Dependence of the relative retention of compounds on the average pressure of helium as a carrier gas in capillary GLC

The dependence of retention factork _i , relative retention time α _i , and retention indexI _i of organic compounds on the average pressure (p _av) of the carrier gas (helium) was studied experimentally using a long narrow-bore capillary column with the SE-30 nonpolar phase at 120°C. The linear dependencesk _i =f(p _av), α _i =φ(p _av), andI _i =φ(p _av) obtained previously were found to be in good agreement with experimental data. Invariant relative retention valuesk _0,i , α _0,i , andI _0,i , which do not depend on the helium pressure, were determined for some organic compounds of various chemical classes. The dependence of the relative retention on the carrier gas pressure needs to be taken into account in precision measurements and in experiments with narrow-bore capillary columns. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 314–316, February, 1998.     

Specific features of matrix correction in the X-ray fluorescence analysis of samples of widely varied composition

The authors critically analyze the paper “Corrections for matrix effects in X-ray fluorescence analysis” [1], which was declared by R. Rousseau as a tutorial but contains some inaccuracies. Conclusions are confirmed by the results of experiments and theoretical calculations. It is shown that uniform linear calibration function I _i /I _i ^m = f(R _i ^th ) can hardly be obtained for test samples of any composition because of the difference in their microstructure and the variation of the background. At the same time, in the XRF analysis of multicomponent materials, such as steels, the Lucas-Tooth and Jongh equations provide a good alternative to the Rousseau algorithm.     

Chemical effects on K and L shell production cross sections and transfer probabilities in Nb compounds

In this study, the chemical effects on σ_Ki (i = α, β), σ_Lα cross sections, K_β/K_α X-ray intensity ratios and vacancy transfer probabilities from K to L (η _KL) for pure Nb and Nb compounds were investigated. The samples were excited by 59.5 keV γ-rays from ²⁴¹Am and 5.96 keV photon energy from a ⁵⁵Fe annular radioactive sources. K and L X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV. While it was observed that the chemical bonding had an effect on the σ_Kβ, σ_Lα cross sections and K_β/K_α X-ray intensity ratios for compounds, it was almost negligible for σ_Kα cross section because K_α transitions (2P_3/2,1/2→1S_1/2) occurred in inner shells. It is well known that interactions between central element atom and ligands come into existence in valence state, so outer energy levels are sensitive to the chemical environment. The experimental values of σ_Kα cross section and η _KL are in good agreement with theoretically calculated and other experimental values of pure niobium, but the experimental values of the σ_Kβ, σ_Lα cross sections and K_β/K_α X-ray intensity ratios have differences for some compounds because valence electrons have different bond distances and binding energies in different compounds.     

A note on overpotential dependence of AC impedance data

Charge-transfer resistance [R _ct = (dη/di)_{η = 0}] and Tafel plots of current density (i) versus overpotential (η) data are generally known to yield values of the energy-transfer coefficient (α) and exchange current density (i _o) of an electrochemical reaction. In the present investigation, the resistance (dη/di)_η≠0 that could be calculated by differentiating a wide range of i−η curves was also shown to provide the values of α and i _o, by plotting ln(dη/di)_η≠0 against η. Since α and i _o could also be evaluated directly from the experimental DC polarization data, the procedure was not of significant importance. Nevertheless, it was considered important in evaluating α and i _o from AC impedance data, because the procedure was based on data analysis, which was much simpler than that reported in the literature. A cobalt electrode prepared from fine metal powder was used in 1 M KOH electrolyte and the hydrogen evolution reaction was studied by AC impedance at several potentials. The resistance values measured from the complex plane impedance diagram were plotted against the potential, and the values of α and i _o were evaluated. Received: 8 October 1998 / Accepted: 11 January 1999     

Electronic absorption spectra of charge-transfer complexes and effects of substituents in radical cations

The effects of X substituents on the energies of charge-transfer bandshv _CT in electronic absorption spectra of charge-transfer complexes of π-, n-, or σ-donors (DX) with π- or σ-acceptors (A) as well as on the ionization potentialsI _D of individual DX molecules are described by the equationhv _CT(l _D)=a +bσ₁ +cσ _R ⁺ +dσ_α. When DX and A are fixed, the inductive (bσ₁), resonance (cσ _R ⁺ ), and polarization (dσ_α) contributions tohv _CT andI _D are virtually identical. The electronic structure of the D^.+X donor component of the compact [A^.−, D^.+X] radical-ionic pair in a solution is similar to that of the radical cation generated upon photoionization of the individual DX molecule in the gaseous phase. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1002–1006, June, 2000.     

