ß-Cyclodextrin Encapsulation of Synthetic AHLs: Drug Delivery Implications and Quorum-Quenching Exploits.

Many bacteria, such as Pseudomonas aeruginosa, regulate phenotypic switching in a population density-dependent manner through a phenomenon known as quorum sensing (QS). For Gram-negative bacteria, QS relies on the synthesis, transmission, and perception of low-molecular-weight signal molecules that are predominantly N-acyl-l-homoserine lactones (AHLs). Efforts to disrupt AHL-mediated QS have largely focused on the development of synthetic AHL analogues (SAHLAs) that are structurally similar to native AHLs. However, like AHLs, these molecules tend to be hydrophobic and are poorly soluble under aqueous conditions. Water-soluble macrocycles, such as cyclodextrins (CDs), that encapsulate hydrophobic guests have long been used by both the agricultural and pharmaceutical industries to overcome the solubility issues associated with hydrophobic compounds of interest. Conveniently, CDs have also demonstrated anti-AHL-mediated QS effects. Here, using fluorescence spectroscopy, NMR spectrometry, and mass spectrometry, we evaluate the affinity of SAHLAs, as well as their hydrolysis products, for ß-CD inclusion. We also evaluated the ability of these complexes to inhibit wild-type P. aeruginosa virulence in a Caenorhabditis elegans host infection study, for the first time. Our efforts confirm the potential of ß-CDs for the improved delivery of SAHLAs at the host/microbial interface, expanding the utility of this approach as a strategy for probing and controlling QS.

X-ray optics and beam characterization using random modulation: theory.

X-ray near-field speckle-based phase-sensing approaches provide efficient means of characterizing optical elements. Presented here is a theoretical review of several of these speckle methods within the framework of optical characterization, and a generalization of the concept is provided. As is also demonstrated experimentally in a parallel paper [Berujon, Cojocaru, Piault, Celestre, Roth, Barrett & Ziegler (2020), J. Synchrotron Rad. 27, (this issue)], the methods theoretically developed here can be applied to different beams and optics and within a variety of situations where at-wavelength metrology is desired. By understanding the differences between the various processing methods, it is possible to find and implement the most suitable approach for each metrology scenario.

X-ray optics and beam characterization using random modulation: experiments.

A parallel paper [Berujon, Cojocaru, Piault, Celestre, Roth, Barrett & Ziegler (2020), J. Synchrotron Rad. 27, 284-292] reviewed theoretically some of the available processing schemes for X-ray wavefront sensing based on random modulation. Shown here are experimental applications of the technique for characterizing both refractive and reflective optical components. These fast and accurate X-ray at-wavelength metrology methods can assist the manufacture of X-ray optics that transport X-ray beams with a minimum amount of wavefront distortion. It is also recalled how such methods can facilitate online optimization of active optics.

Wavefront sensing at X-ray free-electron lasers.

Here a direct comparison is made between various X-ray wavefront sensing methods with application to optics alignment and focus characterization at X-ray free-electron lasers (XFELs). Focus optimization at XFEL beamlines presents unique challenges due to high peak powers as well as beam pointing instability, meaning that techniques capable of single-shot measurement and that probe the wavefront at an out-of-focus location are desirable. The techniques chosen for the comparison include single-phase-grating Talbot interferometry (shearing interferometry), dual-grating Talbot interferometry (moiré deflectometry) and speckle tracking. All three methods were implemented during a single beam time at the Linac Coherent Light Source, at the X-ray Pump Probe beamline, in order to make a direct comparison. Each method was used to characterize the wavefront resulting from a stack of beryllium compound refractive lenses followed by a corrective phase plate. In addition, difference wavefront measurements with and without the phase plate agreed with its design to within λ/20, which enabled a direct quantitative comparison between methods. Finally, a path toward automated alignment at XFEL beamlines using a wavefront sensor to close the loop is presented.

X-ray pulse wavefront metrology using speckle tracking.

An instrument allowing the quantitative analysis of X-ray pulsed wavefronts is presented and its processing method explained. The system relies on the X-ray speckle tracking principle to accurately measure the phase gradient of the X-ray beam from which beam optical aberrations can be deduced. The key component of this instrument, a semi-transparent scintillator emitting visible light while transmitting X-rays, allows simultaneous recording of two speckle images at two different propagation distances from the X-ray source. The speckle tracking procedure for a reference-less metrology mode is described with a detailed account on the advanced processing schemes used. A method to characterize and compensate for the imaging detector distortion, whose principle is also based on speckle, is included. The presented instrument is expected to find interest at synchrotrons and at the new X-ray free-electron laser sources under development worldwide where successful exploitation of beams relies on the availability of an accurate wavefront metrology.

X-ray diffraction imaging of metal-oxide epitaxial tunnel junctions made by optical lithography: use of focused and unfocused X-ray beams.

X-ray diffraction techniques are used in imaging mode in order to characterize micrometre-sized objects. The samples used as models are metal-oxide tunnel junctions made by optical lithography, with lateral sizes ranging from 150 µm down to 10 µm and various shapes: discs, squares and rectangles. Two approaches are described and compared, both using diffraction contrast: full-field imaging (topography) and raster imaging (scanning probe) using a micrometre-sized focused X-ray beam. It is shown that the full-field image gives access to macroscopic distortions (e.g. sample bending), while the local distortions, at the micrometre scale (e.g. tilts of the crystalline planes in the vicinity of the junction edges), can be accurately characterized only using focused X-ray beams. These local defects are dependent on the junction shape and larger by one order of magnitude than the macroscopic curvature of the sample.

Physics of reflective optics for the soft gamma-ray photon energy range.

