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471.
472.
Jadwiga Laska Adam Pro Serge Lefrant 《Journal of polymer science. Part A, Polymer chemistry》1995,33(9):1437-1445
Aliphatic and aromatic diesters of phosphoric acid were tested as dopants improving pro-cessability of polyaniline (PANI) in its doped (conducting) state. It has been found that both aromatic and aliphatic diesters effectively protonate polyaniline, inducing at the same time its solubility. The protonated state has been confirmed by three independent spec-troscopic methods (FTIR, Raman, and UV-vis-NIR). Both aromatic and aliphatic diesters of phosphoric acid plasticize polyaniline which, in turn, allows for the preparation of highly conducting films of PANI or highly conducting blends of PANI with classical nonconducting polymers by thermal processing. © 1995 John Wiley & Sons, Inc. 相似文献
473.
The protonation constants logK
Hj of the acidH
J
are determined by regression analysis of potentiometric titration data whencommon parameters (logK
Hj,j = 1,...,J) andgroup parameters (E
0,L
0,H
T
) are refined. Two kinds of systematic error have been investigated: the error from an uncertainty of group parameters and the error from a computational strategy of the minimization algorithm used. An analysis of variance of logK
Hj matrix was made for 6 reproduced titrations and 7 computational strategies of 6 various regression programs. It was concluded that the influence of the program used is negligible. From two ways of calibration of the glass electrode cell,the internal calibration (performed during titration) was slightly more accurate thanthe external calibration (done separately). Of programs tested, the ESAB and ACBA are most powerful because they permit refinement of group parameters and internal calibration. D-tartaric acid was chosen as model substance.Previous Part III.: Iraqi J. Sci.1981,22, 67. 相似文献
474.
N. Etxebarria M. J. Zapatero J. M. Castresana L. A. Fernández M. A. Olazabal J. M. Madariaga 《Journal of solution chemistry》1991,20(12):1213-1225
The protonation constant in 1.0 mol-dm–3 KNO3, and partition coefficient of 4-methylpyridine (B) between 1.0 mol-dm–3 KNO3, and toluene have been determined at 25°C by measuring the H3O+ ion concentration with a glass electrode. The experimental work consisted of two sets of potentiometric titrations. In the first case, the titrations were carried out in an aqueous system of constant ionic strength and in the second, two-phase titrations using toluene as organic phase were performed. All the titrations were conducted automatically by the use of a computer controlled potentiometric system. The results were treated using graphical and numerical methods and the systematic erros were also considered. The formation constant of the protonated 4-methylpyridine was correlated with the composition of the aqueous phase by means of Bromley's theory.Recently deceased. This paper is dedicated to the memory of Dr. José Maria Castresana. 相似文献
475.
Zexing Cao Xi Jin Zhaohui Zhou Qianer Zhang 《International journal of quantum chemistry》2006,106(9):2161-2168
Protonation of the metal‐bound oxy‐bidentate ligand in the model complexes of [(HS)3(NH3)M(OCH2COO)]q (M = Mo, Fe, V, Co; q = ?2, ?1) in the gas phase and in solutions of water and acetonitrile has been explored by the density functional approach. Calculations show that protonation of the carboxyl oxygen can open the α‐hydroxycarboxylate chelate ring ligated to a transition‐metal center under specific oxidation and spin states. The feasibility of the chelate ring opening by protonation depends on the electronic nature of the metal site in tune with conversion of a six‐coordinate with a five‐coordinate metal atom. Such selective dissociation of the metal‐bound chelate ligand manipulates the availability of an empty site at the metal center and significantly affects reactivity of the metal‐mediated chemical processes. Protonation changes the stability of species with different spin multiplicities and impels spin transition at the metal center in dissociation of the oxy‐bidentate ligand. Solvent environments of water and acetonitrile play an important role in stabilizing the negatively charged species. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
476.
Nonlinear regression program DHMINOPT has been used for an analysis of a set of values expressing the dependence of mixed dissociation constant on ionic strength according to the extended Debye-Hueckel law. Efficiency of program has been examined on simulated data loaded with generated random errors. Goodness-of-fit brings various regression diagnostics enabling to prove a reliability of a regression process and parameter estimates. For five selected sulphonephtalein indicators, i.e. Bromocresol Green, Bromophenol Red, Bromocresol Purple, Bromothymol Blue and Phenol Red, the thermodynamic dissociation constant has been determined at 25°C together with the ion-size parameter and the salting-out coefficient.Previous Part IV.: Mikrochim. Acta1992,108, 227. 相似文献
477.
Side-chain proton affinities for a series of peptide-forming amino acids have been calculated using ab initio Hartree-Fock-Roothaan SCF method; the order of proton affinities is Arg > His > Ser Tyr Lys. Protonation of some side-chains in a protein may introduce new energy levels in the band gaps thus fundamentally altering the conduction properties of the proteins.This paper is dedicated to Professor H. Hartmann for his 65th birthday.Guest at the Laboratory of the National Foundation for Cancer Research at the Chair of Theoretical Chemistry, University of Erlangen-Nürnberg. 相似文献
478.
M KwitJ Gawronski 《Tetrahedron》2003,59(47):9323-9331
Derivatives of trans-1,2-diaminocyclohexane (DACH), useful as chiral ligands, scaffolds and building blocks, differ in their conformation. The conformation of N,N′-diaryl-DACH derivatives was studied by the semiempirical and DFT computational methods and by exciton-coupled circular dichroism. It was found that, contrary to M-helical N,N′-diimine, N,N′-diimide and N,N′-diamide derivatives, the aromatic residues in N,N′-diphenyl derivatives are oriented to form a P-helix for the (R,R)-DACH absolute configuration. The helicity of the bis-aryl system is modified in the case of 1-naphthyl or 2-naphthyl derivatives. Further switching of helicity has been demonstrated by either protonation or mono-N-acetylation of N,N′-diaryl DACH derivatives. 相似文献
479.
A. A. Kamyshova A. Z. Kreindlin M. I. Rybinskaya P. V. Petrovskii 《Russian Chemical Bulletin》1999,48(3):581-585
Decamethylmetallocenes Cp*
2M (M=Ru, Os) in the presence, of acids (CF3CO2H, CF3SO3H) give thepprotonation products [Cp*
2MH]+An−. Broad-band UV photolysis of their solutions results in the formation of the salts of onium cations
. A preparative procedure for the synthesis of these salts has been developed. Hydrolysis of the salts gives the carbinol
Cp*MC5Me4CH2OH.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 587–591. March, 1999. 相似文献
480.
The protonation of o-, m-and p-benzotoluidide in sulfuric acid solutions is studied by UV spectroscopy in the 190–350 nm region. Principal component analysis
is applied to estimate the contributions of the effect of protonation and the medium effect. For the substances studied in
this work, the first principal component (PC) captures about 98 % of the variance and the second PC ∼100 % of the cumulative
percentage variance in the 210–350 nm region. The same spectral region is used for calculation of the ionization ratio from
the coefficients of the first PC and mole fractions of the base and its conjugate acid. Using these data and Hammett's equation
(pK
BH
+ = H
X
+ log I), the pK
BH
+ values for the protonation reaction are obtained. The dissociation constants as well as the solvent parameters m* (∼0.43)
and ϕ (∼0.60) are calculated using the Excess Acidity Method (-pK
BH
+= 2.28–2.30) and the Bunnett-Olsen Method (-pK
BH
+= 2.24–2.28). The probable sites of protonation are discussed. 相似文献