DFT and QTAIM study of the tetra-tert-butyltetraoxa[8]circulene regioisomers structure

Mannich bases of hydroxycoumarins: synthesis, DFT/QTAIM computational study and assessment of biological activity

The synthesis of six Mannich bases derived from hydroxycoumarins was carried out in moderate yields, two of these derivatives were described for the first time. Conformational analysis was performed through DFT theoretical calculations explaining the formation of stable six membered rings based on intramolecular hydrogen bonds within the structure. These findings were correlated with the antiproliferative activity. The biological activity of the Mannich bases through their antiproliferative activity in the HeLa cancer cell line is described for the first time, showing that the compounds were able to inhibit proliferation in cervical cancer by more than 60%. Likewise, the theoretical modeling of the photophysical properties was realized with promising results, showing that the HOMO–LUMO energies of the new compounds present the lowest electronic gap values for those with donor groups in their structure, which makes them potential fluorophores.

Mannich bases derived from hydroxycoumarins as interesting scaffolds for several applications.

Halogen bonds on substituted dibromonitrobenzene derivatives

Halogen bonding is a noncovalent interaction that has attracted great attention because of its importance in several areas, such as photonics, nonlinear optics, pharmaceutical products, supramolecular engineering, biochemistry, protein-ligand complexes, and polymer interactions. In this context, we describe the synthesis, molecular structure, supramolecular arrangement, and theoretical calculations of five dibromonitrobenzene derivatives, which present different halogen atoms substituted. The solid-state characterization was carried out by X-ray diffraction with the contribution of Hirshfeld surfaces for analysis of molecular interactions. The frontier molecular orbital, molecular electrostatic potential, and quantum theory of atoms in molecules were carried out at the M06-2X/6-311+G(d,p) level of theory. Those observed halogen interactions indicate the crystalline solid-state stabilization for the dibromonitrobenzene derivatives.

Exploring the Polymorphism of Drostanolone Propionate

2α-Methyl-4,5α-dihydrotestosterone 17β-propionate, known as drostanolone propionate or masteron, is a synthetic anabolic-androgenic steroid derived from dihydrotestosterone. The crystal structures of two polymorphs of drostanolone propionate have been determined by single crystal X-ray diffraction and both crystallizes in the monoclinic crystal system. One is belonging to the P21 space group, Z = 2, and has one molecule in the asymmetric unit while the second belongs to the I2 space group, Z = 4, and contains two molecules in the asymmetric unit. Another polymorph has been investigated by an X-ray powder diffraction method and solved by Parallel tempering/Monte Carlo technique and refined with the Rietveld method. This polymorph crystallizes in the orthorhombic P212121 space group, Z = 4 having one molecule in the asymmetric unit. The structural configuration analysis shows that the A, B, and C steroid rings exist as chair geometry, while ring D adopts a C13 distorted envelope configuration in all structures. For all polymorphs, the lattice energy has been computed by CLP (Coulomb-London-Pauli), and tight-binding density functional theory methods. Local electron correlation methods were used to estimate the role of electron correlation in the magnitude of the dimer energies. The nature of the intermolecular interactions has been analyzed by the SAPT0 energy decomposition methods as well as by Hirshfeld surfaces.

Structural insights into the anti-cancer activity of quercetin on G-tetrad, mixed G-tetrad, and G-quadruplex DNA using quantum chemical and molecular dynamics simulations

Human telomerase referred as 'terminal transferase' is a nucleoprotein enzyme which inhibits the disintegration of telomere length and act as a drug target for the anticancer therapy. The tandem repeating structure of telomere sequence forms the guanine-rich quadruplex structures that stabilize stacked tetrads. In our present work, we have investigated the interaction of quercetin with DNA tetrads using DFT. Geometrical analysis revealed that the influence of quercetin drug induces the structural changes into the DNA tetrads. Among DNA tetrads, the quercetin stacked with GCGC tetrad has the highest interaction energy of -88.08 kcal/mol. The binding mode and the structural stability are verified by the absorption spectroscopy method. The longer wavelength was found at 380 nm and it exhibits bathochromic shift. The findings help us to understand the binding nature of quercetin drug with DNA tetrads and it also inhibits the telomerase activity. Further, the quercetin drug interacted with G-quadruplex DNA by using molecular dynamics (MD) simulation studies for 100 ns simulation at different temperatures and different pH levels (T = 298 K, 320 K and pH = 7.4, 5.4). The structural stability of the quercetin with G-quadruplex structure is confirmed by RMSD. For the acidic condition (pH = 5.4), the binding affinity is higher toward G-quadruplex DNA, this result resembles that the quercetin drug is well interacted with G-quadruplex DNA at acidic condition (pH = 7.4) than the neutral condition. The obtained results show that quercetin drug stabilizes the G-quadruplex DNA, which regulates telomerase enzyme and it potentially acts as a novel anti-cancer agent.Communicated by Ramaswamy H. Sarma.

