18 research outputs found
Formation and Structure of a Cobalt(III) Complex Containing a Nonstabilized Pyridinium Ylide Ligand
The
reaction of [Co<sup>III</sup>(4,4ā²dmsalen)Ā(CH<sub>2</sub>Cl)Ā(S)], where 4,4ā²dmsalen = 4,4ā²-dimethylsalen
and S = solvent, with pyridine led to the formation of [Co<sup>III</sup>(4,4ā²dmsalen)Ā(CH<sub>2</sub>py)Ā(Cl)], containing a nonstabilized
pyridinium ylide as axial ligand. The complex has been unambiguously
characterized by single-crystal X-ray diffraction analysis. Time-resolved <sup>1</sup>H NMR spectra showed that the formation of [Co<sup>III</sup>(4,4ā²dmsalen)Ā(CH<sub>2</sub>py)Ā(Cl)] occurs in a two-step
process involving a metallacyclized intermediate, <i>cis</i>-Ī²-[Co<sup>III</sup>(4,4ā²dmsalenCH<sub>2</sub>)Ā(py)Ā(S)]<sup>+</sup>. A similar experiment carried out in the presence of different
nitrogen bases having higher p<i>K</i><sub>a</sub> values
(4-Me-py or 4-<i>t</i>-Bu-py) allowed a better separation
of the two consecutive reactions. The almost complete conversion of
[Co<sup>III</sup>(4,4ā²dmsalen)Ā(CH<sub>2</sub>Cl)Ā(S)]
in the cyclized intermediate before the formation of the ylide indicates
that the ylide complex forms exclusively through the nucleophilic
attack of the nitrogen base at the āCH<sub>2</sub>Oā
carbon of the cyclized species, whereas a parallel direct conversion
through the displacement of Cl<sup>ā</sup> from the axial CH<sub>2</sub>Cl group of [Co<sup>III</sup>(4,4ā²dmsalen)Ā(CH<sub>2</sub>Cl)Ā(S)] may be ruled out
Formation and Structure of a Cobalt(III) Complex Containing a Nonstabilized Pyridinium Ylide Ligand
The
reaction of [Co<sup>III</sup>(4,4ā²dmsalen)Ā(CH<sub>2</sub>Cl)Ā(S)], where 4,4ā²dmsalen = 4,4ā²-dimethylsalen
and S = solvent, with pyridine led to the formation of [Co<sup>III</sup>(4,4ā²dmsalen)Ā(CH<sub>2</sub>py)Ā(Cl)], containing a nonstabilized
pyridinium ylide as axial ligand. The complex has been unambiguously
characterized by single-crystal X-ray diffraction analysis. Time-resolved <sup>1</sup>H NMR spectra showed that the formation of [Co<sup>III</sup>(4,4ā²dmsalen)Ā(CH<sub>2</sub>py)Ā(Cl)] occurs in a two-step
process involving a metallacyclized intermediate, <i>cis</i>-Ī²-[Co<sup>III</sup>(4,4ā²dmsalenCH<sub>2</sub>)Ā(py)Ā(S)]<sup>+</sup>. A similar experiment carried out in the presence of different
nitrogen bases having higher p<i>K</i><sub>a</sub> values
(4-Me-py or 4-<i>t</i>-Bu-py) allowed a better separation
of the two consecutive reactions. The almost complete conversion of
[Co<sup>III</sup>(4,4ā²dmsalen)Ā(CH<sub>2</sub>Cl)Ā(S)]
in the cyclized intermediate before the formation of the ylide indicates
that the ylide complex forms exclusively through the nucleophilic
attack of the nitrogen base at the āCH<sub>2</sub>Oā
carbon of the cyclized species, whereas a parallel direct conversion
through the displacement of Cl<sup>ā</sup> from the axial CH<sub>2</sub>Cl group of [Co<sup>III</sup>(4,4ā²dmsalen)Ā(CH<sub>2</sub>Cl)Ā(S)] may be ruled out
Trans and Cis Effects of Axial Fluoroalkyl Ligands in Vitamin B<sub>12</sub> Analogues: Relationship between Alkyl- and Fluoroalkyl-Cobalamins
<b>CF<sub>2</sub>HCbl</b>,
<b>CF<sub>3</sub>Cbl </b>, and <b>CF<sub>3</sub>CH<sub>2</sub>Cbl</b> have been synthesized and characterized in solution by <sup>1</sup>H NMR and UVāvis spectroscopy, and their X-ray crystal
structures have been determined using synchrotron radiation. The structure
of <b>CF<sub>3</sub>CH<sub>2</sub>Cbl</b> is reported for the
first time, whereas those of <b>CF<sub>2</sub>HCbl</b> and <b>CF<sub>3</sub>Cbl</b> are re-examined to obtain more precise structural
data. Comparison of the structural data obtained with the alkylcobalamin
analogues, MeCbl and EtCbl, indicates that the CoāC and CoāNB3
bond lengths are shorter in the fluoroalkylcobalamins. The structural
data of the fluoroalkylcobalamins previously reported in the literature
had been conflicting in this regard. Thus, a much less dramatic shortening
of the two axial bonds was found for <b>CF<sub>3</sub>Cbl</b>, whereas in the case of <b>CF<sub>2</sub>HCbl</b>, the CoāNB3
bond length is shorter than in MeCbl. Direct comparison of the structures
of <b>CF<sub>3</sub>CH<sub>2</sub>Cbl</b> and EtCbl indicates
a large distortion of the axial fragment in the former case that can
be attributed to steric effects. A number of previously reported correlations
of the effect of the Ī²-ligand on the structure and properties
of cobalamins are re-examined in light of the present results. Particular
emphasis is placed on the axial fragment. This analysis substantially
confirms and, with the new data reported here, adjusts and expands
