1,042 research outputs found
A Potential Iterative Approach to 1,4-Dihydro-N-Heteroacene Arrays
Acknowledgements We are grateful to the UK EPSRC National Mass Spectrometry Service Centre for mass spectrometric data.Peer reviewedPublisher PD
APA2[Zn3(HPO4)4(H2O)2], a layered zincophosphate featuring template-to-framework N-H⋯O and "synergic" framework-to-template O-H⋯N hydrogen bonds and C-H⋯O interactions (APA = 2-Amino-1-phenyleneammonium, C6H9N2 +)
Peer reviewedPublisher PD
Metal complexes of saccharin and thiosaccharin as potential anticancer and antimicrobial agents
Acknowledgements The support provided by our universities (KTU, EOGU and UA) in accessing scientific databases (WOS, Scopus, SciFinder and CCDC) was greatly appreciated.Peer reviewe
[KDy(Hptc)3(H3ptc)]n·2n(Hbipy)·5n(H2O), a layered coordination polymer containing DyO6N3 tri-capped trigonal prisms (H3ptc = Pyridine 2,4,6-Tricarboxylic Acid, C8H5NO6; Bipy = 2,2'-Bipyridine, C10H8N2)
Peer reviewedPublisher PD
Crystal structure of 1-butyl-2,3-di-methylimidazolium dicarba-7,8-nido-undecaborate
AL thanks Professor Maitland Jones for the generous donation of the starting orthocarborane stock and Dr John Holbrey for the supply of imidazolium halide reagents. The research support by ACS PRF and Cottrell College awards (44692.01-GB and CC6755) is gratefully acknowledged.Peer reviewedPublisher PD
Synthesis and structural features of copper(II) complexes of N,N,N′,N′-tetramethylethylenediamine with 2-chlorobenzoate1− and 2-hydroxybenzoate1−
Published online 22 Jan 2019.Peer reviewedPostprin
Geomagnetic storm dependence on the solar flare class
Content. Solar flares are often used as precursors of geomagnetic storms. In
particular, Howard and Tappin (2005) recently published in A&A a dependence
between X-ray class of solar flares and Ap and Dst indexes of geomagnetic
storms which contradicts to early published results.
Aims. We compare published results on flare-storm dependences and discuss
possible sources of the discrepancy.
Methods. We analyze following sources of difference: (1) different intervals
of observations, (2) different statistics and (3) different methods of event
identification and comparison.
Results. Our analysis shows that magnitude of geomagnetic storms is likely to
be independent on X-ray class of solar flares.Comment: 3 pages, 1 tabl
Recommended from our members
In Situ Template Generation for Zincophosphate Synthesis Leading to C2H7N4O-ZnPO4 Containing Template-to-Template N--H...O Hydrogen Bonds
The synthesis, structure and some properties of C{sub 2}H{sub 7}N{sub 4}O {center_dot} ZnPO{sub 4} (guanylurea zinc phosphate) are reported. The cationic template was prepared in situ by partial hydrolysis of the neutral 2-cyanoguanidine starting material. The resulting structure contains a new, unprotonated, zincophosphate layer topology as well as unusual N-H-O template-to-template hydrogen bonds which help to stabilize a ''double sandwich'' of templating cations between the inorganic sheets. Crystal data: C{sub 2}H{sub 7}N{sub 4}O {center_dot} ZnPO{sub 4}, M{sub r} = 229.44, monoclinic, P2{sub 1}/c, a = 13.6453 (9) {angstrom}, b = 5.0716 (3) {angstrom}, c = 10.6005 (7) {angstrom}, {beta} = 95.918 (2){sup 0}, V = 729.7 (1) {angstrom}{sup 3}, R(F) = 0.034, wR(F) = 0.034
3-Fluoro-4-hydroxyprolines:Synthesis, conformational analysis and stereoselective recognition by the VHL E3 ubiquitin ligase for targeted protein degradation
Hydroxylation and
fluorination of proline alters the pyrrolidine
ring pucker and the trans:cis amide bond ratio in a stereochemistry-dependent
fashion, affecting molecular recognition of proline-containing molecules
by biological systems. While hydroxyprolines and fluoroprolines are
common motifs in medicinal and biological chemistry, the synthesis
and molecular properties of prolines containing both modifications,
i.e., fluoro-hydroxyprolines, have not been described. Here we present
a practical and facile synthesis of all four diastereoisomers of 3-fluoro-4-hydroxyprolines
(F-Hyps), starting from readily available 4-oxo-l-proline
derivatives. Small-molecule X-ray crystallography, NMR spectroscopy,
and quantum mechanical calculations are consistent with fluorination
at C<sup>3</sup> having negligible effects on the hydrogen bond donor
capacity of the C<sup>4</sup> hydroxyl, but inverting the natural
preference of Hyp from C<sup>4</sup>-exo to C<sup>4</sup>-endo pucker.
