NMR study and quantum mechanical calculations on the 2-[(2-aminoethyl)amino]-ethanol-H2O-CO2 system.

13C and 1H NMR spectra were obtained for AEEA (2-[(2-aminoethyl)amino]-ethanol)-H2O-CO2 systems and quantum mechanical calculations were carried out for the different AEEA species. The results suggest that the main AEEA species under the conditions studied are free amine, primary carbamate, and secondary carbamate. There is also some indication that a dicarbamate species is formed, this species does however only appear to be formed in small amounts. Comparison between experimental data and quantum mechanical calculations suggest that most AEEA species take on conforms with some degree of intramolecular hydrogen bonding.

Analyzing equilibrium water exchange between myocardial tissue compartments using dynamical two-dimensional correlation experiments combined with manganese-enhanced relaxography.

Water compartments were identified and equilibrium water exchange was studied in excised rat myocardium enriched with intracellular manganese (Mn(2+)). Standard relaxographic measurements were supplemented with diffusion-T(2) and T(1)-T(2) correlation measurements. In nonenriched myocardium, one T(1) component (800 ms) and three T(2) components (32, 120, and 350 ms) were identified. The correlation measurements revealed fast- and slow-diffusing water fractions with mean diffusion coefficients of 1.2 x 10(-5) and 3.0 x 10(-5) cm(2) s(-1). The two shortest T(2) components, which had different diffusivities, both originated from water in intracellular compartments. A component with longer relaxation time (T(1) approximately equal 2200 ms; T(2) approximately equal 1200 ms), originating from extra-tissue water, was also observed. The presence of this component may lead to erroneous estimations of water exchange rates from multiexponential relaxographic analyses of excised tissues. The tissue T(1) value is strongly reduced with increasing enrichment of Mn(2+), and eventually a second tissue T(1) component emerges, indicating a shift in the equilibrium water exchange between intra- and extracellular compartments from the fast-exchange limit to the slow-exchange regime. Using a two-site water exchange analysis, the lifetime of intracellular water, T(ic), was found to be 475 ms, with a fraction, p(ic), of 0.71.

Structure elucidation of C80, C81 and C82 isoprenoid tetraacids responsible for naphthenate deposition in crude oil production.

A series of C(80) isoprenoid 20-bis-16,16'-biphytanyl tetraacids has previously been found to be responsible for calcium naphthenate scaling in crude oil processing. This paper describes the structure elucidation by high-field NMR spectroscopy of the structures of the series of homologous C(80) tetraacids containing 4-8 five-membered rings. In addition, the structures of methyl-substituted C(81) and C(82) analogues containing 7 and 8 five-membered rings have been determined for the first time. The biosynthetic implications are discussed.

Analysis of 'ARN' naphthenic acids by high temperature gas chromatography and high performance liquid chromatography.

Examination by high temperature GC (HTGC) of the methyl esters of the so-called 'ARN' naphthenic acids from crude oils of North Sea UK, Norwegian Sea and West African oilfields revealed the distributions of resolved 4-8 ring C80 tetra acids and trace amounts of other acids. Whilst all three oils contained apparently the same major acids, the proportions of each differed, possibly reflecting the growth temperatures of the archaebacteria from which the acids are assumed to have originated. The structures of the 4, 5, 7 and 8 ring acids are tentatively assigned by comparison with the known 6 ring acid and related natural products and an HPLC method for the isolation of the individual acids is described. ESI-MS of individual acids isolated by preparative HPLC established the elution order of the 4-8 ring acids on the HPLC and HTGC systems and revealed the presence of previously unreported acids tentatively identified as C81 and C82 7 and 8 ring analogues.

Archaeal C80 isoprenoid tetraacids responsible for naphthenate deposition in crude oil processing.

The structure of a novel class of octaterpene tetracarboxylic acids which is responsible for naphthenate deposition in crude oil processing has been determined by NMR and mass spectroscopy.

