171 research outputs found
Secondary ionization of pyrimidine nucleobases and their microhydrated derivatives in helium nanodroplets
Radiation damage in biological systems by ionizing radiation is predominantly
caused by secondary processes such as charge and energy transfer leading to the
breaking of bonds in DNA. Here, we study the fragmentation of cytosine (Cyt)
and thymine (Thy) molecules, clusters and microhydrated derivatives induced by
direct and indirect ionization initiated by extreme-ultraviolet (XUV)
irradiation. Photofragmentation mass spectra and photoelectron spectra of free
Cyt and Thy molecules are compared with mass and electron spectra of Cyt/Thy
clusters and microhydrated Cyt/Thy molecules formed by aggregation in
superfluid helium (He) nanodroplets. Penning ionization after resonant
excitation of the He droplets is generally found to cause less fragmentation
compared to direct photoionization and charge-transfer ionization after
photoionization of the He droplets. When Cyt/Thy molecules and oligomers are
complexed with water molecules, their fragmentation is efficiently suppressed.
However, a similar suppression of fragmentation is observed when homogeneous
Cyt/Thy clusters are formed in He nanodroplets, indicating a general trend.
Penning ionization electron spectra (PIES) of Cyt/Thy are broad and nearly
featureless but PIES of their microhydrated derivatives point at a sequential
ionization process ending in unfragmented microsolvated Cyt/Thy cations.Comment: 9 pages, 8 figure
All-Optical Experimental Control of High-Harmonic Photon Energy
We generate high-order harmonics in gaseous medium with tunable photon energy
using time domain interferometry of double pulses in a non-collinear generation
geometry. The method is based on the fact that the generated harmonics inherit
certain spectral properties of the driving laser. The two temporally delayed
ultrashort laser pulses, identical in all parameters, are produced by a
custom-made split-and-delay unit utilizing wave front splitting without a
significant energy loss. The arrangement is easy to implement in any attosecond
pulse generation beamline, and is suitable for the production of an extreme
ultraviolet source with simply and quickly variable central photon energy,
useful for a broad range of applications.Comment: 6 pages, 5 figures, after peer-revie
Spectrally tunable ultrashort monochromatized extreme ultraviolet pulses at 100 kHz
We present the experimental realization of spectrally tunable, ultrashort,
quasimonochromatic extreme ultraviolet (XUV) pulses generated at 100 kHz
repetition rate in a user-oriented gas high harmonic generation (GHHG) beamline
of the Extreme Light Infrastructure - Attosecond Light Pulse Source (ELI ALPS)
facility. Versatile spectral and temporal shaping of the XUV pulses are
accomplished with a double-grating, time-delay compensated monochromator
accommodating the two composing stages in a novel, asymmetrical geometry. This
configuration supports the achievement of high monochromatic XUV flux
(2.8e10+/-0.9e10 photons/s) combined with ultrashort pulse duration (4.0+/-0.2
fs using 12.1+/-0.6 fs driving pulses) and small spot size (sub-100 um).
Focusability, spectral bandwidth, and overall photon flux of the produced
radiation were investigated covering a wide range of instrumental
configurations. Moreover, complete temporal (intensity and phase)
characterization of the few-femtosecond monochromatic XUV pulses - a goal that
is difficult to achieve by conventional reconstruction techniques - has been
realized using ptychographic algorithm on experimentally recorded XUV-IR
pump-probe traces. The presented results contribute to in-situ, time-resolved
experiments accessing direct information on the electronic structure dynamics
of novel target materials.Comment: 20 pages, 8 figure
Visualization of the joining of ribosomal subunits reveals the presence of 80S ribosomes in the nucleus
In eukaryotes the 40S and 60S ribosomal subunits are assembled in the nucleolus, but there appear to be mechanisms preventing mRNA binding, 80S formation, and initiation of translation in the nucleus. To visualize association between ribosomal subunits, we tagged pairs of Drosophila ribosomal proteins (RPs) located in different subunits with mutually complementing halves of fluorescent proteins. Pairs of tagged RPs expected to interact, or be adjacent in the 80S structure, showed strong fluorescence, while pairs that were not in close proximity did not. Moreover, the complementation signal is found in ribosomal fractions and it was enhanced by translation elongation inhibitors and reduced by initiation inhibitors. Our technique achieved 80S visualization both in cultured cells and in fly tissues in vivo. Notably, while the main 80S signal was in the cytoplasm, clear signals were also seen in the nucleolus and at other nuclear sites. Furthermore, we detected rapid puromycin incorporation in the nucleolus and at transcription sites, providing an independent indication of functional 80S in the nucleolus and 80S association with nascent transcripts