In spite of this, F-Hyps still bind to the von Hippel–Lindau
(VHL) E3 ligase, which naturally recognizes C<sup>4</sup>-exo Hyp
in a stereoselective fashion. Co-crystal structures and electrostatic
potential calculations support and rationalize the observed preferential
recognition for (3<i>R</i>,4<i>S</i>)-F-Hyp over
the corresponding (3<i>S</i>,4<i>S</i>) epimer
by VHL. We show that (3<i>R</i>,4<i>S</i>)-F-Hyp
provides bioisosteric Hyp substitution in both hypoxia-inducible factor
1 alpha (HIF-1α) substrate peptides and peptidomimetic ligands
that form part of PROTAC (proteolysis targeting chimera) conjugates
for targeted protein degradation. Despite a weakened affinity, Hyp
substitution with (3<i>S</i>,4<i>S</i>)-F-Hyp
within the PROTAC MZ1 led to Brd4-selective cellular degradation at
concentrations >100-fold lower than the binary <i>K</i><sub>d</sub> for VHL. We anticipate that the disclosed chemistry
of 3-fluoro-4-hydroxyprolines
and their application as VHL ligands for targeted protein degradation
will be of wide interest to medicinal organic chemists, chemical biologists,
and drug discoverers alike
Accuracy and Limitations of Fitting and Stereoscopic Methods to Determine the Direction of Coronal Mass Ejections from Heliospheric Imagers Observations
Using data from the Heliospheric Imagers (HIs) onboard STEREO, it is possible
to derive the direction of propagation of coronal mass ejections (CMEs) in
addition to their speed with a variety of methods. For CMEs observed by both
STEREO spacecraft, it is possible to derive their direction using simultaneous
observations from the twin spacecraft and also, using observations from only
one spacecraft with fitting methods. This makes it possible to test and compare
different analyses techniques. In this article, we propose a new fitting method
based on observations from one spacecraft, which we compare to the commonly
used fitting method of Sheeley et al. (1999). We also compare the results from
these two fitting methods with those from two stereoscopic methods, focusing on
12 CMEs observed simultaneously by the two STEREO spacecraft in 2008 and 2009.
We find evidence that the fitting method of Sheeley et al. (1999) can result in
significant errors in the determination of the CME direction when the CME
propagates outside of 60deg \pm 20 deg from the Sun-spacecraft line. We expect
our new fitting method to be better adapted to the analysis of halo or limb
CMEs with respect to the observing spacecraft. We also find some evidence that
direct triangulation in the HI fields-of-view should only be applied to CMEs
propagating approximatively towards Earth (\pm 20deg from the Sun-Earth line).
Last, we address one of the possible sources of errors of fitting methods: the
assumption of radial propagation. Using stereoscopic methods, we find that at
least seven of the 12 studied CMEs had an heliospheric deflection of less than
20deg as they propagated in the HI fields-of-view, which, we believe, validates
this approximation.Comment: 17 pages, 6 figures, 2 tables, accepted to Solar Physic
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