High-resolution MAS 1H NMR spectroscopic analysis of rabbit cornea after treatment with dexamethasone and exposure to UV-B radiation.

Metabolic changes in rabbit cornea after combined long-term steroid treatment and UV-B exposure were investigated. Corneas were exposed to UV-B radiation (2.05 J/cm2) after 36 days topical pretreatment with either 0.1% dexamethasone or saline. Twenty-four hours after UV-B exposure, corneas were excised and aqueous humour aspirated. Intact corneal tissues were analyzed by magic angle spinning proton NMR spectroscopy and pattern recognition methods. UV-B decreased corneal ascorbate (63% reduction), taurine (62%), and choline (63%), whereas glucose was elevated. Dexamethasone pretreatment further depleted corneal taurine and ascorbate, decreased aqueous ascorbate (85%), and accumulated glucose in cornea and aqueous humour. The results reflect antioxidative mechanisms and osmoregulation.

Time dependency of metabolic changes in rat lens after in vivo UVB irradiation analysed by HR-MAS 1H NMR spectroscopy.

The lens ability to protect against, and repair ultraviolet radiation (UVR) induced damages, is of crucial importance to avoid cataract development. The influence of UVR-induced damage and repair processes on the lens metabolites are not fully understood. Observation of short- and long-term changes in light scattering and the metabolic profile of pigmented rat lenses after threshold UVR exposure might serve to better understand the protective mechanisms in the lens. By using high resolution magic angle spinning (HR-MAS) 1H NMR spectroscopy it was possible to investigate the metabolites of intact rat lenses. Brown-Norway rats were exposed to 15 kJm(-2) UVB irradiation. One eye was exposed and the contralateral served as control. The rats were sacrificed 5, 25, 125, and 625 hr post-exposure and the lenses were removed. The degree of cataract was quantified by measurement of lens forward light scattering. Thereafter, proton NMR spectra from intact lenses were obtained and relative changes in metabolite concentrations were determined. The light scattering in the lens peaked at 25 hr post-exposure and decreased thereafter. The lowest level of light scattering was measured 625 hr after exposure. No significant changes in concentration were observed for the metabolites 5 and 25 hr post-exposure except the total amount of adenosine tri- and diphosphate (ATP/ADP) that showed a significant decrease already 5 hr after exposure. At 125 hr the lens concentrations of lactate, succinate, phospho-choline, taurine, betaine, myo-inositol, and ATP/ADP showed a significant decrease (p<0.05). Phenylalanine was the only metabolite that revealed a significant increase 125 hr post-exposure. At 625 hr most of the metabolic changes seemed to normalise back to control levels. However, the concentration of betaine and phospho-choline were still showing a significant decrease 625 hr after UVB irradiation. The impact of UVB irradiation on the metabolic profile did not follow the same time dependency as the development of cataract. While the light scattering peaked at 25 hr post-exposure, significant changes in the endogenous metabolites were observed after 125 hr. Both the metabolic changes and the light scattering seemed to average back to normal within a month after exposure. Significant decrease in osmolytes like taurine, myo-inositol and betaine indicated osmotic stress and loss of homeostasis. This study also demonstrated that HR-MAS 1H NMR spectroscopy provides high quality spectra of intact lenses. These spectra contain a variety of information that might contribute to a better understanding of the metabolic response to drugs or endogenous stimuli like UVB irradiation.

Characterization of monofluorinated polycyclic aromatic compounds by 1H, 13C and 19F NMR spectroscopy.

Monofluorinated polycyclic aromatic hydrocarbons (F-PAHs) have attracted much attention in analytical, environmental, toxicological and mechanistic studies because of their physico-chemical properties, which are closely similar to those of the parent PAHs. Because of this, full NMR characterization has become of interest. Complete 1H, 13C and 19F NMR chemical shifts, and also 1J(H,C), (n)J(C,F), (n)J(H,F) and (n)J(H,H) coupling constants, have been assigned for the F-PAHs 1-fluoronaphthalene, 2-fluorofluorene, 5-fluoroacenaphthylene, 2-fluorophenanthrene, 3-fluorophenanthrene, 3-fluorofluoranthene, 1-fluoropyrene, 1-fluorochrysene, 2-fluorochrysene, 3-fluorochrysene and 9-fluorobenzo[k]fluoranthene. To allow comparison with the corresponding parent PAHs, the 1H and 13C chemical shifts of acenaphthylene, phenanthrene, fluoranthene, pyrene and benzo[k]fluoranthene were determined. Chemical shift increments and the effects on the coupling constants from the fluorine substitution are discussed.

