Magnetic shielding tensors of carbon nuclei in 3,5-dichlorophenylacetylene,a theoretical ab initio and experimental study

Ab initio GIAO-CHF and DFT(B3LYP) molecular geometry optimization and magnetic shielding tensor calculations of carbon nuclei of 3,5-dichlorophenylacetylene have been performed using 6–311G?? and 6–311+G(2d,p) basis sets. The isotropic ¹³C chemical shifts, needed for comparison, have been measured in C₆D₁₂ solution. The principal elements of the shielding tensor of the carbon nuclei in the investigated molecule in the solid state have been determined from an intensity analysis of the spinning sidebands in ¹H-¹³C CP/MAS NMR spectra. Shielding anisotropy parameters of the acetylenic carbons have been independently determined using the method based on proton-coupled ¹³C nematic phase spectra as well as from the interpretation of the ¹³C longitudinal relaxation rates. The latter data have been analysed assuming the molecular reorientation to be the rotational diffusion of an asymmetrical top, which has provided, apart from the diffusion coefficients, an additional check on the reliability of the theoretical calculation of the shielding tensors. In general, satisfactory agreement between the theoretical and experimental results has been achieved.     

Synthesis and Characterization of a Biologically Active Lanthanum(III)–Catechin Complex and DNA Binding Spectroscopic Studies

A lanthanum(III) complex of catechin has been synthesized and characterized by elemental analysis, molar conductance, UV-Vis spectra, infrared spectra, thermal analysis, and ¹H NMR. The complex behaves as a nonelectrolyte in methanol solvent. The spectral and thermal properties of the complex are examined. A thermogravimetric (TGA) study showed the hydrated nature of the complex. ¹H NMR spectra of the lanthanum and the catechin (CT) ligands measured in CD₃OD-d₄ also show metal ligand coordination. The lanthanum–catechin complex shows bright luminescence in methanol solution. The interaction of the complex with calf thymus DNA has been investigated by absorption and emission spectroscopic measurements. Experimental spectral results suggest CT–DNA binding with catechin complex via an intercalative mode.     

Prediction of the 1H NMR spectra of epoxy-fused cyclopentane derivatives by calculations of chemical shifts and spin–spin coupling constants

¹H NMR spectra of epoxy-fused cyclopentane derivatives have been computationally investigated with density functional calculations in order to unravel the shielding effect of the epoxy ring on the ¹H NMR chemical shifts of N-substituted epoxy-fused cyclopentane-3, 5-diol derivatives. Both ¹H NMR chemical shifts and spin–spin coupling constants have been calculated with the WP04/cc-pVTZ level of theory in solution. The WP04/cc-pVTZ// B3LYP/6-31+G(d) methodology has been found to reproduce the best experimental results on epoxy-fused cyclopentane derivatives. This study is expected to lead experimentalists in their endeavour to characterize epoxy-fused cyclic systems with ease.     

H, C NMR and JCH coupling constants investigation of 4-Phenylpyridine: A combined experimental and theoretical study

Proton coupled and uncoupled ¹³C, ¹H, DEPT, COSY and HETCOR NMR spectra of 4-Phenylpyridine (4-Phpy) have been reported for the first time except for its ¹H NMR spectrum. In order to provide a precise structural elucidation for carbon atoms those have very close chemical shifts to each other, the magnitude of ⁿJ_CH (n=1,2,3) coupling constants of 4-Phpy (C₁₁H₉N) have also been investigated. ¹³C, ¹H NMR chemical shifts and ^1-3J_CH coupling constants of 4-Phpy have been calculated by means of B3LYP density functional method with 6-311++G(d,p) basis set. Moreover, the optimized parameters (bond lengths, bond and torsion angles) of 4-Phpy have been calculated with B3LYP at 6-31G(d) level in methanol (ε=32.63). Comparison between the experimental and the theoretical results indicates that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties.     

In situ solid-state 1H NMR studies of hydration of the solid acid catalyst ZSM-5 in its ammonium form

Hydration of the ammonium form of the solid acid catalyst ZSM-5 is investigated by applying a technique that has been developed recently for carrying out in situ solid-state NMR studies of adsorption processes. From ¹H MAS NMR spectra recorded as a function of time and temperature during the hydration process, insights are established on the nature of the interaction between the adsorbed water molecules and the ammonium cations in the ZSM-5 material. The change in isotropic chemical shift for the ammonium cations is consistent with the formation of N–H?O hydrogen bonding with the water molecules. Studies of the adsorption of deuterated water, and dehydration of the hydrated material, are also reported.     