Synchrotron-radiated X-ray and neutron diffraction study of native cellulose

Precise determination of d-spacings and compositional ratio of cellulose I_α and I_β in various native cellulose samples was successfully carried out by synchrotron-radiated X-ray diffraction and time-of-flight (TOF) neutron diffraction from quasi-powder specimens. X-ray diffraction peaks were separated by the deconvolution method using six types of profile function: Gaussian, Lorentzian, intermediate Lorentzian, modified Lorentzian, pseudo-Voigt, and Pearson VII. In terms of R-factors, the pseudo-Voigt function gave the best fit with the observation, and was used for determination of d-spacings. The numerical results for Valonia cellulose were: dI_α (1 0 0) = 0.613 nm; dI_β (1 1 0) = 0.603 nm; dI_β (1 1 0) = 0.535 nm; dI_α (0 1 0) = 0.529 nm; I_α content = 0.65. The differences determined between dI_α (1 0 0) and dI_β (1 1 0) and between dI_β (1 1 0) and dI_α (0 1 0) were similar to those previously reported. Comparison between unresolved peaks for the two types of cellulose samples revealed a small but definite difference between dI_α (1 1 0) and dI_β (2 0 0). The TOF neutron diffractometry using deuterated samples confirmed this difference. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dependence of analytical signal on the concentration of analyte in X-ray spectral analysis

The dependence of the intensity of analytical signals on the element concentrations expressed in weight percentages I(c) and atomic percentages I(a) in X-ray spectrochemical analysis is considered. It was shown that the change-over from the dependence I(a) to the dependence I(c), which took place in the 1950s, had no theoretical grounds, was based on an incorrect application of the concepts of density and Avogadro’s constant, and was accepted because of practical convenience. In the dependence I(c), the calibration characteristics becomes more complex; it requires corrections for matrix effects, even if these effects are absent. Analytical data published in weight percentages and obtained in the analysis of various samples by conventional X-ray fluorescence analysis (XRFA), X-ray radiometric analysis with an energy-dispersive spectrometer, absorption analysis, and electron probe microanalysis are recalculated into atomic percentages. These results and the data obtained by the author in the analysis of alloys and steels demonstrate a correlation between the intensity of characteristic lines and the atomic concentration of the components. If the calibration curve is based on I(a), a linear dependence over a wide range or the entire concentration range is observed in the majority of systems, the number of the necessary reference standard materials sharply decreases (to one), the sensitivity coefficient increases, and the corrections for matrix effects decrease or the necessity for them disappears.     

Physicochemical constants as a factor determining the need for the derivatization of organic substances in analysis by gas chromatography

A criterion was proposed to estimate the necessity of the derivatization of organic substances for their determination on conventional nonpolar phases, based on such characteristic of analytes as molecular weight (M _r), normal boiling point (T _bp), and molar refraction (MR _D). All these constants can be presented as indices relative to nonpolar n-alkanes (similarly to chromatographic retention indices), I(M), I(T), and I(MR _D), which can be compared to each other as differences Δ_{T − M} = I(T) − I(M) and Δ_{T − M} R _D = I(T) − I(MR _D). Substances do not require derivatization if Δ_{T − M} < 400 and Δ_{T − M} R _D < 600, while at Δ_{T − M} > 600 and Δ_{T − MRD} > 800, derivatization is necessary.     

First ionization potentials and conjugation in molecules of ethylene derivatives containing organoelemental substituents of Group IV elements

Unlike theE _HOMO energies, the first vertical ionization potentials (I ₁) of monosubstituted ethylenes dependen not only on both the inductive and resonance effects but also on the polarizability of the substituents, which can be characterized by the σ_α parameters. The σ _R ⁺ , σ _p ⁺ , and σ_α parameters for 12 silicon-, germanium-, and tin-containing groups were determined using the equations relating theI ₁ values and the σ_I, σ _R ⁺ , σ _p ⁺ and σ_α parameters of the substituents in the molecules of organic compounds. The conjugation of organoelemental substituents with the double bond is stronger than that with benzene ring; the σ _R ⁺ parameters in the ethylene and benzene series are related by a linear dependence. Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya, No. 9, pp. 1626–1631, September, 1997.     

