Fourier transform 13C NMR analysis of benzodiazepines

The natural abundance carbon-13 nuclear magnetic resonance spectra of diazepam, clonazepam, flurazepam and chlordiazepoxide were recorded in suitable solvent using the Fourier transform technique on a JEOL FX-60 spectrometer. The relaxation time (T₁) of these compounds were also measured. The chemical shift of the various carbon resonances have been assigned on the basis of chemical shift theory, multiplicity generated in single-frequency off-resonance decoupled spectra, relaxation time and the chemical shifts of the model compounds.     

Carbon-13 NMR spectra of fusicoccin and its derivatives

The ¹³C NMR spectra of fusicoccin, some of its cometabolites and derivatives were studied. Using standard Fourier transform techniques, T₁ relaxation time measurements and lanthanide shift reagents, the resonances of individual carbon-13 nuclei were assigned.     

Ultra-rapid-scanning Fourier transform infrared spectrometry

Several applications of Fourier transform infrared (FT-IR) spectrometry are discussed where both conventional rapid-scanning interferometers and step-scan interferometers are unable to provide the needed information. A new interferometer is described by which it is possible to acquire interferograms with 0.25 cm optical path difference (4 cm⁻¹ spectral resolution) in less than 1 ms. The moving element of this interferometer is a tilted mirror that continuously rotates at a speed of up to 500 Hz. The performance of this spectrometer is demonstrated by examining the spark-initiated combustion of ethane and methane in air. The formation of vibrationally excited CO₂ and H₂O, with lifetimes approaching 50 ms, was observed.     

Fourier transform Raman spectroscopic studies on sterically hindered aryl dichalcogenides

The Fourier transform Raman spectra of trisubstituted aryl dichalcogenides (2,4,6-R₃C₆E)₂ (R = Me, Prⁱ, Bu^t; E = Se, Te) in the region 600-100 cm⁻¹ are reported. Contrary to expectations, the ν(E-E) stretching frequencies increase slightly with increasing steric bulk of the aryl substituents but are less substituent-dependent than in previously reported examples.     

Fourier transform Raman spectroscopy of kandite clays

The Raman spectra of the kandite clay minerals, kaolinite, halloysite, dickite and nacrite, have been measured in the 180–3000 cm⁻¹ region using Fourier transform near-IR Raman spectroscopy. These clays have a very small Raman cross-section and long data collection times were often required to obtain good spectra. Each clay has its own unique characteristic Raman spectrum which enables each kandite to be identified easily. In contrast, it is quite difficult to distinguish kandite clays by IR spectroscopy. Nacrite and dickite have relatively intense Raman peaks in the 1000–1100 cm⁻¹ region, whereas kaolinite is characterized by an intense peak at 685 cm⁻¹ and halloysite at 470 cm⁻¹.     

Fourier transform infrared spectra and micelle formation of sodiumn-alkanesulfonates in aqueous solution

The concentration dependences of the Fourier transform infrared spectra of aqueous solutions of sodiumn-pentanesulfonate,n-hexanesulfonate,n-heptanesulfonate, andn-octanesulfonate were studied in concentration ranges encompassing the critical micellization concentrations (c.m.c). Changes in wavenumber, bandwidth, and intensity of infrared absorption bands were used to monitor the changes in molecular association with concentration. The premicellar aggregation below the c.m.c. may accompany the association of the alkyl chain, but not the counter-ion binding with the SO ₃ ^– group. Above the c.m.c, the front location of the counter-ion against the SO ₃ ^– group at the micelle surface is demonstrated.     

Combined Fourier transform infrared and Raman spectroscopic studies of some carbonyl-diphosphine-indenyl-iron cations

The Fourier transform infrared and Raman spectra of the cations [η⁵-C₉H₇Fe(CO)_n dppa]⁺ (n = 1, 2; dppa=bisdiphenylphosphinoalkane, where alkane=methane, ethane, butane, hexane and octane) and [{η⁵-C₉H₇Fe(CO)₂}₂-μ-dppa]²⁺ indicate that the alkyl chain lengths have effects on the structures of the bidentate cations resulting in increased back-donation to carbonyl groups as the chain length increases. In contrast the alkyl chain lengths have no similar effects in the unidentate mononuclear and bridged cations.     

Fourier transform ion cyclotron resonance spectroscopy

An ion cyclotron resonance (ICR) absorption spectrum has been obtained by exciting an ICR spectral segment with a fixed-frequency electric field pulse, followed by broad-band detection, digitization of the (time-domain) transient response, and digital Fourier transformation to produce the (frequency-domain) absorption spectrum. For a given signal-to-noise ratio and resolution, the FT-ICR method generates a spectrum in a time which is two orders of magnitude shorter than that required in conventional slow-sweep ICR detection. In the present example, a signal-to-noise ratio of 8:1 and a mass resolution of about 0.005 amu for CH₄⁺ (from CH₄ at a pressure of 8 X 10^?7 torr) have been achieved, using a single data acquisition period of 25.6 msec.     

