Synthesis of L-tryptophan labeled with hydrogen isotopes in the indole ring

The isotopomers of L-tryptophan (L-Trp) labeled with hydrogen isotopes in the indole ring were obtained by isotope exchange method. Heavy and tritiated water were used as the sources of stable and radioactive label. Three isotopomers, i.e., [4′-²H]-L-Trp, [4′-³H]-L-Trp, and doubly labeled [4′-²H/³H]-L-Trp were synthesized by isotope exchange enhanced by irradiation with a mercury discharge lamp. The indole whole ring labeled isotopomers, i.e., [2′,4′,5′,6′,7′-²H₅]-L-, [2′,4′,5′,6′,7′-³H₅]-L-, and doubly labeled [2′,4′,5′,6′,7′-²H/³H]-L-Trp were synthesized by isotope exchange between L-Trp and D₂O or DTO in the presence of deuteriated trifluoroacetic acid.     

Radiochemical scheme for the quantitative isolation and gamma-spectrometric determination of La,Ga, Hf and Sc in neutron activation analysis of refractory materials

A new radiochemical scheme for the quantitative isolation of Ga, Sc, Hf and La, based on ion exchange and extraction chromatography, was devised, Ga and Sc were selectively retained on a Dowex 50WX2 [H⁺] column from 10 M HBr at 50°C. Ga was then eluted with ethyl acetate 0.25M in HBr, and scandium with 4M HBr. Hf was separated from 10M HBr at 75°C on a Kel-F column impregnated with tri-n-octylphosphine oxide (TOPO). The lanthamm fraction, after evaporation to dryness, was purified by ion-exchange chromatography in the system: Dowex 50WX8 [H⁺]−HCl. The effect of accompanying elements, and also the differences in the mechanism of uptake by the resin of various elements from concentrated HBr solution are briefly discussed. The scheme has been used for the determination of these four elements in refractory materials by activation analysis. As this procedure assured practically quantitative isolation of Ga, Sc, Hf and La, the addition of carriers and determination of chemical yield were unnecessary. The radiochemical purities of the respective fractions were as a rule high, and the measurements were performed by NaI(Tl) spectrometry. The detection limits were of the order of fractions of ppm, and could be considerably improved if necessary by increasing the counting time and sample weight.     

Separation and Removal of Mercury(II) from Water Samples Using (Acetylacetone)‐2‐Thiol‐Phenyleneimine Immobilized on Anion‐Exchange Resin Prior to Determination by Cold Vapor Inductively Coupled Plasma Atomic Emission Spectroscopy

Abstract

(Acetylacetone)‐2‐thiol‐phenyleneimine (H₂L) immobilized on an anion‐exchange resin (Dowex) was used for separation and removal of mercury from natural water samples and for preconcentration prior to its determination by cold vapor inductively coupled plasma atomic emission spectroscopy. The metal was eluted from the column using a solution of 10% thiourea in 0.1 M HCl. The modified resin is higly selective with an exchange capacity of 1.60 mmol g^?1. Various parameters like pH, column flow rate, and desorbing agents are optimized. The proposed method has a linear calibration range of 15–1000 ng/ml Hg(II), with a relative standard deviation at the 15 ng/ml level of 3.5%. The precision of the method (evaluated as the relative standard deviation obtained after analyzing six series of five replicates) was ±4.2% at the 50 ng/ml level of Hg(II). The method has been used for routine determination of trace levels of mercury species in natural waters. The potential application of modified resin for the removal of mercury(II) from two natural water samples (top water and lake water) spiked with 50 ng/ml of mercury (II) was studied by ICP‐AES, and the results proved that excellent percent extraction of mercury(II) from both natural water samples was obtained by column method using modified resin.     

