The application of Westcott Formalism k0 NAA method to estimate short and medium lived elements in some Ghanaian herbal medicines complemented by AAS

The epithermal neutron shape factor, α of the inner and outer irradiation sites of the Ghana Research Reactor-1 (GHARR-1) was determined obtaining results of 0.105 for the inner (Channel 1) Irradiation site and 0.020 for the outer (channel 6) irradiation site. The neutron temperatures for the inner and outer irradiation sites were 27 °C and 20 °C, respectively. The α values used in Westcott Formalism k₀ INAA was applied to determine multi elements in 13 Ghanaian herbal medicines used by the Centre for Scientific Research into Plant Medicine (CSRPM) for the management of various diseases complemented by Atomic Absorption Spectrometry. They are namely Mist. Antiaris, Mist. Enterica, Mist. Morazia, Mist. Nibima, Mist. Modium, Mist. Ninger, Mist Sodenia, Mist. Tonica, Chardicca Powder, Fefe Powder, Olax Powder, Sirrapac powder and Lippia Tea. Concentrations of Al, As, Br, K, Cl, Cu, Mg, Mn, Na and V were determined by short and medium irradiations at a thermal neutron flux of 5×10¹¹ ncm⁻² s⁻¹. Fe, Cr, Pb, Co, Ni, Sn, Ca, Ba, Li and Sb were determined using Atomic Absorption Spectrometry (AAS). Ba, Cu, Li and V were present at trace levels whereas Al, Cl, Na, Ca were present at major levels. K, Br, Mg, Mn, Co, Ni, Fe and Sb were also present at minor levels. Arsenic was not detected in all samples. Standard Reference material, IAEA-V-10 Hay Powder was simultaneously analysed with samples. The precision and accuracy of the method using real samples and standard reference materials were evaluated and within ±10% of the reported value. Multivariate analytical techniques, such as cluster analysis (Q-mode and R-mode CA) and principal component analysis (PCA)/factor analysis (FA), have been applied to evaluate the chemical variations in the herbal medicine dataset. All the 13 samples may be grouped into 2 statistically significant clusters (liquid based and powdered herbal medicines), reflecting the different chemical compositions. R-mode CA and PCA suggest common sources for Co, Mg, Fe, Ca, Cr, Ni, Sn, Li and Sb and Na, V, Cl, Mn, Al, Br and K. The PCA/FA identified 3 dominant factors as responsible for the data structure, explaining 84.5% of the total variance in the dataset.     

Reductive dehalogenation of halophenols in sulfite-bisulfate medium

The KHSO₄-Na₂SO₃ system is found to be simple and inexpensive for reductive elimination of halogens (Br, I) from the corresponding halophenols under reflux conditions in dry methanol. Under similar conditions the reaction is sluggish with chlorophenols.     

Vibrational spectra and structural parameters of some XNCO and XOCN (X = H, F, Cl, Br) molecules

Ab initio calculations with full electron correlation by the perturbation method to second order and hybrid density functional theory calculations by the B3LYP method utilizing the 6-31G(d), 6-311+G(d, p), and 6-311+G(2d, 2p) basis sets have been carried out for the XNCO and XOCN (X = H, F, Cl, Br) molecules. From these calculations, force constants, vibrational frequencies, infrared intensities, Raman activities, depolarization ratios, and structural parameters have been determined and compared to the experimental quantities when available. By combining previously reported rotational constants for HNCO, ClNCO and BrNCO with the ab initio MP2/6-311+G(d, p) predicted structural values, adjusted r₀ parameters have been obtained. The r₀ values for BrNCO are: r(BrN) = 1.857(5); r(NC) = 1.228(5); r(CO) = 1.161(5) Å; BrNC = 117.5(5) and NCO = 172.3(5)°. For ClNCO the determined r₀ parameters are in excellent agreement with the previously determine r_s values, whereas those for HNCO the HNC angle is larger with a value of 126.3(5)° compared to the previous reported value of 123.9(17)°. However, considering the relatively large uncertainty in the value given initially the two results are in near agreement. Structural parameters are also estimated for FNCO and XOCN (X = H, F, Cl, Br). The centrifugal distortion constants have been calculated and are compared to the experimentally (XNCO: X = H, Cl, Br) determined values. Predicted values for the barriers of linearity are given for both the XNCO (X = H, F, Cl, Br) molecules and the results were compared to the corresponding isothiocyanate molecules. The predicted frequencies for the fundamentals of the XNCO molecules compare favorably to the experimental values but some of the predicted intensities differ significantly from those in the observed spectra. The two OCN bends for HOCN have been assigned and the frequencies for the two corresponding fundamentals of DOCN are predicted.     

