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

We synthesized novel pyrido[2,3- b ]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 ( E gap ) values; compound 7 with lower E gap (3.444 eV), exhibited smaller value of hardness (1.722 eV) with greater softness value (0.290 eV -1 ). The dipole moment ( μ ), average polarizability 〈 α 〉, first ( β tot ) and second 〈 γ 〉 hyper-polarizabilities were calculated for compounds (4-7). Compound 7 showed less E gap , highest absorption wavelength and remarkable NLO response. The highest 〈 α 〉, β tot and 〈 γ 〉 values for compound 7 were observed as 3.90 × 10 -23 , 15.6 × 10 -30 and 6.63 × 10 -35 esu, respectively. High NLO response revealed that pyrido[2,3- b ]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 n vitro antioxidant and antiurease activity.