scholarly journals Experimental and theoretical determinations of hydrogen isotopic equilibrium in the system CH4-H2-H2O from 3 to 200°C

2021 ◽  
Author(s):  
Andrew C. Turner ◽  
Roman Korol ◽  
Daniel L. Eldridge ◽  
Markus Bill ◽  
Mark E. Conrad ◽  
...  
Keyword(s):  
Isotopic Equilibrium

EFFECT OF PROPYLTHIOURACIL ON THE IODINATION AND MATURATION OF RAT THYROGLOBULIN

1966 ◽  
Vol 53 (2) ◽  
pp. 271-285 ◽  
Author(s):  
Claude Simon ◽  
Marie Roques ◽  
Janine Torresani ◽  
Serge Lissitzky
Keyword(s):  
Single Injection ◽  
Freezing And Thawing ◽  
Isotopic Equilibrium ◽  
Sedimentation Constant

ABSTRACT The effect of propylthiouracil on the maturation of rat thyroglobulin in vivo has been investigated. Newly iodinated thyroglobulin dimer is labile to freezing and thawing. This observation has been used to interpret the findings in the present experiments. From experiments using rats in isotopic equilibrium with 125I, and treated with propylthiouracil or propylthiouracil and tri-iodothyronine and also given a single injection of 131I, the following conclusions were formulated 1) the appearance of iodinated S12 thyroglobulin monomer is due to the dissociation of labile iodinated thyroglobulin dimer and appears more readily if the dimer is poorly iodinated, 2) uniodinated thyroglobulin dimer is the most probable substrate for iodination in vivo, 3) maturation of thyroglobulin dimer (as shown by increasing sedimentation constant from 16—17 to 19) is accompanied by increasing amounts of iodine in the molecule, 4) it is not possible to say at present if iodination and iodothyronine formation is the cause or the consequence of thyroglobulin dimer maturation, 5) propylthiouracil might inhibit thyroglobulin maturation by decreasing iodine organification.

Late Pleistocene chronology and paleoclimate of Vancouver Island determined from cave deposits

1981 ◽  
Vol 18 (11) ◽  
pp. 1643-1652 ◽  
Author(s):  
M. Gascoyne ◽  
D. C. Ford ◽  
H. P. Schwarcz
Keyword(s):  
Late Pleistocene ◽  
Growth Period ◽  
Vancouver Island ◽  
Isotopic Equilibrium ◽  
South Central ◽  
Cave Deposits ◽  
Short Period ◽  
Thermal Buffering

Speleothems from four caves in south-central Vancouver Island have been analysed by the 230Th/234U method. Only speleothems from one cave, Cascade Cave, near Port Alberni, contained sufficient uranium for them to be dated. Twenty-seven ages determined for seven speleothems were found to cluster in two periods: 67–28 ka, corresponding to the Olympia interstadial, and <23–10 ka (or <15 ka if corrected for detrital thorium contamination), corresponding to the Fraser (late Wisconsin) deglaciation and Holocene periods. Two speleothems were found to be deposited in isotopic equilibrium with their seepage waters. Profiles of variations in δ18O of the calcite (δ18Oc) of each of the two deposits show a decrease of 1.3‰ over the growth period, 64–28 ka. At all times, δ18Oc was less than δ18O of modern calcite in the cave. Using modern cave temperature and the variation of δ18O of seawater over the dated period, the profiles of δ18Oc are interpreted in terms of a paleotemperature record for the Olympia interstadial in Vancouver Island. The results show a gradual cooling from 4 °C at 64 ka, to 0 °C between 35 and 28 ka. These results are consistent with conditions necessary for speleothem growth and with published work on surficial Wisconsin deposits in the area. No distinct, short-period warming or cooling events are seen in the record, probably due to thermal buffering by the adjacent ocean.

