10 μ m-thick four-quadrant transmissive silicon photodiodes for beam position monitor application: Electrical characterization and gamma irradiation effects

Silicon photodiodes are very useful devices as X-ray beam monitors in synchrotron radiation beamlines. Owing to Si absorption, devices thinner than 10 μ m are needed to achieve transmission over 90% for energies above 10 keV . In this work, new segmented four-quadrant diodes for beam alignment purposes are fabricated on both ultrathin (10 μ m-thick) and bulk silicon substrates. Four-quadrant diodes implementing different design parameters as well as auxiliary test structures (single diodes and MOS capacitors) are studied. An extensive electrical characterization, including current-voltage (I-V) and capacitance-voltage (C-V) techniques, is carried out on non-irradiated and gamma-irradiated devices up to 100 Mrad doses. Special attention is devoted to the study of radiation-induced charge build-up in diode interquadrant isolation dielectric, as well as its impact on device interquadrant resistance. Finally, the devices have been characterized with an 8 keV laboratory X-ray source at 108 ph/s and in BL13-XALOC ALBA Synchroton beamline with 1011 ph/s and energies from 6 to 16 keV . Sensitivity, spatial resolution and uniformity of the devices have been evaluated.Peer reviewe

Fasciola hepatica calcium-binding protein FhCaBP2: structure of the dynein light chain-like domain

The common liver fluke Fasciola hepatica causes an increasing burden on human and animal health, partly because of the spread of drug-resistant isolates. As a consequence, there is considerable interest in developing new drugs to combat liver fluke infections. A group of potential targets is a family of calcium-binding proteins which combine an N-terminal domain with two EF-hand motifs and a C-terminal domain with predicted similarity to dynein light chains (DLC-like domain)

Axial disposition of myosin heads in isometrically contracting muscles.

Meridional x-ray diffraction diagrams, recorded with high angular resolution, from muscles contracting at the plateau of isometric tension show that the myosin diffraction orders are clusters of peaks. These clusters are due to pronounced interference effects between the myosin diffracting units on either side of the M-line. A theoretical analysis based on the polarity of the myosin (and actin) filaments shows that it is possible to extract phase information from which the axial disposition of the myosin heads can be determined. The results show that each head in a crown pair has a distinct structural disposition. It appears that only one of the heads in the pair stereospecifically interacts with the thin filament at any one time

Versatile wide angle diffraction setup for simultaneous wide and small angle x-ray scattering measurements with synchrotron radiation

5 pages, 10 figures.Here we present a novel, simple, and versatile experimental setup aimed to perform wide angle x-ray scattering (WAXS) measurements alone or in simultaneous combination with small angle x-ray scattering measurements. The design of the WAXS goniometer allows one to obtain high resolution diffraction patterns in a broad angular range. The setup can incorporate a hot stage in order to evaluate temperature resolved experiments. The performance of the equipment has been verified in the BM16 beam line of the European Synchrotron Radiation Facility with different well known samples such as alumina, isotropic film of high density polyethylene (HDPE), and oriented HPDE fiber.The authors are indebted to the Spanish Ministry of Science and Education (Grant No. FPA2001-2139) and to the EU, Marie-Curie reintegration grant (MERG-CT-2004-511908)for the financial support of this project.Peer reviewe

Phase transfer of rhodium(II)-based metal-organic polyhedra bearing coordinatively bound cargo enables molecular separation

The transfer of nanoparticles between immiscible phases can be driven by externally triggered changes in their surface composition. Interestingly, phase transfers can enhance the processing of nanoparticles and enable their use as vehicles for transporting molecular cargo. Herein we report extension of such phase transfers to encompass porous metal-organic polyhedra (MOPs). We report that a hydroxyl-functionalized, cuboctahedral Rh(II)-based MOP can be transferred between immiscible phases by pH changes or by cation-exchange reactions. We demonstrate use of this MOP to transport coordinatively bound cargo between immiscible layers, including into solvents in which the cargo is insoluble. As proof-of-concept that our phase-transfer approach could be used in chemical separation, we employed Rh(II)-based MOPs to separate a challenging mixture of structurally similar cyclic aliphatic (tetrahydrothiophene) and aromatic (thiophene) compounds. We anticipate that transport of coordinatively bound molecules will open new avenues for molecular separation based on the relative coordination affinity that the molecules have for the Rh(II) sites of MOP.Thais Grancha, Arnau Carné-Sánchez, Laura Hernández-López, Jorge Albalad, Inhar Imaz, Judith Juanhuix, and Daniel Maspoc

Crystallization and preliminary X-ray diffraction analysis of vaccinia virus H1L phosphatase

