Determination of trace halogens in rock samples by radiochemical neutron activation analysis coupled with the k0-standardization method

Radiochemical neutron activation analysis coupled with the k₀-standardization method (k₀-RNAA method) was applied to silicate rock samples for the simultaneous determination of trace halogens (Cl, Br and I). Analytical results obtained by the k₀-RNAA method for geological standard rocks and meteorite samples agreed with those determined by the conventional comparison method conducted in the same set of experiments, suggesting that the k₀-RNAA method is as reliable as the conventional method. Our data for these samples are in good agreement with their literature values except for rare cases. Detection limits calculated under the present experimental condition are sufficiently low for Cl and Br but not for I for typical geologic and meteoritic samples. The k₀-RNAA method coupled with longer neutron-irradiation is expected to yield satisfactorily low detection limits for halogens including I in these samples.     

A simple method for non-parametric estimation of the probability distribution function of diatomic molecules by electron diffraction

Treating the Debye intensity relationship as a linear Fredholm integral equation of the first kind, a method is developed for a non-parametric estimation of the probability distribution function P/r) for diatomic molecules from electron-diffraction data. Since the problem is an ill-posed one, Tikhonov's regularization procedure was used for the solution. The method was applied to iodine for which the non-parametric P/r) function is obtained. Based on this function the electron-diffraction parameters r_g, r_a and l_a are estimated by the linear least-squares method without a priori assumptions about the form of the vibrational potential. Approximating the potential by the Dunham expansion, the parameters r_e, ω_e, K₃ and K₄ are also estimated. The results are compared with those obtained from conventional analytical representation of an intensity function. Comparison is also made with spectroscopic data for iodine.     

Chromatographic methods for determination of S-substituted cysteine derivatives—A comparative study

A novel HPLC method for determination of a wide variety of S-substituted cysteine derivatives in Allium species has been developed and validated. This method allows simultaneous separation and quantification of S-alk(en)ylcysteine S-oxides, γ-glutamyl-S-alk(en)ylcysteines and γ-glutamyl-S-alk(en)ylcysteine S-oxides in a single run. The procedure is based on extraction of these amino acids and dipeptides by methanol, their derivatization by dansyl chloride and subsequent separation by reversed phase HPLC. The main advantages of the new method are simplicity, excellent stability of derivatives, high sensitivity, specificity and the ability to simultaneously analyze the whole range of S-substituted cysteine derivatives. This method was critically compared with other chromatographic procedures used for quantification of S-substituted cysteine derivatives, namely with two other HPLC methods (derivatization by o-phthaldialdehyde/tert-butylthiol and fluorenylmethyl chloroformate), and with determination by gas chromatography or capillary electrophoresis. Major advantages and drawbacks of these analytical procedures are discussed. Employing these various chromatographic methods, the content and relative proportions of individual S-substituted cysteine derivatives were determined in four most frequently consumed alliaceous vegetables (garlic, onion, shallot, and leek).     

Fracture characterization of ductile polymers through methods based on load separation

The applicability of load separation property based methods of determining J–R curves of ductile polymers is analysed in this work. Two methods are analysed: the load normalization method and the S_pb method. The load normalization method is based on the use of a plastic deformation dependent function which has an explicit functional form, H, whereas the S_pb method is based on the S_pb parameter, which was defined as the calculated load ratio between two specimens, one having a growing crack and the other with a non-propagated crack. The obtained J–R curves have been compared with those obtained experimentally in order to study the applicability and accuracy of both methods. Although both methods have been shown to be applicable, the load normalization method is the most accurate and the easiest to apply.     

VSCF in internal coordinates and the calculation of anharmonic torsional mode transitions

The vibrational self-consistent field (VSCF) method assumes separability in normal modes in its usual version. However, the method fails in cases such as soft torsional modes which are better treated by angular variables. We develop VSCF equations based on the assumption of wave function separability in internal coordinates. To test the method, simple illustrative applications to small systems are provided: trans-HONO, cis-HONO, H₂S₂, and H₂O₂. The code directly uses points from ab initio calculations, and the method proves to be accurate for all types of transitions. For typical torsional transitions, the error in the computed frequency is smaller than that of VSCF in normal coordinates. The wave functions for the torsional mode are compared with the corresponding normal mode wave functions. The differences are substantial. The results are encouraging for extension of the model for large polyatomic systems. Work along these lines is in progress.     

