HPLC preparation of nitrate from ice cores for mass spectrometric 15N/14N measurements

Summary A method for the analysis of ¹⁵N-data of nitrate at ultratrace levels in ice cores is described. Samples are pre-concentrated using a HPLC-system. Nitrate is then reduced using the Dumas method to molecular nitrogen, which is analysed by mass spectrometry. The overall analytical precision of the method is ±0.4¹⁵N at a sample size of 35 bar l N₂. First results of deep ice-core analyses from Dome Summit, Greenland, are given.     

Pore-water anomalies in gas hydrate-bearing sediments of the deeper continental margins: Facts and problems

Naturally occurring gas hydrates, discovered under the deeper parts of the continental margins (generally below 500 m water depth) during the Deep Sea Drilling Project and the Ocean Drilling Program, impregnate terrigenous sediments 0.5 to 1 km thick. They form from biogenic as well as thermogenic hydrocarbon gases and are associated with characteristic chemical and isotopic anomalies in the pore waters resulting from hydrate decomposition. Typical downward trends derived from water samples squeezed on board ship show decreasing chlorinity coupled with increases in the heavy oxygen and hydrogen isotopes resulting from the combined effects of sediment compaction and salt and isotope fractionation by hydrates. Carbon isotopes can be used to differentiate between biogenic ( ¹³C < –55) and thermogenic ( ¹³C > –559) gas hydrates except where acetate-derived methane is involved. Smooth downward trends in the chemical and isotopic anomalies suggest steady increases in the proportion of hydrates among the pore-filling substances. Spikes are attributed to high local hydrate concentrations (or massive hydrate layers or nodules). Problems encountered in delineating the detailed relationships between hydrate occurrence and pore-water anomalies concern (i) the roof-effect of a hydrate zone which should be marked by a positive Cl^– and a negative ¹⁸O anomaly (the opposite of the hydrate decomposition effect) (ii) the composition ofin-situ pore waters from within hydrate zones; (iii) the suppression of a positive ¹⁸O hydrate-decomposition anomaly due to superposition of other oxygen-isotope fractionation effects (such as volcanic glass alteration); and (iv) the non-linear correlation between Cl^– depletion and¹⁸O enrichment, and the magnitude of the¹⁸O enrichment. The hydrate-decomposition mechanism still provides the most successful explanation for the chemical and isotopic porewater anomalies observed in hydrate-bearing sediments, but the problems encountered underscore the urgency for future research through deep-sea drilling in hydrate zones.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

Preparation of carbon dioxide from magnesite for isotopic analysis

Summary Since the application of the isotope geochemical method to obtain information on the formation mechanism of magnesite deposits was considered promising, we have developed a method to prepare carbon dioxide from magnesite samples for oxygen and carbon isotope analyses, using phosphoric acid reaction at an elevated temperature of 95° C. Data showing the reproducibility of the method (better than ±0.2 for both carbon and oxygen) are presented. The oxygen isotope fractionation factor between the evolved CO₂ and magnesite at 95° C is 1.0080.

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Freisetzung von Kohlendioxid aus Magnesit zur Isotopenanalyse

Zusammenfassung Mit dem Ziel, durch isotopen-geochemische Untersuchungen den Bildungsmechanismus von Magnesitablagerungen aufzuklären, wurde ein Verfahren zur Freisetzung von Kohlendioxid aus den Magnesitproben zur O- und C-Isotopenanalyse ausgearbeitet. Dazu dient die Reaktion mit Phosphorsäure bei 95° C. Die Reproduzierbarkeit ist besser als ±0,2 für beide Elemente. Der Fraktionierungsfaktor für das Sauerstoffisotop zwischen CO₂ und Magnesit bei 95° C beträgt 1,0080.

