Determination of enantiomeric purity of nicotine in pharmaceutical preparations by 13C-NMR in the presence of a chiral lanthanide shift reagent

A method for the determination of enantiomeric composition of nicotine samples, based on 13C-NMR spectroscopy in the presence of the chiral lanthanide shift reagent, tris[3-(trifluoromethylhydroxymethylene)-(+)-camphorato]ytte rbium [Yb(tfc)3], was developed. Observation at 100.6 MHz of the C2' resonance of nicotine in the presence of 0.15-0.20 mol of the ytterbium complex, either in ordinary 13C[1H]-NMR spectra or in carbon spectra enhanced by polarization transfer (refocused INEPT), allowed precise determination of the ratios of (S)- to (R)-nicotine. At least 1% of (R)-nicotine could be determined in samples of (S)-nicotine, milligram amounts being required for the analysis. Use of the 13C-NMR spectra is more advantageous than use of 1H-NMR spectra. Thus, Yb(tfc)3 induced separation of the proton resonances of the enantiomers of nicotine, and the shifted resonances of nicotine enantiomers could be assigned by use of 1H-13C heteronuclear chemical shift correlation, but the proton resonances were broad, their chemical shifts were sensitive to small variations of the ratio between Yb(tfc)3 and nicotine, and signals of the enantiomer present in small amounts were easily obscured by impurities. Therefore, although 13C-NMR is more time consuming, this method is more suitable for routine analysis. The method was applied for the determination of enantiomeric purity of (S)-nicotine in pharmaceutical formulations, including chewing gums, skin absorption patches, inhalators, and nasal sprays.     

Regional vascular and cardiac responses to systemic neuropeptide-Y in normal and diabetic rats

Using a new method of xenon laser-polarization that permits the generation of liter quantities of hyperpolarized 129Xe gas, the first 129Xe imaging results from the human chest and the first 129Xe spectroscopy results from the human chest and head have been obtained. With polarization levels of approximately 2%, cross-sectional images of the lung gas-spaces with a voxel volume of 0.9 cm3 (signal-to-noise ratio (SNR), 28) were acquired and three dissolved-phase resonances in spectra from the chest were detected. In spectra from the head, one prominent dissolved-phase resonance, presumably from brain parenchyma, was detected. With anticipated improvements in the 129Xe polarization system, pulse sequences, RF coils, and breathing maneuvers, these results suggest the possibility for 129Xe gas-phase imaging of the lungs with a resolution approaching that of current conventional thoracic proton imaging. Moreover, the results suggest the feasibility of dissolved-phase imaging of both the chest and brain with a resolution similar to that obtained with the gas-phase images.     

Application of cognitive scales to medical records of schizophrenia inpatients

Studies with proton magnetic resonance spectroscopy (MRS) have reported abnormalities in N-acetyl-aspartate (NAA), amino acids (AA) and choline (Cho) to creatine (Cr) ratios associated with schizophrenia. We report data on the three ratios in a sample of 18 neuroleptic naive patients with first-episode schizophrenia (eight studied in the dorsolateral prefrontal and 10 in the midtemporal lobe) and 24 healthy controls (14 studied in prefrontal and 10 in midtemporal lobes). Frontal lobe proton spectra were acquired with the stimulated-echo acquisition mode (STEAM) pulse sequence (echo time 21 ms, repetition time 2 s). Temporal lobe proton spectra were acquired with the point-resolved spectroscopy (PRESS) pulse sequence (echo time 16-21 ms, repetition time 2 s). Upon comparison with normal controls, NAA/Cr ratios were reduced in patients both for the frontal and the temporal lobe. By contrast, Cho/Cr ratios were slightly elevated in frontal and reduced in temporal lobes; whereas, AA/Cr ratios were normal in frontal and markedly increased in the temporal lobe. The reduced NAA/Cr ratios suggest lower neuronal viability in patients and is consistent with findings of reduced brain volume in both frontal and temporal regions.     

