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D/H Ratios (h + ratio)
Selected AbstractsWater Resource Implications of 18O and 2H Distributions in a Basalt Aquifer SystemGROUND WATER, Issue 6 2000Kathryn R. Larson Ongoing decline of water levels in the confined basalt aquifers of the Pullman-Moscow Basin of Washington and Idaho has prompted study of the timing, amount and distribution of recharge to the system. Previous radiocarbon ages indicate residence times on the order of 103 years and greater and suggest a low rate of recharge to the lower basalt aquifer since the end of Pleistocene time. By contrast, more recent hydrodynamic flow modeling studies invoke a larger Holocene recharge rate through the unconfined loess unit to the upper and lower basalt aquifers, which implies relatively short residence times (102 years). Stable isotopes were used to independently assess contrasting recharge models by comparing 18O/16O and D/H ratios of late-Holocene shallow ground water and deep ground water. Linear regression of local precipitation ratios yields ,D = 6.9 ,18O ,18.5. There is no evidence of fractionation of ground water ratios by recharge processes or water-rock interactions. Deep basalt ground water ,18O values are depleted by 0.4 to 4.9 per mil relative to shallow, recently recharged ground waters and have ,18O values statistically distinct from waters sampled from other stratigraphic units. These findings suggest that the deep waters in the basin were not precipitated under current climate conditions and that aquifer recharge rates to the deep basalt aquifer are substantially lower than have been recently estimated. This in turn suggests that a sustainable ground water exploitation scheme must reduce reliance on the deep ground water resource. [source] Water Sources and Water-Use Efficiency in Mediterranean Coastal Dune VegetationPLANT BIOLOGY, Issue 3 2004G. A. Alessio Abstract: In coastal environments plants have to cope with various water sources: rainwater, water table, seawater, and mixtures. These are usually characterized by different isotopic signatures (18O/16O and D/H ratios). Xylem water reflects the isotopic compositions of the water sources. Additionally, water-use efficiency (WUE) can be assessed with carbon isotope discrimination (,) analyses. Gas exchange, , of leaf dry matter, and isotopic composition (,18O) of xylem water were measured from June to August 2001 in herbaceous perennials of mobile dunes (Ammophila littoralis, Elymus farctus) and sclerophyllous shrubs and climbers (Arbutus unedo, Pistacia lentiscus, Phillyrea angustifolia, Qercus ilex, Juniperus oxycedrus, Smilax aspera) of consolidated dunes. Assimilation rates were rather low and did not show clear seasonal patterns, possibly due to limited precipitation and generally low values of stomatal conductance. The lowest values were shown in S. aspera. Different physiological patterns were found, on the basis of ,18O and , analyses. Values of ,18O of xylem water of phanerophytes were remarkably constant and matched those of the water table, indicating dependence on a reliable water source; values of , were relatively high, indicating low intrinsic WUE, with the exception of J. oxycedrus. Surprisingly, very high ,18O values were found for the xylem water from S. aspera in August. This suggests retrodiffusion of leaf water to xylem sap in the stem or direct uptake of water by leaves or stems, owing to dew or fog occurrence. Low , values indicated high WUE in S. aspera. Contrasting strategies were shown by the species of mobile dunes: E. farctus relied on superficial water and exhibited low WUE, accordingly to its therophyte-like vegetative cycle; on the contrary, A. littoralis used deeper water sources, showing higher WUE in relation to its long-lasting vegetative habit. [source] Gas chromatography flow rates for determining deuterium/hydrogen ratios of natural gas by gas chromatography/high-temperature conversion/isotope ratio mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2008Wanglu Jia The effects of the gas chromatography flow rate on the determination of the deuterium/hydrogen (D/H) ratios of natural gas utilising gas chromatography/high-temperature conversion/isotope ratio mass spectrometry (GC/TC/IRMS) have been evaluated. In general, the measured ,D values of methane, ethane and propane decrease with increase in column flow rate. When the column flow rate is 1,mL/min or higher, which is commonly used for the determination of D/H ratios of natural gas, the organic H in gas compounds may not be completely converted into hydrogen gas. Based on the results of experiments conducted on a GC column