Coordination of Alkaline Earth Metal Ions in the Inverted Cucurbit[7]uril Supramolecular Assemblies Formed in the Presence of [ZnCl4]2− and [CdCl4]2−

A convenient method to isolate inverted cucurbit[7]uril (iQ[7]) from a mixture of water‐soluble Q[n]s was established by eluting the soluble mixture of Q[n]s on a Dowex (H⁺ form) column so that iQ[7] could be selected as a ligand for coordination and supramolecular assembly with alkaline earth cations (AE²⁺) in aqueous HCl solutions in the presence of [ZnCl₄]^2? and [CdCl₄]^2? anions as structure‐directing agents. Single‐crystal X‐ray diffraction analysis revealed that both iQ[7]–AE²⁺–[ZnCl₄]^2?–HCl and iQ[7]–AE²⁺–[CdCl₄]^2?–HCl interaction systems yielded supramolecular assemblies, in which the [ZnCl₄]^2? and [CdCl₄]^2? anions presented a honeycomb effect, and this resulted in the formation of linear iQ[7]/AE²⁺ coordination polymers through outer‐surface interactions of Q[n]s.     

Determination of uranium, thorium, and 20 other elements in high-purity tungsten by radiochemical neutron activation analysis

A radiochemical neutron activation analysis method for the determination of 22 elements in high-purity tungsten has been developed. For the assay of indicator radionuclides with long half-lives, the radiochemical separation was performed from HF/H₂O₂, HF/NH₄F and HCl/H₂SO₄ media by a combination of cation and anion exchange on a Dowex 50 W × 8 and Dowex 1 × 8 column. An effective removal of the matrix-produced radionuclides of W and Re was achieved. U was determined via ¹⁴⁰La, the daughter nuclide of the fission product ¹⁴⁰Ba. Limits of detection of 2 ng/g for U and 0.02 ng/g for Th can be achieved. For the other elements, the limits of detection are between 0.004 ng/g (Sc) and 200 ng/g (Sr). The elements Hf, Ta and Sb could be determined by instrumental neutron activation analysis. This method was applied to the analysis of two tungsten powder samples of different purity grade. The results and limits of detection are compared with those of other methods.     

Bis(N,N′‐dimethylimidazol‐2‐yl­idene)mercury chlorotriiodo­mercury dimethyl sulfoxide solvate

The double mercury salt [Hg(C₅H₈N₂)₂][HgClI₃]·C₂H₆OS was prepared and its structure characterized. The [Hg(C₅H₈N₂)₂]²⁺ cation lies about an inversion centre and the [HgClI₃]^2? anion lies on a mirror plane. Cations and anions are linked to form a one‐dimensional polymer by weak Hg?Cl interactions [Hg?Cl 3.3744 (3) Å]. The mercury–carbene bond distance [2.076 (7) Å] is typical of a dicationic mercury–carbene species.     

Efficient Synthesis and Properties of Single‐Crystalline [SnTe4]4− Salts

Single‐crystalline K⁺, Rb⁺, and Cs⁺ salts of the ortho‐tellurostannate anion have been prepared by a very efficient fusing/extraction/evaporation method. The resulting compounds with the general composition [A₄(H₂O)_n][SnTe₄] can be transferred into mixed H₂O/en solvates by solving the hydrates in 1,2‐diaminoethane (en) and ensuing layering by toluene. A mixed Rb⁺/Ba²⁺ salt results from a partial cation exchange of the Rb⁺ hydrate phase in solution. All hydrates react to polytellurides when exposed to air and represent useful starting materials for the synthesis of transition metal complexes with [SnTe₄]^4? groups as binary main group elemental ligands. [K₄(H₂O)_0.5][SnTe₄] ( 1 ), [Rb₄(H₂O)₂][SnTe₄] ( 2 ), [Cs₄(H₂O)₂][SnTe₄] ( 3 ), [K₄(H₂O)(en)][SnTe₄] ( 4 ), [Rb₄(H₂O)_0.67(en)_0.33][SnTe₄] ( 5 ), [Cs₄(H₂O)_0.5(en)_0.5][SnTe₄] ( 6 ), and [Rb₂Ba(H₂O)₁₁][SnTe₄] ( 7 ) were characterized by means of X‐ray diffractometry and optical absorption spectroscopy.     