Measurement of diffusion and partition coefficients of ferrocyanide in protein-immobilized membranes

True diffusion (D_m) and partition (α) coefficients for the transport of potassium ferrocyanide through diaphorase (Dp)- and bovine serum albumin (BSA)-glutaraldehyde (GA) membranes with different cross-linking degrees of 1-8% GA concentrations immobilized on gold electrodes are investigated by using potential-step method and rotating-disk-electrode method. The thickness of dry and hydrated immobilized membranes is accurately measured by the focus-difference method with a reflection microscope. The thickness of hydrated Dp-GA and BSA-GA membranes are about 1.4 and 2.4 times that of dry membranes, respectively. In addition, the actual area of electrode surface is calculated by the charge amount of chemisorbed oxygen on gold electrode. Owing to the increase of swelling degree and net negative charge of the immobilized membranes, the values of D_m and α for both of Dp-GA and BSA-GA membranes enlarge and decrease with increase of GA concentration, respectively. Furthermore, BSA-GA membranes possess greater D_m and α than those of Dp-GA membranes due to the thinner thickness and the greater swelling degree of BSA-GA membranes.     

Possibilities of applying the Piloyan method of determination of decomposition activation energies in the differential thermal analysis of polynitroaromatic compounds and of their derivatives

Conditions are presented for application of the Piloyan method to the DTA of poly-nitro aromatic compounds. Activation energies (E) of the thermal decomposition and the initial valuesT _D of the exotherms are determined for trinitrotoluene, trinitro-m-xylene, trinitromesitylene, picryl chloride and dichlorotrinitrobenzene. Linear relationships are derived between the termsE · T _D ^? and published kinetic data on these compounds, obtained by an isothermal manometric method. The mechanisms of the primary steps in the thermolyses of these polynitro compounds are discussed. A negative influence on their thermal stability has been confirmed, arising from the contact of the measured compounds with the glass surface.     

Non-ideal polymerization. Treatment of non-ideality due to primary radical termination and degradative chain transfer

A method is proposed for analysing the problems associated with non-ideal polymerizations reflected mainly in the variability of R_p/[I]^0·5[M] where R_p is the rate of polymerization and [I] and [M] are the initiator and monomer concentrations, respectively. Primary radical termination and degradative chain transfer are treated jointly and the entirely different mathematical natures of the two processes are described. The method could dispense with the need to use the uninhibited rate of polymerization which does not lend itself to reliable measurements for many systems. It is found to be efficient in detecting the active species in a polymerization system that leads to non-ideality due to degradative chain transfer.This method is applied to vinyl chloride polymerization data from the literature, the values of constants obtained therefrom are found to agree well with the existing values.     

Innovative Green Chemistry Approach to Synthesis of Sn2+-Metal Complex and Design of Polymer Composites with Small Optical Band Gaps

