13C Nuclear Magnetic Resonance Chemical Research Articles

Use of Replaced Chalcones to Generate a 13C Chemical Shift Staging Factor for Chalcone and Its Derivate

Chalcones have attracted the attention of researchers for decades, they are biologically classified as secondary metabolites of low molecular weight. These are considered as the precursors of flavonoids and they are widely distributed in plants such as vegetables, fruits, teas and spices. It has been demonstrating that chalcones possess many important bioactivities including properties of antioxidants and other evidence of its potential beneficial effects on health. Chalcone compounds and its derivatives have been showing a growing interest in the therapeutic properties. Nuclear magnetic resonance (NMR) spectroscopy is one of the most important tools for determining the structures of organic molecules. In the work present a 13C Nuclear magnetic resonance chemical shift protocol of chalcones and derivative based on the application of scaling factor with chalcone molecules. This protocol consists of using density functional theory with gauge-including atomic orbital method to calculating 13C chemical shifts and the application of a parameterized scaling factor in order to ensure accurate structural determination of chalcones and derivative.

Normal coordinate analysis, molecular structure, vibrational, electronic spectra and NMR investigation of 4-Amino-3-phenyl-1H-1,2,4-triazole-5(4H)-thione by ab initio HF and DFT method

In the present work, the characterization of 4-Amino-3-phenyl-1H-1,2,4-triazole-5(4H)-thione (APTT) molecule was carried out by quantum chemical method and vibrational spectral techniques. The FT-IR (4000–400cm−1) and FT-Raman (4000–100cm−1) spectra of APTT were recorded in solid phase. The UV–Vis absorption spectrum of the APTT was recorded in the range of 200–400nm. The molecular geometry, harmonic vibrational frequencies and bonding features of APTT in the ground state have been calculated by HF and DFT methods using 6-311++G(d,p) basis set. The complete vibrational frequency assignments were made by normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMF). The molecular stability and bond strength were investigated by applying the natural bond orbital analysis (NBO) and natural localized molecular orbital (NLMO) analysis. The electronic properties, such as excitation energies, absorption wavelength, HOMO and LUMO energies were performed by time depended DFT (TD-DFT) approach. The 1H and 13C nuclear magnetic resonance chemical shift of the molecule were calculated using the gauge-including atomic orbital (GIAO) method and compared with experimental results. Finally, the calculation results were analyzed to simulate infrared, FT-Raman and UV spectra of the title compound which shows better agreement with observed spectra.

Experimental spectroscopic (FTIR, FT-Raman, FT-NMR, UV–Visible) and DFT studies of 1-ethyl-1,4-dihydro-7-methyl-4oxo-1,8 napthyridine-3-carboxylic acids

The solid phase FTIR and FT-Raman spectra of 1-ethyl-1,4-dihydro-7-methyl-4oxo-1,8 napthyridine-3-carboxylic acid (EDMONCA) have been recorded in the regions 4000–500 and 4000–400cm−1 respectively. The equilibrium geometry, harmonic vibrational frequencies have been investigated by DFT/B3LYP and B3PW91 methods with 6-311G (d,p) basis set. The different between the observed and scaled wave number values of most of the fundamental is very small. The assignments of the vibrational spectra have been carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFFM). Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV–Visible spectrum of the compound was recorded and the electronic properties HOMO and LOMO energies were measured. The electric dipole moment (μD) and first hyperpolarizability (βtot) values of the investigated molecule were computed using ab initio quantum mechanical calculations. The calculated results also show that the EDMONCA molecule may have microscopic nonlinear optics (NLO) behavior with non-zero values. 1H and 13C NMR spectra were recorded and 1H and 13C nuclear magnetic resonance chemical shift of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. Thermal stability of EDMONCA was studied by thermogravimetric analysis (TGA). Next Fukui function was calculated to explain the chemical selectivity or reactivity site in EDMONCA. Finally molecular electrostatic potential (MEP) and other molecular properties were performed.

Quantum chemical calculation and experimental measurement of the 13C chemical shift tensors of vanillin and 3,4-dimethoxybenzaldehyde

The principal values of the 13C nuclear magnetic resonance chemical shift tensors in vanillin and 3,4-dimethoxybenzaldehyde are reported. Theoretical results of the 13C chemical shift tensors were obtained by employing the gauge included atomic orbital (GIAO) approach. The geometrical parameters were optimized by using the MNDO method. The observed chemical shifts of these two compounds were determined in powders by using the recently introduced magic angle turning (MAT) experiment. The results presented in this paper clearly demonstrate the importance of using tensor information in the study of molecular structures.

Interchain effect of 13C nuclear magnetic resonance chemical shift and electronic structure of polyoxymethylene chains in the solid state

The tight-binding MO calculations of the 13C NMR chemical shifts and electronic structure for seven polyoxymethylene chains having trigonal and orthorhombic forms were carried out within the CNDO/2 sum-over-state framework, taking into account the interchain interactions. The calculation explains reasonably the experimental data. Based on these results, the interchain interactions were discussed.

The ionization behavior of fatty acids and bile acids in micelles and membranes.

The ionization behavior of carboxylic acids including aliphatic chain fatty acids and bile acids in solutions, micelles, membranes and proteins is of considerable biological interest. The 13C nuclear magnetic resonance chemical shift of carboxyl carbon of a variety of acids has been shown to be a linear function of the state of ionization of the carboxyl group. Thus, by measuring the chemical shift as a function of the amount of acid or base added to a solution, the state of ionization and the apparent pKa of the carboxyl group may be determined. The method is illustrated in this paper using butyric acid, and results (given as apparent pKa values) are tabulated for a variety of fatty acids and cholic acid in different environments such as monomeric solutions, micelles, membranes and bound to albumin. The apparent pKa varies greatly depending upon the environment. For instance, the apparent pKa of oleic acid is about 4.2 when bound to albumin whereas it is about 7.5 when incorporated in the bilayer of a phospholipid vesicle. Cholic acid shows similar changes in the apparent pKa, being approximately 5.2 in sodium taurocholate micelles and at least 6.8 in phospholipid vesicles. The use of 13C nuclear magnetic resonance (NMR) and, in particular, 13C NMR of 13C-enriched carboxyl groups provides a method for direct observation of the state of ionization of the carboxyl group in biologically interesting acids. Such techniques may be adapted for use in biological systems, such as cells or tissues.

Acid-induced 13C nuclear magnetic resonance chemical shift changes of ether and ester carbon atoms

13 C N.m.r. chemical shifts of ethers dissolved in tetrachloromethane are displaced on addition of trifluoroacetic acid. The displacements result from independent interactions of the acid with the substrate oxygen atoms and alkyl residues. The structure-dependent and stereoselective shift changes are useful for signal assignments, structure determination, conformational analysis, assessment of the distribution of rapidly interconverting conformers of esters, and estimation of the relative basicity of ethers.

A 13C nuclear magnetic resonance chemical shift study of trans-fused hexopyranoside derivatives

A detailed analysis of the 13C n.m.r. spectra of methyl 4,6-O-benzylidene-D-glycopyranosides (and one ethylidene analogue) and their various C-2 and C-3 derivatives has led to complete assignment of chemical shifts. This study has enabled the effects of a variety of stereochemical features and a variety of functional groups (OH, OMe, O·COR, O·SO2R, NH2, N3) to be established.