Probing the Inverse Trans Influence in Americium and Lanthanide Tribromide Tris(tricyclohexylphosphine oxide)

The synthesis, characterization, and theoretical analysis of meridional americium tribromide tris(tricyclohexylphosphine oxide), mer-AmBr3(OPcy3)3 has been achieved and is compared with its early lanthanide (La to Nd) analogs. The data show that homo trans ligands show significantly shorter bonds than the cis or hetero trans ligands. This is particularly pronounced in the americium compound. DFT along with multiconfigurational CASSCF calculations show that the contraction of the bonds relates qualitatively with overall covalency, i.e. americium shows the most covalent interactions compared to lanthanides. . However, the involvement of the 5p and 6p shells in bonding follows a different order, namely cerium > neodymium ~ americium. This study provides further insight into the mechanisms by which ITI operates in low-valent f-block complexes

Why p-OMe- and p-Cl-β-Methylphenethylamines Display Distinct Activities upon MAO-B Binding.

Despite their structural and chemical commonalities, p-chloro-β-methylphenethylamine and p-methoxy-β-methylphenethylamine display distinct inhibitory and substrate activities upon MAO-B binding. Density Functional Theory (DFT) quantum chemical calculations reveal that β-methylation and para-substitution underpin the observed activities sustained by calculated transition state energy barriers, attained conformations and key differences in their interactions in the enzyme's substrate binding site. Although both compounds meet substrate requirements, it is clear that β-methylation along with the physicochemical features of the para-substituents on the aromatic ring determine the activity of these compounds upon binding to the MAO B-isoform. While data for a larger set of compounds might lend generality to our conclusions, our experimental and theoretical results strongly suggest that the contrasting activities displayed depend on the conformations adopted by these compounds when they bind to the enzyme

Influence of protonation on substrate and inhibitor interactions at the active site of human monoamine oxidase-A

Although substrate conversion mediated by human monoaminooxidase (hMAO) has been associated with the deprotonated state of their amine moiety, data regarding the influence of protonation on substrate binding at the active site are scarce. Thus, in order to assess protonation influence, steered molecular dynamics (SMD) runs were carried out. These simulations revealed that the protonated form of the substrate serotonin (5-HT) exhibited stronger interactions at the protein surface compared to the neutral form. The latter displayed stronger interactions in the active site cavity. These observations support the possible role of the deprotonated form in substrate conversion. Multigrid docking studies carried out to rationalize the role of 5-HT protonation in other sites besides the active site indicated two energetically favored docking sites for the protonated form of 5-HT on the enzyme surface. These sites seem to be interconnected with the substrate/inhibitor cavity, as revealed by the

Altering the Spectroscopy, Electronic Structure, and Bonding of Organometallic Curium(III) Upon Coordination of 4,4-bipyridine

Structural and electronic characterization of (Cp\u273Cm)2(4,4\u27-bpy) (Cp\u27 = trimethylsilylcyclopentadienyl, 4,4\u27-bpy = 4,4\u27-bipyridine) is reported and provides a rare example of curium-carbon bonding. Cp\u273Cm displays unexpectedly low energy emission that is quenched upon coordination by 4,4\u27-bipyridine. Electronic structure calculations on Cp\u273Cm and (Cp\u273Cm)2(4,4\u27-bpy) rule out significant differences in the emissive state, rendering 4,4\u27-bipyridine as the primary quenching agent. Comparisons of (Cp\u273Cm)2(4,4\u27-bpy) with its samarium and gadolinium analogues reveal atypical bonding patterns and electronic features that offer insights into bonding between carbon with f-block metal ions

Molecular dynamics simulation of halogen bonding mimics experimental data for cathepsin L inhibition

Artículo de publicación ISIA MD simulation protocol was developed to model halogen bonding in protein–ligand complexes by inclusion of a charged extra point to represent the anisotropic distribution of charge on the halogen atom. This protocol was then used to simulate the interactions of cathepsin L with a series of halogenated and non-halogenated inhibitors. Our results show that chloro, bromo and iodo derivatives have progressively narrower distributions of calculated geometries, which reflects the order of affinity I[Br[Cl, in agreement with the IC50 values. Graphs for the Cl, Br and I analogs show stable interactions between the halogen atom and the Gly61 carbonyl oxygen of the enzyme. The halogen-oxygen distance is close to or less than the sum of the van der Waals radii; the C–X O angle is about 170 ; and the X O=C angle approaches 120 , as expected for halogen bond formation. In the case of the iodo-substituted analogs, these effects are enhanced by introduction of a fluorine atom on the inhibitors’ halogenbonding phenyl ring, indicating that the electron withdrawing group enlarges the r-hole, resulting in improved halogen bonding properties.FONDECYT Grant 111014

Altering the spectroscopy, electronic structure, and bonding of organometallic curium(III) upon coordination of 4,4′−bipyridine

Abstract Structural and electronic characterization of (Cp′3Cm)2(μ−4,4′−bpy) (Cp′ = trimethylsilylcyclopentadienyl, 4,4′−bpy = 4,4′−bipyridine) is reported and provides a rare example of curium−carbon bonding. Cp′3Cm displays unexpectedly low energy emission that is quenched upon coordination by 4,4′−bipyridine. Electronic structure calculations on Cp′3Cm and (Cp′3Cm)2(μ−4,4′−bpy) rule out significant differences in the emissive state, rendering 4,4′−bipyridine as the primary quenching agent. Comparisons of (Cp′3Cm)2(μ−4,4′−bpy) with its samarium and gadolinium analogues reveal atypical bonding patterns and electronic features that offer insights into bonding between carbon with f-block metal ions. Here we show the structural characterization of a curium−carbon bond, in addition to the unique electronic properties never before observed in a curium compound

Radium Revisited: Revitalization of the Coordination Chemistry of Nature’s Largest 2+ Cation

The crystallization, single-crystal structure, and Raman spectroscopy of Ra(NO3)2 have been investigated by experiment and theory, which represent the first, pure radium compound characterized by single crystal X-ray diffraction. The Ra2+ centers are bound by six chelating nitrate anions to form an anticuboctahedral geometry. The Raman spectrum acquired from a single crystal of Ra(NO3)2 generally occurs at a lower frequency than found in Ba(NO3)2 as expected. Computational studies on Ra(NO3)2 provide an estimation of the bond orders via Wiberg bond indices and indicate that Ra–O interactions are weak with values of 0.025 and 0.026 for Ra–O bonds. Inspection of natural bond orbitals and natural localized molecular orbitals suggest negligible orbital mixing. However, second-order perturbation interactions show that donation from the lone pairs of the nitrate oxygen atoms to the 7s orbitals of Ra2+ stabilize each Ra–O interaction by ca. 5 kcal mol−1

Hydrogen bond network.

<p>In a) p-CMP and b) p-MMP at the active site of MAO-B.</p

Non-covalent interaction (NCI) surface for binding site models in TS complexes with p-CMP and p-MMP after QM optimization.

<p>Red squares indicate hydrogen bonds (blue surfaces) and favorable van der Waals interactions (light green surfaces). a) the reactive region of p-CMP; b) p-substituent region of p-CMP, c) the reactive region of p-MMP and d) p-substituent region of p-MMP. p-CMP is depicted in cyan ball and sticks while p-MMP is depicted in yellow ball and sticks. NCI indexes isovalues range from 0.035 to -0.035 (au). p-MMP (p-methoxy-β-methylphenylethylamine); p-CMP (p-chloro-β-mehtylphenylethylamine), respectively.</p