D. Starodub

Bio: D. Starodub is an academic researcher from Arizona State University. The author has contributed to research in topics: Diffraction & Laser. The author has an hindex of 18, co-authored 27 publications receiving 2959 citations. Previous affiliations of D. Starodub include Stanford University & Arizona's Public Universities.

Single mimivirus particles intercepted and imaged with an X-ray laser

Abstract: The start-up of the Linac Coherent Light Source (LCLS), the new femtosecond hard X-ray laser facility in Stanford, California, has brought high expectations of a new era for biological imaging. The intense, ultrashort X-ray pulses allow diffraction imaging of small structures before radiation damage occurs. Two papers in this issue of Nature present proof-of-concept experiments showing the LCLS in action. Chapman et al. tackle structure determination from nanocrystals of macromolecules that cannot be grown in large crystals. They obtain more than three million diffraction patterns from a stream of nanocrystals of the membrane protein photosystem I, and assemble a three-dimensional data set for this protein. Seibert et al. obtain images of a non-crystalline biological sample, mimivirus, by injecting a beam of cooled mimivirus particles into the X-ray beam. The start-up of the new femtosecond hard X-ray laser facility in Stanford, the Linac Coherent Light Source, has brought high expectations for a new era for biological imaging. The intense, ultrashort X-ray pulses allow diffraction imaging of small structures before radiation damage occurs. This new capability is tested for the problem of imaging a non-crystalline biological sample. Images of mimivirus are obtained, the largest known virus with a total diameter of about 0.75 micrometres, by injecting a beam of cooled mimivirus particles into the X-ray beam. The measurements indicate no damage during imaging and prove the concept of this imaging technique. X-ray lasers offer new capabilities in understanding the structure of biological systems, complex materials and matter under extreme conditions1,2,3,4. Very short and extremely bright, coherent X-ray pulses can be used to outrun key damage processes and obtain a single diffraction pattern from a large macromolecule, a virus or a cell before the sample explodes and turns into plasma1. The continuous diffraction pattern of non-crystalline objects permits oversampling and direct phase retrieval2. Here we show that high-quality diffraction data can be obtained with a single X-ray pulse from a non-crystalline biological sample, a single mimivirus particle, which was injected into the pulsed beam of a hard-X-ray free-electron laser, the Linac Coherent Light Source5. Calculations indicate that the energy deposited into the virus by the pulse heated the particle to over 100,000 K after the pulse had left the sample. The reconstructed exit wavefront (image) yielded 32-nm full-period resolution in a single exposure and showed no measurable damage. The reconstruction indicates inhomogeneous arrangement of dense material inside the virion. We expect that significantly higher resolutions will be achieved in such experiments with shorter and brighter photon pulses focused to a smaller area. The resolution in such experiments can be further extended for samples available in multiple identical copies.

Gas dynamic virtual nozzle for generation of microscopic droplet streams

Abstract: A nozzle for producing a single-file stream of droplets of a fluid, methods using the nozzle, and an injector, comprising the nozzle of the invention, for providing the single-file stream of droplets of a fluid to a high-vacuum system are described. The nozzle comprises two concentric tubes wherein the outer tube comprises a smoothly converging-diverging exit channel and the outlet end of the first tube is positioned within the converging section of the exit channel.

Gas Dynamic Virtual Nozzle for Generation of Microscopic Droplet Streams

Abstract: As shown by Ganan-Calvo and co-workers, a free liquid jet can be compressed in iameter through gas-dynamic forces exerted by a co-flowing gas, obviating the need for a solid nozzle to form a microscopic liquid jet and thereby alleviating the clogging problems that plague conventional droplet sources of small diameter. We describe in this paper a novel form of droplet beam source based on this principle. The source is miniature, robust, dependable, easily fabricated, and eminently suitable for delivery of microscopic liquid droplets, including hydrated biological samples, into vacuum for analysis using vacuum instrumentation. Monodisperse, single file droplet streams are generated by triggering the device with a piezoelectric actuator. The device is essentially immune to clogging.

X-ray diffraction from isolated and strongly aligned gas-phase molecules with a free-electron laser

Abstract: We report experimental results on x-ray diffraction of quantum-state-selected and strongly aligned ensembles of the prototypical asymmetric rotor molecule 2,5-diiodobenzonitrile using the Linac Coherent Light Source The experiments demonstrate first steps toward a new approach to diffractive imaging of distinct structures of individual, isolated gas-phase molecules We confirm several key ingredients of single molecule diffraction experiments: the abilities to detect and count individual scattered x-ray photons in single shot diffraction data, to deliver state-selected, eg, structural-isomer-selected, ensembles of molecules to the x-ray interaction volume, and to strongly align the scattering molecules Our approach, using ultrashort x-ray pulses, is suitable to study ultrafast dynamics of isolated molecules

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Femtosecond X-ray protein nanocrystallography

Abstract: X-ray crystallography provides the vast majority of macromolecular structures, but the success of the method relies on growing crystals of sufficient size. In conventional measurements, the necessary increase in X-ray dose to record data from crystals that are too small leads to extensive damage before a diffraction signal can be recorded(1-3). It is particularly challenging to obtain large, well-diffracting crystals of membrane proteins, for which fewer than 300 unique structures have been determined despite their importance in all living cells. Here we present a method for structure determination where single-crystal X-ray diffraction 'snapshots' are collected from a fully hydrated stream of nanocrystals using femtosecond pulses from a hard-X-ray free-electron laser, the Linac Coherent Light Source(4). We prove this concept with nanocrystals of photosystem I, one of the largest membrane protein complexes(5). More than 3,000,000 diffraction patterns were collected in this study, and a three-dimensional data set was assembled from individual photosystem I nanocrystals (similar to 200 nm to 2 mm in size). We mitigate the problem of radiation damage in crystallography by using pulses briefer than the timescale of most damage processes(6). This offers a new approach to structure determination of macromolecules that do not yield crystals of sufficient size for studies using conventional radiation sources or are particularly sensitive to radiation damage.

Frontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO2 Fixation

Abstract: Two major energy-related problems confront the world in the next 50 years. First, increased worldwide competition for gradually depleting fossil fuel reserves (derived from past photosynthesis) will lead to higher costs, both monetarily and politically. Second, atmospheric CO_2 levels are at their highest recorded level since records began. Further increases are predicted to produce large and uncontrollable impacts on the world climate. These projected impacts extend beyond climate to ocean acidification, because the ocean is a major sink for atmospheric CO2.1 Providing a future energy supply that is secure and CO_2-neutral will require switching to nonfossil energy sources such as wind, solar, nuclear, and geothermal energy and developing methods for transforming the energy produced by these new sources into forms that can be stored, transported, and used upon demand.

Femtosecond diffractive imaging with a soft-X-ray free-electron laser

Abstract: Theory predicts that with an ultrashort and extremely bright coherent X-ray pulse, a single diffraction pattern may be recorded from a large macromolecule, a virus, or a cell before the sample explodes and turns into a plasma. Here we report the first experimental demonstration of this principle using the FLASH soft X-ray free-electron laser. An intense 25 fs, 4 x 10{sup 13} W/cm{sup 2} pulse, containing 10{sup 12} photons at 32 nm wavelength, produced a coherent diffraction pattern from a nano-structured non-periodic object, before destroying it at 60,000 K. A novel X-ray camera assured single photon detection sensitivity by filtering out parasitic scattering and plasma radiation. The reconstructed image, obtained directly from the coherent pattern by phase retrieval through oversampling, shows no measurable damage, and extends to diffraction-limited resolution. A three-dimensional data set may be assembled from such images when copies of a reproducible sample are exposed to the beam one by one.