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排序方式: 共有213条查询结果,搜索用时 50 毫秒
1.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and
their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically
using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition
on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content
in contrast those of L-lysine and L-histidine esters. 相似文献
2.
R. A. Stukan T. V. Dudareva Yu. N. Kil’yanov A. V. Polyakova 《Russian Journal of Inorganic Chemistry》2006,51(1):1-4
A tetragonal 123 phase with the composition close to CeLa2 { Cu
2
2+
} [Mg2+]O8 (the braces indicate the Cu(2) positions; the brackets indicate the Cu(1) positions) with the parameters a = b = 0.3909(3) nm, c = 1.6591(8) nm was prepared at 860°C under an oxygen atmosphere with an elevated oxygen pressure. When the lanthanum-for-barium
substitution was incomplete, the resulting 123 phase had the composition close to CeLa1.7Ba0.3{ Cu
1.7
2+
} [Mg]O8 with the unit cell parameters a = b = 0.3868(3) nm, c = 1.6578(8) nm that contains Cu3+ in the Cu(2) positions. The partial substitution of barium for lanthanum (the melting point of barium oxide is almost 500°C
lower that of the lanthanum oxide) appreciably facilitated the synthesis: the 123 phase in this sample was more than 90%.
The existence of Cu3+ in the Cu(2) positions enhanced the electrical conductivity of the sample. 相似文献
3.
The Chebychev polynomials associated to any given moments μn ∞ 0 are formally orthogonal with respect to the formal δ-series $$w(x)= {\sum^\infty_0}(- 1)^{n}\mu_{{n}}\delta^{(n)}(x)/n!.$$ We show that this formal weight can be a true hyperfunctional weight if its Fourier transform is a slowly increasing holomorphic function in some tubular neighborhood of the real line. It provides a unifying treatment of real and complex orthogonality of Chebychev polynomials including all classical examples and characterizes Chebychev polynomials having Bessel type orthogonality. 相似文献
4.
5.
Sik Min K Weyhermuller T Wieghardt K 《Dalton transactions (Cambridge, England : 2003)》2004,(1):178-186
The potentially tridentate ligand 2-(8-aminoquinolino)-4,6-di-tert-butylphenol, H[1LAP], has been synthesized and its coordination chemistry with Mn(IV), Fe(III), and Co(III) has been investigated by X-ray crystallography, electro- and magnetochemistry, electronic, Mossbauer and EPR spectroscopies. The following complexes have been prepared [MnIV(1LAP-H)2](1), St=3/2; [MnIV(1LAP-H)(1LISQ)](PF6).CH2Cl2 (2), St= 1; [FeIII(1LISQ)2](ClO4).0.5H2O (3), St=1/2; [FeIII(1LISQ)(3,5-dtcat)]2 (4), St= 0; K[CoII(1LISQ)(1LIBQ)](NCS)2 (5), St= 1; [CoIII2(NCS)2(1LAP-H)2(AQ)] (6), St=0, where (1LAP-H)2- corresponds to the o-iminophenolate(2-) dianion, (1LISQ)- is the o-iminobenzosemiquinonate(1-) pi radical derivative of the ligand H[1LAP], (1LIBQ)0 is the neutral iminobenzoquinone ligand, and 3,5-dtcat is 3,5-di-tert-butylcatecholate(2-) and N,N-coordinated (AQ) is 8-aminoquinoline. It is shown that the pi radical anions in 2, 3, 4 couple antiferromagnetically to the respective paramagnetic metal ion. Complex 4 is a dinuclear neutral complex with weak antiferromagnetic coupling between two [FeIII1LISQ)(3,5-dtcat)] halves. The asymmetrically ligated complex 6 contains two bridging (1LAP-H)2- ligands and two diamagnetic CoIII ions. In contrast, 5 is correctly described as [CoII(1LISQ)(1LIBQ)]+ rather than [CoIII(1LISQ)2]+ since it possesses a temperature-independent magnetic moment of mueff(10-298 K)= 3.0 muB indicating an St=1 ground state which is attained via strong antiferromagnetic coupling (|J> or =200 cm(-1)) between a high spin cobalt(II) ion (SCo=3/2) and a single pi radical anion (Srad=1/2). 相似文献
6.