The RNA helicase UPF1 associates with mRNAs co-transcriptionally and is required for the release of mRNAs from gene loci
UPF1 is an RNA helicase that is required for efficient nonsense-mediated mRNA decay (NMD) in eukaryotes, and the predominant view is that UPF1 mainly operates on the 3'UTRs of mRNAs that are directed for NMD in the cytoplasm. Here we offer evidence, obtained from Drosophila, that UPF1 constantly moves between the nucleus and cytoplasm by a mechanism that requires its RNA helicase activity. UPF1 is associated, genome-wide, with nascent RNAs at most of the active Pol II transcription sites and at some Pol III-transcribed genes, as demonstrated microscopically on the polytene chromosomes of salivary glands and by ChIP-seq analysis in S2 cells. Intron recognition seems to interfere with association and translocation of UPF1 on nascent pre-mRNAs, and cells depleted of UPF1 show defects in the release of mRNAs from transcription sites and mRNA export from the nucleus
Combined Forward-Backward Asymmetry Measurements in Top-Antitop Quark Production at the Tevatron
The CDF and D0 experiments at the Fermilab Tevatron have measured the asymmetry between yields of forward- and backward-produced top and antitop quarks based on their rapidity difference and the asymmetry between their decay leptons. These measurements use the full data sets collected in proton-antiproton collisions at a center-of-mass energy of TeV. We report the results of combinations of the inclusive asymmetries and their differential dependencies on relevant kinematic quantities. The combined inclusive asymmetry is . The combined inclusive and differential asymmetries are consistent with recent standard model predictions
Molecular Taxonomy: An Approach Based on Molecular Markers
Molecular markers developed during the last decade of molecular biology research and successfully utilized for various applications in the field of plant molecular taxonomy, are reviewed. It is always desirable to perform detailed genetic analyses, in addition to morphological studies, to segregate taxonomically different individuals particularly at or below the species level. It enables understanding of the evolutionary processes and reconstruction of phylogenetic relationships in groups of plants that are significant from multifaceted standpoints
Simultaneous Exfoliation and Functionalization of 2H-MoS2 by Thiolated Surfactants: Applications in Enhanced Antibacterial Activity
Two-dimensional transition metal dichalcogenides (TMDs), such as MoS2, generally exist in two different polymorphic structures, metallic (1T phase) and semiconducting (2H phase). In context of their wide spectrum of applications ranging from electronic to biomedicine, the aspects of ligand conjugation and solution processability are highly significant. In addition, the assessment of their antibacterial property and biocompatibility is equally important to explore their biomedical applications. Here we report a new method for the exfoliation and direct functionalization of 2H-MoS2 using surfactant molecules with thiol functionality. We found that the exfoliated MoS2 using thiolated ligands are functionalized with desired functionality and the processing scheme can be extended to other TMDs. Functionalized 2H-MoS2 exhibits highly enhanced antibacterial efficiency compared to similarly functionalized metallic 1T-MoS2 against pathogenic bacteria. The newly synthesized functionalized 2H-MoS2 exhibits better hemocompatibility, which makes it suitable for in vivo applications. This convenient functionalization method opens the door for many other applications of functionalized semiconducting 2H-MoS2 and other TMDs
Isothiocyanyl Alanine as a Synthetic Intermediate for the Synthesis of Thioureayl Alanines and Subsequent Aminotetrazolyl Alanines
The
synthesis of unnatural amino acids with small side-chain functionalities
usable for further transformations is highly demanding for the expansion
of the genetic code and other possible biotechnological applications.
To this end, we wanted to report the utility of an unexplored unnatural
amino acid, isothiocyanyl alanine (<sup>NCS</sup>Ala = Ita), for the
synthesis of another class of unnatural amino acids, thioureayl alanines
(<sup>TU</sup>Ala = Tua). The synthesis of a third class of unnatural
amino acids, amino tetrazolyl alanines (<sup>ATz</sup>Ala = Ata),
in a very good yield was subsequently achieved utilizing thioureayl
alanines. Thus, a variety of aliphatic- and aromatic-substituted thioureayl
alanines and aromatic-substituted amino tetrazolyl alanines were successfully
synthesized in good to excellent yields. The photophysical properties
of three of the fluorescent unnatural amino acids from two classes
were also studied and presented herein
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