Chemical Isomer Shift Research Articles

Experimental and computational studies of 3-(N-morpholinylcarbodithioate)-2-(4-methoxyphenyl)chroman-4-one, a flavanone with potential therapeutical properties

In this paper we are reporting the results obtained regarding 3-(N-morpholinylcarbodithioate)-2-(4-methoxyphenyl)chroman-4-one, mainly by IR and NMR spectroscopy combined with Density Functional Theory calculations. The structural and vibrational characterization of this synthetic flavanone was carried out by performing quantum mechanical calculations in the ground state and by using several hybrid functionals (B3LYP, PBE1PBE, CAM-B3LYP and ωB97X-D) in conjunction with the same basis set, namely 6-311G(d,p). A complete assignment of all the absorption bands present in the vibrational spectrum has been performed.The theoretical 1H and 13C NMR chemical shifts (with respect to TMS) of both isomers of the investigated flavanone were obtained with four DFT-GIAO functionals, i.e. B3LYP, WP04, WC04 and PBE1PBE, in conjunction with the 6-311++G(d,p) and cc-pVDZ basis sets. The values of the theoretical 1H and 13C NMR chemical shifts have been compared with the experimental ones. The effect of different functionals and basis sets on the accuracy and precision in predicting the1H and 13C NMR chemical shifts was also assessed.The chemical potential and oral bioavailability of the studied compound was explored by computing several quantum molecular descriptors that characterize the electronic interactions between a compound and its biological receptor, such as the dipole moment, the energy of frontier molecular orbitals, the gap energy, the electronegativity, the chemical hardness/softness and the electrophilicity index. The druglikeness of the targeted compound was evaluated by using filters known to be efficient in estimating the potential of a molecule to be a bioavailable oral drug.

Comparison of spectroscopic, structural, and molecular docking studies of 5-nitro-2-fluoroaniline and 2-nitro-5-fluoroaniline: An attempt on fluoroaniline isomers

Density Functional Theory (DFT) and Hartree-Fock (HF) approaches were used to study the spectroscopic, pharmacological and other molecular properties of structural isomers of fluoroaniline such as 5-nitro-2-fluoroaniline (5N2FA) and 2-nitro-5-fluoroaniline (2N5FA). The geometrical properties, vibrational properties, electronic properties, and chemical shifts of fluoroaniline isomers have been thoroughly investigated. In the gas phase, the energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of fluoroaniline isomers is found to be 3.874 / 8.248 eV (DFT/HF) for 5N2FA and 3.979 / 8.176 eV (DFT/HF) for 2N5FA. The current study reveals that the dipole moment values for 5N2FA and 2N5FA were computed (using DFT / HF) to be approximately 4.5318 / 4.2777 D and 3.6551 / 3.5440 D, respectively. Absorption, distribution, metabolism, and excretion (ADME) properties have been predicted to evaluate the toxicity and pharmacokinetic profile of fluoroaniline isomers. Moreover, the Natural Bond Orbital (NBO), Mulliken population, and Molecular Electrostatic Potential Surface (MESP) analyses have been performed to get a crystal clear insight into the bonding characters, and reactive sites of structural isomers of fluoroaniline. Molecular docking simulation is used to investigate the biological activities of fluoroaniline isomers by forming a stable complex with inducible Nitric Oxide Synthase (iNOS) with a binding affinity of -5.6 kcal/mol (5N2FA), and -5.3 kcal/mol (2N5FA), which shows that of an enzyme inhibitor.

DFT Calculations of 1H NMR Chemical Shifts of Geometric Isomers of Conjugated Linolenic Acids, Hexadecatrienyl Pheromones, and Model Triene-Containing Compounds: Structures in Solution and Revision of NMR Assignments.

