Multicomponent synthesis of pyrido[2,3-]pyrazine derivatives: electrochemical DNA sensing, nonlinear optical properties and biological activity.

We synthesized novel pyrido[2,3-]pyrazin based heterocyclic compounds (4-7) and their chemical structures were ascertained by spectral techniques (NMR, FT-IR). Besides experimental investigation, density functional theory (DFT) computations with B3LYP/6-31G(d,p) level of theory were executed to obtain spectroscopic and electronic properties. Nonlinear optical (NLO) properties, frontier molecular orbitals (FMOs), UV-visible, vibrational analysis, natural bond orbitals (NBOs), transition density matrix (TDM) and density of states (DOS) analyses of molecules (4-7) were accomplished at B3LYP/6-31G (d,p) level. Global reactivity parameters (GRPs) were correlated with the band gap () values; compound 7 with lower (3.444 eV), exhibited smaller value of hardness (1.722 eV) with greater softness value (0.290 eV). The dipole moment (), average polarizability 〈〉, first () and second 〈〉 hyper-polarizabilities were calculated for compounds (4-7). Compound 7 showed less , highest absorption wavelength and remarkable NLO response. The highest 〈〉, and 〈〉 values for compound 7 were observed as 3.90 × 10, 15.6 × 10 and 6.63 × 10 esu, respectively. High NLO response revealed that pyrido[2,3-]pyrazin based heterocyclic compounds had very remarkable contributions towards NLO technological applications. Further compounds (4-7) are utilized for the first time in electrochemical sensing of DNA, i antioxidant and antiurease activity.