Determination of water compartments in rat myocardium using combined D-T1 and T1-T2 experiments.

We have used combined D-T1 and T1-T2 correlation experiments to explore water compartments in rat heart tissue (myocardium). The results show that two main compartments can be identified, which we assign to extracellular (ec) and intracellular (ic) water. The exchange rate of water across the cell membrane was found to be on the order of 0.1 Hz. In addition, the T1-T2 correlation measurements indicate that the ic compartment contain two T2 populations.

Correlations between diffusion, internal magnetic field gradients, and transverse relaxation in porous systems containing oil and water.

The main focus in this study is to investigate the correlations between internal magnetic field gradients (G0) and transverse relaxation times in liquid-saturated packings of glass beads of different wettabilities. We show how these correlations can be expressed as two-dimensional (2D) diagrams of distribution functions between internal magnetic field gradients and T2 values. In the case where it is difficult to distinguish the signals from oil and water, we separate them based on their difference in diffusivity. In addition to using such diffusion weighting in the G0-T2 diagrams, we also show results from experiments where the direct correlation between diffusion and T2 (D-T2) is determined. The overall results show that the wettability of the glass beads has a strong influence on the appearance of these diagrams, in particular on the location of the fast diffusing water molecules. However, due to their lower diffusivity, the transverse magnetization of the oil molecules is not so greatly influenced by either the presence of the glass beads or their wettability properties. Thus, the wettability properties of a liquid-filled porous material can be determined from the location of the water signal in such 2D diagrams. In particular, we show that this is the case not only for D-T2 diagrams, but also for G0-T2 diagrams.

High-resolution magic angle spinning 1H NMR spectroscopy of metabolic changes in rabbit lens after treatment with dexamethasone combined with UVB exposure.

BACKGROUND: Long-term steroid treatment and UVB exposure are well-known cataractogenic factors. The purpose of this study was to investigate metabolic changes in the rabbit lens after long-term dexamethasone treatment in combination with UVB exposure, using high-resolution magic angle spinning proton nuclear magnetic resonance (HR-MAS (1)H NMR) spectroscopy to analyse intact lens tissues. METHODS: Rabbits received topical doses of 0.1% dexamethasone or 0.9% saline (50 microl) four times daily for 36 days. On day 37, the eyes were exposed to UVB radiation (2.05 J/cm(2)). Twenty-four hours later the animals were killed, and HR-MAS (1)H NMR spectra of lens tissues were obtained. RESULTS: More than 15 major metabolites were assigned in NMR spectra of rabbit lenses. The combined treatment with dexamethasone and UVB induced large reductions in the concentration of reduced glutathione, inositols, taurine and lactate compared with normal lenses. Concurrently, the levels of glucose, sorbitol and sorbitol-3-phosphate were increased. After exposure to UVB radiation only, the most significant finding was a decrease in the concentration of lactate. No lens opacities were detected. CONCLUSIONS: HR-MAS (1)H NMR spectroscopy was found to be an efficient tool for analysis of intact lens tissues. High-resolution NMR spectra of intact lens tissue enabled metabolic changes to be quantified. Long-term treatment with dexamethasone combined with UVB exposure induced substantial metabolic changes, dominated by osmolytic regulation processes and loss of glutathione.

On the structure of carotenoid iodine complexes.