NMR study of heterogeneity in pyridine-N-oxide...HCl crystal

An origin of narrow ¹H NMR signals in pyridine-N-oxide (PyO)...HCl crystal has been investigated by means of MAS, SPEDAS, NOESY and COSY techniques. Spectra of crystalline samples are compared with those of solid phase obtained from liquid PyO...HCl solutions (in acetonitile/H₂O) after the heterogeneous phase separation. It has been concluded that partially resolved peaks in ¹H NMR spectra of solids are related with heterogeneity of spin system and presence of different H-bond clusters of water molecules. NOESY spectra show no cross-peaks even at very long mixing time (500 ms). This indicates there is no exchange process between spins causing different peaks, and thus the corresponding molecular aggregates are captured in “islands of mobility8 without any channels sufficient for exchange. Appearance of MAS side bands as “pseudo8 cross-peaks in 2D NMR spectra using MAS/COSY technique is reported. In the case of accidental coincidence of spinning frequency (ω _MAS ) with spectral distances between some diagonal signals, intensive non-diagonal peaks are observed at the corresponding cross-positions. A misleading conclusion concerning spin coupling is easy to avoid using various ω _MAS . This work is dedicated to Professor Robert Blinc on the occasion of his 70^th birthday.     

13C NMR and 2D (H,H and H,C COSY) Spectra of Triazolo-triazino-indole Derivatives and the Conformational Analysis of the Respective C-Nucleoside Analogues

¹³C NMR and 2D (H,H and H,C COSY) spectra of selected examples of sugar (5H-1,2,4-triazino[5,6-b]-indol-3-yl) hydrazones, peracetylated sugar-1-acetyl -1- (5-acetyl-1,2,4-triazino[5,6-b]indol-3-yl)hydrazones, and 10-acetyl-3-(per-0-acetylalditol-1-yl)-1,2,4-triazolo[4′, 3′:2,3][1,2,4]triazino[5,6-b]indole have been reported. The conformation of the latter C-nucleoside analogues have been determined by analysis of their ¹H NMR spectra. The D-galacto, D-manno and L-arabino isomers are preponderantly existing in the planar zigzag arrangement of carbon atoms.     

Unusual Hindered Rotation of an Unsubstituted Phenyl Group. Variable Temperature 1H NMR Studies and Preliminary 13C Assignments in Ketazolam

An unusual hindered rotation of an unsubstituted phenyl group in the drug, ketazolam, has been found at ambient temperature. Variable temperature lH NMR has been employed to examine the two- fold rotation about the C(sp²)-C(sp³) bond. Chemical shift as- signments of the IH NMR spectra and partial assignments of the ¹³C spectra are supported by off-resonance decoupling, gated decou- pling, and low temperature 2D ^l3C-¹H heteronuclear chemical shift correlation experiments at 200.1 MHz for IH and 50.3 MHz for ¹³C.     

Synthesis and Spectroscopic Studies of 3-(3 N-Arylidenehydrazino-1,2,4-triazol-5-yl)-coumarins and Their Biological Activities

The electronic absorption spectra of 3-(3 N-arylidenehydrazino-1,2,4-triazol-5-yl) coumarin III are investigated in organic solvents of varying polarities and buffer solutions of different PH. The behaviour of the latter is utilized in calculating pka values of these compounds. The important bands in the IR spectra and the main ¹H NMR signals are assigned and discussed in relation to molecular structure. The antimicrobial activity of these compound has been investigated.     

1H and 13C NMR Spectral Study of Some 2r-Aryl-6c-phenylthian-4-ones,Their 1-Oxides and 1,1-Dioxides

ABSTRACT

Four 2r-aryl-6c-phenylthian-4-ones 1b?1e and their 1-oxides 2b?2e and 1,1-dioxides 3b?3e have been newly synthesized. ¹H and ¹³C NMR spectra have been recorded for all these compounds and 2r,6c-diphenylthian-4-one 1-oxide 2a. ¹³C NMR spectrum has been recorded for the sulfone 3a of 1a. For selected compounds ¹H-¹H COSY, HSQC, HMBC, and NOESY spectra have been recorded. The vicinal proton–proton coupling constants suggest that in all these compounds, the heterocyclic ring adopts chair conformation with equatorial orientations of the aryl and phenyl groups. Proton and carbon chemical shifts suggest that in the sulfoxides, the S=O bond is axial and enhances the J _aa value by some special effect. The S = O bond causes a significant upfield shift even on carbons without hydrogens. Significant solvent shifts also were observed.     

