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1.
The polarity of the polyethylene oxide(PEO)/silica interface in 1,2-dichloroethane as solvent is classified by means of linear
solvation energy (LSE) relationships . The properties of the bare silica particle surface and the silica/PEO interface is
expressed by two terms: the dipolarity/polarizability (π*) of the interface and the hydrogen-bond donating ability (α) of
the surface silanols. These terms can be defined by using the Kamlet–Taft solvent parameters α and π* as a reference system.
The interfacial polarity parameters α and π* were calculated by means of correlation analyses of the energy of the UV/vis
absorption maxima of the surface polarity indicators: di-cyano-bis(1,10-phenanthroline) iron II, bis-4,4′-(N,N-dimethylamino) benzophenone, and 2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridino)phenolate when adsorbed onto the PEO/silica particle surface. The experimental values of the E
T(30) parameter of the PEO/silica interface are compared with independently calculated values employing specific LSE relations
derived for well-behaved regular solvents and functionalized silicas. PEO adsorption on silica causes a decrease in the value
of the α parameter of the silica surface and an evident increase in the dipolarity/polarizability of the interface.
Received: 16 December 1998 Accepted in revised form: 8 January 1999 相似文献
2.
Jaw-Cherng Hsu Chin-Hung Chang C.-Y. Liu 《Analytical and bioanalytical chemistry》1998,362(6):514-521
A silica based sorbent with an anion complexone polymer coating, [24]ane-N6 macrocycle, was prepared. The chelation properties of this material were investigated by elemental analysis, infrared spectra
and Voige’s method. The polymer-coated silica column (25– 40 μm, 100 × 4.6 mm i.d.) was employed for trace metal analyses.
Oxalic acid, malonic acid, succinic acid, citric acid, phthalic acid and acetic acid were used as mobile phases. Their retention
characteristics were elucidated. Oxalic acid was found to be the most effective eluent. With a mobile phase consisting of
oxalic acid (25 mM) and sodium nitrate (25 mM) at pH 4.2, the separation of copper(II), cadmium(II), cobalt(II) and zinc(II)
in sea water could be achieved. The identification of metal ions was performed at 510 nm using 4(2-pyridylazo)resorcinol (1
× 10–4 M) as post column reagent. The limits of detection were 5 × 10–7 M, 1 × 10–5 M, 3 × 10–5 M and 2 × 10–6 M for copper(II), cadmium(II), cobalt(II) and zinc(II) based on three times the standard deviation of the response for the
lowest concentration (n = 5) in the chromatogram with a sample volume of 50 μL. For evaluation of data reliability, oyster
tissue (NIST SRM 1566 a) was studied with the proposed system.
Received: 9 February 1998 / Revised: 15 May 1998 / Accepted: 16 June 1998 相似文献
3.
Jun-ichi Aihara 《Theoretical chemistry accounts》1999,102(1-6):134-138
A very simple but general index of kinetic stability, T, is proposed for π-electron systems, which is defined as a highest occupied molecular orbital (HOMO)- lowest unoccupied molecular orbital (LUMO)
energy separation multiplied by the number of conjugated atoms. This new index can be justified by relating it to the approximate
form of the superdelocalizability, an index of chemical reactivity defined by Fukui et al. It is best suited for predicting
the kinetic stability of fullerenes. All isolable fullerene isomers have T values larger than 13.
Received: 24 June 1998 / Accepted: 3 September 1998 / Published online: 17 December 1998 相似文献
4.
Abul K. Mallik Kaori Shingo Usha Ghimire Gautam Tsuyoshi Sawada Makoto Takafuji Hirotaka Ihara 《Analytical and bioanalytical chemistry》2010,397(2):623-629
Poly(2-N-carbazolylethyl acrylate) with terminal trimethoxysilyl groups was prepared as an organic phase and immobilized onto silica.
The retention behavior of the column packed with this carbazole-based polymer-immobilized silica (Sil-CEA) was investigated
by using various estrogenic steroids and corticoids in both reversed-phase and normal-phase liquid chromatography. As a result,
complete separation was confirmed for eight kinds of steroids with Sil-CEA. The most specific separation with Sil-CEA can
be emphasized by the high separation factor (e.g., α = 1.39 in methanol–water (7:3, v/v) at 35 °C) for 17α and 17β-estradiols, one of the most difficult pairs of isomers in chromatographic separation, whereas
for two kinds of commercially available polymeric ODS columns as references α = 1.01, only, under the same conditions. Because the excellent separation and retention order with Sil-CEA was maintained
even in a normal-phase mobile phase such as a hexane–2-propanol, it is estimated that the CEA phase has multiple interaction
mechanisms through stronger interactions such as dipole–dipole, carbonyl–π, and hydrogen bonding interactions than the hydrophobic
effect expected with ODS. 相似文献
5.
