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At least 1,045 records · Page 58Linked to original sources
PubMed2004

Comparisons of the interactions between two analytes and two structurally similar chiral stationary phases using high-performance liquid chromatography, suspended-state high-resolution magic angle spinning nuclear magnetic resonance and solid-state nuclear magnetic resonance spectroscopy.

A study of the retention behaviour of the enantiomers (R)- and (S)-1,1'-binaphthyl-2,2'-diol as well as (+) and t-)-O,O'-dibenzoyl-tartaric acid was performed using the two chiral stationary phases (CSPs) Kromasil-DMB and Kromasil-TBB. Detailed information about the interactions between the analytes and the two CSPs was obtained from suspended-state HR/MAS transferred NOESY NMR experiments as well as suspended-state HR/MAS 1H NMR titration experiments. Good correlation between the suspended-state HR/MAS NMR experiments and the corresponding HPLC experiments was obtained. This shows that suspended-state HR/MAS NMR as well as solid-state CP/MAS NMR spectroscopy can be used to investigate interactions between stationary phases and analytes under conditions that are similar to those used in HPLC.

Chromatography, High Pressure Liquid↗
PubMed2000

Identification and quantification of metabolites of 2,3,5,6-tetrafluoro-4-trifluoromethylaniline in rat urine using 19F nuclear magnetic resonance spectroscopy, high-performance liquid chromatography-nuclear magnetic resonance spectroscopy and high-performance liquid chromatography-mass spectrometry.

The urinary excretion profile and identity of the metabolites of 2,3,5,6-tetrafluoro-4-triflouromethylaniline, following i.p. administration to the rat at 50 mg kg(-1), were determined using a combination of 19F-NMR, HPLC-NMR and HPLC-MS. A total of 38% of the dose was eliminated in the urine as five metabolites. The major routes of metabolism were N-glucuronidation, sulfation and oxidation with a significant amount of metabolic defluorination to give a number of ortho-ring hydroxylated metabolites. The oxidised metabolites were excreted as glucuronide and/or sulfate conjugates.

Aniline Compounds↗
PubMed1993

Heteronuclear nuclear magnetic resonance studies of cobalt corrinoids. 15. The structure of glutathionylcobalamin: a 1H and 13C two-dimensional nuclear magnetic resonance study at 600 MHz.

Glutathionylcobalamin (GSCbl), the complex formed between glutathione (GSH, gamma-glutamylcysteinylglycine) and aquacobalamin (H2OCbl), has been implicated as an intermediate in the pathway for the formation of the cobalamin coenzymes. In chemical model studies, GSCbl has been shown to be a substrate for methylcobalamin formation in the presence of S-adenosylmethionine and a thiol reductant. Although GSCbl was first described in 1964, the structure of this compound, particularly the site of GSH coordination, has been unknown. GSCbl was prepared by reacting GSH (5-fold molar excess) with H2OCbl in 0.1 M sodium phosphate (pH 6.5) and was purified by gel-permeation chromatography on a Bio-Gel P2 polyacrylamide column. By use of a combination of homonuclear [homonuclear J-correlated spectroscopy (COSY), homonuclear Hartmann-Hahn spectroscopy (HOHAHA), and absorption-mode nuclear Overhauser effect spectroscopy (NOESY)] and inverse detected heteronuclear [1H-detected heteronuclear multiple-quantum coherence (HMQC) and 1H-detected multiple-bond heteronuclear multiple-quantum coherence (HMBC) spectroscopies] two-dimensional NMR methods at 600 MHz, the complete 1H and 13C NMR spectra of GSCbl have now been assigned. Comparison of the 1H and 13C NMR chemical shifts of the GS moiety of GSCbl to those of free GSH and GS- shows that by far the largest differences occur at the cysteine alpha and beta positions. This result strongly suggests that GSH is coordinated to the cobalt atom in GSCbl via the cysteine sulfur atom.

Carbon Isotopes↗
PubMed1981

Nuclear magnetic resonance characterization of aromatic residues of alpha-lactalbumins. Laser photo chemically induced dynamic nuclear polarization nuclear magnetic resonance studies of surface exposure.