Previous work on carotenoid-iodine complexes is briefly reviewed. The formation of iodine complexes of beta,beta-carotene and of (3R,3' R )-beta,beta-carotene-3,3'-diol (zeaxanthin) has been studied by modern methods including UV/VIS/NIR, IR MS, EPR, ENDOR and NMR (1H, 1H-1H COSY, TOCSY, 2D ROESY, 1H-13C HSQC and 1H-13C HMBC) spectroscopy, and chemical reactions monitored by HPLC, TLC and spectral analysis (VIS, MS, 1H NMR). beta,beta-Carotene formed a solid complex C40H56 x 4I with iodine in hexane and a solvent complex with lambdamax 1010 nm in chlorinated solvents. Iodine was not covalently bound to the carotene. Spectroscopic and chemical evidence is consistent with the representation of the beta,beta-carotene-iodine complex containing iodine in a pi complex with cationic/radical cationic properties. Extensive E/Z isomerisation was noted for all quenching products obtained in acetone, with thiosulfate, by dilution, or by reaction with nucleophile (MeOH). Key products obtained from the beta,beta-carotene-iodine complex were 4',5'-didehydro-4,5'-retro-beta,beta-carotene (isocarotene) and 4-methoxy-beta,beta-carotene. The zeaxanthin-iodine complex was not suitable for a practical synthesis of (3S,3'S)-4',5'-didehydro-4,5'-retro-beta,beta-carotene-3,3'-diol (eschscholtzxanthin).

Intracellular manganese ions provide strong T1 relaxation in rat myocardium.

The efficacy of manganese ions (Mn2+) as intracellular (ic) contrast agents was assessed in rat myocardium. T1 and T2 and Mn content were measured in ventricular tissue excised from isolated perfused hearts in which a 5-min wash-in with 0, 30, 100, 300, or 1000 microM of Mn dipyridoxyl diphosphate (MnDPDP) was followed by a 15-min wash-out to remove extracellular (ec) Mn2+. An inversion recovery (IR) analysis at 20 MHz revealed two T1 components: an ic and short T1-1 (650-251 ms), and an ec and longer T1-2 (2712-1042 ms). Intensities were about 68% and 32%, respectively. Tissue Mn content correlated particularly well with ic R1-1. A two-site water-exchange analysis of T1 data documented slow water exchange with ic and ec lifetimes of 11.3 s and 7.5 s, respectively, and no differences between apparent and intrinsic relaxation parameters. Ic relaxivity induced by Mn2+ ions in ic water was as high as 56 (s mM)(-1), about 8 times and 36 times higher than with Mn2+ aqua ions and MnDPDP, respectively, in vitro. This value is as high as any reported to date for any synthetic protein-bound metal chelate. The increased rotational correlation time (tauR) between proton and electron (Mn2+) spins, and maintained inner-sphere water access, might make ic Mn2+ ions and Mn2+ -ion-releasing contrast media surprisingly effective for T1-weighted imaging.

Delocalized carotenoid cations in relation to the soliton model.

A series of charge-delocalized carotenoid mono- and dications have been prepared by treatment of selected carotenoids with Brønsted and Lewis acids. The detailed structures of the carbocations were established by NMR studies in the temperature range from -10 to -20 degrees C. The general strategy for structure elucidation by NMR of several cationic components in a mixture is outlined. Bond type and regions of bond inversion were established, as well as the charge distribution, which was determined from the difference in (13)C chemical shift at each carbon. This method gave a more accurate estimate for the partial charges than by using the Spiesecke-Schneider relationship. The resulting charge distribution was used as models for the structure of charged solitons. These carotenoid cations have the most delocalized charge so far determined, and the monocations represent the first experimental structure determination of positively charged solitons. The soliton width determined here is in good agreement with the results of previous AM1 calculations.

Metabolic changes in rat lens after in vivo exposure to ultraviolet irradiation: measurements by high resolution MAS 1H NMR spectroscopy.