E. Morosanova A. Velikorodny Y. Zolotov 《Fresenius' Journal of Analytical Chemistry》1998,361(3):305-308
Two approaches to immobilize complex-forming analytical reagents (PAN, PAR, Xylenol orange, Brombenzothiazo, Crystal violet,
Cadion, and Sulfochlorophenolazorhodanine) for the preparation of new sorbents and indicator powders are suggested: on-line
coating of reversed-phase silica gel by reagents or doping of porous sol-gel silica with reagents. The retention of Ag, Cd,
Cu(II), Co(II), Fe(III), Mn(II), Ni, Pb, and Zn on the sorbents developed was investigated. Quantitative sorption and desorption
conditions were optimized. Procedures for the determination of Cd, Cu(II), Fe(III), Pb, and Zn with flame atomic absorption,
spectrophotometric, and diffusion scattering spectrometric detection were elaborated. Detection limits for Cd, Cu(II), Fe(III),
Pb, and Zn were 3 μg/L, 6 μg/L, 5 μg/L, 40 μg/L, and 1 μg/L, respectively. The procedures were used for the analysis of various
real samples, e.g., natural and waste waters, and food.
Received: 17 July 1997 / Revised: 20 January 1998 / Accepted: 5 February 1998 相似文献
6.
L. N. Mazalov G. K. Parygina É. S. Fomin N. V. Bausk S. B. Érenburg S. M. Zemskova S. V. Larionov 《Journal of Structural Chemistry》1998,39(6):923-927
SKβ spectra are studied for a series of nickel(II), zinc(II), and cadmium(II) dithiocarbamate complexes. Model quantum chemical
calculations of the electronic structure of planar chelate rings are reported. It is shown that the metal-ligand interaction
forming a coordination bond between the dithiocarbamate ligand and the metal mainly involves the nonbonding n-electrons and
the weakly bonding π-electrons localized on the sulfur atoms.
Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 6, pp. 1121–1126, November–December, 1998. 相似文献
7.
The capillary electrophoretic separation of Fe(II), Cu(II) and Zn(II) ions in an acidic buffer solution (pH 2.5) by complexation
with 1,10-phenanthroline is investigated. As 1,10-phenanthroline is a neutral ligand, the positively charged metal complexes
formed migrate in the same direction as the EOF, providing a rapid separation of metal ions in acidic buffers. The method
was applied to the determination of metal ions in vitamin tablets.
Received: 5 January 1998 / Revised: 27 March 1998 / Accepted: 15 May 1998 相似文献
8.
The capillary electrophoretic separation of Fe(II), Cu(II) and Zn(II) ions in an acidic buffer solution (pH 2.5) by complexation
with 1,10-phenanthroline is investigated. As 1,10-phenanthroline is a neutral ligand, the positively charged metal complexes
formed migrate in the same direction as the EOF, providing a rapid separation of metal ions in acidic buffers. The method
was applied to the determination of metal ions in vitamin tablets.
Received: 5 January 1998 / Revised: 27 March 1998 / Accepted: 15 May 1998 相似文献
9.
The molecular structures of the model systems of the polaron and the bipolaron in poly-para-phenylene (PPP) were calculated
by an ab initio molecular orbital (MO) method with fairly sophisticated approximations. The calculated models are monocations,
dications, monoanions and dianions of biphenyl, para-terphenyl, para-quaterphenyl, para-quinquephenyl and para-hexaphenyl.
The calculations show that the longer the PPP oligomer is, the stronger is the tendency to take on a non-planar twisting structure.
This was accounted for by the combination of repulsions between proximate ortho-hydrogen atoms with resonance interactions
between benzene π MOs. The magnitude of the resonance interactions was assessed by using the symmetry of benzene π MOs as
well as an analytical Hückel solution of the π MO for polyene. In addition, negatively charged polarons and bipolarons were
found to have a stronger tendency to take on a planar structure than positively charged ones. This result was also explained
by comparing the benzene π HOMO with the benzene π LUMO.
Received: 30 June 1998 / Accepted: 9 September 1998 / Published online: 23 February 1999 相似文献
10.
Susan Londesborough J. Mattusch Rainer Wennrich 《Analytical and bioanalytical chemistry》1999,363(5-6):577-581
The HPLC separation of eight anionic, cationic or neutral arsenic species (arsenite, arsenate, monomethylarsonic acid, dimethylarsinic
acid, arsenobetaine, arsenocholine, trimethylarsine oxide and tetramethylarsonium ion) on a high-capacity, anion-exchange
column (Ion Pac AS 7, Dionex) was studied. The separation was performed during one run with a nitric acid gradient ranging
from pH 4–1.3. The influence of sodium dodecyl sulfate (SDS), sodium octyl sulfate (SOS) and 1,2-benzenedisulfonic acid (BDSA)
as ion pairing eluent modifiers was investigated. In addition the effect of elevated temperatures (30 to 40 °C) was studied.