the data set for correlations between trans and cis influences of
the Ī²-ligand of cobalamins and their structure (CoāX
and CoāNB3 distances and corrin fold angle) and properties
(UVāvis spectra, NMR spectra, and p<i>K</i><sub>baseāoff</sub>)
Trans and Cis Effects of Axial Fluoroalkyl Ligands in Vitamin B<sub>12</sub> Analogues: Relationship between Alkyl- and Fluoroalkyl-Cobalamins
<b>CF<sub>2</sub>HCbl</b>,
<b>CF<sub>3</sub>Cbl </b>, and <b>CF<sub>3</sub>CH<sub>2</sub>Cbl</b> have been synthesized and characterized in solution by <sup>1</sup>H NMR and UVāvis spectroscopy, and their X-ray crystal
structures have been determined using synchrotron radiation. The structure
of <b>CF<sub>3</sub>CH<sub>2</sub>Cbl</b> is reported for the
first time, whereas those of <b>CF<sub>2</sub>HCbl</b> and <b>CF<sub>3</sub>Cbl</b> are re-examined to obtain more precise structural
data. Comparison of the structural data obtained with the alkylcobalamin
analogues, MeCbl and EtCbl, indicates that the CoāC and CoāNB3
bond lengths are shorter in the fluoroalkylcobalamins. The structural
data of the fluoroalkylcobalamins previously reported in the literature
had been conflicting in this regard. Thus, a much less dramatic shortening
of the two axial bonds was found for <b>CF<sub>3</sub>Cbl</b>, whereas in the case of <b>CF<sub>2</sub>HCbl</b>, the CoāNB3
bond length is shorter than in MeCbl. Direct comparison of the structures
of <b>CF<sub>3</sub>CH<sub>2</sub>Cbl</b> and EtCbl indicates
a large distortion of the axial fragment in the former case that can
be attributed to steric effects. A number of previously reported correlations
of the effect of the Ī²-ligand on the structure and properties
of cobalamins are re-examined in light of the present results. Particular
emphasis is placed on the axial fragment. This analysis substantially
confirms and, with the new data reported here, adjusts and expands
the data set for correlations between trans and cis influences of
the Ī²-ligand of cobalamins and their structure (CoāX
and CoāNB3 distances and corrin fold angle) and properties
(UVāvis spectra, NMR spectra, and p<i>K</i><sub>baseāoff</sub>)
Trans and Cis Effects of Axial Fluoroalkyl Ligands in Vitamin B<sub>12</sub> Analogues: Relationship between Alkyl- and Fluoroalkyl-Cobalamins
<b>CF<sub>2</sub>HCbl</b>,
<b>CF<sub>3</sub>Cbl </b>, and <b>CF<sub>3</sub>CH<sub>2</sub>Cbl</b> have been synthesized and characterized in solution by <sup>1</sup>H NMR and UVāvis spectroscopy, and their X-ray crystal
structures have been determined using synchrotron radiation. The structure
of <b>CF<sub>3</sub>CH<sub>2</sub>Cbl</b> is reported for the
first time, whereas those of <b>CF<sub>2</sub>HCbl</b> and <b>CF<sub>3</sub>Cbl</b> are re-examined to obtain more precise structural
data. Comparison of the structural data obtained with the alkylcobalamin
analogues, MeCbl and EtCbl, indicates that the CoāC and CoāNB3
bond lengths are shorter in the fluoroalkylcobalamins. The structural
data of the fluoroalkylcobalamins previously reported in the literature
had been conflicting in this regard. Thus, a much less dramatic shortening
of the two axial bonds was found for <b>CF<sub>3</sub>Cbl</b>, whereas in the case of <b>CF<sub>2</sub>HCbl</b>, the CoāNB3
bond length is shorter than in MeCbl. Direct comparison of the structures
of <b>CF<sub>3</sub>CH<sub>2</sub>Cbl</b> and EtCbl indicates
a large distortion of the axial fragment in the former case that can
be attributed to steric effects. A number of previously reported correlations
of the effect of the Ī²-ligand on the structure and properties
of cobalamins are re-examined in light of the present results. Particular
emphasis is placed on the axial fragment. This analysis substantially
confirms and, with the new data reported here, adjusts and expands
the data set for correlations between trans and cis influences of
the Ī²-ligand of cobalamins and their structure (CoāX
and CoāNB3 distances and corrin fold angle) and properties
(UVāvis spectra, NMR spectra, and p<i>K</i><sub>baseāoff</sub>)
Recent Advances in the Understanding of the Influence of Electric and Magnetic Fields on Protein Crystal Growth
In
this contribution we use nonconventional methods that help to
increase the success rate of a protein crystal growth, and consequently
of structural projects using X-ray diffraction techniques. In order
to achieve this purpose, this contribution presents new approaches
involving more sophisticated techniques of protein crystallization,
not just for growing protein crystals of different sizes by using
electric fields, but also for controlling crystal size and orientation.
