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1.
Mylonaki S Kiassos E Makris DP Kefalas P 《Analytical and bioanalytical chemistry》2008,392(5):977-985
An experimental setup based on a 23 full-factorial, central-composite design was implemented with the aim of optimising the recovery of polyphenols from olive
leaves by employing reusable and nontoxic solutions composed of water/ethanol/citric acid as extracting media. The factors
considered were (i) the pH of the medium, (ii) the extraction time and (iii) the ethanol concentration. The model obtained
produced a satisfactory fit to the data with regard to total polyphenol extraction (R
2 = 0.91, p = 0.0139), but not for the antiradical activity of the extracts (R
2 = 0.67, p = 0.3734). The second-order polynomial equation obtained after analysing the experimental data indicated that ethanol concentration
and time mostly affected the extraction yield, but that increased pH values were unfavourable in this regard. The maximum
theoretical yield was calculated to be 250.2 ± 76.8 mg gallic acid equivalent per g of dry, chlorophyll-free tissue under
optimal conditions (60% EtOH, pH 2 and 5 h). Liquid chromatography–electrospray ionisation mass spectrometry of the optimally
obtained extract revealed that the principal phytochemicals recovered were luteolin 7-O-glucoside, apigenin 7-O-rutinoside and oleuropein, accompanied by smaller amounts of luteolin 3′,7-O-diglucoside, quercetin 3-O-rutinoside (rutin), luteolin 7-O-rutinoside and luteolin 3′-O-glucoside. Simple linear regression analysis between the total polyphenol and antiradical activity values gave a low and
statistically insignificant correlation (R
2 = 0.273, p > 0.05), suggesting that it is not the sheer amount of polyphenols that provides high antioxidant potency; instead, this
potency is probably achieved through interactions among the various phenolic constituents. 相似文献
2.
E. V. Osintseva L. K. Neudachina Yu. G. Yatluk 《Russian Journal of Inorganic Chemistry》2010,55(10):1644-1650
The azo coupling reaction of N-(2-carboxyethyl)anthranilic acid and N,N,N′,N′-tetrabis(2-carboxyethyl)-1,3-phenylenediamine with diazosulfanilic acid yielded the complexones sodium 4-N-(2-carboxyethyl)amino-5-carboxyazobenzene-4′-sulfonate
(I) and 2,4-N,N,N′,N′-tetrabis(2-carboxyethyl)diaminoazobenzene-4′-sulfonic acid (II), respectively. The acidity constants of I and II (20°C, μ = 0.1M KCl) were determined to be as follows: for I, pK
00 = 1.29 ± 0.13, pK
0 = 2.92 ± 0.07, pK
1 = 3.92 ± 0.05, pK
2 = 5.16 ± 0.03; for II, pK
00 = 2.35 ± 0.06, pK
0 = 2.81 ± 0.09, pK
1 = 3.21 ± 0.11, pK
2 = 3.81 ± 0.09, pK
3 = 4.34 ± 0.04, pK
4 = 5.03 ± 0.06, pK
5 = 6.67 ± 0.07. The electronic absorption spectra of I and II were measured, and acid-base equilibrium scheme for I and II in aqueous solutions were suggested. The complexation constants of I and II with copper(II) ions were determined to be logK
CuQI= 5.47 ± 0.06 and logK
CuQII= 5.72 ± 0.13 (20°C, μ = 0.1 M KCl). 相似文献
3.
Two new complexes with formula VOL2·nH2O ((1) L: 4′,5,7-trihydroxyflavone-7-rhamnoglucoside (naringin), n = 8; (2) L: 3′,4′,7-tris[O-(2-hydroxyethyl)]rutin (troxerutin), n = 0) were synthesised and characterised. The IR and UV–Vis spectral data indicate that these flavones act as bidentate chelating
ligands and generate VO(II) complexes with a square-pyramidal stereochemistry. The thermal analysis (TG, DTA) elucidated the
composition and also the number and nature of the water molecules. The thermal behavior indicates also a strong interaction
between oxovanadium (IV) and these oxygen donor ligands. 相似文献
4.