with an i.d. of 0.32,mm, a GC flow rate of 0.6,mL/min is proposed for determining the D/H ratios of natural gas by GC/TC/IRMS. Although this value may be dependent on the instrument conditions used in this work, we believe that correct ,D values of organic compounds with a few carbon atoms are obtained only when relatively low GC flow rates are used for D/H analysis by GC/TC/IRMS. Moreover, as the presence of trace water could significantly affect the determination of D/H ratios, a newly designed inlet liner was used to remove trace water contained in some gas samples. Copyright © 2008 John Wiley & Sons, Ltd. [source] NMR Quantification of Tautomeric Populations in Biogenic Purine BasesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2009Bartl Abstract Purine bases such as purine, adenine, hypoxanthine, and mercaptopurine are known to exist in several tautomeric forms. Characterization of their tautomeric equilibria is important not only for predicting the regioselectivity of their N -alkylation reactions, but also for gaining knowledge of the patterns with which these compounds of significant biological activity form hydrogen bonds with their biological targets. The tautomeric equilibria of purine and some purine derivatives in methanol and N,N -dimethylformamide solutions were investigated by low-temperature 1H and 13C NMR spectroscopy. The N(7)H and N(9)H tautomeric forms were quantified by integrating the individual 1H NMR signals at low temperatures. The Gibbs free energy differences were calculated and the effects of substitution on the N(7)H/N(9)H ratio discussed. A previously published theoretically predicted mechanism of the tautomeric exchange is compared with our measurements in deuteriated solvents. The influence of concentration on the temperature of coalescence indicates that supramolecular clusters play a significant role in this proton transfer process. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] A neutron crystallographic analysis of T6 porcine insulin at 2.1,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2009Wakari Iwai Neutron diffraction data for T6 porcine insulin were collected to 2.1,Å resolution from a single crystal partly deuterated by exchange of mother liquor. A maximum-likelihood structure refinement was undertaken using the neutron data and the structure was refined to a residual of 0.179. The hydrogen-bonding network of the central core of the hexamer was observed and the charge balance between positively charged Zn ions and their surrounding structure was interpreted by considering the protonation and/or deprotonation states and interactions of HisB10, water and GluB13. The observed double conformation of GluB13 was essential to interpreting the charge balance and could be compared with the structure of a dried crystal of T6 human insulin at 100,K. Differences in the dynamic behaviour of the water molecules coordinating the upper and lower Zn ions were observed and interpreted. The hydrogen bonds in the insulin molecules, as well as those involving HisB10 and GluB13, are discussed. The hydrogen/deuterium (H/D) exchange ratios of the amide H atoms of T6 porcine insulin in crystals were obtained and showed that regions highly protected from H/D exchange are concentrated in the centre of a helical region of the B chains. From the viewpoint of soaking time versus H/D-exchange ratios, the amide H atoms can be classified into three categories. [source] A neutron crystallographic analysis of phosphate-free ribonuclease A at 1.7,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2009Daichi Yagi A neutron crystallographic analysis of phosphate-free bovine pancreatic RNase A has been carried out at 1.7,Å resolution using the BIX-4 single-crystal diffractometer at the JRR-3 reactor of the Japan Atomic Energy Agency. The high-resolution structural model allowed us to determine that His12 acts mainly as a general base in the catalytic process of RNase A. Numerous other distinctive structural features such as the hydrogen positions of methyl groups, hydroxyl groups, prolines, asparagines and glutamines were also determined at 1.7,Å resolution. The protonation and deprotonation states of all of the charged amino-acid residues allowed us to provide a definitive description of the hydrogen-bonding network around the active site and the H atoms of the key His48 residue. Differences in hydrogen-bond strengths for the ,-helices and ,-sheets were inferred from determination of the hydrogen-bond lengths and the H/D-exchange ratios of the backbone amide H atoms. The correlation between the B factors and hydrogen-bond lengths of the hydration water molecules was also