High-resolution 19F NMR Spectroscopy Research Articles

Products of electrochemical fluorination of tripropylamine and triallylamine

Products of electrochemical fluorination of tripropylamine and triallylamine were studied by gas chromatography-mass spectrometry and high-resolution 19F NMR spectroscopy. The use of these methods allowed identification of the structures and isomeric composition of components of the electrolysis products.

A 19F NMR Signal Assignment and a Detailed Structural Study of Alternating Tetrafluoroethylene-Propylene Copolymer by High Resolution 19F NMR Spectroscopy and Computational Chemistry

A 19 F NMR Signal Assignment and a Detailed Structural Study of Alternating Tetrafluoroethylene-Propylene Copolymer by High Resolution 19 F NMR Spectroscopy and Computational Chemistry

Fluorine incorporation in silica glass by the MCVD process: Study of fluorine incorporation zone, evaluation of optical properties and structure of the glass

Abstract A theoretical approach was made to find out a complete fluorine incorporation zone on a ternary diagram which serves as a useful graphical representation to select the flows of the supplied reagents for incorporation of the suitable amount of fluorine into cladding glass of optical fiber preform made by the MCVD process using CCl2F2 as a source of fluorine under oxygen abundance, oxygen deficiency and intermediate oxygen state conditions. The possible mechanism for incorporation of fluorine into cladding glass of optical fiber is also evaluated on the basis of the thermodynamical data. The fluorine incorporation mechanism in silica glass by the MCVD process is found to be dependent on the CCl2F2/SiCl4 ratio in the input gas mixture. Fluorine doping is found to be effective for removing the strained Si–O–Si bonds, which govern the optical transparency in deep ultra-violet (DUV) and vacuum ultra-violet (VUV) regions. The maximum refractive index depression of −0.5 × 10−3 is obtained with incorporation of fluorine into silica cladding glass by the MCVD process using CCl2F2 as a dopant precursor with suitable flow of SiCl4 vapor along with O2 through backward deposition pass. The structure of fluorine doped silica glass preform samples containing 1.70–1.79 mol% fluorine incorporated by the MCVD process based on the analyses of 19F MAS spectra done by high-resolution 19F NMR spectroscopy reveal the presence of two distinct types of fluorine environments. The majority of the fluorine environments are formed in SiO1.5F polyhedral and less abundant species is observed to be highly unusual, yielding a fivefold coordinated silicon of the type SiO2F polyhedral which become increased with increasing the fluorine content.

Vitamin C metabolomic mapping in experimental diabetes with 6-deoxy-6-fluoro-ascorbic acid and high resolution 19F-nuclear magnetic resonance spectroscopy

Metabolomic mapping is an emerging discipline geared at providing information on a large number of metabolites as a complement to genomics and proteomics. Here we have probed ascorbic acid homeostasis and degradation in diabetes using 6-deoxy-6-fluoro ascorbic acid (F-ASA) and 750 MHz 19F-nuclear magnetic resonance (NMR) spectroscopy with proton decoupling In vitro, Cu2+-mediated degradation of F-ASA revealed the formation of 4 major stable degradation products at 24 hours. However, when normal or diabetics rats were injected with F-ASA intraperitoneally (IP) for 4 days, up to 20 fluorine-labeled compounds were observed in the urine. Their composition resembled, in part, metal catalyzed degradation of F-ASA and was not explained by spontaneous degradation in the urine. Diabetes led to a dramatic increase in urinary F-ASA loss and a relative decrease in most other urinary F-compounds. Diabetes tilted F-ASA homeostasis toward oxidation in liver (P < .01), kidney (P < .01), spleen (P < .01), and plasma (P < .01), but tended to decrease oxidation in brain, adrenal glands, and heart. Surprisingly, however, besides the major oxidation product fluoro-dehydroascorbic acid (F-DHA), no F-ASA advanced catabolites were detected in tissues at 5 μ mol/L sensitivity. These findings not only confirm the key role of the kidney in diabetes-mediated loss of ascorbic acid, but demonstrate that only selected tissues are prone to increased oxidation in diabetes. While the structure of most degradation products needs to be established, the method illustrates the power of high resolution 19F-NMR spectroscopy for the mapping of complex metabolomic pathways in disease states.

A novel 19F-NMR method for the investigation of the antioxidant capacity of biomolecules and biofluids