Error of sample preparation in pressing emitters for X-ray fluorescence analysis

When determining element concentrations in geological samples by X-ray fluorescence spectrometry using emitters obtained by pressing tablets from powder samples, we revealed the effect of a significant difference in line intensities of characteristic long-wavelength emission (ΔI _i) from opposite sides of the emitter. The effects of compacting pressure, mass of emitter, and its surface area on ΔI _i were investigated. It was shown that the account of this effect can reduce the error of sample preparation in using compacting pressures lower than 20 t.     

A novel 2D organic-inorganic hybrid 3d–4f polyoxometalate built by [Gd(α-PW11O39)2]11? units and [Cu(Dap)2]2+ bridges

A novel 2D organic-inorganic hybrid 3d–4f polyoxometalate [Cu(Dap)₂(H₂O)][Cu(Dap)₂]_4.5[Gd(α-PW₁₁O₃₉)₂] · 5H₂O (I) (Dap = 1,2-diaminopropane) built by [Gd(α-PW₁₁O₃₉)₂]¹¹⁻ units and [Cu(Dap)₂]²⁺ bridges has been synthesized hydrothermally by the reaction of GdCl₃, CuCl₂ · 2H₂O, Na₉[A-α-PW₉O₃₄] · 7H₂O, and Dap and characterized by elemental analysis, IR spectrum, UV spectrum, powder X-ray diffraction, and single-crystal X-ray diffraction. Single-crystal structural analysis shows that I displays an interesting 2D 3d–4f heterometallic sheet architecture with a 5-connected topology constructed from 1: 2-type [Gd(α-PW₁₁O₃₉)₂]¹¹⁻ subunits and [Cu(Dap)₂]²⁺ bridges. To the best of our knowledge, I represents a rare organic-inorganic hybrid 2D 3d–4f heterometallic monovacant Keggin phosphotungstate.     

Evaluation of charges on sulfur atom from refraction

Approximate dependence of the refraction of sulfur atom (R _D) on its charge (q _S) is determined. On its basis R _D S values in different sulfur compounds were calculated. Refraction of the unshared electron pair on sulfur atom was found to be equal to 0.96. Refraction increments (Δ = MR _Dfound − MR _Dcalc) of sulfur-containing saturated heterocycles were calculated (thietanes Δ = −0.28, thiolanes Δ = −0.28, thianes Δ = −0.24) as well as the refraction of deuterium atom bound with carbon (1.10). The values of q _S and R _D S in sulfoxides (−0.1 and 6.5 respectively), in sulfones (0.72 and 3.73 respectively), q _S in dialkyl sulfides (−0.25), and also R _D of S⁴⁺ ion (0.77) were refined.     

Polar steroidal compounds from the Far-Eastern starfish <Emphasis Type="Italic">Lethasterias fusca</Emphasis>

Nine steroidal compounds including three new steroidal glycosides, viz., sodium (24S)-3,24-di-O-(β-D-xylopyranosyl)-5α-cholestane-3β,6β,8,15α,24-pentol 15-sulfate (fuscaside A), (24S)-3,24-di-O-(β-D-xylopyranosyl)-5α-cholestane-3β,6β,8,15α,24-pentol (fuscaside B), and (22E,24R)-24-O-(β-D-xylopyranosyl)-5α-cholest-22-ene-3β,6α,8,15β,24-pentol (desulfated minutoside A); three previously known glycosides, viz., distolasterosides D₁ and D₂ and pycno-podioside A; two previously known polyhydroxysteroids, viz., 5α-cholestane-3β,6α,8,15β,16β,26-hexaol and 5α-cholestan-3β,4β,6α,7⇇8,15β,16β,26-octol; and the known sodium 24,25-dihydro-marthasterone 3-sulfate were isolated from the Far-Eastern starfish Lethasterias fusca. The structures of these compounds were elucidated by NMR spectroscopy and mass spectrometry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 196–200, January, 2008.     

