Monthly sea surface temperature records reconstructed by δ~(18)O of reef-building coral in the east of Hainan Island, South China Sea

Stable oxygen isotopic compositions of a coral colony of Porites lutea obtained on acore allowed the reconstruction of a 56-a (1943-1998) proxy record of the sea surface tempera-tures. This coral δ~(18)O data are from the east of Hainan Island water (22°20＇N, 110°39＇E), SouthChina Sea. The relationship between δ~(18)O in the skeletal aragonite carbonate and the sea surfacetemperature (SST) is SST=-5.36 δ~(18)O_(PDB)-3.51 (r=0.73, n=470), dδ~(18)O/d(SST)=-0.187‰/℃; and the thermometer was set at monthly resolution. The 56-a (1943-1998) proxy record of thesea surface temperatures reflected the same change trend in the northern part of South China Seaas the air temperature change trend in China.     

Variation of <Superscript>231</Superscript>Pa, <Superscript>230</Superscript>Th and <Superscript>231</Superscript>Pa<Subscript>ex</Subscript>/<Superscript>230</Superscript>Th<Subscript>ex</Subscript> in surface sediments of the Sabah–Sarawak coastal waters

Protactinium and thorium activities were measured in eight surface sediment taken in 2004 to determine effectiveness scavenging of ²³¹Pa at Sabah–Sarawak coastal waters. The result found that activity ratios of ²³¹Pa_ex/²³⁰Th_ex were ranged from 0.07 to 0.13 at all sampling stations. The high ²³¹Pa_ex/²³⁰Th_ex activity ratio than the production ratio of 0.093 in seawater at station SR 01, SR 02, SR 04, SB 02 and SB 05, revealed that ²³¹Pa is effectively removed from the water column into the sediment in comparison with ²³⁰Th at those stations. Low percentage of ²³⁰Th_ex (90–95%) in comparison with ²³¹Pa_ex at all stations can be attributed to less efficiently scavenged of ²³⁰Th onto particles prior deposited at the marine sediment bed.     

Short-lived <Superscript>224</Superscript>Ra and <Superscript>223</Superscript>Ra isotopes in the Anadyr River–Bering Sea system

The first results of activity measurement of short-lived radium isotopes dissolved in water in the Anadyr River–Bering Sea transit system are presented. The trends of the radionuclide behavior after passage through high-gradient river–coastal sea water mixing zone were identified and the exchange rate of the horizontal mixing was determined. The ²²⁴Ra/²²³Ra activity ratio was used to construct the “radium age” model, which served for estimating the residence time of brackish water in the Anadyr River estuary. The factors affecting this value were elucidated.     

A study of the hydrolysis of ZrF<Stack><Subscript>6</Subscript><Superscript>2−</Superscript></Stack> and the structure of intermediate hydrolysis products by <Superscript>19</Superscript>F and <Superscript>91</Superscript>Zr NMR in the 9.4 T field

The high-field ¹⁹F and ⁹¹Zr NMR method is used to study the hydrolysis and polycondensation of hexafluorozirconate ZrF₆²⁻ in aqueous and water-peroxide solutions. During hydrolysis in aqueous solutions only ZrF₆²⁻ and F⁻ ions were observed by NMR, however, in the water-peroxide medium, an intermediate product of hydrolysis ([F₅Zr-OO-ZrF₅]⁴⁻ dimer) was detected. The dimer structure is confirmed by ¹⁹F and ⁹¹Zr NMR. In high fields (¹⁹F NMR frequency > 200 MHz), the fluorine exchange between ZrF₆²⁻ and F⁻ is slow in the ¹⁹F NMR scale and has a multisite character.     

Experimental Determination of the Isotherm at 15°C of the System Mg<Superscript>2+</Superscript>/Cl<Superscript>−</Superscript>, SO<Subscript>4</Subscript><Superscript>2</Superscript>–H<Subscript>2</Subscript>O

Summary.  The diagram of the ternary system Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O was established at 15°C by means of analytical and conductimetric measurements. Three compounds were found in this diagram, which are MgSO₄·6H₂O, MgSO₄·7H₂O, and MgCl₂·6H₂O. The solubility field of MgSO₄·7H₂O is important whereas those of MgSO₄·6H₂O and MgCl₂·6H₂O are small. The compositions (mass-%) of the two invariant points determined by the two methods are: MgSO₄:MgCl₂=2.73:33.80 and MgSO₄: MgCl₂=3.38:28.91. Both the measured and the calculated isotherm at 15°C have been used for modelling of the diagram Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O between 0 and 35°C. The polythermal invariant point was approximately located between 15 and 10°C.  Corresponding author. E-mail: ariguib@planet.tn Received October 16, 2002; accepted (revised) December 3, 2002 Published online April 24, 2003 RID="a" ID="a" Dedicated to Prof. Dr. Heinz Gamsj?ger on the occasion of his 70^th birthday     

Cyclopropanol intermediates in the synthesis of the C<Superscript>5</Superscript>–C<Superscript>14</Superscript> fragment of laulimalides

Two novel schemes have been developed for the synthesis of the C⁵–C¹⁴ fragment of the macrocyclic antitumor drug laulimalide and its analogs via transformations of cyclopropanol intermediates.     