Equilibrium Temperature Calculation of the Sulfur Isotope in Dongzhongla Pb-Zn Deposit in Tibet

2015 ◽  
Vol 1092-1093 ◽  
pp. 1394-1397
Author(s):  
Guang Chun Fei ◽  
Yi Fan Yu ◽  
Ke Qiang Hua
Keyword(s):  
Sulfur Isotope ◽  
Equilibrium Temperature ◽  
Mining Area ◽  
Isotopic Equilibrium ◽  
The North ◽  
Geological Conditions ◽  
Typical Type ◽  
Lead Zinc ◽  
Block Based ◽  
Exploration Area

The Dongzhongla Pb-Zn deposit, a newly-discovered medium-sized deposit, is located in the north margin of the eastern Gangdese, central Lhasa block. Based on the analysis of the ore-forming geological conditions in this deposit, sulfur isotope of this deposit were analyzed, and S isotopic equilibrium temperature of mineral pairs (sphalerite and galena) were calculated. This study has shown that the sulfur isotopic equilibrium temperature of sphalerite and galena in Dongzhongla Pb-Zn deposit ranged from 185℃ to 296℃. It indicated that the equilibrium temperature decreased gradually from the skarn stage to sulfide stage. The equilibrium temperature can be used as the reference of metallogenic temperature for Dongzhongla Pb-Zn deposit. DongzhongLa deposit is the typical type of skarn Lead-zinc deposit. East of the Dongzhongla mining area is the priority exploration area.

scholarly journals Oxygen and silicon β-factors of zircon estimated from first principles

2019 ◽  
Vol 27 (4) ◽  
pp. 420-430
Author(s):  
D. P. Krylov
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Isotope Fractionation ◽  
Isotopic Equilibrium ◽  
Functional Theory ◽  
Empirical Calibration ◽  
The Density Functional Theory ◽  
Cubic Polynomials ◽  
Semi Empirical ◽  
Fractionation Factors

Zircon β-factors have been calibrated against temperature for isotopic substitutions of 18O/16O and 30Si/28Si. Calculations were performed using the density functional theory (DFT) with the “frozen phonon” approach. The deduced geometric parameters of the zircon unit cell, and the phonon frequencies calculated, agree well with the experimental data. The results are expressed by the cubic polynomials on x = 106/T(K)2: 1000lnβzrn(18O/16O) = 9.83055x – 0.19499x2 + 0.00388x3;  1000lnβzrn(30Si/28Si) = 7.89907x – 0.17978x2 + 0.00377x3. The expressions deduced can be utilized to construct geothermometers if combined with β-factors of coexisting phases. New calibrations of quartz-zircon are given. The new values of 1000lnβzrn and the estimated isotope fractionation factors between quartz and zircon (1000lnβqtz–1000lnβzrn) deviate considerably from previously used experimental, empirical, and semi-empirical calibration of the isotopic equilibrium.

Brush-border disaccharidase synthesis in infant pigs measured in vivo with [2H3]leucine

1994 ◽  
Vol 267 (6) ◽  
pp. G1128-G1134 ◽  
Author(s):  
M. A. Dudley ◽  
F. Jahoor ◽  
D. G. Burrin ◽  
P. J. Reeds
Keyword(s):  
Brush Border ◽  
Slow Rate ◽  
Chemical Ionization ◽  
Gas Chromatography Mass Spectrometry ◽  
Isotopic Enrichment ◽  
Isotopic Equilibrium ◽  
Fractional Synthesis ◽  
High Mannose ◽  
Plasma Leucine

Conscious unrestrained piglets were fasted overnight and infused intravenously with [2H3]leucine for 6 h. Sucrase isomaltase and lactase phlorizin hydrolase were immunoprecipitated from jejunal mucosal membranes, and the immunoprecipitates were electrophoresed on polyacrylamide gels. Bands corresponding to the pro and mature isoforms of both enzymes were acid hydrolyzed. [2H3]leucine isotopic enrichment was measured by gas chromatography-mass spectrometry using negative chemical ionization. Plasma leucine reached isotopic steady state within 90 min. The isotopic enrichment of mucosal leucine was 73% of that of plasma leucine. The high mannose and complex glycosylated forms of prolactase were in isotopic equilibrium, and their isotopic enrichment was 94% of mucosal leucine. The fractional synthesis rates of total and membrane protein were 0.45 and 0.65 days-1, whereas the processing rates of mature lactase, sucrase, and isomaltase were 0.90, 0.23, and 0.21 days-1, respectively. Approximately 65% of the label in the sucrase isomaltase immunoprecipitate was in the complex glycosylated precursor, whereas 73% of the label in lactase phlorizin hydrolase was in the mature (160 kDa) form. We conclude that the low rate of brush-border sucrase synthesis reflects a slow rate at which the complex glycosylated precursor is processed to the brush-border form.