A new assay for the measurement of the antioxidant capacity of biomolecules by high resolution 19F-NMR spectroscopy is presented here. This method is based on the use of trifluoroacetanilidic detectors, namely trifluoroacetanilide, N-(4-hydroxyphenyl)-trifluoroacetamide and 2-hydroxy-4-trifluoroacetamidobenzoic acid. Upon hydroxyl radical attack, such fluorinated detectors yield trifluoroacetamide and trifluoroacetic acid that can be quantitatively determined by 19F-NMR spectroscopy. Trifluoroacetamide was found to be a reliable reporter of hydroxyl radical attack on the fluorinated detectors, whereas N-(4-hydroxyphenyl)-trifluoroacetamide was found to be the most sensitive detector amongst the ones considered. Therefore, N-(4-hydroxyphenyl)-trifluoroacetamide has been used in competition experiments to assess the antioxidant capacity of a number of low and high molecular weight antioxidants. The antioxidant capacity of a given compound has been scaled in terms of an adimensional parameter, k F , that represents the ratio between the scavenger abilities of the fluorinated detector and the competitor. k F values obtained for low-molecular-mass compounds fall in the range 0.17 < k F < 1.5 and are in good agreement with second order rate constants ( k 2 OH ) for the reaction of the antioxidant with hydroxyl radicals. The k F value for serum albumin is much larger (46.9) than that predicted from the reported k 2 OH value. This finding supports the view that the protein can very effectively scavenge hydroxyl radicals as well as secondary radicals. Human blood serum showed that its antioxidant capacity is even higher than that shown by aqueous solutions of albumin at physiologic concentration suggesting a further contribution from other macromolecular serum components.

Rapid multi-component detection of fluorinated drug metabolites in whole urine from a ‘cassette’ dose study using high resolution 19F NMR spectroscopy

High resolution 19F NMR spectroscopy has been successfully applied to the analysis of drug metabolites in whole rat urine from a ‘cassette’ dose study of 6 fluorinated test compounds dosed at 10 mg kg–1 per compound. A total of 21 compound-related molecules were rapidly detected in the 0–8 h urine samples. The metabolic fate of the compounds after cassette administration appeared to be the same as when the compounds were dosed individually. 19F NMR may thus enable metabolism to be estimated for several compounds simultaneously, with minimal sample preparation, and without interference from endogenous molecules in the biofluid. This analytical approach may therefore be of value at the drug discovery stage in the development of ‘high throughput’ in vivo metabolic screens.

5-Fluorouracil metabolite patterns in viable and necrotic tumor areas of murine colon carcinoma determined by 19F NMR spectroscopy.

High-resolution 19F NMR spectroscopy at 9.4 T was used to study the difference in the metabolite pattern of 5-fluorouracil (5-FU) between viable and necrotic tissues of C38 murine colon tumors grown in C57BI/6 mice. Studies were performed on perchloric acid extracts of these tumor fractions after 5-FU treatment. The 19F nuclear magnetic resonance spectra exhibited resonances representing 5-FU, the catabolites alpha-fluoro-beta-ureidopropionic acid and alpha-fluoro-beta-alanine, as well as several fluoronucleotide anabolites. The absolute concentrations of anabolites and catabolites and the anabolite-to-catabolite ratio were significantly lower in the necrotic fraction than in the viable tumor fraction 50 min after administration of 5-FU, whereas the absolute concentration of 5-FU was the same. Therefore, in 5-FU metabolism studies with NMR spectroscopy, it is important to consider the necrotic contribution to the tumor volume.

NMR spectroscopic and theoretical chemistry studies on the internal acyl migration reactions of the 1-O-acyl-beta-D-glucopyranuronate conjugates of 2-, 3-, and 4-(trifluoromethyl) benzoic acids.

High resolution 19F NMR spectroscopy has been used to investigate the kinetics of internal acyl migration and hydrolysis of the synthetic beta -1-O-acyl-D-glucopyranuronates of 2-, 3-, and 4-(trifluoromethyl) benzoic acids (TFMBAs) in phosphate buffer solutions at 30 degrees C as models of drug ester glucuronides. Apparent first-order degradation of the 1-O-acyl glucuronide and the sequential appearance of 2-, 3-, and 4-O-acyl isomers as both alpha- and beta-anomeric forms were observed for each TFMBA isomer. The overall degradation rate constants of the 2-, 3-, and 4-TFMBA 1-O-acyl isomers were 0.065 h-1, 0.25 h-1, and 0.52 h-1. In order to probe the reasons for these differences in reactivity, theoretical structural and electronic parameters for the beta-anomers of the 1-O-acyl glucuronides, their beta-2-O-acyl isomers, and both structures of the postulated ortho-acid ester intermediate were computed using semiempirical molecular orbital (AM1 and PM3) methods. The distinction between the slowly reacting 2-TFMBA glucuronide and the much faster reacting 3- and 4-TFMBA glucuronides could be observed by calculation of the relative bond order of the C-O bonds in the ortho-acid ester intermediates. The slow internal acyl migration rate of the 2-TFMBA isomer was also partly attributed to the high degree of steric hindrance of the trifluoromethyl group obstructing attack by the glucuronic acid 2-hydroxy group on the carbonyl carbon to form the ortho-acid ester intermediate. Some calculated molecular orbital properties, namely, dipole moment, energy of the lowest unoccupied molecular orbital (LUMO), LUMO density, and nucleophilic frontier density on the carbonyl carbon, were also shown to be related to the measured half-lives. This work gives insight into the molecular physicochemical properties that influence the acyl migration kinetics of simple model drug glucuronides and is of potential importance in understanding more complex drug glucuronide acyl migration reactions of toxicological interest.

Prediction of urinary sulphate and glucuronide conjugate excretion for substituted phenols in the rat using quantitative structure-metabolism relationships.