A DFT study of the 1H NMR chemical shifts, δ(1H), of geometric isomers of 18:3 conjugated linolenic acids (CLnAs), hexadecatrienyl pheromones, and model triene-containing compounds is presented, using standard functionals (B3LYP and PBE0) as well as corrections for dispersion interactions (B3LYP-D3, APFD, M06–2X and ωB97XD). The results are compared with literature experimental δ(1H) data in solution. The closely spaced “inside” olefinic protons are significantly more deshielded due to short-range through-space H…H steric interactions and appear close to or even beyond δ-values of aromatic systems. Several regularities of the computational δ(1H) of the olefinic protons of the conjugated double bonds are reproduced very accurately for the lowest-energy DFT-optimized single conformer for all functionals used and are in very good agreement with experimental δ(1H) in solution. Examples are provided of literature studies in which experimental resonance assignments deviate significantly from DFT predictions and, thus, should be revised. We conclude that DFT calculations of 1H chemical shifts of trienyl compounds are powerful tools (i) for the accurate prediction of δ(1H) even with less demanding functionals and basis sets; (ii) for the unequivocal identification of geometric isomerism of conjugated trienyl systems that occur in nature; (iii) for tackling complex problems of experimental resonance assignments due to extensive signal overlap; and (iv) for structure elucidation in solution.

DFT Calculations of 1H- and 13C-NMR Chemical Shifts of Geometric Isomers of Conjugated Linoleic Acid (18:2 ω-7) and Model Compounds in Solution.

A density functional theory (DFT) study of the 1H- and 13C-NMR chemical shifts of the geometric isomers of 18:2 ω-7 conjugated linoleic acid (CLA) and nine model compounds is presented, using five functionals and two basis sets. The results are compared with available experimental data from solution high resolution nuclear magnetic resonance (NMR). The experimental 1H chemical shifts exhibit highly diagnostic resonances due to the olefinic protons of the conjugated double bonds. The “inside” olefinic protons of the conjugated double bonds are deshielded than those of the “outside” protons. Furthermore, in the cis/trans isomers, the signals of the cis bonds are more deshielded than those of the trans bonds. These regularities of the experimental 1H chemical shifts of the olefinic protons of the conjugated double bonds are reproduced very accurately for the lowest energy DFT optimized single conformer, for all functionals and basis sets used. The other low energy conformers have negligible effects on the computational 1H-NMR chemical shifts. We conclude that proton NMR chemical shifts are more discriminating than carbon, and DFT calculations can provide a valuable tool for (i) the accurate prediction of 1H-NMR chemical shifts even with less demanding functionals and basis sets; (ii) the unequivocal identification of geometric isomerism of CLAs that occur in nature, and (iii) to derive high resolution structures in solution.

Features of the Magnetic Structure of Y3Fe5O12 Polycrystals Synthesized by Radiation Thermal Sintering

Samples of polycrystalline yttrium-iron garnet synthesized using radiation-thermal sintering and ceramic processing have been studied by the Mossbauer spectroscopy method. The best decomposition of the Mossbauer spectroscopy spectra of the research objects, which is a simulation of the experimental spectrum with five sextets, has been selected. An additional fifth sextet is caused by Fe3+ ions, which are surrounded by oxygen vacancies leading to distortion of Fe-tetrahedra, which is reflected in an increase in the quadrupole splitting of Fe3+. An increase in the density of s-electrons on Fe ions in distorted tetrahedra has been found, resulting in a decrease in the isomeric chemical shift δ of Fe ions to a value close to the δ value for Fe4+ ions. It has been shown that the optimal crystal structure is realized in Y3Fe5O12 polycrystals when they are sintered for 40–60 min in the temperature range of 1350–1400°C by the radiation-thermal sintering method.

Особенности магнитной структуры поликристаллов Y-=SUB=-3-=/SUB=-Fe-=SUB=-5-=/SUB=-O-=SUB=-12-=/SUB=-, синтеризованных методом радиационно-термического спекания

The Mössbauer spectroscopy (MS) method was used to study polycrystalline iron yttrium garnet (YIG) samples synthesized by radiation thermal sintering (RTS) technology and by standard ceramic technology (CT). The best option for decomposing the MS spectra of the objects of study was selected, which is a model of the experimental spectrum with five sextets. An additional fifth sextet is caused by Fe3 + ions, surrounded by oxygen vacancies which lead to distortion of the Fe tetrahedra which reflected by an increase in the quadrupole splitting of Fe3+. An increase in the density of s-electrons on Fe ions in distorted tetrahedra lead to a decrease in the isomeric chemical shift δ of Fe ions up to a values closed to the δ value for Fe4+ ions. It was shown that the optimal crystalline structure realizes for Y3Fe5O12 polycrystals upon sintering by RTS method in the temperature range of 1350–1400 ° C for a time from 40 to 60 min.

