Czech Institute of Macromolecular Chemistry

Prague, Czech Republic

Czech Institute of Macromolecular Chemistry

Prague, Czech Republic
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Schulz J.,Charles University | Vosahlo P.,Charles University | Uhlik F.,Czech Institute of Macromolecular Chemistry | Cisarova I.,Charles University | Stepnicka P.,Charles University
Organometallics | Year: 2017

The stereoelectronic influence of phosphine substituents on the coordination and catalytic properties of phosphinoferrocene carboxamides was studied for the model compounds R2PfcCONHMe (1a-d), where fc = ferrocene-1,1′-diyl and R = i-Pr (a), t-Bu (b), cyclohexyl (Cy; c), Ph (d), using experimental and DFT-computed parameters. The electronic parameters were examined via 1JSeP coupling constants determined for R2P(Se)fcCONHMe (6a-d) and CO stretching frequencies of the Rh(I) complexes trans-[RhCl(CO)(1-κP)2] (7a-d); the steric properties of 1a-d were assessed through Tolman’s ligand cone angles (θ) and solid angles (Ω). Generally, a very good agreement between the calculated and experimental values was observed. Whereas the donor ability of the amidophosphines was found to increase from 1d through 1a,c to 1b, the trends in steric demand suggested by the two parameters differed, reflecting the different spatial properties of the phosphine substituents. In situ NMR studies and catalytic tests on the Suzuki-Miyaura cross-coupling of 4-bromoanisole with a bicyclic 4-tolylborate to give 4-methyl-4′-methoxybiphenyl using [Pd(η2:η2-cod)(η2-ma)] (cod = cycloocta-1,5-diene, ma = maleic anhydride) as a Pd(0) precursor revealed that different Pd-1 species (precatalysts) were formed from different ligands and participated in the reaction. Specifically, the bulky and electron-rich donor 1b favored the formation of [Pd(1b)(ma)], while the remaining ligands provided the corresponding bis-phosphine complexes [Pd(1)2(ma)]. The best results in terms of catalyst longevity and efficacy were observed for ligands 1a,c. © 2017 American Chemical Society.


Kozich V.,Charles University | Sokolova J.,Charles University | Klatovska V.,Charles University | Krijt J.,Charles University | And 3 more authors.
Human Mutation | Year: 2010

Misfolding of mutant enzymes may play an important role in the pathogenesis of cystathionine β-synthase (CBS) deficiency. We examined properties of a series of 27 mutant variants, which together represent 70% of known alleles observed in patients with homocystinuria due to CBS deficiency. The median amount of SDS-soluble mutant CBS polypeptides in the pellet after centrifugation of bacterial extracts was increased by 50% compared to the wild type. Moreover, mutants formed on average only 12% of tetramers and their median activity reached only 3% of the wild-type enzyme. In contrast to the wild-type CBS about half of mutants were not activated by S-adenosylmethionine. Expression at 18°C substantially increased the activity of five mutants in parallel with increasing the amounts of tetramers. We further analyzed the role of solvent accessibility of mutants as a determinant of their folding and activity. Buried mutations formed on average less tetramers and exhibited 23 times lower activity than the solvent exposed mutations. In summary, our results show that topology of mutations predicts in part the behavior of mutant CBS, and that misfolding may be an important and frequent pathogenic mechanism in CBS deficiency. © 2010 Wiley-Liss, Inc.


Riesova M.,Czech Institute of Macromolecular Chemistry | Svobodova J.,Czech Institute of Macromolecular Chemistry | Tosner Z.,Charles University | Benes M.,Czech Institute of Macromolecular Chemistry | And 2 more authors.
Analytical Chemistry | Year: 2013

