How do electron donating substituents affect the electronic structure, molecular topology, vibrational properties and intra- and intermolecular interactions of polyhalogenated pyridines?

Design of electron-donating group substituted 2-PAM analogs as antidotes for organophosphate insecticide poisoning

The use of organophosphate (OPs) pesticides is widespread in agriculture and horticulture, but these chemicals can be lethal to humans, causing fatalities and deaths each year. The inhibition of acetylcholinesterase (AChE) by OPs leads to the overstimulation of cholinergic receptors, ultimately resulting in respiratory arrest, seizures, and death. Although 2-pralidoxime (2-PAM) is the FDA-approved drug for treating OP poisoning, there is difficulty in blood-brain barrier permeation. To address this issue, we designed and evaluated a series of 2-PAM analogs by substituting electron-donating groups on the para and/or ortho positions of the pyridinium core using in silico techniques. Our PCM-ONIOM2 (MP2/6-31G*:PM7//B3LYP/6-31G*:UFF) binding energy results demonstrated that 13 compounds exhibited higher binding energy than 2-PAM. The analog with phenyl and methyl groups substituted on the para and ortho positions, respectively, showed the most favorable binding characteristics, with aromatic residues in the active site (Y124, W286, F297, W338, and Y341) and the catalytic residue S203 covalently bonding with paraoxon. The results of DS-MD simulation revealed a highly favorable apical conformation of the potent analog, which has the potential to enhance reactivation of AChE. Importantly, newly designed compound demonstrated appropriate drug-likeness properties and blood-brain barrier penetration. These results provide a rational guide for developing new antidotes to treat organophosphate insecticide toxicity.

Intermolecular interactions in the crystalline structure of some polyhalogenated Di- And triamino Pyridines: Spectroscopical perspectives

Supramolecular synthon is identified as a unit and provides important structural and energetic information in the study of organic crystals. However, the direct estimation of the supramolecular interaction remains challenging. In the present work six polyhalogenated di- or triamino pyridines were synthesised, their crystalline structure was characterised, and corresponding supramolecular synthons were studied using a combination of quantum mechanical calculations and FT-IR and Raman spectroscopy. Some distinctive features were identified especially for three vibrational normal modes (RNMs) related to the pyridine ring (viz. RNM₁, RNM₃ and RNM₇) in the vibrational spectra (FT-IR and Raman) of the solid samples, which are due to the supramolecular interactions, hydrogen bond (hb) in particular, according to the quantum mechanical calculations. The comparison between the IR and Raman spectra of experimental and simulated results indicates that the adjacent intermolecular hydrogen bonds between two same molecules extensively exist in the solid samples. Moreover, some quantitative correlation was established among the dimerisation energies for hb dimers (hb1 dimers for compounds 1 and 2), the ring structure defined by the distribution of the substituents and quantitative characteristics of the vibrational spectra, for instance, the splitting magnitudes for RNM₃(2) in IR spectra and the peak gap between RNM₁ and RNM₂ in Raman spectra.