determined. [source] Cardiac Resynchronization Therapy Upregulates Cardiac Autonomic ControlJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 10 2008YONG-MEI CHA M.D. Objective: To determine the effect of cardiac resynchronization therapy (CRT) on sympathetic nervous function in heart failure (HF). Background: Neurohormonal dysregulation and cardiac autonomic dysfunction are associated with HF and contribute to HF progression and its poor prognosis. We hypothesized that mechanical resynchronization improves cardiac sympathetic function in HF. Methods: Sixteen consecutive patients receiving CRT for advanced cardiomyopathy and 10 controls were included in this prospective study. NYHA class, 6-minute walk distance, echocardiographic parameters, plasma norepinephrine (NE) were assessed at baseline, 3-month and 6-month follow-up. Cardiac sympathetic function was determined by 123iodine metaiodobenzylguanidine (123I-MIBG) scintigraphy and 24-hour ambulatory electrocardiography. Results: Along with improvement in NYHA class (3.1 ± 0.3 to 2.1 ± 0.4, P < 0.001) and LVEF (23 ± 6% to 33 ± 12%, P < 0.001), delayed heart/mediastinum (H/M) 123I-MIBG ratio increased significantly (1.8 ± 0.7 to 2.1 ± 0.6, P = 0.04) while the H/M 123I-MIBG washout rate decreased significantly (54 ± 25% to 34 ± 24%, P = 0.01) from baseline to 6-month follow-up. The heart rate variability (HRV) measured in SD of normal-to-normal intervals also increased significantly from baseline (82 ± 30 ms) to follow-up (111 ± 32 ms, P = 0.04). The improvement in NYHA after CRT was significantly associated with baseline 123I-MIBG H/M washout rate (r = 0.65, P = 0.03). The improvement in LVESV index was associated with baseline 123I-MIBG delayed H/M ratio (r =,0.67, P = 0.02) and H/M washout rate (r = 0.65, P = 0.03). Conclusion: After CRT, improvements in cardiac symptoms and LV function were accompanied by rebalanced cardiac autonomic control as measured by 123I-MIBG and HRV. [source] MIBG scintigraphy for differentiating Parkinson's disease with autonomic dysfunction from Parkinsonism-predominant multiple system atrophy,MOVEMENT DISORDERS, Issue 11 2009Eun Joo Chung MD Abstract Parkinson's disease (PD) with autonomic dysfunction is difficult to differentiate from Parkinsonism-predominant multiple system atrophy (MSA-p). This study aimed to analyze the validity of MIBG scintigraphy for PD with autonomic dysfunction and MSA-p. Thirty-nine patients (PD: 27 patients, MSA-p type: 12) and 12 age-matched controls were prospectively enrolled and underwent MIBG scintigraphy and autonomic function test (AFT). We separately calculated early and delayed heart-to-mediastinal (H/M) ratio and washout rates (WRs). AFT was composed of sympathetic skin reflex and parasympathetic tests based on heart rate variability. Abnormal AFT was observed in 17 (63%) of PD and 10 (83%) of MSA-p. On comparing PD with abnormal AFT with MSA-p, either the early or delayed H/M ratio in PD was not different from that in MSA-p (P > 0.05). Only the WR could differentiate PD with abnormal AFT from MSA-p (47.07 ± 57.48 vs. 31.39 ± 31.52, respectively) (P = 0.026). According to the results, WR may be more useful than the early and delayed H/M ratio to distinguish MSA-p from PD with abnormal AFT. Furthermore, the MIBG uptake did not reflect the disease duration or severity. © 2009 Movement Disorder Society [source] Cardiac 123I-MIBG scintigraphy in patients with essential tremorMOVEMENT DISORDERS, Issue 8 2006Phil Hyu Lee MD Abstract In some cases, it is difficult to differentiate essential tremor (ET) from Parkinson's disease (PD), especially in the early stages of the disease. We investigated cardiac sympathetic dysfunction using 123I-metaiodobenzylguanidine (MIBG) myocardial scintigraphy in 22 patients with ET, in comparison with early PD and tremor-dominant PD (TDPD). The mean ratio of 123I-MIBG uptake in the region of interest in the heart to that in the mediastinum (H/M ratio) was significantly greater in patients with ET (1.99 ± 0.21) than in those with either TDPD (1.28 ± 0.11) or early PD (1.28 ± 0.17; each P < 0.001). The H/M ratio in all patients with ET was greater than two standard deviations above the range of the ratio in the patients with early PD or TDPD. © 2006 Movement Disorder Society [source] Chronic Hypoxia Delays Myocardial Lactate Dehydrogenase Maturation in Young RatsEXPERIMENTAL PHYSIOLOGY, Issue 3 2003Z. Daneshrad The effect of exposure to hypobaric hypoxia for 4 weeks (oxygen pressure = 106 hPa), equivalent to 5500 m in altitude) on myocardial total lactate dehydrogenase (tLDH) activity and isoform (H and M) composition was comparatively studied in