Fourier transform of spherical Laguerre Gaussian functions and its application in molecular integrals

The Fourier transform of the spherical Laguerre Gaussian‐type function (LGTF), L ${}_{\text{n}}^{\text{l}\text{+½}}$ (αr²)r^lY_lm( r̂ )e, was derived. Applying the Fourier transform convolution theorem, the basic two‐center integrals over the general two‐electron irregular solid harmonic operator, Y_LM( r̂ ₁₂)/r (which becomes Coulomb repulsion, spin–other‐orbit interaction or spin–spin interaction when L=0, 1, or 2, respectively) as well as the overlap were evaluated analytically. These basic integral results generate the two‐electron integrals of the Coulomb type, hybrid type, and exchange type as well as that of three‐ and four‐center. The formulas obtained, which are general for electronic wave functions of unrestricted quantum numbers n, l, and m, are expressed explicitly in terms of nuclear spherical LGTFs of internuclear geometrical variables. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 265–273, 1999     

Time-resolved Fourier transform infrared emission spectroscopy of laser ablation products

Time-resolved Fourier transform infrared spectroscopy was applied for observations of emission spectra from ablation products induced by a Nd:YLF laser with a 2.5 kHz repletion rate. The infrared emission spectra from Fe, Cu, Zn, and Al atoms were observed in the 2.5–5 μm region. The observed emission spectrum from iron ablation in the 2500 cm⁻¹ region agrees very well with solar absorption spectrum, where new lines have been detected in the present experiment in addition to the lines observed from a hollow cathode discharge. When O₂ was added to the carbon ablation, emissions from vibrationally excited CO were observed with non-equilibrium vibrational distribution.     

Laser-induced molecular ion formation and gas-phase ion formation from polycyclic aromatic hydrocarbons,coals and coal products detected by Fourier transform mass spectrometry

The results from the laser-ablation Fourier transform mass spectrometric examination of a variety of polyaromatic hydrocarbons (PAHs), coals and other geochemically related materials are presented. Both molecular and quasi-molecular ions have been detected from different ring-sized PAHs. A relationship between the ease of sodium-adduct ion formation and the size of the aromatic array is observed. Nevertheless, suppression of [M + Na]⁺ ion formation in PAHs can be achieved by the addition of coal. In addition, distributions of low-mass positive- and negative-ion carbon clusters (C_n ⁺, 14 ? n ? 27 and C_n, ^?, 4 ? n ? 30), high-mass positive-ion carbon clusters (C_n⁺, 60 ? n ? 260) and low relative molecular mass organic compounds (< 600 daltons) have been observed from the coals. It appears that the ease of C formation may be used as an indicator of coal rank. Irradiance conditions also influence the observed distribution of high-mass positive-ion carbon clusters. Furthermore, distributions of the high-mass positive-ion carbon clusters at different irradiances supports an earlier proposal that their formation is kinetically controlled.     

The effect of apodization and finite resolution on Fourier transform Raman spectra

The effects that finite resolution and choice of apodization function have on Fourier transform (FT) Raman spectra are illustrated by the 839 cm⁻¹ (ν₁) and 914 cm⁻¹ bands of KMnO₄. FT-Raman spectra were recorded at 0.5, 1, 2, 4, 8, 16 and 32 cm⁻¹ resolution using boxcar, Norton—Beer (strong, medium and weak) and triangular apodization functions at each resolution. The results show the dramatic changes in bandshape that occur as the ratio (resolution/true full width at half height of band) increases. The changes were measured in terms of the full width at half height of the band, the height of the band, the area of the band and the bandshape (expressed as a sum of Lorentzian and Gaussian lines). At a given resolution the degree to which each of these characteristics is affected is strongly dependent on the choice of the apodization function.     

Step-scan Fourier transform infrared absorption spectroscopy of liquid benzene cluster in a pulsed supersonic jet

We have obtained the infrared absorption spectrum of the jet-cooled C₆H₆ in the 800–5000 cm⁻¹ region using step-scan Fourier transform infrared spectrometer combined with a pulsed supersonic jet system. The experimental spectrum was in good agreement with the convolution spectrum of the monomer band with the rotational temperature of ∼37 K and the broadbands of liquid C₆H₆, indicating the first spectroscopic evidence for the formation of supercooled liquid C₆H₆ cluster in the supersonic jet.     

Fourier transform ion cyclotron resonance study of ion-molecule reactions of [M – OCH3]+ ions of methyl 2,3,4,6-tetra-O-methyl-d-hexopyranosides with ammonia

Glycosidic oxocarbenium ions A₁⁺ were formed by isobutane chemical ionization from methyl 2,3,4,6-tetra-O-methyl-β-D -mannopyranoside, methyl 2,3,4,6-tetra-0-methyl-β-D -galactopyranoside and methyl 2,3,4,6-tetra-O-methyl-β-D -glucopyranoside (the ring - O-being converted into ? O ? ), and then- reaction with ammonia was studied by Fourier transform ion cyclotron resonance Spectrometry. Very slow formation (reaction efficiency 0.6-1.4%) of the adduct ion [A₁ + NH₃]⁴ was observed as the main process for carefully thermalized ions A₁⁺. Interestingly, the efficiency of the adduct ion formation depends on the sterochemistry of ions A₁⁺.     