Tetrakis-acridinyl peptide: distance dependence of photoinduced electron transfer in deoxyribonucleic acid assemblies

A simple determination method for halogens (Cl, Br, and I) in plant samples using inductively coupled plasma-mass spectrometry (ICP-MS) was developed. In order to extract these halogens into aqueous solution, a leaching step with tetramethyl ammonium hydroxide (TMAH) under mild conditions was carried out, i.e. a 0.1-g dried sample was left overnight (ca. 12 h) in contact with 1 mL of 25% TMAH in a small PFA vial at 60 °C. Then the sample was transferred to a 50-mL centrifuge tube and diluted to 50 mL with deionised water. After centrifugation, halogens in the supernatant were determined by ICP-MS. When standard reference materials were measured by the method, the data were within the 95% confidence range of the certified values. The results also agreed well with the values obtained by neutron activation analysis with correlation factor r > 0.99.     

高温热水解离子色谱法快速同时测定粘土中的卤素

建立高温热水解分解粘土样品,离子色谱快速同时测定其中的氟、氯、溴和碘含量的方法。优化了影响粘土高温热水解的主要参数,得到以下最佳测定条件:2.0 g粘土,反应温度1000℃,停留时间10 min,样品与催化剂V2O5质量比为1∶1,空气流量90 mL/min,15 mL 5.4 mmol/L Na2CO3和5.1 mmol/L NaHCO3混合溶液为粘土释放卤素的吸收液;考察了粘土高温热水解后卤素的赋存形态。结果表明,这些卤素在吸收液中以F!、Cl!、Br!和I!形式存在,且能被离子色谱很好地分离。粘土样品较好的卤素加标回收率和较小的相对标准偏差及土壤标准物质中卤素的评估说明本方法的准确度和精密度良好。分析了4个粘土样品,氟、氯、溴和碘的检出限分别为0.030,0.043,0.09和0.13#g/g,本方法简单、可靠、低消耗和快速,每小时可分析5个样品,可同时分析粘土和其它无机基质中的氟、氯、溴和碘的含量。     

Zirconium-catalyzed methylalumination of heterosubstituted arylethynes: Factors affecting the regio-, stereo-, and chemoselectivities

The Zr-catalyzed methylalumination of heterosubstituted arylethynes containing O, S, Cl, and Si can proceed in high yields (>70%) and in a highly regio- and stereoselective manner (?98-99%), although SO₂Ph, Br, and Cl in a benzylic position present serious chemoselectivity-related problems. The low regioselectivity of 60% initially observed with o-ethynylphenol (1a) has been elevated to ?98% through the use of either a catalytic amount of Zr(ebi)Cl₂ or Zr(2-Me-Ind)₂Cl₂ or, more conveniently, the stoichiometric amount of ZrCp₂Cl₂, ZrCp₂MeCl, or ZrCp₂Me₂ in conjunction with the use of a deficient amount (0.9 molar equiv.) of I₂ for subsequent iodinolysis.     

Assessment of amination reactions via nucleophilic aromatic substitution using conventional and eco-friendly energies

The efficiency of conventional heating energy source compared with Infrared (IR), Ultrasound (US), Microwave and the simultaneous combination US–IR eco-friendly approaches for preparation of new N-(5-R¹ _-amino-2-nitrophenyl)acetamides and 5-R¹-amino-2-nitroaniline by Nucleophilic Aromatic Substitution (S_NAr) via addition–elimination reactions on the halogens F, Cl, Br, I, employing amines as nucleophiles were explored. Moreover, phenyldiazenyl derivatives in good yields by an oxidative one-pot S_NAr-based amination reaction from an unusual oxidation of 2-phenylhydrazinyl derivatives in DMSO was prepared.     

High dielectric constant PrYxOy sensing films electrolyte-insulator-semiconductor pH-sensor for the detection of urea

In this paper, we describe the structural and sensing properties of high-k PrY_xO_y sensing films deposited on Si substrates through reactive co-sputtering. Secondary ion mass spectrometry and atomic force microscopy were employed to analyze the compositional and morphological features of these films after annealing at various temperatures. The electrolyte-insulator-semiconductor (EIS) device incorporating a PrY_xO_y sensing membrane that had been annealed at 800 °C exhibited good sensing characteristics, including a high sensitivity (59.07 mV pH⁻¹ in solutions from pH 2 to 12), a low hysteresis voltage (2.4 mV in the pH loop 7 → 4 → 7 → 10 → 7), and a small drift rate (0.62 mV h⁻¹ in the buffer solution at pH 7). The PrY_xO_y EIS device also showed a high selective response towards H⁺. This improvement can be attributed to the small number of crystal defects and the large surface roughness. In addition, the enzymatic EIS-based urea biosensor incorporating a high-k PrY_xO_y sensing film annealed at 800 °C allowed the potentiometric analysis of urea, at concentrations ranging from 1 to 16 mM, with a sensitivity of 9.59 mV mM⁻¹.     

