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1.
Summary This paper deals for the first time with a direct method for analysis of the α and β anomers of bile acid esters of glucose
by capillary gas chromatography (CGC) without the need for a hydrolytic step. The bile acid esters were derivatized to their
trimethylsilyl (TMS) ethers, which in turn were chromatographed on a short (7m) metal capillary column chemically coated with
a thin (0.15 μm) film of thermostable, non-polar polydimethylsiloxane. Satisfactory CGC separation of the isomeric bile acid
esters was achieved on the column; the β anomers eluted before the corresponding α isomers. Particularly noteworthy is that
the α anomers are partially isomerized to the corresponding β anomers, and that both anomers are partially decomposed during
CGC analysis, demonstrating the chemical specificity and thermal instability of the bile acid esters. 相似文献
2.
Ab initio calculations have been performed to study the molecular structures and vibrational levels of the four low-lying
ionic states (1, 22Π, and 1, 22Σ+) of carbonyl sulfide. The global regions of the potential-energy surfaces have been obtained by multireference single and
double excitation configuration interaction calculations. Vibrational calculations using explicit vibrational Hamiltonians
have been used for vibrational analysis. The equilibrium molecular structures and a vibrational analysis of the four ionic
states are presented. The theoretical ionization intensity curves including the vibrational structures of the ionic states
are also presented and are compared with the photoelectron spectrum.
Received: 20 January 2001 / Accepted: 22 August 2001 / Published online: 30 October 2001 相似文献
3.
An on-line automated flow injection system with microwave-assisted sample digestion was used to perform silicate rock dissolution in acid medium for iron determination. For this purpose, a continuous flow system was built up by using an automatic flow injection analysis (FIA) system coupled to a flame atomic absorption spectrometer (FAAS), including a focused microwave oven unit. Inside the microwave cavity was inserted a polytetrafluoroethylene (PTFE) reactor coil (300 cm length and 0.8 mm i.d.) where the dissolution takes place. Chemical and flow variables as well as iron determination parameters were studied. In the flow system, a slurry of the rock sample (50 mg in 200 ml of acid mixture HF+HCl+HNO3) is pumped through the reaction coil and the microwaves are turned on. After elapsed the time required to complete the sample dissolution, the mixture is pumped again in order to fill the sampling loop (500 μl). Then, by changing the valve position, a water carrier stream pushes the sample solution through the flame atomic absorption spectrometer nebulizer. To achieve an accurate determination of the rock certified materials, the slurry sample was irradiated during 210 s at 90 W power. Working in that condition, a detection limit of 0.80 μg ml−1 (which corresponds to an Fe2O3 content of 0.46%) and an analytical throughput of 10 h−1 were achieved. The relative standard deviation (R.S.D.) of the method varied between 1 and 11% when applied to the rock certified materials. 相似文献
4.
E. D. Matveeva T. A. Podrugina M. V. Prisyazhnoi I. N. Rusetskaya N. S. Zefirov 《Russian Chemical Bulletin》2007,56(4):798-805
Interaction of aliphatic and aromatic aldehydes and ketones with optically active L-α-amino acids or their esters in the three-component catalytic one-pot synthesis of α-aminophosphonates was studied. The
corresponding α-amino phosphonates are formed in high yields as mixtures of diastereomers.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 768–774, April, 2007. 相似文献
5.
Peter Brodelius Kjell Nilsson Klaus Mosbach 《Applied biochemistry and biotechnology》1981,6(4):293-307
Whole cells ofTrigonopsis variabilis were immobilized by entrapment in Ca2+-alginate and used for the production of α-keto acids from the corresponding D-amino acids. The D-amino acid oxidase within
the immobilized cells has a broad substrate specificity. Hydrogen peroxide formed in the enzymatic reaction was efficiently
hydrolyzed by manganese oxide co-immobilized with the cells. The amino acid oxidase activity was assayed with a new method
based on reversed-phase HPLC. Oxygen requirements, bead size, concentration of cells in the beads, flow rate, and other factors
were investigated in a “ trickle-bed ” reactor. 相似文献
6.
