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91.
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
92.
93.
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
94.
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
95.
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
96.
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
97.
In this paper, calculating the molecular internal rotating steric factor of polymers by the radiation crosslinking method is studied and a relationship between the molecular internal rotating steric factor (σ) and crosslinking parameter βis established~([1]) by taking account of the effect of polymer chain flexibility on βvalue, σvalue of polymer obtained by this method is in agreement with that given with other method. 相似文献
98.
The considered mathematical model of the decomposition of valerate presents three unknown kinetic parameters, two unknown
stoichiometric coefficients, and three unknown initial concentrations for biomass. Applying a structural identifiability study,
we concluded that it is necessary to perform simultaneous batch experiments with differenitial conditions for estimating these
parameters. Four simultaneous batch experiments were conducted at 55°C, characterized by four different initial acetate concentrations.
Product inhibition of valerate degradation by acetate was considered. Practical identification was done optimizing the sum
of the multiple determination coefficients for all measured state viariables and for all experiments simultaneously. The estimated
values of kinetic parameters and stoichiometric coefficients were characterized by the parameter correlation matrix, the confidence
interval, and the student's t-test at 9% significance level with positive results except for the saturation constant, for which more eperiments for improving
its identifiability should be conducted. In this article, we discussekinetic parameter estimation methods. 相似文献
99.
H. L. Stalford 《Journal of Optimization Theory and Applications》1995,86(3):685-718
Using a class of linear static controllers, we stabilize the Petersen open-loop two-dimensional linear system (Ref. 1), which consists of one time-varying uncertainty in the state matrixA and one timevarying uncertainty in the input matrixB. We show that the worst-case uncertainty strategy for the closed-loop system is a piecewise constant strategy of the angular state with three switches on the half-turn, –/2/2; it is unique with respect to a set of measure zero. Formulas are derived for the worst-case half-turn radius gainr
HT
as a function of the parameters of the class of stabilizing linear static controllers. Using the class of scalar-quadratic Lyapunov functions, we show that a necessary and sufficient condition for the closed-loop system to be robustly stable against all time-varying admissible uncertainties is thatr
HT
be less than unity. The bound on the time-varying real parameter uncertainties for the closed-loop system to be robustly stable is derived for the class of linear static feedback controllers. We obtain stabilizing linear static controllers such that the bound is as close to infinity as desired. The derived results are compared with numerical results obtained using commerical robust-control software. 相似文献
100.
Schock (Ref. 1) considered a general a posteriori parameter choice strategy for the Tikhonov regularization of the ill-posed operator equationTx=y which provides nearly the optimal rate of convergence if the minimal-norm least-squares solution
belongs to the range of the operator (T
*
T)
v
, o<v1. Recently, Nair (Ref. 2) improved the result of Schock and also provided the optimal rate ifv=1. In this note, we further improve the result and show in particular that the optimal rate can be achieved for 1/2v1.The final version of this work was written while M. T. Nair was a Visiting Fellow at the Centre for Mathematics and Its Applications, Australian National University, Canberra, Australia. The work of S. George was supported by a Senior Research Fellowship from CSIR, India. 相似文献