Lutz Preu Wolfgang Kliegel Steven J. Rettig James Trotter 《Monatshefte für Chemie / Chemical Monthly》2001,132(10):1213-1224
Summary. The structure of the dehydrogenation product 1′,3a′-dihydro-3′-((1,3-dioxoindan-2-ylidene)-phenyl-methyl)-5′-phenyl-spiro-(indan-2,1′-pyrrolo[3,4-c]pyrrole)-1,3,4′,6′-(5′H, 6a′H)-tetrone derived from the cycloadducts (±)-(3a′S,6a′R)-1′,3a′-dihydro-3′-((R)-α-(1,3-dioxoindanyl)-benzyl)-5′-phenyl-spiro-(indan-2,1′-pyrrolo[3,4-c]pyrrole)-1,3,4′,6′(5H,6a′H)-tetrone and/or (±)-(3a′S,6a′R)-1′,3a′-dihydro-3′-((S)-α-(1,3-dioxoindanyl)-benzyl)-5′-phenyl-spiro-(indan-2,1′-pyrrolo[3,4-c]pyrrole)-1,3,4′,6′(5H,6a′H)-tetrone, which were synthesized by 1,3-dipolar cycloaddition of N-phenylmaleimide to 2-((2-(1,3-dioxoindan-2-yl)-2-phenyl-ethenyl)-imino)-indan-1,3-dione,
was determined by X-ray analysis. Crystal data (CCD, 180 K): rhombohedral, R&3macr;;, a = 34.0871(7), c = 13.9358(5) ?, Z = 18; the structure was solved by direct methods and refined by full-matrix least-squares procedures to R(F, I ≥ 3σ(I)) = 0.053. The molecule contains a central folded ring system of two cis-fused 5-membered heterocyclic rings; each ring is nearly planar, and the angle between the rings amounts to 59.0°. Dynamic
1H NMR spectroscopy of the product revealed an exchange process caused by restricted rotation of the double bonded 1,3-indandione
moiety and the phenyl group about the Csp2-Csp2 single-bonds. Molecular modeling and complete lineshape analysis indicated a four site exchange process for which free energies
of activation and free energies could be established. ΔG
‡ values for the barriers of rotation are in the range of 57–59 kJ · mol − 1 at 273 K, which is unusually high for an unsubstituted phenyl group.
Received May 3, 2001. Accepted (revised) June 8, 2001 相似文献
5.
Lemonia Valianou Konstantina Stathopoulou Ioannis Karapanagiotis Prokopios Magiatis Eleni Pavlidou Alexios-Leandros Skaltsounis Yannis Chryssoulakis 《Analytical and bioanalytical chemistry》2009,394(3):871-882
Young fustic (Cotinus coggygria Scop.; Anacardiaceae) has been used as a dyestuff since antiquity. Phytochemical investigation of the methanol extract of
the heartwood has led to the isolation and structure elucidation by nuclear magnetic resonance and mass spectrometry (MS)
of 3′,4′,6-trihydroxyaurone (sulfuretin) and 3′,4′,7-trihydroxyflavonol (fisetin) as well as 3′,4′,7-trihydroxyflavanol (fustin),
3′,4′,5,7-tetrahydroxyflavonol (quercetin), 3′,4′,5,7-tetrahydroxyflavanol (taxifolin), 4′,7-dihydroxyflavanol, 3′,4′,7-trihydroxyflavanone
(butin), 4′,7-dihydroxyflavanone (liquiritigenin), trans-2′,3,4,4′-tetrahydroxychalcone (butein), 4′,5,7-trihydroxyflavanone and trans-2′,4,4′-trihydroxychalcone (isoliquiritigenin). The isolated compounds were used as reference materials for the development
of a high-performance liquid chromatography–diode array detector–MS method, which was then applied to analyse (1) fresh silk
samples dyed with young fustic, (2) dyed silk subjected to artificially accelerated light ageing and (3) historical silk micro-samples,
extracted from ecclesiastical post-Byzantine garments (fifteenth to eighteenth century), which belong to monasteries of Mount
Athos. Sulfuretin and fisetin, which are usually used as markers for the identification of the yellow dye and, for the first
time, some of the aforementioned flavonoid components of young fustic were identified in the historical extracts. Furthermore,
preliminary experiments suggested that although the amounts of the dye components decrease with light ageing, the relative
ratio of fisetin and sulfuretin, after a first step of ageing, seems to be almost unaffected by such degradation processes
raised by light. The effect of the latter on the morphology of the dyed silk fibres is briefly investigated by scanning electron
microscopy. 相似文献
6.