growing (4.5 weeks old) and in adult (4.5 months old) male rats. The consequences of the hypoxia-induced anorexia were checked in growing rats using a pair-fed group. Exposure to hypoxia induced a significant decrease in the H/tLDH ratio in the left (LV) and right ventricle (RV) of growing and adult rats. In adult rats this alteration was mainly a consequence of the significant increase in the specific activity of the M isomer, which resulted in an increase in the overall LDH activity. In contrast, in the LV of young rats exposed to hypoxia, the specific activity of the M isomer was similar to that of normoxic animals while the H isomer activity was significantly lower than in normoxic rats, and the overall LDH activity remained unchanged. These effects were specifically due to hypoxia per se since no significant alterations were observed in pair-fed animals. In the hypertrophied RV, the alteration of H and M isomers following hypoxia was similar to that observed in adults (i.e. no change in H and an increase in M isoform). We conclude that the well-known hypoxia-induced decrease in the H/tLDH ratio is governed by different age-dependent mechanisms. In adult rats, hypoxia may induce in both ventricles a stimulating effect on M isomer expression. In the LV of growing rats this stress could inhibit the H isomer maturation without any effect on the M isomer. In the RV of growing rats this effect could have been counteracted by the growth effect of the hypertrophying process. [source] Quantification of algal endosymbionts (Symbiodinium) in coral tissue using real-time PCRMOLECULAR ECOLOGY RESOURCES, Issue 1 2009J. C. MIEOG Abstract Understanding the flexibility of the endosymbioses between scleractinian corals and single-cell algae of the genus Symbiodinium will provide valuable insights into the future of coral reefs. Here, a real-time polymerase chain reaction (PCR) assay is presented to accurately determine the cell densities of Symbiodinium clades C and D in the scleractinian coral Acropora millepora, which can be extended to other coral,symbiont associations in the future. The assay targets single- to low-copy genes of the actin family of both the coral host and algal symbiont. Symbiont densities are expressed as the ratio of Symbiodinium cells to each host cell (S/H ratio, error within 30%), but can also be normalized to coral surface area. Greater accuracy in estimating ratios of associations involving multiple clades is achieved compared with previous real-time PCR assays based on high-copy ribosomal DNA loci (error within an order of magnitude). Healthy adult A. millepora containing ~1.4 × 106 zooxanthellae per cm2 (as determined by haemocytometer counts) had S/H ratios of c. 0.15, i.e. ~15 symbiont cells per 100 host cells. In severely bleached colonies, this ratio decreased to less than 0.005. Because of its capacity to accurately determine both densities and ratios of multiple symbionts within one sample, the assay will open the door for novel research into the mechanisms of symbiont shuffling and switching. [source] Comparative bioavailability of two oral formulations of ranitidineBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 1 2006Francisco J. Flores-Murrieta Abstract The current requirement of the Mexican Authorities to demonstrate the interchangeability of ranitidine formulations is to establish that the dissolution profile of the drug shows similarity. In order to establish if this requirement is adequate, the bioavailability of two formulations that did not meet this similarity were compared. Twenty-five female volunteers received 150 mg ranitidine (Azantac® or Midaven®) under fasting conditions in two separate sessions using a cross-over design. Plasma samples were obtained at selected times for a period of 12 h and stored frozen at ,80°C until analysed. Ranitidine plasma levels were determined and pharmacokinetic parameters were obtained. Values (mean ± SEM) were: Cmax 528.85 ± 25.34 and 563.03 ± 33.25 ng/ml, tmax 2.76 ± 0.19 and 2.79 ± 0.18 h, and AUC12 h 2694.94 ± 99.50 and 2648.51 ± 133.38 ng.h/ml, for Azantac® or Midaven®, respectively. No statistically significant difference was obtained in the parameters evaluated. Moreover, 90% confidence limits were 96.6%,116.2% and 90.7%,105.1% for Cmax and AUC12 h ratios, respectively, indicating that the formulations tested are bioequivalent, despite the dissimilarity in the dissolution profile of the formulations. These results suggest that the comparative dissolution profile is not an adequate test to demonstrate the interchangeability of ranitidine formulations. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||||||||