Fourier transform spectra of carbon disulfide in the 2800–3000 cm−1 region

Fourier transform spectra were recorded for carbon disulfide in the region between 2800 and 3000 cm⁻¹. A total of 20 bands for the carbon disulfide isotopologue ¹²C³²S₂, 2 for ¹²C³²S³³S, 8 for ¹²C³²S³⁴S, 1 for ¹²C³⁴S₂ and 5 for ¹³C³²S₂ have been investigated. Two bands 13¹1–01¹0 of ¹²C³²S₂ and 12⁰1–00⁰0 of ¹²C³²S³⁴S present local perturbations.Vibrational frequencies and rotational constants have been determined for the bands.     

Carbon-13 pulse Fourier transform NMR : Conformational preference of the hydroxyl and the acetoxyl group in 2-cyclohexenol and its acetate

¹³C Fourier transform NMR spectra of cis and trans 5-t-butyl-2-cyclohexenols, 2-cyclohexenol and their acetates have been examined indicating that the pseudo-axial orientation of the hydroxyl and the acetoxyl group at the allylic position is favoured in 2-cyclohexenol and its acetate.     

The pure rotational spectrum of cyclobutane-d1 observed by microwave Fourier transform spectroscopy

Pure rotational transitions of both equatorial and axial conformers of cyclobutane-d₁ in their vibronic ground state have been observed between 12 and 40 GHz with a pulsed microwave Fourier transform (MWFT) spectrometer. Twenty-four transitions of the equatorial as well as 29 transitions of the axial conformer with J⩽40 have been measured. Their assignment has been confirmed by microwave-microwave double-resonance experiments. Rotational constants and the quartic centrifugal distortion constants have been determined for both conformers from the measured frequencies. The r₀ structure has been deduced from these rotational constants.     

Keeping PASE with WEFT: SHWEFT–PASE pulse sequences for 1H NMR spectra of highly paramagnetic molecules

Metalloproteins are a category of biomolecules in which the metal site is usually the locus of activity or function. In many cases, the metal ions are paramagnetic or have accessible paramagnetic states, many of which can be studied using NMR spectroscopy. Extracting useful information from ¹H NMR spectra of highly paramagnetic proteins can be difficult because the paramagnetism leads to large resonance shifts (~400 ppm), extremely broad lines, extreme baseline nonlinearity, and peak shape distortion. It is demonstrated that employing polychromatic and adiabatic shaped pulses in simple pulse sequences, then combining existing sequences, leads to significant spectral improvement for highly paramagnetic proteins. These sequences employ existing technology, with available hardware, and are of short duration to accommodate short nuclear T₁ and T₂. They are shown to display uniform excitation over large spectral widths (~75 kHz), accommodate high repetition rates, produce flat baselines over 75 kHz while maintaining peak shape fidelity, and can be used to reduce spectral dynamic range. High‐spin (S = 5/2) metmyoglobin, a prototypical highly paramagnetic protein, was used as the test molecule. The resulting one‐dimensional (1D) pulse sequences combine shaped pulses with super‐water elimination Fourier transform, which can be further combined with paramagnetic spectroscopy to give shaped pulses with super‐water elimination Fourier transform–paramagnetic spectroscopy. These sequences require, at most, direct current offset correction and minimal phasing. The performance of these sequences in simple ¹H 1D, 1D NOE, and two‐dimensional NOESY experiments is demonstrated for metmyoglobin and Paracoccus denitrificans Co²⁺‐amicyanin (S = 3/2), and employed to make new heme hyperfine resonance assignments for high‐spin metBjFixLH_151–256, the heme sensing domain of Bradyrhizobium japonicum FixL. Copyright © 2013 John Wiley & Sons, Ltd.     

Chemistry of the phenoxathiins and isosterically related heterocycles. XXIII . 1-azathianthrene: First reported synthesis of a monoazathianthrene and the investigation of the 13C-NMR spectrum using two-dimensional NMR techniques

The reaction of the dianion of 3-mercaptopyridin-2(1H)-thione with 2-chloronitrobenzene in N,N-dimethylformamide leads to the formation of 1-azathianthrene, the first reported mono-aza analog of the thianthrene ring system. A partial assignment of the ¹³C-nmr spectrum of the title compound is reported, the assignment based on chemical shift arguments, spin-lattice (T₁) relaxation times and ¹H-¹³C spin coupling constants. Amplitude modulated two-dimensional Fourier transform (AM2DFT) techniques were employed for the acquisition of the heteronuclear spin-coupling constants.     

Accurate calculation of Fourier transform of two-center Slater orbital products

A method is presented which leads to accurate Fourier transform values of any 1s?1s Slater-type orbital overlap distribution. The numerical merits are discussed and illustrated by some examples.