Terézia Vojtylová Dana Dospivová Olga Třísková Iveta Pilařová Přemysl Lubal Marta Farková Libuše Trnková Petr Táborský 《Chemical Papers》2009,63(6):731-737
Acidobasic properties of purine and pyrimidine bases (adenine, cytosine) and relevant nucleosides (adenosine, cytidine) were
studied by means of glass-electrode potentiometry and the respective dissociation constants were determined under given experimental
conditions (I = 0.1 M (NaCl), t = (25.0 ± 0.1) °C): adenine (pK
HL = 9.65 ± 0.04, pK
H2L = 4.18 ± 0.04), adenosine (pK
H2L = 3.59 ± 0.05), cytosine (pK
H2L = 4.56 ± 0.01), cytidine (pK
H2L = 4.16 ± 0.02). In addition, thermodynamic parameters for bases: adenine (ΔH
0 = (−17 ± 4) kJ mol−1, ΔS
0 = (23 ± 13) J K−1 mol−1), cytosine (ΔH
0 = (−22 ± 1) kJ mol−1, ΔS
0 = (13 ± 5) J K−1 mol−1) were calculated. Acidobasic behavior of oligonucleotides (5′CAC-CAC-CAC3′ = (CAC)3, 5′AAA-CCC-CCC3′ = A3C6, 5′CCC-AAA-CCC3′ = C3A3C3) was studied under the same experimental conditions by molecular absorption spectroscopy. pH-dependent spectral datasets
were analyzed by means of advanced chemometric techniques (EFA, MCR-ALS) and the presence of hemiprotonated species concerning
(C+-C) a non-canonical pair (i-motif) in titled oligonucleotides was proposed in order to explain experimental data obtained according to literature. 相似文献
7.
M. Teresa Barros João Martins Rui M. Pinto Mónica S. Santos Helena M. V. M. Soares 《Journal of solution chemistry》2009,38(12):1504-1519
As part of a search for environmentally friendly metal chelating ligands, the stability constants of N, N′-ethylenedi-L-cysteine
(EC) complexes with Ca(II), Cu(II), Mg(II) and Mn(II) were determined by potentiometry with a glass electrode in aqueous solutions
containing 0.1 mol⋅L−1 KCl at 25 °C. Final models are proposed. For the Ca(II)–EC system, the overall stability constants are log 10
β
CaHL=14.53±0.03, log 10
β
CaL=4.79±0.01 and log 10
β
CaL2=8.38±0.04. For the M(II)–EC systems, where M=Cu(II) or Mg(II), the overall stability constants are log10
β
CuHL=31.19±0.02 and log 10
β
CuL=27.02±0.06 for Cu(II), and are log 10
β
MgHL=14.84±0.02 and log 10
β
MgL=6.164±0.008 for Mg(II). For the Mn(II)–EC system, the overall stability constant is log 10
β
MnL=10.12±0.01.
Metal–chelate speciations simulations showed that EC is an efficient chelating agent for Cd(II), Co(II), Cu(II), Ni(II), Pb(II)
and Zn(II) for pH≥7. 相似文献
8.
M. López-Sánchez M. J. Ayora-Cañada A. Molina-Díaz M. Siam W. Huber G. Quintás S. Armenta B. Lendl 《Analytical and bioanalytical chemistry》2009,394(8):2137-2144
A mid-infrared enzymatic assay for label-free monitoring of the enzymatic reaction of fructose-1,6-bisphosphatase with fructose
1,6-bisphosphate has been proposed. The whole procedure was done in an automated way operating in the stopped flow mode by
incorporating a temperature-controlled flow cell in a sequential injection manifold. Fourier transform infrared difference
spectra were evaluated for kinetic parameters, like the Michaelis–Menten constant (K
M) of the enzyme and V
max of the reaction. The obtained K
M of the reaction was 14 ± 3 g L−1 (41 μM). Furthermore, inhibition by adenosine 5′-monophosphate (AMP) was evaluated, and the K
MApp value was determined to be 12 ± 2 g L−1 (35 μM) for 7.5 and 15 μM AMP, respectively, with V
max decreasing from 0.1 ± 0.03 to 0.05 ± 0.01 g L−1 min−1. Therefore, AMP exerted a non-competitive inhibition. 相似文献
9.