PURPOSE: In the present study, high-resolution magic angle spinning proton nuclear magnetic resonance (HR-MAS (1)H NMR) spectroscopy was used to investigate changes in the metabolic profile of intact rat lenses after UVB irradiation of the eyes. METHODS: Three groups of Sprague-Dawley rats were exposed to UVB radiation at 2.5, 5.0, and 7.5 kJ/m(2). One eye was exposed, and the contralateral eye served as the control. One week after exposure, the lenses were removed and forward light-scattering was quantified. Thereafter, proton NMR spectra from the intact lenses were obtained. Relative changes in metabolite concentrations were determined. RESULTS: The lenses in all three groups showed significant increases in light-scattering after UVB irradiation. The high-quality HR-MAS (1)H NMR spectra permitted more than 30 different metabolites to be identified. UVB irradiation caused a significant decrease (P < 0.05) in concentrations of taurine, hypotaurine, tyrosine, phenylalanine, valine, myo-inositol, phosphocholine, betaine, succinate, and glutathione at all three UV doses. For glycine, glutamate, and lactate, significant decreases in concentration were observed at the two lowest UVR-B doses. The total amount of adenosine tri- and diphosphate and (ATP, ADP) decreased significantly and that of adenosine monophosphate AMP increased significantly at the two highest doses. Alanine was the only amino acid that increased after UVB irradiation. None of these metabolites exhibited a significant UVB dose-dependent relationship. CONCLUSIONS: This study demonstrates for the first time the potential of HR-MAS (1)H NMR spectroscopy as an analytical tool for use on intact lenses. Near-threshold UVR-B doses led to a generally significant decrease in water-soluble metabolites 1 week after exposure. The lack of dose-dependent changes in the metabolites indicates that repair processes during the first week after UVB irradiation overcome the immediate metabolic disturbances.

Structural elucidation by 1D and 2D NMR of three isomers of a carotenoid lysophosphocholine and its synthetic precursors.

A carotenoic acid was used to obtain a long-chain unsaturated lysophosphocholine. The carotenoid lysophosphocholine was synthesized by two methods. The first method resulted in mixtures of regioisomers for each step in the synthetic route. Homo- and heteronuclear 1D and 2D NMR methods were employed to elucidate the structures of the individual isomers and their intermediates. The pure regioisomer [1-(beta-apo-8'-carotenoyl)-2-lyso-glycero-3-phosphocholine] was obtained by a second method, but in low yield. The 1D 1H NMR subtraction spectrum of the mixture and the pure regioisomer was used to interpret the 1H shifts of the unsaturated acyl moieties. The 1H and 13C signals of the acyl chain show characteristic shifts depending on the positions of the choline and the acyl group attached to the glycerol backbone. Therefore, the unsaturated acyl chain signals have diagnostic values for the identification of isomers of unsaturated (lyso)phosphocholines. Chemical shifts and indirect coupling constants are reported for each of the major components of the mixtures. The methods used were 1D (1H, 13C and 31P) and 2D (H,H-COSY, HMBC, HSQC and HETCOR) NMR.

Characterization of a beta-D-(1-->3)-glucan from the marine diatom Chaetoceros mülleri by high-resolution magic-angle spinning NMR spectroscopy on whole algal cells.

High-resolution magic-angle spinning (hr-MAS) NMR spectroscopy was used to record NMR spectra of a cell paste from the marine diatom Chaetoceros mülleri. This gave information on a cellular storage polysaccharide identified as a beta-D-(1-->3)-linked glucan, using hr-MAS one-dimensional 1H and 13C, two-dimensional 1H,1H-COSY and 13C,1H-correlation spectroscopy. The same structural information was deduced from the liquid state NMR data on the glucan extracted from C. mülleri. The extracted glucan proved to be a beta-D-(1-->3)-linked glucan with a degree of polymerization of 19 and a degree of beta-D-(1-->6) branching of 0.005. The hr-MAS spectrum of the diatom showed several nonglucan resonances in the carbohydrate region of the NMR spectrum (60-103 ppm) that were shown to be noncarbohydrate resonances by means of two-dimensional 13C,1H- and 1H,1H-correlated NMR data.