In this work, the green method was used to synthesize Sn²⁺-metal complex by polyphenols (PPHs) of black tea (BT). The formation of Sn²⁺-PPHs metal complex was confirmed through UV-Vis and FTIR methods. The FTIR method shows that BT contains NH and OH functional groups, conjugated double bonds, and PPHs which are important to create the Sn²⁺-metal complexes. The synthesized Sn²⁺-PPHs metal complex was used successfully to decrease the optical energy band gap of PVA polymer. XRD method showed that the amorphous phase increased with increasing the metal complexes. The FTIR and XRD analysis show the complex formation between Sn²⁺-PPHs metal complex and PVA polymer. The enhancement in the optical properties of PVA was evidenced via UV-visible spectroscopy method. When Sn²⁺-PPHs metal complex was loaded to PVA, the refractive index and dielectric constant were improved. In addition, the absorption edge was also decreased to lower photon. The optical energy band gap decreases from 6.4 to 1.8 eV for PVAloaded with 30% (v/v) Sn²⁺-PPHs metal complex. The variations of dielectric constant versus wavelength of photon are examined to measure localized charge density (N/m*) and high frequency dielectric constant. By increasing Sn²⁺-PPHs metal complex, the N/m* are improved from 3.65 × 10⁵⁵ to 13.38 × 10⁵⁵ m⁻³ Kg⁻¹. The oscillator dispersion energy (E_d) and average oscillator energy (E_o) are measured. The electronic transition natures in composite films are determined based on the Tauc’s method, whereas close examinations of the dielectric loss parameter are also held to measure the energy band gap.     

Absolute detection of metastable rare gas atoms by a cw laser photoionization method

A novel, accurate method for the absolute detection of metastable rare gas atoms is described and demonstrated. It involves a direct in situ determination of the electron emission coefficient γ for impact of the respective metastable atom on a conducting surface. γ is reliably obtained by a cw two-photon ionization — depletion technique: the reduction ΔI _S in electron current from the detector surface due to efficient photoionization removal of the metastable flux is compared with the photoelectron current ΔI _P (γ = ΔI _S/ΔI _P). The principle of the method, possible realization schemes for the different metastable rare gas atoms and the apparatus are described in detail. The method has been applied so far to metastable Ne* (3s ³ P ₂), Ar* (4s ³ P ₂), and Kr* (5s ³ P ₂) atoms, and corresponding results for γ, obtained with five different chemically clean, polycrystalline surface materials and at two surface temperatures (300 K, 360 K) are reported. Whereas for Ne*, the value of γ (≈0.35) showed only a rather weak dependence on the surface material and temperature (as also found for a mixed He* (2³ S, 2¹ S) beam), strong variations in γ, especially at 300 K, were detected for Ar* and Kr* (values between 0.25 and 0.003). Some applications of the described method, especially with regard to the determination of absolute reaction cross sections involving metastable rare gas atoms, are discussed.     

A new synthesis of amides and γ-lactones based on the conjugate addition of lithium enolate of amides to 1-chlorovinyl p-tolyl sulfoxides

Reaction of 1-chlorovinyl p-tolyl sulfoxides, which were synthesized from chloromethyl p-tolyl sulfoxide and ketones or aldehydes, with lithium enolate of N,N-dimethylacetamide gave the adducts in good to quantitative yields. The adducts were converted to several kinds of amides in high overall yields. Treatment of the adducts with trifluoroacetic anhydride in the presence of NaI resulted in the formation of γ-tolylsulfanylated γ-lactones in high yields. The scope and limitations of this method and the mechanism of the reactions are also discussed. These procedures offer a new and effective method for the synthesis of amides and γ-lactones having substituents on the β-carbon from N,N-dimethylacetamide with carbon elongation.     

Deoxygenation of tertiary amine N-oxides under metal free condition using phenylboronic acid

A simple and efficient method for the deoxygenation of amine N-oxides to corresponding amines is reported using the green and economical reagent phenylboronic acid. Deoxygenation of N,N-dialkylaniline N-oxides, trialkylamine N-oxides and pyridine N-oxides were achieved in good to excellent yields. The reduction susceptible functional groups such as ketone, amide, ester and nitro groups are well tolerated with phenylboronic acid during the deoxygenation process even at high temperature. In addition, an indirect method for identification and quantification of tert-amine N-oxide is demonstrated using UV–Vis spectrometry which may be useful for drug metabolism studies.     

Microwave-assisted synthesis of substituted phenanthrenes, anthracenes, acenaphthenes, and fluorenes

Rapid coupling reactions of polycyclic aromatic halides with various N-, S-, and Se-nucleophiles under focused microwave irradiation are described. Using this method, the desired products are obtained with good to excellent yields in a short reaction time.     