     

Thermodynamics of the dissociation of Bis H+ in seawater from 5 to 40°C

Electromotive-force measurements of cells without transference were used to determine the dissociation constant of the protonated form of the weak base 2-amino-2-methyl-1, 3-propanediol (Bis) in synthetic seawaters corresponding to salinities of 20, 35, and 45. Hydrogen electrodes and silver-silver chloride electrodes were used, together with standard potentials determined in an earlier investigation. The pK increases in linear fashion with the salinity (S) of the medium, for values of S from 0 to 45. The solvent effect is given by 8.802+0.00378S at 25°C with a mean deviation of 0.001. The medium effect of seawater on H° at 25°C is less than 200 cal-mol^–1 and less than 0.2 cal-^oK-mol^–1 on S°.     

Metal-betaine interactions. Part 17: A study of intradimer Cu · · · Cu distance variation in copper(II) betaine complexes containing [Cu2 (carboxylato-O,O′)4L2]n+ species

Four copper(II) complexes of betaines, [Cu₂(BET)₄Cl₂][Cu(BET)₂Cl₂]Cl₂ (2), [Cu₂(pyBET)₄Cl₂]₃[CuCl₄]₂Cl₂ (3), [Cu, (pyBET)₄ (H₂O)₂] (NO₃)₄ · 2H₂O (4), and [Cu₂(ppBET)₄(H₂O)₂](ClO₄)₄ · 4H₂O (5), (BET = Me₃N⁺CH₂COO^–; pyBET = C₅H₅N⁺CH₂COO^–; ppBET=C₅H₅N⁺CH₂CH₂COO^–), have been prepared and characterized by X-ray crystallography. These complexes all contain dimeric [Cu₂ (carboxylato-O,O)₄L₂] structures [basal Cu-O=1.955(4) 1.991(2), Cu Cu=2.602(1) 2.759(1) Å] with the apical ligand L=Cl^– in (2) and (3) [Cu-Cl=2.415(1) 2.436(3) Å] and L = H₂O in (4) and (5) [Cu-OH₂=2.158(4) 2.192(3) Å]; also present are a discrete [Cu(BET)₂Cl₂] molecule with a compressed tetrahedral CuO₂Cl₂ chromophore involving two unidentate carboxylate ligands [Cu-O=1.916(2), Cu-Cl=2.254(1) Å] in (2), and a discrete C_3v [CuCl₄]^2– anion in (3). Generally the intradimer Cu Cu distance may be correlated to the electronic repulsion of the metal-ligand bonds in the CuO₄L chromophore, as well as the steric interaction between the carboxylate moieties and the apical ligand.     

Stable isotope variation as a tool to trace the authenticity of beef

Organic beef coming principally from Germany was analysed for the hydrogen, carbon, oxygen, nitrogen and sulfur stable isotopic composition to test the possibility of tracing back the geographical origin. Since there is a well-known pattern of D/H and ¹⁸O/¹⁶O in meteoric water and in ground water, there is an existing link to tissue water in the beef. By including the stable isotope ratios of the other elements of life further information is available: soils show different isotope ratios of ¹⁵N/¹⁴N and ³⁴S/³²S depending on the geological composition, cultivation and atmospheric sulfur deposition. As organic farming is mainly obliged to use only their produced fodder, that ratio is reflected in the beef as well.Different organic beef samples from various German farms have been collected and analysed over nearly two years. To check the differentiation of foreign beef, samples from Argentina and Chile were also included in the study. The analyses of meat samples indicate that it is possible to trace back the region (e.g. Argentina and Germany) by using isotopes of oxygen and hydrogen. A local geographical differentiation can be done by using the stable isotopes of nitrogen and sulfur, as was demonstrated for three farms in Colonia Bay. An optimal differentiation also depends on the quality of further information (e.g. the season, kind of cattle breeding or the declaration of the local geographical origin). Certainly authenticity of beef is not only linked with the geographical origin but can also reflect the differentiation of organic and conventional farming. The fodder of organic cattle farming consists mainly of C₃ plants and the use of C₄ plants is more usual in conventional cattle farming. A ¹³C/¹²C ratio above –20 appears as a limit for organic farming. Increased values have to be controlled based on their authenticity.     

