaxation shows abnormal temperature dependence, suggesting that superstructures composed of water droplets and confined 5CB molecules exist. This superstructure possibly possesses a confined nanoscaled liquid crystal ordering and may correspond to the notion of the transparent nematic phase.

Holographic DFB Dye Lasers

A new simple type of DFB dye laser is proposed. The laser consists of a dye cell and a transparent phase holographic grating mounted on the front window of the cell. In the experiment, high-quality stable transparent holographic gratings were recorded in bichromated gelatine with a single mode He-Cd laser. When pumped perpendicular to the surface of the grating the DFB laser emitted a narrow spectral line independently of the width and the position of the pump spectrum. A linewidth of 0·01 nm was measured under pumping with broadband radiation of 20 nm spectral width. Either a set of holographic gratings of a different period or a fan-shaped grating may be used in the laser for stepped or continuous spectral tuning.

Computer simulation of the zernike phase contrast in hard x-ray radiation using refractive lenses and zone plates

Computer simulation of an experiment on imaging transparent (phase) microobjects using the Zernike phase contrast method under hard X-ray radiation has been performed. The beam parameters typical for synchrotron radiation sources of the third generation were used in calculations. Both a refracting lens and a zone plate have been considered as a focusing element. The phase shifting quarter-wave plate is located at a spot of the point source image. The results of calculations have shown that the method can be successfully used for objects with the sizes greater than 0.1 μm along and 1 μm across the beam. It has been shown that the contrast is caused not only by increasing the intensity within the shadow of the objects, but also by decreasing the intensity in the area beyond the objects, which is necessary to retain the integral intensity.

Interaction of pneumococcal phase variation, host and pressure/gas composition: Virulence expression of NanA, HylA, PspA and CbpA in simulated otitis media

Streptococcus pneumoniae, a leading cause of otitis media (OM), adapts to the host environment and undergoes spontaneous intra-strain phase variations in colony morphology. Transparent (T) phase variants are more efficient in colonizing the nasopharynx while the opaque (O) phase variants exhibit greater virulence during systemic infections. We recently demonstrated that T phase variants exhibited a higher growth rate and greater epithelial adherence and destruction than did O phase variants during interactions with human middle ear (ME) epithelial cells. This study was to delineate the underlying molecular mechanisms. Human ME epithelial cells were preconditioned for 24 h under one of the three simulated ME gas/pressure conditions designed to reflect those for 1) normal ME, 2) ME with Eustachian tube obstruction (ETO) and 3) ME with tympanostomy tube (TT) placement; subsequently exposed to a dose (˜107 CFU/ml) of either T or O phase variants of S. pneumoniae (6A), and then incubated for 1h and 3 h. Gene expressions coding for pneumococcal NanA, HylA, PspA, and CbpA virulence factors in inoculum, epithelium-attached and free-floating bacteria were assayed using real-time PCR. Result showed significantly higher basal expression levels for NanA and HylA in T inoculums than in O inoculum. Furthermore, striking differences between the two phase variants were observed in the forms of the inocula, significantly higher expression levels for PspA in T inoculum, but for CbpA in O inoculum. The TT condition enhanced the molecular activities of NanA, HylA, and PspA virulence factors in epithelium-attached T phase variants and fluid-floating O variants, followed by the ETO condition. Our study suggests that the pneumococcal virulence of the phase variations are modulated by the pathological ME environment and host–pathogen interaction during the pathogenesis of OM.

Fast optical computerized topography

The topography of samples is recovered from the phase reconstruction by solving the Transport Intensity Equation (TIE). The TIE is solved by expanding the equation into a series of Zernike polynomials, leading to a set of appropriate algebraic equations. In the experiments laser light was used and the illuminated region defined the boundary conditions on the target. The phase was uniquely reconstructed and the geometry of the target was calculated. The novel technique has been successfully tested on a transparent phase plate as well as on a gold coated one. Using this technique with illumination of a short laser pulse makes it well suited for reconstructing surfaces of moving objects.

Body-Centered TetragonalC4: A Viablesp3Carbon Allotrope

We have investigated by first principles the electronic, vibrational, and structural properties of bct ${\mathrm{C}}_{4}$, a new form of crystalline $s{p}^{3}$ carbon recently found in molecular dynamics simulations of carbon nanotubes under pressure. This phase is transparent, dynamically stable at zero pressure, and more stable than graphite beyond 18.6 GPa. Coexistence of bct ${\mathrm{C}}_{4}$ with $M$ carbon can explain better the x-ray diffraction pattern of a transparent and hard phase of carbon produced by the cold compression of graphite. Its structure appears to be intermediate between that of graphite and hexagonal diamond. These facts suggest that bct ${\mathrm{C}}_{4}$ is an accessible form of $s{p}^{3}$ carbon along the graphite-to-hexagonal diamond transformation path.