Water exchange rates and mechanisms in tetrahedral [Be(H2O)4]2+ and [Li(H2O)4]+ complexes using DFT methods and cluster‐continuum models

The water exchange reactions in aquated Li⁺ and Be²⁺ ions were investigated with density functional theory calculations performed using the [Li(H₂O)₄]⁺·14H₂O and [Be(H₂O)₄]²⁺·8H₂O systems and a cluster‐continuum approach. A range of commonly used functionals predict water exchange rates several orders of magnitude lower than the experimental ones. This effect is attributed to the overstabilization of coordination number four by these functionals with respect to the five‐coordinated transition states responsible for the associative ( A ) or associative interchange ( I_a ) water exchange mechanisms. However, the M06 and M062X functionals provide results in good agreement with the experimental data: M062X/TZVP calculations yield a concerted I_a mechanism for the water exchange in [Be(H₂O)₄]²⁺·8H₂O that gives an average residence time of water molecules in the first coordination sphere of 260 μs. For [Li(H₂O)₄]⁺·14H₂O the water exchange reaction is predicted to follow an A mechanism with a residence time of inner‐sphere water molecules of 25 ps.     

Alkali Metal/Ammonia Reductions of Ketones Should Be Run in the Presence of Ammonium Ion

Reduction of (+)-[3,3?²H₂]camphor ([3,3?²H₂] 1 ) with lithium, sodium or potassium in ammonia and a co-solvent gave; 1) the enolate of [3,3?²H₂] 1 and the alcoholates of (?)-[2,3,3?²H₃]isoborneol ([2,3,3?²H₃] and (+)-[2,3,3?²H₃]borneol ([2,3,3?²H₃] 3 ); 2) the alcoholates of [3,3?²H₂] 2 and [3,3?²H₂] 3 ; 3) the dialcoholates of the pinacols [3,3,3′,3′?²H₄] 4 and [3,3,3′,3′?²H₄] 5 . It is proposed that these are formed from the ketyls [3,3?²H₂] 1 - M⁺, by: 1) disproportionation; 2) H-atom abstraction from the medium; 3) dimerization. Protonation upon work-up afforded [endo?3²H] 1 , [2,3,3?²H₃] 2 , [2,3,3?²H₃] 3 ,[3,3?²H₂] 2 , [3,3?²H₂] 3 , [3,3,3′,3′?²H₄] 4 and [3,3,3′,3′?²H₄] 5 . Pinacol [3,3,3′,3′?²H₄] 5 was the main and pinacol [3,3,3′,3′?²H₄] 4 a minor product in the reductions with lithium and both were minor products in the reductions with sodium; pinacols were not formed in the reductions with potassium. Parallel reductions of 1 , unlabeled, analogously led to 2 , 3 , 4 and 5 , and the ratios 2/3 differed from the ratios ([2,3,3?²H₃] 2 +[3,3?²H₂] 2 /([2,3,3?²H₃]+[3,3?²H₂] 3 ) under certain conditions. Different values for these ratios were found in the reductions with each metal, all of which corresponded to low overall diastereoselectivities. Reactions 1 and 3 persisted when the reductions were carried out in ammonia/water/co-solvent mixtures and the enolate formed via reaction 1 was protonated and the resulting [endo-3-²H] 1 recycled. Reaction 2 cannot be monitored under these conditions. Reactions 1 and 3, and by inference also reaction 2, were almost completely suppressed when analogous reductions were carried out in the presence of ammonium chloride, [3,3?²H₂] 2 and [3,3?²H₂] 3 being obtained almost exclusively, in a 6: 94 ratio. It is proposed that the mechanism outlined in House [1] was dominant when, and only when, ammonium ion was the proton source; it may have competed when water was the proton source.     