A comparative study of 1H NMR lineshape fitting analyses and biochemical lipid analyses of the lipoprotein fractions VLDL, LDL and HDL, and total human blood plasma

The purpose of this work was two-fold. In the first instance, 1H NMR spectra of the ultracentrifuged lipoprotein fractions (VLDL, LDL and HDL) from six volunteers with different clinical conditions were measured. The methylene regions of the experimental spectra were modelled in the frequency domain using non-linear lineshape fitting analyses. In this way the resolvable Lorentzian component structures of the methylene regions of these lipoprotein fraction spectra could be determined. Second, the lipoprotein fraction analyses were used to construct simplified component structures, which interpreted the lipoprotein fraction spectra well, and were feasible to use in the total plasma spectra analyses. The considerable overlap problem of the resonances was properly handled in this way. The NMR-based relative amounts of the lipoproteins (relative integrated intensities of the lipoprotein model signals) obtained were compared to the biochemically resolved relative molar percentages of the lipoprotein fractions and also of the lipid contents between the lipoprotein complexes. It was noticed that nearly all correlations were extremely good. Thus, it is suggested that the developed methodology could be used as a fast method to predict the relative amounts of the lipoproteins and also possibly the relative lipid contents between the major lipoprotein categories directly from the proton NMR spectrum of a total blood plasma sample. Furthermore, if internal or external reference for the integrated intensities of the proton NMR resonances were used, it should also be possible to obtain the absolute amounts of these quantities.     

Comparison of localized proton NMR signals of skeletal muscle and fat tissue in vivo: two lipid compartments in muscle tissue

In vivo 1H NMR spectra of small volumes-of-interest (VOI) were localized in human soleus muscle (8 ml) and compared with volume selective spectra of subcutaneous fat tissue and femoral yellow bone marrow (2 ml). All examinations were performed by the double spin echo (PRESS) localization technique. To provide comparability, spectra of different tissues were recorded using identical sequence timing. Clearly improved resolution of the lipid signals of muscle tissue was obtained using long echo times TE > 200 ms. The spectra of muscle tissue exhibit lipid signals that stem from two compartments with a difference of their resonance frequencies of about 0.2 ppm (Larmor frequency difference 12-13 Hz at 1.5 T). The existence of two fatty acid compartments is supported by measurements of the relaxation times and line shape analysis. Both compartments contain fatty acids or triglycerides with similar composition. Probably one compartment corresponds to fat cells within muscle tissue, the other compartment with lower Larmor frequency is located within muscle cells.     

Angular dependence of electron paramagnetic resonances of an azide-NO complex of cytochrome c oxidase: orientation of the haem-copper axis in cytochrome aa3 from ox heart

In localized proton magnetic resonance spectroscopy very short echo times (TE) are achieved to diminish signal loss due to T2 relaxation and to avoid phase distortions due to J-coupling. A sequence for single volume spectroscopy in human brain is described with a TE as low as 5 ms. Examinations were performed on a 1.5 T whole-body imager with actively shielded gradients. A self-designed stimulated echo acquisition mode (STEAM) sequence with very high amplitude spoiling gradients of 24 mT/m was used to take advantage of the whole potential of the gradient system. Optimization of TE was carried out by controlling spectral quality and localization in both phantom and volunteer measurements. Proton spectra of human brain were acquired in 21 healthy volunteers. Spectra of occipital white matter, parieto-occipital grey/white matter, and cerebellum revealed none or only small eddy current distortions at a TE of 5 ms. The volume of interest was 8-12 ml, repetition time was 1.5 s, and mixing time was 5 ms. Peak ratios of major metabolites referring to creatine were estimated and the relative standard deviations were calculated to determine interindividual reproducibility. The relative standard deviation of myo-inositol ranged from 6% to 11% within these brain regions whereas for glutamine and glutamate 7% to 16% were found.     