J. F. Ogilvie S.-L. Cheah Y.-P. Lee S. P. A. Sauer 《Theoretical chemistry accounts》2002,108(2):85-97
From quantum-chemical calculations of rotational g factor and new experimental measurements of strengths of lines in infrared spectra of vibration–rotational bands v′–0 in absorption, with 1≤v′≤4, of 12C16O, and from analysis of 16,947 frequencies and wave numbers assigned to pure rotational and vibration–rotational transitions
within electronic ground state X
1Σ+, including new measurements of band 4–0 of 12C16O, we evaluate radial functions for potential energy and electric dipolar moment, the latter both in polynomial form and as
a rational function that has qualitatively correct behaviour under limiting conditions.
Received: 8 November 2001 / Accepted: 5 February 2002 / Published online: 14 August 2002 相似文献
7.
S. Calvo-Losada T. L. Sordo F. J. López-Herrera J. J. Quirante 《Theoretical chemistry accounts》2000,103(5):423-430
The influence of protecting the hydroxyl group of a β-oxy-α-diazo carbonyl compound on the competition between the Wolff
rearrangement (WR) and the [1,2]-hydrogen shift (HS) was investigated theoretically. Stationary points on the potential-energy
surface were located with the B3LYP density functional and the 6-31G** basis set. For the basic system geometry optimisations
at B3LYP/6-311+G** were performed to validate the reliability of the B3LYP/6-31G** calculations. Single-point energy calculations
were carried out at the B3LYP/6-311+G** level on the B3LYP/6-31G**-optimised geometries. Further insight into the processes
was achieved with the aid of the theory of “atoms in molecules” of Bader. The calculated energy barriers qualitatively predicted
the yields of HS and WR obtained experimentally. In order to rationalise the calculated energy barriers, it was necessary
to take into account not only the electronegativity of the protective groups but also the alignment of the migrating groups
with the depletion sites at the carbene centre. Further, when the hydroxyl group was not protected the existence of an intramolecular
hydrogen bond played an important role in both HS and WR.
Received: 30 December 1998 / Accepted: 7 May 1999 / Published online: 4 October 1999 相似文献
8.
A unified theory for the kinetic analysis of solid state reactions under any thermal pathway 总被引:1,自引:0,他引:1
Criado J. M. Pérez-Maqueda L. A. Gotor F. J. Málek J. Koga N. 《Journal of Thermal Analysis and Calorimetry》2003,72(3):901-906
The Ozawa concept of generalized time has been used for developing master plots for the different kinetic models describing
solid state reactions. These plots can be indistinctly used for analysing isothermal or non-isothermal experimental data.
It is demonstrated that it is not possible to discriminate the kinetic model from a single non-isothermal curve without a
previous knowledge of the activation energy. However, it has been shown that the ln [(da/dt)/f(a)] data taken from a set of DTG curves obtained at different heating rates lie on a single straight line when represented
as a function of 1/T only if the kinetic model really obeyed by the reaction is considered. Moreover, the true values of E and A are obtained from the slope and the intercept of this straight line.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Electronic stress tensor analysis of molecules in gas phase of CVD process for gesbte alloy
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Hiroo Nozaki Yuji Ikeda Kazuhide Ichikawa Akitomo Tachibana 《Journal of computational chemistry》2015,36(16):1240-1251
We analyze the electronic structure of molecules which may exist in gas phase of chemical vapor deposition process for GeSbTe alloy using the electronic stress tensor, with special focus on the chemical bonds between Ge, Sb, and Te atoms. We find that, from the viewpoint of the electronic stress tensor, they have intermediate properties between alkali metals and hydrocarbon molecules. We also study the correlation between the bond order which is defined based on the electronic stress tensor, and energy‐related quantities. We find that the correlation with the bond dissociation energy is not so strong while one with the force constant is very strong. We interpret these results in terms of the energy density on the “Lagrange surface,” which is considered to define the boundary surface of atoms in a molecule in the framework of the electronic stress tensor analysis. © 2015 Wiley Periodicals, Inc. 相似文献
10.