Syntheses of (R) [4-2H2] 2-Amino-3-Butenoic Acid (Vinylglycine) and (R) [4-2H2, 5-2H3] Methionine

Treatment of (R) methionine sulfoxide with NaOD led to exchange of the C-4 methylene and C-5 methyl protons; exchange of the chiral C-2 proton did not occur. Reducation with mercaptoacetic acid gave (R)-[4-²H₂, 5-²H₃] methionine. The latter was converted into its carbobenzyloxy methyl ester sulfoxide, pyrolysis of which followed by deprotection yielded (R)-[4-²H₂] vinylglcine as the hydrochloride.     

Structural characterization of ammonium molybdophosphate with different amount of cesium adsorption

Powdered crystal AMP was synthesized by precipitation method and different Cs-loading AMP samples were prepared in this work. They were studied by modern methods of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) to gain a better understanding of the ion exchange mechanism of ammonium molybdophosphate (AMP). The XRD patterns combined with the FT-IR analysis indicate that the Keggin structure is retained after Cs adsorption, while the changes of certain characteristic diffraction peaks show crystal lattice distortion caused by the mismatching sizes of Cs⁺ and [NH₄]⁺. The TGA showed that the weight percent of H₂O and [NH₄]⁺ decreases as the amount of Cs adsorbed onto AMP increases, which corresponds with the theory of isomorphous exchange.     

Determination of uranium, thorium, and 20 other elements in high-purity tungsten by radiochemical neutron activation analysis

A radiochemical neutron activation analysis method for the determination of 22 elements in high-purity tungsten has been developed. For the assay of indicator radionuclides with long half-lives, the radiochemical separation was performed from HF/H₂O₂, HF/NH₄F and HCl/H₂SO₄ media by a combination of cation and anion exchange on a Dowex 50 W × 8 and Dowex 1 × 8 column. An effective removal of the matrix-produced radionuclides of W and Re was achieved. U was determined via ¹⁴⁰La, the daughter nuclide of the fission product ¹⁴⁰Ba. Limits of detection of 2 ng/g for U and 0.02 ng/g for Th can be achieved. For the other elements, the limits of detection are between 0.004 ng/g (Sc) and 200 ng/g (Sr). The elements Hf, Ta and Sb could be determined by instrumental neutron activation analysis. This method was applied to the analysis of two tungsten powder samples of different purity grade. The results and limits of detection are compared with those of other methods. Received: 28 July 1997 / Revised: 29 October 1997 / Accepted: 1 November 1997     

Ligand Exchange Processes on Solvated Beryllium Cations. II [Be(solvent)(12‐Crown‐4)]2+

The solvation and solvent exchange mechanism of [Be(12‐crown‐4)]²⁺ in water and ammonia was studied by DFT calculations (RB3LYP/6‐311+G**). In solution, five‐fold coordinated Be²⁺ species of quadratic pyramidal [Be(H₂O)(12‐crown‐4)]²⁺ and [Be(NH₃)(12‐crown‐4)]²⁺ exist. The water and ammonia exchange reactions follow an associative interchange mechanism, similar to that found for the pure solvent complexes [Be(H₂O)₄]²⁺ and [Be(NH₃)₄]²⁺. The activation barriers are clearly smaller than for the pure solvent complexes, viz. [Be(H₂O)(12‐crown‐4)]²⁺: 6.0 kcal/mol and [Be(NH₃)(12‐crown‐4)]²⁺: 15.3 kcal/mol.     

Synthesis,structure, and characterization of picolyl- and benzyl-linked biphenyl palladium N-heterocyclic carbene complexes and their catalytic activity in acylative cross-coupling reactions

N-heterocyclic carbene ligands with picolyl (L¹H₂Br₂, L³H₂Br₂) and benzyl (L²H₂Br₂, L⁴H₂Br₂) linked biphenyl backbone were synthesized and characterized. Their palladium(II) complexes [PdL¹]Br₂ ( 1 ), [PdL²Br₂] ( 2 ), [PdL³]Br₂ ( 3 ), and [PdL⁴Br₂] ( 4 ) were synthesized by direct method using Pd(OAc)₂. All complexes ( 1 – 4 ) were characterized by CHN analysis, electrospray ionization-MS, nuclear magnetic resonance, and single-crystal X-ray diffraction. Molecular structures confirm the distorted square planar geometry around the Pd(II) center. All of them showed good catalytic activity in acylative Suzuki cross coupling of phenyl boronic acid with benzoyl chloride to afford benzophenone in good yields.     