The role of the neurotransmitters acetylcholine and noradrenaline in the pathogenesis of stress ulcers

Molecular self-diffusion coefficients of water (0.75 +/- 0.05), N-acetylaspartate (0.27 +/- 0.04), creatines (0.27 +/- 0.04), and cholines (0.28 +/- 0.08) x 10(-5) cm2 s-1 were obtained from localized proton NMR spectra of rat brain in vivo using diffusion-weighted stimulated-echo (STEAM) sequences with a diffusion time of (delta--delta/3) = 17 ms.     

Localized proton spectroscopy of focal brain pathology in humans: significant effects of edema on spin-spin relaxation time

Localized proton nuclear magnetic resonance (NMR) spectroscopy of human brain in two common focal pathologies producing brain edema (peritumor edema and acute edematous ischemic stroke) was performed utilizing point resolved spectroscopy (PRESS). The spectra obtained from the pathological tissues were characterized by a reduced N-acetyl-aspartate (NAA) to total creatine (Cr) ratio (NAA/Cr) and high level of lactate. While the spin lattice relaxation time (T1) of the main metabolite resonances, namely, those of NAA, Cr, and choline containing compounds (Cho), showed values similar to those of normal brain, the spin-spin relaxation time (T2) of these metabolites exhibited a dramatic shortening in pathological tissues. Serial postoperative measurements of T2 in two patients with peritumor edema showed a gradual recovery of the T2 shortening corresponding to improvement of the edema. The majority of localized spectroscopy studies in humans is performed using a sequence which utilizes spin echo signals with a fixed single echo time. Hence, the signal intensities of the metabolite resonances obtained are inherently T2 dependent. The current study underscores that cautious interpretation of clinical data with respect to metabolite quantification is warranted.     

Expression and epitopic conservation of calponin in different smooth muscles and during development

The synaptic organization of the saccade-related neuronal circuit between the superior colliculus (SC) and the brainstem saccade generator was examined in an awake monkey using a saccadic, midflight electrical-stimulation method. When microstimulation (50-100 microA, single pulse) was applied to the SC during a saccade, a small, conjugate contraversive eye movement was evoked with latencies much shorter than those obtained by conventional stimulation. Our results may be explained by the tonic inhibition of premotor burst neurons (BNs) by omnipause neurons that ceases during saccades to allow BNs to burst. Thus, during saccades, signals originating from the SC can be transmitted to motoneurons and seen in the saccade trajectory. Based on this hypothesis, we estimated the number of synapses intervening between the SC and motoneurons by applying midflight stimulation to the SC, the BN area, and the abducens nucleus. Eye position signals were electronically differentiated to produce eye velocity to aid in detecting small changes. The mean latencies of the stimulus-evoked eye movements were: 7.9 +/- 1.0 ms (SD; ipsilateral eye) and 7.8 +/- 0.9 ms (SD; contralateral eye) for SC stimulation; 4.8 +/- 0.5 ms (SD; ipsilateral eye) and 5.1 +/- 0.7 ms (SD; contralateral eye) for BN stimulation; and 3.6 +/- 0.4 ms (SD; ipsilateral eye) and 5.2 +/- 0.8 ms (SD; contralateral eye) for abducens nucleus stimulation. The time difference between SC- and BN-evoked eye movements (about 3 ms) was consistent with a disynaptic connection from the SC to the premotor BNs.     

Proton-decoupled 31P chemical shift imaging of the human brain in normal volunteers

Proton-decoupled, 31P three-dimensional (3-D) chemical shift imaging (CSI) spectra have been acquired from the entire human brain using a new dual tuned resonator. The resonator operates in quadrature mode to provide improved sensitivity, excellent B1 homogeneity and reduced power deposition at both frequencies. Proton-decoupled and fully NOE enhanced, 31P spectra were acquired from normal volunteers using Waltz-4 proton decoupling with continuous wave bi-level excitation applied through a second radio frequency channel. Well resolved peaks in the phosphomonoester (PME) and phosphodiester regions were obtained from nonlocalized FIDs and spectra localized with 3-D CSI without processing for resolution enhancement. pH measurements made over large regions of the brain using the P(i) resonance show no significant variations (6.9 +/- 0.02) for a single individual. The improved spectral resolution and sensitivity of the PME resonances results in more well defined metabolite images of the PME peak region.     