Characteristics Optimization of the Resonant Detector for Mössbauer Spectroscopy Using Resonance 57Fe

This paper considers the converter materials having different mean thickness, isomeric chemical shift, and various cationic surroundings of the iron atoms in the converter matrix for resonance detectors. The influence of the converter material parameters on the characteristics of the Mossbauer spectra taken by the resonance detector has been estimated. The value of resonance absorption, experimental linewidth, and the measurement time of the Mossbauer spectra has been calculated taking into account the material converter parameters. It has been found that beryllium ferrocyanide with efficient thickness equal to 2 is the most appropriate converter for emission experiments, and potassium-magnesium ferrocyanide with effective thickness equal to 4 proves to be optimal for transmission Mossbauer experiments.

Electron Reconfiguration and Enhanced Phonon Activation in the Superconducting State of a FeSe0.3Te0.7 Single Crystal, as Evidenced by Mössbauer Spectroscopy

The Mossbauer spectra of a FeSe0.3Te0.7 single crystal grown by the Bridgman method were analysed across the superconducting transition by considering the interplay between the structure and electron configuration of the transition metal. The magnetically determined superconducting critical temperature is TC ∼ 14 K. The 57Fe Mossbauer spectra collected in the temperature range from 5 to 200 K mainly have an asymmetric doublet pattern, which was conveniently fitted by the full Hamiltonian method. No effective magnetic moment ascribed to the superconducting phase was observed down to 5 K. The unusual behaviour observed below ∼17 K for the chemical isomer shift and quadrupole splitting may be associated with an electron reconfiguration process intimately related to an unusual lattice distortion accompanying the superconducting transition. The decreasing trend of the total absorption spectral area and second-order Doppler shift during cooling the sample below the critical temperature, point to enhanced phonon...

Hardness and Bonding of Silicate Garnets

The chemical bond properties of the andradite garnet Ca3Fe2Si3O12, grossular garnet Ca3Al2Si3O12, and pyrope garnet Mg3Al2Si3O12 have been investigated using a chemical bond theory of complex crystals. The calculated hardness, isomer shifts of these garnets are in good agreement with the available experimental data. Predictions are made for those cases where no experimental data have been reported. The chemical bond properties, hardness and isomer shifts of the andradite garnet Ca3Fe2Si3O12, grossular garnet Ca3Al2Si3O12, and pyrope garnet Mg3Al2Si3O12 have been investigated using a chemical bond theory of complex crystals.

Theoretical Study on Mössbauer Isomer Shift of Layered Compounds

Using the expended chemical bond dielectric theory of complex crystals, we have calculated chemical bond parameters and Mossbauer isomer shift of LnOFeAs as well as AFe2As2 which had been chosen due to their layered structures. Results are in good agreement with available experimental data, demonstrating the accuracy of our calculations and theories. The relationship between chemical bond parameters and Mossbauer isomer shift is discussed.

ChemInform Abstract: Stereospecific Thionation of 2-Ethoxy-1,2-oxaphosphorinane 2-Oxide and Its Derivatives with Lawesson′s Reagent.

The parent phostone, 2-ethoxy-1,2-oxaphosphorinane 2-oxide 1, and derivatives with substituents at the 3-position (methyl, phenyl, and benzyl; compounds 2-4) were converted with Lawesson's reagent to provide the corresponding sulfide analogues 5-8 in moderate yields. The conversion of 2-4 occurred with retention of configuration at the phosphorus center. This was implied from the relative Rf values and 13C and 31P NMR chemical shifts of the individual isomers and confirmed for the transformation of 3b to 7b by X-ray structures of each of these. Oxidation of 7b, 8a, and 8b with m-chloroperoxybenzoic acid alone led to the corresponding oxides 3b, 4a, and 4b with retention. The presence of trifluoroacetic acid during this oxidation process led to varying degrees of epimerization about phosphorus and was dependent on the relative molar equivalents of this acid.Key words: 2-ethoxy-1,2-oxaphosphorinane 2-oxide, 2-ethoxy-1,2-oxaphosphorinane 2-sulfide, phostone, thiophostone, Lawesson's reagent, stereoselective ...