Three-dimensional microscopy with single-beam wavefront sensing and reconstruction from speckle fields

Generally, 3D digital holographic microscopy requires the interference of the object wave with a known reference beam under coherent illumination to perform numerical focusing. This configuration may be challenging for some applications, including the use of exotic wavelengths such as x rays, miniaturized instrumentation, etc. Single-beam intensity measurement followed by phase retrieval techniques is attractive for wavefront sensing and reconstruction, including applications with low coherence. We use this method to construct a 3D microscope using volume speckle fields. Transparent phase objects are investigated using this principle. To the best of our knowledge, this is the first report on the application of this principle applied to microscopy.

Novel fluorinated double-tail surfactant having high microemulsifying ability in water/supercritical CO 2 system

In order to develop an efficient surfactant for a water-in-scCO 2 microemulsion (W/scCO 2 μE), we synthesized a novel double-tail anionic surfactant, sodium bis(1 H,1 H,2 H,2 H-heptadecafluorodecyl)-2-sulfoglutaconate (8FG(EO) 2), and examined the phase behaviour of an 8FG(EO) 2/water/CO 2 mixture at pressures lower than 400 bar and several water-to-surfactant molar ratios. 8FG(EO) 2 yielded a transparent single phase having a higher amount of water than that soluble in pure scCO 2, i.e. a W/scCO 2 μE phase. Through visual observation and UV-visible absorption spectral measurement, 8FG(EO) 2 was interestingly found to microemulsify at least 52 water molecules by one surfactant at 45 °C and pressures higher than 195 bar.

High-dynamic-range quantitative phase imaging with spectral domain phase microscopy

Phase microscopy for high-dynamic-range quantitative phase-contrast imaging of a transparent phase object was demonstrated. Using a common path Fourier domain optical coherence tomography system, this technique is capable of displacement measurement with a sensitivity of 34 pm. The limitation of 2pi ambiguity restriction was overcome by the use of a phase retrieval approach performed in spectral domain. Two-dimensional quantitative phase imaging of human neonatal dermal keratinocyte cells was demonstrated to evaluate the performance of the system for cell imaging.

Microscopic phase behavior of supercritical carbon dioxide + non-ionic surfactant + water systems at elevated pressures

The microscopic phase behavior of the supercritical carbon dioxide (scCO 2) + polyethylene oxide-2,6,8-trimethyl-4-nonyl ether (TMN) + water systems at about 3 wt% of TMN were investigated using a synthetic method with a microscope. The two types of TMN (TMN-3 and TMN-10) used in this work had molecular weight distributions caused by the distribution of the number of ethylene oxide groups. Two different types of phase transition were observed when pressure was decreased gradually at a constant temperature from the high pressure at which the transparent phase was observed to the low pressure at which the separate vapor–liquid phases were observed for the scCO 2 + TMN-3 + water system at 3 wt% of TMN-3. The transparent phase was colorless under all experimental conditions and the phase transition from a transparent phase to a turbidity phase with small, dispersed droplets was observed at the higher side phase transition (higher phase transition pressure). As the pressure continued to decrease, another phase transition was observed from the phase with small droplets to a state with an accelerating aggregation of droplets (lower phase transition pressure). In the turbidity phase between the higher and the lower phase transition, the degree of turbidity became higher with decreasing pressure. On the other hand, in the phase observed below the lower phase transition, a new liquid phase adhered to the sapphire windows and the wall inside the optical cell. The effect of water concentration on the phase transition pressures for the scCO 2 + TMN-3 + water system was investigated from the results at 1 wt% and 3 wt% of TMN-3. The higher phase transition pressures at 3 wt% of TMN-3 were lower than those at 1 wt%, as measured in our previous work. Moreover, the minimal values of the higher phase transition pressure were observed for the system at 3 wt% of TMN-3 as well as those at 1 wt%. The lower phase transition pressures of the scCO 2 + TMN-3 + water system at 3 wt% of TMN-3 decreased as the water concentration increased to about 1 wt%, and the lower phase transition pressures stayed constant in the range of water concentration from about 1 to 3.62 wt%. On the other hand, the homogeneous phase was not established at water concentrations higher than about 3.86 wt%. As for the scCO 2 + TMN-10 + water system, a transparent homogeneous phase could not be observed in the range of the investigation at 3 wt% of TMN-10.