Temporal and regional changes during focal ischemia in rat brain studied by proton spectroscopic imaging and quantitative diffusion NMR imaging

The early development of focal ischemia after permanent occlusion of the right middle cerebral artery (MCA) was studied in six rats using interleaved measurements by diffusion-weighted NMR imaging (DWI) of water and two variants of proton spectroscopic imaging (SI), multiecho SI (TE: 136, 272, 408 ms) and short TE SI (TE: 20 ms). Measurements on a 4.7-T NMR imaging system were performed between the control phase and approximately 6 h postocclusion. In the center of the ischemic lesion of all rats, the apparent diffusion coefficient (ADC) decreased rapidly to 84.4 +/- 4.2% (mean +/- SD) of the control values approximately 2 min postocclusion. Approximately 6 h postocclusion, the ADC was reduced to 67.1 +/- 5.9%. In contrast, large differences between the animals were observed for the temporal increase of lactate (Lac) in the ipsilateral hemisphere. The maximum Lac signal was reached in four rats after 0.5-1.5 h, and in two rats was not reached even after 6 h postocclusion. Six h postocclusion, SI spectra measured at a TE of 136 ms revealed a decrease in the CH3 signal of N-acetylaspartate (NAA) to 67 +/- 13% of the control values. Differences were observed between the spatial regions of decreased NAA and increased Lac. In the lesions, a T2 relaxation time of Lac of 292 +/- 40 ms, considering a J-coupling constant of 6.9 Hz, was measured. Furthermore, a prolongation of the T2 of the CH3 signal of creatine/phosphocreatine (Cr/PCr) was observed in the lesion, from 163 +/- 22 ms during control to 211 +/- 41 ms approximately 6 h postocclusion. The experiments proved that DWI and proton SI are valuable tools to provide complementary information on processes associated with brain infarcts.     

Stage I non-Hodgkin''s lymphoma treated with doxorubicin-containing chemotherapy with or without radiotherapy

Assess the feasibility of proton MR spectroscopic imaging (1H-MRSI) of the striatum (putamen and caudate nucleus) in patients with Parkinson's disease and evaluate striatal neuronal density. Proton MRSI of the striatum and thalamus with 2 cc spatial resolution was performed in 10 patients with Parkinson's disease, 1 patient with atypical parkinsonism, and 13 control subjects. Single voxel proton MR spectra with signals from choline metabolites (Cho), creatine metabolites (Cr), and the putative neuronal marker, N-acetyl-aspartate (NAA), were obtained from the putamen and thalamus, but not the caudate nucleus, of patients with parkinsonism and control subjects. Metabolite rations in controls and patients were: in putamen NAA/Cho 1.70 +/- 0.25 vrs 1.74 +/- 0.32, NAA/Cr 2.80 +/- 0.79 vrs 2.36 +/- 0.42, Cho/Cr 1.63 +/- 0.25 vrs 1.39 +/- 0.3; in thalamus, NAA/Cho 1.78 +/- 0.15 vrs 1.62 +/- 0.22, NAA/Cr 2.78 +/- 0.34 vrs 2.64 +/- 0.41, Cho/Cr 1.57 +/- 0.25 vrs 1.65 +/- 0.28. There were no statistically significant differences between patients and controls. The putaminal NAA/Cho ratio of the single subject with atypical parkinsonism was lower than that of 9 of the 10 patients with classic Parkinson's disease and 11 of the 13 control subjects. Likewise, the putaminal NAA/Cr ratio in the single subject with atypical parkinsonism was lower than that of 7of the patients with guided selection of spectra from very small brain volumes, is a technique that can be used to evaluate neuronal density in individual subcortical gray nuclei in the brains of patients with parkinsonism. Using this technique, we have shown that Parkinson's disease produces no change in relative levels of the neuronal marker, NAA, in the putamen.     