Theoretical evaluation of the radiative lifetimes of LiCs and NaCs in the A<Superscript>1</Superscript>Σ<Superscript>+</Superscript> state

Calculations of the adiabatic potential energy curves and the transition dipole moments between the ground (A¹Σ⁺) and the first excited (A¹Σ⁺) states have been determined for the LiCs and NaCs molecules. The calculations are performed using an ab initio approach based on non-empirical pseudopotentials for Cs⁺, Li⁺ and Na⁺ cores, parameterized l-dependent polarization potentials and full configuration interaction calculations. The potential energy curves and the transition dipole moment are used to estimate the radiative lifetimes of the vibrational levels of the A⁺Σ⁺ state using the Franck–Condon (FC) approximation and the approximate sum rule method. The radiative lifetimes associated with the A⁺Σ⁺ state are presented here for the first time. These data can help experimentalists to optimize photoassociative formation of ultracold molecules and their longevity in a trap or in an optical lattice.     

Production possibility of <Superscript>186</Superscript>Re via the <Superscript>192</Superscript>Os(p,α3n)<Superscript>186</Superscript>Re nuclear reaction

Experimentally measured cross-sections are presented for the first time for the ¹⁹²Os(p,α3n)¹⁸⁶Re nuclear reaction up to 67 MeV. Highly enriched thin ¹⁹²Os targets (15 pcs), prepared by electro-deposition onto Cu backings, were irradiated with an external proton beam delivered by the SSC cyclotron of iThemba LABS. The excitation function curve of the ¹⁹²Os(p,α3n)¹⁸⁶Re reaction shows a maximum cross-section of ~82 mb at about 24 MeV. According to the yield calculations based on the present results, the available cumulative no-carrier-added ¹⁸⁶Re yield is 7.76 MBq/μAh (0.21 mCi/μAh) over the energy region 13.4 → 27.3 MeV.     

Photochemistry of the IrCl<Subscript>6</Subscript><Superscript>2−</Superscript> complex in aqueous solutions in the presence of the bromide anions

Laser flash photolysis (308 nm) was applied to study photochemistry of the IrCl₆ ²⁻ complex in aqueous solutions in the presence of the Br⁻ anions. The formation of the Br₂ ^·− radical anions in the reaction between the Br⁻ ion and secondary radical pair formed after the photon absorption by the initial complex was observed. The Br₂ ^·− radical anions decay both in recombination and in the reaction with the initial IrCl₆ ²⁻ complex.     

Pulse radiolysis study of the oxidation of the I<Superscript>−</Superscript> ions with the radical anions Br<Subscript>2</Subscript><Superscript>·−</Superscript> in an aqueous solution: formation and properties of the radical anion BrI<Superscript>·−</Superscript>

The radiation chemical redox transformations in solutions of bromides in the presence of minor additives of iodides were studied by pulse radiolysis. The change in the concentrations of the Br⁻ and I⁻ ions changes the ratio of the formed short-lived radical anions Br₂ ^·−, BrI^·−, and I₂ ^·−. The spectrum of the mixed radical anion BrI^·− contains a broad optical band at 370 nm with ɛ₃₇₀ = 9650 L mol⁻¹ cm⁻¹. The reduction potential of the BrI^·−/Br⁻, I⁻ pair is 1.25 V. The rate constants for the forward and backward reactions Br₂ ^·− + I⁻ ⇌ BrI^·− + Br⁻ are k _f = 4.3·10⁹ and k _r = 1.0·10⁵ L mol⁻¹ s⁻¹, respectively; for the reactions BrI^·− ⇌ Br⁻ + I^·, k _f = 5.7·10⁸ s⁻¹ and k _r = 1.0·10¹⁰ L mol⁻¹ s⁻¹. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1787–1792, September, 2008.     