The scaled-particle theory and solvent isotope effects on the thermodynamic properties of inert solutes in water and methanol

The scaled-particle theory has been applied to the calculation of the thermodynamic changes associated with the formation of a cavity in several isotopic varieties of liquid water and methanol. From these results, the thermodynamic functions for the transfer of a cavity (or a hard-sphere solute) have been computed for the following solvent pairs: H₂OD₂O, H₂OH₂ ¹⁸O, H₂ ¹⁸OD₂ ¹⁸O, D₂OD₂ ¹⁸O, CH₃OHCH₃OD. For the last two of these solvents, density measurements required for the calculations were carried out as a function of temperature. The calculated deuterium solvent isotope effect on the heats and entropies of hard-sphere solutes in water is much greater than the¹⁸O isotope effect; the former also exhibits a more pronounced temperature dependence. The transfer functions computed for hard-sphere solutes are compared to experimental data on the transfer of various solutes from H₂O to D₂O and from CH₃OH to CH₃OD. In most of the cases examined, the cavity effect accounts for a large part of the transfer quantities measured for rare gases, hydrocarbons, and solutes containing a significant hydrocarbon substituent.     

Synthesis and crystal structure ofN,N′-DicyclohexylpiperazineN,N′-dioxide octahydrate

N,N-DicyclohexylpiperazineN,N-dioxide octahydrate, C₁₆H₄₆N₂O₁₀,M _r=426.55, monoclinic, space groupC2/m (No. 12),a=12.961(4),b=11.533(4),c=7.907(1) Å, =98.37(2)^o,V=1169.3(6) ų,Z=2. The structure was solved by the direct method and refined toR=0.045 for 1192 observed MoK reflections. TheN,N-dioxide molecule occupies a site of symmetry 2/m. The piperazine ring takes the chair form with the two N–O bonds oriented axially in atrans configuration. Hydrogen bonding between the water molecules, as well as between theN-oxide groups and water molecules, gives rise to a puckered layer composed of edge-sharing four-membered, five-membered, six-membered, and eight-membered rings. Adjacent layers are cross-linked by theN,N-dicyclohexylpiperazine moieties lying between them, thereby generating a sandwich structure consolidated by covalent and hydrogen bonding. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82062 (8 pages).     

Supramolecular Assembly Formation in Monolayers of tert-Butyl Substituted Copper Phthalocyanine and Tetrabenzotriazaporphin

The effect is studied of the layer formation conditions on the molecular arrangement of copper tetra- tert-butyl phthalocyanine (CuPctBu₄) and copper tetra- tert-butyl tetrabenzotriazaporphin (CuThptBu₄) at the air–water interface. The decrease in initial surface concentration of these compounds is shown to affect the molecular orientation, as indicated by the increase in the area per molecule. The data are interpreted in terms of formation of CuPctBu₄ and CuThptBu₄ monolayers with a face-on molecular arrangement when the initial surface concentration is sufficiently small (N less than 1.6 × 10^–7 mole/m² for CuPctBu₄ and N less than 4 × 10^–7 mole/m² for CuThptBu₄) and changes in the molecular orientation to edge-on when the N values are higher. It is emphasized that the edge-on orientation on the water surface is not only a molecular but a collective property of the azaporphyrine supramolecular assembly.     

The dependence of build-up233U,232U,233Pa and fission products from ThO2 irradiated in HFETR on integral thermal neutron fluxes and neutron spectra

In this paper the dependence of build-up²³³U,²³²U,²³³Pa and fission products from ThO₂ irradiated in HFETR on integral thermal neutron fluxes and neutron spectra have been investigated. The yields of all above nuclides in ThO₂ increase with the increase of integral thermal neutron fluxes at different neutron spectra. The values of²³³U/²³²Th increase with the increases of _th and decreases with the increase of fast/thermal neutron ratios (_f/_th). The values of²³²U/²³³U increase with the increase of both _th and _f/_th ratio. The amount of fission products relative to original irradiated thorium decreases with the increase of _f/_th ratios. These results could be used to evaluate the behaviour of thorium-based nuclear fuel in reactor.     