The best results were obtained at room temperature of 20 °C with 0.05 mM benzenedisulfonic acid as the eluent modifier. The
chromatograph was connected to an ICP-MS via a cross-flow nebulizer. Detection limits obtained with the optimized chromatographic
separation were 0.16–0.60 μg As L–1 for different species. The proposed speciation method was applied to the determination of arsenic species in the DORM-2 reference
material (Dogfish Muscle) and in aqueous extracts of mushrooms collected on arsenic contaminated ground.
Received: 3 August 1998 / Revised: 17 September 1998 / Accepted: 21 September 1998 相似文献
11.
Gerald Remberg Pat Sandra Wolfgang Nyiry Norbert Winker A. Nikiforov 《Fresenius' Journal of Analytical Chemistry》1998,362(4):404-408
The distribution of the 8557 theoretically possible structures of polychlorinated terphenyls (PCT) over the different degrees
of chlorination and basic terphenyl backbones has been calculated and is presented in detail. As congeners missing chlorine
atoms in an ortho position are suspected to be as noxious to organisms as dioxins, the number of these congeners is specified
as well. The gas chromatographic retention behavior of 14 PCT single standards is studied on four stationary liquid phases
for capillary columns (HP-Ultra 1, HP-5MS, RSL-300 and Polycarbonate) relative to 2,2′,3,4,4′,5,5′-heptachlorobiphenyl and
shows no consequent separation of PCT in terms of the degree of chlorination. Individual congeners have been assessed for
their suitability as internal standards in PCT analysis.
Received: 16 January 1998 / Revised: 3 April 1998 / Accepted: 7 April 1998 相似文献
12.
S. Pozdniakova R. Ragauskas A. Dikčius A. Padarauskas 《Analytical and bioanalytical chemistry》1999,363(1):124-125
A capillary electrophoretic method for the determination of EDTA has been developed. EDTA was converted to Ni(II)-EDTA prior
to separation, separated from Fe(III)-EDTA, thiosulphate, bromide and polythionates using a fused silica capillary (57 cm
× 75 μm I.D.) filled with a borate buffer (50 mmol L–1; pH 8.5; applied voltage, 30 kV) and detected at 214 nm. The separation time is about 6 min. The detection limit achieved
is 2 × 10–6 mol L–1 for EDTA. This method was applied for the determination of free EDTA in used fixing solutions.
Received: 27 February 1998 / Revised: 28 April 1998 / Accepted: 20 May 1998 相似文献
13.
S. Pozdniakova R. Ragauskas A. Dikius A. Padarauskas 《Fresenius' Journal of Analytical Chemistry》1999,363(1):124-125
A capillary electrophoretic method for the determination of EDTA has been developed. EDTA was converted to Ni(II)-EDTA prior
to separation, separated from Fe(III)-EDTA, thiosulphate, bromide and polythionates using a fused silica capillary (57 cm
× 75 μm I.D.) filled with a borate buffer (50 mmol L–1; pH 8.5; applied voltage, 30 kV) and detected at 214 nm. The separation time is about 6 min. The detection limit achieved
is 2 × 10–6 mol L–1 for EDTA. This method was applied for the determination of free EDTA in used fixing solutions.
Received: 27 February 1998 / Revised: 28 April 1998 / Accepted: 20 May 1998 相似文献
14.
The conformational stabilities of the α- and β-substituted enamines and vinyl ethers were predicted by orbital phase theory
and confirmed by ab initio molecular orbital calculations. Cyclic interaction significantly occurs among the nonbonding orbital
n
Y for the lone pair on the hetero atom Y (N in the enamines or O in the ethers), the π and π* orbitals of the CC bond, and the
σC-H or σ*C-X orbitals on the substituent CH2X. The cyclic -n
Y-π-σC-H-π*- interaction is favored by the orbital phase continuity in the α-substituted molecules, while the cyclic -n
Y-π-σ*C-X-π*- interaction is favored in the β-substituted molecules. The most stable conformation was then predicted to be synperiplanar
or (pseudo)equatorial in the α-substituted molecules and anticlinical or (pseudo)axial in the β-substituted molecules.
Received: 8 May 1998 / Accepted: 30 July 1998 / Published online: 16 November 1998 相似文献
15.