Study of a new derivatizing reagent that improves the analysis of amino acids by HPLC with fluorescence detection: application to hydrolyzed rape bee pollen

A simple and sensitive method for evaluating the chemical compositions of protein amino acids, including cystine (Cys)₂ and tryptophane (Try) has been developed, based on the use of a sensitive labeling reagent 2-(11H-benzo[α]-carbazol-11-yl) ethyl chloroformate (BCEC–Cl) along with fluorescence detection. The chromophore of the 1,2-benzo-3,4-dihydrocarbazole-ethyl chloroformate (BCEOC-Cl) molecule was replaced with the 2-(11H-benzo[α]-carbazol-11-yl) ethyl functional group, yielding the sensitive fluorescence molecule BCEC–Cl. The new reagent BCEC–Cl could then be substituted for labeling reagents commonly used in amino acid derivatization. The BCEC–amino acid derivatives exhibited very high detection sensitivities, particularly in the cases of (Cys)₂ and Try, which cannot be determined using traditional labeling reagents such as 9-fluorenyl methylchloroformate (FMOC-Cl) and ortho-phthaldialdehyde (OPA). The fluorescence detection intensities for the BCEC derivatives were compared to those obtained when using FMOC-Cl and BCEOC-Cl as labeling reagents. The ratios I _BCEC/I _BCEOC = 1.17–3.57, I _BCEC/I _FMOC = 1.13–8.21, and UV_BCEC/UV_BCEOC = 1.67–4.90 (where I is the fluorescence intensity and UV is the ultraviolet absorbance). Derivative separation was optimized on a Hypersil BDS C₁₈ column. The detection limits calculated from 1.0 pmol injections, at a signal-to-noise ratio of 3, ranged from 7.2 fmol for Try to 8.4 fmol for (Cys)₂. Excellent linear responses were observed, with coefficients of >0.9994. When coupled with high-performance liquid chromatography, the method established here allowed the development of a highly sensitive and specific method for the quantitative analysis of trace levels of amino acids including (Cys)₂ and Try from bee-collected pollen (bee pollen) samples.     

A unique borotungstate containing a discrete Keggin-type anion and a trimeric saturated Keggin-type anion

A unique hybrid borotungstate, [Cu(En)(Phen)(H₂O)]₄[α-BW₁₂O₄₀]{[Cu(En)(Phen)]₂[Cu(En)₂ · (H₂O)]₂[Cu(En)(Phen)(H₂O)]₂[α-BW₁₂O₄₀]₃]} sd 10H₂O (I) (Phen = 1,10-phenanthroline, En = ethylenediamine), has been hydrothermally synthesized and characterized by elemental analyses, IR, and UV spectra, powder X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, and singlecrystal X-ray diffraction analysis. X-ray crystallography shows that I contains a discrete saturated Keggin-type [BW₁₂O₄₀]⁵⁻ polyoxoanion and a rare trimeric saturated Keggin-type polyoxoanion {[Cu(En)(Phen)]₂[Cu(En)₂(H₂O)]₂[Cu(En)(Phen)(H₂O)]₂[α-BW₁₂O₄₀]₃]}³⁻. It is noteworthy that I represents the first example of borotungstate containing four saturated Keggin-type units in one molecule.     

Avrami exponent of crystallization in tellurite glasses

Nucleation process and crystal growth for three samples of the (20-x)Li₂O–80TeO₂–xWO₃ glass system were studied using X-ray diffraction and differential scanning calorimetry techniques. X-ray diffraction data confirmed the amorphous characteristic of the as-quenched samples and indicated the growth of crystalline phases formed due to the thermal treatment for annealed samples. These results reveal the presence of three distinct γ-TeO₂, α-TeO₂ and α-Li₂Te₂O₅ crystalline phases in the TL sample, and two distinct α-TeO₂ and γ-TeO₂ crystalline phases in the TLW5 and TLW10 samples. The activation energy and the Avrami exponent were determined from DSC measurements. The activation energy values X-ray diffraction data of the TLW10 glass sample suggest that γ-TeO₂ phase occur before the α-TeO₂. The results obtained for the Avrami exponent point to that the nucleation process is volumetric and that the crystal growth is two or three-dimensional.     

