Search for Osme Bonds with π Systems as Electron Donors

The Osme bond is defined as pairing a Group 8 metal atom as an electron acceptor in a noncovalent interaction with a nucleophile. DFT calculations with the ωB97XD functional consider MO4 (M = Ru, Os) as the Lewis acid, paired with a series of π electron donors C2H2, C2H4, C6H6, C4H5N, C4H4O, and C4H4S. The calculations establish interaction energies in the range between 9.5 and 26.4 kJ/mol. Os engages in stronger interactions than does Ru, and those involving more extensive π-systems within the aromatic rings form stronger bonds than do the smaller ethylene and acetylene. Extensive analysis questions the existence of a true Osme bond, as the bonding chiefly involves interactions with the three O atoms of MO4 that lie closest to the π-system, via π(C-C)→σ*(M-O) transfers. These interactions are supplemented by back donation from M-O bonds to the π*(CC) antibonding orbitals of the π-systems. Dispersion makes a large contribution to these interactions, higher than electrostatics and much greater than induction.

Synthesis, characterization, and molecular modeling of phenylenediamine-phenylhydrazine-formaldehyde terpolymer (PPHF) as potent anti-inflammatory agent

Inflammation, a characteristic physiological response to infections and tissue damage, commences with processes involving tissue repair and pathogen elimination, contributing to the restoration of homeostasis at affected sites. Hence, this study presents a comprehensive analysis addressing diverse aspects associated with this phenomenon. The investigation encompasses the synthesis, spectral characterizations (FT-IR, ¹H NMR, and ¹³C NMR), and molecular modeling of p-phenylenediamine-phenylhydrazine-formaldehyde terpolymer (PPHF), a potent agent in promoting inflammation. To explore the reactivity, bonding nature, and spectroscopy, as well as perform molecular docking for in-silico biological evaluation, density functional theory (DFT) utilizing the def2svp/B3LYP-D3BJ method was employed. The results reveal significant biological activity of the tested compound in relation to anti-inflammatory proteins, specifically 6JD8, 5TKB, and 4CYF. Notably, upon interaction between PPHF and 6JD8, a binding affinity of -4.5 kcal/mol was observed. Likewise, the interaction with 5TKB demonstrated an affinity of -7.8 kcal/mol. Furthermore, a bonding affinity of -8.1 kcal/mol was observed for the interaction with 4CYF. Importantly, these values closely correspond to those obtained from the interaction between the proteins and the standard drug ibuprofen (IBF), which exhibited binding affinities of -5.9 kcal/mol, -7.0 kcal/mol, and -6.1 kcal/mol, respectively. Thus, these results provide compelling evidence affirming the tremendous potential of p-phenylenediamine-phenylhydrazine-formaldehyde (PPHF) as a highly promising anti-inflammatory agent, owing to the presence of nitrogen-a heteroatom within the compound.

Interchangeability and Disorder in the Solid-State Structures of "Two Wall" Calix[4]pyrroles Equipped with Iodine and Ethynyl para-Substituents

Herein, the synthesis and X-ray structures of three α,β "two wall" aryl-extended calix[4]pyrroles having either identical (symmetrically substituted) or different (non-symmetrically substituted) meso-aryl substituents (aryl=4-ethynylphenyl and 4-iodophenyl) are reported. The X-ray structure of the co-crystal formed by the two symmetrically substituted calix[4]pyrroles is also described. In the solid state, all studied α,β-calix[4]pyrroles exhibit a 1,3-alternate conformation with two co-crystallized acetonitrile solvent molecules H-bonded to adjacent cis-pyrrole rings. Remarkably, the 1,3-conformer of the non-symmetrically substituted iodophenyl/ethynylphenyl compound is intrinsically chiral. The two enantiomers are present in the average asymmetric unit in a 65 : 35 occupancy ratio displaying a head-to-tail directional disorder. This is due to the functional complementarity and the isosteric and isoelectronic properties of the para-substituents: iodo and ethynyl. That is, the negative belt of iodine is similar to the negative π-system of the C≡C triple bond and the σ-hole in the iodine atom is similar to the positive proton at the C≡C-H group.

