184 research outputs found
Economical and scalable synthesis of 6-amino-2-cyanobenzothiazole
2-Cyanobenzothiazoles (CBTs) are useful building blocks for: 1) luciferin derivatives for bioluminescent imaging; and 2) handles for bioorthogonal ligations. A particularly versatile CBT is 6-amino-2-cyanobenzothiazole (ACBT), which has an amine handle for straight-forward derivatisation. Here we present an economical and scalable synthesis of ACBT based on a cyanation catalysed by 1,4-diazabicyclo[2.2.2]octane (DABCO), and discuss its advantages for scale-up over previously reported routes
Emergence of double- and triple-gene reassortant G1P[8] rotaviruses possessing a DS-1-like backbone after rotavirus vaccine introduction in Malawi
To combat the high burden of rotavirus gastroenteritis, multiple African countries have introduced rotavirus vaccines into their childhood immunization programs. Malawi incorporated a G1P[8] rotavirus vaccine (Rotarix) into its immunization schedule in 2012. Utilizing a surveillance platform of hospitalized rotavirus gastroenteritis cases, we examined the phylodynamics of G1P[8] rotavirus strains that circulated in Malawi before (1998 to 2012) and after (2013 to 2014) vaccine introduction. Analysis of whole genomes obtained through next-generation sequencing revealed that all randomly selected prevaccine G1P[8] strains sequenced (n = 32) possessed a Wa-like genetic constellation, whereas postvaccine G1P[8] strains (n = 18) had a DS-1-like constellation. Phylodynamic analyses indicated that postvaccine G1P[8] strains emerged through reassortment events between human Wa- and DS-1-like rotaviruses that circulated in Malawi from the 1990s and hence were classified as atypical DS-1-like reassortants. The time to the most recent common ancestor for G1P[8] strains was from 1981 to 1994; their evolutionary rates ranged from 9.7 × 10−4 to 4.1 × 10−3 nucleotide substitutions/site/year. Three distinct G1P[8] lineages chronologically replaced each other between 1998 and 2014. Genetic drift was the likely driver for lineage turnover in 2005, whereas replacement in 2013 was due to reassortment. Amino acid substitution within the outer glycoprotein VP7 of G1P[8] strains had no impact on the structural conformation of the antigenic regions, suggesting that it is unlikely that they would affect recognition by vaccine-induced neutralizing antibodies. While the emergence of DS-1-like G1P[8] rotavirus reassortants in Malawi was therefore likely due to natural genotype variation, vaccine effectiveness against such strains needs careful evaluation.
IMPORTANCE: The error-prone RNA-dependent RNA polymerase and the segmented RNA genome predispose rotaviruses to genetic mutation and genome reassortment, respectively. These evolutionary mechanisms generate novel strains and have the potential to lead to the emergence of vaccine escape mutants. While multiple African countries have introduced a rotavirus vaccine, there are few data describing the evolution of rotaviruses that circulated before and after vaccine introduction. We report the emergence of atypical DS-1-like G1P[8] strains during the postvaccine era in Malawi. Three distinct G1P[8] lineages circulated chronologically from 1998 to 2014; mutation and reassortment drove lineage turnover in 2005 and 2013, respectively. Amino acid substitutions within the outer capsid VP7 glycoprotein did not affect the structural conformation of mapped antigenic sites, suggesting a limited effect on the recognition of G1-specific vaccine-derived antibodies. The genes that constitute the remaining genetic backbone may play important roles in immune evasion, and vaccine effectiveness against such atypical strains needs careful evaluation
Observation of an Exotic Baryon in Exclusive Photoproduction from the Deuteron
In an exclusive measurement of the reaction , a
narrow peak that can be attributed to an exotic baryon with strangeness
is seen in the invariant mass spectrum. The peak is at
GeV/c with a measured width of 0.021 GeV/c FWHM, which is largely
determined by experimental mass resolution. The statistical significance of the
peak is . The mass and width of the observed peak are
consistent with recent reports of a narrow baryon by other experimental
groups.Comment: 5 pages, 5 figure
Measurement of Beam-Spin Asymmetries for Deep Inelastic Electroproduction
We report the first evidence for a non-zero beam-spin azimuthal asymmetry in
the electroproduction of positive pions in the deep-inelastic region. Data have
