Comparison of the performance of different DFT methods in the calculations of the molecular structure and vibration spectra of serotonin (5-hydroxytryptamine, 5-HT)

CO2 Adsorption by Carbon Quantum Dots/Metal Ferrites (M = Co2+, Ni2+, and Zn2+): Electrochemical and Theoretical Studies

In this study, we investigated the adsorption of CO2 by carbon quantum dot-based ferrites (MFe2O4, M = Co2+, Ni2+, and Zn2+) in the context of industrial CO2 emissions and global warming. The ferrites have been characterized using various analytical techniques [X-ray powder diffraction, FTIR, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS)], showing cubic spinel for CoFe2O4, reverse cubic spinel for NiFe2O4, and typical spinel for ZnFe2O4. A TGA study revealed a significant weight loss around 740-780 °C, indicating structural change occurred with increasing temperature. SEM and TEM images displayed spherical particles with sizes ranging from 10 to 50 nm. XPS confirmed the presence of C, O, and Fe atoms with specific cations (Co2+, Ni2+, and Zn2+). Electrochemical impedance Nyquist diagrams suggest a linear relationship between Z″ (ohm) and Z' (ohm) at low frequencies, but the semicircular loop obtained was significantly increased at higher frequencies. This suggests that the charge transfer resistance (R CT) at the electrode boundaries (interface) is much higher than at low frequencies, indicating the resistance per area was 1853 Ω cm2 for carbon paste electrodes (CPE)/CoFe2O4 and it decreased to 1652 Ω cm2 for CPE/NiFe2O4 and 1672 Ω cm2 for CPE/ZnFe2O4. However, improved electron transfer with lower resistance was seen due to the composite nature of the samples (CQDs@MFe2O4), revealing a lower resistance (1163 Ω cm2) for CQD@MFe2O4-CO2 as compared to 1567 Ω cm2 for MFe2O4. Thus, the adsorption of CO2 was studied electrochemically, and interaction between ferrates with CO2 was enhanced by the presence of CQDs in the samples. This is consistent with the adsorption of CO2 with the samples as it follows the Langmuir pseudo-second-order kinetics (k = 4.9, qe = 121.93 for CQD@CoFe2O4, k = 2.9, qe = 156.52 for CQD@NiFe2O4, and k = 3.0, qe = 141.71 for CQD@ZnFe2O4), and the data show that the adsorption efficiency has been decreased by around 1.0% after 7-8 cycles. Lastly, density functional theory analysis demonstrated the interaction of CO2 on the surface of the ferrites, deforming the CO2 linearity, which leads to a subsequent C-O interaction to form carbonate.

Spectroscopic signatures and structural motifs in isolated and hydrated serotonin: a computational study

The conformational landscapes of neutral serotonin characterized by MP2, CC2 and DFT methods. The Gph-out/anti conformation is found most stable.

Molecular structure and vibrational spectra studies on antipyrine derivative, 4-(2,3,4-trihydroxybenzylideneamino) antipyrine

The molecular geometry, theoretical harmonic frequencies and infrared intensities of 4-(2,3,4-trihydroxybenzylideneamino) antipyrine (THBAP) were calculated using different density functional methods (LSDA, mPW1PW91, B3LYP and HCTH) with various basic sets, including 3-21G, 6-311G, LanL2DZ, and SDD. The purpose of this research is to compare the performance of different density functional theory (DFT) methods at different basis sets in predicting geometry and vibration spectrum of THBAP. The optimized geometric band lengths and bond angles obtained by using mPW1PW91 at both LanL2DZ and SDD basic sets show the best agreement with the experimental data. A comparison between the observed fundamental vibrational frequencies of THBAP and the calculated results has been made and the result indicates that the mPW1PW91/6-311G level is superior to all the remaining levels for predicting all the vibration spectra on average for THBAP.

Theoretical DFT study on spectroscopic signature and molecular dynamics of neurotransmitter and effect of hydrogen removal

Vibrational spectroscopic study has been made for the serotonin molecule and its deprotonated form. The Infrared and Raman spectra in optimum geometry of these two molecules are calculated using density functional theorem and the normal modes are assigned using potential energy distributions (PEDs) which are calculated using normal coordinate analysis method. The vibrational frequencies of these two molecules are reported and a comparison has been made. The effect of removal of the hydrogen atom from the serotonin molecule upon its geometry and vibrational frequencies are studied. Electronic structures of these two molecules are also studied using natural bond orbital (NBO) analysis. Theoretical Raman spectrum of serotonin at different exciting laser frequencies and at different temperatures are obtained and the results are discussed. Present study reveals that some wrong assignments had been made for serotonin molecule in earlier study.