Solvent dependent structural, electronic, and optical properties of ureidopeptidomimetics: a DFT and TD-DFT study on the effects of donor and acceptor functional groups

Abstract

Abstract This study provides a comprehensive examination of the structural, electronic, optical, and reactivity properties of ureidopeptidomimetics (UPMs) featuring various donor and acceptor functional groups using density functional theory (DFT) and time-dependent DFT (TD-DFT). To systematically explore their effects on charge transfer, HOMO-LUMO energy gaps, and molecular stability, the molecular models were intentionally designed with both electron-donating groups (–CH3, –OCH3, –OH, –NH2) and electron-accepting groups (–SH, –COCl, –CF3). A detailed analysis of the bond lengths confirmed the electron-rich nature of the substituents, revealing that the introduction of electron-donating groups at the ureido and carboxylate terminals of the UPMs decreased the C–O and C–N bond lengths by 0.005 Å and 0.0003 Å, respectively, compared to the unsubstituted UPM. Polar solvents, notably water and DMSO, enhance the stabilization of HOMO and LUMO energy levels, thus improving the electronic stability and reactivity of UPM molecules, as demonstrated by DFT and TD-DFT calculations. In the case of UPM, the molecular orbitals (HOMO: −6.8646 eV to −6.9027 eV, LUMO: −0.3957 eV to −0.4248 eV) experienced slight stabilization as it transitioned from the gas phase to the aqueous phase. This transition increased the chemical potential (χ) and global hardness (η), signifying enhanced electronic stability. UV-Vis experiments revealed that UPM's λmax values remained around 218.6 nm across various solvents, with polar solvents, particularly water, exhibiting more robust oscillators. In water, λmax decreased to 207.58 nm for D2-UPM-A2 and shifted to 227.86 nm for D1-UPM-A1. For D3-UPM-A3, λmax in water exhibited a redshift to 249.28 nm along with reduced absorption. Specifically, for A1-UPM-D1 and A2-UPM-D2, the polarity of the solvent influenced transitions and increased transition probabilities, indicating their potential in optoelectronic applications.