The complexation of buffer constituents with the complexation agent present in the solution can very significantly influence the buffer properties, such as pH, ionic strength, or conductivity. These parameters are often crucial for selection of the separation conditions in capillary electrophoresis or high-pressure liquid chromatography (HPLC) and can significantly affect results of separation, particularly for capillary electrophoresis as shown in Part II of this paper series (Beneš, M.; Riesová, M.; Svobodová, J.; Tesařová, E.; Dubský, P.; Gaš, B. Anal. Chem. 2013, DOI: 10.1021/ac401381d). In this paper, the impact of complexation of buffer constituents with a neutral complexation agent is demonstrated theoretically as well as experimentally for the model buffer system composed of benzoic acid/LiOH or common buffers (e.g., CHES/LiOH, TAPS/LiOH, Tricine/LiOH, MOPS/LiOH, MES/LiOH, and acetic acid/LiOH). Cyclodextrins as common chiral selectors were used as model complexation agents. We were not only able to demonstrate substantial changes of pH but also to predict the general complexation characteristics of selected compounds. Because of the zwitterion character of the common buffer constituents, their charged forms complex stronger with cyclodextrins than the neutral ones do. This was fully proven by NMR measurements. Additionally complexation constants of both forms of selected compounds were determined by NMR and affinity capillary electrophoresis with a very good agreement of obtained values. These data were advantageously used for the theoretical descriptions of variations in pH, depending on the composition and concentration of the buffer. Theoretical predictions were shown to be a useful tool for deriving some general rules and laws for complexing systems. © 2013 American Chemical Society.


Svobodova J.,Czech Institute of Macromolecular Chemistry | Benes M.,Czech Institute of Macromolecular Chemistry | Hruska V.,Czech Institute of Macromolecular Chemistry | Hruska V.,Agilent Technologies | And 2 more authors.
Electrophoresis | Year: 2012

The complete mathematical model of electromigration in systems with complexation agents introduced in the Part I of this article (V. Hruška et al., Eletrophoresis, 2012, 33, this issue), which was implemented into our simulation program Simul 5, was verified experimentally. Three different chiral selector (CS) systems differing in the type of the CS, the magnitude of the complexation constants as well as in the experimental conditions were selected for verification. The experiments and simulations were performed at various concentrations of the CSs in order to discuss the influence of the concentration of the CS on the separation. The simulated and experimental electropherograms show very good agreement in the position, shape and amplitude of the analyte peaks. The new Simul 5 Complex offers a deep insight into electrophoretical separations that take place in systems containing complexing agents, for example into enantiomer separations. Using Simul 5 Complex we were able to predict and explain the significant electromigration dispersion of analyte peaks. It was clarified that the electromigration dispersion in these systems results directly from complexation. The new Simul 5 Complex was also shown to be a useful and powerful tool for the prediction of the results of enantioseparations. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Benes M.,Czech Institute of Macromolecular Chemistry | Svobodova J.,Czech Institute of Macromolecular Chemistry | Hruska V.,Czech Institute of Macromolecular Chemistry | Hruska V.,Agilent Technologies | And 3 more authors.
Journal of Chromatography A | Year: 2012

The complete mathematical model of electromigration dispersion in systems that contain a neutral complex forming agent and a fully charged analyte was introduced in the previous part of this series of papers (Part III - Theory). The model was implemented in the newest version of our simulation program PeakMaster 5.3 that calculates the effective mobility of the analyte and its nonlinear electromigration mobility slope, SEMD, in the presence of a complex forming agent in the background electrolyte. The mathematical model was verified by both experiments and simulations, which were performed by our dynamic simulator Simul 5 Complex. Three separation systems differing in the chiral selector used (having different values for the complexation constant and the mobility of the complex) were chosen for the verification. The nonlinear electromigration mobility slope values were calculated from the simulations and the experiments that were performed at different complex forming agent concentrations. These data agree very well with those predicted by the mathematical model and provided the foundation for the discussion and explanation of the electromigration dispersion process that occurs in systems which contain a complex forming agent. The new version of PeakMaster 5.3 was shown to be a powerful tool for optimization of the separation conditions by minimizing electromigration dispersion which improves the symmetry of the analyte peaks and their resolution. © 2012 Elsevier B.V.