Effect of pH and ionic strength on the interaction of humic acid with aluminium oxide 总被引:4,自引:0,他引:4
E. Tombácz Á. Dobos M. Szekeres H. D. Narres E. Klumpp I. Dékány 《Colloid and polymer science》2000,278(4):337-345
The effect of pH and neutral electrolyte on the interaction between humic acid/humate and γ-AlOOH (boehmite) was investigated.
The quantitative characterization of surface charging for both partners was performed by means of potentiometric acid–base
titration. The intrinsic equilibrium constants for surface charge formation were logK
a,1
int=6.7±0.2 and logK
a,2
int = 10.6±0.2 and the point of zero charge was 8.7±0.1 for aluminium oxide. The pH-dependent solubility and the speciation of
dissolved aluminium was calculated (MINTEQA2). The fitted (FITEQL) pK values for dissociation of acidic groups of humic acid were pK
1 = 3.7±0.1 and pK
2 = 6.6±0.1 and the total acidity was 4.56 mmol g−1. The pH range for the adsorption study was limited to between pH 5 and 10, where the amount of the aluminium species in the
aqueous phase is negligible (less than 10−5 mol dm−3) and the complicating side equilibria can be neglected. Adsorption isotherms were determined at pH ∼ 5.5, ∼8.5 and ∼9.5,
where the surface of adsorbent is positive, neutral and negative, respectively, and at 0.001, 0.1, 0.25 and 0.50 mol dm−3 NaNO3. The isotherms are of the Langmuir type, except that measured at pH ∼ 5.5 in the presence of 0.25 and 0.5 mol dm−3 salt. The interaction between humic acid/humate and aluminium oxide is mainly a ligand-exchange reaction with humic macroions
with changing conformation under the influence of the charged interface. With increasing ionic strength the surface complexation
takes place with more and more compressed humic macroions. The contribution of Coulombic interaction of oppositely charged
partners is significant at acidic pH. We suppose heterocoagulation of humic acid and aluminium oxide particles at pH ∼ 5.5
and higher salt content to explain the unusual increase in the apparent amount of humic acid adsorbed.
Received: 20 July 1999 /Accepted in revised form: 20 October 1999 相似文献
10.
Silvia Castrignanò Sheila J. Sadeghi Gianfranco Gilardi 《Analytical and bioanalytical chemistry》2010,398(3):1403-1409
Human flavin-containing monooxygenases are the second most important class of drug-metabolizing enzymes after cytochromes
P450. Here we report a simple but functional and stable enzyme-electrode system based on a glassy carbon (GC) electrode with
human flavin-containing monooxygenase isoform 3 (hFMO3) entrapped in a gel cross-linked with bovine serum albumin (BSA) by
glutaraldehyde. The enzymatic electrochemical responsiveness is characterised by using well-known substrates: trimethylamine
(TMA), ammonia (NH3), triethylamine (TEA), and benzydamine (BZD). The apparent Michaelis–Menten constant (K′M) and apparent maximum current (I′max) are calculated by fitting the current signal to the Michaelis–Menten equation for each substrate. The enzyme-electrode has
good characteristics: the calculated sensitivity was 40.9 ± 0.5 mA mol−1 L cm−2 for TMA, 43.3 ± 0.1 mA mol−1 L cm−2 for NH3, 45.2 ± 2.2 mA mol−1 L cm−2 for TEA, and 39.3 ± 0.6 mA mol−1 L cm−2 for BZD. The stability was constant for 3 days and the inter-electrode reproducibility was 12.5%. This is a novel electrochemical
tool that can be used to investigate new potential drugs against the catalytic activity of hFMO3. 相似文献
11.
