Nuclear magnetic resonance, collection

Aqueous GPC can also be semiprepped in manner just like nonaqueous GPC. In this case one must consider carefully the buffers, salts, and biocides used in the eluant. If the fractions are destined for nuclear magnetic resonance experiments it will be imperative to either reduce the salt concentration in the eluant or remove salt after the initial fractionation. Likewise, if the collected samples are destined for infrared (IR) analysis, it is important to choose salts and buffers that have good IR transparency in the wavenumber ranges of interest. 

It is an unfortunate fact that several preexisting theories have tried to explain complicated mechanical phenomena of CB-reinforced rubbery materials but they have not been so successful." " However, a recent report might have a capability of explaining them collectively," when the author accepted the existence of the component whose molecular mobility is different from that of matrix mbber component in addition to the existence of well-known bound rubber component. The report described that this new component might be the most important factor to determine the reinforcement. These mbber components have been verified by spin-spin relaxation time 2 by pulsed nuclear magnetic resonance (NMR) technique, ° while the information obtained by NMR is qualitative and averaged over the sample and, therefore, lacking in the spatial... 

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... 

Ludlow, M., Louden, D., Handley, A., Taylor, S., Wright, B., and Wilson, I.D., Size-exclusion chromatography with on-line ultraviolet, proton nuclear magnetic resonance, and mass spectrometric detection and on-line collection for off-line Fourier transform infrared spectroscopy, /. Chromatogr. A, 857,89,1999. 

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. 

Infrared (IR) spectra were measured on a Beckmann Microlab 600 model spectrophotometer. Nuclear magnetic resonance (NMR) spectra were measured on a Varian EM360 spectrometer, with 19F-spectra collected using trifluoroacetic acid as a standard, or with H-spectra collected using tetramethylsilane as a standard. 

While the broad mission of the National Bureau of Standards was concerned with standard reference materials, Dr. Isbell centered the work of his laboratory on his long interest in the carbohydrates and on the use of physical methods in their characterization. Infrared spectroscopy had shown promise in providing structural and conformational information on carbohydrates and their derivatives, and Isbell invited Tipson to conduct detailed infrared studies on the extensive collection of carbohydrate samples maintained by Isbell. The series of publications that rapidly resulted furnished a basis for assigning conformations to pyranoid sugars and their derivatives. Although this work was later to be overshadowed by application of the much more powerful technique of nuclear magnetic resonance spectroscopy, the Isbell— Tipson work helped to define the molecular shapes involved and the terminology required for their description. 

The isolated 1-indanol was collected and 1 L of the solution was submitted for GC-MS analysis, as described above, and the compound identity was confirmed by nuclear magnetic resonance spectrometry. ... 

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... 

The carbon-13 nuclear magnetic resonance spectrum of a 4.7% (w/v) solution of dorzolamide hydrochloride was obtained in deuterated dimethyl sulfoxide, and is shown in Figure 9. The spectrum was recorded using a Brucker model AM-400 NMR spectrometer. The band assignments were referenced relative to dimethyl sulfoxide-ds (39.5 ppm), and the carbon atom assignments (using the same numbering system as just described) are collected in Table 5. 

Fig. 7.4.3a,b Nuclear magnetic resonance (NMR 500 MHz) urine spectra from a patient with severe trimethylaminuria, a Before eating sea fish (TMA = 44 pmol/mmol creatinine, TMA N-oxide not detectable), b After a 300-g sea fish meal [Nijmegen protocol urine collection during the 6-h postprandial period TMA = 322 pmol/mmol creatinine, TMA N-oxide (TMA + TMA N-oxide) = 84%]. The NMR spectrum shows the presence of increased TMA in the pre-load sample as well as the absence of TMA N-oxide. After eating fish the TMA concentration is very high and the ratio is clearly abnormal... 

Male Fischer 344 rats were exposed by inhalation to 1% 2-chloro-1,1,1 -trifluoroethane for 2 h and then urine was collected for 24 h. Urinary metabolites identified by 19F nuclear magnetic resonance and gas chromatography/mass spectrometry were 2,2,2-trifluoroethyl glucuronide (16%), trifluoroacetic acid (14%), trifluoroacetaldehyde hydrate (26%), trifluoroacetaldehyde-urea adduct (40%) and inorganic fluoride (3%). A minor, unidentified metabolite was also detected. No covalent binding of fluorine-containing metabolites was observed in the liver and kidney from the exposed rats (Yin et al., 1995). In-vitro incubation of 2-chloro-1,1,1-trifluoroethane with rat liver microsomes and an NADPH-generating system has been shown to involve a dechlorination reaction (Salmon et al., 1981) that produced trifluoroacetaldehyde hydrate as the only metabolite (Yin et al., 1995). 

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. 

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