Phospholipid head-group conformations; intermolecular interactions and cholesterol effects

The predominant orientation of the phosphorylcholine polar head group in phosphatidylcholine and sphingomyelin bilayers and cholesterol perturbations of that orientation have been identified by exploiting the 31P (1H) nuclear Overhauser effect (NOE) in the 31P NMR spectra of phospholipid bilayers. In pure egg phosphatidylcholine bilayers, a NOE of 40% is observed. The magnitude of the NOE has been measured as a function of continuous-wave proton-decoupler frequency in order to identify the proton source of the NOE. In pure egg phosphatidylcholine bilayers, the maximum NOE occurs at the N-methyl proton resonance position of the choline moiety. In a modified phosphatidylcholine in which all the N-methyl protons were replaced by deuterium, the NOE arose from methylene protons next to the phosphate. In mixed systems of phosphatidylcholine and phosphatidylethanolamine, and phosphatidylcholine and diphosphatidylglycerol, both phospholipid resonances attained maximum NOE at the position of the N-methyl proton resonance of phosphatidylcholine. An analogous result was obtained with pure sphingomyelin. These results are explained by orienting the phosphorylcholine portion of the molecule parallel to the surface of the bilayer so that the positively charged N-methyl moiety is located close to the negatively charged phosphate on a neighboring phospholipid in an intermolecular interaction. Addition of cholesterol is shown to disrupt the intermolecular interaction in phosphatidylcholine bilayers.     

Interaction of calcium channel antagonists with calcium: spectroscopic and modeling studies on diltiazem and its Ca2+ complex

Using spectral techniques, the solution conformation of diltiazem was studied in acetonitrile with special reference to the effect of Ca2+ on the drug structure. Complete assignment of the proton resonances in the 1H-NMR spectrum of the drug was made using one-and two-dimensional spectral analyses. A two-dimensional 1H-NOESY spectrum (in the phase-sensitive mode) was obtained to identify the interproton connectivities in the drug molecule. A molecular modeling program involving Monte Carlo simulation and energy minimization was employed to arrive at the structure of the drug. The program was run with and without the input of the interproton distances derived from the NOESY cross peaks. Both the protocols led to a structure of the drug which was generally similar to that reported from X-ray diffraction data on crystalline diltiazem hydrochloride (Kojic-Prodic, et al. Helv. Chim. Acta 1984, 67, 916-926). However, significant differences between the two structures were seen in the orientations of the substituent groups attached to the benzothiazepine ring. Substantial changes in the circular dichroic (CD) and 1H-NMR spectra of diltiazem were observed on addition of Ca2+ up to a mole ratio of 0.5 Ca2+ per drug. Relatively large changes were seen in 1H resonances of the N-methyl protons and the methylene protons attached to the heterocyclic nitrogen. Analysis of the binding isotherms from CD data at 22 +/- 1 degrees C indicated a 2:1 drug:Ca2+ "sandwich" complex with an estimated dissociation constant of 140 microM. One-dimensional difference NOE and two-dimensional NOESY spectra revealed interproton connectivities between two drug molecules that were compatible with the sandwich complex formation. The interproton distances derived from the volume integrals of the NOESY cross peaks were used as geometrical constraints in modeling the Ca(2+)-bound conformation of diltiazem. The minimum-energy conformation corresponded to the sandwich complex where Ca2+ was coordinated to three oxygens in each of the two drug molecules. Combined with our earlier data on the ability of diltiazem to translocate Ca2+ across the lipid bilayer in synthetic liposomes (Ananthanarayanan, V.S.; Taylor, L.; Pirritano, S.Biochem. Cell Biol. 1992, 70, 608-612), the structural data presented here point to a role for Ca2+ in the interaction of diltiazem with its membrane-bound receptor.     