The Effect of Concentration Parameters on Complexation in the Iron(0)–Iron(II)–Glycine–Water System

The processes of formation of iron(II) complexes in aqueous glycine solutions in the pH range of 1.0–8.0 at 298 K and ionic strength of 1 mol/L (NaClO₄) are studied using Clark and Nikolskii’s oxidation potential method. The type and number of coordinated ligands, the nuclearity, and the total composition of the resulting complexes are determined. The following complex species are formed in the investigated system: [Fe(OH)(H₂O)₅]⁺, [FeHL(H₂O)₅]²⁺, [Fe(HL)(OH)(H₂O)₄]⁺, [Fe(OH)₂(H₂O)₄]⁰, [Fe₂(HL)₂(OH)₂(H₂O)₈]²⁺, and [Fe(HL)₂(H₂O)₄]²⁺. Their formation constants are calculated by the successive iterations method using Yusupov’s theoretical and experimental oxidation function. The model parameters of the resulting coordination compounds are determined.     

Determination of trace mercury by solid substrate-room temperature phosphorimetry based on catalytic effect of Hg(2+) on formation of the ion association complex [Fe(bipy)(3)](2+)[(FinBr(4))(2)](2-)

A new solid substrate-room temperature phosphorimetry method for the determination of trace mercury has been established. It bases on the fact that in acetic acid medium, Hg²⁺ ion can catalyze the substitute reaction of CN⁻ ligand in [Fe(CN)₆]⁴⁻ by 2,2′-bipyridyl (bipy), and the resultant [Fe(bipy)₃]²⁺ cation can react with FinBr₄⁻ anion of tetrabromofluorescein (HFinBr₄) to form ion association complex [Fe(bipy)₃]²⁺[(FinBr₄)₂]²⁻ which can emit phosphorescent signal on filter paper substrate. Under the optimum condition, the linear dynamic range of this method is 1.6-16 fg per spot with a detection limit (LD) of 0.18 fg per spot (0.4 μl sample solution per spot), and the regression equation of working curve is ΔI_p=1.058+7.671 C_Hg²⁺ (fg per spot ), n=7, correlation coefficient is 0.9990. This method has been applied to the determination of trace mercury in hair and cigarette samples with satisfactory result. The reaction mechanism for formation of the ion association complex is also discussed.     

Synthesis of a re(VI)-catecholato complex by air oxidation of oxorhenium(V)

The complex [Re(ddcat)₃] (H₂ddcat?=?3,5-di-tert-butylcatechol) was prepared by the reaction of either cis-[Re^VO₂I(PPh₃)₂] or (n-Bu₄N)[Re^VOCl₄] with H₂ddcat in toluene in air. X-ray structure determination of the product unequivocally illustrates that the bidentate chelates are in the catecholato rather than the semiquinone form and that the metal has a formal oxidation state of +VI.     

Immersed solvent microextraction of aryloxyphenoxypropionate herbicides from aquatic media