Some CNDO Calculations and Structural Spectroscopic Studies of Paracetamol Complexes

Through complete neglect of differential overlap (CNDO) calculations of the electronic energy among different possible structures of paracetamol (PA) molecule, it has been concluded that its structure has C_s point group symmetry of the cis‐form in which the methyl group has a restricted free rotation around its bond with the carbon atom of the amide group. The electronic spectra of PA compound were studied in different polar and nonpolar solvents. The temperature effect on the electronic spectra confirms the presence of one conformer only. The hydrogen bonding and the orientation energies of the polar solvents were determined from the studies of mixed solvents. Complexes of PA with metal ions M(II) (Cu⁺⁺, Zn⁺⁺, or Fe⁺⁺) of ratio 2:1, respectively, were prepared, and their structure has been confirmed by elemental analysis, atomic absorption spectra, IR spectra, and ¹H‐NMR spectra. It has been concluded that the structure of the complexes has C_2h point group symmetry in which two PA molecules are chelated to any one of the metal ions Cu⁺⁺, Zn⁺⁺, and Fe⁺⁺.     

NMR Studies of Hindered Rotation. The Diels-Alder Adduct of N-n-Butylmaleimide With Phencyclone: Restricted Motion of Bridgehead Phenyls

The Diels-Alder adduct of phencyclone and N-n-butylmaleimide has been prepared, and NMR studies have been carried out in CDCl₃ solution at ambient temperatures by one-and two-dimensional ¹H NMR (300 MHz) and ¹³C NMR (75 MHz) techniques. The resulting spectra appear to be consistent with slow rotation about the hindered C(sp²)-C(sp³) bonds to the bridgehead unsubstituted phenyls, i.e., slow exchange limit (SEL) spectra. Full rigorous ¹H spectral assignments have been made via high-resolution COSY experiments. The number of signals in the ¹³C NMR aryl region were also consistent with hindered phenyl rotations; preliminary ¹³C assignments are given. Striking evidence for magnetic anisotropic effects due to the phenanthrene moiety, bridging ketone carbonyl, and bridgehead phenyls are discussed, supporting endo stereochemical assignment of the adduct.     

Effect of pulsed ion irradiation on the electronic structure of multi-walled carbon nanotubes

The effect of pulsed ion irradiation and vacuum annealing on the ratio of sp ²- and sp ³-hybridized orbitals of carbon atoms in the layers of oriented multi-walled carbon nanotubes has been studied by analyzing the photoemission spectra of the C1s core level and the valence band of carbon, which were obtained using the equipment of the BESSY II Russian-German beamline of synchrotron radiation and a Riber analytical system. It has been shown that the ion irradiation leads to a significant decrease in the fraction of atoms with the sp ³ hybridization of electrons. On the contrary, the annealing reduces the fraction of the sp ³-component in the spectra of carbon. Typical features of the valence band of multi-walled carbon nanotubes in the annealed and irradiated states have been established.     

Parallel-plate RF resonator imaging of chemical shift resolved capillary flow

Magnetic resonance imaging has been introduced to study flow in microchannels using pure phase spatial encoding with a microfabricated parallel-plate nuclear magnetic resonance (NMR) probe. The NMR probe and pure phase spatial encoding enhance the sensitivity and resolution of the measurement. In this paper, ¹H NMR spectra and images were acquired at 100 MHz. The B₁ magnetic field is homogeneous and the signal-to-noise ratio of 30 μl doped water for a single scan is 8×10⁴. The high sensitivity of the probe enables velocity mapping of the fluids in the micro-channel with a spatial resolution of 13×13 μm. The parallel-plate probe with pure phase encoding permits the acquisition of NMR spectra; therefore, chemical shift resolved velocity mapping was also undertaken. Results are presented which show separate velocity maps for water and methanol flowing through a straight circular micro-channel. Finally, future performance of these techniques for the study of microfluidics is extrapolated and discussed.     

Local structure analysis of YSZ by Y-89 MAS-NMR

The local coordination structure around Yttrium ions in yttria stabilized zirconia (YSZ) has been investigated by ⁸⁹Y MAS-NMR. The NMR spectrum showed multiple peaks corresponding to yttrium ions in different coordination numbers. The compositional dependence of spectra was observed. Yttrium ions of different oxygen coordination number were quantified. The oxygen vacancy concentration around the cations was determined. It was found that the vacancies were distributed around Zirconium ions in lower Y₂O₃ concentrations, and the vacancy concentration located to Yttrium began increasing at concentrations above 10 mol% Y₂O₃. The local structure change was able to be directly observed by ⁸⁹Y NMR measurements.     