Hruska V.,Czech Institute of Macromolecular Chemistry | Hruska V.,Agilent Technologies | Svobodova J.,Czech Institute of Macromolecular Chemistry | Benes M.,Czech Institute of Macromolecular Chemistry | Gas B.,Czech Institute of Macromolecular Chemistry
Journal of Chromatography A | Year: 2012

We introduce a new nonlinear electrophoretic model for complex-forming systems with a fully charged analyte and a neutral ligand. The background electrolyte is supposed to be composed of two constituents, which do not interact with the ligand. In order to characterize the electromigration dispersion (EMD) of the analyte zone we define a new parameter, the nonlinear electromigration mobility slope, SEMD,A. The parameter can be easily utilized for quantitative prediction of the EMD and for comparisons of the model with the simulated and experimental profiles. We implemented the model to the new version of PeakMaster 5.3 Complex that can calculate some characteristic parameters of the electrophoretic system and can plot the dependence of SEMD,A on the concentration of the ligand. Besides SEMD,A, also the relative velocity slope, SX, can be calculated. It is commonly used as a measure of EMD in electrophoretic systems. PeakMaster 5.3 Complex software can be advantageously used for optimization of the separation conditions to avoid high EMD in complexing systems. Based on the theoretical model we analyze the SEMD,A and reveal that this parameter is composed of six terms. We show that the major factor responsible for the electromigration dispersion in complex-forming electrophoretic systems is the complexation equilibrium and particularly its impact on the effective mobility of the analyte. To prove the appropriateness of the model we showed that there is a very good agreement between peak shapes calculated by PeakMaster 5.3 Complex (plotted using the HVLR function) and the profiles simulated by means of Simul 5 Complex. The detailed experimental verification of the new mode of PeakMaster 5.3 Complex is in the next part IV of the series. © 2012 Elsevier B.V.


Mullerova L.,Czech Institute of Macromolecular Chemistry | Dubsky P.,Czech Institute of Macromolecular Chemistry | Gas B.,Czech Institute of Macromolecular Chemistry
Journal of Chromatography A | Year: 2014

We introduce an easy but highly descriptive model of separation efficiency of dual-selector systems in capillary electrophoresis. The model expresses effective mobilities of analytes in dual-selector mixtures as a function of mixture composition and total concentration. The effective mobility follows the pattern familiar from single-selector systems, while complexation constant and mobility of the complex are replaced by the same but "overall" parameters and a total concentration of the mixture takes the role of a selector concentration. The overall parameters can be either calculated from the individual ones (an arbitrary mixture) or measured directly (a particular mixture). We inspected two model dual-selector systems consisting of heptakis(2,6-di-O-methyl)-β-CD and β-CD and of heptakis(2,6-di-O-methyl)-β-CD and 6-O-α-maltosyl-β-CD, and ibuprofen and flurbiprofen as model analytes (pH 8.2, non-enantioselective separation). Adopting any optimization strategy typically used in single-selector systems and finding an optimal mixture composition and total concentration is perhaps the prime benefit of the model. We demonstrate this approach on the selectivity parameter and show that the model is precise enough to be used in analytical practice. It also results that an electromigration order (reversal) of analytes can exhibit a rather curious dependency on the mixture composition and concentration. Last, the model can be used for better understanding of separation principles in dual-selector systems in general. © 2014 Elsevier B.V.


Benes M.,Czech Institute of Macromolecular Chemistry | Riesova M.,Czech Institute of Macromolecular Chemistry | Svobodova J.,Czech Institute of Macromolecular Chemistry | Tesarova E.,Czech Institute of Macromolecular Chemistry | And 2 more authors.
Analytical Chemistry | Year: 2013

