Intensified effects of multi-Cu modification on the electronic properties of the modified base pairs containing hetero-ring-expanded pyrimidine bases

Theoretical investigation of the mechanism of DMAP-promoted [4 + 2]-annulation of prop-2-ynylsulfonium with isatoic anhydride

The mechanism for DMAP-promoted [4 + 2]-annulation of prop-2-ynylsulfonium with isatoic anhydride is investigated using the M06-2X functional. The reaction comprises isomerization of prop-2-ynylsulfonium in stage 1. Stage 2 includes DMAP-promoted deprotonation, nucleophilic addition, ring opening, and decarboxylation. Three steps of intramolecular cycloaddition, DMAP-promoted protonation, and dealkylation occur in stage 3, generating methylated DMAP and neutral thioether, which undergo double-bond isomerization to yield 3-methylthio-4-quinolone. The ability of DMAP to promote the reaction lies in the barrier decrease for alkyne isomerization, deprotonation/protonation of allenes, and dealkylation as effective bases for transferring protons and methyl groups. The roles of prop-2-ynylsulfonium and isatoic anhydride were demonstrated to be C2 and C4 synthons via Multiwfn analysis on the frontier molecular orbital. An alternative path was also confirmed by the Mayer bond order of the vital transition states.

Computational design of three Cu-induced triangular pyrimidines based DNA motifs with improved conductivity

Novel DNA triangular pyrimidine derivatives are designed by metal decoration through replacement of H by Cu in the Watson–Crick hydrogen bond region. The DFT method is used to examine the coordination of triangle-arranged Cu with three pyrimidines in nonplanar three-bladed turbine geometries. The Cu···Cu cuprophilic bonds are ascribed to the partially occupied d orbitals without direct molecular orbital (MO) interactions. Four-center bonds depend on Cu–N/O bonds, which are contributed by p orbitals of N/O atoms along or perpendicular to the bond axis. The activity of frontier MOs is modulated, leading to the decrease of gaps, ionization potentials (IPs), and electron affinities (EAs) desired for the improvement of conductivity. The hole trapping ability is assured by virtue of the spin density distributed on Cu. On average, the single electron density is located on π orbitals of three aromatic base rings. There is paramagnetic electron delocalization on the inner d orbitals of triangle region. The analysis of electron localization function ELF-π and electrostatic potential maps reveals that the outer strong π–π stacking interaction together with the inner d orbital channel enable effective transduction of electrical signals along the Cu–DNA nanowires. The 3Cu-induced triangular pyrimidines have important potential applications as structural motifs of molecular electronic devices.