The coordination chemistries of the potential tetradentate ligands N,N'-bis(3,5-di-tert-butyl-2-hydroxyphenyl)ethylenediamine, H4[L1], the unsaturated analogue glyoxal-bis(2-hydroxy-3,5-di-tert-butylanil), H2[L2], and N,N'-bis(2-hydroxy-3,5-di-tert-butylphenyl)-2,2-dimethylpropylenediamine, H4[L3], have been investigated with nickel(II), palladium(II), and copper(II). The complexes prepared and characterized are [Ni(II)(H3L1)2] (1), [Ni(II)(HL2)2].5/8CH2Cl2 (2), [Ni(II)(L3**)] (3), [Pd(II)(L3**)][Pd(II)(H2L3) (4), and [Cu(II)(H2O)(L4)] (5), where (L4)2- is the oxidized diimine form of (L3)4- and (L3**)2- is the bis(o-iminosemiquinonate) diradical form of (L3)4-. The structures of compounds 1-5 have been determined by single crystal X-ray crystallography. In complexes 1 and 2, the ligands (H3L1)- and (HL2)- are tridentate and the nickel ions are in an octahedral ligand environment. The oxidation level of the ligands is that of an aromatic o-aminophenol. 1 and 2 are paramagnetic (mu(eff) approximately 3.2 mu(B) at 300 K), indicating an S = 1 ground state. The diamagnetic, square planar, four-coordinate complexes 3 and [Pd(II)(L3**)] in 4 each contain two antiferromagnetically coupled o-iminobenzosemiquinonate(1-) pi radicals. Diamagnetic [Pd(II)(H2L3)] in 4 forms an eclipsed dimer via four N-H.O hydrogen bonding contacts which yields a nonbonding Pd.Pd contact of 3.0846(4) A. Complex 5 contains a five-coordinate Cu(II) ion and two o-aminophenolate(1-) halves in (L4)2-. The electrochemistries of complexes 3 and 4a ([Pd(II)(L3**)] of 4) have been investigated, and the EPR spectra of the monocations and -anions are reported. 相似文献
7.
8.
The use of ionic liquids in capillary electrophoresis, either as coating material or as components of the background electrolyte needs systematic standardization to set up optimal conditions. Excellent separation of the proteins was achieved using 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]) or 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) ionic liquids using the properly made ionic-liquid–water binary mixtures for the experiments. The binary mixture has a distinctly stable and well perceptible low pH, which depends on the concentration of the ionic liquid, and on the preparation time of the mixture. Optimal conditions for the electrophoretic separation were obtained upon a multivariate analysis of the experimental parameters (applied voltage, migration time, concentration, and type of the ionic liquid). The standardized condition provides a low electroendosmotic flow toward the anode, which, however, did not hinder the proteins to migrate toward the cathode. The migration of cytochrome c, lysozyme, myoglobin, trypsin, and apo-transferrin at a pH around 2, far below the isoelectric points of the proteins, showed RSD values of the migration times less than 7.5% and less than 6.5% when using [emim][BF4] or [bmim][BF4], respectively, either in run-to-run or day-to-day experiments. The determination of the extent of the EOF is not possible with the commonly used EOF markers, due to interaction with the ionic-liquid constituents. The interaction of the ionic liquids with the proteins influences the migration order in zone electrophoresis. This method has been applied successfully for the analyses of real biological samples such as proteins from egg whites and human tears. 相似文献
9.
Yoon Yeol Yoon Kil Yong Lee Kyung Seok Ko 《Journal of Radioanalytical and Nuclear Chemistry》2010,284(3):591-595
The contents of H-3 and C-14 in groundwater and surface waters around low and medium-level atomic waste repository site in
Korea were determined. The concentrations of C-14 were in the range 0.186–0.287 Bq/L. The H-3 concentration of the groundwaters
and surface waters were <0.06–5.75 and 1.22–4.74 Bq/L. The average H-3 contents of west, north and south direction were 1.18 ± 0.12,
1.11 ± 0.78 and 2.85 ± 2.66. H-3 and C-14 concentrations in the south direction were relatively higher than west and north
direction samples. The surface waters sampled from catchment were four times higher than average H-3 concentration in precipitation.
The concentrations of H-3 and C-14 within 5 km area samples were much higher than other samples. 相似文献
10.
Soon Kil Ahn Nam Song Choi Byeong Seon Jeong Kye Kwang Kim Duck Jin Journ Joon Kyum Kim Sang Joon Lee Jung Woo Kim Chung Hong Sang‐Sup Jew 《Journal of heterocyclic chemistry》2000,37(5):1141-1144
A practical semi‐synthetic method of (S)‐7‐(2‐isopropylamino)ethylcamptothecin hydrochloride has been developed. The Mannich reaction of (S)‐7‐methylcamptothecin with isopropylamine hydrochloride in dimethyl sulfoxide as a formaldehyde source gave the desired product in moderate yield. 相似文献