Perfect polar stacking of parallel beloamphiphile layers. Synthesis, structure and solid-state optical properties of the unsymmetrical acetophenone azine DCA

Perfect Polar Alignment of Parallel Beloamphiphile Layers: Improved Structural Design Bias Realized in Ferroelectric Crystals of the Novel "Methoxyphenyl Series of Acetophenone Azines"

An improved design is described for ferroelectric crystals and implemented with the "methoxyphenyl series" of acetophenone azines, (MeO-Ph, Y)-azines with Y=F (1), Cl (2), Br (3), or I (4). The crystal structures of these azines exhibit polar stacking of parallel beloamphiphile monolayers (PBAMs). Azines 1, 3, and 4 form true racemates whereas chloroazine 2 crystallizes as a kryptoracemate. Azines 1-4 are helical because of the N-N bond conformation. In true racemates the molecules of opposite helicity (M and P) are enantiomers A(M) and A*(P) while in kryptoracemates they are diastereomers A(M) and B*(P). The stacking mode of PBAMs is influenced by halogen bonding, with 2-4 showcasing a kink due to directional interlayer halogen bonding, whereas fluoroazine 1 demonstrates ideal polar stacking by avoiding it. Notably, (MeO-Ph, Y)-azines display a stronger bias for dipole parallel alignment, attributed to the linearity of the biphenyl moiety as compared to the phenoxy series of (PhO, Y)-azines with their non-linear Ph-O-Ph moiety. The crystals of 1-4 all feature planar biphenyls and this synthon facilitates their crystallization through potent triple T-contacts and enhances their nonlinear optical (NLO) performance by increasing conjugation length and affecting favorable chromophore conformations in the solids.

Importance of Solvent-Bridged Structures of Fluorinated Diphenylalanines: Synthesis, Detailed NMR Analysis, and Rotational Profiles of Phe(2-F)-Phe(2-F), Phe(2-F)-Phe, and Phe-Phe(2-F)

The crystal structure of l-phenylalanyl l-phenylalanine (Phe-Phe, FF, a.k.a. diphenylalanine) is not merely noncentrosymmetric, but it is highly dipole parallel aligned. It is for this reason that FF is a nonlinear optical (NLO) material and exhibits strong second harmonic generation (SHG). Enhancement of the SHG response by ortho fluorination was demonstrated. Crystallization is nontrivial, and learning about the zwitterion structures in solution is important for the rational improvement of the crystallization process. Here, we present an NMR study of di-fluorinated FF (Phe(2-F)-Phe(2-F)) and mono-fluorinated FF isomers (Phe(2-F)-Phe and Phe-Phe(2-F)). The dipeptides were prepared by solid-phase synthesis and purified by high-performance liquid chromatography (HPLC). Their ¹H and ¹³C NMR spectra were recorded in partially deuterated water (10% D₂O), and two-dimensional (2D) NMR techniques were employed for signal assignments. The unambiguous assignments are reported of all chemical shifts for the aliphatic H and C atoms and of the C atoms of the carboxylate, the amide carbonyl, the CF carbons, and of every arene C atom in each phenyl ring. The dipeptides are trans amides and intramolecular hydrogen bonding between the ammonium group and the amide carbonyl restricts the H₃N-CH-C(O) geometry. We explored the rotational profile of the diphenylalanines as a function of the τ = ∠(C-N-C-CO₂) dihedral angle at the SMD(B3LYP/6-31G*) level without and with specific hydration and report the associated Karplus curves J(θ) vs θ = ∠(H-N-C-H). The rotational profiles show a maximum of three stationary structures, and relative conformer stabilities of the free diphenylalanines show that the conformation found in the crystal M1 is the least stable among the three, M3 > M2 ≫ M1. Specific water solvation makes all of the difference and adds a large competitive advantage to the water-bridged ion pair M1a. In fact, M1a becomes the most stable and dominant conformation for the parent diphenylalanine and mono1 F-FF and M1a becomes competitive with M3c for mono2 F-FF and di F-FF. Implications are discussed regarding the importance of the conformational preorganization of diphenylalanines in solution and the facility for their crystallization.

Perfect Polar Alignment of Parallel Beloamphiphile Monolayers: Synthesis, Characterization, and Crystal Architectures of Unsymmetrical Phenoxy-Substituted Acetophenone Azines

It remains a great challenge to achieve polar order in organic molecular crystals because anti-parallel alignment of side-by-side molecules is intrinsically preferred. We have addressed this problem with a rational design that focuses on the polar stacking of parallel beloamphiphile monolayers (PBAMs) with strong lateral quadrupole-quadrupole attractions. We employ arene-arene interactions as lateral synthons. The first successes were achieved with unsymmetrical donor (X), acceptor (Y) substituted acetophenone azines which form polar PBAMs with double T-contacts between the azines. Near-perfect alignment was achieved with the methoxy series of (MeO, Y)-azines with Y=Cl, Br, I. Here, we report on the synthesis, the characterization (GC/MS, ¹ H NMR, ¹³ C NMR, FTIR), the crystallization, and the single-crystal X-ray analyses of the phenoxy series of (PhO, Y)-acetophenone azines with Y=F, Cl, Br, I. Properties of (RO, Y) azines were computed at the APFD/6-311G* level and are discussed with reference to p-nitroaniline (PNA). This (PhO, Y) series embodies an improved PBAM design based on triple T-contacts which is shown to facilitate faster crystallization and to produce larger crystals. Perfect polar-alignment has been achieved for the phenoxy series of (PhO, Y)-azines with Y=Cl, Br, I and the (PhO, F)-azine also features near-perfect dipole alignment.

New bis hydrazone: Synthesis, X-ray crystal structure, DFT computations, conformational study and in silico study of the inhibition activity of SARS-CoV-2

The aim of this work was to synthesize new bis hydrazone derived from benzil in good yield, namely: (1Z,2Z)-1,2-bis (3-Chlorophenyl Hydrazino) Benzil, encoded by 3-Cl BHB. The benzil (or 1,2-diphenyl ethanedione) reacts with 3-Cl phenyl hydrazine by reflux method using ethanol as solvent to obtain the target compound. The obtained product is depicted by UV-Vis, IR spectroscopy and XRD-crystals analysis. All various contacts intra and intermolecular found in 3-Cl BHB were determined by the X-ray diffraction technique performed on single crystals. On the other hand, the optimized geometric structure of 3-Cl BHB was computed by the DFT/B3LYP method with 6-31 G (d, p) level. So, the bond lengths and angles, frontier molecular orbitals (FMO), surface electrostatic potential of the molecule (MEP), global reactivity descriptors, Mulliken atomic charges, computed vibrational analysis and electronic absorption spectrum were determined to get a good understanding of the electronic properties and the active sites of 3-Cl BHB, then to compare them with experimental data. Additionally, a conformational study was carried out using the same method (DFT). The structure-activity relationships established through molecular docking studies showed that 3-Cl BHB structure strongly binds to the receptors Mpro (-8.90 Kcal/mol) and RdRp (-8.60 Kcal/mol) which confirm its inhibition activity against COVID-19.

Azines: synthesis, structure, electronic structure and their applications

Azines (2,3-diaza-1,3-butadienes): structure, electronic structure, tautomerism, and their applications in organic synthesis, medicinal chemistry and materials chemistry.