Combined QTAIM and ETS-NOCV investigation of the interactions in ClnM[PhB(NtBu)2] complexes with M = Si & Ge (n = 0), As & Sb (n = 1), Te & Po (n = 2)

In this work, the nature of the chemical interactions between the metalloid atom (M = Si, Ge, As, Sb, Te, Po) and the nitrogen atoms in the bora-amidinate (bam) complexes (Cl_nM[PhB(N^tBu)₂]) are investigated, mainly via density-based indices. The descriptors used are derived using the quantum theory of atoms in molecules and natural orbitals for chemical valence approaches. It is shown that the strongest interaction is achieved with silicon. Indeed, it is generally the lightest metalloid in a particular group of the periodic table (i.e., Si, As, and Te for groups 14-16, respectively) that exhibits the strongest bond in the bam complex. This suggests that the atomic radius of the metalloid is a useful parameter for predicting the bonding strength. Extended transition state (ETS) decomposition results indicate that the interactions are more electrostatic than due to orbital interactions.

Behavior of interactions between hydrogen chalcogenides and an anthracene π-system elucidated by QTAIM dual functional analysis with QC calculations

The nature of the interactions between chalcogenides and the anthracene p-system, EH₂-*-p(C₁₄H₁₀), is predicted to be close to that of EH₂-*-p(C₁₀H₈), although the partial structures around the central rings can be found in EH₂-*-p(C₆H₆).

A computational study of aromaticity and photophysical properties of unsymmetrical azatrioxa[8]circulenes

In the present work we have studied a series of unsymmetrical azatrioxa[8]circulenes in order to explain the impact of outer substituents and benzoannelation on photophysical constants and aromaticity of these compounds.

Structure and electrochemical properties for complexes of nitrocompounds with inorganic ions: A theoretical approach

Reduction and oxidation (redox) reactions are widely used for removal of nitrocompounds from contaminated soil and water. Structures and redox properties for complexes of nitrocompounds, such as 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), 2,4-dinitroanisole (DNAN), and 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO), with common inorganic ions (Na(+) , Cl(-) , NO3-) were investigated at the SMD(Pauling)/PCM(Pauling)/MPWB1K/TZVP level of theory. Atoms in molecules (AIM) theory was applied to analyze the topological properties of the bond critical points involved in the interactions between the nitrocompounds and the ions. Topological analyses show that intermolecular interactions of the types O(N)…Na(+) , C-H…Cl(-) ( ONO2-), and C…Cl(-) ( ONO2-) may be discussed as noncovalent closed-shell interactions, while N-H···Cl(-) ( ONO2-) hydrogen bonds are partially covalent in nature. Complexation causes significant decrease of redox activity of the nitrocompounds. Analysis of the reduction potentials of the complexes obtained through application of the Pourbaix diagram of an iron/water system revealed that sodium complexes of NTO might be reduced by metallic iron. © 2016 Wiley Periodicals, Inc.

Structure and spectroscopic characterization of tetrathia- and tetraselena[8]circulenes as a new class of polyaromatic heterocycles

The FTIR, Raman and UV-vis spectra of the recently synthesized tetrathia[8]circulene and tetraselena[8]circulene compounds have been measured and interpreted in details by the density functional theory (DFT) calculations taking into account the molecular symmetry constrains. The structural and electronic features of the studied compounds have also been discussed in connection with the observed spectroscopic characteristics. Particularly, we have found that despite a slightly non-planar conformation the neutral tetrathia[8]circulene and tetraselena[8]circulene molecules demonstrate bifacial aromatic/antiaromatic nature. The inner octatetraene core is characterized by the presence of paratropic ("antiaromatic") ring currents, whereas the outer macrocycle constructed of benzene, thiophene or selenophene rings possesses the strong magnetically-induced diatropic ("aromatic") ring current. This fact suggests the general electronic and magnetic similarity of the tetrathia- and tetraselena[8]circulenes with the strictly planar isoelectronic tetraoxa[8]circulene and related azaoxa-derivatives discussed earlier. However, the vibrational and UV-vis absorption spectra of the studied circulenes are rather different from those of the parent tetraoxa[8]circulene which indicates a clear manifestation of the symmetry selection rules.

Design of novel tetra-hetero[8]circulenes: a theoretical study of electronic structure and charge transport characteristics

Tetra-hetero[8]circulenes were theoretically designed and emerged as good candidates for ambipolar organic semiconductors.

Quantum-mechanical calculations on molecular substructures involved in nanosystems

In this review article, four ideas are discussed: (a) aromaticity of fullerenes patched with flowers of 6-and 8-membered rings, optimized at the HF and DFT levels of theory, in terms of HOMA and NICS criteria; (b) polybenzene networks, from construction to energetic and vibrational spectra computations; (c) quantum-mechanical calculations on the repeat units of various P-type crystal networks and (d) construction and stability evaluation, at DFTB level of theory, of some exotic allotropes of diamond D5, involved in hyper-graphenes. The overall conclusion was that several of the yet hypothetical molecular nanostructures herein described are serious candidates to the status of real molecules.