Carina M. M. Machado Paula Gameiro Helena M. V. M. Soares 《Journal of solution chemistry》2008,37(5):603-617
The complexation behavior of eight M–(buffer)
x
–(OH)
y
systems involving two divalent ions (cobalt and nickel) and four zwitterionic biological buffers (AMPSO, DIPSO, TAPS and
TAPSO) were characterized. Complex formation was detected for all eight M–(buffer)
x
–(OH)
y
systems studied, but fully defined final models were obtained for only four of these systems. For systems involving cobalt
or nickel with AMPSO or TAPS, a complete characterization of the systems was not possible in the studied buffer pH-range.
Metal complexation was studied by glass-electrode potentiometry (GEP) and UV-Vis spectroscopy at 25.0 °C and I=0.1 mol⋅dm−3 KNO3 ionic strength. For the Ni–(L)
x
–(OH)
y
and Co–(L)
x
–(OH)
y
systems, with L = TAPSO or DIPSO, the proposed final models and overall stability constants were obtained by combining results
from both techniques. For the Ni–(L)
x
–(OH)
y
systems, the measured values of the stability constants are log 10
β
NiL=3.0±0.1 and log 10
β
NiL2=4.8±0.1 for L = TAPSO, and log 10
β
NiL=2.7±0.1 and log 10
β
NiL2=4.6±0.1 for L = DIPSO. For the Co–(L)
x
–(OH)
y
systems, the overall stability constants are log 10
β
CoL=2.2±0.1, log 10
β
CoL2=3.6±0.2 and log 10
β
CoL(OH)=7.6±0.1 for L = TAPSO, and log 10
β
CoL=2.0±0.1 and log 10
β
CoL(OH)=7.8±0.1 for L = DIPSO. For both buffers, the CoL(OH) species is characterized by a major structural rearrangement. 相似文献
12.
Fattori Alberto Peter Laurence M. McCall Keri L. Robertson Neil Marken Frank 《Journal of Solid State Electrochemistry》2010,14(10):1929-1936
The electrochemical and spectroelectrochemical properties of the sensitizer dye Z907 (cis-RuLL'(SCN)2 with L=4,4′-dicarboxylic acid-2,2′-bipyridine and L'=4,4′-dinonyl-2,2′-bipyridine) adsorbed on fluorine-doped tin oxide (FTO) and TiO2 surfaces have been investigated. Langmuirian binding constants for FTO and TiO2 are estimated to be 3 × 106 M−1 and 4 × 104 M−1, respectively. The Ru(III/II) redox process is monitored by voltammetry and by spectroelectrochemistry. For Z907 adsorbed
onto FTO, a slow EC-type electrochemical reaction is observed with a chemical rate constant of ca. k = 10−2 s−1 leading to Z907 dye degradation of a fraction of the FTO-adsorbed dye. The Z907 adsorption conditions affect the degradation
process. No significant degradation was observed for TiO2-adsorbed dye. Degradation of the Z907 dye affects the electron hopping conduction at the FTO–TiO2 interface. 相似文献
13.
Vesna Kunti? Dusěan Malesěev Zorica Radovi? Vladana Vukojevi? 《Monatshefte für Chemie / Chemical Monthly》2000,18(5):769-777
In the present work, rutin (3,3′ ,4′ ,5,7-pentahydrohyflavone-3-rhamnoglucoside) was determinated via a complexing reaction with a titanyloxalate anion. K2[TiO(C2O4)2] and rutin react in 50% ethanol forming a 1:2 complex in a pH range from 4.00 to 11.50, in which the TiO(C2O4)2 2− ion is linked to rutin through the 4-carbonyl and 5-hydroxyl group. The thermodynamic stability constant log β2 0 of the complex is determined to 10.80 at pH = 6.50. The change of the standard Gibbs free energy Δ G0 amounts to −61 kJċ mol−1, indicating that the process of complex formation is spontaneous. The optimal conditions for the spectrophotometric determination of microconcentrations of rutin are at pH=6.40 and λ= 430 nm, where the complex shows an absorption maximum with a molar absorption coefficient a 430=(60±2)ċ103 dm3ċ mol−1ċ cm−1. The method is applied rutin determination from tablets. 相似文献
14.