Lewis acid catalyzed asymmetric halohydrin reactions of chiral α,β-unsaturated carboxylic acid derivatives with N-halosuccinimide (NXS) as the halogen source

Lewis acid catalyzed asymmetric halohydrin reactions—(halohydroxylation as well as halomethoxylation) of chiral α,β-unsaturated carboxylic acid derivatives were performed using N-halosuccinimide (NXS; X = Br, I) as the halogen source. Regio- and anti-selectivity of 100% and moderate to good diastereoselectivity with good yields were observed when Oppolzer’s sultam was used as the chiral auxiliary. Among the Lewis acids, Yb(OTf)₃ was found to be the best catalyst. Alkenoyl and cinnamoyl substrates smoothly underwent bromohydrin reactions and the more electron-rich cinnamoyl substrates preferred to undergo iodohydrin reactions. However, electron-deficient cinnamoyl substrates did not respond to this Lewis acid catalyzed halohydrin reaction with NXS (X = Cl, Br, I).     

Palladium-catalyzed trans-selective alkynylation-alkylation tandem process for the synthesis of (E)-3-alkyl-1-trialkylsilyl-3-alken-1-ynes

The Pd-catalyzed trans-selective monoalkynylation of 1,1-dihalo-1-alkenes with XZnCCSiMe₃, where X is Br or Cl, can proceed generally in excellent yields in the presence of Pd(DPEphos)Cl₂ or Pd(dppf)Cl₂, and subsequent alkylation with methyl- and ethylzincs can proceed in excellent yields with ≥98% retention of configuration in the presence of Pd(^tBu₃P)₂ as a catalyst.     

ICP-AES determination of trace elements after preconcentrated with p-dimethylaminobenzaldehyde-modified nanometer SiO2 from sample solution

A new method that utilizes p-dimethylaminobenzaldehyde-modified nanometer SiO₂ (SiO₂-p-DMABD) as a solid phase extractant has been developed for simultaneous preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) prior to the measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). The preconcentration conditions of analytes were investigated, including the pH value, the shaking time, the mass of sorbent, the sample flow rate and volume, the elution condition and the interfering ions. The adsorption capacity of nanometer SiO₂-p-DMABD was found to be (mg g^− 1) Cr(III): 6.2, Cu(II): 18.6, Fe(III): 4.7 and Pb(II): 6.0 at pH 4. The adsorbed metals were quantitatively eluted with 4 mL of 1.0 mol L^− 1 HCl. According to the definition of IUPAC, the detection limits (3σ) of this method for Cr(III), Cu(II), Fe(III) and Pb(II) were 0.79, 1.27, 0.40 and 1.79 ng mL^− 1, respectively. The proposed method achieved satisfied results when it was applied to the determination of trace Cr(III), Cu(II), Fe(III) and Pb(II) in biological and water samples.     

Application of k0-based internal mono standard instrumental neutron activation analysis method method for composition analysis of stainless steel clad sample

The k₀-based internal mono standard instrumental neutron activation analysis (INAA) method was used for the composition analysis of some irregular shape stainless steel (SS) samples of type SS 316M, which is used as fuel cladding in Indian fast breeder test reactor (FBTR). The method utilizes in situ relative detection efficiency using γ-rays of the activation products present in the sample for overcoming γ-ray self-attenuation. Samples were neutron activated using the thermal column as well as the core position of the reactor and the assay of radioactivity was carried out by high-resolution gamma ray spectrometry. The elements determined were Fe, Cr, Ni, Mo, Mn, Co, Cu, As and W. Since all the major elements (Fe, Cr, Ni, Mo and Mn) were amenable to NAA, the relative elemental concentrations with respect to Fe, obtained by this method, were converted to their absolute values by mass balance. The results were compared with specified compositions and found to be satisfactory. In order to validate these results obtained by the standard-less approach, sub samples of SS 316M in solution forms were analyzed by prevalent relative and k₀ methods of INAA, and results were found to be in good agreement. The accuracy of the internal mono standard INAA method has been evaluated by analyzing an alloy steel certified reference material, CRM 225/1 of British Chemical Standards (BCS).     