Stabilization of [Sc(NCS)<Subscript>6</Subscript>]<Superscript>3−</Superscript> anion by [M(18C6)]<Superscript>+</Superscript> complexes in solvation systems

The [M(18C6)]₄[Sc(NCS)₆]Cl · nH₂O complexes were established to form in the solutions ScCl _x -Solv-MNCS-18C6, where Solv is ethanol, THF, acetonitrile, or isopropyl alcohol; M = Na, K; 18C6 is 1,4,7,10,13,16-hexaoxocyclooctadecane. X-ray diffraction analysis of [K(18K6)]₄[Sc(NCS)₆]Cl · 3.33H₂O showed that the thiocyanate ion was coordinated by Sc through the N atom. The structure consists of octahedral Sc(NCS) ₆ ^3? that are united via nonvalent K-S interaction with macrocyclic dimers [M(18C6)]₂ into chains. Each 18C6 molecule coordinates one K atom.     

Optimization of the labeling yield by determination of the Cu<Superscript>+</Superscript>–acetonitrile complex constant in Cu<Superscript>+</Superscript>-catalyzed nucleophilic exchange reactions in mixed solvent conditions

To apply the Cu⁺-assisted nucleophilic exchange based radioiodination of aromatic compounds for more lipophilic compounds the reaction is carried out in mixed solvent conditions. Due to its physicochemical properties acetonitrile is an attractive solvent. Although acetonitrile forms complexes with Cu⁺ decreasing the labeling yield. This article describes a method for the determination of the complex constant at labeling temperature based on a Lineweaver–Burk approach, relating the reaction rate constant and the concentration of precursor in presence of different amounts of acetonitrile. The method also allows to calculate the adjusted amount of copper salt in order to obtain the same high labeling yield as obtained in absence of acetonitrile.     

Counterion effects on the isotopic properties of the Cl<Superscript>−</Superscript> and Li<Superscript>+</Superscript> ions in aqueous solutions

The reduced partition function ratios between isotopic forms (β-factors) were calculated by the ab initio RHF/6-311++G**(3df, 3p) and MP2/6-311++G**(3df, 3p) quantum-chemical methods for hydrated chloride ion and ion pair hydrates NaCl·nH₂O and LiOH · nH₂O. The influence of the Na⁺ cation on the β-factor value and the chlorine isotope separation factor in the precipitation of NaCl from concentrated aqueous solutions was found to be substantial. At the same time, the presence of OH^? counterions had no noticeable effect on the β-factor of the hydrated Li⁺ cation.     

Stereo-dynamics study of O + HCl → OH + Cl reaction on the <Superscript>3</Superscript>A″, <Superscript>3</Superscript>A′, and <Superscript>1</Superscript>A′ states

Using three accurate potential energy surfaces of the ³A″, ³A′, and ¹A′ states constructed recently, we present a quasi-classical trajectory (QCT) calculation for O + HCl (v = 0, j = 0) → OH + Cl reaction at the collision energies (E _col) of 14.0–20.0 kcal/mol. The three angular distribution functions—P(q_r ) P(\theta_{r} ) , P(j_r ) P(\varphi_{r} ) , and P(q_r ,j_r ) P(\theta_{r} ,\varphi_{r} ) , together with the four commonly used polarization-dependent differential cross-sections, \frac2ps \fracds₀₀ dw_t , \frac2ps \fracds₂₀ dw_t , \frac2ps \fracds_{22 +} dw_t , \textand \frac2ps \fracds_{21 -} dw_t {\frac{2\pi }{\sigma }}\,{\frac{{d\sigma_{00} }}{{d\omega_{t} }}},\,{\frac{2\pi }{\sigma }}\,{\frac{{d\sigma_{20} }}{{d\omega_{t} }}},\,{\frac{2\pi }{\sigma }}\,{\frac{{d\sigma_{22 + } }}{{d\omega_{t} }}},\,{\text{and}}\,{\frac{2\pi }{\sigma }}\,{\frac{{d\sigma_{21 - } }}{{d\omega_{t} }}} are exhibited to get an insight into the alignment and the orientation of the product OH radical. There is a similar behavior of the tendency scattering direction for the two triplet electronic states (³A″ and ³A′)—backward scattering dominates, however, forward scattering prevails for the case of ¹A′ state. Also, obvious differences have been found in the stereo-dynamical information, which reveals the influences of the potential energy surface and the collision energy. The degrees of polarization and the influence of the collision energy on the stereo-dynamics characters of the title reaction are both demonstrated in the order of ³A′ > ³A″ > ¹A′.     