Vesna Kuntić Dusěan Malesěev Zorica Radović Vladana Vukojević 《Monatshefte für Chemie / Chemical Monthly》2000,131(7):769-777
Summary. In the present work, rutin (3,3′ ,4′ ,5,7-pentahydrohyflavone-3-rhamnoglucoside) was determinated via a complexing reaction with a titanyloxalate anion. K2[TiO(C2O4)2] and rutin react in 50% ethanol forming a 1:2 complex in a pH range from 4.00 to 11.50, in which the TiO(C2O4)2
2− ion is linked to rutin through the 4-carbonyl and 5-hydroxyl group. The thermodynamic stability constant log β2
0 of the complex is determined to 10.80 at pH = 6.50. The change of the standard Gibbs free energy Δ G0 amounts to −61 kJċ mol−1, indicating that the process of complex formation is spontaneous. The optimal conditions for the spectrophotometric determination
of microconcentrations of rutin are at pH=6.40 and λ= 430 nm, where the complex shows an absorption maximum with a molar absorption coefficient a
430=(60±2)ċ103 dm3ċ mol−1ċ cm−1. The method is applied rutin determination from tablets.
Received January 4, 2000. Accepted (revised) February 17, 2000 相似文献
15.
Jana Ehlerova Liliana Trevani Josef Sedlbauer Peter Tremaine 《Journal of solution chemistry》2008,37(6):857-874
The UV-visible spectra of aqueous o-, m-, and p-nitrophenol were measured as a function of pH at temperatures from 50 to 225 °C at a pressure of 7 MPa. These were used to
determine equilibrium constants for the acid ionization reaction of each isomer. The new results were combined with literature
data on the ionization of nitrophenols and used for parameter optimization in the thermodynamic model of Marshall and Franck
(J. Phys. Chem. Ref. Data 10:295–304, [1981]), to describe the dependence of ionization properties on temperature and pressure. The model yields predictions of the ionization
constants for o-, m-, and p-nitrophenol, log 10
K
a, to at least 250 °C and 20 MPa with an estimated uncertainty in log 10
K
a of less than ±0.06. 相似文献
16.
A 66-kDa thermostable family 1 Glycosyl Hydrolase (GH1) enzyme with β-glucosidase and β-galactosidase activities was purified
to homogeneity from the seeds of Putranjiva roxburghii belonging to Euphorbiaceae family. N-terminal and partial internal amino acid sequences showed significant resemblance to plant GH1 enzymes. Kinetic
studies showed that enzyme hydrolyzed p-nitrophenyl β-d-glucopyranoside (pNP-Glc) with higher efficiency (K
cat/K
m = 2.27 × 104 M−1 s−1) as compared to p-nitrophenyl β-d-galactopyranoside (pNP-Gal; K
cat/K
m = 1.15 × 104 M−1 s−1). The optimum pH for β-galactosidase activity was 4.8 and 4.4 in citrate phosphate and acetate buffers respectively, while
for β-glucosidase it was 4.6 in both buffers. The activation energy was found to be 10.6 kcal/mol in the temperature range
30–65 °C. The enzyme showed maximum activity at 65 °C with half life of ~40 min and first-order rate constant of 0.0172 min−1. Far-UV CD spectra of enzyme exhibited α, β pattern at room temperature at pH 8.0. This thermostable enzyme with dual specificity
and higher catalytic efficiency can be utilized for different commercial applications. 相似文献
17.
Maria das Graças Nunes Matos Vivian Gouveia Diniz Cesar Augusto Moraes de Abreu Augusto Knoechelmann Valdinete Lins da Silva 《Adsorption》2009,15(1):75-80
Heavy metals can be removed from effluents and recovered using physico-chemical mechanisms as biosorption processes. In this
work “Arribada” seaweed biomass was employed to assess its biosorptive capacity for the chromium (Cr3+) and lead (Pb2+) cations that usually are present in waste waters of plating industries. Equilibrium and kinetic experiments were conducted
in a mixed reactor on a batch basis. Biosorption equilibrium and fluid-solid mass transfer constants data were analyzed through
the concept of ion exchange sorption isotherm. The respective equilibrium exchange constants (K
eqCr=173.42, K
eqPb=58.86) and volumetric mass transfer coefficients ((k
mCr
a)′=1.13×10−3 s−1, (k
mPb
a)′=0.89×10−3 s−1) were employed for the dynamic analysis of Cr and Pb sorption in a fixed-bed flow-through sorption column. The breakthrough
curves obtained for both metals were compared with the predicted values by the heterogeneous model (K
eqCr=171.29, K
eqPb=60.14; k
mCr
a=7.81×10−2 s−1, k
mPb
a=2.43×10−2 s−1), taking into account the mass transfer process. The results suggest that these algae may be employed in a metal removal/recovery
process at low cost.