Direct spectrophotometric determination of calcium in clinical samples with carboxyazo-p-CH3

A highly sensitive and relatively interference-free spectrophotometric method for determination of calcium is described. The method is based on the reaction between calcium ions and carboxyazo-p-CH₃ in aqueous citrate medium of pH 7, to form a blue complex with maximum absorption at 716 nm. The calibration is linear up to 0.12 μg ml⁻¹ calcium with a repeatability (R.S.D.) of 1.0% at a concentration of 0.04 μg ml⁻¹ (n=5). The molar absorptivity of the complex and Sandell’s sensitivity are 3.5×10⁵ l mol⁻¹ cm⁻¹ and 0.11 ng cm⁻², its 10σ limit of quantification and the 3σ limit of detection were found to be 0.3 ng ml⁻¹ and 0.09 ng ml⁻¹ respectively. The influence of reaction variables and the effect of interfering ions are studied; no interference was observed in clinical samples. The proposed method has been applied directly to the determination of calcium in clinical samples without the need for pre-concentration, masking metal ions and digesting samples.     

Synthesis and characterization of La2Mo2O9 obtained from freeze-dried precursors

La₂Mo₂O₉ ceramics have been prepared from freeze-dried precursors and their properties compared to those of lantanum molybdate obtained by conventional solid state (SS) reaction. All materials have been characterized by X-ray diffraction, scanning electron microscopy and thermal analysis (TGA/DTA/DSC and dilatometry) to characterize the phase formation and phase transition. When the freeze-dried method was applied, the synthesis temperature required to obtain dense samples was much lower than that for powders obtained by SS reaction. The morphology and structure of the oxide particle are significantly dependent on the synthesis method. The grain size is smaller, whereas the density of sintered pellets is higher for the freeze-dried precursor powder when compared with the SS reaction method. Impedance spectroscopy was used to measure the electrical conductivity of La₂Mo₂O₉ from 548 to 1123 K, in air, and to characterize the blocking effects of grain boundaries.     

Selectfluor-mediated mild oxidative halogenation and thiocyanation of 1-aryl-allenes with TMSX (X = Cl,Br, I,NCS) and NH4SCN

Presence of TMSX (X = Cl, Br, I) unleashes the oxidative character of Selectfluor and provides a mild dihalogenation method for 1-arylallenes. Preference for 2,3-addition was observed with TMSCl in MeCN irrespective of the nature of the substituent on the aryl moiety, whereas 1,2-addition was preferred in [BMIM][BF₄]. With TMSBr and TMSI only products corresponding to 2,3-addition were observed. Reactions carried out with TMSBr in IL solvents gave the corresponding monobromoalkenes as a major product along with the isomeric dibromo-alkenes. Reaction with NH₄SCN provided convenient access to dithiocyanate derivatives. The same products were formed via TMS-NCS/Selectfluor. Formation of common products via TMSNCS and NH₄SCN points to the formation and interplay of SCN⁺/NCS⁺ as incipient electrophiles.     

Synthesis, structures and photocatalytic activities of microcrystalline ABi2Nb2O9 (A=Sr, Ba) powders

Microcrystalline ABi₂Nb₂O₉ (A=Sr, Ba) photocatalysts were successfully synthesized by a citrate complex method. The as-prepared samples were characterized by the X-ray diffraction technique, BET surface area analysis, UV-vis diffuse reflectance spectrum, transmission electron microscopy, X-ray photoelectron spectroscopy and inductively coupled plasma-atomic emission spectrometry. The results indicated that single-phase orthorhombic SrBi₂Nb₂O₉ could be obtained after being calcined above 650 °C, while BaBi₂Nb₂O₉ was tetragonal. Based on the diffuse reflectance spectra, the band gaps of the obtained samples were calculated to be around 3.34-3.54 eV. For the photocatalytic redox reaction of methyl orange under UV-light irradiation, SrBi₂Nb₂O₉ exhibited higher photocatalytic activity than that of BaBi₂Nb₂O₉. The effects of the crystallinities, BET surface areas and crystal structures of the samples on the photocatalytic activities were discussed in detail.     