1. The quantitative urinary excretion of the sulphate and glucuronide metabolites of 15 substituted phenols dosed to rat has been determined using high resolution 19F-nmr spectroscopy. 2. The urinary metabolic fate of each of the compounds was related to a series of calculated physicochemical properties for each compound to produce quantitative structure-metabolism relationships (QSMRs). Using these calculated molecular properties it was possible to predict the urinary recovery of xenobiotic material as a percentage of the administered dose, to classify the compounds according to their 'dominant' metabolite pattern and to predict quantitatively the proportions of glucuronide and sulphate conjugates in the urine by the use of multiple linear regression. 3. The quantitative predictions were tested by cross-validation and good prediction of total xenobiotic urinary recovery as a percentage of the administered dose was achieved based on an equation involving the electrophilic superdelocalizability at C4 (para to the hydroxyl function), the smallest principal ellipsoid axis dimension and the heat of formation. The largest moment of inertia and the electrophilic superdelocalizability at C3 were found to be the most significant factors for the prediction of the percentage glucuronide in the urine, and the urinary excretion of sulphate conjugates as a percentage of total urinary recovery was negatively correlated with the glucuronide excretion as little parent compound was excreted.

Perfluoroalkyliodine(III) derivatives with two or three iodine-carbon bonds

[I(CF 3) 2] +, I(CF 3) 3 and [(ICF 3) 2F 2] − can be prepared from I(CF 3)X 2 and Cd(CF 3) 2 complexes by variation of the stoichiometry, the solvent, the reaction temperature and by addition of Lewis acids. The unstable compounds have been intensively studied by high-resolution 19F NMR spectroscopy. Major differences in the reaction behaviour are observed for the pentafluoroethyl- and heptafluoro-iso-propyl derivatives. Reactions of R fI with non-common oxidizers will be described.

Incorporation of 19F-substituted aromatic amino acids into membrane proteins from chromatophores of Rhodospirillum rubrum G9 +

Chromatophore membranes were isolated from cells of the carotenoidless mutant Rhodospirillum rubrum G9 + grown in the presence of several fluorinated aromatic amino acids, solubilized using SDS and the extent of incorporation analyzed using high-resolution 19F-NMR spectroscopy. 3- and 4- 19F-phenylalanine, 6- 19F-tryptophan and 3- 19F-tyrosine were biosynthetically incorporated into membrane proteins whereas 5- 19F-tryptophan and 2- 19F-phenylalanine were inhibitors of cell growth. The polypeptide chains of the major chromatophore membrane protein the light-harvesting complex, were isolated and shown by high-resolution 19F-NMR to contain 3- 19F-phenylalanine, which is known to be situated principally within the membrane hydrocarbon layer. Broad-band 19F-NMR spectra of 3- 19F-phenylalanine-labelled chromatophores showed the phenyl ring to be immobilized within the membrane.

Solid-state high-resolution NMR K 2PO 3F·KF

In melts of potassium monofluorophosphate and potassium fluoride the new compound K 2PO 3F.KF is formed at 850 °C. According to x-ray powder diffraction data this compound and K 2SO 4.KF [1] are isostructural. Only one mole fluoride per mole monofluorophosphate reacts. Solid-state high-resolution 19F NMR spectroscopy shows that different types of fluorine atoms exist in the investigated samples. In solid-state NMR spectra natural broadening due to strong direct dipolar F-F interactions masks the chemical shift and indirect spin-spin coupling. To overcome this obstacle we used the multipulse technique (four pulse cycle WHH 4 with γ = 4,1 μs). The shape of the resulting high-resolution 19F NMR spectra of polycrystalline samples is dominated by the F-P coupling tensor as well as the 19 F chemical shift tensor. On the basis of the tensor data it is possible to differentiate the covalent bonded fluorine atoms from the ionic bonded ones and to get new insights into the structure of the title compound.

Regulation of intracellular pH by human peripheral blood lymphocytes as measured by 19F NMR.

We have measured the intracellular pH of human peripheral blood lymphocytes by means of high-resolution 19F NMR spectroscopy using D,L-2-amino-3,3-difluoro-2-methylpropanoic acid (F2MeAla) as a probe. Lymphocytes readily took up the methyl ester of F2MeAla, and endogenous esterase hydrolyzed the ester to the free amino acid inside the cell. This alpha-methyl amino acid is not metabolized by the cell, and its 19F NMR spectrum exhibits large pH-dependent shifts as the alpha-amino group is protonated. The size of the 19F shifts, the high sensitivity of 19F NMR, and the favorable pKa of the alpha-amino group of F2MeAla (pKa = 7.3) allowed us to measure intracellular pH of lymphocytes at 25-30 degrees C with approximately 5-min acquisition times. Measurements at various external pH values demonstrated that human peripheral blood lymphocytes regulate their internal pH, a process requiring expenditure of metabolic energy. In the pH range between 6.8 and 7.4, lymphocytes maintain a constant internal pH of 7.17 +/- 0.06 pH unit. Outside this range, intracellular pH changes with extracellular pH. The accuracy of this 19F pH probe has been confirmed by independent measurements of intracellular pH using equilibrium distributions of 5,5-dimethyloxazolidine-2,4-dione.