The alpha-lactalbumins are involved as modifier proteins in lactose biosynthesis. Lactalbumins from different mammalian species are cross-reactive with the galactosyltransferases from others because of their homologous primary and tertiary structure. We have studied the surface exposure of several alpha-lactalbumins (bovine, goat, human, guinea pig, and rabbit) by the laser photo-CIDNP technique, an NMR method which measures the access of a photoexcited flavin dye to surface exposed Tyr, Trp, and His residues. An exposed histidine-68 residue exists in the bovine and goat species but is missing in other species and is replaced with a His-10 in the guinea pig species. The only exposed tryptophan residue was Trp-104, which cross-relaxed to nearby Trp-60. Cross-polarization to the latter residue was proven by taking free induction decays after extremely short light pulses (0.1 s). Furthermore, this cross-polarized Trp-60 resonance was absent in the guinea pig species, which has a substitution at position 60. The chemical shifts of these Trp residues were extremely similar in all species but rabbit, which has substituted His for a Tyr at position 103, situated close to both Trp-104 and -60. Three of the four tyrosines in bovine, goat, human, and guinea pig alpha-lactalbumin were exposed (the latter species has an extra Tyr in its sequence which was apparently not accessible). The rabbit species contains only two Tyr residues, the one which was not accessible (Tyr-50) being common to all species.

Animals↗
PubMed1979

Lithium-7 nuclear magnetic resonance, water proton nuclear magnetic resonance, and gadolinium electron paramagnetic resonance studies of the sarcoplasmic reticulum calcium ion transport adenosine triphosphatase.

The interactions of gadolinium ion, lithium, and two substrate analogues, beta,gamma-imido-ATP (AMP-PNP) and tridentate CrATP, with the calcium ion transport adenosine triphosphatase (Ca2+-ATPase) of rabbit muscle sarcoplasmic reticulum have been examined by using 7Li+ NMR, water proton NMR, and Gd3+ EPR studies. Steady-state phosphorylation studies indicate that Gd3+ binds to the Ca2+ activator sites on the enzyme with an affinity which is approximately 10 times greater than that of Ca2+. 7Li+, which activates the Ca2+-ATPase in place of K+, has been found to be a suitable nucleus for probing the active sites of monovalent cation-requiring enzymes. 7Li+ nuclear relaxation studies demonstrate that the binding of Gd3+ ion to the two Ca2+ sites on Ca2+-ATPase increases the longitudinal relaxation rate (1/T1) of enzyme-bound Li+. The increase in 1/T1 was not observed in the absence of enzyme, indicating that the ATPase enhances the parmagnetic effect of Gd3+ on 1/T1 of 7Li+. Water proton relaxation studies also show that the ATPase binds Gd3+ at two tight-binding sites. Titrations of Gd3+ solutions with Ca2+-ATPase indicate that the tighter of the two Gd3+-binding sites (site 1) provides a ghigher enhancement of water relaxation than the other, weaker Gd3+ site (site 2) and also indicate that the average of the enhancements at the two sites is 7.4. These data, together with a titration of the ATPase with Gd3+ ion, yield enhancements, epsilonB, of 9.4 at site 1 and 5.4 at site 2. Analysis of the frequency dependence of 1/T1 of water indicates that the electron spin relaxation taus of Gd3+ is unusually long (2 X 10(-9) s) and suggests that the Ca2+-binding sites on the ATPase experience a reduced accessiblity of solvent water. This may indicate that the Ca2+ sites on the Ca2+-ATPase are buried or occluded within a cleft or channel in the enzyme. The analysis of the frequency dependence is also consistent with three exchangeable water protons on Gd3+ at site 1 and two fast exchanging water protons at site 2. Addition of the nonhydrolyzing substrate analogues, AMP-PNP and tridenate CrATP, to the enzyme-Gd3+ complex results in a decrease in the observed enhancement, with little change in the dipolar correlation time for Gd3+, consistent with a substrate-induced decrease in the number of fast-exchanging water protons on enzyme-bound Gd3+. From the effect of Gd3+ on 1/T1 of enzyme-bound Li+, Gd3+-Li+ separations of 7.0 and 9.1 A are calculated. On the assumption of a single Li+ site on the enzyme, these distances set an upper limit on the separation between Ca2+ sites on the enzyme of 16.1 A.

Animals↗