1H and 13C NMR Spectra of Alditolyl Derivatives of 3-Hydrazino-5-Methyl[1,2,4]triazino[5,6-b]indole and Their Cyclized Products.

The ¹H and ¹³C NMR spectra of sugar (5-methyl [1, 2, 4]-triazino [5, 6-b] indol-3-yl) hydrazones (1), per-0-acetyl aldehydo sugar 1-acetyl-1-(5-methyl [1, 2, 4] triazino [5, 6-b]-indol-3-yl) hydrazones (2), l- (penta-0-acetyl-pentitol-1-yl)-10-methyl [l, 2, 4] triazolo [3′, 4′:3, 4] [l, 2, 4] triazino [5, 6-b]-indoles (3) have been investigated. The 2 D NMR (H, C COSY) spectrum of 2a has been studied.     

Local structure of amorphous and microcrystalline Fe-B alloys

Amorphous and microcrystalline Fe-B alloys in the composition range (4–25) at % B, fabricated by melt spinning, were investigated by pulse nuclear magnetic resonance (NMR) on ¹¹B nuclei at 4.2 K. Alloy samples were prepared both from a natural mixture of isotopes and an isotope mixture ⁵⁶Fe-¹¹B. The NMR spectra were measured at different boron contents. The local atomic structure of amorphous Fe-B alloys has been determined. The amorphous alloys consist of microregions (clusters) with short-range order of the tetragonal and orthorhombic Fe₃B-phase types, as well as of the α-Fe type.     

Determination of the quadrupole splitting distributions of the A- and B-site ferrous ions in Fe2TiO4

Fe₂TiO₄ has been investigated using⁵⁷Fe Mössbauer spectroscopy with the aim of determining the shape and the temperature dependence of the separate A- and B-site quadrupole splitting distributions. This has been impossible hereto because both contributions are strongly overlapping and the normal doublet spectra do not contain enough information to differentiate between both. It is found that, through th use of external magnetic fields, the necessary information to perform the separation is unveiled. Furthermore, the change in shape as a function of temperature of the distributions thus obtained is well understood from the known behaviour of Fe²⁺.     

NMR Studies of Hindered Rotation. The Diels-Alder Adduct of Phencyclone with N-n-Propylmaleimide: Restricted Motion of Bridgehead Phenyls

The Diels-Alder adduct of phencyclone and N-n-propylmaleimide has been studied in CDCl₃ solution at ambient temperatures by one-and two-dimensional ¹H NMR (300 MHz) and ¹³C NMR (75 MHz) techniques. Clear evidence is presented from slow exchange limit (SEL) spectra for hindered rotation of the bridgehead phenyls in the adduct. Full ¹H spectral assignments have been made via selective homonuclear decoupling and high resolution COSY experiments. The number of signals in the aryl region of ¹³C NMR spectra also indicated slow rotation about the C(sp²)-C(sp³) bond to the unsubstantiated bridgehead phenyls. Striking evidence of magnetic anisotropic effects, seen from ¹H NMR, permits stereochemical assignment of the adduct as endo.     

Magic-angle-spinning NMR on solid biological systems. Analysis Of the origin of the spectral linewidths

Magic-angle-spinning (MAS) high-power ¹H-decoupled ¹³C and ³¹P NMR has been applied to solid biological materials to obtain information about the mechanisms that determine the spectral linewidths. The line broadening in MAS ³¹P NMR spectra of solid tobacco mosaic virus (TMV) has been investigated by selective saturation and T₂ measurements. About 90 Hz stems from homogeneous effects, whereas the inhomogeneous contribution is approximately 100 Hz. The inhomogeneous line broadening is assigned to macroscopic inhomogeneities in the sample and not to variations in the nucleotide bases along the RNA strand in TMV. It is concluded that sample preparation is of vital importance for obtaining well-resolved spectra. Under optimal preparation techniques the isotropic values of the chemical shift of the different ³¹P sites have been determined to obtain information about the secondary structure of the viral RNA. The chemical shift anisotropy has been determined from the relative intensities of the spinning side bands in the spectra. The chemical shift information is used to make a tentative assignment of the resonance in terms of the three structurally distinguishable phosphate groups in TMV. The origin of the linewidths in MAS NMR has been examined further by ¹³C NMR of approximately 10% ¹³C-enriched coat protein of cowpea chlorotic mottle virus, using selective excitation and saturation techniques, as well as measurements of the relaxation times T_1γ and T₂. The CO resonance in the spectrum is composed of an inhomogeneous and homogeneous part with a total linewidth of 700 Hz. The homogeneous linewidth, contributing with 200 Hz, is found to arise from slow molecular motions in the solid on a millisecond timescale.