Duplicating the Retention of Cationic Analytes Obtained with Ammonium Formate Mobile Phases when Switching to UV Transparent Mobile Phase Additives in RP-LC

This study explored feasibility of utilizing sodium phosphate and mixtures of sodium phosphate and sodium perchlorate salts in mobile phases as UV transparent alternatives to the ammonium formate salts commonly used in LC–MS mobile phases. Chromatography experiments were run at pH 3.5 in 25% acetonitrile mobile phase, using several model cationic analytes to evaluate cation retention on two different C18 columns as the type or amount of salt was varied. For both columns, phosphate consistently showed less cation retention than formate. In other respects, the two columns showed very different behavior. The study suggests that it is feasible to use UV transparent mobile phase additives to provide comparable cation retention of formate mobile phases, but that the exact composition needed for optimal retention agreement is column dependent.

Transparent dense sodium

Under pressure, metals exhibit increasingly shorter interatomic distances. Intuitively, this response is expected to be accompanied by an increase in the widths of the valence and conduction bands and hence a more pronounced free-electron-like behaviour. But at the densities that can now be achieved experimentally, compression can be so substantial that core electrons overlap. This effect dramatically alters electronic properties from those typically associated with simple free-electron metals such as lithium (Li; refs 1-3) and sodium (Na; refs 4, 5), leading in turn to structurally complex phases and superconductivity with a high critical temperature. But the most intriguing prediction-that the seemingly simple metals Li (ref. 1) and Na (ref. 4) will transform under pressure into insulating states, owing to pairing of alkali atoms-has yet to be experimentally confirmed. Here we report experimental observations of a pressure-induced transformation of Na into an optically transparent phase at approximately 200 GPa (corresponding to approximately 5.0-fold compression). Experimental and computational data identify the new phase as a wide bandgap dielectric with a six-coordinated, highly distorted double-hexagonal close-packed structure. We attribute the emergence of this dense insulating state not to atom pairing, but to p-d hybridizations of valence electrons and their repulsion by core electrons into the lattice interstices. We expect that such insulating states may also form in other elements and compounds when compression is sufficiently strong that atomic cores start to overlap strongly.

Structural studies of ionic liquid-modified microemulsions

This work is focused on the influence of an ionic liquid (IL), i.e. ethyl-methylimidazolium hexylsulfate, on the spontaneous formation of microemulsions with ionic surfactants. The influence of the ionic liquid on structure formation in the optically clear phase region in water/toluene/pentanol mixtures in presence of the cationic surfactant CTAB was studied in more detail. The results show a significant increase of the transparent phase region by adding the ionic liquid. Conductometric investigations demonstrate that adding the ionic liquid can drastically reduce the droplet–droplet interactions in the L 2 phase. 1H nuclear magnetic resonance ( 1H NMR) diffusion coefficient measurements in combination with dynamic light scattering measurements clearly show that inverse microemulsion droplets still exist, but the droplet size is decreased to 2 nm. A more detailed characterisation of the isotropic phase channel by means of conductivity measurements, dynamic light scattering (DLS), 1H NMR and cryo-scanning electron microscopy (SEM), allows the identification of a bicontinuous sponge phase between the L 1 and L 2 phase. When the poly(ethyleneimine) is added, the isotropic phase range is reduced drastically, but the inverse microemulsion range still exists.

Characterization of Water/Supercritical CO2 Microemulsion by UV-visible Spectroscopy and Dynamic Light Scattering

A water/supercritical CO(2) microemulsion (W/scCO(2) microE) with methyl orange (MO) and sodium bis(1H,1H,2H,2H-heptadecafluorodecyl)-2-sulfosuccinate, 8FS(EO)(2), was characterized by means of UV-visible absorption spectral and dynamic light scattering (DLS) measurements. Visual observation of the scCO(2) mixtures revealed transparent and reddish scCO(2) phases with and without separated excess water; they were identified as Winsor-II and Winsor-IV W/scCO(2) microE, respectively. The polarities of the aqueous cores in the Winsor-IV W/scCO(2) microE were examined by observing the spectral shift of the absorbance maximum of MO. It was observed that with an increase in the water-to-surfactant molar ratio (W(0)(c)), the measured absorbance maximum shifted from 418 to 423 nm, which suggests that the polarity of the environment surrounding the MO molecules was methanol-like, and the polarity increased with W(0)(c). The hydrodynamic diameter of Winsor-IV W/scCO(2) microE increased drastically with W(0)(c) but gradually with a decrease in the CO(2) density. The increase in the diameter was a result of the aggregation of the microE droplets and the fusion promoted by the increase in W(0)(c) and the decrease in the CO(2) density, in addition to the swelling of reversed micelles.