This article elucidates the practical impact of the complexation of buffer constituents with complexation agents on electrophoretic results, namely, complexation constant determination, system peak development, and proper separation of analytes. Several common buffers, which were selected based on the pH study in Part I of this paper series (Riesová, M.; Svobodová, J.; Tošner, Z.; Beneš, M.; Tesařová, E.; Gaš, B. Anal. Chem., 2013, DOI: 10.1021/ac4013804); e.g., CHES, MES, MOPS, Tricine were used to demonstrate behavior of such complex separation systems. We show that the value of a complexation constant determined in the interacting buffers environment depends not only on the analyte and complexation agent but it is also substantially affected by the type and concentration of buffer constituents. As a result, the complexation parameters determined in the interacting buffers cannot be regarded as thermodynamic ones and may provide misleading information about the strength of complexation of the compound of interest. We also demonstrate that the development of system peaks in interacting buffer systems significantly differs from the behavior known for noncomplexing systems, as the mobility of system peaks depends on the concentration and type of neutral complexation agent. Finally, we show that the use of interacting buffers can totally ruin the results of electrophoretic separation because the buffer properties change as the consequence of the buffer constituents' complexation. As a general conclusion, the interaction of buffer constituents with the complexation agent should always be considered in any method development procedures. © 2013 American Chemical Society.


Dubsky P.,Czech Institute of Macromolecular Chemistry | Mullerova L.,Czech Institute of Macromolecular Chemistry | Dvorak M.,Czech Institute of Macromolecular Chemistry | Gas B.,Czech Institute of Macromolecular Chemistry
Journal of Chromatography A | Year: 2015

The model of electromigration of a multivalent weak acidic/basic/amphoteric analyte that undergoes complexation with a mixture of selectors is introduced. The model provides an extension of the series of models starting with the single-selector model without dissociation by Wren and Rowe in 1992, continuing with the monovalent weak analyte/single-selector model by Rawjee, Williams and Vigh in 1993 and that by Lelièvre in 1994, and ending with the multi-selector overall model without dissociation developed by our group in 2008. The new multivalent analyte multi-selector model shows that the effective mobility of the analyte obeys the original Wren and Row's formula. The overall complexation constant, mobility of the free analyte and mobility of complex can be measured and used in a standard way. The mathematical expressions for the overall parameters are provided. We further demonstrate mathematically that the pH dependent parameters for weak analytes can be simply used as an input into the multi-selector overall model and, in reverse, the multi-selector overall parameters can serve as an input into the pH-dependent models for the weak analytes. These findings can greatly simplify the rationale method development in analytical electrophoresis, specifically enantioseparations. © 2015 Elsevier B.V.


Mullerova L.,Czech Institute of Macromolecular Chemistry | Dubsky P.,Czech Institute of Macromolecular Chemistry | Gas B.,Czech Institute of Macromolecular Chemistry
Journal of Chromatography A | Year: 2015

Interactions among analyte forms that undergo simultaneous dissociation/protonation and complexation with multiple selectors take the shape of a highly interconnected multi-equilibrium scheme. This makes it difficult to express the effective mobility of the analyte in these systems, which are often encountered in electrophoretical separations, unless a generalized model is introduced. In the first part of this series, we presented the theory of electromigration of a multivalent weakly acidic/basic/amphoteric analyte undergoing complexation with a mixture of an arbitrary number of selectors. In this work we demonstrate the validity of this concept experimentally. The theory leads to three useful perspectives, each of which is closely related to the one originally formulated for simpler systems. If pH, IS and the selector mixture composition are all kept constant, the system is treated as if only a single analyte form interacted with a single selector. If the pH changes at constant IS and mixture composition, the already well-established models of a weakly acidic/basic analyte interacting with a single selector can be employed. Varying the mixture composition at constant IS and pH leads to a situation where virtually a single analyte form interacts with a mixture of selectors. We show how to switch between the three perspectives in practice and confirm that they can be employed interchangeably according to the specific needs by measurements performed in single- and dual-selector systems at a pH where the analyte is fully dissociated, partly dissociated or fully protonated. Weak monoprotic analyte (R-flurbiprofen) and two selectors (native β-cyclodextrin and monovalent positively charged 6-monodeoxy-6-monoamino-β-cyclodextrin) serve as a model system. © 2015 Elsevier B.V.

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