An erratum to this article can be found at 相似文献
18.
Miraç Ocak Hakan Alp Halit Kantekin Hülya Karadeniz Ümmühan Ocak 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(1-2):17-24
Three new macrocyclic crown ether ligands containing nitrogen–oxygen donor atoms were designed and synthesized from 1,4-bis(2′-formylphenyl)-1,4-dioxabutane
and 4-nitro-o-phenylenediamine. Ion-pair extraction of metal picrates such as Ag+, Hg2+, Cd2+, Zn2+, Cu2+, Ni2+, Mn2+, Co2+, and Pb2+ from aqueous phase to the organic phase was carried out using the novel ligands. The solvent effect over the metal picrate
extractions was investigated at 25 ± 0.1 °C by using UV–visible spectrometry. The extractability and the values of the extraction
constants (log Kex) were determined for the extracted complexes. 相似文献
19.
Contracted Gaussian-type function (CGTF) basis sets are reported for valence p orbitals of the six alkali and alkaline-earth atoms Li, Be, Na, Mg, K, and Ca for molecular applications. These sets are
constructed by Roothaan–Hartree–Fock calculations for the ns → np excited states of atoms, in which both linear and nonlinear parameters of CGTFs are variationally optimized. The present
CGTF sets reproduce well the numerical Hartree–Fock ns → np excitation energies: the largest error is 0.0009 hartrees for Li. New CGTFs are tested with diatomic Li2, Na2, K2, and MH molecules, where M = Li, Be, Na, Mg, K, and Ca, by self-consistent-field (SCF) and multiconfiguration SCF calculations.
The resultant spectroscopic constants compare well with those of more elaborate calculations and are sufficiently close to
experimental values, supporting the efficiency of the present set for the valence p orbitals.
Received: 9 July 1998 / Accepted: 17 September 1998 / Published online: 1 February 1999 相似文献
20.
Isotope ratio measurements characterizing 202Hg/200Hg in NIST SRM 3133 Mercury Standard Solution were undertaken by multicollector inductively coupled plasma mass spectrometry
employing NIST SRM 997 Tl for mass bias correction by use of the slope and the intercept obtained from a natural logarithmic
plot of each session of measurements of 202Hg/200Hg against 205Tl/203Tl. The calculated value of 1.285333 ± 0.000192 (mean and one standard deviation, n = 40) for the mass bias corrected 202Hg/200Hg was then used for mass bias correction of other Hg isotope pairs. Ratios of 0.015337 ± 0.000011, 1.68770 ± 0.00054, 2.3056 ± 0.0015,
1.3129 ± 0.0013, 2.9634 ± 0.0038, and 0.67937 ± 0.0013 (expanded uncertainty, k = 2) were obtained for 196Hg/198Hg, 199Hg/198Hg, 200Hg/198Hg, 201Hg/198Hg, 202Hg/198Hg, and 204Hg/198Hg, respectively. Reduction of Hg(II) to Hg0 in solutions of SRM 3133 was then undertaken using SnCl2, NaBH4, UV photolysis in the presence of formic acid, and ethylation of Hg(II) using NaBEt4. These reactions induced significant isotope fractionation with maximum values of 1.17 ± 0.07, 1.08 ± 0.09, 1.34 ± 0.07, and
3.59 ± 0.09‰ (one standard deviation, 1SD, n = 5) for δ
202/198Hg relative to the initial isotopic composition in the solution following 85–90% reduction of the Hg by SnCl2, NaBH4, UV photolysis, and ethylation with NaBEt4, respectively. Mass-dependent fractionation was found to be dominant for all reduction processes.
Figure Mass dependence of fractionation for all samples from Hg fractionation experiments using NaBEt4. Solid lines are the theoretically predicted MDF based on δ′ 202/198
Hg using equation 7. Error bars displayed are one standard deviation of the mean of 5 measurements of each sample 相似文献