Tissue-specific isotope trophic discrimination factors and turnover rates in a marine elasmobranch: empirical and modeling results

2012 ◽  
Vol 69 (3) ◽  
pp. 551-564 ◽  
Author(s):  
Luis Malpica-Cruz ◽  
Sharon Z. Herzka ◽  
Oscar Sosa-Nishizaki ◽  
Juan Pablo Lazo
Keyword(s):  
Natural Populations ◽  
Nitrogen Isotope ◽  
Cartilage Tissue ◽  
Turnover Rates ◽  
Isotopic Equilibrium ◽  
Isotope Turnover ◽  
Discrimination Factors ◽  
Triakis Semifasciata ◽  
Leopard Sharks ◽  
Trophic Discrimination

There are very few studies reporting isotopic trophic discrimination factors and turnover rates for marine elasmobranchs. A controlled laboratory experiment was conducted to estimate carbon and nitrogen isotope trophic discrimination factors and isotope turnover rates for blood, liver, muscle, cartilage tissue, and fin samples of neonate to young-of-the-year leopard sharks ( Triakis semifasciata ). Trophic discrimination factors varied (0.13‰–1.98‰ for δ13C and 1.08‰–1.76‰ for δ15N). Tissues reached or were close to isotopic equilibrium to the new diet after about a threefold biomass gain and 192 days. Liver and blood exhibited faster isotope turnover than muscle, cartilage tissue, and fin samples, and carbon isotopes turned over faster than those of nitrogen. Metabolic turnover contributed substantially to isotopic turnover, which differs from most reports for young marine teleosts. We modeled the relationship between muscle turnover rates and shark size by coupling laboratory results with growth rate estimates for natural populations. Model predictions for small, medium, and large wild leopard sharks indicate the time to isotopic equilibrium is from one to several years.

EFFECT OF THE EXPOSURE TO COLD ON THE EXTRATHYROIDAL CONVERSION OF L-THYROXINE TO TRIIODO-L-THYRONINE, AND ON INTRAMITOCHONDRIAL α-GLYCEROPHOSPHATE DEHYDROGENASE ACTIVITY IN THYROIDECTOMIZED RATS ON L-THYROXINE

1975 ◽  
Vol 78 (3) ◽  
pp. 481-492 ◽  
Author(s):  
J. Bernal ◽  
F. Escobar del Rey
Keyword(s):  
Dehydrogenase Activity ◽  
Paper Chromatography ◽  
Cold Exposure ◽  
Isotopic Equilibrium ◽  
Glycerophosphate Dehydrogenase ◽  
Exposure To Cold ◽  
Constant Dose ◽  
And Control

ABSTRACT Thyroidectomized rats have been injected daily with 125I labelled L-thyroxine (T4*) and, once isotopic equilibrium was attained, divided into cold-exposed (4–10°C) and control (21–24°C) groups, the daily T4* administration being continued till the end of the experiment. Fourteen days after onset of cold exposure, the total I* of different organs and of the carcass was determined and the tissues submitted to extraction and paper chromatography for the separation of T4 and T4-derived I-containing compounds. The activity of intramitochondrial α-glycerophosphate dehydrogenase (α-GPD) was measured in kidneys and liver. It was found that the total amount of I* was intensely decreased in all samples from cold-exposed animals. The proportion of this I* which was non-extractable was the same, in all tissues, for cold-exposed and control rats. The % of extractable tissue radioactivity in the form of T4 was decreased, and that found as T4-derived T3 was increased, in all samples from cold-exposed animals. The T3/T4 ratio was increased more than two-fold in all tissues studied. The concentration of T4 decreased significantly in all tissues, whereas the concentration of T3 in tissues of cold-exposed rats did not decrease. It actually increased in kidneys and lungs, and remained the same in liver and carcass. Despite the decrease in the concentration of T4 in the kidneys, α-GPD activity was increased in this tissue, where the concentration of T3 was increased. No change in the α-GPD activity was found for the liver, where the concentration of T3 was the same for cold-exposed and control rats. Thus, it appears likely that the conversion of T4 to T3 is increased by the exposure to cold of thyroidectomized rats on a constant dose of T4. α-GPD activity in a given tissue appears to be more closely related to the concentration of T3, than to that of T4.

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