Preparative synthesis of the Corey chiral controller for enantioselective dihydroxylation of olefins
A five-step synthesis of both enantiomers of 1,2-di(2,4,6-trimethylbenzylamino)-1,2-diphenylethane,i.e., Corey (R,R)- and (S,S)-controllers for enantioselective dihydroxylation of olefins by osmium tetroxide, starting from α,α′-diphenylglyoxime, has
been developed. The key operations in the synthesis are the optical resolution of intermediaterac-1,2-diamino-1,2-diphenylethane into two enantiomers using only (R,R)-tartaric acid and the subsequent enhancement of the enantiomeric purity to >98% by crystallizations of the corresponding
Schiff's bis-bases. Analysis of the enantiomeric purity of the controllers can be easily performed using1H NMR spectra of their salts with (R)-α-methoxy-α-(trifluoromethyl)phenylacetic acid (MosherR-acid).
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 101–105, January, 1997. 相似文献
11.
L. A. Krinitskaya 《Russian Chemical Bulletin》1997,46(6):1140-1142
3-Bromo-2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl reacts with NH4OH to give 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl, a product of the Favorsky rearrangement. 3-Bromo-2,2,6,6-tetramethyl-4-piperidinone
is transformed under these conditions into a bicyclic amino ketone, while its 1-hydroxy derivative affords acyclic nitrosoenone.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1189–1191, June, 1997. 相似文献
12.
The numerical properties of the radial part of overlap integrals with the same screening parameters in the form of polynomials
in p = ξR over Slater-type orbitals have been studied and obtained by using three different methods. For that purpose, the characteristics
of auxiliary functions were used first, then Fourier transform convolution theorem, and recurrence relations for the basic
coefficients of A
s
n
l
λ,
n
′
l
′λ were used. The calculations of the radial part of overlap integrals with the same screening parameters were made in the range
1 ≤ n ≤ 75, 1 ≤ n′ ≤ 75, and 10−6 ≤ p.
Received: 18 January 2001 / Accepted: 5 April 2001 / Published online: 27 June 2001 相似文献
13.
N. A. Keiko Yu. A. Chuvashev T. A. Kuznetsova L. V. Sherstyannikova M. G. Voronkov 《Russian Chemical Bulletin》1998,47(12):2426-2428
The reaction of α-ethoxyacrolein with diethyl malonate in the presence of EtONa, lithium diisopropylamide, or the Na2CO3−benzene−Et3(PhCH2)NCl catalytic system proceeds as the Michael addition. In the presence of an equimolar amount of triethylamine, selective
1,2-addition followed by dehydration of the 1,2-adduct occurs. Owing to the strong +M effect of the EtO group, α-ethoxyacrolein
is a substantially less active Michael acceptor than acrolein.
Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2508–2510, December, 1998. 相似文献
14.
M. Cieslak-Golonka E. Ingier-Stocka A. Bartecki 《Journal of Thermal Analysis and Calorimetry》1995,43(1):157-167
The activation energy,E a taken from the thermal decomposition of KMnO4 and AgMnO4 was compared with the energy of the longest wavelength O→Mn ‘charge transfer’ (CT) transition. TheE a and CT correlation was found in these systems. However, such relationship can be valid when in the dissociation process the electron transfer is assumed to be the rate determining step. Thus, the permanganates as well as the previously studied chromates, are positive examples showing that in some cases, the energies derived from both methods can be comparable. 相似文献
15.
Validation criteria for developing ion-selective membrane electrodes for analysis of pharmaceuticals
The problem of validation criteria for developing ion-selective membrane electrodes for the analysis of pharmaceuticals arises
from the connection between the reliability of ion-selective membrane electrodes construction and the reliability of the analytical
information. Liquid membrane selective electrodes are more suitable for validation than the solid variety. The influence of
the stability of ion pair complexes from the membrane on various parameters (e.g. response, limit of detection, and selectivity)
is discussed. Validation criteria are proposed.
Received: 18 September 1997 · Accepted: 17 November 1997 相似文献
16.
