Vibrational spectroscopy and density functional theory study of ninhydrin

Periodic and non-periodic DFT studies of an organic semiconductor material: Structural, electronic, optical, and vibrational properties of ninhydrin

The main purpose of the present study is to explore details of the structural, electronic, optical and vibrational properties of ninhydrin. To achieve this aim, the results of extensive DFT calculations have been employed. Because the accuracy of the results is essential in this study, some periodic DFT approximations have first been subjected to rigorous computational tests, and the RPBE-TS functional is finally selected. Then, the analysis of the RPBE-TS results has revealed that the studied crystal is a semiconductor with a direct band gap of 2.17 eV. The variation of some optical properties (dielectric constant, absorption coefficient, and refractive index) as a function of the polarization directions of the incident electromagnetic wave has also been presented. In addition, the complementarity of anharmonic isolated molecule and harmonic solid-state calculations is exploited in order to give precise assignments of the experimental IR spectrum in the region 400-3800 cm-1. The combination of these two theoretical approaches allows the precise identification of the four red-shifted OH-stretching bands based on the periodic DFT-calculations, and also to attribute, by using the isolated molecule model, some anharmonic bands in the CH/OH stretching regions 2700-3800 cm-1.

Indirect glyphosate detection based on ninhydrin reaction and surface-enhanced Raman scattering spectroscopy

Glyphosate is one of the most commonly-used and non-selective herbicides in agriculture, which may directly pollute the environment and threaten human health. A simple and effective approach to assessment of its damage to the natural environment is thus quite necessary. However, traditional chromatography-based detection methods usually suffer from complex pretreatment procedures. Herein, we propose a simple and sensitive method for the determination of glyphosate by combining ninhydrin reaction and surface-enhanced Raman scattering (SERS) spectroscopy. The product (purple color dye, PD) of the ninhydrin reaction is found to SERS-active and directly correlate with the glyphosate concentration. The limit of detection of the proposed method for glyphosate is as low as 1.43×10^-8mol·L^-1 with a relatively wider linear concentration range (1.0×10^-7-1.0×10^-4mol·L^-1), which demonstrates its great potential in rapid, highly sensitive concentration determination of glyphosate in practical applications for safety assessment of food and environment.