Quantum mechanical assessment on the optical properties of capsanthin conformers.

As optical properties, the ultraviolet-visible (UV-Vis) absorption spectra of capsanthin-based red natural dye are a decisive parameter for their usage in various applications. Thus, accurately predicting the maximum UV-Vis wavelength ( λ max ) values is critical in designing dye-conjugated material. Extensive metadynamics simulations were carried out to generate capsanthin conformers at various levels of the extended tight-binding method. Benchmarking the time-dependent density-functional theory (TD-DFT) methods help understand the results of a particular functional and allows a comparison between results obtained with different functional. The long-range correction (LC) scheme in LC-TD-DFT-D4/ωB97X/def2-SVP has been found to reproduce the experimental λ max , and exhibited the effect of conformational changes to the calculated wavelengths. On the other hand, an inexpensive yet efficient LC-TD-DFTB method reproduced the experimental λ max insensitive to conformational changes.

Revealing the incorporation of an NH2 group into the edge of carbon dots for H2O2 sensing via the C-N⋯H hydrogen bond interaction.

We investigated hydrogen peroxide (H2O2) sensing on NH2-functionalized carbon dots (Cdots) for three different -NH2 positions, and the N atom was found to be the active site using a quantum computational approach. B3LYP and 6-31G(d,p) were used for density functional theory (DFT) ground state calculations, whereas CAM-B3LYP and the same basis set were used in time-dependent density functional theory (TD-DFT) excited state calculations. Structural optimization showed that the H2O2 is chemisorbed on 1-sim via a C-N⋯H hydrogen bond interaction with an adsorption energy of -10.61 kcal mol-1. Mulliken atomic charge distributions and electrostatic potential (ESP) analysis were both used to determine reactivity of the molecules at the atomic level. For in-depth analysis of the ground states, we utilized Frontier molecular orbital (FMO) theory, quantum theory of atoms in molecules (QTAIM), and non-covalent interaction (NCI) index analysis. In addition, we also present UV-vis absorption spectra and charge transfer lengths to understand the mechanism of H2O2 sensing in excited states. Based on the molecular and electronic properties of the NH2-Cdots, it was shown that 1-sim is a potential candidate for use as an electrochemical sensor for H2O2 sensing. Whereas 3-sim is believed to be a potential candidate for use as an optical sensor of H2O2 based on the UV-vis characteristics via photoinduced charge transfer.

Quantum Chemical Calculation for Intermolecular Interactions of Alginate Dimer-Water Molecules.

The abundance of applications of alginates in aqueous surroundings created by their interactions with water is a fascinating area of research. In this paper, computational analysis was used to evaluate the conformation, hydrogen bond network, and stabilities for putative intermolecular interactions between alginate dimers and water molecules. Two structural forms of alginate (alginic acid, alg, and sodium alginate, SA) were evaluated for their interactions with water molecules. The density functional theory (DFT-D3) method at the B3LYP functional and the basis set 6-31++G** was chosen for calculating the data. Hydrogen bonds were formed in the Alg-(H2O)n complexes, while the SA-(H2O)n complexes showed an increase in Van der Walls interactions and hydrogen bonds. Moreover, in the SA-(H2O)n complexes, metal-nonmetal bonds existed between the sodium atom in SA and the oxygen atom in water (Na…O). All computational data in this study demonstrated that alginate dimers and water molecules had moderate to high levels of interaction, giving more stability to their complex structure.