Background Intensity as a Function of the Particle Size of a Radiating Sample in X-ray Fluorescence Spectroscopy

The background intensity I _bin the short-wave (0.065–0.15 nm) and long-wave (0.19–0.85 nm) X-ray regions is studied experimentally as a function of the particle size D(15–360 m) for single-phase and multiphase samples. It is found that, for single-phase samples, I _bdecreases with D, and the effect is connected with the surface quality of the radiating sample. For multiphase samples, I _bin the short-wave region can either increase or decrease as Dincreases, depending on the wavelength and the sample composition. The causes of the effects observed are revealed. For multiphase samples, we found no well-defined regularity I _b= f(D) in the long-wave region.     

Extending the applicability of TG measurements to industry and to quality ensuring by dimensionless analysis

TheI _i=E _i/RT _i dimensionless evaluation is very suitable for describing the TG measurements according to theE _i/RT _i=lnA +n[ln(1–)_i]–ln(d/dr)_i equation. TheI _i andE _i functions make the comparison of the different TG measurements possible quantitatively in the case of more DTG peaks as well.TheI _i andE _i values as function of (1-)_i and 1/T _i open new way for further theoretical and practical studies by TG measurements. Such types of results are the quantitative determination of the effect of the measuring conditions, the measuring of the mechanochemical effect of grinding and among others the explanation of the self-hardening process of fly ashes of power stations.Strict connections exist between theI _i functions and the constants of the compensation effect (CE). These constants (tan, axis intersect) can be calculated directly from the average of the measured data of theI _i function making the introduction and theoretical and practical application of the idea of general activation energy (¯E) possible. The quantitative characterisation of the examined materials of the fine structure ofCE and of the thermal processes together proves the extending importance of TG measurements from industrial and material qualification aspects as well.The author thanks gratefully to Professor Márta Fehér mathematicien, Head of the Department of Philosophy at the Technical University of Budapest for the consultations and for the encouragements.     

Ionization potentials of non-metal monosulfides. Conjugation in radical cations containing Group IV elements

The first vertical ionization potentialsI(n_s) of 69 monosulfides XSY (X, Y=H, Hal, organic, or heteroorganic substituent) are related to the inductive σ_I resonance (σ _R ⁺ ) and polarizability (σ_α) constants of the substituents by dependences of theI(n_S)=a+bΣσ_I+bΣσ_R+bΣσ_α type. TheI(n_s) values are also affected by hyperconjugation which increases on going from XSH to XSY (Y≠H) compounds. The first calculations of the σ _R ⁺ parameters characterizing the conjugation of Si-, Ge-, Sn-, and Pb-containing substituents with the S^.+ radical cation center are reported. The reasons for weakening of resonance donor properties of heteroorganic substituents of the +M-type in the systems studied as compared to those of the same substituents in the corresponding aromatic radical cations are considered. Translated fromIzvestiya Akademii Nauk. Seriya Khmicheskaya, No. 1, pp. 25–31, January, 2000.     

Effect of the directionality of the ester group on the formation of hairpins in polyesters containing naphthalene and a flexible spacer

Steady-state fluorescence measurements and molecular dynamics simulations have been used to study the intramolecular formation of excimers in five model compounds for polyesters containing naphthalene groups separated by flexible spacers. The model compounds are derived from 2-hydroxynaphthalene and HOOC (CH₂)_n COOH, n = 2–6. The ratio of the intensity of excimer and monomer emissions, I_D/I_M, is nearly independent of the viscosity of the medium, η, over the range covered in dilute solution. Although I_D/I_M is always very small, it shows an odd–even effect for the first four members of the series, with maxima when n is odd. Molecular dynamics simulations provide an explanation for the small values of I_D/I_M, their weak dependence on η, and the trend of I_D/I_M with n. The results for the present series of model compounds are compared with previous work, which reported larger values of I_D/I_M, and a stronger dependence of I_D/I_M on η, for bichromophoric compounds derived from 2-naphthoic acid and aliphatic glycols, where the direction of the ester groups is reversed. The origin of the difference in the behavior of I_D/I_M in the two series is identified. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1127–1133, 1997