1H MR spectroscopy monitoring of changes in choline peak area and line shape after Gd-contrast administration

Fifteen percent loss in the peak area of choline containing compounds (Cho) was recently observed in 1H MR spectra of contrast-enhancing tumor at 5-10 min after Gd-contrast administration [Magn. Reson. Med. 37:222-225, 1997]. In this study, chemical shift imaging (CSI, 1500/135 ms PRESS) was used to assess the spectral changes in 47 Gd-enhancing glial brain tumors and metastatic brain tumors measured at 0-5, 5-10, and/or 10-15 min after administration of Gd-contrast. Percent Cho peak area losses measured at these times, 3 +/- 3, 12 +/- 2, and 14 +/- 3 SEM, respectively, coincided with trends of line narrowing and up-field shift of the Cho peak. Significant changes in creatine and N-acetyl acetate signals were not observed. It is concluded that the Gd-induced loss of tumor Cho signal measured after 5 min, typically required for post contrast-MRI and the positioning of the CSI volume on tumor, shows little further change with time, if any.     

Ethical aspects to be considered in brain banking

OBJECTIVE: To investigate MRI and proton spectroscopy changes in five patients with HIV associated dementia complex (HADC) treated with antiretroviral therapy. METHODS: Three markers were evaluated: (1) CSF/intracranial volume ratio; (2) T2 weighted signal ratio between parieto-occipital white and subcortical grey matter; and (3) metabolite ratios from long echo time (TE=135 ms) single voxel proton spectra of parieto-occipital white matter. RESULTS: Spectroscopic changes indicated initial increases in N-acetyl/(N-acetyl + choline + creatine) ratio (NA/(NA+ Cho+Cr)) and progression of atrophy after initiation of antiretroviral therapy in four of five patients. When the neurological status of the patients subsequently deteriorated (two of five patients), the NA/(NA+Cho+Cr) ratio also declined. CONCLUSIONS: Spectroscopic changes mirror reversible neuronal dysfunction. These objective, non-invasive techniques may be used for monitoring the neurological effects of antiretroviral drug therapy in patients with HADC.     

The site-specific recombination system of the Lactobacillus species bacteriophage A2 integrates in gram-positive and gram-negative bacteria

We present three experiments which serve to identify carbon and proton sidechain resonances in 13C-labeled proteins. The first is an improvement on the previously published H(C)CH-COSY experiment and comprises the application of gradients for coherence selection and a reduction in the phase cycle. The second experiment is a new (H)CCH-COSY with two carbon dimensions. The (H)CCH-COSY presents several advantages over the H(C)CH-COSY experiment in terms of better sensitivity, improved resolution and easier identification of amino acid spins systems. The third experiment is a 2D proton-edited (H)C(C)H-COSY that allows suppression of methylene resonances. All three HCCH-COSY experiments show good sensitivity and excellent solvent suppression. The 2D version can be acquired in as little as 45 minutes and the 3D versions acquired overnight. The experiments are demonstrated on a 13C-labeled sample of the second PDZ domain from human phosphatase PTP1E in H2O solution.     

Ternary complex between elongation factor Tu.GTP and Phe-tRNA(Phe)

The effect of aminoacylation and ternary complex formation with elongation factor Tu.GTP on the tertiary structure of yeast tRNA(Phe) was examined by 1H-NMR spectroscopy. Esterification of phenylalanine to tRNA(Phe) does not lead to changes with respect to the secondary and tertiary base pair interactions of tRNA. Complex formation of Phe-tRNA(Phe) with elongation factor Tu.GTP results in a broadening of all imino proton resonances of the tRNA. The chemical shifts of several NH proton resonances are slightly changed as compared to free tRNA, indicating a minor conformational rearrangement of Phe-tRNA(Phe) upon binding to elongation factor Tu.GTP. All NH proton resonances corresponding to the secondary and tertiary base pairs of tRNA, except those arising from the first three base pairs in the aminoacyl stem, are detectable in the Phe-tRNA(Phe)-elongation factor Tu-GTP ternary complex. Thus, although the interactions between elongation factor Tu and tRNA accelerate the rate of NH proton exchange in the aminoacyl stem-region, the Phe-tRNA(Phe) preserves its typical L-shaped tertiary structure in the complex. At high (> 10(-4) M) ligand concentrations a complex between tRNA(Phe) and elongation factor Tu-GDP can be detected on the NMR time-scale. Formation of this complex is inhibited by the presence of any RNA not related to the tRNA structure. Using the known tertiary structures of yeast tRNA(Phe) and Thermus thermophilus elongation factor Tu in its active, GTP form, a model of the ternary complex was constructed.     

