Experimental (FT-IR, FT-Raman, 1H, 13C NMR) and theoretical study of alkali metal 2-aminonicotinates

A mystery of a cup of coffee; an insight look by chemist

Fruits, vegetables as well as processed food products of plant origin are a rich source of beneficial for human health constituents. Among them the polyphenols constitute a large group of compounds. The presented literature survey is devoted to chlorogenic acid the most abundant representative of cinnamate acids esters. Its chemical as well as biological properties are described. © 2017 BioFactors, 43(5):621-632, 2017.

The spectroscopic (FT-IR, FT-Raman, dispersive Raman and NMR) study of ethyl-6-chloronicotinate molecule by combined density functional theory

In this study, ethyl-6-chloronicotinate (E-6-ClN) molecule is recorded in the region 4000-400 cm(-1) and 3500-100 cm(-1) (FT-IR, FT-Raman and dispersive Raman, respectively) in the solid phase. ((1))H and ((13))C nuclear magnetic resonance (NMR) spectra are recorded in DMSO solution. The structural and spectroscopic data of the molecule are obtained for two possible isomers (S1 and S2) from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. The geometry of the molecule is fully optimized, vibrational spectra are calculated and fundamental vibrations are assigned on the basis of the potential energy distribution (PED) of the vibrational modes. ((1))H and ((13))C NMR chemical shifts are calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, oscillator strengths, wavelengths, HOMO and LUMO energies, are performed by time-dependent density functional theory (TD-DFT). Total and partial density of state and overlap population density of state diagrams analysis are presented for E-6-ClN molecule. Furthermore, frontier molecular orbitals (FMO), molecular electrostatic potential, and thermodynamic features are performed. In addition to these, reduced density gradient of the molecule is performed and discussed. As a conclusion, the calculated results are compared with the experimental spectra of the title compound. The results of the calculations are applied to simulate the vibrational spectra of the molecule, which show excellent agreement with the observed ones. The theoretical and tentative results will give us a detailed description of the structural and physicochemical properties of the molecule. Natural bond orbital analysis is done to have more information stability of the molecule arising from charge delocalization, and to reveal the information regarding charge transfer within the molecules.

A combined experimental and theoretical analysis on molecular structure and vibrational spectra of 2,4-dihydroxybenzoic acid

The FT-IR and FT-Raman spectra of 2,4-dihydroxybenzoic acid (2,4-DHBA) in the solid phase have been recorded in the regions 4000-400 cm(-1) and 3700-100 cm(-1), respectively. The total energies of sixteen stable conformers for 2,4-DHBA have been calculated by density functional theory (DFT) using the B3LYP method with 6-311++G (d, p) basis set, and the C1 conformer with the lowest energy was obtained, the geometrical parameters between X-ray experiment diffraction and DFT calculation show good consistency. Furthermore, the vibrational frequencies of 2,4-DHBA were computed, and the detailed analysis of vibrational spectra was made on the basis of the potential energy distribution (PED) by combining experimental with theoretical data. In addition, frontier molecular orbitals, atomic charge distribution and molecular electrostatic potential (MEP) were also given.

Molecular structure and spectroscopic characterization of ethyl 4-aminobenzoate with experimental techniques and DFT quantum chemical calculations

The FT-IR and FT-Raman spectra of ethyl 4-aminobenzoate (EAB) in the solid phase were recorded. The fundamental vibrational wavenumbers, intensities of vibrational bands and the optimized geometrical parameters of the compound were evaluated using DFT (B3LYP) method with 6-311++G(d,p) basis set. The stable geometry of the compound was determined from the potential energy surface scan. Complete vibrational assignments and Natural Bond Orbital (NBO) analysis for the title compound were carried out. The assignments of the vibrational spectra were carried out with the help of normal co-ordinate analysis (NCA) following the Scaled Quantum Mechanical Force Field (SQMFF) methodology. The molecule orbital contributions were studied by using the total (TDOS), partial (PDOS), and overlap population (OPDOS) density of states. UV-visible spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies were performed by time-dependent DFT (TD-DFT) approach. Mulliken population analysis on atomic charges were also calculated. Besides, molecular electrostatic potential (MEP) and thermodynamic properties were performed.

Spectroscopic (FT-IR, FT-Raman, UV absorption, 1H and 13C NMR) and theoretical (in B3LYP/6-311++G** level) studies on alkali metal salts of caffeic acid

The effect of some metals on the electronic system of benzoic and nicotinic acids has recently been investigated by IR, Raman and UV spectroscopy [1-3]. Benzoic and nicotinic acids are regarded model systems representing a wide group of aromatic ligands which are incorporated into enzymes. In this work the FT-IR (in solid state and in solution), FT-Raman, UV absorption and (1)H and (13)C NMR spectra of caffeic acid (3,4-dihydroxycinnamic acid) and its salts with lithium, sodium, potassium, rubidium and caesium were registered, assigned and analyzed. The effect of alkali metals on the electronic system of ligands was discussed. Studies of differences in the number and position of bands from the IR, Raman, UV absorption spectra and chemical shifts from NMR spectra allowed to conclude on the distribution of electronic charge in the molecules, the delocalization energy of π electrons and the reactivity of ligands in metal complexes. Optimized geometrical structures of studied compounds were calculated by B3LYP method using 6-311++G** basis set. Bond lengths, angles and dipole moments for the optimized structures of caffeic acid and lithium, sodium, potassium caffeinates were also calculated. The theoretical wavenumbers and intensities of IR spectra were obtained. The calculated parameters were compared to the experimental characteristics of investigated compounds. Microbial activity of studied compounds was tested against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Proteus vulgaris.

Molecular structure (monomeric and dimeric structure) and HOMO-LUMO analysis of 2-aminonicotinic acid: a comparison of calculated spectroscopic properties with FT-IR and UV-vis

The experimental (UV-vis and FT-IR) and theoretical study of 2-aminonicotinic acid (C(6)H(6)N(2)O(2)) was presented in this work. The ultraviolet absorption spectrum of title molecule that dissolved in ethanol and water were examined in the range of 200-400 nm. The FT-IR spectrum of the title molecule in the solid state were recorded in the region of 400-4000 cm(-1). The geometrical parameters and energies of 2-aminonicotinic acid have been obtained for all four conformers/isomers (C1, C2, C3, C4) from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. C1 form has been identified the most stable conformer due to computational results. Therefore, spectroscopic properties have been searched for the most stable form of the molecule. The vibrational frequencies were calculated and scaled values were compared with experimental FT-IR spectrum. The complete assignments were performed based on the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Also the molecular structures, vibrational frequencies, infrared intensities were calculated for a pair of molecules linked by the intermolecular O-H⋯O hydrogen bond. Moreover, the thermodynamic properties of the studied compound at different temperatures were calculated. Besides, charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap, molecular electrostatic potential (MEP) were calculated and presented. The spectroscopic and theoretical results are compared to the corresponding properties for monomer and dimer of C1 conformer. The optimized bond lengths, bond angles, calculated frequencies and electronic transitions showed the agreement with the experimental results.