Comparison of several sorbents for continuous in situ derivatization and preconcentration of low-molecular mass aldehydes prior to liquid chromatography–tandem mass spectrometric determination in water samples

A comparative study of six SPE conventional and non-conventional sorbent materials (silica RP-C₁₈, LiChrolut EN, Amberlite XAD-2, C₆₀ fullerene, multiwall carbon nanotubes and graphitized carbon black) was carried out for the in situ derivatization/preconcentration of eight aldehydes with 2,4-dinitrophenylhydrazine. Although two of the sorbents, LiChrolut EN and RP-C₁₈, turned out to be the most suitable for ultratrace analysis of the aldehydes, LiChrolut EN showed higher capacity for 2,4-dinitrophenylhydrazine trapping (higher efficiency for the in situ derivatization reaction) and superior performance in terms of sensitivity (likely a result of its increased sample breakthrough volume). The LiChrolut EN-based method combined with LC–MS/MS allowed the determination of aldehydes over the linear range of 0.02–15 μg l⁻¹, with limits of detection at 6–24 ng l⁻¹ and precision of 3.2–7.2%. The method was applied to determine low-molecular mass aldehydes in water samples. These results indicate that the method proposed is a straightforward and sensitive tool for the determination of these aldehydes in water samples providing better results than those LC–MS/MS reported alternatives in terms of the limit of detection, sample requirements for analysis and cost.     

Synthesis and characterization of metal substituted AlxCr1−x(acetylacetonate)3 single-source precursors for their application to MOCVD of thin films

A detailed study, involving the synthesis of a single-source precursor containing two metal ions sharing the same crystallographic site, has been undertaken to elucidate the use of such a single-source precursor in a CVD process for growing thin films of oxides comprising these two metals, ensuring a uniform composition and distribution of metal ions. The substituted complexes Cr_1−xAl_x(acac)₃, where acac = acetylacetonate, have been prepared by a co-synthesis method, and characterized using UV–Vis spectroscopy, TGA/DTA measurements, and single crystal X-ray diffraction at low temperature. All the studied compositions crystallize in the monoclinic space group P2₁/c with Z = 4 in the unit cell. It was observed that the ratio (Al:Cr) of the site occupancy for the metal ions, obtained from single crystal refinement, is in agreement with the results obtained from complexometric titrations. All the solid state structures have the metal in an octahedral environment forming six-membered chelate rings. M–O acac bond lengths and disorder in the terminal carbon have been studied in detail for these substituted metal–organic complexes. One composition among these was chosen to evaluate their suitability as a single-source precursor in a LPMOCVD process (low-pressure metal–organic chemical vapour deposition) for the deposition of a substituted binary metal oxide thin film. The resulting thin films were characterized by X-ray diffraction, scanning electron microscopy, and infrared spectroscopy.     

k 0-RNAA used in determination of 129I in a mixed resin sample

A k ₀-RNAA procedure was developed to determine ¹²⁹I in a mixed resin sample. CH₄ extraction and (NH₄)₂SO₃ back-extraction were used to separate ¹²⁹I in ashed samples. The ¹²⁹I target sample for irradiation in the reactor was prepared by heating the (NH₄)₂SO₃ back-extraction solution to reduce its volume and then to dry it in a quartz ampoule. No MgO and LiOH were needed during the target sample preparation. After irradiation, the nuclide ¹³⁰I was purified by combining hydrated antimony pentoxide column and CH₄ extraction separations. A k-factor was determined for the reaction of ¹²⁷I (n, 2n) ¹²⁶I and used for iodine chemical yield determination. The apparent ¹²⁹I concentrations of five nuclear reaction interferences were calculated. The relative standard deviation of three ¹²⁹I determinations was found to be 3.5 %. The ¹²⁹I content in the analyzed resin was found to be 1.36 × 10^?9 g/g (8.63 × 10^?3 Bq/g) with a relative uncertainty of 9.1 %. The detection limit of ¹²⁹I was calculated to be 7.4 × 10^?13 g (4.7 × 10^?6 Bq) in a k ₀-RNAA of a blank sample.     

Theoretical study of the thermochemistry and the kinetics of the SFxCl (x = 0-5) series

A systematic thermodynamic and kinetic study of the entire SF_xCl (x = 0-5) series has been carried out. High-level quantum chemical composite methods have been employed to derive enthalpy of formation values from calculated atomization and isodesmic energies. The resulting values for the SCl, SFCl, SF₂Cl(C₁), SF₃Cl(C_s), SF₄Cl(C_s) and SF₅Cl molecules are 28.0, −36.0, −64.2, −134.3, −158.2 and −237.1 kcal mol⁻¹. A comparison with previous experimental and theoretical values is presented. Statistical adiabatic channel model/classical trajectory, SACM/CT, calculations of selected complex-forming and recombination reactions of F and Cl atoms with radicals of the series have been performed between 200 and 500 K. The reported rate coefficients span over the normal range of about 6 × 10⁻¹² and 5 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ expected for this type of barrierless reactions.