An immersed solvent microextraction (SME) method was successfully developed for the trace enrichment of aryloxyphenoxypropionate herbicides from aquatic media. A microdrop of toluene was used as the extraction solvent. Some important extraction parameters such as type of solvent, solvent dropsize, stirring rate, ionic strength and extraction time were investigated and optimized. The microdrop volume of 1.5?µL, a sampling time of 25?min, and use of toluene were major parameters for achieving high enrichment factors. The linearity was studied by preconcentration of 4?mL of the water samples spiked with a standard solution of aryloxyphenoxypropionates at the concentration range of 0.15 to 30?ng?mL^?1. The coefficient of determination was satisfactory (r ^2?>?0.99) for all the studied analyte and the relative standard deviations (RSD%) values under the optimized condition were found to be 1.7 to 14.2% at the concentrations of 1 and 10?ng?mL^?1. The enrichment factors were from 217 to 403 for the samples spiked at 1?ng?mL^?1. Detection limits were obtained to be in the range of 0.05 to 0.15?ng?mL^?1 using time-scheduled selected ion monitoring (SIM). The EI mass spectra of these herbicides revealed that fenoxaprop-P-ethyl and quizalofop-P-ethyl exhibited [M-COOC₂H₅]⁺ as the base peak while, clodinafop-propargyl, haloxyfop-etotyl and haloxyfop-P-methyl showed [M-C₂H₄COOC₃H₃]⁺, [M-CH₂COOC₄H₈O]⁺ and [M-COOCH₃]⁺ as the base peaks, respectively. The developed method was successfully applied to the extraction and determination of aryloxyphenoxypropionates in river water samples.     

Simultaneous determination of mercury and selenium in biological materials by radiochemical neutron activation analysis

A simple and sensitive radiochemical neutron activation analysis (RNAA) method has been developed for the simultaneous determination of mercury and selenium in biological materials. The radiochemical procedure is based upon the digestion of irradiated samples with sulphuric and nitric acids followed by subsequent extractions of mercury and selenium into toluene, first of mercury from 7.5 M H₂SO₄-0.01M HBr media and after of selenium from 7M H₂SO₄-1 M HBr media. After washing of the organic phases with similar media, the mercury bromide was back-extracted into 0.034M EDTA in 5% aqueous ammonia and the selenium bromide into 0.14M H₂O₂ in aqueous solution. The¹⁹⁷Hg and the⁷⁵Se were counted on a Ge(Li) detector. The precision and accuracy of the method was checked by analysing NBS Standard Reference Materials: orchard leaves and bovine liver.     

Mass spectra of organometallic compounds—IX: Compounds with metal-metal bonds

The mass spectra of the following compounds have been investigated: (i) The organotin derivatives (CH₃)₃SnMo(CO)₃C₅H₅ and (CH₃)₃SnNCW(CO)₅; (ii) The mercury derivatives Hg[Mn(CO)₅]₂, Hg[Co(CO)₄]₂, Hg[Mo(CO)₃C₅H₅]₂ and ClHgMo(CO)₃C₅H₅; (iii) The polynuclear cyclopentadienyl metal derivatives [C₅H₅Ru(CO)₂]₂, [C₅H₅Cr(CO)₃]₂, [C₅H₅Cr(NO)₂]₂ and [C₅H₅Fe-CO]₄; (iv) The trinuclear cobalt carbonyl derivatives YCCo₃(CO)₉ (Y = Cl and CH₃); (v) The binuclear triene-iron carbonyl derivatives C₄H₄Fe₂(CO)₆ and C₈H₁₀Fe₂(CO)₆. The mass spectra of the trimethyltin derivatives exhibited stepwise loss of methyl groups as well as of carbonyl groups. The mass spectra of the mercury derivatives exhibited the facile loss of mercury. The mass spectrum of [C₅H₅Cr(CO)₃]₂ indicated a very weak chromium-chromium bond since it exhibited no ion containing two chromium atoms. The mass spectrum of the nitrosyl derivative [C₅H₅Cr(NO)₂]₂ exhibited the stepwise loss of its four nitrosyl groups. The mass spectrum of [C₅H₅FeCO]₄ was rather complex and exhibited a variety of unusual processes including eliminations of neutral Fe and C₅H₅Fe fragments. Unusual ions observed in the mass spectrum of CH₃CCo₃(CO)₉ include the bare polymetallic ions [Co_n]⁺ (n = 3 and 2). Many examples of the elimination of neutral CO, C₂H₂ and H₂ fragments were noted in this work.