Kinetics of the light-induced proton translocation associated with the pH-dependent formation of the metarhodopsin I/II equilibrium of bovine rhodopsin

The kinetics of the formation of the metaII (MII) state of bovine rhodopsin was investigated by time-resolved electrical and absorption measurements with rod outer segment (ROS) fragments. Photoexcitation leads to proton transfer in the direction from the cytosolic to the intradiscal side of the membrane, probably from the Schiff base to the acceptor glutamate 113. Two components of comparable amplitude are required to describe the charge movement with exponential times of 1.1 (45%) and 3.0 ms (55%) (pH 7.8, 22 degreesC, 150 mM KCl). The corresponding activation energies are 86 and 123 kJ/mol, respectively (150 mM KCl). The time constants and amplitudes depend strongly on pH. Between pH 7.1 and 3.8 the kinetics becomes much faster, with the faster and slower components accelerating by factors of about 8 and 2, respectively. Complementary single-flash absorption experiments at 380 nm and 10 degreesC show that the formation of MII also occurs with two components with similar time constants and pH dependence. This suggests that both signals monitor the same molecular events. The pH dependence of the two apparent time constants and amplitudes of the optical data can be described well over the pH range 4-7.5 by two coupled equilibria between MI and two isochromic MII species MIIa and MIIb: MI MIIa(380) MIIb(380), with k0 proportional to the proton concentration. This model implies that deprotonation of the Schiff base and proton uptake are tightly coupled in ROS membranes. Models with k2 proportional to the proton concentration cannot describe the data. Photoreversal of MII by blue flashes (420 nm) leads to proton transfer in a direction opposite to that of the signal associated with MII formation. In this transition the Schiff base is reprotonated, most likely from glutamate 113. At pH 7.3, 150 mM KCl, 22 degreesC, this electrical charge reversal has an exponential time constant of about 30 ms and is about 10 times slower than the forward charge motion.     

Spectroscopic imaging of the knee with line scan CPMG sequences

OBJECTIVE: A line scan spectroscopic imaging method providing variable T2-weighted spectra from many small voxels along selected tissue columns was applied to study the chemical composition of hematopoietic and fatty marrow in the knees of adults and children. MATERIALS AND METHODS: Line scan Carr-Purcell-Meiboom-Gill (CPMG) spectroscopic imaging sequences were implemented on a 1.5 T clinical scanner. Variable T2-weighted proton spectra from 128 locations along 20 cm long, 5 mm2 columns oriented superiorly to inferiorly through knees were collected from eight healthy adults and eight children. RESULTS: In adult yellow marrow, olefinic protons, water, a composite lipid proton peak, and methyl/methylene protons contributed 6.4 +/- 0.4, 4.2 +/- 1.5, 7.2 +/- 0.5, and 82.2 +/- 1.9% (mean +/- SD) to the spectra, respectively. Marrow spectra were largely independent of position along the column. Marrow spectra of normal children showed distinct positional dependences. Epiphyseal marrow spectra of children (8-16 years old) resembled adult spectra but with more water (mean 15 vs. 4%). Metaphyseal marrow had higher, variable water content, reflecting the extent of marrow conversion and generally obscuring the olefinic proton peak. CONCLUSIONS: Spectroscopic imaging of columns is a time-efficient method for sampling extensive regions of bone marrow with high spatial resolution. It should prove useful for proton spectroscopic studies of hematologic pathologies and conditions requiring the monitoring of lipid composition.