Jean-Pierre Duneau Serge Crouzy Yves Chapron Monique Genest 《Theoretical chemistry accounts》1999,101(1-3):87-91
The structure and dynamics of the ErbB-2 transmembrane domain have been examined using molecular dynamics techniques both
in vacuum and within an explicit hydrated L-α-dilauroyl-phosphatidyl-ethanolamine environment. In-vacuum simulations show that a highly cooperative structural transition
occurs frequently within the α-helical transmembrane domain which converts to local π-helices. We show that the α-helix alteration
does not depend upon the force field or initial side-chain conformations but is intimately related to the sequence. The membrane-like
environment does not prevent the structural transition in the helix but slows down the peptide dynamics indicating that the
appearance of a π-bulge is not an artifact of the vacuum approximation. The consequences of π-helix formation could be very
huge for the ErbB-2 receptor which is involved in numerous human cancers and also for other membrane proteins wherein similar
local structures are also observed experimentally.
Received: 9 May 1998 / Accepted: 3 September 1998 / Published online: 17 December 1998 相似文献
16.
José L. F. C. Lima C. Delerue-Matos M. Carmo M. C. V. F. Vaz Jeanine Silva 《Fresenius' Journal of Analytical Chemistry》1999,364(3):266-269
A flow injection analysis (FIA) system with potentiometric detection has been developed for the determination of citric acid
in commercial fruit juices using a copper-selective tubular electrode. It consists of the complexation of citrate ion with
copper (II) ion, monitoring the free copper (II) concentration. Linear relationships between the potential and log concentrations
of citric acid in the range of 1 × 10–3 mol/L – 1 × 10–2 mol/L were attained with samples injected in the system without prior treatment. Repeatability was determined by assessing
the relative standard deviation for ten replicate injections of different juice samples which varied from 1.2% to 3.0%. The
results provided by the automated system were compared with those of an enzymatic conventional method used for the analysis
of citric acid in food and a relative deviation of less than 4.0% was found. Recovery trials resulted in values from 97.0%
to 101.0%. The system allows a sampling frequency of 60 samples/h.
Received: 22 October 1998 / Revised: 14 December 1998 / Accepted: 16 December 1998 相似文献
17.
Summary The effect of column temperature on solute retention was investigated for 10 PCBs with different degrees of planarity (degree
of ortho position substitution). The variation of retention values (lnk) with temperature was measured using two solvents, n-hexane and dichloromethane, as mobile phase: retention decreases as
temperature increases. The relationship between lnk values and temperature (1/T) exhibits a good linearity. The ΔH
0 values calculated are in the −2 to −5 kcal mole−
1 range: they are very similar for compounds with the same degree of ortho-substitution and are significantly higher for non-ortho
substituted congeners. High temperature significantly improves separation efficiency (plate number significantly increases):
this effect is the dominant factor controlling chromatographic resolution, which improves with increasing temperature. Operating
at 40 °C, an efficient separation of planar PCBs was obtained with low solvent consumption. 相似文献
18.
Stepnowski P Nichthauser J Mrozik W Buszewski B 《Analytical and bioanalytical chemistry》2006,385(8):1483-1491
Current research indicates that replacing organic solvents with room-temperature ionic liquids may lead to remarkable improvements
in well-known processes. Ionic liquids have already been utilized as alternative solvents in organic synthesis and catalysis,
and also in electrochemistry and in separation sciences. Their wide applicability will soon result in their production on
an industrial scale. Therefore, analytical methods applicable to various matrices for product control and environmental monitoring
will be very much in demand. In this study, the usefulness of π...π interactions between alkylimidazolium and pyridinium cations
and the aromatic π...π active moiety of the stationary phase was investigated for the selective separation and analysis of
some ionic liquids. With phenyl-bonded phases, very good separations of the cations were achieved. Special attention was paid
to the short-chain hydrophilic entities, known to be poorly separated on conventional reversed-phase columns. Further, the
nature of the interactions occurring in the system under study was investigated by varying the content of methanol/acetonitrile
used as organic modifiers in the mobile phases. The analytical method developed here is simple and reproducible, and its quantitative
analytical performance was excellent. The paper also discusses the applicability of the method for monitoring degraded cations
of 1-butyl-3-methylimidazolium salts obtained in the Fenton process. 相似文献
19.
Maja Nendel Bernd Goldfuss K. N. Houk Klaus Hafner Udo Grieser 《Theoretical chemistry accounts》1999,102(1-6):397-400
B3LYP/6-31G* calculations on bis-periazulene (cyclohepta[def]-fluorene) predict a triplet ground state for this molecule. The singlet has an aromatic 14π-electron periphery but is 2 kcal/mol
higher in energy. The results agree with earlier predictions by Heilbronner.
Received: 19 August 1998 / Accepted: 6 October 1998 / Published online: 23 February 1999 相似文献