Investigation on stabilities and spectroscopy of C80O2 based on C80 (D5d) using density functional theory

AbstractThe relative stabilities of the 17 possible isomers for C80O2 based on C80 (D5d) were studied using Becke three parameters plus Lee, Yang, and Parr's (B3LYP) method and 6‐31G (d) basis set in density functional theory. The most stable geometry of C80O2 was predicted to be 23,24,27,28‐C80O2 (A) with annulene‐like structures, where the additive bonds are those between two hexagons (6/6 bonds) near the equatorial belt of C80 (D5d). Electronic spectra of C80O2 isomers were calculated based on the optimized geometries using intermediate neglect of differential overlap (INDO) calculation. Compared with those of C80 (D5d), the first absorptions in the electronic spectra of C80O2 are blue‐shifted owing to the wide energy gaps. 13C nuclear magnetic resonance spectra and nucleus independent chemical shifts of the C80O2 isomers were computed at B3LYP/6‐31G level. The chemical shifts of the bridged carbon atoms in the epoxy structures of C80O2 compared with those of the bridged carbon atoms in the annulene‐like structures are changed upfield. Generally, the isomers with the annulene‐like structures of C80O2 are more aromatic than those with the epoxy structures. The addition of the oxygen atoms near the pole of C80 (D5d) is favorable to improving the aromaticities of C80O2. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Theoretical study of structure and stability of fullerene derivative: C50O

AbstractA total of eight possible isomers of C50O, an oxide of fullerene C50 (D5h), have been investigated by B3LYP/3‐21G calculations. The isomer, which has an annulene‐like structure with oxygen bridging across a [5,6] type CC bond at the site between the pole and the equatorial belt, is found being the ground state of C50O. Four isomers are relatively more stable and the energy differences between them are not large. This result indicates that more than one C50O isomer will coexist once C50O is synthesized. The relative stabilities of the C50O isomers may be determined mainly by the strain release and by the formation of the cyclic phenylene substructure at the equatorial belt of the cage. The calculated nucleus independent chemical shifts (NICS) of the C50O isomers will be useful because from them one can expect outstanding NMR properties that can lead to their identification and characterization. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Theoretical 13C NMR chemical shifts of the stable isomers of fullerene C90

Density functional theory has been employed to study fullerene C 90 . Structures of all 46 IPR isomers were optimized at the B3LYP/STO-3G level. Geometry optimization for those isomers with relative energies less than 25 kcal/mol were performed using basis sets up to 6-31G, and the 13 C NMR chemical shifts were calculated using the GIAO method. Isomer 45 is the most stable species, while other stable isomers include 28 , 30 , 32 , 35 , 40 and 46 . Comparison between prediction and experiment shows that the reported NMR spectrum likely arises from isomers 35 and 46 instead of isomer 36 and one C 2 isomer.

13C NMR spectra for IPR isomers of fullerene C 86

Structures of all the 19 isolated-pentagon-rule abiding isomers of fullerene C 86 have been optimized using density functional theory at the B3LYP/6-31G level of theory. Isomers 16 and 17 have low total energies and large HOMO–LUMO gaps. 13C NMR chemical shieldings are obtained employing the gauge-independent atomic orbital method. The good agreement between the predicted and the measured NMR spectra allows us to conclusively assign the observed C 2 isomer as isomer 17 and the C s isomer as isomer 16. Quantum mechanically predicted NMR chemical shifts of other isomers are also presented for future reference.

Theoretical evidence for the major isomers of fullerene C84 based on 13C NMR chemical shifts

Geometry optimizations for three isomers of fullerene C84, 21, 22 and 23, have been performed by density functional theory (DFT) at the B3LYP/6-31G* level of theory. 13C NMR chemical shifts were evaluated by the GIAO method employing 6-31G* and 6-311G** basis sets. Isomers 22 and 23 are predicted to have essentially equal energies and isomer 21 to be 16 kcal mol−1 less stable. The calculated 13C NMR chemical shifts of isomers 22 and 23 agree nicely with experimental data while the results of isomer 21 show large differences, indicating that isomer 22 is the experimentally observed D2 isomer.

