Nuclear magnetic resonance data collection

Electrochemical nuclear magnetic resonance (NMR) is a relatively new technique that has recently been reviewed (Babu et al., 2003). NMR has low sensitivity, and a typical high-held NMR instrument needs 10 to 10 NMR active atoms (e.g., spins), to collect good data in a reasonable time period. Since 1 cm of a single-crystal metal contains about 10 atoms, at least 1 m of surface area is needed to meet the NMR sensitivity requirement. This can be met by working with carbon-supported platinum... 

In order to co clarify the role of complex formation, the new data on stability constants should be accumulated, being collected at strictly similar conditions. It should be also mentioned that any analysis of equilibrium in solutions involving anions of polybasic hydroxy carboxylic acids requires the data on the deprotonation constants of the acid in question. This information would be crucial for conclusions regarding the presence and stability of mixed complexes in the system. Valuable knowledge about the structure of complex compounds present in solutions (and in precursors as well, see later) may be gained by means of vibrational spectroscopy (IR and Raman spectra) and nuclear magnetic resonance. 

A reevaluation of molecular structure of humic substances based on data obtained primarily from nuclear magnetic resonance spectroscopy, X-ray absorption near-edge structure spectroscopy, electrospray ionization-mass spectrometry, and pyrolysis studies was presented by Sutton and Sposito (2005). The authors consider that humic substances are collections of diverse, relatively low molecular mass components forming dynamic associations stabilized by hydrophobic interactions and hydrogen bonds. These associations are capable of organizing into micellar structures in suitable aqueous environments. Humic components display contrasting molecular motional behavior and may be spatially segregated on a scale of nanometers. Within this new structural context, these components comprise any molecules... 

Use of an integrated system incorporating CCC separation, PDA detector, and LC-MS proved to be a valuable tool in the rapid identification of known compounds from microbial extracts.6 This collection of analytical data has enabled us to make exploratory use of advanced data analysis methods to enhance the identification process. For example, from the UV absorbance maxima and molecular weight for the active compound(s) present in a fraction, a list of potential structural matches from a natural products database (e.g., Berdy Bioactive Natural Products Database, Dictionary of Natural Products by Chapman and Hall, etc.) can be generated. Subsequently, the identity of metabolite(s) was ascertained by acquiring a proton nuclear magnetic resonance ( H-NMR) spectrum. 

Fig. 3.53 >3C nuclear magnetic resonance spectrum of benzyl alcohol in CDC13 sweep width 200 p.p.m. Data reproduced from the Standard Carbon-13NMR Spectra Collection, Sadder Research Laboratories, Division of Bio-Rad Laboratories, Inc. 

Some of the new spectroscopic data are taken from the collections of the School of Chemistry, Thames Polytechnic, and we wish to acknowledge particularly the assistance of Dr E. Vidgeon for specifically recording the majority of the 13C-n.m.r. spectra. We acknowledge the inclusion of other spectroscopic data from the Sadtler Collections, Standard Infrared Spectra, Standard Ultraviolet Spectra and Standard Nuclear Magnetic Resonance Spectra, Sadtler Research Laboratories, Philadelphia, USA, and from Compilation of Mass Spectral Data, A. Cornu and R. Massot (1966-1971), Heyden and Son Ltd in collaboration with Presses Universitaires de France. 

Tphe application of nuclear magnetic resonance to the study of the compounds of the platinum group metals has been limited by the properties of these nuclei. Data are collected in Table I for all of the isotopes of these elements which have nonzero spins. 

Basic information on the nuclear magnetic resonance (NMR) properties of pyrroles and their benzo derivatives is collected in CHEC(1984) <1984CHEC(4)155> and CHEC-II(1996) <1996CHEC-II(2)1>. Only recently acquired data or new structurally relevant interpretations of old data based are reported here. 

In a paper that appeared in 1979, R.P.J. Merks and R. DeBeer pointed out that the sinusoidal dependence of the stimulated echo ESEEM experiment on x and T (equation 8), presented the opportunity to collect ESEEM data in both time dimensions and then apply a two-dimensional EFT to derive two important benefits. The first benefit was that suppression-free spectra should be obtained along the zero-frequency axis for each dimension while the second benefit would be the appearance of cross-peaks at (tUo, cofs) and (tw, co ) that would allow one to identify peaks that belonged to the same hyperfine interaction. This ESEEM version of the NMR COSY experiment (see Nuclear Magnetic Resonance (NMR) Spectroscopy of Metallobiomolecules) would prove invaluable for ESEEM analysis of complex spin systems. However, the disparity in spin relaxation times in the x and T time dimensions precluded the general application of this method. 

H and nuclear magnetic resonance (NMR) spectroscopic data for all indicated dithiiranes have been reported and important chemical shifts are collected in Table 1. The configurations of the sulfmyl sulfur of 18 and 19 have been assigned by comparison of the chemical shifts of the geminal methyl groups with those of known cis- and trans-dithiirane A-oxides <1995TL1867>. 

From the analysis of the data in the LIPID AT database (41), more than 150 different methods and method modifications have been used to collect data related to the lipid phase transitions. Almost 90% of the data is accounted for by less than 10 methods. Differential scaiming calorimetry strongly dominates the field with two thirds of all phase transition records. From the other experimental techniques, various fluorescent methods account for 10% of the information records. X-ray diffraction, nuclear magnetic resonance (NMR), Raman spectroscopy, electron spin resonance (ESR), infrared (IR) spectroscopy, and polarizing microscopy each contribute to about or less than 2-3% of the phase transition data records in the database. Especially useful in gaining insight into the mechanism and kinetics of lipid phase transitions has been time-resolved synchrotron X-ray diffraction (62,78-81). 

Resolution and sensitivity are essential to the collection of analytical chemical data with accuracy and precision. It is well known that mathematical transformation techniques enhance the resolution and sensitivity of spectroscopic methods. Fourier transform (FT), cross correlation (CC), and Fladamard transform (FIT) techniques allow for high resolution and high sensitivity of infrared spectroscopy (IR), fiuorometry, nuclear magnetic resonance... 

The characterization of the physical properties of pharmaceutical compounds under development is often conducted using a variety of techniques including DSC, TGA, XRD, HSM, solid-state nuclear magnetic resonance (NMR), infrared (IR) and Raman spectroscopy, moisture uptake, particle size analysis, scanning electron microscopy (SEM), and micromeritic assays. A typical initial analysis of a pharmaceutical compound under development in a materials characterization group would include DSC, TGA, HSM, and XRD analyses. These four techniques are chosen because the data generated from them, when viewed collectively, comprise a relatively complete initial analysis of the physical properties of the compound. The DSC, TGA, and HSM assays... 

Experiments in which specifically labeled deuteriotoluene was passed through the RF. discharge afforded additional experimental data which supported the importance of radical intermediates leading to condensable products. The materials formed from the labeled toluene were collected, separated by chromatographic techniques, and the distribution of the deuterium label determined by infrared and nuclear magnetic resonance spectroscopy and mass spectrometry. 

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