Dual-template imprinted polymer electrochemical sensor for simultaneous determination of malathion and carbendazim using graphene quantum dots.

Malathion (MAL) and carbendazim (CBZ) are organophosphate pesticides and fungicides, respectively. They are often used simultaneously in agriculture, and both have been shown to have harmful effects on humans and animals. Therefore, it is important to be able to measure both of these toxins simultaneously in order to assess their potential risks. This study aims to design a dual template electrochemical sensor using a cost-effective graphite-epoxy composite electrode (GECE) modified with molecularly imprinted polymers (MIPs) coated on graphene quantum dots (GQDs) for simultaneous detection of MAL and CBZ in real samples. GQDs were synthesized initially, and their surface was coated with MIPs that were formed using MAL and CBZ as the template molecules, ethylene glycol dimethyl acrylate as the cross-linker, and methacrylic acid as the functional monomer. The GQDs@MIP were characterized using Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, and X-ray scattering spectroscopy. Parameters affecting the sensor response, such as the percentage of GQDs@MIP in the fabricated electrode, the pH of the rebinding solution and analysis solution, and the incubation time, were optimized. The optimum pH values of the rebinding solution were verified using density functional theory (DFT) calculations. Under the optimized conditions, differential pulse voltammetry (DPV) response calibration curves of MAL and CBZ were generated, and the results showed that the sensor had a linear response to MAL in the range of 0.02-55.00 µM with a limit of detection (LOD) of 2 nM (S/N = 3) and to CBZ in the range of 0.02-45.00 µM with a low LOD of 1 nM (S/N = 3). The results also demonstrated the proposed sensor's long-term stability and anti-interference capability. The practical applicability of the fabricated electrode was evaluated for real sample analysis, and good recovery values were obtained.

Theoretical insight into the hybridization effect of donor and acceptor atoms on the cooperativity of C-H···N hydrogen bonds.

In the present work, the influence of hybridization on cooperativity between C-H···N hydrogen bonds is theoretically investigated. Here, C2H6, C2H4, and C2H2 are considered as hydrogen bonding donor while NH3, N2H4, N2H2, and N2 act as the hydrogen bonding acceptor. The calculations are performed at MP2/aug-cc-pVTZ level. It is observed that the stability of systems is amplified as C(sp) > C(sp2) > C(sp3) and also N(sp3) > N(sp2) > N(sp). The role of interaction and deformation energies on the stability of the systems is examined. The results indicate the contribution of interaction energy is dominant in all complexes. The strength of C-H···N hydrogen bond is estimated using interaction energy. In agreement with cooperative energies, the C-H···N hydrogen bond is respectively weakened/strengthened in the triads containing C(sp) and C(sp2)/C(sp3) where two hydrogen bonds coexist. On the other hand, the C-H···N hydrogen bond is strengthened in the ternary systems including N(sp3) and N(sp2) while an opposite behavior is obtained in the triad having N(sp).

The influence of Cu+ binding to hypoxanthine on stabilization of mismatches involving hypoxanthine and DNA bases: a DFT study.

In the present work, the influence of Cu+ binding to N3- and N7-positions of hypoxanthine on energetic, geometrical and topological properties of hypoxanthine-guanine, hypoxanthine-adenine, hypoxanthine-cytosine, hypoxanthine-thymine and hypoxanthine-hypoxanthine mismatches is theoretically investigated. The calculations, in gas phase, are performed at B3LYP/6-311++G(3df,3pd) level of theory. Unlike the other mispairs, Cu+ binding to N3-position of hypoxanthine causes the proton transfer process from enol form of hypoxanthine to imino forms of adenine and cytosine. This process also occurs in all mismatches having enol form of hypoxanthine when Cu+ binds to N7-position of hypoxanthine. The mismatches are stabilized by hydrogen bonds. The influence of Cu+ on hydrogen bonds is also examined by atoms in molecules (AIM) and natural bond orbital (NBO) analyses. Communicated by Ramaswamy H. Sarma.

A theoretical survey of substituent effects on the properties of pnicogen and hydrogen bonds in cationic complexes of PH4+ with substituted benzonitrile.

In this paper, we analyze the substituent effects on the nature and characteristics of P⋯N and H⋯N interactions in X-PhCN:PH4+ complexes (X=H, F, Cl, Br, CN, NH2, NO2, CH3 and N(CH3)2) as a working model at MP2(FC)/6-311++G(d,p) level of theory. The natural bond orbital (NBO) method as well as the quantum theory of atoms in molecules (AIM) is applied to characterize interactions in the studied complexes. In general, the pnicogen bonded systems are more stable than the corresponding hydrogen bonded cases. The strength of the interactions generally correlates well with the magnitudes of the negative electrostatic potentials of the nitrogen atom of isolated substituted benzonitrile (Vs,min(N)). The results indicate that increase in the electron withdrawing power of substituents is accompanied by decrease in the absolute value of Vs,min(N). Also, there are meaningful relationships between Vs,min(N) values and the results of AIM and NBO analyses in studied systems. Moreover, it is found that substituent effects on characteristics of P⋯N pnicogen and H⋯N hydrogen bonds can be expressed by Hammett constants.

The effects of tautomerization and protonation on the adenine-cytosine mismatches: a density functional theory study.

In the present work, we demonstrate the results of a theoretical study concerned with the question how tautomerization and protonation of adenine affect the various properties of adenine-cytosine mismatches. The calculations, in gas phase and in water, are performed at B3LYP/6-311++G(d,p) level. In gas phase, it is observed that any tautomeric form of investigated mismatches is more stabilized when adenine is protonated. As for the neutral mismatches, the mismatches containing amino form of cytosine and imino form of protonated adenine are more stable. The role of aromaticity on the stability of tautomeric forms of mismatches is investigated by NICS(1)ZZ index. The stability of mispairs decreases by going from gas phase to water. It can be explained using dipole moment parameter. The influence of hydrogen bonds on the stability of mismatches is examined by atoms in molecules and natural bond orbital analyses. In addition to geometrical parameters and binding energies, the study of the topological properties of electron charge density aids in better understanding of these mispairs.