Stereospecific thionation of 2-ethoxy-1,2-oxaphosphorinane 2-oxide and its derivatives with Lawesson's reagent

The parent phostone, 2-ethoxy-1,2-oxaphosphorinane 2-oxide 1, and derivatives with substituents at the 3-position (methyl, phenyl, and benzyl; compounds 2-4) were converted with Lawesson's reagent to provide the corresponding sulfide analogues 5-8 in moderate yields. The conversion of 2-4 occurred with retention of configuration at the phosphorus center. This was implied from the relative Rf values and 13C and 31P NMR chemical shifts of the individual isomers and confirmed for the transformation of 3b to 7b by X-ray structures of each of these. Oxidation of 7b, 8a, and 8b with m-chloroperoxybenzoic acid alone led to the corresponding oxides 3b, 4a, and 4b with retention. The presence of trifluoroacetic acid during this oxidation process led to varying degrees of epimerization about phosphorus and was dependent on the relative molar equivalents of this acid.Key words: 2-ethoxy-1,2-oxaphosphorinane 2-oxide, 2-ethoxy-1,2-oxaphosphorinane 2-sulfide, phostone, thiophostone, Lawesson's reagent, stereoselective synthesis, X-ray diffraction.

A tin-119 Mössbauer spectroscopic investigation of some chalcogen-containing Zintl phases

The 119Sn Mössbauer parameters for some chalcogen-containing Zintl phases of composition M 4Sn X 4 ( M=Na, K; X=S, Se, Te), Na 2SnSe 3, M 3SnTe 3 ( M=K, Rb, Cs), Cs 4Sn 2Te 7 and M 2SnTe 5 ( M=K, Rb) are reported. All the compounds contain tetrahedrally coordinated tin and the chemical isomer shift data show the tin to be involved in covalent bonding with the chalcogen atoms. The dependence of the 119Sn Mössbauer parameters on the local coordination of tin, the extent of polymerisation of the anionic sub units, the transfer of electrons from the alkali metal to the anionic units, and the electronegativity of the chalcogen atoms are discussed.

Conformational analysis by NMR spectroscopy and molecular simulation in water of methylated glutamic acids, agonists at glutamate receptors

We have undertaken a conformational analysis by 1H and 13C NMR spectroscopy and molecular modelling of five glutamic acid analogues substituted in position-3 or -4 by a methyl (3T, 3E, 4T, 4E) or a methylene group (4M). These analogues interact with glutamate receptors of the central nervous system, especially the ligand 4T, at one cloned metabotropic receptor (mGluR1a), and the ligand 4E, at the ionotropic receptor (KA). A combination of one- and two-dimensional NMR techniques was used to completely assign the 1H and 13C NMR chemical shifts of the different isomers according to the geometrical isomerism of the methyl. Hetero- and homo-nuclear coupling constants were measured in order to assign the diastereotopic methylene protons at C(3) or C(4), and used for comparison in molecular dynamics (MD) simulations. The system with two carbon–carbon single bonds allows the possibility of trans and gauche forms ‘A, B, C’ and ‘a, b, c’ corresponding to the χ1 and χ2 backbone torsion angles, respectively. The hydrogen-bonding possibility, steric effect or electrostatic interaction may be a considerable influence in stabilizing the different conformations in D2O solution. The conformations may be grouped by the two characteristic distances between the potentially active functional groups, αN+⋯γCO2–(d1) and αCO2–⋯γCO2–(d2) and by the two backbone torsion angles, χ1[α-CO2––C(2)–C(3)–C(4)] and χ2[+NC(2)–C(3)–C(4)–γCO2–].

Bonding in Some Zintl Phases: A Study by Tin-119 Mössbauer Spectroscopy

The 119Sn Mössbauer parameters for a range of Zintl phase compounds are reported. The compounds containing tetrahedrally coordinated tin of composition M5SnX3 (M = Na, K; X = P, As, Sb) have chemical isomer shifts close to that of grey-tin and can be considered to be covalently bonded species. The layer structures of composition KSnX (X = As, Sb) and double-layer compounds M Sn2X2 (M = Na, Sr; X = As, Sb) have tin in a distorted octahedral environment. The chemical isomer shifts are closer to that of white-tin and can be interpreted in terms of metallic bonding.