N. A. Keiko Yu. A. Chuvashev L. G. Stepanova M. G. Voronkov 《Russian Chemical Bulletin》1998,47(12):2422-2425
The first stage of the reactions of alcohols with α-alkoxyacroleins in an acidic medium at 20°C under kinetically controlled
conditions is the Markovnikoff addition at the C=C bond to form 2,2-dialkoxypropanals (methylglyoxal ketals). Under conditions
of thermodynamic control, subsequent acetalization of the aldehyde group occurs to form 1,1,2,2-tetraalkoxypropanes. When
the duration of the reaction is further increased in the absence of a water acceptor, the ketal group undegroes hydrolysis
and methylglyoxal acetals are formed. A method was developed for the preparation of methylglyoxal ketals.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2504–2507, December, 1998. 相似文献
17.
The preparation and analysis of the oxygen mass fraction of three pure copper reference materials (BAM-379/1, BAM-379/2, BAM-379/3)
intended for the calibration of spark emission spectrometry are described here. Data of homogeneity testing and round robin
certification in collaboration with 12 independent laboratories from metalworking industry and research are reported. Problems
with the establishment of traceability in this special case are discussed.
Received: 20 July 2001 Accepted: 13 October 2001 相似文献
18.
Marti E. Kaisersberger E. Emmerich W.-D. 《Journal of Thermal Analysis and Calorimetry》2004,77(3):905-934
The definitions of the temperature resolution, the so-called resolution of DSC instruments given in literature are discussed.
A new definition of the resolution for DSC instruments is presented and outlined. The main characteristic introduced in this
new definition is a minimum between two caloric events as a prerequisite of an existing resolution. Possible candidates of
test substances have been evaluated. The oligomer n-hexatriacontane is revealing an interesting phenomenon, namely a lambda
transition which is in the peak temperature only 2 K lower than the melting temperature of 76°C. The substance was selected
as an ideal test substance for the quantification of the resolution of DSC instruments. The lambda transition is a second
order process which may reach under certain conditions the saturation of the occurring molecular dislocation within 0.2 K,
and after saturation the heat flow rate drops sharply down. Investigations concerning the main characteristics of n-hexatriacontane
in respect to the temperatures of transition (lambda transition and melting), to the involved enthalpies, and to the resolution
factors were performed as functions of the sample mass and the heating rate. The importance of relevant evaluation procedures
increasing the resolution factors of DSC curves are discussed and these procedures are integrated into the testing of the
resolution. The necessity for widening the experimental scope from instruments to evaluation procedures is forced by the existence
of instruments with built-in signal treatments based on electronic devices and software procedures. A comparison with literature
data is outlined for all of the mentioned characteristic values of n-hexatriacontane.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
S. Korhammer Rolf Herzig Peter Schramel Jorma Kumpulainen Bernd Markert Herbert Muntau Philippe Quevauviller 《Accreditation and quality assurance》2000,5(6):238-242
Cabbage is frequently used in environmental monitoring and food control, and, hence, cabbage reference materials (RMs) are
required for ensuring quality assurance. A cabbage RM was prepared in view of certification of specific elements from the
"black list" of high toxicological interest and nutritive importance. All tasks of the RM production (production of the plant
material, cutting and freeze-drying, determination of the residual water content, preparation of the RM, homogeneity testing,
stability testing, certification measurements) are described in detail.
Received: 12 November 1999 / Accepted: 29 January 2000 相似文献
20.
Absract The methodology for statistical processing of reports on nonconforming work and unexpected situations which occur in the laboratory
of Gamma-Ray Spectrometry Group at the Jožef Stefan Institute is presented. The results of statistical analyses are discussed.
Pareto analysis has shown that the majority of cases of nonconforming work originates in errors made by personnel. The sociological
and psychological aspects of strategies aimed at preventing careless work are discussed. It is proposed that motivation should
be used as a tool against habits that lessen awareness during routine operations. Specific recommendations regarding communication
with personnel are given.
Received: 20 July 2001 Accepted: 24 October 2001 相似文献