Practice of fluorous biphase chemistry: convenient synthesis of novel fluorophilic ethers via a Mitsunobu reaction

The evolution of the term fluorous is addressed first, then a concise terminology is proposed, including fluorous partition coefficient, specific fluorophilicity and fluorousness. Some examples are shown for the design of higher generation fluorophilic molecules, involving Class I to Class III ponytails. Fluorophilic ethers of the structure of ArC(CF₃)₂O(CH₂)_m(CF₂)_nF (m=1, n=1, 7; m=3, n=8) are obtained in high yields, when 2-aryl-1,1,1,3,3,3-hexafluoro-propanols are reacted either with trifluoroethyl- and 1H,1H-perfluorooctyl triflates (NaH/DMF, Williamson ether synthesis) or with 3-perfluorooctyl-propanol (Ph₃P/EtO₂CNNCO₂Et/PhCF₃, Mitsunobu reaction), respectively. Fluorophilic phenol- and perfluoro-tert-butyl ethers can also be prepared effectively by the latter method. In case of higher homologues (n=7, 8) product isolation can be facilitated using fluorous extraction (C₆F₁₄/CH₃OH). Specific fluorophilicity values of target molecules are estimated using a 2D method and compared with experimentally determined ones.     

Facile monoprotection of trans-1,2-diaminocyclohexane

A new method of monoprotection of C₂-symmetric trans-1,2-diaminocyclohexane as the N-phthaloyl, N-tetrachlorophthaloyl or N-1,8-naphthaloyl derivative is presented. The first two derivatives are obtained with high yields and can be readily transformed into other unsymmetrical derivatives of trans-1,2-diaminocyclohexane.     

Enzymatic resolution of methyl N-alkyl-azetidine-2-carboxylates by Candida antarctica lipase-mediated ammoniolysis

A facile method for the synthesis of optically active azetidine-2-carboxylic acid derivatives is presented. Racemic N-alkylated azetidine esters are resolved by lipase from Candida antarctica in an ammoniolysis reaction, and both the S-amide and the R-ester are obtained with excellent stereoselectivity.     

Simulation of the triplet EPR spectra of randomly oriented molecules with an exact method of resonance field calculation

A simple method for the calculation of the resonance fields of the triplet EPR transitions is given, which are the solutions of a cubic equation with coefficients depending on the parameters g, D, and E. This method is very useful for the simulation of EPR powder spectra.     

Effects of gold catalysts and thermal evaporation method modifications on the growth process of Zn1−xMgxO nanowires

In this paper, we investigate the roles of gold catalysts and thermal evaporation method modifications in the growth process of Zn_1−xMg_xO nanowires. Zn_1−xMg_xO nanowires are fabricated on silicon substrates with and without using a gold catalyst. Characterizations reveal that Mg acts in a self-catalyst role during the growth process of Zn_1−xMg_xO nanowires grown on catalyst-free substrate. The optical properties and crystalline quality of the Zn_1−xMg_xO nanowires are characterized by room temperature photoluminescence (PL) measurements and Raman spectroscopy, respectively. The Raman and PL studies demonstrate that the Zn_1−xMg_xO nanowires grown using the catalyst-free method have good crystallinity with excellent optical properties and have a larger band-gap in comparison to those grown with the assistance of gold.     

Structure and spectra of 1,3-dioxanes. microwave spectrum, structural parameters, and ab initio calculations of 5-methyl-1,3-dioxane

In the microwave spectrum of a 5-methyl-1,3-dioxane sample, the rotational transitions of a and c types with 4 ≤ J ≤ 11 for five isotopomers of a molecule with ¹³C and ¹⁸O isotopes in different sites are identified in a frequency range of 18 GHz to 42 GHz. The spectroscopic constants of isotopomers are found. The substituted r _s and effective r _o structural parameters of 5-methyl-1,3-dioxane are determined. By the B3PW91/aug-cc-pVDZ density functional method the equilibrium structure of the molecule is calculated. The results of quantum chemical calculations are compared to the experimental data.