Kinetic studies on the formation of ternary complexes in the reaction of diaquonitrilotriacetatonickelate(II) with amino acids in aqueous solution

Summary Kinetics of formation of ternary complexes in the reaction of Ni(NTA)(H₂O) ₂ ^– with several amino acids, LH^± (glycine, -alanine, -alanine, L-valine and L-phenylalanine) have been studied by a pH indicator method using stopped-flow spectrophotometry. The results conform to 1/k_obs = 1/k + [H⁺]/ kKT_L where K is the equilibrium constant for formation of Ni(NTA)(–L)(H₂O)^2–, and k is the specific rate constant for the subsequent rate-determining ring-closure step leading to Ni(NTA)(=L)^2–. For the different amino acids studied, the k values decrease in the sequence: glycine > -alanine > L-phenylalanine > L-valine > -alanine. These k values areca. 1000 times lower than the values for complexation of Ni(NTA)(H₂O) ₂ ^– with NH₃ and imidazole and the spread in k values is much less than the pK_a values of the amino acids. The relative rates are enthalpy controlled and the S values are highly negative in conformity with ring closure as the rate determining step.     

Vibrational spectra and structure of 4-amino-1H-quinazolin-2-one 3-oxide

On the basis of a study of the vibrational spectra in the solid state of the product of the reaction of 2-cyanophenyl isocyanate with hydroxylamine and its isotopic analogs (¹⁵N O and ¹⁵NH₂) it was demonstrated that the compound obtained has the 4-amino-1H-quinazolin-2-one 3-oxide structure.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 968–972, July, 1981.     

Plutonium-244 and strange xenon components in the solar system

A number of strange xenon components have been reported in the literature during the past three decades; for example, AVCC (average carbonaceous chondrite), CCF (carbonaceous chondrite fission) xenon, xenon-X, xenon-H, xenon-L, xenon-S, xenon-U, SUCOR (surface correlated xenon), BEOC (Bern Oberflächen-Correliert) xenon, and so on. It is often assumed that they reprsent the isotopic compositions of more or less pure or primordial components of xenon. If one attempts to interpret the existing xenon isotope data for meteorites and lunar samples, assuming that they are pure or primordial, however, one encounters all sorts of problems and no coherent theory concerning the variation of the isotopic composition of xenon in the solar system emerges. We have therefore re-examined over 4,000 sets of existing xenon isotope data for meteorites and lunar samples. The results indicate that these strange xenon components are mixtures of²⁴⁴Pu fission xenon and atmospheric xenon, whose isotopic compositions have been altered by the processes of a) mass-fractionation, b) spallation and c) neutron-capture reactions.     

Diffusion of linear aliphatic esters in polyethylene as a function of chain length of the esters,pressure and temperature

Diffusion of linear aliphatic mono- and diesters (C _N ) havingN main chain atoms (N=13–68) in bulk medium-density polyethylene (MDPE) has been studied under hydrostatic pressures up to 2500 bar at temperatures between 60°C and 125°C. Three triglycerides, phenyl stearate, and p-aminoazobenzene (pAAB, 80°C) as the diffusants and low-density (LDPE) and high-density (HDPE) polyethylenes as polyethylene substrate were used for comparison. Diffusion coefficientD was determined from concentration distribution of the diffusants through stacked PE sheets as substrate. Regarding the linear esters at 90°C, the relationshipD N holds at constant pressures. Under the atmospheric pressure, became –2.10 in accordance with de Gennes's proposal (1971)D N ^–2 as well as with the experimental results reported by Klein and Briscoe (1979) forN larger than 30.D's for the glycerides deviate from the relationshipD N ^–2 toward the smaller values by comparison at the sameN. The exponent is pressure-dependent. It decreases with increasing pressure according to =–2.10–0.000942P, whereP is measured by the unit of bar. Plots of lnD vsP for all the diffusants show linear relationships with negative slopes, from which activation volume for the diffusion V was calculated. At 90°C, V increases slowly with increasingN and increasingV _Ki, the intrinsic molecular volume of the diffusant, from 39.3 cm³/mol for ethyl caprate (C ₁₃,V _Ki=136 cm³/mol) to 76.8 cm³/mol for behenyl behenate (C₄₅,V _Ki=466 cm³/mol). Observed V s are explainable on the basis of the reptation mode of the chain molecule diffusion. V s for C₂₅ and C₄₅ are found to increase with increasing degree of crystallinity where MDPE, heat-treated MDPE, LDPE, and HDPE were used. The results obtained by varying temperature are as follows. V for C₄₅ was always found to be larger than C₂₅. Both decreased linearly with increasing temperature, giving two linear lines with different slopes whose extensions intersected at 132°C, the melting point of the MDPE, where the difference in V disappeared. The apparent activation energiesE _Ds for the diffusion of C₂₅ and C₄₅ increased linearly with increasing pressure, whose slopes are explainable according toE _D=E ₀+PV [1-(dln V /dlnT) _P ].     