been obtained using a polarized electron beam of 4.3 GeV with the CLAS detector
at the Thomas Jefferson National Accelerator Facility (JLab). The amplitude of
the modulation increases with the momentum of the pion relative to
the virtual photon, , with an average amplitude of for range.Comment: 5 pages, RevTEX4, 3 figures, 2 table
Measurement of the Polarized Structure Function for in the Resonance Region
The polarized longitudinal-transverse structure function
has been measured in the resonance region at and 0.65
GeV. Data for the reaction were taken at Jefferson Lab
with the CEBAF Large Acceptance Spectrometer (CLAS) using longitudinally
polarized electrons at an energy of 1.515 GeV. For the first time a complete
angular distribution was measured, permitting the separation of different
non-resonant amplitudes using a partial wave analysis. Comparison with previous
beam asymmetry measurements at MAMI indicate a deviation from the predicted
dependence of using recent phenomenological
models.Comment: 5 pages, LaTex, 4 eps figures: to be published in PRC/Rapid
Communications. Version 2 has revised Q^2 analysi
Onset of asymptotic scaling in deuteron photodisintegration
We investigate the transition from the nucleon-meson to quark-gluon
description of the strong interaction using the photon energy dependence of the
differential cross section for photon energies above 0.5 GeV and
center-of-mass proton angles between and . A possible
signature for this transition is the onset of cross section scaling
with the total energy squared, , at some proton transverse momentum, .
The results show that the scaling has been reached for proton transverse
momentum above about 1.1 GeV/c. This may indicate that the quark-gluon regime
is reached above this momentum.Comment: Accepted by PRL; 5 pages, 2 figure
First Measurement of Transferred Polarization in the Exclusive e p --> e' K+ Lambda Reaction
The first measurements of the transferred polarization for the exclusive ep
--> e'K+ Lambda reaction have been performed in Hall B at the Thomas Jefferson
National Accelerator Facility using the CLAS spectrometer. A 2.567 GeV electron
beam was used to measure the hyperon polarization over a range of Q2 from 0.3
to 1.5 (GeV/c)2, W from 1.6 to 2.15 GeV, and over the full center-of-mass
angular range of the K+ meson. Comparison with predictions of hadrodynamic
models indicates strong sensitivity to the underlying resonance contributions.
A non-relativistic quark model interpretation of our data suggests that the
s-sbar quark pair is produced with spins predominantly anti-aligned.
Implications for the validity of the widely used 3P0 quark-pair creation
operator are discussed.Comment: 6 pages, 4 figure
Observation of Nuclear Scaling in the Reaction at 1
The ratios of inclusive electron scattering cross sections of He,
C, and Fe to He have been measured for the first time. It is
shown that these ratios are independent of at Q1.4 (GeV/c) for
1.5 where the inclusive cross section depends primarily on the
high-momentum components of the nuclear wave function. The observed scaling
shows that the momentum distributions at high-momenta have the same shape for
all nuclei and differ only by a scale factor. The observed onset of the scaling
at Q1.4 and 1.5 is consistent with the kinematical expectation that
two nucleon short range correlations (SRC) are dominate the nuclear wave
function at 300 MeV/c. The values of these ratios in the scaling
region can be related to the relative probabilities of SRC in nuclei with
A3. Our data demonstrate that for nuclei with A12 these
probabilities are 5-5.5 times larger than in deuterium, while for He it is
larger by a factor of about 3.5.Comment: 11 pages, 10 figure
Single pi+ Electroproduction on the Proton in the First and Second Resonance Regions at 0.25GeV^2 < Q^2 < 0.65GeV^2 Using CLAS
The ep -> e'pi^+n reaction was studied in the first and second nucleon
resonance regions in the 0.25 GeV^2 < Q^2 < 0.65 GeV^2 range using the CLAS
detector at Thomas Jefferson National Accelerator Facility. For the first time
the absolute cross sections were measured covering nearly the full angular
range in the hadronic center-of-mass frame. The structure functions sigma_TL,
sigma_TT and the linear combination sigma_T+epsilon*sigma_L were extracted by
fitting the phi-dependence of the measured cross sections, and were compared to
the MAID and Sato-Lee models.Comment: Accepted for publication in PR
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