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61.
Elena V. Parfenyuk Olga I. Davydova Nataliya Sh. Lebedeva 《Journal of solution chemistry》2004,33(1):1-10
Calorimetric titrations have been performed at 298.15 K in aqueous solutions to derive the stability constants and thermodynamic parameters of the interactions of D-maltose and sucrose with some amino acids (glycine, DL-alanine, DL-leucine, and L-serine). The apparent molal volumes of the disaccharides in dilute aqueous solutions of the amino acids have been determined from density measurements at 298.15 K. In contrast to D-maltose, sucrose was found to associate with the amino acids and these associated species are preferentially entropy stabilized. These results are interpreted in terms of the influence of the nature of the solutes, their specific conformations, and hydration, on the ability of the disaccharides to form associated complexes with the amino acids. 相似文献
62.
A method for the quantitative preconcentration of lead based on an existing batch process was developed for implementation in a flow system including a flame AAS detector. Lead can be quantitatively preconcentrated as pyrrolidinedithiocarbamate or dithizonate on an activated carbon minicolumn. The chelates are eluted in methyl isobutyl ketone and introduced directly into the nebuliser-burner. An enrichment factor of 50 is typically obtained for a preconcentration time of 2 min (lead can be determined at concentrations between 15 and 400 ng/ml), which results in a throughput of ca. 25 samples per hr. The sensitivity achieved with the two reagents is similar, but the selectivity provided by APDC exceeds that of dithizone. Based on the results obtained in the determination of lead in reference materials (minerals and skim milk), the proposed APDC method is applicable to real samples. 相似文献
63.
Aviñó A Cubero E González C Eritja R Orozco M 《Journal of the American Chemical Society》2003,125(51):16127-16138
The structural, dynamical, and recognition properties of antiparallel DNA triplexes formed by the antiparallel d(G#G.C), d(A#A.T), and d(T#A.T) motifs (the pound sign and dot mean reverse-Hoogsteen and Watson-Crick hydrogen bonds, respectively) are studied by means of "state of the art" molecular dynamics simulations. Once the characteristics of the helix are defined, molecular dynamics and thermodynamic integration calculations are used to determine the expected stabilization of the antiparallel triplex caused by the introduction of 8-aminopurines. Finally, oligonucleotides containing 8-aminopurine derivatives are synthesized and tested experimentally using several approaches in a variety of systems. A very large stabilization of the triplex is found experimentally, as predicted by simulations. These results open the possibility for the use of oligonucleotides carrying 8-aminopurines to bind single-stranded nucleic acids by formation of antiparallel triplexes. 相似文献
64.
González-Núñez ME Mello R Royo J Asensio G Monzó I Tomás F López JG Ortiz FL 《The Journal of organic chemistry》2005,70(9):3450-3457
[reaction: see text] Data on the apparent dipole moment of thianthrene-5-oxide (1) and (1)H NMR spectra in different solvents support the conformational mobility of 1, which flaps between two limit boat conformations with the sulfinyl group in pseudoequatorial and pseudoaxial positions, respectively. The conformational equilibrium of 1 occurs too fast for the (1)H NMR (500 MHz) time-scale even at -130 degrees C, and the equilibrium constant has not been determined. The apparent dipole moments of 1 in n-hexane and 1,4-dioxane and the (1)H NMR spectra of 1 and the model compounds cis- and trans-thianthrene-5,10-dioxides (2) and thianthrene (5) in different solvents and at various temperatures confirm that the relative position of the conformational equilibrium of 1 is solvent-dependent, and more polar solvents favor the conformation with the sulfoxide group in the pseudoaxial position (1(')(ax)). Variable-temperature (1)H NMR spectra have established the interconversion barrier of trans-2 and confirmed that the conformational equilibrium of cis-2 is strongly displaced toward the conformation with both sulfinyl groups in the pseudoequatorial position. The (1)H NMR data support the transannular interaction of the functional groups in 1 and trans-2. 相似文献
65.
Determination of sulfametoxazole, sulfadiazine and associated compounds in pharmaceutical preparations by capillary zone electrophoresis 总被引:3,自引:0,他引:3
Berzas Nevado JJ Castañeda Peñalvo G Guzmán Bernardo FJ 《Journal of chromatography. A》2001,918(1):205-210
A capillary zone electrophoresis method is presented to separate sulfadiazine, sulfamethoxazole, trimethoprim, bromhexine and guaiacol by using a fused-silica capillary (60.2 cm x 75 microm I.D.). The separation was carried out at 30 kV and 25 degrees C in a 15 mM phosphate buffer adjusted to pH 6.2 as electrolyte. Under these conditions, the run time was 6 min and the limits of quantification were about 1 mg/l for every component. The method was applied to pharmaceutical preparations and the results provided recoveries close to 100%. 相似文献
66.