Polyanionic cyano-fullerides for CO2 capture: a DFT prediction

The reaction of C₆₀ fullerene with 'n' molecules (n = 1 to 6) of 1,3-dimethyl-2,3-dihydro-2-cyano-imidazole (IMCN) results in the exothermic formation of imidazolium cation-polyanionic fulleride complexes, (IM⁺)_n⋯((C₆₀(CN)_n)^n-). The binding energy of IM⁺ with (C₆₀(CN)_n)^n- in the imidazolium-fulleride ionic complexes increased from -69.6 kcal mol^-1 for n = 1 to -202.9 kcal mol^-1 for n = 6. The energetics of the complex formation and cation-anion interaction energy data suggest the formation of imidazolium-fulleride ionic liquid (IL) systems. Furthermore, the dimer formation of such ionic complexes showed more exergonic nature due to multiple cooperative electrostatic interactions between oppositely charged species and suggested improved energetics for higher order clusters. The molecular electrostatic potential (MESP) analysis has revealed that the extra 'n' electrons in the ionic complex as well as that in the bare (C₆₀(CN)_n)^n- are delocalized mainly on the unsaturated carbon centers of the fullerene unit, while the CN groups remain as a neutral unit. The MESP minimum (V_min) values of (C₆₀(CN)_n)^n- on the carbon cage have shown that the addition of each CN^- unit on the cage enhances the negative character of V_min by ∼54.7 kcal mol^-1. This enhancement in MESP is comparable to the enhancement observed when one electron is added to C₆₀ to produce (^-62.5 kcal mol^-1) and suggests that adding 'n' CN^- groups to the fullerene cage is equivalent to supplying 'n' electrons to the carbon cage. Also the high capacity of the fullerene cage to hold several electrons can be attributed to the spherical delocalization of them onto the electron deficient carbon cage. The interactive behavior of CO₂ molecules with (IM⁺)_n⋯(C₆₀(CN)_n)^n- systems showed that the interaction becomes stronger from -2.3 kcal mol^-1 for n = 1 to -18.6 kcal mol^-1 for n = 6. From the trianionic fulleride onwards, the C⋯CO₂ noncovalent (nc) interaction changes to C-CO₂ covalent (c) interaction with the development of carboxylate character on the adsorbed CO₂. These results prove that cyano-fullerides are promising candidates for CO₂ capture.

Noncovalent Interactions Involving Group 6 in Biological Systems: The Case of Molybdopterin and Tungstopterin Cofactors

In this study we propose to coin the term Wolfium bond (WfB) to refer to a net attractive force (noncovalent interaction) between any element of group 6 and electron donor atoms (neutral molecules or anions) and to differentiate it from a coordination bond (metal-ligand interaction). We provide evidence of the existence of this interaction by inspecting the X-ray crystal structure of proteins containing Molybdopterin and Tungstopterin cofactors from the Protein Data Bank (PDB). The plausible biological role of the interaction as well as its physical nature (antibonding Wf-Ligand orbital involved) are also analyzed by means of ab initio calculations (RI-MP2/def2-TZVP level of theory), Atoms in Molecules (AIM), Natural Bond Orbital (NBO) and Noncovalent Interactions plot (NCIplot) analyses.

Meta-Hybrid Density Functional Theory Prediction of the Reactivity, Stability, and IGM of Azepane, Oxepane, Thiepane, and Halogenated Cycloheptane

The application of plain cycloalkanes and heterocyclic derivatives in the synthesis of valuable natural products and pharmacologically active intermediates has increased tremendously in recent times with much attention being paid to the lower cycloalkane members. The structural and molecular properties of higher seven-membered and nonaromatic heterocyclic derivatives are less known despite their stable nature and vast application; thus, an insight into their structural and electronic properties is still needed. Appropriate quantum chemical calculations utilizing the ab initio (MP2) method, meta-hybrid (M06-2X) functional, and long-range-separated functionals (ωB97XD) have been utilized in this work to investigate the structural reactivity, stability, and behavior of substituents on cycloheptane (CHP) and its derivatives: azepane, oxepane, thiepane, fluorocycloheptane (FCHP), bromocycloheptane (BrCHP), and chlorocycloheptane (ClCHP). Molecular global reactivity descriptors such as Fukui function, frontier molecular orbitals (FMOs), and molecular electrostatic potential were computed and compared with lower members. The results of two population methods CHELPG and Atomic Dipole Corrected Hirshfeld Charges (ADCH) were equally compared to scrutinize the charge distribution in the molecules. The susceptibility of intramolecular interactions between the substituents and cycloalkane ring is revealed by natural bond orbital analysis and intramolecular weak interactions by the independent gradient model (IGM). Other properties such as atomic density of states, intrinsic bond strength index (IBSI), and dipole moments are considered. It is acclaimed that the strain effect is a major determinant effect in the energy balance of cyclic molecules; thus, the ring strain energies and validation of spectroscopic specificities with reference to the X-ray crystallographic data are also considered.

Hydrogen- and halogen bond synergy in the self-assembly of 3,5-dihalo-tyrosines: structural and theoretical insights

Halogenation, generally introduced on aromatic aminoacids, is becoming a key supramolecular tool in peptides. Herein, we report the crystal structures and DFT study of two bis-halogenated tyrosines showing the subtle...