The charge delocalised beta,beta-carotene dication--preparation, structure elucidation by NMR and reactions with nucleophiles.

The reaction between beta,beta-carotene and BF3-etherates has been investigated, leading to structural elucidation of the blue product, formed in appropriate organic solvents, as a symmetrical charge delocalised dication (lambda(max) 985 nm at room temperature in CHCl3) with considerable stability. The reaction, monitored by EPR studies at -25 degrees C, occurred via free radical intermediates. A C40H56BF3 intermediate was captured by EIMS. The detailed structure of the dication was established by COSY, HSQC, HMBC and 1D and 2D ROESY NMR techniques (600 MHz, CDCl3, -20 degrees C) leading to complete assignments of 1H and 13C chemical shifts and 3J(H,H) coupling constants. The effects of the two delocalised charges on chemical shift (charge distribution) and bond distance (3J(H,H)) were considered. The results are consistent with charge delocalisation mainly in the C-5-C-9 and C-5'-C-9' regions and with bond inversion to retro shifted double bonds in the central C-13-C-13' region. A convention for denoting the charge delocalisation and bond types is presented. The experimental results are discussed relative to previous theoretical calculations of the beta,beta-carotene dication structure. (All-E) and (15-Z)-beta,beta-carotene provided the same dication. The NIR spectra and stability of dications prepared in the same manner from the related carotenes 20,20'-dinor-beta,beta-carotene, heptapreno-beta,beta-carotene and nonapreno-beta,beta-carotene were examined for comparison. Reactions of the beta,beta-carotene dication with selected nucleophiles provided products including isocryptoxanthin, isocarotene and mutatochrome with H2O as nucleophile, and isocryptoxanthin methyl ether, 8-methoxy-7,8-dihydro-beta,beta-carotene and isocarotene with CH3ONa as nucleophile. The formation of these products is rationalised from the structure assigned to the dication.

Proton magic angle spinning NMR reveals new features in photodynamically treated bacteria.

The bacterium Propionibacterium acnes is light-sensitive due to porphyrin-induced photosensitization. The light sensitivity increases with incubation of 5-aminolevulinic acid, ALA. For the first time, 1H magic angle spinning NMR spectroscopy is used to describe the photoinduced changes in the bacterium after ALA incubation. Successful photosensitization was performed with light-emitting diodes in the blue and red regions (430 and 654 nm, respectively). The irradiation setup, suitable for irradiation of bacterium suspensions in petri dishes is described. For NMR studies blue light diodes with about 90 micromol/m2s were chosen. After blue light irradiation, the endogenous glycine betaine, proline, glutamate and choline levels in P. acnes decreased with increasing irradiation time. For sublethal light doses (50% survival fraction), the endogenous glycine betaine level decreased 80% on average. The corresponding percentages for proline, choline and glutamate were about 40, 25 and 10, respectively. It is hypothesized that the irradiation, inducing porphyrin photosensitization amplified by ALA incubation, leads to elimination of the osmolyte glycine betaine and possibly also proline by so-called regulatory volume decrease (RVD) mechanisms. These mechanisms are known to be active in several prokaryotic and eukaryotic cells when exposed to hypotonic stress. They are also known to be present in several eukaryotic cells during photodynamic therapy (PDT) exposure leading to hypotonoc stress. The findings contribute to the knowledge of the inactivation mechanisms of P. acnes in photosensitization, and could therefore be of interest in the efforts to use PDT as treatment of the acne disease.

Structure elucidation of polyene systems with extensive charge delocalization-carbocations from allylic carotenols.

[structure: see text] The structures of two diastereomeric cations, readily prepared from beta, beta-caroten-4-ol (1) by treatment with trifluoroacetic acid, have been determined by NIR and NMR spectroscopy, resulting in the complete structure elucidation of the most extensively delocalized carbocations so far described. Higher partial charge was observed toward the center of the polyene chain (larger filled red circles). Bond reversion occurs in the central region of the molecule.