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101.
The surface behavior of solutions of the rhamnolipids, R1 and R2, were investigated in the absence and presence of an electrolyte (NaCl) through surface tension measurements and optical microscopy at pH 6.8. The NaCl concentrations studied are 0.05, 0.5 and 1 M. Electrolytes directly affect the carboxylate groups of the rhamnolipids. The solution/air interface has a net negative charge due to the dissociated carboxylate ions at pH 6.8 with strong repulsive electrostatic forces between the rhamnolipid molecules. This negative charge is shielded by the Na+ ions in the electrical double layer in the presence of NaCl, causing the formation of a close-packed monolayer, and a decrease in CMC, and surface tension values. The maximum compaction is observed at 0.5 M NaCl concentrations for R1 and R2 monolayers, with the R1 monolayer more compact than R2. The larger spaces left below the hydrophobic tails of R1 with respect to that of R2, due to the missing second rhamnosyl groups are thought to be responsible for the higher compaction. The rigidity of both R1 and R2 monolayers increases with the electrolyte concentration. The rigidity of the R1 monolayer is greater than that of R2 at all NaCl concentrations due to the lower hydrophilic character of R1. The variation of CMC values as a function of NaCl concentration obtained from the surface tension measurements and critical packing parameter (CPP) calculations show that spherical micelles, bilayer and rod like micelles are formed in the rhamnolipid solutions as a function of the NaCl concentration. The results of optical microscopy supported these aggregation states indicating lamellar nematic liquid crystal, cubic lamellar and hexagonal liquid crystal phases in R1 and R2 solutions depending on the NaCl concentration. 相似文献
102.
103.
Riccardo d'Agostino Vincenzo Colaprico Francesco Cramarossa 《Plasma Chemistry and Plasma Processing》1981,1(4):365-375
The spectroscopic emission intensities from excited F atoms in SF6-O2 discharges at 1 torr have been correlated to the densities of atoms in their ground electronic state by measuring the excitation efficiencies of the electrons in the energy range 11 to 17 eV with a method which essentially consists in the analysis of the emission of Ar or N2, added as actinometer gases to the discharge mixtures. The general applicability of the method has been tested by a direct titration of F atoms with chlorine. The spectroscopic analysis has allowed the determination of useful information on the trends of both the electron densities and their energies as a function of the oxygen percent in the feed. 相似文献
104.
Sonia E. Blanco 《Tetrahedron letters》2007,48(14):2577-2581
By applying the B3LYP/6-31G(d) method with the SCIPCM model on seven 4X substituted 2-hydroxybenzaldehydes, some structural characteristics related with their conformational equilibria and intramolecular hydrogen bonds have been clarified. The compounds are almost completely under the planar conformation characterized by a strong intramolecular hydrogen bond, which decreases in those solvents that possess a higher hydrogen bond donating capability and polarity. The substituents exert a marked influence on the conformational equilibrium constants and the strength of the IHB. Moreover, the excellent Hammett-type equations obtained support the proposed conformational reactions to quantify the IHB in the o-hydroxybenzaldehydes studied. 相似文献
105.
106.
用高效毛细管电泳前沿分析法研究了酸性药物那格列奈与人血浆白蛋白的结合常数、结合位点和结合率。使用未涂层的毛细管柱 (4 0cm× 5 0 μmi.d .;有效柱长 32cm) ,磷酸盐缓冲溶液 (pH 7.4 ,离子强度0 .17)为背景溶液 ,在紫外检测波长 2 14nm、运行电压 18kV和重力进样 10 0s的条件下 ,利用那格列奈谱峰的平台高度和游离药物浓度的良好线性关系 (r>0 .999,n =6 ) ,测定了那格列奈的游离药物浓度。固定药物浓度 (2 0 0 μmol L ,2 5 0 μmol L) ,考察不同的蛋白质浓度对结合的影响 ;固定蛋白质浓度 (10 0 μmol L) ,考察不同的药物浓度对结合的影响。实验数据采用非线性拟和程序进行处理 ,得到了那格列奈的蛋白质结合参数。高效毛细管电泳前沿分析法测定的数据重现性良好 (RSD <2 .5 % ,n =3) ,在药代动力学和药效学研究方面具有简便、准确的优点。 相似文献
107.