The energy of the N→O bond in 3-nitroisoxazoline N-oxide

The enthalpy of combustion of 3-nitroisoxazoline has been determined as H _c ^298.15 =–414±0.3 kcal/mole and that of 3-nitroisoxazoline N-oxide as H _c ^298.15 =–406.6±0.5 kcal/mole. From the values for the heats of combustion and evaporation, the standard enthalpies of formation have been calculated and the energy of the NO bond has been evaluated at 64±3 kcal/mole.     

ESR spin-trapping study of the radicals produced in the photochemical reaction of Cr, Mo, W hexacarbonyls with carbon tetrachloride

The effect of UV and visible light on the catalytic reaction has been investigated in the systems containing Cr, Mo and W hexacarbonyls, nitrone and nitroso type of spin-traps in carbon tetrachloride. Under these reaction conditions not only radical CCl ₃ ^. but also dialkyl-, diphenyl- and acyl-phenylnitroxides have been trapped.

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, Cr, Mo W, . CCl ₃ ^. , , .

     

Kinetics and mechanism of aquation of [Cr(NCS)(edtrp)]-, [Cr(NCS)(R-pdtrp)]-, [Cr(edtrp)(NCSHg)]+ and [Cr(R-pdtrp) (NCSHg)]+ complexes. Unexpected rate retardation in strongly acidic media for NCS- ligand release

Three new complex ions, [Cr(NCS)(R-pdtrp)]^-, [Cr(R-pdtrp)(NCSHg)]⁺ and [Cr(edtrp)(NCSHg)]⁺, that are derivatives of the trans-equatorial isomers of [Cr(R-pdtrp)(H₂O)]⁰ and [Cr(edtrp)(H₂O)]⁰ (edtrp= ethylenediamine-N,N,N-tripropionate, R-pdtrp= R-propane-1,2-diamine-N,N,N-tripropionate) have been obtained and characterized in solution. Rate constants and activation parameters, including, in two cases, volumes of activation, have been determined. Rate retardation for NCS^- ligand release has been observed with increasing acidity within the pH 0–2 range. The mechanism of the reactions has been discussed.     

Error of Atomic Charges Derived from Electrostatic Potential

The purpose of this article is to show that CHELP, CHELPG, and Merz and Kollman undergo error for the charge on atoms of HCOO^– (H₂O) _n for n = 1 6. We also demonstrate that the CHELP, CHELPG, and Merz and Kollman show error for the tendency toward change in the charges on carbons for CH₃NH⁺ ₃ (CH₃)₂NH⁺ ₂ (CH₃)₃NH⁺ (CH₃)₄N⁺.     

Absorption spectra and bond type in Co(II) aquoamino complexes

Absorption spectra are reported for solutions containing Co(II) and ammonia. Spectra are calculated for five Co(II) aquoamino complexes. The spectra are used to determine Dq and B, parameters of the bonds in these compounds. It is found that Dq and B change nonlinearly and nonadditively. The parameters _c, Dt, Ds, and have also been established for [Co(H₂O)₆]²⁺ and [Co(NH₃)₆]²⁺. The parameter variation can be explained if the H₂O molecules form weaker bonds to the central atom than do the NH₃ molecules, but are capable of d-p interaction.