Formation and Structure of a Cobalt(III) Complex Containing a Nonstabilized Pyridinium Ylide Ligand

The reaction of [Co^III(4,4′dmsalen)­(CH₂Cl)­(S)], where 4,4′dmsalen = 4,4′-dimethylsalen and S = solvent, with pyridine led to the formation of [Co^III(4,4′dmsalen)­(CH₂py)­(Cl)], containing a nonstabilized pyridinium ylide as axial ligand. The complex has been unambiguously characterized by single-crystal X-ray diffraction analysis. Time-resolved ¹H NMR spectra showed that the formation of [Co^III(4,4′dmsalen)­(CH₂py)­(Cl)] occurs in a two-step process involving a metallacyclized intermediate, <i>cis</i>-β-[Co^III(4,4′dmsalenCH₂)­(py)­(S)]⁺. A similar experiment carried out in the presence of different nitrogen bases having higher p<i>K</i>_a 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^III(4,4′dmsalen)­(CH₂Cl)­(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 −CH₂O– carbon of the cyclized species, whereas a parallel direct conversion through the displacement of Cl^– from the axial CH₂Cl group of [Co^III(4,4′dmsalen)­(CH₂Cl)­(S)] may be ruled out

Formation and Structure of a Cobalt(III) Complex Containing a Nonstabilized Pyridinium Ylide Ligand

The reaction of [Co^III(4,4′dmsalen)­(CH₂Cl)­(S)], where 4,4′dmsalen = 4,4′-dimethylsalen and S = solvent, with pyridine led to the formation of [Co^III(4,4′dmsalen)­(CH₂py)­(Cl)], containing a nonstabilized pyridinium ylide as axial ligand. The complex has been unambiguously characterized by single-crystal X-ray diffraction analysis. Time-resolved ¹H NMR spectra showed that the formation of [Co^III(4,4′dmsalen)­(CH₂py)­(Cl)] occurs in a two-step process involving a metallacyclized intermediate, <i>cis</i>-β-[Co^III(4,4′dmsalenCH₂)­(py)­(S)]⁺. A similar experiment carried out in the presence of different nitrogen bases having higher p<i>K</i>_a 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^III(4,4′dmsalen)­(CH₂Cl)­(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 −CH₂O– carbon of the cyclized species, whereas a parallel direct conversion through the displacement of Cl^– from the axial CH₂Cl group of [Co^III(4,4′dmsalen)­(CH₂Cl)­(S)] may be ruled out

Trans and Cis Effects of Axial Fluoroalkyl Ligands in Vitamin B₁₂ Analogues: Relationship between Alkyl- and Fluoroalkyl-Cobalamins

<b>CF₂HCbl</b>, <b>CF₃Cbl </b>, and <b>CF₃CH₂Cbl</b> have been synthesized and characterized in solution by ¹H NMR and UV–vis spectroscopy, and their X-ray crystal structures have been determined using synchrotron radiation. The structure of <b>CF₃CH₂Cbl</b> is reported for the first time, whereas those of <b>CF₂HCbl</b> and <b>CF₃Cbl</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 Co–C and Co–NB3 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>CF₃Cbl</b>, whereas in the case of <b>CF₂HCbl</b>, the Co–NB3 bond length is shorter than in MeCbl. Direct comparison of the structures of <b>CF₃CH₂Cbl</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 β-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 β-ligand of cobalamins and their structure (Co–X and Co–NB3 distances and corrin fold angle) and properties (UV–vis spectra, NMR spectra, and p<i>K</i>_base‑off)

Trans and Cis Effects of Axial Fluoroalkyl Ligands in Vitamin B₁₂ Analogues: Relationship between Alkyl- and Fluoroalkyl-Cobalamins

<b>CF₂HCbl</b>, <b>CF₃Cbl </b>, and <b>CF₃CH₂Cbl</b> have been synthesized and characterized in solution by ¹H NMR and UV–vis spectroscopy, and their X-ray crystal structures have been determined using synchrotron radiation. The structure of <b>CF₃CH₂Cbl</b> is reported for the first time, whereas those of <b>CF₂HCbl</b> and <b>CF₃Cbl</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 Co–C and Co–NB3 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>CF₃Cbl</b>, whereas in the case of <b>CF₂HCbl</b>, the Co–NB3 bond length is shorter than in MeCbl. Direct comparison of the structures of <b>CF₃CH₂Cbl</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 β-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 β-ligand of cobalamins and their structure (Co–X and Co–NB3 distances and corrin fold angle) and properties (UV–vis spectra, NMR spectra, and p<i>K</i>_base‑off)

Trans and Cis Effects of Axial Fluoroalkyl Ligands in Vitamin B₁₂ Analogues: Relationship between Alkyl- and Fluoroalkyl-Cobalamins

<b>CF₂HCbl</b>, <b>CF₃Cbl </b>, and <b>CF₃CH₂Cbl</b> have been synthesized and characterized in solution by ¹H NMR and UV–vis spectroscopy, and their X-ray crystal structures have been determined using synchrotron radiation. The structure of <b>CF₃CH₂Cbl</b> is reported for the first time, whereas those of <b>CF₂HCbl</b> and <b>CF₃Cbl</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 Co–C and Co–NB3 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>CF₃Cbl</b>, whereas in the case of <b>CF₂HCbl</b>, the Co–NB3 bond length is shorter than in MeCbl. Direct comparison of the structures of <b>CF₃CH₂Cbl</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 β-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 β-ligand of cobalamins and their structure (Co–X and Co–NB3 distances and corrin fold angle) and properties (UV–vis spectra, NMR spectra, and p<i>K</i>_base‑off)

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)–Pd(II) Porous Metal–Organic Framework with Square-Octahedron Topology Displaying High CO₂ Uptake and Selectivity toward CH₄ and N₂

The targeted synthesis of metal–organic 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 In­(III)/Pd­(II)-based MOF with square-octahedron (<b>soc</b>) topology. The new MOF, formulated as [In₃O­(<b>L</b>)_1.5(H₂O)₂Cl]·n­(solv) (<b>1</b>), features the oxo-centered trinuclear clusters, [In₃(μ₃-O)­(−COO)₆], acting as trigonal-prismatic 6-connected nodes that linked together with the metalloligand <i>trans</i>-[PdCl₂(PDC)₂] (<b>L</b>^<b>4–</b>) (PDC: pyridine-3,5-dicarboxylate) to form a 3D network. After successful activation of <b>1</b> using supercritical CO₂, high-resolution microporous analysis revealed the presence of small micropores (5.8 Å) with BET area of 795 m² g^–1 and total pore volume of 0.35 cm³ g^–1. The activated solid shows high gravimetric (92.3 cm³ g^–1) and volumetric (120.9 cm³ cm^–3) CO₂ uptake at 273 K and 1 bar as well as high CO₂/CH₄ (15.4 for a 50:50 molar mixture) and CO₂/N₂ (131.7 for a 10:90 molar mixture) selectivity, with moderate <i>Q</i>_st⁰ for CO₂ (29.8 kJ mol^–1). Slight modifications of the synthesis conditions led to the formation of a different MOF with an anionic framework, having a chemical formula [Me₂NH₂]­[In­(<b>L</b>)]·<i>n</i>(solv) (<b>2</b>). This MOF is constructed from pseudotetrahedral, mononuclear [In­(−COO)₄] nodes bridged by four <b>L</b>^<b>4–</b> 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 90°. β-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