Chemical Bonding in the Complexes XeF<Stack><Subscript>5</Subscript><Superscript>+</Superscript></Stack>XF<Stack><Subscript>6</Subscript><Superscript>−</Superscript></Stack> (X = P,As, Sb,and Bi)

Ab initio quantum-chemical calculations of the complexes XeF ₅ ⁺ XF ₆ ^? (X = P, As, Sb, and Bi) were performed with the use of relativistic pseudopotentials for heavy atoms and full-electron basis sets. The chemical bonds were characterized by the parameters of critical points (electron density, its Laplacian, total electron energy, and its kinetic and potential components). It was demonstrated that the interaction between the XeF ₅ ⁺ cation and the XF ₆ ^? anion in XeF ₅ ⁺ XF ₆ ^? follows a key-lock scheme involving directed interactions of bridging fluorine atoms F_b → Xe and that the structuring function of the lone electron pair of the Xe atom is to compensate the destabilizing electrostatic interaction between the Xe and X atoms bearing excess positive charges.     

Yb<Superscript>3+</Superscript> → Er<Superscript>3+</Superscript> energy transfer in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and temperature characteristic of near-infrared photoluminescence

For the Er³⁺–Yb³⁺ codoped Al₂O₃ powders, the strong near-infrared photoluminescence (PL) centered at 1.535 μm derived from the energy transfer (ET) from Yb³⁺ to Er³⁺ was detected by a 978 nm laser diode excitation. Compared with that of Er³⁺ doped Al₂O₃ powders, the PL intensity enhanced about 9 times, the full width at half maximum (FWHM) extended from 82 to 90 nm, and the lifetime increased from 3.22 to 4.17 ms for Er³⁺–Yb³⁺ codoped Al₂O₃ powders at room temperature. The ET coefficient of 2.18 × 10⁻¹⁸ cm³ s⁻¹ from Yb³⁺ to Er³⁺ was obtained based on the rate equations. The decrease of PL intensity with increasing temperature in the range of 298–733 K was observed, due to thermally enhanced nonradiative relaxation ⁴I_13/2 → ⁴I_15/2 dominated over thermally enhanced phonon-assisted ET in the Er³⁺–Yb³⁺ codoped Al₂O₃.     

Diffusions of β-cyclodextrins in mucus studied by <Superscript>19</Superscript>F diffusion NMR

β-Cyclodextrin (β-CD) based materials have been widely used as drug carriers for pharmaceutical applications. To understand the diffusion of β-CDs in mucus is important for selecting β-CD based drug carriers for applications targeting mucosal absorption because the surfaces of many biological membranes are covered with a highly viscous aqueous mucus layer which forms relatively effective diffusion barriers for drugs. In this study, ¹⁹F self-diffusion NMR technique has been applied to study the self-diffusions of β-CDs in mucus. The ¹⁹F NMR signals arose from 1-fluoroadamantane molecules entrapped in the cavities of β-CDs. The diffusive abilities of different β-CDs in mucus were assessed through analyzing the diffusion coefficients using the presented kinetic model, and Ogston’s and Renkin’s diffusion models for hydrogel systems. The kinetic results show that 2-hydroxypropyl-β-CD and 2-Carboxyethyl-β-CD have the smallest binding affinities to bovine submaxillary mucin and human nasal mucin among five tested β-CDs. The mesh sizes of the bovine submaxillary mucus at different concentrations and that of the human nasal mucus were evaluated using the diffusion models. We hope that this ¹⁹F diffusion method will be useful to study the diffusion of β-CD based materials in other biological systems.     

Separation of phosphorous by liquid–liquid extraction for the measurement of <Superscript>32</Superscript>P

Phosphorous containing radioisotope waste was separated and determined by liquid–liquid extraction method through liquid scintillation counter (LSC). In this process, ammonium phosphate was converted to phosphomolybdate (PMo) by the reaction of ammonium molybdate (Mo) in HCl solution (0.02 M) and maximum UV/VIS absorbance (λ_max) 218 nm was observed. The PMo solution was extracted with TOA (Tri-n-Octylamine)/xylene mixture and λ_max 290 nm was found for this organic layer. Absorbance of aqueous and organic layer was linear through concentration. The impurities such as Co, Cr, Gd, etc. remain in aqueous layer by treating with Mo which was determined by ICP-AES and AAS. The quenching correction curve for ³²P was calculated using LSC results. No counting change was observed as the volume of quenchers increased. The recovery was 98% and 81% for the extraction and separation process from the test using H₃³²PO₄ as standard tracer.     

Molecular dynamics of ≡SiOC<Superscript>·</Superscript>O radicals “grafted” onto the Aerosil surface in adsorption layers of carbon dioxide

As the formation of adsorption layers of carbon dioxide on the Aerosil surface proceeds, the character of rotational mobility of grafted radicals SiOC^·O changes from the anisotropic Brownian motion in vacuo to Brownian motion in a potential of 1.7–1.9 kcal mol^–1. The SiOC^·O radicals were proposed for use as probes to study the dynamic characteristics of adsorbates on the Aerosil surface.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2573–2578, December, 2004.