Elena Levi Eli Lancry Yossi Gofer Doron Aurbach 《Journal of Solid State Electrochemistry》2006,10(3):176-184
A crystallographic approach was applied to elucidate the influence of the nature of the surface films on the electrochemical
behavior of Li and Mg intercalation compounds. This paper presents two examples: (1) protection of graphite electrodes by
Li2CO3 surface films, and (2) the unique electrochemical behavior of Mg-containing Chevrel phases (MgCP) obtained by different synthetic
routes. In the former case, the elucidation of the protection mechanism and the explanation of the high performance of such
protected electrodes are based on the analysis of possible Li-ion motion in the carbonate crystal structure. In the latter
case, a combination of synthesis, electrochemistry and XRD analysis was used to explain an unusual phenomenon: the difference
between the excellent electrochemical behavior of the Chevrel phase (CP) based on Cu-leached Cu2Mo6S8 (CuCP), and the poor electrochemical activity of the high-temperature synthesized MgCP, with the same phase composition.
It is shown that this phenomenon is caused by MgO formation on the surface of the latter material. The different surface chemistry
of the MgCPs obtained by the two different synthetic routes was substantiated by revealing the correlation between the electrochemical
activity and the chemical stability of these materials under ambient atmosphere conditions.
Dedicated to Prof. Mikhail A. Vorotyntsev on the occasion of his 60th birthday. 相似文献
67.
Elena V Chubarova Denis G. Samsonenko Maxim N. Sokolov Olga A. Gerasko Vladimir P. Fedin Javier G. Platas 《Journal of inclusion phenomena and macrocyclic chemistry》2004,48(1-2):31-35
A new inclusion compound which is a supramolecular adduct of cucurbit[8]uril with two guest molecules of phenylphosphonic acid, PhP(O)(OH)2, included into the cavity as ``two guests in host'' is reported. The guests match both size and hydrophilicity/hydrophobicity requirements. Two phenyl groups of molecules of PhP(O)(OH)2 are directed toward the center of the large hydrophobic cavity whereas the PO(OH)2 groups are outward-looking and bound with each hydrophilic portal of cucurbit[8]uril by a short hydrogen bond. 相似文献
68.
R. L. Arenosa R. G. Rubio C. Menduiña M. Díaz Peña 《Journal of solution chemistry》1985,14(5):345-354
The molar excess enthalpies for the ethylbenzene + n-decane and ethylbenzene + n-tetradecane systems have been measured at 25°C over the complete concentration range. These results and others from the literature for alkanes + ethylbenzene, and alkanes + toluene have been discussed in terms of the Prigogine-Flory-Patterson theory. 相似文献
69.
Eneyskaya EV Ivanen DR Shabalin KA Kulminskaya AA Backinowsky LV Brumer Iii H Neustroev KN 《Organic & biomolecular chemistry》2005,3(1):146-151
Transglycosylation catalyzed by a beta-D-xylosidase from Aspergillus sp. was used to synthesize a set of 4-methylumbelliferyl (MU) beta-1-->4-D-xylooligosides having the common structure [beta-D-Xyl-(1-->4)]2-5-beta-D-Xyl-MU. MU xylobioside synthesized chemically by the condensation of protected MU beta-D-xylopyranoside with ethyl 2,3,4-tri-O-acetyl-1-thio-beta-D-xylopyranoside was used as a substrate for transglycosylation with the beta-D-xylosidase from Aspergillus sp. to produce higher MU xylooligosides. The structures of oligosaccharides obtained were established by 1H and 13C NMR spectroscopy and electrospray tandem mass spectrometry. MU beta-D-xylooligosides synthesized were tested as fluorogenic substrates for the GH-10 family beta-D-xylanase from Aspergillus orizae and the GH-11 family beta-D-xylanase I from Trichoderma reesei. Both xylanases released the aglycone from MU xylobioside and the corresponding trioside. With substrates having d.p. 4 and 5, the enzymes manifested endolytic activities, splitting off MU, MUX, and MUX2 primarily. 相似文献
70.
Talapin DV Shevchenko EV Murray CB Kornowski A Förster S Weller H 《Journal of the American Chemical Society》2004,126(40):12984-12988
We demonstrate the self-organization of CdSe nanorods into nematic, smectic, and crystalline solids. Layered colloidal crystals of CdSe nanorods grow by slow destabilization of a nanocrystal solution upon allowing the diffusion of a nonsolvent into the colloidal solution of nanocrystals. The colloidal crystals of nanorods show characteristic birefringence, which we assign to specific spherulite-like texture of each nanorod assembly. To demonstrate the general character of nanorod self-assembly technique, CdSe/CdS heterostructure nanorods were organized into highly luminescent superlattices. 相似文献