Traditional multilayer reflective optics that have been used in the past for imaging at x-ray photon energies as high as 200 keV are governed by classical wave phenomena. However, their behavior at higher energies is unknown, because of the increasing effect of incoherent scattering and the disagreement between experimental and theoretical optical properties of materials in the hard x-ray and gamma-ray regimes. Here, we demonstrate that multilayer reflective optics can operate efficiently and according to classical wave physics up to photon energies of at least 384 keV. We also use particle transport simulations to quantitatively determine that incoherent scattering takes place in the mirrors but it does not affect the performance at the Bragg angles of operation. Our results open up new possibilities of reflective optical designs in a spectral range where only diffractive optics (crystals and lenses) and crystal monochromators have been available until now.

Grating-based at-wavelength metrology of hard x-ray reflective optics.

A mean of characterizing the tangential shape of a hard x-ray mirror is presented. Derived from a group of methods operating under visible light, its application in the x-ray domain using an x-ray absorption grating allows recovery of the mirror shape with nanometer accuracy and submillimeter spatial resolution. The method works with incoherent light, does not require any a priori information about the mirror characteristics and allows shape reconstruction of x-ray reflective optics under thermal and mechanical working conditions.

Two-dimensional x-ray beam phase sensing.

We present a new method to analyze quantitatively the wave front of a partially coherent x-ray beam. The technique is based on the use of two-dimensional speckle patterns combined with digital image correlation algorithms and offers a pixel size resolution, a high accuracy, and a reduced sensitivity to mechanical vibrations thanks to a very simple setup. The requirements on transverse and longitudinal coherence are also low. Finally, we show how the method can be used for phase contrast imaging applications by a single sample exposure process.

X-ray wavefront characterization using a rotating shearing interferometer technique.

A fast and accurate method to characterize the X-ray wavefront by rotating one of the two gratings of an X-ray shearing interferometer is described and investigated step by step. Such a shearing interferometer consists of a phase grating mounted on a rotation stage, and an absorption grating used as a transmission mask. The mathematical relations for X-ray Moiré fringe analysis when using this device are derived and discussed in the context of the previous literature assumptions. X-ray beam wavefronts without and after X-ray reflective optical elements have been characterized at beamline B16 at Diamond Light Source (DLS) using the presented X-ray rotating shearing interferometer (RSI) technique. It has been demonstrated that this improved method allows accurate calculation of the wavefront radius of curvature and the wavefront distortion, even when one has no previous information on the grating projection pattern period, magnification ratio and the initial grating orientation. As the RSI technique does not require any a priori knowledge of the beam features, it is suitable for routine characterization of wavefronts of a wide range of radii of curvature.

Exact determination of the phase in time-resolved X-ray reflectometry.

An exact solution of the phase retrieval problem is described as applied to in-situ X-ray reflectometry of a growing layered film. The following statement is proved: if the reflectivity R and the derivative dR/dt are known at the time t, then the real and the imaginary parts of the amplitude reflectivity r(t) are found uniquely at this point t.

Molybdenum(VI)-Catalyzed Rearrangement of Prebiotic Carbohydrates in Formamide, a Candidate Prebiotic Solvent.

It has been four decades since formamide was first suggested to perform roles as a precursor and/or a solvent in prebiotic chemistry. However, little work has sought to integrate formamide into larger prebiotic schemes that might create prebiotic RNA, often proposed to have been the first Darwinian biopolymer. Here, we report that formamide can be used as a solvent to perform the Bílik reaction, which uses molybdenum(VI) oxo species as catalysts at near-neutral pH to rearrange branched carbohydrates to give linear carbohydrates; the branched carbohydrates are produced from formaldehyde (HCHO) in alkaline mixtures containing borate, whereas the linear carbohydrates are the precursors needed for ribonucleosides and ribonucleotides. Under conditions wherein the Bílik reaction does this rearrangement, carbohydrate reaction products do not require stabilization by borate. These results, therefore, connect aqueous and formamide-based processes for the prebiotic formation of RNA components. Based on data from Hadean zircons that show that the mantle of the early Earth was near the fayalite-quartz-magnetite fugacity, molybdenum in its 6+ oxidation state was likely available in the Hadean. Together, these allow us to conjecture a process that delivers ribonucleosides and ribonucleotides from hydrogen cyanide and HCHO from a Hadean atmosphere on a Hadean geosphere, without needing precisely timed transitions from one solvent system to the other.

X-ray phase imaging with a grating interferometer.

Using a high-efficiency grating interferometer for hard X rays (10-30 keV) and a phase-stepping technique, separate radiographs of the phase and absorption profiles of bulk samples can be obtained from a single set of measurements. Tomographic reconstruction yields quantitative three-dimensional maps of the X-ray refractive index, with a spatial resolution down to a few microns. The method is mechanically robust, requires little spatial coherence and monochromaticity, and can be scaled up to large fields of view, with a detector of correspondingly moderate spatial resolution. These are important prerequisites for use with laboratory X-ray sources.

W/SiC x-ray multilayers optimized for use above 100 keV.

We have developed a new depth-graded multilayer system comprising W and SiC layers, suitable for use as hard x-ray reflective coatings operating in the energy range 100-200 keV. Grazing-incidence x-ray reflectance at E = 8 keV was used to characterize the interface widths, as well as the temporal and thermal stability in both periodic and depth-graded W/SiC structures, whereas synchrotron radiation was used to measure the hard x-ray reflectance of a depth-graded multilayer designed specifically for use in the range E approximately 150-170 keV. We have modeled the hard x-ray reflectance using newly derived optical constants, which we determined from reflectance versus incidence angle measurements also made using synchrotron radiation, in the range E = 120-180 keV. We describe our experimental investigation in detail compare the new W/SiC multilayers with both W/Si and W/B4C films that have been studied previously, and discuss the significance of these results with regard to the eventual development of a hard x-ray nuclear line telescope.