The cysteine-based protein phosphatase H1L was the first reported dual-specificity protein phosphatase. H1L is encapsidated within the vaccinia virus and is required for successful host infection and for the production of viable vaccinia progeny. H1L has therefore been proposed as a target candidate for antiviral compounds. Recombinant H1L has been expressed in a catalytically inactive form using an Escherichia coli host, leading to purification and crystallization by the microbatch method. The crystals diffract to 2.1 Å resolution using synchrotron radiation. These crystals belong to space group P422, with unit-cell parameters a = b = 98.31, c = 169.15 Å, and are likely to contain four molecules in the asymmetric unit. A sulfur SAD data set was collected to 2.8 Å resolution on beamline BM14 at the ESRF to facilitate structure determination. Attempts to derivatize these crystals with xenon gas changed the space group to I422, with unit-cell parameters a = b = 63.28, c = 169.68 Å and a single molecule in the asymmetric unit. The relationship between these two crystal forms is discussed

Enzymatic, LC-MS/MS, crystallography and SAXS data of AKR1B1

Enzymatic, mass spectrometry, crystallography and SAXS data of AKR1B1This work was started and partly supported by a grant from the Spanish Nuclear Council (CSN).Peer reviewe

Enhanced Stability Against Radiation Damage of Lysozyme Crys-tals Grown in Fmoc-CF Hydrogels

Lysozyme crystals grown in Fmoc-CF (Cys-Phe) hydro-gels, unlike those grown in agarose, give rise to compo-site crystals that have an enhanced resistance against degradation caused by an intense exposure to X-ray irradiation. Fmoc-CF dipeptide shows a clear protection of the most sensitive groups (disulfide bonds and methi-onines) of the protein. The protection mediated by cys-teine is exerted only in its gel state since cysteine in solution has an adverse effect. Probably the reactive thiols groups of cysteine being locked within the rigid peptide fibers minimize cross-reactions with the proteins favoring the formation of protein crystals. Once located inside the protein crystal the long peptide fibers are able to protect the protein against radiation damage.Projects BIO2016-74875-P (JAG) and FIS2017-85954-R (LAC) (Ministerio de Economía, Industria y Competitivid-ad, MINECO, and Agencia Estatal de Investigación, AEI, Spain, co-funded by Fondo Europeo de Desarrollo Region-al, FEDER, European Union) and by Junta de Andalucía (Spain) projects P12-FQM-2721 and P12-FQM-790

Peroxisomal catalases from the yeasts Pichia pastoris and Kluyveromyces lactis as models for oxidative damage in higher eukaryotes

12 p.-7 fig.-2 tab.Catalases are among the main scavengers of reactive oxygen species (ROS) present in the peroxisome, thereby preventing oxidative cellular and tissular damage. In human, multiple diseases are associated with malfunction of these organelles, which causes accumulation of ROS species and consequently the inefficient detoxification of cells. Despite intense research, much remains to be clarified about the precise molecular role of catalase in cellular homeostasis. Yeast peroxisomes and their peroxisomal catalases have been used as eukaryotic models for oxidative metabolism, ROS generation and detoxification, and associated pathologies. In order to provide reliable models for oxidative metabolism research, we have determined the high-resolution crystal structures of peroxisomal catalase from two important biotechnology and basic biology yeast models, Pichia pastoris and Kluyveromyces lactis. We have performed an extensive functional, biochemical and stability characterization of both enzymes in order to establish their differential activity profiles. Furthermore, we have analyzed the role of the peroxisomal catalase under study in the survival of yeast to oxidative burst challenges combining methanol, water peroxide, and sodium chloride. Interestingly, whereas catalase activity was induced 200-fold upon challenging the methylotrophic P. pastoris cells with methanol, the increase in catalase activity in the non-methylotrophic K. lactis was only moderate. The inhibitory effect of sodium azide and β-mercaptoethanol over both catalases was analyzed, establishing IC50 values for both compounds that are consistent with an elevated resistance of both enzymes toward these inhibitors. Structural comparison of these two novel catalase structures allows us to rationalize the differential susceptibility to inhibitors and oxidative bursts. The inherent worth and validity of the P. pastoris and K. lactis yeast models for oxidative damage will be strengthened by the availability of reliable structural-functional information on these enzymes, which are central to our understanding of peroxisomal response toward oxidative stress.Spanish Ministry of Economy, Industry and Competitiveness (CTQ2015-66206-C2-2-R, SAF2015-72961-EXP, RTI2018-102242-B-I00), Regional Government of Madrid (S2017/BMD-3673), and CSIC (PIE 20160E064) to M.C.V. All grants were co-funded with European Union ERDF funds (European Regional Development Fund).Peer reviewe