V. V. Davydov V. L. Sokol E. V. Balebanova Yu. V. Shklyaev S. V. Sergeev V. A. Nikanorov B. E. Zaitsev M. A. Porai-Koshits 《Russian Chemical Bulletin》1993,42(2):288-294
3,3-Dimethyl- and 3-methyl-1-(4,4-dimethyl-2,6-dioxocyclohex-1-yl)-3,4-dihydroisoquinolines have been synthesized. Crystal and molecular structures of the 3,3-dimethyl derivative have been determined. In the crystalline state this compound exists as a tautomeric form where a hydrogen atom is located at the N atom of the dihydroisoquinoline fragment of the molecule. The tautomeric equilibrium does not shift noticeably in solutions, as shown by IR, UV, and NMR spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 331–336, February, 1993. 相似文献
108.
Mu-Shih Lin Kuen-Tay Jeng Kun-Yui Huang Yen-Fong Shih 《Journal of polymer science. Part A, Polymer chemistry》1993,31(13):3317-3325
Simultaneous interpenetrating polymer networks (SINs) based on diglycidyl ether of bis-phenol A (DGEBA) and poly(ethylene glycol) diacrylate (PEGDA) in weight ratios of 100/0, 50/50, and 0/100 were blended and cured simultaneously by using benzoyl peroxide (BPO) and m-xylenediamine (MXDA) as curing agents. A kinetic study during SIN formation was carried out at 45, 55, 63, and 70°C. Concentration changes for both the epoxide and C?C bond were monitored with FTIR. A rate expression for DGEBA cure kinetics was established with a model reaction of phenyl glycidyl ether (PGE) and benzylamine. Experimental results revealed that lower rate constants and higher activation energy for the SIN were found, compared with those for the constituent DGEBA and PEGDA network formation. A model of network interlock was proposed to account for this phenomenon. During simultaneous cure of DGEBA and PEGDA, the interlock (mutual entanglement) between DGEBA and PEGDA networks provided a sterically hindered environment, which subsequently increased the activation energy and reduced cure rates for both DGEBA and PEGDA. © 1993 John Wiley & Sons, Inc. 相似文献
109.
The interlaboratory variability in the quantification of adsorbable organically bound halogens (AOX) in industrially contaminated
soil is presented. Three consecutive rounds of a proficiency testing scheme, in which between 88 and 119 routine laboratories
participated, yielded relative reproducibility standard deviations between 7 and 20% at AOX contents between 10.9 and 268 mg
kg−1. Nineteen laboratories with established proficiency were invited to participate in the certification of the AOX content in
three soil reference materials meant for the internal quality control in analytical laboratories. The certified values are
(1349 ± 59) mg kg−1, (80 ± 7) mg kg−1 and (102 ± 8) mg kg−1, respectively. 相似文献
110.
The solvation parameter model is used to elucidate the retention mechanism on a perfluorohexylpropylsiloxane-bonded (Fluophase
RP) and octadecylsiloxane-bonded (Betasil C18) stationary phases based on the same silica substrate with acetonitrile–water
and methanol–water mobile phase compositions. Dewetting affects the retention properties of Fluophase RP at mobile phase compositions
containing less than 20% (v/v) acetonitrile or 40% (v/v) methanol. It results in a loss of retention due to an unfavorable change in the phase ratio as well as changes in specific
intermolecular interactions. Steric repulsion reduces retention of bulky solutes on fully solvated Betasil C18 with methanol–water
(but not acetonitrile–water) mobile phase compositions but is not important for Fluophase RP. The retention of weak bases
is affected by ion-exchange interactions on Fluophase RP with acetonitrile–water, and to a lesser extent, methanol-water mobile
phases but these are weak at best for Betasil C18. The system constants of the solvation parameter model and retention factor
scatter plots are used to compare selectivity differences for Fluophase RP, Betasil C18 and a perfluorophenylpropylsiloxane-bonded
silica stationary phase Discovery HS F5 for conditions where incomplete solvation, steric repulsion and ion-exchange do not
significantly contribute to the retention mechanism. Lower retention on Fluophase RP results from weaker dispersion and/or
higher cohesion moderated to different extents by polar interactions since solvated Fluophase RP is a stronger hydrogen-bond
acid and more dipolar/polarizable than Betasil C18. Retention factors for acetonitrile–water mobile phases are highly correlated
for Fluophase RP and Betasil C18 except for compounds with a large excess molar refraction and weak hydrogen-bonding capability.
Selectivity differences are more significant for methanol–water mobile phases. Retention factors on Fluophase RP are strongly
correlated with those on Discovery HSF5 for acetonitrile–water mobile phases while methanol–water mobile phases retention
on Fluophase RP is a poor predictor of the retention order on Discovery HS F5. 相似文献