This latter was possible through the use of magnetic fields that allow
to obtain protein crystals suitable for both high-resolution X-ray
and neutron diffraction crystallography where big crystals are required.
This contribution discusses some pros, cons and realities of the role
of electromagnetic fields in protein crystallization research, and
their effect on protein crystal contacts. Additionally, we discuss
the importance of room and low temperatures during data collection.
Finally, we also discuss the effect of applying a rather strong magnetic
field of 16.5 T, for shorts and long periods of time, on protein crystal
growth, and on the 3D structure of two model proteins
Heterometallic In(III)āPd(II) Porous MetalāOrganic Framework with Square-Octahedron Topology Displaying High CO<sub>2</sub> Uptake and Selectivity toward CH<sub>4</sub> and N<sub>2</sub>
The targeted synthesis of metalāorganic
frameworks (MOFs) with open metal sites, following reticular chemistry
rules, provides a straightforward methodology toward the development
of advanced porous materials especially for gas storage/separation
applications. Using a palladated tetracarboxylate metalloligand as
a 4-connected node, we succeeded in synthesizing the first heterobimetallic
InĀ(III)/PdĀ(II)-based MOF with square-octahedron (<b>soc</b>)
topology. The new MOF, formulated as [In<sub>3</sub>OĀ(<b>L</b>)<sub>1.5</sub>(H<sub>2</sub>O)<sub>2</sub>Cl]Ā·nĀ(solv) (<b>1</b>), features the oxo-centered trinuclear clusters, [In<sub>3</sub>(Ī¼<sub>3</sub>-O)Ā(āCOO)<sub>6</sub>], acting
as trigonal-prismatic 6-connected nodes that linked together with
the metalloligand <i>trans</i>-[PdCl<sub>2</sub>(PDC)<sub>2</sub>] (<b>L</b><sup><b>4ā</b></sup>) (PDC:
pyridine-3,5-dicarboxylate) to form a 3D network. After successful
activation of <b>1</b> using supercritical CO<sub>2</sub>, high-resolution
microporous analysis revealed the presence of small micropores (5.8
Ć
) with BET area of 795 m<sup>2</sup> g<sup>ā1</sup> and
total pore volume of 0.35 cm<sup>3</sup> g<sup>ā1</sup>. The
activated solid shows high gravimetric (92.3 cm<sup>3</sup> g<sup>ā1</sup>) and volumetric (120.9 cm<sup>3</sup> cm<sup>ā3</sup>) CO<sub>2</sub> uptake at 273 K and 1 bar as well as high CO<sub>2</sub>/CH<sub>4</sub> (15.4 for a 50:50 molar mixture) and CO<sub>2</sub>/N<sub>2</sub> (131.7 for a 10:90 molar mixture) selectivity,
with moderate <i>Q</i><sub>st</sub><sup>0</sup> for CO<sub>2</sub> (29.8 kJ mol<sup>ā1</sup>). Slight modifications of
the synthesis conditions led to the formation of a different MOF with
an anionic framework, having a chemical formula [Me<sub>2</sub>NH<sub>2</sub>]Ā[InĀ(<b>L</b>)]Ā·<i>n</i>(solv) (<b>2</b>). This MOF is constructed from pseudotetrahedral, mononuclear
[InĀ(āCOO)<sub>4</sub>] nodes bridged by four <b>L</b><sup><b>4ā</b></sup> linkers, resulting in a 3D network
with <b>PtS</b> topology
Data collection statistics for native and selenomethionine substituted AmyR.
<p>Values in parentheses are for the highest resolution shell.</p
Ribbon representation of the overall structure of the AmyR monomer.
<p>The AmyR monomer is coloured by secondary structure. Secondary structure elements are labelled with residue numbers. The right panel is rotated 90Ā°. Ī²-strand 1 interacts with the equivalent residues in the dimer, shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0176049#pone.0176049.g002" target="_blank">Fig 2</a>.</p
Unmodelled density at crystal contact between molecules.
<p>(A) Electron density and difference map of the unmodelled density at the crystal contact. The main crystal contact forming density is central, while the two other chains are seen below. (B) An alternative view of the two chains.</p